Patent Publication Number: US-2012045558-A1

Title: Method for the vacuum skin packaging of products with irregular sharp surfaces

Description:
TECHNICAL FIELD 
     The present invention relates to a vacuum skin packaging process suitable for the packaging of products with irregular and sharp surfaces. The process is particularly suitable for the packaging of food products provided with mechanically abusive surfaces, like bones, claws or hard shells, such as crustaceans or shellfish. 
     BACKGROUND ART 
     Vacuum skin packaging (VSP) is a process well known in the art using a thermoplastic packaging material to enclose a food product. The vacuum skin packaging process is in one sense a type of thermoforming process in which an article to be packaged serves as the mold for a forming web. An article may be placed on a rigid or semi-rigid support member, that can be flat or shaped, e.g., tray-shaped, bowl-shaped or cup-shaped (called “bottom” web), and the supported article is then passed to a chamber where a “top” web is first drawn upward against a heated dome and then draped down over the article. The movement of the top web is controlled by vacuum and/or air pressure, and in a vacuum skin packaging arrangement, the interior of the container is vacuumized before final welding of the top web to the bottom web. The distinguishing feature of a vacuum skin package is that the upper heated film forms a tight skin around the product and is sealed to the whole surface of the support not covered by the product. 
     The terms “vacuum skin packaging” or “VSP” as used herein indicate that the product is packaged under vacuum and the space containing the product is evacuated from gases at the moment of packaging. The top flexible film is referred to as “skin-forming” or “skin” film. 
     Vacuum skin packaging is described in many references, including FR 1,258,357, FR 1,286,018, AU 3,491,504, U.S. RE 30,009, U.S. Pat. No. 3,574,642, U.S. Pat. No. 3,681,092, U.S. Pat. No. 3,713,849, U.S. Pat. No. 4,055,672, and U.S. Pat. No. 5,346,735. 
     U.S. Pat. No. 5,896,994 relates to VSP packages comprising an oxygen scavenger film strip for limiting the exposure of oxygen-sensitive products to oxygen, thus enhancing their shelf-life. The oxygen scavenger film strip does not cover the entire dimension of the package. This document does not mention the possible drawbacks in packaging sharp and irregular products. 
     U.S. Pat. No. 5,560,182 describes meat packages comprising a plastics material base, goods on the base, a plastics material flexible web which skin the goods to the base and an outer lid. At retail display the impermeable outer lid can be peeled off to allow oxygen to permeate the remaining permeable inner skin to restore the original colour of the meat (blooming). This document neither discloses simultaneous draping and welding of the two top films over the goods on the base nor deals with the possible problems arising in VSP packaging of sharp and irregular products. 
     Although a wide variety of products, especially food products, are being offered in visually attractive packages made using the vacuum skin packaging process, limitations still remain for the packaging of products provided with highly irregular and sharp surfaces. Particularly demanding is the vacuum skin packaging of food products like bone-in meat, and more particularly, crustaceans, such as crabs, lobsters, prawns etc. or shellfish, such as oysters, mussels etc. These products are not only provided with extremely sharp and tough edges but they also have very irregular shapes which require the skin film to be highly stretched in some areas which are then more prone to puncturing. 
     DISCLOSURE OF INVENTION 
     It has now been found that the limitations encountered so far in the packaging of products with irregular and sharp surfaces can be overcome by a vacuum skin packaging (VSP) process wherein a twin skin film is fed to a conventional vacuum chamber and draped over the product. 
     In particular, it has been surprisingly found that in VSP packaging of irregular and sharp products it is possible to overcome the mentioned drawbacks of puncturing and unsatisfactory draping of the top film by using a twin film instead of a single film of comparable thickness and composition in a conventional VSP process. 
     The expressions “twin skin film” and “twin film” are used herein to indicate a composite film comprising at least two separate films superimposed the one on the other. When referred to films or webs the term “superimposed” is used herein to indicate films which are contiguously placed the one in contact with the other without any chemical or physical connection between them. In other words superimposed films are not welded, bonded, adhered, glued or sealed together. 
     Preferably the component films of the twin film have substantially the same longitudinal and transversal dimensions at any stage of the packaging process, as well as in the final package, said same dimensions being suitable for providing a satisfactory draping on the products and welding to the part of the support not covered by the products of both the films. 
