WO2014171874A9

WO2014171874A9 - Method for production of a plastic bag with draining valve, a plastic bag and use of a plastic bag

Info

Publication number: WO2014171874A9
Application number: PCT/SE2014/000051
Authority: WO
Inventors: Vilho Eriksson
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-04-18
Filing date: 2014-04-15
Publication date: 2014-12-04
Anticipated expiration: 2015-10-18
Also published as: WO2014171874A1; SE1350489A1

Abstract

A method for production of a plastic bag (1) for liquid is described together with such a plastic bag (1). The method comprises the steps of providing a plastic web (4) which has been manufactured by extrusion in an extrusion direction (3) and to arrange 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 said at least one longitudinal welding line (18) which essentially follows the extrusion direction (5), and to weld together said at least two layers along transverse welding lines (7) which extend transverse to the longitudinal welding line (18), and which are arranged at predetermined distances from each other, so that a number of connected plastic bags (1) are formed. The application also includes a plastic bag and use of a plastic bag.

Description

METHOD FOR PRODUCTION OF A PLASTIC BAG WITH DRAINING VALVE, A PLASTIC

BAG AND USE OF A PLASTIC BAG

Technical field

The present invention relates to a method for production of a plastic bag for a liquid and preferably such a plastic bag with a draining valve. The present invention also relates to a production method for such a plastic bag.

Prior art

Plastic bags for liquid exist in many different forms and for many different purposes. One purpose is to use plastic bags for wine, wherein the plastic bag often is arranged in a paper box. Such a package with a plastic bag in a paper box is usually called Bag-In-Box. Such packages may of course be used also for other purposes than wine. The PCT application WO 2010/062247 describes a package for liquid. The package is provided with a draining device which is arranged so that spillage during manoeuvring of the draining device is eliminated. The draining device is also arranged so that the package is not broken until the first draining occasion. The draining is controlled using a rotary valve, which is connected to a knife, which breaks the package at rotation of the valve, as well as a draining tube through which the liquid may be drained.

GB 2 152 019 describes an alternative package with which the package is not broken until the first draining occasion, similarly to WO 2010/062247. The breaking of the package and the draining of the liquid occur with two different means. The breaking of the package occurs by a pointed end of a tube being punched into the package while the draining of the liquid is controlled with a crane being arranged in the other end of the tube.

US 2008/0247682 describes the production of an upright standing bag and a method for its manufacturing. The bag may be composed of one or more panels which are welded together. The bags are manufactured with their height axis transverse to the feeding direction of the web, so that an opening in the bags is provided either by leaving a side open or by attaching a tube opening in the plastic.

US 3,668,046 describes a method for production of flat plastic bags from a plastic web. The purpose is to provide an apparatus for performing welding- or hot gluing operations on continuously advanced webs of material. The welding is performed along the folding line and transverse the folding line while one short side is left open. The bags are produced with their long side transverse the feeding direction of the web.

Usually the bag is a plastic bag in the packages according to the inventions above and similar packages. The plastic bag is usually placed in a paper box. The plastic bags are usually manufactured by one of two different methods, namely by extrusion of plastic which is then welded together to plastic bags or by blowing melted plastic in tube form which is first cut to a flat film and which is then welded together to plastic bags.

Summary of the invention

An object of the present invention is to provide a plastic bag and a method for production of such a bag, which are alternatives to known plastic bags and methods for manufacturing of such bags.

Another object of the present invention is to provide a plastic bag and a method for manufacturing of such a bag which provide a reduced risk for contamination of the liquid which is to be filled into the plastic bag. A further object of the present invention is to provide a method for manufacturing of a plastic bag with a draining device and a plastic bag provided with a draining device, wherein the draining device is intended to break the plastic bag at the first use, with which the breaking of the plastic bag is facilitated compared with the prior art.

At least one of the objects above is fulfilled with a method and a plastic bag according to the appended independent claims.

