CA1127363A - Moulding plastic film material - Google Patents
Moulding plastic film materialInfo
- Publication number
- CA1127363A CA1127363A CA305,083A CA305083A CA1127363A CA 1127363 A CA1127363 A CA 1127363A CA 305083 A CA305083 A CA 305083A CA 1127363 A CA1127363 A CA 1127363A
- Authority
- CA
- Canada
- Prior art keywords
- film
- concavity
- cavity
- junction
- container
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
- B29C51/26—Component parts, details or accessories; Auxiliary operations
- B29C51/30—Moulds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
- B65D1/00—Containers having bodies formed in one piece, e.g. by casting metallic material, by moulding plastics, by blowing vitreous material, by throwing ceramic material, by moulding pulped fibrous material, by deep-drawing operations performed on sheet material
- B65D1/22—Boxes or like containers with side walls of substantial depth for enclosing contents
- B65D1/26—Thin-walled containers, e.g. formed by deep-drawing operations
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Ceramic Engineering (AREA)
- Moulds For Moulding Plastics Or The Like (AREA)
- Containers Having Bodies Formed In One Piece (AREA)
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
- Shaping Of Tube Ends By Bending Or Straightening (AREA)
- Table Devices Or Equipment (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of packaging an object in flexible thermo-plastic film material comprises moulding the film by differential pressure in a die cavity to form in the film a recess having the same surface area but a different contour to that of the object, the film then being re-shaped after removal from the die cavity to form a container having a contour corresponding to that of the object, the object then being deposited in the container which is closed by another film sealed around the mouth of the container. The parts of the recess corresponding to corners and edges of the object have a larger radius of curvature, prior to re-shaping of the film, then the radius of curvature of the corresponding edges or corners of the object, so that the stretch of the film during the moulding operation is less than if the film was moulded in a die cavity in the shape of the object.
A method of packaging an object in flexible thermo-plastic film material comprises moulding the film by differential pressure in a die cavity to form in the film a recess having the same surface area but a different contour to that of the object, the film then being re-shaped after removal from the die cavity to form a container having a contour corresponding to that of the object, the object then being deposited in the container which is closed by another film sealed around the mouth of the container. The parts of the recess corresponding to corners and edges of the object have a larger radius of curvature, prior to re-shaping of the film, then the radius of curvature of the corresponding edges or corners of the object, so that the stretch of the film during the moulding operation is less than if the film was moulded in a die cavity in the shape of the object.
Description
1~2~31~;~
BAC~GROUND OF THE INVENTION
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.
Subsequently9 another flat film of thèrmo-plastic material is placed over the containers and sealed round the extremlties 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 v~cuum-forming machines form recesses in thermo-plastic film by the fo]lowing 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 rilm 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 d;e cavity or vacuum is drawn in the die cavity. Under the differetltial 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 ln 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 sligllt 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 tbinnest.
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 prac~icable to mould a f~ilm 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 corncr is too casily damagcd and- the original flat film thickness is chosen which gives this result. Since the corner thickness is ~ \
l~Z7363 the minimum of satisfactory strength and since it is the thinnest part oE the pack it follows that the rest of the pack is formed of film of a heavier gauge than is necessary.
E~revious attempts to soLve the problem of excessive thinning of plastic film moulded in a die cavity have relied on moulding the parts of tlle film whicll arc subjccted to excessive thinning in a mirror image inversion of tlle desired shape and, when the moulded film is removed from the rlie cavity, turning the mirror image portions inside .
out to provide the deslred final shape. One example of this method is illustrated in British Patent Specification No. 1443688 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 bu- fitted with inserts in the corners of the die cavity, the inserts having a shape which is a mirror irnage 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 frorn the die cavity. This method providcs thickcr corners to the moulded film, but does not overcome the problem of excessive thinning along the junctlons between the base and the side walls and at the ~unctions 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 improvcd cons~ructioll of dic, for forming a containcr havillg a junction of small radius between adjacent walls, without the excessive thinning, which would occur by moulding the film in a ~1 .. . .
l~Z7363 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 a side wall connected to the base by a junction of relatively small radius of curvature, characterised by the steps of:
Ao moulding the film so as to stretch the film into a concavity having an open mouth, the internal surface of said concavity having an area substantially equal to that of the internal surface of the desired container, and the ~ -side wall of said concavity having a peripheral length substantially equal to the peripheral length of the side wall of the desired container at the same distance from the mouth measured on the surface of the side wall, but said concavity having a contour that differs frorn 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 su~stantially greater than the radius of curvature of said junction; and . 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.
