Improvements in or relating to film packaging

Abstract: Packaging apparatus, using an upper film (6) pre-heated before contact with a lower film (9) on which products (not shown) are placed, has at least the central region heated by radiant heaters (7) and the marginal regions heated by hot air nozzles (10) at least in the region immediately preceding contact (8) between the upper and lower films.

Description: The present invention relates to a packaging process and apparatus in which one or more articles can be placed between opposing film sheets which are sealed together, and often vacuum draped or shrunk into intimate contact with the enclosed article(s). In known forms of such apparatus a base film, which may or may not be thermoformed into a succession of trays, is advanced along a packaging table and the articles are then placed on that film and subsequently covered by a second flexible packaging film which descends into contact with the base film and the articles thereon in order to become sealed where the two films come in contact with one another hence enclosing completely the articles which may either be arranged as a succession of individual articles or as a succession of groups of articles which are intended to form a package comprising a respective said group. One example of such an apparatus is disclosed in EP-A-0270208 in which Figure 1 shows the base film being unwound at one end of the packaging table and thermoformed into trays, following which the cover film is paid out from a downstream overhead roll and is brought into contact with the articles on the base film. The present invention is particularly concerned with such an apparatus in which the cover film is pre-heated before coming into contact with the base film. It has been known to pre-heat the cover film before contacting it with the base film, for example by feeding the cover film past an array of heat-emitting lamps. There are circumstances when this heating is not fully effective. For example, when packaging a tall product which has to pass below all of the heat-emitting lamps, and be sufficiently below them to avoid damage due to exposure to their radiant heat, the last lamps nearest the point of juxtaposition of the cover film with the base must be positioned a long way ahead of the sealing location giving the cover film time to cool down before sealing. This cooling is all the more noticeable along the margins of the cover film where the clamps advancing the cover film tend to be relatively cool and serve to absorb heat from the margins of the cover film. There is thus a tendency for at least the marginal seals to be weak and possibly also for the ends of the transverse seal lines to be insufficiently hot at the time of sealing so the leading corners of the package are inadequately sealed. Accordingly, one aspect of the present invention proposes apparatus as defined in claim 1. A second aspect of the present invention proposes a process as defined in claim 5. US-A-4133163 discloses the use of a hot air nozzle 25 extending along the line of contact between an upper film and a lower film which are to be brought together for forming a skin pack, and calls for this heating to be downstream of a heated drum 23 which initially pre-heats the cover film. Hence the heat is applied to the cover film in two stages, both being across the full width of the cover film which is freely stretched between the heating drum 23 and roller clamps 26. US-A-4133163 has been used as the basis for the pre-chacterizing portion of claim 1 and of claim 6. In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings in which:- FIGURE 1 is a side view showing the overall machine in accordance with the present invention; FIGURE 2 is a detail showing the path of the cover film as it approaches the base film near the sealing station; FIGURE 3 is a view of the apparatus and film of Figure 2 when seen along the direction of arrow 3 thereof; and FIGURE 4 is a detail of one row of packages being formed using the apparatus in accordance with the present invention, and illustrating the potential areas of weak seal which have been eliminated by use of the present invention. Figure 1 shows a side elevational view of a machine capable of dispensing a lower polyethylene film (9 in Figure 2) from a supply roll 1 and feeding it along a table 2 where products (not shown) can be placed on the film by non-illustrated means, following which the products and the lower film are covered by an upper polyethylene film (6 in Figure 2) from a supply roll 3, The two films 6 and 9, with the products between them, then pass through a sealing station 4, in this case a vacuum skin packaging (VSP) station, where the upper and lower films are sealed to one another, and subsequently the thus formed packs are severed from one another at a severing station 5. In the VSP process the space between the two films is evacuated and at least one of the films is heated to soften it sufficiently for it to drape on to the other film and on to the product therebetween, so as to form an evacuated package which conforms to the contours of the product like a skin. The region directly below the supply roll 3 of the covering film is shown in more detail in Figure 2 where the covering film 6 is illustrated as being guided, by a chain of grippers (not shown), past a battery of infra-red heater elements 7 for pre-heating the film in a known manner before it arrives at the point of contact 8 with the lower film 9 having the product (not shown) thereon. Over the last part of the travel of the upper film 6 toward the line of contact 8, the marginal portions of that film web pass directly below elongate nozzles 10 through which hot air is injected to be dispensed directly above and in contact with the corner region where the marginal portions 11 of the upper film 6 intersect the line of contact 8 between the upper and lower films 6 and 9, respectively. To some extent the region of the film 6 passing alongside each elongate nozzle 10 may be heated by radiation at a low rate from the nozzle and hence there is a two-stage heating process which is concluded when the hot air issuing from the nozzles 10 contacts the upper face of the upper film 6. This second, independent heating action is sufficient to ensure that the contact between the upper and lower films is adequate to seal the heated upper film 6 to the lower film 9 completely over the whole of its width and hence no unsealed areas such as areas 12 in Figure 4 will arise. Although the products are omitted from Figures 1 and 2, a typical array of three products 13 a , 13 b and 13 c is shown in Figure 4 which also defines the leading edge 14 a and the trailing edge 14 b of a pack (the pack itself being defined once the film assemblies have passed through the severing station 5 of Figure 1). The direction of movement of the products and films in Figure 4 is illustrated by the arrow 15. As will be evident from the above description, the use of the infra-red heating lamps 7 to pre-heat the film 6 is well known but has been found to be in some circumstances unsatisfactory as regards the heating of the marginal portions 11 of the upper film 3, partly because of the limited extent of the lamps 7 across the width of the cover film 6, partly because of the need for the marginal regions 11 of the upper film 6 to be held by the movable grippers which conceal the film from the heat radiation in order for that holding action to guard against contact of the film 6 with the radiant heaters 7, partly due to the loss of heat by conduction to the conveyor grippers, and partly due to the fact that there is a long run of the cover film between the last heat-emitting lamps and the sealing means during which the pre-heated cover film tends to cool down. For example, whereas most of the cover film may be pre-heated to the level of 100°C to 110°C required for good sealing, the marginal portions may only be in the range 80°C to 90°C in the absence of the hot air nozzles. The air from the nozzles 10 brings the temperature of the margins up to 100°C to 110°C. As indicated above, the application of air heating near the line of contact 8 is adequate to overcome the deleterious effects on the seal, resulting from the lower temperature of the marginal portions of the upper film 6. If these unsealed corner regions were to be left in the finished pack, there would be a loss of vacuum experienced in cases where the space immediately around the products 13 a , 13 b and 13 c and between the films 6 and 9 is intended to be evacuated in an airtight manner in the package. As indicated above, although the present invention is intended to have primary application in the type of VSP process where the lower film is flat and the products stand proud of it, it can equally apply to cases where the lower film is thermoformed into usually shallow trays, and the covering film is intended to drape onto both the tops of the articles and the bases of the trays. The process and apparatus of the present invention are particularly useful in the formation of packages using a multi-layer film which may, for example, have a thickness in the range 75 µm to 150 µm. One such film is an oxygen barrier film incorporating a barrier layer of EVOH and known by the Registered Trade Mark "DARFRESH". It would also be possible for the second film 9 forming the base for the products to be advanced by means of a chain of grippers which can have its grippers open just before the point of convergence of the covering film 6 with the path of movement of the base film 9, in order to allow the same set of grippers to advance the two films together, in contact with one another, into the VSP station where they are intimately contacted with one another and with the product therebetween. In this case the action of these lower grippers receiving the covering film 6 as well as the base film 9 may be adequate to convey the covering film 6 past the infrared heaters 7 and the heating nozzles 10, but it is nevertheless possible for there still to be a separate chain of grippers to advance the covering film 6 towards the line of contact between the films 6 and 9.

