Package with strip closure system, method for making same

Abstract

The subject of the invention is a package comprising at least two sheets (2, 3) and two flexible films (10a, 10b) placed between them and welded to the sheets (2, 3) by the welds (11a, 11b) respectively, and welded together and to the sheets (2, 3) by the welds (12a, 12b), at least one of the two films being folded over the other at that end of the films on the opposite side to the welds (11a, 11b).

Description

[0001] The subject of the invention is a novel flat closure system, suitable for packages of the bag type, especially those made of plastic. These packages or bags may be “Doypack” or so-called “three weld” bags.

[0002] Many plastic packages or bags, provided with a valve or otherwise, are already known.

[0003] GB-A-826 784 discloses a bag obtained by successively folding a plastic film. This film is folded firstly along a straight line having a central orifice, two V-shaped weld regions are applied, and then the film is folded over on itself. The three free sides are welded, together with part of the fourth side having the bellows with the V-welds. The presence of the opening at the bottom of the bellows, and the presence of the two V-shaped welds and the partial weld on the side of the opening, allow the valve formed by the central orifice to operate properly.

[0004] FR-A-2 711 115 discloses an inflatable bag provided with a valve. This bag is obtained by forming two parallel welds in a film folded over on itself, which is then again folded over on itself, in a manner similar to that of GB-A-826 781. However, in this case the film doubly folded over on itself is welded so as to leave the folded-over edges of the film accessible from the outside.

[0005] WO-A-95/23742 discloses a complex system obtained by successive folding with intermediate weld steps. According to a first variant, the bag obtained is double-walled. According to one embodiment, based on this first variant, it is possible to produce a flexible pocket with a single wall. In this case, the valve system consists of an attached film, which is pierced by application of a straw. This film may be made of aluminium or of polymer. According to that document, an orifice is firstly provided by welding along two parallel lines (between which the straw will be placed). This part is then folded over on the sheet which is welded along its ends. Another sheet is then added, to form the container. The straw pierces the membrane, but when the straw is removed the two walls are pressed against each other by the pressure of the fluid.

[0006] Document JP-A-09-254999 discloses a bag made of synthetic resin. The bag consists of two films hermetically joined together laterally. A strip is placed parallel to a jaw between the two films. The strip is provided partly with a non-adhesive part. This non-adhesive part serves as a flow opening.

[0007] FR-A-1 436 217 discloses a method for manufacturing a bag for packaging drinks. According to that process, a container formed from a sheet of synthetic thermoplastic is emptied by means of a straw. The container is manufactured starting from a tube having lateral folds, the said tube being drawn from a synthetic thermoplastic sheet. The straw is introduced into the container between the lateral folds pressed against one another.

[0008] However, the above systems have several drawbacks. They are complicated and require a complicated folding device. They do not allow the incorporation of stoppers, which are often associated with this type of product.

[0009] The invention makes it possible to remedy the drawbacks of the systems of the prior art. Thus, the invention provides a package comprising at least two sheets and two flexible films placed between them and welded to the sheets by the welds respectively, and welded together and to the sheets by the welds, at least one of the two films being folded over the other at that end of the films on the opposite side to the welds.

[0010] According to one embodiment, the two films are folded over on themselves at that end of the films on the opposite side to the welds.

[0011] According to another embodiment, the package comprises at least two sheets and two flexible films placed between them and welded to the sheets by the welds respectively, and welded together by the welds and to the sheets by the welds, the welds being between the welds, at least one of the two films being folded over the other at that end of the films on the opposite side to the welds.

[0012] According to one embodiment, the two films are folded over on themselves at that end of the films on the opposite side to the welds.

[0013] According to yet another embodiment, the package comprises at least two sheets, a flexible film placed between them and folded over on itself and welded to the sheets by the welds respectively and welded to itself and to the sheets by the welds.

[0014] According to one embodiment, the fold formed by the film(s) can be unfolded by inserting a straw between the films.

[0015] According to yet another embodiment, the fold formed by the film(s) cannot be unfolded by inserting a straw.

[0016] According to another embodiment, the package has an additional weld between the sheets.

[0017] According to yet another embodiment, the flexible film is made of PE, EVA, PP, OPP, PET or PA.

[0018] Provision may also be made for the sheets to be semi-rigid.

