EP3481638B1 - Method and device for multiple-colour inkjet printing on containers - Google Patents

Description

The invention relates to a method for multicolored inkjet printing on containers according to the preamble of claim 1, as is known from U.S. 2013/176358 A1 and EP 1 769 916 , as well as a corresponding device.

The labeling of containers in bottling plants or the like is increasingly carried out by means of ink jet printing directly on the container due to the flexibility in terms of design and the adaptation to different products. For this purpose are from the DE 10 2014 109 948 A1 and from the DE 10 2011 009 393 A1 Methods and devices are known in which the containers are moved along stationary print heads during direct printing, and in which the transport speed of the containers relative to the print heads is temporarily reduced during printing in order to enable high average transport speeds and machine outputs. Furthermore, it is from the DE 10 2012 213 080 A1 known to distribute the incoming stream of containers in parallel to several printing units in order to increase overall machine performance. Alternatively, the DE 10 2010 020 958 A1 proposed to move printing stations on a track parallel to the means of transport of the containers.

The fundamental problem here is that the individual printing colors for the multicolored ink jet printing are printed one after the other by separate print heads onto the containers. Deviations in the positioning of the containers in front of the individual print heads then cause an unwanted offset of the individual printing colors in relation to one another, as a result of which the quality of the finished printed motif suffers.

As a makeshift, the DE 10 2014 116 201 A1 propose to print test containers or the like in a first printing station with a test pattern, to inspect this and to adjust a subsequent printing station on the basis of the inspection result. However, separate test containers must be provided for this and introduced into the machine.

From the DE 10 2012 209 305 A1 it is also known to compare relief-like surface contours with the position of a multicolor direct print after printing and, if necessary, to change printing parameters on the basis of the comparison and/or if necessary to carry out an additional correction print. However, this method depends on the presence of characteristic print features in the printed image and more appropriately in relief Comparison structures dependent. Furthermore, a correction of parameters and/or print images is only possible later than after the multicolored print image has been completed.

From the DE 10 2014 112 483 A1 a method is also known in which a multi-color printing machine is taught step by step on the basis of inspection results after all colors have been printed completely. However, this requires a comparatively complex analysis of print images and special training phases for the printing operation.

There is therefore a need for improved methods and devices with regard to the print quality of the multicolor print and the machine performance.

The task is solved with a method according to claim 1. Accordingly, this is used for multicolored inkjet printing on containers and comprises the following steps: S1) joint printing of a motif or a first motif layer and at least one print mark arranged in particular within the motif in a first printing color on the containers; S2) mechanical optical inspection of the at least one print mark; S3) aligning the containers based on step S2 and printing the motif or a second motif layer, and in particular the print mark, in a subsequent printing color; and S4) overprinting of the print mark.

As a result, the print quality for each printing color or motif layer can be optimized during regular printing operations with regard to the printing colors already printed. In this case, the print mark enables a simplified inspection of the print quality compared to the motif and/or features of the container, for example with regard to the position of the motif and with regard to the quality of individual printing colors. Furthermore, the print mark can be concealed by the overprinting in the final printed image and thus the appearance of the finished printed container can be optimized.

Print marks within the meaning of the present invention are in particular registration marks for checking the location/position of the motif printed with a specific printing ink or a specific motif layer and color marks for checking the uniformity of the print quality of a specific printing ink or motif layer. Also conceivable are print marks that have the function of registration marks as well as color marks. In principle, the print marks could also be arranged outside of the motif, for example above and/or below the motif.

The motif is a printed image which, based on a digital print template, is printed step by step in the form of several motif layers directly onto the containers using an ink jet. The motif layers have inks of a specific color model such as CMYK. An initial motif layer may be the background color of the motif, specifically white. The background can be part of the printed motif or the printed container.

Steps S2 and S3 are preferably carried out on the condition that there is a fixed spatial relationship between the inspection units and print heads used for this purpose, in the sense that the position of the print mark determined in step S2 corresponds to a specific rotational position of the containers and specific active nozzles of the print head to be used can be assigned, particularly within a certain vertical working range of the print head.

According to the invention, steps S2 and S3 are repeated in pairs for at least two further subsequent printing colors. As a result, the print quality can also be optimized for the other subsequent printing colors directly and in the sense of an inspection loop that is closed separately for each subsequent printing color.

