DE102017101527A1 - Method for detecting a faulty application of a coating material which is invisible in the applied state, in particular a primer, for printing on a recording medium and corresponding printing system - Google Patents

Abstract

The present invention relates to a method for detecting a faulty application of an invisible in the applied state coating material, in particular a primer, for printing a recording medium, comprising the following steps: printing a printing area of a recording medium with a coating material by means of an inkjet printhead; Printing a first color across the width of the printing area of the recording medium printed with the coating material; Printing a thin line of a second color across the width of the print area to the first color; Analyze the bleeding behavior of the first and second colors along the thin line. The present invention further relates to a corresponding printing system.

Description

The invention relates to a method for detecting a faulty application of an invisible in the applied state coating material, in particular a primer, for printing a recording medium and a corresponding printing system.

The present invention and the problems underlying it are explained in more detail below with reference to inkjet printers, also called inkjet printers. However, the invention is not limited thereto, but transferable to a variety of printing methods.

Inkjet or inkjet printers use multicolor, non-contact, direct printing based on thermal or electrophysical principles. For example, the inkjet printing in the document DE 102 33 409 A1 explained.

There are numerous measures to improve the quality of inkjet printing. For example, if the throughput is too low, ink in the printheads may change, usually increase, its viscosity. Therefore, especially in high-speed printing systems and / or in continuous printing systems, regularly interspersed regeneration print images, so-called refresh lines, are used to regenerate the nozzles (print nozzles) of the print heads between the printing of print data-based print images. For example, this is in the document DE 10 2014 108 342 A1 described.

Another problem of so-called "bleeding" or "color bleeding" can occur when an ink of one color is applied to or in the immediate vicinity of an ink of another color. This problem manifests itself in mixing or bleeding together of two inks at their interfaces, making a boundary at the transition from one ink to another ink unclear, e.g. the edges of the touching inks blur. This phenomenon is caused by capillary forces, which draw the printing inks into adjacent areas. By pretreatment with a coating material, for. B. the fixation of ink drops are increased on the surface of the recording medium, so that the Bleeding is avoided.

If the coating material is likewise applied to the recording medium by means of an inkjet station or by inkjet printing, locally limited failures of individual print heads or printing nozzles can occur. This can have a variety of causes, such as local short circuits, for example due to detergent residues, or droplet formation on the print head, for example due to condensation. Such locally limited failures of an inkjet station can sometimes be difficult to detect in the printing operation, especially since the coating material on the recording medium is usually invisible in order not to influence the printing result. One recognizes a failure therefore often only in itself accumulating quality losses of the finished printing result.

Against this background, the object of the present invention is to specify an improved method for detecting a faulty application of a coating substance, in particular a primer, invisible in the applied state for printing a recording medium.

The object is solved by the features of the independent method claim 1 or by the features of the independent apparatus claim 15.

The invention relates to a method for detecting an erroneous application of an invisible in the applied state coating material, in particular a primer, for printing a recording medium, comprising the following steps: printing a printing area of a recording medium with a coating material by means of an inkjet printhead; Printing a first color across the width of the printing area of the recording medium printed with the coating material; Printing a thin line of a second color across the width of the print area to the first color; and analyzing the bleeding behavior of the first and second colors along the thin line.

The invention further relates to a printing system, in particular for carrying out a method according to the invention for detecting a faulty application of an invisible in the applied state coating material, in particular a primer, for printing a recording medium, comprising: a primer inkjet station with a plurality of printing nozzles for printing a Printing area of a recording medium with a coating material; an ink-inkjet station for printing a first color across the width of the printing area of the recording medium printed with the coating material and for printing a thin line of a second color across the width of the printing area onto the first color; a sensor for sensory detection of the printed printing area; a controller coupled to the sensor and the primer inkjet station for analyzing the local bleeding behavior of the first and second colors along the thin line based on sensory detection and for identifying any localized failures of print nozzles the primer inkjet station from any bleeding affected portions of the thin line.

The idea on which the invention is based is now to make nozzle failures of an inkjet printhead used for printing the recording medium detectable on the basis of targeted examination of the bleeding behavior on a thin test line of a second color printed on a first color for this purpose.

