EP3023253B1 - Method and device for ink-jet printing on containers - Google Patents

Description

The invention relates to a method and apparatus for ink jet printing on containers.

For ink jet printing on containers, such as beverage bottles or the like, it is for example from EP 2 669 088 A1 and the DE 10 2011 113 150 A1 It is known to guide containers to be printed along circular transport paths along stationary printing stations or to circulate printing stations together with the containers on carousels or the like. By rotating the container around itself, an advance of the side walls of the containers to be printed is then produced in front of the respectively activated printheads.

The printheads used for this purpose generally have rows of nozzles extending transversely to the printing direction, with individual printheads possibly not covering the entire width of a printed image defined transversely to the printing direction as a result of the design. In this case, printheads are used whose pressure areas abut or overlap transversely to the printing direction. Depending on the accuracy of the adjustment of such adjacent pressure ranges occur between the part imprints produced visible and the printed image disturbing transitions, for example, at double-printed areas or to gaps in the printed image.

To counteract this problem, it is for example from the US 2004/0252152 A1 and the US 2011/0012949 A1 known to overlap transversely to the printing direction abutting partial imprints and form the transition areas meshing with each other to disguise double pressures and connection gaps. The requirements for the most accurate alignment of adjacent printheads to each other can be reduced, in particular because the relative position of the printheads and containers can be maintained transversely to the printing direction usually reproducible and does not change during printing.

The EP 2 769 848 A2 Proposes to compensate for an inaccurate height of the containers in front of different stationary printheads by selectively adding nozzles in a vertical overlap area of the printheads. The containers are moved on turntables standing by a container table on the printheads successively and determines the vertical position transverse to the printing direction of the containers in the region of the individual printheads. When changing the vertical position, a corresponding connection or disconnection of individual nozzles is triggered. A gridded meshing of partial imprints transversely to the printing direction is described as rather problematic. Instead, vertical position changes of the containers are to be compensated for by switching on / off printheads only in a minimized overlapping area.

The EP 2 208 541 A2 further describes the painting of body surfaces, wherein printing webs are printed consistently meandering and then overlap transversely to the printing direction with a uniform in the overall layer thickness / flow into each other. The pressure paths are sharply delimited in the printing direction.

However, there is still the problem that for the direct printing of containers, several components of a color model over a predetermined circumferential region of the container, possibly also in full, must be printed from different printheads. In addition, often only peripheral portions of the container surface to be printed can be positioned in front of a specific row of nozzles and printed continuously in the required in beverage filling positions machine performance and associated transport speeds. It is therefore often also add in the printing direction partial imprints to each other to produce a continuous printing direction on the images on the containers.

This is made more difficult by dimensional tolerances which, depending on the actual container cross-section, cause a side wall to be printed differently long in the circumferential direction. Depending on the dimensional tolerances and the circumferential extent of the printed image, the problem arises in the printing direction of qualitatively defective connection areas between partial imprints due to overlapping double pressure and / or connection gaps.

Thus, there is a need for methods and apparatus for inkjet printing on containers that can overcome or at least alleviate at least one of the above problems.

The stated object is achieved by a method according to claim 1. Accordingly, this is suitable for inkjet printing on containers, wherein at least a first and a second partial imprint are added in the printing direction to a printed image complementary to each other. According to the invention, first the first partial imprint is printed from one or up to a connection area. Thereafter, the second partial imprint is printed at a pressure feed in the direction of the connection region, such that the first and second partial imprints overlap one another in the connection region.

Thus, partial imprints, in particular for direct printing on curved container surfaces whose length to be printed may vary due to dimensional tolerances of the containers, can be combined with a transition region which is less conspicuous to the viewer than conventional methods. By intermeshing is to be understood here that the partial imprints in the connection region do not adjoin one another along a straight line running transversely to the printing direction, but that an interlocking and / or mosaic interlocking connection region is formed in the image contents of both the first and the second partial imprint are distributed so that the transition between the image areas blurred to the viewer.

