LASER INDUCED STRUCTURAL MODIFICATION OF PAPERBOARDS

Abstract

A method for locally modifying a structure of a paperboard. A penetrating region (114) of the paperboard (110) is penetrated by laser radiation (102) such that moisture in the penetrating region (114) evaporates for locally modifying the structure of the penetrating region (114) e.g. by weakening the paperboard at the region and for deforming it there.

Claims

1. A method for locally modifying a structure of a paperboard further comprising: providing the paperboard; penetrating a penetrating region of the paperboard by laser radiation such that moisture in the penetrating region evaporates for modifying the structure of the penetrating region.

2. A method according to claim 1, further comprising: after evaporation of the moisture creasing the paperboard along the penetrating region, wherein the penetrating region describes a creasing line along which the paperboard is intended to be bent.

3. A method according to claim 1, wherein the provided paperboard comprises a first cover layer covering a core section of the paperboard; wherein during the step of penetrating the penetrating region, penetrating the penetrating region such that the evaporated moisture deforms at least the first cover layer; wherein the penetrating region then describes an embossing structure a Braille letter, a number or a symbol.

4. A method according to claim 3, further comprising: adjusting a swelling level within the core section at the penetrating region before the step of penetrating the penetrating region; and wherein the step of adjusting the swelling level comprises introducing at least one swelling additive adapted for swelling under influence of the laser radiation such that the embossing structure of the first layer is generated.

5. A method according to claim 1, further comprising: adjusting a moisture level within the core section at the penetrating region before the step of penetrating the penetrating region; wherein the step of adjusting the moisture level comprises introducing at least one moisture levelling additive for causing gas generation by the laser radiation within a core section of the paperboard at the penetrating region such that the penetrating region is weakened.

6. A method according to claim 1, wherein the laser radiation comprises a power density of 10.sup.4 W/cm.sup.2 to 10.sup.6 W/cm.sup.2, preferably 10.sup.5 W/cm.sup.2.

7. A method according to claim 1, wherein the laser radiation comprises deposited power of 10 W/cm.sup.2 to 10.sup.3 W/cm.sup.2, preferably 10.sup.2 W/cm.sup.2 W/cm.sup.2.

8. A method according to claim 1, wherein the laser radiation has a wavelength of 1000 nm to 11000 nm, in particular 4000 nm to 8000 nm.

9. A method according to claim 1, wherein the laser radiation is a pulsed laser radiation generated by a pulsed laser device.

10. A method according to claim 1, wherein the laser radiation is a continuous laser radiation generated by a continuous laser device.

11. A method according to claim 1, wherein the laser radiation is generated by a diode laser.

12. A method according to claim 1, wherein the laser radiation is generated by Nd:YAG 1064 nm laser or a Ytterbium doped fibre laser 1074 nm.

13. A method according to claim 1, wherein the laser radiation is generated by a carbon dioxide laser.

14. A device for locally modifying a structure of a paperboard, the device comprising: a holding device for holding the paperboard; a laser device configured for penetrating a penetrating region of the paperboard by laser radiation such that the moisture in the penetrating region evaporates for locally modifying the structure of the penetrating region.

15. A device according to claim 14, further comprising a bending device for bending the paperboard along the penetrating region.

16. A method according to claim 1, wherein the provided paperboard comprises a first cover layer covering a core section of the paperboard; and wherein during the step of penetrating the penetrating region, penetrating the penetrating region such that the evaporated moisture deforms at least the first cover layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The aspects defined above and further aspects of the present invention are apparent from the examples of embodiments to be described hereinafter and are explained with reference to the examples of embodiments. The invention will be described in more detail hereinafter with reference to examples of embodiments but to which the invention is not limited.

[0041] FIG. 1 shows a schematic view of a device for modifying the structure a paperboard according to an exemplary embodiment of the present invention.

[0042] FIG. 2 shows a schematic view of a continuous penetration line along a paperboard according to an exemplary embodiment of the present invention.

[0043] FIG. 3 shows a schematic view of a penetration spots along a paperboard according to an exemplary embodiment of the present invention.

[0044] FIG. 4 shows a schematic view of a flow chart of the method for modifying the structure a paperboard according to an exemplary embodiment of the present invention.

[0045] FIG. 5 shows a schematic view of a paperboard onto which first cover layer a letter is formed according to an exemplary embodiment of the present invention.

[0046] FIG. 6 shows a sectional view of a paperboard according to an exemplary embodiment of the present invention.

[0047] FIG. 7 shows a schematic view of a paperboard comprising a plurality of creasing lines according to an exemplary embodiment of the present invention.

[0048] FIG. 8 shows a schematic view of a conventional creasing device.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0049] The illustrations in the drawings are schematic. It is noted that in different figures similar or identical elements are provided with the same reference signs.

[0050] FIG. 1 shows a device 100 for locally modifying a structure of a paperboard 110. The paperboard 110 is supported on a holding device 103, e.g. a workbench. A laser device 101 is arranged relative to the paperboard 110 for penetrating a penetrating region 114 of the paperboard 110 by laser radiation 102 such that moisture in the core section 113 evaporates for modifying the structure (e.g. weakening or embossing) of a penetrating region 114. The paperboard 110 illustrated is comprised of a first cover layer 111 and a second cover layer 112 between which a core section 113 of the paperboard 110 is arranged. A penetrating region 114 of the paperboard 110 is penetrated by laser radiation 102 such that moisture in the core section 113 is evaporated for modifying the structure of the penetrating region 114.

