EP3681724A1

EP3681724A1 - Direct printer for applying a printed layer to containers

Info

Publication number: EP3681724A1
Application number: EP18728586.1A
Authority: EP
Inventors: Georg Gertlowski
Original assignee: Krones AG
Current assignee: Krones AG
Priority date: 2017-09-04
Filing date: 2018-05-28
Publication date: 2020-07-22
Anticipated expiration: 2038-05-28
Also published as: EP3681724B1; EP3681724C0; CN213413297U; DE102017215433A1; WO2019042600A1

Abstract

The present invention relates to a direct printer for applying a printed layer to containers (130), such as bottles in the beverage-processing industry, with at least one print head (101) which comprises at least two nozzle rows for ejecting ink droplets onto a surface of a container, characterized in that the print head is oriented in such a way that the nozzle rows enclose an angle of greater than 0° with a plane (133) perpendicularly with respect to the transport direction (132) of the containers; and to a corresponding method. In one alternative embodiment, the printer can have two print heads (301, 302) which are arranged behind one another in the transport direction of the containers and are offset with respect to one another perpendicularly with respect to the transport plane, in which the containers are transported, by a distance (h) which is smaller than the spacing of two adjacent nozzles in a nozzle row.

Description

Direct printing machine for applying a printing layer to containers

The present invention relates to a direct printing machine for applying a printing layer to a container according to the preamble of claims 1 and 8 and to a direct printing method for applying a printing layer to a container according to the preamble of claim 13.

State of the art

Direct printing methods for printing on containers are known in the art over a wide range of resolution.

For example, EP 2 089 234 B1 proposes a direct printing method in which a primer is applied to the container before it is provided with a printed image. From this it is known that ink drops with a resolution of 200 to 1200 drops / inch (dpi) and also different drop sizes can be applied to the surface of the container, for example to form a primer or at least a part of the printed image.

Although the known method generally allows the application of a primer and the subsequent application of a printed image, but can not be ensured over the entire surface of the container due to the usable resolutions of a maximum of 1 .200 dpi and a drop size of 10 to 200 μηη that the applied Printing layer or primer is flat or nearly flat. Such unevenness may result in the subsequent application of a printed image to the flow of the printing ink in accordance with the relief produced by the primer, thereby reducing the print quality.

task

Starting from the known prior art, the technical problem to be solved is therefore to improve direct printing processes and direct printing machines for printing on containers with regard to the quality of the printed images.

solution

This object is achieved by the direct printing machines for applying a printing layer to containers according to claim 1 or claim 8 and the direct printing method for applying a printing layer to a container according to claim 13. Advantageous developments of the invention are covered in the subclaims. The direct printing machine according to the invention is characterized in that the print head is oriented so that the nozzle rows form an angle greater than 0 ° with a plane perpendicular to the transport direction of the container. This clearly indicates that the print head is inclined with respect to the container in the transport direction. This reduces the spacing of the individual nozzles of the nozzle rows at least in the vertical direction, so that the pixel density in this direction can be increased beyond the output pixel density of the print head. Depending on the angle of attack, for example, twice the ink drop density can be achieved, at least in the vertical direction. In this way, a much more uniform layer can be produced when the printing layer is applied, so that a color layer applied later to the printing layer can be produced more levelly and therefore with a higher quality.

In this case, "printing layer" is to be understood as any layer applied to the surface of a container by a printing module of a direct printing machine. These include in particular colored layers (for example yellow, red or blue), but also functional layers, such as primers, which are applied to the container before the actual print motif is applied. Although this primer may already be part of the image (for example, it may be white or cause certain other optical properties, or it may also have any color), it need not. The primer may also be formed as a transparent layer or at least as a partially transparent layer, and e.g. affect the adhesive properties of the applied color layers for the printed image. For example, the primer may be made of a material that reduces or increases the surface tension compared to the actual surface of the container, which may be beneficial for wetting with the actual printing inks.

The fact that the nozzle rows enclose an angle that is perpendicular to the transport direction at an angle greater than 0 ° does not mean that they are arbitrary misalignments, for example due to a not completely exact alignment of another vertically arranged pressure module (the nozzle rows run as planned parallel to the plane perpendicular to the transport direction), but are intentional inclinations. As a result, they will generally be larger, even significantly larger than the tolerances acceptable for vertical alignment and will be in the range of a few degrees, in particular 5 ° to 30 °.

In one embodiment, it is provided that the nozzle rows are arranged in a plane in the print head, which is perpendicular to the transport plane. This means that the print head does not move in the direction of the transport plane or in the direction of a transport plane in the transport plane. th container is tilted, but just stands. Distortions of the printed image can be avoided.

