GB2218037A

GB2218037A - Reinforcing plastics sheet; making bags

Info

Publication number: GB2218037A
Application number: GB8910394A
Authority: GB
Inventors: Michael S Johnstone
Original assignee: AJ Bingley Ltd
Current assignee: AJ Bingley Ltd
Priority date: 1988-05-06
Filing date: 1989-05-05
Publication date: 1989-11-08
Also published as: GB8810681D0; GB8910394D0

Abstract

A defined area of a sheet of plastics film material is reinforced by applying a coating to a surface of the sheet only in the defined area. The coating is applied in a molten or uncured flowable form and adheres to the sheet before solidifying. This method forms part of a bag making process in which a moving (6) flattened tubular plastics web (3) is slit (4) longiiudinally in its upper layers, the cut edges are folded outwards, said coating (2) is applied to four areas on the exposed inner surfaces (7, 8) of the upper and lower layers, the cut edges are folded back so that the reinforced areas overlay each other, the lower layer is cut longitudinally, the two webs are sealed transversely, and carrying holes are punched through the reinforced areas. The coating is applied directly by printing, spraying, pouring, painting, extrusion; or by transferring. The web comprises polyethylene, and the coating comprises polyethylene or foamed polyurethane. <IMAGE>

Description

REINFORCING PLASTICS SHEET The present invention is concerned with reinforcing plastics sheet and in particular embodiments, reinforcing the areas of plastics film material in which the carrying holes would be formed when the film is made up as a plastics bag.

Bags of plastics film material are typically made of polyethylene film of either high or low density. One of the problems with such bags is the tendency for the carrying holes which form handles for the bag to tear if the bag is overloaded. It has been the normal practice hitherto to reinforce the region around these carrying holes by doubling over the material of the film in these regions, or else by sticking an additional layer of material to the film.

The present invention is concerned with an improved method of reinforcing plastics sheet material, particularly for the handles of plastics bags, which provides for a simpler manufacturing process, especially in an automated production line.

According to one aspect of the invention, a method of reinforcing a defined area of a sheet of plastics film material comprises applying a coating to a surface of the sheet only in said defined area, said coating being applied in flowable form and comprising a material which adheres to the sheet when applied thereto and solidifies after application to reinforce said area.

Normally the plastics film material to be reinforced is polyethylene of low, medium or high density or mixtures of coextrusions thereof.

The material of the coating is preferably either a thermoplastic material such as polyethylene or a thermosetting plastics material and is applied to the surface of the sheet in a molten or uncured flowable state. The coating material may be a hot-melt composition, e.g. a mixture of polymers, resins and/or waxes selected and blended to provide desired properties. The coating may be a foam, or may be essentially gas-free. The desired properties of the coating are that it bonds readily with the film when applied, is strong, and is dry to the touch when solidified on cooling or curing.

Preferably, the coating is applied directly to the surface of the sheet by printing, spraying, pouring, painting or slot-die coating. However instead the material of the coating may first be applied to an intermediate surface and subsequently transferred from said intermediate surface to the surface of the sheet.

Very conveniently, the method may form part of a process for making bags of plastics film material, wherein the defined areas which are reinforced correspond to the positions of the carrying holes formed in the bags. Then, where the sheet of plastics film material is in the form of a continuous flattened tubular web, the method may include the steps of slitting the tube along its length, folding outwards the two cut edges of the upper layer of the tube to expose inner surface portions of both layers, applying said coating simultaneously to four said adjacent areas on the exposed inner surface positions, folding the cut edges back so that the layers of the tube overlay each other, and then cutting the carrying holes for a pair of bags through the reinforced areas.

The present invention also envisages a bag of plastics film material having carrying holes through defined areas of the material of the bag, where said areas have been reinforced by the above described method.

In another aspect, the invention provides a continuous web of plastics film material having defined areas thereon regularly spaced along the web, said areas having self-adherent coatings on a surface thereof, providing reinforcement of the areas. Also, the invention provides a bag of plastics film material having carrying holes through defined areas of the bag material, said areas having self-adherent coatings on a surface thereof providing reinforcement of the areas.

Examples of the invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates the application of reinforcing patches to a web of plastics film material; Figures 2 and 3 illustrate a preferred arrangement for applying the reinforcing patches in a bag making process, where Figure 3 is a cross sectional view; Figure 4 illustrates a bag of plastics film material embodying the present invention.

In the example illustrated in Figure 1, a web 10 of thermoplastics film material is moving in the direction of an arrow 11 past an applicator head 12.

The web 10 may be formed of polyethylene film, made from low, medium or high density polyethylene or a mixture or coextrusion of polyethylenes of differing density. In preferred arrangements, the web 10 may be made of low density polyethylene or linear low density polyethylene.

The applicator head 12 is fed with a plastics material in molten or uncured flowable form by means of an inlet pipe 13, and serves to extrude the flowable thermoplastics material on to a surface 14 of the web 10 in a predefined patch or area shown at 15.

When extruded on to the surface 14 of the web 10, the extruded plastics material adheres or bonds to the material of the web 10 and solidifies, e.g. on cooling if thermoplastic or by a chemical curing reaction if thermosetting, to form a solid coating 16 covering the patch.

The applicator head 12 is arranged to apply sufficient quality of the plastics material, in relation to the speed of transport of the web 10, to apply a coating of a desired thickness. In a convenient arrangment, a thermoplastics material is extruded from the head 12 and comprises a hot-melt composition, extruded at sufficient temperature to maintain the composition molten or flowable until the coating is applied. After application, the coating cools to solidify and simultaneously bond firmly with the underlying material of the web 10.

