Laser treatment of materials, in particular cutting and welding

For elevator, particularly of cutting or welding field of the invention the invention relates to methods that use a laser to transform materials, in particular for welding, cutting, incising or labeling materials, particularly materials in strips or sheets comprising a plastic layer.

State of the technique the applications of laser materials processing have received a very large number of jobs and publications.

By way of example, typical documents include the following: the international application WO 89/10231 describes a method for socket weld a sheet comprising a layer of thermoplastic material, by melting, under laser irradiation, portions to be welded.

European patent number 237,192 ΔBL describes a method for welding plastics surfaces using the laser beam reflecting surfaces.

The French request the n 2,289 588 AI describes a method for attaching two elements [...] thermoplastic material using a laser operating in a portion of the absorption spectrum of said thermoplastic material.

There is also, in the literature, very many articles on the use of lasers.

By way of example, include of the article I-A by Jones and TT Taylor's "high speed downlink struggling d'Transparent estimation using laser" in [...]' 94 to 1363 1360 page, as well as the article of j.

Korte and H. [...] Taylor's "the laser Stratford struggling semicrystalline [...] OC" in [...] ' 96 page 1255 to 1259.

Problem is the problem regarding treatment by a laser, on line industrial, materials, typically web or sheet, comprising a plastic material.

Indeed, when the applicant has tried to use known laser to replace, on industrial line continuously operating, a conventional thermal energy input (e.g. electrical resistance, induction, andc...) for welding a multilayer material comprising a layer of plastic, it has failed to different problems: -'d ' one hand, it has firstly observed large variations in quality (or even a non-weldability) depending on the nature of the plastic materials used and following the laser used.

-'d ' on the other hand, it has also observed, MME to an MME plastics used, quality variations according to the desired rates. It has been decided that the great difficulty, if not impossibility of ensuring a constant energy output by a suitable adjustment of the laser, which is convenient, inexpensive, compact, ergonomic and flexible.

It has therefore sought a solution in these problems.

Description of the invention according to the invention, the laser processing a material, typically in the form of strip, comprising at least one layer absorbs energy of laser radiation, typically plastic, in particular to perform a cutting operation, incision, for marking at least said layer, said material on solder or [...] or with a second material, by energy of the laser beam located on all or part of said layer to heat said layer at least to the temperature required to perform step, is characterized in that, typically once and for all before said feeding, and for any new material to be treated, has) is first established, if it is not known, the spectral absorption curve in at least one of said layer,

to determine a frequency interval corresponding to an absorption peak, and b) said laser is selected among the lasers whose frequency, or corresponding wavelength, the beam is adjustable over a range of frequencies comprising at least said frequency interval relative to said absorption peak, and c) tuning the laser to a frequency of said vW or, said work, said frequency interval absorption, selected to enable reaching said temperature and to perform said operation within a predetermined time of said treatment.

Thus, the preceding means, and particularly the use of a variable frequency laser on a frequency given, adjustable to a range of given corresponding to an absorption peak of the material m of said layer, solve a fundamental problem of the invention.

Indeed, on the one hand, most plastic materials have absorption peaks in an MME portion of the IR absorption spectrum. Thus, for example, many plastic materials having carbon-hydrogen bonds have, enerally absorption peaks in frequency intervals corresponding to some neighboring common or vibration modes C-H bonds. An MME the laser will therefore TREs usable for a large number of plastic materials.

On the other hand, for an MME plastic, the variety of treatments and experimental conditions causes an equal variety of energy inputs by the laser to the plastics and thus required temperatures. It is not surprising that, according to which coact engagement for example cutting or welding, the temperature to be reached in said energy absorbing layer will not be the MME.

The invention allows this adaptation of an MME laser to requirements by adjusting its on said working frequency, in view of the absorption curve of said plastic material and of the nature of the work.