In a further embodiment, it is provided that the print head has a normal resolution of 1200 dpi. The normal resolution means that this is the resolution that can be achieved on a flat substrate when the ink droplets strike the surface vertically. The fact that the printhead is tilted and thus the resolution on the substrate can be increased at least in the vertical direction, an even higher resolution than the 1200 dpi, especially 1440 dpi, can be achieved, which for the applied print layer even more even distribution the surface of the container means.

It can further be provided that the printing press comprises two print heads arranged one after the other in the transport direction, which are offset from each other perpendicular to the transport plane and each have a normal resolution of 600 dpi, wherein both print heads comprise at least two rows of nozzles and are aligned so that the nozzle rows with the Level perpendicular to the transport direction of the container include an angle greater than 0 °. By the vertical offset of the two printheads from each other and the simultaneous skew according to the invention, a suitable offset of the ink droplets applied by the printheads can be achieved, so that even with the comparatively low resolution of 600 dpi / printhead an ink droplet density can be achieved on the surface of the container , which is significantly larger than the sum of the ink drop densities of the individual printheads, for example, much greater than 1200 dpi, so that a layer as flat as possible is applied.

In a further development of this embodiment, the print heads are offset from one another by a distance h which corresponds to half the distance between two adjacent nozzles of a nozzle row in the direction of the surface normal of the transport plane. That is, the ink droplets of the second printhead are placed on the surface of the container just in the interstices of the ink drops of the first printhead. In order for a uniform printed layer can be generated, which facilitates the application of the subsequent print layers and leads to an improved print image.

Furthermore, the printhead or printheads can be designed so that they can eject ink drops with a diameter of 10 to 50 μm. The diameter of the ink droplets refers to the dimensions of an ink drop at normal pressure and room temperature in the equilibrium of forces, that is to say without any forces acting on the ink droplets in total. Moreover, in embodiments having two printheads, one of the printheads may be configured to eject ink droplets having a smaller diameter than the other printhead. In this way, embodiments can be realized in which the gaps between the relatively large ink droplets can be filled by the smaller ink drops and thus a surface which is as flat as possible can be produced.

Another direct printing machine according to the invention for applying a printing layer to containers is characterized in that the print heads are arranged offset from one another perpendicular to the transport plane by a distance h which is smaller than the distance between two adjacent nozzles in the nozzle row. The ink drop density can be doubled in this direction (ie perpendicular to the transport plane of the container). Thus, the most uniform printing layer can be applied, which can improve the quality of printed images applied to this printing layer.

Furthermore, it can be provided that the distance h is equal to half the distance between two adjacent nozzles in a row of nozzles.

Further, one of the printheads may be configured to dispense ink drops having a smaller diameter than the other printhead. When the ink drops of the printhead come into contact with the ink droplets of the other printhead to eject smaller drops of ink, a uniform print layer can be achieved because the smaller ink drops fill the gaps.

It may further be provided that the print heads have a normal resolution of 720 dpi and / or at least four rows of nozzles. The achievable with such printheads maximum resolutions show good results in terms of the homogeneity of the applied print layer and thus improve the conditions for it to be applied printed images or other print layers.

Furthermore, it can be provided that each of the direct printing machines described so far comprises one or more adjusting devices, which are assigned to a print head and designed to change the relative position of the print head to the transport plane. It is intended in particular to a change in the position perpendicular to the transport direction and a change in the angle enclosed by a plane perpendicular to the transport direction and the rows of nozzles. Thus, the settings of the printheads can be adapted to the requirements of the printing layer for the container, for example, depending on the container type or the degree of quality to be achieved. The inventive method for printing on containers is characterized in that the containers are transported in a direct printing machine according to one of the preceding embodiments along a transportation line defining a transport plane and are equipped during transport with the print layer.

In this case, "during transport" does not necessarily mean that the containers undergo a movement along a transport direction in the transport device during the printing process. The containers may also be stationary relative to the printheads during the printing process, or at least undergo rotation.

In one embodiment of the method, it is provided that the ink drops applied to the container at normal temperature and pressure have a volume of 3 to 30 pl and / or a diameter of 10 to 50 μm and / or a distance of the center points after application to the container of FIG to 20 μηη, preferably 17.5 μηη have.

In a further embodiment, the alignment of the print heads takes place relative to the transport plane by means of an adjusting device to a predetermined value. An adaptation of the printheads to different requirements is possible.

Brief description of the figures

Fig. 1 a + b schematic representation of a known arrangement of a print head (Fig.

