A high-speed single-pass inkjet printing method

Abstract

A single-pass inkjet printing method comprising the steps: a) providing a substrate (S); b) forming on the substrate (S) at a printing speed higher than two meters per second (Pspeed) a monochromatic image (I), comprising a plurality of printed dots, by driving with a waveform (W) a plurality of piezoelectric printheads (H1..M), having one or more nozzle rows (R1..N), for jetting ink per printed dot of the plurality of printed dots; wherein the formed monochromatic image has a first print resolution (PRES,1) aligned the one or more nozzle rows (R1..N); and a second print resolution (PRES,2) substantially perpendicularly aligned the one or more nozzle rows (R1..N); and wherein the first print resolution (PRES,1) is more than two times the second print resolution (PRES,2); and where each printed dot of the plurality of printed dots has a dot size (Dsize) which is at least equal to a dot pitch (DPRES,2) according the second print resolution (PRES,2).

Description

DescriptionTitle of Invention: A high-speed single-pass inkjet printing method

[0001] [The present invention is a high-speed single-pass inkjet printing method suitable to produce printed products containing a printable substrate such as corrugated cardboard. The present invention can also be used in other applications like folding carton printing, object printing, label printing, flexible packaging, document printing … with high-speed single-pass inkjet printing technology.Technical Field

[0002] The technical field relates to single-pass inkjet printing methods suitable for manufacturing printed products containing printable substrate such as manufacturing corrugated cardboard by decorating paper substrate at high printing speeds above 100 m / min (= meters per minute) with piezoelectric printheads to achieve high printing quality.Background Art

[0003] Corrugated cardboard is a packaging material as it is low cost and lightweight.Lightweight packaging material reduces transportation costs and facilitates the handling during delivery to the customer. A further benefit is that corrugated cardboard boxes are stackable, making them easy to store and transport.

[0004] Corrugated cardboard is formed by gluing one or more fluted sheets of paperboard (also called corrugating medium) to one or more flat sheets of linerboard (also called facings). Commonly, two types of corrugated cardboard are used as packaging material: single face cardboard with one fluted sheet glued to one facing (total two sheets) and single wall cardboard with one fluted sheet sandwiched between two facings (total three sheets).

[0005] One could use up to seven paper sheets for the production of corrugated boards (resulting in so-called triple wall corrugated boards).

[0006] The main part of the used corrugated board for packaging applications requires a decorative appearance or requires information and / or coding, which is typically achieved by printing an image, text or (bar or QR) codes. Most of thecorrugated board for packaging applications is printed by analogue flexographic printing, either in single or in multiple colors. The manufacturing of the printing cylinder, which is required for flexographic printing, is very complex and costly and therefore can be economically justified only at high numbers of the printed parts of the same design. As soon as any change in the printing design is required, new printing cylinders need to be manufactured. The cylinders may be stored to avoid making new ones; however, this requires large storage room.

[0007] When the number of forming monochromatic images is low or variable data has to be printed such as bar codes or QR codes, only digital printing is an industrially relevant, alternative printing technique such as inkjet printing may be used for different substrates. In inkjet printing, printhead(s) may be driven according to an electronical pattern across the substrate or may be fixed above the substrate (which is typically moved through the machine by a conveying system), thereby producing an image on the substrate when passing the printhead(s) once (single-pass printing) or repeatedly (multi-pass printing).

[0008] Inkjet printing is a suitable method for applying a print on printable substrate such as corrugated board, especially when the so-called pre-print technique (the print is applied to a paper liner before the manufacturing of the corrugated board) and / or the so-called post print technique (the print is applied onto the readymade corrugated board) is used.

[0009] A newer method is the integration of a digital printing unit (typically an inkjet printing unit) into an industrial manufacturing machine using printable substrate, such as a corrugator or a corrugated board production line (see e.g.,DE102013202871 A1 or WO2014128115 A1), or an existing printing line such as an offset press. This method has advantages as compared to the analogue flexography printing in regard of the manufacturing costs and in production flexibility.

[0010] State of the art industrial manufacturing machines using printable substrate, such as corrugators, produce at conveying speeds of substrate, such as paper board or liner, in the order of 150 m / min up to 450 m / min. This requires a challenging high-speed inkjet printing method which achieves high printing quality with good color saturation such as machine-readable bar codes; machine-readable QR codes; human-readable printed characters; thin lines of logo’s... even if they are printed inverse (e.g., white text on a black background) or small.

[0011] State-of-the-art industrial manufacturing machines using printable substrate, such as corrugators, are capable of producing products containing said printable substrate, such as paperboard or liner, at conveying speeds ranging from 150 m / min to 450 m / min. This necessitates an advanced high-speed inkjet printing method that ensures high-quality printing. Such printing must accommodate machine-readable barcodes and QR codes, human-readable text, thin logo lines, brightness, and even inverted prints (e.g., white text on a black background) or small fonts.

[0012] US2017225460A1 discloses systems and methods for printing graphics on substrates, particularly components used in manufacturing absorbent articles such as diapers, using non-contact inkjet printing processes, which addresses limitations of traditional contact printing methods which often necessitate shutdown and restart of entire converting operations when graphic designs change, whereas non-contact inkjet printing processes provide relatively high degrees of flexibility and ease with regard to the ability to change printed graphic designs. The system enables printing at substrate speeds ranging from 0.5 to 15 meters per second, with some configurations operating at speeds equal to or greater than 6 meters per second.

[0013] US2006203024A1 discloses an image forming apparatus and method using radiation-curable ink, particularly ultraviolet-curable ink systems, wherein droplets are ejected onto a recording medium and cured by radiation irradiation to form images which addresses the technical problem of landing interference, which occurs when subsequently ejected droplets land on or near previously deposited droplets before sufficient curing has occurred, causing the droplets to combine undesirably on the recording medium surface. To prevent landing interference, preliminary curing light sources are provided immediately after each head to preliminarily cure or semi-cure ink droplets deposited by a preceding head, thereby curing the surface of the deposited ink droplet to a prescribed thickness such that deposited ink droplets do not combine on the surface of the recordingmedium with ink droplets of the same color or different color ejected from subsequent heads.Summary of Invention

[0014] It is the objective of the present invention to provide a solution to the above stated problems. The objective has been achieved by providing a high-speed single-pass inkjet printing method especially for production of printed products, containing printable substrate, such as corrugated cardboard, as defined in claim 1.

[0015] Other features, elements, steps, characteristics, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention. Specific embodiments of the invention are also defined in the dependent claims.Technical Problem

[0016] One of the technical problems of inkjet printing above 100 m / min on a substrate, preferably paper substrate, especially for production of printed corrugated cardboard is achieving a high quality of printing such as high jetting reliability, machine-readable barcodes and QR codes, human-readable text, thin logo lines, and even inverted prints (e.g., white text on a black background) or small fonts.

