FR2807392A1 - Ultrasonic welding device for making food packaging, etc., by welding flexible plastic sheets has passage between ultrasonic source and anvil with projecting ridge parallel to sheet movement - Google Patents

Abstract

An ultrasonic welding device has an ultrasonic source and an anvil forming a passage through which two superposed sheets to be joined can pass. The passage decreases in section between its inlet and its outlet. The source and/or the anvil has a ridge projecting into the passage and extending parallel to the direction of relative movement between the sheets and the device. Independent claims are included for: (a) Welding sheets as above; (b) Flexile packaging made as in (a).

Description

The present invention generally relates to cutting welding operations of at least two superimposed flexible sheets.

More particularly, it relates in a first aspect to a device of the type comprising a sonotrode and an anvil arranged facing each other so that their facing surfaces define a passage gap of the superimposed sheets to be welded, with a section of input and output section, the sonotrode vibrating at high frequencies to emit ultrasonic waves.

The invention also relates, according to a second aspect, to a welding and / or cutting process using a device of the aforementioned type, said method being able to be used for welding and possibly cutting two films or flexible sheets.

More particularly, advantageous applications according to the invention relate to the welding and possibly also the cutting, using a device of the aforementioned type, of the two lateral edges of flexible packaging, as well as the sealing by welding, using a device type above, packaging as evoked above.

It also relates to a flexible package, made in particular according to one of the methods mentioned above.

Such packaging can be made from monolayer plastic films, or multilayer.

Advantageous, but not limiting, application of the invention is the production of pouches or flexible bags containing food materials, for example animal feed materials, such pouches or bags being generally intended to be hermetically closed and heat-treated after filling and filling. closing (in the remainder of this text, the terms "packaging" or "pouch" will be used interchangeably to designate flexible packaging).

These pouches can, once filled, be sterilized by being heated in a humid environment and under pressure.

To resist such heat treatment, they are made from one or more film (s) of particular structure.

More particularly, they are generally made from one or more film (s), each film comprising an upper layer and a lower layer intended to constitute the outer and inner faces of said packages made of plastic, a central layer sandwiched. between said upper and lower layers, made of light metal.

Even more specifically, the films from which these packages are made may have the following characteristics: the upper layer is generally a polyethylene terephthalate layer optionally associated with a polyamide layer, the central layer is made of a gas-tight material, in particular aluminum, and the lower layer is polypropylene layer or not associated with a polyamide layer, # between each layer, there is provided an adhesive coating for bonding the different layers together, # furthermore, the layer polyethylene terephthalate can be printed on the inside to decorate the outside of said pouch. Indeed, polyethylene terephthalate layer generally serves as a printing medium and gives the appearance of the pouch.

 # aluminum core layer forms a barrier to gas, especially oxygen, and water vapor, to isolate from the outside the materials contained inside the pouch, # layer of polyamide constitutes an anti-aging layer perforation when necessary depending on the subsequent applications of the pouch, the polypropylene layer serves as a solder for making pouch, gives the general mechanical strength of the pouch and seals at the welds of said pouch.

Such pouches may contain solids, wet solids, liquids or a combination of solids and liquids. Currently, such pouches have various forms.

They can be flat, three or four welds, or bellows with three welded sides and a welded bottom in the form of bellows.

Such pouches may also include two side gussets, or two bellows positioned at the top and bottom of the pouch with welded side edges.

A widespread configuration, because particularly simple, these pouches is the flat configuration, in which the pouch is simply made by the assembly of two sheets. Such an assembly is carried out in two stages. Initially, a pouch is formed, one edge of which remains open, by welding the two sheets on three of the four sides of the pouch (which generally has a generally rectangular shape).

To achieve this welding, use a folded sheet on itself in a line that will form an edge of the pouch, or two separate sheets that are superimposed.

In both cases, the welding of the sides of the sheets can be associated with a cut to detach each sheet of plastic film.

In a second step, it closes the last side of the pouch after filling; such a closure is also by welding, which can also be associated with a cut.

In any case, the welds made must ensure a very good seal of the interior of the pouch not only to the liquid, but also to the gas (in particular if the pouch contains liquid, moist or perishable products), very good mechanical strength of the pouch.

