Apparatus for manufacturing a web of plastic bags

Abstract

A web of interconnected plastic bags with gusset folds. Each bag is provided with first fold part seals (8, 9, 10, 11) and with second fold part seals (13, 14, 15, 16). Additional seals (36) extend parallel to fold edges of the foil and are connected with subsequent first and second fold part seals. The additional seals (30) are in the region between inner (4, 4a) and outer (2, 3 and 2a, 3a) fold edges.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a web of a plurality of interconnected plastic bags with longitudinal gusset folds, at least comprising a central and two outer longitudinal gusset fold edges which bound a first and a second gusset fold part, by providing a continuously supplied tubular plastic foil by heatsealing with a first transverse bottom seal which extends across the entire width of the tubular foil and moving the tubular foil over a predetermined distance to another sealing position.

2. Description of the Prior Art

A method of this type has been used in the prior art. In the prior art methods the first transverse bottom seal is produced by heatsealing the various different foil layers across the entire width of the bag after having applied first and second fold part seals slopingly extending with respect to one another, preferably under an angle of 45.degree., at both ends of the bag.

The first fold part seals contact the first transverse bottom seal so that a filled bag can be given a block shape at the bottom side. The second fold part seals likewise form, together with a final heatseal to be applied, a block bottom, thus causing a filled bag to have a block shape at either side.

The difficulty with the said prior art method is, that it is inappropriate, as the quality of the first transverse bottom seal leaves much to be desired, which is inherent with the fact that in a heatsealing process two foil layers have to be heatsealed to each other in the central part of a tubular foil web, whilst four foil layers have to be heat-sealed to each other in gusset fold parts. Especially the transition from the two-layer-seal seal toward the four-layer-seal will involve problems and particularly a weakening of the foil material.

SUMMARY OF THE INVENTION

In view of the foregoing factors and conditions of the prior art it is a primary object of the present invention to provide a method overcoming these drawbacks.

According to the present invention this aim is attained in that

(a) a tubular foil is provided at both sides with at least bottom fold part seals, each bottom fold part seal obtained by heatsealing a gusset fold part to the opposite outer foil layer, said bottom fold part seals extending from an outer gusset fold edge to the nearest central gusset fold edge;

(b) subsequently the tubular foil as obtained under step (a) is moved over a predetermined distance and immediately after having reached another sealing position a transverse bottom seal is formed by simultaneously heatsealing the opposite foil layers, extending between the central gusset fold edges and opposite bottom fold part seals to each other.

It has appeared that in this manner a first transverse bottom seal is obtained of a much better quality than before, as according to the present invention only two layers need be interconnected across the entire width of the tubular foil layer, said layers consist of superimposed central tubular foil layers of the tubular foil and the bottom fold part seals which are now integrated while forming the first transverse bottom seal.

As forming the first transverse bottom seal is now less timeconsuming than in prior art methods, the production speed can be indreased. Actually, when heatsealing the first transverse bottom seal in the second step, heat is employed which was added to the material in the first step on forming the bottom fold part seals, so that less heat need be supplied during the second step, thus allowing an economy on the time of heatsealing of about 20%, or in other words, energy is saved.

Moreover, the reduced sealing time allows a longer cooling period before coiling the web. In this respect it should be noted that during coiling the tubular foil is subjected to a stretching load which might tear an insufficiently cooled heatseal. This last mentioned problem is now overcome by the present invention.

A preferred embodiment of the present invention comprises the following steps:

a. At both sides of the tubular foil, two first fold part seals are formed, whereby each first fold part seal always connects an outer foil layer with an opposite gusset fold part.

b. At a predetermined distance from said first fold part seals always at least two second fold part seals are formed at both sides of the tubular foil, which second fold part seals connect an outer foil layer part with the opposite gusset fold part.

c. First and second fold part seals are formed between the central and outer longitudinal fold part seals, in the direction of the nearest bag end.

d. The first fold part seals or their extensions are formed to intersect the first transverse bottom seal, substantially in the area near the intersection of a first transverse bottom seal with the central longitudinal gusset fold edges.

e. Forming bottom fold part seals, and

f. Forming said first transverse seal after said first and second fold part seals have passed the sealing zone for forming the first transverse bottom seal.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims.

