WO2020109615A1

WO2020109615A1 - Method and device for position-selective carbonization of a substrate

Info

Publication number: WO2020109615A1
Application number: PCT/EP2019/083195
Authority: WO
Inventors: Venkatesh SESHAIYA DORAISWAMY CHANDRASEKAR
Original assignee: Macsa Id, S.A.
Priority date: 2018-11-30
Filing date: 2019-11-29
Publication date: 2020-06-04

Abstract

The invention relates to a method for position-selective carbonization of a substrate wherein at least one predefined area of said substrate is heated prior the selective carbonization. The invention also relates to a device configured for performing the method.

Description

METHOD AND DEVICE FOR POSITION-SELECTIVE CARBONIZATION OF A SUBSTRATE

DESCRIPTION

The invention relates to a method for position-selective carbonization of a substrate. The invention also relates to a device for position-selective carbonization of a substrate.

Inkless printing devices rely on the thermal process of selective carbonization to print or mark on substrates comprising cellulose such as paper and cardboard without the need of ink. This selective carbonization, i.e. the inkless printing, can be applied to regular substrates omitting the need of special coatings, special heat sensitive paper or special wavelength-sensitive paper. Another benefit is that there is no need for the use of consumables such as toners which is beneficial from environmentally point of view. This also applies to the omission of ink.

For the quality of the print it is important that the contrast between the print and the substrate is sufficient. An adequate contrast is in particular relevant when printing text, numbers and/or barcodes. Laser-based inkless devices can already achieve a desired, and therefore optimal, contrast, however, therefore the printing needs to be performed at relatively low scan speeds. Additionally, it is recommended that the print is made on a white background such as white paper or white cardboards, since further types of non white substrates, such as brown cardboards, may result in a decreased contrast between the substrate and the print, resulting in a lower quality of the print. Applying a relatively low scan speed, compared to conventional printers, is also required for optimising the blackness of the print. When operating at low scan speed the print can achieve the lowest lightness value, which corresponds to an optimum blackness. However, the low scan speed results in a relatively long printing time. A further drawback of the state of the art is that the print depth of the print with respect to the substrate for a fixed power density of the laser increases with time. Hence, when operating at low scan speed the print will be deeper into the material, and by defect decreasing the strength of the substrate material and increasing the probability of burning through the material leading till hole formation.

It is therefore desired to provide an improved method and/or device for inkless printing wherein an optimized contrast between the print and the substrate can be obtained. It is also a desired to provide an improved method and/or device for inkless printing wherein the scan speed during printing can be increased. It is a goal of the invention to provide at least one solution for abovementioned aims.

The invention provides thereto a method for position-selective carbonization of a substrate, comprising the steps of:

a) providing at least one carbonizable substrate, in particular a cellulose substrate,

