Method and apparatus for printing a substrate using inkjet printing

Abstract

The invention relates to a method for printing a substrate using inkjet printing, wherein on the substrate in a grid of inked areas formed by inked area rows and inked area columns inked areas are given and by means of one or several print head nozzles of a print head single patterns composed of one or several droplets are printed for the inked areas, wherein the print head nozzles are caused to travel along an imaginary nozzle track over the substrate surface during printing. The invention also relates to a device for printing a substrate having a grid of inked areas formed by inked area rows and inked area columns using inkjet printing. In order to provide a method and a device for printing a substrate using inkjet printing, which efficiently and simply achieve a substrate printing, wherein the printing result is particularly uniform and interference-free and the printed surface is particularly free from lines and Moire effects, it is proposed in the method that on the substrate in a grid of inked areas formed by inked area rows and inked area columns inked areas are given and by means of print head nozzles of a print head single patterns composed of droplets are printed for the inked areas, wherein the print head nozzles and the substrate surface are caused to move relative to each other along an imaginary nozzle track during printing. Therein, all single patterns of one print nozzle track are printed in several passes, wherein in each pass only a part of the single pattern and / or only a part of all single patterns is printed into the inked area along the nozzle track and in at least one of the subsequent passes the missing part of the single pattern or the other entire single pattern is printed into the incomplete or empty inked area. Furthermore, between the passes the print head and the substrate surface are caused to move relative to each other transversely to the nozzle track with a transverse offset.

Description

Technical Field

[0001] The present invention relates to a method for printing on a substrate using inkjet printing, and an apparatus for printing on a substrate having an inking zone grid consisting of rows and columns of inking zones using inkjet printing. Background Technology

[0002] Various technical solutions for printing substrates using inkjet printing and corresponding apparatus have been disclosed in the prior art and applied to a wide range of applications, such as printing rigid and flexible substrates. These methods and apparatuses are particularly suitable for specific applications that require the precise placement of functional liquids into several precisely defined surface areas (corresponding ink application areas) of the substrate. Such applications include, for example, process or medical sensor surfaces, reactive surfaces for medical applications, or pixel surfaces of displays such as LCDs, TFTs, OLEDs, or electronic paper.

[0003] Especially when printing RGB patterns as color filters onto electronic paper displays, a large number of inked areas are typically printed. The size of each individual pattern to be printed can vary considerably, ranging from very small (e.g., 40 × 40 μm) to large (e.g., 200 × 1000 μm). A typical size for a single pattern is approximately 60 × 200 μm. To achieve color display using electronic paper, the printed color layers are visible in the white areas of the underlying electronic paper, particularly the red (R), green (G), and blue (B) pixel faces that act as filters. The black electronic paper pixels absorb light, making the printed RGB color filters only very faintly visible, thus these electronic paper pixels appear almost colorless. For color electronic paper, a pixel typically consists of three color subpixels (RGB) and possibly one white subpixel forming a high-resolution pixel array. Each (color) subpixel is an inked area for printing.

[0004] To achieve high-quality printing results, especially high-quality electronic paper surfaces, it is necessary to uniformly construct sub-pixels across the entire surface of the substrate. The positioning and size of the pixels, as well as the amount of color filters released into each sub-pixel, which serves as the ink-receiving area within narrow boundaries, are all of great importance.

[0005] To achieve repeatable and interference-free printing results, the commonly used quantitative method in inkjet printing applications is to place the exact same number of inkjet droplets in each ink zone of an ink zone type, that is, in all ink zones with the same function, color, shape and / or size.

[0006] Nevertheless, slight differences in droplet volume between printheads, or slight deviations in nozzle position and / or nozzle orientation from their rated positions within the printhead, can leave a clearly visible visual impression that differs from the average, as a large number of single patterns in a row are printed onto the substrate along the printing direction through the same defective printhead nozzles or adjacent defective printhead nozzles. If the printing characteristics of a single printhead nozzle are significantly different from the average of all printhead nozzles, it particularly results in the formation of visible streaks.

[0007] An observer's eye can very keenly detect such intensity differences in the substrate, especially in the case of color filters for electronic paper, at least when several printed single patterns are side by side and / or have the same defect characteristics, these characteristics are slightly different from the remaining single patterns in adjacent areas.

[0008] In practice, these subtle differences are often caused by inherent fluctuations in the printhead nozzles. Specifically, when the printing area differs, even with identical ink volumes, the visual impression of a sub-pixel remains significantly different from the others. Conversely, even with the same area but slight differences in ink volume, the impression remains remarkably different. Therefore, fluctuations in printhead nozzle position that cause area variations, and / or fluctuations in ink volume, can both lead to these undesirable effects.

[0009] The arrival of droplets with a single pattern at different times on the substrate can also result in several different visual impressions of a single pattern, because the printing medium may not be absorbed on the substrate immediately, and the surface tension effect of freshly printed droplets may cause the printing medium to flow systematically toward previously printed droplets.

[0010] Finally, the digital quantization of printhead resolution and the pattern to be printed on the electronic paper display can cause inconsistent visual impressions, particularly resulting in stripes, leading to the classic moiré effect. Especially when the size of the substrate's inking grid is not an integer multiple of the original printhead resolution or print line spacing, misalignment occurs between inking columns under the printhead. This misalignment can accumulate with the number of printhead nozzles arranged side-by-side on the printhead, resulting in visible inking column misalignment in the printed result, or even severe interference, such as lines not being printed or identifiable changes in the distance of the printed pattern. Summary of the Invention

[0011] In view of this, the object of the present invention is to provide a method and an apparatus for printing on a substrate using inkjet printing, which achieves printing on the substrate efficiently and simply, wherein the printing result is particularly uniform and interference-free, and the printed surface is particularly free of stripes and moiré effects.