[0017] But printing at a high speed above 100 m / min (≈1.67 m / s), even with a singlepass inkjet printing method, needs high fire frequencies by the piezoelectric printheads which causes the forming of satellites; start-up effects which is the presence of a fast drop before the rest of the printed dot and not well aligned printed dots. These anomalies cause a low jetting reliability and bad print quality whereby barcodes, QR codes are not machine-readable or inverted thin lines or small fonts are not recognizable.Brief Description of Drawings

[0018] Figure 1. A shows a cross-section of an end shooter piezoelectric printhead, where the print head walls (10) encompass an ink channel (14) supplied with inkjet ink via an ink inlet (12), which can only leave the print head as an ejected ink droplet (17) via ink ejection (11) through a nozzle (16) in the nozzle plate (15)of the print head. The piezo element of the print head for forming the ejected droplet (17) is not shown in the schematic drawing.

[0019] Figure 1. B shows a cross-section of a throughflow piezoelectric printhead, where the print head walls (10) encompass an ink channel (14) supplied with inkjet ink via an ink inlet (12) and which continuously leaves the ink channel (14) via an ink outlet (13) and only when required leaves the ink channel (14) as an ejected ink droplet (17) via ink ejection (11) through a nozzle (16) in the nozzle plate (15) of the print head. The piezo element of the print head for forming the ejected droplet (17) is not shown in the schematic drawing.

[0020] Both illustrated cross-sections of piezoelectric printheads in Figure 1 are driven with a waveform (W) and the nozzle is part of a nozzle row having a plurality of nozzles, which is not shown, formed in the nozzle plate.

[0021] Figure 2 illustrates a print pulse (1) of a waveform (W) having a rising segment (2) to reach a certain voltage, a dwell segment (3) for maintaining the voltage and a falling segment (4) for removing the voltage applied. The voltage applied gives the print pulse (1) its amplitude (5), determined in voltage (V). The moment at which the voltage is no longer applied is called the end segment (6) of the print pulse.

[0022] Figure 3 illustrates a waveform according to a preferred embodiment wherein the waveform is having 3 subsequent print pulses followed by a cancel pulse at the end. The 3 print pulses and cancel pulse encompasses four acoustic resonance periods (ARP), each ARP including a printing pulse having an amplitude A1, A2, A3 and a cancel pulse having an amplitude A4. The term "acoustic resonance period" (ARP) of a piezoelectric printhead is the time-period that refers to the time that it takes for a pressure wave to travel both ways in an ink chamber. It is a characteristic for each print head type and can differ depending on the ink used. The period is namely related to the speed of sound in the ink. The acoustic resonance period can be measured by changing the timing between two ceramic movements in a single drop wave form.Solution to Problem

[0023] By using the presented invention with a single-pass inkjet printing method at a printing speed above 100 m / min the above technical problem is overcomewhereby the print quality is acceptable for machine-reading and human reading even with (inverted) small fonts and thin lines and the jetting reliability is tremendous higher. The single-pass inkjet printing method of the present invention here forms on a provided substrate (S), preferably paper substrate, a monochromatic image (I), comprising a plurality of printed dots, by driving with a waveform (W) a plurality of piezoelectric printheads (H1..M), having one or more nozzle rows (R1..N), for jetting ink per printed dot of the plurality of printed dots; - wherein the formed monochromatic image has a first print resolution (PRES,1) aligned the one or more nozzle rows (R1..N); and a second print resolution (PRES,2) substantially perpendicularly aligned the one or more nozzle rows (R1..N); and - wherein the first print resolution (PRES,1) is more than two times the second print resolution (PRES, 2), thus PRES,1 > 2 × PRES,2; and- where each printed dot of the plurality of printed dots has a dot size (Dsize) minimal a dot pitch (DPRES,2) according the second print resolution (PRES, 2), thus where each printed dot of the plurality of printed dots has a dot size (Dsize) at least equal to said dot pitch (DPRES,2).The invention provides a solution to the problem by combining printing speeds higher than hundred meters per minute with a resolution configuration wherein the first print resolution is more than two times the second print resolution in perpendicular directions, using piezoelectric printheads arranged to form a monochromatic image across the substrate width.The differences in resolution between one direction and the other direction can be called anisotropic printing resolution.Advantageous Effects of Invention

[0024] By using dot sizes at least equal to the dot pitch (DPRES,2) according the second print resolution (PRES, 2), the printed dots are concatenating (or having a small overlap) neighboring printed dots along the second print resolution (PRES, 2) whereby the aforementioned technical problem is solved and high quality printing with a printing speed above 100 m / min is achievable with a good jetting reliability.

[0025] The claimed invention addresses the technical challenge of achieving high- quality monochromatic image formation in single-pass inkjet printing operations atprinting speeds exceeding two meters per second. At such elevated operational speeds, conventional inkjet printing systems encounter significant technical difficulties in maintaining acceptable print quality while managing ink deposition characteristics on substrates. The fundamental technical problem relates to balancing competing requirements in high-speed printing operations: achieving sufficient print resolution to produce acceptable image quality, controlling ink dot placement and sizing to prevent undesired overlap or gaps between adjacent dots, managing ink absorption and drying behavior on substrates particularly porous materials, and maintaining these performance parameters consistently across the entire printed image while the substrate moves at speeds exceeding two meters per second relative to the printheads. The technical problem is particularly acute in printed parts where only one ink is used where coverage uniformity and dot placement precision directly determine visible print quality without the masking effects that multiple color layers can provide.Description of Embodiments

[0026] Monochromatic Image (I)

[0027] By using inkjet technology, more precisely by using a plurality of piezoelectric printheads (H1..M); and a single pass inkjet printing method a monochromatic image (I) is formed on a substrate (S), preferably paper substrate. A monochromatic image is formed by using a single ink which is jettable by the plurality of printheads (H1..M) of a printing device. Hereby the monochromatic image comprises a plurality of printed dots. The plurality of printed dots is by the present invention arranged in a certain print grid determined by the first printing resolution (PRES ) and the second printing resolution (PRES,2).

[0028] The printing device may be capable of printing more than one ink for a forming multichromatic images, such as a CMYK image with a cyan, magenta, yellow and black ink, by forming multiple monochromatic images on the substrate (S), sometimes called printed separations.

[0029] In a preferred embodiment each printed dot of the plurality of printed dots has a dot size (Dsize) between a dot pitch (DPRES,2) according the first print resolution (PRES, 2) and three times the dot pitch (DPRES,2); more preferably two times the dot pitch (DPRES,2) and most preferably one and a half times the dot pitch (DPRES,2).Too large dot size (Dsize) makes it difficult to have a good print quality for inverted characters I fonts so the dot size may not too large.

[0030] As known by a person skilled in the art of producing inkjet printed corrugated cardboard dot pitch of a print resolution (DPRES) can be determined by one dividing the print resolution (PRES).