Further advantages are provided with the features in the following dependent claims.

A method according to the invention for production of a plastic bag for liquid comprises the steps of providing at least one plastic web which is extruded in an extrusion direction, and to arrange said at least one plastic web in at least two layers. The method is characterized in that the method comprises the steps of welding said at least two layers together along at least one longitudinal welding line which essentially follows the extrusion direction, and to weld together said at least two layers along transverse welding lines which extends transverse to the longitudinal welding line, and which are arranged at predetermined distances from each other, so that a number of connected sealed plastic bags are formed. The method comprises also the step of attaching, on the outside of the plastic bag, a draining device comprising a knife member, which is arranged to cut open the plastic bag along a cutting line at the first use. The draining device is arranged so that the cutting line is essentially parallel with the extrusion direction, wherein the cutting line deviates no more than 10 degrees from the extrusion direction, preferably no more than 5 degrees and advantageously no more than 2 degrees. Thus, the method comprises the step of attaching a draining device on the outside of each plastic bag. By attaching the draining device on the outside of the plastic bag already during the manufacturing of the plastic bag this step is facilitated at the same time as any surfaces on the outside of the plastic bag underneath the draining device which come into contact with the contents in the plastic bag, may be held free from contamination. An inside which is protected against contamination by for example bacteria is provided also by the fact that the plastic bags are sealed until they are cut from said plurality of connected plastic bags. By the inside of the plastic bags being protected from

contamination by bacteria the amount of preservatives that is added to food which is to be filled into the plastic bag may be reduced or totally eliminated.

Thus, the draining device comprises a knife member which is arranged to cut open the plastic bag along a cutting line at the first use. It is particularly in connection with such draining devices that the largest advantages with the invention may be achieved. The inventor has surprisingly discovered that the breaking of the package with a knife member is facilitated considerably if the knife may act along a cutting direction which is essentially parallel with the extrusion direction of the plastic. One of the explanations to this is that the molecules preferably orientate parallel with the extrusion direction.

As the knife may act along a cutting direction which is essentially parallel with the extrusion direction of the plastic a cut with straight edges is achieved. I contrast thereto frayed edges are achieved if the cutting direction is transverse to the extrusion direction. Frayed edges may hinder the outflow of liquid from the package.

The draining device is, thus, preferably arranged so that the cutting line is essentially parallel with the extrusion direction, wherein the cutting line does not deviate more than 10 degrees from the extrusion direction, preferably no more than 5 degrees and

advantageously no more than 2 degrees. This provides the advantage that has been mentioned above that the cutting resistance becomes considerably lower than what is the case when the cutting direction is transverse to the extrusion direction.

With a method according to the present invention the advantage is achieved that the plastic bags are sealed directly after the manufacturing which prevents contamination of the plastic bags before they are filled. This is especially important for example when the liquid that is to be filled into the bag is food such as, e.g., wine or fruit juice.

The connected bags are separated before the filling of the plastic bags wherein 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 folding line which is parallel with the extrusion direction so that the plastic web becomes folded in two, and wherein the plastic web folded in two is welded at the side of the web folded in two being opposite to the folding line. By using only one plastic web which is folded in two the number of welds in the plastic bag may be minimized. In order for the plastic bags to be sealed it is required that the welds along the transverse welding lines extend all the way between the longitudinal welding line and the folding line. As it is cumbersome to achieve a transverse welding line all the way to the folding line it may be preferable to have two longitudinal welding lines also in the case with a folded plastic web. One of the longitudinal welding lines is then placed close to the folding line.

Alternatively two plastic webs may 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 welding lines may run between the two welds along the longitudinal welding lines. This gives a more secure seal as none of the welds along the transverse welding lines then has to be welded at a folding line.