[0012] The solution of the present invention to achieve the above-mentioned objective is a method according to claim 1, and an apparatus according to claim 16. Advantageous improvements of the present invention are described in the dependent claims.

[0013] In the method of printing on a substrate using inkjet printing according to the present invention, ink zones are defined on the substrate in an ink zone grid consisting of ink zone rows and columns. A single pattern consisting of one or more droplets is printed in each ink zone using one or more printhead nozzles of one or more printheads, wherein the one or more printhead nozzles move relative to the surface along an imaginary nozzle trajectory during the printing process. To obtain a particularly uniform and interference-free printing result, all single patterns of an ink zone row and / or an ink zone column or a printhead trajectory are printed in several passes. In each pass, only a portion of a single pattern, and / or only a portion of all single patterns, is printed into the ink zone along the nozzle trajectory or within the area of ​​the printhead, particularly within the areas of all ink zone rows and / or ink zone columns located below the printhead. In at least one subsequent pass, missing portions of a single pattern or other entire single patterns are printed into incomplete or empty ink zones. Furthermore, between each pass, the printhead and the substrate surface move relative to each other with a certain lateral offset from the nozzle trajectory.

[0014] The apparatus of the present invention for printing on a substrate having an inked area grid consisting of rows and columns of inked areas using inkjet printing comprises: a print head having a plurality of print head nozzles spaced apart from each other, for printing a single pattern consisting of one or more droplets into the inked area of ​​the inked area grid by means of one or more print head nozzles; and a positioning driver for moving the print head and the substrate surface relative to each other along an imaginary nozzle trajectory of each of the print head nozzles and in a direction transverse to the nozzle trajectory. The apparatus also includes a control unit for controlling the printing operation, particularly for controlling the positioning driver, wherein the control unit is designed such that all single patterns of an inked row and / or an inked column or a printing nozzle track are printed in several passes, wherein in each pass, only a portion of a single pattern, and / or only a portion of all single patterns, is printed into the inked area along the nozzle track or in the area of ​​the print head, particularly in the area of ​​all inked rows and / or columns of inked areas located below the print head, and in at least one of subsequent passes, missing portions of a single pattern or other entire single patterns are printed into incomplete or empty inked areas, and between each pass, the print head and the substrate surface are moved laterally relative to each other by a certain lateral distance from the nozzle track.

[0015] The inventors discovered that printing should be performed in several passes, and particularly preferably in several layers, to compensate for the relatively distinct visual impressions of different sections of the substrate surface, especially the rows of inked areas, which are easily recognizable by the observer's eye. In one pass, only a portion or the entirety of a single pattern is printed (pseudo)randomly. Between passes, the print head is moved laterally relative to the substrate to another position, so that, if it is desired to print again in the changed lateral position of the print head, the previously printed portion or the previously printed complete single pattern is printed by other print head nozzles of the print head. Accordingly, for the free positions located between printed single patterns, especially the unprinted inked areas, the print head nozzles used are different from those used when printing the previous single patterns, thereby preventing the adverse effects of each print head nozzle from affecting the entire row of inked areas and effectively avoiding the formation of interference or streaks.

[0016] For example, in a case where 100,000 red single patterns need to be printed on a display, and printing is carried out in three passes, approximately one-third of the single patterns are (pseudo) randomly selected in each pass and are to be printed in the corresponding pass. Each single pattern is preferably printed in exactly one pass, and all 100,000 single patterns are printed sequentially. Between the passes, the print head is offset laterally by a predetermined distance, wherein this distance is preferably at least greater than one printed single pattern, and particularly preferably several millimeters, i.e., significantly greater than a single pattern.

[0017] Printing, in principle, refers to a method in which a liquid or flowable printing medium is applied to a surface, wherein the application is performed according to a stencil, a given pattern, and / or at a given location. According to the invention, the printing method is inkjet printing, i.e., matrix printing, in which the printing medium to be applied is applied to a substrate in the form of droplets or as jets. Accordingly, it is preferably non-contact, i.e., printing is performed in a manner in which the printing apparatus does not directly contact the substrate.

[0018] For printing, the apparatus has one or more printheads that are movable relative to the substrate to be printed, so as to print at different positions on the substrate. This can be either a case where the printhead is fixed and the substrate moves, or vice versa. In principle, the printhead has at least one printhead nozzle for releasing droplets or a jet of printing media. Preferably, a large number of printhead nozzles are arranged in a row on the printhead, and particularly preferably, they are arranged at equal intervals. Alternatively, the printhead nozzles can be arranged in several rows on the printhead, particularly sequentially along the printing direction and / or laterally staggered. Particularly preferably, the rows of printhead nozzles are laterally staggered in a certain way, such that all nozzle trajectories of the printhead have the same distance from each other, thereby achieving uniform lateral resolution.