[0031] [Math. 1]DPRES =‘ RES

[0032] E.g., if the print resolution is 300 dots per inch (PRES), which is around 118,11 dots per cm, then the dot pitch (DPRES) is around 84,66 pm which is the distance between the centers of the printed dots along said print resolution.

[0033] As known, the printed dot formed on a substrate by a jetted droplet is substantially circular. The dot size of the printed dot determines the diameter of said substantially circular dot. With machine vision products of manufacturer ImageXpert™, especially for print quality analyses according to ISO 13660, the dot sizes of printed dots; dot placement of printed dots; distances between printed dots; print resolutions can be measured. “Interpretation of Dot Area and Dot Shape of Inkjet Dots Based on Image Analysis” January 2002 NIP & Digital Fabrication Conference 18(1): p 474-477 by P. D. Fleming and co. also discloses similar methods of inkjet printed dot analysis.

[0034] The first print resolution (PRES,1) is preferably more than 236 dots per cm.Higher the first print resolution (PRES,1), better the print quality, such as machine readable QR codes, human readable small characters / fonts shall be.

[0035] The second print resolution (PRES,2) is more than 118 dots per cm. Higher the second print resolution (PRES, 2), better the print quality, such as machine readable QR codes, human readable small characters I fonts shall be.

[0036] Preferably the first print resolution (PRES,1) is equal or more than three times the second print resolution (PRES,2) or equal or more than four times the second print resolution (PRES,2) so a good print quality, such as machine readable QR codes, human readable small characters / fonts, at high printing speed above 100 m / min can be achieved, thus at PRES,1 ≥ 3 × PRES,2 or PRES,1 ≥ 4 × PRES,2.

[0037] The formed monochromatic image may represent one or more digital image elements such as a photo, a logo, a text, a QR-code, a bar-code. By using raster image processor (RIP), such as ASANTI™ of manufacturer AGFA™, the one or more digital image elements are formed to one or more raster images by using halftoning technologies, preferably an error diffusion method, to data in a printable format, such as RTL-format (Raster Transfer Language), that is transferred to the printing device, eventually stored in a memory of the printing device first, for forming the monochromatic image.

[0038] However, in-line digital printing in a corrugated board production line requires inks with exceptional requirements, like high frequency jettability, good drying performance, high stability, good wetting performance on a wide range of substrates, high water resistance of the printed corrugated cardboard as well as high abrasion resistance of the printed corrugated cardboard, in particular under heat exposure.

[0039] Printing device capable performing the present invention

[0040] The printing device may for performing the present invention comprises a transport mechanism for providing a substrate (S), preferably paper substrate, to a plurality of piezoelectric printheads (H1..M) for forming the monochromatic image (I). The substrate (S) is preferably a substrate web, more preferably a paper substrate web.

[0041] The printing device is capable of performing a single pass inkjet printing method thus the printing device is sometimes called a single-pass inkjet printing device.

[0042] As the method according to the invention is useful for paper substrate widths of 1.2 m, 1.6 m, 2.8 m and even up to 3.5 m. The width of the one or more printbars is here preferably at least larger than 1.2 m, 1.6 m, 2.8 m and even up to 3.5 m respectively. The width of paper substrate and a printbar are determined in the same direction as the one or more nozzle rows (R1..N).Especially for being incorporated in corrugators or corrugated cardboard production lines, the printing unit should have a width of 2.8 m or more.

[0043] The transport mechanism for providing the substrate (S) is not particularly limited but comprises preferably a rotatable conveyer belt, a rotatable vacuumconveyer belt or a composition of one or more transport rollers whereof minimum one is driven by a motor. Providing a paper substrate as a paper substrate web is preferably done by a transport mechanism comprising means of a rotatable impression cylinder or means of transport rollers whereof minimum one is driven by a motor.

[0044] The plurality of printheads (H1..M) are preferably arranged into a line or more lines for performing the single inkjet printing method of the present invention. Each arrangement into a line is called a print bar. Such printbar may be pagewide technology such as the HP PageWide Technology of manufacturer HP (Hewlett Packard™).

[0045] To achieve the forming of monochromatic images having a high image quality, the nozzle resolution of the inkjet printhead should be preferably equal to 225 nozzles / inch or more, more preferably equal to 500 nozzles / inch or more, most preferably equal to 1000 nozzles / inch or more. The nozzles may be arranged in one or more nozzle rows (R1..N) such as disclosed in US20180370234 A1. Most actual commercial inkjet printheads have a nozzle density of 1200 nozzles / inch or more along a first axis corresponding with the longest dimension of the nozzle plate of the inkjet printhead. The inkjet printheads may be arranged in an array along this first axis. This array forms a printing bar which is positioned above the first surface of the paper substrate according to a direction perpendicular to the conveying direction of the paper substrate.

[0046] The printheads in the present invention are piezoelectric printheads.Piezoelectric inkjet jetting is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print printhead creating a void, which is then filled with aqueous inkjet ink. When the voltage is again removed, the ceramic expands to its original shape, ejecting a drop of pretreatment liquid from the inkjet printhead.

[0047] Particularly suitable piezoelectric inkjet printheads are Gen5 and Gen5S from RICOH™, KJ4B from KYOCERA™, Samba G3L and G5L from FUJIFILM DIMATIX™ and the 5601printhead from XAAR™.

[0048] A piezoelectric printhead can be driven by either positive-going and / or negative-going pulses, depending on how it is manufactured. A combination of pulses with a certain amplitude; whether or not with slopes; duration of a pulse; timings between pulses determines what is happening at the nozzle and the jetting of ink. The combination is called a waveform (W).Typically, a waveform comprises one or more print pulses and / or cancel pulse. A print pulse may comprise:rise segment: an increase in voltage that causes the piezoelectric element to expand, pushing ink towards the nozzle; dwell segment: a period of constant voltage where the element remains expanded to allow ink to form a meniscus at the nozzle; fall segment: a decrease in voltage that causes the element to contract, creating a pressure that ejects ink from the nozzle.The amount of the ejected ink and the velocity of the ejected ink are determined by the slope and the amplitude of the print pulse. Typically, the amount of ejected ink grows if the number of print pulses is higher.A cancel pulse, sometimes called dampening pulse, may also comprise several similar segments, but a cancel pulse is causing to dampen any oscillations and to stabilize the printhead for the next ejection of ink. A cancel pulse results mainly in minimizing satellites and mist formation.Other type of pulses may be comprised in the waveform (W) such as a pre-pulse that come shortly before the first print pulse. It can help the ink moving so that the print pulse has less energy to overcome. They have typically a low amplitude.

