Method and system for digital printing with ink ejection control

Abstract

Digital printing method and system with ink volume control, using an inkjet printer (10) provided with ink ejection nozzles to provide preset ink drop volume levels per nozzle and print resolution. The method is characterised by comprising the step of reprocessing the ejection commands so that the drop volume level corresponding to each of at least one of the original printing points (P) is redistributed between the original printing point (P) itself and / or at least one generated printing point (Q). The generated printing points (Q) are introduced close to the original printing point (P).

Description

[0001] DIGITAL PRINTING PROCEDURE AND SYSTEM WITH INK EJECTION CONTROL

[0002] DESCRIPTION

[0003] OBJECT OF THE INVENTION

[0004] The present invention relates to a method and system for digital printing using an inkjet printer. More specifically, the invention aims to improve the way in which ink droplets are ejected onto the printing points through the printer's ink nozzles. The invention also relates to a computer program that facilitates the implementation of the method of the invention.

[0005] BACKGROUND OF THE INVENTION

[0006] Inkjet printing has been widely adopted in the field of digital printing, both at an industrial and personal level, due to its inherent ability to print digital images with high resolution, quality and performance.

[0007] Inkjet printers work by the controlled ejection of ink droplets through nozzles. This process begins with the digital image to be printed, which is processed to generate ink droplet ejection commands. Each print point within the printing area corresponds to the ejection, at that point, of a specific droplet volume level, through one of the nozzles, at a specific moment in time.

[0008] Print resolution is predetermined by the number of nozzles available during the printing process for the various points in the print area where ink droplets are ejected. Conventionally, print resolution is expressed in dots per inch (dpi).

[0009] Furthermore, the droplet volume levels ejected by each nozzle are preset. Currently available inkjet printers are typically configured with multiple droplet volume levels, as a greater number of droplet volume levels allows for more precise control of the amount of ink deposited, improving, among other aspects, the gradation of color tones in the print and, therefore, the print quality.

[0010] For example, in the case of single-pass inkjet printers, the nozzles are typically arranged in printhead bars with nozzles aligned along the bar, perpendicular to the direction of substrate transport. In this case, the print resolution, in the horizontal direction (perpendicular to the substrate transport direction), is determined by the number of nozzles per unit length arranged along that horizontal direction for each color.

[0011] The resolution in the vertical direction (parallel to the substrate's transport direction) is determined by the number of distinct print points, with their corresponding droplet volume levels, that the printer can place per unit length in the vertical direction. Vertical resolution depends, in particular, on the number of nozzles aligned vertically and / or the number of sprays each nozzle can make per unit length of substrate travel in that direction.

[0012] The digital image is processed to transform it into print dots in the print area, at the given print resolution. The different colors of the image are formed by overlapping print dots of ink droplets from a limited number of colors. For this purpose, primary colors such as cyan, magenta, yellow, and black, or mixtures of primary colors such as green, violet, orange, etc., are typically used. Furthermore, the varying droplet depths of each print dot allow for the creation of color gradation effects or grayscale.

[0013] Digital image processing is typically performed using a computer program called a RIP (Raster Image Processor). This program converts digital image files into ink ejection commands for the nozzles, managing the distribution of print dots, droplet volumes, colors, and other parameters based on the print resolution, print area size, image definition, and other factors to optimize print quality. Digital image processing, particularly through the RIP, primarily controls ink ejection. For example, the droplet volume levels ejected at each print dot are determined after processing to achieve the desired print resolution with optimized print quality.

[0014] Therefore, an inkjet printer user or operator has little to no control over ink ejection, as it is determined by the digital image processing, particularly through the RIP (Recording Processor). This significantly limits the versatility of known inkjet printing procedures and systems.

[0015] In particular, it is worth highlighting the limitation of current procedures and systems in relation to the dependence of the ink on the substrate priming on which it is printed, which forces the type of priming to be adapted according to the ink and substrate used.

[0016] The invention aims to overcome the limitations of current technologies such as the dependence of the ink on the substrate priming, improving its versatility, as well as maintaining, or even improving, the quality, availability and performance of known digital inkjet printing procedures and systems.

[0017] EXPLANATION OF THE INVENTION

[0018] To achieve the aforementioned objective, as well as additional technical advantages that may be derived from this invention, the invention provides a digital printing method with ink volume control by means of an inkjet printer. The printer is equipped with ink ejection nozzles to provide a predefined print resolution and ink droplet volume levels per nozzle.

[0019] The method according to the invention, as in known digital inkjet printing methods, comprises processing a digital image to obtain ink droplet ejection commands onto a printing area of ​​a substrate, such that each printing point on the printing area corresponds to the ejection, at that point, of a certain droplet volume level, by one of the nozzles and at a specific instant in time. Subsequently, printing is performed on a substrate following the final ejection commands.

