WO2000027576A1

WO2000027576A1 - Laser treatment of materials, in particular cutting and welding

Info

Publication number: WO2000027576A1
Application number: PCT/FR1999/002731
Authority: WO
Inventors: Didier Bauchiere; Jean-Charles Pinoli; Michel Duvaley
Original assignee: Cebal S.A.
Priority date: 1998-11-10
Filing date: 1999-11-08
Publication date: 2000-05-18
Also published as: AU1053200A; FR2785564A1; FR2785564B1

Abstract

The invention concerns the laser treatment (2) of a material in the form of a strip (1), comprising at least a layer (10) of material M absorbing the laser radiation energy, to bring at least said layer to the temperature required for performing said treatment. The invention is characterised in that for each new material to be transformed, it consists in: a) first, elaborating the spectral curve Ai of said layer (10) of material Mi, so as to determine a frequency spacing (106) corresponding to an absorption peak (101); b) selecting said laser (2) among lasers whereof the beam frequency, or corresponding wavelength, is adjustable on the frequency domain (102) comprising at least said frequency spacing (106); c) tuning said laser frequency on a frequency ξw (103) of said selected spacing to reach said temperature and perform said treatment in a predetermined time interval.

Description

TREATMENT OF LASER MATERIALS, IN PARTICULAR CUTTING OR WELDING

FIELD OF THE INVENTION

The invention relates to the field of methods which use a laser to transform materials, in particular to weld, cut, incise or mark materials, in particular materials in strips or sheets comprising a material layer. plastic.

STATE OF THE ART

Laser applications in materials processing were the subject ^of a very large number of works and publications.

For example, there may be mentioned typical following documents: International patent application WO 89/10231 discloses a tubular welding method ^for a sheet comprising a layer of thermoplastic material, by melting, under laser irradiation, portions to solder.

European Patent No. 237,192 B1 describes a method for welding plastic surfaces using surfaces reflecting the laser beam.

French Application No. 2,289,588 A1 describes a method for fixing two elements coated with thermoplastic material using a laser operating in part of the absorption spectrum of said thermoplastic material.

There are also numerous articles in the literature on the use of lasers. As an example, we can cite the LA article. Jones and NS Taylor "High speed welding of plastics using lasers" in ANTEC'94 pages 1360 to 1363, as well as the article by J. KORTE and H. POTENTE Taylor "Laser butt welding of semi-crystalline thermoplastics" in ANTEC96 pages 1255 to 1259. PROBLEM

The problem posed relates to the treatment by a laser, on an industrial line of materials, typically in a strip or in a sheet, comprising a plastic material. Indeed, when the applicant has tried to use a conventional laser to replace, on an industrial line operating in continuous, a contribution of conventional thermal energy (for example by electrical resistance, by induction, etc.) in order to weld a multilayer material comprising a layer of plastic material, it encountered various problems - on the one hand, it first observes large variations in quality (or even a non-weldable) depending on the nature of the plastics used and depending on the laser used - on the other hand, it also observes, even for the same plastic used, variations in quality according to the desired rates It has therefore noted the great difficulty, if not the impossibility of ensuring a constant supply of energy by appropriate regulation πee laser, which is convenient, inexpensive, compact, ergonomic and flexible She therefore sought an overall solution to these problems

DESCRIPTION OF THE INVENTION

According to the invention, the laser treatment of a material, typically in the form of a strip, comprising at least one layer absorbing the energy of the laser radiation, typically made of plastic, in order to carry out in particular a cutting operation of incision, of marking at least said layer, or of welding of said material on itself or with a second material, by supply of energy from the laser beam located on all or part of said layer in order to carry at least said layer at the temperature necessary for carrying out said operation, is characterized in that, typically once and for all before said supply, and for any new material to be treated, a) first, if not known, the spectral absorption curve of at least said layer is established, in order to determine a frequency interval corresponding to an absorption peak, b) said laser is chosen from lasers whose frequency, or length ^of corresponding wave beam is adjustable over a range of frequencies including at least said frequency interval relative to said absorption peak, c) gives the frequency of said laser at a frequency v _w, said working, of said absorption frequency interval, chosen to allow reaching said temperature and to perform said operation in a predetermined time of said treatment.

Thus, the above means, and in particular the use of a laser with variable frequency over a given frequency range, adjustable over a given frequency interval corresponding to an absorption peak of the material M of said layer, make it possible to resolve a essential problem of the invention. On the one hand, most plastics have absorption peaks in the same part of the IR absorption spectrum. Thus, for example, many plastics with carbon-hydrogen bonds generally have absorption peaks in common or neighboring frequency intervals corresponding to certain modes of vibration of C-H bonds. The same laser can therefore be used for a large number of plastics.

