Bag having an elastic band, and method for the production thereof

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DESCRIPTION

Bag with elastic band and procedure for its manufacture.

The present invention relates to a bag, especially made of plastic material, in particular a bag for storing household rubbish, of the so-called "elastic band" type, which borders the opening of the bag to allow the bag to be retained elastically on a bucket. for garbage, and a method of making such a bag.

In general, in industrialized countries, waste and garbage, especially household garbage, are stored in plastic bags. These bags of plastic material generally have two faces of plastic material joined to one another at their periphery, providing an opening area. These bags are mostly rectangular in shape, although other shapes are possible: for example, the bottom of the bag may have a rounded shape. In the following of the description, for ease of use, it will refer to bags of rectangular shape, although it is understood that bags according to the present invention are not limited to this shape.

The bags can be prepared from two rectangular sheets of plastic material, welding three sides of the rectangle and leaving the fourth side open. They can also be prepared from a single sheet of plastic material that is folded, either to form the bottom of the bag, or to form a side side of the bag, the other two sides being heat-sealed. In a known way, in bags, the faces can be connected to each other by a bellows at the bottom level and / or at the level of one lateral side, preferably both lateral sides.

It is also known to manufacture so-called sliding tie element bags, in which the opening of the bag, whatever it may be, is bordered by a cover in which a tie element is capable of sliding. The tying element can be constituted by a single branch, the two ends of the tying element being fixed to each other. It can also consist of two threads, each thread being fixed at each of its ends to the sheath. The tying element is preferably a tape of plastic material capable of being heat-welded.

The sleeve is generally made by folding the sheet of plastic material parallel to the opening and heat sealing it parallel to the edge of the film. The sleeve can be continuous or formed by two independent parts. This is particularly the case when the bags are formed by heat sealing the lateral sides and in which the cover is formed by folding the sheet of plastic material before carrying out the heat sealing of the lateral sides.

Such bags with a sliding tie element made of a substantially non-elastic plastic material are described in patents EP-953,511 and EP-1,232,954 belonging to the applicant.

It has also been proposed in the state of the art, for example in patent US-5,133,607, in the German utility model DE-201 10 350-U1 and in the international application WO 03/035500, a bag of the type of slip tie, in which the slip tie element is made of elastic or extensible material. This closed-loop elastic tying element is characterized by the fact that the length of its periphery is less than that of the opening of the bag, so that the user must elastically elongate the sliding tying element to fix it around the periphery of a receptacle, for example a garbage can. Thus, this sliding tie element allows the bag to be elastically retained on the rubbish bin, in a wide range of bin sizes, limiting the risk of the bag sliding into the rubbish bin, for example by the effect of the weight of the waste inside the bag.

However, the aforementioned bags with an elastic sliding tie element have a double drawback, due to the presence of relatively deep lateral joints which are arranged at the longitudinal opening edge of the bag. The presence of these relatively wide joints has, on the one hand, the drawback of not allowing the total closure of the bag, when the sliding fastening elements are knotted, after filling the bag. Indeed, during transport or storage of bags filled with waste, waste could escape through these joints. On the other hand, the presence of these relatively wide joints decreases the length of the sleeve in contact with the tying element and therefore makes the bag brittle when it is transported full using the elastic sliding tying element as a grip location.

Furthermore, all these bags with an elastic sliding tie element have as a common drawback the fact that the elastic tie element cannot have a sufficient tensile strength to support a significant weight of waste in the bag during transport. For the rest, even if the tear resistance is sufficient, if the weight of the waste in the bag is important, the sliding tying element, which is generally used as a grip by the user during the transport of the bag, has the risk of elastic elongation, which may cause the bag to drag or lower it low enough to bump into obstacles, which is a significant annoyance for the user.

