WO2001054997A1

WO2001054997A1 - A multiple-wall sack with glue between layers, and method of manufacturing

Info

Publication number: WO2001054997A1
Application number: PCT/FI2001/000070
Authority: WO
Inventors: Valter Sievers; Pentti Rikassaari; Jarmo Juvonen
Original assignee: Upm-Kymmene Corporation
Priority date: 2000-01-28
Filing date: 2001-01-26
Publication date: 2001-08-02
Also published as: AU3178701A; FI111617B; FI20000174A; FI20000174A0

Abstract

The application describes a barrier bag comprising a tubular housing that has an inner layer (1) made of paper, further out a barrier layer (2) that is impermeable to air, and yet further out an outer layer (3) made of paper. The barrier layer (2) is provided with holes (11), through which the inner layer (1) and the outer layer (3) are glued together. Owing to said holes, the inner layer and the outer layer can be easily glued together. The application also describes a method of manufacturing bag.

Description

A multiple-wall sack with glue between layers, and method of manufacturing

FIELD OF THE INVENTION

The invention relates to paper bags and more particularly to a multilayer bag, where in between the paper layers, there is provided a barrier layer.

BACKGROUND OF THE INVENTION

When manufacturing multilayer valve bags made of paper, superimposed paper webs are arranged to form a tube, the tube is cut into desired lengths and their apertures are closed in order to provide a bottom. Moisture-proof valve bags can be manufactured by inserting a separate plastic film between the layers. The type of the employed plastic has been polyethylene, in particular.

The strength of a multilayer bag can be increased, when the layers are attached together by gluing. A reinforcing gluing is made especially at the bag orifice by means of a transversal glue bond. The gluing also helps in aligning the bag layers during the manufacturing process. If plastic film is provided in between the paper layers, gluing is difficult, when materials with radically different properties must be attached together. The gluing process requires the use of soft dispersion glues, which as such are difficult to handle. Moreover, their drying periods are long, even up to a week. The final result can still be uncertain, and it cannot be easily checked, because the g fl^Aue bond is not visible.

For instance the patent publication FI-A-972664 describes a bag where a plastic film is provided in between the paper layers.

GENERAL DESCRIPTION OF THE INVENTION

The present invention relates to a bag according to claim 1 , and to the manufacturing method thereof. Preferred embodiments of the invention are described in the dependent claims.

In the bag according to the invention, in between the paper layers, there can be used a barrier film that is completely impermeable to air and moisture. The paper layers are glued together, so that they are easily aligned in the manufacturing process. At the same time, the strength of the bag is improved. Ordinary glues suited to gluing paper can be used in the process. DRAWINGS

The appended drawings form part of the detailed description of the invention. In the drawings

figure 1 illustrates a bag blank prior to making the bottoms, figure 2 illustrates a blank provided with a valve piece, figure 3 illustrates a blank where the bottom sealings are made, figure 4 illustrates a blank where the side flaps that are placed underneath are folded, and figure 5 illustrates a ready-made bag.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The bag according to the drawings is made of a three-layered material. Innermost there is an inner layer 1 made of paper, next a barrier layer 2 that is impermeable to air, and outermost a outer layer 3 made of paper. At both ends of the flattened tube- like blank (Fig. 1), there are made sections 4 in order to create side flaps 5 and end flaps 6. At the side flaps 5, the blank is somewhat longer than at the end flaps 6. In the drawings, there are also marked the transversal side creasings 7 and the diagonal end creasings 8 of the bottom, along which the flat bottom is formed by folding, as well as the folding creasings 9, along which the bottom is folded against the bag housing.

The inner layer 1 and the outer layer 3 can be made of some bag paper that is suited to this purpose (strength for example 95 g/m^). The barrier layer 2 can be made of a suitable plastic film (for example HDPE).

