HK1070862A - Method for drying a printing ink on a printing substrate, and print unit suited for implementing the method - Google Patents

Description

Method for drying printing ink on printing material and printing device for carrying out said method

Technical Field

The invention relates to a method for drying printing ink on a printing material in a printing press, wherein the printing material is moved through the printing press along a path, the printing material is printed with at least one printing ink having at least one pigment at one point of the path, and the printing material is irradiated with light from a laser light source at least one further point in the path at a subsequent time. The invention further relates to a printing device having a laser light source for carrying out the method.

Background

Depending on the type of printing ink and the specific drying program on which it is based, various devices are known in printing presses, in particular flat presses such as offset, rotary, offset, flexographic printing presses, etc., which process sheet-like or web-like printing materials, in particular paper, cardboard and the like, which cause or support the adhesion of the ink to the printing material in that: radiation energy, in particular in the form of light, is introduced into the ink on the printing material.

So-called UV inks harden by polymerization, which is triggered by photoinitiation by means of UV light. In contrast, solvent-containing printing inks are generally available which can be subjected not only to physical but also to chemical drying treatments. Physical drying includes evaporation of the solvent and diffusion (penetration) in the print substrate, whereas chemical drying or oxidative drying is understood on the basis of polymerization of the oils, resins, binders, etc. contained in the ink formulation, which polymerization is sometimes carried out in the presence of oxygen in the air. These drying processes are often interdependent in that separation between the solvent and the resin occurs inside the binder system by penetration of the solvent, whereby the resin molecules approach each other and can sometimes be polymerized more easily.

A device for drying printed products is known, for example, from EP 0355473 a2, which comprises a radiation energy source in the form of a laser. The radiation can be directed onto the surface of the printing material between the individual printing units or at a location behind the last printing unit, in front of or inside the delivery unit, the printing material being moved through the printing press on a path by means of a transport device. The radiation source can be an ultraviolet laser for UV inks or a laser light source for heating solvent-containing printing inks. The radiation energy source is provided outside the printing press to avoid heating of parts of the printing press which are not intended to be heated due to unavoidable or isolatable waste heat. The disadvantages of this solution are: additional system components for the printer must be provided separately.

Furthermore, for removing solvents and/or water from solvent-containing printing materials, it is known, for example, from document US 6,026,748: a printing press is provided with a drying device with an infrared lamp which emits short-wave infrared light (near infrared light) or medium-wave infrared light. The emission spectrum of the lamp light source is broadband, resulting in a number of wavelengths being provided. The disadvantages of such an infrared drying device are: a considerable part of the energy is absorbed in the paper, wherein the ink is heated only indirectly. Rapid drying can only be achieved by a correspondingly high energy input. However, there is a major risk of uneven drying of the printing material and formation of waves.

In xerographic printing technology, for example, DE 4437077 a1 discloses: the tone fixation on the record carrier is performed by near infrared radiation energy emitted by a diode laser. The heating of the tonal particles is achieved by using a narrow-band light source to melt them, form a colour layer and fix them on the surface of the record carrier. Since most common paper types have a minimum absorption value in this spectral region, a significant portion of the energy can be absorbed directly into the tonal particles.

DE 10107682 a1 also discloses: the xerographic printer or copier may have a plurality of tone fixing devices, wherein each of the fixing devices emits electromagnetic radiation in a wavelength range corresponding to a maximum absorption wavelength corresponding to the tone type of the fixing device, but no or only little absorption at the absorption wavelengths of the other tone types.

However, the simple knowledge of the absorption window in the paper absorption spectrum cannot be directly applied in printing techniques using solvent-containing printing inks, since it is based on different chemical or physical drying methods as described above. In the context of the present invention, the concept of solvent-containing printing inks refers in particular to such inks: its solvent component, which may be aqueous or organic, is built on the basis of binder systems which allow oxidative, ionic or radical polymerization. The input energy for drying the solvent-containing printing ink should support or promote the solvent evaporation effect and/or the effect of penetration into the printing material and/or the polymerization effect, while avoiding undesirable side effects, such as excessive heating of the solvent-containing printing ink in particular, which can lead to decomposition of the components or overheating of the solvent. The input energy should not be used only to melt the particles, as is the case for tone fixation.

