METHOD AND SYSTEM FOR MARKING PAPER, CARDBOARD AND/OR FABRIC

Abstract

A method for marking at least one portion of a surface of an object, said surface being made of a material that is paper, cardboard or fabric, the method comprising the following steps: heating the surface of the material by means of a heat source to a temperature lower than a temperature at which the visual appearance of the material changes; marking the heated surface by means of a marking laser, so that the light beam of the laser raises the temperature on the surface of the material enough to change the visual appearance of said surface;

in which the marking laser is a laser with a light beam that belongs to the visible or ultraviolet spectrum.

Claims

1. A method for marking at least one portion of a surface of an object, said surface being made of a material that is paper, cardboard or fabric, the method comprising the following steps: heating the surface of the material by means of a heat source to a temperature lower than a temperature at which the visual appearance of the material changes; marking the heated surface by means of a marking laser, so that the light beam of the laser raises the temperature on the surface of the material enough to change the visual appearance of said surface; wherein marking laser is a laser with a light beam that belongs to the visible or ultraviolet spectrum.

2. The method according to claim 1, wherein the heat source used in the heating step is an infrared laser.

3. The method according to claim 2, wherein the infrared laser is a CO.sub.2 laser.

4. The method according to claim 1, wherein the marking laser has a wavelength of 590 to 10 nm.

5. The method according to claim 1, wherein the marking laser has a wavelength of 590 to 280 nm.

6. The method according to claim 1, wherein the marking laser has a wavelength of 532 to 355 nm.

7. The method according to claim 1, wherein the heat source used in the heating step goes along the same path over the surface of the object as the marking laser.

8. The method according to claim 7, wherein the marking laser acts after the heat source used in the heating step with a time difference of less than 100 ms.

9. The method according to claim 1, wherein it does not include a step of fixing marking by-products.

10. A system for marking at least one portion of the surface of an object by means of the method according to claim 1, said object being made of a material that is paper, cardboard or fabric, wherein it comprises two lasers that act on a surface to be marked of the material, the first of said lasers being a heating laser configured to heat the surface of the material to a temperature lower than the temperature at which the visual appearance of the material changes, and the second of these two lasers being a marking laser that is a laser with a light beam that belongs to the visible or ultraviolet spectrum, configured to raise the temperature on the surface of the object enough to change the visual appearance of said surface; the system comprising means for guiding both lasers, the guiding means being configured so that both lasers follow the same path, in order for the heating laser to pass over said path first, followed by the marking laser.

11. The system according to claim 10, wherein the marking laser has a wavelength of 590 to 10 nm.

12. The system according to claim 10, wherein the marking laser has a wavelength of 590 to 280 nm.

13. The system according to claim 10, wherein the marking laser has a wavelength between 532 and 355 nm.

14. The system according to claim 16, wherein the infrared laser is a CO.sub.2 laser.

15. The system according to claim 10, wherein the guiding means are configured so that the marking laser follows the same path as the heating laser with a time difference of less than 100 ms.

16. The system according to claim 10, wherein the heating laser is an infrared laser.

Description

[0025] A diagram and a drawing of one embodiment of the present invention are appended to ensure better understanding through explanatory but non-exhaustive examples.

[0026] FIG. 1 shows a diagram of one embodiment of a marking method according to the present invention.

[0027] FIG. 2 shows a diagrammatic example of one embodiment of a marking method according to the present invention.

[0028] FIG. 1 shows an embodiment of a method 100 for marking an object which, in the example, is made of a material that is paper or cardboard. The marking method according to the present invention comprises two steps: a first step 1 of heating the surface of the material, and a second step 2 of marking the surface of the material.

[0029] In the heating step 1, the area or region of the surface of the material on which a certain character, logo, code, image, etc. is to be marked or printed is heated by means of a heat source, without requiring any previous treatment of the surface to be printed (without requiring the use of any type of pigment or ink).