Thus, a linear double print or a line-like gap between the adjoining partial imprints can be avoided or at least made inconspicuous to the viewer. The intermeshing pressure also decreases the requirements for the dimensional accuracy of the container and the accuracy of the printhead positioning and / or the rotational position of the position of the container with respect to at least one printhead used for inkjet printing.

According to the invention, the printing direction extends laterally around a main axis of the containers. Thus, the inventive method is particularly suitable for the joining of partial prints that cover the peripheral portions of the container. Thus, the container can be in the partially circumferential areas, in particular during transport of the container print with a required print quality. Furthermore, dimensional tolerances, in particular with regard to the container circumference, can be compensated.

The connection region preferably covers a circumferential arc segment with a length of 5 to 50 pixels, in particular 10 to 30 pixels, based on the print resolution of the printed image. Also conceivable is an absolutely defined length of the circumferential arc segment of 0.1 to 1 mm or in particular from 0.2 to 0.5 mm. The circumferential arc segment is to be understood as a section of the outer container cross section. The connection region thus defines an overlap region with the length defined above, in which the partial imprints overlap one another in the circumferential direction. Thus, with the dimensional tolerances customary for plastic containers in particular, visually distinct double prints or gaps in the printed image can be avoided with sufficient reliability.

Preferably, the containers are at least fully printed over a pressure range of at least 362 degrees, in particular at least 365 degrees. The containers can be easily printed in this way completely. For each ink only one print head is needed.

Preferably, the containers are rotated around themselves before at least one print head. This allows a feed especially curved container surfaces in front of the print head. Rotation of the containers about themselves can nevertheless be combined with a pressure feed of the containers in front of the print head caused by a transport. In particular, in the case of container walls to be printed with infinite or very large radii of curvature, a suitable feed in front of the print head can also be generated exclusively by a transport movement of the containers with respect to the print head.

Preferably, the first and second partial imprints are printed by means of different printheads. Thus, the print image can be composed of several complementary in the circumferential direction partial imprints in visually appealing way. This is particularly advantageous when the full rotation of the container before a single printhead for lack of time during the container transport is not possible and / or if not rotationally symmetric container cross sections require the use of different printheads for printing circumferential portions of the container.

Preferably, the end of the second partial imprint connects to the beginning of the first partial imprint. The beginning and end of the partial imprints are to be understood here in terms of a chronological sequence when printing on the container. For example, the first partial imprint in Print direction seamlessly transition into the second partial imprint, for example, in a full rotation of the container around itself in front of a single printhead. The beginning of the printing process then defines the beginning of the first partial imprint. The end of the second partial imprint then results from reaching the beginning of the first partial imprint after full rotation by definition.

Since the circumference of the container to be printed may vary due to dimensional tolerances, the joining according to the invention at the beginning of the first partial imprint and at the end of the second partial imprint allows for a continuous and without double impression printed image in the connection area for the viewer.

Preferably, at least two connection areas distributed around the container in the circumferential direction are produced simultaneously for each container. For this purpose, for example, at least two printheads distributed in the circumferential direction around the container are present, which emit ink with simultaneous rotation of the container in temporally overlapping printing processes. It is then necessary, for example, only a teilumfängliche rotation of the container for a full-scale print with inventively juxtaposed partial imprints. Thus, direct printing can be performed faster and / or with multiple components of a color model.

Preferably, at least two components of a color model are printed on one another in such a way that connection areas of different components are offset from one another in the printing direction. This means that, for example, a connection region between two partial imprints of one component lies in a different circumferential partial region of the printed image than a connection region of another component of the color model. Thus, overlapping areas between the partial imprints in the printed image as a whole can be made particularly inconspicuous. For example, artefacts caused by the intermeshing pressure would not overlap in the same circumferential area of the print image but would be distributed to different peripheral areas of the print image for the individual components of the color model.

