EP3571052B1 - Method for printing films which deform under thermal loads - Google Patents

Description

The present invention relates to a method for printing films that deform under thermal stress.

A printer for printing foils is known from the prior art, comprising: I) A printing roller which can be rotated about an axis and has a cylindrical roller shell, to which a printing module with four rows of nozzles arranged one behind the other in the direction of rotation of the printing roller and spaced apart from the roller shell is assigned , whereby different colors can be printed with the respective rows of nozzles; II) Means for tempering the roll shell to a temperature between 20 and 90 degrees Celsius, the printer being designed to be able to print on the film while the film is being advanced over the roll shell.

The U.S. 6,154,232 A describes a printing device for printing on sheets of paper, comprising: I) a printing drum with a drum outer surface for receiving a sheet of paper, to which a printing module comprising two sets of two rows of nozzles, which are spaced apart from the outer surface of the drum, is assigned, the width of a print stripe of the ink printed on the sheet of paper being im The sum of the print stripes of two rows of nozzles of the first set essentially corresponds; II) means for driving the print drum in a first direction of rotation, the printer being designed to be able to print on paper while the print drum is rotated in the direction of rotation. The printing drum in (I) is formed as a vacuum drum to prevent the paper sheet from falling during rotation in the direction of rotation. For this purpose, the printing drum is perforated with vacuum openings, which extend between the interior of the printing drum and the outer surface of the drum and can be subjected to negative pressure.

From the DE102009007565A1 discloses a guiding device for guiding flexible flat material, such as paper or plastic film, in the form of a material web or sheets of material, with at least one guiding surface which can run away from the flat material and at which gas blow-out channels serving to blow out air or other gases open out.

In the DE102013007300B4 also discloses a web guiding device for guiding a material web consisting of a flexible flat material, with at least one web deflection unit.

With the documents DE102009007565A1 and DE102013007300B4 it is therefore only about web guiding devices for deflecting flexible flat materials. The present invention, on the other hand, is about a printing device for printing on a film.

The document U.S. 6,983,692 B2 discloses a print drum having a vacuum source for drawing a vacuum on the surface of the print drum. In addition, a radiation source is arranged in the printing drum. The radiation source serves to dry, or partially dry, ink that is applied to a medium that rests on the outer surface of the print drum.

Different factors influence the printing process of a film. These include, among other things, the temperature, the heat capacity, the mass, the geometric dimensions and the material composition of the film used, as well as the energy that is supplied to or withdrawn from the film depending on its distribution on the film. It should be noted that these factors also influence each other.

Another factor that influences the printing process is the thermal expansion coefficient of a material of a film to be printed. A problem that causes poor print quality when printing on films with relatively high coefficients of thermal expansion is that they tend to expand and contract during processing when subjected to thermal stresses.

The inventors have observed that printing a film with a device from the prior art with ink drops at a lower selected temperature of the drops than the film increases the distortion and thus the deterioration of the printed image. On the other hand, it can be observed that with higher energy input in the form of, for example, IR and/or NIR radiation during the printing process in order to at least partially vaporize and/or harden the ink droplets, the distortion of the printed image increases as well.

It can therefore be stated in general that an increase or decrease in temperature of the film during the printing process resulting from the influences described above can lead to image deterioration which is based on a Deformation of the film is due, whereby the ink drops can no longer hit their intended target positions during the gradual build-up of the printed image. This means that in the prior art, a temperature change in the film during the printing process must be avoided or at least kept as low as possible in order to obtain an attractive printed image.

If you consider that when a print image is built up step by step, for example during a single-pass printing process with a single-pass printing device, a foil with a foil width of 500 mm and a dot density of 600 dpi, i. H. at a drop-to-drop distance of 42 µm, during which it first experiences a shrinkage of 2 millimeters and then an expansion of 3 millimeters, it becomes immediately clear what a negative impact the deformation will have on the appearance of the print motif .

In the context of this description, a single-pass printing device is understood to mean a printing device with a printing module for printing a film, in which the film is moved continuously in the operating mode and the printing module sees a region of the film only once, with the printing module not being operated in accordance with known scanning method (i.e. moving a printing module back and forth line by line), but is arranged in a stationary manner.

