GB1601924A

GB1601924A - Moulding stretch-deformable film material

Info

Publication number: GB1601924A
Application number: GB24809/77A
Authority: GB
Original assignee: St Ivel Ltd
Current assignee: St Ivel Ltd
Priority date: 1977-06-14
Filing date: 1977-06-14
Publication date: 1981-11-04
Also published as: NZ187437A; NL7806443A; DE2825889A1; AU3694178A; FR2394382A1; ZA783384B; CH625456A5; BE868098A; JPS5425970A; FR2394382B1; IT7824568A0; LU79804A1; IL54861A; SE7806266L; DK259278A; SE432559B; IT1095400B; IL54861A0; CA1127363A; ES470742A1

Abstract

The method for forming a film (p) of flexible and deformable material, by drawing, into an open container intended for packaging a food product, consists in moulding the film in a mould cavity in order to form therein a recess having a surface whose area and perimeter (10, 15, 16, 13) are essentially equal to those of the internal surface (10, 11, 12, 13) of the desired container. That part of the mould cavity corresponding to a join between a side wall and the base of the container has a radius of curvature greater than that of this join. In each corner of the cavity, the surface of the cavity has a protrusion (18) extending into the cavity. During moulding, the film is moulded around these protrusions (18) in order to form folds (pleats) having opposed sides. After having withdrawn the moulded film from the cavity, the opposed sides are opened out in order to obtain the desired container. This method enables a moulded container to be obtained from a plastic film having approximately equal wall thicknesses. <IMAGE>

Description

(54) IMPROVEMENTS IN MOULDING STRETCH-DEFORMABLE FILM MATERIAL (71) We, ST. IVEL LIMITED (formerly Unigate Foods Limited), a British Company of, Unigate House, Western Avenue, London W3 OSH, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the moulding of a film of flexible stretch-deformable material to form a container for the reception of food or non-food products to be packaged in the material.

In large scale production of food or other products, vacuum-forming machines are generally used for packaging the products in thermo-plastic material. These machines are supplied with a film of thermo-plastic flexible material in flat reeled form and under the effect of heat and differential pressure mould a series of recesses or concavities in the film so as to form containers into which the product is loaded. Subsequently, another flat film of thermo-plastic material is placed over the containers and sealed round the extremities while under vacuum or gas to form sealed packs or pouches containing the product. The thermo-plastic material prevents the ingress of bacteria or the harmful components of the atmosphere.

Conventional constructions of vacuumforming machines form recesses in thermoplastic film by the following method. The thermo-plastic film is gripped at its edge and moved into an area of the machine where its temperature is rapidly increased. This is generally accomplished by radiant heat or by forcing the film into contact with a heated surface. Once the film has reached the desired temperature it is held over the cavity of a rigid die. Compressed air is then applied to the space above the die cavity or vacuum is drawn in the die cavity. Under the differential pressure the film distorts being curved between the extremities of the die cavity. The hot plastic film continues to expand and lose thickness until it touches the cold surface of the die cavity. This surface is normally chilled and on contact the hot plastic film sets, loosing its plasticity but still retaining its flexibility. Since the plastic film always expands in a curved form it will not touch all parts of a rectangular section die cavity at the same moment. Those parts which touch first will thus chill after only slight stretching and thinning whilst those touching last will have been stretched longer and be subsequently thinner. In a die having a cavity of rectangular section or any section having square corners, the corners and edges are the last to be formed and are therefore the thinnest. Thus the most vulnerable part of the pack, namely the corner, is formed of the thinnest and most fragile plastic. It is in fact not practicable to mould a film into a die cavity having right-angled edges or corners due to excessive thinning of the material at the edges and corners, and it is necessary to provide a small radius at the corners and along the junctions between adjacent walls inside the die cavity. To achieve a satisfactory pack it is current practise to set a minimum thickness below which the corner is too easily damaged and the original flat film thickness is chosen which gives this result. Since the corner thickness is the minimum of satisfactory strength and since it is the thinnest part of the pack it follows that the rest of the pack is formed of film of a heavier gauge than is necessary.