b) heating at least one predefined area of said substrate, and

position-selectively carbonizing at least a part of at least one heated area of said substrate by position- selectively irradiating said at least one heated area, by using at least one primary irradiation source, to form at least one printed marking within said area. The method according to the invention focusses on preheating at least one predefined area of the carbonizable substrate before said area is position-selectively irradiated. The position-selectively irradiation up to temperature exceeding the carbonization temperature of the substrate can be referred to as inkless printing. The preheating of at least one predefined area provides that the heating step to be made during step c) to reach a temperature exceeding the carbonization temperature of the substrate is deceased. This reduces the temperature difference between the temperature of the area of the substrate to be position-selectively irradiated and the carbonization temperature provides the advantage that the position-selective carbonization can be achieved in a shorter time interval. Due to the relatively short temperature difference to overcome with respect to a conventional method of carbonization of substrate being at for example room temperature it is experimentally found that the intensity and/or power density and/or exposure time of the irradiation source can be reduced. Despite a lower intensity and/or power density an equal level of blackness of the position-selectively carbonized print can be obtained. A further benefit of preheating the substrate before the position-selective carbonization is that the final carbonization and this print of the surface will be more superficial. Due to step b) of the method according to the invention the temperature of the area to be carbonized is above and initial temperature of the substrate, generally the room temperature, wherefore the temperature increase of the substrate towards carbonization temperature, which is generally above 270 degrees Celsius, more in particular above 400 degrees Celsius, is reduced. A known effect of a relatively large and sudden temperature increase is that such temperature increase may cause ablation. This undesired ablation can be prevented by the method according to the invention, in particular by step b) thereof. Furthermore step b) of the method according to the invention provides photothermal activation of at least one predefined area of the substrate. This photothermal activation causes a higher blackness of the inkless print, compared to non-thermally activated carbonization of a substrate. A higher blackness of the print generally corresponds to a higher contrast of the print with respect to the substrate, resulting in a better visibility of the print. A further benefit of the method according to the invention is that a higher scan speed of at least one beam of the primary irradiation source, in particular at least one laser beam of the laser, can be used. This will subsequently result in a reduced printing time. It is beneficial to heat at least one predefined area and possibly multiple predefined areas of the substrate, since this may improve the energy efficiency of the heating step. The area(s) to be heated can be limited to the area(s) of the substrate which are carbonized. Therefore the risk of discolouring and/or damaging of the substrate due to unnecessary heating of the substrate or parts thereof can be omitted.

The carbonization used during step c) of the method according to the invention is typically based upon pyrolysis, and hence is also referred to as pyrolytic carbonization. The advantages of pyrolytic carbonization is that carbon can be produced in a relatively simple and cost-efficient manner, without needing complicated facilities. Typically, at an early stage of pyrolysis (400°C<T<600°C), cyclization and aromatization proceed in the carbonizable substrate, typically formed by an organic precursor, with the release of various organic compounds like hydrocarbons, and inorganic matters such as CO, C0₂, H₂0, mainly because some of the C-C bonds are weaker than C-H bonds. Over 600°C, out-gassing is typically hydrogen (H₂) due to the polycondensation of aromatics. Up to 1500°C, though this temperature doesn’t have to be necessarily reached, the residues which have“suffered” from carbonization may be called carbonaceous solids though they might still contain hydrogen. Above 1500, graphitization begins so the residues contain more than 99% of C which are thus called carbon materials. The occurrence of reactions, including cyclization, aromatization, polycondensation and graphitization, depends strongly on the substrate used as well as heating conditions. Sometimes these processes overlap with each other throughout pyrolysis and therefore, the whole process from precursor to the final carbon residues is often simply called “the carbonization”. In the method according to the invention at least cyclization and aromatization take place.

It has been found that the flame retardants could facility and stabilize the pyrolysis process of the carbonizable substrate. For example, the preferred presence of dihydrogen phosphate (GDP), ammonium phosphate (DAP), and diguanidine hydrogen phosphate (DHP) in and/or on the substrate leads to an increase of 33% on carbon yield. Moreover, water-soluble organosilicon, whether alone or mixed with other ammonium additives, also helps increasing carbon yield to an important extent and improving simultaneously mechanical resistivity of carbon particles and carbon fibres. It was also found that impregnation of the substrate with a diluted sulfuric acid solution before step b) and/or c) is performed, or conducting the pyrolysis process of step c) in a hydrogen chloride (HCI) atmosphere helps increase the carbon yield to 38%. Hence, it is preferred that the substrate is treated with at least one of the aforementioned additives prior to performing step c) and preferably prior to step b) and/or to subject the substrate during at least step c) in an acidic environment. Instead of applying an acidic environment during step c), it will be clear that step c) may also be applied in air (atmospheric conditions) or in an inert atmosphere.

Carbonizable substrates refer to substrates, in particular sheets or layers, which can get carbonised at elevated temperature, typically temperatures of 270 degrees Celsius and higher, more specifically temperatures of 400 degrees Celsius and higher. Examples of carbonizable substrates are cellulose based materials like paper, brown carton, wood, etcetera. Also the use of coloured substrates is possible when applying the method according to the invention. It is also conceivable that the substrate is formed by a carbonizable polymer, like polyimide or polyamide.

