A METHOD AND AN APPARATUS FOR WELDING TOGETHER PLASTICS FOIL STRIPS

Abstract: By the welding together of two webs (1, 2) of plastics foil by heating action of the foil webs along a welding line (20) or in a welding zone the heating action is performed in that the sides of the webs that are to face each other are during synchronous movement of the foil webs brought into pressure contact with heating elements provided in the guiding surface, e.g. rollers (8) for the foil webs, subsequent to which the webs are immediately attached to each other under pressure action.

Description: A METHOD AND AN APPARATUS FOR WELDING TOGETHER PLASTICS FOIL STRIPS. This invention relates to a method for welding together two webs of plastics foil along a welding line or in a welding zone by heating action on the foil webs by means of one or more heating elements which are brought into pressure contact with one or both foil webs, e.g. for the manufacture of closed bag items. * ' In connection with numerous different productions it is a more or less fondamental task to weld together foil webs along a continuous line or zone, e.g. in order to close a top or bottom edge area of a double web from which the bag items now welded together may be successively cut off by transverse cutting. The welding attachment is carried out in that an appro- priately heated welding jaw presses the foils, which are in contact with each other, against an appropriate counterpart this pressure being exerted exactly ϊn the area where the jaw at the same time produces such a heating that the foils are melted together. It is further known to use heated welding rollers capable of providing the welding during continuous passage of the foil webs. In order to obtain a high quality welding the process must be controlled quite exactly because the fact that the heating of the proper welding area must take place through the foil layer against which the welding tool presses makes this process difficult. This also sets narrow limits to the welding speed since a quick welding requires a high temperature of the welding tool so as to quickly distribute the heat to the welding area, but at such a high -temperature of the tool the external side of the foil is exposed to excessive melting, which normally should be avoided. The present invention is based on the idea that it is possible in a simple manner to perform the heating action for the welding from the inside, namely by suppling heat directly to the zones concerned of the foil webs immediately before bringing these together. By the method according to the invention this is accomplished in that the heating action in said welding line or zone is carried out during syn¬ chronous movement of the foil webs by bringing the sides of the webs that are to face each other into pressure contact with heating elements provided in guiding surfaces for the foil webs, subsequent to which the foil webs are immediately attached to each other by a pressure action. It is thus possible to accelerate the working speed quite considerably while obtaining a high quality welding, because the material is heated to melt locally precisely in the welding area without the heat being transmitted trough the foil. It is even so that the heating action can be controlled in a less critical manner the higher the conveying speed is, so that a rather high working temperature may be used without getting completely through the respective foils. In principle optimum working conditions have therefore been provided for, namely an intense melting of the welding zones facing each other so as to allow the welding to be performed by a slight compression of the webs without this giving rise to separating problems in connection with the compression itself since the melting area does not extend completely to the external side of the foils. A high working speed also means that the period between the final heating and the compression of the webs is short which implies that the welding temperature neigther is essentially lowered nor gets through to the external side of the foil. An apparatus designed to carry out this method includes means for conveying the foil webs and one or more heating elements for imposing a heating action of the foil webs by pressure contact, and is characte- rized in that a configuration of heating elements adapted to the desired welding lines or zones are provided in a guiding surface for each foil web, in that the conveying means for the foil webs are designed to guide each foil web past said guiding surface with the side intended to face the other foil web in enga¬ gement with the guiding surface, and in that means are arranged downstream of the guiding surface for attaching the foil webs to each other by pressure action. The invention will now be described further in with reference to the drawing which is a schematic perspective view of an apparatus for the execution of a welding action according to the invention. The apparatus is supplied with two foil webs 2 and 4 from supply rolls (not shown), but these webs may also be two sides of one single web folded in V-shape at its lower part. The webs are introduced around respective guiding rollers 6 wherefrom they are guided outwardly to partly entwine the larger rollers 8 wherefrom they are led towards each other so as to be conveyed together through a pair of com¬ pression rollers 10 and preferably then through a pair of opposite rolling belts 12 wherefrom they are finally conveyed in the form of a double layer web 14, e.g. welded together along a top welding line 16. This double web may then in a manner not shown be exposed to a transverse cutting by welding so as to form successive bag items. The wide rollers 8 are at the top provided with heating means along a narrow circumferential belt 18 so that both of the foil webs 2 and 4 during their passage through the apparatus are heated along the lines indicated -by 20 on the sides of the foils facing each other. As mentionned above, the passage may be quick so that the heating can be controlled so as to provide a local melting or considerable smoo¬ thing of the foil material at said inner sides of the webs, without the associated high temperature reaching the external side of the foils before these are brought together between the rollers 10. By this attachment the melting areas 20 are pressed against each other to create a welding along the welding line 16. The rollers 10 have a cooling effect on the external sides of the foil webs so as to prevent a melting through of the foils. This cooling or heat-absorbing effect may also be obtained by the pressure belts 12 so that when using such belts an extra security is provided against a melting through of the foil webs and assuring that they are kept effec- tively together until the material in the melting zones 20 has hardened to complete the welding. It will be possible to expose the foil webs to an active cooling on their external sides during the passage around the rollers 8 whereby the heating along the roller zones 18 can be very considerable without a melting through of the webs which allows an extra high conveying speed. The invention involves important consequences not only concerns the choice of material since this invention allows the control of a very quick welding of polyethylene foils whereas until now when high production speeds have been requested it has only been possible to use less attractive PVC foils. Without difficulty various construction elements may by provided between the welded areas of the foil webs, such as connection hoses for the manufactured bag items since the respective rollers 8, 10 and pos¬ sible belt 12 may be designed with recesses for acco- modating such elements. In the case of connection hoses for liquidtight connection with the bag items, e.g. for urine or stomi bags, the hose ends may be preheated before being inserted in these recesses whereby a safe welding to the welding zones 20, in the foil webs is made possible. The rollers 8 may be replaced by a doublesided heating plate dividing the conveyed foils 2 and 4 so that these are heated at the zones 20 during the passage along this dividing plate.