Previous attempts to solve the problem of excessive thinning of plastic film moulded in a die cavity have relied on moulding the parts of the film which are subjected to excessive thinning in a mirror image inversion of the desired shape and, when the moulded film is removed from the die cavity, turning the mirror image portions inside out to provide the desired final shape. One example of this method is illustrated in British Patent Specification No. 1 443688 in the name of Wrightcel Limited, which describes a die for moulding a container, the die having a cavity corresponding to the shape of the container but fitted with inserts in the corners of the die cavity, the inserts having a shape which is a mirror image inversion of the shape of the corners. A film moulded in the cavity is thus formed at the corners with protrusions which extend inwardly into the recess moulded in the film, the protrusions being turned inside out after the film is removed from the die cavity. This method provides thicker corners to the moulded film, but does not overcome the problem of excessive thinning along the junctions between the base and the side walls and at the junctions of the inserts and the walls of the die cavity.

The object of the invention is to provide an improved method of moulding a film of stretch-deformable material and an improved construction of die, for forming a container having a junction of small radius between adjacent walls, without the excessive thinning, which would occur by moulding the film in a die cavity having the shape of the desired container.

According to the present invention there is provided a method of forming a film of flexible stretch-deformable material into an open-mouthed container of predetermined shape and size having a base and one or more side walls connected to the base by a junction of relatively small radius of curvature, characterised by the steps of: A. moulding the film so as to stretch the film into a concavity having an open mouth and an internal surface substantially equal to that of the internal surface of the desired container in area and in the peripheral length around the wall or walls at the same distance from the mouth measured along the wall, but having a contour that differs from the contour of the desired container in that the moulded film has at least one fold which projects into the concavity as a ridge-shaped protrusion extending across the wall portion of the concavity that is to form part of said junction, said fold having opposing sides which can be splayed apart, so that the wall portions of the concavity on opposite sides of said fold that are to form other parts of said junction have a radius of curvature which is substantially greater than the radius of curvature of said junction; and B. splaying apart the opposing sides of said fold or folds so as to unfold the moulded film and re-contour said concavity to form said container of predetermined shape and size.

The film may be moulded by differential pressure and/or by a plug in a die cavity.

It is to be understood that the peripheral length around the side walls of the concavity is the length of a line extending around the surface of the concavity at a fixed distance from the mouth of the concavity measured along the surface thereof. In the case of a container having a tapered side wall, the peripheral length around the side wall will vary with the distance from the top of the side wall, and in the method of the invention the peripheral lengths of the side walls of the concavity and container are of course measured at the same distance from the top of the side walls.

In the method of the invention the film of stretch-deformable material is stretched less than would be the case if the film was moulded in a die cavity corresponding in contour to the desired container. The original film of material may thus be of thinner gauge than was possible hitherto, resulting in use of less film material and consequent saving in production cost.

Moreover, the method of the invention has the further advantage that the container formed by re-contouring the moulded film may have sharp corners and sharp edges of substantially the same thickness as the remainder of the container. A container for packaging a product having sharp corners and edges can thus be made the same shape as the product and only slightly large to provide sufficient clearance to enable the product to be placed in the container.

The flexible stretch-deformable material may be aluminium or other metallic foil, but can conveniently be a synthetic resin which is thermo-plastic.

In one aspect of the invention there is provided a die for use in forming a film of flexible stretch-deformable material into an open-mouthed container of substantially rectangular parallelepiped shape having a substantially flat base and four side walls connected to said base by ajunction of relatively small radius of curvature, said die having a cavity for moulding the film therein by stretching the film into contact with the entire surface of the cavity, said cavity having a mouth and a surface substantially equal to that of the external surface of the desired container in area and in the peripheral length around the walls at the same distance from the mouth measured along the surface of the die cavity, but havirig a contour which comprises a concave base, four walls connected to the base by a junction having a radius of curvature substantially larger than that of the junctions between the base and walls of the desired rectangular container, and four ridge shaped protrusions extending into the interior of the cavity one from each of the corners at the ends of said walls, said protrusions being adapted to form folds in the wall of a film moulded in the cavity, each fold having opposing sides which can be splayed apart upon removal of the moulded film from the die cavity to unfold the wall of the moulded film into the desired container of rectangular parallelepiped shape.

In use in a moulding operation with a film of thermoplastic material, the film in a hot plastic condition is clamped to the die around the mouth of the cavity and differential pressure applied to opposite sides of the film to force or draw the film into the cavity.