[0019] According to one embodiment, the sheets and the flexible film have the following characteristics, where H is the thickness in mm and E is the equivalent modulus of the film in N.mm−2:

sheet: H3E = 0.1 to 50 N · mm;
film:  H3E = 0.5 × 10−3 to 5 N · mm;
with preferably:
sheet: H3E = 0.5 to 25 N · mm;
film:  H3E = 0.05 to 1 N · mm;
with, in both cases, the relationship:
film H3E < sheet H3E.

[0020] According to another embodiment, the package is in the form of a Doypack or three-weld bag.

[0021] The invention also relates to a method for manufacturing a package according to the teaching of the invention, comprising the following steps:

[0022] insertion of a screen-film between the films;

[0023] welding of the films to the sheets along the welds respectively;

[0024] extraction of the screen-film;

[0025] optionally, welding of the films together along the welds; and

[0026] welding of the films and the sheets together along the welds.

[0027] According to one embodiment, the manufacturing method comprises the following steps:

[0028] insertion of a screen-film in the fold formed by the film;

[0029] welding of the film to the sheets along the welds respectively;

[0030] extraction of the screen-film; and

[0031] welding of the film and the sheets together along the welds.

[0032] According to yet another embodiment of the process, the screen-film is made of PTFE or of Teflon®-coated fabric.

[0033] The invention will now be described in greater detail in the description which follows and with reference to the drawings, in which:

[0034] FIG. 1 shows a first package;

[0035] FIGS. 2 a and 2b show the operation of this first package;

[0036] FIG. 3 shows a method for manufacturing this first package;

[0037] FIGS. 4 a and 4b show the filling of this first package;

[0038] FIGS. 5 a and 5b show two embodiments of a second package;

[0039] FIG. 6 shows this second package;

[0040] FIG. 6 a shows an alternative embodiment of this second package;

[0041] FIGS. 7 a and 7b show the operation of this second package;

[0042] FIGS. 8 a and 8b show a method for manufacturing this second package;

[0043] FIGS. 9 a and 9b show the filling of this second package;

[0044] FIGS. 10 and 11 show a third package;

[0045] FIG. 12 shows a stopper designed to be used with this third package;

[0046] FIGS. 13 a and 13b show a method for manufacturing this third package;

[0047] FIGS. 14 a and 14b show the filling of this third package; and

[0048] FIG. 15 shows an alternative embodiment of the first and second packages.

[0049] Referring to the exploded view in FIG. 1, a bag 1 comprises two sheets 2, 3 facing each other. These sheets are made of a material conventional in the art, especially a plastic such as PET, OPP, PA, etc. These two sheets are in particular semi-rigid in the sense that they can be deformed in order to accept the expansion of the bag, while still holding the bag together. The thickness of these two sheets is conventional in the art, for example a thickness of between 50 and 1000 μm and preferably between 60 and 250 μm. Placed between these sheets 2 and 3 is a flexible film 4. This flexible film is made of a suitable material, especially a plastic. This film 4 may especially be made of PE, or else of EVA, PP, OPP, PET, PA, etc. This film has a thickness of between 10 and 500 μm, and preferably between 30 and 100 μm.

[0050] In general, these sheets 2 and 3 and this flexible film 4 have moduli and thicknesses such that, with H the thickness in mm and E the equivalent modulus of the film in N.mm−2:

semi-rigid sheet: H3E = 0.1 to 50 N · mm;
flexible film:    H3E = 0.5 × 10−3 to 5 N · mm;
ith preferably:
semi-rigid sheet: H3E = 0.5 to 25 N · mm;
flexible film:    H3E = 0.05 to 1 N · mm;
with, in both cases, the relationship:
flexible film H3E < semi-rigid sheet H3E.

[0051] This film 4 is welded, over part of its length, to one end of the sheet 3 along the weld 5 (which is shown here by cross hatching). This film is also welded, over part of its width, to the sheet 2 along two welds 6a and 6b which define the width of the valve. These valves may or may not be parallel or may or may not be perpendicular to the weld 5. These welds 5 and 6a and 6b are made so that the weld 5 lies approximately between the welds 6a and 6b, thereby contributing to the sealing. Preferably, the weld 5 lies completely between the welds 6a and 6b. The welds 6a and 6b extend approximately over the width of the strip of film 4, or even extend beyond this width. This very simple system affords the same advantages as the prior art, in particular WO-A-95/23742, but without the drawbacks of the many successive folds and welds.

[0052] As an example, the film is in the form of a strip having a width of between 5 and 200 mm, and preferably between 10 and 50 mm. The length of the strip (in fact this time the width of the bag) is between 20 and 1500 mm, preferably between 50 and 400 mm.