Other claims and many of the attendant advantages will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts throughout the figures.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first web of plastic bags comprising a plurality of interconnected plastic bags according to the present invention;

FIG. 2 shows the members for forming first and second fold part seals;

FIG. 3 is a tubular foil comprising first, second and bottom fold part seals as obtained in this manner;

FIG. 4 shows how first transverse bottom seals are formed with the present apparatus;

FIG. 5 is the web during the formation of the first transverse bottom seals, and

FIG. 6 is a variant of the web during its formation.

DESCRIPTION OF A PREFERRED EMBODIMENT

Initially referring to FIG. 1, a web of bags in accordance with the present invention comprises consecutive plastic bags 27 with longitudinal gusset folds, each bag 27 including two outer longitudinal gusset fold edges 2, 3, 2a, 3a respectively and a central longitudinal gusset fold edge 4, 4a respectively.

One end of the bag is provided with a first transverse bottom seal 12, so that the superimposed web foil layers 1a, 1b, are at least interconnected in the region between the central longitudinal gusset fold edges 4, 4a.

As can be seen, the first transverse bottom seal 12 also extends upon the outer longitudinal gusset fold edges 2, 3, 2a, 3a, whereby in first instance the superimposed foil layers 1a and 1b are interconnected with each other, whilst the foil layers 1a and 1b and first gusset fold part 5 and second gusset fold part 6 are all interconnected.

In order to give the completed bag a blockbottom-shape, a first fold part seal 8 extends from intersection 8a of the transverse bottom seal 12 with the central longitudinal gusset fold edges 4, 4a to the outermost longitudinal gusset fold edges 2, 3 and 2a, 3a. In a flat condition of the bag a second fold part seal 9 is situated below said seal, said second fold part seal 9 extending in a manner corresponding with that of the fold part seal 8.

At the other side of the bag also similar first fold part seals 10, 11 extend between the intersection 8a' of the first transverse bottom seal 12 with the central longitudinal gusset fold edge 4a and a point upon one of the outer longitudinal gusset fold edges 2a, 3a. The first fold part seals 8, 9, 10 and 11 extend advantageously under an angle of 45.degree. with respect to the outer longitudinal gusset fold edges.

At the other end the bag is provided with second fold part seals 13, 14 which extend from the outer longitudinal gusset fold edges 2 and 3 to upon the central longitudinal gusset fold edge 4, whilst fold part seals 15 and 16 extend from the longitudinal gusset fold edges 2a and 3a to upon the central longitudinal gusset fold edge 4a.

The second fold part seals 13, 14, 15, 16 appropriately extend under an angle of 45.degree. with respect to the extension of the line interconnecting the end points 17 and 18 of the aforementioned four second fold part seals 13, 14, 15 and 16.

Referring now to FIG. 3, the first step is shown of forming a web of plastic bags in accordance with the present invention, To that end the bag is provided with first and second fold part seals 8, 9, 10, 11 and 13, 14, 15, and 16. In order to prevent a heatsealing of for instance a gusset fold part 5a together with a second gusset fold part 6a, a separating means 26, for instance a Pertinax sheet, is disposed between said gusset fold parts 5 and 6 and 5a and 6a. The heatsealing members 25a, 25b will then form the desired fold part seals. Said seals may be produced in about 1,5 sec. (see FIG. 2).

Simultaneously with forming the first fold part seals, bottom fold part seals 23, 24 and 21, 22 are applied at either side of the tubular foil, which bottom fold part seals 21, 22 and 23, 24 intersect the first fold part seals 10, 11 and 8, 9 at the inner longitudinal gusset fold edges 4a, 4.

As the respective superimposed fold part seals are not yet sealed to each other, the separating means 26 need not be removed during transport of the tubular foil over a predetermined distance A to another sealing zone or another position, which strongly facilitates the processing of said tubular foil.

After having displaced the tubular foil over a distance A from a first transverse bottom seal, a new first transverse bottom seal 12 is formed by heatsealing to each other the foil web parts 1a and 1b between the intersections of the first and bottom fold part seals, while simultaneously the still hot superimposed bottom fold part seals 23, 24, 21, 22 are likewise heatsealed to each other.

In order to form the first transverse bottom seal 12, a support 19 is used, and a heatsealing bar 20. It will be obvious, however, that said support 19 may also be a heatable support.

The upper foil layer of the tubular foil 1a between consecutive bags is cut through thereby forming a cut 28, whilst the other side of the bag is perforated or superficially incised by means of an incision 29.

