SE1350489A1 - Process for making plastic bag with drain valve - Google Patents

Abstract

A process for producing a plastic bag (1) for liquid is described together with such a plastic bag (4). The method comprises the steps of providing a plastic web (4) which has been manufactured by extrusion in a spray direction (3) and arranging said at least one plastic web (4) in at least two layers. The method also comprises the steps of welding together said at least two layers along at least one longitudinal welding line (18) which substantially follows the spray direction (5), and welding together said at least two layers along transverse welding lines (7) which run across the longitudinal welding line (18), and which are arranged at predetermined distances from each other, so that a plurality of continuous plastic bags (1) are formed.

Description

SUMMARY OF THE INVENTION An object of the present invention is to provide a plastic bag and a method of making one which is alternative to known plastic bags and methods of making the same.

Another object of the present invention is to provide a plastic bag and a method of making the same which provide a reduced risk of contamination of the liquid to be filled into the plastic bag.

A further object of the present invention is to provide a method of manufacturing a plastic bag with a tapping device and a plastic bag provided with a tapping device, the tapping device being intended to break the plastic bag in first use, with which the breaking of the plastic bag is simplified compared with prior art. At least one of the above objects is fulfilled by a method and a plastic bag according to the appended independent claims.

Additional advantages are obtained with the features of the appended dependent claims.

A method according to the invention for producing a plastic bag for liquid comprises the steps of providing at least one plastic web which is extruded in a spray direction, and arranging said at least one plastic web in at least two layers. The method is characterized in that the method comprises the steps of welding together said at least two layers along at least one longitudinal welding line which substantially follows the spray direction, and welding together said at least two layers along transverse welding lines running across the longitudinal welding line, and arranged at predetermined distances a number of continuous plastic bags are formed.

With a method according to the present invention, the advantage is obtained that the plastic bags are closed immediately after manufacture, which prevents contamination of the plastic bags before they are filled.

This is especially important, for example, when the liquid to be filled in the bag is a food such as wine or fruit juice.

The continuous bags are divided before filling the plastic bags, whereby an opening in the plastic bag is created at the same time as the bag is separated from the other plastic bags.

The method may comprise the step of providing only one plastic web, which plastic web is folded along a fold line parallel to the spray direction so that the plastic web becomes double folded, and wherein the double-folded plastic web is welded in the fold line opposite side of the double-folded plastic web. By using a single plastic web that is double-folded, the number of welds in the plastic bag can be minimized.

Alternatively, two plastic webs can be provided which are welded together along two longitudinal welding lines arranged on each side of the plastic webs. Such a method has the advantage that no folding is required and that the welds along the transverse weld lines can run between the two welds along the longitudinal weld lines, which provides a more secure closure.

The method may also include the step of attaching a drain device to the outside of each plastic bag. By attaching the tapping device to the outside of the plastic bag already during the manufacture of the plastic bag, this step is facilitated at the same time as any surfaces on the outside of the plastic bag under the tapping device which come into contact with the contents of the plastic bag can be kept free from contamination.

Advantageously, the tapping device is attached to one of said at least one plastic web before said at least one plastic web is folded or welded. This enables welding of the tapping device to the plastic web, which requires heating from the opposite side of the plastic.

It is advantageous to weld the drain device to the plastic bag as it provides a secure adhesion. Alternatively, it is possible to glue the draining device to the plastic bag. In the latter case, it is possible to attach the tapping device to the plastic bag after it has been folded.

The tapping device may comprise a knife means which is arranged to cut up the plastic bag along a cutting line in the first use. It is in particular in connection with such tapping devices that the greatest advantages of the invention can be obtained.

The inventor has surprisingly discovered that the breaking of the package with a knife member is considerably facilitated if the knife is allowed to act along a cutting direction which is substantially parallel to the spraying direction of the plastic. One of the explanations for this is that the molecules preferably orient themselves parallel to the spray direction.

The tapping device is thus advantageously arranged so that the cutting line is substantially parallel to the spraying direction, the cutting line not deviating more than 10 degrees from the spraying direction, preferably not more than 5 degrees and advantageously not more than 2 degrees.

