APPARATUS FOR THE HEAT-WELDING OF THE SUPERIMPOSED EDGES OF THERMOPLASTIC FILM

Abstract: The product (P) to be heat-welded is inserted between a pair of conveyors which are arranged one above the other and are both motorized and horizontal, the upper conveyor (2) performing the opposing function, while the lower conveyor (1) is formed by a plurality of spaced parallel rollers (14) arranged in succession and having a body (214) made of suitable resilient and yielding material such that, as a result of the pressure exerted by the said opposing conveyor, the rollers of the lower conveyor are deformed and are adapted to the irregularities on the bottom surface of the packaged tray and this surface is subjected to a uniformly distributed pressure. Some of the rollers (14'') of the lower conveyor may oscillate about a parallel axis, in opposition to resilient means (20) which keep them raised, so that these rollers may exert a correct degree of pressure also on the front side and on the rear side of the packaging. The heat for the heat-welding operation is produced by infrared-ray generators (32) which are located underneath the rollers of the lower conveyor (1) and which emit radiation at a wavelength suitable for the film to be welded.

Description: TITLE "Apparatus for the heat-welding of the superimposed edges of thermoplastic film" DESCRIPTION The present invention relates to the techniques for packaging, using extensible and heat-weldable film, products of any type inside trays, for example those techniques described in document WO 98/12111 which discloses how it is possible to package products placed in trays, using a wound strip of extensible and protective film, i.e. with controlled impermeability to gases, in the inside of which a modified atmosphere having a pressure equal to or different from atmospheric pressure is created, this being useful for better conservation of the packaged product. In this technical sector, the edges of the packaging film are extended and superimposed on the bottom and to a limited extent also on the bottom side surface of the trays and it is envisaged that the said edges may, at the end of the cycle, be fixed together by means of a heat- welding operation, so as to ensure the sealed closure of the packaging and the conservation, over time, of the modified atmosphere inside the packaging itself. In order to perform this heat-welding operation, according to the known art the packaged trays are fed on a flat conveyor belt heated by suitable means and the tray itself is kept suitably pressed against this conveyor by means of an upper opposition conveyor. On account of the flat and rigid surface of the lower welding conveyor and because sometimes the trays have on the bottom a not perfectly flat or an irregular surface, for example owing to the presence of stiffening ribs or other raised and/or recessed parts and also because the edges of the packaging film are superimposed in a non-uniform manner, creating zones of varying thickness, the known means are unable to produce the desired sealed heat-welding of the edges of the packaging film, so that the modified atmosphere created inside the packaging may, within a short space of time, be contaminated by the surrounding atmosphere. The known means, since they are rigid and flat, are also unable to act on the portions of the edges of the winding film located on the bottom side zones of the tray where openings allowing the modified atmosphere to escape may remain. The invention intends to overcome this technical problem using the following proposed solution. The packaged product to be heat-welded is inserted between a pair of conveyors which are arranged one above the other and are both motorized and substantially horizontal, the upper conveyor performing the usual opposing function, while the lower conveyor is formed by a plurality of parallel rollers arranged in succession and made of a suitable resilient and yielding material such that, as a result of the compression exerted by the opposing conveyor located above, the rollers of the lower conveyor are deformed and are adapted perfectly to the irregularities on the bottom surface of the packaged tray so as to subject this surface to a uniformly distributed pressure, useful for ensuring perfect welding of the superimposed edges of the packaging. At least some of the rollers of the lower conveyor may perform an oscillation, by a predetermined amount, about a parallel axis, in opposition to the action of resilient means which tend to bring the rollers back into the raised position, such that the same rollers are able to exert a correct degree of