Aseptic packaging

Abstract: A method of forming an aseptic package and an aseptically filled package using a construction of flexible plastics material (12,13) sandwiching a material (10,11) which is impervious to micro-organisms, the longitudinal seal being made between two surfaces of the same material, and an end closure (20) including a plug (22) of resilient material which ensures the integrity of the closure.

Description: This invention relates to a method of continuously forming and filling flexible aseptic packages. In present aseptic packaging methods there are three areas in which the integrity of the package can break down. In the first of these, if the film or foil, hereinafter called film, is not impervious to the transmission of micro-organisms, oxygen, other gases or water vapour, then there can be degradation of the product by transmission through the film. For ease in this specification we will refer generally to micro-organisms and such reference is considered to relate to other things which can pass through the film and which can degrade the product. In practice, this has normally been overcome, and generally quite satisfactorily, by using a composite film which may preferably have two parent components of a polyester, which may satisfactorily be polypropylene, which are adhesively secured. Generally each of the parent materials has a very thin layer of an impervious material coated thereon, and in many cases this material may be polyvinylidene chloride, and at least one of the layers may also have a film of a metal, such as aluminium vacuum deposited thereon. Such films do provide a good barrier to micro-organisms but, where they are to be connected, such as along a longitudinal seam, if a cylindrical package is being formed, or about the periphery of a differently shaped package, connection is normally by means of heat welding. The weld is made between two very thin layers of PVDC and this can cause the second area of difficulty which is encountered in that the PVDC layer can partially separate from its parent layer and the weld may thus not be microbiologically continuous. Also, physically, it may be that the weld can break if the package is distorted as by being dropped. Further, as PVDC is relatively non-elastic, if there is physical distortion of the package, as when a package is dropped, then the PVDC tends to split and the whole package can split and, not only is the integrity of the package destroyed, the contents may spill. Such packages are generally, not acceptable to distributors and retailers. A further area where there have been difficulties with such packages, particularly when they are in the form of cylinders, has to do with the closing of the cylinders. Normally during formation the filled cylinder, where it is to form the ends of adjacent packages, is compressed and a pair of metallic clips are passed around the compressed cylinder and are deformed to draw the package closed and, after the clips have been closed, the packages are severed between the clips. Because the film is bunched beneath the clip it is possible that there can be a path through the seal to permit degradation of the contents of the package. Also, because the clips are simply crimped, it is possible that, on physical mishandling of the package, there can be deformation of the clip which can destroy the integrity of the package. EP-A-0038075 relates to a packaging material for aseptic packages. A laminate material is formed consisting of a relatively rigid base layer of paper or cardboard one side of which is covered by a polyethylene coating. A layer of aluminium foil is laminated to the base layer by means of an intermediary thin polyethylene layer, although this aluminium layer may not always be provided. A thicker polyethylene layer is then provided and on this a thermoplastic boundary layer and an outer polypropylene layer are provided. In the manufacture of packages, the polypropylene layer is pulled off the laminate which is formed into a tube, filled and sealed at its end by a sealing device which presses the sides of the tube together. DE-B-2106556 relates to a packaging method in which a filled tube of material is pinched and sealed at one packaging station and then has two ties applied at the seal and a cut made between the ties at a second station. The invention is designed to overcome, or at least minimise, the disadvantages set out hereinbelow. According to the invention, a method of continuously forming and filling flexible aseptic packages from a film which has outer layers of a flexible plastic material having sandwiched therebetween a flexible layer of a material which is impervious to microorganisms, comprises the steps of forming a continuous substantially cylindrical package from the film with adjacent edges thereof being in contact to form a cylinder, heat sealing said adjacent edges of the film, with the plastic materials of the adjacent edges which are sealed together being the same, filling the cylinder, compressing the filled cylinder at the positions where the cylinder is to be divided into individual packages, placing two clips about the cylinder in the compressed area, tightening the clips to close the adjacent ends of the individual packages and separating the cylinder between the clips into individual packages. A package produced in accordance with the invention is illustrated in the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view showing the arrangement of the foodstuff package; Fig. 2 is an enlarged view at 2 of Fig. 1 showing the constituents of the film; Fig. 3 is a partial view along line 3-3 of Fig. 1 showing a form of lap joint; Fig. 4 is a Figure similar to Fig. 3 showing a fin joint before this is turned over against the package; Fig. 5 is a view similar to that of Fig. 3 but showing the addition of an adhesive which aids the mechanical stability of the package; and Fig. 6 is an end view of the package showing the location of the adhesive plug in the area where the package is sealed. Referring initially