EP2183057A2

EP2183057A2 - Method and apparatus for the application of plastics coatings

Info

Publication number: EP2183057A2
Application number: EP08785039A
Authority: EP
Inventors: Dirk Schlatterbeck; Andre F. Ceppi
Original assignee: Schmid Rhyner AG
Current assignee: Actega Schmid Rhyner AG
Priority date: 2007-07-24
Filing date: 2008-07-24
Publication date: 2010-05-12
Anticipated expiration: 2028-07-24
Also published as: CN101827658A; WO2009012996A2; EP2183057B1; ES2385119T3; RU2010106649A; US20100221449A1; RU2481959C2; CN101827658B; WO2009012996A3; DE102007034877A1

Abstract

The invention relates to an apparatus for the application of coatings to surfaces of substrates in the form of paper, paperboard, or plastics foils, preferably for the finishing of print products. The apparatus encompasses a coating unit for the application of coating material in fluid form to the substrate surface, and equipment for smoothing of the film while it is still fluid after it has been applied by means of the coating unit to the substrate surface, where the equipment encompasses equipment for generating a gas stream orientated onto the substrate surface coated with the film, where the gas stream smooths the film with at least partial elimination of undesired structures in the film surface, e.g. depressions, elevations and craters, prior to the hardening of the coating material.

Description

Method and device for applying plastic coatings

description

The invention generally relates to the application of coatings, such as paints. In particular, the invention relates to devices and measures for the targeted influencing of the surface structure of the still fluid film such. the smoothing of coated coating films. By smoothing is meant in particular the elimination of undesirable structures or disturbances of the coating surface, which will be explained in more detail below.

Due to the application process for lacquers or the substrate to be coated with a lacquer or coating material, applied coating films may have undesirable structures or defects. Such structures or perturbations may include, but are not limited to, roll structures, roll transfer longitudinal structures, longitudinal streaks of uneven application, or transfer coating coating defects.

Another cause of disruptive surface structures may be the substrate. The surface finish of the substrate can cause structures or perturbations on the coating surface. For example, by not wetted wells in the substrate, craters on the Coating surface arise. This may be the case in particular, but not exclusively in the case of contactless application of the coating material, in particular in the case of non-contact application by nozzles.

From the state of the art, the smoothing of coatings by doctor blade, air knife or air knife or smooth rollers is well known. Here, however, there is the problem that such methods can not be applied to laterally structured lacquer layers in which, for example, parts of the surface coating are to be recessed (partial coating). The treatment with a squeegee or a roller leads, in addition to a smoothing of the surface, to the fact that the still-liquid coating layer also spreads on the surface and also reaches areas which are to be recessed from the coating.

From DE 44 43 261 Al a method for smoothing layers is further known, in which applied to a pad liquid or dough-like layers are smoothed by means of ultrasound. For this purpose, an ultrasonic transducer is provided, which transmits to the layer. The substrate with the layer is brought into contact with the ultrasonic vibrator from the rear for effective transmission of the ultrasonic vibrations, wherein the substrate is curved or bent over the ultrasonic vibrator.

Smoothing of a coated film by ultrasound is also described in JP 59225772 A. Here, the coating is applied with roller application. The substrate passes over a roller, which is arranged opposite the ultrasonic oscillator. The ultrasound is touchless over the air on the layer side coupled. Again, similar to the

DE 44 43 261 Al a curvature of the substrate at the place of

Ultrasound application performed.

However, depending on the substrate, this may be undesirable or impractical, for example if the substrate is too stiff or if damage is to be expected. Since in both cases described above also the direction of movement of the substrate in the respective device for selectively influencing the surface of the fluid

As such coating material is changed, such a design can be difficult to integrate into existing equipment such as printing presses or printing finishing equipment.

The object of the invention is to eliminate or smooth surface disturbances occurring during the coating application in order to produce a smooth surface regardless of the applied application method and the substrates used.

Also, the course of coating systems should be reduced by means of the invention.

Accordingly, the invention provides a device and a

A method for applying coatings on surfaces of substrates, wherein a coating unit for applying coating material in fluid form to the substrate surface, and a conveyor is used to the substrate surface relative to

Coating unit along a running direction to move past the coating unit. For this purpose, the substrate is preferably moved past a stationary coating unit. It is also conceivable to hold the substrate and move the coating unit.

Furthermore, a device for selectively influencing the coating surface, such as e.g. the smoothing of the still applied to the substrate surface by means of the coating unit, still provided fluid film. This device includes means for generating a gas stream which is directed to the film-coated substrate surface and smoothes the film, at least partially eliminating spurious structures of the film surface such as pits, bumps and craters prior to curing of the coating material. The smoothing is carried out accordingly by the gas flow contactless.

