Method for folding an edge on a continuous material web

Abstract: The disclosure relates to an apparatus for folding an edge (11) on a continuous web (10) in which the continuous web (10) is caused to pass a belt (1) between two wheels (2, 3) and in which the belt (1), which is twisted through 180°, folds over the edge (11) in its twisting action. The belt (1), which is endless, runs over a further two wheels (4, 5) in order to be returned.

Description: The present invention relates to a method for folding an edge on a continuous material web, according to the preamble of claim 1 and as known from US-A- 3 073 217. The material which is employed for disposable packages for liquid foods such as milk or juice normally consists of a paper or cardboard layer which is laminated on both sides with a thermoplastic. The laminate may occasionally also include a thin aluminium foil. After production of the laminate, this is cut in suitable widths and formed into packages in a filling machine. The point of departure for this operation is that the packaging material supplied from a roll is formed into a tube which is transversely sealed and then cut in the transverse seals, in order finally to be formed into the finished package. Since the longitudinal joint is sealed in that the two edges overlap one another so that the material web becomes a tube, the edge located inside the tube must be protected in some manner so that the filled contents do not come into direct contact with the paper layer in the laminate. Otherwise, this could result in the contents wetting the paper layer and, in aseptic packages or cartons, such a joint would give rise to unsterility. Normally, the inner longitudinal edge is protected by a loose strip which is sealed against the outer thermoplastic layer in the laminate. It is also possible, in production of the laminate, to allow a narrow edge of thermoplastic, possibly laminated with aluminium foil, to protrude outside the edge of the packaging material proper. Such an edge of thermoplastic, possibly with adhering aluminium foil, must, before arrival of the packaging material at the filling machine, be folded over the open laminate edge in order thereby to protect this edge. Today, this operation is carried out in that the edge is heated by hot air or by an IR lamp and is folded by means of a number of rollers at different angles of inclination. Such an apparatus provides for adequate folding. However, friction will be great and allows but limited output capacity. Moreover, prior art apparatuses are also complex and contain many moving parts. Such an apparatus is described in US-A- 4 606 784. One object of the present invention is to realise an apparatus for folding an edge on a continuous material web, the apparatus having no or insignificant friction and, therefore, being capable of operation at high speed. A further object of the present invention is to realise an apparatus which is simpler and more economical than existing prior art apparatuses. These and other objects have been attained according to the present invention by the method as defined in claim 1. The nature of the present invention and its aspects will be more readily understood from the following brief description of the accompanying Drawings, and discussion of one preferred embodiment relating thereto. In the accompanying Drawings: Fig. 1 is a schematic top plan view of the apparatus according to the invention; Fig. 2 is a schematic side elevation of the apparatus according to the invention; Fig. 3 is another schematic side elevation of the apparatus according to the invention; Figs. 4 to 6 show different cross-sections of the belt and how the edge is folded towards the belt; and Fig. 7 shows how the apparatus according to the invention is incorporated in a particular context. The accompanying Drawings illustrate only those details which are essential to an understanding of the present invention. Referring to the Drawings, the apparatus according to the invention includes a belt 1, of rectangular or trapezoidal cross-section. The belt runs over at least four wheels 2, 3, 4 and 5 which are preferably designed as conventional belt pulleys but may also be designed without grooves. Fig. 2 shows how the belt 1 runs from the wheel 2, twists through 180° before reaching the wheel 3, runs about the wheel 3 and passes further to the wheel 4, down over the wheel 5 and back to the wheel 2. In order to return the belt 1 after the twisting operation, the wheels 4 and 5 must be inclined in relation to the wheels 2 and 3, which is clearly apparent from Fig. 1. However, Fig. 1 shows only the shafts 6, 7, 8 and 9, respectively, of the wheels, 2, 3, 4 and 5. The centre line of the belt 1 determines the design and thereby also determines the size of the wheels, for which reason the wheels 4 and 5 will of necessity be somewhat larger than the wheels 2 and 3. In the preferred embodiment, the wheels 2 and 3 are disposed in the same plane, while the wheels 4 and 5 are disposed at an angle in relation to the common plane of the wheels 2 and 3. The direction of movement of the belt is shown by arrows in Fig. 3. A continuous material web 10 is led through the apparatus, the web having a projecting edge 11 along the one laterally defining line of the web 10. The edge 11 of the continuous material web is in contact with the belt 1 for the greater part of that distance in which the belt 1 is twisted through 180°, i.e. between the wheels 2 and 3. Thereafter, the continuous material web 10 reaches a roller 12 which, in this embodiment, serves both as squeezer for the inwardly folded edge 11 and as return roller for the continuous material web 10. Naturally, two different rollers may be provided for both of these purposes. The belt 1 may be of rubber, plastics or the like, possibly reinforced or strengthened with cord, with at least one planar face 13 against which the edge 11 is to be folded. In the preferred embodiment, the belt 1 is of trapezoidal cross-section. The planar face 13 against which the edge 11 is folded should be at least twice as wide as that edge 11 on the continuous material web 10 which is to be folded. The belt 1 is driven at the same speed as the continuous material web 10. Driving of the belt 1 (not shown) is provided in a suitable manner by means of, for instance, an electric motor, via one of the wheels. The active part of the belt 1 which is in contact with the continuous material web 10 and which executes the folding operation proper is that part between the wheels 2 and 3 where the belt 1 twists through 180°. This part should be as short as possible, in order that the belt will not be capable of moving laterally when it folds the edge 11. If the belt is unstable in this part, there is the risk of a resultant uneven folding which does not tightly enclose the material web 10. It is also possible to solve this problem by providing the apparatus with guide rollers (not shown) for the belt and the material web. Consequently, it is vitally important to keep the belt taut, so the apparatus should be provided with some form of tensioning screw or the like (not shown). The total length of the belt 1 may vary but the so-called inactive part constitutes a cooling facility for the slight frictional heat which occurs in the active part, for which reason the belt may readily be long without necessarily taking up too much space. In the preferred embodiment, the apparatus is oriented such that the material web 10 moves vertically through the apparatus and the active part of the belt 1 is thereby also vertically oriented. However, it is fully possible to orient the web and, thereby also the apparatus proper, horizontally. Figs. 4 to 6 show three different cross-sections through the active part of the belt 1, where the planar face 13 of the belt against which the edge 11 is folded is twisted through 180° from section line C/C to section line E/E. When the continuous material web 10 first comes into contact with the belt 1, the projecting edge 11 constitutes an extension of the material web (Fig. 4). In Fig. 5, the belt has half-completed its twisting and, hence, turned the planar face 13 and therewith the projecting edge 11 through 90°. In Fig. 6, both twisting of the belt and folding of the edge have been completed and the planar face 13 of the belt 1 is now oriented at 180° from the starting position. Fig. 7 shows how the apparatus according to the present invention may be integrated into a complete plant in which the continuous material web, from a magazine reel 14 where the edge 11 of the material web 10 projects straight out, is processed through the plant until it reaches a new magazine reel 15 where the projecting edge 11 is folded in and sealed against the material web 10. From the magazine reel 14, the material web 10 moves between the nip of a pair of rollers 16 consisting of two rollers, of which one is provided with a projecting ridge. The material web is guided through the roller pair 16 such that the ridge impinges on the material web 10 slightly inside the projecting edge 11 and thereby presses together the material web 10, at least so much that it corresponds to the thickness of the projecting edge 11, since the folded edge would otherwise "build up" the one side of the web and render winding-up of the web impossible. From the roller pair 16 via the return rollers 17 and 18, the material web 10 moves vertically downwards. Just before folding of the edge takes place, the outermost portion of the material web against which the edge is to be sealed is heated. A suitable heating unit 19 for hot air or IR light is disposed along the edge of the material web and heats the web to that temperature at which the thermoplastic melts. Thereupon, the web 10 reaches the apparatus according to the invention for folding of the edge 11, the belt folding over the projecting edge 11. Where the edge 11 is wholly folded-in, the material web also reaches the roller 12 which constitutes both return roller and counter-pressure roller - or squeezer - on sealing of the edge 11 against the heated material web 10. The material web 10 is now ready for renewed winding-up on a new magazine reel 15. Instead of sealing with the aid of the thermoplastic on the surface of the material web 10, it is possible to supply a binder to the material web before the edge is folded over. As will have been apparent from the above description, the present invention realises a simple and economical apparatus for folding of one edge on a continuous material web, the apparatus being capable of achieving high output capacity and suffering from no or insignificant friction. Nor is an apparatus according to the present invention sensitive to any possible joints in the continuous material web, since there is a certain resilience in the belt so that this may move slightly when a joint passes through the apparatus.