A bag of the type of sliding tie element made of plastic material is also known from document EP-A1,013,567, and which has an elastic tape whose ends are fixed by a hot-melt glue to one of the outer faces of the bag, on the proximity, but at a distance, to the sheath that encloses the plastic sliding tie element. This elastic band is grippable from the outside by the user, after the edge of the bag has been folded around the neck of the garbage can, and can be elastically elongated by the user so that the tape forms a closed loop that can enclose the periphery of the container, allowing the bag to be elastically held over the garbage can. Although the elastic tape, preferably rubber, can be chosen to have a maximum elongation of 800%, this elastic tape preferably has an elastic elongation of less than 500%. In a first example, the elastic band has a length at rest of the order of one fourth of the length of the periphery of the container. In a first variant, the elastic band is elongated so that it only surrounds three sides of the container, which corresponds to an elastic elongation of the order of 200%, that is to say three times its length. In another variant, the elastic band is elongated so that

ES 2 281 019 T3 forms a closed loop that squeezes the entire periphery of the container, which corresponds to an elastic elongation of the order of 400%, that is to say five times its length at rest. In another example, the elastic band has a length slightly less than the semi-periphery of the container, so that it is necessary to form a closed loop with the elastic band to ensure the elastic retention of the bag on the container, which corresponds to an elastic elongation. at least equal to 200%, that is to say at least three times its length. Advantageously, this elastic strap is only used for the elastic holding of the bag in the container, while the plastic sliding tie element is used for knotting, to close the bag.

Similarly, document EP-A-1,266,837 describes a bag of the type with a sliding fastening element made of plastic material, which also has an elastic strap that is fixed at its ends to the side edges of the bag and is, in a A variant, housed in the same sleeve as the plastic sliding tie element, or arranged on the outer face of said sleeve. As in EP-A-1,013,567, to ensure elastic retention of the bag in the garbage can it is necessary to form a closed loop with the elastic tape, and for this it has been provided that the elastic elongation of the tape it should be more than 200%, for example 250%, and preferably 300% or more.

However, these two documents, EP-A1,013,567 and EP-A-1,266,837, which refer to the same type of bag with a plastic sliding tie element provided with an elastic strap for keeping the bag in a container, resort to elastic tapes that have a high degree of elastic elongation, greater than 200%, which therefore requires the use of particular elastic materials, which can be difficult to weld or to join to the bag, and that they are also difficult to apply in a process of continuous manufacturing of a chain of bags, since the high degree of elasticity of the tape means that there is the risk of disturbing the multiple welding, folding and cutting operations that are involved. necessary to manufacture, for example, a continuous roll of a chain of bags. Indeed, in the course of such a continuous manufacturing process, the plastic sheets that form the faces of the bag, as well as the different elements of bundles and tapes, are driven on multiple rollers or drive wheels in order to ensure a in minimum tension of all these elements. Now, a very elastic tape subjected to such tensioning could experience elastic deformations during the manufacturing process of the bag chain, damaging the quality of the heat seals, even causing the bag to fold, if these heat seals are not made correctly.

It is also for this reason that in EP-A-1,013,567 the elastic tapes are individually and separately glued on each bag of the bag chain, either transversely to the direction of advance of the bag chain, or parallel to that direction.

The object of the invention is therefore to propose a bag of the elastic band type that makes it possible to elastically fix the periphery of the bag in a receptacle and that makes it possible to avoid the aforementioned drawbacks. Another object of the invention is to avoid the risks of the waste falling out of the bag, after the bag has been closed. The invention also aims to limit the risk of breakage or tearing of the elastic band or the risks of deformation of the elastic band during the transport of the bag mostly filled with waste.

For this, the invention has as its object a bag made up of two faces joined together along their entire periphery, with the exception of a longitudinal edge, the bag having an opening that leads to said longitudinal edge, the two faces being welded to each other. along two opposite side edges, at least one face being provided, in the vicinity of said opening, with at least one elastic band joined to said face by two joining zones, so that the useful length at rest of said elastic band between the two joining zones corresponds to the separation between the two joining zones in the bag and is less than the length of the longitudinal edge of said face of the bag, a such bag in EP-A-1,013,567. The bag according to the invention is characterized in that the elastic band extends over the entire length of the bag, from one longitudinal edge to the other, said elastic band being welded to the two faces of the bag along said edges lateral, with at least one of the two aforementioned joining zones forming a so-called intermediate joining zone located at a distance from the two aforementioned lateral edges. In the sense of the invention, the useful length of the elastic band at rest can vary slightly depending on the elasticity of the band and its small deformation during its welding to the bag. This elastic band, which is not housed in a sheath, can thus be manufactured continuously in a process for manufacturing a chain of bags, having a reduced useful length, which corresponds to the narrowing of the extensible and compressible part of the outside of said elastic band due to the presence of the intermediate joining zone between the two side edges of the bag.

