EP3031610A1 - Zuverlässiges Kalibrierverfahren für industrielle Tintenstrahlsysteme - Google Patents

Zuverlässiges Kalibrierverfahren für industrielle Tintenstrahlsysteme Download PDF

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Publication number
EP3031610A1
EP3031610A1 EP14196696.0A EP14196696A EP3031610A1 EP 3031610 A1 EP3031610 A1 EP 3031610A1 EP 14196696 A EP14196696 A EP 14196696A EP 3031610 A1 EP3031610 A1 EP 3031610A1
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European Patent Office
Prior art keywords
calibration
industrial inkjet
printhead
optical
machine
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EP14196696.0A
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English (en)
French (fr)
Inventor
Peter Baeyens
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Agfa NV
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Agfa Graphics NV
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Priority to EP14196696.0A priority Critical patent/EP3031610A1/de
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J29/00—Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
    • B41J29/38—Drives, motors, controls or automatic cut-off devices for the entire printing mechanism
    • B41J29/393—Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J29/00—Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
    • B41J29/38—Drives, motors, controls or automatic cut-off devices for the entire printing mechanism
    • B41J29/393—Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns
    • B41J2029/3935—Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns by means of printed test patterns

Definitions

  • the present invention relates to a reliable calibration method of a large inkjet printing system, such as an industrial inkjet system.
  • the maximum printing size of inkjet printing system is enlarged to print on large or multiple ink receivers such as wood or textile.
  • a large inkjet printing system has to be manufactured with a large amount of printheads.
  • a maximum use of printheads results in a better productivity (high volume industrial inkjet systems) which is economically beneficial, especially in single pass industrial inkjet systems wherein the width of the printing area covers the total width of the ink receivers.
  • the printing of large ink receivers exists in the state-of-the-art such as the INCATM Onset S40 or Agfa GraphicsTM :M-PRESS TIGER which are capable to handle very large ink receivers for sign& display print jobs and HYMMENTM JPT-L for printing furniture panels, doors, laminate floorings or façade elements or REGGIANI MACHINETM ReNOIR for printing on fabric web with a maximum web-width up to 3.40 m or DIEFFENBACHERTM Colorizer for furniture production with formats up to 2.070 mm x 3.600 mm. They have all a large amount of printheads.
  • the print quality of industrial inkjet printed objects may also be enhanced by applying more printheads in an industrial inkjet system to enhance the print resolution or to enhance the colour gamut by adding more colors, which results in more heads.
  • DotrixTM :Transcolor a duplex single-pass industrial inkjet system had at each side (recto & verso) twenty-four printheads of 150 DPI per color (C,M,Y,K) thus 192 printheads.
  • the DotrixTM :Transcolor was provided for two additional colors to enlarge the color gamut which resulted in 288 printheads in total to be calibrated.
  • Another example as industrial inkjet system is the ChromoJET MT 4000c x 1024 from ZIMMERTM for printing rugs and carpets with 1024 valve-jets for each of the 16 colors so in total of 16384 valve-jets that have to be calibrated.
  • the throw distance is defined as the distance from the printhead to the ink receiver. It is a function of many factors including: the jet velocity, the printhead flight path, the variation in jet velocities across the array, nozzle straightness, drive position errors, air turbulence, printhead perpendicularity and alignment, timing errors, and nozzle pitch variation.
  • An industrial inkjet system has several working parameters to control this throw distance which have all to be calibrated for each printhead.
  • the state-of-the-art calibration method of an industrial inkjet system comprises the steps of jetting on an ink receiver a calibration patch for a working parameter; and evaluating the calibration patch for example by a measuring tool or a human visual measurement method, such as viewing by the naked eye; and inputting the result of the evaluation in the industrial inkjet system to adapt a value of the working parameter.
  • care have to be taken that an operator doesn't input wrong calibrated values of working parameters by a human input error, such as mistyping.
  • the calibration method of Agfa GraphicsTM :M-PRESS TIGER the input is controlled against a range of values for the working parameter or against values of other working parameters to detect anomalies in the input.
  • a calibration patch may be measured by a densitometer to know the maximum density of the jetted ink from a printhead. If the density is too low, a voltage on the printhead is altered to get a darker maximum density.
  • the working parameter is in this example the voltage of a printhead, the density of the calibration patch is a sensitive field.
  • a calibration patch that comprises a color-on-color registration between two colors by visual evaluating with a microscope. The color-on-color registration can be determined by a distance-difference between the two colors in a pattern of the calibration patch. The color-on-color registration may be corrected by adapting the time-of-firing of the printhead which printed one of the colors in the calibration patch.