[0019] During printing, and preferably during each pass of the printhead relative to the substrate surface, the substrate surface below the area of ​​the printhead nozzles is referred to as the printhead trajectory, and the vertical projection of each individual printhead nozzle onto the substrate surface of the motion trajectory realized during printing is referred to as the nozzle trajectory. Accordingly, the nozzle trajectory is not necessarily physically mapped onto the substrate, but is initially a hypothetical trajectory. If the printhead continuously releases printing medium during its linear movement through the maximum printing range or along the ink zone row, the nozzle trajectory is reflected by the printing medium on the substrate surface. The nozzle trajectory can, in principle, extend linearly or have any other non-linear orientation. Preferably, the nozzle trajectory forms an angle of <10°, particularly preferably <5°, further particularly preferably <2° with the ink zone row, and especially preferably is completely parallel to the ink zone row; alternatively, the nozzle trajectory is correspondingly parallel to the ink zone column, and forms the aforementioned angle with the ink zone column as appropriate. However, alternatively, the printhead trajectory can also form any angle with the ink zone row or ink zone column. According to a particularly preferred embodiment of the method, the method is implemented in an alignment-free manner, i.e., without aligning the substrate relative to the printing nozzle trajectory (particularly according to alignment features) prior to printing. During a single pass through the substrate, a printhead comprising several printhead nozzles arranged in a row generates several imaginary nozzle trajectories over the substrate surface, wherein the distance between the nozzle trajectories corresponds to the original lateral resolution of the printhead.

[0020] The printing medium can, in principle, be any liquid and be used for any purpose. The printing medium can be, for example, based on aqueous or non-aqueous solvents and may also contain any other functional components, such as dyes and pigments, but may also contain substances with chemical and / or biochemical activity. Particularly preferably, the printing medium is an ink or color filter dye solution for printing sub-pixels of a display.

[0021] The substrate can, in principle, be made of any material and have any shape. Preferably, the substrate has a flat, printable surface, and particularly preferably employs a flat construction, especially as a plate or thin film. The substrate can be either rigid or flexible. An example of a flexible substrate is a flexible EPD (electronic paper display), which, as an unprinted substrate, has a native black / white resolution of 150 ppi and a TFT pixel size of 170 μm. To generate a color display based on this EPD, RGB filters are printed from top to bottom onto each black / white TFT pixel, where each color pixel is typically slightly smaller than the TFT pixel size, for example, only 150 μm. In this case, the resulting color display resolution is, for example, 75 ppi. Preferably, several, for example, four, inking grids are provided on the surface of the substrate in a staggered manner, wherein one grid is printed with a red filter, one grid with a green filter, one grid with a blue filter, and the fourth grid remains unprinted. More preferably, each TFT pixel has at least one ink area of ​​an ink area type (e.g., color).

[0022] A key criterion for high quality is that color pixels are precisely placed in a given location within each TFT pixel. These nominal locations are typically defined by the substrate, for example, as recesses in the substrate or as TFT grids, forming ink areas. While other applicable standards may exist, a fundamental condition in most cases is that, for all pixels in an active matrix display, color pixels or subpixels within a TFT pixel are not allowed to encroach on adjacent TFT pixels; instead, they must remain within the TFT pixel area.

[0023] Accordingly, the inked area is the underlying structure within the display, such as the TFT driving pixel of the display, wherein, preferably, the inked area is printed with exactly a single pattern. In principle, the inked area can be practically given on the substrate, or the inked area only represents a specific location on the entire surface, and these locations are not directly visible on the substrate itself. A substrate can have one or more different inked area types. Different inked area types can be printed with different printing media, have different amounts of printing media, or different geometries. Preferably, the inked area types are arranged systematically on the substrate, or in a manner that periodically repeats along at least one spatial direction, preferably along two spatial directions, or form a repeating upper-level pattern. Particularly preferably, the electronic paper or EPD has at least three inked area types, namely red, green, and blue. Furthermore, for one or more of these colors, inked area types of different shapes and / or sizes can be given, thereby correspondingly increasing the total number of inked area types to be printed on the substrate. Therefore, a plurality of ink-receiving area grids are provided on the substrate surface in a staggered manner, wherein the plurality of ink-receiving area grids are preferably arranged in the gaps between other ink-receiving area grids, particularly in such a manner that the ink-receiving areas of different ink-receiving area grids are arranged in a manner that repeats periodically along the substrate surface. Particularly preferably, a plurality of ink-receiving area grids are provided with slightly staggered origins, wherein the ink-receiving area grids are particularly preferably formed in the same manner as each other.

[0024] According to the invention, the ink-receiving areas of the substrate are arranged in an ink-receiving area grid consisting of rows and columns of ink-receiving areas. Preferably, the rows and columns of ink-receiving areas are positioned at fixed angles to each other and / or in a constant mutual arrangement across the entire substrate surface. Particularly preferably, the rows and columns of ink-receiving areas are perpendicular to each other and / or arranged in a rectangular matrix. Furthermore, the ink-receiving area grid is preferably aligned relative to the print head, such that the columns of ink-receiving areas extend substantially parallel to the printing direction, thereby enabling particularly simple line-by-line printing. Although the rows and columns of ink-receiving areas are preferably identical, their dimensions and / or layout may differ, or even the ink-receiving areas may be randomly placed within the ink-receiving area grid, in which case it is a pseudo-random grid. To align the substrate relative to the printing apparatus or relative to the nozzle control device, the substrate may also have alignment features, which are preferably detectable by optical or other sensing methods.

[0025] However, the substrate, and particularly the grid of ink-printed areas, need not, in principle, be oriented or aligned in a parallel and / or defined manner relative to the nozzle trajectory. Specifically, the rows or columns of ink-printed areas can be arbitrarily aligned relative to the nozzle trajectory. Accordingly, it is not mandatory for this invention that the nozzle trajectory follows a row or column of ink-printed areas. Accordingly, during the crossing, it is also permissible for the nozzle trajectory to intersect with the rows of ink-printed areas; that is, the ink-printed area of ​​the first row of ink-printed areas is printed in the first segment of the crossing, followed by crossing the boundary between at least two adjacent rows of ink-printed areas, in which case no printing is performed, and finally a single pattern or a portion thereof is printed into the ink-printed area of ​​another row of ink-printed areas.