It is surprising here that it is possible to achieve a very effective removal of disruptive structures in the film surface with the gas stream without the coating material being transported over long distances along the surface. The transport of the coating material through the gas stream is preferably kept smaller than 1 mm, more preferably smaller than 0.25 mm along the surface. The contours of the edges of coated areas remain particularly preferably unaffected by the smoothing. This means that the smoothing does not introduce coating material into uncoated areas.

The invention is particularly in connection with a non-contact coating order by a

Nozzle arrangement suitable. In this regard, furthermore, a computer-aided control device for controlling the coating nozzles is advantageous, so that laterally patterned by appropriate control of the nozzles Coatings, here in particular to produce a recess of areas of the substrate surface. Particularly preferred is a drop-on-demand, or demand droplet coating unit with nozzles for dispensing each individual droplets of the coating material in response to control signals used. The nozzles of the coating unit are preferably arranged in at least one row transversely to the direction of travel.

Especially in a non-contact process, such as coating by a drop-on-demand or ink jet printing unit, many, especially porous substrates such as paper or cardboard, have the coating forming a film in which over the surface distributed small craters or pits, or Pinholes are present, which disturb the desired appearance. Thus, these craters or pinholes are clearly visible on both glossy and matt coatings on printed matter. Even with coated paper or cardboard, these can

Wells occur. By means of the invention, these craters can be at least significantly reduced in their number by applying the not yet solidified paint or coating film in a very simple manner.

In order to achieve a rapid application of the coating material by means of a non-contact coating, in particular by means of drop-on-demand technology, it is further particularly preferred that the nozzles of the coating unit are arranged in at least one row, which extends transversely to the direction and the processable substrate width spans at least three quarters perpendicular to the direction of rotation, wherein the nozzles are preferably arranged rigidly in the direction transverse to the direction. The nozzles thus cover the entire area of the substrate to be coated only by movement along one direction, namely the direction of travel.

Also in other coating methods, such as

Roller application or screen printing, however, can also lead to undesirable structures of the surface which, inter alia, arise due to material splitting when the roller or screen separates from the substrate surface. In a development of the invention, the coating unit can therefore also comprise a device for roller application and / or a screen printing device. In the case of a coating with roller application is particularly thought of flexographic printing, gravure and simple, full-surface roller painting. The flexo printing process rolls with a

Printing form coated form roller on the substrate and selectively applies the coating material to the substrate surface.

In gravure printing, the wells of a selectively engraved cylinder are filled with coating material or ink. The cylinder is brought into direct contact with the paper, with the coating material or the ink being transferred to the paper. In screen printing, through a partially permeable fabric with a squeegee, the ink or coating material at the open locations is transferred through the fabric to the paper. All of the above-mentioned methods, except for the full surface roll coating, as well as the drop-on-demand technique, can also be used for the laterally structured coating with the exception of regions of the substrate surface. It turns out that a uniform gas flow is disadvantageous in terms of the smoothing effect. Thus, with a slit nozzle, which sweeps over the surface with a uniform gas flow, only a comparatively poor smoothing effect could be generated. Rather, it is favorable to guide a gas flow over the surface, which varies with respect to the direction and / or flow velocity for the respective points of the surface to be smoothed. Measures to generate such gas flow are outlined below.

In the simplest case, individual nozzles are used in a row or grid arrangement. It is advantageous if the device for generating a gas stream comprises at least one row of gas nozzles which extends transversely to the direction of travel.

In order to produce gas streams at a suitable speed, pre-pressures on the nozzle (s) in the range from at least 1 bar, preferably at least 0.5 bar or at least 0.1 bar, have proved suitable. With larger nozzle diameters, higher pressures, for example up to 2 bar, 4 bar, 6 bar or 12 bar, possibly even 20 bar, can be used.

Also, the gas flows may be adjusted by suitable nozzle shapes and nozzle sizes for the purpose of the invention. Preferably, the nozzles of a smoothing device have a diameter of at least 0.05 millimeters to at most 10 millimeters, more preferably between 0.1 to 5 millimeters, particularly preferably between 0.2 and 2 millimeters or between 0.5 and 1 millimeters. One way to improve the smoothing effect is to provide a nozzle assembly that generates air streams that strike the substrate surface under different spatial directions and / or have gradients in the flow velocity in multiple directions along the surface.

Another measure is the use of nozzles that generate a turbulent gas flow. For this purpose, turbulators can be provided, for example, in the nozzle or nozzles, which swirl the gas stream.

Also, the or the gas streams can be acted upon by ultrasonic waves.

Furthermore, it may be favorable if, during the deflection of the gas flow through the substrate along the surface thereof, a preferred direction is present. For this purpose, in addition to vertically impinging gas streams or the gas streams preferably at an oblique angle to the

Substrate surface to be addressed. The angle of the gas flow is for this purpose between an angle greater than 0 ° and up to 90 °, preferably in the range of 10 ° or 20 ° to 80 °, preferably in the range of 30 ° to 70 °, particularly preferably in the range of 40 ° to 60 ° measured from the solder to the surface.

