Digital printing procedure and system with ink ejection control

Abstract

Method and system for digital printing with control over the volume of ink, by means of an inkjet printer (10) provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined. The method is characterized in that it comprises reprocessing the ejection commands such that the droplet volume level corresponding to each one of at least one of the original print dots (P) is redistributed between the original print dot itself (P) and / or at least one generated print dot (Q). The generated print dots (Q) are introduced close to said original print dot (P).

Description

SUBJECT MATTER OF THE INVENTION

[0001] The present invention relates to a method and a system for digital printing by means of an inkjet printer. More specifically, the invention aims to provide improvements to the way in which the droplets of ink are ejected at the print dots through the ink injection nozzles of the printer. The invention also relates to computer software that facilitates the implementation of the method of the invention.BACKGROUND ART

[0002] Inkjet printing has been widely used in the field of digital printing, both on an industrial level and by individuals, owing to its inherent capacity to print digital images with a high resolution, quality and performance.

[0003] Inkjet printers work by controlled ejection of droplets of ink through nozzles. To this end, the starting point is the digital image to be printed, which is processed so as to obtain commands for the ejection of ink droplets, in such a way that each print dot of the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time.

[0004] The printing resolution is predetermined by the number of nozzles available for the duration of printing for the various dots in the printout area at which the droplets of ink are ejected. Conventionally, the printing resolution is expressed in dots per inch.

[0005] Likewise, the droplet volume levels that can be ejected by each nozzle are predetermined. The inkjet printers that are currently available are usually configured with various droplet volume levels, since a higher number of droplet volume levels allows more precise control over the amount of ink deposited, improving among other things the gradation of colour tones in the printout and, therefore, the quality of printing.

[0006] For example, in the case of single pass inkjet printers, the nozzles are usually arranged on bars of heads with nozzles aligned along the bar, perpendicularly to the direction in which the substrate to be printed is conveyed. In this case, the printing resolution is determined, in the horizontal direction (perpendicular to the direction in which the substrate is conveyed), by the number of nozzles per unit length that are arranged in said horizontal direction for each colour.

[0007] As for the resolution in the vertical direction (parallel to the direction in which the substrate is conveyed), this is determined by the number of different print dots, with their corresponding droplet volume levels, that the printer can deposit per unit length in the vertical direction. The vertical resolution depends, in particular, on the number of nozzles aligned in the vertical direction, and / or on the number of ejections that each nozzle can produce per unit length that the substrate moves in said direction.

[0008] The digital image is processed so as to be converted into print dots in the printout area, with the printing resolution determined. The various colours of the image are formed by superposition of print dots of ink droplets of a limited number of colours. To this end, use is usually made, in particular, of basic colours such as cyan, magenta, yellow and black, or mixtures of basic colours such as green, violet, orange, etc. Furthermore, the different droplet levels of each print dot make it possible to produce gradated colour tones or grayscale effects.

[0009] Usually, the digital image is processed by means of computer software called RIP (raster image processor). This software converts the digital image files into commands for the ejection of ink by the nozzles, managing the distribution of the print dots, droplet volumes, colours, etc. depending on the printing resolution, the size of the printout area, the definition of the image, etc. so as to optimize printing quality.

[0010] Processing of the digital image, in particular using the RIP, allows fundamental management of the control over the ejection of ink such that, for example, the droplet volume levels ejected at each print dot are determined after said processing, so as to obtain the predetermined printing resolution with optimized printing quality.

[0011] Therefore, a user or operator of the inkjet printer has little or no leeway for control over the ejection of ink, as this is dictated by the processing of the digital image, specifically by the RIP. This limits, in particular, the versatility of known inkjet printing methods and systems.

[0012] Mention must be made in particular of the limitation of current methods and systems as regards the dependency of the ink on the priming of the substrate on which it is printed, which requires that the type of priming be adapted to the ink and substrate used.

[0013] An aim of the invention is to overcome the limitations of current technologies, such as the dependency of the ink on the priming of the substrate, improving versatility while maintaining, and even improving, the quality, availability and performance of known inkjet digital printing methods and systems.SUMMARY OF THE INVENTION

[0014] To achieve the stated aim, and other technical advantages that may become clear from this description, the invention proposes a method for digital printing with control over the volume of ink by means of an inkjet printer. The printer is provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined.

[0015] The method according to the invention, as in known inkjet digital printing methods, comprises processing a digital image to obtain commands for the ejection of ink droplets in a printout area of a substrate, such that each print dot in the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time. Subsequently, printing is carried out on a substrate following the definitive ejection commands.

[0016] Unlike known inkjet digital printing methods, the method according to the invention further comprises reprocessing the ejection commands such that the droplet volume level corresponding to each one of at least one of said print dots, original, according to the non-reprocessed ejection commands, is redistributed between the original print dot itself and / or at least one generated print dot, which is introduced close to said original print dot, by means of respective reassigned droplet volume levels, which are ejected by nozzles.

[0017] The invention thus allows controlled reduction of the ink droplet volume deposited per original print dot, redistributing said volume to generated print dots, which are located close to said original print dot.

[0018] Because the droplet volume ejected is reduced, the ink droplets of smaller volume expand to a lesser extent once deposited on the substrate, since they have a smaller quantity of liquid that can spread on the surface of the substrate.

[0019] The expansion of the ink droplets on the substrate, in general, may also depend on other factors, including properties of the ink droplets, such as viscosity or surface tension, properties of the substrate, such as surface energy, porosity or hydrophilicity, or environmental conditions, such as temperature or relative humidity. However, the droplet volume significantly influences the expansion of the droplets.

[0020] The invention therefore makes it possible, in particular, to minimize or eliminate the dependency relationship between the printing method and the ink and the substrate or priming of the substrate, with regards to the influence thereof on the expansion of the ink droplets. In particular, it is even possible to dispense with priming of the substrate, unlike in conventional printing methods.

[0021] Furthermore, the resolution and quality of printing are not affected by the application of the method of the invention, compared to a digital printing method applied under the same conditions but according to non-reprocessed ejection commands. This is because the introduction of the generated print dots is carried out per original print dot, and they are located close to the latter, with only a redistribution of the droplet volume, such that the visual appearance of the printed image and its apparent quality are maintained.

[0022] In the context of the invention, "print dot" means a theoretical or nominal dot in the printout area, at which, like a target or objective, a droplet volume level is ejected, by a nozzle and at an instant in time which are predetermined, so as to generate the printed damage. The print dot, therefore, does not necessarily coincide with the dot at which the nozzle ejects said droplet volume at said instant in time, there being tolerances that are managed in a controlled manner.

[0023] In general, at each print dot, a plurality of droplet volume levels may be ejected, by different nozzles or by the same nozzle at different instants in time. For example, single pass inkjet printers are usually configured such that for each print dot, each nozzle of a different colour, for example cyan, magenta, yellow and black, ejects a droplet volume level.

[0024] "Droplet volume level" means each of the quantities of a theoretical or nominal volume of an ink droplet that is ejected by the nozzle so as to be deposited at each print dot. The term "droplet volume level" includes the level zero when the quantity ejected is zero.

[0025] Unlike the prior art, the invention comprises a reassignment of droplet volume levels per original print dot between the original print dot itself and generated print dots. Instead of the corresponding droplet volume level being ejected at the original print dot according to the non-reprocessed ejection commands, said droplet volume level is redistributed between the original print dot itself and / or at least one generated print dot, by means of respective reassigned droplet volume levels.

[0026] According to the invention, the reassignment of droplet volume levels by means of the step of reprocessing may be carried out, in particular, for any of the original print dots or for each and every one of said original print dots, of the printout area or part of the printout area.

[0027] "Redistribution of the droplet volume level" means that the volume corresponding to the original print dot, according to the non-reprocessed ejection commands, is split between the original print dot itself and / or the generated print dots, preferably equally.

[0028] Therefore, said volume corresponding to the original print dot is, in particular, substantially equal, or as close as possible, to the sum of the redistributed droplet volumes, corresponding to the reassigned droplet volume levels, more particularly, exceeding or not exceeding said volume corresponding to the original print dot.

[0029] According to the invention, the generated print dot or dots are introduced close to the corresponding original print dot. In the context of the invention, "close to" means in a zone surrounding said original print dot corresponding to the printing resolution of the printer. In particular, at a distance from the original dot which is smaller than the distance separating original print dots corresponding to the printing resolution. Preferably, located at a distance of less than half of said separation distance, more preferably less than one third.

[0030] An increasing proximity of the generated print dots to the original print dot promotes the similarity of the image printed with the method of the invention, with respect to the same printed image if it was printed according to the non-reprocessed ejection commands.

[0031] If printing is in colour, the colour that is reassigned to the original print dot itself and / or the at least one generated print dot after reprocessing is, preferably, the colour of the ink that would be ejected at the corresponding original print dot according to the non-reprocessed ejection commands.

[0032] Colours usually used in inkjet printing are basic colours such as, for example, cyan (C), magenta (M), yellow (Y) and black (K). Furthermore, depending on the type of substrate to be printed or on the chromatic characteristics of the image to be printed, other colours are often used, such as for example, green (G), violet (V), orange (O), light black (LK), light magenta (LM), etc.

[0033] In general, preferably, any characteristic of the ink (such as the colour) at the original print dot according to the non-reprocessed ejection commands is reassigned, by means of the reprocessing according to the invention, to the original print dot itself and / or the at least one corresponding generated print dot.

[0034] In this regard, the underlying criterion is to replicate these characteristics at all the dots between which the droplet volume level per original print dot is redistributed, to ensure that the appearance of the printed image resulting from the application of the method of the invention is similar to what would have been the result if it had been applied without the reprocessing step.

[0035] The printing method according to the invention is not limited to the printing of decorative images, monochrome or in colour, but may also be used, as an alternative or in addition to the generation of decorative images, for generating textures.