[0026] A single pattern refers to a single printed surface, wherein each single pattern is composed of one or more droplets of printing medium or ink originating from one or more printhead nozzles. Preferably, each single pattern is printed within exactly one inking zone, or each inking zone contains at least one single pattern printed through one or more printhead nozzles. Particularly preferably, for a given type of inking zone, all single patterns are identical to each other, and even more particularly preferably, they are printed with the same layout and / or number of printing medium droplets.

[0027] According to the invention, all individual patterns, particularly for each individual inked row, are printed in several passes, i.e., more than one pass of the print head, wherein only a portion and / or a part of the individual pattern is printed in each pass. Preferably, in any pass, no individual pattern is printed onto an already printed individual pattern. Particularly preferably, printing is performed in a manner during the passes such that after the last pass through the inked row, all the individual patterns to be printed for an inked row have been printed.

[0028] In each pass, a single pattern is printed along the nozzle trajectory, preferably only in the inked area. Alternatively, it is preferable not to print in areas outside the inked area or at the boundary between two inked areas, thus preventing the printing medium from simultaneously entering two adjacent inked areas.

[0029] The advantageous effects of this invention are largely achieved as follows: between each traversing printing operation, the printhead and substrate are moved laterally relative to each other by a certain lateral distance from the nozzle trajectory. This initially means only that the printhead or printhead nozzle moves laterally relative to the substrate, or the substrate relative to the printhead, at any angle or with a non-zero component perpendicular to the nozzle trajectory. This lateral movement is preferably performed at a defined angle, along a defined motion vector, and / or, particularly preferably, perpendicular to the nozzle trajectory, at least for each individual inked area, preferably across the entire substrate. The degree of lateral movement can be the same distance each time, a sequence of different distances, and / or random distances.

[0030] This distance can be either an integer multiple of the distance between two adjacent printhead nozzles, allowing printing at the printhead's original resolution, or an additional increment to improve the actual lateral resolution, making it higher than the original resolution. Particularly preferably, the printhead moves laterally to the printing direction in each pass, thereby improving the lateral resolution through n passes of the printhead relative to the substrate. Accordingly, the actual lateral resolution a res This refers to the number of nozzle trajectories per unit length.

[0031] By utilizing lateral displacement, visual differences in the appearance of different segments on the substrate surface can be avoided, thus eliminating the need, in principle, to measure the volume of droplets released from each specific printhead nozzle. Furthermore, it is unnecessary to print a single pattern or inked area with particularly precise volumetric accuracy. Accordingly, according to a preferred embodiment of the method, the volume of the printing medium is generally, and particularly preferred, disregarded when measuring the lateral displacement to be performed. Not measuring and / or disregarding the volume released from each specific printhead nozzle is particularly advantageous because numerous factors can cause variations in the volume typically measured for printhead nozzles. Accordingly, the method is implemented in a manner that disregards droplet volume.

[0032] In a preferred improvement of the method for printing a substrate according to the invention, in layers following the first layer and / or in passes following the first pass, and preferably in each layer or each pass, only missing portions or the entire single pattern of a single pattern are printed into incomplete or empty inked areas, without printing into inked areas already containing the complete single pattern. This ensures, on the one hand, that the surface is covered with the single pattern in a desired manner after printing the final layer and / or after the final pass, and on the other hand, that a large amount of printing medium is not applied to any inked area, thereby avoiding perceptible visual interference. In a particularly preferred improvement of the method, each single pattern is printed completely in exactly one layer and / or one pass, thereby printing the single pattern particularly uniformly and effectively preventing uneven extension of the printing medium during application to partially printed single patterns.

[0033] In a preferred embodiment of the printing substrate method of the present invention, after all layers have been printed, or after all passes of the print head relative to the corresponding areas of the substrate, particularly within each row and / or column of inked areas, all individual patterns are printed, and / or no empty or unprinted inked areas remain. Thus, the complete printing is divided into only a few passes, and / or, in terms of the number and layout of individual patterns, the final printed result is indistinguishable from conventional printing in the prior art. However, the quality of printed matter produced using the method of the present invention is far superior to that of printed matter in the prior art.

[0034] In principle, any proportion of all individual patterns can be printed in each pass, but in a preferred embodiment of the method for printing a substrate according to the invention, printing is performed in u passes, particularly for each individual inked area row, and approximately 1 / u of all individual patterns, or approximately 1 / u of all portions of a single pattern, is printed in each pass. Particularly preferably, ±25% of all individual patterns or portions of a single pattern is printed in each pass; particularly preferably, ±10% of all individual patterns or portions of a single pattern is printed; and even more particularly preferably, ±5% of all individual patterns or portions of a single pattern is printed.

[0035] In principle, any criteria can be used to select the single pattern to be printed in a pass, but preferably, all portions of the single pattern to be printed in the pass and / or portions of the single pattern to be printed in its entirety are selected randomly or pseudo-randomly, particularly individually for each inked row. For each pass of the print head and / or for each inked row, particularly preferably, the single pattern or portions thereof to be printed are randomly selected again and / or independently of the previously printed inked rows.

[0036] Furthermore, preferably, between some or all passes, the printhead and the substrate surface are offset relative to each other by a certain distance or lateral offset, which is greater than a single pattern and particularly greater than the lateral extension of a single pattern. This avoids the same printhead nozzle from participating in printing when two single patterns of an inked area are printed in different passes, thereby preventing the recurrence of printing errors caused by the properties of a particular printhead nozzle. Preferably, the lateral offset is less than 50% of the width of the printhead or the portion of the printhead with the printhead nozzle, particularly preferably less than 33%, and even more preferably less than 25%. Furthermore, preferably, the lateral offset is smaller than the lateral width of the printhead or the portion of the printhead with the printhead nozzle divided by the number of passes and / or layers.

