FR2787058A1 - Ultrasonic welding of films to make packages and e.g. disposable nappies is carried out between sonotrode and form rotated by drum, with speed differential to elongate or foreshorten shape of weld - Google Patents

Abstract

Films (3, 4) and drum (6) carrying welding forms (10), pass an ultrasonic emitter (5), moving at differing speeds (V1, V2). This bonds the films along a welding zone differing in shape from that of the welding forms. Preferred features: The first assembly (comprising both films, 3, 4), is moved along at constant speed. The speed (V2) of the second assembly (comprising the welding drum and forms, 6, 10) is varied. V1 = Vn initially, a nominal speed. V2 is increased to an accelerated speed Va, then decreased back to nominal (Vn) to obtain a welding zone reduced in extent, i.e. foreshortened, in comparison with the size of the welding form (10). Between acceleration and deceleration, the drum runs at constant speed or is stopped. At least one acceleration or deceleration of the drum is instantaneous. The welding zone includes a straight line portion parallel to film motion. The speed V2 is varied. Either or both films are printed with a series of impressions. The process assures suitable matching between positions of printing and those of welding. If necessary, the films are re-positioned with respect to the matrix.

Description

METHOD OF WELDING TWO FILMS BY ULTRASOUND

  The invention relates to a process for welding at least two films, used for the manufacture of many and various products such as sachets

  packaging, diapers, and other such assemblies.

  There are mainly two types of film welding process.

  The first method, by heat sealing, uses two heating dies, of cylindrical shape, each supporting a plurality of welding imprints in relief and in slight pressure against each other along a generator. For mass production, for example, of a plurality of bags welded on four sides forming a rectangle, the rollers used support a plurality of rectangular welding imprints of format corresponding to that of the bags. During manufacture, two films are driven concomitantly in translation by passing them between the two heating rollers driven in rotation in opposite directions, the driving speed of the two films being equal to that of the two rollers. The two films, thus brought into contact with one another and brought to a softening temperature, are welded to each other along welding zones of shape and format identical to those of the welding imprints . The second method, by ultrasound, uses a matrix, generally of cylindrical shape, supporting a plurality of raised welding impressions and an ultrasonic emitter extending along a generator of the matrix, at a determined distance from this one. During the manufacture of sachets, to use this example again, under the action of the rotary drive of the impression support roller, the two films are made to pass in front of the ultrasonic emitter, in contact with one another , and by sliding support against the support roller. The profile of the impression support roller, along each generatrix, has ridges and valleys corresponding to a relief weld imprint. The ultrasonic emitter is slightly moved away from the impression support matrix in order to allow the passage of the two films between the emitter and the matrix and to provide a slight clearance between the emitter and the two films entrained in movement. While scrolling,

  the two films come into contact with the ridges of the weld footprint.

  The ultrasonic radiation induces vibrations at the molecular level in the areas of the films in contact with the ridges of the impression of

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  welding. As a result, the two films are welded to each other, along welding zones of shape and format identical to those of the imprint

welding of the matrix.

  With the two known methods explained above, the format and more generally the shape of the welding zones are identical to those of the welding imprints. To weld the films along welding zones with a shape different from that of the welding indentations, it is therefore advisable to

  change the fingerprint support matrix.

  The present invention aims to overcome this drawback.

  To this end, the invention relates to a method of ultrasonic welding of at least two films, in which the two films and a matrix are displaced in displacement, supporting at least one welding imprint of given shape, in front of a transmitter. ultrasound, characterized in that the two sets of the two films and the matrix are driven at two different speeds, respectively, in order to weld the two films along an area of

  welding with a shape different from that of the welding footprint.

  In the case where the impression support matrix is cylindrical, the drive speed of the matrix must obviously be understood to be the speed

  tangential drive of the matrix.

  Thanks to the invention, it is therefore possible to manufacture sachets of shapes

  different with the same matrix, to use this example again.