Preferably, the draining device is attached on one of said at least one plastic web before said at least one plastic web is folded or welded. This enables welding of the draining device to the plastic web which requires heating from the opposite side of the plastic. It is preferable to weld the draining device onto the plastic bag as this gives a secure attachment. Alternatively it is possible to glue the draining device onto the plastic bag. In the latter case it is possible to attach the draining device on the plastic bag after it has been folded.

The draining device may comprise a housing part with an attachment surface and a draining part, wherein the draining device is attached against the plastic bag by attaching the attachment surface against the plastic bag, so that the housing part creates a chamber together with the plastic bag, wherein the draining part comprises a rotational part which is suspended in the housing part rotatable around a rotational axis which is essentially parallel with the attachment surface when the draining device is attached to the plastic bag, and a draining tube which extends from the rotational part and which is attached to the rotational part. The housing part comprises a channel towards the rotational part and the rotational part comprises a channel towards the housing part. The draining part may be rotated between a closed position in which the channel in the rotational part does not overlap the channel in the housing part, and an open position in which the channel in the rotational part at least partly overlaps the channel in the housing part so that the liquid in the plastic bag may be emptied through the draining tube. The knife member is arranged to cut open the plastic bag inside the fastening surface. This is an advantageous way of arranging the draining device which enables spillage to be avoided.

The fastening surface may define a plane, wherein the draining device is arranged on the plastic bag in the closed position of the draining part, in which position the knife member is arranged in the chamber inside the plane of the fastening surface. With such an arrangement of the knife member there is no risk for the knife member to cut open the plastic unplanned. The draining tube is preferably arranged so that it in the closed position of the draining part not deviates more than 10 degrees from the plane of the fastening surface. This results in that the draining device becomes compact.

The knife member may be arranged to be manoeuvred independently of the draining part. However, it is preferable if the knife member is connected frictionally to the rotational part so that the first rotation of the rotational part from the closed position to the open position results in that the knife member is rotated so that the plastic bag is cut open. This minimizes the number of parts in the draining device.

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

Alternatively, the plastic web may comprise plastic of at least two different types which are arranged in at least two different plastic layers. By combining many different types of plastic the characteristics of the plastic bag may 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 a second type of plastic which is impermeable to water. This results in that a relatively cheap and strong plastic such as polyethene may be used for the outer layers of the plastic while a good barrier against oxygen penetration may be provided by the middle layer. This is especially preferable when the content of the plastic bag is wine which is often stored a relatively long time and is sensitive to oxidation.

According to a second aspect of the present invention a plastic bag for a liquid is provided which comprises at least one plastic web of extruded plastic arranged in two layers. The plastic bag is characterised in that said at least two layers are welded together along at least one longitudinal welding line which essentially extends along the extrusion direction of the plastic web, and said at least two layers are welded together along a transverse welding line which extends transverse to said at least one longitudinal welding line, and which is arranged at one edge of the plastic bag. The plastic bag comprises, attached on the outside of each plastic bag, a draining device which comprises a knife member which is arranged to cut open the plastic bag along a cutting line at the first use. The draining device is arranged so that the cutting line is essentially parallel with the extrusion direction in which the extruded plastic has been extruded, wherein the cutting line deviates no more than 10 degrees from the extrusion direction, preferably no more than 5 degrees and

advantageously no more than 2 degrees.

With a plastic bag according to the present invention the advantage is achieved that the plastic bag is sealed 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 into the bag is a foodstuff such as, e.g., milk, wine or fruit juice. The plastic bags are delivered put together. The connected plastic bags are divided before the filling of the plastic bags, wherein an opening in the plastic bag is created at the same time as the bag is separated from the other bags.