The irradiation which is required and applied during step c) is sometimes referred to as heat. This irradiation applied during step c) is generated by using a primary irradiation source, in particular laser, more in particular a gas laser, even more in particular a carbon dioxide laser (C0₂ laser). Carbon dioxide lasers are the highest-power continuous wave lasers that are currently available. And they are also quite efficient: the ratio of output power to pump power can be as large as 20%. The C0₂ laser typically produces a beam of infrared light with the principal wavelength bands centering on 9.4 and 10.6 micrometres (pm). Lasers typically operate relatively fast and, moreover, are flexible, as a result of which lasers are ideally suitable to create different track, pads, or electronic circuits, or parts thereof, within a short time frame. Instead of using a laser, it is also imaginable that the substrate is irradiated position- selectively in another manner, for example by using a heated stamp to physically burn, position- selectively, the substrate. Alternatively, a mask may be applied onto the substrate after which the uncovered parts of the substrate are heated, for example by means of a heated air flow, to temperature above the carbonization temperature. Stamps and masks are typically useful in case a standard track layout and/or pad layout would be desired. Optionally, step c) is repeated a plurality of times, such that at least one irradiated part of the substrate is irradiated a plurality of times. However, step b) may event prevent that multiple irradiation of a part of the substrate is necessary.

In a possible embodiment, the method according to the invention comprises the step of determining at least one marking to be printed during step C), and predefining at least one area to be heated based upon said determination of the at least one marking. This determination step preferably takes places between step a) and step b). During this determination in particular the shape and/or the size of the at least one marking are determined, and/or the position of the at least one marking is determined with respect to the substrate. It is imaginable that merely the area to be carbonized during step c) is (pre)heated during step b). It is also imaginable that only a part of the area to be carbonized during step c) is (pre)heated during step b). Moreover, it is conceivable that not only the area to be carbonized during step c) is (pre)heated during step b), but that also at least one other part, and possibly the complete substrate, is (pre)heated during step b). The carbonized part of the substrate may represent text, drawings, pictures, dots, and/or by any other graphical representation. Here, it is conceivable that the carbonized part in fact is based upon and/or formed by a plurality of carbonized (sub)parts, each carbonized (sub)part forming, for example, a dot, text, character making part of a greater graphical representation.

In a preferred embodiment, the total area of a substrate is heated during step b) at least equals the total area of said substrate which is position-selectively carbonized during step c). It is also conceivable that the total area of a substrate heated during step b) is larger the total area of said substrate which is position-selectively carbonized during step c). It is also possible that the total area of a substrate heated during step b) is equal to or smaller than the total area of said substrate which is position-selectively carbonized during step c). Abovementioned embodiments are beneficial since the total area to be heated can be reduced to merely the minimum required in order to perform the method according to the invention.

In a possible embodiment of the method according to the invention, at least one predefined area during step b) is heated to a temperature below the (minimum) carbonization temperature of the substrate, in particular up to 10 degrees Celsius below the carbonization temperature and more in particular up to 5 degrees Celsius below the carbonization temperature. The minimum carbonization temperature may deviate slightly dependent on the type of carbonizable substrate used and/or be dependent on one or more process conditions, such as the exposure time. Hence, the (minimum) carbonization temperature could either by fixed (predefined, and thus independent of the circumferential factors (process conditions)) and/or could be dependent on circumferential factors (process conditions). However, generally the carbonization temperature is above 270 degrees Celsius, more in particular above 400 degrees Celsius. The temperature chosen for the preheating is for example in the range of 20 to 5 degrees Celsius below the carbonization temperature. It is also possible that during step b) at least one predefined area is heated to a temperate in the range of 100 degrees Celsius to 270 degrees Celsius, preferably in the range of 200 degrees Celsius to 250 degrees Celsius. In a preferred embodiment of the method according to the invention, during step b) at least one predefined area of the substrate is heated for a period of time situated in between 0 and 5 seconds. The temperature of the substrate can for example be measured using a non-contact temperature sensor, such as an infrared temperature sensor. The preheating of the substrate can be stopped once the desired local substrate temperature for step b) is obtained.