  Preferably, the first of the two is driven at a constant speed.

  sets and the drive speed of the second set is varied.

  Advantageously, the first set is driven at a nominal speed and, concomitantly, the driving speed of the second set is increased from the nominal speed to an accelerated speed and then it is reduced to the nominal speed, in order to obtain a zone shape welding

  shrunk from that of the weld footprint.

  Advantageously again, which one drives the first set at nominal speed and, concomitantly, the driving speed of the second set is reduced from nominal speed to a slow speed and then

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  increases it to nominal speed, in order to obtain a welding zone

  of enlarged form compared to that of the weld footprint.

  In a particular embodiment, between the acceleration phase and the deceleration phase of the second assembly, the latter is trained to a

constant speed.

  In an alternative embodiment, between the deceleration phase and the acceleration phase of the second set, the training is stopped.

io displacement of it.

  Advantageously, at least one of the acceleration and

  deceleration of the second set is instantaneous.

  Thanks to this, an oblong-shaped welding zone can be formed from a circularly shaped welding imprint, without creating defects.

of form.

  Advantageously also, the welding zone comprising at least one rectilinear portion extending parallel to the direction of movement of the films, the drive speed of the second assembly is varied during the

  welding of the two films along said straight portion.

  Thanks to this, we avoid creating defects in shape.

  The invention will be better understood using the following description of a

  particular embodiment of the process for welding two films of the invention, with reference to the attached drawing in which: - Figure 1 shows a schematic view of a device for welding two films; 2 shows a top view of a welding imprint of a matrix of the device of Figure 1; - Figure 3 shows a sectional view of the footprint of Figure 2, along the line III-III; - Figure 4a shows a top view of a first welding area of the two films of Figure 1; - Figure 4b shows a graph of the time evolution of the drive speed of the two films and the drive speed of the die, for welding the two films along the welding area of Figure 4a;

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  - Figure 5a shows a top view of a second welding area of the two films of Figure 1; FIGS. 5b and 5c each represent a graph of the temporal evolution of the drive speed of the two films and of the drive speed of the matrix, for welding the two films along a welding zone such that that of FIG. 5a; - Figure 6a shows a top view of a third welding area of the two films of Figure 1; - Figures 6b, 6c and 6d each show a graph of the time evolution of the drive speed of the two films and the drive speed of the die, for welding the two films along a welding area such as that of FIG. 6a; - Figure 7 shows a top view of a circular welding footprint; - Figure 8a shows a top view of an oblong area for welding two films made using the welding imprint of Figure 7 and - Figure 8b shows a graph of the time evolution of the speed drive of a matrix supporting the welding footprint of

  Figure 7 and the drive speed of the two films, to weld them

  Ci along the welding area of Figure 8a.

  At the outset, it will be noted that on the graphs of the temporal evolution of the speeds of FIGS. 4b, 5b, 5c, 6b-6d and 8b, time and speeds

  respectively represented on the abscissa and on the ordinate.

  The welding process of the invention makes it possible to weld two films, using a welding device explained below, for the manufacture here of

  packaging bags intended to contain a substance.

  The welding device, shown in FIG. 1, comprises two rollers 1, 2 for supplying film 3, 4, an ultrasound emitter 5, a welding matrix 6, a pair of deflection rollers 8, 8 'and a pair of

  rollers 9, 9 'for driving the films 3, 4.

  The welding matrix 6 consists of a cylinder, of axis 1 1, rotatably mounted and supporting a plurality of welding imprints 10 in relief, on its wall

cylindrical outer.

  In the following description of the matrix 6, the cylindrical support wall

  of fingerprints 10 is developed on a plane. Welding footprints 10

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  are arranged side by side, perpendicular to the axis ll, and separated from each other by a welding pitch Ps. Each cavity 10 here comprises four sides 12-15 comprising a plurality of welding ribs 16, here four in number , generally rectilinear, and generally forming a rectangle, and, inside this rectangle, a central rectangular recess 18. The two sides 12 and 14 extend parallel to the axis 11 and the other two sides 13 and 15 generally extend perpendicular to this axis 1 1. The welding footprints 10 of the

  matrix 6 here all have the same shape and therefore the same format.