[0036] "Texture" refers to a surface with a relief. To generate textures, use may be made of a coating, for example in the form of a base layer, on which the impact, contact and / or mixture of the ejected ink droplets produces or helps to produce protruding and / or recessed reliefs on the surface of the base layer. Preferably, use may be made of substantially transparent ink to generate textures, in particular in combination with decorations. Moreover, a varnish, especially a substantially transparent varnish, may be used as base layer.

[0037] In particular, the droplet volume ejected at each print dot corresponding to the respective reassigned droplet volume levels has an influence on the depth and / or height of the texture generated at said print dots, and therefore the method according to the invention makes it possible to obtain various textures on various substrates, printout areas, digital images or parts thereof, according to the various reassigned droplet volume levels at the various print dots.

[0038] Therefore, by controlling the volume of ink according to the invention, in other words, specifically, the reassigned ink volume levels, it is possible to control the depth and / or height of the texture generated. In particular, this may also be used to control the degree of matt or gloss of a printed decoration, mainly as a result of the effect of the lower reflection of light on rough surfaces.

[0039] Advantageously, in general, owing to the fact that ink droplets of smaller volume expand to a lesser extent once deposited on the substrate, in particular, this being controllable according to the invention, it is possible to obtain printouts with greater definition, specifically textures with greater definition. Moreover, as mentioned above, the dependency of the printing on the coating, base layer or priming of the substrate on which the ink droplets are ejected is reduced or eliminated.

[0040] Moreover, as regards the nozzles used in the method according to the invention, in the invention use may preferably be made of the same nozzles as would be used for printing with the predetermined resolution and droplet volume levels according to the non-reprocessed ejection commands, in other words ejecting the droplet volume levels, without reassignment, only at the original print dots. In the context of the invention, these nozzles are referred to as the main nozzles.

[0041] Alternatively or in addition to the use of the main nozzles, the respective reassigned droplet volume levels may be ejected by additional nozzles, which are additional to the main nozzles, of the inkjet printer. In particular, use may also be made of only the main nozzles or only the additional nozzles for the ejection of the reassigned droplet volume levels.

[0042] The option of including additional nozzles offers the additional advantage of having redundant nozzles, in particular when selectively the digital printing method is not applied and therefore printing is carried out directly from the ejection commands. Availability of the machine is thereby increased.

[0043] The additional nozzles may be selected to have an arrangement or configuration such that, by themselves and independently of the main nozzles, they provide a printing resolution that is greater than or equal to the main nozzles, and / or to have a maximum droplet volume level per nozzle that is smaller than or equal to that of the main nozzles. It is thus possible to obtain arrangements of generated print dots closer to original print dots according to the invention.

[0044] Preferably, the same nozzle, main or additional, may eject the respective reassigned droplet volume levels at a plurality of generated print dots, per original print dot.

[0045] In this way, the same nozzle is used to generate multiple print dots. In particular, the main nozzles, which in principle are used to eject a single print dot, corresponding to the original print dot associated with the predetermined printing resolution, may be used to eject more than one print dot. In particular, they may be used to eject at least one original dot and at least one generated dot, or at least two generated dots.

[0046] This is possible according to the invention, for example, by reducing the printing speed, since this makes it possible to increase the number of discharges per nozzle per unit area of a printout. It is also possible by limiting the number of droplet volume levels of the nozzles. For example, if only one droplet volume level (in addition to the zero level) is ejected, it is possible to maximize the number of discharges of droplet volume levels.

[0047] Advantageously, the method according to the invention may be applied selectively to substrates, printout areas, digital images or parts of the same substrate, printout area or digital image. In particular, the selective application may be carried out with respect to other substrates, printout areas, digital images or parts of the same substrate, printout area or digital image for which ink is ejected only at original print dots according to the non-reprocessed ejection commands.

[0048] Selective application of the method according to the invention means, in particular, the activation or deactivation of reprocessing of the ejection commands for certain original print dots as desired. Such print dots may correspond, in particular, to physical dots of the substrate or of the printout area, or to pixels of the digital image, according to the processing of the digital image carried out.

[0049] Likewise, the method according to the invention may also be applied differently to substrates, printout areas, digital images or parts of the same substrate, printout area or digital image. In particular, the method may be applied such that the introduction of generated print dots, and / or the redistribution of the droplet volume level, is different for different substrates, printout areas, digital images or parts of the same substrate, printout area or digital image.

[0050] In particular, the reprocessing step may be carried out in a different manner for different substrates, printout areas, digital images or parts thereof, as desired. This may be useful, for example, so as to be able to print areas of saturated colour, with droplets of larger size, and areas that require greater gradation of colour, or definition, using droplets of smaller size.

[0051] "Different introduction of the generated print dots" means, for example, that the number of generated print dots, per original print dot, is different and / or that the location of the generated print dots with respect to the original print dot is different, for example following a different pattern.

[0052] "Different redistribution of the generated print dots" means the different ways in which the volume of ink can be split between the reassigned droplet volume levels, per original print dot. For example, different modes of redistribution may be based on setting a maximum droplet volume or different maximum reassigned droplet volume levels.

[0053] Any mode of redistribution that can be envisaged may be applied according to the invention. A priori, once the number of generated print dots and their location have been decided, there are as many modes of redistribution as there are possibilities of sharing the volume of ink between the different ink volume levels available.

[0054] Likewise, when applying the reprocessing according to the invention, introduction and / or redistribution criteria may be set, these being selectable by means of other control variables by the operator implementing the method. For example, a general criterion may be based on a minimum distortion of original droplet volume levels, so that the original droplet volume level, which would be ejected according to the non-reprocessed ejection commands, is reduced as little as possible.

[0055] Another example of a selection criterion may be based on choosing one of the possible reassigned droplet volume levels when the possibilities are that their sum exceeds or does not exceed the original droplet volume level.

[0056] In general, the introduction and / or redistribution may also be random, in particular in combination with other criteria or modes of introduction and / or redistribution. This is compatible with the use of stochastic inkjet printing techniques, which are usually used in the processing of the digital images for printing.

[0057] According to the invention, the method may also be applied selectively and / or differently to different substrates, depending on properties of the ink and / or depending on whether or not there is a coating on the substrate on which the ink is ejected, in particular depending on properties of the coating or of the substrate, more particularly depending on the thickness of the coating.

[0058] The properties, of the ink or of the coating or of the substrate, may be, in particular, physical or chemical properties, for example viscosity, surface tension, chemical composition, etc.

[0059] "Coating" means, in particular, a primer, the main function of which is to prepare the surface of the substrate to receive the ink, in particular ensuring adhesion of the ink to the substrate, and / or a base layer, the function of which is to act as a base for generating a texture.

[0060] Thus, the invention makes it possible for the same method to be used with different types of coatings and / or different types of ink for printing on a substrate, adapting the mode of application of the method to the type of coating and / or ink.

[0061] In particular, the invention makes it possible to dispense with a coating or primer, for example, by selecting maximum reassigned droplet volume levels that are sufficiently small to minimize or disregard the expansion of the droplets of ink deposited on the surface of the substrate.

[0062] According to another aspect, the invention relates to computer software for carrying out a method for digital printing as described above. The software comprises instructions such that, when the software is executed by a computer, the computer performs the reprocessing of the ejection commands, obtained, in particular, using computer software for processing digital images (RIP), from the digital image, so as to provide new ejection commands for ejection at original print dots and / or generated print dots.

[0063] The computer software according to the invention may include or be included in software for processing the digital image such as, for example, the RIP.

[0064] Lastly, the invention also relates to a system for digital printing with control over the volume of ink. The system comprises an inkjet printer, in particular a single pass inkjet printer, provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined.

[0065] According to the invention the system is configured to carry out a method as described above. In particular, the system comprises a computer on which computer software as described above may be installed or is installed.BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The invention is described in more detail below, by way of non-limiting illustration, and with reference to a preferred embodiment by way of example, with reference to the attached drawings. In the drawings: Figure 1 shows a flow chart of an inkjet digital printing method according to the prior art. Figure 2 shows a flow chart of an inkjet digital printing method according to the invention. Figures 3, 4 and 5 relate to an embodiment of a printing method and system of the prior art or in which the nozzles of the inkjet printer eject the droplet volume levels according to non-reprocessed ink ejection commands. Figures 6, 7, 8 and 9 depict various embodiments according to the invention corresponding to various positions of the generated print dots, with respect to the original print dots. Figures 10 and 11 depict two exemplary embodiments of the invention, in correspondence with the embodiment depicted in Figure 9. Figures 12 and 13 depict various arrangements of main and additional nozzles, for various embodiments of a printing system according to the invention in which the inkjet printer is a single pass inkjet printer. Figure 14 shows an embodiment of a nozzle head for a single pass inkjet printer. Figure 15 depicts droplets of ink deposited on the substrate to be printed. It can be seen in the figure that the droplets of greater volume are spread over a greater area than the droplets of smaller volume. Figure 16 shows an exemplary embodiment according to the invention in which the printing is used to generate a texture. It can be seen in the figure that the droplets of greater volume are introduced at a greater depth than the droplets of smaller volume. Figure 17 schematically depicts an embodiment of a printing system according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0067] In the description of all of the figures, the reference signs relate to the system shown in Figure 17.

[0068] Figure 1 shows a flow chart of a known method for digital printing by means of an inkjet printer (10). The inkjet printer (10) is configured to provide a printing resolution and droplet volume levels which are predetermined.

[0069] To print a digital image with a given image definition or resolution, in a printout area of a substrate and with the printing resolution of the inkjet printer (10), the digital image is processed, for example using RIP processing software. The RIP software converts the pixels of the digital image into ejection commands for the ejection of droplets of ink in the printout area of the substrate.

[0070] The inkjet printing of the image is carried out in such a way that each print dot of the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time.

[0071] In the context of the present invention, the term "digital image" includes the concept of a digital file that stores digital information in a format suitable for printing. The digital image may be in raster or vector format. "Raster format" refers to the form of storage of information on the image in which the image is composed of a map or matrix of pixels, wherein each pixel individually stores a value of colour, depth or height of relief (in the case of textures), location, etc., which is produced in the printout.