Yet another measure is to pulse the gas stream (s) instead of evenly flowing out of the nozzle (s).

Furthermore, it is also possible to provide a device for screening the gas stream or streams over in each case at least one subregion of the substrate surface. This way you can with one or more gas streams, each having flow gradients in multiple directions along the surface, yet sweeping the entire surface to be smoothed.

It has been found that crater-like depressions, depending on the nature of the substrate, in particular occur at small layer thicknesses. The application of the invention is therefore particularly suitable for thinner coating films. In a further development of the invention, it is provided that a film with a layer thickness less than 100 microns, preferably less than 50 microns, more preferably less than 30 microns is applied and then smoothed before solidification. Even very thin coatings with layer thicknesses of less than 20 microns, even smaller than 10 microns layer thickness can be smoothed with elimination of wells and / or openings. Even coating surfaces of films with layer thicknesses of less than 5 micrometers can be positively influenced by the method according to the invention.

As a purposeful influencing of the surface structure, the smoothing of a film of still fluid coating material may apply, in which by means of the gas flow crater-like depressions or structures which are transferred from the substrate or by the coating process are removed or closed. At the same time, new, desired as desired structures can be generated, for example, to give the cured film a special look and / or haptic appearance. For this purpose, the gas flow in the angle of incidence and flow rate is adjusted so that smaller depressions not only smoothed, but at the same time additional by local displacement and / or redeployment of the coating material Structures are created. Such selectively generated structures can be, among other things, crimping structures, undulations, depressions, ribs or grooves.

In a particularly preferred embodiment of the invention, the film after the targeted influencing of the surface, e.g. the smoothing by means of a separate curing or drying device for curing or drying of the coating material in a solid form. This device is arranged downstream in the direction of the device for influencing the surface, so that the substrate surface passes first the coating unit, then the device for influencing the surface and then the curing device. Particularly suitable in this case is the application of UV-curable coatings, in particular UV overprint varnish and curing of the coating material by irradiation of UV light after smoothing. Accordingly, in this embodiment of the invention, the curing device comprises a light source, preferably a UV light source.

Other alternative or additional possibilities of curing after the targeted influence consist in the heating in an oven and / or with a radiant heater and / or by means of a microwave source. For curing under heating, for example, known thermally crosslinkable or curable systems can be used. Thermally crosslinkable coatings, for example, as well as UV-crosslinkable systems can be based on acrylates.

In order to be able to effect an effective influencing of the surface, for example a smoothing, it is furthermore favorable to observe a certain range in the dynamic viscosity. Is the viscosity of the applied coating material too small, it may quickly cause by the gas flow to a blowing and undesirable redistribution and bleeding of the film at the edges. On the other hand, if the dynamic viscosity is too high, unwanted structures of the film, such as, in particular, crater-like depressions, may not be smoothed at a desirable rate. In an advantageous embodiment of the invention, a coating material is applied to it, which at the processing temperature has a dynamic viscosity of at least 10 seconds and at most 1000 seconds, preferably at most 500 seconds, more preferably at most 200 seconds, possibly even at most 100 seconds, measured as the flow time of a volume of 100 cm ³ from a DIN cup with a 4 mm diameter outlet nozzle. The adjustment of the viscosity can also be done by adjusting the temperature, so that even highly viscous or low-viscosity coating materials can be applied and smoothed.

The targeted influencing of the surface with a gas stream, such as in particular an air stream represents the particularly preferred, because very effective and simple way of influencing the surface. In addition, however, other methods have also been found, which also a simple and effective influencing of the Enable surface. Thus, according to a further, alternative or additional embodiment of the invention, a device for applying coatings to surfaces of substrates is provided, which likewise comprises a coating unit for applying coating material in fluid form, as well as a conveying device, to the substrate surface move relative to the coating unit along a running direction on the coating unit, preferably in turn by moving the substrate to a fixed coating unit.

A device is provided for selectively influencing the coating surface, in particular for smoothing the still fluid film applied to the substrate surface by means of the coating unit, wherein the device for selectively influencing the surface of the fluid coating material comprises an arrangement of needles which, for influencing the surface, in particular for smoothing, touch the surface. In particular, the needles can pierce into the film. The piercing of the needles causes a localized movement of the liquid coating material which results in the compensation of surface irregularities present in the puncture site or in areas near the puncture site.

In doing so, use is made of the interfacial tension between the liquid and the needle, which leads to adhesion of the liquid coating material to the needles. , When pulling out the needle from the material, the material accumulated in this way on the needle runs again. In particular, crater-like recesses, as occur with certain substrate materials and non-contact coating, can also be closed. Since only a punctual contact with the film takes place with the needles, at most little coating material is distributed by the repeated piercing and contact of needles with uncoated areas of the substrate surface. The problems with smoothing with a Roller or a squeegee, are accordingly avoided as well as in a smoothing with a gas stream.