Claims: Method of folding and sealing an edge (11) on a continuous material web (10) by means of an endless belt (1) which runs over wheels (2, 3, 4, 5) and is twisted between wheels of a number of at least four wheels (2, 3, 4, 5) and being in contact with the web (10) during a part of that distance where the belt (1) ist twisted and by means of a sealing device, characterized in that said edge (11) of said web (10) is moved in contact with an active part of said belt (1) which active part is twisted by two succeeding wheels (2, 3) by about 180° and is short compared with the inactive part of said belt (1) and that said web (10) at least one face thereof being coated with thermoplastic is pre-heated in the region most proximal the projecting edge (11) and sealed against said web (10). Method as claimed in claim 1, characterized in that both said web (10) and said belt (1) are advanced at the same speed. Method as claimed in claim 1 or 2, characterized in that said active part of said belt (1) is moved substantially vertically. Method as claimed in any one of the preceding claims, characterized in that said pre-heating is performed before said folding. Method as claimed in any of the preceding claims, characterized in that said belt (1) has at least one planar face (13). Method as claimed 5, characterized in that said belt (1) is of trapezoidal cross-section. Method as claimed in claim 5 or 6, characterized in that said planar face (13) of said belt (1) is at least twice as wide as the projecting edge (11) on said web (10).

Inventors: LOEVENBRANT JAN, LOEVENBRANT, JAN, Lövenbrant, Jan
Applicants: TETRA LAVAL HOLDINGS & FINANCE, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 1990
Main classification: B31B1
IPC codes: B65B61, B65H45, B31F1, B65B51, B65B49, B31F5, B31B1