pressure also on the bottom zone of the front and rear side surface of the packaged trays, where superimposed edges of the packaging film to be welded may be present. The heat necessary for heat-welding of the packaging is produced by infrared-ray generators which are located underneath the rollers of the lower conveyor and which emit radiation at a wavelength suitable for the film to be welded. These generators heat the film directly, by means of irradiation, through the gaps which are present between the rollers of the lower conveyor and indirectly, by means of conduction, via the same rollers which provide the film with the necessary pressure for heat-welding. Further characteristic features of the invention and the advantages arising therefrom will appear more clearly from the following description of a preferred embodiment thereof, illustrated purely by way of a non-limiting example, in the figures of the accompanying sheets of drawings, in which: - Fig. 1 shows a side elevation view of the apparatus with sectioned parts; - Fig. 2 shows a top plan view of the lower conveyor of the apparatus; - Fig. 3 shows a front view of the apparatus, seen from the front side for entry of the packaged product to be heat-welded. The apparatus in question is located immediately downstream of a packaging machine so as to receive the products P as soon as they have left the packaging station or have been discharged from the conventional end welding apparatus onto the flat lower conveyor of the said packaging machine, as indicated schematically by T in Figure 1. From the figures it can be seen that the apparatus comprises a pair of conveyors 1 and 2 which are substantially horizontal, rectilinear and parallel with each other, the upper conveyor 2 for example being of the type having pressing tracks 102 which are made of suitable elastomeric material and being supported with the possibility of oscillation, while maintaining the horizontal position, by a known hinged parallelogram structure 3, the side 103 of which is integral with the frame of the conveyor in question, while the side 203 is fixed to a support structure 4 fastened to one end of the frame of the lower conveyor 1. The hinging axis 5 of the parallelogram 3 corresponds to the end axis of the conveyor 2 which is driven by the movement transmission 6 (Fig. 3) connected to the motor 7, all of which so that the lower section of the conveyor 2 travels in the direction indicated by the arrow F2 and at a speed which is the same as the working speed of the lower conveyor 1 (see below). The conveyor 2 is kept with the lower section at a distance from the conveyor 1 which is suitably less than the height of packaged product P to be welded, but with the possibility of freely oscillating upwards for interference with the product itself, such that the latter is acted on by the weight of the said conveyor 2 and if necessary also by the action of special resilient opposition means, not shown. For this purpose (Figs. 1 and 3), the frame 202 of the conveyor 2 is hinged at an intermediate point 8 with an overhead gantry cross-piece 9 to which there is connected the bottom end of a screw 10 which slidably passes through a bracket 11 in the form of an overturned "L" which is fixed to the frame 15 of the lower conveyor 1 , the said screw 10 having, screwed onto it, a nut 12 which, via a damping element 13, rests on the said bracket 11. Upon variation in the dimensions of the product P, the position of the nut 12 on the screw 10 is adjusted so as to raise or lower the conveyor 2 depending on the height of the said product P. It is understood that the action of the nut 12 may be automated by means of a servo-control device and sensors of the known type which detect the dimensions of the product at the entry point into the packaging machine. What characterizes mostly the apparatus in question is the lower conveyor 1 which is formed by a plurality of rollers 14 which are parallel to each other and transverse to the direction of travel of the product and are suitably spaced for the reasons mentioned further below. The rollers in question consist of a steel shaft 114 onto which a body of suitable thickness 214 consisting of any suitable material which is sufficiently resilient and yielding, for example a silicone sponge rubber. The front and end rollers indicated by 14' are arranged on a travel plane which is coplanar with the conveyor T supplying the product and are rotatably supported at the ends of their axial shaft 114 by the support frame 15 of the lower conveyor in question, while all the other intermediate rollers indicated by 14" have their