At the side flaps 5, the layer ends are arranged to have varying lengths in a stepping fashion, so that at the upper blank end, on the front face of the housing, the inner layer 1 is longest and the outer layer 3 is shortest, and that on the rear face of the housing, the inner layer is shortest and the outer layer is longest. At the bottom end of the blank, on the front face of the housing, the inner layer 1 is shortest, and the outer layer 3 is longest, and on the rear face the inner layer is longest and the outer layer is shortest. The arrangement of the material in a stepping fashion makes it possible to attach all materials together in the bottom structure.

At the end flaps 6, at the top end, the inner layer 1 is somewhat longer than the barrier film 2 and the outer layer 3. At the bottom end, the inner layer 1 is somewhat shorter than the barrier film 2 and the outer layer 3. The layers 1, 2 and 3 are at both ends attached together by means of a transversal point by point sealing 10. The sealings help to align the layers. Moreover, they reinforce the bag, because strains are directed more evenly to all layers.

The sealings are made so that prior to placing the layers on top of each other, in the barrier layer 2 there is made a row of holes 11. and the paper layers are glued together through these holes. Thus the gluing proper can be carried out by means of conventional methods and materials used in the manufacturing of bags, for instance by using starch glue. Starch glue is cheap and easy to use and dries quickly. The end result is extremely reliable.

The holes 11 can be made in the barrier film by cutting, for instance by using a suitable punching tool. In a film that melts by heating, the holes can be melted by using a suitable hot pin.

In the next step (Fig. 2), at one end of the top side of the blank, there is attached a valve piece 13 made of paper. The valve piece 13 is glued to the end flap 6 by two glue strips. Inside the valve piece 13, there is provided a fold 14. The side flaps 5 of the front face are turned open along the fold creasing 9, and simultaneously the end flaps 6 are folded inwards along the end creasings 8. Moreover, the sides of the valve piece 13 are folded inwards at the side creasings 7, and on top of the folded sides, there are formed glue strips 15 inwardly from the fold edge. In the area of the double end edge of the valve piece 13, the glue strip 15 is somewhat wider. Thereafter the side edges of the valve piece 13 are again turned open, and they are tightly glued to the end flap 6, to the inner layer of the side flaps 5.

In the next step (Fig. 3), there are made glue strips, whereby the bottoms are sealed. In the side flap 5.1 that goes underneath, and where the inner layer 1 is longest, there are formed end glue strips 16.1 starting from the outer surface of the end flap 6, from the side creasing 7, and extending to inner surface of the side flap, as long as the end thereof. In the side flap 5.2 that comes on top, and where the inner layer 1 is shortest, there are made corresponding shorter end glue strips 16.2. Moreover, the end glue strips 16.2 are interconnected, along the edge of the inner layer 1, by means of a narrower inner side glue strip 17. At the end of the outer layer 3, on the inner side thereof, there is made a fairly narrow outer side glue strip 18 that extends from one end to the other. At the valve piece 13, the end glue strips 16.1 and 16.2, as well as the inner glue strip 17. naturally fall on the valve piece. In the next step (Fig. 4), there are folded the side flaps 5.1 that are placed lowest against the bottom, so that the inner surface of their inner layer 1 sticks tightly to the end flaps 6 by means of the end glue strips 16.1, and at the valve end respectively to the valve piece 13. When finally there are folded the side flaps 5.2 that go topmost against the bottom, the outer layer 3 thereof sticks to the outer layer of the lower side flap 5.1 by means of the outer side glue strip 18, and the inner layer 1 sticks to the end flap 6, at the valve corner to the valve piece 13 and to the inner layer of the lower side flap by means of the end glue strips 16.2 and the inner side glue strip 17.

Consequently, in the bottom structure the paper layers 1 and 3 are glued, in the longitudinal direction of the bag, against themselves (laminated arrangements) by means of glue bonds 17 and 18. In the longitudinal direction, the laminated barrier layer 2 is not glued to itself, but it is attached, with respect to the paper layers, owing to the sealings 10. Thus the free, unglued film structure enables the exhaustion of air via the bottom ends, but in a laminated structure it creates a moisture lock in the bottom structure. The barrier layer can be glued by means of a cheap process gluing method; expensive and staining special glues are not needed.