Specification of Figures Figure 1 illustrates the principle of the invention and represents diagrams (100) absorption AI, a2 and A3, relating respectively to three materials ml., m2 m3 and constituting said layer (10) energy absorbing. On these 3 schematic layouts where the V-fig. abscissa and ordinate to absorption takes, are represented absorption peaks (101) to which correspond intervals (106). The superposition of these three diagrams absorption AI, a3 a2 and thus defining a common domain (102), wherein each material has at least one absorption peak, this range of frequencies, which extends from va to vb, being that of the laser selected.

Depending on the material, a working frequency (103) vW or is selected for each material: [...] for ml., vw2 for [...][...]; for m3.

Figures 2 and 3 illustrate a modality of the invention in which the frequency of said laser may vary stepwise (104) about said working frequency (103) vW or, on a working range (105) extending from a V-, to a frequency v2, as shown in Figure 2. Figure 2 represents a portion (1010) of absorption curve (101) corresponding to said working range (105), and a portion of curve corresponding temperature T, plotted with the V and the ordinate, the absorption has left for the curve portion (1010), the temperature T at right for the curve portion (1011).

Figure 3 is in connection with Figure 2 and represents a curve portion (1012), called 'isothermal ", giving the relative speed of travel of the material relative to the laser beam as a function of frequency V such that, in view of the absorption curve (1010) of Figure 2, the I' received energy per unit time, and thus the temperature of the absorbent material remains constant.

Thus, desired variations or accidental speed on production line can TRE to automatically compensated by changes in frequency of the laser. Figure 4 represents schematically a regulating method and represents both a web material (1) to be treated passes across the speed V between a tape drive (6) and (7) a retractor in a treatment laser (2) comprising means (21) moving and/or focusing the beam (20) in the directions X and/or Y, and/or Z, and a regulating means (22), typically a computer having stored the absorption curve has=(P-(volts), and the curves t=f (V-, V-) leading to the curves v=f (V-) for T=to verbs.

Said regulating means comprises links (220.221) with the laser and with 1' (7) to ensure retractor typically regulation between the instantaneous speed VI of the strip (1) and the instantaneous frequency VI of the laser beam (20).

Figure 5 is a perspective view schematically illustrating the formation of a cylindrical tube (3) by folding, using means, particular tensioning means (8), not shown, the edges (11) of a web material (1) comprising outer layers per ml and M2, as shown in Figure its, plastic or welded by absorbing the energy of the laser (2) to form a junction (30) with solder (12), as shown in Figures 5b and 5c, Figure 5b corresponding to a lap joint and weld (12) layers ml and NT2, and Figure 5c at a junction edge to edge and weld (12) layers m1 ni1 on one side and m2 on m2 on the other side.

Figure 6 is a perspective view schematically illustrating the formation of bags (5) from a material web (1), by folding the strip relative to the longitudinal center line (16) to 1 'by means not shown, and forming, using the laser (2) (20) whose beam can be moved and/or TRE to distributed using said moving means and/or focusing (21), according to the directions longitudinal XX', cross-Y [...] vertical Z-Z', (14) transverse welds equally spaced apart and perpendicular to a fold line (15). After cutting (not shown) between two transverse seals (14.14 ') (51) along lines, the bags (5) are obtained, the open side (50) being at the top of the sachet, STRP to TREs filled.

Figure 7 is a perspective view schematically illustrating the formation of bags (5) from two web materials (1), by welding, using the laser (2) which can be moved and/or dispensed TRE to i 'by said moving means and/or focusing (21) according to the directions X [...] longitudinal cross-X-X ', the two films to form, for each bag, a longitudinal seam (13) and (14) two transverse seals. (5) the bags have an opening (50) in the longitudinal direction.

Figure S illustrates the kinematics of the laser beam in the case of Figure 7 and in the case where said strips (1) advance continuously to speed V constant. In this case, the beam, initially at the point a is moved diagonally to the point b in the X-Y plane, so as to form a transverse seal (14) which is perpendicular to the direction of feed of the strips. Once in b, the beam remains stationary, the time that the longitudinal seam (13) is formed and point c is reached. Then, the beam is moved diagonally up point c, with a very rapid return to point A prosecution following weld cycle. The beam thus has followed a path (23) predetermined.