axial shaft 114 rotatably supported by one of the ends of pairs of parallel levers 16 which are substantially in the form of a "U", are pivotably mounted at their other end at 17 on the said frame 15, are provided with a lug 116 directed downwards and have a hole 18 through which a pin 19 fixed to the adjacent side of the frame 15 passes, the said lug 116 being connected to a resilient means 20, for example a tensile spring, which keeps the rollers 14" suitably raised with respect to the rollers 14' by a predetermined identical amount ensured by resting of the pins 19 against a side of the holes 18 of the levers 16. All the rollers 14 are driven in the direction indicated by the arrow F1 and their peripheral speed is the same as that of the upper conveyor 2. From Figure 2 it can be seen that the pivot axes 17 of the adjacent levers 16 are arranged on one side of the frame 15 so as to project by the correct amount and these axes have, mounted on them, pulleys 21 of identical diameter which, by means of belts 22, transmit the movement to respective pulleys 23 of identical diameter which are keyed onto the shafts of the oscillating rollers 14" associated with said pivots, the bodies of the said first pulleys having keyed onto them identical bevel pinions 24 which mesh with respective identical bevel pinions 25 keyed onto a shaft 26 parallel to the longitudinal axis of the conveyor 1 and rotatably supported by brackets 27 fixed to the frame 15 and connected to an actuating motor 28 flanged to one of the said brackets 27. The non- oscillating end rollers 14', for example, derive their movement from the closest pulleys 21 , by means of associated belt and pulley transmissions indicated by 29, 30 and 31. When a packaged product P therefore arrives from the conveyor T, said product passes onto the first motorized rollers 14' and is then gripped between these rollers and the overlying track conveyor 2 which is also motorized and such as to exert on the product itself a correct downwards pressure. Viewing Figure 1 from left to right, the packaged product P gradually encounters the raised rollers 14' and with its front side causes lowering thereof against the action of the associated springs 20 and as soon as the product leaves these rollers, the said rollers return into the high position, applying a correct pressure also onto the rear side of the product itself. Owing to the compression to which they are subjected (Figs. 1 and 3), the rollers 14" are deformed along the part in contact with the product and with this part subject the lower side portions and the bottom of the product itself to a uniformly distributed pressure useful for ensuring the sealed welding of the superimposed edges of the thermoplastic packaging film which wraps the product itself, also when there are uneven and irregular surfaces. The heating necessary for plasticization of the film portions in contact with the rollers 14 is ensured by a beam of infrared radiation, with a wavelength suitable for the film to be heat-welded, which is emitted by cup elements 32 which are suitably arranged underneath the rollers 14 and supported, for example, by a housing 33 fixed to the sides of the frame 15 and which heat the film directly by means of irradiation through the gaps which are present between the rollers 14 and, indirectly, by means of conduction, via the said rollers 14. The pressure of the rollers 14" may be kept constant or varied by means of the resilience of the material which makes up the body 214 of the said rollers and/or by means of the resilience of the springs 20. The heating performed by the cup elements 32 may also be kept constant or varied. Finally, programmable means, not shown, may be provided in order to ensure that the speed of travel of the conveyors 1 and 2 and/or the intensity of the heating performed by the cup elements 32 may also vary automatically depending on the type and the thickness of the film which forms the packaging and depending on the characteristic features of the tray which contains the packaged product. The end part of the apparatus may be provided with means for cooling the heat-welded packaging, for example a device blowing air at the ambient temperature. It is, for example, possible for at least the shaft of the last roller 14' to be hollow (Fig. 2) and to be connected with one end, by means of a rotating coupling 34, to a source 35 delivering air at the correct pressure and for the said shaft to be provided laterally with holes as indicated by 36, so as to supply fresh air through the pores of the material which form the sponge rubber body 214 of the said last roller.