This has the advantage mentioned above that the cutting resistance becomes considerably less than is the case when the cutting direction is transverse to the spraying direction.

The draining device may comprise a housing part with a fastening surface intended to be fastened to the plastic bag and a draining part, the housing part forming a chamber together with the plastic bag when the housing part is attached to the plastic bag and wherein the draining part comprises a rotating part suspended in a housing part rotatable about a shaft substantially parallel to the mounting surface, and a drain pipe extending from the pivot member and attached to the pivot member. The housing part comprises a channel against the rotating part and the rotating part comprises a channel against the housing part. The drain part can be rotated between a closed position in which the channel in the turning part does not overlap the channel in the housing part, and an open position in which the channel in the turning part at least partially overlaps the channel in the housing part so that the liquid in the plastic bag can be emptied through the drain pipe. The knife means is arranged to cut up the plastic bag inside the fastening surface. This is an advantageous way of arranging the draining device which means that spills can be avoided.

The fastening surface can define a plane, wherein the knife means in the closed position of the tapping part is arranged inside the plane of the fastening surface so that the knife means is arranged in the chamber when the tapping device is arranged on the plastic bag. With such an arrangement of the knife member, there is no risk of the knife member cutting the plastic unplanned.

The drain pipe is advantageously arranged so that in the closed position of the drain part it does not deviate more than 10 degrees from the plane of the fastening surface. This means that the draining device becomes compact.

The knife member can be arranged to be operated independently of the tapping part. However, it is advantageous if the knife member is frictionally coupled to the rotating part so that the first rotation of the rotating part from the closed position to the open position causes the knife member to be rotated so that the plastic bag is cut open. This minimizes the number of parts in the drain device.

The plastic web may comprise a single layer. This is the simplest and cheapest solution because the plastic web can then be produced in one step by extrusion.

Alternatively, the plastic web may comprise plastics of at least two different varieties which are arranged in at least two different plastic layers. By combining several different types of plastics, the properties of the plastic bag can be optimized.

The plastic web may comprise a first plastic layer of a first type of plastic which is impermeable to oxygen and a second and a third plastic layer on each side of the first plastic layer, which are of second type of plastic which is impermeable to water. This means that a relatively cheap and strong plastic such as polyethylene can be used for both outer layers of the plastic, while a good barrier against oxygen penetration can be provided by the intermediate layer. This is especially advantageous when the plastic bag contents are wine that is often stored for a relatively long time and is sensitive to oxidation.

According to a second aspect of the present invention, there is provided a plastic bag for liquid comprising at least one plastic web of extruded plastic arranged in two layers.

The plastic bag is characterized in that said at least two layers are welded together along at least one longitudinal welding line which is substantially extending along the extrusion direction of the plastic web, and said at least two layers are welded along a transverse welding line running transversely to said at least one, at one edge of the plastic bag.

With a plastic bag according to the present invention, the advantage is obtained that the plastic bag is closed, which prevents contamination of the inside of the plastic bags before they are filled. This is especially important, for example, when the liquid to be filled in the bag is a food such as milk, wine or fruit juice. The plastic bags are delivered assembled. The continuous plastic bags are divided before filling the plastic bags, whereby an opening in the plastic bag is created at the same time as the bag is separated from the other plastic bags.

The plastic bag may also comprise a draining device which is welded to the outside of each plastic bag. By welding the tapping device to the outside of the plastic bag already during the manufacture of the plastic bag, this step is facilitated at the same time as any surfaces on the outside of the plastic bag under the tapping device, which surfaces come into contact with the contents of the plastic bag, can be kept free from contamination.

The tapping device may comprise a knife means which is arranged to cut up the plastic bag along a cutting line in the first use. There are of course other ways to break the plastic bag. For example, it is possible to punch a hole in the bag. However, the solution of cutting the plastic bag along a cutting line is an uncomplicated way of effecting the breaking of the plastic bag.