  • the time-of-firing of a printhead is a working parameter; the distance difference between two colors is a sensitive field. So a value for a working parameter in the state-of-the-art calibration method is the result of translating the evaluation for a sensitive field, located in a calibration patch.
  • US8118385 discloses an automation in a calibration method for industrial inkjet systems wherein the calibration patch is scanned to evaluate the calibration patch. This automation is beneficial for a fast calibration method but asks for optical sensors and movement means for the optical sensors. The movement means and the optical sensors are expensive and not sustainable in an industrial printing environment.
  • the number of working parameters, especially working parameters of printheads, is in industrial inkjet systems very large so there is a need to have a reliable calibration method to avoid mistakes by the operator who performs the calibration method and there is need to have fast and affordable calibration method. These needs are beneficial for economic reasons to have a fast, payable and correct start-up from the industrial inkjet system.
  • the object of the invention is realized by the method according to claim 1
  • the present invention provides a reliable and fast calibration method for industrial inkjet systems.
  • the industrial inkjet system comprises a plurality of printheads which are mounted and positioned in a matrix of N rows and M columns.
  • the total amount of printheads is larger than one (MxN>1) and preferably the industrial inkjet systems comprise minimum one row with a plurality of printheads or minimum one column with a plurality of printheads.
  • the calibration method for industrial inkjet systems ( Figure 1 ) comprises the steps:
  • the calibration method for industrial inkjet systems of the present invention is performed by an industrial inkjet system calibration unit which is comprised in an industrial inkjet system.
  • the calibration patches (P i,j,1 ... P i,j,P ) in the calibration target are evaluated by the operator or service engineer.
  • the operator or service engineer may use a microscope or other visualization means and may optionally measure the calibration patches.
  • the method links the encoded identification (I i,j ) of the printhead and the encoded sensitive value (V r ) to each other to adapt a value of the working parameter correctly for the printhead (H i,j ) which is identified by the identification (I i,j ).
  • the value of the working parameter for that printhead (H i,j ) is adapted by interpreting (INTERPRET) the sensitive value (V r ).
  • all printheads are mounted in the industrial inkjet system in one printhead unit to position the printheads in a matrix of N rows and M columns or in N parallel printhead units, positioned in rows in the industrial inkjet system, each comprising M printheads or in M parallel printhead units, positioned in columns in the industrial inkjet system, each comprising N printheads.
  • printheads which are positioned in one row or in one column are jetting the same liquid.
  • printheads which are positioned in one row or in one column are jetting the same liquid.
  • the adaption may be reviewed by repeating the steps of calibration method for industrial inkjet systems in the present invention ( Figure 2 ).
  • the set of sensitive values (V 1 ,..., V p ) are selected from a range of sensitive values and at repeating the steps of calibration method for industrial inkjet systems embodiment the set of sensitive values (V 1 ,..., Vp) are selected from a smaller range of sensitive values to improve the result of the calibration method for industrial inkjet systems at each repeat.
  • the smaller range may be calculated automatically depending on a previous sensitive value of a selected calibration patch.
  • the industrial inkjet system calibration unit may also enlarge the range in a repeat when for example an anomaly in the input or adaption occurred.
  • each optical-machine-readable codes (C i,j,1 ,...,C i,j,P ) in the calibration target is generated immediately adjacent located to the calibration patch (P i,j,k ) where the optical-machine-readable code (C i,j,k ) refers to. If the distance between the optical-machine-readable code (C i,j,r ) and its selected calibration patch (P i,,j,r ) is to larger, the change of mistaking by the operator becomes larger.
  • the time of taking and handling the optical-machine-readable coder to scan the optical-machine-readable code (C i,j,r ) and time of movement of the optical-machine-readable coder to the optical-machine-readable code (C i,j,r ) may result in human mistakes due to lost of concentration by the operator.
  • the distance between an optical-machine-readable code and its corresponding calibration patch is preferably between 0 and 100 mm, more preferably between 0 and 50 mm and most preferably between 0 and 20 mm.
  • the selection of a calibration patch is difficult because two calibration patches, comprising consecutive sensitive values, may both be selected but an intermediate value of the consecutive sensitive values is more preferred by the operator.
  • the forming of the calibration target comprises the generation of an optical-machine-readable code, between two optical-machine-readable codes, that both refer to another generated calibration patch; to encode the identification of the printhead (H i,j ) and a sensitive value between the sensitive values, which are encoded in the two optical-machine-readable codes ( Figure 3 ).