Claims: Apparatus for packaging products in film, comprising sealing means (4) for bringing first (6) and second (9) films into contact with one another and with at least one product therebetween to seal said first and second films about the product; radiant heating means (7) for heating a web of said first film before contact with said second film; and a hot air nozzle for further heating said web of the first film; characterised by the fact that there are said hot air nozzles positioned at the marginal portions of said web of the first film for conductively heating said marginal portions of the first film web before contact of said first and second films (6 and 9), independently of said radiant heating means (7), said further heating means being operative on the web of the first film after it has been heated by said radiant heating means (7). Apparatus according to claim 1, characterised in that the means for bringing the first and second films (6 and 9) into contact with one another is a vacuum skin packaging chamber (4). Apparatus according to any one of the preceding claims, characterised by movable grippers engaging the margins of said web of the first film (6) and advancing the gripped film web towards the means for contacting the films. Apparatus according to claim 2, characterised by movable grippers advancing a web of said second film towards said means for contacting the first and second films, said grippers being openable to receive said web of the first film before said web of the second film enters said vacuum skin packaging chamber (4). A process for packaging articles between heat sealable thermoplastic films, comprising introducing product articles between first and second films, heating a web of said first film by radiant heating means across at least the majority of said web of the first film extending outwardly from a centre line of the web of the first film, and thereafter contacting said first and second films with the product therebetween to seal the first film to the second film, and independently further heating said first film using a hot air nozzle; characterised in that there are said hot air nozzles positioned for heating the opposed marginal regions of said web of the first film before the films contact one another but after exposure of said first film to the radiant heating means. A process according to claim 5, characterised in that said radiant heating is infra-red heating. A process according to either of claims 5 and 6, characterised in that said first and second heat sealable films are polyethylene.

Inventors: BREMBILLA SANDRO C O PACKAGING, BREMBILLA, SANDRO, BREMBILLA, SANDRO, C/O PACKAGING TECHNICAL CENTER
Applicants: GRACE W R & CO, W.R. GRACE & CO.-CONN.
Application year: 1990
Main classification: B65B11
IPC codes: B65B11, B29C65