[0072] In particular, when the digital image is in vector format, the step of processing to obtain the ink droplet ejection commands may include a rasterizing sub-step for changing the digital image from vector format to raster format and subsequent processing of pixels.

[0073] The definition of the digital image, also referred to as the resolution of the digital image, of the digital images in raster format, represents the quality of the actual digital image and depends on the number of pixels it contains, the quality being higher the greater said number of pixels.

[0074] In comparison with Figure 1, Figure 2 shows a flow chart of a method for digital printing by means of an inkjet printer (10) according to the invention.

[0075] Unlike prior art methods for inkjet digital printing, the printing method according to the invention comprises a step of reprocessing of the ejection commands so as to generate new ejection commands.

[0076] With the new ejection commands generated by the reprocessing, the droplet volume level that would correspond to each one of the original print dots (P) according to the non-reprocessed ejection commands are redistributed between the original print dot itself (P) and / or at least one generated print dot (Q), which is introduced close to said original print dot (P), by means of respective reassigned droplet volume levels. Printing is carried out by ejecting said reassigned droplet volume levels.

[0077] In particular, the way in which the reprocessing is carried out may be controlled, for example, by requesting a droplet volume or reassigned droplet volume level or by means of other control variables.

[0078] The phases of processing and reprocessing may be carried out simultaneously, merged, with identical results.

[0079] With reference to Figures 3 to 5, an embodiment of a prior art method and system is explained below, before then explaining the changes made, in this embodiment, according to the invention.

[0080] Figure 3 shows the droplets of ink deposited in a sub-area of the printout area, with their corresponding colours (C, M, Y, K) according to an exemplary embodiment. A single circle means that the droplet volume level of the droplet of ink deposited is level 1, two concentric circles represent a level 2 and three concentric circles a level 3.

[0081] The sub-area in question measures 3x3 cells, wherein each cell corresponds to a print dot. The printing resolution is determined by the number of print dots per unit area. The processing of the digital image, in particular the RIP, makes it possible to convert pixels of the digital image, or associated with the digital image, into print dots of the various cells, adjusting the digital image to the printout area selected.

[0082] To adjust the digital image to the printout area selected, the processing of the digital image may comprise generating new pixels from native pixels of the digital image, by interpolating the information therefrom, or deleting native pixels of the digital image, eliminating the information from the digital image. Likewise, the processing may comprise carrying out an adjustment of the digital image consisting in modifying native pixels on the basis of native pixels neighbouring said pixels, for example, so as to simulate colours or tones to be produced in the printout. The new pixels, specifically pixels that have been interpolated, modified, etc., are examples of pixels associated with the digital image in the context of the invention.

[0083] For the sake of simplicity but without thereby limiting the invention, in the exemplary embodiments illustrated, a droplet of a single colour of ink has been ejected at each print dot of the sub-area. However, in particular, several droplets of different colours may be ejected, and would be superposed on one another, at one and the same print dot.

[0084] Figure 4 shows the positions of the print dots in the printout sub-area. It depicts original print dots (P), since these are the print dots at which the droplets of ink are ejected according to the non-reprocessed ejection commands. The original print dots (P) are represented in the figures with an "x".

[0085] Figure 5 shows the arrangement of the nozzles (each nozzle is represented by a triangle in the figures) according to an embodiment of the invention in which a single pass inkjet printer (10) is used, wherein the nozzles are grouped together in heads for the different colours (C, M, Y, K). These are main nozzles (C-PR, M-PR, Y-PR, K-PR).

[0086] The sub-area to be printed is shown in the lower part of Figure 5. As the substrate with the printout area moves in the (vertical) direction indicated by the arrows, the main nozzles (C-PR, M-PR, Y-PR, K-PR) corresponding to each colour eject the corresponding droplet volume level in the printout sub-area, so as to obtain the distribution of droplets of ink shown in Figure 3.

[0087] Preferably, a single pass inkjet printer (10) is used according to the invention, although any type of inkjet printer may be used. The nozzles are usually arranged as shown in Figure 5, aligned with one another in rows parallel to the horizontal direction, perpendicular to the vertical direction in which the substrate is conveyed.

[0088] Likewise, the nozzles arranged in rows are usually arranged in print heads, which are also grouped together aligned with one another in printing bars (11, 12, 13 and 14; 21, 22, 23, 24), with one bar per colour. In order to have redundancy or alternating use of the nozzles, and therefore greater availability of the inkjet printer (10), there is usually more than one printing bar per colour.

[0089] With reference now to Figures 6 to 9, in comparison with Figure 4, these figures show the positions of the generated print dots (Q), in addition or as an alternative to the original print dots (P). The generated print dots (Q) are represented in the figures by a cross ("+"), being distinguished from the original print dots (P), which are shown with an "x".

[0090] As shown in each of Figures 6 to 9, the generated print dots (Q) are positioned close to the respective original print dot (P). Specifically, they are located within the cell associated with the original print dot (P) with which they are linked.

[0091] The size of each cell of the printout sub-area is directly related to the printing resolution. Thus, the printing resolution is given by the number of cells per unit length in the printed area, in other words the number of original print dots (P) available for the ejection of the droplets of ink according to the non-reprocessed ejection commands.

[0092] Indeed, when applying the method according to the invention, the printing resolution is not changed since the generated print dots (Q) replicate the information associated with each original print dot (P) with which they are linked per cell.

[0093] For example, in Figure 6 the generated print dots (Q) are located at a distance from the respective original print dot (P) which is equal to ¼ of the separation between original print dots (P) in the printout sub-area, which separation is equal to the length of the side of the corresponding cell.

[0094] In the example of Figure 7, unlike that in Figure 6, for each original print dot (P) there are two generated print dots (Q), which are located on either side of said print dot (P). A greater number of print dots (P, Q) makes it possible to increase the versatility, as well as the availability of the method and system of the invention.

[0095] Figure 8 shows another example of the distribution of generated print dots (Q) according to the invention. In this case, each original print dot (P) is split into two generated print dots (Q) aligned in the vertical direction, dispensing with the original print dot (P). As can be seen, the distance from each generated print dot (Q) to the original print dot (P), which is in this case imaginary, is 1 / 6 of the separation between original print dots (P), which separation is equal to the length of the side of the corresponding cell.

[0096] The distribution of the generated print dots (Q) in Figure 8 may be achieved when the same main nozzles (C-PR, M-PR, Y-PR, K-PR) are used, without the need to add additional nozzles (C-AD, M-AD, Y-AD, K-AD), with a single pass inkjet printer (10). In this case, the main nozzles (C-PR, M-PR, Y-PR, K-PR) are reconfigured so as to eject the respective droplet volume levels at two dots instead of a single dot for each cell.

[0097] Figure 9 shows a fourth example of the distribution of generated print dots (Q). In this case, the original print dot (P) is maintained and two generated print dots (Q) per cell or original print dot (P) are introduced, aligned in the vertical direction. As in the case of Figure 8, this arrangement of generated print dots (Q) may be achieved when the same, additional (C-AD, M-AD, Y-AD, K-AD) printing nozzle is used to eject the two dots of each cell, with a single pass inkjet printer (10).

[0098] Returning to Figure 3, and in conjunction with Figures 10 and 11, an embodiment of a method and system according to the invention is described below. The embodiment described is applied to the case in which it is desired to print the same sub-area as in Figure 3, which corresponds to the ejection of droplets of ink according to the non-reprocessed ejection commands, by means of the main nozzles (C-PR, M-PR, Y-PR, K-PR) and at the original print dots (P) distributed as shown in Figure 4.

[0099] To this end, as well as using the original print dots (P), two generated print dots (Q) per original print dot (P), or per cell, are introduced, in accordance with a distribution like that shown in in Figure 9.

[0100] The method according to this embodiment is applied by selecting a maximum droplet volume level for the respective reassigned droplet volume levels. The reassigned droplet volume levels are determined by redistributing the droplet volume level that would correspond to each original print dot (P), if they were ejected following the non-reprocessed ejection commands (as in Figure 3), between the new print dots, in this case between the original print dot itself (P) and the two generated print dots (Q).

[0101] As regards the colour of the ink of the new droplets ejected, the same colour of ink is chosen as would be ejected at the original print dot (P) according to the non-reprocessed ejection commands. In other words, the colour of the ink is maintained according to the new ejection commands after reprocessing.

[0102] Figure 10 shows an exemplary embodiment in which the maximum droplet volume level selected is level 2. As in Figure 3, a single circle means that the droplet volume level of the droplet of ink deposited is level 1, two concentric circles represent level 2 and three concentric circles would represent level 3.

[0103] Thus, for example, the ejection in the cell of row 1 and column 1 is not changed, since it was already level 2 originally. However, in the case of, for example, the ejection in the cell of row 1 and column 3 it is modified, the level being reduced from 3 to 2 at the original print dot itself (P) and, so that the total droplet volume level of the cell remains equal to the original level 3 (P), a droplet of level 1 is introduced at one of the two generated print dots (Q). Randomly, the lower generated print dot (Q) has been selected for this cell.

[0104] Therefore, for the purposes of this reassignment of droplet volume levels, a criterion of minimum distortion of the original droplet is followed. That is, for example, in the cells with original level 3, another option would have been to select level 2 at any of the generated print dots (Q) and level 1 at the original print dot itself (P). However, this option would involve greater distortion with respect to the original droplet, in which the greater part of the ink ejected in the cell is concentrated.

[0105] In the exemplary embodiment of Figure 11 the maximum droplet volume level selected is level 1, the droplets being represented by a single circle at the corresponding print dots.