The tapping device can be arranged so that the cutting line is substantially parallel to the spraying direction in which the extruded plastic is sprayed, the cutting line not deviating more than 10 degrees from the spraying direction, preferably not more than 5 degrees and advantageously not more than 2 degrees. The inventors have surprisingly discovered that the breaking of the package with a knife member is considerably facilitated if the knife is allowed to act along a cutting direction which is substantially parallel to the spraying direction of the plastic. One explanation for this is that the molecules preferably orient themselves parallel to the spray direction.

The draining device may comprise a housing part with a fastening surface which is fastened to the plastic bag and a draining part, the housing part forming a chamber together with the plastic bag.

The drain member includes a pivot member suspended in the housing member rotatable about an axis substantially parallel to the mounting surface, and a drain pipe extending from the pivot member, the housing member comprising a channel toward the pivot member and the pivot member comprising a channel toward the housing member. a closed position in which the channel in the rotating part does not overlap the channel in the housing part and an open position in which the channel in the rotating part at least partially overlaps the channel in the housing part.

The fastening surface of the tapping device can define a plane, the knife means in the closed position of the tapping part being arranged inside the plane of the fastening surface so that the knife means is arranged in the chamber when the tapping device is arranged on the plastic bag. With such an arrangement of the knife member, there is no risk that the knife member cuts the plastic unplanned.

The drain pipe is advantageously arranged so that in the closed position of the drain part it does not deviate more than 10 degrees from the plane of the fastening surface. This means that the draining device becomes compact.

The knife member can be arranged to be operated independently of the tapping part. However, it is advantageous if the knife member is frictionally coupled to the rotating part so that the first rotation of the rotating part from the closed position to the open position causes the knife member to be rotated so that the plastic bag is cut open. This minimizes the number of parts in the drain device.

The plastic web can be formed by spraying plastic of at least two different varieties through at least two different extruder nozzles in a spray direction to form plastic layers which are assembled to the plastic web. By combining olika your different types of plastics, the properties of the plastic bag can be optimized.

The plastic web may comprise at least two different types of plastic in at least two different plastic layers.

By combining olika your different types of plastics, the properties of the plastic bag can be optimized.

The plastic web may comprise a first plastic layer of a first type of plastic which is impermeable to oxygen and a second and a third plastic layer on each side of the first plastic layer, which are of second type of plastic which is impermeable to water. This means that a relatively cheap and strong plastic such as polyethylene can be used for both outer layers of the plastic, while a good barrier against oxygen leakage can be provided by the intermediate layer. This is especially advantageous when the plastic bag contents are wine that is often stored for a relatively long time and is sensitive to oxidation.

The features described above can, as far as possible, be combined in the same embodiment.

In the following, preferred embodiments will be described with reference to the accompanying figures.

According to a third aspect of the present invention, there is a use of a plastic bag according to the second aspect of the invention or a plastic bag made by a method according to the first aspect of the present invention. The bag is primarily intended for use in products that are sensitive to oxygen and / or with limited shelf life.

Examples of such products are fruit juices, dairy products, wine and juice. Other possible uses are cooking oil, spirits, and vinegar. In addition, it is possible to use the plastic bag for various chemical products in liquid form such as engine oil and paint or other oils, solvents and acids. In the case of solvents, however, care must be taken so that the solvent does not dissolve the plastic in the plastic bag.

The plastic bag is advantageously combined with a cardboard package to increase the handling of the plastic bag.

Brief Description of the Drawings Fig. 1 schematically illustrates a prior art method of making plastic bags for liquid.

Fig. 2 schematically illustrates a method according to an embodiment of the present invention for manufacturing plastic bags for liquid.

Fig. 3 schematically shows an assembly for the manufacture of plastic bags according to an embodiment of the invention.

Fig. 4 schematically shows an assembly for manufacturing plastic bags according to an alternative embodiment of the invention.

Fig. 5 shows in greater detail a plastic bag with a tapping device according to an embodiment of the present invention.

Fig. 6 shows how schematically in section a plastic web with several different plastic layers.

Fig. 7 shows in greater detail in partial section a draining device according to an embodiment of the present invention.