With regard to the formation of the coating unit and the curing unit, the device may be designed in the same way as the device described above. In addition to a non-contact coating so may alternatively or additionally, for example, a device for roller application, such as for the simple full-surface, flexo or gravure job, or be provided for screen printing.

A particularly preferred embodiment of the device for selectively influencing the surface of the fluid coating material provides a needle provided

Roller or a needled tape before, which roll on the film. The rolling avoids that the needle tips move along the film and then in turn insert unwanted structures in the form of grooves in the film.

The needles can generally also be controlled with a control so that they selectively touch the film selectively or in a predetermined pattern.

In order to further improve the effect of the device for selectively influencing the surface of the fluid coating material, according to a further development of the invention, an ultrasonic oscillator can be provided, which is coupled to the needles. In this way, the needles are subjected to ultrasonic vibrations and transmit them via the needle tips in the film. The needles can be selectively controlled by electromechanical devices such as piezo control or a suitable control via compressed air to z. B. only to touch areas on which coating material has been applied. The piezo or compressed air control can also be used, for example, to generate a vertical or lateral movement of the needles in order to expand or support the smoothing effect. Furthermore, with partial coating, this movement can at least reduce the smearing of the coating film.

According to yet another alternative or additional embodiment of the invention, a targeted influencing of the surface of the film by means of a targeted, non-contact heating by the means for selectively influencing the surface of the fluid coating material is provided.

Generally, in the method according to the invention for

Application of coatings on surfaces of substrates accordingly,

coated with a coating unit coating material in fluid form, while -with a conveyor, the substrate surface is moved relative to the coating unit along a running direction of the coating unit, preferably by moving the substrate to a fixed coating unit, which on the substrate surface by means of

Coating unit applied, still fluid film is specifically influenced before its solidification, wherein for influencing the coating surface at least one of the measures is carried out: a gas stream is generated and directed onto the substrate surface coated with the film,

- The film surface is touched by means of an array of needles, - The film is heated without contact.

The heating may be by an oven, a radiation source (e.g., an IR emitter), preferably a laser, and / or by means for generating electromagnetic radiation of other wavelengths, preferably microwaves.

Also, the individual smoothing methods can be combined with each other. Thus, inter alia, a heating device for heating the at least one gas stream can be provided, so that a smoothing takes place with a heated gas stream. Temperatures of the gas stream in the range from 0 to 500 ^° C., preferably in the range from 100 to 400 ^° C., particularly preferably in the range from 150 to 300 ^° C., are suitable for this purpose

Surface with one or more gas streams carried out a separate heating, such as by means of a suitable radiation source or by microwaves.

Is a source for generating electromagnetic

Radiation used for local heating, a means for scanning the beam or beams over the substrate surface, or at least a portion of which may be provided. In this way, an energetic, localized beam or multiple such beams can sweep the entire surface to be smoothed.

In principle, coated surfaces of any material and any geometry can target the targeted Influencing the still liquid coating surface preferably be smoothing by the inventive device.

The device can be designed in particular for coating paper, cardboard or plastic films. Thought is particularly to the coating of printed products, preferably for their refinement. Especially with substrates such as paper or cardboard, which have a certain porosity, otherwise often the problem of occurring in the coating crater-like depressions, especially here in conjunction with a contract of the coating material in the drop-on-demand method or another non-contact coating process.

In general, it is also intended to use the device according to the invention in a printing machine, such as an offset, flexo, gravure or screen printing machine. In this way, printed products can be printed in a single

Plant then printed and finished. It is also intended to retrofit a coating device, such as a printing machine with coating unit, or a coating device, with a device for selectively influencing the surface of the fluid coating material, so that a coating device according to the invention is obtained. Likewise, a printing press-regardless of the printing process used-can be retrofitted with a coating unit which contains a device according to the invention for selectively influencing the coating surface. The invention will be explained in more detail by means of embodiments and with reference to the accompanying drawings. In this case, the same reference numerals designate the same or similar parts. Show it:

Fig. 1 is a schematic view of an apparatus for

Finishing of printed products with

Coating films

Fig. 2 is a view of a sheet-fed offset printing machine with a coating unit for applying and

Smoothing of paint,

Fig. 3 is a schematic view of another

Embodiment of a coating device,

Fig. 4 parts of a device for selectively influencing surfaces of liquid

Coating films

5A and 5B lattice representations of a paint film before and after the targeted influencing of the surface,

Fig. 6 shows a further embodiment of a device for selectively influencing coating surfaces, with which a smoothing by local heating of the

Coating material takes place,

Fig. 7 is an electron micrograph of a crater-like depression in one applied paint film before the targeted influencing with the inventive method,

Fig. 8 recording of crater-like depressions as in

7 is shown with white light microscopy,

Fig. 9 section through one of the two crater-like

Depressions from FIG. 8.