The prior application document DE 10149844.6 discloses: an infrared absorber, i.e. a material which absorbs in the near infrared spectral range, is mixed in the printing ink to be printed in the printing unit. The printing ink on the printing material is irradiated by means of a narrow-band radiation energy source, preferably a laser light source, arranged downstream of the printing gap. The input of light of a wavelength which is essentially resonant with the wavelength of the infrared absorber enables or supports the input of energy into the printing ink such that the printing ink is dried. The wavelength of the radiation energy source and the absorption wavelength of the infrared absorber are selected such that the wavelength used is not at the same time resonant with water, in order to reduce or prevent energy input into the printing material.

Disclosure of Invention

The object of the present invention is to provide a method for the photo-drying of printing inks in a printing press by means of a narrow-band radiation energy source, in which the incorporation of infrared-absorbing materials into the printing ink to be printed can be dispensed with. A printing device suitable for carrying out the method is also provided.

According to the invention, this object is achieved by a printing ink drying method having the features of claim 1 and by a printing unit according to claim 8. Advantageous further configurations and embodiments of the invention are the features of the dependent claims.

In the method according to the invention for drying printing ink on a printing substrate, the printing substrate is moved through a printing press along a path. At a position, a section or a coordinate value of the path, the printing material is printed with at least one printing ink, in particular an offset printing ink, having at least one pigment. At a subsequent time, the printing material is irradiated at least one further point of the path with light from a narrow-band radiation energy source, i.e. a laser light source, wherein the light has a wavelength, in particular only a wavelength, which is between 350nm and 700nm, substantially resonant with an absorption wavelength of the at least one pigment of the at least one printing ink. By narrow band is meant that the light source emits only wavelengths around a central wavelength of 20.0nm, preferably 10.0nm, in particular 2nm, or even only a narrow line of the spectrum. In other words, a laser light source is used or introduced in the method according to the invention, which emits light with a wavelength between 350nm and 700nm, wherein this light is essentially resonant with an absorption wavelength of the at least one pigment of the at least one printing ink. In this way, an efficient and rapid drying can be achieved. The infrared absorbing material in the ink may be omitted.

The inventive method is based on the knowledge that: the excellent absorption capacity of pigments used in printing inks, in particular offset printing inks, in particular of the current standard pigments, can be used to couple energy input in the form of light into an ink layer of a substrate which has just been printed with the printing ink. In other words, the absorption of the radiation energy can be supported, allowed, caused or at least accelerated by at least one ink pigment in the printing ink. The influence on the drying process is achieved by the heat generated. The chemical reaction is initiated by the heat generated when required. For the present pigments which absorb a certain wavelength, preferably a certain wavelength at maximum, a special laser light source emitting light at this certain wavelength can be used.

In a preferred embodiment of the method, the wavelength of the light used is between 450nm and 750 nm. The pigments of popular offset printing inks (standard: cyan C, magenta M, yellow Y and black K) absorb very well between 350nm and 700 nm: typically printing inks C, M, Y, K at 400nm to 500 nm; c, M, K at 400nm to 600nm and C and K at 400nm to 750 nm. For a typical pigment, the maximum absorption is on the following scale: c (Clariant standard pigment blue 15:3) 650. + -.100 nm, even below 550nm up to 400nm with a low absorption value; m (Clariant standard pigment Red 57:1) 500. + -. 100 nm; and Y (Clariant standard pigment yellow 13) 400. + -.100 nm. In this spectral range, the printing material paper and water (H)₂O) has a low absorption capacity. The water absorption is less than 10%, in a preferred embodiment less than 1%, most preferably less than 0.1%. The absorption of the printing material web drops strongly above 400nm, and in the range between 450nm and 750nm this does not matter (that is to say in any case less than 20%, in preferred embodiments less than 20%)Less than 10%, especially less than 5% in the examples). The wavelength of the light is preferably substantially resonant with the absorption maximum of the at least one pigment of the at least one printing ink. In other words, the radiation energy source emits a wavelength corresponding to the absorption of the ink pigments. That is, the light emitted by the radiation energy source is preferably substantially resonant or nearly resonant, in particular resonant, with the absorption wavelength, in particular the maximum absorption, of the pigment, so that the absorption of the pigment coincides as well as possible with the maximum emission of the laser light source. A pigment may have one or more local absorption maxima. The wavelength of the emitted light is substantially resonant with the absorption wavelength of the pigment when the wavelength of the light is at least within the edges of the (spectral) absorption line of the pigment. At least the absorption wavelength and the wavelength should differ by less than +/-50 nm.

