BACKGROUND OF THE INVENTION. The present invention relates -to a method for manufacturing a film to be used for the production of bags which, during a product filling procedure, are formed into closed individual bags. The invention also relates to a bag produced from a substantially endless film which, during a product filling procedure, is formed into closed individual bags. The invention also relates to the film for the produc- tion of a bag according to the invention and the use of a film according to the invention for filling in known packing machines.

It is well known to produce bags, generally to be considered as a sales packa¬ ging and produced from flat film webs which are produced in a single layer or in a tubular shape. Such bags are primarily produced from resin materials in which a closure is obtained by weldings lengthwise and crosswise on the film. However, the invention also relates to bags produced from other materials, including webs of technical textiles, papers, and others.

The prior art bags which are formed into closed individual bags during the filling process will be closed permanently. This means that the bag must be cut or torn open in order to use its contents. If only part of the contents is used, the opening must be reclosed temporarily. This may be accomplished in various ways, e.g. by the use of clips, bands or by folding. This may be undesirable if the goods contained in the bag are exposed to deterioration due to improper or insufficient reclosing. Moreover, an improper or insufficient reclosure may imply a risk that the goods will fall out of the bag during subsequent storage.

The goods contained in the bag may be of many kinds. They may be foods, such as chips, coffee, flour, oats or others. They may also be any kind of grain material such as corn, gravel or others. The goods which are filled into the bags may also have a fully or partially liquid substance, as known e.g. from ketchup, mustard, mayonnaise and others.

Hitherto, the consumers have had the disadvantage of insufficient reclosure. Such disadvantages have so far been insurmountable unless one would use bags with special reclosable arrangements, e.g. zip systems or adhesive systems. Ho¬ wever, such special reclosable arrangements cannot be used in processes where a film is used for the production of bags which are formed into closed individual bags during the filling of goods.

Furthermore, zip systems will be particularly disadvantageous for use in a mass production. Owing to the considerable thickness of a zip compared to a film, it would involve big difficulties to use a film provided with zips when the film is to be conducted through machines by rollers. Furthermore, it would be very difficult to handle film with zips on rolls because of its poor rolling geometry.

It is known, e.g. from the European Patent Application No. 0,032,006, to pro- duce bags in which an adhesive is provided between overlapping parts of a film. However, the film and the bag according to the prior art are produced as in¬ dividual bags, without the filling of goods. The filling of goods is accomplished during a subsequent handling of the individual bags. This is disadvantageous for a broad range of goods since it is desirable to fill them into bags while the bag is being formed.

Although a bag according to the European Patent Application provides the abili¬ ty to be reclosed in a relatively tight and safe way after partial emptying of the bag's contents, this bag would be unsuitable for common filling machines of the so-called VFFS type (Vertical Filling, Forming, Sealing).

It is the object of the present invention to remedy the above-mentioned disad¬ vantages of the prior art by disclosing a method for manufacturing a film to be used in the production of bags, as well as bags which, while being produced, are formed into closed individual bags and which may, during subsequent use, be reclosed and reopened for partial emptying of the bag's contents.

According to the present invention this is achieved by a method of the above-

mentioned type which is characterized in that a continuous and substantially endless film is manufactured, that the film is cut up longitudinally, that the two lateral areas adjacent to the cut are put into an overlapping position, and that between the two overlapping surfaces facing each other an adhesive is applied which is sensitive to pressure and able to glue several times, and that the over¬ lapping lateral areas are put into contact with the adhesive applied between them.

A film which is manufactured in this manner is fit to be handled in packing machines having rollers. Furthermore, the film may be stored in rolls as the variations in thickness across the width of the film are insignificant. The method is further advantageous in that the film may be designed in such a manner as to provide, in the finished bag, safety against unintended access to the bag's con¬ tents without this being noticeable. This is achieved in that in one lateral area and parallel to the cut a line of weakening is formed, preferably a perforation, that in the overlapping position this lateral area is placed in such a manner that it will turn outward in the finished bag, and that the overlapping lateral areas are sealed by a longitudinally extending welding in a position between the per¬ foration and the outmost edge of said lateral area in which said perforation has been maid.

When the film is used for the manufacture of a bag, said bag will have a line of weakening which must be broken before the two overlapping lateral areas can be separated for access to the inside of the bag. Thus, unintended access to the inside of the bag is prevented, which is very desirable, e.g. for bags used as sales packaging in retailing.

