IE47675B1 - Valve sacks and methods of making them - Google Patents

Abstract

A valve sack is made from tubular material whose opposed longitudinal edges have been gusseted. There is formed in one of the gussets an aperture (S) which extends along the gusset for a distance appreciably less than the width (D) of eventual sack. The outer longitudinal edges of the gusset are then sealed together, either directly or via a further sheet of material, over a distance greater than the length of said aperture, to form a tube running along one longitudinal edge of the material. The material is then sealed together along two lines which run across the material and are spaced apart to define the width of the eventual sack. One end of the tube is sealed off. A further aperture overlapping the first mentioned aperture if formed in the tube.

Description

47673 The invention relates to valve sacks.

It is known to construct valve hags or sacks from paper, polythene and the like in so-called block bottom style. The flat tube of material which forms the bag is folded and sealed, across its length, at each end but at one end a valve is incorporated in the folds. The valve is a flat tube of paper, polythene or the like which allows access through the folds into the bag. When the bag is filled, and stored with the valve at the base of the bag, the contents cannot inadvertently be poured out of the bag because the pressure of the contents on the flat tube of the valve effectively seals off the valve opening. The bag must be cut open to release its contents.

These conventional block-bottom valve sacks are very widely used, but they have drawbacks: they are relatively expensive to make, they are confined to a relatively limited range of overall sizes, and there is a tendency for plastics block-bottom sacks to balloon” during filling.

To make bags by a method according to the invention .,-. involves two major departures from the accepted block-bottom :-. - - - construction outlined above. Firstly, an initially seamless tube of film is used, and is gusseted along its opposed longitudinal edges; and secondly, when the film is subsequently sealed across its length, the sealed regions define 2.5 the sides, not the ends, of the finished bag. - 3 In one broad aspect, the invention provides a method of making a valve sack, the method comprising the steps of taking a length of flexible tubular material whose opposed longitudinal edges have been gusseted; forming in one of the gussets an aperture (or a weakened area which can subsequently be broken to form an aperture) which extends longitudinally of the gusset for a distance appreciably less than the width of the eventual sack; sealing the outer longitudinal edges of the gusset together, either directly or via a further sheet of material, to form a tube running along one longitudinal edge of the material; sealing off one end of said tube and leaving the other end open to form a further aperture, or sealing off both ends of the tube and forming a further aperture (or a weakened area which can subsequently be broken to form an aperture) in the tube; and sealing the material together along two lines which run across the material and are spaced apart to define the width of the eventual sack; said further aperture (or weakened area) being spaced along the tube from the first-mentioned aperture (or weakened area) and extending transversely of the tube, and said tube being formed by sealing the outer longitudinal edges of the gusset together over a distance which comprises the full width of the eventual sack.

In another broad aspect, the invention provides a valve sack in which two overlying sheets of material defining the walls of the sack are joined together, along an edge incorporating the sack's valve means, by an integral gusset of flexible material; the outer longitudinal edges of the gusset being sealed together, either directly or via a further sheet of material, to form an elongate tube; a valving aperture (or a weakened area which can subsequently be - 4 broken to form an aperture) being formed in the gusset and extending longitudinally of the gusset for a distance appreciably less than the full length of the gusset; both ends of the tube being sealed off and a filling aperture being formed in the tube, or one end of the tube being sealed off and the other end being left open to form a filling aperture; the filling aperture being spaced along the tube from the valving aperture (or weakened area) and extending transversely of the tube; and the other longitudinal edges of the gusset being sealed together along the full length of the gusset.

The single Figure of the accompanying drawings shows diagrammatically a first method of making valve sacks from clear plastics film.

Xn the accompanying drawing, arrow A indicates the direction of feed of a longitudinally continuous and initially seamless gusseted tube. As the tubing advances intermittently, slits are made in the base of one of the gussets. This slitting is performed by a thin blade (not shown) lying flat within one of the gussets so that the film normally slides past it. At intervals, the blade is pushed deeper into the gusset to cut through the base of the gusset and make a slit S. The position of this slit will normally be arranged to fall within the range of approximately one-fifth to threefifths of the distance D between the subsequent cross-seals which define the side edges of the finished bag. As shown, the slit does not extend as far as either of these crossseals.

After the slit is made in the base of the gusset , a strip of centre-folded film equal in measurement to the width - 5 of the finished bag is fed into the gusset as indicated at B. The longitudinal edges of this strip are then welded to the outer longitudinal edges of the gusset a ion9· te;c -*c s. x - -. the lengths of the welds being equal to the desired width “ΰ·! of the bag being made. This has the effect of making a tubular form between the strip of centre-folded film and the sides of the gusset, and, as the drawing shows, the slit S in the gusset is covered by the strip of film.

Either before or after the additional strip of film has been welded to the gusset, it is itself slit (or perforated; as indicated at C. As shown in the drawing, the slit is at an angle (specifically, at right angles) to the slit S” ir; the gusset and is longitudinally displaced from it.

The sealing technique uses a side welding bar H positioned across the direction of feed A of the gusseted film.

At intervals synchronised with the operations of slitting the gusset and welding-in the additional strip of film,the welding bar is pressed against the film to make cross-weIds indicated by broken lines in the drawing and spaced apart by a distance D equal to the desired width of the finished bag. Whilst the film is still molten and held under the welding bar, the film is pulled apart at the weld leaving a seal at each side of the break. As the film advances and the sealing is repeated at suitably spaced intervals, bags are formed between the weIds.

These welds then become the side edges of the bag, and when the welds have cooled the bag can be pushed out around its gusseted ends to give a square base (and top) similar to a block bottom sack.