     Accordingly, a first object of the present invention is a VSP process wherein a twin skin film is used as the top web. The VSP process comprises the steps of placing a product loaded support in a vacuum chamber, positioning a twin skin film above the product loaded support, allowing the twin skin film to drape itself over the product and to weld to the whole surface of the support not covered by the product to obtain a vacuum skin package. 
     At the entrance of the vacuum chamber the component films of the twin skin film are still not welded, bonded, adhered, glued or sealed together, i.e. they are superimposed. Once fed to the vacuum chamber, the twin skin film is draped over a product loaded on the support as in a conventional VSP cycle and welded to the whole surface of the bottom web which is not covered by the product. 
     The at least two separate films superimposed the one on the other forming the twin skin film of the present invention, when subjected to the VSP process as described above, simultaneously drape themselves over the product and weld together to the whole surface of the support not covered by the product. 
     In a first aspect of the VSP process of the invention the twin skin film is fed to the vacuum chamber from a single roll. The single roll comprises the component films of the twin film wound together. 
     In a second aspect the films composing the twin skin film are unwound from separate rolls and combined together to form the twin skin film before being fed to the vacuum chamber. 
    
    
     
       The present invention will be described in detail with reference to the following drawings, wherein: 
         FIG. 1  schematically shows a VSP process according to a first embodiment of the present invention; 
         FIG. 2  schematically shows a VSP process according to a second embodiment of the present invention. 
       The same reference numbers will be used throughout the following description for indicating the same or functionally equivalent parts. 
     
    
    
     A first embodiment of the VSP process of the present invention is illustrated in  FIG. 1 , wherein the working direction is indicated by arrow X and it is from right to left. In  FIG. 1 , sheet-like material  3  to form the support or bottom web is unrolled from roll  2 . 
     As the material moves to the left it passes over a bottom forming station  4 . At this station, a thermoforming operation takes place in which the web  3  is heated to its softening and forming temperature and then drawn into the mold where it assumes the shape of the mold. After cooling the now formed tray  5  is moved to the left to the product loading station  6 . Alternatively, bottom forming station  4  can be eliminated and preformed supports can be used instead. At the loading station  6 , product to be packaged  7  is loaded into the tray. 
     Once the product has been properly positioned on the tray, the product loaded tray  8  moves to the vacuum chamber  9 . 
     Before being fed to the vacuum chamber  9  the twin skin film  10  may be optionally preheated. When a preheating station is present it is possible to heat all or only part of the component films of the twin skin film. For instance, when the twin skin film consists of only two component films only one of them may be preheated by passage through the preheating station. When the twin skin film consists of more than two component films all of the component films, only one of them or alternative more than one of the component films may be preheated by passage through the preheating station depending on the nature of the films. 
     In the embodiment shown in  FIG. 1 , twin skin film  10  is unwound from a single roll  11  and preheated at station  12 . In a typical VSP apparatus the vacuum chamber  9  comprises an upper dome  13  and a lower or bottom cavity  14 . Inside the dome the twin film  10  is drawn up against the heated interior of the dome and held there while the product containing space is evacuated. When the chamber has been evacuated, the twin skin film  10  which has been held by vacuum in contact with the dome interior heated surface is released and atmospheric pressure is applied from above, thus causing the pressure differential in the evacuated chamber to force the heated twin film down around the product to assume the product&#39;s shape. Once the twin film is welded to the tray all around the product, the vacuum chamber is ventilated and opened in order to move the sealed packages to the transversal and longitudinal cutting stations  15 , thus leaving the vacuum chamber ready for a new cycle. Unitary packages  16  are obtained at the end of the cutting operations. 
     It has been observed that although the films composing the twin film are only superimposed the one on the other when they enter the vacuum chamber, without any physical or chemical bonding in between, they drape simultaneously over the product without forming any pleat. Final packages are obtained with smooth, pleat-free skin surfaces. 
       FIG. 2  shows an alternative embodiment of the VSP process of the present invention wherein the films composing the twin film  10 ,  10   a  and  10   b,  are wound on two separate rolls  11   a  and  11   b  and are brought together before the vacuum chamber. The respective positions of rolls  11   a  and  11   b  are selected only on the basis of design efficiency of the apparatus. In the specific embodiment shown in  FIG. 2  rolls  11   a  and  11   b  are close to each other roughly above the vacuum chamber. 