In this way, otherwise visually unrecognizable local defects in the application of the coating material, for example in the form of a local in the region of a pressure nozzle due to a failure of the pressure nozzle occurring lack of coating material, made visible. This advantageously makes it possible to initiate countermeasures at an early stage, in particular before the faulty application has repeatedly adversely affected the finished printing result.

The analysis of the Bleedingverhaltens can be done in various ways, either manually, semi-automated or automated, if necessary. Also embedded in a control loop, made. In particular, it permits a conclusion as to the location of the failure of a printing nozzle or at least to the inkjet printing head of the primer inkjet printing station which is affected by the failure. Thus, early targeted countermeasures can be initiated.

For example, as a countermeasure (especially in a first escalation stage), attempts can be made to readjust the applied quantity. Furthermore, a warning message could be issued (in particular in a second escalation stage) and / or a cleaning routine, in particular for self-cleaning of the print head, be initiated. It would also be conceivable (in particular in a third escalation stage) to stop the pressure if necessary and request a repair and / or cleaning measure.

If the analysis is not carried out manually, an often already existing in a printing system for monitoring the print image sensor, for example, a so-called inline camera, can be used. In addition, due to their design, inkjet printheads are always provided with only locally acting pressure nozzles, the local effect of which may possibly be influenced individually by control technology. The sensory detection by the sensor therefore allows within certain limits a readjustment of the applied amount by a local increase in the amount of coating material which is applied by arranged in the immediate vicinity of the failed nozzle pressure nozzles. In this way it can be attempted to compensate for a detected failure of a pressure nozzle and thus to keep the print quality constant despite the failure.

The inkjet printing of the printing area with a coating material is usually a flat inkjet printing over the entire width of the printing area.

The analysis of the Bleedingverhaltens can thus in one embodiment, the, in particular sensory, detecting the printed image, preferably over the entire width of the printing area along the thin line include.

The printing area may be a maximum printing area technically predetermined by the printing system used or a maximum printing area predetermined by the width of the recording medium or a freely selected or set maximum printing area.

The method according to the invention can preferably be used on an inkjet printing system. The printing system according to the invention is accordingly preferably designed as an inkjet printing system.

Further advantageous embodiments of the invention are given in the dependent claims.

The above embodiments and developments can, if appropriate, combine with each other as desired. In particular, all features of the method for detecting a faulty application of an invisible in the applied state coating material, in particular a primer, for printing a recording medium on a corresponding printing system are transferable, and vice versa.

Further possible refinements, developments and implementations of the invention also include combinations, not explicitly mentioned, of features of the invention described above or below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

• 1 ein Blockdiagramm eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens;
• 2 ein schematisches Schaltbild eines Ausführungsbeispiels eines erfindungsgemäßen Drucksystems;
• 3A - 3D verschiedene Zustände des Aufzeichnungsträgers gemäß einem Ausführungsbeispiel des Verfahrens;
• 4 eine beispielhafte sensorische Erfassung eines Abschnitts des Druckbereichs mit Teils ausgefallenen Druckdüsen der Primer-Inkjet-Station;
• 5 eine beispielhafte sensorische Erfassung eines Abschnitts des Druckbereichs mit vollständig funktionierenden Druckdüsen der Primer-Inkjet-Station;
• 6 eine beispielhafte Analyse einer lokalen Linienbreite;
• 7 eine beispielhafte Analyse einer lokalen Kantenglätte;
• 8 eine beispielhafte Analyse einer lokalen Kantenschärfe; und
• 9 eine schematische Darstellung einer Primer-Inkjet-Station.

In the following, embodiments of the invention will be described in more detail with reference to the schematic drawing. Showing:

• 1 a block diagram of an embodiment of a method according to the invention;
• 2 a schematic diagram of an embodiment of a printing system according to the invention;
• 3A - 3D various states of the record carrier according to an embodiment of the method;
• 4 an exemplary sensory detection of a portion of the print area with partially failed print nozzles of the primer inkjet station;
• 5 an exemplary sensory detection of a portion of the printing area with fully functioning printing nozzles of the primer inkjet station;
• 6 an exemplary analysis of a local line width;
• 7 an exemplary analysis of a local edge smoothness;
• 8th an exemplary analysis of a local edge sharpness; and
• 9 a schematic representation of a primer inkjet station.

