A method of heating part of a continuous material web

Abstract: The disclosure relates to a method of heating a part of a continuous material web (4), in that IR lamps (1) with radiation-concentrating reflectors (2) are aimed towards a restricted area (7) of the continuous material web (4).

Description: The present invention relates to a method of heating a restricted area along a side of a continuous material web consisting of a paper or cardboard layer laminated with thermoplastic, according to the preamble of claim 1. Heating a restricted area of a packaging material sheet consisting of a thermoplastic with IR light in order to obtain a heated zone for, for instance, deep-drawing of plastic lids, is previously known in this Art. Within the packaging industry, use is made of continuous material webs for packaging material. This packaging material normally consists of a paper or cardboard layer laminated on both sides with a thermoplastic. The laminate may also include a thin aluminium foil. After production, the laminate is cut to suitable widths and stored on so-called jumbo reels. In a packaging machine, the packaging material is formed into a tube which is transversely sealed, cut in the transverse seals and finally formed into a finished package. In the majority of cases, it is necessary to protect the inner laminate edge when the packaging material is formed into a tube. This may be effected in that a loose thermoplastic strip is sealed against the inside of the laminate, or also in that a narrow edge of thermoplastic is allowed, on production of the packaging material, to project out beyond the one laterally defining line of the laminate. The thermoplastic edge, which may possibly be laminated with adhering aluminium foil, is, in a later process ahead of the filling machine, to be folded over the open laminate edge and sealed against the laminate surface of thermoplastic. In this instance, it is necessary to heat the packaging material web before the edge is folded so that sealing of the edge against the laminate surface may take place. In this case, a restricted heating of the continuous material web is desirable. Also in the application of loose plastic strips, a restricted heating of the continuous material web is desirable. According to prior art technology, the edge of the continuous material web has hitherto been heated, before the folding operation, by hot air. A hot air jet is directed from a hot air nozzle towards the edge of the continuous material web. In this instance, a scattered heating effect is obtained which is difficult to restrict in physical terms. In addition to the laminate edge, the thermoplastic edge is also heated, which entails that this becomes soft and intractible for handling in a subsequent folding operation. This is particularly true when the thermoplastic edge is laminated with aluminium foil, since heating of the edge may entail crack-formation and crease-formation in the thin aluminium foil, with a resultant edge folding which is not completely gas-tight, which in turn may cause insterility in aseptic packaging. The subsequent folding operation may be effected with a series of rollers of different angles of inclination, or alternatively with a belt which folds over the edge. It is known by US-A-4 617 081 to direct infra-red radiation by means of a reflector onto edges of flexible plastic prepunched blanks in order to cause a quick temperature rise of the edges which are overfold by a flap in order to form a disk envelope. It is an object of the invention to heat a restricted area of a continuous material web without adjacent portions of the packaging material web being affected by the heat. The invention is characterized in claim 1 and preferred embodiments are claimed in sub-claims. According to the invention heating to a restricted area is carried out by a combination of the effect of radiation concentrating reflectors on the one hand and of a dark colour strip on the other hand. According to a preferred embodiment of the invention the IR lamp or lamps are situated with regard to said restricted area in such a manner that the focal point of the concentrating radiation is disposed in a certain distance from said restricted area so that the radiation is concentrated on a certain width. The colour strip should comprise the same width. 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 with reference thereto. In the accompanying Drawings: Fig. 1 schematically illustrates how an IR lamp is aimed towards a continuous material web; and Fig. 2 schematically illustrates a part of the continuous material web. The accompanying Drawings illustrate only those details which are essential to an understanding of the present invention. Referring to the Drawings, Fig. 1 shows an IR lamp 1 or alternatively a battery of IR lamps connected in series, fitted with a conventional reflector screen 2. The reflector 2 has a predetermined distance to a focal point 3 where radiation is concentrated. By placing the IR lamp 1 with the reflector 2 at a certain distance from a continuous material web 4, the focal point 3 will be sited at the distance A ahead of the material web 4. This implies that the radiation behind the focal point 3 is scattered on the width B on the packaging material web 4. If the distance A is increased, the width B increases, and vice versa. Hence, B constitutes the restricted area 7 on the packaging material which is heated. The number of IR lamps 1 connected in series depends upon the speed at which the web 4 is advanced, so that the greater the speed of advancement of the web 4, the larger will be the number of series-connected lamps 1 required in order to achieve the contemplated effect. Fig. 1 also shows the thermoplastic edge 5 projecting out from the continuous material web, possibly laminated with aluminium foil. When the continuous material web 4 passes the IR lamp 1 or the IR lamps connected in series to form a battery, the thermoplastic surface of the continuous material web 4 is heated to a temperature which corresponds to the melting point of the thermoplastic in a restricted area 7 immediately inside the projecting edge 5. The restricted heating area 7 then consists of a zone which extends along the edge of the continuous material web 4 in the direction of movement of the web 4. When the heating operation is physically restricted in this manner, the edge 5 is not affected but may (being unheated and easily manageable) be folded over in a subsequent folding process using, for example, rollers or belts, and be sealed against a continuous material web 4 with a uniform and smooth seal, without any risk that the aluminium foil, which may possibly adhere to the thermoplastic, cracks or crinkles. Fig. 2 illustrates a portion of the continuous material web 4 in which that area 7 which is to be heated before the folding process has been provided with a pre-printed colour strip 6. This colour strip 6 is suitably printed on the continuous material web 4 in an earlier printing process when the graphic artwork is applied to the packaging material. The colour strip 6 consists of a dark, matted colour, preferably black mat. The IR lamp 1 is selected so as to operate on a wavelength which is particularly adapted to respond to black. On being exposed to heating from the IR lamp 1, the colour strip 6 will absorb the heat, and practical experiments have demonstrated that this process may reduce the power requirements for heating by as much as 50%. The colour strip 6 also contributes in concentrating the thermal radiation so that an insignificant amount of heat is scattered outside the colour strip 6. As will have been apparent from the foregoing, the present invention realises a method of heating a restricted area of a continuous material web without other parts of the web, above all the thermoplastic edge, being affected by the heat, with resultant negative consequences for the subsequent folding operation. The present invention should not be considered as restricted to that described above and shown on the Drawings, many modifications being conceivable without departing from the spirit and scope of the appended Claims.

Claims: Method of heating a restricted area (7) along a side of a continuous material web (4) consisting of a paper or cardboard layer laminated with thermoplastic, characterized in that the heating is carried out by an IR lamp (1), or a battery of IR lamps provided with radiation concentrating reflectors (2) and in that the restricted heating area (7) is pre-printed with a colour strip (6) consisting of a dark colour. Method as claimed in claim 1, characterized in that the colour strip (6) consists of a matted dark colour. Method as claimed in claim 1 or 2, characterized in that the radiation is concentrated on a certain width (B) which substantially complies with width of the colour strip (6). Method as claimed in any of the preceding claims, characterized in that the wave length of the infra-red radiation is selected so as to be responded by said colour strip (6).

Inventors: ANDERSSON ANDERS, KJELGAARD TOM, ANDERSSON, ANDERS, KJELGAARD, TOM
Applicants: TETRA LAVAL HOLDINGS & FINANCE, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 1990
Main classification: B31B1
IPC codes: B29C65, B65B51, C08J7, B29C35, B65D65, B32B27, B32B29, B29C51, B29C67, B29B13, B31B1