[0106] Thus, for example, the ejection in the cell of row 1 and column 1 is modified, such that in order for the total droplet volume level to be level 2, at the actual original dot (P) a droplet of level 1 is ejected and at one of the generated print dots (Q) another droplet of level 1 is ejected. In this cell, for the ejection of the other droplet the lower generated print dot (Q) has been selected at random, but the upper generated print dot (Q) could have been selected, as in the case of the cell of row 2 and column 2.

[0107] Figure 12 shows a detail of the arrangement of the nozzles in a single pass inkjet printer (10), according to an embodiment of the system of the invention, and for the purpose of carrying out the exemplary embodiment of the method which has been described with reference to Figures 10 and 11.

[0108] The nozzles are arranged in bars of nozzles (11, 12, 13, 14; 21, 22, 23, 24). For example, Figure 12 shows, for the colour K, a bar of main nozzles and a bar of additional nozzles. The additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged staggered with respect to the main nozzles (C-PR, M-PR, Y-PR, K-PR), offset by a distance "δ".

[0109] With this configuration of offset nozzles, the distribution of original print dots (P) and generated print dots (Q) shown in Figure 9 may be obtained. The additional nozzles (C-AD, M-AD, Y-AD, K-AD) eject at two generated dots (Q) per cell, which makes it possible to use the same additional nozzle (C-AD, M-AD, Y-AD, K-AD) to generate two print dots and, therefore, improve the efficiency of the method and of the system.

[0110] In general, for a single pass inkjet printer (10), for example, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) may be arranged interspersed or staggered with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR). Likewise, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) may be arranged aligned with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR) in rows parallel to the vertical direction, as shown in Figure 13.

[0111] As stated above, the option of including additional nozzles offers the additional advantage of having redundant nozzles, in particular when selectively the digital printing method is not applied and therefore printing is carried out directly from the ejection commands. This is applicable, for example, to the arrangements of nozzles (aligned) shown in Figure 13. Equally, it may also be applicable to the arrangements of nozzles (offset) shown in Figure 12, considering that the distance "δ" would be sufficiently small to be noticeable in the printout.

[0112] Figure 14 shows another embodiment of a head or bar of nozzles (11, 12, 13 and 14; 21, 22, 23, 24) that may be used in the invention. In this embodiment, the nozzles are in a staggered arrangement forming part of the same head. A staggered arrangement gives a greater printing resolution (there being double the nozzles per unit length) and the same droplet volume levels, compared to a head in which the same nozzles are arranged in a single row.

[0113] Preferably, as shown in Figures 12 to 14, the nozzles are arranged grouped together in sets of nozzles for each colour. Likewise, the main nozzles (C-PR, M-PR, Y-PR, K-PR) and the additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged, respectively, grouped together.

[0114] Advantageously, the nozzles of redundant bars may be used as additional nozzles (C-AD, M-AD, Y-AD, K-AD), without negatively affecting the performance of the inkjet printer (10). Or seen another way, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) may be used as redundant nozzles, increasing the availability of the inkjet printer (10) and, therefore, of the method and system.

[0115] There are many options regarding the design of the distribution of the print dots, depending on the arrangement of the main nozzles (C-PR, M-PR, Y-PR, K-PR) and / or additional nozzles (C-AD, M-AD, Y-AD, K-AD), and on the instant of discharge of the nozzles. For example, the inkjet printer (10) may be configured such that the generated print dots (Q) are arranged vertically, horizontally and / or diagonally with respect to the original print dot (P).

[0116] More particularly, with respect to an original print dot (P), at least one generated print dot (Q) may be arranged, for example, in a direction of alignment of original dots (P), in a direction perpendicular to said direction of alignment and / or in a direction diagonal to the above, preferably along any of the bisectors thereof, and, for each one of said directions, to one side and / or to the other side of the original print dot (P).

[0117] Preferably, the invention is designed for printing with small reassigned droplet volume levels, in particular with a droplet volume deposited per print dot which is smaller than or equal to 15 pL (picolitres), preferably than 10 pL, more preferably than 5 pL.

[0118] The use of small droplet volumes makes it possible to achieve a greater resolution and quality of printing. Furthermore, as stated above, it has the advantage of allowing printing that has a reduced or no effect on the properties of the substrate, coating and / or ink, such that it is even possible to dispense with primer to control the expansion of the droplets.

[0119] Figure 15 shows the effect resulting from the reduction of the droplet volume or of the reassigned droplet volume level in the area of deposition of the droplet. For droplets of greater volume, the area of deposition ("α") is greater than the area of deposition ("α'") for droplets of smaller volume, thus minimizing the interaction between the ink and the substrate or coating on which the droplet is deposited.

[0120] The printing method and system according to the invention is not limited to decorative printing, but is also applicable to textures. Thus, as shown in Figure 16, the printing may be used to generate a texture in a substrate or coating of the substrate onto which the ink is directly ejected.

[0121] A smaller droplet volume produces a smaller expansion of the droplets and therefore more defined textures. Moreover, a smaller droplet volume may contribute to creating a relief of smaller depth ("ξ'") than the depth ("5") resulting from a droplet of greater volume.

[0122] Lastly, Figure 17 schematically depicts an embodiment of a digital printing system according to the invention. The system (1) comprises a single pass inkjet printer (10), provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined.

[0123] The system (1) is configured to carry out a method as described above, in particular comprising a computer (20) on which, in particular, computer software for carrying out said method has been installed.

[0124] The substrate (2) to be printed is supplied to the system (1) and conveyed through the various stations of the system (1) by a conveyor means (30) which comprises a conveyor belt (31).

[0125] First, the substrate passes through a station for applying a coating (40) by roller so as to spread a primer onto which the droplets of ink of the printout are ejected directly. The coating is partially cured in the curing station (50) before being printed, so as to optimize the properties of adhesion of the ink to the coating and adhesion of the coating to the rest of the substrate (2).

[0126] Next, the substrate is printed by means of the inkjet printer (10). The inkjet printer (10) comprises main nozzles (C-PR, M-PR, Y-PR, K-PR) and additional nozzles (C-AD, M-AD, Y-AD, K-AD) for each colour (C, M, Y, K), grouped together in respective bars, with their corresponding heads. Thus, the bars (11, 12, 13 and 14) are bars of main nozzles (C-PR, M-PR, Y-PR, K-PR), respectively, for the colour C, M, Y and K, whereas the bars (21, 22, 23 and 24) are bars of additional nozzles (C-AD, M-AD, Y-AD, K-AD), respectively, for the colour C, M, Y and K.

[0127] After each group of bars of nozzles of each colour, the system (1) includes respective pinning lamps for pinning the droplets of ink (15, 16, 17, 18). Finally, the system (1) includes a curing station (60) to complete the curing of the printout and coating.

[0128] To sum up, as stated in the present specification, the invention provides a method and system that overcome the limitations of the prior art, making it possible, in particular, to reduce the dependency of the ink on the primer of the substrate and providing additional technical advantages.

[0129] To this end, the invention is not limited to the embodiments set out, but includes all variants, modifications and combinations that fall within the scope of the attached claims.List of reference signs

[0130] 1Printing system 2Substrate to be printed 10Inkjet printer 11, 12, 13, 14Printing bars of main nozzles 15, 16, 17, 18Pinning lamps 20Computer processor 21, 22, 23, 24Printing bars of additional nozzles 30Conveyor means 31Conveyor belt 40Station for applying the coating 50Station for curing the coating 60Station for curing the printout

Examples

Embodiment Construction

[0067]In the description of all of the figures, the reference signs relate to the system shown in Figure 17.

[0068]Figure 1 shows a flow chart of a known method for digital printing by means of an inkjet printer (10). The inkjet printer (10) is configured to provide a printing resolution and droplet volume levels which are predetermined.

[0069]To print a digital image with a given image definition or resolution, in a printout area of a substrate and with the printing resolution of the inkjet printer (10), the digital image is processed, for example using RIP processing software. The RIP software converts the pixels of the digital image into ejection commands for the ejection of droplets of ink in the printout area of the substrate.

[0070]The inkjet printing of the image is carried out in such a way that each print dot of the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time.

[0071]In the context of t...

SUBJECT MATTER OF THE INVENTION

[0001] The present invention relates to a method and a system for digital printing by means of an inkjet printer. More specifically, the invention aims to provide improvements to the way in which the droplets of ink are ejected at the print dots through the ink injection nozzles of the printer. The invention also relates to computer software that facilitates the implementation of the method of the invention.BACKGROUND ART

[0002] Inkjet printing has been widely used in the field of digital printing, both on an industrial level and by individuals, owing to its inherent capacity to print digital images with a high resolution, quality and performance.

[0003] Inkjet printers work by controlled ejection of droplets of ink through nozzles. To this end, the starting point is the digital image to be printed, which is processed so as to obtain commands for the ejection of ink droplets, in such a way that each print dot of the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time.

[0004] The printing resolution is predetermined by the number of nozzles available for the duration of printing for the various dots in the printout area at which the droplets of ink are ejected. Conventionally, the printing resolution is expressed in dots per inch.

[0005] Likewise, the droplet volume levels that can be ejected by each nozzle are predetermined. The inkjet printers that are currently available are usually configured with various droplet volume levels, since a higher number of droplet volume levels allows more precise control over the amount of ink deposited, improving among other things the gradation of colour tones in the printout and, therefore, the quality of printing.

[0006] For example, in the case of single pass inkjet printers, the nozzles are usually arranged on bars of heads with nozzles aligned along the bar, perpendicularly to the direction in which the substrate to be printed is conveyed. In this case, the printing resolution is determined, in the horizontal direction (perpendicular to the direction in which the substrate is conveyed), by the number of nozzles per unit length that are arranged in said horizontal direction for each colour.

[0007] As for the resolution in the vertical direction (parallel to the direction in which the substrate is conveyed), this is determined by the number of different print dots, with their corresponding droplet volume levels, that the printer can deposit per unit length in the vertical direction. The vertical resolution depends, in particular, on the number of nozzles aligned in the vertical direction, and / or on the number of ejections that each nozzle can produce per unit length that the substrate moves in said direction.