[0020] Unlike known digital inkjet printing processes, the process according to the invention further comprises reprocessing the ejection commands, such that the droplet volume level corresponding to each of at least one of the original print points, according to the unreprocessed ejection commands, is redistributed between the original print point itself and / or at least one generated print point, which is introduced close to the original print point, by means of respective reassigned droplet volume levels, which are ejected by nozzles. In preferred embodiments, the droplet volume level is redistributed between the original print point itself and a generated print point, between the original print point itself and several generated print points, or between several generated print points.

[0021] In this way, the invention allows for a controlled reduction of the volume of ink droplet deposited per original printing point, redistributing said volume towards generated printing points, which are located close to said original printing point.

[0022] As a result of the reduced volume of the ejected drop, smaller volume ink droplets expand less once deposited on the substrate, because they have less liquid that can spread over the substrate surface.

[0023] The spread of ink droplets on the substrate can 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; and environmental conditions, such as temperature or relative humidity. However, droplet volume significantly influences droplet spread.

[0024] Therefore, the invention makes it possible, in particular, to minimize or eliminate the printing process's dependence on the ink and the substrate or substrate primer, with respect to their influence on the spread of the ink droplets. Specifically, it even makes it possible to dispense with substrate priming, in contrast to conventional printing processes.

[0025] Furthermore, the resolution and print quality are not altered by the application of the invention's procedure compared to a digital printing procedure applied under the same conditions but with the ejection commands not reprocessed. This is because the generated print dots are introduced by the original print dot, located close to it, and only a redistribution of the droplet volume is carried out, so that the visual appearance of the printed image and its apparent quality are maintained.

[0026] In the context of the invention, a printing point is understood to be a theoretical or nominal point in the printing area where, like a target, a specific droplet volume is ejected by a nozzle at a specific instant in time to generate the printed image. The printing point, therefore, does not necessarily coincide with the point at which the nozzle ejects said droplet volume at that instant in time; tolerances exist and are managed in a controlled manner.

[0027] In general, at each print point, multiple droplet volume levels can be ejected, either by different nozzles or by the same nozzle at different times. For example, single-pass inkjet printers are usually configured so that for each print point, each nozzle of a different color—for example, cyan, magenta, yellow, and black—ejects a different droplet volume level.

[0028] Drop volume level refers to each of the theoretical or nominal volume quantities of ink droplets ejected from the nozzle to be deposited at each printing point. The term drop volume levels includes the zero level, where the amount ejected is zero.

[0029] Unlike the prior art, the invention involves a reallocation of droplet volume levels per print point between the original print point and generated print points. Instead of the droplet volume level corresponding to the original print point being ejected according to the unreprocessed ejection commands, this droplet volume level is redistributed between the original print point and / or at least one generated print point by means of respective reallocated droplet volume levels. In preferred embodiments, the droplet volume level is redistributed between the original print point and a generated print point, between the original print point and several generated print points, or between several generated print points.

[0030] According to the invention, the reassignment of droplet volume levels by means of the reprocessing stage can be carried out, in particular, for some of the original printing points or for each and every one of said original printing points, of the printing area or part of the printing area.

[0031] By redistribution of the drop volume level, it can be understood that the volume corresponding to the original print point, according to the unreprocessed ejection orders, is divided between the original print point itself and / or the generated print points, preferably, equally.

[0032] Therefore, the volume corresponding to the original print point is, in particular, substantially equal to, 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 the volume corresponding to the original print point.

[0033] According to the invention, the generated print point(s) are introduced close to the corresponding original print point. In the context of the invention, "close" means within the vicinity of the original print point corresponding to the printer's print resolution. In particular, at a distance from the original point less than the separation distance between original print points corresponding to the print resolution. Preferably, located at a distance less than 1 / 2 of said separation distance, and more preferably less than 1 / 3.

[0034] An increasing proximity of the generated printing points to the original printing point favors the similarity of the printed image with the procedure of the invention, with respect to the same printed image if it were printed according to the ejection orders without reprocessing.

[0035] If printing is done in color, the color that is reassigned to the original print point and / or the at least one print point generated after reprocessing is, preferably, the color of the ink that would be ejected at the corresponding original print point according to the unreprocessed ejection commands.

[0036] Inkjet printing typically uses basic colors such as cyan (C), magenta (M), yellow (Y), and black (K). Depending on the printing substrate or the image's color characteristics, other colors are also commonly used, such as green (G), violet (V), orange (O), light black (LK), light magenta (LM), and so on.

[0037] In general, preferably, any characteristic of the ink (such as, for example, the color) at the original printing point according to the unreprocessed ejection commands, is reassigned, by reprocessing according to the invention, to the original printing point itself and / or the corresponding generated at least one printing point.

[0038] In this sense, the underlying criterion is to replicate such characteristics at all points between which the drop volume level per original printing point is redistributed, in order to assimilate the appearance of the printed image resulting from applying the procedure of the invention to that which would result if it were applied without the reprocessing stage.