  • each generated optical-machine-readable code is generated to encode the selected working parameter and/or a value of the selected working parameter.
  • this extra information may be used by the industrial inkjet system calibration unit to verify the input and to enhance the reliability.
  • each generated optical-machine-readable code is generated to encode another working parameter of the industrial inkjet system and/or a value of the another working parameter.
  • this extra information may be used to adapt the value of the working parameter according to the sensitive value (V r ) and identification (I i,j ) of the decoded scanned optical-machine-readable code (P i,j,r ) and according to the value of the another working parameter or may be used to control for example an anomaly in the input or selection.
  • This preferred embodiment ensures to have a higher reliable calibration method for industrial inkjet systems.
  • Any other kind of information may be encoded to the optical-machine-readable code to enhance the reliability of the calibration method for industrial inkjet systems.
  • an identification (I i,j ) is encoded in the optical-machine-readable code to know which printhead H(i,j) was used to jet the calibration target. This doesn't mean that the calibration target was printed only with this printhead H(i,j), also other printheads in the industrial inkjet system may be used to jet the calibration target.
  • the identification may comprise the position of the printhead in the printhead unit; type of a printhead; type of inkjet ink in the printhead; and/or color of inkjet ink in the printhead.
  • This information in the identification code in this preferred embodiment enhances the reliability of the calibration method for industrial inkjet systems, for example to prevent that a value of a working parameter from a printhead with cyan ink is changed because the value exceeds the range of printheads with cyan ink.
  • the range of printheads with magenta ink may be different than the range of printheads with cyan ink. If the industrial inkjet system calibration unit has identified the color of the selected printhead (H i,j ) mistakes in this preferred embodiment of the calibration method for industrial inkjet systems can be prevented, which enhances the reliability of the method.
  • a preferred embodiment further comprises in the scanning-step: inputting a measurement from the selected calibration patch (P i,j,r ); and wherein the step of adapting a value of the working parameter is according to the measurement, for example the density of the selected calibration patch (P i,j,r ) may be measured by a densitometer which transmits the density to the industrial inkjet system. The measurement may be used to control the input of the scanned optical-machine-readable code to enhance the reliability of this preferred embodiment.
  • the measurement is the result of a human visual measuring method, for example the operator or service engineer evaluates or judges the selected calibration patch (P i,j,r ) by a number in a range or type from a list, such as ⁇ bad , good, best ⁇ , and input his evaluation or judgment in the industrial inkjet system.
  • a human visual measuring method for example the operator or service engineer evaluates or judges the selected calibration patch (P i,j,r ) by a number in a range or type from a list, such as ⁇ bad , good, best ⁇ , and input his evaluation or judgment in the industrial inkjet system.
  • optical-machine-readable code is in a preferred embodiment insensitive for the selected working parameter else de decoding may be influenced. It may be one-dimensional barcode-type or a two-dimensional barcode-type.
  • the calibration patches (P i,j,1 ...P i,j,P ) of the calibration target is jetted by more than one printhead from the same row or column in the industrial inkjet system and/or the calibration patches (P i,j,1 ...P i,j,P ) of the calibration target comprises more than one color.
  • the dots, printed by a nozzle row in a printhead must be aligned such that they are closely registered relative to the dots printed by the other nozzle rows. If they are not well registered, then the maximum density attainable by the printer will be compromised, banding artifacts will appear and inferior color registration will lead to blurry or noisy images and overall loss of detail.
  • These problems make good calibration, such as registration and alignment, of all the nozzle rows within an industrial inkjet system critical to ensure good image quality. That is, not only should a nozzle row be well registered with another that jets the same color ink, but it should be well registered with nozzle rows that jet ink of another color.
  • nozzle count may be increased is by simply adding extra nozzle rows. This has the advantage that the same printhead design may be used. However, this adds to the number of nozzle rows that must be aligned, thereby increasing the possibility for misalignment and the labour required to properly align all the nozzle rows.
  • the industrial inkjet system may have several allowable discrete gaps between the nozzle rows and the printer platen to accommodate these different receivers.
  • the gap between the nozzle rows and the top of the receiver referred to as the throw-distance
  • the throw-distance can vary significantly because of the range of receiver thicknesses and the limited number of discrete nozzle row heights. Due to the carriage velocity, the flight path of the drop is not straight down but really is the vector sum of the drop velocity and carriage velocity. This angular path and the differences in throw-distance make nozzle row registration sensitive to both the average of throw-distance as well as the variation in the throw-distance. These sensitivities further complicate the nozzle row alignment process.