[0037] In an advantageous refinement of the method according to the invention, the lateral offset x is not equal to the minimum printing nozzle distance or the minimum nozzle track distance a of the printing nozzle head, such that by printing in a plurality of traverses, a position resolution higher than the original position resolution of the print head is achieved, and the minimum distance a between two nozzle tracks of the actual position resolution res is less than a.

[0038] Furthermore, particularly preferably, in order to increase the position resolution to be higher than the original position resolution of the print head, each ink application area row is printed in k staggered traverses, where in each case the print head is offset relative to the substrate surface by a certain lateral staggering distance where a is the minimum distance between two nozzle tracks of the original printing resolution, in particular, or the distance a between two adjacent print head nozzles of the print head. Furthermore, it is particularly preferred to select j < k. Here, j is preferably selected from the set of all non-zero natural numbers. For each traverse, the integer j can be different from each other, but can also be the same for several traverses or for the entire printing. Therefore, the number k of staggerings is used to increase the printing resolution, so that an effective printing resolution of 2400 ppi can be achieved on the substrate with an original printing resolution of 600 ppi and k = 4.

[0039] In a preferred embodiment of the method for printing a substrate according to the invention, the total number u of traverses is at least twice the number k of staggered traverses, and / or the total number u of all traverses of an ink application area row is divided into n levels each consisting of k staggered traverses, where particularly preferably, in each level, the actual position resolution a obtained by staggering is achieved res . Furthermore, particularly preferably, for each of the n levels, the number k of staggered traverses is the same.

[0040] Furthermore, preferably, the lateral offset of a single or all traverses is at least equal to the minimum nozzle track distance a of the printing nozzle head, so as to prevent the same print head nozzle from being positioned above an ink application area row in two traverses, where the degree of the lateral offset x is preferably at least one printing nozzle distance x = i × a, where and particularly preferably, Furthermore, particularly preferably, at least for a part of the traverses, preferably for all traverses other than one level, and in particular for all traverses, the lateral offset is carried out both at the staggering distance and at the printing nozzle distance. Accordingly, in the case of printing with k staggered traverses in each of the n levels, and thus with a total of at least u = k × n traverses, it is preferably that after each traverse, the print head is offset relative to the substrate surface by a certain distance where Here, a is the minimum distance between the trajectories of two nozzles. i is preferably selected separately for each pass, and it is preferably selected that j < k, and particularly preferably j = 1.

[0041] Preferably, the k staggered passes of each ink application zone row together form a complete layer. Although all the staggered passes of each layer can in principle be carried out successively, between the staggered passes of each layer, any passes for other ink application zone rows can also be carried out, and / or any misalignments of the degree of the printing nozzle distance and / or the staggered distance can be carried out. In this way, the printing of a layer can be interrupted by other passes, especially with a large lateral misalignment. Generally, however, preferably, k staggered passes are finally carried out for each individual ink application zone row, so as to achieve a complete staggered resolution for each ink application zone row.

[0042] Although most visual disturbances in the printing result can already be prevented by using the method of the present invention, in individual cases, clearly visible disturbances, especially in the form of stripes, still occur. The coherent effects of the nozzle properties can in particular cause recognizable fluctuations in the optical properties of a single pattern on the substrate, the typical repetition distance (wavelength) of which is several single nozzle pattern distances, often several millimeters or even several centimeters. Accordingly, in an advantageous improvement of the method according to the present invention, a first test print is created by the print head, and this test print is inspected for laterally recurring disturbances. Where one or more periodic lateral disturbances occur, especially where intensity maxima and / or stripe formation occur, at least one lateral disturbance distance λ is determined, and in the subsequent printing of the substrate where and n = the number of layers, the lateral distance x between the layers and / or the passes is determined, so that by appropriately selecting the lateral misalignment x between the printing layers, the coherent effect with a wavelength of λ that may be recognizable on the substrate can be reduced, and even the periodic lateral disturbances can be efficiently eliminated. For each layer or each pass, the integer i can be different from each other, but it can also be the same for the entire ink application zone row or the entire printing. Here, the lateral disturbance distance λ is the minimum distance between two laterally periodically recurring disturbances, such as between two intensity maxima. As a supplement or alternative, the lateral distance x of the passes can be selected in such a way that in the interval [0, λ] including λ, the average lateral position of all the passes is between 1 / 4λ and 3 / 4λ, and especially 1 / 2λ ± 10%. Generally, when printing the substrate, the lateral layout of the passes is preferably selected in such a way that the passes suppress the periodic disturbances.

[0043] Preferably, a new test print is performed before each new print run and / or after each modification of at least one print parameter. This is because the occurrence of periodic interference depends on a large number of influencing variables, such as the shape and size of a single pattern, the layout of a single pattern, print resolution, and the print head used; therefore, it is necessary to check for the presence of such periodic interference in principle. Furthermore, the test print can be checked for other interferences that do not occur laterally, which can also be taken into account when determining the ideal lateral distance x. In this method, the test print can be used only to check for potential interferences, but it can also be a pre-production print. Therefore, in continuous production or printing processes, at least one pre-production print can be used as a test print for subsequent print runs. Particularly preferably, a large number of pre-production prints are used as test prints, and the state of lateral and, particularly, periodic interferences is evaluated based on these large number of pre-production test prints, and these interferences are utilized individually or collectively when determining the lateral distance x to avoid such interferences.