The plastic bag comprises a draining device which is welded onto the outside of each plastic bag. By the draining device being welded onto the outside of the plastic bag already at the manufacturing of the plastic bag this step is facilitated at the same time as any surfaces on the outside of the plastic bag underneath the draining device, which surfaces come into contact with the contents in the plastic bag, may be kept free from

contamination. The draining device comprises a knife member which is arranged to cut open the plastic bag along a cutting line at the first use. There are of course other ways of breaking the plastic bag. It is for example possible to punch a hole in the bag. However, the solution of cutting the bag open along a cutting line is an uncomplicated way of achieving the breaking of the plastic bag. The draining device is arranged so that the cutting line is essentially parallel with the extrusion direction in which the extruded plastic has been extruded, wherein the cutting line deviates no more than 10 degrees from the extrusion direction, preferably no more than 5 degrees and advantageously no more than 2 degrees. The inventors have

surprisingly discovered that the breaking of the package with a knife member is facilitated considerably if the knife may act along a cutting direction which is essentially parallel with the extrusion direction of the plastic. One explanation to this is that the molecules orientate themselves parallel with the extrusion direction.

The draining device may comprise a housing part with an attachment surface which is attached to the plastic bag and a draining part, wherein the draining part forms a chamber together with the plastic bag. The draining part comprises a rotational part which is suspended in the housing part rotatable around an axis which is essentially parallel with the attachment surface, and a draining tube which extends from the rotational part, wherein the housing part comprises a channel towards the rotational part and wherein the rotational part comprises a channel towards the housing part, wherein the draining part may be rotated from a closed position in which the channel in the rotational part does not overlap the channel in the housing part and an open position in which the channel in the rotational part at least partly overlaps the channel in the housing part.

The attachment surface of the draining device may define a plane, wherein the knife member in the closed position of the draining part is arranged inside the plane of the attachment surface so that the knife member is arranged in the chamber when the draining 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 draining tube is preferably arranged so that, in the closed position of the draining part, it deviates no more than 10 degrees from the plane of the attachment surface. This results in the draining device becoming compact.

The knife member may be arranged to be manoeuvred independently of the draining part. It is, however, advantageous if the knife member is frictionally connected to the rotational part so that the first rotation of the rotational part from the closed position to the open position results in that the knife member rotates so that the plastic bag is cut open. This minimises the number of parts in the draining device.

The plastic web may be formed by extrusion of plastic of at least two different types through at least two separate extruder dies in an extrusion direction for creation of plastic layers which are put together to the plastic web. By combining many different types of plastic the properties of the plastic bag may be optimized.

The plastic web may comprise at least two different types of plastic in at least two different plastic layers. By combining many different types of plastic the properties of the plastic bag may be optimized.

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

The above describe embodiments may, to the extent that it is possible, be combined in the same embodiment. In the following preferred embodiments will be described with reference to the appended drawings.

A third aspect of the present invention relates to a use of a plastic bag according to the second aspect of the invention or a plastic bag produced with a method according to the first aspect of the present invention. Primarily, the bag is intended to be used for products that are sensitive to oxygen and/or with a limited shelf-life. Examples of such products are fruit juice, dairy products, wine and syrup. Other possible fields of application are cooking oil, spirits and wine vinegar. It is also possible to use the plastic bag for different chemical products in liquid form such as motor oil and paint or other oils, solvents and acids. In the case of solvents care must be taken so that the solvent does not dissolve the plastic in the plastic bag.

The plastic bag is preferably combined with a paper package in order to increase the manageability of the plastic bag. Short description of the drawings

Fig. 1 illustrates schematically a method according to the prior art for manufacturing of plastic bags for liquid.

Fig. 2 illustrates schematically a method according to an embodiment of the present invention for manufacturing of plastic bags for liquid. Fig. 3 shows schematically an assembly for manufacturing of plastic bags according to an embodiment of the invention.

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

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

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

Fig. 7 shows in larger detail partly in cross 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 different figures will be denoted with the same reference numeral.