Description of Preferred Embodiments In the following description of preferred embodiments of the invention, similar features in the various figures will be designated by the same reference numerals.

Fig. 1 schematically illustrates a method according to the prior art for manufacturing plastic bags 1 for liquid. The process begins with the step of providing extruded plastic from a roll 2, which plastic has been extruded in a spray direction 3. A plastic web 4 is discharged from the roll 2, which is followed by the step of arranging a tapping device 10 on the plastic web 4 which is preferably done by welding fixed the draining device 10 to the plastic web 4.

In the figure, the draining device 10 is arranged on the underside of the plastic web 4, but it could just as easily be arranged on the upper side. This is followed by the step of folding the plastic web along a fold line 5 which is parallel to the spray direction so that the plastic web becomes double-folded, which step is illustrated at 6. Then follows the step of welding the double-folded plastic web along transverse weld lines 7 running across the fold line and longitudinal weld line. , and which are arranged at predetermined distances from each other, so that a number of continuous plastic bags are formed. As can be seen from the figure, the welds along the cross-weld lines 7 are double between two adjacent plastic bags 1. The space 8 between the cross-weld lines 7 can be used to separate the plastic bags 1 from each other by making a cut in the gap 8.

As can be seen from Fig. 1 and the above description, the fold line 5 opposite the edge 9 of the plastic bags 1 is open so that the finished plastic bags 1 can be filled from that edge 9.

The tapping device 10 may be of the type described in WO 2010/062247 which comprises a knife means (not shown) which is operated with a tapping part 11 which is rotatable about a rotation axis 12 which in Fig. 1 is parallel to the spray direction 3. By turning the tapping part 11 the knife means is actuated to cut up the plastic bag during the first use along a cutting line 13 which is perpendicular to the spraying direction 3.

Fig. 2 schematically illustrates a method according to the present invention for manufacturing plastic bags 1 for liquid. The process begins with the step of providing a roll 2 of plastic film which has been extruded through an extruder nozzle in a spray direction 3.

A plastic web 4 is rolled by the roller 2 which is followed by the step of attaching the tapping device 10 to the underside of the plastic web and the step of folding the plastic web 4 along a fold line 5 parallel to the spray direction so that the plastic web 4 becomes double folded, which step is illustrated at 6. The tapping device 10 is attached advantageously on the plastic web before folding, since the tapping device 10 is advantageously welded to the plastic web, which is done with heating from the opposite side of the plastic web. It is of course also possible to fasten the draining devices by gluing, which can take place after folding and welding of the bag. Then follow the steps of welding the double-folded plastic web along the longitudinal weld line 18 arranged at the fold line 5 opposite the edge of the plastic web and to weld the double-folded plastic web along transverse weld lines 7 which run across the fold line and are arranged at predetermined distances from each other. In this way, a number of continuous plastic bags are formed. It is also possible to weld the double-folded plastic web 4 along a second longitudinal weld line 38 in the vicinity of the fold line 5. Such a second longitudinal weld line can also be arranged in the case that the plastic bag is made of two or two separate plastic webs. As can be seen from the figure, the welds along the transverse welding lines 7 are simple. The tapping devices 10 will be shown in greater detail in Fig. 4 and are of the type described in WO 2010/062247 which comprises a knife member (Fig. 4) which is operated with a tapping part 11 which is rotatable about an axis of rotation 12 which in Fig. 1 is perpendicular by turning the drain part 11, the knife means is operated to cut the plastic bag in the first use along a cutting line 13 which is substantially parallel to the spraying direction 3. By substantially parallel is meant that the cutting line does not deviate more than 10 degrees from the spraying direction, preferably not more than 5 degrees and advantageously not more than 2 degrees. After welding, the bags 1 are completely sealed and delivered in suitable lengths to the place where they are to be filled with liquid. At the place where the bags are to be filled with liquid, the bags are cut off next to a weld, whereby an opening in the bag is formed at the same time as the bag is cut off. Because the bag has been closed from manufacture until it is cut off, there is no risk that it would have been contaminated, which is an advantage, for example, if the plastic bag 1 is to be used for food.

