WO2004026522A1

WO2004026522A1 - Method for laser working a film material and film material to be worked using that method.

Info

Publication number: WO2004026522A1
Application number: PCT/NL2002/000601
Authority: WO
Inventors: Gert Jan Huizinga
Original assignee: Gert Jan Huizinga
Priority date: 2002-09-19
Filing date: 2002-09-19
Publication date: 2004-04-01
Also published as: AU2002324368A1

Abstract

A method for laser working a film material (1). A second layer of the film material is provided that is more absorptive to laser light of at least one wavelength than a first layer of the film. By irradiating at least a part of the second layer with a laser beam (7) of the at least one wavelength, a part of the second layer is heated up. Parts of the first layer adjacent the heated up parts of the first layer are at least partially weakens by heat (8) transferred from the second layer to the first layer.

Description

TITLE: Method for laser working a film material and film material to be worked using that method

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a method for working a film material. The invention further relates to a film material specifically adapted to be worked by that method. It is known from practice to weld or cut film material with a laser. In the known method, the welding or cutting is performed by irradiating the film material with a laser beam. The laser beam heats the film material until the film melts in the area where the beam hits the film, causing the material to be cut. It is also possible to melt the film partially and to bring the melted material in contact with another material to weld the materials.

However, in many cases the known method is disadvantageous because it requires a large amount of energy to work the film material. Specifically, a relatively large amount of laser energy is required to melt or weaken the material. In for example the packaging of food products mostly film including polyethylene (PE) is used which is difficult to be worked with a laser.

PE is substantially transparent to the laser radiation. Hence, a large amount of laser energy is required to melt the PE, since most of the laser radiation is not absorbed by the PE. Even if reflection of the laser radiation back into the PE increases the amount of laser radiation absorbed by the PE because a layer of aluminium is included in a laminate film, which is common in packaging because of the favourable barrier properties of aluminium, still a very large amount of laser energy is required to work the material.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for working a film material which requires less laser energy. According to the invention, this object is achieved by providing a method according to claim 1. The invention further provides a film material according to claim 14.

Because the second layer is heated by the laser beam and the first layer is melted by heat from the second layer and the second layer has a higher absorption than the first layer, a larger percentage of the laser energy is absorbed in the second layer and used to at least weaken the first layer. Hence a smaller amount of laser energy is required to at least weaken the first layer than when the first layer is only heated directly by the laser beam. Specific examples of embodiments of the invention are set forth in the dependent claims. Further details, aspects and embodiments of the invention will be described with reference to the examples of the figures in the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically shows a first example of a film material according to the invention.

Fig. 2 schematically shows a second example of a film material Fig. 3 schematically illustrates the welding of a film material according to the invention. Fig. 4 schematically shows a fourth example of a film material according to the invention.

DETAILED DESCRIPTION

The example of a laminate film material 1 of Fig. 1 is composed of first layer 2 and a second layer 3. Both layers lie beneath a laminate surface 4. In this example, the first layer 2 lies adjacent to the surface 4 and the second layer 3, is separated from the surface 4 by the first layer 2. However, the first layer may likewise lie deeper in the film material and for example be separated from the surface by one or more other layers transparent for laser radiation of one or more wavelengths. Seen from the surface 4, the second layer 3 lies beneath the first layer 2. The second layer may likewise lie further away from the first layer and for instance be separated from the first layer by a heat conducting material. The first layer 2 has a lower absorption of laser radiation than the second layer 3 for at least one wavelength.