The accompanying figures of the drawing are intended to convey a further understanding of the embodiments of the invention. They illustrate embodiments and, together with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the stated advantages will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale to each other.

In the figures of the drawing are the same, functionally identical and same-acting elements, features and components - unless otherwise stated - each provided with the same reference numerals.

1 shows a block diagram of an embodiment of a method according to the invention.

It is a method for detecting an erroneous application of a coating material which is invisible in the applied state, in particular a primer, for printing on a recording medium, in particular in an inkjet printing system.

The method comprises a step S1 of printing on a printing area 3 a record carrier 4 with a coating material 5 by means of an inkjet printhead 20 , as in 3B displayed. The inkjet printhead 20 can be provided in particular in a primer inkjet station 2, which in particular also several inkjet printheads 20 may contain. Accordingly, in one embodiment, across the width of the print area 3 several inkjet printheads 20 for applying the coating material 5 be provided. Thus, analyzing the bleeding behavior can be an indication of any failure of pressure nozzles 21 on a single printhead 20 include, as in the 2 and 9 displayed.

As a coating material 5 In the case of a later inkjet printing of the inks to be printed, a primer is preferably applied or printed on which improves the adhesion of the color particles of the subsequently applied colored ink or causes the ink to flocculate, so that it is deposited on the recording medium 4 directly liable. It will do this with the preferably several across the width of the printing area 3 arranged inkjet printheads, each containing a variety of, in particular individually controllable, pressure nozzles, a uniform application of the coating material 5 printed.

According to one embodiment, the printhead 20 , as in 9 shown, over the width of its associated pressure range a plurality of pressure nozzles 21 for applying the coating material 5 Analyzing the bleeding behavior is an indication of any localized failures in the range of fewer or individual pressure nozzles 21 includes. If appropriate, this can be used for readjusting the applied quantity of coating material by setting or controlling the nozzles adjacent to a failed nozzle to an increased output of coating material, for example in the form of an increased drop size.

According to a development can thus upon detection of a failure in the range of less or individual pressure nozzles 21 to compensate for the failure, the drop size of the coating material 5 for pressure nozzles arranged in the area and / or near the area 21 be enlarged.

In a further step S2 of the method is the printing of a first color 7 across the width of the with the coating material 5 printed print area 3 of the record carrier 4 provided as in 3C displayed.

The method further comprises a step S3 of printing at least one thin line 8th a second color 9 across the width of the print area 3 on the first color 7, as in 3D displayed.

The printing of the first color 7 is at least a small area, preferably made as a flat print. The first color 7 is preferably over the entire width of the printing area 3 applied over the entire printing area 3 Any incorrect application of the coating material 5 to make recognizable. It is, for example, a continuous surface of the first color 7 over the entire width of the print area 3 printed.

According to one embodiment, the first color becomes 7 over a predetermined length and over the entire width of the printing area printed with the coating material 3 of the record carrier 4 printed. If appropriate, this may also be a surface of short length, for example a thick line with a thickness of several points. The surface printed with the first color, in particular its length, is selected such that the thin line 8th the second color 9 across the width of the print area 3 can be printed on it. It is therefore at least a significant overlap of the first color throughout 7 and the second color 9 provided in printing or longitudinal direction. Preferably, the thin line 8th completely on the second color 9 applied or printed.

According to a preferred embodiment, the thin line 8th is printed in the form of a one-dot line. That is, it is a printable line that is thinnest possible with the printing system. That's how sections are 19 in which bleeding occurs or caused by bleeding deviations from the thin line 8th particularly easy to recognize.

According to one embodiment, the thin line 8th the second color 9 in the form of a regular pattern of several thin lines on the first color 7 printed. This regular pattern can have a wide variety of configurations, for example a plurality of parallel lines.