Fig. 1 illustrates schematically a method according to the prior art for manufacturing of plastic bags 1 for liquid. The method starts with the step of providing extruded plastic from a roll 2, which plastic has been extruded in an extrusion direction 3. A plastic web 4 is supplied from the roll 2, which is followed by the step of arranging a draining device 10 on the plastic web 4 which preferably is done by welding the draining device 10 onto the plastic web 4. In the figure the draining device 10 is arranged on the lower side of the plastic web 4, but it could just as well be arranged on the upper side. This is followed by the step of folding the plastic web along a folding line 5 which is parallel with the extrusion direction so that the plastic web becomes folded in two which step is illustrated at 6. Then follows the step of welding the plastic web folded in two along transverse welding lines 7 which extend transverse to the folding line and the longitudinal welding line, and which are arranged at predetermined distances from each other, so that several connected plastic bags are formed. As is evident from the figure the welds along the transverse welding lines 7 are double between two adjacent plastic bags 1. The space 8 between the transverse welding lines 7 may be used to separate the plastic bags 1 from each other by placing a cut in the space 8. As is evident from Fig. 1 and the above description the edge 9 of the plastic bags 1 opposite to the folding line 5 is open so that the finished plastic bags 1 may be filled from that edge 9. The draining device 10 may be of the type that is described in WO 2010/062247 which comprises a knife member (not shown) which is manoeuvred with a draining part 11 which is rotatable around a rotational axis 12 which in Fig. 1 is parallel with the extrusion direction 3. By rotating the draining part 11 the knife member is manoeuvred at the first use to cut open the plastic bag along a cutting line 13 which is perpendicular to the extrusion direction 3.

Fig. 2 illustrates schematically a method according to the present invention for

manufacturing of plastic bags 1 for liquid. The method begins with the step of providing a roll 2 of plastic film which has been extruded through an extruder die in an extrusion direction 3. A plastic web 4 is rolled of the roll 2, which is followed by the step of attaching the draining device 10 on the lower side of the plastic web and the step of folding the plastic web 4 along a folding line 5 which is parallel with the extrusion direction so that the plastic web 4 becomes folded in two, which step is illustrated at 6. The draining device 10 is preferably attached on the plastic web before folding as the draining device 10 preferably is welded onto the plastic web which is performed using heating from the opposite side of the plastic web. It is of course also possible to attach the draining devices by gluing, which may be done after folding and welding of the bag. Then follows the step of welding the plastic web folded in two along the longitudinal welding line 18 which is arranged at the edge of the plastic web being opposite to the folding line 5 and to weld the plastic web folded in two along transverse welding lines 7 which extend transverse to the folding line and are arranged at predetermined distances from each other. In this way several connected plastic bags are formed. It is also possible the weld the plastic web 4 folded in two along a second longitudinal welding line 38 adjacent to the folding line 5. Such a second longitudinal welding line may also be arranged in the case that the plastic bag is produced by two or more separate plastic webs. As is evident from the figure the welds along the transverse welding lines 7 are single. The draining devices 10 will be shown in larger detail in Fig. 4 and are of the type that is described in WO 2010/062247 which comprises a knife member (Fig. 4) which is manoeuvred with a draining part 11 which is rotatable around a rotational axis 12 which in Fig. 1 is perpendicular to the extrusion direction 3. By rotating the draining part 11 the knife member is manoeuvred at the first use to cut open the plastic bag along a cutting line 13 which is essentially parallel with the extrusion direction 3. By essentially parallel is meant that the cutting line deviates no more than 10 degrees from the extrusion direction, preferably no more than 5 degrees and advantageously no more than 2 degrees. After the welding the bags 1 are completely sealed and are delivered in suitable lengths to the location where they are to be filled with liquid. On the location where the bags are to be filled with liquid the bags are cut off close to a weld, wherein an opening in the bag is formed at the same tine at the bag is cut off. By the bag having been sealed from the manufacturing until it is cut off, there is no risk that it could have been contaminated which is an advantage for example if the plastic bag is to be used for foodstuff. Fig. 3 shows schematically an assembly for manufacturing of plastic bags according to the invention. A plastic roll 2 functions as a store from which a plastic web 4 is fed to a welding device 19 for welding of the draining device 10. Then the plastic web is conveyed to a folding device 20 which folds the plastic web 4 in two. The plastic web folded in two is then conveyed to a welding device 21 which welds the plastic web folded in two along the longitudinal welding line 18 and possibly also along the second longitudinal line 38 and along the transverse welding lines 7. The welds along the transverse welding lines extend all the way to the welds along the longitudinal welding lines so that sealed plastic bags are formed which are delimited by the welds along the transverse welding lines and the longitudinal welding lines. Finally, the plastic web is conveyed to a cutting device 22 which cuts the plastic web in suitable lengths with a number of plastic bags in each cut off part.

