CH637078A5 - PLASTIC BAG WITH AT LEAST ONE BELLOWS AND ITS MANUFACTURING METHOD. - Google Patents

Description

The invention relates to a plastic bag which can be heat sealed with at least one bellows and its manufacturing method.

Methods of making plastic bags with bellows sides and sides are well known. U.S. Patents Nos. 4046065, 3980225,3319540, 3395622 and 3839128 describe certain typical prior art processes for the manufacture of plastic bellows pouches.

In the prior art, it appeared that the bottom of plastic bags with bellows had two weak points located at the intersections of the central fold line of the bellows and the lateral edges. A previous solution to this problem consists in using diagonal heat-sealing zones, descending from the weak points towards the bottom of the sachet by forming a certain angle with this bottom. The diagonal heat-sealing zones can take two different forms. If they join the four thicknesses of the sachet together, the bellows is restricted and the sachet cannot open completely, so that its ability and ability to hold in a standing position are affected.

If the diagonal heat-sealing zones join only two adjacent thicknesses of the sachet rather than the four thicknesses, a separation plate must be used during the sealing operation. The use of a separate plate placed between the different thicknesses prevents the heat-sealed diagonal area from reaching and reinforcing the weak sealing points, so that the effectiveness of the diagonal sealing cannot be total. In addition, the use of a separate plate requires that the heat sealing be carried out independently on each side of the bag, which has the effect of increasing manufacturing and equipment costs.

Likewise, weaknesses have been discovered in the side bellows pouches and this problem has also been addressed by diagonal heat sealing.

The invention can be implemented inexpensively and is surprisingly effective in reinforcing plastic bags with bellows.

The sachet according to the invention is defined by claim 1.

In general, each heat-sealed point is preferably in the form of a semicircle having a diameter disposed along the corresponding lateral edge and divided approximately in its middle by the central fold line. This point heat-sealed zone can take other forms, for example annular, triangular, hexagonal, polygonal, etc. shapes.

The plastic bag may include a closing device allowing it to be opened and closed. This device can be any of the devices of the prior art or the device described in United States patent application No. 892432, filed March 31, 1978.

The invention also relates to a method for manufacturing a sachet, which is defined in claim 8.

The heat-sealed areas are preferably spaced a predetermined distance equal to the width of the bag, and they preferably have a circular shape.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples and in which:

fig. 1 is an elevation of the plastic bag according to the invention;

fig. 2 is a section along line 2-2 of FIG. 1;

fig. 3 is a perspective view of the plastic bag of FIG. 1, shown in the open position;

fig. 4 is a diagram of an apparatus implementing the method of the invention;

fig. 5 is a schematic elevation showing a detail of the operations indicated in FIG. 4, and fig. 6 is an elevation of a variant of the plastic bag according to the invention.

The invention will be described with reference to FIGS. 1 to 6 in certain embodiments chosen by way of nonlimiting examples.

The plastic bag according to the invention may optionally include a closure device disposed at its end

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637,078

opened. Fig. 1 shows an embodiment comprising a closure device 10. The side walls 11 of the bag are made of material which can be heat-sealed, and the bottom 12 with bellows, as shown in FIG. 2, is constituted by a part folded inwards along a central and longitudinal line 13 and along external lines 15.

According to prior practice, the side edges 14 are formed during a cutting and sealing operation. Thermosealed point zones 16 are formed at the intersections of the central fold 13 and the lateral edges 14 in order to reinforce the bottom 12 with bellows, in particular when the sachet is open and loaded and the bottom 12 is subjected to a certain load . The heat-sealed zones 16 join together the four thicknesses of the bottom 12 with bellows, as shown in FIGS. 2 and 3.

Fig. 4 schematically shows an apparatus implementing the method of the invention for producing the plastic bag according to the invention. In general, the production of a plastic bag with bellows bottom is known to those skilled in the art.

Thin strips 17 of plastic material are cut, for example, from a coil 18 of material which can be heat-sealed. In its simplest form, the strip 17 can consist of a single thickness. However, this strip 17 can also consist of several layers or thicknesses, provided that the two outer thicknesses can be heat sealed to allow the production of the plastic bag according to the invention. A device 19 folds the strip 17 in the middle and thus forms a part folded inwards along a central and longitudinal line to form a bellows. The device 19 is well known to those skilled in the art and described, for example, in United States patent No. 3059549. The strip 17 is preferably folded in the middle, but it can be desirable, for certain uses, to fold the strip so that the plastic bag finally obtained has a side wall projecting from the other side wall.

A closing device can be fixed by means of an apparatus 22 to the folded strip 21 coming from the device 19, in accordance with the previous methods, or else the strip 21 can pass directly into a point heat sealing apparatus 23, intended to reinforce the bottom with bellows. The point heat sealing process is well known to those skilled in the art. The point heat-sealing zones 25 are spaced apart by a distance equal to the width of the sachets to be produced. The heat-sealed strip 24 is then cut and sealed in a device 26 so that the plastic bag according to the invention is obtained.