The fact is, however, that common plastic materials used, for example, in packaging films almost always have a high coefficient of thermal expansion, which makes them very sensitive to temperature fluctuations during their processing, as illustrated in Table 1 below: <b>Table 1</b> material Thermal expansion coefficient α [°K ^-1 ] Material width S0 [mm] ΔT1 [K] ΔS1 [mm] ΔT2 [K] ΔS2 [mm] Paper ∼13 x 10 ^-6 500 10 0.065 40 0.26 Aluminum (Al) ∼23 x 10 ^-6 500 10 0.115 40 0.46 polyethylene ∼80 x 10 ^-6 500 10 0.4 40 1.6 Polyamide (Nylon) ∼120 x 10 ^-6 500 10 0.6 40 2.4 polypropylene ∼150 x 10 ^-6 500 10 0.75 40 3.0 polyvinyl chloride ∼175 x 10 ^-6 500 10 0.875 40 3.5 polyethylene (PE) ∼200 x 10 ^-6 500 10 1 40 4.0

The thermal expansion ΔS1 or ΔS2 of typical plastic materials is many times that of paper, for example, with the same temperature increase. For polyamide, polyvinyl chloride and polyethylene it is about 6 to 15 times higher than for paper.

Another factor that influences the printing process and plays a crucial role is the heat capacity of the foil used. The thermal capacity C of a substrate is by definition the ratio of the heat supplied to it (ΔQ) to the temperature increase (ΔT) caused by it. The heat capacity of a substrate made of a homogeneous material can be calculated as the product of its specific heat capacity C and its mass m.

Because foils are inherently relatively thin gauges (i.e., calipers), typically in the range 5 to 200 µm, preferably in the range 10 to 100 µm, they are susceptible to temperature changes generated when energy is applied to or removed from the foil.

A combination of factors that also influence the printing of films that deform under thermal stress is when the film is a composite film that consists of a number of materials, in particular if they are built up in layers. This is the case, for example, when, in the case of flexible foils, an effective barrier, e.g. B. is required against migrating UV ink components. Such can be realized by providing a two-layer or multi-layer composite film comprising at least one metal layer, for example an aluminum layer.

A problem that can occur when printing composite foils with different thermal expansion coefficients is a deterioration in print quality due to the so-called bimetallic effect, in such a way that, in processes according to the prior art, it bulges under thermal stress and the ink drops are therefore no longer available reach their target positions.

The composite film could even bulge in such a way that it comes into contact with the pressure nozzles located opposite one another, which are usually only a few millimeters from the surface of the composite film. B. would result in smearing of the printing ink on the composite film.

There is therefore a need for a device and a method for printing films that deform under thermal stress and have a relatively high coefficient of thermal expansion, in which the negative effects of thermal stress can be suppressed at least partially, preferably completely.

It is therefore the object of the present invention to specify a device and a method for printing films which deform under thermal stress and have a relatively high coefficient of thermal expansion, in which films can be kept largely dimensionally stable despite thermal stress during a printing process.

This object is achieved by a method according to claim 1. Preferred embodiments of the method according to the invention are described in the dependent claims.

The application of the holding forces according to the method according to claim 1 is therefore not used solely and exclusively for the purpose of securing a substrate against a possible falling of the film from a receiving means, as in the U.S. 6,154,232 A is the case, but serves according to the invention for the purpose of preventing expansion and thus deformation of the area of the film applied to the receiving surface during the printing process, so that the film is kept largely dimensionally stable during the printing process. A deterioration in the print quality can only be effectively avoided by the solution disclosed above. On the other hand, deformations of the film before it is applied to the receiving surface described above or after the film has been detached from the same receiving surface cannot be avoided—on the contrary, they can even be desirable or at least not disturbing.

At the same time, the invention overcomes another problem associated with conventional methods for printing films with relatively high coefficients of thermal expansion, when the area of the film experiences an inhomogeneous temperature distribution due to the supply and/or removal of energy, because even this negative effect is eliminated by the solution according to the invention largely prevented.

The cause of such an inhomogeneous temperature distribution can be based on various factors. This includes, for example, the color of the ink and/or the application of the ink.

As is well known, dark inks usually heat up much more than light ones when exposed to heat. The cause lies, among other things, in the interaction of the affected ink with near infrared radiation (NIR), which is not limited to the absorption of electromagnetic radiation, in which the electromagnetic waves are converted into heat, but also to the thermal radiation of the surface of the ink Ink, i.e. the emission in the far infrared.