[0008] The digital image is processed so as to be converted into print dots in the printout area, with the printing resolution determined. The various colours of the image are formed by superposition of print dots of ink droplets of a limited number of colours. To this end, use is usually made, in particular, of basic colours such as cyan, magenta, yellow and black, or mixtures of basic colours such as green, violet, orange, etc. Furthermore, the different droplet levels of each print dot make it possible to produce gradated colour tones or grayscale effects.

[0009] Usually, the digital image is processed by means of computer software called RIP (raster image processor). This software converts the digital image files into commands for the ejection of ink by the nozzles, managing the distribution of the print dots, droplet volumes, colours, etc. depending on the printing resolution, the size of the printout area, the definition of the image, etc. so as to optimize printing quality.

[0010] Processing of the digital image, in particular using the RIP, allows fundamental management of the control over the ejection of ink such that, for example, the droplet volume levels ejected at each print dot are determined after said processing, so as to obtain the predetermined printing resolution with optimized printing quality.

[0011] Therefore, a user or operator of the inkjet printer has little or no leeway for control over the ejection of ink, as this is dictated by the processing of the digital image, specifically by the RIP. This limits, in particular, the versatility of known inkjet printing methods and systems.

[0012] Mention must be made in particular of the limitation of current methods and systems as regards the dependency of the ink on the priming of the substrate on which it is printed, which requires that the type of priming be adapted to the ink and substrate used.

[0013] An aim of the invention is to overcome the limitations of current technologies, such as the dependency of the ink on the priming of the substrate, improving versatility while maintaining, and even improving, the quality, availability and performance of known inkjet digital printing methods and systems.SUMMARY OF THE INVENTION

[0014] To achieve the stated aim, and other technical advantages that may become clear from this description, the invention proposes a method for digital printing with control over the volume of ink by means of an inkjet printer. The printer is provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined.

[0015] The method according to the invention, as in known inkjet digital printing methods, comprises processing a digital image to obtain commands for the ejection of ink droplets in a printout area of a substrate, such that each print dot in the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time. Subsequently, printing is carried out on a substrate following the definitive ejection commands.

[0016] Unlike known inkjet digital printing methods, the method according to the invention further comprises reprocessing the ejection commands such that the droplet volume level corresponding to each one of at least one of said print dots, original, according to the non-reprocessed ejection commands, is redistributed between the original print dot itself and / or at least one generated print dot, which is introduced close to said original print dot, by means of respective reassigned droplet volume levels, which are ejected by nozzles.

[0017] The invention thus allows controlled reduction of the ink droplet volume deposited per original print dot, redistributing said volume to generated print dots, which are located close to said original print dot.

[0018] Because the droplet volume ejected is reduced, the ink droplets of smaller volume expand to a lesser extent once deposited on the substrate, since they have a smaller quantity of liquid that can spread on the surface of the substrate.

[0019] The expansion of the ink droplets on the substrate, in general, may also depend on other factors, including properties of the ink droplets, such as viscosity or surface tension, properties of the substrate, such as surface energy, porosity or hydrophilicity, or environmental conditions, such as temperature or relative humidity. However, the droplet volume significantly influences the expansion of the droplets.

[0020] The invention therefore makes it possible, in particular, to minimize or eliminate the dependency relationship between the printing method and the ink and the substrate or priming of the substrate, with regards to the influence thereof on the expansion of the ink droplets. In particular, it is even possible to dispense with priming of the substrate, unlike in conventional printing methods.

[0021] Furthermore, the resolution and quality of printing are not affected by the application of the method of the invention, compared to a digital printing method applied under the same conditions but according to non-reprocessed ejection commands. This is because the introduction of the generated print dots is carried out per original print dot, and they are located close to the latter, with only a redistribution of the droplet volume, such that the visual appearance of the printed image and its apparent quality are maintained.

[0022] In the context of the invention, "print dot" means a theoretical or nominal dot in the printout area, at which, like a target or objective, a droplet volume level is ejected, by a nozzle and at an instant in time which are predetermined, so as to generate the printed damage. The print dot, therefore, does not necessarily coincide with the dot at which the nozzle ejects said droplet volume at said instant in time, there being tolerances that are managed in a controlled manner.

[0023] In general, at each print dot, a plurality of droplet volume levels may be ejected, by different nozzles or by the same nozzle at different instants in time. For example, single pass inkjet printers are usually configured such that for each print dot, each nozzle of a different colour, for example cyan, magenta, yellow and black, ejects a droplet volume level.

[0024] "Droplet volume level" means each of the quantities of a theoretical or nominal volume of an ink droplet that is ejected by the nozzle so as to be deposited at each print dot. The term "droplet volume level" includes the level zero when the quantity ejected is zero.

[0025] Unlike the prior art, the invention comprises a reassignment of droplet volume levels per original print dot between the original print dot itself and generated print dots. Instead of the corresponding droplet volume level being ejected at the original print dot according to the non-reprocessed ejection commands, said droplet volume level is redistributed between the original print dot itself and / or at least one generated print dot, by means of respective reassigned droplet volume levels.

[0026] According to the invention, the reassignment of droplet volume levels by means of the step of reprocessing may be carried out, in particular, for any of the original print dots or for each and every one of said original print dots, of the printout area or part of the printout area.

[0027] "Redistribution of the droplet volume level" means that the volume corresponding to the original print dot, according to the non-reprocessed ejection commands, is split between the original print dot itself and / or the generated print dots, preferably equally.

[0028] Therefore, said volume corresponding to the original print dot is, in particular, substantially equal, or as close as possible, to the sum of the redistributed droplet volumes, corresponding to the reassigned droplet volume levels, more particularly, exceeding or not exceeding said volume corresponding to the original print dot.

[0029] According to the invention, the generated print dot or dots are introduced close to the corresponding original print dot. In the context of the invention, "close to" means in a zone surrounding said original print dot corresponding to the printing resolution of the printer. In particular, at a distance from the original dot which is smaller than the distance separating original print dots corresponding to the printing resolution. Preferably, located at a distance of less than half of said separation distance, more preferably less than one third.

[0030] An increasing proximity of the generated print dots to the original print dot promotes the similarity of the image printed with the method of the invention, with respect to the same printed image if it was printed according to the non-reprocessed ejection commands.

[0031] If printing is in colour, the colour that is reassigned to the original print dot itself and / or the at least one generated print dot after reprocessing is, preferably, the colour of the ink that would be ejected at the corresponding original print dot according to the non-reprocessed ejection commands.

[0032] Colours usually used in inkjet printing are basic colours such as, for example, cyan (C), magenta (M), yellow (Y) and black (K). Furthermore, depending on the type of substrate to be printed or on the chromatic characteristics of the image to be printed, other colours are often used, such as for example, green (G), violet (V), orange (O), light black (LK), light magenta (LM), etc.

[0033] In general, preferably, any characteristic of the ink (such as the colour) at the original print dot according to the non-reprocessed ejection commands is reassigned, by means of the reprocessing according to the invention, to the original print dot itself and / or the at least one corresponding generated print dot.

[0034] In this regard, the underlying criterion is to replicate these characteristics at all the dots between which the droplet volume level per original print dot is redistributed, to ensure that the appearance of the printed image resulting from the application of the method of the invention is similar to what would have been the result if it had been applied without the reprocessing step.

[0035] The printing method according to the invention is not limited to the printing of decorative images, monochrome or in colour, but may also be used, as an alternative or in addition to the generation of decorative images, for generating textures.

[0036] "Texture" refers to a surface with a relief. To generate textures, use may be made of a coating, for example in the form of a base layer, on which the impact, contact and / or mixture of the ejected ink droplets produces or helps to produce protruding and / or recessed reliefs on the surface of the base layer. Preferably, use may be made of substantially transparent ink to generate textures, in particular in combination with decorations. Moreover, a varnish, especially a substantially transparent varnish, may be used as base layer.

[0037] In particular, the droplet volume ejected at each print dot corresponding to the respective reassigned droplet volume levels has an influence on the depth and / or height of the texture generated at said print dots, and therefore the method according to the invention makes it possible to obtain various textures on various substrates, printout areas, digital images or parts thereof, according to the various reassigned droplet volume levels at the various print dots.

[0038] Therefore, by controlling the volume of ink according to the invention, in other words, specifically, the reassigned ink volume levels, it is possible to control the depth and / or height of the texture generated. In particular, this may also be used to control the degree of matt or gloss of a printed decoration, mainly as a result of the effect of the lower reflection of light on rough surfaces.

[0039] Advantageously, in general, owing to the fact that ink droplets of smaller volume expand to a lesser extent once deposited on the substrate, in particular, this being controllable according to the invention, it is possible to obtain printouts with greater definition, specifically textures with greater definition. Moreover, as mentioned above, the dependency of the printing on the coating, base layer or priming of the substrate on which the ink droplets are ejected is reduced or eliminated.

[0040] Moreover, as regards the nozzles used in the method according to the invention, in the invention use may preferably be made of the same nozzles as would be used for printing with the predetermined resolution and droplet volume levels according to the non-reprocessed ejection commands, in other words ejecting the droplet volume levels, without reassignment, only at the original print dots. In the context of the invention, these nozzles are referred to as the main nozzles.

[0041] Alternatively or in addition to the use of the main nozzles, the respective reassigned droplet volume levels may be ejected by additional nozzles, which are additional to the main nozzles, of the inkjet printer. In particular, use may also be made of only the main nozzles or only the additional nozzles for the ejection of the reassigned droplet volume levels.

[0042] The option of including additional nozzles offers the additional advantage of having redundant nozzles, in particular when selectively the digital printing method is not applied and therefore printing is carried out directly from the ejection commands. Availability of the machine is thereby increased.

[0043] The additional nozzles may be selected to have an arrangement or configuration such that, by themselves and independently of the main nozzles, they provide a printing resolution that is greater than or equal to the main nozzles, and / or to have a maximum droplet volume level per nozzle that is smaller than or equal to that of the main nozzles. It is thus possible to obtain arrangements of generated print dots closer to original print dots according to the invention.