As is shown in Fig. 1, the film material 1 according to the invention can be worked with a method according to the invention. First, the first layer 2 and the second layer 3 are irradiated with a laser beam 7. In Fig. 1, the laminate surface 4 side of the film 1 faces in the direction from which the laser radiation 7 is irradiated. However, the laser beam 7 may likewise be applied to the other side of the film. The laser beam 7 is at least partially absorbed by the second layer 3 and only very little if any significant amount of the laser radiation 7 is absorbed by the first layer 2. Accordingly, the second layer 3 is heated substantially more by the conversion of laser energy into heat than the first layer 2 in which, per unit of thickness of the layer, less laser energy is converted into heat than in the second layer 3. Due to the temperature difference between the first and the second layer, thermal energy 8 is then transferred from the second layer 3 to the first layer 2. Because of this transfer of thermal energy 8, the first layer 2 heats up as well. The first layer 2 then breaks down because of the increase in temperature. In the examples of Figs. 1-3, the first layer 2 breaks down due to melting, however, the first layer 2 may likewise evaporate of chemically degrade due to the increase in temperature. Furthermore, the first layer 2 may be broken down or be weakened over a portion of its thickness only or over its entire thickness. In the example shown in Fig. 1, the first layer 2 is made of a PE material. The second layer 3 is made of PP material and the laser beam 7 is generated with a carbon dioxide laser with a wavelength in the range of 9 to 11.5 μm. As is generally known in the art, and for example described in United States patent 5 010 231, in this range a CO2-laser with a C¹²O2¹⁶ isotope has about 80 transitions or wavelengths, distributed over four wings or ranges. For PE-PP laminates, a wavelength in the third wing of the CO2-laser, also known in the art as the 10R wing, is particularly suited because PP absorbs most of the radiation in this wavelength range. More in particular, for a wavelength of 10.25 μm, PP has a very good absorption of the laser radiation. Hence, for this wavelength laminates containing PP can be worked in a method according to the invention with a very low intensity of laser energy. Thus, the PP, e.g. the second layer 3, is heated by the 10.25 μm laser radiation, while the PE in the first layer 2 is not directly affected to a significant extent by that radiation. However, the PE will melt because of the transfer of heat from the PP to the PE.

During or after the melting of the first layer 2, the second layer 3 may be broken down as well, whereby the film material is cut. The cutting may also be repeatedly performed over different parts of the laminate, such that the film material is not cut over its entirety, but only local cuts or perforations are made, e.g. a pattern of perforated lines or spots or holes may be made. It is also possible to bring the melted material in contact with another material and thereafter let the melted material solidify, thus welding the film material to the other material, as is described below in more detail with reference to Fig. 3.

In Fig. 1, the materials of the first layer 2 and the second layer 3 are chosen such that the first layer 2 absorbs less of the laser radiation than the second layer 3. Thus, most of the laser energy will be absorbed in the second layer 3. Hence, the first layer 2 is heated with a higher efficiency then when the laser beam 7 directly heats the first layer 2 only. However, the difference in absorption between the first layer and the second layer can also be obtained in a different manner than by selecting different materials. For example, by using different filler materials in layers of similar bulk material, the first and second layer may be made different in absorption. If the first layer 2 has a melting temperature lower than second layer 3, the amount of laser energy required can be reduced further, because the material of the second layer 3 is able to continue transferring heat to the first layer 2 until the first layer is molten and is not molten and thereby displaced beforehand.

Fig. 2 shows a second example of a material according to the invention. The film material comprises a first layer 2 and a second layer 3. The first layer is made of a PE-material and the second layer of a PP-material. Seen from the material surface 4, a cardboard layer 5 lies beneath the second layer 3. Between the cardboard layer 5 and the second layer 3 lays a reflecting layer 6. The reflecting layer 6 can for example be made of a metal material, such as aluminium, which also forms an effective barrier layer for shielding products to be packaged from the environment. The reflecting layer reflects radiation of a laser beam 7 that has passed the first and second layer 2,3 without having been absorbed back into the first and second layer 2,3, thus increasing the proportion of laser energy absorbed by the second layer 3 and hence increasing the efficiency with which the laser energy is used to work the film material. Experiments show that, for example, at least ten times less energy is required to seal a PE/PP/aluminium/cardboard laminate according to the invention, than the energy that is required to seal a comparable PE/aluminium/cardboard laminate lacking the PP layer for absorbing laser energy.