-- S --:, ,;
1~2~363 It is to be unùerstood thst the peripheral lentth around the side walls of the concavity is the length of a line extending around the surface of the concavity at a fixed distance Erom 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 w~th 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 filrn 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 larger to provide sufficierlt 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.
:
1~;Z73~3 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 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 die cavity, said die cavity having a mouth, the surface of the die cavity having an area substantially equal to that of the external surface of the desired container, and the side walls of the die cavity having a peripheral length substantially equal to the external peripheral length of the side walls of the desired container at the same distance from the mouth measured on the surface of the side walls, but said die cavity 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.
In use in a moulding operation with a film of thermo- ¦
plastic 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 - 7 ~
L _ 31.~.Z7 36 3 to atmosphere. Tlle film may, if desired, be subjccted simultaneously or consecutively to both a vacuum and fluid under pressure.
Alternatively, the film may be forced into the cavity by a plug, with or without application of a vacuum or fluid under pressure to the film.
The filrn will contact the protrusion or protrusions in the die cavity bcfore the film contacts the rernainder of the wall Or the cavity, so that the portions of film which contact the protrusions will conse4uently be thicker than the remainder of the moulaed 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 thiclclless than the remainder of the container. It will of course be apprcciated that the protrusions do not only provide the corners of the containers but aLso provide t-he addltional material to enable the remainder of the moulded film to be re~shaped into the container o~ thc desircd 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 tlme thaL it contacts the side wall and base, so that the part of the film extending across the side walls and base and across the jùnction 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 opcn-moutllcd container having a substantially part-spherical side wall and a substantially flat base co-operating with the part~spherical wall to provide an interior to the container which is appro~imately in the shape of a sector of a sphere, the junction between the base and the part-spherical wall of the container having ':: ~"
~27363 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, the surface of the die cavlty having an area substantially equal to that of-the external surface of the desired container, and the wall of the die cavity having a peripheral length substantially equal to the external peripheral length of the wall of the desired container at the same distance from the mouth measured - ~ -on the surface of the wall, but said die cavity having a contour which differs from that of the desired container in that the wall of the die cavity has a rldge-shaped 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 Eorm 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 mouIded f1lm into:the desired container.
The reshaping of the moulded film to form a container of the desired shape and s1ze may be efEected 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 ~s ~ 9 _ ` ~ :
i, -- ~Z7363 bcing witlldrawll alld tlle objcct del)ositcd in thc rcccss or concavity.
The conLaillcr m;ly Lhcn bc closcd by placirlg anotllcr filln Or matcrial across thc rnouth Or Lhe container and scaling thc two films together aroullcl thc mou~ll ot tllc container.
The contour of a die cavity for use in shaping a film of flexible plas~ic material in accordance with the invention into a concavity which ~an subsequently be re-contoured into a container of a particular sbapc and si~e having a junction of small radius between the base and a si~e 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 thc cavity, alld then folding thc rnoulded film across part of the junction of srllall radius so that tlle ilm material which is drawn into ~hc fold causcs a re-shaping o Lhe rcrnaindcr of thc 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 rilm will of course be very rnuch thinncr than the rcmainder of the fillll as explained pLev:iously, but Lhe contour of the mouldcd film WilCll folded is the contour of ~hc dic cavity suitable for use in sllapillg the film of flexible plastic rnaterial into the desired container without excessive thinning of the film material in accordancc with the present invention.:
~ xamples of dies suitable for use in shaping films of thermo-plastic material into containers by the method of the invention~
are illustratcd in the accompanying drawin~sr in wl,icll l~'igure 1 is a perspccLivc view of .i die suita~le for use in moulding a film into a concavity which can be re-contoll~ed into an open-mouthed container of rcctangular parallelepipcd shape, ~ 10 -~""~
~ ~Z7363 Figure 2 is a plan view of the die of Figure 1, Figurc 3 is a sccLiorlal view of thc die of Figure 1 talcen along the Line LII-III in Figure 1, Figure 4 is a plan view Or the die of Figure 1 showing contour lines, Figure 5 is a perspective view of a known construction of die for use in Inoulding 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 re-contoured 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, Figurc 8 is a sectional view of the die of Figures 6 and 7 taken along the line VIII-VIII in Figure 7, and Figure 9 is a sectional view of the die of Figures 6 and 7 taken alollg the line [X-IX in Figure 7.