If, in the prior art, a printed image was printed according to four-color printing and with an inhomogeneous color ink distribution and then exposed to IR and/or NIR radiation, it inevitably experienced an inhomogeneous temperature distribution and thus an inhomogeneous deformation.

The problem of an inhomogeneous temperature distribution occurring in the film during the printing process is thus also effectively remedied by the present invention.

The invention will now be described in detail and by way of example with reference to the figures.

1 shows a schematic side view of a particularly preferred embodiment of a printing device in cross section.

figure 1 shows a roll-to-roll inkjet printing device for printing a film 100 with a means for receiving 101 a region of the film 100 with a receiving surface 103, wherein the means for receiving 101 is designed as a pressure roller rotatable about an axis and the receiving surface 103 as a cylindrical roll shell is formed.

Four pressure modules 105a, 105b, 105c, 105d, each comprising at least one row of nozzles (not shown), which are spaced apart from the roll shell, are associated with the cylindrical roll shell. The respective printing modules 105a, 105b, 105c, 105d are assigned an electromagnetic radiation source 106a, 106b, 106c, 106d downstream in the direction of rotation (arrow) of the printing roller for at least partially curing and/or at least partially evaporating the ink droplets applied to film 100.

Advantageously, by using one or more electromagnetic radiation sources, such as an IR and/or NIR radiation source and/or UV radiation source, undesirable wetting behavior of the ink drops printed on the film can be avoided, since they no longer have enough time to separate to run or to contract (depending on the wetting behavior: no wetting, partial wetting, complete wetting).

For pre-tempering the film 100, the printing device comprises a pre-tempering roller 115 with two associated pressure or nip rollers 117, which are designed to press the film 100, which can be moved away over the pre-tempering roller 115, against the pre-tempering roller 115.

This arrangement can advantageously improve the energy transfer from the roller to the film. The pre-tempering roller can be set in a range between 20 and 100 degrees Celsius, preferably between 50 and 90 degrees Celsius.

As in figure 1 shown, the film 100 can be removed by means of an unwinding device (not shown) from a film roll 127 via a device for controlling the clothing, which is designed as a dancer roller 133, and via a pre-tempering roller 115, a deflection roller 119, a pressure roller, a further deflection roller 121, a cooling roller 123 for cooling the film 100 and a second dancer roller 135 and are rolled up again as a film roll 129 by means of a winding device (not shown).

The rollers or rollers described are mounted on a frame 131 of the printing device, with feet 134 being attached to the frame.

The chill roll 123 is also assigned three pressure or nip rolls 125 which are designed to press the film 100 that can be moved past the chill roll 123 against the chill roll 123 .

The pressure roller with a cylindrical roller shell comprises means for temperature control of the receiving surface 103 and activatable holding means, which are formed by suction channels that can be subjected to vacuum and which extend through a layer 104 to the cylindrical roller shell and open out on the cylindrical roller shell as suction openings (not shown). In this case, the layer 104 forms the receiving surface 103 .

The activatable holding means are designed in such a way that during this time the area of the film 100 in contact with the receiving surface 103 experiences a temperature change under the action of an energy change, which is generated when energy is supplied and/or withdrawn in such a way, at the same time as holding forces can be applied to the area of the film 100 via the receiving surface 103, which are so large that they counteract at least the deformation forces caused by the temporary temperature change in the area of the film 100 parallel to the receiving surface 103.

The pressure roller is mounted on a hollow shaft 102, whereby the pressure roller and thus the cylindrical roller shell can be subjected to a specific negative pressure by means of a vacuum generator (not shown) via a tube (not shown) penetrating the hollow shaft. The cylindrical roller shell can be temperature-controlled to any desired temperature in a range between 20 and 100 degrees Celsius, preferably between 50 and 90 degrees Celsius, either via a second tube passing through the hollow shaft 102 using a temperature-controlled liquid or via current means (not shown).

A current means can be a heating resistor capable of converting electrical energy into thermal energy.

The printing device further comprises a drive means (not shown) which can apply a predetermined torque directly or indirectly unidirectionally or bidirectionally to the printing roller.

The printing device also includes a control unit 132 for carrying out a printing method according to the invention.