[0044] To further optimize the method for printing substrates of the present invention, particularly within the range of each individual ink-printing area row, the number of layers n can be selected to be the same as the number of staggered or staggered crossings k, and / or, the lateral distance is x = (n × i + 1) × a res in Where a res It is the minimum distance between two nozzle tracks that achieve actual positional resolution through interleaving, thereby enabling highly efficient printing operations while preventing the nozzle tracks from precisely overlapping and extending in each layer. In other words, the actual positional resolution here is determined by... It is given that, particularly preferably, n>1 and / or k>1. The number of passes is the number of times the print head passes through a single inked area with any print head nozzle. Accordingly, when selecting the lateral distance x, it is preferable not to select an integer multiple of the minimum print nozzle distance or the minimum nozzle trajectory distance a, so that subsequent layers are printed with a slight lateral offset relative to the print nozzle grid or nozzle trajectory of the previous layer, thereby effectively preventing the formation of stripes. In this regard, it is particularly preferable to use several staggered passes to improve resolution, wherein a single pattern is distributed equally to each stagger, for example, four staggers.

[0045] According to a preferred improvement of the method of the present invention, when selecting the lateral distance, it is preferable not to select an integer multiple of the minimum printing nozzle distance or the minimum nozzle trajectory distance a, so as to print subsequent layers in a manner that is slightly laterally offset relative to the printing nozzle grid or printing nozzle trajectory of the previous layer.

[0046] Finally, in an advantageous embodiment of the method of the present invention, the lateral interference distance λ is taken into account when selecting the lateral misalignment x, and simultaneously the minimum printing nozzle distance or minimum nozzle trajectory distance a and / or the minimum distance a between two nozzle trajectories at the actual position resolution are considered. res The fraction or non-integer multiple of the x is chosen as the lateral distance x, wherein the coefficient i is chosen in a manner that minimizes the lateral distance x. Particularly preferably, this is achieved by... in And n = the number of levels and simultaneously through x2 = (n × i2 + 1) × a res in Measure the lateral distance x, where the absolute value |x2-x1| is minimized, specifically by appropriately choosing the integer i. 1,2 accomplish. Attached Figure Description

[0047] An embodiment of the method of the present invention will be described in detail below with reference to the accompanying drawings. Wherein:

[0048] Figure 1 This is a schematic diagram of a first embodiment where the printhead is first traversed through the printed substrate, with the printhead aligned accordingly.

[0049] Figure 2 For after the second printing, as Figure 1 The schematic diagram of the substrate is shown, in which the printhead is aligned accordingly.

[0050] Figure 3 For after the last third cross-printing, as Figure 2 The schematic diagram of the substrate is shown, in which the printhead is aligned accordingly.

[0051] Figure 4 This is a schematic diagram of a second embodiment with the first printhead traversing the printed substrate, wherein the printhead is aligned accordingly.

[0052] Figure 5 For after the second printing, as Figure 4 The schematic diagram of the substrate is shown, in which the printhead is aligned accordingly.

[0053] Figure 6 This is a schematic diagram of a third embodiment with two printed substrates, including printed sub-patterns.

[0054] Figure 7 This is a schematic diagram of a fourth embodiment with the first staggered printing across a rotating substrate, wherein the printheads are aligned accordingly.

[0055] Figure 8 For example, after the second interlaced printing, Figure 7The schematic diagram of the substrate shown illustrates that the printheads are aligned accordingly, and

[0056] Figure 9 For example, after the final third interlacing printing, Figure 8 The diagram shows a substrate in which the printhead is aligned accordingly. Detailed Implementation

[0057] Using a flexible electronic paper display with a black / white resolution of 150 ppi and a TFT pixel size of 170 μm as an example, a single color filter is illustratively printed on the flexible substrate 1. Each color pixel should be slightly smaller than the TFT pixel size, approximately 150 μm. Accordingly, an inking area 2 is provided on the substrate 1 to accommodate the color filter within a rectangular grid consisting of inking area rows Zx and inking area columns Rx. The inking area rows Zx extend along the printing direction DR, and the substrate 1 can be moved along the printing direction below a printhead 5 containing sixteen printhead nozzles Dx arranged in a row for printing on the substrate 1. Each printhead Dx follows a linear nozzle trajectory 6 along the surface of the substrate 1. In practice, unlike this greatly simplified example, instead of printing a single inking area grid, several staggered inking area grids are typically printed, where each inking area 2 of a certain inking area type is repeatedly arranged on the substrate 1. Typically, at least one ink area 2 of an ink area type (e.g., color) is printed into the color pixel.

[0058] To compensate for the specific properties of individual printhead nozzles Dx, and especially the effects of errors, and to obtain a uniform, streak-free printing result, several passes are used, in this case three passes (see...). Figure 1-3 (to be printed.)

[0059] In the first step, one-third of all single patterns 3 to be printed into the inking area 2 of each inking area row Zx are randomly selected, and these single patterns are printed by the print head 5 as it travels through the substrate 1 along the printing direction DR (see...). Figure 1 In this case, each individual pattern 3 is printed using two side-by-side single printhead nozzles Dx of printhead 5, wherein, for example, the first inked area row Z1 is printed through printhead nozzles D1 and D2. For this purpose, six droplets 4 of filter dye are printed into each inked area 2 through each of the printhead nozzles Dx.

[0060] After printing 1 / 3 of all the single patterns 3 onto the substrate 1 in the first pass, the print head 5 is moved laterally L so that the nozzles D1 and D2 in front of the first inking zone row Z1 are no longer the print head nozzles D1 and D2, but two print head nozzles D5 and D6 (see...). Figure 2The same printing operation is then performed, wherein, during the pass-through, another third of all the single patterns 3 in the inked area row Zx are printed again. However, in this case, more single patterns 3 are printed only in the unprinted empty inked areas 2, so after the second pass of the print head 5, 2 / 3 of all single patterns 3 are printed.