     In this second embodiment the VSP process of the invention offers the additional advantage of greater flexibility as it is possible to switch between using a twin skin film or a single film easily and rapidly, by simply excluding one of the two component films from the VSP process. 
     Depending on the chemical composition of the component films of the twin skin film, it may or may not be possible to separate them in the final package. 
     The packaging method according to the first embodiment of the present invention can be run on any conventional VSP machine. The packaging method according to the second embodiment of the present invention can be run on a conventional VSP machine by introducing therein only minor modifications, such as the addition of a second roll unwinding station. 
     Bottom web  3  is typically a rigid or semi-rigid material. Preferably the bottom web is made of a multilayer material comprising, in addition to a heat-sealable layer to allow welding of the twin skin film to the part of the support not covered by the product, at least one bulk layer for the mechanical properties. 
     In a number of applications the bottom web is required to have gas barrier properties, in particular oxygen barrier properties. Thus, in addition to a bulk and a heat-sealable layer, bottom web  3  will be provided with a gas barrier layer. The thickness of the gas barrier layer will be typically set in order to provide the support with an oxygen transmission rate lower than 30, lower than 15, preferably lower than 10 cm 3 /m 2 .d.atm (as measured according to ASTMD-3985 at 23° C. and 0% relative humidity). 
     Generally the heat-sealable layer is selected among polyolefins, such as ethylene homo- or co-polymers, propylene homo- or co-polymers, ethylene/vinyl acetate copolymers, ionomers. Suitable heat-sealable layers may also include peelable blends to provide the package with an easy-to-open feature. 
     As used herein, the term “copolymer” refers to a polymer derived from two or more types of monomers, and includes terpolymers. 
     Ethylene homopolymers include high density polyethylene (HDPE) and low density polyethylene (LDPE). 
     The term “ethylene copolymer” is used herein to refer to ethylene/alpha-olefin copolymers. Ethylene/alpha-olefin copolymers generally include copolymers of ethylene and one or more comonomers selected from alpha-olefins having from 4 to 12 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like. 
     Ethylene/alpha-olefin copolymers generally have a density in the range of from about 0.86 to about 0.94 g/cm 3 . The term linear low density polyethylene (LLDPE) is generally understood to include that group of ethylene/alpha-olefin copolymers which fall into the density range of about 0.915 to about 0.94 g/cm 3  and particularly about 0.915 to about 0.925 g/cm 3 . Sometimes linear polyethylene in the density range from about 0.926 to about 0.94 g/cm 3  is referred to as linear medium density polyethylene (LMDPE). Lower density ethylene/alpha-olefin copolymers may be referred to as very low density polyethylene (VLDPE) and ultra-low density polyethylene (ULDPE). Ethylene/alpha-olefin copolymers may be obtained by either heterogeneous or homogeneous polymerization processes. 
     Ethylene/unsaturated ester copolymers are copolymers of ethylene and one or more unsaturated ester monomers. Useful ethylene/unsaturated ester copolymers are ethylene/vinyl acetate copolymers (EVA), copolymers of ethylene and alkyl esters of acrylic or methacrylic acid, where the esters have from 4 to 12 carbon atoms. 
     The term “ionomer” (Io) refers to the ionized or partially ionized form of a copolymer of ethylene with a copolymerisable ethylenically unsaturated carboxylic acid monomer selected from acrylic acid and methacrylic acid wherein the neutralizing cation can be any suitable metal ion, e.g. an alkali metal ion, a zinc ion, or other multivalent metal ions. 
     Useful propylene copolymers include propylene/ethylene copolymers (EPC), which are copolymers of propylene and ethylene having a majority weight percent content of propylene, and propylene/ethylene/butene terpolymers (EPB), which are copolymers of propylene, ethylene and 1-butene. 
     Suitable thermoplastic materials with low oxygen transmission characteristics to provide packaging materials with gas barrier properties are PVDC, EVOH, polyamides, polyesters or blends thereof. 
     PVDC is any vinylidene chloride copolymer wherein a major amount of the copolymer comprises vinylidene chloride and a minor amount of the copolymer comprises one or more unsaturated monomers copolymerisable therewith, typically vinyl chloride, and alkyl acrylates or methacrylates (e.g. methyl acrylate or methacrylate) and the blends thereof in different proportions. Generally a PVDC barrier layer will contain plasticisers and/or stabilizers as known in the art. 