Fig. 4 shows schematically an alternative assembly for manufacturing of a plastic bag from two plastic webs 35, 36. A first plastic web 35 is fed from a first roll 33 and a second plastic web 35 is fed from a second roll 34. The second plastic web is conveyed to a welding device 19 for welding on the draining device 10. Then both plastic webs are conveyed to a welding device 21 which welds together the plastic webs along the longitudinal welding line 18, along the second longitudinal welding line 38 and along the transverse welding lines 7. Finally the plastic web is conveyed to a cutting device 22 which cuts the plastic web in suitable lengths. Fig. 5 shows in larger detail a plastic bag 1 with a draining device 10 according to an embodiment of the present invention. The draining device 10 comprises a housing part 23 which is attached to the plastic bag 1 and a draining part 1 1 with a rotational part 24 which is suspended in the housing part 23 rotatable around the rotational axis 12 and a draining tube 25 which extends from the rotational part and which is attached to the rotational part. The draining part 11 comprises an opening 26 through which liquid may be drained and a handle 27 which facilitates the manoeuvring of the draining part 11. The plastic bag 1 comprises a part of a plastic web 4 folded in two and is welded along a longitudinal welding line 18 which extends along the side of the plastic bag 1 being opposite to the folding line 5 and along a transverse welding line 7 between the folding line 5 and the longitudinal welding line 18.

In the description above the plastic web has been described as a plastic web with a single plastic layer. It is, however, possible to have the plastic web composed by several different layers with different types of plastic in the different layers. Such a plastic web is shown schematically in cross section in Fig. 6. The method for producing a plastic film with different layers is known from the prior art and will not be described in detail here. The plastic web preferably 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 a second type of plastic which is impermeable to water. Plastics which are impermeable to oxygen rarely have sufficient mechanical strength to function as a single plastic in a plastic bag. Such mechanical strength is given by the two outer layers. The two outer layers may for example be of polyethene. In case the requirements on impermeability to oxygen are not too high a single layer of polyethene may be sufficient. The second and third layers are preferably of a plastic which enables welding.

Fig.7 shows in larger detail partly in cross section a draining device 10 attached to a plastic bag 1 according to an embodiment of the present invention. The draining device 10 comprises a housing part 23 with an attachment surface 28 defining a plane and which is intended to be attached to the plastic bag 1. The draining device 10 also comprises a draining 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 draining part 11 comprises a rotational part 24 which is suspended in the housing part 23 rotatable around the rotational axis 12 which is essentially parallel with the fastening surface 28. The draining part 11 comprises a draining tube 25 which extends from the rotational part 24 and which is attached to the rotational part 24. The housing part 23 comprises a channel 30 towards the rotational part 24 and the rotational part 24 comprises a channel 31 towards the housing part 23. The draining part 11 may be rotated between a closed position in which the channel 31 in the rotational part 24 does not overlap the channel 30 in the housing part 23, and an open position in which the channel 31 in the rotational part 24 overlaps the channel 30 in the housing part 23. The draining part 11 comprises also a knife member 32 which is arranged rotatable around the rotational axis 12. The knife member 32 is arranged with a frictional coupling to the rotational part 24 so that the knife member 32 is rotated when the rotational part is rotated. Preferably, the movement of the knife member 32 is limited so that it stays in the position which provides the largest opening through the opening cut open in the plastic bag 1 even if the rotational part is rotated further. The knife member 32 is arranged to cut open the plastic bag 1 inside the attachment surface 28. In the closed position of the draining part the knife member 32 is arranged inside the plane of the attachment surface 28 so that the knife member 32 is arranged in the chamber 29. The first rotation of the rotational part 24 from the closed position to the open position results in that the plastic bag 1 is cut open along a cutting line 13 which is perpendicular to the rotational axis 12 and parallel with the extrusion direction.