On the other hand, for the same plastic material, the variety of treatments and experimental conditions results in an equal variety of energy inputs by the laser to the plastic materials and therefore of the required temperatures. It is easily understood that, depending ^on whether it is for example cutting or welding, the temperature to be reached in said energy absorbing layer will not be the same.

The invention allows this adaptation of the same laser to the conditions required by adjusting its frequency on said working frequency, taking into account the absorption curve of said plastic material and the nature of said work.

DESCRIPTION OF THE FIGURES FIG. 1 illustrates the principle of the invention and represents absorption diagrams (100) A1, A2 and A3, relating respectively to three materials Ml, M2 and M3 constituting said layer (10) absorbing energy. On these 3 schematic diagrams where the frequency v appears on the abscissa and the absorption A on the ordinate, are represented absorption peaks (101) to which correspond frequency intervals (106). The superposition of these three absorption patterns A1, A2 and A3 makes it possible to define a common frequency domain (102), in which each material has at least one absorption peak, this frequency domain, which extends from v _α to v _b . being that of the chosen laser. Depending on the material, a working frequency v _w (103) is chosen for each material v „ι for Ml, v _w2 for M2, v _w3 for M3.

Figures 2 and 3 illustrate a method of the invention in which the frequency of said laser can vary step by step (104) around said working frequency v _w (103), over a working range (105) extending from 'a frequency vi at a frequency v ₂ , as shown in Figure 2. Figure 2 shows a portion (1010) of absorption curve (101) corresponding to said working range (105), and a portion of curve corresponding temperature T, with the frequency v on the abscissa and the ordinate, the absorption A on the left for the portion of the curve (1010), the temperature T on the right for the portion of the curve (101 1).

FIG. 3 is related to FIG. 2 and represents a portion of the curve (1012), called "isothermal", giving the relative speed of travel of the material with respect to the laser beam as a function of the frequency v so that , taking into account the absorption curve (1010) of FIG. 2, the energy received per unit of time, and therefore the temperature of the absorbent material remains constant, thus, desired or accidental variations in speed on the production line can be compensated for by automatic frequency variations of the laser FIG. 4 schematically represents a regulation of said process and represents ^{on the} one hand a strip material (1) to be treated moving at speed V between an unwinder (6) and a rewinder (7) under a treatment laser (2) comprising a means of displacement (21) and / or of focusing of the beam (20) in the directions X and / or Y, and / or Z, and on the other hand a means of regulation (22), typically a computer having in memory the absorption curve A = φ (v), and the curves T = f (V, v) leading to the curves v = F (V) for T = To

Said regulating means comprises links (220, 221) with the laser and with the reel (7) to typically ensure regulation between the instantaneous speed Vi of the strip (1) and the instantaneous frequency vi of the laser beam (20).

Figure 5 is a schematic perspective view illustrating the formation of a cylindrical tube (3) by folding, using means, in particular traction means (8), not shown, the edges (1 1) of a strip material (1) comprising external layers M1 and M2, as shown in FIG. 5a, which can be welded by absorbing the energy of the laser (2) to form a junction (30) with solder (12), as shown in FIGS. 5b and 5c, FIG. 5b corresponding to a junction by covering and welding (12) of the layers Ml and M2, and FIG. 5c to an edge-to-edge junction and welding (12) of the layers Ml on Ml on one side and M2 on M2 on the other side

FIG. 6 is a schematic perspective view illustrating the formation of sachets (5) from a material (1) in a strip, by folding the strip relative to the longitudinal center line (16) by means not shown, and forming, using the laser (2) whose beam (20) can be moved and / or distributed using said displacement and / or focusing means (21), in the longitudinal directions X -X ', transverse Y- Y' and vertical Z-Z ', transverse welds (14) regularly spaced and perpendicular to a fold line (15). After cutting (not shown) between two transverse welds (14, 14 ') along the lines (51), the bags (5) are obtained, the open rib (50) being at the top of the bag, ready to be filled. Figure 7 is a schematic perspective view illustrating the formation of sachets (5) from two strip materials (1), by welding, using the laser (2) which can be moved and / or distributed to the using said displacement and / or focusing means (21) in the longitudinal XX 'and transverse Y- Y' directions, the two films to form, for each bag, a longitudinal weld (13) and two transverse welds (14) . The bags (5) have an opening (50) in the longitudinal direction.