     EVOH is the saponified product of ethylene-vinyl ester copolymers, generally of ethylene-vinyl acetate copolymers, wherein the ethylene content is typically comprised between 20 and 60% by mole and the degree of saponification is generally higher than 85% preferably higher than 95%. 
     The term “polyamides” includes aliphatic homo- or co-polyamides commonly referred to as e.g. polyamide 6, polyamide 69, polyamide 610, polyamide 612, polyamide 11, polyamide 12, polyamide 6/12, polyamide 6/66, polyamide 66/610, modifications thereof and blends thereof. Said term also includes crystalline or partially crystalline, aromatic or partially aromatic, polyamides, such as polyamide 6I/6T or polyamide MXD6. 
     The term “polyesters” refers to polymers obtained by the polycondensation reaction of dicarboxylic acids with dihydroxy alcohols. Suitable dicarboxylic acids are, for instance, terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid and the like. Suitable dihydroxy alcohols are for instance ethylene glycol, diethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Examples of useful polyesters include poly(ethylene 2,6-naphtalate), poly(ethylene terephthalate), and copolyesters obtained by reacting one or more dicarboxylic acids with one or more dihydroxy alcohols, such as PETG which is an amorphous co-polyesters of terephthalic acid with ethylene glycol and 1,4-cyclohexanedimethanol. 
     Additional layers, such as tie layers, to better adhere the gas barrier layer to the adjacent layers, may be present in the bottom web material for the support and are preferably present depending in particular on the specific resins used for the gas barrier layer. 
     In case of a multilayer structure, part of it can be foamed and part can be cast. For instance, the bottom web may comprise (from the outermost layer to the innermost food-contact layer) one or more structural layers, typically of a material such as polystyrene, polyester, poly(vinyl chloride), polypropylene or cardboard; a gas barrier layer and a heat-sealable layer. 
     The overall thickness of the support will typically be up to 8 mm, preferably it will be comprised between 0.2 and 7 mm and more preferably between 0.2 and 6 mm. 
     In the VSP process of the present invention the top web is a twin film, that is a composite film consisting of at least two superimposed component films, i.e. at least two films adjacent the one to the other without any chemical or physical bonding in between. When the twin film enters the vacuum chamber the two component films are not bonded, sealed or welded to each other in any area, even when a preheating step is provided for in the process. At the exit of the preheating station it is possible that the component films may loosely stick to each other, however no permanent bond or seal exists between them. 
     Preferably, the component films of the twin film have substantially the same longitudinal and transversal dimensions at any stage of the packaging process, as well as in the final package. 
     When required, the oxygen transmission rate of the overall twin skin film will be set to be lower than 25, lower than 15, preferably lower than 10 cm 3 /m 2 .d.atm when measured at 23° C. and 0% RH. 
     Twin skin&#39;s component films may have any number of layers. For example each component film may independently have a total of any of the following: from 1 to 20 layers, at least 2 layers, at least 3 layers, at least 5 layers, from 5 to 10 layers, from 5 to 9 layers. First and second component films suitable for this application have a thickness in the range of from 20 to 200 microns, from 50 to 160 microns, from 70 to 150 microns. 
     Twin skin&#39;s component films are obtained by any suitable extrusion or co-extrusion process, either through a flat or a round extrusion die, preferably by cast or by hot blown extrusion techniques. 
     Typically at least one of the component films, or only one or more of the thermoplastic layers thereof, is cross-linked to e.g. improve the strength of the film and/or the heat resistance when the film is brought in contact with the heated dome during the vacuum skin packaging process. Cross-linking may be achieved by using chemical additives or by subjecting the film layers to an energetic radiation treatment, such as a high-energy electron beam treatment, to induce cross-linking between molecules of the irradiated material. 
     Packaging films often includes printed images to provide the consumer with visual information. The images may be printed on the outermost surface of the twin film, that is the surface forming the exterior of the final package. Preferably, the images are printed on the internal surface of at least one of the component films, that is on the surface of one component film which faces and is in contact with the inner surface of another component film when the films are brought together in the twin skin film. 
