Method and device for inkjet printing on containers

Abstract

In a method and a device for inkjet printing on containers, at least a first and a second subprint complementing each other in the printing direction so as to form a print image are joined. The first subprint is printed starting from a connection area or up to a connection area. Subsequently, the second subprint is printed with a feed towards the connection area such that the first and second subprints interleavingly overlap in the connection area. This allows a joining of subprints with unobtrusive transitions even in the case of dimensional tolerances and complicated cross-sections of the respective container.

Claims

1. A method for inkjet printing on containers, comprising the steps of joining at least a first and a second subprint complementing each other in the printing direction so as to form a print image, wherein the first subprint is printed first starting from a connection area or up to a connection area and the second subprint is printed subsequently with a feed towards the connection area such that the first and second subprints interleavingly overlap in the connection area, wherein the first and second subprint do not adjoin one another in the connection area along a straight line extending transversely to the printing direction, but the connection area is formed in an intermeshing manner distributing image contents of the first and second subprint in a gear tooth configuration, and wherein the printing direction runs laterally about a main axis of the containers, and the first and second subprint interleavingly overlap in a circumferential direction of the containers.

2. The method according to claim 1, wherein the connection area covers a circumferential arc segment whose length comprises 5 to 50 pixels of the print image.

3. The method according to claim 1, wherein the containers are printed on one of at least over their full circumference, over a print area of at least 362°, or over a print area of at least 365°.

4. The method according to claim 1, wherein the containers are rotated about their own axis in front of at least one print head.

5. The method according to claim 1, wherein an end area of the second subprint adjoins a starting area of the first subprint.

6. The method according to claim 1, wherein, for each container, at least two connection areas distributed around the container in a circumferential direction are produced simultaneously.

7. The method according to claim 1, wherein at least two components of a color model are printed one on top of the other such that connection areas of different components are displaced relative to one another in the printing direction.

8. The method according to claim 1, wherein image contents of a digital master copy comprised in the first and/or second subprint are distributed by means of an image processing algorithm to pixel patterns complementing one another in the connection area so as to form a print image.

9. The method according to claim 1, wherein, in addition, at least a third and a fourth subprint are joined to the first and second subprints in a direction transversely to the printing direction such that the respective adjacent subprints interleavingly overlap in the associated connection areas.

10. The method according to claim 1, wherein the containers (18) are specially shaped bottles.

11. The method according to claim 10, wherein the specially shaped bottles have a curved cross-section in at least one circumferential subarea of their sidewall to be printed on.

12. The method according to claim 11, wherein the curved cross-section has a varying radius of curvature.

13. A device for executing the method according to claim 1, comprising at least one print head, at least one rotatable support for a container, and a control unit for controlling the print head and the support such that, in the connection area, the first and second subprints can be printed onto the container in an interleaving fashion.

14. The device according to claim 13, comprising at least two print heads, which are displaced relative to one another in the printing direction and which are coordinated such that they can be used for composing a print image from subprints that interleave in the printing direction.

15. The method according to claim 1 wherein the connection area covers a circumferential arc segment whose length comprises 10 to 30 pixels of the print image.

16. A method for inkjet printing on containers, comprising the steps of joining at least a first and a second subprint complementing each other in the printing direction so as to form a print image, wherein the first subprint is printed first starting from a connection area or up to a connection area and the second subprint is printed subsequently with a feed towards the connection area such that the first and second subprints interleavingly overlap in the connection area, wherein the first and second subprint do not adjoin one another in the connection area along a straight line extending transversely to the printing direction, but the connection area is formed in at least one of an intermeshing and a mosaic-like manner distributing image contents of the first and second subprint, wherein the first and second subprint are printed by different print heads, and wherein one print head ejects a suitable number of subdroplets of a pixel in the connection area, and another print head ejects the rest of the subdroplets of the respective pixel.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) Preferred embodiments of the present invention are shown in the drawing, in which:

(2) FIG. 1 shows an example of two subprints which are to be sequentially joined so as to form a print image in a conventional manner;

(3) FIG. 2 shows an example of an interleaving connection area in accordance with the present invention;

(4) FIG. 3a shows a schematic top view of a first device according to the present invention;

(5) FIG. 3b shows a schematic top view of an alternate device of the present invention;

(6) FIG. 4 shows an example of connection areas interleaving in the printing direction and transversely to the printing direction; and

(7) FIG. 5 shows an example of printing on a specially shaped bottle with a connection area according to the present invention.

(8) FIG. 1 exemplarily illustrates the fundamental problem to be solved when a first and a second subprint 1, 2 are joined in the printing direction 3 so as to form a continuous print image 4. The respective subprints 1, 2 are to be produced successively from a starting area 1a, 2a to an end area 1b, 2b such that image contents 1c, 2c of the first and second subprints 1, 2 will abut on one another on an imaginary target butt line 5 extending transversely to the printing direction 3 and smoothly complement each another in the print image 4.

