Specification

The present invention relates to a printing machine and to a method for printing workpieces.

The publication DE 10 2011 076 410 Al teaches a method for working surfaces of a machine element. A coating is applied on the surface with the PVD method. The surface itself is worked by a geometrically not defined cutting method in such a manner that an isotopic structure is obtained .

A method for working a coating of hard carbon is furthermore known from the publication DE 10 2006 010 916 Al . In it, brush-like or plate-like elements are used to smooth the surface .

The invention has the problem of indicating a printing machine and a corresponding method for printing workpieces with which machine and with which method workpieces can be effectively printed in the simplest manner possible even if these workpieces are provided with a coating which should prevent the adhering of any particles or which furthers an insufficient adhesion.

This and other problems are solved as regards the printing machine in accordance with the invention by the subject matter of the independent Claim 1 and as regards the printing method by the subject matter of the coordinate Claim 15, wherein advantageous further developments of the printing machine according to the invention are indicated in the dependent Claims 2 to 12.

Accordingly, the invention relates in particular to a printing machine for printing workpieces, wherein the printing machine comprises a pretreatment station for pretreating the surface of a workpiece to be printed and comprises a printing station connected in after the pretreating station. The pretreating station is designed to selectively structure the surface of the workpiece to be printed. The printing station comprises an inkjet printing unit in order to print in a contactless manner on at least selectable areas of the surface areas of the workpiece to be printed, which surface areas are selectively structured in the pretreatment station.

Advantages which can be achieved with the solution according to the invention are obvious: since in the case of the printing machine according to the invention a printing station with an inkjet printing unit is used, no fixed printing form is required for printing the workpieces. In other words, different information such as, for example, writings or variable graphics can be printed one after the other, wherein only one database needs to be used for this. Therefore, the inkjet technology used in the printing machine according to the invention makes it possible to economically operate the printing machine already starting with a lot size of one. The reason for this is the preparation of the printing data which takes place exclusively in a digital workflow. This saves the supposed expenses of the conventional printing methods which arise in particular on account of the manufacture of the printing plates required in them.

In addition, the problems and disadvantages which are unavoidable in the case of printing methods known from the prior art and based on inkjet technology no longer occur with the printing machine according to the invention and the printing method according to the invention. These disadvantages include in particular the strongly regulated formulations of the inks available in the inkjet printing method which are conditioned by the mechanical components of this technology such as, for example, the printing head and the color system. Therefore, it is not possible with traditional printing methods known from the prior art and based on the inkjet technology to print workpieces with a satisfactory result and a reliable process whose surface qualities do not further the adhesion of the printing ink to the substrate of the workpiece.

There are currently a few applications which cannot be realized in inkjet printing due to the previously described, limited chemical plurality of the printing inks available in inkjet technology. This can be traced back to the difficult wetting qualities of the workpieces since they frequently have special coatings in order to meet special qualities, wherein these special coatings, however, as a rule counteract the adhesion between the printing ink and the surface to be adhered to. In order to solve this problem, previous attempts known from the prior art provide pretreating the coating on the workpiece to be printed in such a manner that there is a wettability and an adhesion. The concept "pretreat" used here denotes different chemical, physical and mechanical methods for either removing the coating and/or applying an adhesion-promoting layer in order to ensure a necessary adhesion. However, the disadvantage of the previously used attempts is that the coatings which were problematic for the inkjet printing method could be removed or modified only over the entire surface.

With the solution according to the invention such as it is indicated in particular in the independent Claims 1 and 15, it is in particular possible to achieve an adhesion between the printing color (ink) applied by the inkjet printing unit and the workpiece without a coating present on the workpiece, in particular an anti-adhesion coating, having be completely removed or modified and therefore destroyed.

The invention provides to this end placing a pretreatment station in front of the printing station with the inkjet printing unit in order to selectively structure or process the areas/positions to be printed onto the surface of the workpiece.