In Fig. 1, an embodiment of a device 1 for the processing of printed products is shown.

For this purpose, a lacquer coating is applied to the surface 21 of a preferably printed paper or cardboard substrate 2 by means of the device 1. For this purpose, a conveying device is provided, which in the illustrated example comprises rollers 11, on which the substrate 2 with the side 22 resting on a coating unit 5 in the form of a coating unit is moved along a running direction 13. The coating unit 5 carries a film 7 initially still fluid coating material in the form of a UV-curable coating controlled by a computer 15.

The coating unit 5 operates on the drop-on-demand principle, the nozzles 51 of the coating unit 5, in response to control signals from the computer 15, hurling individual drops onto the substrate surface 21 to be coated, the drops forming a preferably closed film. The nozzles 51 are arranged in a row to the running direction, wherein the row spans at least 3/4 of the width, preferably the entire width of the substrate 2. To high To be able to achieve coating speeds, it is preferable to use an arrangement of nozzles 51 which, during the coating, are held rigidly in the direction transverse to the running direction. Unlike shown in Fig. 1, a plurality of rows of nozzles arranged one behind the other in the running direction can also be provided.

Downstream in the direction of the coating unit, a device for selectively influencing the coating surface, e.g. provided for smoothing the surface 9. This comprises a series of nozzles 91 directed towards the substrate surface. The row of nozzles 91, as well as the at least one row of coating nozzles 51, likewise runs transversely to the direction of rotation 13.

The nozzles 91 of this device 9 are connected to at least one source of compressed air, so that escape from the nozzles 91 air flows 93, which hit the substrate surface 21, and the film applied thereto. By virtue of the preferably turbulent air streams, a slight horizontal shift in the film 7 is effected, so that crater-like recesses 71 are formed which are formed during the drop-on-demand coating of the porous paper or cardboard substrate 2. In order to further improve the smoothing effect, it may be useful to pulse and / or heat the air streams and / or provide one or more ultrasonic vibrators in the gas supply to the nozzles 91 to apply ultrasonic waves to the air streams 93.

The smoothing effect of the air currents is also improved by the axes of the nozzles, and accordingly the exiting air currents obliquely below directed at an angle 92 to the solder on the side 21 of the substrate 2. The angle 92 is between 0 ° and 90 °, preferably between 20 ° to 80 °, in particular between 30 ° to 70 °, particularly preferably between 40 ° to 60 °.

An improvement of the smoothing effect is already achieved by having a plurality of discrete gas streams through the plurality of nozzles and / or gradients in the flow velocity in several directions along the surface instead of a single gas stream, such as can be generated with a slot nozzle.

After the film 7 has been smoothed by means of the air streams 91 of the device 9, the film is cured. For this purpose, a curing device for curing the coating material is provided, which is arranged downstream in the running direction of the device 9. In the illustrated example, the curing device comprises a UV light source 10. This light source emits UV light with a spectrum which is suitable for the curing reaction in combination with the photoinitiator used.

By the UV light of the UV light source 10, a radical polymerization of the hitherto still fluid UV varnish is set in motion. Suitable examples are UV-curing acrylate-based coatings.

The device 1 can not only a device for

Finishing of printed products. According to a variant, the printed products can also be produced with the device, with the nozzles 51 of the coating unit 5 printing inks as a coating be applied, the surface of which is then smoothed with the device 9. Also in this case UV curing inks can be used, which are then solidified by the UV light of the UV light source 10.

FIG. 2 shows a further embodiment in which a device 1 according to the invention is integrated in an offset printing machine 30. The offset printing machine 30 is formed in the illustrated example as a sheet-fed offset printing machine for printing substrates 2 in the form of individual paper or cardboard sheets. Likewise, however, a web offset printing press can also be used. The printing press 30 comprises an inking unit 31, with which ink 32 is applied to the plate cylinder 38 via a series of rollers 33. On the plate cylinder 38, the pressure plate is attached. A dampening unit 34 applies water 35 via a further arrangement of rollers 36 on the printing plate on the plate cylinder 38, wherein the ink is displaced by the non-illustrated points of the printing plate. From the plate cylinder 38, the printed image is transferred to the printing cylinder 39 provided with a blanket. This then carries the ink, or the printed image on the pressed with a counter-pressure cylinder 37 against the printing cylinder

Substrates 2, which are conveyed along the direction 13 by the printing press 30. Downstream of the printing cylinder 39 in the direction of rotation 13, a coating device is arranged, as shown for example in FIG. The coating device 1 accordingly comprises a coating unit 5 for the structured application of coating material, a unit 9, with which the applied paint film is smoothed, and a UV light source 10 for curing the of the Coating unit 5 optionally structured coated film of a UV-curing paint. As a conveyor, the printing machine 30 itself serves. In addition, suitable, especially with the device 1 cooperating, or belonging to the device

Conveyors may be provided. In the example shown, a belt 110 running over rollers 11 is provided, on which the substrates 2 rest.

