Inkless printing method, inkless printer, and printed substrate

Abstract

The invention relates to an inkless printing method. The invention also relates to an inkless printing device, in particular configured to perform at least a part of the method according to the invention. The invention furthermore relates to a substrate provided with at least one printed marking realised by applying the method according to the invention and/or the device according to the invention.

Claims

1. An inkless printing method, comprising a sequence of steps which are performed in the following order: A) providing at least one carbonizable substrate, B) determining at least one carbonization related characteristic of said at least one carbonizable substrate, C) defining at least one printing zone of the at least one carbonizable substrate, D) position-selectively carbonizing said at least one defined at least one printing zone of the at least one carbonizable substrate by at least one time position-selectively irradiating of said at least one defined printing zone of the at least one carbonizable substrate, by using at least one primary beam irradiation to form at least one printed marking within said defined at least one printing zone, and E) at least one time irradiating of at least a part of said at least one defined printing zone, by using at least one secondary beam irradiation, such that each printing zone is irradiated at least twice during the execution of D) and E), wherein during B) a carbonization temperature of the at least one carbonizable substrate is determined, and wherein during E) the complete at least one carbonizable substrate is heated to a temperature below the carbonization temperature defined during B).

2. The method according to claim 1, wherein during E) the complete at least one carbonizable substrate is heated to the temperature below the carbonization temperature defined during B).

3. The method according to claim 1, wherein the at least one secondary beam irradiation is an infrared (IR) light beam.

4. The method according to claim 1, wherein the at least one primary beam and the at least one secondary beam are emitted from a primary irradiation source.

5. The method according to claim 4, wherein the primary irradiation source is configured to transform the irradiated beam between a narrow beam and a broad beam, wherein the narrow beam acts as the at least one primary beam irradiation and is configured to only irradiate at least a part of the at least one printing zone, and wherein the broad beam acts as the at least one secondary beam irradiation and is configured to irradiate at least a part of the substrate beyond said at least one printing zone.

6. The method according to claim 5, wherein the broad beam is configured to irradiate both at least a part of the at least one defined printing zone and at least a part of the at least one carbonizable substrate beyond said at least one defined printing zone.

7. The method according to claim 5, wherein during D) the narrow beam is used, and wherein during E) the broad beam is used.

8. The method according to claim 1, wherein a color of the at least one defined printing zone remains unchanged during irradiating of said at least one defined printing zone according to E).

9. The method according to claim 1, wherein a color of the at least one defined printing zone is effected during irradiating of said at least one defined printing zone according to E).

10. The method according to claim 1, wherein the at least one secondary beam irradiation is emitted by a laser with a wavelength of between 455 and 529 nm.

11. The method according to claim 1, further comprising a step E′) comprising irradiating of said at least one defined printing zone, by using the at least one secondary beam irradiation, wherein E′) is initiated prior to D).

12. The method according to claim 1, wherein each defined printing zone is irradiated at least three times during the execution of D) and E).

13. The method according to claim 1, wherein the at least one primary beam irradiation is emitted by a CO.sub.2 laser.

14. The method according to claim 1, wherein the at least one primary beam irradiation is emitted by a tuneable laser.

15. The method according to claim 1, wherein the at least one carbonizable substrate provided during A) is formed by a cellulose based substrate.

16. The method according to claim 1, further comprising: F) transferring the at least one printed marking during D) onto a transfer substrate.

17. The method according to claim 16, wherein the original carbonizable substrate is removed from the at least one transferred marking after F).

18. The method according to claim 1, wherein during D) the at least one defined printing zone of the at least one carbonizable substrate is irradiated at least a plurality of times by at least one primary beam irradiation.

19. The method according to claim 1, further comprising: G) position-selectively whitening at least a part of the at least one defined printing zone of the at least one carbonizable substrate by position-selectively irradiating of said at least one defined printing zone of the at least one carbonizable substrate by using the at least one primary beam irradiation having an output power up to 30 Watt, wherein the scanning speed is at least 1 m/s.

20. The method according to claim 19, wherein during G) at least one substrate part beyond the at least one defined printing zone is whitened.

21. The method according to claim 19, wherein the the at least one primary beam irradiation used during G) is emitted by a primary irradiation source.

22. The method according to claim 19, wherein G) is initiated prior to D).

23. The method according to claim 1, wherein the method comprises H), comprising increasing the bond strength between at least one marking printed and/or to be printed during D) and the at least one carbonizable substrate.

24. A substrate provided with at least one printed marking realized by applying the method according to claim 1.

25. The substrate according to claim 24, wherein at least a part of the at least one printed marking has a lightness level L, defined by a CIELAB colour space, which is equal to or below 30.

26. The substrate according to claim 24, wherein at least a part of the at least one printed marking is black and/or comprises more char than tar.

27. The substrate according to claim 24, wherein at least a part of the at least one printed marking is brown and/or comprises more tar than char.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1a shows a schematic representation of a print obtainable via selective carbonization of a substrate;

(3) FIGS. 1b-1e show examples of the predefined area to heated prior to the selective carbonization;

(4) FIGS. 2a and 2b show a schematic representation of an irradiation source to be used in the method, and device, according to the invention;

(5) FIG. 3 shows the effect of pre-heating of the substrate before selective carbonization according to the invention;

(6) FIG. 4 shows a schematic representation of a substrate printed via a method according to the invention; and

(7) FIG. 5 shows a schematic representation of a device according to the invention.

(8) FIG. 6a illustrates a graph of heat treatment temperatures (HTT) vs. electrical resistivity for different carbonizable substrates,

(9) FIG. 6b illustrates a graph of pyrolysis temperature vs. char yield for heating rate from 70 to 0.03 degrees Celsius per minute (° C./min).

(10) FIG. 7 shows transfer process of the marking.

(11) FIG. 8 illustrates a graph of the lightness L of the carbonizable substrate vs. laser output power for an ‘in focus’ laser beam and for an ‘out of focus’ laser beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

(13) FIG. 1a 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 FIGS. 1b-1e.

(14) FIG. 1b shows the substrate (2) as shown in FIG. 1a, 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.

(15) FIG. 1c 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 FIG. 1b, resulting in a reduced energy requirement for heating.

(16) FIG. 1d 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).

(17) FIG. 1e 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 FIGS. 2a and 2b.

(18) 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).

(19) FIGS. 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). FIG. 2a shows both a beam of a laser (4) which is in focus (6) and a beam which is out of focus (5). FIG. 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.

(20) FIG. 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 20×20 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.

(21) FIG. 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.

(22) FIG. 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 (11) 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.

(23) 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.