The dic showrl in Figures 1-4 is designed for rnoulding a filrn of thermo-plastic ma~erial reprcsented by tl~e line P ln 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 10-11-12-13 in Figuré 3. As explained above, moulding of the sheet P in a die cavity of a contour 10-11-12-13 in transverse cross section wou]d produce a container in which the wall at tlle edges 11 and 12 was very mucl~ thinner than the remainder of the container and thus vulnerable to rupture.
1 1 _ , ~-~.273Ç;3 'l`he cavity oL the die shown in Figures 1-4 has a surface represented in l~igure 4 by contour lines Al, A2, A3, A4, A5, A6 at the leveLs Al-~6 respectively below the mouLI~ of tlle cavity as shot~tl in Figure 3, the surface area of the cavity and its periplleral lcngtll around the side walls (as hercinbefore defined) being the same as those oE the external surface of a rectangular --parallelep:il)ed container having a lengtll and breadth cqual to that of the mouth of the cavity of the die and a rectangular cross sectioli as shown at 10-11-12-13 in Figure 3.
Figure 3 shows in full lines a transverse cross section through the centre of the die cavlty along the line III-III in Figures 1 and 4. The line 10-14~15-16-17-13 representing the surfacc of the cavity has the same length as Lhe line 10-11-12-~3 but has a large radius of curvature at the junctions between the side walls10-:l4 13-17 and the base 15-16.
Similarly in a longiLudinal cross section through the ccnLre of the die cavity along the Line IV-IV In Figure 4-there is a large radius of curvature at tbe ionc~tions between the end walls and the base of tlle cavity, as:shot~n by the contour lines in li"ur~: 4. ~L Ll~ cor~ rs ~,r tll. c~lviLy, wll~rc i~ ~
is 110t possible to have large;curvatures between Lhe base and both the adjacent end wall and the adjacent side wall, the surface oL the cavity forms a protruslon 18 at each corner extending into the interior of the cavity, the protrusions being of a si~e such that the peripheral length around the walls of the cav:ity at ally ~iVCtl di.stance less th<ln the distance lO-ll below Lhe mouth oL Lhe caviLy, measured along Lhe surface of the cavity, is equal to the peripheral lengLh around the mouth of the cavity.
:12 ~
~27363 ~ hen the fiLm ~ is moulded in the die of Figures 1-4 to forrn a concavity in the film, the parts of the film which are moulded around the ridge-sllaped protrusions 18 form folds having opposing sides which, upon remova] 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 10-11-12-13 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 filmj is the same as tXe 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 constan- thickness in transverse and longitudinal section due to tlle large radius of culvature at the junctlons between the side walls and the base, as shown by the line 10-14-15-16-17-13 in Figure 3. The portions of the film which are moulded ;~
around the protrusions 18 are slightly thlcker tban the portions moulded a~ainst the remainder of Lhe wall of the die cavity due to the fact that the film contacts the proerusions during its expansion into the die cavLty 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 sectol of a sphcre. When a film is moulded into the cavity, the part of the film at Lhe juDction between the base 20 and side wall 21 is much thinner than at other parts of the cavity, for the reasons ~27363 describcd hercinbcEorc, and to avoid excessive thinning of the film at thc 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.
~he cavity of the die shown in Figures 6-9 has a surface ~ represented in Figure 7 by contour lines Bl, B2, B3, B4, B5, B6 : ~ at the levels Bl-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 '''~ ~' . , ' , ' :
' , ' i r, .
!, sallle as those ur Lhc e~tc~r~ l surC.Icc of a contaillc~r in the shape of a one-eighth scctor Or a sphere having a transverse cross sectlon through the plane oL symmetry as shown at 25-26-27 in l~`igurc 9~
Figurc! 8 shows in full lines 28-29-30 a transverse cross section Lhrougll tlle clie cavity along the line VIII-VIII in Figure 7, and im broken lines 2~-3~-30 a correspond:ing transverse cross section Lhrougll a contai.ller in the shape of a one-elgll~ll sccLor Or a spllere. It will be noted that the line 28-29-30 has a comparatively large raùius 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 sllows 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-:LX is a plane of synunetry ~lle line 25-32-33-27 is the same length as the broken line 25-26-27 representing a corresponding transverse cross section Lhrough a container.in the shape of a one eighth sector of a sphere The line 25-'2-33-27 has a sma].l radius of curvature at points 32 and 33 but a rilm Irl-Julcled 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 moulded in a die cavity of cross section 25-26-27 sillce the poi.nts 32 and 33 are closer to the mouth of the cavity than point 26. As will be seen from the contour lines in Figu-re 7, the line 32-33 forms the ape~ of a protrusion whicll e~Len(ls i.nto Lhe intcrior of the cavity.