to the formation of the film, this comprises a central polyester layer 10, a deposited metal film 11 and two outer layers 12, 13 of a flexible plastics material, preferably polyethylene. Whilst the layers 10, 12 and 13 may not be completely impervious to the transmission of micro-organisms, oxygen, other gasses or water vapour, the imperviability is provided by the metal film 11. Preferably this is a film of aluminium which is deposited on the central polyester film 10 prior to the location of the outer films 12, 13 thereover, the outer films being formed either by coextrusion or adhesive securing to the central film. The deposited layer 11 can be very thin, whilst giving a complete coverage and complete imperviability, but, at the same time, is very flexible, as will be discussed hereinafter. Preferably the deposited layer can be printed to provide an attractive pack for the product. The outer layers are preferably of linear low density polythene and these may have additives, known in the packaging art, for example to increase clarity and for other purposes. The film is basically made of very thin layers and an exemplification could be that the central layer 10 of polyester may be 10 µm thick; the deposited film 11 may be of aluminium and may be of 1-2µm thick; and the outer layers 12, 13 may of a linear low density polyethylene and may be 30,µm thick, giving a total thickness of the order of 72-75 µm when the securement of the layers is considered. We have found a film of this thickness gives a good package integrity, including a good feel. This is distinguished from the films which are used in non-aseptic packaging processes, normally called retort packaging, in which the product is initially hermetically sealed within the package and then goes through a retorting process which cooks the product and, at the same time, destroys any micro-organisms which are within the package. It will be appreciated that, physically, the packaging for such products must be strong, and any seals must be extensive, as there is a substantial increase in pressure within the package during the retorting process. Also, very often, an aluminium foil is incorporated in the packaging material which adds to the expense and, as indicated herein, is unsatisfactory for an aseptic package where the ends of the package are drawn together and crimped, as the aluminium tends to pinhole or crack. If deposited aluminium is used, this can degrade at retorting temperatures. Further, such films need to use adhesives which are stable at temperatures of the order of 120°C, whereas, using the process described, stability to the order of 80°C is all that is required. With the package, described, the product, whilst it is fed to the package hot, has been sterilised during the cooking procedure and the filling process is aseptic so that there is no contamination introduced during this procedure and post filling treatment is not required. It is for this reason that films can be used which are, over all, very much thinner, and thus cheaper, than the films used in retort packages. The film has substantial advantages over previous films, and particularly those which included layers of PVDC, which is a relatively non-elastic material. The film, as a whole, has a high degree of elasticity and, thus, it can accept substantial physical mishandling without damage. By using the film described, even a relatively heavy package will not be damaged by being dropped, for example, onto a floor from a substantial height. The package is sufficiently resilient to absorb such treatment without damage. This is, of course, important from a sales point of view. The main competitive forms of packaging for the type of foodstuffs to which this invention relates are canned packages or retort packages. Canning is basically expensive, because of the cost of the can and the cost in sealing the can and, for some products, is not completely satisfactory as the products are treated under high temperatures and pressures to destroy microorganisms. On the other hand, physically, a can is a very satisfactory method of storing products as cans are strong, but cans can be badly distorted if dropped from a height and can be pierced on striking a sharp object, although this is unusual. Retort packaging suffers from a disadvantage similar to cans in that the product is treated to high temperatures and pressures, often to its detriment, and, generally, retort packages tend to be damaged if, say, dropped onto a surface from a height. Also, as discussed earlier, the films used for retort packaging are relatively expensive because they are thick. The film described thus has substantial advantages over both these previously used forms of packaging whilst having only minor disadvantages. Referring now to Figs. 3 and 5, means are shown whereby the longitudinal seal of a package can be made. Fig. 3 shows the most usual type of seal, a lap seal, and it will be seen that the outer layer 13 along one edge of the film is in contact with the inner layer 12 along the other edge of the film and it is these two layers which are connected together. As previously explained, these layers are of a similar material, in the specific example, polyethylene, and it is thus possible to make a good and continuous seal between these layers thus preventing ingress of micro-organisms or other deleterious gasses into contact with the food contained in the package. Also, as each of these films can be strongly laminated to the central layer 10, there is no likelihood of delamination when the seal is made and thus a good and coherent package is formed. The example of Fig. 4 is somewhat different as, in this case, the abutting surfaces, which form a fin 15, are both the inner layer 12. This, of course, ensures, once again, a good seal being achieved but this arrangement can be used where the inner and outer layers are of different material. In the form of arrangement shown in Fig. 4, there would normally be another step in the formation of the cylindrical package, that is by