[0061] Subsequently, the print head 5 is moved a certain distance laterally along the L direction, thereby using the print head nozzles D8 and D9 to print the first inking zone Z1 (see...). Figure 3 During the final pass of the print head 5 through the substrate, the remaining one-third of the single pattern 3 is printed, so that after printing with all three passes, all inked areas 2 are filled with filter dye.

[0062] Furthermore, after printing a defined number of inked areas Zx, the printed substrate 1 is checked for any visually perceptible repeating stripe patterns. If such stripe patterns are identified, the repeating distance λ of the stripes is then determined. If this repeating distance in the lateral direction is, for example, λ = 12 mm, and printing is still performed with three passes, then the lateral offset x of the printhead 5 between each of these three passes is chosen such that x approximately satisfies x = 12 * (Z + 1 / 3) mm, where, for example, Z = 0: x = 4 mm. Furthermore, a lateral offset of x = 12 mm is avoided, as this would enhance the repeating stripe pattern because, in this case, in each pass, stronger stripes would fall onto stronger stripes in other passes.

[0063] In such Figure 4 and Figure 5 In the alternative embodiment shown, to improve the actual printing resolution above the original printing resolution of the print head 5, printing is performed in an interleaved manner, thereby printing each single pattern 3 at one level within two passes. Specifically, in the first pass (see...) Figure 4 In the process, the first part of a single pattern 3 is printed in the area of ​​the nozzle trajectory 6. Then, the print head 5 is moved along the transverse direction L with a certain staggered shift to reach a nozzle trajectory 6 located between the nozzle trajectories 6 of the two adjacent print head nozzles Dx that were previously crossed, and then the second part of the single pattern 3 can be printed with improved effective resolution.

[0064] In this scenario, all traversals of a single level can proceed sequentially, such as... Figure 4 and Figure 5 As shown, but it is also possible to print a portion of the single pattern 3 or the entire single pattern 3 at other levels first, such as... Figure 6 As shown. In addition, if advantageous or necessary, each individual pattern 3 may be printed incompletely.

[0065] at last, Figure 7–9 illustrates three successive passes in another embodiment, wherein the substrate 1 is not parallel to the nozzle trajectory 6, but is arbitrarily oriented, here at a certain angle. Furthermore, printing is performed with several staggered passes, thereby improving the actual printing resolution to be higher than the original resolution of the printhead 5. Within the range of the first pass, if the nozzle trajectory 6 extends within or does not exceed the ink zone boundary, each droplet 4 of a single pattern 3 is always printed into the ink zone 2, and at the ink zone boundary, printing is simultaneously performed in two adjacent ink zones 2 (see [reference]). Figure 7 ).

[0066] In subsequent crossings, if the nozzle trajectory 6 extends within or does not exceed the boundary of the ink zone 2 (see...) Figure 8 If this is not the case, then only the droplets 4 of a single pattern 3 are printed into the inking area 2, thus adding the other parts of the single pattern 3. Finally, following the same rules, a third traversal through the same inking area row Lx is performed, where the initial single pattern 3 is completed (see...). Figure 9 In the first two inked rows L1 and L2, 50% of all inked areas 2 are printed. Therefore, three more passes are made to print the still empty inked areas 2 with the same staggered resolution, thus completing the entire pattern.

[0067] Appendix Label Table

[0068] 1 Substrate

[0069] 2. Ink application area

[0070] 3. Single pattern

[0071] 4 droplets

[0072] 5 Printing Head

[0073] 6. Nozzle trajectory

[0074] DR printing direction

[0075] L horizontal

[0076] Dx Printhead Nozzle x

[0077] Rx Ink Zone Column x

[0078] Zx Ink Zone x

Claims

1. A method for printing on a substrate using inkjet printing, wherein... - Ink zones are defined on the substrate within an ink zone grid consisting of ink zone rows and columns. - Using the nozzles of the printhead, a single pattern consisting of one or more droplets is printed onto the inking area, wherein... - During the printing process, the printhead nozzle and the surface of the substrate move relative to each other along an imaginary nozzle trajectory. in, - To print all the single patterns in a single inked area using several traversal lines, where - In each pass, only a portion of a single pattern and / or only a part of all single patterns are printed into the inking area along the nozzle trajectory, and - In at least one of the subsequent passes, the missing portion of a single pattern or other entire single pattern is imprinted into an incomplete or empty inked area, and - Between each pass, the surface of the printhead and the substrate are offset laterally to the nozzle trajectory by a certain amount. Relative to each other in motion; as well as The process involves creating a first test print using a printhead and inspecting it for recurring transverse interference. Specifically, in the event of periodic transverse interference, the distance of the transverse interference is measured. λ And in subsequent printing of the substrate, through To measure the lateral displacement between different levels ,in and =Number of layers, and / or, select the lateral displacement of the crossing. , such that in the interval [0, λ] including λ, the average lateral position of all crossings is between ¼ λ and ¾ λ.

2. The method for printing on a substrate according to claim 1, characterized in that, In each pass, only the missing part of a single pattern or the entire single pattern is imprinted into the incomplete or empty ink area of ​​the ink area row.

3. The method for printing on a substrate according to claim 1, characterized in that, After all the traversals of an inked row have been completed, all the individual patterns of the inked row are printed, and no unprinted inked areas remain.