r ~ hell a film of Llcxible plastic material is moulded in the die of Figures 6-9, tlle part oE the film which is rnouldcd around the ridge-shaped protrusions 32-33 forms a fold having opposing sides which, upon ren-oval 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 onc-c`;gll~ll sector of a sphere having a transverse cross section 25-26-27 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 ccntre 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 splayea apart in the general direction of the cnds of the junction.
_ 16 _ ..
~S
BAC~GROUND OF THE INVENTION
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.
Subsequently9 another flat film of thèrmo-plastic material is placed over the containers and sealed round the extremlties 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 v~cuum-forming machines form recesses in thermo-plastic film by the fo]lowing 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 rilm 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 d;e cavity or vacuum is drawn in the die cavity. Under the differetltial 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 ln 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 sligllt 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 tbinnest.
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 prac~icable to mould a f~ilm 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 corncr is too casily damagcd and- the original flat film thickness is chosen which gives this result. Since the corner thickness is ~ \
l~Z7363 the minimum of satisfactory strength and since it is the thinnest part oE the pack it follows that the rest of the pack is formed of film of a heavier gauge than is necessary.
E~revious attempts to soLve the problem of excessive thinning of plastic film moulded in a die cavity have relied on moulding the parts of tlle film whicll arc subjccted to excessive thinning in a mirror image inversion of tlle desired shape and, when the moulded film is removed from the rlie cavity, turning the mirror image portions inside .
out to provide the deslred final shape. One example of this method is illustrated in British Patent Specification No. 1443688 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 bu- fitted with inserts in the corners of the die cavity, the inserts having a shape which is a mirror irnage 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 frorn the die cavity. This method providcs thickcr corners to the moulded film, but does not overcome the problem of excessive thinning along the junctlons between the base and the side walls and at the ~unctions 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 improvcd cons~ructioll of dic, for forming a containcr havillg a junction of small radius between adjacent walls, without the excessive thinning, which would occur by moulding the film in a ~1 .. . .
l~Z7363 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 a side wall connected to the base by a junction of relatively small radius of curvature, characterised by the steps of:
Ao moulding the film so as to stretch the film into a concavity having an open mouth, the internal surface of said concavity having an area substantially equal to that of the internal surface of the desired container, and the ~ -side wall of said concavity having a peripheral length substantially equal to the peripheral length of the side wall of the desired container at the same distance from the mouth measured on the surface of the side wall, but said concavity having a contour that differs frorn 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 su~stantially greater than the radius of curvature of said junction; and . 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.
-- S --:, ,;
1~2~363 It is to be unùerstood thst the peripheral lentth around the side walls of the concavity is the length of a line extending around the surface of the concavity at a fixed distance Erom 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 w~th 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 filrn 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 larger to provide sufficierlt 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.
:
1~;Z73~3 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 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 die cavity, said die cavity having a mouth, the surface of the die cavity having an area substantially equal to that of the external surface of the desired container, and the side walls of the die cavity having a peripheral length substantially equal to the external peripheral length of the side walls of the desired container at the same distance from the mouth measured on the surface of the side walls, but said die cavity 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.
In use in a moulding operation with a film of thermo- ¦
plastic 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 - 7 ~
L _ 31.~.Z7 36 3 to atmosphere. Tlle film may, if desired, be subjccted simultaneously or consecutively to both a vacuum and fluid under pressure.
Alternatively, the film may be forced into the cavity by a plug, with or without application of a vacuum or fluid under pressure to the film.