It is possible to produce the film by providing the cut and the line of weakening simultaneously with forming the film. Alternatively, this may be accomplished in two subsequent steps. It is also possible to apply an adhesive simultaneously with providing the cut and the line of weakening. Alternatively, these three steps may also be accomplished separately. The adhesive may be applied in a strip in the longitudinal direction of the film simultaneously with providing the

cut. Subsequently, the lateral areas are put into an overlapping position and brought into contact with each other.

It is normally preferred that the adhesive is applied in a separate step prior to forming the cut and the line of weakening. Thus, it is preferred that the adhesi¬ ve is applied in a first step, in which the bag is also provided with a print on the bag as this is accomplished at a speed of conveyance for the film which is very high.

It will also be preferred that the line of weakening or the safety perforation in the bag is made simultaneously with forming the cut whereas sealing the two overlapping parts is only performed in immediate connection with the filling of the bag. In this manner one obtains the least variation in thickness (best rolling geometry) across the width of the wound film.

Forming the film may be performed in a separate machine in which the finished film is wound and in which the resulting roll is subsequently used in a packing machine. Alternatively, the production of the film with overlapping seal may be performed in immediate connection with the packing machine itself.

The bag according to the invention is characterized in that between two closed ends the bag has an overlapping joint which extends parallel to a longitudinal welding of the film's lateral edges, which welding has been made when forming the closed individual bag, and that surfaces facing each other in the overlapping joint are provided with an adhesive of a known type which is able to glue se¬ veral times.

In the bag, a reclosable opening is provided in the sales packing. This opening may be secured against unintended manipulation of the contents if a line of wea- kening, preferably a perforation, is provided in the overlapping joint, and if the two overlapping lateral areas are welded in a position between the line of wea¬ kening and the outer edge of the outward lateral area in the bag.

At the overlapping joint, a closure is provided which is sufficiently tight to be used for foods where sanitary authorities require airtight packaging. The consu¬ mer may open the packaging at the overlapping joint, possibly after first having broken the line of weakening, and empty the bag of the desired amount of go- ods. Thereafter, the packaging may be reclosed at the overlapping joint.

It is preferred for a bag that is formed by providing a welding of the two op¬ posed free edges of the film in a welding seam that the overlapping joint extends parallel with the joint of the two opposed edges of the film and parallel with the side edge of the bag. The two side edges of the film will ordinarily be joined through welding. When the overlapping seal is in a position immediately next to a side edge of the bag, said side edge of the bag may subsequently be seen as a bag top by the consumer. This is achieved through the fact that the reclosable opening of the bag will be situated at one end of the packaging, which also facilitates emptying the packaging of its contents.

The film for use in the manufacture of a bag according to the invention is cha¬ racterized in that in a position between the film's lateral edges at least one overlapping joint has been provided wherein - between two overlapping surfaces facing each other - an adhesive is provided which is of a known type and able to glue several times. The film may easily be used in connection with existing packing machines for the manufacture of the bag, since the variation in thick¬ ness across the film does not prevent the use of the film in existing packing machines. The film is particularly well suited for use in packing machines of the VFFS type.

Thus, with the film according to the invention it is possible to manufacture bags in exactly the same manner as in the filling methods of the prior art without important investments in special machines for the manufacture of the bags.

The manufacture of the film is very simple and subsequent use of the film for the manufacture of bags which are formed during filling is easily accomplished. Thus, a film is produced which is wider than the intended film for use in the

manufacture of the bag. The film is produced with an excessive width corre¬ sponding to the width of the overlap and so the film may be used directly in an existing packing machine.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be further explained with reference to the accompanying drawing, wherein

fig. 1 shows a bag according to the invention, fig. 2 shows a sectional view through the bag according to fig. 1, fig. 3 shows a fragmentary picture of a film according to the invention, after application of adhesive but prior to formation of the overlap¬ ping joint, fig. 4 shows a fragmentary picture of the film shown in fig 3, after for- mation of the overlapping joint, fig. 5 a sectional view along the line V-V in fig. 4, figs. 6-8 show pictures corresponding to figs. 3-5 through a second embodi¬ ment of the film according to the invention, and fig. 9 shows a schematic picture intended to illustrate the production of a bag according to the invention with the use of a film according to the invention.

A bag 1 for foods, e.g. deep-frozen goods, may be designed as shown in figs. 1 and 2. The bag 1 is produced from polyethylene film extruded in a single layer, whereupon the film is assembled and welded in a first welding seam 3 and subsequently in a second transversal welding seam 5, whereupon the bag shape has been formed. After the filling of the contents 7, the bag is closed by a third welding seam 9. Alternatively, the film may be co-extruded or laminated from several layers, which may be in different materials. This may in particular be advantageous for bags in which rigidity in the bag sides is required at the same time as good welding qualities.