The differential pressure may be obtained by extracting air from the cavity to generate a vacuum therein, or by applying a fluid under pressure, conveniently compressed air, to the external surface of the film and venting the cavity to atmosphere. The film may, if desired, be subjected simultaneously or consecutively to both a vacuum and fluid under pressure. Alternatively the film may be formed into the cavity by a plug, with or without application of a vacuum or fluid under pressure to the film.

The film will contact the protrusion or protrusions in the die cavity before the film contacts the remainder of the wall of the cavity, so that the portions of film which contact the protrusions will consequently be thicker than the remainder of the moulded film. Thus, in a die for forming a substantially rectangular parallelepiped shape as defined above, the protrusions in the corners will provide the container with corners which have a thicker wall thickness than the remainder of the container. It will of course be appreciated that the protrusions do not only provide the corners of the containers but also provide the additional material to enable the remainder of the moulded film to be reshaped into the container of the desired shape. The curvature at the junction between each side wall and the base is preferably such that the film contacts the curved junction at approximately the same time that it contacts the side wall and base, so that the part of the film extending across the side walls and base and across the junction therebetween will have substantially the same thickness.

In another aspect of the invention there is provided a die for use in forming a film of flexible stretch-deformable material into an open-mouthed container having a substantially part-spherical side wall and a substantially flat base co-operating with the partspherical wall to provide an interior to the container which is approximately in the shape of a sector of a sphere, the junction between the base and the part-spherical wall of the container having a relatively small radius of curvature, said die having a cavity for moulding the film therein by stretching the film into contact with the entire surface of the cavity, the die cavity having an open mouth and a surface substantially equal to that of the external surface of the desired container in area and in the peripheral length around the side wall at the same distance from the mouth measured along the surface of the die cavity, but having a contour which differs from that of the desired container in that the wall of the die cavity has a ridgeshaped protrusion which projects into the cavity and extends across the wall portion of the cavity that is to form the centre section of said junction and the wall portions of the cavity on opposite sides of said protrusion that are to form other parts of said junction have a radius of curvature which is substantially larger than the radius of curvature of said junction, said ridge-shaped protrusion being adapted to form a fold in the wall of a film moulded in the cavity, said fold having opposing sides which can be splayed apart upon removal of the moulded film from the die cavity to unfold the wall of the moulded film and thereby re-contour the moulded film into the desired container.

The reshaping of the moulded film to form a container of the desired shape and size may be effected by depositing in the recess or concavity in the moulded film a product to be packaged therein, the product having a shape corresponding to that of the desired container. Alternatively, a moulded film may be reshaped by inserting in the recess a plug having a shape and size corresponding to the object to be packaged, the plug then being withdrawn and the object deposited in the recess or concavity. The container may then be closed by placing another film of material across the mouth of the container and sealing the two films together around the mouth of the container.

The contour of a die cavity for use in shaping a film of flexible plastic material in accordance with the invention into a concavity which can subsequently be re-contoured into a container of a particular shape and size having ajunction of small radius between the base and a side wall can conveniently be determined by first moulding a sheet of flexible plastic material in a die cavity having the same contour as that of the desired container, removing the moulded film from the cavity, and then folding the moulded film across part of the junction of small radius so that the film material which is drawn into the fold causes a re-shaping of the remainder of the moulded film and enlarges the radius of curvature of the remaining part of the junction which is not included in the fold.

The junction of the moulded film will of course be very much thinner than the remainder of the film as explained previously, but the contour of the moulded film when folded is the contour of the die cavity suitable for use in shaping the film of flexible plastic material into the desired container without excessive thinning of the film material in accordance with the present invention.

Examples of dies suitable for use in shaping films of thermo-plastic material into containers by the method of the invention are illustrated in the accompanying drawings, in which Figure 1 is a perspective view of a die suitable for use in moulding a film into a concavity which can be recontoured into an open-mouthed container of rectangular parallelepiped shape, Figure 2 is a plan view of the die of Figure 1, Figure 3 is a sectional view of the die of Figure 1 taken along the line IIIIII in Figure 1, Figure 4 is a plan view of the die of Figure 1 showing contour lines, Figure 5 is a perspective view of a known construction of die for use in moulding a container having an interior in the shape of a sector of a sphere.

Figure 6 is a perspective view of one form of die according to the invention suitable for use in moulding a container which can be recontoured to form the interior into the shape of a sector of a sphere, Figure 7 is a plan view of the die of Figure 6 showing contour lines, Figure 8 is a sectional view of the die of Figures 6 and 7 taken along the line VI II-VIII in Figure 7, and Figure 9 is a sectional view of the die of Figures 6 and 7 taken along the line IX-IX in Figure 7.