The filrn will contact the protrusion or protrusions in the die cavity bcfore the film contacts the rernainder of the wall Or the cavity, so that the portions of film which contact the protrusions will conse4uently be thicker than the remainder of the moulaed 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 thiclclless than the remainder of the container. It will of course be apprcciated that the protrusions do not only provide the corners of the containers but aLso provide t-he addltional material to enable the remainder of the moulded film to be re~shaped into the container o~ thc desircd 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 tlme thaL it contacts the side wall and base, so that the part of the film extending across the side walls and base and across the jùnction 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 opcn-moutllcd container having a substantially part-spherical side wall and a substantially flat base co-operating with the part~spherical wall to provide an interior to the container which is appro~imately in the shape of a sector of a sphere, the junction between the base and the part-spherical wall of the container having ':: ~"
~27363 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, the surface of the die cavlty having an area substantially equal to that of-the external surface of the desired container, and the wall of the die cavity having a peripheral length substantially equal to the external peripheral length of the wall of the desired container at the same distance from the mouth measured - ~ -on the surface of the wall, but said die cavity having a contour which differs from that of the desired container in that the wall of the die cavity has a rldge-shaped 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 Eorm 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 mouIded f1lm into:the desired container.
The reshaping of the moulded film to form a container of the desired shape and s1ze may be efEected 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 ~s ~ 9 _ ` ~ :
i, -- ~Z7363 bcing witlldrawll alld tlle objcct del)ositcd in thc rcccss or concavity.
The conLaillcr m;ly Lhcn bc closcd by placirlg anotllcr filln Or matcrial across thc rnouth Or Lhe container and scaling thc two films together aroullcl thc mou~ll ot tllc container.
The contour of a die cavity for use in shaping a film of flexible plas~ic material in accordance with the invention into a concavity which ~an subsequently be re-contoured into a container of a particular sbapc and si~e having a junction of small radius between the base and a si~e 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 thc cavity, alld then folding thc rnoulded film across part of the junction of srllall radius so that tlle ilm material which is drawn into ~hc fold causcs a re-shaping o Lhe rcrnaindcr of thc 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 rilm will of course be very rnuch thinncr than the rcmainder of the fillll as explained pLev:iously, but Lhe contour of the mouldcd film WilCll folded is the contour of ~hc dic cavity suitable for use in sllapillg the film of flexible plastic rnaterial into the desired container without excessive thinning of the film material in accordancc with the present invention.:
~ xamples of dies suitable for use in shaping films of thermo-plastic material into containers by the method of the invention~
are illustratcd in the accompanying drawin~sr in wl,icll l~'igure 1 is a perspccLivc view of .i die suita~le for use in moulding a film into a concavity which can be re-contoll~ed into an open-mouthed container of rcctangular parallelepipcd shape, ~ 10 -~""~
~ ~Z7363 Figure 2 is a plan view of the die of Figure 1, Figurc 3 is a sccLiorlal view of thc die of Figure 1 talcen along the Line LII-III in Figure 1, Figure 4 is a plan view Or the die of Figure 1 showing contour lines, Figure 5 is a perspective view of a known construction of die for use in Inoulding 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 re-contoured 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, Figurc 8 is a sectional view of the die of Figures 6 and 7 taken along the line VIII-VIII in Figure 7, and Figure 9 is a sectional view of the die of Figures 6 and 7 taken alollg the line [X-IX in Figure 7.
The dic showrl in Figures 1-4 is designed for rnoulding a filrn of thermo-plastic ma~erial reprcsented by tl~e line P ln 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 10-11-12-13 in Figuré 3. As explained above, moulding of the sheet P in a die cavity of a contour 10-11-12-13 in transverse cross section wou]d produce a container in which the wall at tlle edges 11 and 12 was very mucl~ thinner than the remainder of the container and thus vulnerable to rupture.
1 1 _ , ~-~.273Ç;3 'l`he cavity oL the die shown in Figures 1-4 has a surface represented in l~igure 4 by contour lines Al, A2, A3, A4, A5, A6 at the leveLs Al-~6 respectively below the mouLI~ of tlle cavity as shot~tl in Figure 3, the surface area of the cavity and its periplleral lcngtll around the side walls (as hercinbefore defined) being the same as those oE the external surface of a rectangular --parallelep:il)ed container having a lengtll and breadth cqual to that of the mouth of the cavity of the die and a rectangular cross sectioli as shown at 10-11-12-13 in Figure 3.
Figure 3 shows in full lines a transverse cross section through the centre of the die cavlty along the line III-III in Figures 1 and 4. The line 10-14~15-16-17-13 representing the surfacc of the cavity has the same length as Lhe line 10-11-12-~3 but has a large radius of curvature at the junctions between the side walls10-:l4 13-17 and the base 15-16.