Preferably, the first color 7 and the second color 9 each also printed with an inkjet process. For example, this is a conventional ink-jet ink station 6 intended.

According to a preferred embodiment, the first color and the second color are selected with a high contrast to each other. For example, the first color may be a lightest color or primary ink of the ink-inkjet station 6 , in particular yellow, and in the second color to a darkest color or a darkest primary ink of the ink-inkjet station 6 , especially black, act.

According to an advantageous embodiment, the printing of the first color 7 and printing the thin line 8th the second color 9 during a regular printing operation during routine printing of a regeneration print image. In particular, the regeneration print image may be refresh lines. The printing of the first color 7 and printing the thin line 8th the second color 9 can be provided in addition to the refresh lines, integrated with the refresh lines, or in the form of refresh lines. For example, a surface of the recording medium which has been inserted into the print job or a section of the recording medium provided for the purpose of cutting is suitable as the surface.

In a further step S4 of the method, an analysis of the Bleedingverhaltens of the first and second color 7 . 9 along the thin line 8th performed.

According to one embodiment, the analyzing comprises deriving any of them across the width of the record carrier 4 locally incorrect application of the coating material 5 from the bleeding behavior. It may consist of the position, type and frequency sections 19 at which bleeding occurs, the position and frequency of nozzle failures of the inkjet printhead 20 for applying the coating material 5 be derived.

In particular, the Bleedingverhalten is based on the course of the line width 14 , Edge smoothness and / or edge sharpness 18 the thin line 8th assessed. For this purpose, the line width, edge smoothness and / or edge sharpness are first determined, with reference to 6 to 8th will be discussed in more detail. In particular, an adjustment can then be made with predetermined setpoint values and / or tolerances.

According to one embodiment, the conclusion of the failure of an inkjet printhead or a pressure nozzle from a local bleeding behavior based on a position of a bleeding affected section 19 along the thin line 8th to be pulled. The position along the width of the printing area can be assigned to the respective print head or optionally the affected nozzle.

In one embodiment, analyzing the bleeding behavior after the printing operation is optically based on the printing result on the recording medium 4 performed.

Another embodiment is analyzing the Bleedingverhaltens during the printing process by means of a sensor 10 performed. In particular, as a sensor in the printing system 1 integrated on the record carrier 4 be directed camera provided. Such a camera, also referred to as an inline camera or ILS camera, is often provided anyway in a printing system for monitoring the printing result. Advantageously, therefore, no additional hardware is necessary.

If a readjustment of the applied amount of the coating material is provided, the sensor 10 a part of my in the printing system 1 provided loop for automatically adjusting the amount of the coating material 5 represent.

According to a further embodiment, analyzing the bleeding behavior comprises scanning the print result on the record carrier 4 by means of a scanner. This can be done in particular during or after the printing process. Accordingly, it may be integrated into the printing system or external scanner. In the case of an integrated scanner, this can be used as a sensor 10 be provided instead of or in addition to the camera. In the case of an external scanner, this can be provided for example for computer-aided downstream analysis.

According to one embodiment, as a result of the analysis of the bleeding behavior, the printing process may be stopped upon detection of a predetermined measure of bleeding behavior, in particular over a predetermined period of time or printing length. For example, stopping may result in cleaning or replacement of the affected printhead 20 be provided. This can in particular be postponed to an unsuccessful attempt at readjustment, ie as a measure of a higher escalation level than readjustment.

2 shows a schematic diagram of an embodiment of a printing system according to the invention 1 ,

The printing system is for performing a method according to 1 educated.

The printing system 1 has a primer inkjet station 2 for printing on a print area 3 a record carrier 4 with a coating material 5 on. Such a primer inkjet station 2 has one or more inkjet printheads not shown in detail herein 20 which each contain a plurality of individually controllable pressure nozzles 21.

In addition, an inkjet inkjet station 6 intended. In principle, the inkjet ink station 6 designed for printing any colors and shapes in any order and / or composition. Ink-inkjet stations are generally known to those skilled in the art and require no further explanation at this point.