  • carriage velocities implies the supporting of the print heads upon a carriage support that moves in the fast-scan direction while being supported for movement by a rail or other support.
  • the angular flight path of the droplets described will be a function of the carriage velocity. This then makes nozzle row alignment sensitive to the carriage velocity.
  • calibration patches are generated wherein a sensitive field (F) is located.
  • the sensitive field shows how the situation is, regarding the calibration of the industrial inkjet system.
  • the situation may be evaluated by the human eye or a measurement device.
  • the calibration patches may be generated with a sensitive value of the sensitive field (F), to know how the calibration shall looks like depending on the sensitive value.
  • a sensitive value of a sensitive field (F) simulates a possible print situation in the calibration patch for a value of a working parameter. By selecting the most pleasing calibration patch by comparing other calibration patches comprising the same sensitive field (F), the working parameter, translated from the selected sensitive value in the selected calibration patch, may be adapted to have a better calibration.
  • the color-on-color registration can be determined by a distance-difference between the two colors in a pattern of the calibration patch.
  • the color-on-color registration may be corrected by adapting the time-of-firing of the printhead which printed one of the colors in the calibration patch.
  • the time-of-firing of a printhead is a working parameter; the distance difference between two colors is a sensitive field. So a value for a working parameter in the state-of-the-art calibration method is the result of translating the evaluation for a sensitive field, located in a calibration patch.
  • the present invention may be used in a landing distance calibration to guarantee dot placement accuracy in bi-directional printing, given the dot speed of the nozzle rows is not the same for all and the height position of the printheads in the printhead unit may be slightly different. Landing distance calibration is done for all each nozzle row in a printhead
  • the present invention may be used in a fastscan calibration which is a software / electronic correction of the mechanical fastscan position of each head in the matrix of printheads from the industrial inkjet system.
  • a calibration target is preferable defined in raster graphics format such as Portable Network Graphics (PNG), Tagged Image File Format (TIFF), Adobe Photoshop Document (PSD) or Joint Photographic Experts Group (JPEG) or bitmap (BMP) but more preferably a calibration target is defined in a raster vector graphics format, also called line-work format, such as Scale Vector Graphics (SVG) or AutoCad Drawing Exchange Format (DXF) and more preferably defined in a page description language (PDL) such as Printer Command Language (PCL): developed by Hewlett Packard, Postscript (PS): developed by Adobe Systems or Portable Document Format (PDF): developed by Adobe Systems.
  • PDL page description language
  • PCL Printer Command Language
  • PS Postscript
  • PDF Portable Document Format
  • the lay-out of the document is created in a desktop publishing (DTP) software package such as Adobe InDesignTM, Adobe PageMakerTM, QuarkXpressTM or Scribus (http://scribus.net/canvas/Scribus).
  • a calibration target may be defined in a document markup language, also called mark-up language, such as IBM's Generalized Markup Language (GML) or Standard Generalized Markup Language (ISO 8879:1986 SGML), more preferably defined in HyperText Markup Language (HTML) and most preferably defined in HTML5, the fifth revision of the HTML standard (created in 1990 and standardized as HTML 4 as of 1997) and, as of December 2012, is a candidate recommendation of the World Wide Web Consortium (W3C).
  • GML Generalized Markup Language
  • ISO 8879:1986 SGML Standard Generalized Markup Language
  • HTML5 HyperText Markup Language
  • a calibration patch comprises an image position error detection technique which is also applicable by an industrial inkjet system.
  • Visual techniques use calibration patches permit an operator or service engineer to simultaneously view various sensitive values, such as alignment settings, and choose the best calibration patch.
  • a calibration patch (P i,j,k ) in a calibration target is preferable defined in raster graphics format such as Portable Network Graphics (PNG), Tagged Image File Format (TIFF), Adobe Photoshop Document (PSD) or Joint Photographic Experts Group (JPEG) or bitmap (BMP) but more preferably a calibration patch (P i,j,k ) in a calibration target is defined in a vector graphics format, also called line-work format, such as Scale Vector Graphics (SVG) or AutoCad Drawing Exchange Format (DXF) and more preferably defined in a page description language (PDL) such as Printer Command Language (PCL): developed by Hewlett Packard, Postscript (PS): developed by Adobe Systems or Portable Document Format (PDF): developed by Adobe Systems.