Alternatively or additionally to this, the wavelength of the light may be in contact with water (H)₂O) do not resonate at the absorption wavelength. In the context of the present invention, the concept of "non-resonance" with respect to the absorption wavelength of water should be understood as: the radiation energy absorbed by water at 20 ℃ is not higher than 10.0%, in a preferred embodiment not higher than 1.0%, in particular not higher than 0.1%. In other words, the narrow band radiation energy source, particularly the laser light source, may emit only very low intensity light resonant with the water absorption wavelength, preferably none.

The process of the invention can be applied to a large number of printing inks to be printed, with particular advantages: the substrate is printed at locations along a path through the printing press with different printing inks, each printing ink having at least one different pigment. At least at another location of the path, the print substrate is illuminated with light of different wavelengths, wherein each of the different wavelengths is substantially resonant with one of the absorption wavelengths of the different pigments. In other words, the method according to the invention can be used for a plurality of printing inks in multicolor printing, wherein for each of the printing inks used a resonance wavelength is used, one for each pigment.

In terms of layout in the printing press, the method according to the invention, which is further developed in this way, can be implemented at least in the following manner: the printing material can be irradiated with light of different wavelengths at other points in the path, wherein the printing material is irradiated with a wavelength which is substantially resonant with the pigments of the printed printing ink, after printing with one of the printing inks and before printing with the other, unprinted printing ink of the printing inks. In particular, the printing material can be irradiated with light of a wavelength which is essentially resonant with the absorption wavelength of one pigment at a location behind the location at which the printing ink with the pigment is applied to the printing material and in front of another location at which another printing ink with another pigment is printed on the printing material.

Alternatively, the printing material can be irradiated with light of the different wavelengths at a point in the path after being printed with the different printing inks in time. In other words, before the printing material is irradiated with light of these wavelengths, the printing material passes through locations on its path through the printing press, at which the printing inks are applied.

The absorption capacity of the pigments is supported by the fact that a relatively high energy input can advantageously be carried out directly into the printing ink without the undesirable input of energy into the printing material. The total input energy required is reduced. The radiation energy absorbed in the printing ink amounts to more than 30%, preferably 50%, in particular 75% and even more preferably to more than 90%.

The inventive concept also relates to a printing unit having at least one laser light source which is assigned to the printing unit, in particular is arranged downstream of the printing gap along the path of the print substrate through the printing unit. The printing device according to the invention is suitable for carrying out the method according to the invention described, wherein the light of the laser light source has a wavelength between 350nm and 700nm in order to achieve emission in the narrowest possible band while having a high spectral power density.

The laser light source is preferably a semiconductor laser (diode)Laser, quantum wave laser, InGaAsP laser), a gas laser (HeNe, argon ion), a solid-state laser (titanium-sapphire, erbium-glass, Nd: YAG, Nd-glass, Nd: YVO)₄Pr ZBLAN, Yb ZBLAN (PR-lasers, Yb-doped fluoride glass lasers, etc.), a diode-pumped, frequency-multiplied solid-state laser (DPSS-laser) or a frequency-multiplied semiconductor laser. The solid state laser may preferably be optically pumped by one or more diode lasers. Advantageously, the laser light source has a wavelength of 450nm +/-50nm, 500nm +/-100nm, 525nm +/-75nm, 550nm +/-50nm, 600nm +/-150nm, 600nm +/-100nm or 600nm +/-50 nm. The laser emission preferably has a spectrally narrow line width, whose center wavelength may be, in particular: 430nm +/-50nm, 442nm +/-50nm, 457nm +/-50nm, 473nm +/-50nm or 532nm +/-50 nm. Such lasers can advantageously be tunable within a limited range. In other words, the output wavelength of the laser is changeable. This can be tuned to a desired wavelength, for example, to be resonant or nearly resonant with the absorption wavelength of a pigment in the printing ink. The light of the laser light source is widened along a light path, on which an imaging optics for generating a widened or focused light beam, in particular a light cone on the surface of the printing material, can be arranged.