[0049] Preferably the waveform (W) comprises more than two print pulses. More preferably the waveform (W) comprises more than two print sequential pulses; The maximum of print pulses in the waveform (W) is preferably less than five. The number of print pulses in the waveform (W) is preferably three, also called a 3 DPD waveform or 3-pulse waveform, or four, also called a 4 DPD waveform or 4-pulse waveform (DPD = Droplets Per Drop).

[0050] After the more than two print pulses the waveform comprises preferably a cancel pulse. By this cancel pulse the preferred embodiment improves jetting reliability at high speed (>100 m / min), reduces satellites and mist formation;giving stable droplet formation even with multiple droplets per dot thus better print quality for fine text and machine-readable codes.

[0051] To achieve a high first print resolution (PRES1) and higher printing speed (Pspeed) and thus a better print quality at high speed (> higher the resolution, better the print quality) all two printed dots which are neighboring each other, aligned along the one or more nozzle rows (R1..N) may be achieved by jetting by a different piezoelectric printhead of the plurality of piezoelectric printheads (H1..M). Preferably the plurality of piezoelectric printheads (H1..M) are arranged in minimum two printbars for forming the first print resolution (PRES, 1). of the formed monochromatic image (I). WO13127889 A1 (AGFA) discloses single pass inkjet printing methods wherein a monochromatic image is formed by using two or more printbars capable of jetting UV curable ink and curing the printed monochromatic image with UV light.

[0052] The printing speed (Pspeed) in the present invention is more than 100 m / min (≈1.67 m / s) but preferably more than 200 m / min (≈3.33 m / s), especially when the present invention is used in a corrugator for producing decorated corrugated cardboard.

[0053] To achieve a high compact design of the printing device e.g., in a corrugator, the inkjet printhead(s) should be preferably positioned such as to wrap around a curved support or impression cylinder carrying the substrate (S) during the forming of the monochromatic image (I). An impression cylinder is particularly suitable for a paper substrate web which is being transported over the outer surface of the cylinder. Indeed, the dimensional stability of the substrate (S) containing ink in the plurality of dots is much more guaranteed than with a conveyor belt or a combination of transport rollers in a curved configuration. As specially the width of the printbar to be incorporated in a corrugator must be preferably equal to or larger than 1.6 m, 2.8 m or even 3.5 m, this dimensional stability of the paper substrate web is very critical. A suitable example how the inkjet printheads can be positioned around an impression cylinder is disclosed in Fig. 1 of US20020168212 A1. Another advantage of an impression cylinder for transporting and providing the paper substrate web when forming amonochromatic image with inkjet technology is that the design of the printing unit is much more compact.

[0054] In a preferred embodiment, all piezoelectric printheads of the plurality of piezoelectric printheads (H1..M) may be configured to recirculate the ink prior or during the forming of the monochromatic image (I), more preferrable the piezoelectric printhead are throughflow piezoelectric printheads (Fig 1. B).Examples of throughflow printheads or methods of (re)circulation of ink are disclosed in W02006030235 A2 and W02006064036 A1. Commercial examples of suitable piezoelectric through-flow print heads are the print heads Samba G3L and G5L from FUJIFILM™ DIMATIX, Ricoh™ Gen5F and MF heads, Epson (D3000) throughflow heads and the 5601 print-head from XAAR™.

[0055] The ink circulation system for feeding and (re)circulating the ink through the piezoelectric printhead, comprises for example an ink tank for containing the ink, a supply buffer tank for receiving the ink from the main tank and supplying the ink to the throughflow piezoelectric printhead, a return manifold for receiving the ink from the through-flow printhead and returning the ink to the main ink tank via a pump.

[0056] In a preferred embodiment, the printing device comprises an inline quality control system configured to monitor the formed monochromatic image during printing. The system may include a machine vision unit capable of detecting dot placement accuracy, barcode readability, and color density in real time, thereby enabling immediate corrective actions without interrupting the printing process.

[0057] The printing device may include an automated printhead maintenance system configured to perform periodic purge and wipe cycles in combination with continuous ink recirculation. This system minimizes nozzle clogging and satellite formation during extended high-speed printing operations exceeding 300 m / min.

[0058] The printing device may integrate a raster image processor (RIP) capable of real-time variable data handling, enabling the printing of dynamic content such as QR codes, barcodes, and serialized text without reducing the printing speed or throughput of the manufacturing line.

[0059] Another embodiment of the invention is a manufacturing line for producing an object wherein the printing device; capable performing the inkjet printing method as claimed in claim 1 and its preferred embodiments; is embedded.

[0060] The manufacturing line comprises: a first process device and a second process device arranged in a sequence along a manufacturing path at a manufacturing speed, wherein: one of the first or second process devices is the printing device or preferred embodiments configured to form a monochromatic image (I) onto a substrate (S); preferably a substrate web; andthe other of the first or second process devices is configured to prepare at a manufacturing speed a material to become the substrate or to convert the substrate, with the applied print layer, into the object or an intermediate material thereof;- a speed sensor for generating movement pulses according to the manufacturing speed;- a print control system for use in the printing device comprising:a fire pulse controller configured to generate fire pulses for a plurality of piezoelectric printheads; having one or more nozzle rows (R1..N); to form the monochromatic image (I) at a printing speed above 100 m / min with a plurality of printed dots;wherein the formed monochromatic image has a first print resolution (PRES,1) aligned the one or more nozzle rows (R1..N); and a second print resolution (PRES,2) substantially perpendicularly aligned the one or more nozzle rows (R1..N); and wherein the first print resolution (PRES,1) is more than two times the second print resolution (PRES, 2), thus PRES,1 > 2 × PRES,2; andwhere each printed dot of the plurality of printed dots has a dot size (Dsize) at least a dot pitch (DPRES,2) according the second print resolution (PRES,2).Especially the synchronization of printing with upstream / downstream processes are here important whereby the print quality is maintained at industrial manufacturing speed and the Inline inkjet printing at industrial manufacturing speeds doesn’t slow down the manufacturing line by using an anisotropic resolution strategy.

[0061] The printing device is preferably part of a manufacturing line for manufacturing wood based laminate panels or thermoplastic laminate panels as objects. Other preferred manufacturing lines are- Metal Coil Coating Lines: Printing on aluminum or steel coils before protective coating or embossing.- Plastic Sheet Extrusion Lines: Printing on extruded sheets for signage or auto motive interiors.

[0062] The printing device may also be part of a manufacturing line for producing laminated corrugated cardboard sheet / web such as a corrugator. Said device, part or not part of a corrugated cardboard plant, is capable of performing producing printed corrugated cardboard sheet / web comprising the present invention. Preferably the corrugated cardboard sheet / web or is single-sided or double-sided laminated corrugated cardboard sheet / web. Steps of producing laminated corrugated cardboard may bea) supplying raw material such as linerboard and fluting medium to a device for producing laminated corrugated cardboard sheet / web;b) optionally: heating and moisture conditioning the fluting medium;c) corrugating the fluting medium using fluted rolls;d) applying adhesive to the tips of the corrugated medium;e) bonding the linerboard to the corrugated medium;f) optionally: cooling and drying the corrugated web;g) optionally: trimming and winding into rolls or cutting into sheets.