Referring to the method according to 1 becomes the inkjet inkjet station 6 for printing S2 of a first color 7 across the width of the with the coating material 5 printed print area 3 of the record carrier 4 and for printing S3 a thin line 8th a second color 9 across the width of the print area 3 used on the first color 7, as in terms of 1 described.

The printing system 1 also has a sensor 10 for sensory detection of the printed printing area 3 on. This is, for example, a camera, in particular a so-called inline camera, which is in the printing system 1 is integrated. The sensory detection by the sensor 10 allows a readjustment of the local amount of the applied coating material 5 for compensation in the event of a detected failure of a pressure nozzle 21 ,

It is also one with the sensor 10 and the primer inkjet station 2 coupled control device 11 intended. This is for analyzing the local bleeding behavior of the first 7 and second colors 9 along the thin line based on sensory detection 12 educated. It is also used to identify any localized limited pressure nozzle failures 21 the primer inkjet station 2 on any bleeding affected sections 19 the thin line 8th educated.

The control device 11 For this purpose, it can have a computing device and a memory, which can have a database of comparison values or nominal values and / or tolerances. On the computing device is in particular an algorithm for analyzing the bleeding behavior, for example by means of examination of the line thickness, edge smoothness and / or edge sharpness of the thin line 8th implemented.

The algorithm includes, for example, the steps of evaluating the line thickness, edge smoothness and / or edge sharpness of the thin line 8th , What follows in relation to the 6 to 8th will be explained in more detail, a comparison with a setpoint, the detection of any affected by bleeding sections based on deviations (peaks) from the setpoint over a predetermined tolerance away, as well as the initiation of a countermeasure. As a countermeasure come, for example, a readjustment of the applied amount of the coating material, the output of an error message, the initiation of a Cleaning routine or possibly stopping the pressure question.

In addition, the control device 11 in the illustrated embodiment also for readjustment of the applied amount of the coating material, ie here for driving the primer inkjet station 2 for locally adjusting the printed amount of the coating material 5 in sections of the thin line affected by bleeding 8th , educated. In particular, it is designed, individual printheads 20 , preferably individual groups of pressure nozzles 21 , more preferably individual pressure nozzles 21 for increased application of the coating material 5 according to the amount of coating material required to compensate for a detected failure 5 head for. For example, to individual pressure nozzles 21 be controlled variably with regard to the droplet size ejected by them.

The printing system 1 preferably has a feed mechanism, not shown, with which the recording medium 4 first the primer inkjet station 2 and then the ink-inkjet station 6 is supplied. It can also be an unillustrated deduction in the wake of the sensor 10 for removing the printed record carrier 4 be provided.

3A to 3D show different states of the record carrier 4 according to an embodiment of the method.

3A schematically shows a recording medium 4 in unprinted condition. For example, it may be a sheet of paper. However, it may also be a web or roll of a recording medium 4 , For example, a paper web or roll of paper act. There come for a variety of paper types, such as glossy or matte paper types, as well as a variety of other suitable as a record carrier substrates, for example, films of plastic and / or metal, especially aluminum, or rolls, sheets or sheets containing cardboard, composites, or the like in question.

3B shows the record carrier 4 with coating material applied thereto 5 , In particular, it is the coating material 5 around a so-called primer. This may be provided, for example, as an aqueous saline solution containing the colored ink of the inkjet inkjet station 6 reacts and causes flocculation of the color, so that they on the record carrier 4 sticks directly when printing.

Such a primer is usually colorless or not visible or recognizable in the printed state on the recording medium. In this way, the printed image is not adversely affected.

The printing of the recording medium 4 with the coating material 5 will be in the primer inkjet station 2 performed. Preferably, this is a continuous process, wherein the coating material 5 across the width of the record carrier 4 is applied evenly and the recording medium 4 with a regular feed v is encouraged, as in 2 drawn with an arrow.

If a failure of a pressure nozzle occurs 21 on, so creates a faulty order or imprint of the coating material 5 ,

In 3B is not visible per se coating material 5 only with on the record carrier 4 applied points shown schematically. The coating material 5 is flat, preferably over the entire surface over the entire pressure range 3 , on the record carrier 4 applied.