[0039] The printing process according to the invention is not limited to the printing of decorative images, monochrome or color, but can also be used, alternatively or complementarily, with the generation of decorative images, for the generation of textures.

[0040] Texture refers to a surface with relief. A coating, such as a base coat, can be used to create textures. The impact, contact, and / or mixing of ejected ink droplets on this base coat produces or contributes to the creation of raised and / or recessed reliefs. Preferably, substantially transparent ink can be used to create textures, especially in combination with decorations. A varnish, particularly one that is substantially transparent, can also be used as a base coat.

[0041] In particular, the droplet volume ejected at each printing point corresponding to the respective reassigned droplet volume levels influences the depth and / or height of the texture generated at said printing points, so the procedure according to the invention allows obtaining different textures on different substrates, printing areas, digital images or parts thereof, according to the different levels of reassigned droplet volumes at the different printing points.

[0042] Therefore, by controlling the ink volume according to the invention, specifically the reallocated ink volume levels, it is possible to control the depth and / or height of the resulting texture. In particular, this can also be used to control the degree of matte or gloss finish of a printed decoration, primarily due to the reduced light reflection on rough surfaces.

[0043] Advantageously, in general, due to the effect that smaller ink droplets expand less once deposited on the substrate, and especially since this effect is controllable according to the invention, it becomes possible to obtain higher-definition prints, particularly with more defined textures. Furthermore, as mentioned previously, the dependence of the print on the coating, base coat, or primer of the substrate onto which the ink droplets are ejected is reduced or eliminated. Moreover, with regard to the nozzles used in the process according to the invention, the invention provides that, preferably, the same nozzles used for printing with the predefined resolution and droplet volume levels can be used, according to the ejection commands without reprocessing; that is, ejecting the droplet volume levels without reassignment only at the original printing points.In the context of the invention, these nozzles are referred to as main nozzles.

[0044] Alternatively or in addition to using the main nozzles, the respective reassigned droplet volume levels can be ejected by additional nozzles on the inkjet printer. Specifically, it is also possible to use either only the main nozzles or only the additional nozzles for ejecting the reassigned droplet volume levels.

[0045] The option to include additional nozzles offers the added advantage of having redundant nozzles, particularly when the digital printing process is selectively omitted and printing is done directly from the ejection commands. This increases machine availability.

[0046] The additional nozzles can be selected with an arrangement or configuration such that, independently of the main nozzles, they provide a print resolution greater than or equal to that of the main nozzles, and / or with a maximum droplet volume per nozzle less than or equal to that of the main nozzles. This allows for the creation of print dot arrangements closer to the original print dots according to the invention.

[0047] Preferably, it is envisaged that the same nozzle, main or additional, ejects the respective reassigned droplet volume levels in a plurality of generated print points, per original print point.

[0048] This allows a single nozzle to be used to generate multiple print points. Specifically, the main nozzles, which are initially used to eject a single print point—corresponding to the original print point associated with the preset print resolution—can be used to eject more than one print point. In particular, they can be used to eject at least one original point and at least one generated point, or at least two generated points.

[0049] This is possible according to the invention, for example, by decreasing the printing speed, since this measure can increase the number of shots per nozzle per unit of printing area. It is also possible by limiting the number of droplet volume levels of the nozzles. For example, if only one droplet volume level is ejected (in addition to the zero level), the number of shots of droplet volume levels can be maximized.

[0050] Advantageously, the process according to the invention can be selectively applied to substrates, print areas, digital images, or parts thereof. In particular, the selective application can be carried out with respect to other substrates, print areas, digital images, or parts thereof, for which ink is ejected only at the original print points according to the unprocessed ejection commands.

[0051] Selective application of the procedure according to the invention involves, in particular, activating or deactivating the reprocessing of the ejection commands for specific original print points as desired. These print points may correspond, in particular, to physical points on the substrate or the printing area, or to pixels in the digital image, depending on the digital image processing performed.

[0052] Furthermore, it is also envisaged that the procedure according to the invention can be applied differently to substrates, printing areas, digital images, or parts thereof. In particular, the procedure can be applied in such a way that the introduction of generated printing dots, and / or the redistribution of the droplet volume level, is different for different substrates, printing areas, digital images, or parts thereof.

[0053] Specifically, the reprocessing stage can be performed differently for different substrates, print areas, digital images, or parts thereof, as needed. This can be useful, for example, to print areas of saturated colors with larger droplets and areas requiring greater color gradation or definition with smaller droplets.

[0054] By different introduction of the generated print points, it can be understood, for example, that the number of print points generated, per original print point, is different and / or that the location of the generated print points with respect to the original print point is different, for example, following a different pattern.

[0055] Different redistribution of generated print points refers to the different ways in which the ink volume can be divided among the reassigned droplet volume levels per original print point. For example, different redistribution methods can be based on setting a maximum droplet volume or different maximum reassigned droplet volume levels.

