GB2100703A

GB2100703A - Plastics bag

Info

Publication number: GB2100703A
Application number: GB08216914A
Authority: GB
Inventors: Gianfranco Luoni
Original assignee: Elba SpA
Current assignee: Elba SpA
Priority date: 1981-06-19
Filing date: 1982-06-10
Publication date: 1983-01-06
Also published as: IT1137100B; IT8122441A0; FR2508020A1; DE3221282A1

Abstract

Heat sealed plastics bags for domestic use have the bag bottom obtained by longitudinal foldings and transverse sealing of a tubular plastic film so as to obtain a bottom which is shorter and thicker than the conventional plastic bag bottoms, this plastic bag taking a so called "tomato" configuration once it is filled. <IMAGE>

Description

SPECIFICATION Heat sealed plastic bag for domestic use and the method of its manufacture This invention relates to a heat sealed plastic bag for domestic use and the method of manufacturing such a bag.

Plastic bags for domestic use generally made of polyethylene, polypropylene and similar plastic-materials intended to be used, for example, in the collection of refuse, garbage or the like, are well known. These bags are made generally starting from a coil of tubular plastic film, wound in a flattened condition or with longitudinal side foldings, from which the single bags are heat-sealed and cut across the longitudinal axis of the tubular film, in order to form the sealed closure of the bag bottom, while the side opposite the bag bottom is kept open to form the bag aperture.

Generally, the final width of the flattened bag corresponds to the initial tubular film width so that the bottom sealing machine must have a corresponding height for accomodating the tubular film. Bags produced by means of the conventional sealing and cutting methods show a sealing line extending along all the bag bottom width and forming in a way the bag bottom proper. When a plastic bag formed either of a simple tubular film or of a tubular film with longitudinal side foldings is being filled, a distribution of the stresses induced by the weight of the materials contained therein occurs, which stresses concentrate along the sealing line and at the end corners thereof so as to induce relatively high tensions in the plastic material forming the bag, which in some circumstances can lead to ruptures and tearings of the bag walls.

The main object of this invention is to overcome these and other drawbacks by providing a bag for domestic use formed of heat sealed plastic material and intended for example to be used in the collection of refuse, garbage or the like, characterized in that, by starting from a coil of a plain tubular plastic film or of a tubular plastic film provided with longitudinal side foldings, the bag has its own bottom formed by the sealing region extending across the longitudinal feeding direction of the tubular film and therefore the longitudinal axis of the flattened and empty bag which is comprised of at least four main overlapping walls, preferably eight main overlapped walls, this wall overlapping resulting in that, before the tubular film comes to the sealing and cutting station, it has been longitudinally folded, namely along its feeding direction in such a manner that the width of the longitudinally folded tubular film coming to the sealing and cutting station is substantially lesser than the initial width thereof.

Therefore, the sealing region forming the bottom of the so obtained bag is shorter and thicker than that of conventional plastic bags in such a manner that, when this bag is filled and therefore put in stretched conditions, the stresses, rather than being concentrated and compelled to act at the sealing region, are evenly distributed on the bag main walls, which, when the bag is filled, form together a unique main wall.

The method of manufacturing the bags according to this invention is characterized in that, by starting from a coil of a simple flattened tubular film or of a tubular film provided with longitudinal side foldings and before this tubular film comes to the sealing and cutting station of the bag bottoms, at least a longitudinal folding is made on the tubular film, which is performed along the feeding direction of the tubular film and therefore along the longitudinal axis of the bags in such a manner that the tubular film comes to the above mentioned station in longitudinally folded condition with its main walls being substantially overlapped, the longitudinal foldings of the tubular film being at least two with the result that, at the sealing station eight main overlapped walls will be present.

The folding method of the tubular film according to this invention is carried out by suitable means arranged between the initial coil and the sealing station, which are adapted to impart to the tubular film the necessary longitudinal folding or foldings to achieve the desired bottom configuration, these folding means being preferably arranged on oblique plans in order to compel the tubular film unwinding from the associated coil to follow a tortuous path.

The folding means can be formed of oblique triangular elements cooperating with associated guide rollers and/or of means forming a folding on both the longitudinal sides of the tubular film.

Advantageously, the tubular plastic film is first folded along its longitudinal center line, so as to have a symmetrical folding of the tubular film resulting in four main overlapped walls, and then the tubular film is again folded along the new longitudinal center line so as to have a tubular film formed of eight overlapped main walls, in such a manner that the resulting width of the tubular film at the sealing station corresponds to 4 of the initial width thereof.

According to another method, the tubular plastic film is first longitudinally folded by simultaneously acting on both the opposite longitudinal edges thereof so as to obtain a folded tubular film having a width which is one half of the initial width and the the so folded tubular film is again folded along its new longitudinal center line in order to obtain a tubular film having a width corresponding to a of the initial width thereof.