The die shown in Figures 1--4 is designed for moulding a film of thermo-plastic material represented by the line P in Figure 3 to form a concavity which can be re-contoured without additional stretching of the film into an open-mouthed rectangular parallelepiped container represented in transverse cross section by the broken line 1-11--122-13 in Figure 3. As explained above, moulding of the sheet P in a die cavity of a contour 1-11--122-13 in transverse cross section would produce a container in which the wall at the edges 11 and 12 was very much thinner than the remainder of the container and thus vulnerable to rupture.

The cavity of the die shown in Figures 1--4 has a surface represented in Figure 4 by contour lines Al, A2, A3, A4, A5, A6 at the levels A1--A6 respectively below the mouth of the cavity as shown in Figure 3, the surface area of the cavity and its peripheral length around the side walls (as hereinbefore defined) being the same as those of the external surface of a rectangular parallelepiped container having a length and breadth equal to that of the mouth of the cavity of the die and a rectangular cross section as shown at 1--111-112-13 in Figure 3.

Figure 3 shdws in full lines a transverse cross section through the centre of the die cavity along the line Ill-Ill in Figures 1 and 4. The line 10--144-115--166-17-13 representing the surface of the cavity has the same length as the line 10-11-12-13 but has a large radius of curvature at the junctions between the side walls 1(3-14 13-17 and the base 15-16. Similarly in a longitudinal cross section through the centre of the die cavity along the line IV-IV in Figure 4 there is a large radius of curvature at the junctions between the end walls and the base of the cavity, as shown by the contour lines in Figure 4. At the corners of the cavity, where it is not possible to have large curvatures between the base and both the adjacent end wall and the adjacent side wall, the surface of the cavity forms a protrusion 18 at each corner extending into the interior of the cavity, the protrusions being of a size such that the peripheral length around the walls of the cavity at any given distance less than the distance 1--11 below the mouth of the cavity, measured along the surface of the cavity, is equal to the peripheral length around the mouth of the cavity.

When the film P is moulded in the die of Figures 1--4 to form a concavity in the film, the parts of the film which are moulded around the ridge-shaped protrusions 18 form folds having opposing sides which, upon removal of the film from the cavity, can be splayed apart so as to re-contour the moulded film into a rectangular container have a transverse section as shown at 10--111-112-13 in Figure 3. This is possible since the surface area and peripheral length around the side walls of the die cavity, and hence the surface area and peripheral length around the side walls of the concavity in the moulded film, is the same as the surface area and the peripheral length around the side walls of the rectangular container.

The film moulded in the die of Figures 1--4 has however a substantially constant thickness in transverse and longitudinal section due to the large radius of curvature at the junctions between the side walls and the base, as shown by the line 10--144-115--166-17-13 in Figure 3. The portions of the film which are moulded around the protrusions 18 are slightly thicker than the portions moulded against the remainder of the wall of the die cavity due to the fact that the film contacts the protrusions during its expansion into the die cavity before it contacts the remainder of the cavity.

The known die of Figure 5 has a flat base 20 and a part-spherical side wall 21 which co-operate to define a cavity having a shape approximately that of a one-eighth sector of a sphere. When a film is moulded into the cavity, the part of the film at the junction between the base 20 and side wall 21 is much thinner than at other parts of the cavity, for the reasons described hereinbefore, and to avoid excessive thinning of the film at the junction it is necessary to provide a small radius to the junction. Due to the radius at the junction, and without any compensating variation in contour as in the present invention, it is necessary to make the surface area of the cavity larger than the surface area of the product to be packaged.

The cavity of the die shown in Figures 6--9 has a surface represented in Figure 7 by contour lines B1, B2, B3, B4, B5, B6 at the levels B l-B6 respectively below the mouth of the cavity as shown in Figures 8 and 9, the surface area of the cavity and its peripheral length around the side walls being the same as those of the external surface of a container in the shape of a one-eighth sector of a sphere having a transverse cross section through the plane of symmetry as shown at 25-2(#27 in Figure 9.