The printing press 30 can in particular also be retrofitted with a device 1. In the event that the printing machine itself is already designed alternatively or in addition to printing for the paint job, a device 9 according to the invention can also be retrofitted.

As in the example shown in FIG. 1, the device 9 may in particular again comprise an arrangement of nozzles for generating gas streams, with which the paint film is smoothed.

Instead of an offset printing machine, the device 1 or the device 9 in a corresponding manner in other printing machines, such as digital printing (inkjet, toner method), screen printing, flexographic or gravure printing and pad printing machines for printing and / or

Print finishing, or even a machine for roller or spray application of paints are installed.

FIG. 3 shows a further embodiment of a coating device 1.

Also in this example, the coating can be carried out with a paint film for producing structured paint films by means of a coating unit 5, which laterally structured films produced by the drop-on-demand method. As substrate 2, a continuous band is shown in the example shown here.

In contrast to the preceding examples, the device 9 here comprises a needled roller 94 instead of a nozzle arrangement. As the roller rolls off, the needles contact the film of the still fluid coating material. With suitable process parameters, this leads to an efficient smoothing of the film surface.

Fig. 4 shows a schematic view of an embodiment of a device 9, which the still fluid paint film according to the embodiments shown in Figs. 1 and 2 by on the

Substrate surface directed gas flows smooth. 4 shows a view along the running direction of the substrate 2. The device 9 comprises, as in the examples shown in FIGS. 1 and 2, a row of nozzles 91 which extends transversely to the running direction. The nozzles are also arranged at different angles to the normal of the substrate, so that gas streams are generated by the individual nozzles, which have different angles to the substrate 2. In addition, the device is, as indicated by the double arrow, moved back and forth transversely to the direction of the substrate 2, so that successively impinge the gas streams at different angles to a respective point of the film and the gas streams are rastered over the substrate surface. In this way a particularly effective smoothing is achieved. Of course, one after the other at different angles to a location of the substrate surface incident gas streams can be achieved with a different arrangement. Just to give you an example can be used, for example, also rotary axes precessing nozzles. It is therefore to be understood that the embodiment illustrated in FIG. 4 is merely exemplary. In order to further improve the smoothing effect, the gas streams may also be pulsed and / or heated and / or acted upon by ultrasonic waves.

With the nozzles 91, not only a smoothing of the paint film by elimination of crater-shaped depressions can be produced. Depending on the strength and / or turbulence of the gas stream and the viscosity of the coating material, it is also possible to additionally introduce specific structures into the film. Such an example is shown in Figs. 5A and 5B. FIG. 5A shows, in a grid representation, a paint film before smoothing, as it is often obtained in particular on paper or cardboard substrates by means of drop-on-demand coating. The crater-like depressions 71 are distributed over the surface of the film 7 and have a diameter dependent on the layer thickness.

As can be seen from Fig. 5B, these recesses are closed by blowing the film with gas streams. Instead, by appropriate adjustment of the viscosity and the flow rate of the gas flow in the film 7, a relief-like structuring with ribs or corrugations 72 has been produced. Such a targeted structuring can be used to achieve a specific desired haptic and / or visual appearance.

6 shows yet another example of a device 9. The principle of the device shown here is based on a smoothing by a targeted, non-contact To achieve warming. For this purpose, one or more radiation sources, for example, as in the example shown, several lasers 95 are provided which emit radiation which is at least partially absorbed by the applied coating material or the substrate and thus heat the film. The lasers 95 are pivotably arranged so that they can be scanned over the substrate surface 21 or respectively regions of the substrate surface 21. The pivoting, preferably also the intensity of the laser, is controlled by means of a computer 15. In the simplest case, the surface 21 can be scanned with the lasers 95 by pivoting.

However, it is also possible to detect imperfections, in particular crater-like depressions 71 in the film 7, and to smoothly level them by directing one or more lasers 95 onto the defect. For this purpose, in the example shown in FIG. 6, a camera 96 is provided, which is connected to the computer 15. With the camera, any existing defects are recorded and their

Position determined by the computer. The computer then controls one or more lasers so that they heat the coating material in the area of the defect and thereby compensate for the defect.

This principle is also applicable to the other, by way of example with reference to FIGS. 1 to 4 illustrated method. Therefore, a device for selectively influencing the coating surface is provided in a further development of the invention also generally, which is a

Detecting means for detecting the position of defects in the film, preferably with a camera. The defects detected by the detection device are targeted by movement or direction of the Gas stream and / or the radiation source for non-contact heating and / or at least one needle balanced.