     The twin film comprises at least two component films. Preferably the twin skin film consists of two component films. Typically the twin skin film consists of a first heat-resistant component film and of a second sealable component film. The heat-resistant component film is the component film that will be in contact with the heated dome of the vacuum chamber in the VSP process of the invention. The sealable component film is the component film which will provide the surface of the twin skin film that will be welded to the bottom web. Each of the heat-resistant component film and the sealable component film have an outer surface and an inner surface. The outer surface of the heat-resistant component film corresponds to the outermost surface of the twin skin film in the final package and to the surface in contact with the heated dome during the VSP process. The term “inner surface” for both the heat-resistant component film and the sealable component film indicates the surface of each component film which faces and is in contact with the inner surface of the other component film when the two films are brought together in the twin skin film. The outer surface of the sealable component film corresponds to the surface of the twin skin film that will be welded to the bottom web in the final package. This surface will be referred to as the “heat-sealable” surface. 
     The materials making up the inner surfaces of the component films of the twin skin film are selected in such a way that the two films will not adhere together even after the preheating phase of the VSP process of the invention, when this is present. That is the materials used for the inner layers are combined in such a way that the inner surface of one of the component films is made of a material that it will not adhere to the material making up the inner surface of the other component film. 
     When a preheating step is present in the process, suitable combination of materials for the inner layers of the twin film are for instance HDPE and ionomer, cross-linked HDPE and cross-linked LDPE, ethylene homo- or co-polymers and polypropylene, ethylene homo- or co-polymers and polyamides, ethylene homo- or co-polymers and EVOH, ethylene homo- or co-polymers and PETG, ethylene homo- or co-polymers and ethylene/norbornene copolymers. An inner layer can be made of either one of the materials in each of the suitable combination of materials, as long as the other inner layer is made of the other material in the combination. 
     When no preheating step is present in the process further suitable combinations of materials for the inner layer of the twin skin&#39;s component films can be for instance LDPE and HDPE, ethylene/vinyl acetate copolymers and HDPE. 
     Preferably when the inner surface of one of the component films is made of HDPE the inner surface of the other component film is made of ionomer. 
     Any suitable combination of a heat-resistant component film and of a sealable film can be used for the twin skin film provided they are suitable for use in a VSP process and their inner layers are suitably selected. First and second component films may have the same or different composition. 
     In a first form of realization the twin skin film may comprise a monolayer film and a multilayer film provided with functional properties. 
     When the monolayer film is the heat-resistant component film suitable polymers to be used are HDPE, optionally cross-linked, polyesters, polyamides, ethylene/norbonene copolymers, cross-linked LDPE or LMDPE, cross-linked ethylene/vinyl acetate. 
     When the heat-resistant component film is a monolayer film then the sealable component film is a multilayer film comprising a heat-sealable layer for welding to the bottom web in the VSP package, optionally a gas barrier layer and an inner layer. Suitable polymers for the heat-sealable layer may be ethylene homo- or co-polymers, like LDPE, ethylene/alpha-olefin copolymers, ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, or ethylene/vinyl acetate copolymers, ionomers, co-polyesters, e.g. PETG. Preferred materials for the heat-sealable layer are LDPE, ethylene/alpha-olefin copolymers, ionomers, ethylene-vinyl acetate copolymers and blends thereof. 
     The multilayer component film may also comprise other layers such as adhesive layers, bulk layers and the like to provide the necessary thickness to the film and improve the mechanical properties thereof, such as puncture resistance, abuse resistance, formability and the like. 
     Alternatively, the monolayer film could be the sealable component film of the twin skin film. In this case suitable resins to be used would be the ones indicated above for the heat-sealable layer. The heat-resistant component film would then be a multilayer film comprising a heat-resistant outer layer, optionally a gas barrier layer and an inner layer in contact with the monolayer sealable component film. Suitable resins for the heat-resistant outer layer and the gas barrier layer are as discussed above. The inner layer of the heat-resistant component film would be selected on the basis of the nature of the monolayer sealable film to avoid sticking or bonding of the two component films during the packaging process as discussed above. Preferred combinations of materials for the monolayer sealable film and for the inner layer of the heat-resistant film are HDPE and ionomer. For instance the monolayer sealable film could be made of ionomer and the inner layer of the multilayer heat-resistant film could be made of HDPE. 
     In another form of realization the twin skin film may comprise two multilayer films which can have the same or different layer composition. 
     For instance the component films of the twin skin film could be films which are typically used in VSP processes. 