In Fig. 3, the welding of a laminate film according the first example to another material is illustrated. In Fig. 3 the other material is a laminate film material 10 similar to laminate film material 1. The laminate films 1,10 are transported between two rolls 11,12 which are spaced apart to form a transport nip 13. Just before the film 1 enters the transport nip 13, the film material is worked with a method according to the invention by irradiating the laminate films 1 and 10 with a laser beam 7 from a CO2-laser 70. In Fig. 3, the laser 70 is placed between the laminate films 1 and 10 and projects the radiation 7 into the nip 13. Hence, the irradiated parts of the first layers 2 in the materials 1 and 10, which face each other, are melted. In the nip 13, the melted first layers 2 are brought in contact with each other. Thereafter, the molten material of the first layers 2 solidifies and hence the films are welded to each other and a welded material 15 is formed. As is shown with the striped line 14, the film is irradiated for a short time and the films are locally welded only. A weld or welds corresponding to the track or pattern of molten material that have been written by the laser beam 7 in the first layers 2 is obtained. Of course, it is in principle possible to weld the entire film. As is indicated with the dotted lines, the laser 70 may also be positioned on one or more of the sides of a film turned away from the other material. Also, the laminate film 1 may be welded to another material, such as for example a PE monolayer film.

In a film material according to the invention, the second layer may for example be applied as a coating. For example, the coating can be selectively present as a line over the width of a band of the film material only. Likewise, the absorbing layer may be present over the entire material. In the sample of film material 1 shown by way of yet another example in Fig. 4, the second layer 3 extends over a part of the first layer 2 only and forms a pear-shaped path or track. A pear-shaped part of the material can be cut from the sample with a small amount of laser energy by moving the laser beam along the pear- shaped track, as is indicated by dotted line 71. An advantage of providing the second layer 3 in the form of a path along which the film is to be cut only, is that the spot where the laser beam hits the film may be moved over the material to a next part of the material to be cut out of the film without cutting or damaging the film, in the areas where the second layer 3 is absent. Thus the need Qf co-ordinated deflection or obscuring of the laser beam between the cutting of, separate subsequent parts the film is obviated. Furthermore, if the second layer^' is provided selectively in areas where the materials needs to be worked only, the amount of material for the second layer used in the manufacturing of the film material can be reduced. Furthermore, the laser beam can be moved along the track as the film is moved along a cutting station including the laser. That is, the material is worked "on the fly". Synchronization between the operation of the laser beam and movement of the film material can for instance be obtained from command pulses in synchronization with movement of the film material in transport direction, so that patterns along which the film material is at least weakened are positioned in sync with other items that may have been provided on the film, such as prints, pouring spouts, pouches or lines along which successive items can be severed from each other after completion. However, such synchronization can also be obtained by scanning markings from the film material and by controlling the laser beam to operate on the film material in response to the detection of such markings. The markings may for instance be formed by items on the film as mentioned above. Such markings may also be formed by the selectively applied material of the second layer that may optionally be a contrasting tint or colour to allow optical recognition, so that no separate processing step is required to apply such a marking. It is also possible to detect the increased absorbance of the laser radiation in the area where the second layer is present and to start a next cycle of movement of the laser beam relative to the film material in response to the detection of increased absorbance.

The invention may also be applied to the processing of layers of different film material that are supplied from different sources, such as rolls, and that are assembled into a multi-layered configuration and subsequently laser welded or of which at least one layer is subsequently laser cut and/or laser perforated. Products can for instance be cut from single layer webs of film material using a method according to the invention, for example if the webs are first combined into a composite film of layers made of polyethylene and polypropylene materials. However, the layers may likewise be made of other materials such as polyester, polyvinyl chloride, polyamide, cellophane, polystyrene, polycarbonate or otherwise. Also here, the relatively low amount of laser energy per unit of cutting length allow the material to be cut very last, for instance "on the fly" from a composite web outputted from an apparatus in which the layers are assembled and a further material may be interleaved between the webs of the top and bottom layers. Heat transfer from the PP layer to the PE layer can for instance be ensured, because the layers have been sealed to each other in the area of the cutting line beforehand. It is also possible to ensure the required heat transfer in other manners, for instance by clamping the layers against each other mechanically or by a vacuum that is operative during cutting. It is then also possible to provide that cutting and welding along the inside of the cutting line along which the product is cut out of the web are both carried out with a laser at the selected wavelength absorbed primarily by the second layer. If the welding action precedes the cutting action or is carried out simultaneously therewith, the relative positioning of the layers along the cutting line is particularly reliably maintained.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternatives without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps than those listed in a claim. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A method for laser working film material comprising: providing film material having a first layer (2) and a second layer (3), said second layer being more absorptive to laser light of at least one wavelength than said first layer, irradiating a part of the second layer with a laser beam (7) of said at least one wavelength, said radiation heating up said part of said second layer, and causing a part of the first layer closely adjacent to said irradiated part of the second layer to at least partially weaken due to heat (8) transferred from said irradiated part of the second layer to said part of the first layer.