  • DTP desktop publishing
  • DTP desktop publishing
  • DTP desktop publishing
  • a calibration patch (P i,j,k ) in a calibration target may be defined in a document markup language, also called mark-up language, such as IBM's Generalized Markup Language (GML) or Standard Generalized Markup Language (ISO 8879:1986 SGML), more preferably defined in HyperText Markup Language (HTML) and most preferably defined in HTML5, the fifth revision of the HTML standard (created in 1990 and standardized as HTML 4 as of 1997) and, as of December 2012, is a candidate recommendation of the World Wide Web Consortium (W3C).
  • GML Generalized Markup Language
  • ISO 8879:1986 SGML Standard Generalized Markup Language
  • HTML5 HyperText Markup Language
  • HTML5 revision of the HTML standard created in 1990 and standardized as HTML 4 as of 1997) and, as of December 2012, is a candidate recommendation of the World Wide Web Consortium (W3C).
  • optical-machine-readable code Different types are well-known, especially in the graphical industry.
  • One of the oldest types of optical-machine-readable code is the one-dimensional barcode. These one-dimensional barcodes are representing the data by varying the widths and spacing's of parallel lines. Barcodes originally were scanned by special optical scanners, called barcode readers. Later, digital imaging devices and interpretive software became available on devices such as portable mobiles.
  • the one-dimensional barcode is nowadays evolved to two-dimensional barcodes, also called matrix barcodes such as the Quick Response Code or QR code.
  • QR code was first designed for the automotive industry in Japan. A QR code on an item is scanned by a digital imaging device to read the content about the item which it is attached.
  • QR code may contain a hyperlink to a web page.
  • QR codes printed on a package, such as pharmaceutical package comprising a medicine, directs the operator of a mobile phone, after the QR code is scanned, to the specifications of the medicine on a web page.
  • the optical-machine-readable code is preferably constructed so it is insensitive for changes in working parameters of the industrial inkjet system for example printing by another printhead or printing in another color.
  • the optical-machine-readable code is preferably a two-dimensional barcode-type but more preferably a one-dimensional barcode-type because this type is less insensitive for changes in working parameters.
  • An optical-machine-readable code in a calibration target is preferable defined in raster graphics format such as Portable Network Graphics (PNG), Tagged Image File Format (TIFF), Adobe Photoshop Document (PSD) or Joint Photographic Experts Group (JPEG) or bitmap (BMP) but more preferably an optical-machine-readable code in a calibration target is defined in a vector graphics format, also called line-work format, such as Scale Vector Graphics (SVG) or AutoCad Drawing Exchange Format (DXF) and more preferably defined in a page description language (PDL) such as Printer Command Language (PCL): developed by Hewlett Packard, Postscript (PS): developed by Adobe Systems or Portable Document Format (PDF): developed by Adobe Systems.
  • DTP desktop publishing
  • DTP desktop publishing
  • An optical-machine-readable code in a calibration target may be defined in a document markup language, also called mark-up language, such as IBM's Generalized Markup Language (GML) or Standard Generalized Markup Language (ISO 8879:1986 SGML), more preferably defined in HyperText Markup Language (HTML) and most preferably defined in HTML5, the fifth revision of the HTML standard (created in 1990 and standardized as HTML 4 as of 1997) and, as of December 2012, is a candidate recommendation of the World Wide Web Consortium (W3C).
  • GML Generalized Markup Language
  • ISO 8879:1986 SGML Standard Generalized Markup Language
  • HTML5 HyperText Markup Language
  • HTML5 revision of the HTML standard created in 1990 and standardized as HTML 4 as of 1997) and, as of December 2012, is a candidate recommendation of the World Wide Web Consortium (W3C).
  • a raster graphic is also known as a bitmap, contone or a bitmapped graphic and represent a two-dimensional discrete image P(x,y).
  • a vector graphic also known as object-oriented graphic, uses geometrical primitives such as points, lines, curves, and shapes or polygon(s), which are all based on mathematical expressions, to represent an image.
  • the scanning of the optical-machine-readable code is performed by an optical-machine-readable code scanner such as optical scanners, barcode readers or digital imaging devices.
  • the decoding or interpreting of the scanned optical-machine-readable code (C i,j,r ) may be done by the optical-machine-readable code scanner or by the industrial inkjet system for example in the industrial inkjet system calibration unit.
  • the optical-machine-readable code scanner is preferably mechanically connect to the industrial inkjet system by a wire to transmit the optical-machine-readable code (C i,j,r ) or to transmit the decoded optical-machine-readable code (C i,j,r ) to the industrial inkjet system, And more preferably connected by wireless communication such as bluetooth or by a wire-less communication channel such as BluetoothTM, WIFI, radio or microwave communication.
  • wireless communication such as bluetooth or by a wire-less communication channel such as BluetoothTM, WIFI, radio or microwave communication.