In an advantageous embodiment, the printing couple according to the invention has laser light sources which are arranged in a one-dimensional field, a two-dimensional field (partially curved, fully curved or flat) or a three-dimensional field and whose light impinges on the print substrate at a plurality of locations. By using individual laser light sources for the individual regions on the printing material, the required maximum output power of the laser light source is reduced. Laser light sources with lower output power are generally lower in cost and have longer life expectancy. Furthermore, the occurrence of unnecessarily high waste heat can be avoided. The energy of radiation per unit area brought about by the input light is in the range of per square centimeter (cm)²) Between 100 and 10,000mJ, preferably between about 100 and 10,000mJ per square centimeter (cm)²) Between 100 and 1,000mJ, in particular between each square centimeter (cm)²) Between 200 and 500 mJ. The duration of irradiation of the substrate is withinBetween 0.01ms and 1s, preferably between 0.1ms and 100ms, in particular between 1ms and 10 ms.

It is particularly advantageous that for each laser light source the light falling on a location on the print substrate can be controlled in terms of its intensity and duration of irradiation independently of the other laser light sources. For this purpose, a control unit can be provided separately or integrated in the printing press machine control. The control of the laser light source parameters enables the energy input at different positions of the printing material to be adjusted. The energy input can thereby be adapted to the print substrate at the current position of the print substrate. It is also advantageous if the printing couple according to the invention is equipped with laser light sources in such a way that the light of at least two radiation energy sources impinges on a location on the printing material. In this case, on the one hand, partially overlapping light beams and, on the other hand, completely overlapping light beams can be involved. The required maximum output power of the individual laser light sources is reduced and, furthermore, if one laser light source fails, there is still a redundant laser light source.

The printing press according to the invention is characterized by at least one printing unit described with a laser light source. In a further embodiment of the printing press according to the invention with at least two printing units, the latter printing unit with a plurality of laser light sources is used to carry out the method according to the invention on a number of printing inks to be printed, the light of the laser light sources having a number of wavelengths between 350nm and 700 nm. When the printing press is a sheet-fed printing press, the laser light source or the laser light sources of the downstream printing unit can be located in the delivery unit. The expression "downstream printing unit with several laser light sources" is also understood to mean such a geometric arrangement. In other words, the delivery of the printing press can have laser light sources suitable for carrying out the described method, wherein these laser light sources emit wavelengths between 350nm and 700 nm.

The printing press of the present invention may be a direct or indirect flat press, lithographic press, offset press, flexographic press, etc. On the one hand, the position of the light falling on the print substrate in the path through the printing press can be arranged after the last printing gap of the last of these printing units, i.e. after all printing gaps. On the other hand, this position can also be arranged after a first printing gap and before a second printing gap, i.e. at least between two printing units. The printing press may be a sheet-processing printing press or a web-processing printing press. Sheet-fed printing presses can have a sheet feeder, at least one printing unit, possibly a finishing unit (punching unit, varnishing unit, etc.) and a delivery unit. The web-processing printing press may comprise a roll changer, a plurality of printing units for printing the printing material web from both sides, a dryer and a folding device.

Drawings

Further advantages and advantageous further embodiments of the invention are described below with the aid of the figures and their description. The figures each show:

figure 1 is a schematic view for explaining the method of the invention in a printing press,

FIG. 2 is a schematic view of an advantageous configuration of a printing unit according to the invention in a printing press, and

fig. 3 is a schematic illustration of a printing press with different laser light sources which can be arranged alternately on the printing unit or after the last printing unit.

Detailed Description

Fig. 1 shows a schematic diagram for explaining the method according to the invention used in a printing press. A laser light source 10, preferably a diode-pumped, frequency-multiplied solid-state laser, emits laser light having a wavelength between 350nm and 700nm, and is arranged in a printer in such a way that: so that the light 12 emitted by it falls on a substrate 14 which is transported through the printing press on a path 16. The orientation of the path 16 is indicated by an arrow. The path 16 passes through a print gap 18 between a print cylinder 110 and a counter cylinder 112. The print cylinder 110 may be a plate cylinder or a blanket cylinder, depending on the particular printing process in the printing press. At the location of the printing gap 18 of the path 16, the print substrate 14 is printed with at least one printing ink having at least one pigment. In fig. 1, the printing substrate 14 is represented by way of example as a sheet, but in a variant it can also be moved in the form of a strip through the printing press along the path 16. The path 16 is shown here as a straight line, without being limited to a generally curved or non-straight course, in particular not to a circular arc.