1 a) and a printhead according to the invention (Figure 1 b);

Fig. 2a-c is a schematic representation of an embodiment of the invention with two printheads and different ink drop distributions;

Fig. 3 is a schematic representation of another embodiment with two printheads.

Detailed description

In Fig. 1 a, an arrangement of a container 30 is shown on a transport path 31. The container 30 is transported along the arrow 32 shown. The transport section shown here is exemplified as a conveyor belt on which the containers 30 are transported. Such transport is not mandatory. Alternatively, it is known that a transport in neck handling or on a stand or turntable can be done in conjunction with a centering device. All of these embodiments for the transport of the containers are already known in the art and may be used with the invention described herein.

It will also be understood that each of these particular embodiments may be assigned a "transport plane" for transport, in which the containers are transported, which need not coincide with or be explicitly defined by a region of the transport device. The longitudinal axis of the container usually extends from the bottom of the container to the opening and corresponds in particular in the case of rotationally symmetrical or substantially rotationally symmetrical container whose axis of symmetry.

In the prior art, a print head 1 in the direct printing machine (which is not fully illustrated here) is arranged so that the individual nozzles of the nozzle rows 1 1 and 12 point in the direction of the surface of a container guided past the print head. The individual pressure nozzles of the nozzle rows 1 1 and 12 can then, as shown in dashed lines, deploy ink drops and apply them to the surface of the container. Thus, a printed image or a coating of the container surface can take place. Various printing inks (in particular with different colors) and functional substances which are present under normal conditions (pressure, temperature, etc.) as liquids and can be applied to the surface of the container are already known from the prior art.

In the prior art, the rows of nozzles 1 1 and 12 are arranged together with the print head 1 such that the rows of nozzles 1 1 and 12 and an imaginary line connecting the individual nozzles of each nozzle row parallel to a plane 33, which in turn perpendicular to the transport direction of Container stands. Thus, the maximum resolution in the vertical direction starting from the transport plane, ie in the direction of the surface normal n-i, for an applied print image is equal to the resolution of the print head in this direction, that is given by the distance of the individual nozzles in the nozzle rows in the direction n-i.

In contrast, Fig. 1 b shows an embodiment of a direct printing machine (here at least the transport device 131 and a print head 101) according to the invention. The properties of the transport device are unchanged from those in FIG. 1a. However, the printhead 101 is compared with the Fig. 1 a arranged such that the nozzle rows 1 1 1 and 1 12 with the plane 133 include an angle α and not, as shown in Fig. 1, parallel thereto. This reduces in the direction of the surface normal ni of the transport plane the distance between adjacent nozzles of a row of nozzles, so that the image resolution or the density with which ink droplets can be applied in this direction can be increased.

In particular, the angle can be in a range between 5 ° and 30 °, which allows for common printheads with a maximum resolution of 1200 dpi, an increase to at least 1400 dpi and thus a 1/6 higher ink drop density, whereby a much more level print layer are applied can.

Although not shown here, the plane of the nozzle rows, which is denoted by 1 13, not perpendicular to the plane defined by the transport device 131 transport plane (ie not parallel to ni run). Thus, in some embodiments, the printhead may also be inclined to the transport plane, for example, in cases where the neck area of the container is to be printed. Similarly, methods may be provided in which the printhead is moved along the contour of the container and between a position in which the nozzle rows in the plane 1 13 are perpendicular to the transport plane, and a position in which the plane 1 13 with the therein arranged nozzle rows form an angle smaller than 90 ° with the transport plane. Such movements leave the angle α invariant with respect to the plane 133 perpendicular to the transport plane, so that the increased density of the ink drops perpendicular to the transport plane can be maintained.

Although not explicitly shown here, one or more adjusting devices can be provided which can effect an adjustment of the orientation of the print head as a whole or at least an adjustment of the alignment of the nozzle rows, so that the angle α is changed to the plane 133. These adjusting devices may be actuators or the like, which are connected to a control unit, such as a computer, running a control program, which makes these settings either on input of the user and / or based on the container to be printed and the Regulating device controls accordingly.

Figures 2a-c show an embodiment of the invention in which two printing heads are provided in the printing machine according to the embodiment described in Figure 1b. A container 130 in a transport path 131, as already described, passes along the transport direction 132 first the printhead 201 and then the printhead 202. Both can either at the same angle with respect to the plane perpendicular to the transport direction obliquely arranged rows of nozzles (for example 25 ° ) or the angles may differ. In addition, the print heads 201 and 202 are offset from each other perpendicular to the transport plane, ie parallel to the surface normal ni. This is also shown in Fig. 2a. The height offset is h and may preferably be a fraction of the offset of two nozzles of adjacent rows of nozzles along the normal ni. Thus, depending on the choice of the height difference h, the vertical spacing of the nozzles of the nozzle heads can be adjusted so that the density of the ink drops, which finally form the pressure layer on the container, is further increased.