     Typical films used as skin films in VSP applications comprise an outer sealable layer, a first bulk layer, a tie layer, a gas barrier layer, a tie layer, a second bulk layer and an outer heat-resistant layer. 
     Bulk layers provide the necessary thickness to the film and improve the mechanical properties thereof, i.e. increase puncture resistance, increase abuse resistance, etc. Typical resins for the bulk layers are ethylene homo- and copolymers, ethylene/vinyl acetate copolymers, propylene/alpha-olefin copolymers, ionomers. Tie layers have the primary purpose of improving the adherence of two layers to each other. Tie layers may include polymers, e.g. ethylene copolymers, having grafted polar groups so that the polymer is capable of covalently bonding to polar polymers such as EVOH. 
     Suitable skin films for use as component films for the twin skin film are for instance those sold by Cryovac® under the trade names T5201®, TC201®, TH300®, T5270® or TH301®. 
     Specific examples of suitable skin films for use as component films for the twin skin film have the following layer composition (starting from the heat-resistant layer to the heat-sealable layer):
         FILM A: HDPE/EVA/tie/EVOH/tie/EVA/LDPE (150 microns)   FILM B: HDPE/Io/tie/EVOH/tie/Io/EVA/Io (130 microns)   FILM C: HDPE/LDPE/EVA/tie/EVOH/tie/EVA/LDPE/Io (100 microns)   FILM D: HDPE/EVA/LLDPE/LDPE/LLDPE/EVA/LDPE (100 microns)       

     Specific examples of twin skin films obtained by combining multilayer component films are:
         FILM A//FILM A; FILM A//FILM B; FILM B//FILM B; FILM B//FILM A; FILM B//FILM C; FILM B//FILM D; FILM C//FILM A; FILM C//FILM C; FILM C//FILM D;
 
wherein the layer sequence of each of the films is in the order indicated above and the symbol “//” is used to indicate the interface between the component films.
       

     Preferably, In the VSP process and in the final package of the present invention, the twin films do not comprise oxygen scavenger films. As far as oxygen scavenger films definition is concerned, reference is made to U.S. Pat. No. 5,896,994. 
     The following non-limiting examples will illustrate the advantages of the VSP process of the invention. 
     EXAMPLE 1 AND COMPARATIVE EXAMPLE 1  
     Packaging tests using dummies with nails and razor blades protruding from their surface, loaded on a commercially available bottom web (sold by Cryovac® under the trade name RSC03X25) were packaged using a R272CD vacuum skin packaging machine supplied by Multivac GmbH under standard conditions. The following packaging materials were used as the top skin film: 
     Example 1 
     FILM C//FILM C wound on same roll; 
     Comp. Example 1 
     FILM  2 C, a film having the same layer sequence and relative layer thickness of FILM C but with a total overall thickness of 200 microns instead of 100 microns. 
     No holes or tears were present in the packages obtained with the twin film of Example 1 and the skin film was properly draped around the product. The packages obtained with the film of Comp. Example 1 showed poor formability of the top around the product. 
     EXAMPLE 2 AND COMPARATIVE EXAMPLE 2  
     Packaging tests using lobsters loaded on a commercially available bottom web (sold by Cryovac® under the trade name RSC03X25) were packaged in a VSP process using a R272CD vacuum skin packaging machine supplied by Multivac GmbH at standard conditions. The following top web materials were used: 
     Example 2 
     FILM B//FILM B wound on same roll; 
     Comp. Example 2 
     FILM B 
     With the twin film of the invention packages with no defects, even with high vacuum in the package, were obtained whereas a high number of tears were observed with the standard single film B. 
     The VSP process of the present invention has the advantage over prior art processes that the properties of the skin film in the final package can be modulated even by the packer by suitably selecting the component films of the twin skin film. 
     The VSP process of the present invention is particularly suitable for the packaging of mechanically abusive products having irregular surfaces as the twin film provides more resistance to the damage caused by the sharp edges of the product. Food products which may benefit from the VSP process of the invention are in particular bone-in meat and, preferably, crustaceans like lobsters, prawns, crabs, and shellfish like oysters, mussels and the like. 
     Accordingly there is provided a VSP package comprising a food product selected from the group consisting of crustaceans and shellfish loaded on a support and a twin skin film draped over the product and welded to the part of the support not covered by the product.