FIG. 8 illustrates the kinematics of the laser beam in the case of FIG. 7 and in the case where said bands (1) advance continuously at constant speed V. In this case, the beam, initially at point A is moved diagonally to point B in the X-Y plane, so as to form a transverse weld (14) which is perpendicular to the direction of advancement of the bands. Once at B, the beam remains stationary, as long as the longitudinal weld (13) is formed and point C is reached Then, the beam is moved diagonally to point C, with a very rapid return to point A to continue the next welding cycle. The beam therefore followed a predetermined path (23).

The other option would be to advance the strip (s) (1) step by step, to immobilize it during the welding and to move the laser beam while the strip is immobilized

Figure 9 illustrates a variant of Figure 7, wherein the bags are oriented ⁱⁿ a different way since each bag comprises two longitudinal seams (13) and one transverse weld (14). The bags (4) formed have openings (40) in the transverse direction.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows schematically the general principle of the invention. from the absorption curves of the various materials Mi to be treated, an adjustable frequency laser is chosen for its frequency domain (102), a domain which includes a certain number of frequency intervals (106) corresponding to peaks of absorption (101) belonging to each of the absorption curves Ai of each material Mi. Thus, the same laser can potentially be suitable for a large number of plastic materials, and be finely adjusted for each of them at a working frequency v _wi .

In order to carry out the treatment according to the invention, said laser can be a solid-state laser using a pumped diode.

This type of laser can deliver an adjustable wavelength, typically using a parametric optical oscillator.

Said parametric optical oscillator may be made of lithium niobate and have an adjustable frequency between 1 and 5 μm, that is to say between 10,000 and 2,000 cm ^" ', an area which corresponds in particular to infrared and in which most of the plastics have absorption peaks.

Preferably, the range 2400 - 3200 cm ^"1 is chosen as the frequency range (102) which corresponds in particular to a certain mode of vibration of the CH bonds, so that most of the plastics constituting said layers, in particular said outer layer, having absorption peaks between 2400 and 3200 cm ^-1 , the same laser, typically with lithium niobate, can be used for most common plastics.

It is advantageous to choose a laser whose frequency is adjustable with a pitch of less than 0.1 μm, and typically with a pitch of 10 nm.

According to the invention, by adjusting said frequency, an initial frequency range, called the working range (105), is chosen, going from v, to v ₂ as illustrated in FIG. 2, and corresponding to an area of strong variation, typically a side, of a portion (1010) of an absorption peak (101) of said absorption curve Ai, and it is varied step by step. and preferably with a pitch (104) less than 0.01 μm, in one direction or the other of said zone, the frequency of said laser, so as to be able to adjust in a substantially proportional manner the quantity of energy absorbed , and thus the temperature of said layer to be treated. FIG. 2, which illustrates this concept, clearly shows that the portion of the absorption curve (1010) corresponds to a portion of the temperature curve (101 1) and that thus, a fine adjustment of the frequency v corresponds a fine adjustment of the temperature of the energy absorbing material and therefore an operational control of said treatment.

According to a first practical modality of said treatment, said material can be a material in the form of a very long strip which is scrolled at a determined speed, the laser beam being fixed or mobile, so as to carry out said treatment of said material on a small width, less than 5 mm and typically equal to 2 mm (or even edge to edge), and the step-by-step variation of the frequency of said laser is controlled by the relative speed variation Vr of said material with respect to the laser beam, way to

10 that the amount of energy absorbed by said outer layers, and therefore the temperature of said layers of the material to be treated, is substantially constant regardless of said running speed of said strip.

This concept is illustrated in FIG. 3 which, taking into account in particular the curves (1010) and (101 1) of FIG. 2, gives the relationship between the relative speed Vr between beam and

15 material to be treated to maintain a constant supply of energy per unit of time, and therefore the same temperature of the absorbent layers. The curve (1012) of FIG. 3 is therefore an isotherm calculated for a given temperature T≈To. FIG. 4 schematically represents a possible solution of the global regulation making it possible to control the treatment line to have a treatment temperature

20 constant despite variations in the relative speed Vr, which may be due to variations in the speed V of the strip to be treated.