On the contrary, in EP-A-1,013,567 the elastic band has a length at rest clearly less than the width of the bag. Even if a passage, purely general and without any application example, indicates that this band can extend over the entire width of the bag, it is not provided in any way that can be welded to the side edges of the bag. This band is in practice fixed by a thermoadhesive glue that cannot, therefore, be located at the level of the welds on the side edges of the bag without impairing the good adhesion of the bands to the bag. Each band is glued, individually and discontinuously, as can be seen in Figures 7 and 17, which alienates the person skilled in the art from the present invention that is adapted to the welding of a continuous elastic band along the length of a chain of bags.

Advantageously, each face of the bag has a sheath that borders said opening and in which is arranged a non-elastic sliding tie element that is grippable from the outside by at least one joint arranged through said sheaths, so that this element The non-elastic sliding tie essentially serves as the knotting for the closure of the bag, while the elastic band serves mainly for the elastic retention of the bag in a container.

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In this case it can be envisaged that each face of the bag is folded inwards, along the longitudinal edge of the bag, so that a part of the fold forms the aforementioned cover and extends beyond a skirt, being said elastic band attached to the corresponding face of the bag overlapping at least partially on said skirt. Thus, the intermediate joining zone can be made at least partially in a double thickness of plastic sheets made up of one face of the bag and the aforementioned skirt. Preferably, this intermediate connecting zone does not extend into the part of the fold that forms the sheath, in order to allow the non-elastic binding element to slide freely in the sheath. The fact of welding the elastic band at the level of its intermediate joint area in a double thickness of sheets makes it possible to reinforce this intermediate weld, which is subject to strong tensile stresses.

As a variant, each face of the bag associated with the elastic band is folded inwards along the longitudinal edge of the bag, so that the elastic band is attached to said face, overlapping, at least partially, said fold. Thus, even when the bag does not have a sliding fastening element in a cover, it is advantageous to provide an internal fold to ensure a double thickness of plastic sheets at the level of the intermediate connection zone of the elastic band in the bag.

According to another characteristic, the other of the aforementioned joint zones forms another intermediate joint zone located at a distance from the two aforementioned side edges and from the first intermediate joint zone.

As a variant, the other of the aforementioned joining zones is constituted by the welding zone of the elastic band with the lateral edge of the bag farthest from the aforementioned intermediate joining zone. In this case, the two faces of the bag form a double thickness of sheets for the attachment of the elastic band at the level of the lateral edge.

Preferably, each elastic band is attached to an inside face of the bag. However, as a variant, each elastic band can be attached to an outer face of the bag.

In another particular embodiment, each elastic band is longitudinally cut into two vertically contiguous branches, the respective joining zones of which are in the vertical extension of each other, so that the two branches form a closed loop with the bag, of which each Branch is intended to squeeze an opposite side of a container. In this case, one of the branches will remain along the face of the bag that carries it, while the other branch will be elastically housed to tighten the opposite side of the container. The intermediate connecting zone of the elastically supported branch, which is subject to the strongest stresses, is thus locally reinforced by the intermediate connecting zone of the adjacent branch.

According to another characteristic of the invention, the elastic band has a degree of elongation of less than 150% and preferably of the order of 100%. For example, this elastic band is made from Ethylene Vinyl Acetate (EVA).