Preferably, at least one predefined area of the substrate is heated via radiative heating, in particular via illumination by at least one secondary irradiation source, in particular a light source. Radiative heating is advantageous compared to for example heating via conduction or heating via convection, since it enables relatively controlled and localized heating of a predefined area. The localized heating can for example be done by using a light source, such as a laser, an infrared light source and/or a single- or multipoint illumination element.

In a preferred embodiment of the method according to the invention, steps b) and c) are successive steps. It is however also possible that step b) and step c) are substantially simultaneously performed. It is also possible that step b) and step c) are partially overlapping in time. The time interval between step b) and step c) is preferably chosen such that the preheated area remains at a sufficient temperature till the step c) is performed. The time interval between step b) and step c) is preferably at most 2 seconds, preferably at most 1 second.

In a preferred embodiment of the method according to the invention, during step c) a part of the substrate is position-selectively irradiated for a period of time situated in between 0 and 5 seconds. Typically, this time interval will be sufficient to convert the substrate position-selectively into char (carbon particles/fibres).

It is commonly advantageous in case, during step c), the substrate and the at least one irradiation source, preferably a laser, and more preferably a diode laser and/or a C0 laser, are mutually displaced by using a speed which is at least 10 mm/s. This speed is also called the printing speed, the marking speed, or the carbonization speed.

In a possible embodiment it is conceivable that step b) is conducted by using said primary irradiation source. The process parameters of the primary irradiation source possibly need to be adapted to the step to be performed.

In a further possible embodiment of the invention, the primary irradiation source is configured to generate at least one beam having a core (centre beam) and a sheath (peripheral beam), wherein said sheath of the beam is configured to heat at least a part of the substrate according to the step b), and wherein said core of the beam is configured to conduct the position-selective carbonization in accordance with step c). This means that said beam can be or is shaped such that the sheath of the beam heats at least a predefined area of the substrate before the core of the beam position-selectively carbonizes said predefined area of the substrate. Typically, the power density of the core is larger than the power density of the sheath. The power density of the beam of the primary irradiation source, in particular the laser, is preferably adjustable, and more preferably such that the beam spills over with respect to the core of the beam (forming a sheath), resulting in that the sheath of the beam serves as heating source for heating a predefined are of the substrate before it is selectively carbonized. Basically, the beam of the primary irradiation source is out of focus when it reaches the substrate. However, since in this embodiment the beam comprises a (high-power density) core it is still possible to achieve a relatively sharp marking. In this embodiment the heating source thus forms integral part of the primary irradiation source. The sheath of the beam can also be used for post-heating and/or post-irradiating of at least part of the surface, in particular the at least one carbonized substrate part generated during step c). This post-heating step may further contribute to the blackness of the print.

An embodiment of the method according to the invention is possible, wherein at least part of the substrate is subjected to at least one photochemical bleaching step, preferably prior to step b). By applying such chemical bleaching step at least part of the substrate will be whitened due to irradiation. With the term bleached or whitened it is meant that the lightness value (L^*), as defined in the CIELAB colour space, is increased. An increased lightness value of a substrate corresponds to a lighter colour of the substrate. This advantageous since the contrast between the print and the substrate is substantially dependent on the difference is lightness value of the substrate and the lightness value of the print. A larger difference between these values consequently corresponds to a better contrast. The photochemical bleaching step is preferably applied before selective carbonization of the substrate and preferably before step b). Applying at least one photochemical bleaching step is in particular useful when using an non-white substrate, such as but not limited to, brown cardboard. This embodiment is for example in particular beneficial when printing a (matrix) bar code or QR code, since these codes require a sufficient contrast between the print and the substrate.