The welding operations used to form these pouches are generally carried out using conduction welding technology of the edges close to the flanks of each pouch, so as to heat the polypropylene inner layer of each flank by conduction through the central layer. in aluminium.

following the conduction welding, it is expected a cooling that strengthens welding thus achieved.

solder line made by such a method generally has a width of several millimeters, to ensure the strength and sealing tightness.

it would be advantageous to be able to reduce the width of the weld line in order to save material.

Indeed, pouches are usually manufactured in very large quantities so that it is interesting for manufacturers to look for all possible savings on the unit cost of pouches; the relatively large width of the weld line is therefore a first drawback of conductive welding.

Moreover, the implementation of this conduction welding process with continuously moving plastic films proves problematic, in particular because of the friction between the fixed elements and the moving elements of the welding device.

The type of process is therefore generally implemented in a fractional mode, on films scrolling step by step.

Step welding principle has a rate limit. Even by performing a simultaneous advance of two no poches, this method reaches its mechanical operating limits, in particular because it is necessary to decelerate and accelerate the bags before and after the welding station, and that the system has certain inertia.

In order to increase the rate of sealing of such packages or pouches, and to pass for example a rate of 120 packages / min (current limit of the rates for the processes of welding by heating) 'a value much higher (of the order of 500 packages / min or more), considered using an ultrasonic welding device with continuous packaging scrolling.

In this field, documents EP 333390 and GB-A 952581 are already known, ultrasonic welding devices between an anvil and an ultrasonic frequency oscillating sonotrode, of at least two superimposed sheets made of plastic material which run continuously following a determined path.

The ultrasonic welding devices described in these documents have, as a common feature, a gap between the two superposed sheets to be welded, defined between the surfaces facing the sonotrode and the anvil, which has a section which decreases and then increases. between his entry and his exit.

According to EP 333390, this section configuration of the passage gap, is performed exclusively so that the force applied by the device on the surfaces to be welded is homogeneous over the entire length of the welding gap.

But nothing indicates that the configuration of EP 333390 can significantly reduce the width of the weld lines.

In addition, the device of EP 333390 is not intended to cut the sheets to be welded. On the contrary, it is specified that for the applications of the device described in this document it is sought to avoid any cutting or perforation of the materials to be welded. However, as has been said, it may be desirable to associate a section with the welding of the sheets, particularly in the widespread case where it is desired at the same time to make a cut to form the sheets of the pouch from films moving in continuous, # and welding the edges of the folded sheet, or superimposed sheets, to form the pouch.

Thus, device EP 333390 does not satisfactorily fulfill objectives of the manufacturers as presented above (significant reduction of weld width while allowing a high rate and ensuring very good qualities of mechanical strength and sealing, as well as that possibility to perform a cut simultaneously welding).

And it is the same for the device of GB - A - 952581.

Indeed, regarding the width of the weld line, it is specified that the document device aims on the contrary to keep it relatively large, by increasing the width of the contact zone between the sheets to be welded the device (the width of the line the solder being in the case of the device of - A - 952581 always lower than that of the contact area between the sheets the device).

And this document also does not mention the possibility of cutting in the sheets to be welded.

Finally, there are documents disclosing ultrasonic devices for performing not only welding, but also film cutting. An example of such a device can be found in the document FR 2 665. However, the device described in this document does not make it possible to process continuously moving films, so that the associated rate is limited by the fractionality of the method. In addition, no indication is given in this document on the width of the weld lines.

The object of the invention is to eliminate the disadvantages mentioned above.

In order to achieve this object, the invention proposes, according to a first aspect, an ultrasonic welding device for at least two superimposed sheets, the device comprising a welding assembly formed of two elements which are respectively an anvil and a sonotrode, arranged facing each other so that their facing surfaces form a passage gap of the sheets to be welded, said gap having an inlet section and an output section, the sonotrode vibrating at high frequencies to emit waves ultrasound characterized in that there is provided means for creating between, on the one hand, the superimposed sheets and, on the other hand, said welding assembly, a relative movement in a direction of scrolling determined with respect to all for welding, that the section of said passage gap decreases between its inlet section outlet section, and at least one element of said welding assembly comprises sill edge nte opening into said passage gap and extending in a direction generally parallel to said direction of travel.