[0051] The laser radiation 102 is adjusted to evaporate moisture within the selected paperboard 110. The moisture may originate from the air within the core section 113 and/or from the paperboard material within the core section 113 itself. The evaporated moisture causes delamination of the layers in the core section of the paperboard. Furthermore, by penetrating the penetrating region 114 by the laser radiation, a very flexible penetrating region 114 may be formed, particularly in contrast to other regions, so that complex graphic structures or creasing lines may be generated.

[0052] The penetrating region 114 weakened due to evaporation of moisture may be used for bending the paperboard 110 along the penetrating region 114, wherein the penetrating region describes a creasing line along which the paperboard 110 is intended to be bent. As described above, a smooth and non-destroying bending of the paperboard 110 along a creasing line 201 (see FIG. 2) may be accomplished.

[0053] FIG. 2 shows a schematic view of a continuous penetration line, such as a creasing line 201, along a paperboard 110 according to an exemplary embodiment of the present invention. The laser radiation 102 that produced the line 201 may be, for example, a continuous laser radiation generated by a continuous laser device such that a constant line (straight and/or curved) along which the moisture evaporates is generated.

[0054] FIG. 3 shows a schematic view of a plurality of penetration spots 301 along a paperboard 110 according to an exemplary embodiment of the present invention. In this embodiment, the laser radiation 102 is a e.g. pulsed laser radiation generated by a pulsed laser device. The laser device 101 may be selected from the group consisting of ultra-short pulsed lasers and short pulsed lasers.

[0055] The penetrating region 114 is penetrated by the laser radiation such that penetration spots 301 at which the moisture evaporates are generated. Two adjacent penetration spots 301 are shown spaced apart from each other at a distance. Alternatively, two adjacent penetration spots 301 may overlap such that a continuous penetration region 114 is formed, wherein the plurality of penetration spots 114 partially overlap with neighboring penetration spots 114.

[0056] FIG. 4 shows a schematic view of a flow chart of the method for modifying the structure of a paperboard 110 according to an exemplary embodiment of the present invention. According to the method, the paperboard 110 to be creased is provided (step 401), wherein the paperboard 110 is made of a first cover layer 111 and a second cover layer 112 between which a core section 113 of the paperboard 110 is arranged. A penetrating region 114 of the paperboard 110 is penetrated by a laser radiation 102 (step 403) such that a moisture in the core section 113 evaporates for modifying the structure of the penetrating region 114.

[0057] The method further comprises adjusting the moisture within the core section at the penetrating region before the step of penetrating the penetrating region (step 402). In order to achieve a sufficient evaporation of moisture in order to have a desired swelling of the penetrating region 114, the moisture within the core section 113 may be adjusted.

[0058] Finally, the paperboard 110 is creased 404 along the penetrating region 114, wherein the penetrating region 114 describes a creasing line 201 along which the paperboard 110 is intended to be bent.

[0059] FIG. 5 shows a schematic view of a paperboard 110 onto which the first cover layer 111 an embossing graphic structure (graphic symbol 501), such as a letter, is formed. In the step of penetrating the penetrating region 114 the core section 113 is penetrated in such a way that the evaporated moisture deforms at least the first cover layer 111, wherein the penetrating region describes the graphic structure 501, in particular a Braille letter, number, or any symbol.

[0060] Hence, by adjusting the laser radiation 102 in such a way that a greater amount of moisture in the core section 113 evaporates, the core section 113 and additionally at least the first cover layer 111 swells due to the high evaporating moisture. The swollen/swelled section of the first cover layer 111 has protrusions and sinks which are visible and haptic sensible. Hence, by the deformation of the at least first cover layer 111 due to the evaporation of moisture, desired graphic symbols 501 can be printed onto the first layer. The graphic symbols 501 may be pictures and letters for example. Specifically, Braille letters, numbers or any symbol may be formed onto the first layer.

[0061] In particular, a swelling additive may be injected into the core section 113, which is adapted to form a hardened structure within the core section 113 and/or the first cover layer 111 in reaction with the laser radiation 102. Hence, a robust and withstanding embossing graphic structure 501 is formed.

[0062] FIG. 6 shows a sectional view of a paperboard 110 according to an exemplary embodiment of the present invention. Specifically, the sectional view in FIG. 6 shows the paperboard 110 as shown in FIG. 5. In order to form an embossing graphic structure, i.e. a graphic symbol, 501 in the first layer 111, the laser radiation 102 evaporates the moisture in the core section 113 within the penetration region 114 such that also the first layer 111 swells. Hence, protrusions which are visible and haptic sensible are formed. After swelling the paperboard 110, the protrusions remain visible and haptic sensible.

[0063] FIG. 7 shows a schematic view of a paperboard 110 comprising a plurality of creasing lines 201 according to an exemplary embodiment of the present invention. The pattern of the creasing lines 201 is formed by the laser radiation 102. The creasing lines 201 form delaminated sections of the paperboard 110. In a next step, the paperboard 110 may be bent along the creasing lines 201, so that e.g. a box may be formed.

[0064] It should be noted that the term comprising does not exclude other elements or steps and a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined.

LIST OF REFERENCE SIGNS

[0065] 100 device [0066] 101 laser device [0067] 102 laser radiation [0068] 103 holding device [0069] 110 paperboard [0070] 111 first cover layer [0071] 112 second cover layer [0072] 113 core section [0073] 114 penetrating region [0074] 401 step of providing [0075] 402 step of adjusting a moisture [0076] 403 step of penetrating [0077] 404 step of creasing [0078] 201 creasing line [0079] 301 penetration spots [0080] 501 graphic structure [0081] 800 conventional paperboard [0082] 801 inner liner [0083] 802 outer liner [0084] 803 conventional creasing rule [0085] 804 conventional support table [0086] 805 cavity