The other option would be to advance the at least one band (I-) stepping, to remain in position during welding and moving the laser beam while the web is stopped.

Figure 9 illustrates a variant of Figure 7, where the bags are oriented in a different manner since each bag comprises two longitudinal seams (13) and a single cross seal (14). (4) formed bags have openings (40) in the transverse direction.

Detailed disclosure of the invention Figure 1 [...] graphic wherein the principle of the invention: from the absorption curves of various materials mid to be treated, a laser with adjustable frequency is selected for its domain (102), domain that comprises a number of slots (106) corresponding to peaks (101) absorption belonging to each of the absorption curves AIs of each material mid. Thus. an MME laser can potentially be suitable for a large number of plastic materials, and finely adjusted TREs were each at a working frequency [...].

In order to perform processing according to the invention, said laser can illustrates a solid state laser using a diode pumped.

This type of laser can supply an adjustable wavelength, typically to 1' using an optical parametric oscillator.

Optical parametric oscillator may TREs lithium niobate and have a frequency adjustable between T and 5 um in. i.e. between 10000 and 2000 cm - ', which corresponds in particular to domain [...]-red and wherein most plastic materials have absorption peaks.

Preferably, chosen is frequency domain (102) the range 2400 - 3200 cm in ' which corresponds in particular to a certain vibration mode C-H bonds, so that, most plastic materials forming said layers, said outer layer in particular, which has peaks between 2400 and 3200 absorptions of Cl ", an MME a laser, typically lithium niobate, can TREs used current most plastic materials.

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

According to the invention, by adjusting said frequency, a frequency range is selected initial, called working (105), ranging from V, to v2 as shown in Figure 2, and corresponding to an area of considerable variation, typically a flank, a portion (1010) one absorption peak (101) of said absorption curve AIs, and is varied stepwise. and preferably with a pitch (104) less than 0.01 a.m., in one direction or the other of said area, said laser frequency, so as to be substantially proportional adjustment of the amount of energy absorbed, and thus the temperature of said layer to be processed.

Figure 2, which illustrates this concept, watch although to the portion of absorption curve (1010) corresponds a portion of temperature curve (1011) and thus, a fine adjustment of the frequency v corresponds a fine adjustment of the temperature of the energy absorbing material and thus control over operation of said treatment.

According to a first modality of said treatment practice, said material may illustrates a strip material of great length that scrolls at a determined speed, the laser beam being fixed or movable, so as to carry out said treatment of said material with a small width, less than 2 mm to 5 mm and typically lift even (or edge-to-edge), and slaving the stepwise varied frequency of said laser to tA relative speed vr variation of said material relative to the laser beam, so that the amount of energy absorbed by said outer layers, said layers and thus the temperature of the material to be treated, is substantially constant irrespective of said speed of movement of said strip.

This concept is illustrated in Figure 3 which, particularly in view of the curves (1010) and (1011) of Figure 2, the relation between the relative speed vr between beam and material to be treated to maintain a constant energy output per unit time, and hence an MME temperature absorber layers. The curve (1012) of Figure 3 is thus a isothermal calculated for at a given temperature T=to verbs. Figure 4 represents schematically a possible solution of the overall control for driving the processing line to have a processing temperature constant despite changes in relative speed vr, which may TREs due to variations in the speed V of the web to be treated.

According to a first application illustrated in Figure 5, said layer is an outer layer (10) plastic, each face of said strip (1) comprising said layer (ml over a face m2 on the other side, as shown in Figure 5 has), and. preferably after close parallel edges (11) of said strip, said treatment is applied on at least one of two edges (11) of said strip for welding, preferably edge to edge, the two parallel sides of said web, to form a cylindrical tube (3) long by longitudinal seam (30) resulting from a weld (11) typically either by cover as illustrated in Figure 5b, either edge to edge as illustrated in Figure 5c.