(9) FIG. 1 additionally shows a first and a second print head 6, 7 by means of which the subprints 1, 2 are printed e.g. onto a sidewall 8a of a container 8. The print heads 6, 7 have provided thereon rows of nozzles 6a, 7a (schematically indicated) extending transversely to the printing direction 3. Depending e.g. on the structural design of the print heads 6, 7, said rows of nozzles 6a, 7a are spaced apart at a distance 9 in the printing direction 3.

(10) As can additionally be seen from FIG. 3, the distance 9 between the print heads 6, 7 may also result from the fact that the latter face different circumferential subareas 8b, 8c of the container 8, displaced e.g. by 180° in a circumferential direction, so as to produce the subprints 1, 2 in a temporally overlapping or simultaneous mode by means of the print heads 6, 7 while the container 8 is rotating about its own axis. A suitable rotation in the printing direction 3 about the main axis 8′ of the container 8 is schematically indicated in FIG. 2.

(11) Irrespectively of the size of the respective distance 9 between individual rows of nozzles 6a, 7a, the subprints 1, 2 have to be joined in the printing direction 3 so as to form the print image 4, as far as possible without connection gaps and/or double-print areas that are visible during normal use of the container 8.

(12) Due to dimensional tolerances and/or shape tolerances existing e.g. in the case of the circumference of the whole sidewall 8a to be printed on and/or in the case of individual circumferential subareas 8b, 8c, the actual length (defined here in the circumferential direction) of the whole printing area to be covered and/or the actual distances between the subprints 1, 2 to be joined in the printing direction 3 may vary.

(13) Contrary to the idealized representation according to FIG. 1, the subprints 1, 2 will then not smoothly follow one after the other along the imaginary target butt line 5. Instead, connection gaps which are not printed on, or an overlapping double print with subprint image contents 1c, 2c printed one on top of the other, form e.g. between the end area 1b and the starting area 2a of the subprints 1, 2. Such boundaries 1d, 2d of the subprints 1, 2 which, erroneously, are not located on the target butt line 5 are exemplarily indicated by a broken line in FIG. 1. The resultant quality losses occurring when the sidewall 8a is directly printed on are counteracted by the interleaving overlap of the first and second subprints 1, 2 explained hereinbelow.

(14) To this end, image contents 1c of the end area 1b of the first subprint 1 and image contents 2c of the starting area 2a of the second subprint 2 are interleavingly distributed within a connection area 10. This is schematically shown in FIG. 2.

(15) Preferably, the connection area 10 according to the present invention covers in the printing direction 3 a circumferential arcuate segment 8d of the sidewall 8a, which, related e.g. to the print resolution of the print image 4, has a length of 5 to 50 pixels, in particular of 10 to 30 pixels, or an absolutely defined length of 0.1 to 1 mm, or in particular 0.2 to 0.5 mm. It follows that, in contrast to the conventional, ideally non-overlapping abutting contact of the subareas 1, 2 along the imaginary continuous target butt line 5, an overlap area extending in the printing direction is obtained.

(16) The term “interleaving” is to be understood such that the image contents 1c, 2c are intermeshed, cf. the upper pattern example 10a in the connection area 10, and/or that pixels of the image contents 1c, 2c are distributed in the connection area 10 in a mosaic-like fashion, cf. the lower pattern example 10b. Making use of image processing algorithms, pixels of the image contents 1c, 2c can flexibly be distributed in the connection area 10, depending on the print image 4 to be produced. This has the effect that conventional continuous straight boundaries 1d, 2d of the subprints 1, 2 are broken through at least in certain sections thereof.

(17) Alternatively or additionally, image contents 1c, 2c in the connection area 10 may be printed in two printing processes. The amount of ink per pixel or fractions of the droplet size of the pixel can then be distributed to the print heads 6, 7. For example, a pixel may be composed of a plurality of subdroplets, a subdroplet being here the respective smallest representable droplet. In a transition area, e.g. one print head 6 may eject a suitable number of subdroplets and the other print head 7 may eject the rest of the subdroplets of the respective pixel.

(18) For example, pixels of the first subprint 1 are, in the connection area 10, displaced relative to the boundary 1d in the printing direction 3 and/or copied and pasted, and pixels of the second subprint 2 are, in the connection area 10, displaced relative to the boundary 2d in a direction opposite to the printing direction 3 and/or copied and pasted. To put it simply, the connection area 10 according to the present invention differs from the prior art especially insofar as the image contents 1c, 2c do not end in an abrupt fashion at boundaries 1d, 2d extending transversely to the printing direction 3. Said boundaries 1d, 2d may be straight and orthogonal to the printing direction 3, jagged, oblique or the like.

(19) By means of image processing of the image contents 1c, 2c, the length of the connection area 10 in the printing direction 3, i.e. for example the length of the arcuate segment 8d, can flexibly be adapted to the dimensional tolerance and/or shape tolerance of the sidewall 8a to be expected and/or the print image 4 to be printed.