In the bag according to the invention there is an overlapping joint 11 consisting

of a first edge area 13, which is the outer edge area and situated on top of anot¬ her edge area 15. The surfaces of the edge areas 13 and 15 which face each other are held together by an adhesive with a relatively weak adhesive capacity and which will not dry. The adhesive further has the quality that the surfaces facing each other may be separated and reclosed.

The overlapping joint 11 extends in the whole of one dimension of the packa¬ ging 1 , as indicated by a dotted line in fig. 1. In the embodiment shown, the welding seams 5 and 9 ensure that an opening may only be formed between the seams 5, 9. However, an embodiment in which the welding seams permit ope¬ ning the joint 11 in the whole of one dimension of the bag may be produced.

When buying goods in bags, such as indicated by the numeral 1, the consumer may manually separate the edge areas 13 and 15, take out the desired amount of the goods 7 and then reclose the joint 11 by pressing the edge areas 13 and 15 together. The closing method used also ensures that the bag may be reclosed airtight after taking out the goods.

A preferred embodiment of the film according to the invention is manufactured after extrusion as a film in one layer, e.g. of polyethylene. The film will nor¬ mally be exposed to graphic treatment in which colours and writing are printed on the film, e.g. as shown in the demarcated fields 21 and 23. The fields 21 , 23 may for example form a coherent text on the package. Simultaneously with the printing, the adhesive is applied in a longitudinal strip 25 and parallel with the lateral edges 17, 19. Subsequently the film is cut transversely, e.g. at the posi¬ tion indicated by arrows 27. Simultaneously with the cutting, the narrowest, cutoff part of the film is led over the strip 25 so that the graphic print in the fields 21 and 23 fit together in a marked position, cf. fig. 4. In this manner, a longitudinal overlapping joint 11 is formed in the length of the film. Then the bag 1 may be produced in the ordinary manner, i.e. first joining the free edges 17, 19 and producing a first welding seam 3, etc.

Figs. 6-8 correspond to figs 3-5 but illustrate a second embodiment of bag. The

parts that are identical in the two embodiments are designated with the same re¬ ference numerals and will not be further explained. The bag shown in figs 6-8 differs in that in the overlapping joint a line of weakening is provided in the form of a perforation 29. The perforation 29 is preferably provided simultane- ously with cutting the film 27. The perforation 29 is provided in the edge area which faces outward in the finished bag 1. The two overlapping edge areas 13, 15 are welded together at 31. The welding 31 extends in a position between the perforation 29 and the outer edge 33 of the edge area 13 in which the perfora¬ tion is provided and which faces outward in the finished bag.

The welding 31 is formed in immediate connection with the filling of the bag. As the welding 31 will result in a variation in thickness, it is not desirable in the film which is wound into a roll that serves to supply a packing machine. The variation in thickness which occurs in the overlapping joint 11 will, however, not result in difficulties in handling the film in traditional packing machines.

The bag 1 which is produced from the film shown in figs 6-8 will prevent unin¬ tended access to the inside of the bag without this being noticeable. Thus, in order to get access to the inside of the bag, it is necessary to break the perfora- tion 29 and separate the overlapping edge areas 13, 15.

Fig. 9 shows schematically the production of a bag according to the invention in a VFFS packing machine. The packing machine itself is illustrated by a filling pipe 35 through which material is filled into the bags 1. which are formed by advancing the film 37 in the direction of arrows 39. The film 37 is led around the filling pipe 35 and folded in a known manner around the pipe, as indicated at 41. Simultaneously with the filling, the longitudinal welding seam 3 and the transverse welding seams 5 and 9 are provided. The film 37 is supplied to the packing machine from a supply roll 43 which has a rolling geometry that per- mits handling in traditional packing machines. The film shown in fig. 9 corre¬ sponds to the one shown in figs. 3-5. Alternatively, a film 37 with a perforation 29 may be used, as shown in figs. 6-8. In the latter case, the welding 31 is pro¬ vided at a position marked by an arrow 45. During production the film 37 is

advanced in a manner known per se synchronously with welding jaws which form the transverse welding seams 5 and 9 having mutual intervals 47. This production will be well-known to those skilled in the art and accordingly will not be explained further.

Alternative embodiments of the film according to the invention are possible. Thus, the film may be produced as a tube of film, where an overlapping joint in longitudinal direction is provided by applying adhesive, cutting and joining, in principle as indicated above. The subsequent production of the bag with a tube- shaped film may be done as with the plane film, leaving out the first welding seam 3 as unnecessary. Furthermore, it would be possible to apply a strip of ad¬ hesive across the film whereupon the overlapping joint is formed by cutting and joining.