[0056] Any conceivable redistribution method is applicable to the invention. Given the number of generated printing points and their location, there are as many redistribution methods as there are possibilities for distributing the ink volume among the different available ink volume levels.

[0057] Furthermore, it is envisaged that, for the application of reprocessing according to the invention, introduction and / or redistribution criteria can be programmed and selected by the operator of the procedure through other control variables. For example, a general criterion could be based on minimal distortion of the original droplet volume levels, with the objective that the original droplet volume level, which would be ejected according to the ejection commands without reprocessing, decreases as little as possible.

[0058] Another example of a selection criterion may be based on choosing one of the possible reassigned drop volume levels when the chances are that their sum will exceed or not exceed the original drop volume level.

[0059] In general, random introduction and / or redistribution is also considered, especially in combination with other criteria or methods of introduction and / or redistribution. This is compatible with the use of stochastic inkjet printing techniques, which are commonly used in digital image processing for printing.

[0060] According to the invention, it is also contemplated that the procedure is applied selectively and / or distinctly to different substrates, depending on properties of the ink and / or depending on the absence or presence of a coating on the substrate onto which the ink is ejected, in particular, depending on properties of the coating or the substrate, more particularly depending on the thickness of the coating.

[0061] The properties of the ink, coating, or substrate can be, in particular, physical or chemical properties, for example, viscosity, surface tension, chemical composition, etc.

[0062] By coating, we can understand, in particular, a primer, with the main function of preparing the substrate surface to receive the ink, in particular, ensuring the adhesion of the ink to the substrate, and / or a base coat, with the function of serving as a base for the generation of a texture.

[0063] Thus, the invention makes it possible for the same procedure to be used with different types of coatings and / or different types of ink to print on a substrate, adapting the application method of the procedure to the type of coating and / or ink.

[0064] In particular, the invention makes it possible to dispense with coating or priming, for example, by selecting sufficiently small maximum reassigned droplet volume levels to minimize or disregard the expansion of the ink drops deposited on the substrate surface.

[0065] According to another aspect, the invention relates to a computer program for performing a digital printing procedure as described above. The program comprises instructions such that, when executed by a computer, the computer reprocesses the ejection commands, obtained, in particular, by means of a digital image processing (RIP) computer program, from the digital image, to provide new ejection commands at original print points and / or generated print points.

[0066] The computer program according to the invention may include or be included in a digital image processing program such as, for example, a RIP.

[0067] Finally, the invention also relates to a digital printing system with ink volume control. The system comprises an inkjet printer, particularly a single-pass printer, equipped with ink ejection nozzles to provide a predetermined print resolution and ink droplet volume levels per nozzle.

[0068] According to the invention, the system is configured to perform a procedure as described above. In particular, the system comprises a computer on which a computer program as described above can be installed, or is installed.

[0069] BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The invention is described in greater detail below for illustrative and non-limiting purposes, as well as with respect to a preferred embodiment by way of example, with reference to the accompanying drawings. In the drawings:

[0071] Figure 1 shows a flow diagram of a digital inkjet printing procedure according to the state of the art.

[0072] Figure 2 shows a flow diagram of a digital inkjet printing procedure according to the invention.

[0073] Figures 3, 4 and 5 refer to an embodiment of a prior art printing process and system in which the inkjet printer nozzles eject droplet volume levels according to ink ejection commands without reprocessing.

[0074] Figures 6, 7, 8 and 9 represent different embodiments according to the invention corresponding to different positionings of the generated printing points, with respect to the original printing points.

[0075] Figures 10 and 11 represent two examples of embodiments of the invention, corresponding to the embodiment represented in Figure 9.

[0076] Figures 12 and 13 represent different arrangements of main and additional nozzles, for different embodiments of the printing system according to the invention in which the inkjet printer is single-pass.

[0077] Figure 14 shows one embodiment of a nozzle head for a single-pass inkjet printer.

[0078] Figure 15 shows ink drops deposited on the substrate to be printed. The figure shows that the larger drops cover a larger area than the smaller drops.

[0079] Figure 16 illustrates an embodiment of the invention in which printing is used to create a texture. The figure shows that larger droplets penetrate to a greater depth than smaller droplets.

[0080] Figure 17 schematically represents an embodiment of a printing system according to the invention.

[0081] DETAILED DESCRIPTION OF THE INVENTION

[0082] In the description of all figures, the reference signs refer to the system shown in Figure 17.

[0083] Figure 1 shows the flow diagram of a known digital printing procedure using an inkjet printer (10). The inkjet printer (10) is configured to provide a preset print resolution and droplet volume levels.

[0084] To print a digital image with a given image definition or resolution, on a printing area of ​​a substrate and with the printing resolution of the inkjet printer (10), the digital image is processed, for example, by a RIP processing program. The RIP program converts the pixels of the digital image into commands for ejecting ink droplets onto the printing area of ​​the substrate.