Similarly in a longiLudinal cross section through the ccnLre of the die cavity along the Line IV-IV In Figure 4-there is a large radius of curvature at tbe ionc~tions between the end walls and the base of tlle cavity, as:shot~n by the contour lines in li"ur~: 4. ~L Ll~ cor~ rs ~,r tll. c~lviLy, wll~rc i~ ~
is 110t possible to have large;curvatures between Lhe base and both the adjacent end wall and the adjacent side wall, the surface oL the cavity forms a protruslon 18 at each corner extending into the interior of the cavity, the protrusions being of a si~e such that the peripheral length around the walls of the cav:ity at ally ~iVCtl di.stance less th<ln the distance lO-ll below Lhe mouth oL Lhe caviLy, measured along Lhe surface of the cavity, is equal to the peripheral lengLh around the mouth of the cavity.
:12 ~
~27363 ~ hen the fiLm ~ is moulded in the die of Figures 1-4 to forrn a concavity in the film, the parts of the film which are moulded around the ridge-sllaped protrusions 18 form folds having opposing sides which, upon remova] 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 10-11-12-13 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 filmj is the same as tXe 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 constan- thickness in transverse and longitudinal section due to tlle large radius of culvature at the junctlons between the side walls and the base, as shown by the line 10-14-15-16-17-13 in Figure 3. The portions of the film which are moulded ;~
around the protrusions 18 are slightly thlcker tban the portions moulded a~ainst the remainder of Lhe wall of the die cavity due to the fact that the film contacts the proerusions during its expansion into the die cavLty 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 sectol of a sphcre. When a film is moulded into the cavity, the part of the film at Lhe juDction between the base 20 and side wall 21 is much thinner than at other parts of the cavity, for the reasons ~27363 describcd hercinbcEorc, and to avoid excessive thinning of the film at thc 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.
~he cavity of the die shown in Figures 6-9 has a surface ~ represented in Figure 7 by contour lines Bl, B2, B3, B4, B5, B6 : ~ at the levels Bl-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 '''~ ~' . , ' , ' :
' , ' i r, .
!, sallle as those ur Lhc e~tc~r~ l surC.Icc of a contaillc~r in the shape of a one-eighth scctor Or a sphere having a transverse cross sectlon through the plane oL symmetry as shown at 25-26-27 in l~`igurc 9~
Figurc! 8 shows in full lines 28-29-30 a transverse cross section Lhrougll tlle clie cavity along the line VIII-VIII in Figure 7, and im broken lines 2~-3~-30 a correspond:ing transverse cross section Lhrougll a contai.ller in the shape of a one-elgll~ll sccLor Or a spllere. It will be noted that the line 28-29-30 has a comparatively large raùius 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 sllows 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-:LX is a plane of synunetry ~lle line 25-32-33-27 is the same length as the broken line 25-26-27 representing a corresponding transverse cross section Lhrough a container.in the shape of a one eighth sector of a sphere The line 25-'2-33-27 has a sma].l radius of curvature at points 32 and 33 but a rilm Irl-Julcled 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 moulded in a die cavity of cross section 25-26-27 sillce the poi.nts 32 and 33 are closer to the mouth of the cavity than point 26. As will be seen from the contour lines in Figu-re 7, the line 32-33 forms the ape~ of a protrusion whicll e~Len(ls i.nto Lhe intcrior of the cavity.
r ~ hell a film of Llcxible plastic material is moulded in the die of Figures 6-9, tlle part oE the film which is rnouldcd around the ridge-shaped protrusions 32-33 forms a fold having opposing sides which, upon ren-oval 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 onc-c`;gll~ll sector of a sphere having a transverse cross section 25-26-27 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 ccntre 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 splayea apart in the general direction of the cnds of the junction.
_ 16 _ ..
~S
Claims (12)
1. 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 a side wall 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, the internal surface of said concavity having an area substantially equal to that of the internal surface of the desired container, and the side wall of said concavity having a peripheral length substantially equal to the peripheral length of the side wall of the desired container at the same distance from the mouth measured on the surface of the side wall, but said concavity 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.
A. moulding the film so as to stretch the film into a concavity having an open mouth, the internal surface of said concavity having an area substantially equal to that of the internal surface of the desired container, and the side wall of said concavity having a peripheral length substantially equal to the peripheral length of the side wall of the desired container at the same distance from the mouth measured on the surface of the side wall, but said concavity 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 a junction 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.