According to a first application illustrated in FIG. 5, said layer is an external layer (10) of plastic material, each face of said strip (1) comprising said

-> layer (Ml on one side - M2 on the other side, as shown in FIG. 5a), and. preferably after bringing the parallel edges (1 1) of said strip together, said treatment is applied to at least one of the two edges (1 1) of said strip in order to weld, preferably edge to edge, the two parallel sides of said strip , so as to form a cylindrical tube (3) of great length thanks to the longitudinal junction (30) resulting from a weld (1 1) typically either by overlapping as illustrated in FIG. 5b, or edge to edge as illustrated in Figure 5c. According to a second practical modality of the invention, said laser beam can be moved, at least over the straight line portions of the path (23), at a predetermined relative speed, said material being typically fixed during said treatment, so as to produce said treatment of said material, and it is possible to control said relative speed and the step-by-step variation of the frequency of said laser so that the quantity of energy absorbed, and therefore the temperature of said layer, is substantially constant whatever said relative speed of movement of said laser beam relative to said material In this case, said strip advances step by step, said treatment being carried out, at least in part, during the stop phase of the strip. In certain cases, this method can be advantageous because, without penalizing the processing speed too much, it can avoid having to resort to expensive kinematic means to ensure the relative displacement of the laser beam according to a desired path. It is a great advantage to be able to slave the frequency to the relative speed of the beam, because, as soon as the path (23) of the beam is not linear and presents changes of direction, there are locally phases of deceleration and ^acceleration of the movement of the laser beam (20) which can not only lead to local temperature variations.

According to another application of the treatment according to the invention illustrated in FIG. 6, said layer can be an external plastic layer on one face of said strip (1), said strip can be folded in the longitudinal direction so as to bring into with regard to the two half-portions of longitudinal strips, and said treatment can be applied transversely over the width of said half-portion, so as to form transverse welds (14, 14 ′), regularly spaced in the longitudinal direction, over a length equal to the half-width of said strip (1). leading, after appropriate cutting, to the formation of sachets (5) open on one side (50). In the figures, and in particular in FIG. 6, the position of the laser (2) is only indicated schematically and symbolically. In practice, it may be advantageous for the laser beam to arrive at a different incidence from that illustrated in the figures and use complementary devices known in themselves to allow a precise location of the energy supply by said beam on said layer to be treated (10). Do not appear in Figure 6 the means, known elsewhere, which allow to fold the strip (1) and apply each half of the strip to form said transverse welds. According to another variant illustrated in FIGS. 7 and 9, said layer may be an external plastic layer, in which said treatment is applied in a "U" shape and a second strip, identical or not to said strip, is applied to said strip, so as to form "U" welds between said strip and said second strip, leading, after appropriate cutting, to the formation of sachets (4,5) open on one side.

The welding is so-called "U" to denote the generic form of a bag (4,5), the bags usually being square or rectangular, but it goes without saying that n ^'there is no limitation of the treatment according to the invention in a particular form of sachet. Figures 7 and 9 are distinguished by the orientation of the bags relative to the direction of travel of the strips (l), the opening (40) being transverse to Figure 9, the opening (50) being longitudinal in Figure 7 .

It is of course possible to envisage obtaining not one but several bags on the same bandwidth, and possibly implementing for this several laser beams simultaneously.

The treatment according to the invention is not limited to the sealing of two layers of plastic material. It also aims to cut, incise, engrave, mark, continuously or discontinuously, over all or part of its thickness, said material, all operations for which it is desirable to control the supply of energy and therefore for which the means of the present invention can be applied advantageously.

In general, it aims to modify the surface of a material to form a discrete trace along a given path. But it can also, by scanning the beam over an entire surface, substantially modify the entire surface as regards its texture. its roughness or its surface energy. To implement the treatment according to the invention, it is possible to use an optical fiber carrying the laser beam, or any deflection and / or separation device of the laser beam, to effect said supply of energy at the desired location of said layer.