Due to the fact that first the bottom gusset fold part seals 21, 22, 23, 24 are formed, a considerable economy of time is obtained for forming the first transverse bottom seal, while furthermore an economy of heat may be obtained. The heat being used for forming the bottom fold part seals 21, 22, 23, 24 extending perpendicularly to the longitudinal central gusset fold edge 4, 4a, is, actually, partially retained in the plastic material until the heatsealing bar 20 is operated for forming the first transverse bottom seal 12. If, for example, the four layers in the gusset fold parts would be simultaneously heatsealed to each other, the above economies could not be obtained. Thus, first applying the bottom fold part seals offers a considerable economy, as the production speed can be increased by about 20%.

Referring now to FIG. 4, the manner in which the first transverse bottom seals are formed is clearly shown, whilst FIG. 5 is a web of plastic bags, comprising three transverse bottom seals.

Finally referring to FIG. 6, being another embodiment of the seals to be applied, it can clearly seen that the first fold part seals 9, 10 and 11 and the second fold part seals 13, 14, 15, 16 are interconnected by means of an additional seal 30 which runs parallel to the longitudinal edges 4, 4a of the tubular foil. A seal 30 of this type may simplify the filling of a bag.

Claims

1. An apparatus for manufacturing a valve free plastic bag (27) with gusset folds formed from a tubular foil, at least comprising a central (4, 4a) and two outer longitudinal gusset fold edges (2, 3, 2a, 3a) which bound a first and second gusset fold part, said bag being open at one end opposite a transverse bottom seal (12) and further comprising:

(a) two first fold part seals (8, 9, 10, 11) at both sides of the bag, which first fold part seals always connect an outer foil layer (1a, 1b) with an opposite gusset fold part (6a, 5a; 6,5) said first fold part seals extending in the region between the central (4, 4a) and outer longitudinal fold edges (2, 3; 2a, 3a) in the region of said transverse bottom seal (12) and diverging from the region of said bottom seal (12) to the outer fold edges (2, 2a; 3, 3a),

(b) second fold part seals (13, 14, 15, 16) at both sides of the bag which second foil part seals always connect an outer foil layer (1a, 1b) with an opposite gusset fold part (6a, 5a; 6, 5) said second fold part seals extending in the region between the central (4, 4a) and outer longitudinal fold edges (2, 3; 2a, 3a) at the end of the bag remote from the transverse bottom seal of this bag, said second fold part seals converging from the outer longitudinal fold edges (2, 3; 2a, 3a) to the open end of said bag (27) wherein least at both sides of the bag an additional seal (30) extends substantially parallel to the fold edges and in the region between inner and outer fold edges and in the region between inner and outer fold edges, said additional seals (30) being at least connected with the second fold part seals (13, 14; 15, 16) and extending from said second fold part seals towards the open end of said bag (27), said apparatus at least comprising:

(1) conveying means for stepwise conveying a tubular plastics foil;

(2) first sealing means for forming said first fold part seals (8, 9; 10, 11);

(3) second sealing means for forming said second fold part seals (13, 14; 15, 16);

(4) transverse sealing means for forming a transverse bottom seal (12);

(5) additional sealing means for forming said additional seals (30) connecting at least said seals with said second sealing means;

(6) separating means being active during the action of said first respectively second sealing means for forming said first respectively second fold part seals.

2. An apparatus according to claim 1 comprising also means for incising the plastic foil.

3. An apparatus according to claim 1, wherein the additional sealing for forming the additional seals (30) are active near the inner fold edges (4, 4a) of a tubular plastics foil.

4. An apparatus according to claim 1, wherein said sealing means form additional seals extending to the filling opening (28) of a bag.

5. An apparatus according to claim 1, wherein additional sealing means form additional seals (30) connecting first fold part seals and extending towards the transverse bottom seal (12) of a bag.

6. An apparatus according to claim 5, wherein the additional sealing means form additional seals (3) extending at both sides of a transverse bottom seal (12) of a bag.

7. An apparatus according to claim 1 wherein the additional sealing means form additional seals (30) connected with the first fold part seals and extending beyond the transverse bottom seal (12) of a bag.

8. An apparatus according to claim 1, wherein the additional sealing means form additional seals (30) connected with the first fold part seals extending to the free end of a bag below a transverse bottom seal.

9. An apparatus according to claim 2, wherein said incision means comprise perforating means being active in the region of the foil forming said open end.