Preferably, image contents of a digital print original contained in the first and / or second partial print are distributed by image processing algorithm to pixel patterns that complement each other in the connection area to the print image. For example, pixel patterns are binary masks that complement each other in the connection area to the printed image. Preferably, no continuous boundary line is then formed between the masks of the first and second partial imprint. Thus, the connection area for the viewer visually unobtrusive disguise. It is both possible image contents of the first partial imprint in the second Partial print to take over as well as vice versa. Likewise, image contents can be distributed in a suitable manner to the first and second partial imprints, depending on the printed image. It is also possible to reproduce image contents by copying and inserting both in the first and in the second partial imprint.

Pixels often consist of different sized drops and associated colors. The print heads are able to print different drop sizes depending on the control or print template preparation.

Alternatively or in addition to the printing described above, each pixel in the transition area could be printed in two printing operations. The required amount of ink or drop size can then be distributed to two print heads. For example, a pixel can be composed of a total of seven sub-droplets, wherein a sub-droplet is to be understood as the smallest droplet that can be represented. In the transition area, for example, one printhead can deliver four sub-drops and the other printhead can deliver the remaining three sub-drops of the pixel.

Preferably, at least a third and a fourth partial imprint are added to the first and second partial imprints transversely to the printing direction such that the respectively adjacent partial imprints overlap one another in the associated connection regions. The print image can thus be tiling-like composed of individual partial imprints.

Thus, partial envelopes adjoining one another in the peripheral direction of the container can be visually inconspicuously joined together and optically combined in the axial direction to increase the printing width.

Preferably, the containers are molding bottles. In particular, with a rotation of form bottles around themselves occur changes in the pressure separation and caused by the pressure feed pressure resolution. By defining individual partial imprints which are advantageously to be printed in front of a printhead and by interleaving these partial imprints, it is possible, despite non-rotationally symmetrical cross-sections, to produce a gap-free and transition-free printed image for the viewer.

The molding bottles preferably have a curved cross section in a side wall section to be printed, in particular with a changing radius of curvature. In these areas, it is particularly difficult to produce a circumferential direction of continuous direct printing from a single printhead having the required print quality. ever After changing the radius of curvature, it is thus possible to insert suitable circumferential partial regions in the compression direction into one another in a meshing manner.

The stated object is also achieved with a device according to claim 13.

Preferably, the device then comprises at least two print heads offset from one another in the printing direction, which are tuned in such a way that they can be used to assemble a print image from partial prints intermeshing in the printing direction.

Fig. 1

ein Beispiel für zwei Teildruckbilder, die auf herkömmliche Weise zu einem Druckbild sequenziell aneinander gefügt werden sollen;

Fig. 2

ein Beispiel für einen erfindungsgemäß ineinander kämmenden Anschlussbereich;

Fig. 3

eine schematische Draufsicht auf erfindungsgemäße Vorrichtungen;

Fig. 4

ein Beispiel für in Druckrichtung und quer zur Druckrichtung ineinander kämmende Anschlussbereiche; und

Fig. 5

ein Beispiel für das Bedrucken einer Formflasche mit einem erfindungsgemäßen Anschlussbereich.

Preferred embodiments of the invention are shown in the drawing. Show it:

Fig. 1

an example of two partial print images to be sequentially joined to one another in a conventional manner;

Fig. 2

an example of an inventive intermeshing connection area;

Fig. 3

a schematic plan view of devices according to the invention;

Fig. 4

an example of in the printing direction and transverse to the printing direction intermeshing connection areas; and

Fig. 5

an example of the printing of a mold bottle with a connection area according to the invention.

The Fig. 1 illustrates the basic problem when joining a first and second partial imprint 1, 2 in the printing direction 3 to a continuous print image 4. The partial imprints 1, 2 are respectively from an initial region 1a, 2a to an end region 1b, 2b to produce such succession that image content 1c, 2c of the first and second partial imprints 1, 2 at an imaginary, transversely to the printing direction 3 extending target line of abutment 5 abut each other and complement each other seamlessly in the printed image 4.