Fig. 3 schematically shows an assembly for the manufacture of plastic bags according to the invention.

A plastic roll 2 acts as a layer from which a plastic web 4 is discharged to a welding device 19 for welding the tapping device 10. The plastic web is then passed to a folding device 20 which doubles the plastic web 4. The double-folded plastic web is then fed to a welding device 21 which welds the double-folded plastic web the longitudinal weld line 18 and possibly also along the second longitudinal weld line 38 and along the transverse weld lines 7.

Finally, the plastic web is conveyed to a cutting device 22 which cuts the plastic web into suitable lengths.

Fig. 4 schematically shows an alternative assembly for manufacturing a plastic bag from two plastic webs 35, 36. A first plastic web 35 is discharged from a first roller 33 and a second plastic web 35 is discharged from a second roller 34. The second plastic web is fed to a welding device 19 for welding the drain device 10. Then both plastic webs are passed to a welding device 21 which welds together plastic webs along the longitudinal weld line 18, along the second longitudinal weld line 38 and along the transverse weld lines 7.

Finally, the plastic web is conveyed to a cutting device 22 which cuts the plastic web into suitable lengths.

Fig. 5 shows in greater detail a plastic bag 1 with a draining device 10 according to an embodiment of the present invention. The tapping device 10 comprises a housing part 23 which is attached to the plastic bag 1 and a tapping part 11 with a pivot part 24 which is suspended in the housing part 23 rotatable about the axis of rotation 12 and a tapping tube 25 which extends from the pivot part and which is attached to the pivot part. The drain pipe 11 comprises an opening 26 through which liquid can be drained and a handle 27 which facilitates operation of the drain part 11. The plastic bag 1 comprises a part of a double-weight plastic web 4 and is welded along a longitudinal weld line 18 running along the fold line 5 opposite side of the plastic bag. 5 and along a transverse weld line 7 between the fold line 5 and the longitudinal weld line 18.

In the description above, the plastic web has been described as a plastic web with a single plastic layer.

However, it is possible to have the plastic web composed of olika your different layers, but different 10 15 20 25 30 10 kinds of plastic the different layers. Such a plastic web is shown schematically in section in Fig. 6. The method for producing a plastic film with different layers has been known since the beginning and will not be described in detail here. The plastic web advantageously comprises a first plastic layer 39 of a first type of plastic which is impermeable to oxygen and a second 40 and a third plastic layer 41 (not shown) on each side of the first plastic layer 39, which are of second type of plastic which is impermeable to oxygen. water. Plastics that are impermeable to oxygen rarely have sufficient mechanical strength to function as the only plastic in a plastic bag.

Such mechanical strength is provided by the two outer layers. The two outer layers can, for example, be made of polyethylene. If the requirements for oxygen impermeability are not too high, a single layer of polyethylene may be sufficient. The second and third layers are advantageously of a plastic that allows welding.

Fig. 7 shows in greater detail in partial section a tapping device 10 attached to a plastic bag 1 according to an embodiment of the present invention. The tapping device 10 comprises a housing part 23 with a fastening surface 28 which defines a plane and which is intended to be fastened to the plastic bag 1. The tapping device 10 also comprises a tapping part 11.

The housing part 23 forms a chamber 29 together with the plastic bag 1 when the housing part 23 is attached to the plastic bag 1. The drain part 11 comprises a rotating part 24 which is suspended in the housing part 23 rotatable about the axis of rotation 12 which is substantially parallel to the fastening surface 28.