The present invention also has as its object a process for the continuous manufacturing of a chain of bags, said process comprising the steps consisting of:

a) arranging inside a folded sheet at least one elastic tape, along one of the longitudinal edges of the sheet;

b) performing, at regular intervals corresponding to the width of a bag, at least one transverse heat sealing limited in the height of the elastic tape only, to form an intermediate joining zone of the elastic tape on the corresponding inner face of the sheet;

c) making, at regular intervals corresponding to the width of a bag, a plurality of pairs of adjacent transverse heat-welds corresponding to the side edges of the bags, so that the aforementioned elastic tape is heat-welded with the side edges of the bags, said pairs of transverse heat-welds being made at a distance from the aforementioned limited transverse heat-welds;

d) pre-trimming, at regular intervals, the sheet between the transverse seals of each pair to form a chain of pre-trimmed bags. This manufacturing method has the advantage of allowing the continuous manufacture of a chain of elastic band bags whose useful length at rest is less than the width of one face of the bag, without the risk of folding the body of the bag.

Advantageously, the procedure comprises the supplementary stage consisting of:

e) before step a) or b), bending each longitudinal edge of the sheet inwards to form an internal fold, the aforementioned elastic tape being arranged in a fold, with at least partial overlap, so that the elastic tape is welded in step b) at least a double thickness of material at the level of its intermediate joining zone.

According to another characteristic of the invention, the process comprises the additional steps consisting before step a) of:

f) cutting film parts in the vicinity of the two longitudinal edges of the folded sheet at regular intervals corresponding to at least the width of a bag, for example one or two bag widths;

g) arranging inside said folded sheet two ribbons of non-elastic material, to the right of said cut-out parts on each face of the sheet, so that each non-elastic ribbon is housed inside a fold;

h) heat sealing the folds parallel to the longitudinal direction to form a sheath in which each non-elastic tape is housed, the elastic tape overlapping at least partially the remaining part that forms the skirt of the fold.

The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly during the following description of various particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings in which that:

FIG. 1 is a perspective elevation view of a first embodiment of a bag according to the invention, with an elastic band and with a non-elastic sliding tie element;

figure 2 is a sectional view according to line II-II of figure 1, in the open position of the bag;

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FIG. 3 is a partially broken away and perspective view of a second embodiment of the bag according to the invention mounted on the neck of a container, before the elastic band is tensioned;

FIG. 4 is a view similar to that of FIG. 3, but showing the elastic band during elongation;

FIG. 5 is a view analogous to that of FIG. 4, but showing the elastic band in the final elastic holding position on the opposite edge of the container;

FIG. 6 is an elevation view of a third embodiment of the bag according to the invention, which has an outer elastic band;

FIG. 7 is a view similar to that of FIG. 6, but showing a fourth embodiment of the bag according to the invention, in which the elastic band is cut into two branches;

figure 8 is a schematic view showing the bag of figure 1 in a closed position of the bag, with the plastic sliding tying element arranged to be knotted;

FIG. 9 is a partially broken away perspective view of a stage in the method of manufacturing a chain of bags according to the first embodiment of the invention; Y

FIG. 10 is a view similar to that of FIG. 1, but showing a fifth embodiment of the bag according to the invention, without a plastic sliding tie element.

In the first embodiment illustrated in Figures 1 and 2, it can be seen that the bag 1 according to the invention is made up of two substantially parallel rectangular faces 1a, 1b, being made up of the same sheet of plastic material that is folded to form the bottom 1c of the bag, this bottom being rounded when the bag is in the transport position, as represented in figure 2. In the storage position, the faces 1a and 1b are brought against each other and are joined at the level of the bottom 1c by means of a flat fold, as shown in figure 1. At their lateral edges 2 and 3, the faces 1a and 1b are joined together by the corresponding welds 2a and 3a. These welds 2a and 3a extend substantially over the entire height of the bag 1 and form a vertical line, but these welds could not be linear but extend over the entire area of ​​the lateral margin of the bag.

On the side opposite the bottom 1c, the periphery of the bag has an opening zone 1d defined along the longitudinal edge of each face 1a and 1b, the longitudinal edge of each face 1a and 1b extending at the level of the zone of opening 1d, by an inner fold 4, the end of which is welded to the corresponding face of the bag by means of a longitudinal weld 4a. This fold 4 extends beyond the longitudinal seal 4a in a skirt 4b, which can be free or be welded to the corresponding face of the bag.