Preferably, active printing nozzles are selected in step S3 based on the inspection of step S2. It would also be conceivable to select the print time for individual print nozzles and/or for the print head as a whole depending on the inspection of step S2. With the selection of active print nozzles, a vertical print area for the subsequent motif layer can be defined within a total vertical working area available on the print head.

Preferably, a vertical area of an assigned print head that is active in step S3 is shifted vertically by targeted activation of print nozzles in order to cover a vertical print area required for the motif. The vertical working area of the print head is then higher than the motif. This enables a vertical adjustment of the motif layer to be applied with the respective subsequent ink. However, a vertical adjustment of the print head would also be conceivable.

Furthermore, by adjusting the printing time, the horizontal position of the motif layer to be applied with the subsequent printing ink can be adjusted and/or corrected, taking into account a relative transport movement between the container and the print head.

The rotational position of the containers is preferably adjusted in step S3 based on the inspection in step S2 for the printing of the motif in the respective subsequent printing color.

Preferably, step S4 is finally executed after step S3 has been executed for the last time. Thus, the direct printing with all printing inks of the color model can be controlled separately for each motif layer using the print mark before the print mark is made unrecognizable by overprinting in step S4.

Step S4 is preferably carried out in a separate correction station for multi-color printing. The print mark can be made unrecognizable in step S4, for example, in that the print mark is multicolored overprinted with a component of the motif. It is also conceivable to make the print mark unrecognizable by overprinting it outside of the motif with a color and/or a pattern that is present on the container in the area around the print mark.

The first printing ink is preferably white and is excited to fluoresce in particular in step S2 with UV light. White is suitable as a background color for a brilliant multi-page motif. Fluorescence can be used to achieve improved contrast for the inspection of the print mark, especially compared to a light-colored or white container wall.

Preferably, the print mark is then omitted from the print in step S3. It is possible to only print the print mark when printing with the background color white and to align the direct print with all subsequent print colors of the color model using the print mark printed with the background color. The print mark would then only be overprinted in step S4, in particular with black printing ink, blue printing ink, red printing ink or a mixed color. In other words, this variant is particularly suitable if the print mark is in a dark area of the motif. The absence of the background color white in the area of the print mark is then not noticeable in the finished printed motif.

According to the invention, the containers are excited to fluoresce in step S2 with UV light. Transparent (opaque) white plastic containers or translucent (translucent) white plastic containers that fluoresce when exposed to UV light are particularly suitable for this purpose. In contrast, the first printing color, in particular a white background color, is then essentially non-fluorescent. As a result, a particularly white pressure mark can be compared to the unprinted container wall locate dark contrast in step S2. The print mark is then preferably opaque.

The print mark is preferably printed within the motif and, in step S4, overprinted with a partial area of the motif, in particular in multiple colors. Alternatively, the print mark is printed outside of the motif and, in step S4, overprinted with the color and/or a pattern of the container wall surrounding the print mark. As a result, the printed mark can be made unrecognizable with respect to the final appearance of the container, regardless of its position on the container.

In the case of a print mark arranged outside of the motif, it would also be conceivable as an alternative or in addition to overprint the print mark with a solvent and suck off the detached print mark. It would also be conceivable to overprint a print mark located outside of the motif with a bleaching agent, for example with hydrogen peroxide or the like, in order to make the print mark unrecognizable in relation to a surrounding and, in particular, white container wall.

The print mark preferably includes a registration mark, with rotary mounts for the containers and/or print head nozzles for printing with the subsequent printing ink also being controlled as a function of a determined position of the registration mark. This allows the rotational position of the container to be corrected for the subsequent printing ink. In addition, a specific, in particular vertical, area of the print head can be specifically activated for printing with the subsequent printing ink in order to align the motif to be printed with it precisely in relation to the motifs previously printed with other printing inks.

Preferably, the print mark comprises a color mark, with the printing of the same container with the subsequent printing ink being released or suppressed depending on a determined print quality of the color mark, and/or the printing of subsequent containers with the same printing color being corrected depending on a determined print quality of the color mark . The color mark is, for example, a field with a uniform color tint or a predetermined color tint gradient. Deviations from this can be recognized as printing errors in step S2 in order to specifically trigger actions for the further treatment of the same container and/or to correct the print with the printing ink recognized as defective for subsequent containers.