[0053] FIGS. 2 a and 2b show the operation of the valve thus formed. In FIG. 2a, the valve is in the open position (for example after insertion of a straw). The film 4 is then in contact with the sheet 3. When the system is relaxed, the internal pressures (for example owing to only the weight of the contents) press the film 4 against the sheet 2 to which it is welded along the welds 6a and 6b. Thus, a seal is obtained.

[0054] FIG. 2 b illustrates this case, a cut along the weld 6b being made so as to more clearly indicate the phenomenon. The arrows indicate the thrust exerted, for example, by a fluid in the bag.

[0055] FIG. 3 shows, in cross section, and illustrates a way of manufacturing the bag in FIG. 1. The manufacture makes use of a screen-film which allows the flexible film 4 to be selectively welded either to the sheet 2 or to the sheet 3. In a first step, the film 4 in the form of a strip is welded to the sheet 3 along a weld 5. Next, a film 7 forming a screen between the strip of film 4 and the sheet 3 is inserted. The sheet 2 is then placed against the above structure and the combination is placed between two jaws of a welding machine or welding bars. One of them, the jaw 8a, is for example at room temperature while the jaw 8b is at a temperature high enough to weld the film 4 to the sheet 2 along the welds 6a and 6b. It is also possible to have a heated bar on a silicone counterpart. It is also possible for both jaws to be at the welding temperature, depending on the film and the rate. As an example, the welding temperature may be between 130 and 250° C., depending on the material to be welded. Once the weld has been made, the screen-film 7 is removed. Thus, the closure system shown in FIG. 1 is obtained. This film 7 forming a screen is made of a substantially heat-insensitive material that does not adhere to the film at the welding temperature. It may for example be made of PTFE or of another material, such as Teflon®-coated fabric. The method could also be in the reverse sequence, with formation of the welds 6a and 6b, insertion of a sheet 7 between these welds and then formation of the weld 5.

[0056] The closure system shown in FIG. 1 (termed type I hereafter) may be fitted for little cost onto existing bags. These are conventional bags such as a “Doypack” bag, a three-weld bag, etc. Reference may be made, for example, to Application FR 9 811 622, to U.S. Pat. No. 3,380,646 and to the Certificate of Addition to Patent FR-A-1 327 875. The closure system may be placed in the centre or on one side of the bag, according to convenience. In most cases, a straw or other similar instrument will be provided with the bag. This straw, inserted between the sheets 2 and 3, is guided up to the system described, separates the sheets 2 and 3 at the weld 5 and is naturally positioned between the welds 6a and 6b. When the straw is removed, the walls formed on one side by the film 4 and on the other side by the sheet 2 are pressed against each other. A seal is thus obtained.

[0057] This system may also include, as film 4 (or possibly as sheet 2), a repositionable film. Such films are known and comprise a support film 4a, a layer of adhesive 4b and a welding layer 4c. The welding layer is welded along a seam to the sheet 2 which is facing it (or to a welding layer placed against the said sheet 2). Upon tearing, the strip corresponding to the welded part is fastened to the sheet 2, thereby exposing the adhesive. After the straw has been removed, pressure may then be applied in order to completely reseal the system.

[0058] Such repositionable films are described for example in WO-A-97/19867. It is also possible to use, not a repositionable film, but a peelable film. Such films are known and, unlike the above films, do not include a layer of permanent adhesive but an interlayer 4d. These films ensure, as above, the integrity of the bag before being pierced by a straw, but they are not repositionable. In both these cases, the strip of film 4 may be welded to the sheet 2 along an additional weld 6c, lying between the welds 6a and 6b, at the lower end of the welds 6a and 6b (the weld 5 being at the upper end). This weld 6c may be made at the same time as the welds 6a and 6b, or subsequently, depending on the conventional techniques indicated in the abovementioned documents of the prior art.

[0059] The bag provided with the type I closure system is filled conventionally, as illustrated in FIGS. 4a and 4b (the closure system being on one side of the bag). The weld 5 extends, as shown, over the entire length of the sheet 3 (but weld 5 could be only over that part between the welds 6a and 6b). In so far as the film 4 is welded to the sheet 2 only at the welds 6a and 6b, there is therefore a space between this film 4 and the sheet 2 in the region lying between the weld 6a and the rest of the bag. There is therefore a filling region, shown by the arrow. Once the bag has been filled, the weld 9 is formed, this weld extending from the weld 6a to the end of the bag, as shown in FIG. 4b. The sheets 2 and 3 and the film 4 are welded together by this weld.