In particular, the pretreatment station of the printing machine according to the invention is designed to structure selectable areas of the surface of the workpiece to be printed on, in particular in the micro- and nanometer range. The selectable areas of the surface of the workpiece to be printed which are structured in the pretreatment station are in particular precisely those areas of the surface of the workpiece which are subsequently printed in the printing station with the inkjet method.

In preferred embodiments of the solution according to the invention the pretreatment station comprises a unit for emitting high energy radiation. This is, for example, a laser unit, a unit for emitting UV radiation or a plasma unit. Moreover, it is advantageous to associated the unit for emitting high energy radiation with an appropriate focusing lens located downstream via which the selectable areas of the surface of the workpiece to be printed can be loaded with appropriate high energy radiation. The loading of the selected areas takes place in particular according to a previously determined or settable operating cycle by means of which the radiation time, the intensity of the high energy radiation and/or other radiation parameters such as, for example, a pulse frequency, etc. can be determined or set.

It is especially preferable if the pretreatment station comprises a laser unit which is designed to load selectable areas of the surface of the workpiece to be printed with laser light, preferably according to a previously determined or settable operating cycle.

The unique quality of the laser radiation is made use of here, namely, in particular its spatial coherency and the monochromaticity of the laser light. The spatial coherency of the laser radiation permits an extreme ability to focus the surface areas of the workpiece to be printed and which are to be selectively structured. The monochromaticity of the laser light makes possible - together with a changing of the wavelength - a selective and spatially localized stimulation of atoms or molecules of any coating present on the surface of the workpiece to be printed and which coating is to be selectively removed or structured in the pretreatment station. With the aid of pulsed laser radiation or of continuous laser beams which are moved relative to the workpiece to be pretreated, a localization in time of the interactive processes can be achieved.

In particular, it is provided in embodiments of the present invention that an ablation of the coating provided on the workpiece to be printed takes place with the aid of the laser unit at least in areas in the pretreatment station. Here the coating is selectively stoichiometrically removed preferably under the effect of short, intensive laser pulses, wherein the interaction time is preferably selected to be so short that material of the coating cannot segregate into individual components . It should be taken into account here that it is not absolutely required in the pretreatment station to selectively and completely remove the coating on the workpiece to be printed and which coating is problematic and disadvantageous for the inkjet printing process. It is frequently already sufficient, as a function of the coating type, to modify, in particular to structure the coating selectively in the areas of the coating into which the printing ink is to be subsequently applied in the printing station with the aid of the inkjet printing unit .

According to embodiments of the present invention the printing machine comprises a positioning system for positioning a workpiece to be pretreated in the pretreatment station and for the subsequent positioning in the printing station of the workpiece which was pretreated in the pretreatment station and is to be printed in the printing station. The positioning system is designed in such a manner that the workpiece pretreated in the pretreatment station and to be printed in the printing station is positioned in the printing station in such a manner that that a printing image to be generated by the inkjet printing unit is transferred exactly onto the surface area of the workpiece which was selectively structured in the pretreatment station.

There is the opportunity here to design the positioning system as an absolute positioning system, that is, as a positioning system which is designed to position the workpiece in the pretreatment station and in the printing station in a coinciding manner. A positioning system is cited as an example for such an absolute positioning system which comprises at least one linear drive via which the workpiece can be transferred along a linear axis from the pretreatment station to the printing station of the printing machine.

It is basically advantageous if an optical monitoring unit (especially a camera system) is associated with the positioning system ( whether it is designed as an absolute positioning system or as a relative positioning system) in order to monitor and correct, if necessary, a local position of the workpiece in the pretreatment station, in the printing station and/or between the pretreatment station and the printing station.

It is mentioned as regards the inkjet printing unit that in principle inkjet systems known from the prior art can be used. The inkjet printing unit can have one print head but preferably several, i.e., at least two print heads are used.

In particular, the inkjet printing unit is designed to apply optionally and/or selectively different inks onto surface areas structured in the pretreatment station. The concept "selective application of ink" denotes an application of ink onto certain previously determined or settable structured areas of the workpiece.