A correction for subsequent containers is possible, for example, by replacing or compensating for pressure nozzles identified as defective by at least one adjacent pressure nozzle. For example, in normal operation, multicolor printing takes place at half the resolution of the respective print head, ie using every second print nozzle. If a specific printing nozzle fails, it can be replaced, for example, by the immediately adjacent printing nozzle or by an adjacent group of printing nozzles.

Preferably, the suppressed pressure containers are selectively discarded. The containers identified as faulty are then preferably no longer printed with the subsequent printing inks or the correction print for the printing mark in order to save printing ink. Defective containers are preferably rejected automatically downstream of the device used for multicolor printing.

The motif is preferably composed of partial circumferential print areas and at least one print mark is printed on each print area. The individual partial circumferential print areas can then be aligned and checked separately on their respectively assigned print mark. This compensates for inaccuracies when repositioning the containers for printing on the individual print areas. All print marks are then overprinted in step S4.

The task is also solved with a device according to claim 13. Accordingly, this is used for multicolored inkjet printing on containers and comprises: several consecutive color stations each with at least one print head for printing the containers in an assigned printing color and with a subsequent inspection unit for optically inspecting the printed motif and/or at least one print mark printed in the color stations by stimulation the container (12) with UV light for fluorescence; a correction station which follows the color stations and has at least one print head for selectively overprinting the print mark; a transport means with rotating supports for successively positioning the containers in the color stations and in the correction station; and a control unit for driving the rotating posts and the print heads depending on results from the inspection units.

The inspection unit is preferably designed in such a way that it spatially selectively inspects the print marks in contrast to a complete inspection of the entire motif. The inspection unit is then particularly capable of fault detection based on an imaging detection of contrast gradients and/or color gradients in the print marks is based, in particular by means of targeted evaluation of the previously applied printing ink. In particular, evaluation algorithms then run in the inspection unit, which are designed specifically for determining the position of registration marks and for evaluating color gradients or brightness gradients in color marks.

The print heads are preferably designed in such a way that they continuously cover at least the entire height of the motif to be printed. In principle, however, it would also be conceivable to arrange a plurality of print heads so that they overlap in the vertical direction in order to cover the entire height of the motif. The print heads preferably have a resolution of at least 1200 dpi.

Preferably the rotary mounts comprise servomotors and the maximum print height of the printheads is greater than the height of the motif. This will provide an exact correction of the situation motifs to be printed with a specific ink, both vertically and horizontally.

The inspection units preferably include cameras for imaging the containers all around. For example, a plurality of cameras can be present at least in the entry-side inspection unit in order to inspect the containers with a plurality of partial-circumference camera images over the entire circumference without any gaps. This allows the entire area of the motif to be printed and the printed print mark to be monitored and the quality of the print to be determined on the basis of the print mark. This configuration could also be used on the subsequent inspection units.

However, it would also be conceivable for the subsequent inspection units to inspect only the partial peripheral area of the container in which the print mark was printed and initially recognized. It would also be conceivable to carry out a rough alignment of the rotational position before printing with the first printing ink, so that only the partially circumferential printing area with the printing mark to be inspected then has to be examined.

A rough alignment of the rotational position would be possible, for example, using container contours, such as embossing. Since the rotational position of the container is then fundamentally known on the basis of such an incoming inspection of the container and/or can be corrected accordingly, only a comparatively small correction of the rotational position is necessary during the subsequent inspection and correction of the rotational position using the print marks in order to avoid deviations during positioning and Transporting the containers in the individual color stations or to compensate in between.

For this purpose, an optical sensor, possibly also non-imaging, could be present directly in front of each color station, which localizes the print mark comprising a registration mark and causes the immediately following color station and/or the rotary table assigned to the container to correct the subsequent imprint by means of the control unit.

• Figur 1 eine schematische Darstellung eines Druckmotivs mit Druckmarken und eines zugeordneten Druckkopfs; und
• Figur 2 eine schematische Draufsicht auf eine Vorrichtung mit Farbstationen und einer Korrekturstation für den Mehrfarben-Direktdruck.