  • a printhead is a means for jetting an inkjet ink on an ink receiver through a nozzle.
  • the nozzle may be comprised in a nozzle plate (600) which is attached to the printhead.
  • a set of ink channels, comprised in the printhead corresponds to a nozzle of the printhead which means that the inkjet ink in the set of ink channels can leave the corresponding nozzle in the jetting method.
  • the inkjet ink is preferably an ink, more preferably an UV curable inkjet ink or water based inkjet ink, such as a water based resin inkjet ink
  • a printhead may be any type of printhead such as a valvejet printhead, piezoelectric printhead, thermal printhead, a continuous printhead type, electrostatic drop on demand printhead type or acoustic drop on demand printhead type or a page-wide printhead array, also called a page-wide inkjet array.
  • a printhead comprises a set of master inlets to provide the printhead with an inkjet ink from a set of external inkjet ink feeding units.
  • the printhead comprises a set of master outlets to perform a recirculation of the inkjet ink through the printhead.
  • the recirculation may be done before the droplet forming means but it is more preferred that the recirculation is done in the printhead itself, so called through-flow printheads.
  • the continuous flow of the inkjet ink in a through-flow printheads removes air bubbles and agglomerated particles from the ink channels of the printhead, thereby avoiding blocked nozzles that prevent jetting of the inkjet ink.
  • the continuous flow prevents sedimentation and ensures a consistent jetting temperature and jetting viscosity. It also facilitates auto-recovery of blocked nozzles which minimizes inkjet ink and ink receiver wastage.
  • the recirculation of an inkjet ink results also in less inertia of the inkjet ink.
  • the printhead is a through-flow piezoelectric printhead or through-flow valvejet printhead, wherein the high viscosity inkjet ink is recirculated in a continuous flow through an inkjet ink transport channel where the pressure to the inkjet ink is applied by a droplet forming means and wherein the inkjet ink transport channel is in contact with the nozzle plate.
  • the droplet forming means in these printheads applies a pressure in the same direction as the jetting directions towards the ink receiver to activate a straight flow of pressurized inkjet ink to enter the nozzle that corresponds to the droplet forming means.
  • the advantage of such through-flow printheads is a better dot-placement on an ink receiver than the non through-flow printheads for example by less sedimentation in the printhead.
  • the number of master inlets in the set of master inlets is preferably from 1 to 12 master inlets, more preferably from 1 to 6 master inlets and most preferably from 1 to 4 master inlets.
  • the set of ink channels that corresponds to the nozzle are replenished via one or more master inlets of the set of master inlets.
  • the amount of master outlets in the set of master outlets in a through-flow printhead is preferably from 1 to 12 master outlets, more preferably from 1 to 6 master outlets and most preferably from 1 to 4 master outlets.
  • a set of inkjet inks is mixed to a jettable inkjet ink that replenishes the set of ink channels.
  • the mixing to a jettable inkjet ink is preferably performed by a mixing means, also called a mixer, preferably comprised in the printhead wherein the mixing means is attached to the set of master inlets and the set of ink channels.
  • the mixing means may comprise a stirring device in an inkjet ink container, such as a manifold in the printhead, wherein the set of inkjet inks are mixed by a mixer.
  • the mixing to a jettable inkjet ink also means the dilution of inkjet inks to a jettable inkjet ink.
  • the late mixing of a set of inkjet inks for jettable inkjet ink has the benefit that sedimentation can be avoided for jettable inkjet inks of limited dispersion stability.
  • the inkjet ink leaves the ink channels by a droplet forming means, through the nozzle that corresponds to the ink channels.
  • the droplet forming means are comprised in the printhead.
  • the droplet forming means are activating the ink channels to move the inkjet ink out the printhead through the nozzle that corresponds to the ink channels.
  • the amount of ink channels in the set of ink channels that corresponds to a nozzle is preferably from 1 to 12, more preferably from 1 to 6 and most preferably from 1 to 4 ink channels.
  • the printhead of the present invention is suitable for jetting an inkjet ink having a jetting viscosity of 5 mPa.s to 3000 mPa.s.
  • a preferred printhead is suitable for jetting an inkjet ink having a jetting viscosity of 20 mPa.s to 200 mPa.s.
  • a preferred printhead for the present invention is a so-called Valvejet printhead.
  • Preferred valvejet printheads have a nozzle diameter between 45 and 600 ⁇ m.
  • the valvejet printheads comprising a plurality of micro valves, allow for a resolution of 15 to 150 dpi that is preferred for having high productivity while not comprising image quality.