The longitudinal seal 4a is preferably continuous over the entire width of the bag. It may also be non-continuous, dashed, or dotted.

In the embodiment shown in Figures 1 and 2 it can be seen that the inner fold 4 forms a cover 8 in which a non-elastic sliding tie element 6 is arranged. On the skirt 4b of the face 1a of the bag there is arranged a band of elastic material 16 which is attached to the lateral edges 2 and 3 by transverse weld lines 2a and 3a. As best seen in Figure 2, the elastic band 16 completely overlaps the skirt 4b without, however, interfering with the cover 8, so that the non-elastic sliding tie element, for example made of plastic, can freely slide between its ends, which are also welded with the 2nd and 3rd transverse welds. The lower edge of the elastic band 16 may exceed or exactly correspond to the lower edge of the skirt 4b. The elastic band 16 has a so-called intermediate junction zone 17 with the face 1a of the bag, which is formed by a vertical welding or gluing line or other, this line 17 being limited to the height of the band 16. Advantageously, the elastic band 16 overlaps the longitudinal weld 4a, without, however, interfering with the sliding tying element 6, so that the tensile forces exerted at the level of the line 17 are taken up again by weld 4a, thus reinforcing the resistance of line 17 to tearing. Of course, as a variant, each side of the bag could have an elastic band.

Figures 1 and 2 show a joint 12, substantially in the middle part of each cover 8, along the longitudinal edge of the opening of the bag, the joint 12 passing through the faces 1a and 1b of the bag in each side of it. This connection is represented here with a substantially semicircular shape, but it could have any shape, for example oval or square, or another, and it is not necessary for the sliding tie element 6 to be visible throughout its height through the connection 12. This connection 12 can be provided laterally, in a substantially analogous way to the connection 112 that will be described later with reference to the embodiments of Figures 6 and⁷.

The main function of the elastic band 16 is to allow the periphery of the bag to be adjusted elastically over the edge of a receptacle, while the non-elastic tying element 6 will be used mainly to carry the bag once filled with waste and / or to tie the tie elements 6 for closing the bag (see figure 8). Taking into account the arrangement of the tie 6 and of the band 16, it is understood that the closure of the bag will be completely closed, avoiding or limiting the risk of waste falling out of the bag during transport or storage. During the transport of the filled bag, it is the other plastic material tie element 6 that is used to prevent deformation of the elastic band.

In figure 2, the inside of the bag, in the open position, has been indicated by the reference figure I.

The elastic band 16 is arranged over the entire width of the bag, from one side edge 2 to the other 3, in a taut but not elastically elongated state when the bag is flat, to avoid any folding of the bag. The limited weld line 17 is made in the vicinity of a lateral edge 3 of the bag, so that the externally compressible and elastically deformable part of the band 16 is that between the line 17 and the opposite side edge 2 which is farthest away. . Thus, the distance L2 between the two welds 2a and 17 in the elastic band 16 is substantially less than the length L1 between the welds of the two side edges 2 and 3 of the bag, which allows

ES 2 281 019 T3 to produce an elastic band having a useful length at rest less than that of the opening of the bag. By way of non-limiting example, it can be envisaged for a bag having a capacity of 30 liters and a length l1 equal to approximately 50 cm (semi-perimeter) that the joining zone 17 is arranged so as to obtain a separation L2 of the order of 34 cm. Thus, to maintain the bag in a rubbish bin that has a perimeter of the order of 1 meter, it is necessary to lengthen the elastic band from 34 cm to 66 cm by turning the band on the opposite side of the rubbish bin. to that where the band is initially arranged, which corresponds to a degree of elastic elongation of the order of 94%. In practice it is desirable that the material be chosen with a slightly higher degree of elastic elongation to facilitate the placement of the band on the opposite side of the container. Generally, the necessary degree of elastic elongation is still less than 150% and is preferably of the order of 100%. Thus, the length L2 can advantageously be chosen on the order of 2/3 of L1.