Preferred but non-limiting aspects of the device according to the invention are the following: said projecting edge is formed on the anvil.

 # the surface of the anvil facing the sonotrode has a pointed profile formed by inclined planes forming an acute angle between them.

said acute angle is of the order of 140 degrees.

 # The surfaces facing the anvil and the sonotrode are generally flat.

 # the inlet section of said passage gap is greater by a factor of between 1.2 and 2 approximately to the outlet section of said interstice.

 # means are provided for scrolling through the sheets and the welding set is fixed.

 the welding assembly is mounted on a movable carriage so that it can move relative to the sheets in a desired welding direction.

 # there is provided a cylinder or a counterweight in combination with the sonotrode so that it exerts on the sheets to be welded a determined pressure between 0.2.105 and 6.105 a.

 # means are provided for increasing the determined pressure so that the device cuts the sheets in combination with welding.

the speed of travel of the sheets relative to the welding assembly is between 50 and 150 m / min, preferably between 60 and 80 m / min. According to a second aspect, the invention proposes a method of welding flexible packages, characterized in that by means of a device as evoked above, welding of two flexible sheets is carried out to form sidewalls of the 'packaging. Preferred but not limiting aspects of the method according to the invention are as follows: the passage of the sheets in said passage gap causes a creep of the material of the sheets on each side of said edge.

 # said creep creates on each side of said edge a creep bead which constitutes a primary welding line.

 # simultaneously with the welding of the sheets makes a cut of said sheets.

 # during cutting the sheets advance continuously with respect to the welding assembly # prior to welding, heating the sides of the package to soften the internal faces of each sidewall.

 # the sides of the package consist of a flexible sheet comprising a central layer of gas-tight material between two layers of plastic materials.

 # The central layer includes aluminum.

 during the welding, the respective inner layers of the two sheets facing each other merge and the central layers of the two respective sheets come into contact with each other.

 the inner layer of each sheet comprises polypropylene.

According to a third aspect, the invention provides a flexible package comprising two sheet portions facing each other, characterized in that the sheet portions are welded by a method as mentioned above.

Preferred but not limiting aspects of the flexible package according to the invention are the following: it can be obtained by a process according to one of the aspects mentioned above, used to carry out at least one weld along a line welding machine, characterized in that the width of said weld line is of the order of one millimeter, # the central layers of the sides of the package which are in contact with each other constitute a watertight barrier to the air leakage rate associated with the package is the order of 2.4.10 'cm' / day. The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be achieved.

1 is a diagrammatic perspective view of the sonotrode and the anvil ultrasonic welding device according to the invention; FIG. 2 is a diagrammatic view in longitudinal section of detail at the scale of the sonotrode; and the anvil of the ultrasonic welding device according to the invention, - Figures 3 and 4 are schematic side and top views of the ultrasonic welding device according to the invention, according to a first embodiment particularly well. adapted to a closure application of pouches whose side edges have already been assembled, - Figure 5 is a schematic cross-sectional representation of two superposed films received in a device according to the invention to be welded together, and possibly cut, - FIG. 6 is a graph showing the evolution of a mechanical strength characteristic of a pouch produced according to the invention, in FIG. unction of the evolution of parameters of the method according to the invention.

In the figures, there is shown schematically an ultrasonic welding device 100 of at least two superimposed sheets 1,2 made of plastic material, for example polypropylene, which continuously scroll in a determined path F.

In this regard, the device comprises means for scrolling the sheets. Such means may be known and will not be detailed further. It is specified that if the examples which will be described in detail below concern pouches made simply from two sheets 1 and 2, the invention also finds particularly advantageous applications in the production of pouches from multilayer films of the type mentioned. higher (aluminum layer between two plastic layers).

The device 100 comprises a sonotrode 101 which vibrates at high frequencies to emit ultrasonic waves, and an anvil 102.

The sonotrode 101 and the anvil 102 are arranged facing each other so that their facing surfaces 101 ', 102' define a passage gap 103 of the two superimposed sheets to weld 1.2, passage gap having an inlet section 104 and an outlet section In the example shown in FIG. 3 and the sonotrode 101 and the anvil 102 extend in a generally horizontal plane and the superimposed sheets to be welded are intended to run in a generally vertical plane. Of course, it is possible according to a variant not shown, to arrange sonotrode and the anvil vertically with sheets superimposed solder running in a horizontal plane.

height of the inlet section 104 of the passage gap 1 is slightly greater than the sum of the thicknesses of the superimposed sheets to be welded 1, Here, the thickness of the superimposed sheets to be welded is of the order 200 wm and the height of the input section 104 is about 220 #tm. This allows the solder sheets to easily enter the passage gap provided between the sonotrode anvil of the ultrasonic welding device.