Figure 8 shows in full lines 28-29-30 a transverse cross section through the die cavity along the line VIlI-VIlI in Figure 7, and in broken lines 28-31-30 a corresponding transverse cross section through a container in the shape of a one-eighth sector of a sphere. It will be noted that the line 28-29 30 has a comparatively large radius of curvature throughout its length, so that a film moulded onto surface 28-29-30 would have a comparatively uniform thickness throughout its length.

Figure 9 shows in full lines 25-32 33-27 a transverse cross section through the die cavity along the line IX-IX in Figure 7. Since IX-IX is a plane of symmetry the line 25-32-33-27 is the same length as the broken line 25-26-27 representing a corresponding transverse cross section through a container in the shape of a one eighth sector of a sphere. The line 25-32-33-27 has a small radius of curvature at points 32 and 33 but a film moulded in a die cavity of this section would have a much thicker wall at these points than the thickness of film at point 26 if mounted in a die cavity of cross section 262627 since the points 32 and 33 are closer to the mouth of the cavity than point 26. As will be seen from the contour lines in Figure 7, the line 32-33 forms the apex of a protrusion which extends into the interior of the cavity.

When a film of flexible plastic material is mounted in the die of Figures 69, the part of the film which is moulded around the ridge-shaped protrusions 32-33 forms a fold having opposing sides which, upon removal of the film from the cavity, can be splayed apart so as to re-contour the moulded film into a container in the shape of a one-eighth sector of a sphere having a transverse cross section 25-2(#27 as shown in Figure 9.

This is possible since the surface area and peripheral length around the side walls of the cavity of the die of Figures 6-9 is the same as the surface area and peripheral length around the side walls of a container having the shape of a sector of a sphere. It will be noted that the fold formed by the protrusion 32-33 extends across the part of the film which forms the centre of the junction between the base and the part-spherical side wall, and that upon re-contouring the moulded film the opposing sides of the fold are splayed apart in the general direction of the ends of the junction.

WHAT WE CLAIM IS: 1. A method of forming a film of flexible stretch-deformable material into an openmouthed container of predetermined shape and size having a base and one or more side walls connected to the base by a junction of relatively small radius of curvature, characterised by the steps of: A. moulding the film so as to stretch the film into a concavity having an open mouth and an internal surface substantially equal to that of the internal surface of the desired container in area and in the peripheral length around the wall or walls at the same distance from the mouth measured along the wall, but having a contour that differs from the contour of the desired container in that the moulded film has at least one fold which projects into the concavity as a ridge-shaped protrusion extending across the wall portion of the concavity that is to form part of said junction, said fold having opposing sides which can be splayed apart, so that the wall portions of the concavity on opposite sides of said fold that are to form other parts of said junction have a radius of curvature which is substantially greater than the radius of curvature of said junction; and B. splaying apart the opposing sides of said fold or folds so as to unfold the moulded film and re-contour said concavity to form said container of predetermined shape and size.