These and other features of the present invention will be now more apparent from the following description taken in connection with the accompanying drawings, the description and the drawings being given by way of example only and being therefore not intended to limit the scope of the invention In the drawings: Figure 1 shows a bag obtained from a simple plastic tubular film in its empty and flattened condition.

Figure 2 shows a bag obtained from a longitudinally folded plastic tubular film, also in its empty and flattened condition.

Figure 3 is a diagrammatic view of a first way of carrying-out the longitudinal folding operation of a simple tubular film from the associated coil for obtaining bags provided with narrow and thick bottom according to the invention.

Figure 4 shows an alternative way of carrying-out the method of Fig. 3.

Figure 5 is a diagrammatic perspective view of a bag according to the invention in its filled condition.

Figure 6 is a view of the bag of Fig. 1 in its filled condition, and Figure 7 shows the bag of Fig. 2 in its filled condition.

Referring now to the drawings and particularly to Fig. 3, A designates a coil of plain tubular plastic film, which of course may also be provided with longitudinal side foldings as shown in Fig. 2.

From this coil the tubular film B is unwound, which is moved in the direction of the arrow X by means not shown in the drawings.

In the first path extending from the line 10 to the roller 12, the tubular film B is flattened as indicated in B1 so as to present two equal and opposite main walls 14-16 which have been indicated slightly spaced apart for clarity of the drawings but which actually are in abutting relationship to each other. C and D designate the longitudinal folding means employed in this case, which are formed of oblique triangular elements cooperating with associated rollers 12-18 and 20-22 arranged in oblique relationship to each other.

When the tubular film B passes over the roller 1 2 and therefore on the oblique triangular element associated thereto, it is folded along its longitudinal center line 24, being guided by the rollers 18, the symmetrical longitudinal folding of the tubular film occurring in the path between the roller 1 2 and the rollers 18.

At the exit from the rollers 1 8. the width L of the initial tubular film has been reduced by one half since the tubular film B has taken the configuration B2, being folded according to the above mentioned way. Then, the tubular film already two-folded along the folding line F forming four main overlapped walls is again folded by the elements D along the center line 26 so that, at the exit from the guiding rollers 22, the width of the tubular film in the configuration B2 will be again halved, with the tubular film taking the final configuration B3, the width of which will be 4 of the initial 4 width L.

With this configuration B3 the tubular film will have eight main overlapped walls 28-30, 32-34, 36-38 and 40-42 deriving from the initial main walls 14-16 which have been double folded as discussed hereinbefore.

In the practice, the method according to the invention consists in providing the tubular film with a first curved edge F forming the fold along the center line 24 and then with a second curved edge G forming the fold along the line 26.

As it is seen, the longitudinal folding elements C-D are arranged on different and oblique levels so that the path of the tubular film B is tortuous with the initial path 44 parallel to the final path 46; in the initial path 44 the overlapping of the two main walls 14-16 only occurs, while in the final path 46 the overlapping of the eight main walls 28 to 42 occurs.

By keeping this double folded configuration B3. the tubular film comes to the bag bottom sealing and cutting station, not shown.

In this station, the heat sealing of the bottom P of the bag N obtained according to the invention is performed in the same manner as the sealing of the bottoms of the conventional bags H-M, this bottom P being much narrower and thicker that the bottom 0 of the conventional bags. In fact, while the conventional bag bottom is formed by a sealing line 52 connecting the two main walls 16-14 only, according to the invention the bottom P is formed by a sealed region including the eight main walls 28 through 42 which have a width corresponding to 4 of the width of the main walls 14, 16.

It is also to be noted that while in the filled condition of Figs. 6 and 7 the weight of the content of the conventional bags concentrates the stresses at the sealing lines 52 and particularly at the corners 54-56 with the result that breakings or tearings of the bag can occur. the new bag N, once it is filled, will take at the bottom P a particular so called "tomato" configuration, so that the single walls 28 through 42 are stretched in such a manner that the dangerous stresses are distributed along a strip Z, thereby reducing the pressure exerted on the bottom P and avoiding the danger of ruptures and tearings. It is also to be noted than another advantage offered by the bag N formed according to the described method is to permit small sized sealing machines to be used in order to perform the sealing operation of the bottom P and the cutting operation of the bags, since the final width of the tubular film configured as in B3 is 41 of the initial width of the tubular firlm configured as in B. If, in order to obtain a conventional bag H or N having a width of 700 mm a sealing machine having a height of 800 mm is employed, then the same sealing machine permits four strips of longitudinally folded bags to be accomodated.

It is also to be noted that the minimum sizes exhibited by this bag N will reduce the packaging operations, thereby facilitating the operator work.