[0044] Preferably, the same nozzle, main or additional, may eject the respective reassigned droplet volume levels at a plurality of generated print dots, per original print dot.

[0045] In this way, the same nozzle is used to generate multiple print dots. In particular, the main nozzles, which in principle are used to eject a single print dot, corresponding to the original print dot associated with the predetermined printing resolution, may be used to eject more than one print dot. In particular, they may be used to eject at least one original dot and at least one generated dot, or at least two generated dots.

[0046] This is possible according to the invention, for example, by reducing the printing speed, since this makes it possible to increase the number of discharges per nozzle per unit area of a printout. It is also possible by limiting the number of droplet volume levels of the nozzles. For example, if only one droplet volume level (in addition to the zero level) is ejected, it is possible to maximize the number of discharges of droplet volume levels.

[0047] Advantageously, the method according to the invention may be applied selectively to substrates, printout areas, digital images or parts of the same substrate, printout area or digital image. In particular, the selective application may be carried out with respect to other substrates, printout areas, digital images or parts of the same substrate, printout area or digital image for which ink is ejected only at original print dots according to the non-reprocessed ejection commands.

[0048] Selective application of the method according to the invention means, in particular, the activation or deactivation of reprocessing of the ejection commands for certain original print dots as desired. Such print dots may correspond, in particular, to physical dots of the substrate or of the printout area, or to pixels of the digital image, according to the processing of the digital image carried out.

[0049] Likewise, the method according to the invention may also be applied differently to substrates, printout areas, digital images or parts of the same substrate, printout area or digital image. In particular, the method may be applied such that the introduction of generated print dots, and / or the redistribution of the droplet volume level, is different for different substrates, printout areas, digital images or parts of the same substrate, printout area or digital image.

[0050] In particular, the reprocessing step may be carried out in a different manner for different substrates, printout areas, digital images or parts thereof, as desired. This may be useful, for example, so as to be able to print areas of saturated colour, with droplets of larger size, and areas that require greater gradation of colour, or definition, using droplets of smaller size.

[0051] "Different introduction of the generated print dots" means, for example, that the number of generated print dots, per original print dot, is different and / or that the location of the generated print dots with respect to the original print dot is different, for example following a different pattern.

[0052] "Different redistribution of the generated print dots" means the different ways in which the volume of ink can be split between the reassigned droplet volume levels, per original print dot. For example, different modes of redistribution may be based on setting a maximum droplet volume or different maximum reassigned droplet volume levels.

[0053] Any mode of redistribution that can be envisaged may be applied according to the invention. A priori, once the number of generated print dots and their location have been decided, there are as many modes of redistribution as there are possibilities of sharing the volume of ink between the different ink volume levels available.

[0054] Likewise, when applying the reprocessing according to the invention, introduction and / or redistribution criteria may be set, these being selectable by means of other control variables by the operator implementing the method. For example, a general criterion may be based on a minimum distortion of original droplet volume levels, so that the original droplet volume level, which would be ejected according to the non-reprocessed ejection commands, is reduced as little as possible.

[0055] Another example of a selection criterion may be based on choosing one of the possible reassigned droplet volume levels when the possibilities are that their sum exceeds or does not exceed the original droplet volume level.

[0056] In general, the introduction and / or redistribution may also be random, in particular in combination with other criteria or modes of introduction and / or redistribution. This is compatible with the use of stochastic inkjet printing techniques, which are usually used in the processing of the digital images for printing.

[0057] According to the invention, the method may also be applied selectively and / or differently to different substrates, depending on properties of the ink and / or depending on whether or not there is a coating on the substrate on which the ink is ejected, in particular depending on properties of the coating or of the substrate, more particularly depending on the thickness of the coating.

[0058] The properties, of the ink or of the coating or of the substrate, may be, in particular, physical or chemical properties, for example viscosity, surface tension, chemical composition, etc.

[0059] "Coating" means, in particular, a primer, the main function of which is to prepare the surface of the substrate to receive the ink, in particular ensuring adhesion of the ink to the substrate, and / or a base layer, the function of which is to act as a base for generating a texture.

[0060] Thus, the invention makes it possible for the same method to be used with different types of coatings and / or different types of ink for printing on a substrate, adapting the mode of application of the method to the type of coating and / or ink.

[0061] In particular, the invention makes it possible to dispense with a coating or primer, for example, by selecting maximum reassigned droplet volume levels that are sufficiently small to minimize or disregard the expansion of the droplets of ink deposited on the surface of the substrate.

[0062] According to another aspect, the invention relates to computer software for carrying out a method for digital printing as described above. The software comprises instructions such that, when the software is executed by a computer, the computer performs the reprocessing of the ejection commands, obtained, in particular, using computer software for processing digital images (RIP), from the digital image, so as to provide new ejection commands for ejection at original print dots and / or generated print dots.

[0063] The computer software according to the invention may include or be included in software for processing the digital image such as, for example, the RIP.

[0064] Lastly, the invention also relates to a system for digital printing with control over the volume of ink. The system comprises an inkjet printer, in particular a single pass inkjet printer, provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined.

[0065] According to the invention the system is configured to carry out a method as described above. In particular, the system comprises a computer on which computer software as described above may be installed or is installed.BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The invention is described in more detail below, by way of non-limiting illustration, and with reference to a preferred embodiment by way of example, with reference to the attached drawings. In the drawings: Figure 1 shows a flow chart of an inkjet digital printing method according to the prior art. Figure 2 shows a flow chart of an inkjet digital printing method according to the invention. Figures 3, 4 and 5 relate to an embodiment of a printing method and system of the prior art or in which the nozzles of the inkjet printer eject the droplet volume levels according to non-reprocessed ink ejection commands. Figures 6, 7, 8 and 9 depict various embodiments according to the invention corresponding to various positions of the generated print dots, with respect to the original print dots. Figures 10 and 11 depict two exemplary embodiments of the invention, in correspondence with the embodiment depicted in Figure 9. Figures 12 and 13 depict various arrangements of main and additional nozzles, for various embodiments of a printing system according to the invention in which the inkjet printer is a single pass inkjet printer. Figure 14 shows an embodiment of a nozzle head for a single pass inkjet printer. Figure 15 depicts droplets of ink deposited on the substrate to be printed. It can be seen in the figure that the droplets of greater volume are spread over a greater area than the droplets of smaller volume. Figure 16 shows an exemplary embodiment according to the invention in which the printing is used to generate a texture. It can be seen in the figure that the droplets of greater volume are introduced at a greater depth than the droplets of smaller volume. Figure 17 schematically depicts an embodiment of a printing system according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0067] In the description of all of the figures, the reference signs relate to the system shown in Figure 17.

[0068] Figure 1 shows a flow chart of a known method for digital printing by means of an inkjet printer (10). The inkjet printer (10) is configured to provide a printing resolution and droplet volume levels which are predetermined.

[0069] To print a digital image with a given image definition or resolution, in a printout area of a substrate and with the printing resolution of the inkjet printer (10), the digital image is processed, for example using RIP processing software. The RIP software converts the pixels of the digital image into ejection commands for the ejection of droplets of ink in the printout area of the substrate.

[0070] The inkjet printing of the image is carried out in such a way that each print dot of the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time.

[0071] In the context of the present invention, the term "digital image" includes the concept of a digital file that stores digital information in a format suitable for printing. The digital image may be in raster or vector format. "Raster format" refers to the form of storage of information on the image in which the image is composed of a map or matrix of pixels, wherein each pixel individually stores a value of colour, depth or height of relief (in the case of textures), location, etc., which is produced in the printout.

[0072] In particular, when the digital image is in vector format, the step of processing to obtain the ink droplet ejection commands may include a rasterizing sub-step for changing the digital image from vector format to raster format and subsequent processing of pixels.

[0073] The definition of the digital image, also referred to as the resolution of the digital image, of the digital images in raster format, represents the quality of the actual digital image and depends on the number of pixels it contains, the quality being higher the greater said number of pixels.

[0074] In comparison with Figure 1, Figure 2 shows a flow chart of a method for digital printing by means of an inkjet printer (10) according to the invention.

[0075] Unlike prior art methods for inkjet digital printing, the printing method according to the invention comprises a step of reprocessing of the ejection commands so as to generate new ejection commands.

[0076] With the new ejection commands generated by the reprocessing, the droplet volume level that would correspond to each one of the original print dots (P) according to the non-reprocessed ejection commands are redistributed between the original print dot itself (P) and / or at least one generated print dot (Q), which is introduced close to said original print dot (P), by means of respective reassigned droplet volume levels. Printing is carried out by ejecting said reassigned droplet volume levels.

[0077] In particular, the way in which the reprocessing is carried out may be controlled, for example, by requesting a droplet volume or reassigned droplet volume level or by means of other control variables.

[0078] The phases of processing and reprocessing may be carried out simultaneously, merged, with identical results.

[0079] With reference to Figures 3 to 5, an embodiment of a prior art method and system is explained below, before then explaining the changes made, in this embodiment, according to the invention.

[0080] Figure 3 shows the droplets of ink deposited in a sub-area of the printout area, with their corresponding colours (C, M, Y, K) according to an exemplary embodiment. A single circle means that the droplet volume level of the droplet of ink deposited is level 1, two concentric circles represent a level 2 and three concentric circles a level 3.

[0081] The sub-area in question measures 3x3 cells, wherein each cell corresponds to a print dot. The printing resolution is determined by the number of print dots per unit area. The processing of the digital image, in particular the RIP, makes it possible to convert pixels of the digital image, or associated with the digital image, into print dots of the various cells, adjusting the digital image to the printout area selected.