It is for example possible that the photochemical bleaching is performed by irradiation of at least part of the substrate with an irradiation source using a power density in a range of 20k W/cm2 to 140 kW/cm2 and applying a irradiation time of at most 55 microseconds. The irradiation source can be either the primary irradiation source used for the carbonization of the substrate or a further secondary irradiation source. The irradiation of at least part of the substrate with an irradiation source, preferably a laser, with a power density in the range of 20 kW/cm2 to 140 kW/cm2, preferably 30 kW/cm2 to 120 kW/cm2, preferably 53 kW/cm2 to 77 kW/cm2. Preferably, an irradiation of 55 microseconds or below results in a thermal shock of the substrate. The thermal shock provides the photochemical bleaching effect. As a further result of the thermal shock at least part of the water content of the treated area will be evaporated. At least part of the evaporated water may optionally be removed via an extractor. The photochemical bleaching step is generally performed as an additional step, however, it is also possible that the chemical bleaching step replaces step b) of the method according to the invention. A table with the corresponding power densities for the whitening depending on the DC value is given below. The values 20 to 140 kW /cm2 is a wider range than the one that we used. The optimum range value is between 53 and 77 kW/cm2.

Power based Power density

DC value (%) Spot size (cm)

on best fit (W) (kW/cm2)

10 7.6746 0.018 30.2

15 13.6261 0.018 53.5

20 19.5776 0.018 76.9

30 31.4806 0.018 123.7 Scan speed Spot size Irradiance time

(mm/s) (mm) (microseconds)

7620 0.18 23.6

7620 0.4 52.5

It is could also be advantageous in case the method comprises step d), comprising of post-irradiating at least the irradiated parts of the substrate after completion of step c), preferably by using at least one laser selected from the group consisting of: a blue laser, a green laser, a blue-green laser. These lasers generate electromagnetic radiation with a wavelength of 455-529 nm. Experiments have shown that this post-irradiation (post-illumination) further improves the blackness of the irradiated, carbonized substrate parts, which is in favour of the contrast of the print with respect to the substrate.

The method according to the invention preferably comprises step e), comprising the step of increasing the bond strength between at least one marking printed and/or to be printed during step c) and the substrate. This will lead to an improved fixation of the printed marking(s) onto the substrate. Increasing the bond strength can be realized in different manners, wherein step e) can be performed prior and/or after step c), and wherein step e) can be performed prior and/or after step b). In particular in case step e) is performed prior to step c), step e) is preferably based upon treating the substrate with a bond strength improving coating, which can, for example, by spraying, preferably by using one or more spray nozzles, onto the substrate prior to step c). This bond strength improving coating may also be applied after carbonization according to step c). The coating may be configured to react with the marking(s) to intensify the bond between the marking and at least one of the substrate and the coating. It is also imaginable that step e) comprises the step of further irradiating the at least one marking, such that the bond strength between said at least one marking and the substrate is improved (intensified). It is also imaginable that step e) comprises the step of apply mechanical pressure onto the at least one marking formed during step c), which may also lead to an increase of the bond strength of said at least one marking onto the substrate. Applying a pressure may, for example, be realized by using a roller. The invention also relates to a printing device for selective carbonization of a substrate, in particular via a method according to the present invention, comprising:

at least one primary irradiation source, in particular a laser, such as a diode laser and/or C02 laser, being configured to position-selectively irradiate at least one part of a carbonizable substrate to a temperature exceeding the carbonization temperature of said substrate, such that the irradiated part of the substrate is carbonized, and

at least one secondary irradiation source, in particular a heating source, for heating at least one predefines area of said substrate.