The invention is not limited to the above described embodiments of the invention, which may be modified in many 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 manoeuvrable with separate means even if it is less complicated to let the knife member be connected to the rotational part and its movement.

The knife member in a plastic bag according to the invention may be manufactured of any of many different materials. For cost reasons it is however preferable to manufacture the knife member of plastic. However, not all plastics are suitable. For example polystyrene should be avoided as polystyrene may form splinters at mechanical failure. A suitable material for the knife member has proven to be Acrylonitrile butadiene styrene (ABS). A man skilled in the art may find other suitable plastics which have sufficient strength and hardness to enable manufacturing of a knife member and which at the same time is tough enough to hardly be able to crack into splinters.

Claims

1. Method for production of a plastic bag (1) for liquid comprising the steps of providing at least one plastic web (4) which is extruded in an extrusion direction (3), and arranging said at least one plastic web (4) in at least two layers, characterized in that the method comprises the steps of welding together said at least two layers along at least one longitudinal welding line (18) which essentially follows the extrusion direction (5), welding together said at least two layers along transverse welding lines (7) which extend transverse to the longitudinal welding line (18), and which are arranged at predetermined distances from each other, so that a number of connected sealed plastic bags (1) are formed, and attaching on the outside of the plastic bag (1) a draining device (10) comprising a knife member (32) which is arranged to cut open the plastic bag (1) along a cutting line (13) at the first use, wherein the draining device ( 10) is arranged so that the cutting line ( 13) is essentially parallel with the extrusion direction (3), wherein the cutting line (13) deviates no more than 10 degrees from the extrusion direction (3), preferably no more than 5 degrees and advantageously no more than 2 degrees.

2. Method according to claim 1, wherein a plastic web (4) is provided which plastic web (4) is folded along a folding line (5) which is parallel with the extrusion direction (3) so that the plastic web (4) becomes folded in two, and wherein the plastic web (4) folded in two is welded at the side of the plastic web (4) folded in two opposite the folding line (5).

3. 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.

4. Method according to claim 1, 2 or 3, wherein the draining device (10) is attached on one of said at least one plastic web before said at least one plastic web is folded or welded.

5. Method according to any one of the preceding claims, wherein the draining device (10) comprises a housing part (23) with an attachment surface (28) and a draining part (11), wherein the draining device is attached to the plastic bag (1) by attaching the attachment surface (28) to the plastic bag (1), so that the housing part (23) forms a chamber (29) together with the plastic bag (1), wherein the draining part (11) comprises a rotational part (24) which is suspended in the housing part (23) rotatable around a rotational axis (12) which is essentially parallel with the fastening surface (28) when the draining device is attached to the plastic bag (1), a draining tube (25) which extends from the rotational part (24) and which is attached to the rotational part (24), wherein the housing part (23) comprises a channel (30) towards the rotational part (24) and wherein the rotational part (24) comprises a channel (31) towards the housing part (23), and wherein the draining part (1 1) may be rotated between a closed position in which the channel (31) in the rotational part (24) does not overlap the channel (30) in the housing part (23), and an open position in which the channel (31) in the rotational part (24) at least partly overlaps the channel in the housing part (23), wherein the knife member (32) is arranged to cut open the plastic bag inside the attachment surface (28).