[0082] To adjust the digital image to the printout area selected, the processing of the digital image may comprise generating new pixels from native pixels of the digital image, by interpolating the information therefrom, or deleting native pixels of the digital image, eliminating the information from the digital image. Likewise, the processing may comprise carrying out an adjustment of the digital image consisting in modifying native pixels on the basis of native pixels neighbouring said pixels, for example, so as to simulate colours or tones to be produced in the printout. The new pixels, specifically pixels that have been interpolated, modified, etc., are examples of pixels associated with the digital image in the context of the invention.

[0083] For the sake of simplicity but without thereby limiting the invention, in the exemplary embodiments illustrated, a droplet of a single colour of ink has been ejected at each print dot of the sub-area. However, in particular, several droplets of different colours may be ejected, and would be superposed on one another, at one and the same print dot.

[0084] Figure 4 shows the positions of the print dots in the printout sub-area. It depicts original print dots (P), since these are the print dots at which the droplets of ink are ejected according to the non-reprocessed ejection commands. The original print dots (P) are represented in the figures with an "x".

[0085] Figure 5 shows the arrangement of the nozzles (each nozzle is represented by a triangle in the figures) according to an embodiment of the invention in which a single pass inkjet printer (10) is used, wherein the nozzles are grouped together in heads for the different colours (C, M, Y, K). These are main nozzles (C-PR, M-PR, Y-PR, K-PR).

[0086] The sub-area to be printed is shown in the lower part of Figure 5. As the substrate with the printout area moves in the (vertical) direction indicated by the arrows, the main nozzles (C-PR, M-PR, Y-PR, K-PR) corresponding to each colour eject the corresponding droplet volume level in the printout sub-area, so as to obtain the distribution of droplets of ink shown in Figure 3.

[0087] Preferably, a single pass inkjet printer (10) is used according to the invention, although any type of inkjet printer may be used. The nozzles are usually arranged as shown in Figure 5, aligned with one another in rows parallel to the horizontal direction, perpendicular to the vertical direction in which the substrate is conveyed.

[0088] Likewise, the nozzles arranged in rows are usually arranged in print heads, which are also grouped together aligned with one another in printing bars (11, 12, 13 and 14; 21, 22, 23, 24), with one bar per colour. In order to have redundancy or alternating use of the nozzles, and therefore greater availability of the inkjet printer (10), there is usually more than one printing bar per colour.

[0089] With reference now to Figures 6 to 9, in comparison with Figure 4, these figures show the positions of the generated print dots (Q), in addition or as an alternative to the original print dots (P). The generated print dots (Q) are represented in the figures by a cross ("+"), being distinguished from the original print dots (P), which are shown with an "x".

[0090] As shown in each of Figures 6 to 9, the generated print dots (Q) are positioned close to the respective original print dot (P). Specifically, they are located within the cell associated with the original print dot (P) with which they are linked.

[0091] The size of each cell of the printout sub-area is directly related to the printing resolution. Thus, the printing resolution is given by the number of cells per unit length in the printed area, in other words the number of original print dots (P) available for the ejection of the droplets of ink according to the non-reprocessed ejection commands.

[0092] Indeed, when applying the method according to the invention, the printing resolution is not changed since the generated print dots (Q) replicate the information associated with each original print dot (P) with which they are linked per cell.

[0093] For example, in Figure 6 the generated print dots (Q) are located at a distance from the respective original print dot (P) which is equal to ¼ of the separation between original print dots (P) in the printout sub-area, which separation is equal to the length of the side of the corresponding cell.

[0094] In the example of Figure 7, unlike that in Figure 6, for each original print dot (P) there are two generated print dots (Q), which are located on either side of said print dot (P). A greater number of print dots (P, Q) makes it possible to increase the versatility, as well as the availability of the method and system of the invention.

[0095] Figure 8 shows another example of the distribution of generated print dots (Q) according to the invention. In this case, each original print dot (P) is split into two generated print dots (Q) aligned in the vertical direction, dispensing with the original print dot (P). As can be seen, the distance from each generated print dot (Q) to the original print dot (P), which is in this case imaginary, is 1 / 6 of the separation between original print dots (P), which separation is equal to the length of the side of the corresponding cell.

[0096] The distribution of the generated print dots (Q) in Figure 8 may be achieved when the same main nozzles (C-PR, M-PR, Y-PR, K-PR) are used, without the need to add additional nozzles (C-AD, M-AD, Y-AD, K-AD), with a single pass inkjet printer (10). In this case, the main nozzles (C-PR, M-PR, Y-PR, K-PR) are reconfigured so as to eject the respective droplet volume levels at two dots instead of a single dot for each cell.

[0097] Figure 9 shows a fourth example of the distribution of generated print dots (Q). In this case, the original print dot (P) is maintained and two generated print dots (Q) per cell or original print dot (P) are introduced, aligned in the vertical direction. As in the case of Figure 8, this arrangement of generated print dots (Q) may be achieved when the same, additional (C-AD, M-AD, Y-AD, K-AD) printing nozzle is used to eject the two dots of each cell, with a single pass inkjet printer (10).

[0098] Returning to Figure 3, and in conjunction with Figures 10 and 11, an embodiment of a method and system according to the invention is described below. The embodiment described is applied to the case in which it is desired to print the same sub-area as in Figure 3, which corresponds to the ejection of droplets of ink according to the non-reprocessed ejection commands, by means of the main nozzles (C-PR, M-PR, Y-PR, K-PR) and at the original print dots (P) distributed as shown in Figure 4.

[0099] To this end, as well as using the original print dots (P), two generated print dots (Q) per original print dot (P), or per cell, are introduced, in accordance with a distribution like that shown in in Figure 9.

[0100] The method according to this embodiment is applied by selecting a maximum droplet volume level for the respective reassigned droplet volume levels. The reassigned droplet volume levels are determined by redistributing the droplet volume level that would correspond to each original print dot (P), if they were ejected following the non-reprocessed ejection commands (as in Figure 3), between the new print dots, in this case between the original print dot itself (P) and the two generated print dots (Q).

[0101] As regards the colour of the ink of the new droplets ejected, the same colour of ink is chosen as would be ejected at the original print dot (P) according to the non-reprocessed ejection commands. In other words, the colour of the ink is maintained according to the new ejection commands after reprocessing.

[0102] Figure 10 shows an exemplary embodiment in which the maximum droplet volume level selected is level 2. As in Figure 3, a single circle means that the droplet volume level of the droplet of ink deposited is level 1, two concentric circles represent level 2 and three concentric circles would represent level 3.

[0103] Thus, for example, the ejection in the cell of row 1 and column 1 is not changed, since it was already level 2 originally. However, in the case of, for example, the ejection in the cell of row 1 and column 3 it is modified, the level being reduced from 3 to 2 at the original print dot itself (P) and, so that the total droplet volume level of the cell remains equal to the original level 3 (P), a droplet of level 1 is introduced at one of the two generated print dots (Q). Randomly, the lower generated print dot (Q) has been selected for this cell.

[0104] Therefore, for the purposes of this reassignment of droplet volume levels, a criterion of minimum distortion of the original droplet is followed. That is, for example, in the cells with original level 3, another option would have been to select level 2 at any of the generated print dots (Q) and level 1 at the original print dot itself (P). However, this option would involve greater distortion with respect to the original droplet, in which the greater part of the ink ejected in the cell is concentrated.

[0105] In the exemplary embodiment of Figure 11 the maximum droplet volume level selected is level 1, the droplets being represented by a single circle at the corresponding print dots.

[0106] Thus, for example, the ejection in the cell of row 1 and column 1 is modified, such that in order for the total droplet volume level to be level 2, at the actual original dot (P) a droplet of level 1 is ejected and at one of the generated print dots (Q) another droplet of level 1 is ejected. In this cell, for the ejection of the other droplet the lower generated print dot (Q) has been selected at random, but the upper generated print dot (Q) could have been selected, as in the case of the cell of row 2 and column 2.

[0107] Figure 12 shows a detail of the arrangement of the nozzles in a single pass inkjet printer (10), according to an embodiment of the system of the invention, and for the purpose of carrying out the exemplary embodiment of the method which has been described with reference to Figures 10 and 11.

[0108] The nozzles are arranged in bars of nozzles (11, 12, 13, 14; 21, 22, 23, 24). For example, Figure 12 shows, for the colour K, a bar of main nozzles and a bar of additional nozzles. The additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged staggered with respect to the main nozzles (C-PR, M-PR, Y-PR, K-PR), offset by a distance "δ".

[0109] With this configuration of offset nozzles, the distribution of original print dots (P) and generated print dots (Q) shown in Figure 9 may be obtained. The additional nozzles (C-AD, M-AD, Y-AD, K-AD) eject at two generated dots (Q) per cell, which makes it possible to use the same additional nozzle (C-AD, M-AD, Y-AD, K-AD) to generate two print dots and, therefore, improve the efficiency of the method and of the system.

[0110] In general, for a single pass inkjet printer (10), for example, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) may be arranged interspersed or staggered with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR). Likewise, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) may be arranged aligned with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR) in rows parallel to the vertical direction, as shown in Figure 13.

[0111] As stated above, the option of including additional nozzles offers the additional advantage of having redundant nozzles, in particular when selectively the digital printing method is not applied and therefore printing is carried out directly from the ejection commands. This is applicable, for example, to the arrangements of nozzles (aligned) shown in Figure 13. Equally, it may also be applicable to the arrangements of nozzles (offset) shown in Figure 12, considering that the distance "δ" would be sufficiently small to be noticeable in the printout.

[0112] Figure 14 shows another embodiment of a head or bar of nozzles (11, 12, 13 and 14; 21, 22, 23, 24) that may be used in the invention. In this embodiment, the nozzles are in a staggered arrangement forming part of the same head. A staggered arrangement gives a greater printing resolution (there being double the nozzles per unit length) and the same droplet volume levels, compared to a head in which the same nozzles are arranged in a single row.

[0113] Preferably, as shown in Figures 12 to 14, the nozzles are arranged grouped together in sets of nozzles for each colour. Likewise, the main nozzles (C-PR, M-PR, Y-PR, K-PR) and the additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged, respectively, grouped together.