  The ultrasonic emitter 5 extends along a generator 19 of the matrix 6, which will hereinafter be called "welding generator", at a determined distance from the matrix 6, allowing the passage of two films 3 , 4 between

the emitter 5 and the matrix 6.

  The films 3, 4, wound around the feed rollers 1, 2, are

  made of ultrasonically weldable material, in this case polyethylene.

  The two feed rollers 1, 2 are mounted to rotate freely and are arranged on either side of a plane P tangent to the matrix, and more

  precisely to the ribs 16, along the welding generator 19.

  The two deflecting rollers 8, 8 'bear against one another in the plane P and mounted free in rotation. The two drive rollers 9, 9 'are pressed against each other in the plane P and mounted to rotate in opposite directions. The pair of diverter rollers 8, 8 'and the pair of drive rollers 9, 9' are respectively located upstream and downstream of the welding generator 19, the upstream designating what is located between the feed rollers 1, 2 and the welding generator 19 and downstream

  designating what is located beyond the welding generator 19.

  The welding device further comprises a speed sensor, intended to measure the speed of the die 6, and a regulation system, connected to the speed sensor, intended to control the drive of the die 6 to that of the rollers. drive 9, 9 ', by varying the drive speed

  of the die 6 as a function of the speed of the drive rollers 9, 9 '.

  The speed sensor and the regulation system are not shown.

  The welding process of the two films 3, 4 will now be explained.

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  The two films 3, 4, unwound from the feed rollers 1, 2, are taken and thus brought closer to each other by the two deflecting rollers 8, 8 ′, and pinched between the two drive rollers 9, 9 ′, being applied and therefore brought into contact with one another, and they thus extend in the plane P. Under the action of the drive in rotation of the drive rollers 9, 9 ′, the two films 3, 4 are concomitantly driven to run, in contact with one another, in the plane P, in front of the ultrasonic transmitter 5, from upstream to downstream, perpendicular to the welding generator 19 , io with a drive speed VI. The direction of travel of the films 3, 4 is indicated by the arrow 7. The two films 3, 4 are thus passed through the

welding generator 19.

  Concomitantly with the drive of the two films 3, 4, the die 6 is driven in i5 rotation, in the direction of rotation indicated by the arrow 7 ', with a drive speed V2. By definition, we qualify as "speed

  drive V2 of the die 6 "the tangential speed of the die 6.

  It will also be emphasized that the direction of rotation 7 ′ of the matrix 6, tangential to the welding generator 19, is identical to the direction of

scroll 7.

  During scrolling, the two films 3, 4 come into temporary contact against the ribs 16 of the matrix 6. Obviously, by the term "contact", it is meant either direct contact, for the first of the two films 3, either an indirect contact, through the first film 3,

for the second film 4.

  The two films 3, 4, moving past the ultrasonic transmitter 5, are subjected to ultrasonic radiation substantially along the welding generator 19. This radiation induces a molecular vibration of the material in the areas of the two films 3 only. , 4 coming into contact with the welding ribs 16. This molecular vibration has the effect of heating and welding the two films 3, 4 along a plurality of welding zones, each corresponding to a welding footprint 10 and comprising four sides generally forming a rectangle and corresponding

  respectively at the four sides 12-15 of the imprint 10.

  During the welding, the substance to be introduced between the two films 3, 4

  pack in bags during manufacture.

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  With reference to FIG. 4, in the case where the two films 3, 4 and the matrix 6 are driven at the same nominal speed v., Constant, the two films 3 and 4 are welded along a plurality of zones of welding 17, each corresponding to a welding footprint 10, having four sides 20-23 generally forming a rectangle, of the same shape and therefore of

  same format as those of the imprints 10.