A preferred embodiment of the invention is illustrated in the drawings. Show it:

• figure 1 a schematic representation of a print motif with print marks and an associated print head; and
• figure 2 a schematic plan view of a device with color stations and a correction station for multi-color direct printing.

the figure 1 shows schematically an intermediate stage during the multicolor inkjet printing of a motif 1. Seen in the printing direction DR, this is preferably composed of several motif parts 1A-1D, which are printed one after the other with a specific printing ink after the rotational position of a container to be printed with respect to a print head. The motif 1 is applied in succession in the form of motif layers with the individual printing inks, as is explained below by way of example.

Inside the motif 1, the motif parts 1A-1D are preferably separately assigned internal print marks 2A-2D including registration marks and internal print marks 3A to 3D including color marks. Register marks and color marks can also be combined in print marks (not shown).

the figure 1 shows a state after printing a first motif layer MS1 in a first ink DF1, which is a white background color in the example shown, and a second motif layer MS2 in a second ink DF2, which is any component of a color model used, such as CMYK. In the example of figure 1 the print marks 2A-2D and 3A-3D have the second print color DF2.

For the sake of completeness are in the figure 1 furthermore, an external printed mark 2E comprising a register mark and an external printed mark 3E comprising a color mark, each outside the motif 1 in the area of a surrounding container wall 4 of a wall color WF, indicated schematically. The external print marks 2E, 3E can be printed in addition to or as an alternative to internal print marks 2A-2D and 3A-3D, preferably above and/or below the motif 1 and have the second printing color DF2 in the example.

The dimensions of the motif 1 are defined by a vertical motif area YM in the sense of a motif height and by a horizontal motif area XM, which is shown as an example as the developed length of the entire motif 1 . The horizontal motif area XM results from the uninterrupted juxtaposition of motif parts 1A-1D.

the figure 1 FIG. 12 also schematically shows a print head 5 for single-color printing with a subsequent printing color DF3 of the color model used. The print head 5 has, for example, two rows of nozzles 6 and 7, which together cover a vertical working area YMAX that is larger than the vertical motif area YM.

The vertical alignment of the motif layers MF1, MF2 of the motif 1 that have already been printed with respect to the print head 5 is determined on the basis of the print marks 2A to 2D and/or 2E. Depending on this, only those printing nozzles 8 of the print head 5 are used for printing with the following Printing ink DF3 activated, which cover the currently determined vertical motif area YM.

The vertical area YA of the print head 5 that is required for the subsequent print and is thereby selectively active can thus be shifted up or down within the vertical working area YMAX by targeted nozzle activation. This enables the subsequent motif layer MS3 to be printed congruently in the printing ink DF3 on the previously printed motif layers MF1 and MF2. The common reference for this is a (not shown) digital color master for motif 1.

In the example shown, the print head 5 has two vertical rows of nozzles 6 and 7 which are offset from one another at a vertical distance YD. On the one hand, it is possible to activate both rows of nozzles 6, 7 together in order to double the vertical resolution (dpi) of the print head 5. On the other hand, however, it is also possible to activate only one row of nozzles 6 and to keep the other row of nozzles 7 in an inactive waiting state. If a defective printing nozzle 9 is found in the active nozzle row 6, its function can be taken over by at least one adjacent intact printing nozzle 8a of the nozzle row 7 that is in the waiting state. In this case, only individual pressure nozzles 8a of the inactive row of nozzles 7 are activated in a targeted manner to compensate.

The rows of nozzles 6, 7 can, for example, be controlled in a known manner with a time offset adapted to the horizontal distance XA between the rows of nozzles 6, 7 in order to align all print dots in a specific column of the print template vertically with one another.

The print head 5 is actuated as a function of the position of the print marks 2A-2D and/or 2E, which is determined in particular by imaging. These have a known spatial relationship to motif 1 in each motif layer and serve as registration marks for determining the relative position, here by way of example of the last printed motif layer MF2 with respect to print head 5 for printing with the subsequent printing ink DF3. However, non-imaging scanning of the print marks 2A-2D and/or 2E would also be conceivable.

The multi-color printing of motif 1 takes place successively during a particularly continuous transport movement 10 of the container to be printed along several preferably stationary print heads 5. The printing direction DR (shown only as an example) results from the superimposition of transport movement 10 with a targeted change in rotational position of the associated container and its container wall 4 in front of the respective print head 5. In the example the figure 1 the print head 5 immediately afterwards prints both the motif 1 and new print marks 2A-2D, 3A-3D, 2E and/or 3E in the next printing color DF3.