The benefits as described above for the method according to the present invention also apply to the corresponding device according to the invention. The device preferably comprises at least one control unit for controlling at least one primary irradiation source and/or at least one secondary irradiation source. At least one secondary irradiation source may for example be an illumination source, in particular an infrared illumination source. In a preferred embodiment forms the secondary irradiation source integral part of the primary irradiation source. Optionally, the device may comprise means for adjusting at least one beam of the primary irradiation source, in particular the laser, such that said beam comprises a core and a sheath, wherein said sheath of the beam is configured to conduct the heating of at least one predefined area of the substrate and wherein said core of the beam is configured to conduct the position- selectively irradiation of at least one part of a carbonizable substrate to a temperature exceeding the carbonization temperature of said substrate, such that the irradiated part of the substrate is carbonized.

The invention will be elucidated on the bases of non-limitative exemplary embodiments shown in the following figures, wherein:

figure 1 a shows a schematic representation of a print obtainable via selective carbonization of a substrate;

figures 1 b-1 e show examples of the predefined area to heated prior to the selective carbonization;

figures 2a and 2b show a schematic representation of an irradiation source to be used in the method, and device, according to the invention;

figure 3 shows the effect of pre-heating of the substrate before selective carbonization according to the invention;

figure 4 shows a schematic representation of a substrate printed via a method according to the invention; and

figure 5 shows a schematic representation of a device according to the invention.

In these figures, corresponding references correspond to similar or equivalent features.

Figure 1 a shows a schematic representation of an example of a print (1 ) obtainable via position-selective carbonization of a substrate (2) via the method according to the present invention. The figure shows the carbonized area (1 ) or print (1 ) in order to be able to indicate the predefined area(s) of the substrate to be heated prior to the carbonization. Examples of the predefined areas are illustrated in figures 1 b-1 e.

Figure 1 b shows the substrate (2) as shown in figure 1 a, wherein a predefined area (3b) to be heated is indicated via highlighting (3b). The determination of the predefined area (3b) is based upon the surface enclosed by the desired the print (1 ) which is to be position-selectively carbonized (printed). The predefined area (3b) is heated via an in the present patent application described heating method, preferably via radiative heating such as illumination. As can be seen in the figure, the predefined area (3) to be heated encloses the print (1 ) entirely.

Figure 1 c shows a further example how the predefined area (3c) of the substrate (2) to be heated can be defined. The predefined area (3c) substantially follows the contours of the final print (1 ). A benefit of this example is that a smaller area (3c) has to be heated compared to the example of figure 1 b, resulting in a reduced energy requirement for heating.

Figure 1 d shows a third example of defining the predefined area (3d) of the substrate (2) which has to be heated prior to the selective carbonization (1 ) according to the method according to the invention. The figures shows that multiple predefined areas (3d) are indicated, wherein each predefined area (3d) substantially follows the contours of the final print (1 ). For this embodiment, the total area of a substrate (2) which is to be heated substantially at least equals the total area of said substrate (2) which is position- selectively carbonized (1 ).

Figure 1 e shows a fourth example falling within the scope of the invention of defining the predefined area (3e) of the substrate (2) which has to be heated prior to the position-selective carbonization (1 ). The predefined area (3e) to be heated is further reduced compared to the previous examples. The figure shows that the predefined areas (3e) are substantially localized with respect to the print (1 ). This localized heating is in particular achievable via shaping a beam of the primary irradiation source such that the beam is out of focus when it reaches the substrate, such that the sheath of the beam heats the substrate before the core of the beam carbonizes the substrate (2). Examples hereof are shown in figures 2a and 2b. For this embodiment, the total area of a substrate (2) which is to be heated substantially equals the total area of said substrate (2) which is position-selectively carbonized (1 ).

Figures 2a and 2b show a schematic representation of an irradiation source (4) to be used in the method, and device, according to the invention. In the shown example is the irradiation source (4) a laser (4). Figure 2a shows both a beam of a laser (4) which is in focus (6) and a beam which is out of focus (5). Figure 2b shows a schematic representation of the beneficial effects of the out of focus beam (5) for selective carbonization without losing on the resolution of the final print. For the out of focus situation is it required that the beam of the primary irradiation source (4) is shaped such that the beam is out of focus when it reaches the substrate, such that the sheath of the beam (5b) heats the substrate (2) before the core of the beam (5a) carbonizes the substrate (2). The beam of the laser (4) can for example pass through beam shaping optics (not shown) which modifies the shape of the beam. The beam shape of the laser is preferably modified such that the beam can be used to both pre-heat and post heat the substrate (2). With this beam shaping, the power distribution can be designed to get the optimal temperature for blackening in the most optimal heating rate by altering the power density distribution.