A printing ink 114 is shown on the substrate 14 after passing through the printing gap 18. After printing, the printing material 14 is irradiated at a point 116 of the path 16 with light 12 of the laser light source 10, wherein the light 12 has a wavelength between 350nm and 700nm and is essentially resonant with an absorption wavelength of the pigments. The light 12 emitted by the laser light source 10 falls in a beam-like or carpet-like manner on the print substrate 14 at the location 116. The printed ink 114 in the location 116 may absorb energy from the light 12. By advantageously selecting or coordinating the wavelength of the light 12 according to the invention, it is achieved that the energy is absorbed by the pigments in the printing ink 14, whereby the energy for drying the printing ink 14 is directly input into the printing ink 14.

Fig. 2 is a schematic illustration of an advantageous embodiment of the configuration of a printing unit 30 according to the invention, in which a number of laser light sources 10 are provided in a printing press 40. A field 20 of laser sources 10 is shown, here 3 by 4, i.e. 12 laser sources 10. In addition to the two-dimensional field 20, a three-dimensional field or a one-dimensional row oriented across the width of the print substrate 14 may also be provided. A two-dimensional field and a three-dimensional field, the optical two-dimensional distribution of which falls on the print substrate 14, have the main advantages: by irradiating a set of locations within a gap of the field 20 in parallel or simultaneously, rapid drying may be achieved. Thus, the speed at which the print substrate 14 moves past the laser source 10 can be higher than if there was only one-dimensional field. The field 20 may also have a different number of radiation energy sources than that shown here in fig. 2. Light 12 is delivered from each of these laser light sources 10 onto a substrate 14. Light 12 lands on the print substrate 14 along a path 16 through the printing press at a location 116, which location 116 is positioned behind a print gap 118 defined by a print cylinder 110 and a counter-print cylinder 112. In this case, the individual positions 116 can partially coincide, as shown in the preceding row of radiation energy sources 10 in fig. 2, or even overlap substantially completely. A control device 24 is associated with the field 20 formed by the radiation energy source 10, with which the field 20 can exchange control signals by means of a connection 22. The control device 24 can control the field 20 in such a way that: so that energy input is made corresponding to the amount of printing ink at location 116 on the substrate 14. In this advantageous embodiment, in particular, the laser light sources 10 in the field 20 can be controlled individually with regard to the irradiation duration and the irradiation intensity.

Fig. 3 shows a schematic representation of a printing press, which in this embodiment is a sheet-fed printing press, with different laser light sources that can be arranged as alternatives to one another in the printing unit according to the invention. By way of example, the printing press has 4 printing units 30, a feeder 32 and a delivery 34. The figures show various cylinders in a printing machine which are used, on the one hand, to convey a sheet through the printing machine and, on the other hand, to provide a printing surface directly as a plate cylinder or indirectly as a blanket cylinder. The typical printing unit 30 in the printing press 40 furthermore has an inking unit and, if necessary, a dampening unit, not shown in the figures. The substrate material passes along path 16 through a printer 40.

Each printing unit 30 comprises a printing cylinder 110 and a counter-printing cylinder 112, which define a printing gap 18, so that the printing material can be printed in a number of positions (number of printing gaps 18) with different printing inks, each printing ink having at least one different pigment. The printing press shown in fig. 3 shows a plurality of possibilities, for example, that the printing material 14 is irradiated with light of different wavelengths at least one further point of the path 16, wherein each of the different wavelengths is essentially resonant with one of the absorption wavelengths of the different pigments. In a specific embodiment of the printing press, one of the possibilities shown can be used for all printing units.

A first possibility of such an arrangement is represented by the first and second printing devices 30: the emitted light is guided from a central laser light source 36 via light-guiding elements 38, for example optical waveguides, mirrors, imaging optics, etc., to projection elements 310, which are arranged in correspondence with the printing unit 30. These projection elements 310 emit light 12 onto a location 116 on the path 16 of the print substrate 14 through the printing press, wherein the print substrate passes the location 116 in time after being printed with printing ink with a pigment corresponding to the wavelength of the light 12. By using the light-conducting element 38, the laser light source 36 can be arranged in a suitable position in or near the printing press 40, in particular the printing unit 30, on which a corresponding installation space is available.

A second possibility of such an arrangement is represented by the third and fourth printing devices 30 with the laser light source 10. Starting from the light source 10, the light 12 is conveyed directly onto a path 16 of the print substrate 14. This possibility of the arrangement has the layout already shown in fig. 1 and 2.