A printing device for printing a film 100 that deforms under thermal stress with at least one means for receiving 101 at least one region of a film 100 with a receiving surface 103 has been disclosed, which has at least one printing module 105a, 105b, 105c, 105d for printing the film with ink drops comprising at least one row of nozzles, which is spaced opposite the receiving surface 103, wherein the means for receiving 103 comprises holding means that can be activated.

The means for receiving 101 includes means for tempering the receiving surface 103.

In a preferred embodiment of the invention, the activatable holding means are designed such that during this time the area of the film 100 in contact with the receiving surface 103 undergoes a temperature change under the action of an energy change that is generated when energy is supplied in such a way and/or is withdrawn, at the same time holding forces can be applied via the receiving surface 103 to the area of the film 100, which are so great that they are at least caused by the temporary temperature change in the area of the film 100 parallel to the receiving surface 103 caused deformation forces overcompensate counteracting.

In a further preferred embodiment, the activatable holding means are configured as suction channels that can be acted upon by a vacuum, which extend from the interior of the means for receiving 101 to the receiving surface 103 and open out on the receiving surface 103 as suction openings.

In a particularly preferred embodiment, the means for receiving 101 includes a layer 104 that includes the suction channels, with the layer 104 forming the receiving surface 103 .

The layer 104 is preferably formed from nanoporous and/or microporous material.

The suction openings are designed as nano and/or micro openings.

When micro-openings are mentioned here within the scope of the disclosure, this means openings with a size between 1 μm and 200 μm, preferably 1 μm and 100 μm. If, on the other hand, nano-openings are mentioned, this means openings with a size of less than 1 μm.

In a particularly preferred embodiment, the at least one means for receiving 101 a region of the film 100 is embodied as a pressure roller that can be rotated about an axis, and the receiving surface 103 is embodied as a cylindrical roller shell, with the pressure roller being designed to rotate the film 100 in one direction of rotation, whereby a feed direction of the film 100 is defined.

In a further particularly preferred embodiment, the pressure roller is mounted on a hollow shaft 102, whereby the pressure roller and thus the cylindrical roller shell can be subjected to a certain negative pressure by means of vacuum means via a tube penetrating the hollow shaft. The cylindrical roller shell can be heated to any desired temperature in a range between 20 and 100 degrees Celsius, preferably between 50 and 90 degrees Celsius, either via a second tube penetrating the hollow shaft 102 using a temperature-controlled liquid or using electricity.

In a preferred embodiment, at least two, preferably at least four, printing modules 105a, 105b, 105c, 105d are arranged on the roll shell at a distance from one another in the direction of rotation.

In a further preferred embodiment, at least one corresponding electromagnetic radiation source 106a, 106b, 106c, 106d is/are downstream of the printing module(s) 105a, 105b, 105c, 105d in the direction of rotation of the printing roller for at least partially curing and/or at least partially evaporating the material applied to the film associated with ink drops.

The at least one electromagnetic radiation source 106a, 106b, 106c, 106d can be embodied as an IR and/or NIR radiation source.

The at least one IR and/or NIR radiation source can be arranged between at least two printing modules 105a, 105b, 105c, 105d.

In a particularly preferred embodiment, the printing device comprises a pre-tempering device for pre-tempering film 100, which can be temperature-controlled preferably in a range between 20 and 100 degrees Celsius, particularly preferably between 50 and 90 degrees Celsius, with the pre-tempering device being opposite the printing roller in the feed direction of film 100 located upstream. The pre-tempering device is preferably designed as a pre-tempering roller 115 .

In a further particularly preferred embodiment, the printing device comprises a cooling device for cooling the film 100, which can preferably be temperature-controlled in a range between 20 and 40 degrees Celsius, the cooling device being arranged downstream in the feed direction of the film 100 opposite the printing roller. The cooling device is preferably designed as a cooling roller 123 .

In another particularly preferred embodiment, the printing device comprises a final curing and/or evaporation device for complete curing and/or evaporation of the printed ink droplets. This can be part of an aftertreatment device.

In a further particularly preferred embodiment of the invention, the printing device comprises a roll-to-roll printing device, in particular a roll-to-roll inkjet printing device.

In a preferred embodiment, the printing device comprises a drive means which can apply a predetermined torque directly or indirectly unidirectionally or bidirectionally to the printing roller. The drive means can be an electric drive motor.