Advantageously, the tying element 6 and the band 16 are of a different color from the color of the sheet that forms the faces 1a and 1b, and the tying element and the band can be distinguished by having different colors.

By way of example, the band 16 of elastic material, for example of ethylene vinyl acetate (EVA) is chosen so as to allow a degree of elastic elongation of less than 150%. The other non-elastic tie 6 is, for example, made of plastic material, for example high-density polyethylene.

In figure 2 the elastic band 16 is represented in a slightly loosened state inside the bag in open position I, that is to say in a position in which the elastic band 16 is no longer necessarily in contact, especially in its part. middle, with the inside wall facing the bag. Thus, the user can easily grip the elastic band 16 from the outside by inserting his hand through the opening 1d.

In the embodiments illustrated in Figures 3 and below, the same reference figures will designate identical or analogous elements.

In the second embodiment illustrated in Figures 3 to 5, the bag differs from that illustrated in Figures 1 and 2 essentially by the fact that the elastic band 16 is connected to the skirt 4b by two intermediate connection zones 17 and 17 'which are symmetrical to each other with respect to a plane passing through the mid-junctions 12. Of course, the two intermediate junction zones 17 and 17 'could be arranged at different distances from the respective lateral edges 3a and 2a, without going outside the scope of the invention. The separation L2 is therefore defined here between the zones 17 and 17 '. By way of example, for a 30-liter bag having a length L1 equal to 500 mm, zones 17 and 17 'can be provided so as to obtain a separation L2 equal to 34 cm, each zone being 17, 17', separated from its corresponding lateral edge 3 and 2 of approximately 8 cm respectively. In a second embodiment, the elastic band 16 is fully arranged on the skirt 4b, while in the first embodiment, the elastic band protrudes from one side of the skirt to the other.

When the bag is placed in a container R, of rectangular, square, circular or other section, the lip of the bag at the level of its opening is turned over the peripheral edge of the container, as can be seen in figure 3, which It advantageously makes the elastic band 16 appear that from now on is oriented towards the outside of the outer wall of the container. When the elastic band is arranged on the outer wall of the bag, as described below with reference to Figures 6 and 7, the elastic band is then hidden between the outer wall of the container and the turned edge of the bag, but the The user can easily grasp the elastic band by sliding their hand between the turned edge of the bag and the outer wall of the container to pull it down and back on the other side of the container.

In figure 4 the elastic band is represented during its stretching by the user, before it is not turned back from the side opposite the container, as shown in figure 5.

In figure 3 the elastic band is at rest while in figure 5 the elastic band is in its elastically elongated state, which creates a sufficient elastic force to maintain the bag in the container R. It is not necessary that this elastic band is elongated to form a closed loop that allows squeezing the entire periphery of the container.

In the third embodiment illustrated in FIG. 6, the bag 101 is essentially distinguished from the previously mentioned bag 1 by the fact that the middle connection 12 is optional, with at least one lateral connection 112 being provided to provide access from the outside. to the non-elastic sliding tie 106. This non-elastic sliding tie element 106 is welded to one end with the side edge 2 of the bag, along the welding line 2a, while the opposite ends of the non-elastic tie element 106 are welded together along of a weld 107 which is made through the joint 112, so that this end of the non-elastic tie element 106 is not joined to the side edge 3 of the bag. This variant of the non-elastic sliding tie element is known per se.

Of course, the bag 101 could have two lateral joints for gripping the plastic tie 106, without going outside the scope of the present invention. Each side joint 112 can have any shape, especially quarter-circle, quarter-ellipse, or rectangular.

The bag 101 also differs in that the elastic band 116 is fixed to the outer wall of the face 1a of the bag, its upper edge being located slightly above the previously mentioned line 4a, while its lower edge is located above lower edge of skirt 4b. Thus, the elastic band 116 partially overlaps the skirt 4b and the part of the fold 4 that forms the sheath for the sliding tying element 106, without the tying element 106 and the band 116 being able to be superimposed.

The use of bag 101 is substantially analogous to that of bag 1, as described with reference to Figures 3 to 5.