EXAMPLES OF REALIZATION

The figures constitute the exemplary embodiments

According to a first example, illustrated in FIG. 5, a very long cylindrical tube (3) was made from a strip (1) of multilayer material having as structure PEι / Adh / EVOH / Adh / PE ₂ , or PEi denotes a layer of polyethylene of 150 μm and PE ₂ denotes a layer of PE of 100 μm, where Adh denotes a layer of adhesive of 10 μm and EVOH a barrier layer, in EVOH, of 15 μm Taking into account the absorption diagram PE, layer (10) absorbing the laser energy, we chose a solid type laser with pumped diode with optical parametric oscillator with lithium niobate, and a frequency domain (102) with v _α equal to 2.8 μm and v _b equal to 4 μm We have chosen a working frequency v _w equal to 3.3 μm, a frequency which belongs to the absorption peak (101) of the PE used, peak having a frequency interval (106) ranging from 3.2 μm to 3.7 μm. In order to regulate the process, as illustrated in FIGS. 2 and 4, a step has been chosen (104) of 10 nm and a working range (105) ranging from Vi = 3, 1 μm to v ₂ = 3.4 μm The two types of welds illustrated in FIGS. 5b and 5c were produced, with M1 = M2 = layer of PE The speed of travel of the strip (1) was fixed at a nominal value of 40 m / min. The speed was varied by - / - 20% around the nominal value and the quality of the weld was examined ( 12) of the junction (30) either with the regulation according to the invention, or without regulation by carrying out tension and delamination tests making it possible to assess the quality of the weld (12) It has thus been observed that the tube obtained according to the invention exhibited a weld of constant quality whatever the speed V, while the tube obtained according to the state of the art, that is to say without regulation according to the invention, exhibited an irregularity in the quality of the welding that can lead to serious problems with the quality of the tubes, typically toothpaste tubes obtained after having cut said cylindrical tube (3) of great length into sections and having molded a head.

According to a second example illustrated in FIG. 6, bags were made from a PE film 60 μm thick forming a strip (1) 30 cm wide. The laser used is the same as that of the previous example. The same is true for experimental conditions, and typically for the working frequency v _w , the energy absorbing layer (10) also being PE. In this example, the strip (1) has been scrolled step by step, so as to have a simplified kinematics for the laser beam (20).

At each step, the strip being stopped, the laser beam (20) was focused and moved along a "V" shaped trajectory, the two half-portions of the film (10) being only partially folded back. moment when said supply of energy by laser beam occurs. The movement of the focal point of the beam (20), controlled by said displacement means (21), comprises a transverse component in the direction Y-Y ', and a vertical component in the direction Z-Z ', the assembly constituting the trajectory in "V" We chose a constant transverse speed in the direction YY' and, taking into account the real trajectory in "V" introduced into the computer (22) of regulation , the vertical component along the axis ZZ ^′ of the movement of the focal point, or height of the focal point, is calculated and imposed on said focal point by means of a corresponding actuator, in the same way as the relative speed Vr of the focal point is calculated.

ADVANTAGES OF THE INVENTION

The invention provides a relevant and flexible solution to the difficult problem of regulating the energy supply by laser beam in all laser material processing where the temperature of the material plays a critical role, which is the case of most treatments involving an energy supply by laser beam In addition, the invention provides a general solution to this problem, in no way limited to the examples according to the invention, each time that an organic material is involved and especially each time what happens is a relative speed of the focal point with respect to the support or material to be treated

The invention therefore makes it possible to treat with the same laser, typically to weld, different plastic materials, by tuning the frequency of the laser, without having to modify the plastic, typically by adding additives, to make it absorbent at lengths d 'predetermined conventional waves, as is known Thus, it is the frequency of the laser according to the invention which adapts to the absorption frequency of the material and not the reverse.