In the following, for example, the crater-like depressions which can be eliminated with the invention are characterized in more detail on the basis of measurement results. FIG. 7 shows an electron micrograph of such a depression 71. As can be seen from the image, the measured depression in the coating shown in this example has a diameter of about 10 micrometers.

FIG. 8 shows a two-dimensional surface profile of another section of a paint film. The surface profile was obtained by white light interferometry. The section shown has a dimension of 1.24 x 0.94 millimeters. In the detail shown two crater-like depressions can be seen. 9 further shows a line profile through the larger of the two depressions (in the viewing angle of FIG. 8, this is the rear of the two depressions 71). The line profile shows that the recess has an outer dimension of about 0.3 millimeters. This dimension results in an approximation of the shape of the recess as a cone or truncated cone. Obviously, the pinholes 71 are very deep, with a cross-section tapering towards the substrate. In particular, the real depth could not be determined with white light interferometry, since the possible measuring range is exceeded. However, the values indicated indicate that the wells reach down to the substrate, which also suggests the appearance of the wells. In general, it is precisely those depressions which can be closed by the method according to the invention. The crater diameter is generally dependent on the layer thickness and can also be greater than in the example shown in FIG. 8. It is believed that these crater-like pits emanate from small chemical and / or topographic perturbations on the substrate. The depression then runs up funnel-shaped. The curvature of the funnel wall is a function of the surface tension. This means that a greater layer thickness does not lead to an improvement of the

Appearance of the coating lead, but on the contrary the recesses with increasing layer thickness emerge more clearly, since the diameter of the coating surface is larger.

Craters, as in the example shown in FIG. 8, are soluble above 2 μm in thickness for the human eye and disturb the appearance of a closed lacquer surface. As the layer thickness increases, its density decreases, but, as stated above, its diameter increases at the surface.

The targeted influencing of the film surface according to the invention is accordingly particularly suitable for closing depressions from about 2 micrometers

Diameter at the surface, preferably 5 micrometers in diameter. Recesses from such a diameter interfere with the appearance of the paint or the coating. The diameter of the crater-like depressions can, as the example shown above illustrates, extend to the surface even down to the millimeter range. Even such major disturbances can be at least partially eliminated by means of the invention. A movement of the coating material over larger However, stretching is not carried out. Preferably, the coating material is laterally moved by the smoothing device by less than one millimeter, more preferably by less than 0.25 millimeters. In particular, the edges to uncoated areas are preferably not affected, so that sharp contours remain at the edges.

It will be apparent to those skilled in the art that the invention is not limited to the above embodiments, but may be varied in many ways. In particular, the individual features of the embodiments can also be combined with each other.

Claims

Claims:

1. A device for applying coatings on surfaces of substrates in the form of paper, cardboard or plastic films, in particular of

Printed products, preferably for the finishing of printed products, with

a coating unit for applying coating material in fluid form to the substrate surface, as well as

a conveyor for moving the substrate surface past the coating unit along a direction of travel relative to the coating unit, preferably by moving the substrate on a fixed coating unit, as well as

-this means for smoothing the applied to the substrate surface by the coating unit, more fluid film, said means comprising means for generating a gas flow which is directed to the surface coated with the film substrate surface and the film ^as' at least partial removal of undesired structures the film surface, such as depressions, elevations and craters before curing of the coating material smoothes.

2. Device according to the preceding claim, characterized in that the coating unit as a drop-on-demand coating unit with nozzles for discharging each individual droplets of the coating material in response to control signals, wherein the nozzle assembly, the coating material contactlessly applied to the substrate surface, and wherein the Nozzles of the coating unit are arranged in at least one row, which extends transversely to the direction and spans the processable substrate width perpendicular to the running direction at least three quarters, and wherein the nozzles are preferably arranged rigidly in the direction transverse to the running direction, and a computer-aided control device for controlling the nozzles ,

3. Device according to one of the preceding claims, characterized in that the coating unit comprises one of the following means:

a device for roller application,

- a gravure device, a flexographic printing device,

-a screen printing device,

-a digital printing facility,

- a pad printing device.

4. Device according to one of the preceding claims, characterized in that the smoothing means comprises means for generating a gas flow with at least one row of gas nozzles, which extends transversely to the running direction.

5. Device according to one of the preceding claims, characterized in that the smoothing device comprises means for generating a gas stream which strikes at an oblique angle to the substrate surface, in particular under a

Angle in the range of greater than 0 ° to 90 °, preferably in the range of 20 ° to 80 °, preferably in the range of 30 ° to 70 °, particularly preferably in the range of 40 ° up to 60 ° measured from the solder on the surface.