In the fourth embodiment illustrated in FIG. 7, the elastic band is cut or split longitudinally into two different branches 116a and 116b, vertically contiguous and arranged, for example, on the outer wall of face 1a of the bag. During the placement of the bag in a container, the branch 116a can remain, by way of example, on the face 1a of the bag, without elongation, while the other ra6

ES 2 281 019 T3 mal 116b is elongated to tighten the other side of the container, analogously to the band 16 mentioned above. In this position, the two branches 116a and 116b can be considered to form a substantially closed loop around the container with the bag 101. Furthermore, the intermediate joint zone 117b which is subjected to strong stress is locally reinforced by the presence of the intermediate weld 117a of the other branch 116a.

In Figures 6 and 7, the supplementary middle connection 12 is represented in broken line, thus giving access to the non-elastic tying element 106. However, such a middle connection 12 is not necessary since the user can already access the tying element non-elastic 106 by side joint 112.

Reference will now be made more particularly to FIG. 9 which represents a step in a process for the continuous production of a chain of bags from which the aforementioned bag 1 can exit.

As described in more detail in patent EP 1,232,954, to begin with, a continuous tube of plastic material sheet, for example polyethylene, is passed through a machine, not shown, which is to be cut longitudinally in its center to obtain two independent half tubes.

Then, in each half tube, circular or elliptical parts are cut at regular intervals corresponding to once the width of a bag (or twice the width of a bag if a single lateral joint per bag is provided), with the in order to form semi-circular or semi-elliptical joints 12 after bending the longitudinal edge of the sheet 20 of the half-tube inwards, as shown in FIG. 9.

Of course, the shape of the cutout can be any, for example square, rectangular or other.

A plastic tape 6 is then introduced inside each fold 4, before closing it by means of longitudinal heat sealing to form the cover. Then, an elastic tape 16 is inserted into the wrapper along the free edge of the fold 4 overlapping it at least partially.

Of course, the operations could be completely reversed by first arranging the elastic tape 16 and then heat sealing the fold 4 to form the sheath.

The procedure is the same in both cases; the inside edge of the fold is heat-welded (following a line 4a) on each face of the sheet 20 to form the sleeves, in the forward direction F.

Then, at regular intervals corresponding to the width of a bag, heat-sealing 2a and 3a are made substantially at a half distance between the semi-circular or semi-elliptical cutouts. Each pair of heat seals 2a or 3a is such that the individual bags can immediately be separated by transverse trimming or by pre-trimming between the seals of each pair.

The machine also performs transverse heat-sealing 17 limited to the part corresponding to the elastic band 16 to form the aforementioned intermediate joint zones that limit the useful length of the elastic band at rest.

Of course, the order of the stages of making the thermowelders 4a, 2a and 3a, and 17 can be modified, without departing from the scope of the invention.

A fifth embodiment will now be described with reference to Figure 10 in which a bag 201 has been represented, which essentially differs from the preceding bags by the fact that it does not have a non-elastic sliding tie element, having the bag 201 simply an elastic band 216 along one face 1b of the bag, on the inside as shown, or on the outside. Preferably, this bag 201 also has an inner fold 4, the lower inner edge of which 4a is not necessarily welded to the rest of the bag, outside of the side edges 2 and 3. Thus, the elastic band 216 is arranged to the right of this fold interior 4, so that the limited transverse weld 217, located between the lateral welds 2a and 3a, is reinforced by the double thickness of material at the level of the bend

4.

Of course, the other variants of embodiment of the elastic band illustrated with reference to Figures 1 to 9, are applicable to the bag 201 devoid of a plastic sliding tie element. In particular, the elastic band 216 could be cut into two branches as in Figure 7, or provided on the outside as in Figure 6, or have two intermediate joining areas as in Figures 3 to 5. Similarly, the overlap of the fold and the elastic band can be total or partial, as illustrated in the other figures.

Although the invention has been described in relation to several particular embodiments, it is evident that it is in no way limited to them and that it encompasses all the equivalent techniques of the described means, as well as their combinations if they fall within the scope of the invention. .