[0060] FIGS. 5 a and 5b show, in cross section, a second package. In this package, the film 4 is replaced with two films 10a and 10b. Each film 10a and 10b is welded to the sheets 2 and 3, respectively along welds 11a and 11b (which are equivalent to the weld 5 in the type I package). In FIG. 5a, the film 10a is not folded, whereas it is folded in FIG. 5b. These two new types are termed type Ia and type IIb, respectively.

[0061] FIG. 6 shows a view of these second packages in the closed state. The presence of two vertical welds 12a and 12b, which weld the two sheets 2 and 3 and the films 10a and 10b together, should be noted. These welds 12a and 12b may or may not be parallel and may or may not be perpendicular to the welds 11a and 11b. These welds 11a and 11b lie approximately between the welds 12a and 12b; preferably, the welds 11a and 11b lie completely between the welds 12a and 12b. The welds 12a and 12b extend over substantially the width of the strips of film 10a and 10b, or even extend beyond this width. The valve defined by the welds 12a and 12b is therefore substantially leaktight.

[0062] FIG. 6 a shows an alternative embodiment of these second packages in the closed state (in which the welds 11a and 11b have not been shown and in which, however, all the films and sheets have been shown). The presence of two vertical welds 12′a and 12′b, which weld the films 10a and 10b together, in their unfolded position should be noted. These welds 12′a and 12′b lie between the welds 12a and 12b, which themselves weld the sheets 2 and 3 and the films 10a and 10b together, this time in the folded position. This alternative embodiment makes opening easier by increasing the width of blockage of the fold; greater flexibility in the height of the fold is thus obtained. The welds 11a and 11b likewise lie in this case completely between the welds 12a and 12b. The position of the welds 12′a and 12′b relative to the welds 12a and 12b may vary greatly. In general, the distance between these welds 12′a and 12′b will represent between 5 and 50%, preferably between 10 and 35%, of the distance between the welds 12a and 12b. The valve defined by the welds 12′a and 12′b is in this case also substantially leaktight. The other features described with reference to FIG. 6 apply mutatis mutandis.

[0063] The operation of the valve is more clearly explained with reference to FIGS. 7a and 7b (with the type IIa for example—the first embodiment—i.e. without the welds 12′a and 12′b). FIG. 7a shows the valve closed, a fold of the film 10b covering the film 10a and sealing. Insertion of a straw for example between the sheets 2 and 3 causes the films 10a and 10b to move apart and the valve opens as shown in FIG. 7b. When the straw is removed, the films 10a and 10b resume their initial position and the valve is again closed. The straw (or any other equivalent device such as a plug or a funnel) may be present when the bag is emptied. The latter is then filled and the straw removed, thereby closing the bag. This system is particularly suitable when the fold(s) of the film(s) 10a and 10b extend over most of the width (taking into account the separation of the welds). In this case, it is difficult for the user to separate the films 10a and 10b because of the fold; delivery of the empty bag—in the open position—with the straw (or any other device) thereby makes a “rubbish bin” or rubbish bag which, once the straw has been removed, is very well sealed. The latter embodiment is particularly suitable for hazardous substances such as frying oil, sump oil, solvents and industrial waste and sludge.

[0064] Thus, depending on the configuration chosen, the operation is either reversible or irreversible. In the case of reversible operation, with opening/closing cycles, there is a large distance between the respective welds 12a (or 12′a) and 12b (or 12′b) compared with the height of the fold. In the case of irreversible operation, with the bag being delivered open, with only closure possible, there is a small distance between the respective welds 12a (or 12′a) and 12b (or 12′b) compared with the height of the fold. Choosing the respective dimensions lies within the competence of a person skilled in the art.

[0065] The characteristics of the films (thickness, etc.) are substantially the same as for type I. The fold(s) represents (represent), a percentage of the distance between the respective welds 12a (or 12′a) and 12b (or 12′b), between 5 and 50%. If it is desired to open the bag using a straw, the fold(s) represents (represent) in general from 5 to 25%. If it is desired that opening cannot occur, the fold(s) represents (represent) in general from 25 to 50%.

[0066] FIGS. 8 a and 8b illustrate the method of producing the type IIa or IIb bags (here the type IIa—the first embodiment—has been chosen to be shown). FIG. 8a shows the sheets 2 and 3, the films 10a and 10b and a screen-film 7 of the same kind as that used for manufacturing the type I bag. Welding bars 13a and 13b heated to the welding temperature are applied so as to obtain the welds 11a and 11b. The screen-film 7 is removed and then, as shown in FIG. 8b, vertical weld bars 14a and 14b, heated to the temperature for welding the sheets 2 and 3 and the films 10a and 10b together, are applied in order to obtain the welds 12a and 12b. Any other welding device of the bar/counterpart type can also be used.