  In order to weld the two films 3, 4 along welding zones of a shape different from that of the welding imprints 10, and more particularly here of a format different from that of the welding imprints 10, the two films and the matrix are driven. 6, respectively at two speeds V1 and V2 different from each other, here by varying the drive speed V2 of the matrix 6 and by driving the films 3, 4 at a constant speed. This makes it possible to weld the two films 3, 4, along weld zones of either enlarged or narrowed shape relative to the shape of the weld imprints.

  , as will now be explained with reference to FIGS. 5 and 6.

  1) Welding zones of narrowed shape with respect to that of the welding impressions In the case 1) here described, the two films 3, 4 are welded, using one of the welding impressions 10, along a welding zone 29, of narrowed shape relative to that of the cavity 10 and comprising two portions, or sides 30, 32, rectilinear, perpendicular to the direction of travel 7 and two portions 31, 33, or sides, rectilinear, parallel to the direction of travel 7, as shown in FIG. Sa. FIG. 5b represents the time evolution of the respective drive speeds of the two films 3, 4 (VI) and of the matrix 6 (V2), during the welding of the two films 3, 4 along the

welding area 29.

  During the phases 24, 28 of welding on the two sides 30, 32 perpendicular to the direction of travel 7, the two films 3, 4 and the matrix 6 are driven to the

  same nominal speed vn, constant.

  On the other hand, during the simultaneous welding of the two sides 31, 33 parallel to the direction of travel 7, the drive speed V2 of the die 6 is varied, while continuing to drive the films 3, 4 at the speed nominal

vn, constant.

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  In a first acceleration phase 25, the driving speed V2 of the matrix 6 is increased continuously from the nominal speed vn to an accelerated speed Va. Then, in a second phase 26, we

  drives the matrix 6 at constant speed, namely at the accelerated speed va.

  Finally, in a third deceleration phase 27, the driving speed V2 of the matrix 6 is reduced continuously from the accelerated speed to the nominal speed Vn. This increases the average speed

  drive of the die 6 with respect to the nominal speed vn.

  Thus, the two welded sides 31, 33, parallel to the running direction 7, are smaller than the corresponding sides 13, 15 of the welding imprint, while the two welded sides 30, 32, perpendicular to the running direction 7 , are of the same dimension as the corresponding sides 12, 14

of the welding footprint 10.

  2) Welding area of enlarged shape compared to that of the welding imprints In the case 2) here described, the two films 3, 4 are welded, using one of the welding imprints 10, along d '' a welding zone 39, of enlarged shape compared to that of the cavity 10 and comprising two portions, 42, or sides, rectilinear, perpendicular to the direction of travel 7 and two portions 41, 43, or sides, rectilinear, parallel in the direction of travel 7, as shown in FIG. 6a. FIG. 6b represents the temporal evolution of the respective drive speeds of the two films 3, 4 (VI) and of the matrix 6 (V2), during the welding of the two films 3, 4 along the

welding area 39.

  During the phases 34, 38 of welding the sides 40, 42 perpendicular to the direction of travel 7, the two films 3, 4 and the matrix 6 are driven to the

  same nominal speed vn, constant.

  On the other hand, during the welding of the sides 41, 43 parallel to the direction of travel 7, the drive speed V2 of the die 6 is varied, while

  continuing to drive the films 3, 4 at the nominal speed Vn, constant.

  In a first deceleration phase 35, the driving speed V2 of the matrix 6 is decreased continuously from the nominal speed Vn to a slowed down speed Vr. Then, in a second phase 36, we

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  drives the matrix 6 at constant speed, namely at the slowed down speed vr.

  Finally, in a third acceleration phase 37, the driving speed V2 of the matrix 6 is increased continuously from the slowed down speed vr to the nominal speed vn. This reduces the average drive speed of the die 6 relative to the nominal speed vn. Thus, the two welded sides 41, 43, parallel to the direction of travel 7, are larger than the corresponding sides 13, 15 of the weld footprint, while the two welded sides 40, 42, perpendicular to the travel direction 7 , are of the same dimension as the corresponding sides 12, 14

of the welding footprint 10.