[0030] In this step 1, the heat source raises the temperature of the material to a temperature lower than the temperature at which the visual appearance of the material changes, preferably to a temperature close to said temperature. This heating is preferably carried out gradually. In the case of cellulosic materials such as paper or cardboard, the preferred temperature for changing visual appearance is the carbonisation temperature of the material, at which the material changes colour and turns black.

[0031] The heat source used in heating step 1 is an infrared laser 10 (shown in FIG. 2), more preferably a CO.sub.2 laser. CO.sub.2 lasers commonly emit in an infrared wavelength band between 9.3 and 10.8 μm, this type of laser being preferable for its proven ability to heat. Alternatively, other types of heat sources can be used.

[0032] Unlike other prior art documents in which the infrared laser is used to mark or print on the surface of the material, in the embodiment of the present invention the infrared laser is only used to heat the material to a temperature lower than the carbonisation temperature of the material (without reaching it).

[0033] The heating step 1 aims to facilitate the marking that is carried out in the marking step 2, in which a laser 20 (see FIG. 2) is used to raise the surface temperature of the material beyond the colour-change temperature. Since the material does not reach the carbonisation temperature in this heating step 1, no type of marking or printing is carried out on the surface of the material in this step. Due to the heating performed in the heating step 1, the laser 20 used in the marking step 2 needs less energy to raise the temperature of the material to the carbonisation temperature, thus speeding up the marking step 2.

[0034] In addition, the temperature increases gradually, avoiding the creation of volatile by-products and optimising the permanence on the surface of the black-coloured compounds (char, tar) resulting from the process, thus optimising the print quality.

[0035] The exact carbonisation temperature depends on the type of material to be printed or marked. For paper or cardboard, the surface of the material is raised to 100-200° C., always below the carbonisation temperature of the material. The temperature to which the material is heated is achieved by modifying the laser power intensity.

[0036] In the marking step 2, the surface of the material is marked by a process of selective carbonisation of the paper or cardboard. The marking is carried out by means of a laser 20 (see FIG. 2) so that the laser beam 20 raises the temperature on the surface 30 of the material 3 enough to carbonise said surface 30, changing its colour and producing the printing on the material.

[0037] The laser 20 used in the marking step 2 is a visible or ultraviolet spectrum laser, with a wavelength preferably of 590 to 10 nm, more preferably of 590 to 280 nm, and even more preferably between 532 and 355 nm.

[0038] FIG. 2 shows a system for marking a surface 30 of a cellulosic material 3 on which characters, logos, codes, images, etc. are to be printed, by using two lasers 10, 20 and in accordance with the previous method.

[0039] Both lasers 10, 20 serve different purposes, the first laser being a heating laser 10 that locally heats the surface to be printed without changing the visual appearance of the material 3, and the second laser being a marking laser 20 that produces a carbonisation reaction on the affected surface so that the colour of the surface 30 of the material 3 changes from a light colour to a black colour, achieving a high contrast. More specifically, the heating laser 10 is an infrared laser, more preferably a CO.sub.2 laser, while the marking laser 20 is a visible or ultraviolet spectrum laser.

[0040] The marking system of FIG. 2 also comprises means for guiding the lasers 10, 20 over the surface 30 of the material 3 to be marked. The heating laser 10 is guided over the surface of the material in such a way that it only strikes the surface 30 of the material 3 to be printed or marked, forming characters, logos, codes, images, etc. The marking laser 20 is guided in a similar fashion, and acts on the same surface of the material as the heating laser 10, without affecting the characteristics of the adjoining surface. Both lasers 10, 20 act only on the desired surface 30, without affecting the characteristics of the nearby surface that it is not to be printed.

[0041] The guiding means are configured so that the marking laser 20 passes over the same path as the heating laser 10 with a time difference of less than 100 ms, the action of both lasers 10, 20 being practically simultaneous. To achieve this effect, the diameter of the first laser beam can be adjusted to affect only the surface over which the second beam will pass.

[0042] While the invention has been described and represented based on a representative example, it should be understood that said exemplary embodiment has no limiting effect on the present invention, so any of the variations that are included directly or by way of equivalence in the content of the appended claims should be considered to be included in the scope of the present invention.