3C shows the record carrier 4 with on the coating material 5 printed first color 7 ,

The first color is purely schematic and exemplary 7 here also all over the record carrier 4 shown printed. However, it may also be only over a predetermined length (in printing or feed direction) and over the entire width of the recording medium 4 flat printed area of the first color 7 act. It would also be conceivable, the first color 7 only as a line, preferably a relatively thick line with a thickness of at least several points apply. In this case, the strength would have to be chosen sufficiently so that at least one overlap with the thin line of the second color 9 is possible.

3D shows the record carrier 4 with the on the first color 7 printed thin line 8th the second color 9 , By way of example, a plurality of parallel thin lines 8 are applied here. These are preferably one-dot lines, ie lines with a thickness of only one pixel, which represents the line thickness which can be printed on the thinnest.

4 shows an exemplary sensory detection of a portion of the printed printing area 3 with partly failed pressure nozzles of the primer inkjet station 2 ,

The detection is provided here in the form of an image recording. Other types of sensory detection are possible.

Shown are areas of first color 7 and a thin line 8th with the second color 9 , The first 7 and the second color 9 are along the line 8th at several sections 19 partially merged. This merging of the colors, which is commonly referred to as Bleeding, it is necessary to avoid the production of a high print quality.

The reason for the bleeding is a locally too small amount of coating material or amount of primer on the recording medium 4 due to pressure nozzle failures at the primer inkjet station 2 are traceable. Accordingly, the first and second colors adhere 7 , 9 in the sections 19 not ideal on the record carrier 4 and thus partially run into each other due to capillary effects.

5 shows an exemplary sensory detection of a portion of the print area 3 with fully functioning printing nozzles of the primer inkjet station 2 ,

It is easy to see here a much sharper delineation of the areas of first color 7 and the thin line 8th with the second color 9 recognizable. The second color 9 applied thin line 8th also has one compared to 4 much more uniform and thinner line width.

By a sufficient amount of coating material or primer adhere to the first and the second color 7 . 9 here directly after printing on the recording medium 4 so it does not affect the effect of bleeding as in 4 comes.

6 shows an exemplary analysis of a local line width.

For the determination of the line width, also called line width, the strongest change of the brightness becomes on both edges of the line 8th determined. This is preferably done using the so-called gradient method for the transitions of the first color 7 to the second color 9 performed.

For this purpose, firstly by means of image processing gradient contours 13 identifies and a distance between the gradient contours 13 measured. The distance between the two gradient contours 13 sets the line width 14 represents.

The measurement principle is based in particular on the draft of ISO 13660 "Measurement of Image Quality Attributes for Hardcopy Output"; Section 6.3 "Line Width".

Exceeds the measured line width 14 a predetermined value (depending on the printing resolution, type of recording medium and used primer for a single-dot line eg 50 microns, 100 microns or 200 microns), this allows a conclusion on locally occurring bleeding and thus on a pressure nozzle failure.

7 shows an exemplary analysis of a local edge smoothness.

First, the position of an ideal edge 15 determined, with the strongest change in brightness according to the gradient method for the transition from the first color 7 also with the second color 9 printed line element is determined.

The mean absolute deviation of the real geometry 16 to the ideal edge 15 describes the edge smoothness.

The valuation is based in particular on ISO 13660 "Information Technology - Office Equipment - Measurement of image quality attributes for hard copy output - Binary monochrome text and graphic images".

If the measured local edge smoothness exceeds a predetermined value (for example, depending on the recording medium and the primer used 20 μm, 50 μm or 100 μm), this allows a conclusion on local bleeding and thus on a pressure nozzle failure.

8th shows an exemplary analysis of a local edge acuity.

For the determination of the edge sharpness, first a 20% threshold contour is calculated 16 and an 80% threshold contour 17 of the respective edge for the transition from the first color 7 to the one with the second color 9 determined printed line element.

To determine the threshold contours 16 . 17 become the reflection values, ie a reflection factor (also called the reflection coefficient) of the first color 7 and the second color 9 determined.