According to a first particularly advantageous characteristic of the ultrasonic welding device 100, the facing surfaces 101 ', 102' of the sonotrode and of the anvil 102 converge towards one another so that the section of said passage gap 103 decreases continuously between its inlet section 104 and its outlet section 105 (see Figure 2 in particular).

In a preferred embodiment, the surfaces 101 'and 102' are made of planar surfaces, and the anvil 102 is fixed.

According to the particular example described, the inlet section 104 of the passage gap is approximately a factor of about 1.3 greater than the outlet section 105 of said gap. Thus, the height of the outlet section 105 of said interstice 103 here is around 70pm. This height of 170pm gives a solder thickness made the welding device of the order of 135 .mu.m.

superimposed sheets 1.2 scrolling at a constant speed, the passage gap defined between the sonotrode 101 and the anvil 102 has a length determined according to the determined speed, constant or variable, scroll said sheets for a contact time of the vibration sonotrode and the anvil 102 with said sheets 1, 2 chosen, so as to obtain a sealed sealing of the sheets together over a given welding width.

According to the example shown, the running speed of said sheets is constant and of the order of 62.5 mlmin, which gives a length of the passage gap equal to about 75 millimeters, for a contact time of 72 ms and a width of the weld band of about 1 millimeter.

As shown more particularly in Figure 3, and according to another essential feature of the invention, the surface 102 'of the anvil 102 opposite the sonotrode 101 has a tip-shaped profile formed by inclined faces 102a, 102b forming an acute angle between them. Here, the angle formed between the inclined faces 102a, 102b is of the order of 140 degrees. This angle can in any case be in a range extending from 120 to 160 degrees.

In this way, the sides 102a, 102b of the anvil and the flat surface of the sonotrode facing each other form an angle here of the order of 20 degrees. Thus, using such a welding device, is formed between the sheets to be welded and the welding device (and more particularly the anvil and sonotrode) a contact zone which corresponds essentially to the line of edge l 'anvil.

And contact zone is extremely narrow (of a millimeter smaller width, tip of the profile of the anvil actually having a radius of curvature less than millimeter, for example 0.5 millimeter or preferably 0.25 millimeter).

therefore, the weld line in the two superimposed plastic sheets, which is of a thickness of the order of 135m, has a width of the order of a millimeter, which is a significant improvement over the performance of known devices .

It is important to note that the configuration of the welding device according to the invention, comprising the combination of a converging gap 103, which is in the example described above defined the flat surfaces of the anvil and the sonotrode, # and the tip profile of the surface 102 'of the anvil, so as to form a sharp edge, is particularly advantageous.

Indeed, this configuration makes it possible to receive in the interstice 103 sheets 1, to be welded continuously scrolling with respect to the anvil and sonotrode, to produce next to the edge line of the anvil a very small width weld leaves.

More precisely, and as shown in FIG. 5 (on which, as in FIG. 1, the angles and dimensions are not to scale, this figure simply illustrating the principle of the invention), the combination of the convergence of generally flat surfaces of the sonotrode 101 and the anvil 102, with tip profile of this anvil, not only allows to weld the sheets and 2 which scroll continuously in the direction F relative to the anvil and sonotrode.

Indeed, because of the shape of the anvil, the orientation of the edge of this anvil parallel to the direction of the relative movement between the films to be welded, and the distance between anvil and sonotrode (the amplitude of oscillations of the sonotrode being defined so that the sonotrode can come very close to the anvil at the end stroke of oscillation, and even flush the anvil for application to the cut combined with welding), the material films 1 and 2 is pushed back the sides and undergoes a creep on each side of the contact zone Z which is located in the middle of the passage gap 103.

This creep thus creates on each side of the contact zone a bead B within which the materials that constitute the sheets 1 and 2 are mixed and constitute an amalgam that creates an extremely strong bond.