The drain part 11 comprises a drain pipe 25 extending from the rotating part 24 and which is attached to the rotating part 24. The housing part 23 comprises a channel 30 against the rotating part 24 and the rotating part 24 comprises a channel 31 against the housing part 23. The draining part 11 can be rotated between a closed position in which the channel 31 in the rotating part 24 does not overlap the channel 30 in the housing part 23, and an open position in which the channel 31 in the rotating part 24 overlaps the channel 30 in the housing part 23. The draining part 11 also comprises a knife member 32 which is arranged rotatably about the rotation axis 12. The knife member 32 is arranged with a friction coupling to the rotating part 24 so that the knife member 32 is rotated when the rotating part is rotated. Advantageously, the movement of the knife member 32 is limited so that it remains in the position which provides the largest opening through the opening foamed in the plastic bag 1 even if the rotating part is turned further. The knife means 32 is arranged to cut open the plastic bag 1 inside the fastening surface 28. In the closed position of the tapping part the knife means 32 is arranged inside the plane of the fastening surface 28 so that the knife means 32 is arranged in the chamber 29. The first rotation of the turning part 24 from the closed position to the open position that the plastic bag 1 is cut up along a cutting line 13 which is perpendicular to the axis of rotation 12 and parallel to the spraying direction. The invention is not limited to the above-described embodiments of the invention, which can be modified in many different ways without departing from the spirit and scope of the present invention which is limited only by the appended claims.

It is of course possible to have the knife member operable by separate means, although it is less complicated to leave the knife member coupled to the rotating part and its movement.

Claims (25)