In particular, this embodiment is advantageous if the individual print heads 201 and 202 have only a comparatively low resolution, for example 600 dpi. With this embodiment, the resulting density of ink drops in the direction of the normal ni can then be increased to over 1200 dpi.

Analogous to the embodiment described in FIG. 1 b, each of the print heads can be assigned an adjusting device, wherein this is preferably not only designed to change the angle of the nozzle rows to the plane perpendicular to the transport direction, but additionally to influence the height difference h. Analogously to FIG. 1 b, for this purpose, a corresponding control unit, for example a computer, can be in communication with one or more servo drives per pressure module and effect a corresponding control.

Figures 2b and 2c show embodiments of ink drop distributions on the printed surface of a container as may be produced with the printheads of Figure 2a.

FIG. 2 b shows a container with the printed image 250, wherein a cutout 251 is shown in a schematically enlarged form. Between two sets of ink droplets 21 1 and 212, which were applied to the container by the same print head, another, slightly offset row of ink drops 221 can be seen. This was applied by the second printhead.

In the embodiment shown in FIG. 2b, the print heads 201 and 202 emit ink droplets of the same size, which for example all have a diameter of 10 to 50 μm.

Alternatively, in the embodiment according to FIG. 2 c, a section 252 of a print image 250 or a print layer 250 is also shown on the surface of a container 130. Here, however, the sizes of the ink drops of the different print heads are different. While the ink drops of the ink droplet rows 21 1, 212 have the same diameter (for example, 50 μm) and were applied with the same print head, the ink droplets of the ink droplet row 221 have a smaller diameter and are additionally in the gaps between the individual ink droplets of the ink droplet rows 21 1 and 212 arranged. The size of these drops of ink can be for example only 10 μηι.

Preferably, the ink drops of the ink drop row 221 are applied to the surface of the container such that the connecting lines of the center of such ink drop with the centers of the directly adjacent ink droplets from the ink droplet rows 21 1 and 212 form an angle of exactly 60 °, so that the ink droplet of the ink droplet row 221 are accurately positioned in the gap between the ink drops of the ink droplet row 21 1 and the ink droplets of the ink droplet row 212.

Basically, the previously described and subsequent examples of the size of the ink droplets are not restrictive. Thus, the ink drops can basically have a size of 10 to 50 μm. In addition, they can have a volume under normal conditions (normal temperature and normal pressure) of 3 to 30 .mu.l and on the surface of the container, the centers of the ink droplets may have a distance from each other, for example 15-20 μηη, preferably 17.5 μηη. These statements also apply to the descriptions of the subsequent embodiments.

FIG. 3 shows a further embodiment in which likewise two printheads 301 and 302 are arranged one after the other in the direction of transport of the containers 130, so that the container 130 passes through these in succession during transport in the direction 132. In this embodiment, the rows of nozzles are arranged so that they parallel to the surface normal of the transport plane, here denoted by ni run, however, as also shown in Fig. 3, the printheads spaced in the direction of the surface normal η-ι, so that two to each other corresponding nozzles of the two print heads (for example, the respective first nozzle of the nozzle row), a distance h in the direction of the surface normal ni, which is smaller than the distance between two immediately adjacent nozzles of a nozzle row of the print head. Preferably, this distance is exactly half as large as the distance between two adjacent nozzles of a row of nozzles, so that the ink droplets, which are discharged from the second printing head 302 in the transport direction of the container 130, get into the gaps between the ink droplets of the first print head 301 exactly.

Thus, the ink drop density can be doubled in principle. In particular, printheads with a dpi number in the direction of the surface normal ni of 720 dpi can be used here, so that the total density can be increased to 1440 dpi. Again, an adjusting device not shown may be provided, which is for example in the form of one or more servomotors and the distance h of the print heads can be adjusted to each other by either only one or both printheads are moved.

While the above description has been made of general inks, implementations using UV-curable inks are preferred. These are commonly used inks for printing on containers. These harden when irradiated with UV light from suitable sources and have very good adhesion properties with respect to PET. Since the present invention can also be used in particular in connection with PET-based containers, such good results can be achieved.

The measurement of the parameters given for the ink droplets, in particular droplet size, volume, diameter, contact angle on the surface of the container can also be carried out with a drop shape analyzer DSA30 Micro available from KRÜSS.

For this purpose, a test body can be equipped with a transparent PET film, which is for example 25-50μηΊ thick. The film may have the shape of a label and be fixed to the container, for example by means of adhesive strips.