When this has been done, the slit C in the base of - 6 the bag defines a flap which will lift to give an entrance to the space between the extra welded-in strip of film and the sides of the gusset which that strip covers.

The bag can then be filled by pouring or blowing material with a suitable nozzle under this flap and into the bag through the slit S in the gusset. During filling, the filling aperture would normally be at the top of the bag. Subsequently, the material cannot be poured out of the bag because, when the bag is inverted, after filling, to stand on its base, pressure of the material in the bag presses the gusset walls against the welded-in film strip and this seals off the exit.

A variation of the above construction can be achieved still using a similar technique and gusseted tubing, but this time no extra strip of centre-folded sheeting is fed into the gusset after slitting- The slit “S in the base of the gusset is made in the same manner as previously described. It is then arranged that a heat-sealing bar welds across the gusseted tubing at X after the slitting operation in the gusset.

A shim of P.T.F.E. is allowed to trail in the gusset and under this sealing bar so that the two inner faces of the gusset do not weld together at any point. To prevent this cross-weld parting, while soft, under the normal tension of the machine, an arrangement of cooling air jets and extra feed rollers may be necessary.

After leaving this welding position, the film is moved forward a distance equal to the required width of the bag.

At the same time the two longitudinal edges of the gusset are now welded together for a length equal at least to the width of the bag and encompassing the slit contained in the base of the gusset. A further heat-sealing bar then welds across the film, in a position closely adjacent the first cross-weld - 7 and this time including welding the gusset together. A cutting blade between these two closely-adjacent welds parts ;he bag across the film, and the process is repeated sequentially. The gusseted edges of the film form the ends of the finished bags.

Bags made in this manner will have a tube across the top of the bag with an opening at one end. Material poured into this opening will fall into the body of the bag through the slit in the bottom of the gusset but when the bag is turned upside down the material cannot get out again because the tube forms a valve. The gusseted base of the bag will open out to a square form similar to a block bottom” sack.

It is sometimes necessary, particularly when powders are being forcibly blown into a valve sack, for the air to be able to escape. This is very easily accommodated with a sack incorporated the extra strip of film in the gusset. If the bottom corners of the empty sacks are perforated within a right-angled triangle defined in the corner, the short sides of the triangle being of a length not exceeding the depth of the gusset, the perforations will allow the pressurised air to escape when the bag is being filled and the filling tube is open, but will automatically be sealed off when the bag is subsequently inverted. The perforated holes may also be utilized to give moisture permeability to the bag, the size and number of the holes being determined so as to suit requirements.

Although the invention is ideally suited to plastics film—such as polythene—which can be heat-welded, the same principle can be applied to paper, woven polypropylene, Hessia., and other materials where adhesives or sewing methods are used. The formation of the sack is the same but the method of sealing is that most appropriate to the material being used. 4767S In a modification to the construction described and illustrated, either or both of the slits S and C are formed as lines of weakening or perforations in the fim: when the bag comes to be filled, the filling nozzle punches through the weakened or perforated lines and creates the slits which admit the contents to the bag. A similar modification can be made to the second construction described.

Claims (6)

1. CIAIMS:1. A method of making a valve sack, the method comprising the steps of taking a length of flexible tubular material whose opposed longitudinal edges have been gusseted; forming in one of the gussets an aperture (or a weakened area which can subsequently be broken to form an aperture) which extends longitudinally of the gusset for a distance appreciably less than the width of the eventual sack; sealing the outer longitudinal edges of the gusset together, either directly or via a further sheet of material, to form a tube running along one longitudinal edge of the material; sealing off one end of said tube and leaving the other end open to form a further aperture, or sealing off both ends of the tube and forming a further aperture (or a weakened area which can subsequently be broken to form an aperture) in the tube; and sealing the material together along two lines which run across the material and are spaced apart to define the width of the eventual sack; said further aperture (or weakened area) being spaced along the tube from the first-mentioned aperture (or weakened area) and extending transversely of the tube, and said tube being formed by sealing the outer longitudinal edges of the gusset together over a distance which comprises the full width of the eventual sack.

2. A method according to claim 1, in which one or both corners of the end of the sack along which the said tube extends is or are perforated, to allow escape of air during the eventual filling of the sack, the perforations being confined within one or both of two right-angled corner triangles whose non-hypotenuse side length is defined by the width of the flattened tube. - 10

3. A method of making a valve sack, substantially as described herein with reference to either of the major examples.

4. A valve sack in which two overlying sheets of material defining the walls of the sack are joined together, along an

5. Edge incorporating the sack's valve means, by an integral gusset of flexible material; the outer longitudinal edges of the gusset being sealed together, either directly or via a further sheet of material, to form an elongate tube; a valving aperture (or a weakened area which can subsequently be broken 10 to form an aperture) being formed in the gusset and extending longitudinally of the gusset for a distance appreciably less than the full length of the gusset; both ends of the tube being sealed off and a filling aperture being formed in the tube, or one end of the tube being sealed off and the other end being 15 left open to form a filling aperture; the filling aperture being spaced along the tube from the valving aperture (or weakened area) and extending transversely of the tube? and the outer longitudinal edges of the gusset being sealed together along the full length of the gusset. 20 5. A valve sack according to claim 4, in which one or both corners of the end of the sack along which the said tube extends is or are perforated, to allow escape of air during the eventual filling of the sack, the perforations being confined within one or both of two right-angled corner tri25 angles whose nonhypotenuse side length is defined by the width of the flattened tube.

6. A valve sack made by a method according to any of claims 1 to 3. F. R. KELLYS CO.