As a result, a strongly reinforced patch 16 is formed on the web.

The hot-melt composition is a blend of polymers, resins and/or waxes selected to provide the desired adhesion when applied to the polyethylene film, and to be strong and dry to the touch on cooling.

Instead of the hot-melt composition, the extruded material may be a foamed polyurethane which is thermosetting.

Conveniently, the supply of plastics material along the inlet 13 to the head 12 is controlled intermittently to apply patches at regular intervals along the length of the web 10 as the web moves in the direction of the arrow 11. Alternatively, a shutter arrangement is provided in the head 12 to cut off the flow of plastics material from the head on to the surface of the web 10 to form the desired patches.

In a typical arrangement, two sets of patches may be formed near opposite lateral edges of the moving web 10 so that when the web 10 is folded in half longitudinally the patches at opposite edges register with one another. When the folded web is then divided and sealed to form individual bags of plastics film material, carrying holes may then be punched simultaneously through the two overlying reinforced patches, thereby providing a suitably strengthened handle for the formed bag.

Referring now to figures 2 and 3a flattened tubular web 3 of thermoplastics film material moves in the direction of arrow 6 and the top layer of the web is cut by a knife edge 4. The cut edges are then folded outwards to expose their interior surfaces 7 as well as the interior surface 8 of the lower layer of the tubular web 3.

These exposed surfaces 7 and 8 are passed under an applicator 9 equiped with four heads 1, positioned in a line across the tubular web 3 such that the central two heads align with the interior surface 8 of the lower web layer and the two outer applicator heads align with the interior surface 7 of the upper web layer.

The applicator heads 1 is supplied with plastics material in a molten form or uncured flowable form by means of a manifold inlet 5 and the supply of flowable plastics is controlled to extrude this plastics material onto the surfaces 7 and 8 in predetermined areas or patches 2.

As in the previous example the thickness of the plastics material is dependent on the rate of application and the speed of transport of the tubular web and the position of the patches is controlled by either controlling the flow of the patches material or by the use of shutters. All four patches are applied to the web simultaneously at intervals along the length of the web corresponding to the bags being formed.

After the patches have been formed the cut edges 7 of the tubular web are folded back into their original positions so that there are now two pairs of overlying patches to form bags of plastic film material, the lower layer of the tubular web 3 is cut longitudinally thus separating the adjacent pairs of reinforced patches. The two webs thus formed are then sealed transversely to form pairs of bags. Carrying holes are also punched simultaneously through the pairs of overlying patches.

A bag of thermoplastics film material formed by the methods described above is illustrated in Figure 4 and comprises a single sheet of polyethylene film 20 folded in half at 21 to form the two sides of a plastics bag. When separating from the continuous web of material, seals are formed at the sides 22 and 23 of the bag, leaving an opening 24 at the top of the bag. Reinforced patches 25 and 26 are provided on each of the sides of the bag and these are pierced through to form carrying holes 27 and 28 respectively. The advantage of this type of strengthening of the handle area of plastic bags is that the strengthening material is bonded strongly to the plastics material and is unlikely to become separated.

In the illustrated examples, the reinforcing coating is applied to one surface only of the sheet of plastics film material, but it may be appreciated that such a coating may be applied to the corresponding areas of both surfaces if additional reinforcement is required.

Claims

CLAIMS:

1. A method of reinforcing a defined area of a sheet of plastics film material comprising applying a coating to a surface of the sheet only in said defined area, said coating being applied in flowable form and comprising a material which adheres to the sheet when applied thereto and after application to reinforce said area.

2. A method as claimed in claim 1 wherein the plastics film material is polyethylene.

3. A method as claimed in claim 1 or claim 2 wherein the material of the coating is a thermoplastic or thermosetting plastics material and is applied to the surface of the sheet in an uncured flowable state.

4. A method as claimed in claim 3 wherein the material of the coating is polyethylene.

5. A method as claimed in any preceding claim wherein the coating is applied directly to the surface of the sheet by printing, spraying, pouring, painting or slot-die coating.

6. A method as claimed in any of claims 1 to 4 wherein the material of the coating is first applied to an intermediate surface and subsequently transferred from said to intermediate surface to the surface of the sheet.

7. A method as claimed in any preceding claim wherein the method forms part of a process for making bags of plastics film material, wherein the defined areas which are reinforced correspond to the positions of the carrying holes formed in the bags.

8. A method as claimed in claim 7, wherein said sheet of plastics film material is in the form of a continuous flattened tubular web and including the steps of slitting the tube along its length, folding outwards the two cut edges of the upper layer of the tube to expose inner surface portions of both layers, applying said coating simultaneously to four said defined areas on the exposed inner surface portions, folding the cut edges back so that the reinforced areas on the upper and lower layers of the tube overlay each other, and then cutting the carrying holes for a pair of bags through the reinforced areas.

9. A continuous web of plastics film material having defined areas areas thereon regularly spaced along the web, said areas having self-adherent coatings on a surface thereof, providing reinforcement of the areas.

10. A bag of plastics film material having carrying holes through defined areas of the bag material, said areas having self-adherent coatings on a surface thereof providing reinforcement of the areas.

11. A method of making bags of plastics film material substantially as hereinbefore described with reference to the accompanying drawings.

12. A bag of plastics film material made by the method claimed in any of claims 7, 8 or 11.