Thus, the weld line between the films 1 and 2 comprises the two beads B which extend longitudinally on the films, each of these beads constituting in itself a primary weld line.

The Applicant has carried out tensile strength tests of two sheets welded together using this technique; these results are shown in Figure 6.

More precisely, this figure represents in Newtons the right axis of the ordinates the traction N corresponding to the breaking of the mechanical connection between the two welded sheets (curve in thick lines), and on the abscissa axis the reference height of the gap 103 (that is to say the distance between the tip of the anvil and the face 101 'of the sonotrode when said sonotrode is in its reference position around which it oscillates), in microns.

The results of FIG. 6 show that the tensile strength levels are quite satisfactory, of the order of 20 to 35 Newtons, or even more. These results also show that there is a range of values of the reference height of the gap 103 (between 140 and 160 microns in the case described) for which the breaking strain N is high, with a maximum for a height 150 microns.

The ordinate axis on the left indicates in Watts the power consumed by the device for welding (curve in fine lines). This power increases from 200 Watts to 340 Watts when the reference height decreases from 170 to 110 microns.

A creep result described above is that the width of the weld zone, delimited by the two beads B, is as it is said of the order of only one millimeter (each bead having by itself a width substantially less than one millimeter ).

Another result of this configuration, and the associated creep that causes the amalgam described above, is the very good quality of the welding performed at each bead in terms of sealing and mechanical strength, in combination with the very low width of the weld lines that correspond to the beads.

More specifically, the Applicant has carried out airtightness tests on pouches whose sheets, each consisting of three layers including an aluminum core layer, were welded by the method described above.

The results showed that the watertightness of the bags thus obtained was greater than the usual values, the measured air leakage rate being of the order of 2.4 × 10 -4 cubic centimeters of air per bag per day ( for pouch whose four sides were thus welded).

And it will be noted that this process can be carried out on continuously moving films, allowing a yield of the order of 500 pouches / minute or more for welding, and a scroll speed of the sheets with respect to the device of the order of 25 mlminute for cutting applications.

In place of a pointed profile defined by two planes forming a straight edge, the anvil may have any projecting profile which defines a sharp edge, as long as the contact zone between the sheets and the device is very narrow, order of the tenth of a millimeter, and that the following combination is present # convergence of the gap in the direction of scrolling sheets, and # existence of a protruding edge of the anvil.

It is also possible to produce in a converging gap 103 a narrow contact zone along an edge associated not with the anvil 102, but with the sonotrode, the face (s) of the anvil turned towards the sonotrode. can have a flat profile, or whatever. It is also possible that both the anvil and sonotrode have protruding profiles.

However, it is preferable to associate with the anvil, and only with it, the protruding edge profile, because it is known that the face of the films which is turned towards the sonotrode is the one which undergoes the most mechanical stresses due to the vibration of the sonotrode. And to avoid damaging the films that are welded, it is better only the anvil has a protruding profile.

 sonotrode 101 vibrates at a frequency of between and about 40 KHz for welding, at an amplitude of between 10 and 00 microns, preferably equal to about 70 microns.

Adjusting screws 110 are provided for adjusting the position of the sonotrode relative to the anvil in the horizontal plane. There is also a comparator 113 which makes it possible to adjust the gap between the anvil 102 and the sonotrode, in addition, the adjusting screws 105 make it possible to adjust the angle between the sonotrode and the anvil 102.

adjustment system makes it possible to adjust, depending on the thicknesses of sheets to be welded, the relative positions of the sonotrode and the anvil and therefore the height of the inlet and outlet sections of the passage gap of said sheets.

Advantageously, this ultrasonic welding device 100 makes it possible to weld superimposed plastic sheets traveling at a speed of between 50 and 100 mlmin, preferably between 60 and 80 mlmin.

According to another aspect of the invention, the ultrasonic welding device described above with reference to the welding of two films 1 and 2 can advantageously be used to manufacture and / or close packagings comprising two sidewalls bound by their lateral edges. each flank comprising inner and outer faces of plastic material and a central layer of light metal sandwiched between the two inner and outer faces.

According to a welding closure method according to the invention, the packages run on a bench being placed vertically one after the other, this here implies the horizontal position of the sonotrode and the anvil as shown in FIGS. 3 and 4.