A second modality according to practice of the invention, said laser beam can TREs moved. at least those portions of straight line course (93), to a predetermined relative speed, said material being typically fixed in said processing, so as to carry out said treatment of said material and said relative velocity may be servo stepping and the variation of the frequency of said laser such that the amount of energy absorbed, and thus the temperature of said layer, is substantially constant irrespective of said relative speed of travel of said laser beam relative to said material.

In this case, said strip is pushed forward, said treatment being carried out, at least in part, during the phase of ARTJ of the strip. In some cases, this modality can TREs attractive because, without thereby penalizing the processing speed, may avoid the need for costly kinematic means for providing the relative movement of the laser beam along a desired path.

It is a great advantage to be able to slave the relative speed of the beam, because, as soon as the path (23) of the beam is not linear and has direction changes, there are locally from lag and acceleration of the movement of the laser beam (20) which can only lead to local variations of temperature.

In another application of the process according to the invention illustrated in Figure 6, this layer can TREs an outer layer of plastic material on one face of said web (I-) web may TREs folded in the longitudinal direction so as to be set facing the two half portions of longitudinal strips, and said treatment may TREs applied transversely across 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 half the width of said strip (1). leading, after appropriate cut, the formation of bags (5) open on one side (50).

In Figures, and especially in Figure 6, the position of the laser (2) is indicated only schematically and symbolic. In practice, it may TREs advantageous if the laser beam comes incident different from that illustrated in Figures and uses complementary devices known per se Mmeas to permit accurate location of the energy input by said beam on said layer to be treated (10). Are not included in Figure 6 the means, also known, which make possible the strip (1) and applying each web-half to form said transverse seals.

In another embodiment illustrated in Figures 7 and 9, said layer may TRE to an outer layer of plastic material, wherein said treatment is applied in "U-shaped" and a second band, identical or not to said band, said band is applied, so as to form welds in "U-shaped" between said band and said second band, leading, after appropriate cut, to the formation of bags (4.5) open on one side.

The weld is called "U-shaped" to designate the generic form of a sachet (4, 5), the bags being usually square or rectangular shape, but of course it is not limiting the treatment according to the invention to a particular form of bag.

Figures 7 and 9 are distinguished by the orientation of the bags relative to the direction of travel of the webs (1), the opening (40) being transverse to Figure 9, the opening (50) being longitudinal in Figure 7.

It is of course possible to imagine provide not one but several bags on an MME bandwidth, and optionally to implement on this more laser beams simultaneously.

The treatment according to the invention is not limited to sealing two plastic layers. II concerns also for cutting, cutting, etching, marking, continuously or discontinuously, over all or part of its thickness, said material, all operations for which it is desirable to control the delivery of energy and therefore for which the means of the present invention can be advantageously applied.

In general, it is intended to modify the surface of a material to form a trace to discretely given course. By may, by scanning the beam across a surface, substantially altering the entire surface with respect to its texture, its roughness or its surface energy. For carrying out the process according to the invention, can be used an optical fiber carrying the laser beam, or any sensing device and/or separation of the laser beam, to effect said power delivery to the desired location of said layer.

Examples of making the Figures constitute the exemplary embodiments.

In one example, illustrated in Figure 5, fabricated a long cylindrical tube (3) from a strip (1) of multilayered material having as a structure of PEI // // ADHs EVOHs ADHs PE2 which, wherein PE; denotes a polyethylene layer of 150 um and pe2 designates a PE-layer of 100 um in, where ADHs denotes an adhesive layer of 10 um and a barrier layer of EVOH, EVOH, of 15, MU.

Taking into account the absorptive pattern PE, layer (10) absorbing the energy of the laser, is chosen type laser diode solid optical parametric oscillator pumped with lithium niobate, and a frequency domain (102) with V, equal to 2, 8 and VB equal to 4 um in U-shape. the m. Has been selected V-work, equal to 3r3 UMN map which belongs to the absorption peak (101) PE used, peak having a frequency interval (106) ranging from 3, 2 um in d-um in 3.7.