The roll-to-roll printing device can comprise a device for unwinding and/or winding up the film in the form of a continuous film web from or onto a winding core, which in each case preferably comprises a drive means which drives the respective winding core directly or indirectly unidirectionally or bidirectionally can be subjected to a predetermined torque.

In a particularly preferred embodiment, the printing device comprises at least two printing rollers working in series, each with a cylindrical roller shell.

In a particularly preferred embodiment, the printing device or the roll-to-roll printing device is designed as a single-pass printing device.

At this point it should be pointed out that the printing device can also include means for cleaning dirt from the film and/or means for aligning the film or film web and/or means for pretreating the film, such as a corona treatment unit.

For the sake of clarity, it should be pointed out that, for a better understanding of the structure of the printing device, it or its components are sometimes shown not to scale and/or enlarged and/or reduced.

Based on figure 1 a particularly preferred embodiment of the method according to the invention for printing films that deform under thermal stress is described below.

In a first step, a printing device with a means for receiving 101 at least one area of a film 100, which is designed as a printing roller, provided. The printing roller comprises a receiving surface 103, which is designed as a cylindrical roller shell, to which four printing modules 105a, 105b, 105c, 105d, each comprising at least one row of nozzles (not shown), which are spaced apart from the receiving surface 103, are assigned.

In the exemplary method, a pressure roller with a cylindrical roller shell with a diameter of 1.4 meters was provided as the pressure roller.

In a second step, the film 100 is pre-tempered to a temperature of 88 degrees Celsius via a pre-tempering roller 115 and, in a third step, onto the roller shell at a temperature T1 of 88 degrees Celsius, which roller shell is tempered to a temperature T2 of 90 degrees Celsius, upset. Temperature T1 and temperature T2 define a temperature difference TU of 2 degrees Celsius.

In a fourth step, the area of the film 100 in contact with the roll shell is printed by ejecting water-based ink drops at a temperature of 40 degrees Celsius from the nozzles of the nozzle rows of the four printing modules 105a, 105b, 105c, 105d.

In a fifth step, the ink droplets are at least partially vaporized successively by means of the electromagnetic radiation sources arranged downstream opposite the printing modules 105a, 105b, 105c, 105d as IR and/or NIR radiation sources 106a, 106b, 106c, 106d.

During which the area of the film 100 in contact with the roll mantle undergoes a temperature change under the action of an energy change generated when energy is withdrawn by printing with ink droplets of a lower temperature than the area of the film 100 in contact with the roll mantle and at the same time by at least partial drying of the water-based ink drops printed on the area of the film 100 in contact with the roller shell is supplied by IR and/or NIR radiation, so that the temperature difference TU between the area of the film 100 and the receiving surface 103 is increased, at the same time holding forces are applied to the area of the film 100 via the receiving surface 103, which counteract at least the deformation forces caused by the temperature change in the area of the film 100 parallel to the receiving surface 103 overcompensate.

A method of printing a thermally deformable film 100 as defined in detail in claim 1 has been disclosed.

A preferred embodiment of the method according to the invention is characterized in such a way that at the same time the area of the film 100 in contact with the receiving surface 103 under the influence of an additional change in energy is supported by energy exchange between the receiving surface 103 and the area of the film 100, a reduction of a current temperature difference TU is supported. and preferably occurs, thereby at least partially realigning a current temperature of the area of the foil 100 to the temperature T2 is supported, and preferably takes place.

According to the method according to the invention, the holding forces are applied as vacuum holding forces via holding means, which are formed by suction channels that can be acted upon by a vacuum, which extend from the inside of the means for holding to the holding surface 103 and open out on the holding surface 103 as suction openings.

In a further preferred embodiment of the method, the means for receiving is provided as a means for receiving comprising a layer 104 which comprises suction channels, the layer 104 forming the receiving surface 103 and the layer preferably being formed from nanoporous and/or microporous material.

The receiving surface 103 can be provided as a receiving surface 103, the suction openings of which are chosen so small that the areas of the film 100 directly affected by the suction openings can be kept dimensionally stable with regard to the action of the vacuum holding forces, i.e. the affected areas of the film 100 by the vacuum holding forces (suction forces) are not plastically deformed.

The receiving surface 103 is a receiving surface 103 whose suction openings are in the form of nano- and/or micro-openings.

Before being applied to the receiving surface 103, the area of the film 100 can be preheated in such a way that at the moment of application to the receiving surface 103 it has a temperature T1 which, compared to the temperature T2, has a temperature difference TU in a range between at least 0 and 10 degrees Celsius , preferably between 0 and 5 degrees Celsius.