With the aid of the welding device 100, it is realized at the upper edges of the flanks of each package running at a fixed speed, constant or variable, ultrasonic welding of the inner faces of the flanks of each package, along a weld line. extending at least over most of the width of each package, and in particular over the width of the pouch.

The packages used here are such that the central layer each of their flanks is made of aluminum, the inner face of each side has a polypropylene layer or a polyamide layer a polypropylene layer, and the outer face of each of their flanks comprises a layer of polyethylene terephthalate optionally coated with an additional layer of polyamide.

The outer layer is intended to serve as a decorative pattern support. The ultrasonic welding device as described with reference to FIGS. 1 4, makes it possible to weld together the internal faces of the flanks of each package through the outer face and the central layer.

Indeed, the polypropylene has a melting temperature lower than the melting temperature of the layer of the outer face and under the action of the oscillations of the sonotrode, there is an excitation of the particles constituting the inner layer which merges to form the beads B.

And this not only causes the creation of a bead resulting from the melting of the inner layers that are in contact with each other, but also the contacting of the aluminum layers of the two sides, which allows obtain the very good sealing properties mentioned above.

As already described above, the weld line of each package has a thickness of the order of about 135 μm and a width of about one millimeter.

Moreover, advantageously, thanks to oscillations of the sonotrode against the sheets to be welded, it is possible to remove particles of food material that can remain at the place where the welding is to be carried out, thereby sealing the said package.

Such a device also makes it possible to close each package scrolling at high speed to the welding station without damaging the outer and central layers of the latter.

According to an advantageous characteristic of the process according to the invention, to accelerate the welding process of the sidewalls of each package, it is possible beforehand to ultrasonically weld each package, to heat each sidewall of each package to soften the internal faces of the sidewalls. each package. This makes it possible to obtain a tight seal of the films with greater flexibility as regards the relative positions of the anvil and the sonotrode.

The heating can be achieved for example by conduction or injection of steam.

In addition, it is possible to adjust the gap between the anvil and the sonotrode and the pressure exerted between the sonotrode and the anvil on the flanks of each package to be welded (via a control of an associated cylinder at the sonotrode), so that when making the weld line in each package, a cutting line is simultaneously produced. This aspect will be detailed later in this text. According to other characteristics of the ultrasonic welding device, as shown more particularly in FIGS. 3 and 4, the sonotrode 101 is mounted on a support 106 in connection with a jack 107 which acts on the sonotrode so that it exercises on the sheets to be welded 101 a determined pressure of between 2.105 and 6.105Pa.

According to the method described, it is also possible to envisage two welding devices as shown in FIGS. 1 to 4 arranged along the packaging run path, at a determined distance and at different heights or at the same height, so that only one is made. weld line or two weld lines juxtaposed flanks of each package (a weld line below the other).

In addition, advantageously, with the aid of the ultrasonic welding device, it is possible to detect the quality of the welding or the presence of undesirable particles in the welding zone of each package, thanks to the detection of the power consumption of the welding device. welding, used as a detection signal.

Such a captured signal can be processed to identify eject the defective packaging, that is to say, not sealed welded.

According to this method, it is possible to close about 500 pouches per minute which represents a considerable gain in the cost of manufacturing pouches. In addition, the method of closing pouches using the device according to the invention makes it possible to seal the flanks of the scrolling pouches. This is confirmed by Table 1 which expresses the results of a biotest carried out on pouches welded according to the method according to the invention using several embodiments of the device according to the invention.

<U> Table <SEP> 1 </ U>
<tb><B><U> SPEED <SEP> OF </ U><SEP> Length <SEP> (mm) <SEP><U> TIME <SEP> FROM <SEP> CONTACT <SEP> RESULTS <SEP> BIOTEST </ U></B>
<tb><U> Pockets </ U><SEP> of <SEP> the <SEP> gap
<tb><B> (mlminute) <SEP> welding <SEP> of the <SEP> device <SEP> Sonotrodelenclume <SEP>% <SEP><B> Sealed <SEP> Pouches </ B>
<tb> according to <SEP> the invention <SEP> From <SEP> device <SEP> according to <SEP> to <SEP> bacteria
<tb> 500 <SEP> poucheslminute <SEP> the invention
<tb><B> 62.5 <SEP> 25 <SEP> 24 <SEP> ms <SEP> 73 </ B>
<tb><B> 62.5 <SEP> 35 <SEP> 34 <SEP> ms <SEP> 92% </ B>
<tb><B> 62.5 <SEP> I <SEP><B> 75 </ B><SEP> I <SEP><B> 72 <SEP> ms </ B><SEP> I <SEP><B> 100 </ B> The application to the closing of pouches described above is of course not limiting, the invention generally relates to the welding of flexible films for other applications than the closure of pouches.