In principle, however, it would also be possible to leave out registration marks in a subsequent print, possibly even in the second printing color DF2. The registration mark can then be used for several subsequent printing colors and only then be overprinted.

Separate rows of nozzles or pairs of rows of nozzles 6, 7, which can be part of a common print head 5 or separate print heads 5, are assigned to the partially circumferential motif parts 1A-1D. The position of the respective motif part 1A-1D in the printing direction DR and the targeted selection of active printing nozzles 8 are then preferably carried out separately using the respectively assigned printing mark 2A-2D.

The number of partially circumferential motif parts 1A-1D and the rows of nozzles 6, 7 per printing color depends, for example, on the length of the motif 1 and/or the machine output and can be adapted to the respective requirements. For the sake of simplicity, a single print head 5 per printing color is always mentioned below.

the figure 2 shows a schematic plan view of a device 11 for multicolor printing on containers 12 with a plurality of stationary consecutive color stations 13-17 and a subsequent correction station 18.

The color stations 13-17 and the correction station 18 each comprise at least one print head 5 for single-color printing and an inspection unit 19 with a light source for VIS and/or UV light and preferably several cameras 20, which are used for imaging all partial-circumference motif parts 1A-1D to serve. A pinning unit 21 is preferably connected in between in order to intermediately cure the ink printed immediately beforehand by means of UV light. The color stations 13-17 are constructed identically in this respect and differ only in that they are used to print different printing colors DF1 to DF5 of a color model, such as CMYK, onto the containers 12.

The correction station 18, on the other hand, is preferably designed with a print head 22 for multicolor printing for overprinting the print marks 2A-2E and/or 3A-3E.

During the multi-color printing, the containers 12 circulate on a container table 23, which in particular can be continuously rotated about itself, which results in the transport movement 10. The container table 23 is a partial circle with rotary mounts 24, such as turntable, for the container 12 schematically in FIG figure 2 implied. The transport movement 10 and one Cyclic rotation 25 of the rotary mounts 24 about themselves result in a cyclic advance of the container wall 4 with respect to the print head 5 in the printing direction DR.

Device 11 also includes components known per se, such as an infeed starwheel 26, an outfeed starwheel 27, an inlet-side inspection unit 28 for detecting the rotational position of incoming containers 12, an outlet-side inspection unit 29 for final inspection of the finished printed containers 12, and a control unit 30. This is for selective Activation of the printing nozzles 8, 8a and for the selective and individual activation of the rotary mounts 24, which are preferably driven by servomotors.

A mechanical assembly block (not shown) would also be possible on device 11 with at least one upstream unit for container pretreatment, for example for flame treatment, corona treatment and/or plasma treatment of the container, and/or with at least one downstream unit for container final treatment, for example for final coating, painting and/or UV irradiation of the containers.

Also conceivable would be a machine block with the device 11 and an upstream container stretch blow molding machine and a downstream filling machine and sealing machine.

The device 11 can be used, for example, as follows:
The incoming containers 12 are checked in the inspection unit 28 for their respective rotational position and the containers 12 are brought to a desired rotational position, if necessary, in which the container table 23, clamped in the rotary mounts 24, transports them to the first color station 13 in a known manner.

The first motif layer MS1, for example a white background of the motif 1, is printed onto the container 12 together with at least one printed mark 2A-2E and/or 3A-3E in the first printing ink DF1. The containers 12 are then optically scanned in the inspection unit 19 of the first color station 13, preferably by imaging, in order to check the position and/or the quality of the print marks 2A-2E and/or 3A-3E.

Printing with the subsequent printing ink DF2 is controlled as a function of the determined position and/or quality of the printing marks 2A-2E and/or 3A-3E of the printing ink DF1.

This can include the rotational position of the container 12 checked in the inspection unit 19 being corrected for the subsequent printing ink DF2 by actuating its assigned rotary mount 24 .

This can also include that the temporal control of the print head 5 for printing with the subsequent printing ink DF2 is adjusted to correct a printing position in the (horizontal) printing direction DR.

Likewise, to correct the print position in the vertical direction, the active print area YA of the print head 5 can be shifted for printing with the subsequent print color DF2.

Consequently, the motif layer MS2 to be applied with the subsequent printing ink DF2 can be printed congruently on the motif layer MS1 previously printed with the printing ink DF1.