[0085] The inkjet printing of the image occurs in such a way that each printing point of the printing area corresponds to the ejection, at that point, of some level of droplet volume, by one of the nozzles and at some certain instant of time.

[0086] 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 way image information is stored in which the image is composed of a map or matrix of pixels, where each pixel individually stores a value of color, depth or relief height (in the case of textures), location, etc., which is materialized in the print.

[0087] In particular, when the digital image is in vector format, the processing stage to obtain the ink drop ejection commands may include a rasterization substage to convert the digital image from vector format to raster format and its subsequent pixel processing.

[0088] The definition of the digital image, or also called the resolution of the digital image, of digital images in raster format, represents the quality of the digital image itself and is a function of the number of pixels they contain, being greater the greater the number of pixels.

[0089] In contrast to Figure 1, Figure 2 shows the flow diagram of a digital printing procedure using an inkjet printer (10) according to the invention.

[0090] Unlike prior art digital inkjet printing procedures, the printing procedure according to the invention comprises a step of reprocessing the ejection commands to generate new ejection commands.

[0091] With the new ejection commands generated by reprocessing, the droplet volume level that would correspond to each of the original print points (P) according to the unreprocessed ejection commands is redistributed between the original print point (P) and / or at least one generated print point (Q), which is inserted close to the original print point (P), using respective reassigned droplet volume levels. Printing is performed by ejecting these reassigned droplet volume levels.

[0092] In particular, the way in which reprocessing is carried out can be controlled, for example, by requiring a reallocated drop volume or drop volume level, or by other control variables.

[0093] The processing and reprocessing phases can be carried out simultaneously, merged, with identical results.

[0094] With reference to Figures 3 to 5, an embodiment of the prior art procedure and system is explained below, followed by an explanation of the modifications introduced in such embodiment according to the invention.

[0095] Figure 3 shows the ink droplets deposited in a sub-area of ​​the printing area, with their corresponding colors (C, M, Y, K) according to an example embodiment. A single circle represents level 1 of the deposited ink droplet volume, two concentric circles represent level 2, and three concentric circles represent level 3.

[0096] The selected subarea is 3x3 cells in size, where each cell corresponds to a print dot. Print resolution is determined by the number of print dots per unit area. Digital image processing, particularly the RIP (Raster Image Processor), allows pixels of the digital image, or pixels associated with the digital image, to be converted into print dots in the different cells, adjusting the digital image to the selected print area.

[0097] For adjusting the digital image to the selected printing area, the digital image processing may involve generating new pixels from existing pixels of the digital image by interpolating their information, or deleting existing pixels of the digital image by reducing its information. The processing may also involve adjusting the digital image by modifying native pixels based on neighboring native pixels, for example, to simulate colors or tones to be achieved in printing. New pixels, particularly interpolated or modified pixels, are examples of pixels associated with the digital image in the context of the invention.

[0098] For simplicity and without loss of generality, the examples shown eject a single-color drop of ink at each printing point in the subarea. However, several drops of different colors can be ejected at a single printing point, overlapping each other.

[0099] Figure 4 shows the positioning of the print points in the printing subarea. These are the original print points (P), as they are the print points where the ink drops are ejected according to the ejection commands without reprocessing. The original print points (P) are represented in the figures with an "x".

[0100] 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, where the nozzles are grouped into printheads for the different colors (C, M, Y, K). These are the main nozzles (C-PR, M-PR, Y-PR, K-PR).

[0101] The printing subarea is shown in the lower part of Figure 5. As the substrate with the printing area is moved in the (vertical) direction indicated by the arrows, the main nozzles (C-PR, M-PR, Y-PR, K-PR) corresponding to each color eject the corresponding droplet volume level into the printing subarea, to obtain the ink droplet distribution shown in Figure 3.

[0102] Preferably, according to the invention, a single-pass inkjet printer (10) is used, although it can be used with any type of inkjet printer. The nozzles are usually arranged as shown in Figure 5, aligned with each other in rows parallel to the horizontal direction, perpendicular to the vertical direction along which the substrate is transported.

[0103] Likewise, the nozzles arranged in rows are usually located in printheads, which are also grouped in alignment with each other in print bars (11, 12, 13 and 14; 21, 22, 23, 24), one bar per color. To achieve redundancy or alternation of nozzle use, and therefore greater availability of the inkjet printer (10), more than one print bar per color is usually provided.

[0104] Referring now to Figures 6 to 9, in comparison with Figure 4, these figures show the positioning of the generated print points (Q), either complementarily or alternatively to the original print points (P). The generated print points (Q) are represented in the figures with a cross (“+”), distinguishing them from the original print points (P), which are represented with an x ​​(“x”).