[0067] In the case of the second embodiment, the method also includes the step for the welds 12′a and 12′b. In such a case, it is possible to separate the sheets 2 and 3 from the films 10a and 10b in order to carry out the welding. The sheets 2 and 3 may also be folded over on themselves, in order to completely free the films 10a and 10b which it is then very easy to weld together.

[0068] FIGS. 9 a and 9b show the filling region. The closure system is shown on one side of the bag. The welds 11a and 11b on the one hand, and 12a and 12b on the other hand, have already been produced. FIG. 9a shows the open space left between the film 10a and the sheet 2, which allows filling, indicated schematically by the arrow. Once filling has been completed, the weld 15 extending from the weld 12a to the edge of the bag is made, as shown in FIG. 9b. The sheets 2 and 3 and the films 10a and 10b are welded together by this weld.

[0069] FIG. 10 shows a third package (termed hereafter type III). In this package, the film 16 in the form of a strip is folded over on itself and welded to the sheets 2 and 3 by the welds 17a and 17b. This film 16 is of the kind similar to that of the films 10a, 10b and 4.

[0070] FIG. 11 shows a side view in which the welds 18a and 18b may be seen. These welds may or may not be parallel and may or may not be perpendicular to the previous welds. The welds 17a and 17b lie approximately between the welds 18a and 18b, preferably completely between them. The welds 18a and 18b extend substantially over the width of the strip of folded-over film 16 or even extend beyond this width.

[0071] The valve thus formed is termed type III. Unlike types I and IIa and IIb, the film 16, in the original state, does not allow a straw to pass through it. It is necessary to pierce the flexible film 16. The piercing tool is preferably a piercer stopper 19, as shown in FIG. 12. The piercing tool may also be a straw.

[0072] The piercer stopper 19 shown in FIG. 12 comprises a body 20 through which a channel 21 passes. Advantageously, the piercer stopper also has a piercer tube 22. The body 20 advantageously has a screw thread or splines, which will allow this stopper to be fastened to the flexible film 16. This film 16 is preferably elastic so as to obtain the effect of a diaphragm gripping the stopper. Thus, this stopper 19 may be provided with a cap 23 which may be screwed on. This stopper may be a simple stopper, one with a pouring lip, reclosable, tamperproof, one with a child-proof safety system, etc.

[0073] FIG. 13 a shows the first type of way to manufacture the type III bag. As previously, the manufacture makes use of a screen-film 7. Firstly, the film 16 is welded to the sheets 2 and 3 along the welds 17a and 17b, the film 7 being inserted into the fold of the film 16. Welding bars 24a and 24b weld along the welds 17a and 17b. The screen-film 7 is then removed and welding bars 25a and 25b weld the sheets 2 and 3 and the folded film 16 together along the welds 18a and 18b.

[0074] FIGS. 14 a and 14b show the filling operation. The closure system is shown on one side of the bag. The welds 17a and 17b on the one hand, and 18a and 18b on the otherhand, have already been produced. FIG. 14a shows the open space left between the film 16 (which is folded) and the sheet 2, which allows filling, indicated schematically by the arrow. Once filling has been completed, the weld 26 extending from the weld 18a to the edge of the bag is made, as shown in FIG. 14b. The sheets 2 and 3 and the folded film 16 are welded together by this weld.

[0075] FIG. 15 shows a package common to types I and IIa/IIb. In this package, the sheets 2 and 3 are also welded along an additional line 27, placed along an extension of the sheets 2 and 3. A line of weakness or a simple marking line 28 may be placed beneath the weld 27 so as to encourage the user to cut the bag along this marking line. The additional weld ensures complete sealing.

[0076] The package, by dint of its embodiments of type I, II (IIa/IIb) and III therefore has many advantages, by the combination of two semi-rigid sheets 2 and 3 forming the body of the bag and one (two) flexible film(s) 4; 10a, 10b; 16. The characteristics of the sheets and films are common between all the packages and the description given with reference to FIG. 1 applies mutatis mutandis to the other embodiments. Likewise, the other features (width, length, operating conditions, welding conditions, etc.), when they are not specifically mentioned in an example of a package, are common to the various embodiments.