  • a Valvejet printhead is also called coil package of micro valves or a dispensing module of micro valves.
  • the way to incorporate valvejet printheads into an inkjet printing device is well-known to the skilled person.
  • US 2012105522 (MATTHEWS RESOURCES INC) discloses a valvejet printer including a solenoid coil and a plunger rod having a magnetically susceptible shank.
  • Suitable commercial valvejet printheads are chromoJETTM 200, 400 and 800 from Zimmer, PrintosTM P16 from VideoJet and the coil packages of micro valve SMLD 300's from Fritz GygerTM
  • a nozzle plate (600) of a Valvejet printhead is often called a faceplate and is preferably made from stainless steel.
  • Valvejet printhead controls each micro valve in the Valvejet printhead by actuating electromagnetically to close or to open the micro valve so that the medium flows through the ink channel.
  • Valvejet printheads preferably have a maximum dispensing frequency up to 3000 Hz.
  • Valvejet printhead has a native print resolution from 10 DPI to 300 DPI, in a more preferred embodiment the Valvejet printhead has a native print resolution from 20 DPI to 200 DPI and in a most preferred embodiment the Valvejet printhead has a native print resolution from 50 DPI to 200 DPI.
  • the jetting viscosity is from 5 mPa.s to 3000 mPa.s more preferably from 25 mPa.s to 1000 mPa.s and most preferably from 30 mPa.s to 500 mPa.s.
  • the jetting temperature is from 10 °C to 100 °C more preferably from 20 °C to 60 °C and most preferably from 25 °C to 50 °C.
  • Piezoelectric printhead also called piezoelectric inkjet printhead
  • Piezoelectric printhead is based on the movement of a piezoelectric ceramic transducer, comprised in the printhead, when a voltage is applied thereto.
  • the application of a voltage changes the shape of the piezoelectric ceramic transducer to create a void in an ink channel, which is then filled with inkjet ink.
  • the ceramic expands to its original shape, ejecting a droplet of inkjet ink from the ink channel.
  • the droplet forming means of a piezoelectric printhead controls a set of piezoelectric ceramic transducers to apply a voltage to change the shape of a piezoelectric ceramic transducer.
  • the droplet forming means may be a squeeze mode actuator, a bend mode actuator, a push mode actuator or a shear mode actuator or another type of piezoelectric actuator.
  • Suitable commercial piezoelectric printheads are TOSHIBA TECTM CK1 and CK1L from TOSHIBA TECTM (https://www.toshibatec.co.jp/en/products/industrial/inkjet/products/cf1/) and XAARTM 1002 from XAARTM (http://www.xaar.com/en/products/xaar-1002).
  • An ink channel in a piezoelectric printhead is also called a pressure chamber.
  • an ink channel and a master inlet of the piezoelectric printheads there is a manifold connected to store the inkjet ink to supply to the set of ink channels.
  • the piezoelectric printhead is preferably a through-flow piezoelectric printhead.
  • the recirculation of the inkjet ink in a through-flow piezoelectric printhead flows between a set of ink channels and the inlet of the nozzle wherein the set of ink channels corresponds to the nozzle.
  • the minimum drop size of one single jetted droplet is from 0.1 pL to 100 nL, in a more preferred embodiment the minimum drop size is from 1 pL to 150 pL, in a most preferred embodiment the minimum drop size is from 1.5 pL to 15 pL.
  • Minimum drop size of one single jetted droplet may be larger than 50 pL by a piezoelectric printhead, such as the XaarTM 001 which is used in the digitalization of ceramics manufacturing processes.
  • the piezoelectric printhead has a drop velocity from 3 meters per second to 15 meters per second, in a more preferred embodiment the drop velocity is from 5 meters per second to 10 meters per second, in a most preferred embodiment the drop velocity is from 6 meters per second to 8 meters per second.
  • the piezoelectric printhead has a native print resolution from 25 DPI to 2400 DPI, in a more preferred embodiment the piezoelectric printhead has a native print resolution from 50 DPI to 2400 DPI and in a most preferred embodiment the piezoelectric printhead has a native print resolution from 150 DPI to 3600 DPI.
  • the jetting viscosity is from 5 mPa.s to 200 mPa.s more preferably from 25 mPa.s to 100 mPa.s and most preferably from 30 mPa.s to 70 mPa.s.
  • the jetting temperature is from 10 °C to 100 °C more preferably from 20 °C to 60 °C and most preferably from 30 °C to 50 °C.