It should be emphasized in this connection that the inkjet printing unit is not only designed to apply colored inks or pigmented inks onto surface areas structured in the pretreatment station but also functional liquids. In this manner, for example, electronic structural components can be imprinted onto the workpiece in order to produce a printed electronics system.

Finally, it is advantageous if the printing machine furthermore comprises a posttreatment station connected in downstream from the printing station in order to subsequently treat the workpiece selectively printed in the printing machine. The posttreatment station is designed here, for example, to carry out an appropriate heat treatment in order to dry or activate the color/ink/liquid previously applied by the inkjet printing unit.

The invention relates not only to a printing machine of the previously described type but also to a method for printing workpieces, wherein this method comprises in particular the following method steps:

(i) Making a workpiece to be printed available;

(ii) Supplying the workpiece to be printed to a pretreatment station in which the surface of the workpiece to be printed is selectively structured; and

(iii) Supplying the workpiece pretreated in the pretreatment station to a printing station in which the surface area of the workpiece to be printed, which surface was selectively structured in the pretreatment station, or at least selected areas of the workpiece are printed without contact with the aid of an inkjet printing unit.

Embodiments of the present invention are described in detail in the following using the attached drawings.

In the drawings: FIG. 1 schematically shows a first exemplary embodiment of the printing machine according to the invention in a side view;

FIG. 2 schematically shows a top view of a second embodiment of the printing machine according to the invention; and

FIG.3 schematically shows a side view of another exemplary embodiment of the printing machine according to the invention.

The invention solves the initially described problem by the implementing of a special pretreatment which occurs in traditional applications known from the prior art. The invention provides to this end the selective working of positions of a workpiece which are to be printed in a first step with the aid, for example, of a laser unit. The laser unit is controlled in particular with a defined intensity so that a problematic coating on the workpiece is selectively removed. This makes it possible for the printing color to be directly connected to the substrate of the workpiece without a barrier layer preventing the adhesion of the printing color.

In detail, it is provided according to the exemplary embodiments shown in the drawings that a coated workpiece 7 is selectively worked in a laser unit in such a manner that only the positions of the workpiece 7 to be printed are worked by the laser beam. The laser intensity is preferably selected as a function of the coating of the workpiece 7, wherein decisive influences are, among others, the pigmenting/color and layer thickness of the coating. A defined ablation of the coating is ensured by a correct parameterization. According to the exemplary embodiments schematically shown in the drawings, the workpiece 7 is worked in a printing station 2 in a second step, wherein in particular an exact positioning is necessary. It should be ensured in particular that the layer previously ablated in the pretreatment station 1 by the laser unit is located coinciding with the printing image in order to ensure the wetting of the substrate of the workpiece 7 and of the printing color. As is shown in the drawings, the exemplary embodiments of the printing machine 10 according to the invention comprise the already cited pretreatment station 1 with the laser unit and the also already cited printing station 2, wherein an inkjet printing unit 3a with at least one print head 3b is associated with the printing station 2 in order to print in a contactless manner at least selectable areas of the surface of the workpiece 7 to be printed, which surface was selectively structured in the pretreatment station 1. In addition, a positioning system 5 is used in the exemplary embodiments of the printing machine 10 according to the invention and schematically shown in the drawings .

The positioning system 5 is constructed especially as an absolute positioning system 5 which is designed to position the workpiece 7 in the pretreatment station 1 and in the printing station 2 in a coinciding manner. According to the exemplary embodiments of the printing machine 10 according to the invention and which are schematically shown in the drawings, the positioning system 5 comprises at least one linear drive by which a workpiece 7 held by a workpiece carrier can be transferred along a linear axis L from the pretreatment station 1 to the printing station 2.

Furthermore, the positioning system 5 is preferably associated with an optical monitoring unit in order to control and, if necessary, correct the local position of the workpiece 7 in the pretreatment station 1, in the printing station 2 and/or between the pretreatment station 1 and the printing station 2.