2. A method as claimed in claim 1 for forming a container having a base and four side walls connected to the base by ajunction of relatively small radius of curvature, comprising moulding said film in such manner that the wall portions of said concavity that are to form the corners of the desired container at the ends of the side walls thereof are each formed with a fold which extends into the interior of the concavity to form a ridge-shaped protrusion, each of said folds having opposing sides which can be splayed apart, whereby the wall portions of said concavity between the folds that are to form parts of said junction have a substantially larger radius of curvature than the junction between the base and side walls of the desired container, the method including the step of splaying apart the opposing sides of all the folds in the moulded film to form the desired container.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. junction it is necessary to provide a small radius to the junction. Due to the radius at the junction, and without any compensating variation in contour as in the present invention, it is necessary to make the surface area of the cavity larger than the surface area of the product to be packaged. The cavity of the die shown in Figures 6--9 has a surface represented in Figure 7 by contour lines B1, B2, B3, B4, B5, B6 at the levels B l-B6 respectively below the mouth of the cavity as shown in Figures 8 and 9, the surface area of the cavity and its peripheral length around the side walls being the same as those of the external surface of a container in the shape of a one-eighth sector of a sphere having a transverse cross section through the plane of symmetry as shown at 25-2(#27 in Figure 9. Figure 8 shows in full lines 28-29-30 a transverse cross section through the die cavity along the line VIlI-VIlI in Figure 7, and in broken lines 28-31-30 a corresponding transverse cross section through a container in the shape of a one-eighth sector of a sphere. It will be noted that the line 28-29 30 has a comparatively large radius of curvature throughout its length, so that a film moulded onto surface 28-29-30 would have a comparatively uniform thickness throughout its length. Figure 9 shows in full lines 25-32 33-27 a transverse cross section through the die cavity along the line IX-IX in Figure 7. Since IX-IX is a plane of symmetry the line 25-32-33-27 is the same length as the broken line 25-26-27 representing a corresponding transverse cross section through a container in the shape of a one eighth sector of a sphere. The line 25-32-33-27 has a small radius of curvature at points 32 and 33 but a film moulded in a die cavity of this section would have a much thicker wall at these points than the thickness of film at point 26 if mounted in a die cavity of cross section 262627 since the points 32 and 33 are closer to the mouth of the cavity than point 26. As will be seen from the contour lines in Figure 7, the line 32-33 forms the apex of a protrusion which extends into the interior of the cavity. When a film of flexible plastic material is mounted in the die of Figures 69, the part of the film which is moulded around the ridge-shaped protrusions 32-33 forms a fold having opposing sides which, upon removal of the film from the cavity, can be splayed apart so as to re-contour the moulded film into a container in the shape of a one-eighth sector of a sphere having a transverse cross section 25-2(#27 as shown in Figure 9. This is possible since the surface area and peripheral length around the side walls of the cavity of the die of Figures 6-9 is the same as the surface area and peripheral length around the side walls of a container having the shape of a sector of a sphere. It will be noted that the fold formed by the protrusion 32-33 extends across the part of the film which forms the centre of the junction between the base and the part-spherical side wall, and that upon re-contouring the moulded film the opposing sides of the fold are splayed apart in the general direction of the ends of the junction. WHAT WE CLAIM IS:

1. A method of forming a film of flexible stretch-deformable material into an openmouthed container of predetermined shape and size having a base and one or more side walls connected to the base by a junction of relatively small radius of curvature, characterised by the steps of: A. moulding the film so as to stretch the film into a concavity having an open mouth and an internal surface substantially equal to that of the internal surface of the desired container in area and in the peripheral length around the wall or walls at the same distance from the mouth measured along the wall, but having a contour that differs from the contour of the desired container in that the moulded film has at least one fold which projects into the concavity as a ridge-shaped protrusion extending across the wall portion of the concavity that is to form part of said junction, said fold having opposing sides which can be splayed apart, so that the wall portions of the concavity on opposite sides of said fold that are to form other parts of said junction have a radius of curvature which is substantially greater than the radius of curvature of said junction; and B. splaying apart the opposing sides of said fold or folds so as to unfold the moulded film and re-contour said concavity to form said container of predetermined shape and size.

3. A method as claimed in claim 1 for

forming a container having an end wall which is approximately part-spherical in shape and a substantially flat base lying in a radial plane of the end wall and connected thereto by a junction of small radius therebetween, the method comprising moulding said film in such manner that the film is formed with a fold which projects into the interior of said concavity to form a ridge shaped protrusion extending across the wall portion of the concavity that is to form the centre section of said junction between the part-spherical wall and the base of the desired container, and the wall portions of the concavity on opposite sides of said fold that are to form other parts of said junction have a radius of curvature substantially larger than the radius of curvature of the junction.

4. A method as claimed in any of claims 1--3, wherein the re-contouring of the concavity in the moulded film is carried out by depositing in the concavity an object having a shape and size corresponding substantially to the interior of the desired container.

5. A method as claimed in any of claims 1H, wherein the film is thermo-plastic and is moulded in a heated condition.

6. A method of packaging an object or product having a base and one or more side walls co-operating therewith to form at least one edge having a small radius of curvature, comprising moulding a film of flexible stretch-deformable material so as to stretch the film into a concavity having a surface area substantially equal to that of the base and side walls of the object and having a peripheral length around its side walls substantially equal to the corresponding peripheral length around the side walls of the object, but said concavity having a contour that differs from the contour of the object in that the moulded film has at least one fold which projects into the concavity as a ridgeshaped protrusion extending across the wall portion of the concavity that is to accommodate part of said edge of the object, said fold having opposing sides which can be splayed apart, so that the wall portions of the concavity on opposite sides of said fold that are to accommodate other parts of said edge of the object have a radius of curvature which is substantially greater than the radius of curvature of said edge, said method further including the step of splaying out the opposing sides of said fold or folds and thereby re-contouring the moulded film to form a concavity corresponding to the contour of the object, and depositing the object of the concavity.