Claims: AMENDED CLAIMS [received by the International Bureau on 12 June 1990 (12.06.90). ; original claims 1,5 and 6 amended; other claims unchanged (2 pages)] 1. A method for welding together two webs (2,4) of plastics foil along a welding line (16) or in a welding zone by heating action on the foil webs by means of one or more heating elements which are brought into pressure contact with one or both foil webs, characterized in that the heating action in said welding line (20) or zone is carried out during synchronous movement of the foil webs (1,2) by bringing the sides of the webs that are to face each other into pressure contact with heating elements provided in guiding surfaces (8) for the foil webs, formed by two opposite rollers rotating synchronously with opposite directions of revolution, subsequent to which the foil webs are immediately attached to each other by a pressure action exerted by at least one pair of counter rotating pressure rollers arranged downstream of the guiding surfaces. 2. A method as claimed in claim 1, charac¬ terized in that the heating action and the subsequent attachment are performed during continuous movement of the foil webs (1,2). 3. A method as claimed in claim 1 or 2, cha¬ racterized in that during the attachment, cooling is provided of the external sides of the foil webs. 4. A method as claimed in claim 1, 2 or 3, characterized in that in connection with the attachment construction elements such as connection hoses are inserted between two zones of the foil webs welded to each other. 5. An apparatus for welding together two webs of plastics foil using the method according to claims 1-4, which apparatus includes means for conveying the foil webs and one or more heating elements for imposing a heating action of the foil webs by pressure contact, characterized in that a configuration of heating elements adapted to the desired welding lines or zones is provided in guiding surfaces (8) for each foil web (1,2) formed by two opposite rollers rotating synchronously with opposite directions of revolution, ~ in that the conveying means (6) for the foil webs are designed to guide each foil web (1,2) past said guiding surface with the side intended to face the other foil web in engagement with the guiding surface, and in that attachment means (10) arranged downstream of the guiding surfaces comprises at least one pair of counter rotating pressure rollers for attaching the foil webs to each other by pressure action. 6. Apparatus as claimed in claim 5 , charac¬ terized in that the attachment means comprises means for cooling the external sides of the webs. 7. An apparatus as claimed in claims 5 and 6, characterized in that said pair of pressure rollers (10) are designed with recesses for accomodating of a construction element such as a connection hose between the two supplied foil webs. STATEMENTUNDERARTICLE19 In order to limit the claims from the prior art dis¬ closed in US-A-2 387 566, US-A-4 146 419, DE-C2-3 640 187 and .GB-A-2 082 500 the feature of original claim 6 has been incorporated into the characterizing part of each of claims 1 and 5.

Inventors: BISGAARD HANS FLINKER, BISGAARD, HANS, FLINKER
Applicants: BISGAARD HANS FLINKER, COLOPLAST AS, BISGAARD, HANS, FLINKER, COLOPLAST A/S
Application year: 1989
Main classification: B29C65
IPC codes: B29C65