In the Fig. 1 Furthermore, a first and second print head 6, 7 are shown, with which the partial imprints 1, 2 are printed, for example, on a side wall 8a of a container 8. At the print heads 6, 7 are (schematically indicated) extending transversely to the printing direction 3 nozzle rows 6a, 7a available. For example, due to the design of the print heads 6, 7, the rows of nozzles 6a, 7a have a spacing 9 relative to one another in the printing direction 3.

Like the farther Fig. 3 can also be caused by the fact that these different peripheral portions 8b, 8c of the container 8 are facing, for example, offset by 180 ° in the circumferential direction to the partial imprints 1, 2 upon rotation of the Container 8 to overlap itself or to produce simultaneously with the print heads 6, 7. A suitable rotation in the printing direction 3 about the main axis 8 'of the container 8 is in the Fig. 2 indicated schematically.

Regardless of how large the respective distance 9 between individual rows of nozzles 6a, 7a, the partial imprints 1, 2 in the printing direction 3 as possible without the normal use of the container 8 recognizable connection gaps and / or double-printed areas to print image 4 together.

Due to dimensional tolerances and / or shape tolerances, which, for example, the extent of the side wall to be printed 8a and / or individual circumferential portions 8b, 8c are afflicted, the (in the circumferential direction defined here) actual length of the total pressure area to be covered and / or actual distances between the printing direction 3 to be joined to each other partial imprints 1, 2 vary.

The partial imprints 1, 2 then lined up against the idealized representation of Fig. 1 not seamlessly along the imaginary desired score line 5 together. Instead, for example, between the end region 1 b and the starting region 2 a of the partial imprints 1, 2 connecting gaps without imprinting or an overlapping double printing with imprinted image contents 1 c, 2 c of the partial imprints 1, 2 are formed. This then incorrectly adjacent to the target-line 5 lying limits 1d, 2d of the partial imprints 1, 2 are in the Fig. 1 indicated by dashed lines as an example. As a result, quality losses during direct printing of the side wall 8a are counteracted by the interleaving overlapping of the first and second partial imprints 1, 2 explained below.

For this purpose, image contents 1 c from the end region 1 b of the first partial imprint 1 with image contents 2 c of the starting region 2 a of the second partial imprint 2 are distributed into one another within a connection region 10. This is in the Fig. 2 shown schematically.

The connection region 10 according to the invention preferably covers a circumferential arc segment 8d of the side wall 8a in the printing direction 3, with a length of 5 to 50 pixels, in particular from 10 to 5, for example, based on the printing resolution of the printed image 4 30 pixels, or with an absolutely defined length of 0.1 to 1 mm or in particular from 0.2 to 0.5 mm. This results in an extended in the direction of pressure overlap area in contrast to the conventional, ideally non-overlapping contiguous abutment of the sections 1, 2 along the imaginary continuous target-puncture line fifth

By intermeshing one understands that the image contents 1c, 2c intermesh with one another, see upper exemplary example 10a in the connection region 10, and / or pixels of the image contents 1c, 2c are distributed like a mosaic in the connection region 10, see the lower exemplary example 10b. Pixels of the image contents 1c, 2c can be flexibly distributed in the connection area 10 with image processing algorithms, depending on the printed image 4 to be produced. As a result, conventional, continuously rectilinear boundaries 1d, 2c of the partial imprints 1, 2 are broken at least in sections.

Alternatively or additionally, image contents 1c, 2c in the connection area 10 could be printed in two printing processes. The amount of ink per pixel or parts of the drop size of the pixel can then be distributed to the print heads 6, 7. For example, a pixel can be composed of several sub-droplets, wherein a sub-droplet is to be understood as the smallest droplet that can be represented. In the transition region, for example, one print head 6 can deliver a suitable number of sub-drops, and the other print head 7 can deliver the remaining sub-drops of the respective image point.