Finally, fig. 3 shows a third possibility for the last printing group 30: the last printing unit 30, which is arranged downstream of the other printing units of the printing press 40, comprises a laser light source 312 in one switchable position 116 toward the delivery unit 34 and a further laser light source 314 in a further switchable position 116. These switchable positions 116 may also be located in the delivery unit 34. In an arrangement according to the third possibility, the printing material can be irradiated at a position 116 of the path 16 with a number of different wavelengths of light 12, after being printed in time with all of these numbers of printing inks.

In a similar manner to the configuration shown by the sheet-fed printing press in fig. 3, the printing couples according to the invention can also be used advantageously in web-fed printing presses, in particular so-called web-fed rotary printing presses, for advertising or newspaper printing.

Claims (15)

1. Method for drying printing ink (114) on a print substrate (14) in a printing press (40), wherein the print substrate (14) is moved through the printing press (40) along a path (16), the print substrate (14) is printed with at least one printing ink (114) having at least one pigment at a position (18) of the path (16), and, after this in time, the print substrate (14) is irradiated with light of a laser light source (10) at least one further position (118) of the path (16), characterized in that: the light (12) has a wavelength between 350nm and 700nm that is substantially resonant with an absorption wavelength of said at least one pigment of said at least one printing ink (114).

2. The drying method according to claim 1, characterized in that: the light (12) has a wavelength between 450nm and 750 nm.

3. Drying method according to claim 1 or 2, characterized in that: the wavelength of the light (12) is substantially resonant with the maximum absorption of the at least one pigment of the at least one printing ink (114).

4. Drying process according to claim 1, 2 or 3, characterized in that: the wavelength of the light (12) and the water (H)₂O) do not resonate at the absorption wavelength.

5. Drying method according to one of the preceding claims, characterised in that: printing the printing material (14) with different printing inks (114) at positions (18) of the path (16), wherein each printing ink (114) has at least one different pigment, and irradiating the printing material (14) with light (12) of different wavelengths at least one further position (116) of the path (16), wherein one of the different wavelengths is essentially resonant with one of the absorption wavelengths of the different pigments.

6. The drying method according to claim 5, characterized in that: the printing material (14) is irradiated with light (12) of different wavelengths at further locations (116) of the path (16), wherein the printing material (14) is irradiated temporally after printing with one of the printing inks (114) and before printing with a printing ink which has not yet been printed in another of the printing inks (114) with a wavelength which is substantially resonant with that printed ink.

7. The drying method according to claim 5, characterized in that: the printing material (14) is irradiated with the light (12) of different wavelengths at a position (116) of the path (16) at a time after being printed by the printing inks (114).

8. Printing device (30) for carrying out the method according to one of claims 1 to 4, having a laser light source (10), characterized in that: the light (12) of the laser light source (10) has a wavelength between 350nm and 700 nm.

9. Printing unit (30) according to claim 8, characterized in that: the laser light source (10) is a semiconductor laser, a gas laser, a solid-state laser, a diode-pumped, frequency-multiplied solid-state laser or a frequency-multiplied semiconductor laser.

10. Printing device (30) according to claim 7 or 8, characterized in that: the printing unit (30) has a plurality of laser light sources (10) which are arranged in a one-dimensional, a two-dimensional or a three-dimensional field and whose light (12) falls on a plurality of locations (116) on the printing material (14).

11. Printing unit (30) according to claim 8, 9 or 10, characterized in that: for each laser light source, the light (12) impinging on the print substrate (14) at one location (116) is controllable with respect to its intensity and/or irradiation duration.

12. Printing unit (30) according to claim 8, 9, 10 or 11, characterized in that: the wavelength of the laser light source (10) is 430nm +/-20nm, 442nm +/-20nm, 457nm +/-20nm, 473nm +/-20nm or 532nm +/-20 nm.

13. Printing unit (30) according to one of claims 8 to 12, characterized in that: the light (12) of at least two laser light sources (10) is incident on a location on the printing material.

14. A printing press (40), characterized by: having at least one printing unit according to one of claims 8 to 13.

15. Printing machine (40) having at least two printing units (30), characterized in that: the downstream printing device (30) has laser light sources (10) suitable for carrying out the method according to claim 7, wherein the light (12) of the laser light sources (10) has wavelengths between 350nm and 700 nm.