. To effect the regulation of the process, as shown in Figures 2 and 4, is chosen not (104) of 10 nm and a working range (i05) ranging from v=3.1 um in to v=3, 4 MU.

Was made both types of welds illustrated in Figures 5b and 5c, with M1===M2 of PE-layer.

The speed V of web running (1) has been set to a nominal value of 40 meters/minute.

This varies the speed of + / - about 20% about the nominal value by examining the quality of the welding of the joint (12) (30) either with the regulation according to the invention. either without regulation by performing tests of tensile and delamination for evaluating the quality of the weld (12). It thus been observed that the resulting tube according to the invention had a quality weld constant regardless of the speed V, while the tube obtained according to the state of the technique, i.e. without regulation according to the invention, had an unevenness in the quality of the weld which can lead to severe problems of quality tubes, toothpaste tubes typically obtained subsequent to said cylindrical tube (3) of great length into sections and have a assessm overmolded.

In a second example illustrated in Figure 6, fabricated bags from a PE film of 60 um in thickness forming a strip (1) of 30 cm wide.

The laser used is that of the MME 1' previous example. II is of MME in experimental conditions, and typically the working frequency of the layer (10) wine energy absorbing being also PE.

In this example was the unseparated web (1) stepping, to have a simplified kinematics for the laser beam (20).

At each step, the strip being to t'a ARTJ, the laser beam (20) has been focused and moved along a path in the form of a ' V-", the two half portions of the film (10) being only partly collapsed upon occurrence at said energy input by laser beam.

The movement of the focal point of the beam (20), driven by said moving means (21), comprises a transverse component in the direction X-X ', and a vertical component in the Z direction to-[...] constituting the path I' vee '.

Has been selected transverse velocity constant in the direction of Y-[...], taking into account the actual trajectory "vee" introduced in the computer (22) control, the vertical component according to 1' axis Z-[...] focal spot movement, or height of the focal point, is calculated and imposed upon the focus through a corresponding actuator, of MMEs that is calculated the relative velocity Vr of the focal point.

Advantages of the invention as a solution relevant and flexible at difficult problem of the regulation of the energy supply by laser beam in all treatments of laser material where the temperature of the material plays a critical role, which is the case of most treatments using an energy supply by laser beam..

Further, the invention provides a general solution to this problem, none at all limited to the examples according to the invention, each time a organic material involved and especially whenever it a relative speed of the focal point relative to the medium or material to be treated.

The invention thus provides for an MME processed with a laser, typically welding. various plastics, by tuning the frequency of the laser, without having to modify the plastic, typically by adding additives, to render it absorbing at predetermined conventional wavelengths, as known. Thus, it is the frequency of the laser according to the invention that adapts to the absorption frequency of the material and not vice versa.

LIST REFERENCES WEB MATERIAL............................... 1 ENERGY ABSORBING LAYER............................... 10 [...][...].................................... 1 ADSORBENT SECTION.............................. 101 TEMPERATURE CURVE......... 1011 ISOTHERMAL CURVE................... 1012 FREQUENCY DOMAIN.............................. 102 WORKING FREQUENCY................................ 103 NOT.............................................. 104 WORKING RANGE............................... 105 OF A PEAK FREQUENCY INTERVAL. 106. EDGE OF THE STRIP 11 12 WELD WELD [...]......... 13 WELD [...].......... 14 [...]....................................... 15 CENTRAL LINE OF THE BAND........................

16 laser-................................ 2 laser beam....................... 20 means seating height, therein, Z-......................... 21 means control overspeed............ 22 path of the laser beam...................... 23 link detected between lasers & [...].......... 220 linking & retractor. control. 221 open side junction 30.................... 50 scribe channel......................... 51 traction means 8