[0063] Substrate (S)

[0064] The substrate (S) which is used in the method according to the invention is not particularly limited to a specific type, but a paper substrate is preferred which shows a certain absorbability towards the ink.

[0065] The substrate may also be a thermoplastic foil, preferably polyvinylchloride foil as used in the manufacturing of thermoplastic laminate panels. Said foil have preferably a coating, also called an ink-receiving layer, which absorb the ink to adhere the formed monochromatic image to the foil.

[0066] Absorbing paper substrates include paper, coated paper, coated paper having an ink receiving layer on at least one surface, offset paper, office paper, newspaper paper, cardboard, white lined chipboard, folding board.

[0067] For packaging applications absorbing paper substrates include cardboard, paper lines, and paper. The paper can be a single layer of a multilayer paper. The paper liner may be brown kraft liner, top kraft liner, white coated kraft liner or bleached paper board.

[0068] The absorbing paper substrate may be manufactured from chemical, wood, or recycled fibre.

[0069] In a preferred embodiment of the invention, the paper may be a liner intended for printing into a corrugator and converted into corrugated boards or boxes. In this aspect, the liner paper may be used as a double face liner and may be converted directly in a corrugator or laminated onto a double face liner after corrugation.

[0070] In a more preferred embodiment of the invention, the substrate (S), such as for example the liner intended for printing into a corrugator, is a porous paper substrate such as an uncoated liner. A porous paper substrate is quite challenging as due to the porosity of the paper; the pigments of the aqueous inkjet ink tend to migrate into the paper when water-soluble organic solvents such as alkyl glycol ethers are used as penetrants to obtain good setoff properties. When the pigment of the ink penetrates into the paper substrate, low image quality of the formed monochromatic image (I) such a low color depths and contrast is obtained.

[0071] Quantitatively, a porous paper substrate indicates a "paper substrate having a porosity, measured using a Gurley air permeability meter, of equal to 100 seconds or less’, also expressed as a Gurley porosity below 100 seconds. A Gurley air permeability meter measures the airflow between the paper substrate, clamped between a flat glass plate and a circular metal head. A suitable Air Permeability Tester measuring the air permeability of a paper substrate is a Bendtsen Porosity Tester (RL-BRAPT-A) from Rycolab™. The Gurley porosity is calculated from the measured values.

[0072] The method according to the invention is useful for a substrate web width of 1.2 m, 1.6 m, 2.8 m and even up to 3.5 m. Especially, corrugators require a paper substrate web width of 1,6m and more.

[0073] The paper substrate may also be separate sheets instead of web-based paper. Boards used for boxes and other packaging applications are also suitable. Most preferably, the paper substrate is an uncoated paper liner. The absence of a coating further improves penetration of the ink vehicle while keeping at least a part of the achromatic or chromatic color of the ink at the surface.

[0074] In a preferred embodiment, the maximum printing speed of the printing device capable performing the present invention or its preferred embodiments is not less than 100 m / min, preferably not less than 250 m / min, most preferably not less than 300 m / min. These printing speeds correspond with conveying speeds used in corrugators. Some corrugators operate at peak conveying speeds of 450 m / min.

[0075] The present invention is preferably limited to a paper substrate but also textile, synthetic foil or plates or any other printable substrate as known in the art have similar advantages with the present invention.

[0076] The substrate (S) used in the highspeed ink-jet printing method according to the present invention preferably comprises a support with at least one inkreceiving layer. The ink-receiving layer may consist of just one single layer, or alternatively it may be composed of two or more layers. The ink-receiving layer or at least one of the ink-receiving layers, in the case of multiple layers, contains at least a polymeric binder and a curable compound.

[0077] The ink-receiving layer or at least one of the ink-receiving layers, in the case of multiple layers, preferably further contains also at least one filler. The inkreceiving layer can be transparent but is preferably translucent or opaque.

[0078] The ink-receiving layer used in the ink-jet printing method according to the present invention may be a coloured layer so thinner formed monochromatic images are achieved which dries faster.

[0079] Ink

[0080] The monochromatic image (I) is formed using inkjet technology whereby printed droplets are formed with a single ink preferably an aqueous inkjet ink.

[0081] The aqueous inkjet ink preferably comprises a pigment, a water-soluble alkane diol in an amount not less than 10 wt.% and not more than 40 wt.% with respect to the total weight of the ink, a water-soluble alkyl glycol ether in an amount not less than 5 wt.% and not more than 20 wt.% with respect to the total weight of the ink and a non-ionic surfactant.

[0082] Without being bound by a theory, it is thought that due to the specific combination of water, water-soluble alkane diol and alkyl glycol ether, the liquid vehicle of the ink (which comprises the water and the water-soluble organic solvents of the ink) penetrates very fast into the paper substrate leading to excellent setoff values, while at least a part of the pigment remains at the surface of the paper substrate leading to excellent color depths of the formed monochromatic image (I).

[0083] The pigment in the aqueous inkjet ink according to the invention may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, and the like. A color pigment may be chosen from those disclosed by HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley - VCH, 2004. ISBN 3527305769.

[0084] Suitable pigments for the invention are disclosed in paragraphs from

[0128] to

[0138] of W02008074548 A1.

[0085] The pigment used in the present invention is not particularly limited and may be either an organic pigment or an inorganic pigment and may also be used in the form of a mixture of these pigments.

[0086] Examples of the organic pigment include at least one pigment selected from the group consisting of condensed polycyclic pigments such as anthraquinone- based pigments, quinacridone-based pigments, indigo-based pigments, dioxazine-based pigments, perylene-based pigments, perinone-based pigments, isoindolinone-based pigments, isoindoline-based pigments, phthalocyanine- based pigments, quinophthalone-based pigments and diketopyrrolopyrrole-based pigments, and azo-based pigments such as diazo-based pigments and condensed azo-based pigments. Of these organic pigments, from the viewpointof improving color reproducibility thereof, preferred is at least one pigment selected from the group consisting of quinacridone-based pigments, azo-based pigments and phthalocyanine-based pigments.