For example, pixels of the first partial imprint 1 in the connection region 10 are shifted and / or copied and past the boundary 1d, and pixels of the second partial imprint 2 are displaced and / or copied and pasted in the connection region 10 opposite the boundary 2d against the printing direction 3 , In simple terms, the connection region 10 according to the invention differs from the prior art in particular in that the image contents 1c, 2c are not sharply demarcated at ends 1d, 2d which extend transversely to the printing direction 3. The latter can be rectilinear orthogonal to the printing direction 3, jagged, oblique or the like

The length of the connection region 10 in the printing direction 3, that is, for example, the length of the sheet segment 8d, can be flexibly adapted to the expected dimensional tolerance and / or shape tolerance of the side wall 8a and / or the printed image 4 to be imprinted by image processing of the image contents 1c, 2c.

The Fig. 3 shows schematic plan views of preferred embodiments 20, 21 of a device according to the invention, which differ by the number of print heads.

On the left side of the Fig. 3 is a container to be printed 8 and two 180 degrees around the container circumference distributed printheads 6, 7 shown. A pressure feed of the container side wall 8a in the printing direction 3 with respect to the print heads 6, 7 is generated by rotation of the container 8 around itself in front of both print heads 6, 7 simultaneously. In the example of Fig. 3 For example, the first partial print 1 with one print head 6 and the second partial print 2 with the other print head 7 could be generated. This results in two connecting regions 10, 11 according to the invention, which are produced essentially simultaneously and according to the invention in the sense of FIG Fig. 2 overlap each other. This is also possible with deviating number and / or extensive division of the print head positions.

On the right side of the Fig. 3 is a full printing of the container 8 with only one print head 6 indicated schematically. In this case, the connection area 10 only results after rotation of the container 8 by more than 360 °, for example by 362 °. The initial region 1a of the first partial imprint 1 is then first produced and the end region 2b of the second partial imprint 2 is added to the initial region 1a without interruption of the printing advance.

However, terminal regions 10 according to the invention can in principle be produced with any desired, even partially circumferential, rotational movements of the container 8 around itself. For this purpose, for example, a rotatable holder 22 for the container 8 and a control unit 23 for controlling the print head 6 and the holder 22 is present.

It is also possible in this way to control print heads 6, 6 'separately for different components of a color model, such as CMYK, in order to form associated connection regions 10, 10' in the circumferential direction offset from one another. This is in the Fig. 3 indicated by dashed lines as an example.

The first and second partial imprint 1, 2 are defined with regard to the connection region 10, 11 to be produced, regardless of the number of printheads 6, 7 used and whether the printing feed in the printing direction 3 is interrupted between individual partial imprints 1, 2. The beginning and end of the partial imprints 1, 2 are related to the printing direction 3 for a better understanding. However, it does not matter for the invention whether the printing direction 3 is reversed for individual partial imprints 1, 2. It is crucial that is printed on an initial area or end portion of a previously created partial imprint out and the respective terminal portion 10, 11 formed meshing with each other.

The Fig. 4 shows a further advantageous variant, in the inventive terminal areas 10, 11 between the first and second partial imprints 1, 2 and between third and fourth partial imprints 12, 13 are produced in the printing direction 3. Furthermore, the partial imprints 1, 2, 12, 13 share a connection region 14 transversely to the printing direction 3. This is possible, for example, with printing heads 15, 16 which are offset from one another both along the printing direction 3 and transversely to the printing direction 3. The connection region 14 is then also formed with partial imprints 1, 2, 12, 13 which mesh with one another transversely to the printing direction 3.

On the right side of the Fig. 4 is also indicated that in the printing direction 3 and transverse to the printing direction 3 intermeshing partial imprints 1, 2, 12, 13 on different partially circumferential areas 8b, 8c in analogy to Fig. 3 also by several correspondingly distributed printheads 15, 16 produce simultaneously or overlapping in time.

The Fig. 5 shows a further advantageous variant for printing formed as molding bottles containers 18 with non-rotationally symmetrical cross-section. By way of example, an elliptical cross section to be imprinted is indicated. Due to the significantly divergent radii of curvature of individual teilumfänglicher areas 18b, 18c of the side wall 18a during rotation of the container 18 about its major axis 18 ', the printed image 4 in the printing direction 3 of several partial imprints 1, 2 must be assembled.