Since the first color here is a light color, the reflection value of the first color represents a highest reflection factor (also called a reflection coefficient) Rmax. The second color is preferably a dark color or black and thus has a minimum reflection factor Rmin. The reflection factors can for example consist of a The manufacturer's instructions are taken or measured with commercially available spectrophotometers.

$$\text{Th80}=\text{Rmax}-8\text{0\%}*\left(\text{Rmax}-\text{Rmin}\right)$$

The 20% threshold (Th20) and the 80% threshold (Th80) are then calculated as follows: $$\text{Th20}=\text{Rmax}-\text{20\%}*\left(\text{Rmax}-\text{Rmin}\right)$$

$$\text{TH80}=\text{Rmax}-\mathrm{8th}\text{0\%}*\left(\text{Rmax}-\text{Rmin}\right)$$

The threshold contours associated with the 20% threshold Th20 and the 80% threshold Th80 16 and 17 are set at the position of the mean value having the respective value. The distance between the 20% threshold contour 16 and the 80% threshold contour 17 then sets the edge sharpness 18 the respective edge.

This evaluation is carried out in accordance with ISO 13660 "Information Technology - Office Equipment - Measurement of image quality attributes for hard copy output - Binary monochrome text and graphic images".

If the measured local edge sharpness exceeds a predetermined value (eg, depending on the recording medium and the primer used) 20 μm, 50 μm or 100 μm), this allows a conclusion on local bleeding and thus on a pressure nozzle failure.

9 shows a schematic representation of a primer inkjet station 2 ,

Shown here is a schematic plan view of the so-called Nozzle- or-pressure nozzle plate, which on a recording medium side facing the primer inkjet station 2 is provided.

In the primer inkjet station 2 Here are purely illustrative five juxtaposed printheads 20 intended. Of course, the number of printheads 20 depending on their size and the width of the printing area 3 vary. It would also be conceivable, only a single printhead 20 provide with the required width or the primer inkjet station 2 as a single over the entire width of the print area 3 form extending printhead.

Each of the printheads 20 has a variety of pressure nozzles 21 on.

Purely for improved clarity are in the presentation of the 9 on each of the printheads 20 only nine pressure nozzles 21 shown, which are arranged in two rows next to each other and offset from each other. In an actual printhead are usually a much higher number of printing nozzles 21 provided, which have compared to the size of the print head much smaller dimensions. Different arrangements of the pressure nozzles are possible. The dimensions as well as the number and type of arrangement of the pressure nozzles 21 can be varied in many ways.

In particular, is for use in the primer inkjet station 2 a conventional inkjet printhead 20 used. This can, for example, before use in the primer inkjet station 2 be thoroughly rinsed to remove any used in industrial quality assurance inks without residue. This is advantageous because otherwise by the coating material 5 flocculating an ink residue in the pressure nozzle 21 could be caused, which would have a direct failure of the nozzle result.

A distance of the pressure nozzles 21 each other depends in particular on the type of printheads used 20 which in turn is the one with the primer inkjet station 2 determine printable resolution. In an exemplary embodiment, the primer inkjet station 2 be formed with a resolution of 600 dpi. This corresponds to a distance of two pressure nozzles of about 42.3 microns. Of course, the pressure nozzle spacing is variable or scalable depending on the desired resolution. By way of example, the printing nozzle spacing with a resolution of 300 dpi would then be 84.6 μm.

Although the present invention has been fully described above with reference to preferred embodiments, it is not limited thereto but is modifiable in a variety of ways.