[0087] Specific examples of the quinacridone-based pigments that are capable of exhibiting a magenta color include C.l. PR (Pigment Red) 122, PR 192, PR 202, PR 207 and PR 209; and C.l. PV (Pigment Violet) 19, etc. Of these quinacridone- based pigments, preferred is at least one pigment selected from the group consisting of C.l. PR 122, C.l. PV 19. Specific examples of the azo-based pigments that are capable of exhibiting a yellow color include C.l. PY (Pigment Yellow) 74, PY 151, PY 154, PY 155, PY 180 and PY 213. Of these azo-based pigments, preferred is at least one pigment selected from the group consisting of C.l. PY 74, C.l. PY154 and C.l. PY 155. Specific examples of the phthalocyanine- based pigments that are capable of exhibiting a cyan color or a green color include C.l. PB (Pigment Blue) 15:1, PB 15:2, PB 15:3, PB 15:4, PB 15:5, PB 15:6 and PB 16; and C.l. PG (Pigment Green) 7 and PG 36. Of these phthalocyanine pigments, from the viewpoint of well exhibiting a cyan color, preferred is at least one pigment selected from the group consisting of C.l. PB 15:3 and C.l. PB 15:4.

[0088] The organic pigment may also include a derivative of the organic pigment as a raw material thereof. The organic pigment derivative may be produced by conducting such a treatment in which a functional group such as a hydroxy group, a carboxy group, a carbamoyl group, a sulfo group, a sulfonamide group and a phthalimidomethyl group is bonded to the surface of the organic pigment.

[0089] Examples of the inorganic pigment include carbon blacks and metal oxides such as alumina and titanium dioxide. These inorganic pigments may be treated with a conventionally known hydrophobization agent such as a titanium coupling agent, a silane coupling agent and a higher fatty acid metal salt, etc.

[0090] The carbon blacks are preferably used for black inks. Examples of the carbon blacks include furnace blacks, gas black, thermal lamp blacks, acetylene blacks and channel blacks, and the carbon blacks may also be surface-treated carbon blacks.

[0091] The pigment particles are preferably dispersed in an aqueous medium using a polymeric dispersant, a surfactant, or a combination thereof or encapsulated by a crosslinked polymeric shell. Self-dispersible pigments can also be used. The latter prevents interaction of the polymeric dispersant with the dispersing groups of binders or capsules which may be included in the inkjet ink.

[0092] A self-dispersible pigment is a pigment having on its surface covalently bonded anionic hydrophilic groups or salt-forming groups, that allow the pigment to be dispersed in an aqueous medium without using a surfactant or a resin.

[0093] Pigment particles in inkjet inks should be sufficiently small to permit free flow of the ink through the inkjet-printing device, especially at the ejecting nozzles. It is also desirable to use small particles for maximum color strength and to slow down sedimentation.

[0094] The pigment particles may also be dispersed in an aqueous medium using a polymeric dispersant, a surfactant or a combination thereof.

[0095] Suitable polymeric dispersants are copolymers of two monomers but they may contain three, four, five or even more monomers. The properties of polymeric dispersants depend on both the nature of the monomers and their distribution in the polymer.

[0096] In a preferred embodiment of the invention the aqueous ink comprises a pigment which is encapsulated by means of a cross-linked polymeric shell.Encapsulated pigments provide printed images having improved physical properties such as water resistance and dry rub resistance with respect to pigments dispersed by means of un-cross-linked polymers.

[0097] Suitable encapsulated pigments are provided by Lubrizol as Diamond HSDX- dispersions and by Fujifilm as RxD pigment dispersions such as APD1000 and APD4000 premium dispersions.

[0098] The pigments are preferably present in the range of 0.05 to 15 %, more preferably in the range of 0.1 to 10 % by weight and most preferably in the range of 0.2 to 6 % by weight, each based on the total weight of the inkjet ink. For white inkjet inks, the white pigment is preferably present in an amount of 3% to 40% byweight of the inkjet ink, and more preferably 5% to 35%. An amount of less than 0.05% by weight cannot achieve sufficient covering power.

[0099] The average pigment particle size is preferably between 0.050 and 1 µm, more preferably between 0.070 and 0.300 µm and particularly preferably between 0.080 and 0.200 µm. Most preferably, the numeric average pigment particle size is no larger than 0.150 µm. The average particle size of pigment particles is determined with a Brookhaven Instruments Particle Sizer BI90 plus based upon the principle of dynamic light scattering.

[0100] The ink composition of the invention contains preferably at least one water- soluble alkane diol in an amount not less than 10 wt.% and not more than 37 wt.%, preferably not more than 35 wt.% with respect to the total amount of the ink.

[0101] This alkane diol is incorporated in the aqueous inkjet ink to prevent drying and clogging of ejection nozzles due to aggregates formed of adhered and dried ink.

[0102] Clogging of the ejection nozzles of a print head impairs severely the jetting reliability, especially at the start-up of the forming process and during long printing jobs.

[0103] A biocide may be added to the aqueous inkjet ink of the invention to prevent unwanted microbial growth, which may occur over time. The biocide may be used either singly or in combination. Suitable biocides for the ink-jet ink of the present invention include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyridinethion-1 -oxide, ethyl p-hydroxybenzoate and 1,2-benzisothiazolin- 3-one and salts thereof.

[0104] Preferred biocides are Proxel™ GXL and Proxel™ Ultra 5 available from ARCH UK BIOCIDES and Bronidox™ available from COGNIS.

[0105] A biocide is preferably added to the aqueous medium in an amount of 0.001 to 3 wt.%, more preferably 0.01 to 1.0 wt. %, each based on the total weight of the ink.

[0106] The aqueous inkjet ink may further comprise at least one thickener for viscosity regulation in the liquid. Suitable thickeners include urea or urea derivatives, hydroxyethylcellulose, carboxymethylcellulose,hydroxypropylcellulose, derived chitin, derived starch, carrageenan, xanthan gum, pullulan, proteins, poly(styrenesulphonic acid), poly(styrene-co-maleic anhydride), poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamid, partially hydrolyzed polyacrylamid, poly(acrylic acid), poly(vinyl alcohol), partially hydrolyzed poly(vinyl acetate), poly(hydroxyethyl acrylate), poly(methyl vinyl ether), polyvinylpyrrolidone, poly(2-vinylpyridine), poly(4-vinylpyridine) and poly(diallyldimethylammonium chloride). Particular suitable thickeners are hydrophilically modified PU thickeners (HEUR) like Thijet 170 from Lamberti and Polyacrylic esters like BYK LP-R21675 from BYK.

[0107] The thickener is added preferably in an amount of 0.01 to 20 wt.%, more preferably 0.1 to 10 wt.% based on the total weight of the ink.

[0108] The aqueous inkjet ink according to the invention may comprise non-wetting coating attack inhibitors. These prevent the attack of the non-wetting coating which usually is present onto the nozzle plate of inkjet printheads. This nonwetting coating prevents accumulation of ink around the ejection nozzles and attack of this coating creates severe jetting reliability issues.

[0109] In a preferred embodiment of the invention, inhibitors are selected from compounds including a six-membered aromatic ring having two hydroxyl groups in para-position and a compound according to Formula 1:wherein R5 is selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl and a substituted or unsubstituted heteroaryl group; R6 to R9 are independently selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, asubstituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl and a substituted or unsubstituted heteroaryl group; or any of R6 to R9 may represent the necessary atoms to form a five to eight membered ring.