Figure 3 shows the effect of pre-heating of the substrate before selective carbonization according to the invention. The figure shows in particular the effect of using a beam of an irradiation source which is out of focus with respect to a beam which is in focus. The x-axis shows the lightness level (L^*) of the print. The values are measured by using a calorimeter. A lightness level below 30 corresponds to an acceptable blackness, and therewith contrast, of the print. The y-axis show the printing time (in seconds). For this experiment blocks of approximately 20x20 mm were printed. The speed of the galvanometer, and therewith the speed of the laser beam, used for printing, has a direct correlation to the printing time. The higher the speed, the shorter the time required for printing. The measurement point for different speeds (mm/s) are indicated in the figure for both an out of focus beam and an in focus beam. The substrate used is conventional brown carton. It can be seen that a higher blackness is obtained when the substrate is preheated via the sheath of the beam which is out of focus. Furthermore, higher laser speeds can be used, and the required printing time is reduced for any laser speed.

Figure 4 shows a schematic representation of a substrate (2) printed via a method according to the invention. The figure show a substrate (2) having a print (1 ) which is printed via selective carbonization of the substrate. The print (1 ) is provided on a predefined area (7) which is subjected to a photochemical bleaching step. The predefined area (7) therefore has a lighter colour than the substrate (2) in its original form, which is beneficial for the contrast between the print (1 ) and the background (7) thereof.

Figure 5 shows a schematic representation of a printing device (8) according to the present invention. The device (8) is configured for selective carbonization of a substrate (2). The device (8) comprises a heating source for at least partially heating at least one substrate, and a primary irradiation source (9), in particular a laser, for at least partially irradiating a substrate such that carbonization of at least part of the substrate occurs. In the shown embodiment forms the heating source an integral part of the primary irradiation source. The device (8) comprises adjusting means for adjusting the beam of the primary irradiation source (9), in particular the laser (9), such that said beam comprises a core (5a) and a sheath (5b), wherein said sheath (5b) is configured for heating at least a predefined area of the substrate (2) before said core (5a) of the beam carbonizes at least part of said predefined area of the substrate (2). The device (8) furthermore comprises a control unit (10) for controlling at least the primary irradiation source (9). Additionally, the device (8) comprises a colour sensor (1 1 ) and a non-contact temperature sensor (12). The device optionally comprises an extractor (13) for removing volatile compounds. The substrate (2) is in the shown embodiment positioned on a moving stage (14).

It will be apparent that the invention is not limited to the working examples shown and described herein, but that numerous variants are possible within the scope of the attached claims that will be obvious to a person skilled in the art.

The verb“comprise” and conjugations thereof used in this patent publication are understood to mean not only“comprise”, but are also understood to mean the phrases “contain”, “substantially consist of”, “formed by” and conjugations thereof. Where the term“print” is used a selective carbonized marking is meant. Where the term“irradiation” is used, this may be interpreted as“direct irradiation”, wherein an, optionally, shaped, irradiated beam directly (without intervention of an intermediate layer or intermediate component) hits the substrate, and may also be interpreted as “indirect irradiation”, wherein an, optionally, shaped, irradiated beam indirectly, via at least one intermediate layer or intermediate component, hits the substrate. An example of an intermediate layer could be, for example, a transparent plate and/or another substrate.

Claims

1. Method for position-selective carbonization of a substrate, comprising the steps of:

b) heating at least one predefined area of said substrate, and

c) position-selectively carbonizing at least a part of at least one heated area of said substrate by position-selectively irradiating at least a part of said at least one heated area, by using at least one primary irradiation source, to form at least one printed marking within said area.