  • the nozzle spacing distance of the nozzle row in a piezoelectric printhead is preferably from 10 ⁇ m to 200 ⁇ m; more preferably from 10 ⁇ m to 85 ⁇ m; and most preferably from 10 ⁇ m to 45 ⁇ m.
  • An industrial inkjet system is a marking device that is using one or more printhead units wherein one or more printheads are mounted.
  • the printheads jet inkjet ink on an ink receiver.
  • a pattern that is marked by jetting of the industrial inkjet system on an ink receiver is preferably an image.
  • the pattern may be achromatic or chromatic colour.
  • Industrial inkjet system essentially means using inkjet technology as a printing or deposition process in manufacturing or on production lines in a large scale.
  • the industrial inkjet system may mark a broad range of ink receivers: sheet-shaped or web-shaped.
  • An ink receiver may be folding carton, acrylic plates, glass, honeycomb board, corrugated board, foam, medium density fibreboard, solid board, rigid paper board, fluted core board, plastics, aluminium composite material, foam board, corrugated plastic, textile, thin aluminium, paper, rubber, adhesives, vinyl, veneer, varnish blankets, wood, flexographic plates, metal based plates, fibreglass, transparency foils, rugs, carpets or adhesive PVC sheets.
  • the industrial inkjet system may comprise a step belt conveyor which is a piece of mechanical handling equipment that carries an ink receiver by moving from a start location to an end location via a porous conveyor belt in successive distance movements, also called discrete step increments.
  • the direction movement from the start location to the end location is called the printing direction or conveying direction.
  • the porous conveyor belt is linked between a plurality of pulleys wherein the porous conveyor belt rotates around the plurality of pulleys.
  • An example of a general belt conveyor system comprising a vacuum table to hold an ink receiver while printing and wherein the vacuum table comprises pneumatic cleaning devices is disclosed in US 20100271425 (XEROX CORPORATION).
  • An industrial inkjet system which prints by a single pass printing process is a preferred embodiment.
  • Such industrial inkjet systems are called industrial single-pass inkjet systems, which can be performed by using page wide inkjet printheads or a printhead unit wherein multiple printheads are staggered to cover the entire width of an ink receiver.
  • the inkjet printheads usually remain stationary and the substrate surface is transported once under the inkjet printheads.
  • An industrial inkjet system may also comprise a printhead unit, comprising one or more printheads, which is designed for reciprocating back and forth across an ink receiver in a fast scan direction FS and for repositioning across the printing table in a slow scan direction SS perpendicular to the fast scan direction.
  • Optional repositioning of the printhead unit is done in between reciprocating operations of the printhead unit, in order to position the printhead unit in line with a non-printed or only partially printed area of the printing medium. The repositioning of the printhead unit is unnecessary in situations where the printhead unit is equipped to print a full-width printing medium in a single fast scan operation.
  • a support frame guides and supports the printhead unit during its reciprocating operation.
  • a printing medium transport system may feed individual ink receivers into the industrial inkjet system along a sheet feeding direction that is substantially perpendicular to the fast scan direction of the printhead unit.
  • the digital printer may also be used with a web-based medium transport system.
  • the printing medium transport may feed web media into the digital printer from a roll-off at the input end of the digital printer to a roll-on at the discharge end of the digital printer. Inside the digital printer the web is transported along the printing table that is used to support the printing medium during printing.
  • the repositioning of the printhead unit along the slow scan direction may be replaced by a repositioning of the web in the feeding direction.
  • the printhead unit then only reciprocates back and forth across the web in the fast scan direction.
  • the industrial inkjet system is preferably a textile industrial inkjet system, ceramic industrial inkjet system, glass industrial inkjet system or decoration industrial inkjet system and on top of more preferably an industrial single-pass inkjet system.
  • the inkjet ink in the present invention may be any type of ink which is jettable by a printhead.
  • the inkjet ink may be a solvent inkjet ink, UV-curable inkjet ink or dye sublimation inkjet ink.
  • An inkjet ink may be a colourless inkjet ink and be used, for example, as a primer to improve adhesion or as a varnish to obtain the desired gloss.
  • the inkjet ink includes at least one colorant, more preferably a colour pigment.
  • the inkjet ink may be a cyan, magenta, yellow, black, red, green, blue, orange or a spot color inkjet ink, preferable a corporate spot color inkjet ink such as red colour inkjet ink of Coca-ColaTM and the blue colour inkjet inks of VISATM or KLMTM.
  • the inkjet ink is an inkjet ink comprising metallic particles or comprising inorganic particles such as a white inkjet ink.
  • optical-machine-readable codes may also be usefull for other calibration in the industrial inkjet system such as:
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