4. The method for printing on a substrate according to claim 1, characterized in that, by u Each pass is used to print each individual inked area row, and approximately 1 / 3 of all the individual patterns of said inked area rows are printed in each pass. u Or approximately 1 / 3 of all single patterned portions u .

5. The method for printing on a substrate according to claim 1, characterized in that, Randomly or pseudo-randomly determine all single pattern portions to be printed in a pass and / or single patterns to be printed in their entirety.

6. The method for printing on a substrate according to claim 1, characterized in that, Between some or all of the passes, the printhead and the surface of the substrate are offset from each other by a certain distance, the distance being greater than the extension of a single pattern.

7. The method for printing on a substrate according to claim 1, characterized in that, The lateral displacement Not equal to the minimum printing nozzle distance or minimum nozzle trajectory distance of the print head This allows for a higher positional resolution than the original positional resolution of the print head by printing through multiple passes.

8. The method for printing on a substrate according to claim 7, characterized in that, To improve the positional resolution, making it higher than the original positional resolution of the printhead, in order to Each ink-printing zone is printed using an alternating pattern, wherein the print head and the surface of the substrate are offset laterally from each other by a certain amount. ,in in, This represents the minimum distance between the two nozzle trajectories.

9. The method for printing on a substrate according to claim 8, characterized in that, Total number of crossings u At least twice as The number of intersecting crossings, and / or the total number of crossings in a line of ink. u Divided into Each by The locations are formed by interlacing, where, at each location, the actual position resolution obtained through interlacing is realized. .

10. The method for printing on a substrate according to claim 1, characterized in that, Lateral displacement, either individually or in all directions At least equal to the minimum nozzle trajectory distance of the printhead This avoids the same printhead nozzle being positioned above an inked area line during two passes, wherein the lateral misalignment... The degree is at least the distance of the printing nozzle. ,in .

11. The method for printing on a substrate according to claim 8, characterized in that, In Each level A series of intersecting crossings, thus totaling at least In the case of printing through multiple passes, after each pass, the print head and the surface of the substrate are laterally offset relative to each other. Displacement, in which ,in, This represents the minimum distance between the two nozzle trajectories.

12. The method for printing on a substrate according to claim 8, characterized in that, Each ink zone The intersecting passages form a complete layer.

13. The method for printing on a substrate according to claim 1, characterized in that, In the presence of periodic lateral interference, the lateral interference distance is measured. λ And in subsequent printing of the substrate, through in and =Number of layers, to determine the lateral displacement between layers. And / or, select the lateral displacement of the crossing. This makes the average lateral position of all crossings in the interval [0, λ], which includes λ, ½ λ ± 10%.

14. The method for printing on a substrate according to claim 8, characterized in that, Select with the above The number of layers in the same number of intersecting inked areas And / or, the lateral displacement ,in, It is the minimum distance between two nozzle trajectories whose actual position resolution is obtained through interleaving, i.e. .

15. The method for printing on a substrate according to claim 14, characterized in that, In selecting the lateral displacement The lateral interference distance will be... λ Taking into account, and simultaneously considering the minimum distance between the two nozzle trajectories at the actual position resolution. The odd multiples of the selection are used as the lateral shift. , whereby, at the same time, lateral displacement is achieved Choose the coefficients to use in the smallest possible way. i .

16. The method of printing on a substrate according to claim 2, wherein each individual pattern is printed completely in exactly one pass.

17. The method for printing on a substrate according to claim 6, wherein, The distance is greater than the lateral extension of a single pattern.

18. The method for printing on a substrate according to claim 8, wherein, 。 19. The method for printing on a substrate according to claim 10, wherein, 。 20. The method for printing on a substrate according to claim 11, wherein, i Select individually for each crossing.

21. The method for printing on a substrate according to claim 11, wherein, 。 22. The method for printing on a substrate according to claim 11, wherein, 。 23. The method for printing on a substrate according to claim 12, wherein, Between each staggered crossing at each level, arbitrary crossings of other inked zones are permitted, and / or the degree of offset is determined by the distance between the printing nozzles and / or lateral displacement. Arbitrary displacement.

24. The method for printing on a substrate according to claim 13, wherein, In the event of periodic transverse disturbances with maximum intensity, the transverse disturbance distance is determined. λ .

25. An apparatus for printing a substrate having a grid of inked areas consisting of rows and columns of inked areas using inkjet printing, comprising: - At least one printhead having a plurality of printhead nozzles spaced apart from each other, for printing a single pattern composed of one or more droplets into the inking area of ​​the inking area grid by means of one or more printhead nozzles. - A positioning driver for moving the printhead relative to the surface of the substrate along an imaginary nozzle trajectory of each of the printhead nozzles and in a direction transverse to the nozzle trajectory. - A control unit used to control the printing operation, wherein - The control unit is designed to print all single patterns through several rows of an inked area, wherein - In each pass, only a portion of a single pattern and / or only a part of all single patterns are printed into the inking area along the nozzle trajectory, and - In at least one of the subsequent passes, the missing portion of a single pattern or other entire single pattern is imprinted into an incomplete or empty inked area, and Between each pass, the surface of the printhead and the substrate are transversely offset relative to each other by a certain amount of displacement from the nozzle trajectory. ,as well as A first test print is created using the printhead, and this first test print is checked for recurring interference in the lateral direction. In the presence of periodic lateral interference, the lateral interference distance is measured. λ And in subsequent printing of the substrate, through To measure the lateral displacement between different levels ,in and =Number of layers, and / or, select the lateral displacement of the crossing. , such that in the interval [0, λ] including λ, the average lateral position of all crossings is between ¼ λ and ¾ λ.

26. The apparatus of claim 25, wherein the control unit is used to control the positioning driver.

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