LIST OF REFERENCE NUMBERS

1

printing system

2

Primer Inkj et station

3

pressure range

4

record carrier

5

coating material

6

Ink Inkjet station

7

first color

8th

print image

9

second color

10

sensor

11

control device

12

sensory detection

13

Gradientenkontur

14

linewidth

15

ideal edge

16

20% -Schwellwertkontur

17

80% -Schwellwertkontur

18

edge sharpness

19

section

20

printhead

21

pressure nozzle

S1-S4

steps

v

feed

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10233409 A1 [0003]
• DE 102014108342 A1 [0004]

Claims (15)

Method for detecting a faulty application of a coating material which is invisible in the applied state, in particular a primer, for printing a recording medium, comprising the following steps: - printing (S1) a printing area of a recording medium (4) with a coating material (5) by means of an inkjet printing head (20); - printing (S2) a first color (7) over the width of the printed material (5) printed area (3) of the recording medium (4); - printing (S3) a thin line (8) of a second color (9) over the width of the printing area (3) on the first color (7); and - analyzing (S4) the Bleedingverhaltens the first and second color (7, 9) along the thin line (8). Method according to Claim 1 , wherein the analyzing (S4) comprises deriving any locally incorrect application of the coating substance (5) from the bleeding behavior across the width of the recording medium (4). Method according to Claim 1 or 2 , Wherein Bleedingverhalten on the basis of the course of the line width (14), edge smoothness and / or edge sharpness (18) of the thin line (8), in particular in the form of a comparison with setpoints, is assessed Method according to one of the preceding claims, wherein over the width of the printing area (3) of one or more inkjet printheads (20) for applying the coating material (5) are provided and analyzing the Bleedingverhaltens a conclusion on a possible failure of pressure nozzles (21) a single printhead (20). Method according to one of the preceding claims, wherein the print head (20) over the width of its associated pressure range a plurality of pressure nozzles (21) for applying the coating material (5) and analyzing (S4) of Bleedingverhaltens a conclusion on any localized failures in the range of fewer or individual pressure nozzles (21). Method according to Claim 5 in which, upon detection of a failure in the region of fewer or individual pressure nozzles (21) to compensate for the failure, the droplet size of the coating substance (5) is increased for pressure nozzles (21) arranged in the region and / or near the region. Method according to one of Claims 4 to 6 wherein the inference from a local bleeding behavior is drawn from a position of a bleeding-affected portion (19) along the thin line (8). Method according to one of Claims 1 to 5 wherein the analyzing (S4) of the Bleedingverhaltens after the printing process is made optically based on the printing result on the recording medium (4). Method according to one of Claims 1 to 7 wherein the analyzing (S4) of Bleedingverhaltens during the printing operation by means of a sensor (10), in particular a in the printing system (1) integrated on the recording medium (4) directed camera is made. Method according to one of Claims 1 to 7 wherein analyzing (S4) the Bleedingverhaltens comprises scanning the printed result on the recording medium (4) by means of a scanner. Method according to one of the preceding claims, wherein the thin line (8) is printed in the form of a one-dot line. Method according to one of the preceding claims, wherein the first and the second color (7, 9), which are provided in particular with a high contrast to each other, each printed with an inkjet method. Method according to one of the preceding claims, wherein the printing (S2) of the first color (7) and the printing (S3) of the thin line (8) of the second color (9) during a regular printing operation in the course of a routine printing a regeneration print image , in particular refreshlines. Method according to one of the preceding claims, wherein the printing process is stopped upon detection of a predetermined measure of Bleedingverhaltens, in particular over a predetermined period of time or printing length, in particular for cleaning or replacement of the affected printhead (20). Printing system (1), in particular for carrying out a method for detecting an application of a coating material invisible in the applied state to detect a recording medium which is invisible in the applied state according to one of the preceding claims, comprising: - a primer inkjet station (2) having a multiplicity of printing nozzles (21 ) for printing (S1) a printing area (3) of a recording medium (4) with a coating material (5); - An ink-inkjet station (6) for printing (S2) of a first color (7) over the width of the with the Coating material (5) printed printing area (3) of the recording medium (4) and for printing (S3) a thin line (8) of a second color (9) over the width of the printing area (3) on the first color (7); - A sensor (10) for sensory detection (S4) of the printed printing area (3); and - a controller (11) coupled to the sensor (8) and the primer inkjet station (2) for analyzing (S5) the local bleeding behavior of the first and second colors (7, 9) along the thin line (8) the sensory detection (12) and for the identification of any localized failures of pressure nozzles (21) of the primer inkjet station (2) on the basis of any affected by bleeding portions (19) of the thin line (8).

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