The gluing of the bottom corners by the bonds 16.1 and 16.2 closes and seals the structure, but allows the dust-free air that has entered in between the layers 1 and 2 to be exhausted via the bottom ends.

The bottom structure is completely leak-proof towards the inside of the bag, except for the valve that is provided with a filling aperture in between the outer surface of the end flap 6 and the valve piece. The material contained in a filled bag presses the end flap 6 tightly against the valve piece 13. When desired, the valve orifice can be separately closed by means of a sealing tape attached against the bottom over the orifice. Owing to the laminated arrangement of the materials, the bottom is provided with an unbroken barrier film 2 throu *Bgh' out.

When filling the bag, air proceeds from the bag to between the inner layer 1 and the barrier layer 2, wherefrom it is exhausted at the end thereof, at the bag bottoms. In the bag bottoms air proceeds, in between the side flaps 5.1 and 5.2, to the ends, where it is exhausted. In order to facilitate the flowing of air, the outer surface of the inner layer 1 can be provided with grooves, but a paper with a smooth surface serves the purpose, too.

Air exhaustion is very efficient, when air flows on both sides of the bag towards both ends thereof. A bottom patch is not needed in order to form an exhaustion air channel or to reinforce the bag.

Bags can be manufactured in an ordinary bag production line; in tube and bottom machines that are provided with additional equipment for making the required sections, laminations and sealings. Extra material is not needed.

Claims

1. A barrier bag comprising a tubular housing that has an inner layer (1) made of paper, further out a separate barrier layer (2) impermeable to air, and yet further out an outer layer (3) made of paper, both ends of said housing being provided with a flat bottom, characterized in that the barrier layer (2) is provided with holes (11), at which holes the inner layer (1) and the outer layer (3) are glued together.

2. A bag according to claim 1, provided with holes (11) in the bottom area.

3. A bag according to claim 1 or 2, provided holes (11) arranged in a row.

4. A bag according to claim 3, provided with holes (11) in a row that runs in the transversal direction of the housin ^•*go.-

5. A bag according to any of the claims 1 - 4, the bottom of which bag is provided with inwards folded end flaps (6) and side flaps (5.1, 5.2) that are folded on top of these, so that in the side flap (5.1) that lies lowest in the bottom, the inner layer (1) is longer than the barrier layer (2), and the outer layer (3) is shorter than the barrier layer (2), and that in the side flap (5.2) that lies on top, the inner layer (1) is shorter than the barrier layer (2) and the outer layer (3) is longer than the barrier layer (2), and that the inner surface of the inner layer (1) of the topmost side flap (5.2) is glued against the outer surface of the inner layer (1) of the lowest side flap (5.1) by means of a inner sided glue strip (17), that the inner surface of the outer layer (3) of the topmost side flap (5.2) is glued against the outer surface of the lowest side flap (5.1) by means of an outer side glue strip (18), so that air can be exhausted at the bottom from between the inner layer (1) and the barrier layer (2), and further to between the side flaps (5.1, 5.2) and out via the end of the bottom.

6. A bag according to claim 5, where air can be exhausted at both ends of the bottom.

7. A bag according to claim 5 or 6, where air can be exhausted at both ends of the bag.

8. A bag according to claim 7, where air can flow in between the inner layer (1) and the barrier layer (2), on both sides of the bag, to both ends thereof.

9. A bag according to any of the claims 1 - 8, where the bottom is not provided with a bottom patch.

10. A method for manufacturing a barrier bag comprising a tubular housing that has an inner layer (1) made of paper, further out a separate barrier layer (2) that is impermeable to air and yet further out an outer layer (3) made of paper, both ends of said housing being provided with a flat bottom, characterized in that holes (11) are made in the barrier layer (2), and that the inner layer (1) and the outer layer (3) are glued together at said holes.