6. Device according to one of the preceding claims, characterized in that the means for generating a gas stream at least one of the following

Facilities includes:

a device for generating a pulsed

Gas stream, a heater for heating the at least one gas stream

- A means for screening the gas flow over at least a portion of the substrate surface

a device for supplying the gas stream with

Ultrasonic waves - at least one nozzle to produce a turbulent

Gas flow.

7. Device according to one of the preceding claims, characterized in that the smoothing means comprises a nozzle arrangement which generates gas streams which strike the substrate surface under different spatial directions and / or have gradients in the flow velocity in several directions along the surface.

8. Device according to one of the preceding claims, characterized by a curing device for curing the coating material, which is arranged downstream in the running direction of the smoothing device, wherein the curing device comprises a UV light source and / or an oven and / or a radiant heater and / or a microwave source.

9. Device according to one of the preceding claims, characterized by a detection device for detecting the position of defects in the film, preferably a camera, and means for moving the gas flow to the defects.

10. Device according to one of the preceding claims, designed as offset printing, gravure, flexographic, screen printing, digital printing or pad printing machine.

11. A method for applying coatings on surfaces of substrates, in which

coating material is applied in fluid form while a conveying device moves the substrate surface relative to the coating unit along a running direction on the coating unit, preferably by moving the substrate on a fixed coating unit, and applying it to the substrate surface by means of

Coating coated, still fluid film is smoothed before solidification, wherein for smoothing a gas stream is generated and is directed to the coated with the film substrate surface.

12. The method according to the preceding claim, characterized in that the coating material is applied contactlessly by means of a nozzle arrangement on the substrate surface, wherein the nozzles are controlled by a computer-aided control device and the film is applied in the drop-on-demand method by the nozzles each individual drops of the coating material below Deliver response to control signals.

13. The method according to any one of the four preceding claims, characterized in that the coating material is applied with nozzles, which are arranged in at least one row, which extends transversely to the direction and spans the processable substrate width perpendicular to the direction of at least three quarters, and wherein the Nozzles are preferably arranged rigidly in the direction transverse to the running direction.

14. The method according to any one of the preceding claims, characterized in that the coating material is applied by roller application, screen, digital or pad printing ^■ .

15. The method according to any one of the preceding claims, characterized in that the gas stream is directed by means of a nozzle row on the substrate, which is arranged transversely to the direction.

16. The method according to any one of the preceding claims, characterized in that the film with

a turbulent or pulsed or an ultrasonic waves acted upon gas flow or with

at least one heated gas stream, wherein the at least one gas stream is heated to a temperature in the range of 50 to 500 ⁰ C, preferably in the range of 100 to 400 ° C, more preferably in the range of 150 to 300 ° C, or with a gas stream which impinges on the substrate surface at an oblique angle, in particular at an angle in the range of greater than 0 ° to 90 °, preferably in the range of 20 ° to 80 °, preferably in the range of 30 ° to 70 °, more preferably in the range of 40 ° to 60 ° measured from the solder on the surface, or with gas streams that meet under different spatial directions on the substrate surface and / or gradients in the flow velocity in multiple directions along the surface, is smoothed

17. The method according to any one of the preceding claims, characterized in that at least one gas stream for smoothing the film is rastered over at least a portion of the substrate surface.

18. The method according to any one of the preceding claims, characterized in that a film having a layer thickness less than 100 microns, preferably less than 50 microns, more preferably less than 30 microns, or less than 20 microns, especially less than 10 microns is applied.

19. The method according to any one of the preceding claims, characterized in that the film is cured after smoothing by means of a curing device, wherein a UV-curable coating material or a

Ink applied and this is cured by irradiation of UV light and / or by heating in an oven and / or with a radiant heater and / or by means of a microwave source after smoothing.

20. The method according to any one of the preceding claims, characterized in that specifically for influencing the fluid film by means of the gas stream structures, in particular crimping, waves, Wells, ribs or grooves are inserted into the film.

21. The method according to any one of the preceding claims, characterized in that a coating material is applied, which in the

Processing temperature has a dynamic viscosity of at least 10 seconds and / or at most 1000 seconds, preferably 500 seconds, more preferably 200 seconds, measured as

Outflow time of a volume of 100 cm ³ from a DIN cup with a 4 mm diameter outlet nozzle (DIN 53211).

22. The method according to any one of the preceding claims, characterized in that the substrate surface is laterally structured with the recess of at least one surface area is coated.

23. The method according to any one of the preceding claims, characterized in that the coating material is transported by the gas flow by less than 1 mm, more preferably less than 0.25 mm along the surface.

24. The method according to any one of the preceding claims, characterized in that by smoothing depressions, in particular crater-like depressions, furthermore depressions in particular, which extend to the substrate, are closed.

25. Method, in particular according to one of the preceding claims, characterized in that a coating device or a printing press with a coating device, or a printing press is equipped with a coating unit with a smoothing device for the fluid coating material, so that a coating device according to claim 1 is obtained.