In the embodiment of the printing machine 10 according to the invention and schematically shown in FIG. 1 the positioning system 5 has a linear axis L as linear drive and/or transport drive. This axis ensure an absolute positioning accuracy. A linear carriage 6 with a workpiece carrier and/or a workpiece receptacle is provided on the linear axis L. The workpiece 7 to be printed is introduced onto this workpiece carrier or into this workpiece receptacle.

The supplying of the workpiece carrier or of the workpiece receptacle takes place in position 1 (POS1) . The linear carriage 6 runs from left to right.

At first, the linear carriage 6 with the workpiece 7 to be worked and/or to be printed runs through the pretreatment station 1 with the laser unit. A defined layer thickness of the workpiece 7 is removed by the laser unit of the pretreatment station 1. The pattern to be removed is digitally supplied to the laser unit.

Depending on the particular application, the pattern to be removed can exactly correspond to the print image to be applied in the printing station 2. However, it is also conceivable as an alternative to the above if the pattern to be removed is dimensioned to be somewhat larger -in comparison to the size of the print image to be applied - in order to make possible a kerning of the printed image. However, the shape of the pattern to be removed should correspond at least substantially to the shape of the print image to be applied in the printing station 2. The workpiece 7 subsequently runs through the printing station 2 with the inkjet printing unit 3a. The inkjet printing unit 3a of the printing station 2 is provided with as many print heads 3b as desired. The individual print heads 3b successively spray the printing ink onto the surface areas of the workpiece 7 which were already processed in the pretreatment station 1 with the laser unit .

The printing inks sprayed by the printing heads 3b of the inkjet printing unit 3a do not necessarily have to be color inks or pigment inks; it is also conceivable that adhesion promotors and/or functional liquid/colors are applied from at least one printing head 3b.

In order to apply the print image into the areas of the workpiece 7 which are selectively structured or processed in the pretreatment station 1, the input of the image to be printed is preferably inputted digitally into the printing station.

In a following step the linear carriage 6 moves through a posttreatment station 4 in order to harden or dry the printing ink in the embodiment of the printing machine 10 according to the invention schematically shown in FIG. 1.

The removal of the printed workpiece 7 can then takes place in the second position (POS2) in in a following process step wherein the linear carriage 6 runs from right to left out of its initial position (POS1) . If the printed workpiece 7 was not unloaded in the second position, this can now take place in the first position.

FIG. 2 and 3 schematically show other constructive embodiments of the process according to the invention. Here, a linear carriage 6 with the pretreatment station 1 and the printing station 2 moves relative to a stationary workpiece 7, for example in the embodiment according to FIG. 2.

The embodiment according to FIG. 3 provides that the linear axis L is interrupted between the pretreatment station 1 and the posttreatment station so that the workpiece 7 can be removed already after the pretreatment station 1. The linear carriage 6 or the workpiece receptacle can be optionally provided with the workpiece 7 directly in front of an optical monitoring unit 8 or directly in front of the printing station 2.

According to the invention laser light is preferably used for the pretreatment since it makes possible an especially selective pretreatment with a high edge sharpness without negatively influencing surrounding areas .

The invention is not limited to the exemplary embodiments shown in the drawings but rather results from an overall view of all features and aspects disclosed herein. In particular, it is conceivable that the surface of the workpiece 7 to be printed is constructed at least in areas as a 3-D surface.

The solution according to the invention is especially suited for printing workpieces 7 which are provided with a coating which should prevent the adhering of any particles or which furthers an insufficient adhesion. Examples for this are high-grade steel sheets with anti- fingerprint coating. This application is frequently used in the area of whiteware .

Any type of work pieces can be considered onto which a functional coating/lacquer (for example, anti-graffiti lacquer, anti-perspiration coating) is applied but which is additionally be printed on. The automobile sector is focused on here.

Furthermore, applications are conceivable which have become known in the area of a functional coating. It would be possible to process full-surface coatings with the laser not as a function of a graphic function but rather in order to realize patterns which make possible another function and to coat them afterwards with a functional ink, for example, a conductive ink or an isolating ink.