Fig. 5 shows the heat-sealed strip 24 on its arrival in the device 26 and the bag 27 ejected from the device 26. The cutting and sealing operations consist in substantially cutting the heat-sealed points 25 in their middle, as shown in FIG. 5.

The surprising improvement obtained with the process of the invention can be appreciated on reading the following test results.

Sachets or bags with bellows bottom in the so-called 5 1 dimension were produced. These sachets were produced using a film of low density polyethylene having a thickness of 0.044 mm.

Their width is 26.5 cm and their depth is 28 cm, the depth of the bottom bellows being 5 cm. The bags are fitted with interlocking closures. Out of a total of 104 sachets produced, half are produced by implementing the method of the invention, while the sachets of the other half do not have any reinforcement and are produced according to the prior art. Each sachet is loaded with 11 of water, closed by means of the interlocking device and released, in a standing position, from a height of 1.2 m in order to fall on a hard surface. The deterioration of each sachet is then examined.

Among the 52 sachets produced according to the invention, only one showed deterioration, while 10 of the 52 sachets produced according to the prior art showed deterioration.

These results show that the sachets produced according to the invention are significantly superior to the anterior sachets which are not reinforced by a point heat sealing operation.

Fig. 6 shows another embodiment of the invention, namely a plastic bag comprising lateral bellows. The side walls 30 are made of material which can be heat-sealed. The side bellows 31 are formed by folding the material inwards along central lines 32 and outside lines 33. According to prior practice, a sealed edge 34 is produced so as to form a skirt 36. The heat-sealed points 37 are located at the intersections of the central fold lines 32 and the heat-sealed edge 34, in order to reinforce the side bellows 31.

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2 drawings sheets

Claims (10)

637,078 2 1. Plastic bag, characterized in that it comprises two side walls (11; 30) of material which can be heat sealed, the side edges of the walls and the edges of the bottom of the walls being connected to each other according to two different arrangements, the first arrangement consisting of a heat-sealed connection along an edge (14; 34), the second arrangement consisting of at least one bellows (12; 31) obtained by folding part of the walls (11; 30) towards the interior along a central line (13; 32) and exterior lines (15; 33), the or each heat-sealed connection (14; 34) of the first arrangement being approximately perpendicular to the exterior fold lines (15; 33) in order to forming the bag, a point heat seal (16; 37) being produced at a certain distance from the outer fold lines and being located at the intersection of the central fold line (13) and the edge (14) in order to join together the four thicknesses of sachet material. 2. Bag according to claim 1, characterized in that it comprises a closure device (10) close to its open end. 3. Bag according to one of claims 1 or 2, characterized in that the heat-sealing point (16; 37) has the shape of at least part of a circle, or else a triangular, rectangular or any other polygon shape. . 4. Bag according to one of claims 1 to 3, characterized in that the lateral edges of the walls (11) are connected according to the first arrangement with a heat-sealed connection along an edge (14) and that the edges of the bottom of the walls are connected in the second arrangement by at least one bellows (12). 5. Bag according to claim 4, characterized in that the heat-sealing point (16) has the shape of a semicircle which is arranged so that its diameter is located along the near lateral edge (14). 6. Bag according to one of claims 1 to 3, characterized in that the edges of the bottom of the walls (30) are connected according to the first arrangement with a heat-sealed connection (34) and that the lateral edges of the walls are connected according to the second arrangement with a side bellows (31) on each side. 7. Bag according to claim 6, characterized in that the heat-sealed connection of the bottom (34) is made at a certain distance from the bottom edges of the walls so that the bag has a skirt (36) which exceeds the heat-sealed connection (34) . 8. A method of manufacturing a plastic bag with at least one bellows according to claim 1, comprising using a material which can be heat sealed, folding inwards this material along a central line (13; 32) and outer lines (15; 33) in order to form a bellows, and to heat-seal along at least one edge approximately perpendicular to the central fold line to form a sachet, the method being characterized in that it also consists to make a heat-sealing point at a certain distance from the outer fold lines and at the intersection of the central fold line and said edge, in order to join together the four thicknesses of material constituting the bag. 9. Method according to claim 8 for the manufacture of a bag according to one of claims 4 or 5, characterized in that it consists in using a strip of material (17) in the form of a continuous sheet with substantially parallel edges, to fold this strip so that its edges are close to each other and arranged approximately parallel to each other, to fold inward part of the strip to establish the center line in the longitudinal direction, to make the heat-sealing points (25) at points spaced along the center line, and to cut and seal (fig. 5) the strip transversely, passing through the heat-sealing points, in order to form the lateral edges of the sachet. 10. Method according to claim 8, characterized in that it consists in fixing a closure device (10) on the strip so that the bag obtained can be closed.