The print marks 3A-3D and/or 3E designed as color marks provide information about the print quality of the motif layer MS1 printed with the inspected print color DF1. If a proper print quality is determined here, then it is only necessary to check the position of the motif layer MS1 that has just been printed using the print marks 2A-2D and/or 2E and, if necessary, to adjust the relative positioning of motif 1 and print head 5 to one another for the subsequent printing color as described above correct.

If, on the other hand, insufficient print quality is determined on the basis of the color marks or print marks 3A-3D and/or 3E, the printing of the same container 12 with the subsequent printing colors DF2 to DF5 and the final correction print KD in the correction station 18 can be suppressed.

On the other hand, for subsequent containers 12, a correction can be made to print head 5, which is responsible for the insufficient print quality, in order to improve the print quality for the print color DF1 in question. Printing marks 3A-3D and/or 3E can be used to identify malfunctioning printing nozzles 9 and to replace or compensate for them with adjacent working printing nozzles 8a, as is shown schematically in FIG figure 1 is indicated.

For this purpose, the print head 5 preferably has a higher vertical print resolution than the motif 1, in particular at least twice the print resolution than the motif 1. For example, the motif 1 could be printed with a nominal print resolution of 600 dpi. The print head 5 then preferably has a print resolution of at least 1200 dpi for the direct replacement of defective print nozzles 9 with adjacent print nozzles 8a in the waiting position.

However, it is also possible to compensate for a defective printing nozzle 9 with a group of adjacent functional printing nozzles 8b. For this purpose, a reduction in the vertical print resolution caused by connecting adjacent print nozzles 8b together can be accepted.

The inspection of the print marks 2A-2D and/or 2E and 3A-3D and/or 3E in the individual color stations 13 to 17 with regard to the position and quality of the motif layer MS1-MS5 just printed with a specific printing ink DF1-DF5 enables direct feedback in the normal printing operation both for the further treatment of the same container 12 by correcting or suppressing subsequent printing and for the treatment of subsequent containers 12 with the same printing ink by targeted compensation for defective printing nozzles 9.

These feedback loops, which work in the production process, can be used along the transport route of the containers 12 for each printing color DF1-DF5 to be printed. In the example shown, the above procedure is repeated in each of the subsequent color stations 14-17.

Finally, the preferably multicolored correction print KD takes place at the correction station 18 in order to overprint all remaining print marks 2A-2D and/or 2E as well as 3A-3D and/or 3E and thereby make them unrecognizable on the motif 1 and/or on the surrounding container wall 4 make or at least conceal.

Both the quality of the finished printed motif 1 and the quality of the correction print KD can be checked in the inspection unit 29 during the final inspection.

Containers 12 recognized as not properly printed can be selectively ejected from the product flow downstream of the device 11 . An improper condition of the container 12 can be determined both in the individual color stations 13-17 and in the correction station 18 and/or in the inspection unit 29 during the final inspection.

The correction station 18 is preferably configured in such a way that only the areas of the print marks 2A-2D and/or 2E and 3A-3D and/or 3E are spatially selectively overprinted and other areas of the motif 1 and the container wall 4 are left out of the correction print KD. This enables high-quality multicolor printing for the final correction of the appearance while rendering the respective print marks unrecognizable at a single correction station 18 with the required machine output.

The internal print marks 2A-2D and 3A-3D can be printed in areas of motif 1 that can be overprinted in a particularly simple manner in correction station 18, for example in areas with comparatively dark and/or well-opaque colors and/or low contrast differences in the finished motif 1.

A positioning of the internal print marks 2A-2D and 3A-3D in areas without special information content, such as in a monochrome background area or the like, is particularly advantageous.

Alternatively, however, the internal print marks 2A-2D and 3A-3D can also be printed at points on the motif 1 where there are characteristic areas of the motif 1 that are suitable for alignment and/or color control, for example with comparatively sharp contrast transitions and/or color transitions. These are then reproduced by the correction print KD.

The print heads 5 preferably have a resolution of at least 1200 dpi and preferably include at least 10,000 nozzles for a vertical working area YMAX of at least 70 mm. Optionally, the working range YMAX (in terms of a maximum nominal print head) can be increased to at least 140 mm or at least 210 mm. For example, for a nominal print height of 210 mm, a print head with a nozzle array that has an actual height of 217.8 mm and 42240 print nozzles is used.