10 15 20 25 30 12 PATENT REQUIREMENTS A method of making a plastic bag (1) for liquid comprising the steps of providing at least one plastic web (4) extruded in a spray direction (3), and arranging said at least one plastic web (4) in at least two layers, characterized the method comprising the steps of welding together at least two layers along at least one longitudinal welding line (18) substantially following the spray direction (5), and welding together said at least two layers along transverse welding lines (7) running across the longitudinal welding line (18), and which are arranged at predetermined distances from each other, so that a plurality of continuous plastic bags (1) are formed. A method according to claim 1, wherein a plastic web (4) is provided which plastic web (4) is folded along a fold line (5) parallel to the spray direction (3) so that the plastic web (4) becomes double-folded, and wherein the double-folded plastic web (4) ) is welded at the fold line (5) opposite the side of the double-folded plastic web (4). A method according to claim 1, wherein two plastic webs (4, 35) are provided which are welded together along two longitudinal welding lines (18, 36) arranged on each side of the plastic webs. A method according to claim 1, comprising the step of attaching a tapping device (10) to the outside of the plastic bag (1). A method according to claim 4, wherein the tapping device (10) is attached to one of said at least one plastic web before said at least one plastic web is folded or welded. A method according to claim 4 or 5, wherein the tapping device (10) comprises a knife means (32) arranged to cut the plastic bag (1) along a cutting line (13) in the first use. A method according to claim 6, wherein the tapping device (10) is arranged so that the cutting line (13) is substantially parallel to the spraying direction (3), the cutting line (13) not deviating more than 10 degrees from the spraying direction (3), preferably not more than 5 degrees and preferably not more than 2 degrees. A method according to claim 6 or 7, wherein the draining device (10) comprises a housing part (23) with a fastening surface (28) which is intended to be fastened to the plastic bag (1) and a draining part (11), wherein the housing part (23) forms a chamber (29) together with the plastic bag (1) when the housing part (23) is attached to the plastic bag (1) and wherein the drain part (1 l) comprises a rotating part (24) which is suspended in the housing part (23) rotatable about a pivot axis (12) substantially parallel to the mounting surface (28), a drain pipe (25) extending from the pivot part (24) and fixed to the pivot part (24), the housing part (23) comprising a channel (30 ) against the rotating part (24) and wherein the rotating part (24) comprises a channel (31) against the housing part (23), and wherein the drain part (11) can be rotated between a closed position in which the channel (31) in the rotating part (24) does not overlap the channel (30) in the housing part (23), and an open position in which the channel (31) in the rotating part (24) at least partially overlaps the channel in the housing the electricity (23), the knife means (32) being arranged to cut up the plastic bag inside the fastening surface (28). A method according to claim 8, wherein the mounting surface (28) defines a plane and wherein the knife means (32) in the closed position of the tapping part is arranged inside the plane of the mounting surface (28) so that the knife means (32) is arranged in the chamber (29) when the tapping device (10) ) is arranged on the plastic bag (l). A method according to claim 8 or 9, wherein the knife means (32) is frictionally coupled to the rotating part (24) so that the first rotation of the rotating part (24) from the closed position to the open position causes the knife means (32) to be rotated so that the plastic bag (1) cut up. 11. ll. A method according to any one of the preceding claims, wherein the plastic web (4) comprises plastic of at least two different varieties which are arranged in at least two different plastic layers. A method according to claim 11, wherein the plastic web (4) comprises a first plastic layer of a first kind of plastic which is impermeable to oxygen and a second and a third plastic layer on each side of the first plastic layer, which are of second kind of plastic which is impermeable. for water. Plastic bag for liquid comprising at least one plastic web (4) of extruded plastic arranged in two layers, characterized in that said at least two layers are welded together along at least one longitudinal welding line (18) which runs substantially along the extrusion direction of the plastic web, and said at least two layers are welded together along a transverse weld line which runs across said at least one longitudinal weld line, and which is arranged at one edge of the plastic bag (1). A plastic bag according to claim 13, comprising a draining device (10) attached to the outside of each plastic bag (1). 10 15 20 25 30 35 14 A plastic bag (1) according to claim 14, wherein the tapping device (10) comprises a knife means (32) arranged to cut the plastic bag (1) along a cutting line (13) in the first use. A plastic bag (1) according to claim 15, wherein the tapping device (10) is arranged so that the cutting line (13) is substantially parallel to the spraying direction (3) in which the extruded plastic is sprayed, the cutting line (13) not deviating more than 10 degrees from spray direction, preferably not more than 5 degrees and advantageously not more than 2 degrees. A plastic bag (1) according to claim 15 or 16, wherein the draining device (10) comprises a housing part (23) with a fastening surface (28) intended to be fastened to the plastic bag (1) and a draining part (11), wherein the housing part (23 ) forms a chamber (29) together with the plastic bag when the housing part is attached to the plastic bag (1) and wherein the drain part (10) comprises a rotating part (24) suspended in the housing part (23) rotatable about a rotation axis (12) which is substantially parallel with the fastening surface (28), a drain pipe (25) extending from the rotating part (24) and which is fastened to the rotating part (24), the housing part (23) comprising a channel (30) against the rotating part (24) and wherein the rotating part (24 ) comprises a channel (31) against the housing part (23), and wherein the drain part (11) can be rotated between a closed position in which the channel (31) in the rotating part (24) does not overlap the channel (30) in the housing part (23), and a open position in which the channel (31) in the rotating part (24) at least partially overlaps the channel (30) in the housing part (23), wherein kn the iv means (32) is arranged to cut the plastic bag inside the fastening surface (28). A plastic bag (1) according to claim 17, wherein the fastening surface (28) defines a plane and wherein the knife means (32) in the closed position of the drain part (11) is arranged inside the plane of the fastening surface (28) so that the knife means (32) is arranged in the chamber ( 29) when the draining device (10) is arranged on the plastic bag (1). Plastic bag (1) according to claim 18, wherein the knife means (32) is frictionally coupled to the rotating part (24) so that the first rotation of the rotating part (24) from the closed position to the open position causes the knife means (32) to be rotated so that the plastic bag (1) is cut open. A plastic bag (1) according to any one of the preceding claims, wherein the plastic web (4) comprises at least two different kinds of plastic in at least two different plastic layers. A plastic bag according to claim 20, wherein the plastic web (4) comprises a first plastic layer of a first kind of plastic which is impermeable to oxygen and a second and a third plastic layer on each side of the first plastic layer, which are of second kind of plastic which is impermeable. for water. 15 Use of a plastic bag prepared by the process according to any one of claims 1 to 12 for a liquid selected from the group consisting of fruit juices, dairy products, wine and juice. Use of a plastic bag prepared by the process according to any one of claims 1 to 12 for a liquid selected from the group consisting of oils, solvents and acids. Use of a plastic bag according to any one of claims 13-21 for a liquid selected from the group consisting of fruit juices, dairy products, wine and juice. Use of a plastic bag according to any one of claims 13-21 for a liquid selected from the group consisting of oils, solvents and acids.