(20) FIGS. 3a and 3b show schematic top views of preferred embodiments 20, 21 of a device according to the present invention differing from one another with respect to the number of print heads.

(21) On the left hand side of each of FIGS. 3a and 3b, a container 8 to be printed on and two 180° spaced-apart print heads 6, 7 distributed around the circumference of the container are shown. A print feed of the container sidewall 8a in the printing direction 3 with respect to the print heads 6, 7 is created through a rotation of the container 8 about its own axis in front of both print heads 6, 7 at the same time. In the examples according to FIGS. 3a and 3b, the first subprint 1 may be produced by means of one of the print heads 6 and the second subprint 2 by means of the other print head 7. In this way, two connection areas 10, 11 according to the present invention are obtained, which are produced substantially simultaneously and which interleavingly overlap in accordance with the present invention in the sense of FIG. 2. This will also be possible in the case of a deviating number of and/or circumferential distribution of the print head positions.

(22) On the right hand side of each of FIGS. 3a and 3b, it is schematically indicated how the container 8 is printed on over its full circumference by means of only one print head 6. In this case, the connection area 10 will only be obtained when the container 8 has been rotated by more than 360°, e.g. by 362°. The starting area 1a of the first subprint 1 is here produced first and the end area 2b of the second subprint 2 is added to said starting area 1a in the way disclosed in the present invention, without interrupting the print feed.

(23) However, connection areas 10 according to the present invention can, in principle, be produced by means of arbitrary rotary movements of the container 8 about its own axis, and also by rotary movements taking place over only part of the circumference of the container 8. To this end, e.g. a rotatable support 22 for the container 8 and a control unit 23 for controlling the print head 6 and the support 22 are provided.

(24) Likewise, print heads 6, 6′ for different components of a color model, such as CMYK, can be controlled separately in this way, so as to create associated connection areas 10, 10′ such that they are displaced relative to one another in a circumferential direction. This is exemplarily indicated in each of FIGS. 3a and 3b by a broken line.

(25) The first and second subprints 1, 2 are defined with respect to the connection area 10, 11 to be created, irrespectively of the number of print heads 6, 7 used and irrespectively of whether the print feed in the printing direction 3 is interrupted between individual subprints 1, 2. For clearer understanding, the beginning and the end of the subprints 1, 2 are related to the printing direction 3. Whether the printing direction 3 is reversed for individual subprints 1, 2 is, however, irrelevant for the present invention. What matters is that printing is effected towards a starting area or an end area of a previously produced subprint and that the respective connection area 10, 11 is configured in an interleaving fashion.

(26) FIG. 4 shows another advantageous variant in the case of which connection areas 10, 11 according to the present invention are produced between first and second subprints 1, 2 and between third and fourth subprints 12, 13 in the printing direction 3. In addition, the subprints 1, 2, 12, 13 share a connection area 14 in a direction transversely to the printing direction 3. This can be accomplished e.g. by means of print heads 15, 16 which are displaced relative to one another along the printing direction 3 as well as transversely to the printing direction 3. Also the connection area 14 is then formed with subprints 1, 2, 12, 13 interleaving in a direction transversely to the printing direction 3.

(27) On the right hand side of FIG. 4 it is additionally outlined that subprints 1, 2, 12, 13, which interleave in the printing direction 3 and in a direction transversely to the printing direction 3, can, analogously to FIG. 3, be produced on different circumferential subareas 8b, 8c also by means of a plurality of suitably distributed print heads 15, 16 simultaneously or in a temporally overlapping mode.

(28) FIG. 5 shows another advantageous variant of printing on containers 18, which are configured as specially shaped bottles and which have an non-rotationally symmetric cross-section. By way of example, an elliptical cross-section to be printed on is outlined. Due to the substantial deviation in the radii of curvature of individual circumferential subareas 18b, 18c of the sidewall 18a during the rotation of the container 18 about its main axis 18′, the print image 4 must be composed of a plurality of subprints 1, 2 in the printing direction 3.

(29) In FIG. 5, the circumferential subareas 18b, 18c have exemplarily associated therewith the first and second subprints 1, 2, which share a connection area 10 according to the present invention in an interleaving fashion. The connection area 10 is identified by oblique hatches.

(30) The circumferential subareas 18b, 18c of the sidewall 18a are, for this purpose, successively printed on from print heads 6, 7 arranged at suitable distances from the main axis 18′, while the container 18 is rotating about its own axis. The containers are then additionally moved along a linear and/or circular conveying path 19 or along a conveying path 19 having some other shape, so as to create a suitable print feed in front of the print heads 6, 7.

(31) The above described embodiments and variants can be combined in a flexible manner so that different containers 8, 18, such as bottles having a rotationally symmetric cross-section or specially shaped bottles, can be printed on directly by means of an inkjet.