[0105] As can be seen in each of Figures 6 to 9, the generated print points (Q) are positioned close to their respective original print point (P). Specifically, they are located within the cell associated with the original print point (P) on which they depend.

[0106] The size of each cell in the printing subarea is directly linked to the printing resolution. Thus, the printing resolution is given by the number of cells per unit length in the printed area, that is, the number of original printing points (P) available for the ejection of ink drops according to the unprocessed ejection commands.

[0107] Indeed, the print resolution when applying the procedure according to the invention is not altered since the generated print points (Q) replicate the information associated with each original print point (P) on which they depend per cell.

[0108] For example, in figure 6 the generated print points (Q) are located at a distance from the respective original print point (P) equal to ! of the separation between original print points (P) in the print subarrea, a separation that is equal to the length of the side of the corresponding cell.

[0109] In the example in Figure 7, unlike that in Figure 6, there are two generated print points (Q) per original print point (P), located on either side of said print point (P). A greater number of print points (P, Q) increases the versatility and availability of the invention's procedure and system.

[0110] Figure 8 shows another example of the distribution of generated print points (Q) according to the invention. In this case, each original print point (P) is split into two generated print points (Q) aligned in the vertical direction, disregarding the original print point (P). As can be seen, the distance from each generated print point (Q) to the original print point (P), imaginary in this case, is 1 / 6 of the separation between original print points (P), a separation that is equal to the length of the side of the corresponding cell.

[0111] The distribution of generated print dots (Q) in Figure 8 can be achieved when using the same main nozzles (C-PR, M-PR, Y-PR, K-PR), 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 to eject the respective droplet volume levels at two points instead of a single point per cell.

[0112] Figure 9 shows a fourth example of generated print dot distribution (Q). In this case, the original print dot (P) is maintained, and two generated print dots (Q) are introduced per cell or original print dot (P), aligned vertically. Similar to the case in Figure 8, this arrangement of generated print dots (Q) can occur when using the same additional print nozzle (C-AD, M-AD, Y-AD, K-AD) to eject the two dots for each cell with a single-pass inkjet printer (10).

[0113] Referring back to Figure 3 and together with Figures 10 and 11, a procedure and system embodiment according to the invention is described below. The described embodiment applies to the case where it is desired to print the same subarea as in Figure 3, which corresponds to the ejection of ink drops according to the unreprocessed ejection commands, through the main nozzles (C-PR, M-PR, Y-PR, K-PR) and at the original printing points (P) distributed as shown in Figure 4.

[0114] To do this, in addition to using the original print points (P), two generated print points (Q) are introduced per original print point (P), or per cell, following a distribution like the one shown in Figure 9.

[0115] The procedure 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 point (P), if they were ejected following the unreprocessed ejection commands (as in Figure 3), among the new print points, in this case, between the original print point (P) and the two generated print points (Q).

[0116] Regarding the ink color of the newly ejected drops, the same ink color is chosen as would be ejected at the original printing point (P) according to the unreprocessed ejection commands. In other words, the ink color remains the same according to the new ejection commands after reprocessing.

[0117] Figure 10 shows an example implementation where the selected maximum drop volume level is level 2. As in Figure 3, a single circle represents the drop volume level of the deposited ink drop as level 1, two concentric circles represent level 2, and three concentric circles would represent level 3.

[0118] Thus, for example, the ejection in the cell in row 1 and column 1 is not modified, as it already has a level of 2. However, in the case of, for example, the ejection in the cell in row 1 and column 3 is modified, reducing the level from 3 to 2 at the original print point (P). To maintain the total drop volume level of the cell at the original level 3 (P), a level 1 drop is introduced at one of the two generated print points (Q). The lower generated print point (Q) has been randomly selected for this cell.

[0119] Therefore, to perform this reassignment of droplet volume levels, a criterion of minimal distortion of the original droplet is followed. That is, for example, in cells with an original level of 3, another option would have been to choose level 2 at one of the generated print points (Q) and level 1 at the original print point itself (P). But this option would have resulted in greater distortion compared to the original droplet, which concentrates most of the ejected ink in the cell.

[0120] In the implementation example of figure 11, the selected maximum drop volume level is level 1, with the drops represented by a single circle at the corresponding print points.

[0121] Thus, for example, the ejection in the cell in row 1 and column 1 is modified so that, in order for the total drop volume level to be level 2, a level 1 drop is ejected at the original point (P) and another level 1 drop at one of the generated impression points (Q). In this cell, the lower generated impression point (Q) has been randomly chosen for the ejection of the other drop, but the upper generated impression point (Q) could have been chosen, as in the case of the cell in row 2 and column 2.

[0122] Figure 12 shows a detail of the nozzle arrangement in a single-pass inkjet printer (10), according to an embodiment of the system of the invention, and to carry out the example embodiment of the procedure described with reference to Figures 10 and 11.