  To weld the two films 3, 4 along welding zones of a shape different from that of the welding imprints, it could be envisaged to vary the drive speed of the matrix according to profiles of temporal evolution, not differing from those explained above only by this

which will now be described.

  With reference to FIG. 5c, in order to weld the two films 3, 4 along a weld zone of shape that is narrower than that of the weld footprints 10, as shown in FIG. 5a, when welding the parallel sides in the direction of travel 7, it would be possible, in a first acceleration phase 44, to increase the speed V2 of the matrix 6 by the nominal speed v. until an accelerated speed goes, then, in a second deceleration phase 45, decrease the speed V2 from the accelerated speed goes to the nominal speed v ,. In this case, the matrix 6 would not be driven at constant speed between the acceleration phase 44 and the deceleration phase 45. Similarly, with reference to FIG. 6d, in order to weld the two films 3, 4 along a weld zone of enlarged shape relative to that of the weld footprints 10, as shown in FIG. 6a, during the welding of the sides parallel to the direction of travel 7, one could, in a first phase 46, deceleration, decrease the speed V2 of the matrix 6 from the nominal speed v ,, to a slow speed vr, then, in a second phase 47, of acceleration, increase the speed V2 by the speed

  slowed down vr to nominal speed v ,.

  With reference to FIG. 6c, in order to weld the two films 3, 4 along a weld zone of enlarged shape relative to that of the indentations of

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  welding 10, as shown in FIG. 6a, one could, in a first phase 48, of deceleration, decrease the driving speed V2 of the matrix 6 from the nominal speed Vn to zero speed, then, in a second phase 49, maintain zero the drive speed V2 of the matrix 6 and finally, in a third phase 50, of acceleration, increase the drive speed V2 of the matrix 6 from the zero speed to the nominal speed vn ,,. In this case, we would stop momentarily

  the rotary drive of the die 6.

  Each of the two films 3, 4 supports, on the face opposite that to be welded, a plurality of printed patterns intended to identify the packaging bags produced. These patterns are arranged side by side in the lengthwise direction of each film and separated from each other by a printing pitch pi equal to the welding pitch Ps separating the imprints of

welding 10 of the die 6.

  In order to produce correctly printed packaging bags, it is necessary to match the printing pitch pi and the welding pitch ps, when welding the two films 3, 4, so that each sachet

  supports a pattern printed on each of its two external faces.

  However, after having welded a succession of packaging bags, a discrepancy may appear between the printing steps p, and the welding steps Ps. In this case, the two films 3, 4 are repositioned relative to the matrix 6 , by driving the two films 3, 4 and the matrix 6 respectively at two different speeds, and here by varying the speed of the matrix 6 while keeping constant the speed of the films 3, 4, as previously described, in order to match and thus readjust the print pitch pi and the

no ps welding.

  The acceleration and deceleration phases could be instantaneous,

  in other words of very short duration, of the order of a few milliseconds.

  In another embodiment of the welding device differing from that of FIG. I only in what will now be explained, the welding matrix supports welding imprints 51 comprising ribs

  circular, as shown in Figure 7.

  Using one of these circular welding imprints and varying the drive speed of the matrix, as explained below with reference to FIG. 8b, while simultaneously driving the two films at nominal speed vn, the two films are welded along an oblong welding zone, of enlarged shape compared to that of the circular imprint, as shown in FIG. 8a, comprising two semicircular portions 57, 60 connected one to the other the other by two straight sides 58, 59. In a first phase 52, the two films and the matrix are driven at the same constant nominal speed v ,, and thus the two films are welded along the first semi-portion circular 57, using a first semi-circular half of the welding imprint 51. In a second phase 53, of instantaneous deceleration, the driving speed V2 of the matrix is instantly reduced to zero speed. In a third phase 54, the drive speed V2 of the matrix is maintained at zero. In a fourth phase 55, of instantaneous acceleration, the drive speed V2 of the matrix is instantaneously increased from zero speed to nominal speed vn. During phases 53 to 55, the two films are concomitantly driven at the constant nominal speed vm. The two films are thus welded along the two straight portions, or sides 58, 59. Finally, in a fifth phase 56, the two films and the matrix are driven at the same nominal speed v ,. The two films are thus welded along the second semicircular portion 60, using

  the second semi-circular half of the welding footprint 5 1.