[0114] Advantageously, the nozzles of redundant bars may be used as additional nozzles (C-AD, M-AD, Y-AD, K-AD), without negatively affecting the performance of the inkjet printer (10). Or seen another way, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) may be used as redundant nozzles, increasing the availability of the inkjet printer (10) and, therefore, of the method and system.

[0115] There are many options regarding the design of the distribution of the print dots, depending on the arrangement of the main nozzles (C-PR, M-PR, Y-PR, K-PR) and / or additional nozzles (C-AD, M-AD, Y-AD, K-AD), and on the instant of discharge of the nozzles. For example, the inkjet printer (10) may be configured such that the generated print dots (Q) are arranged vertically, horizontally and / or diagonally with respect to the original print dot (P).

[0116] More particularly, with respect to an original print dot (P), at least one generated print dot (Q) may be arranged, for example, in a direction of alignment of original dots (P), in a direction perpendicular to said direction of alignment and / or in a direction diagonal to the above, preferably along any of the bisectors thereof, and, for each one of said directions, to one side and / or to the other side of the original print dot (P).

[0117] Preferably, the invention is designed for printing with small reassigned droplet volume levels, in particular with a droplet volume deposited per print dot which is smaller than or equal to 15 pL (picolitres), preferably than 10 pL, more preferably than 5 pL.

[0118] The use of small droplet volumes makes it possible to achieve a greater resolution and quality of printing. Furthermore, as stated above, it has the advantage of allowing printing that has a reduced or no effect on the properties of the substrate, coating and / or ink, such that it is even possible to dispense with primer to control the expansion of the droplets.

[0119] Figure 15 shows the effect resulting from the reduction of the droplet volume or of the reassigned droplet volume level in the area of deposition of the droplet. For droplets of greater volume, the area of deposition ("α") is greater than the area of deposition ("α'") for droplets of smaller volume, thus minimizing the interaction between the ink and the substrate or coating on which the droplet is deposited.

[0120] The printing method and system according to the invention is not limited to decorative printing, but is also applicable to textures. Thus, as shown in Figure 16, the printing may be used to generate a texture in a substrate or coating of the substrate onto which the ink is directly ejected.

[0121] A smaller droplet volume produces a smaller expansion of the droplets and therefore more defined textures. Moreover, a smaller droplet volume may contribute to creating a relief of smaller depth ("ξ'") than the depth ("5") resulting from a droplet of greater volume.

[0122] Lastly, Figure 17 schematically depicts an embodiment of a digital printing system according to the invention. The system (1) comprises a single pass inkjet printer (10), provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined.

[0123] The system (1) is configured to carry out a method as described above, in particular comprising a computer (20) on which, in particular, computer software for carrying out said method has been installed.

[0124] The substrate (2) to be printed is supplied to the system (1) and conveyed through the various stations of the system (1) by a conveyor means (30) which comprises a conveyor belt (31).

[0125] First, the substrate passes through a station for applying a coating (40) by roller so as to spread a primer onto which the droplets of ink of the printout are ejected directly. The coating is partially cured in the curing station (50) before being printed, so as to optimize the properties of adhesion of the ink to the coating and adhesion of the coating to the rest of the substrate (2).

[0126] Next, the substrate is printed by means of the inkjet printer (10). The inkjet printer (10) comprises main nozzles (C-PR, M-PR, Y-PR, K-PR) and additional nozzles (C-AD, M-AD, Y-AD, K-AD) for each colour (C, M, Y, K), grouped together in respective bars, with their corresponding heads. Thus, the bars (11, 12, 13 and 14) are bars of main nozzles (C-PR, M-PR, Y-PR, K-PR), respectively, for the colour C, M, Y and K, whereas the bars (21, 22, 23 and 24) are bars of additional nozzles (C-AD, M-AD, Y-AD, K-AD), respectively, for the colour C, M, Y and K.

[0127] After each group of bars of nozzles of each colour, the system (1) includes respective pinning lamps for pinning the droplets of ink (15, 16, 17, 18). Finally, the system (1) includes a curing station (60) to complete the curing of the printout and coating.

[0128] To sum up, as stated in the present specification, the invention provides a method and system that overcome the limitations of the prior art, making it possible, in particular, to reduce the dependency of the ink on the primer of the substrate and providing additional technical advantages.

[0129] To this end, the invention is not limited to the embodiments set out, but includes all variants, modifications and combinations that fall within the scope of the attached claims.List of reference signs

[0130] 1Printing system 2Substrate to be printed 10Inkjet printer 11, 12, 13, 14Printing bars of main nozzles 15, 16, 17, 18Pinning lamps 20Computer processor 21, 22, 23, 24Printing bars of additional nozzles 30Conveyor means 31Conveyor belt 40Station for applying the coating 50Station for curing the coating 60Station for curing the printout

Examples

Embodiment Construction

[0067]In the description of all of the figures, the reference signs relate to the system shown in Figure 17.

[0068]Figure 1 shows a flow chart of a known method for digital printing by means of an inkjet printer (10). The inkjet printer (10) is configured to provide a printing resolution and droplet volume levels which are predetermined.

[0069]To print a digital image with a given image definition or resolution, in a printout area of a substrate and with the printing resolution of the inkjet printer (10), the digital image is processed, for example using RIP processing software. The RIP software converts the pixels of the digital image into ejection commands for the ejection of droplets of ink in the printout area of the substrate.

[0070]The inkjet printing of the image is carried out in such a way that each print dot of the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time.

[0071]In the context of t...

Claims

1. Method for digital printing with control over the volume of ink, by means of an inkjet printer (10) provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined, such that it comprises processing a digital image to obtain commands for the ejection of ink droplets in a printout area of a substrate (2), such that each print dot in the printout area corresponds to the ejection, at said dot, of a given droplet volume level, by a given nozzle and at a given instant in time, characterized in that it comprises reprocessing the ejection commands such that the droplet volume level corresponding to each one of at least one of said print dots, original (P), according to the non-reprocessed ejection commands, is redistributed between the original print dot itself (P) and / or at least one generated print dot (Q), which is introduced close to said original print dot (P), by means of respective reassigned droplet volume levels, which are ejected by nozzles.

2. Method for digital printing according to Claim 1, characterized in that the respective reassigned droplet volume levels are ejected by main nozzles (C-PR, M-PR, Y-PR, K-PR), with which, according to the non-reprocessed ejection commands, ink would be ejected only at original print dots (P), and / or by additional nozzles (C-AD, M-AD, Y-AD, K-AD) of the inkjet printer (10).

3. Method for digital printing according to Claim 2, characterized in that the same nozzle, main (C-PR, M-PR, Y-PR, K-PR) or additional (C-AD, M-AD, Y-AD, K-AD), ejects the respective reassigned droplet volume levels at a plurality of generated print dots (Q), per original print dot (P).

4. Method for digital printing according to one of the preceding claims, characterized in that the method is applied selectively to substrates (2), printout areas, digital images or parts of the same substrate (2), printout area or digital image, unlike other substrates (2), printout areas, digital images or parts of the same substrate (2), printout area or digital image for which ink is ejected only at original print dots (P) according to the non-reprocessed ejection commands.

5. Method for digital printing according to one of the preceding claims, characterized in that the method is applied differently to substrates (2), printout areas, digital images or parts of the same substrate (2), printout area or digital image, in particular such that the introduction of generated print dots (Q), and / or the redistribution of the droplet volume level, is different for different substrates (2), printout areas, digital images or parts of the same substrate (2), printout area or digital image.

6. Method for digital printing according to either of Claims 4 and 5, characterized in that the method is applied selectively and / or differently to different substrates (2), depending on properties of the ink and / or depending on whether or not there is a coating on the substrate (2) on which the ink is ejected, in particular depending on properties of the coating, more particularly depending on the thickness of the coating.

7. Method for digital printing according to one of the preceding claims, characterized in that the method is applied by selecting a maximum droplet volume level for the respective reassigned droplet volume levels.

8. Method for digital printing according to one of the preceding claims, characterized in that the droplet volume corresponding to the respective reassigned droplet volume levels is smaller than or equal to 15 pL, preferably than 10 pL, more preferably than 5 pL.

9. Method for digital printing according to one of the preceding claims, characterized in that the inkjet printer (10) is a single pass inkjet printer, the substrate (2) being printed while being conveyed in a direction, a vertical direction.

10. Method for digital printing according to Claim 9, characterized in that additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged interspersed or staggered with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR).

11. Method for digital printing according to Claim 9, characterized in that additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged aligned with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR) in rows parallel to the vertical direction.

12. Method for digital printing according to one of the preceding claims, wherein printing is carried out in colour, using inks of a plurality of colours, in particular cyan, magenta, yellow and black, characterized in that the colour of the ink of the original print dot itself (P) and / or of the at least one generated print dot (Q) is the colour of the ink that would be ejected at the original print dot (P) according to the non-reprocessed ejection commands.

13. Method for digital printing according to one of the preceding claims, characterized in that the method is used to generate a texture, in particular in a coating of the substrate (2) onto which the ink is directly ejected.

14. Computer software for carrying out a method for digital printing according to one of the preceding claims, characterized in that the software comprises instructions such that, when the software is executed by a computer (20), the computer (20) performs the reprocessing of the ejection commands, obtained, in particular, using computer software for processing digital images (RIP), from the digital image, so as to provide new ejection commands for ejection at original print dots (P) and / or generated print dots (Q).

15. System for digital printing with control over the volume of ink, which comprises an inkjet printer (10), in particular a single pass inkjet printer, provided with ink ejection nozzles to produce a printing resolution and ink droplet volume levels per nozzle which are predetermined, characterized in that the system (1) is configured to carry out a method according to one of Claims 1 to 13, in particular comprising a computer (20) on which software according to Claim 14 may be installed.

Images