6. Method according to claim 5, wherein the attachment surface (28) defines a plane and wherein the draining device (10) is arranged on the plastic bag (1) in the closed position of the draining part in which position the knife member (32) is arranged in the chamber (29) inside the plane of the attachment surface (28).

7. Method according to claim 5 or 6, wherein the knife member (32) is arranged frictionally coupled to the rotational part (24) so that the first rotation of the rotational part (24) from the closed position to the open position results in that the knife member (32) rotates so that the plastic bag (1) is cut open.

8. Method according to any one of the preceding claims, wherein the plastic web (4) comprises plastic of at least two different types which are arranged in at least two different plastic layers.

9. Method according to claim 8, wherein the plastic web (4) comprises 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 a second type of plastic which is impermeable to water.

10. Plastic bag for liquid comprising at least one plastic web (4) of extruded plastic arranged in two layers, characterised in that said at least two layers are welded together along at least one longitudinal welding line (18) which mainly extends along the extrusion direction of the plastic web, and said at least two layers are welded together along a transverse welding line which extends transverse to said at least one longitudinal welding line, and which is arranged at one edge of the plastic bag (1), comprising, attached on the outside of each plastic bag (1), a draining device (10) comprising a knife member (32) which is arranged to cut open the plastic bag (1) along a cutting line (13) at the first use, wherein the draining device (10) is arranged so that the cutting line (13) is essentially parallel with the extrusion direction (3) in which the extruded plastic has been extruded, wherein the cutting line (13) deviates no more than 10 degrees from the extrusion direction, preferably no more than 5 degrees and advantageously no more than 2 degrees.

11. Plastic bag (1) according to claim 10, wherein the draining device (10) comprises a housing part (23) with an attachment surface (28) which is intended to be attached 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 draining part (10) comprises a rotational part (24) which is suspended in the housing part (23) rotatable around a rotational axis (12) which is essentially parallel with the fastening surface (28), a draining tube (25) which extends from the rotational part (24) and which is attached to the rotational part (24), wherein the housing part (23) comprises a channel (30) towards the rotational part (24) and wherein the rotational part (24) comprises a channel (31) towards the housing part (23), and wherein the draining part (11) may be rotated between a closed position in which the channel (31) in the rotational part (24) does not overlap the channel (30) in the housing part (23), and an open position in which the channel (31) in the rotational part (24) at least partly overlaps the channel (30) in the housing part (23), wherein the knife member (32) is arranged to cut open the plastic bag inside the attachment surface (28).

12. Plastic bag (1) according to claim 11, wherein the fastening surface (28) defines a plane and wherein the knife member (32) in the closed position of the draining part (11) is arranged inside the plane of the fastening surface (28) so that the knife member (32) is arranged in the chamber (29) when the draining device (10) is arranged on the plastic bag (!)■

13. Plastic bag (1) according to claim 12, wherein the knife member (32) is frictionally coupled to the rotational part (24) so that the first rotation of the rotational part (24) from the closed position to the open position results in that the knife member (32) is rotated so that the plastic bag (1) is cut open.

14. Plastic bag (1) according to any one of the preceding claims, wherein the plastic web (4) comprises at least two different types of plastic in at least two different plastic layers.

15. Plastic bag according to claim 14, wherein the plastic web (4) comprises 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 a second type of plastic which is impermeable to water.

16. Use of a plastic bag produced with the method according to any one of claims 1-9 for a liquid chosen from the group consisting of fruit juice, dairy products, wine and syrup.

17. Use of a plastic bag produced with the method according to any one of claims 1-9 for a liquid chosen from the group consisting of oils, solvents and acids.

18. Use of a plastic bag according to any one of claims 10-15 for a liquid chosen from the group consisting of fruit juice, dairy products, wine and syrup.

19. Use of a plastic bag according to any one of claims 10-15 for a liquid chosen from the group consisting of oils, solvents and acids.