  Instead of varying the drive speed of the die, we could

vary that of the two films.

  The matrix could also include an endless band, supporting a succession of welding impressions, mounted around two rollers

drive rotary.

  We could also consider welding more than two films.

  The films could be made of any other material that can be welded by ultrasound (for example thermoplastic) or include at least one

  layer of material weldable by ultrasound, on the side or sides to be welded.

  Finally, one could use welding imprints of shapes different from those previously described, comprising for example sides

  parallel and other sides not parallel to the direction of travel of the films.

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Claims (9)

  1- Method of ultrasonic welding of at least two films (3, 4), in which the two films (3, 4) and a matrix (6) are moved along with it, supporting at least one weld imprint (10; 51) of given shape, in front of an ultrasonic transmitter (5), characterized in that the two sets of the two films (3, 4) and the matrix (6) are driven, respectively at two different speeds (VI , V2), in order to weld the two films (3, 4) along a welding zone (29; 39; 57-60) of a shape different from that of 0o the welding footprint (10; 51).   2- The method of claim 1, wherein, the first of the two assemblies (3, 4) is driven at a constant speed and the speed is varied   drive (V2) of the second set (6).   3- The method of claim 2, wherein the first assembly is driven (3, 4) at a nominal speed (vn) and, concomitantly, the drive speed (V2) of the second assembly is increased (25; 44) 6) from the nominal speed (vn) to an accelerated speed (va) then it is reduced (27; 45) to the nominal speed (vn), in order to obtain a welding zone   (29) with a narrowed shape relative to that of the welding imprint (10).   4- Method according to one of claims 2 and 3, wherein the   first set (3, 4) at nominal speed (vn) and, concomitantly, the driving speed (V2) of the second set is reduced (35; 46; 48) at nominal speed (vn) at a slow speed ( vr) then it is increased (37; 47; 50) to the nominal speed (vj), in order to obtain a weld zone (39) of enlarged shape compared to that of the imprint welding (10).   - Method according to one of claims 3 and 4, wherein, between the phase   acceleration (25; 37; 50) and the deceleration phase (27; 35; 48) of the   second set (6), it is driven at a constant speed (va; vr).   6- Method according to one of claims 4 and 5, wherein, between the phase   deceleration (48) and the acceleration phase (50) of the second set   (6), it stops the driving movement thereof. 13 2787058   7- Method according to one of claims 3 to 6, wherein at least one   acceleration and deceleration phases (53, 55) of the second set (6) is instantaneous.   8- Method according to one of claims 2 to 7, wherein, the area of   welding (29; 39; 57-60) comprising at least one rectilinear portion (31, 33; 41, 43; 58, 59) extending parallel to the direction of movement (7) of the films (3, 4), varying the drive speed (V2) of the second assembly (6) when welding the two films (3,4) along said portion   io rectilinear (31, 33; 41, 43; 58, 59).   9- Method according to one of claims 2 to 8, wherein one varies the   drive speed (V2) of the die (6).   10- Method according to one of claims 1 to 9, wherein, a   succession of patterns being printed with a determined printing pitch on at least one of the two films (3, 4), the two films (3, 4) are welded along successive welding zones separated from each other by a welding pitch equal to the printing pitch, and, if necessary, the two films (3, 4) are repositioned with respect to said matrix (6), driving the two films (3, 4) and said matrix ( 6) respectively at two different speeds,   to match the welding pitch and the printing pitch.