Moreover, the device described above can advantageously be implemented not only for the welding of the sheets of the pouch, but also for simultaneously making a cut of the sheets.

In the case of a combined cut with the weld, the pressure level applied to the sheets will be set at around 6.105Pa, and the reference height of the gap 103 may be reduced, preferably to a value less than 50 microns, for example 20 microns.

In this case, the half amplitude of the vibrations of the sonotrode is adjusted to a very slightly lower value (of the order of one-tenth of a micron) at the height of the reference gap, so that the sonotrode touches the anvil at the end of the race.

This application is advantageous because it makes it possible to form on each side of the section line, which is opposite the edge of the anvil a primary welding line which corresponds to the width of the bead, this width being as it is said significantly less than a millimeter.

Thus, in the case of welding / cutting, the width of the welding lines is substantially less than one millimeter.

And the results of the tests carried out by the Applicant on pouches whose edges were welded and cut according to the invention, so that the flanks of the pouch are sealed only by the primary weld line of a bead, were similar to those performed on welded bags without cutting.

It has been described above (more particularly with reference to FIGS. 3 and 4) an embodiment of the invention in which the top of continuously scrolling pouches is closed by welding, the lateral edges of said pouches having previously been welded together. .

It is also possible to implement the invention films running continuously in the same direction F, with the same speed, to perform a welding and possibly a cut, in any desired direction with respect to the direction of travel F films for example the direction perpendicular to this direction F.

For this, a set consisting of a sonotrode and an anvil taking up the configuration described above (converging surfaces to form the gap 103, edge of the anvil) is placed on a mobile carriage, the whole being able to move so that the films scroll between the oscillating sonotrode and the anvil.

In this case, the assembly comprising the sonotrode and the anvil is oriented so that the inlet and outlet sections delimiting the gap 103 are aligned in direction of the movement of the films to be welded with respect to said assembly. Thus, walls of the gap 103 decrease when a line parallel to this direction is described.

movement of the carriage is in this case controlled to perform alternating # welding sequences (and possibly cutting), during which the carriage leaves a starting position being animated by a movement combining a parallel advance to the direction F with the same the films it will keep during the whole sequence, and a lead according to the desired welding direction. This second component of the movement can be made in a straight line, or not, # repositioning sequences, during which the carriage returns close starting position to start a new welding sequence.

The carriage can thus reciprocate along a line forming an angle between 0 and 90 with the direction F, the speed of the carriage being adjusted during the return sequences to reposition itself at the starting point in time to reattach the films with a desired deviation from the previous weld line traveled.

It is also possible to provide two or more carriages, some performing a welding sequence while others return to desired starting positions.

In the case where the pressure of the sonotode is adjusted to perform cutting simultaneously with the welding, sheets obtained from the cutting of the films are thus obtained according to cutting lines corresponding to the zone of contact between the device and the films, said sheets being welded. between them by their lateral edges due to the creep of the material of the films on each side of each line of cut.

And it is also possible to place a sonotrode on each carriage, and to provide under scrolling films at least one fixed anvil having a peak profile and whose edge is oriented according to the path followed by the carriage during its welding / cutting sequence so that the sonotrode carried by the carriage cooperates with the edge of the anvil. The present invention is not limited to the embodiments described described, but the skilled person can make any variant within his mind.

In particular, it is not obligatory for the sheets to be welded and possibly to be cut continuously; any embodiment in which is established relative movement between the sheets (which will always have to themselves a synchronized movement relative to each other) and welding device (assembly comprising the anvil and the sonotrode) enters into the scope of the present invention.

likewise, the invention is not limited to the application of pouches containing animal feed materials; it obviously covers pouches or bags using bags made from plastic sheets and intended for other applications, including the packaging of food products such as candies or freeze-dried coffee.