2. Method according to claim 1 , comprising the step of determining at least one marking to be printed during step C), and predefining at least one area to be heated based upon said determination of the at least one marking.

3. Method according to any of the previous claims, wherein the total area of the substrate heated during step b) at least equals the total area of said substrate which is position-selectively carbonized during step c).

4. Method according to any of the previous claims, wherein during step b) at least one predefined area is heated to a temperature below the minimum carbonization temperature of the substrate, in particular up to 10 degrees Celsius below the minimum carbonization temperature and more in particular up to 5 degrees Celsius below the minimum carbonization temperature.

5. Method according to any of the previous claims, wherein during step b) at least one predefined area is heated to a temperate in the range of 100 degrees Celsius to 270 degrees Celsius, preferably in the range of 200 degrees Celsius to 250 degrees Celsius.

6. Method according to any of the previous claims, wherein at least one predefined area of the substrate is heated via radiative heating, in particular via illumination by at least one secondary irradiation source.

7. Method according to any of the previous claims, wherein step b) and c) are successive steps, wherein preferably the time interval between step b) and c) is at most 2 seconds, preferably at most 1 second.

8. Method according to any of the previous claims, wherein during step c) a part of the substrate is position-selectively irradiated for a period of time situated in between 0 and 5 seconds.

9. Method according to any of the previous claims, wherein during step c) a part of the substrate is position-selectively irradiated by using a laser, and more preferably a diode laser and/or C0₂ laser.

10. Method according to any of the previous claims, wherein during step c) the substrate and the at least one primary irradiation source, preferably a laser, and more preferably a diode laser and/or C0₂ laser, are mutually displaced by using a speed which is at least 10 mm/s.

1 1. Method according to any of the previous claims, wherein during step c) the temperature of the at least one irradiated part of substrate is brought to at least 270 degrees Celsius, preferably at least 400 degrees Celsius.

12. Method according to any of the previous claims, wherein heating at least one predefined area of said substrate according to step b), is conducted by using said primary irradiation source.

13. Method according to any of the previous claims, wherein the primary irradiation source comprises at least one beam comprising a core and a sheath, wherein said sheath of the beam is configured to heat at least one predefined area of said substrate according to step b), and wherein said core of the beam is configured to conduct the position-selective carbonization according to step c).

14. Method according to any of the previous claims, wherein at least part of the substrate is subjected to a photochemical bleaching step, preferably prior to and/or during step b).

15. Method according to claim 14, wherein the photochemical bleaching is performed by irradiation of at least part of the substrate with an irradiation source using a power density in a range of 20 kW/cm2 to 140 kW/cm2, preferably in a range of 53 and 77 kW/cm2, and applying a irradiation time of at most 55 microseconds.

16. Method according to any of the previous claims, wherein the method comprises step d), comprising of post-irradiating at least one area of the substrate carbonized during step c), preferably by using at least one laser selected from the group consisting of: a blue laser, a green laser, a blue-green laser.

17. Method according to any of the previous claims, wherein the method comprises step e), comprising the step of increasing the bond strength between at least one marking printed and/or to be printed during step c) and the substrate.

18. Printing device for selective carbonization of a substrate, preferably via a method according to any of the previous claims, comprising:

19. Device according to claim 18, comprising at least one control unit for controlling at least one primary irradiation source and/or at least one secondary irradiation source.

20. Device according to any of claims 18-19, wherein at least one secondary irradiation source is an illumination source.

21. Device according to any of claims 18-20, wherein the secondary irradiation source forms integral part of and/or is formed by the primary irradiation source.

22. Device according to any of claims 18-21 , comprising means for adjusting at least one beam of the primary irradiation source, in particular the laser, such that said beam is adjustable to have a core and a sheath, wherein said sheath of the beam is configured to heat at least one predefined area of the substrate and wherein said core of the beam is configured to position-selectively carbonize at least one part of a carbonizable substrate by position-selectively area said at least one part.