In some embodiments of the method according to the invention, in particular when the film 100 is printed with ink drops at a lower temperature than the film 100, it can be advantageous if the film 100 has a slightly lower temperature than the receiving surface 103 at the moment of application. This allows stronger deformation forces, due to of the smaller temperature difference, preventively avoid during the printing process.

The area of the film 100 can therefore be preheated before being applied to the receiving surface 103 so that at the moment of being applied to the receiving surface 103 it has a temperature T1 which is preferably in a range between at least 2 and 10 degrees Celsius compared to the temperature T2 between 2 and 5 degrees Celsius lower.

In a preferred embodiment, the holding forces can be determined as a function of a predetermined maximum temperature change and these can be taken into account when controlling the holding forces in such a way that the deformation forces caused are at least partially compensated, preferably compensated, and particularly preferably overcompensated.

In a particularly preferred embodiment, the printing is performed with ink droplets at a lower temperature than the area of the film 100 that is in contact with the support surface 103, so that the temperature change in the area of the film 100 is generated by energy extraction. The reason for the energy deprivation is the ink with its lower temperature compared to the film.

In a preferred embodiment, according to a method step d), at least partial evaporation and/or hardening of the ink droplets printed on the area of the film 100 in contact with the receiving surface 103 takes place by IR and/or NIR radiation, so that the temperature change is generated by the supply of energy.

In a further preferred embodiment, according to a method step e), instead of method step d) or in addition to it, air at a temperature between 15 and 180° C. is printed by means of a blowing air means on the area of the film 100 that is in contact with the receiving surface 103 Ink drops are blown so that the temperature change is generated by energy extraction or energy input accordingly. This procedure is advantageous because, among other things, it enables an insulating layer of air covering the ink to be removed more quickly.

Steps d) and e) can be carried out at different times or simultaneously.

Instead of or in addition to step d), the ink droplets can be cured in a step f) by UV irradiation.

In a preferred embodiment of the method according to the invention, the receiving surface 103 is heated before step b) to a certain temperature T2 in a range between 50 and 100 degrees Celsius, preferably between 60 and 100 degrees Celsius, particularly preferably between 80 and 100 degrees Celsius tempered and at least during the following steps b) and c) kept at this temperature at least partially constant, preferably kept constant.

In a particularly preferred embodiment, a water-based ink is used as the ink.

Compared to the usual acrylate-based UV inks, which consist largely of one or more monomers, water-based inks make it possible to realize thinner, hardened ink films on a substrate. Advantageously, this also saves on expensive acrylate monomer as the starting material.

The temperature of the ink drops can be a lower temperature than the current temperature of the area of the film 100 in the range between 20 and 60 degrees Celsius, preferably 30 and 50 degrees Celsius.

A water-based hybrid ink comprising as components (a) water, (b) UV-curing oligo- and/or polymer with ethylenically unsaturated functional groups, (c) a humectant and (d) a free-radical photoinitiator can be used as the water-based ink.

When an oligomer is referred to in this specification, it means a molecule having a molecular weight in the range between 1,000 and 10,000 inclusive. If, on the other hand, a polymer is mentioned in the context of this description, a molecule with a molecular weight greater than 10,000 is to be understood.

A preferred hybrid ink includes the following components: (a) 20 to 70%, preferably 40 to 70% component (a), (b) 5% to 50%, preferably 05 to 25% component (b), (c) 02 to 40%, preferably 05 to 30% component (c), (d) 0.1 to 0.5%, preferably 0.5 to 3.0% component (d)

In the context of this description, the percent sign "%" is used in the sense of weight percent.

The application of the film 100 to the receiving surface 103 may be performed under a predetermined first tension in a first direction and a second tension vertically with respect to the first direction, the first and second tensions being zero or non-zero.

In a particularly preferred embodiment, the film is applied to the receiving surface 103 under a first tension of <1500 N, in particular <700 N and a second tension of preferably <300 N, in particular <200 N.

The film 100 can be provided as an elastically deformable film 100 .

The film 100 can be provided as a film 100 which comprises a thermoplastically deformable plastic.

The film 100 can be provided as a multilayer composite film, comprising at least one thermoplastically deformable plastic layer and optionally at least one metal layer and/or at least one paper layer.