Referring now to Fig. 4, there is shown another way of carrying out the method of longitudinal folding the tubular film B. For this purpose, in place of the first folding elements C.in the form of an oblique triangle, a double folding device G1 is employed, the second folding elements D being still present. In this case, the device G1 is formed of a pair of Vshaped opposite folding elements 11-13, which longitudinally fold the side edges 27-25 of the tubular film B so that in the path between the device G1 and the roller 20, the width L of the tubular film is halved since the edges 27 and 25 are turned below the tubular film, which therefore takes the configuration B2, having the curved edges R-S.

As the tubular film is proceeding along its path, it will be converted from the configuration B2 to the configuration B3 in which it is supported by the guiding means D which carry out on the tubular film a second longitudinal folding along the center line of the configuration B2, so that eventually the tubular film has, in addition to the curved edges R-S, also the curved edge T, in this case there being eight main overlapped walls too, which are arranged in a different way with respect to the configuration shown in Fig. 3, this being due to the different folding manner as that instead of two curved edges only, in this case there are three curved edges.

Also in the folding manner shown in Fig. 4, the tubular film in the folded configuration B3 comes to the bottom sealing station, not shown, where the bag bottom P is formed followed by a cutting operation and the formation of a new bag N. This bag with its own bottom formed by eight main overlapped walls has the same characteristics of configuration and strength as the preceding bag, with all the advantages thereof.

In the practice the manufacturing and construction particulars can be changed without departing from the scope of the invention.

Claims

1. Bag for domestic use formed of heat sealed plastic material and intended for example to be used in the collection of refuse, garbage or the like, characterized in that, by starting from a coil of a plain tubular plastic film or of a tubular plastic film provided with longitudinal side foldings, the bag has its own bottom formed by the sealing region extending across the longitudinal feeding direction of the tubular film and therefore the longitudinal axis of the flattened and empty bag which is comprised of at least four main overlapped walls, preferably eight main overlapped walls, said wall overlapping resulting in that, before the tubular film comes to the sealing and cutting station, it has been longitudinally folded, namely along its feeding direction in such a manner that the width of the longitudinally folded tubular film coming to the sealing and cutting station is substantially lesser than the initial width thereof.

2. Bag according to claim 1, characterized in that the sealing region forming the bottom of the so obtaining bag is short-er and thicker than that of conventional plastic bags in such a manner that, when this bag is filled and therefore put in stretched conditions, the stresses, rather than being concentrated and compelled to act at the sealing region, are evenly distributed on the bag main walls, which, when the bag is filled, form together a unique main wall.

3. Bag according to claim 1, characterized in that, when it is in a filled condition, it takes a so called "tomato configuration" since, with the plastic film in a stretched condition, from the small sealing region of the bag bottom bulges of plastic material extend, which are disposed, by starting from the bag bottom, in the form of slices converging in a single wall formed by the plastic film.

4. Method of manufacturing bags for domestic use in a plastic material intended, for example, to be used in the collection of refuse or the like, characterized in that, by starting from a coil of a simple flattened tubular film or of a tubular film provided with longitudinal side foldings and before this tubular film comes to the sealing and cutting station of the bag bottom, at least a longitudinal folding is made on the tubular film, which is performed along the feeding direction of the tubular film and therefore along the longitudinal axis of the bags in such a manner that said tubular film comes to the above mentioned station in longitudinally folded condition with its main walls being substantially overlapped, said longitudinal foldings of the tubular film being at least two with the result that, at the sealing station eight main overlapped walls will be present.

5. Method according to claim 4, characterized in that suitable means arranged between the initial coil and the sealing station are provided, which are adapted to impart to the tubular film the necessary longitudinal folding or foldings to achieve the desired bottom configuration, said folding means being preferably arranged on oblique levels in order to compel the tubular film unwinding from the associated coil to follow a tortuous path.

6. Method according to claim 4, characterized in that said folding means are form-ed of oblique triangular elements cooperating with associated guide rollers and/or of means forming a folding on both the longitudinal sides of the tubular film.

7. Method according to claim 4, characterized in that said tubular plastic film is first folded along its longitudinal center line, so as to have a symmetrical folding of the tubular film resulting in four main overlapped walls.

and then said tubular film is again folded along the new longitudinal center line so as to have a tubular film formed of eight overlapped main walls, in such a manner that the resulting width of the tubular film at the sealing station corresponds to 4 of the initial width thereof.

8. Method according to claim 4. characterized in that said tubular plastic film is first longitudinally folded by simultaneously acting on both the opposite longitudinal edges thereof so as to obtain a folded tubular film having a width which is one half of the initial width and then the so folded tubular film is again folded along its new longitudinal center line in order to obtain a tubular film having a width corresponding to 4 of the initial width thereof.

9. A bag for domestic use formed of heat sealed plastic material and intended for example to be used in the collection of refuse, garbage or the like, arranged, constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.

1 0. A method of manufacturing bags for domestic use in plastics material intended, for example, to be used in the collection of refuse or the like, substantially as hereinbefore described with reference to the accompanying drawings.