2. A method as claimed in claim 1, wherein said part of the first layer (2) is also irradiated with the laser beam during the irradiation of said part of the second layer (3).

3. A method as claimed in claim 2, wherein the laser beam enters the film material at a film surface (4) and the first layer (2) lies between the film surface and the second layer.

4. A method as claimed in any one of the preceding claims, further comprising at least weakening at least a part of the second layer (3) by irradiating said part of the second layer with the laser beam (7).

5. A method as claimed in claim 4, wherein said weakening of the first and second layer causes the film material (1) to be at least partially cut.

6. A method as claimed in claim 4 or 5, wherein said weakening of the first and second layer causes the film material (1) to be perforated.

7. A method as claimed in any one of the preceding claims, further comprising at least partially welding the film material (1) to another material (10).

8. A method as claimed in claim 7, wherein said welding of the film material (1) to another material (10) comprises melting the first layer (2) by transferring heat (8) from the second layer (3) to the first layer, bringing the first layer in contact with said other material; and allowing at least part of the molten material of the first layer to solidify, causing the film material to become attached to said other material.

9. A method as claimed in any one of the preceding claims, wherein the second layer (3) extends along a part of the first layer (2) only and the film material (1) is irradiated only in an area where said second layer extends.

10. A method as claimed in claim 9, wherein the second layer (3) forms a path (71) along the first layer (1) and in said irradiating a spot of said laser radiation is moved along said path.

11. A method as claimed in any one of the preceding claims, wherein the laser beam (7) has a wavelength in the range of 9 to 11.5 μm.

12. A method as claimed in claim 11, wherein the laser beam (7) has a wavelength in the third wing of a Cθ2-laser.

13. A method as claimed in claim 12, wherein the laser beam (7) has a wavelength of 10.25 μm and the second layer contains polypropylene.

14. A film material comprising: a first layer (2), and a second layer (3) in thermal contact with the first layer, said first layer differing from said second layer in absorption of laser radiation of at least one wavelength, such that if the film is irradiated with laser radiation of said at least one wavelength, irradiated parts of said second layer are heated by said radiation (7) of said at least one wavelength and heat (8) is transferred from the irradiated parts of said second layer to the first layer causing parts of the first layer closely adjacent the irradiated parts of the second layer to be at least weakened.

15. A film material as claimed in claim 14, wherein the first and second layer (2,3) are made of different materials and the material of the second layer has a higher absorption of light of said at least one wavelength than the material of the first layer.

16. A film material as claimed in claim 15, wherein the second layer (3) has a higher melting point than the first layer (2).

17 A film material as claimed in any one of claims 14-16, wherein the film material further comprises a reflecting layer (6) beneath the second layer (3) for reflecting the laser beam (7) into the second and first layer (2).

18. A film material as claimed in claim 17, wherein the reflecting layer (6) is made, of an aluminium material.

19 A film material as claimed in any one of the claims 14-18, wherein the first layer (2) is a polyethylene layer.

20. A film material as claimed in any one of the claims 14-19, wherein the second layer (3) contains or is made of a material from of a group consisting of: polypropylene, polyester, polyvinyl chloride, polyamide, cellophane, polystyrene and polycarbonate.

21 A film material as claimed in any one of claims 14-20, further comprising a cardboard layer (5).

22. A film material according to any one of claims 14-21, worked with a method as claimed in any one of claims 1-13.

23. A film material as claimed in claim 22, wherein the material is welded to another material (10).