In a preferred embodiment, a film 100 with at least one layer is selected as the film 100, which has a thermal expansion coefficient α of at least 40*10 ^-6 *°K ^-1 , preferably at least 70*10 ^-6 *°K ^-1 .

The foil 100 is provided with a thickness between 10 and 100 μm.

• Bereitstellung einer um eine Achse 102 drehbare Druckwalze als Mittel zur Aufnahme 101 mit zylindrischem Walzmantel als Aufnahmefläche 103,
• Antreiben der Druckwalze in eine Drehrichtung, wobei beim Drehen ein synchrones Mitführen der Folie 100 in Drehrichtung der Druckwalze erfolgt,
• Bedrucken der Folie 100 mit Tintentropfen

In a particularly preferred embodiment, the method comprises the following steps:

• Provision of a pressure roller rotatable about an axis 102 as a means for receiving 101 with a cylindrical roller shell as receiving surface 103,
• Driving the pressure roller in one direction of rotation, with the film 100 being synchronously carried along in the direction of rotation of the pressure roller when rotating,
• Printing the foil 100 with ink drops

The printing device can be provided as a roll-to-roll printing device, in particular as a roll-to-roll ink jet printing device, so that the film 100 is processed in the form of a continuous film web from the roll and continuously applied to the cylindrical roll mantle.

The pre-tempering can take place by means of a pre-tempering device, which is preferably designed as a pre-tempering roller (115), over which the film 100 is guided.

A foil 100 with a width in a range between at least 100 mm and 1000 mm is typically provided as the foil 100 .

Claims (19)

1. A method for printing a sheet (100) deforming under thermal stress comprising the steps of:

   a) providing a printing device having at least one means for receiving (101) at least one region of the sheet (100) having a receiving surface (103) to which a printing module (105a, 105b, 105c, 105d) comprising at least one row of nozzles is assigned, which row of nozzles is oppositely spaced apart from the receiving surface (103),

   b) applying the region of the sheet (100) having a temperature T1 to the receiving surface (103) having a temperature T2, defining a temperature difference TU,

   c) printing the region of the sheet (100) being in contact with the receiving surface (103) with ink droplets, wherein in the meantime the region of the sheet (100) being in contact with the receiving surface (103) undergoes a temperature change under the influence of an energy change, which is generated when energy is supplied and/or withdrawn, in such a way that the temperature difference TU between the region of the sheet (100) and the receiving surface (103) increases and, at the same time, holding forces are applied via the receiving surface (103) onto the region of the sheet (100), wherein the holding forces are applied as vacuum holding forces by means of activated retaining means which are formed by vacuum-capable suction channels extending from the interior of the receiving means (101) to the receiving surface (103) and entering the receiving surface (103) as suction openings, wherein the holding forces over-compensate for the deforming forces resulting from the temperature change in the region of the sheet (100) parallel to the receiving surface (103) in a counter-acting way,

   wherein the sheet (100) is provided with a thickness of 10 to 100 µm, wherein the suction openings are formed as nano and/or micro openings and are chosen so small that the regions of the sheet (100) directly affected by the suction openings are kept in a stable form with regard to the effects of the vacuum holding forces, wherein the holding forces are determined depending on a maximum predetermined temperature change that can occur and these are taken into account when controlling the holding forces in such a way that the deforming forces caused are overcompensated in a counter-acting way.
2. The method according to claim 1, characterized in that, simultaneously with the region of the sheet (100) being in contact with the receiving surface (103), under the influence of an additional energy change by energy exchange between the receiving surface (103) and the region of the sheet (100), reduction of a current temperature difference TU is supported, and preferably occurs, whereby at least a partial re-adaptation of a current temperature of the region of the sheet (100) to the temperature T2 is supported, and preferably occurs.
3. The method according to at least one of the preceding claims 1 to 2, characterized in that the region of the sheet (100), prior to being applied onto the receiving surface (103), is preheated such that, at the moment of being applied onto the receiving surface (103), it has a temperature T1 that, compared to temperature T2, has a temperature difference TU in a range between 0 and 10 degrees Celsius, preferably between 0 and 5 degrees Celsius.
4. The method according to at least one of the preceding claims 1 to 3, characterized in that the region of the sheet (100), prior to being applied onto the receiving surface (103), is preheated such that, at the moment of being applied onto the receiving surface (103), it has a temperature T1 that is at least 2 to 10 degrees Celsius, preferably 2 to 5 degrees Celsius lower than the temperature T2.
5. The method according to at least one of the preceding claims 1 to 4, characterized in that printing with ink droplets having a lower temperature than the region of the sheet (100) being in contact with the bearing surface (103) is carried out such that the temperature change in the region of the sheet (100) is generated by energy extraction.
6. The method according to at least one of the preceding claims 1 to 5, characterized in that the method comprises a further step of:

   d) at least partially evaporating and/or curing the ink droplets printed onto the region of the sheet (100) being in contact with the receiving surface by IR and/or NIR irradiation and/or UV irradiation,

   such that the temperature change is generated by energy supply.
7. The method according to claim 6, characterized in that in a step
   e) either instead of or in addition to process step d), air having a temperature between 15 and 180°C is blown onto the ink droplets printed on the region of the sheet 100 being in contact with the receiving surface 103 by way of an air blower device, so that the temperature change is accordingly generated by energy extraction or energy supply.
8. The method according to at least one of the preceding claims 1 to 7, characterized in that the receiving surface (103), prior to step b), is heated to a specified temperature T2 in a region between 50 and 100 degrees Celsius, preferably between 60 and 100 degrees Celsius, particularly preferred between 80 and 100 degrees Celsius, by way of temperature controlling means and, at least in the following steps b) and c), is constantly held at that temperature at least temporarily and preferably is held constantly at that temperature.
9. The method according to at least one of the preceding claims 1 to 8, characterized in that the temperature of the ink droplets is a temperature that, compared to the current temperature of the region of the sheet (100), is a lower temperature in the range between 20 and 60 degrees Celsius, preferably 30 and 50 degrees Celsius.
10. The method according to at least one of the preceding claims 1 to 9, characterized in that a water-based ink is used as an ink.
11. The method according to at least one of the preceding claims 10, characterized in that a hybrid ink based on water comprising, as the components, (a) water, (b) UV-curing oligo and/or polymer having ethylenically unsaturated functional groups, (c) a humectant and (d) a radical-forming photoinitiator is used as a water-based ink.
12. The method according to at least one of the preceding claims 1 to 11, characterized in that the application of the sheet (100) onto the receiving surface (103) is performed under a first predetermined pulling tension in a first direction and under a second pulling tension in a direction vertical to the first direction, wherein the first and second pulling tensions are zero or unequal to zero, wherein the application of the sheet (100) onto the receiving surface (103) is preferably done under the first pulling tension of <1500 N, especially <700 N and the second pulling tension of preferably <300 N, especially <200 N.
13. The method according to at least one of the preceding claims 1 to 12, characterized in that the sheet (100) is provided as an elastically deformable sheet (100).
14. The method according to at least one of the preceding claims 1 to 13, characterized in that the sheet (100) is provided as a sheet (100) comprising a thermoplastically deformable plastic material.
15. The method according to at least one of the preceding claims 1 to 14, characterized in that the sheet (100) is provided as a multilayer composite sheet comprising at least a thermoplastically deformable plastic layer and optionally at least a metal layer and/or at least a paper layer.
16. The method according to at least one of the preceding claims 1 to 15, characterized in that a sheet (100) with at least one layer having a thermal coefficient of expansion α of at least 40 * 10^-6 * °K^-1, preferably at least 70 * 10^-6 * °K^-1 is selected as a sheet (100).
17. The method according to at least one of the preceding claims 1 to 16, characterized in that the method comprises the following steps:

    - providing a print roller which is rotatable about an axis (102) as a receiving means (101) having a cylindrical roll shell as a receiving surface (103),

    - driving the print roller in a rotating direction, wherein, while rotating, synchronous entrainment of the sheet (100) in the rotating direction of the print roller occurs,

    - printing the sheet (100) with ink droplets.
18. The method according to claim 17, characterized in that the printing device is provided as a roll-to-roll printing device, especially as a roll-to-roll ink jet printing device, so that the sheet (100) is processed by the roll in the form of a continuous web and is continuously applied onto the cylindrical roll shell.
19. The method according to at least one of the preceding claims 1 to 18, characterized in that pre-heating is done by way of a pre-heating device, which is preferably formed as a pre-heating roll (115), over which the sheet (100) is guided.

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