For the purposes of the present invention, a horizontal orientation is to be understood in each case as the direction of the print feed or in the opposite direction. A vertical orientation is orthogonal and parallel to the printing plane.

Claims (13)

1. Method for multicolour ink jet printing on containers (12), comprising the steps of:

   S1) joint printing, in a first printing ink (DF2) and onto the containers (12), of a motif (1) and at least one print mark (2A-2D, 2E, 3A-3D, 3E) that is arranged in particular within the motif (1);

   S2) mechanical optical inspection of the at least one print mark (2A-2D, 2E, 3A-3D, 3E);

   S3) alignment of the containers (12) on the basis of step S2 and printing of the motif (1) and in particular the print mark (2A-2D, 2E, 3A-3D, 3E) in a subsequent print colour (DF3); and

   S4) overprinting of the print mark (2A-2D, 2E, 3A-3D, 3E),

   characterised in that the containers (12) are excited to fluoresce using UV light in step S2, and steps S2 and S3 are repeated in pairs for at least two further subsequent print colours (DF4-DF5).
2. Method according to claim 1, wherein active print nozzles (8) are selected for step S3 on the basis of the inspection in step S2.
3. Method according to either of the preceding claims, wherein a vertical area (YA) of an associated print head (5), which area is active in step S3, is shifted vertically by targeted activation of print nozzles (8), in order to cover a vertical print area (YM) required for the motif (1).
4. Method according to at least one of the preceding claims, wherein step S4 is finally carried out after step S3 has been carried out for the last time.
5. Method according to at least one of the preceding claims, wherein the first printing ink is white and is excited to fluoresce using UV light in particular in step S2.
6. Method according to claim 6, wherein the print mark (2A-2D, 2E, 3A-3D, 3E) is omitted from the printing in step S3.
7. Method according to at least one of the preceding claims, wherein the print mark (2A-2D, 3A-3D) is printed within the motif (1) and is overprinted in step S4 with a portion of the motif (1), in particular in multiple colours, or wherein the print mark (2E, 3E) is printed outside the motif (1) and is overprinted in step S4 with the colour (WF) of the surrounding container wall (4).
8. Method according to at least one of the preceding claims, wherein the print mark (2A-2D, 2E) comprises a register mark, and wherein rotary mounts (24) for the containers (12) and/or nozzles (8) for printing with the subsequent printing ink (DF2) are controlled according to a determined position of the register mark.
9. Method according to at least one of the preceding claims, wherein the print mark (2A-2D, 2E) comprises a colour mark, and wherein the printing of the same container (12) with the subsequent printing ink (DF3) is enabled or suppressed according to a determined print quality of the colour mark, and/or wherein the printing of subsequent containers (12) with the same printing ink (DF2) is corrected according to a determined print quality of the colour mark.
10. Method according to claim 9, wherein containers having suppressed printing are selectively discarded.
11. Method according to claim 9, wherein a print quality determined to be defective is corrected by deactivating malfunctioning print nozzles (9) and instead printing, by means of adjacent working print nozzles (8a) and by activating and/or controlling said working print nozzles in a targeted manner, pixels assigned to said malfunctioning print nozzles.
12. Method according to at least one of the preceding claims, wherein the motif (1) is composed of partially circumferential motif parts (1A-1D), and at least one print mark (2A-2D, 3A-3D) is printed per motif part.
13. Device (11) for multicoloured ink jet printing on containers (12), in particular in accordance with the method according to at least one of the preceding claims, comprising:

    - a plurality of consecutive colour stations (13-17), each comprising at least one print head (5) for printing on the containers (12) using an assigned print colour (DF1-DF5), and comprising a subsequent inspection unit (19) for inspecting, in an optical and in particular imaging manner and by exciting the containers (12) to fluoresce using UV light, the relevant printed motif (1) and/or at least one print marking (2A-2D, 2E, 3A-3D, 3E) printed in the colour stations (13-17);

    - a correction station (18) following the colour stations (13-17) and having at least one print head (22) for selective overprinting of the print marking (2A-2D, 2E, 3A-3D, 3E);

    - a transport means (23) having rotary mounts (24) for successive positioning of the containers (12) in the colour stations (13-17) and in the correction station (18); and

    - a control unit (30) for controlling the rotary mounts (24) and the print heads (5, 22) according to results of the inspection units (19).

Images