[0123] The nozzles are arranged in nozzle bars (11, 12, 13, 14; 21, 22, 23, 24). For example, in Figure 12, for color K, a main nozzle bar and an additional nozzle bar are shown. The additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged three times in a row with respect to the main nozzles (C-PR, M-PR, Y-PR, K-PR), offset by a distance of “5”.

[0124] With this staggered nozzle configuration, the distribution of original (P) and generated (Q) print points shown in Figure 9 can be obtained. The additional nozzles (C-AD, M-AD, Y-AD, K-AD) eject at two generated points (Q) per cell, which allows the same additional nozzle (C-AD, M-AD, Y-AD, K-AD) to be used to generate two print points and, therefore, improve the efficiency of the procedure and the system.

[0125] In general, for a single-pass inkjet printer (10), for example, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) can be staggered or interleaved with respect to the main nozzles (C-PR, M-PR, Y-PR, K-PR). Alternatively, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) can be aligned with respect to the main nozzles (C-PR, M-PR, Y-PR, K-PR) in rows parallel to the vertical direction, as shown in Figure 13.

[0126] As mentioned previously, the option to include additional nozzles offers the added advantage of having redundant nozzles, particularly when the digital printing procedure is selectively not applied and printing is done directly from the ejection commands. This applies, for example, to the (aligned) nozzle arrangements shown in Figure 13. It can also apply to the (offset) nozzle arrangements shown in Figure 12, considering that the distance “5” would be small enough to be noticeable in the print.

[0127] Figure 14 shows another embodiment of a printhead or nozzle bar (11, 12, 13, and 14; 21, 22, 23, 24) that can be used in the invention. In this embodiment, the nozzles are arranged in a staggered pattern as part of the printhead itself. This staggered arrangement provides higher print resolution (due to having twice as many nozzles per unit length) and the same droplet volume levels compared to a printhead in which the same nozzles are arranged in a single row.

[0128] Preferably, as shown in Figures 12 to 14, the nozzles are arranged in groups of nozzles for each color. 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 in groups with each other.

[0129] Advantageously, the redundant bar nozzles can be used as additional nozzles (C-AD, M-AD, Y-AD, K-AD) without compromising the performance of the inkjet printer (10). Or, put another way, the additional nozzles (C-AD, M-AD, Y-AD, K-AD) can be used as redundant nozzles, increasing the availability of the inkjet printer (10) and, consequently, of the procedure and system.

[0130] There are multiple possibilities for designing the distribution of 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), as well as the nozzle firing time. For example, the inkjet printer (10) can be configured so that the generated print dots (Q) are arranged vertically, horizontally, and / or diagonally with respect to the original print dot (P).

[0131] More specifically, with respect to an originating print point (P), at least one generated print point (Q) can be arranged, for example, along an originating point alignment direction (P), along a direction perpendicular to said alignment direction and / or along a direction diagonal to the above, preferably along one of their bisectors, and, for each of said directions, on one side and / or the other side of the originating print point (P).

[0132] Preferably, the invention is conceived for printing with small reassigned droplet volume levels, in particular with a droplet volume deposited per print spot less than or equal to 15 pL (picoliers), preferably 10 pL, more preferably 5 pL.

[0133] Using small droplet volumes allows for higher resolution and print quality. Furthermore, as previously mentioned, it offers the advantage of printing with minimal or no influence from the properties of the substrate, coating, and / or ink, meaning that a primer to control droplet expansion can even be omitted.

[0134] Figure 15 illustrates the effect of reducing the droplet volume or reallocating the droplet volume level on the droplet deposition area. For larger droplets, the deposition area (“a”) is larger than the deposition area (“a”’) for smaller droplets, thus minimizing the interaction between the ink and the substrate or coating onto which the droplet is deposited. The printing process and system according to the invention are not limited to decorative printing but are also applicable to textures. As shown in Figure 16, the printing can be used to create a texture on a substrate or substrate coating onto which the ink is directly ejected.

[0135] A smaller droplet volume results in less droplet expansion and therefore more defined textures. On the other hand, a smaller droplet volume can contribute to producing a shallower relief (“ ”) than the depth (“ ') caused by a larger droplet volume.

[0136] Finally, Figure 17 schematically shows 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 provide a predefined printing resolution and ink droplet volume levels per nozzle.

[0137] The system (1) is configured to perform a procedure as described, in particular comprising a computer (20) on which, in particular, a computer program has been installed to carry out said procedure.

[0138] The substrate (2) to be printed is supplied to the system (1) and transported through the different stations of the system (1) by a transport means (30) comprising a transport belt (31).

[0139] First, the substrate passes through a roller coating application station (40) to spread a primer onto which the printing ink droplets are directly ejected. The coating is partially cured in the curing station (50) before printing, to optimize the adhesion properties of the ink to the coating and of the coating to the rest of the substrate (2).