[0111] In a preferred embodiment, R5 is selected from the group consisting of a substituted or an unsubstituted alkyl group and a substituted or unsubstituted aryl group, a substituted or unsubstituted aryl group being particularly preferred, a substituted or unsubstituted phenyl group being the most preferred.

[0112] The non-wetting coating attack inhibitors may also be a compound including a six-membered aromatic ring having two hydroxyl groups in para-position such as the ones according to Formula 2:

[0113] [Formula.2]wherein R1 to R4 are independently selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl or heteroaryl group, a halogen, a hydroxyl group, an ether group, an ester group, a carbonate group, an amide group, a urethane group, a carboxylic acid group or salt thereof, a nitrile group an nitro, an amine group, a thiol group, a thioether group, a sulfonic acid group or salt thereof, a sulfonamide group, a sulfonate ester group, a sulfoxide group, a sulfone group, a phosphate group or salt thereof, a phosphate ester group, a phosphonate group or salt thereof, a phosphonate ester group, an aldehyde group and a ketone group, or wherein R1 and R2 and / or R3 and R4 may represent the necessary atoms to form a five to eight membered ring.

[0114] In a preferred embodiment, R1 to R4 are independently selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a carboxylic acid group or saltthereof and a sulfonic acid group or salt thereof.

[0115] In an even more preferred embodiment, R1 to R4 are independently selected from the group consisting of a hydrogen, a C1 to C4 alkyl group, a substituted or unsubstituted phenyl ring, a carboxylic acid group or salt thereof and a sulfonic acid group or salt thereof.

[0116] In the compounds according to Formula 1 and Formula 2, carboxylic acid groups or salts thereof and sulfonic acid groups or salts thereof are particularly preferred substituents. The cations in the salts of the carboxylic acid and the sulfonic acid groups or salts thereof are preferably monovalent and preferably selected from Li+, K+, Na+, NH4+ and monovalent organic cations.

[0117] It has been observed that inkjet inks containing a compound according to Formula 1 or Formula 2 with a carboxylic acid group or salt thereof tends to be more efficient and effective against corrosion than other type of acid groups or salts thereof.

[0118] For preventing ink drying at the ejection nozzles, the alkane diol preferably has a lower vapor pressure than that of water.

[0119] In a preferred embodiment the printing method is suitable for the production of printed corrugated cardboard including the steps of:i. Providing a paper substrate; preferably a paper web as paper substrate; and ii. Adhering an aqueous ink onto a first surface of the paper substrate by means of an inkjet print head to obtain a printed paper substrate, the aqueous ink comprising a pigment, a water-soluble alkane diol in an amount not less than 10 wt.% and not more than 37 wt.% with respect to the total weight of the ink, a water-soluble alkyl glycol ether in an amount not less than 5 wt.% and not more than 20 wt.% with respect to the total weight of the ink and a non-ionic surfactant; andiii. Contacting the first surface of the printed paper substrate with a roller.

[0120] The aqueous ink preferably comprises an alkyl alcohol having an alkyl group comprising 1 to 7 carbon atoms in an amount not less than 1 wt.% and not more than 5 wt.% with respect to the total weight of the ink.

[0121] The pigment is preferably selected from a group consisting of a self- dispersible pigment and a pigment encapsulated by means of a crosslinked polymer.

[0122] The contacting is preferably between 5 and 0.0001 seconds; more preferably between 3.5 and 0.0001 seconds; after the adhering the aqueous ink.

[0123] The paper substate is preferably a paper substrate web and the adhering of the aqueous ink onto the paper web is done by means of at least two inkjet printheads having a first axis and a nozzle resolution of not less than 300 nozzles / inch in the direction of the first axis, both first axis being parallel to each other and perpendicular to the moving direction of the paper web.

[0124] The inkjet printheads are preferably positioned such as to at least double the drop density in the direction of the moving paper web.

[0125] The outer surface of the roller is preferably metallic.

[0126] The paper substrate in step (i) is preferably provided onto an impression cylinder.

[0127] Preferably no forced drying step by applying heat or airflow to the printed substrate is done.

[0128] The pigment is preferably a black pigment to achieve high-quality monochromatic printing (e.g., machine-readable barcodes, inverted text) at high speed (>100 m / min) on porous substrates without jetting reliability issues or poor color depth. If a black aqueous ink is formed with said black pigment which is preferably self-dispersible or encapsulated; said ink comprises preferably water- soluble alkane diol (10-40 wt%) for nozzle reliability and / or alkyl glycol ether (5- 20 wt%) for fast penetration and / or non-ionic surfactant for wetting. So the technical effect of these preferred embodiments are high jetting reliability at >100 m / min; machine-readable barcodes and QR codes even inverted; good color depth and contrast on porous substrates; reduced nozzle clogging and satellites.

[0129] The aqueous ink preferably comprises a non-wetting coating attack inhibitor being a compound including a six-membered aromatic ring having two hydroxyl groups in para-position.ExamplesF0130] Materials

[0131] A) Ink:A.1) ink composition according a preferred embodiment:D.I. Water Up to 100 wt.% Co-solvent Propylene glycol 1,2 - propaandiol 34%Co-solvent n-buthanol 2.95%Co-solvent Propylene glycol monobutyl Ether 7% Surfactant Hydropalat WE 3650 2%Biocide 1,2-Benzisothiazolin-3-one 0.11% Pigment dispersies Cabot CO4107K 30%

[0132] B) paper substrates:B.1) AGFA SherpaProof microporous proofing paperB.2) SUV519 - Austroliner 3 liner paper.

[0133] C) piezoelectric printheads:C.1)FujiFilm Dimatix Samba G5L RJC2, serial #301486-14* temperature during the formation of a monochromatic image ~32°C measured in the piezoelectric printhead;* print distance between nozzles and paper substrate during the formation of a monochromatic image is 1 mm;* recirculation settings ink flow in the range of 29 - 35 ml / min.