The test body prepared in this way is then provided with a test print, wherein preferably only every fifth or every tenth printing nozzle of a print head is used, so that isolated ink drops on the test body or the film result. The film is then removed from the test body and analyzed with the Drop Shape Analyzer DSA30, which allows height, width, diameter and contact angle measurement.

In order to compensate for possible deviations in the context of the operating tolerance of the print heads during the measurement, such tests can be carried out several times, at least 30 times, preferably 300 times, and by subsequent application of a normal distribution or other statistical methods, the mean value of the respective relevant parameters for the ink drops and eventual Deviations (in particular standard deviations) are determined.

Alternatively to applying a film to a test container, a container made of PET may also be used, which is cut after printing and from which a printed piece is further used for measurement according to the method described above. Since pretreatment of the container and subsequent treatments of the printed container can also influence properties of the ink droplets, it is possible to use a test container which is pretreated in accordance with the intended production and after-printed and pre-measured / analyzed according to the desired production.

For the measurement of the volume of an ink drop can advantageously be done by weighing. In this case, a test substrate of known mass is equipped with, for example, 10,000 or 100,000 ink droplets, and the subsequently printed test substrate is then weighed. From the mass difference, the mass of the ink drops as a whole and thus the average mass of an ink droplet can be determined first. From this value, the volume of a single drop of ink can be calculated, for example, at room temperature and normal pressure using the known density of the ink drops.

Claims

claims

1 . Direct printing machine for applying a printing layer to containers (130), such as bottles in the beverage industry, comprising at least one printhead (101) comprising at least two rows of nozzles (1 1 1, 1 12) for dispensing drops of ink onto a surface of a container characterized in that the print head is oriented so that the nozzle rows with a plane (133) perpendicular to the transport direction (132) of the container enclose an angle greater than 0 °.

2. Direct printing machine according to claim 1, wherein a plane in which the rows of nozzles (1 1 1, 1 12) are arranged in the print head (101) is perpendicular to the transport plane.

The direct printing machine according to claim 1 or 2, wherein said print head (101) has a normal resolution of 1200dpi.

4. Direct printing machine according to claim 1 or 2, wherein the printing press two in the transport direction of the container successively arranged printheads (201, 202) which are offset from one another perpendicular to the transport plane and each having a normal resolution of 600dpi, both printheads at least two rows of nozzles and are aligned so that the rows of nozzles with the plane perpendicular to the transport direction of the container enclose an angle greater than 0 °.

5. direct printing machine according to claim 4, wherein the print heads (201, 202) are offset by a distance h to each other, which corresponds to half the distance between two adjacent nozzles of a row of nozzles in the direction of the surface normal of the transport plane.

6. direct printing machine according to one of claims 1 to 5, wherein the one or more printheads are designed for dispensing of ink drops with a diameter of 10 to 50μηι.

A direct printing machine according to claim 4 or 5, wherein one of the print heads (201, 202) is adapted to eject ink drops having a smaller diameter than the other print head.

8. direct printing machine for applying a printing layer on containers (130), such as bottles in the beverage industry, with two successively arranged in the transport direction of the container printheads (301, 302), each having at least two rows of nozzles, characterized in that the printheads perpendicular to the transport plane to a distance h are arranged offset from each other, which is smaller than the distance between two adjacent nozzles in a row of nozzles.

9. Direct printing machine according to claim 8, wherein the distance h is equal to half the distance between two adjacent nozzles in a row of nozzles.

A direct printing machine according to claim 8 or 9, wherein one of the print heads (301, 302) is adapted to eject ink drops having a smaller diameter than the other print head.

1 1. Direct printing machine according to one of claims 8 to 10, wherein the print heads (301, 302) have a normal resolution of 720 dpi and / or at least four rows of nozzles.

12. Direct printing machine according to one of claims 1 to 1 1, wherein each printhead (301, 302) is associated with an adjusting device which is adapted to change the relative position of the print head to the transport plane.

13. Direct printing method for applying a printing layer to a container (130), such as a bottle in the beverage processing industry, characterized in that the containers are transported in a direct printing machine according to one of claims 1 to 12 along a transport plane defining transport plane (131) and be provided with the print layer during transport.

14. direct printing method according to claim 13, wherein the ink drops applied to the container at normal temperature and normal pressure, a volume of 3-30pl and / or a diameter of 10 to 50μηι and / or a distance of the centers after application to the container of 15 to 20μη " ΐ, preferably have 17,5μηΊ.

15. Direct printing method according to 13 or 14, wherein the orientation of the print heads (101, 201, 202, 301, 302) is adjusted to the transport plane by means of an adjusting device to a predetermined value.