[0077] The bag is:

[0078] leaktight

[0079] by welding,

[0080] by film/film contact,

[0081] by folding of the films,

[0082] by film/attached stopper contact,

[0083] by a ZIPLOCK system (two profiles, generally extruded, which cooperate by one fitting into the other),

[0084] by a peelable/repositionable film (type I);

[0085] openable and reclosable

[0086] by an attached stopper (type III),

[0087] by mechanical operation of the sealing system (type I, II);

[0088] tamperproof

[0089] by an attached stopper (type III),

[0090] by welding

[0091] film/sheet or

[0092] sheet/sheet.

[0093] The bag also has the advantage of being flat (before filling), thereby making it easier to handle and decreasing the volumes for packaging the bags.

[0094] The bag has in general an overall thickness of less than 2 mm, preferably less than 500 μm.

[0095] The bags are suitable for all technical fields, especially the food, chemical, detergents and cosmetics fields; and they apply for liquids, powders, granules or solids of small size (for example sweets). As was indicated above, the bag may be of a use-once type, such as a “rubbish bin”.

[0096] The bag of type III (with an attached stopper) makes it possible to integrate the stopper function into the manufacturing logic and into the methods for flexible bags (such as Doypacks and three-weld bags).

[0097] Finally, it will be noted that the sheets and films may include conventional additives and may consist of several layers, as is known in the art. Thus, the films or sheets may comprise several layers, one of which can be welded.

[0098] The invention is not limited to the embodiments shown, but is easily capable of many improvements within the competence of a person skilled in the art.

Claims

1. A package comprising at least two sheets (2, 3) and two flexible films (10a, 10b) placed between them and welded to the sheets (2, 3) by the welds (11a, 11b) respectively, and welded together and to the sheets (2, 3) by the welds (12a, 12b), at least one of the two films being folded over the other at that end of the films on the opposite side to the welds (11a, 11b).

2. The package according to claim 1, the two films being folded over on themselves at that end of the films on the opposite side to the welds (11a, 11b).

3. The package comprising at least two sheets (2, 3) and two flexible films (10a, 10b) placed between and welded to the sheets (2, 3) by the welds (11a, 11b) respectively, and welded together by the welds (12′a, 12′b) and to the sheets (2, 3) by the welds (12a, 12b), the welds (12′a, 12′b) being between the welds (12a, 12b), at least one of the two films being folded over the other at that end of the films on the opposite side to the welds (11a, 11b).

4. The package according to claim 3, the two films being folded over on themselves at that end of the films on the opposite side to the welds (11a, 11b).

5. The package comprising at least two sheets (2, 3), a flexible film (16) placed between them and folded over on itself and welded to the sheets (2, 3) by the welds (17a, 17b) respectively and welded to itself and to the sheets (2, 3) by the welds (18a, 18b).

6. The package according to any one of claims 1 to 4, in which the fold formed by the film(s) can be unfolded by inserting a straw between the films (10a, 10b).

7. The package according to any one of claims 1 to 5, in which the fold formed by the film(s) cannot be unfolded by inserting a straw.

8. The package according to any one of claims 1 to 7, having an additional weld (15) between the sheets (2, 3).

9. The package according to any one of claims 1 to 8, in which the flexible film is made of PE, EVA, PP, OPP, PET or PA.

10. The package according to any one of claims 1 to 9, in which the sheets (2, 3) are semi-rigid.

11. The package according to any one of claims 1 to 10, in which the sheets (2, 3) and the flexible film (10a, 10b; 16) have the following characteristics, where H is the thickness in mm and E is the equivalent modulus of the film in N.mm−2.

12. The package according to any one of claims 1 to 11, in the form of a Doypack or three-weld bag.

13. A method for manufacturing a package according to any one of claims 1 to 4 and 6 to 12, comprising the following steps: insertion of a screen-film (7) between the films (10a, 10b); welding of the films (10a, 10b) to the sheets (2, 3) along the welds (11a, 11b) respectively; extraction of the screen-film (7); optionally, welding of the films (10a, 10b) together along the welds (12′a, 12′b); and welding of the films (10a, 10b) and the sheets (2, 3) together along the welds (12a, 12b).

14. The method for manufacturing a package according to claim 5, comprising the following steps: insertion of a screen-film (7) in the fold formed by the film (16); welding of the film (16) to the sheets (2, 3) along the welds (17a, 17b) respectively; extraction of the screen-film (7); and welding of the film (16) and the sheets (2, 3) together along the welds (18a, 18b).

15. The method according to either of claims 13 and 14, in which the screen-film (7) is made of PTFE or of Teflon®-coated fabric.