Claims: CLAIMS 1. Apparatus for the sealed heat-welding of the superimposed edges of a wound strip of thermoplastic film, in particular extensible and protective film which wraps products arranged in trays, characterized in that it comprises: - at least one first horizontal conveyor (1 ) formed by a plurality of parallel and suitably mutually spaced rollers (14) which are driven so as to cause feeding of the product and formed by a steel shaft (114) on which a tubular body (214) of suitable thickness made of any appropriate suitably 0 resilient and yielding material is fixed; - at least one second horizontal conveyor (2), for example of the type with tracks (102) made of a suitable soft material, which is arranged above the first conveyor and motorized so as to cause feeding of the product to be processed, this conveyor being provided with (3-5, 8-13) which allow it to be 5 positioned at an adjustable distance from the lower conveyor, depending on the dimensions of the product to be processed and so to exert on the said product a pressure which causes the resilient deformation of the body (214) of the rollers of the said lower conveyor (1 ) against the bottom part and the bottom side part of the tray of the packaged product, with the consequent uniform o pressing of the edges of the winding film, even though the wound strip itself has zones of varied thickness and even though the surface of the tray is not perfectly flat and even; - heating radiating means (32) which are located below and if necessary also upstream of the rollers of the said first conveyor (1 ) so as to 5 cause plasticization of the winding film necessary for heat-welding thereof, by means of direct irradiation, through the gap which is present between the rollers (14) of the said conveyor and by means of conduction via the same rollers (14). 2. Apparatus according to Claim 1 , in which the rollers (14) of the lower conveyor (1 ) have a body (214) which is made of a suitable silicone-type 0 sponge rubber with suitable resilient and yielding properties. 3. Apparatus according to Claim 1 , in which the rollers (14) of the lower conveyor (1 ) have the same resilient and yielding properties. 4. Apparatus according to Claim 1 , in which the rollers (14) of the lower conveyor (1 ) have varied resilient and yielding properties. 5. Apparatus according to Claim 1 , in which the first and the last rollers (14') of the lower conveyor (1 ) are rotatably supported by the support frame (15) of the said conveyor and are coplanar with each other and with the conveyor (T) from which the packaged product (P) to be processed arrives, whereas all the intermediate rollers (14") are initially at a height suitably greater than that of the other rollers and are designed to be lowered and to be arranged coplanar with the said end rollers, in opposition to resilient means (20) which tend to bring the said rollers back into the raised position, all of which being envisaged so as to ensure better and uniform distribution of the pressure on the product by these rollers and ensure that they also come into contact with the 5 bottom side portions of the product itself, so as to ensure welding of the film edges superimposed thereon. 6. Apparatus according to Claim 5, in which the movable rollers (14") of the lower conveyor are mounted on oscillating levers (16) which are biased upwards by resilient means (20) and controlled by means (19) which o limit the oscillating movement thereof at least upwards. 7. Apparatus according to Claim 6, in which the levers (16) which support the movable rollers (14") of the lower conveyor are provided with a hole (18) through which a pin (19) fixed to the adjacent shoulder of the conveyor frame passes so as to limit both the upwards oscillation and the downwards 5 oscillation of the said levers. 8. Apparatus according to Claim 1 , in which the heating means (32) consist of cup elements which emit infrared rays at a wavelength suitable for plasticization of the film which wraps the packaged product (P), these cup elements being supported, for example, by a suitable casing (33) which is fixed 0 to the sides of the frame (15) of the lower conveyor (1 ). 9. Apparatus according to the preceding claims, characterized in that at least the last roller (14') of the lower conveyor may have an axially hollow shaft (114) which is provided with lateral holes (36), is closed at one end and is connected at the other end, via a rotating coupling (34), to a pressurized- air delivery source (35) for supplying air at the ambient temperature through the pores of the sponge rubber body (214) of this roller, in order to cool and fix the edges of the packaging film immediately after plasticization and compression by the apparatus in question.

Inventors: CAPPI ANGELO, RIMONDI RENATO, CAPPI, ANGELO, RIMONDI, RENATO
Applicants: AWAX PROGETTAZIONE, CAPPI ANGELO, RIMONDI RENATO, A.W.A.X. PROGETTAZIONE E RICERCA S.R.L., CAPPI, ANGELO, RIMONDI, RENATO
Application year: 1999
Main classification: B65B51
IPC codes: B29C35, B29C65, B65B51, B65B59