[0134] D) waveforms:D.1 ) waveform with two printing pulses; respectively of 30V; 24V followed by a cancel pulse of 10V;D.2) waveform with two printing pulses; respectively of 30V; 23.5V followed by a cancel pulse of 17V;D.3) waveform with three printing pulses; respectively of 30V; 13V; 21V followed by a cancel pulse 20V. (WF202405°6)

[0135] E) print resolutions & print speed:E.1) PRES. I = 1200 printed dots per inch; PRES, 2 = 600 printed dots per inch; speed2.5 m / sE.2) PRES. I = 1200 printed dots per inch; PRES, 2 = 600 printed dots per inch; speed 2.5 m / sE.3) PRES. I = 1200 printed dots per inch; PRES, 2 = 300 printed dots per inch; speed 2.5 m / sE.4) PRES. I = 1200 printed dots per inch; PRES, 2 = 300 printed dots per inch; speed 2.5 m / s

[0136] P) Print qualityThe following parameters are evaluated to have an overview of the overall print quality:P.1 ) Startup effect: the presence of a fast drop before the rest of the printed structure evaluated with imageXpert’s JetXpert w / GIS print head driving electronics;P.2) Bar code: empirical evaluation of the bar code: readable after 1 scan = ++; readable after more than 1 scan but less than 5 scans +; not readable The scans are taken with a smartphone SAMSUNG Galaxy A34 with standard camera app.P.3) QR code 8mm x 8 mm: actual readability test by smartphone SAMSUNG Galaxy A34 with standard camera app. Two different coding systems and contents were tested (link and text). Readable after 1 scan = ++; readable after more than 1 scan but less than 5 scans +; not readableP.4) Satellites: empirical and mutual relative evaluation of the quality: ++ no satellites; + acceptable amount of satellites; -- not acceptable amount of satellites;P.5) Positive text 12 pt with the standard font Times New Roman: ++ readable printed text; + more or less readable printed text; not readable printed text; P.6) Negative text 12 pt with the standard font Times New Roman: ++ readable printed text; + more or less readable printed text; not readable printed text; P.7) L* value: CIE L* values measured with X-Rite eXact, D50 / 27M1.

[0137] [Table.1]A _ C D E P.1 P.2 _ P.3 _ P.4 _ B.1 B.2 B1. B.2 _ A.1 C.1 D.1 E.1 - - - ++A.1 C.1 D.2 E.2 - + - ++A.1 C.1 D.2 E.3 - ++ + ++ ++A.1 C.1 D.3 E.4 ++ ++ + ++ ++ +[Table.2]A _ C D E P.5 _ P.6 _ P.7 _ _ B.1 B.2 B.1 B.2 B.1 B.2 A.1 C.1 D.1 E.1 + ++ + - 36.45 36.32 A.1 C.1 D.2 E.2 - ++ + - 17.88 34.69 A.1 C.1 D.2 E.3 - ++ + - 43.64 38.18 A.1 C.1 D.3 E.4 + ++ + - 30.70 36.38Industrial Applicability

[0138] The present invention is about inkjet printing technology for production of decorated corrugated cardboard and has thus a technical character.Citation List

[0139] Citation list follows:Patent Literature

[0140] PTL1: DE102013202871 A1 (BHS Corrugated Maschinen und Anlagenbau GmbH; 2014-09-04)

[0141] PLT2: WO2014128115 A1 (BHS Corrugated Maschinen und Anlagenbau GmbH; 2014-08-28)

[0142] PLT3: US20020168212 A1 (LaserSoft Management LLC; 2002-11-14)

[0143] PLT4: W02006030235 A2 (Xaar Technology Limited; 2006-03-23)

[0144] PLT5: W02006064036 A1 (Agfa Graphics Nv; 2006-06-22)

[0145] PLT6: W02008074548 A1 (Agfa Graphics Nv; 2008-06-26)

[0146] PLT7: US20180370234 A1 (Fujifilm Dimatix Inc; 2018-12-27)

[0147] PLT8: US2017225460A1 (Procter and Gamble Co; 2017-08-10)

[0148] PLT9: US2006203024A1 (Fujifilm Corp; 2006-09-14)

[0149] PLT10: WO13127889 A1 (AGFA; 2013-09-06)Non Patent Literature

[0150] NPL1: “Interpretation of Dot Area and Dot Shape of Inkjet Dots Based on Image Analysis” January 2002 NIP & Digital Fabrication Conference 18(1): p 474-477 by P. D. Fleming and co.

Claims

GN24014 EPClaims

1. |A single-pass inkjet printing method comprising the steps:a) providing a substrate (S);b) forming on the substrate (S) at a printing speed higher than two meters per second (Pspeed) a monochromatic image (I), comprising a plurality of printed dots,by driving with a waveform (W) a plurality of piezoelectric printheads (H1..M), having one or more nozzle rows (R1..N), for jetting ink per printed dot of the plurality of printed dots;- wherein the formed monochromatic image has a first print resolution (PRESJ) aligned the one or more nozzle rows (R1..N); and a second print resolution (PRES,2) substantially perpendicularly aligned the one or more nozzle rows (R1..N); and- wherein the first print resolution (PRES,1) is more than two times the second print resolution (PRES, 2); and- where each printed dot of the plurality of printed dots has a dot size (Dsize) which is at least equal to a dot pitch (DPRES,2) according to the second print resolution (PRES,2).

2. The printing method according to claim 1 wherein the droplet is formed by more than two print pulses and preferably less than five print pulses in the waveform (W).

3. The printing method according to claim 1 or 2 wherein the ink is an aqueous ink comprising a pigment.

4. The printing method according to claim 3 wherein the pigment is selected from a group consisting of a self-dispersible pigment and a pigment encapsulated by means of a crosslinked polymer.

5. The printing method according to claim 3 or claim 4 wherein the ink further comprises a water-soluble alkane diol in an amount not less than 10 wt.% and not more than 40 wt.% with respect to the total weight of the ink, a water-soluble alkyl glycol ether in an amount not less than 5 wt.% and notGN24014 EPmore than 20 wt.% with respect to the total weight of the ink and a non-ionic surfactant.

6. The printing method according to claim 3 or claim 4 or claim 5 wherein the substrate (S) is a paper substrate having a Gurley porosity equal to hundred seconds or less.

7. The printing method according to claim 6 wherein all two printed dots which are neighboring each other, aligned along the one or more nozzle rows (R1..N) are each jetted by a different piezoelectric printhead of the plurality of piezoelectric printheads (H1..M).

8. The printing method according to claim 6 wherein the plurality of piezoelectric printheads (H1..M) are arranged in minimum two printbars for forming the first print resolution (PRES,1). of the monochromatic image (I).

9. The printing method according to claim 7 or claim 8 wherein the plurality of piezoelectric printheads are throughflow piezoelectric printheads.

10. The printing method according to any of the previous claims wherein the waveform (W) comprises after the more than two print pulses a cancel pulse.

11. The printing method according to any of the previous claims wherein the first print resolution (PRES ) is more than three times the second print resolution (PRES,2).

12. The printing method according to any of the previous claims wherein the first print resolution (PRES,1) is more than 236 dots per cm or the second print resolution (PRES,2) is more than 118 dots per cm.

13. The printing method according to any of the previous claims wherein the dot size (Dsize) is between the dot pitch (DPRES,2) and one and a half times the dot pitch (DPRES,2).

14. The printing method according to any of the previous claims wherein the printing speed (Pspeed) is higher than four meters per second.

15. The printing method according to any of the previous claims for producing printed corrugated cardboard wherein no forced drying step by applying heat or airflow to the formed monochromatic image is done. ]

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