LIST OF REFERENCES

STRIP MATERIAL 1

ENERGY ABSORBING LAYER 10 ABSORPTION DIAGRAM 100

ABSORPTION PIC 101

PORTION OF PIC 1010

TEMPERATURE CURVE 1011

ISOTHERMAL CURVE 1012 FREQUENCY DOMAIN 102

WORKING FREQUENCY 103

PAS 104

WORKING RANGE 105 FREQUENCY INTERVAL OF A PIC 106 EDGE OF THE BAND 1 1

LONGITUDINAL TUBE WELDING 12

LONGITUDINAL WELDING OF BAG 13

CROSS BAG SOLDER 14

FOLDING LINE 15 MEDIAN STRIP LINE 16

LASER 2

LASER BEAM 20

MEANS OF MOVEMENT X, Y, Z 21 MEANS OF REGULATION on SPEED 22

LASER BEAM ROUTE 23

LAISON BETWEEN LASER & REGUALTION 220 LINK BETWEEN HOSE REEL & REGULATION 221

CYLINDRICAL TUBE 3

JUNCTION 30 LONGITUDINAL BAG 4

OPEN SIDE 40

TRANSVERSAL BAG 5

OPEN SIDE 50

CUTTING LINES 51

COIL REWINDER 6 COIL REEL 7

MEANS OF TRACTION 8

Claims

1. Laser treatment (2) of a material, typically in the form of a strip (1), comprising at least one layer (10) of plastic M absorbing the energy of the laser radiation, with a view in particular to carrying out an operation cutting, incising, marking at least said layer, or welding said material to itself or to a second material, by supplying energy from the laser beam (20) located on all or part of said layer with a view to bringing at least the said layer to the temperature necessary for carrying out the said operation, characterized in that, typically once and for all before the said addition, and for any new material to be transformed, a) it is established first, if it n is not known, the spectral absorption curve .Ai of said layer (10) of material Mi, in order to determine a frequency interval (106) corresponding to an absorption peak (101), b) said laser is chosen (2) among the lasers whose frequency, or length ^of ond e corresponding, the beam is adjustable over a frequency domain (102) comprising at least said frequency interval (106) relative to said absorption peak (101), c) the frequency of said laser is tuned to a frequency v _w (103 ), said to be working, of said absorption frequency interval, chosen to allow said temperature to be reached and said operation to be carried out in a predetermined time of said treatment

2. Treatment according to claim 1 wherein said laser (2) is a solid state laser using a pumped diode.

3. Treatment according to claim 2 wherein said laser (2) delivers an adjustable wavelength, typically using a parametric optical oscillator.

4. Treatment according to claim 3 in which said parametric optical oscillator is made of lithium niobate and has an adjustable frequency between 1 and 5 μm, that is to say between 10000 and 2000 cm ^'1 .

5 Treatment according to any one of claims 1 to 4 wherein the frequency of said laser (2) is adjustable with a step less than 0.1 μm, and typically with a step of 10 nm

6 Treatment according to claim 5 in which an initial frequency range (105), called the working range, corresponding to a zone of strong variation, typically a flank, of said absorption curve A is chosen, and it is varied step by step and preferably with a pitch (104) less than 0.01 μm, in one direction or the other of said zone, the frequency of said laser, so as to be able to adjust in a substantially proportional manner the quantity of energy absorbed, and thus the temperature of said layer (10) to be treated

7 Treatment according to claim 6 wherein said material is a material in the form of a strip (1) of great length which is scrolled at a determined speed, the laser beam (20) being fixed or movable, so as to achieve said treatment of said material over a small width, less than 5 mm and typically equal to 2 mm, and the step-by-step variation of the frequency of said laser is controlled by the relative speed variation of said material, so that the quantity of energy absorbed by said outer layer, and therefore the temperature of said layer (10) of the material to be treated is substantially constant regardless of said running speed of said strip (1)

8 Treatment according to claim 7 wherein said layer (10) is an outer plastic layer, each side of said strip comprising said layer, and wherein, preferably after having brought the parallel edges (1 1) of said strip, applying said treatment to at least one of the two edges of said strip to weld, preferably edge to edge, the two parallel ribs of said strip, so as to form a cylindrical tube (3) of great length

9 Treatment according to claim 6 wherein said laser beam (20) is moved at a predetermined relative speed, said material being typically fixed during said processing, so as to carry out said processing of said material, and in which said relative speed and the step-by-step variation of the frequency of said laser (2) are controlled so that the quantity of energy absorbed, and therefore the temperature of said layer (10) is substantially constant whatever said relative speed of movement of said laser beam relative to said material.

10 Treatment according to any one of claims 7 or 9, wherein said layer (10) is an outer plastic layer on one side of said strip (1), and wherein said strip is folded in the longitudinal direction so as to put opposite the two half-portions of longitudinal strips, and in which said treatment is applied transversely over the width of said half-portion, so as to form transverse welds, regularly spaced longitudinally, over a length equal to half -width of said strip, leading, after appropriate cutting, to the formation of sachets (5) open on one side.

1 1 Treatment according to any one of claims 7 or 9, in which said layer (10) is an outer layer of plastic material, in which said treatment is applied in a "U" shape and in which a second strip, identical or not to said strip , is applied to said strip, so as to form "U" welds (13, 14) between said strip and said second strip, leading, after appropriate cutting, to the formation of sachets (4,5) open on one side .

12. Treatment according to any one of claims 7 and 1 1 for cutting, incising, engraving, continuously or discontinuously, over all or part of its thickness. said material.

13. Treatment according to any one of claims 1 to 12 in which the range 2400 - 3200 cm ^"1 is chosen as the frequency domain (102), which corresponds in particular to a certain mode of vibration of the CH bonds, so that the most of the plastics constituting said outer layer having peaks absorption between 2400 and 3200 cm ^{* 1} , the same laser, typically with lithium niobate, can be used for all common plastics.

14. Treatment according to any one of claims 1 to 13 in which an optical fiber, or any device for deflecting the laser beam, is used to effect said supply of energy at the desired location of said layer.