7. A method as claimed in claim 6, wherein the re-contouring of the moulded film is effected by depositing the object in the concavity.

8. A method as claimed in claim 6, wherein the re-contouring of the moulded film is effected by inserting in the concavity a plug having a shape and size corresponding to that of the object to be packaged, the plug then being withdrawn from the concavity and said object deposited therein.

9. A method as claimed in any of claims 6-8, including the step of closing the concavity after the object has been deposited therein by placing another sheet of film material across the mouth of the concavity and sealing the two films together around the mouth of the concavity.

10. A die for use in forming a film of flexible stretch-deformable material into an open-mouthed container of predetermined shape and size having a base and one or more side walls connected to the base by a junction of relatively small radius of curvature, said die having a cavity for moulding the film therein by stretching the film into contact with the entire surface of the cavity, the die cavity having an open mouth and a surface substantially equal to that of the external surface of the desired container in area and in the peripheral length around the walls at the same distance from the mouth measured along the surface of the die cavity, but having a contour which differs from that of the desired container in that the wall of the cavity has at least one ridge-shaped protrusion which projects into the interior of the die cavity and extends across the wall portion of the cavity that is to form part of said junction, the wall portions of the cavity on opposite sides of said protrusion that are to form other parts of said junction having a radius of curvature which is substantially greater than the radius of curvature of said junction, the ridge-shaped protrusion being adapted to form a fold in a film moulded in the cavity, said fold having opposing sides which can be splayed apart upon removal of the moulded film from the die cavity to unfold the moulded film and thereby recontour the moulded film without further stretching into the desired container having said junction of relatively small radius.

11. A die for use in forming a film of flexible stretch-deformable material into an open-mouth container of substantially rectangular parallelepiped shape having a substantially flat base and four side walls connected to said base by ajunction of relatively small radius of curvature said die having a cavity for moulding the film therein by stretching the film into contact with the entire surface of the cavity, said cavity having a mouth and a surface substantially equal to that of the external surface of the desired container in area and in the peripheral length around the walls at the same distance from the mouth measured along the surface of the die cavity, but having a contour which comprises a concave base, four walls connected to the base by a junction having a radius of curvature substantially larger than that of the junctions between the base and walls of the desired rectangular container, and four ridge shaped protrusions extending into the interior of the cavity one from each of the corners at the ends of said walls, said protrusions being adapted to form folds in the wall of a film moulded in the cavity, each fold having opposing sides which can be splayed apart upon removal of the moulded film from the die cavity to unfold the wall of the moulded film into the desired container of rectangular parallelepiped shape.

12. A die for use in forming a film of flexible stretch-deformable material into an open-mouthed container having a substantially part-spherical side wall and a substantially flat base co-operating with the partspherical wall to provide an interior to the container which is approximately in the shape of a sector of a sphere, the junction between the base and the part-spherical wall of the container having a relatively small radius of curvature, said die having a cavity for moulding the film therein by stretching the film into contact with the entire surface of the cavity, the die cavity having an open mouth and a surface substantially equal to that of the external surface of the desired container in area and in the peripheral length around the side wall at the same distance from the mouth measured along the surface of the die cavity, but having a contour which differs from that of the desired container in that the wall of the die cavity has a ridgeshaped protrusion which projects into the cavity and extends across the wall portion of the cavity that is to form the centre section of said junction and the wall portions of the cavity on opposite sides of said protrusion that are to form other parts of said junction have a radius of curvature which is substantially larger than the radius of curvature of said junction, said ridge-shaped protrusion being adapted to form a fold in the wall of a QIm moulded in the cavity, said fold having opposing sides which can be splayed apart upon removal of the moulded film from the die cavity to unfold the wall of the moulded film and thereby re-contour the moulded film into the desired container.

13. A container formed from a film of flexible stretch-deformable material by the method as claimed in any of claims 1--5.

14. A package consisting of an object or product wrapped in flexible stretch-deformable material by the method as claimed in any of claims 6-9.

15. A method of forming a film of flexible stretch-deformable material into an open-mouthed container as claimed in claim l and substantially as hereinbefore described with reference to Figures 14 or Figures 6-9 of the accompanying drawings.

16. A die substantially as hereinbefore described with reference to. Figures 1H or Figures 6--9 of the accompanying drawings.