Claims (25)

<B> <U> CLAIMS </ U> </ B> 1. Device (100) for ultrasonic welding of at least two superposed sheets 2), the device comprising a welding assembly formed of two elements which are respectively an anvil (102) and a sonotrode (1 arranged opposite one another; on the other side so that their facing surfaces (101, 02 ') form a gap (103) for passage of the sheets to be welded, said gap having an inlet section (104) and an outlet section (105), high frequency vibrating sonotrode for emitting ultrasonic waves, characterized in that means are provided for creating between, on the one hand, superimposed sheets and, on the other hand, said welding assembly, a relative movement in one direction (F) determined relative to the welding assembly, in that the section of said passage gap decreases between the inlet section and its outlet section, and at least one element of said welding assembly has a protruding edge protrudingin said passage gap and extending in a direction generally parallel to said running direction (F). 2. Device according to claim 1, characterized in that said projecting edge is formed on the anvil (102). 3. Device according to claim 1 or 2, characterized in that the anvil surface opposite the sonotrode has a tip profile formed by inclined planes (102a, 102b) forming an acute angle between them. 4. Device according to the preceding claim, characterized in that said acute angle is of the order of 140 degrees. 5. Device according to one of the preceding claims, characterized in that the surfaces facing the anvil and the sonotrode are generally flat. 6. Device according to one of the preceding claims, characterized in that the inlet section of said passage gap is greater by a factor between 1.2 and 2 approximately to the outlet section of said gap. 7. Device according to one of the preceding claims, characterized in that there is provided means for scrolling the sheets and the welding assembly is fixed. 8. Device according to one of claims 1 to 6, characterized in that the welding assembly is mounted on a carriage movable so as to move relative to the sheets in a desired welding direction. 9. Device according to one of the preceding claims, characterized in that there is provided a cylinder or a counterweight in combination with the sonotrode so that it exerts on the sheets to be welded a determined pressure between 0.2.105 and 6.105 Pa . 10. Device according to the preceding claim, characterized in that it is provided means for increasing the determined pressure so that the device performs a cutting of the sheets in association with the welding. 11. Device according to one of the preceding claims, characterized in that the speed of travel of the sheets relative to the welding assembly is between 50 and 150 mlmn, preferably between 60 and 80 mlmn. 12. A method of welding flexible packaging, characterized in that with the aid of a device according to one of the preceding claims, is carried out a welding of two flexible sheets to form sidewalls of the package. 13. Method according to the preceding claim, characterized in that the passage leaves in said passage gap causes creep material leaves on each side of said edge. 14. Method according to the preceding claim, characterized in that said creep creates on each side of said edge a flange B creep constitutes a primary welding line. 15. Method according to one of claims 12 to 14, characterized in that simultaneously with the welding of the sheets is carried out a section of said sheets. 16. The method of claim 15, characterized in that during cutting the sheets advance continuously relative to the welding assembly. 17. Method according to one of claims 12 to 16, characterized in that prior to welding, the flanks of the package are heated to soften the internal faces of each flank. 18. Method according to one of claims 12 to 17, characterized in that the sidewalls of the package consist of a flexible sheet comprising a central layer of gas-tight material between two layers of plastic materials. 19. Method according to the preceding claim, characterized in that the central layer comprises aluminum. 20. A method according to claim 18 or 19, characterized in that during welding the respective inner layers of the two sheets which are opposite each other merge, and the central layers of the two respective sheets come into contact with each other. one with the other. 21. Method according to the preceding claim, characterized in that the inner layer of each sheet comprises polypropylene. Flexible package comprising two sheet portions facing each other characterized in that the sheet portions are welded by a method according to one of claims 12 to 21. 23. Flexible packaging obtainable by a process according to one of claims 12 to 21, implemented to perform at least one weld according to the weld line, characterized in that the width of said weld line is of the order of millimeter. 24. Flexible packaging obtained by a process according to the combination of one of claims 20 or 21 with claim 18, characterized in that the central layers of the sides of the package which are in contact with one another constitute a gas-tight barrier. 25. Flexible packaging according to claim 24, characterized in that the air leakage rate associated with the package is of the order of 2.4.104 cm3ljour.