[0140] The substrate is then printed using 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 color (C, M, Y, K), grouped into respective bars, with their corresponding printheads. Thus, bars (11, 12, 13, and 14) are for main nozzles (C-PR, M-PR, Y-PR, K-PR), respectively, for the colors C, M, Y, and K, while bars (21, 22, 23, and 24) are for additional nozzles (C-AD, M-AD, Y-AD, K-AD), respectively, for the colors C, M, Y, and K.

[0141] After each group of nozzle bars for each color, the system (1) includes respective ink droplet pinning lamps (15, 16, 17, 18). Finally, the system (1) includes a curing station (60) to complete the curing of the print and coating.

[0142] In short, as explained in this document, the invention provides a procedure and system that overcomes the limitations of the prior art, making it possible, in particular, to reduce the dependence of the ink on the substrate priming and providing additional technical advantages.

[0143] To that end, the invention is not limited to the embodiments presented, but includes all variations, modifications, and combinations included within the scope of the attached claims.

[0144] List of reference signs

[0145] Printing system

[0146] Substrate to be printed

[0147] 10 Inkjet printer

[0148] 11, 12, 13, 14 Main nozzle print bars

[0149] 15, 16, 17, 18 Fixation curing lamps

[0150] 20 Processing Computer

[0151] 21, 22, 23, 24 Additional nozzle print bars

[0152] 30 Means of transport

[0153] 31 Conveyor belt

[0154] 40 Coating application station Coating curing station Print curing station

Claims

CLAIMS 1. A digital printing method with ink volume control, using an inkjet printer (10) provided with ink ejection nozzles to provide a print resolution and predetermined ink droplet volume levels per nozzle, comprising processing a digital image to obtain ink droplet ejection commands in a printing area of ​​a substrate (2), such that each print point in the printing area corresponds to the ejection, at said point, of some droplet volume level, by one of the nozzles and at some determined instant in time, characterized in that it comprises reprocessing the ejection commands, such that the droplet volume level corresponding to each of at least one of said original print points (P), according to the unreprocessed ejection commands, is redistributed between the original print point (P) itself and / or at least one generated print point (Q),which is introduced close to said original printing point (P), by means of respective reassigned droplet volume levels, which are ejected by nozzles.

2. Digital printing method, 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 unreprocessed ejection orders, ink would be ejected only at original printing points (P), and / or by additional nozzles (C-AD, M-AD, Y-AD, K-AD) of the inkjet printer (10).

3. Digital printing method, 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 drop volume levels into a plurality of generated printing points (Q), per original printing point (P).

4. A digital printing process according to any of the preceding claims, characterized in that the process is selectively applied to substrates (2), printing areas, digital images, or parts thereof, as distinct from other substrates (2), printing areas, digital images, or parts thereof, for which it is not applied. ejects ink only at original print points (P) according to the unreprocessed ejection commands.

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

6. Digital printing process, according to one of claims 4 or 5, characterized in that the process is applied selectively and / or distinctly to different substrates (2), depending on properties of the ink and / or depending on the absence or presence of a coating on the substrate (2) onto which the ink is ejected, in particular depending on properties of the coating, more particularly depending on the thickness of the coating.

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

8. Digital printing method, according to any of the preceding claims, characterized in that the droplet volume corresponding to the respective reassigned droplet volume levels is less than or equal to 15 pL, preferably 10 pL, more preferably 5 pL.

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

10. Digital printing method, according to claim 9, characterized in that additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged interleaved or staggered with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR).

11. Digital printing method, according to claim 9, characterized in that additional nozzles (C-AD, M-AD, Y-AD, K-AD) are arranged in alignment with respect to main nozzles (C-PR, M-PR, Y-PR, K-PR) in rows parallel to the vertical direction.

12. A digital printing method, according to any of the preceding claims, wherein the printing is done in color, using inks of a plurality of colors, in particular cyan, magenta, yellow and black, characterized in that the color of the ink of the original printing point (P) and / or of the at least one generated printing point (Q) is the color of the ink that would be ejected at the original printing point (P) according to the unprocessed ejection commands.

13. Digital printing process, according to any of the preceding claims, characterized in that the process is used to generate a texture, in particular, on a coating of the substrate (2) onto which the ink is directly ejected.

14. Computer program for performing a digital printing procedure, according to any of the preceding claims, characterized in that the program comprises instructions so that, when the program is executed by a computer (20), the computer (20) performs the reprocessing of the ejection commands, obtained, in particular, by means of a digital image processing (RIP) computer program, from the digital image, to provide new ejection commands at original print points (P) and / or generated print points (Q).

15. A digital printing system with ink volume control, comprising an inkjet printer (10), in particular a single-pass printer, provided with ink ejection nozzles to provide a print resolution and ink droplet volume levels per nozzle, characterized in that the system (1) is configured to perform a procedure according to any one of claims 1 to 13, in particular comprising a computer (20) on which a program according to claim 14 can be installed.

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