In the Fig. 5 For example, the first and second partial imprints 1, 2 are associated with the partially circumferential regions 18b, 18c, which parts intersect one another in a connecting region 10 according to the invention. The connection region 10 is characterized by an oblique hatching.

The teilumfbaren wall portions 18b, 18c of the side wall 18a are printed for this purpose successively from at appropriate intervals to the main axis 18 'arranged print heads 6, 7 by rotation of the container 18 to itself. The containers are then also moved along a linear and / or circular or otherwise extending transport path 19 to produce a suitable print feed in front of the print heads 6, 7.

The described embodiments and variants can be flexibly combined to directly print different containers 8, 18, such as bottles with rotationally symmetrical cross section or shaped bottles by means of inkjet.

Claims (14)

1. A method for inkjet printing on containers (8, 18), comprising the steps of joining at least a first and a second subprint (1, 2) complementing each other in the printing direction (3) so as to form a print image (4), wherein the first subprint (1) is printed first starting from a connection area (10, 11) or up to a connection area (10, 11) and the second subprint (2) is printed subsequently with a feed towards the connection area (10, 11) such that the first and second subprints (1, 2) interleavingly overlap in the connection area (10, 11), wherein the printing direction (3) runs laterally about a main axis (8', 18') of the containers (8, 18).
2. The method according to claim 1, wherein the connection area (10) covers a circumferential arc segment (8d) whose length comprises 5 to 50 pixels of the print image (4), in particular 10 to 30 pixels.
3. The method according to claim 1 or 2, wherein the containers (8, 18) are printed on at least over their full circumference, over a print area of at least 362°, in particular of at least 365°.
4. The method according to one of the preceding claims, wherein the containers (8, 18) are rotated about their own axis in front of at least one print head (6, 7, 15, 16).
5. The method according to one of the preceding claims, wherein the first and second subprints (1, 2) are printed by means of different print heads (6, 7, 15, 16).
6. The method according to one of the preceding claims, wherein an end area (2b) of the second subprint (2) adjoins a starting area (1a) of the first subprint (1).
7. The method according to one of the preceding claims, wherein, for each container (8), at least two connection areas (10, 11) distributed around the container (8) in a circumferential direction are produced simultaneously.
8. The method according to one of the preceding claims, wherein at least two components of a color model are printed one on top of the other such that connection areas (10, 10') of different components are displaced relative to one another in the printing direction (3).
9. The method according to one of the preceding claims, wherein image contents (1c, 1d) of a digital master copy comprised in the first and/or second subprint (1, 2) are distributed by means of an image processing algorithm to pixel patterns (10a, 10b) complementing one another other in the connection area (10) so as to form a print image (4).
10. The method according to one of the preceding claims, wherein, in addition, at least a third and a fourth subprint (12, 13) are joined to the first and second subprints (1, 2) in a direction transversely to the printing direction (3) such that the respective adjacent subprints interleavingly overlap in the associated connection areas (10, 11, 14).
11. The method according to one of the preceding claims, wherein the containers (18) are specially shaped bottles.
12. The method according to claim 11, wherein the specially shaped bottles have a curved cross-section in at least one circumferential subarea (18b, 18c) of their sidewall (18a) to be printed on, in particular a curved cross-section with a varying radius of curvature.
13. A device (20, 21) for executing the method according to at least one of the preceding claims, comprising at least one print head (6, 7), at least one rotatable support (22) for a container (8), and a control unit (23) for controlling the print head (6, 7) and the support (22) to produce rotary movements of the container (8) about its own axis such that a first subprint (1) is printed first starting from a connection area (10, 11) or up to a connection area (10, 11) and a second subprint (2) is printed subsequently with a feed towards the connection area (10, 11) such that the first and second subprints (1, 2) interleavingly overlap in the connection area (10, 11).
14. The device according to claim 13, comprising at least two print heads (6, 7), which are displaced relative to one another in the printing direction (3) and which are coordinated such that they can be used for composing a print image (4) from subprints (1, 2) that interleave in the printing direction (3).

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