turning the fin 15 to one side and then securing it to the surface of the package. Fig. 5, as explained, is a view similar to that of Fig. 3 but, in this case, an adhesive material 16 is provided at the edge of the lap joint, which material can assist in aiding the mechanical integrity of the seal as well as adding an additional barrier to the passage of micro-organisms. In the manufacture of a product which is aseptically packaged in film, the film, either in the form of a cylinder or in the form of a sheet which is formed into a cylinder, is filled continuously with a material and where the individual packages are to be formed, means are provided to compress the cylinder thus, basically, removing the material being packaged from the area and when compression is completed, deformable clips 21 are placed about the package at two spaced positions, which clips effect the sealing of the ends of the packages and, after location, the material 22 between the clips is severed. Conventionally, the clips 21 used were of aluminium, as being a metal which is relatively easy to deform, but it is preferred to use steel clips which, although more difficult to deform, once they are deformed, tend to retain their deformed condition and are unlikely to be displaced. In the sealing of the ends, it will be appreciated that the film is bunched whilst the foodstuff in the package is displaced and, provided the final compression is sufficient, there should be no voids through the seal. However, because of this bunching, there is always a possibility that a passage sufficient for the passage of micro-organisms can be left in the sealed end. In order to overcome this, I prefer to locate, at the position at which the seal is to be maintained, an adhesive material, which may be a micro-crystalline wax or some form of silicone adhesive, which material, on compression, flows to fill any interstices which are left in the package and to, thus, increase the integrity of the seal. The wax or adhesive should have properties of a good tack, to adhere to the film, be solvent free, plastic at the clipping stage, be compatible with food and be of relatively low cost. Two suitable materials are those sold under the trade marks "Ultraflex Amber" and "Microflex". This adhesive may be applied to the film as it is passing along its path to the position where it is formed into the package and, preferably, the adhesive sets so that it retains its position on the film during movement. When the actual closing step takes place, as the clip is tightened, the adhesive is caused to flow into any interstices in the film and fill these. It may be preferred that the adhesive softens or melts, at least to a certain degree, when heated by the product which is in contact with the adhesive, to aid this flow. When the product cools, the adhesive sets to form a plug which provides a barrier to the passage of micro-organisms. The adhesive is selected so that it is inert to foodstuffs and does not attract foodstuff to its surface, although this is not critical as the package is normally opened by removing the end inside the clip and the adhesive would normally be discarded with the end of the package and the clip. It will be seen that the adhesive not only provides a physical barrier for micro-organisms and other deleterious substances, but, also, can act to physically strengthen the package at its ends. It will be seen that the invention provides an aseptic package which is more successful than previously proposed packages and, at the same time, provides a package which can permit satisfactory packaging of products at a price which can be substantially less than competitive packages.

Claims: A method of continuously forming and filling flexible aseptic packages from a film which has outer layers (12, 13) of a flexible plastic material having sandwiched therebetween a flexible layer of a material (10, 11) which is impervious to micro-organisms, comprising the steps of forming a continuous substantially cylindrical package from the film with adjacent edges thereof being in contact to form a cylinder, heat sealing said adjacent edges (15) of the film, with the plastic materials of the adjacent edges which are sealed together being the same, filling the cylinder, compressing the filled cylinder at the positions where the cylinder is to be divided into individual packages, placing two clips (21) about the cylinder in the compressed area, tightening the clips to close the adjacent ends of the individual packages and separating the cylinder between the clips into individual packages. A method as claimed in claim 1 wherein an adhesive (22) is located in the cylinder at positions where the cylinder is to be divided into individual packages, the arrangement being such that as the clips (21) are tightened, the adhesive flows to occupy any interstices formed in the film during compression to thereby provide a plug of adhesive material beneath and between the clips. A method as claimed in claim 2 wherein the adhesive (22) is placed on the film during delivery and during the tightening of the clips (21) the adhesive softens because of contact with the hot product in the package and can therefore flow. A method as claimed in claim 2 or claim 3 wherein the adhesive (22) is a microcrystalline wax or a silicone adhesive. A method as claimed in any preceding claim, wherein the impervious material comprises a layer of polyester material (10) and a continuous layer (11) of metal. A method as claimed in claim 5 wherein the metal is aluminium. A method as claimed in claim 5 or claim 6 wherein the layer (11) of metal is deposited on the polyester material (10). A method as claimed in any preceding claim, wherein the outer layers (12, 13) are of polythene. A package which has been aseptically filled made by the method of any of the preceding claims.

Inventors: DONALD ROBERT ARCHIBALD, DONALD, ROBERT ARCHIBALD
Applicants: DONALD ROBERT ARCHIBALD, DONALD, ROBERT ARCHIBALD
Application year: 1986
Main classification: A22C11
IPC codes: A22C13, B65D75