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 1-3, 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 ridge-shaped 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 _ 19 -of the object, and depositing the object in 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 a side wall 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, the surface of the die cavity having an area substantially equal to that of the external surface of the desired container, and the side wall of the die cavity having a peripheral length substantially equal to the external peripheral length of the side wall of the desired container at the same distance from the mouth measured on the surface of the side wall, but said die cavity 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 re-contour 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-mouthed container of substantially rectangular parallelepiped shape having a substantially flat base and four side walls connected to said 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 die cavity, said die cavity having a mouth, the surface of the die cavity having an area substantially equal to that of the external surface of the desired container, and the side walls of the die cavity having a peripheral length substantially equal to the external peripheral length of the side walls of the desired container at the same distance from the mouth measured on the surface of the side walls, but said die cavity 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 part-spherical 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, the surface of the die cavity having an area substantially equal to that of the external surface of the desired container, and the wall of the die cavity having a peripheral length substantially equal to the external peripheral length of the wall of the desired container at the same distance from the mouth measured on the surface of the wall, but said die cavity having a contour which differs from that of the desired container in that the wall of the die cavity has a ridge-shaped 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.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB24809/77 | 1977-06-14 | ||
| GB24809/77A GB1601924A (en) | 1977-06-14 | 1977-06-14 | Moulding stretch-deformable film material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1127363A true CA1127363A (en) | 1982-07-13 |
Family
ID=10217571
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA305,083A Expired CA1127363A (en) | 1977-06-14 | 1978-06-09 | Moulding plastic film material |
Country Status (17)
| Country | Link |
|---|---|
| JP (1) | JPS5425970A (en) |
| AU (1) | AU3694178A (en) |
| BE (1) | BE868098A (en) |
| CA (1) | CA1127363A (en) |
| CH (1) | CH625456A5 (en) |
| DE (1) | DE2825889A1 (en) |
| DK (1) | DK259278A (en) |
| ES (1) | ES470742A1 (en) |
| FR (1) | FR2394382A1 (en) |
| GB (1) | GB1601924A (en) |
| IL (1) | IL54861A (en) |
| IT (1) | IT1095400B (en) |
| LU (1) | LU79804A1 (en) |
| NL (1) | NL7806443A (en) |
| NZ (1) | NZ187437A (en) |
| SE (1) | SE432559B (en) |
| ZA (1) | ZA783384B (en) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1207019A (en) * | 1957-06-25 | 1960-02-12 | Du Pont | Process and apparatus for vacuum thermoforming |
| BE642610A (en) * | 1959-07-02 | |||
| US3737496A (en) * | 1970-11-23 | 1973-06-05 | A Voorhees | Method of reinforcing the wall of a thermo-formed article |
| CA1038582A (en) * | 1973-10-03 | 1978-09-19 | Albert R. Uhlig | Method of making blow molded plastic articles |
| DE2507575A1 (en) * | 1974-02-25 | 1975-08-28 | Wrightcel Ltd | DEEP DRAWING FORM FOR PLASTIC PACKAGING |
-
1977
- 1977-06-14 GB GB24809/77A patent/GB1601924A/en not_active Expired
-
1978
- 1978-05-30 SE SE7806266A patent/SE432559B/en unknown
- 1978-05-31 NZ NZ187437A patent/NZ187437A/en unknown
- 1978-06-05 IL IL54861A patent/IL54861A/en unknown
- 1978-06-08 AU AU36941/78A patent/AU3694178A/en active Pending
- 1978-06-09 DK DK259278A patent/DK259278A/en not_active Application Discontinuation
- 1978-06-09 CA CA305,083A patent/CA1127363A/en not_active Expired
- 1978-06-12 CH CH640778A patent/CH625456A5/en not_active IP Right Cessation
- 1978-06-13 DE DE19782825889 patent/DE2825889A1/en not_active Ceased
- 1978-06-13 ZA ZA00783384A patent/ZA783384B/en unknown
- 1978-06-13 FR FR7817571A patent/FR2394382A1/en active Granted
- 1978-06-13 LU LU79804A patent/LU79804A1/en unknown
- 1978-06-13 ES ES470742A patent/ES470742A1/en not_active Expired
- 1978-06-14 NL NL7806443A patent/NL7806443A/en not_active Application Discontinuation
- 1978-06-14 IT IT2456878A patent/IT1095400B/en active
- 1978-06-14 BE BE188548A patent/BE868098A/en not_active IP Right Cessation
- 1978-06-14 JP JP7100978A patent/JPS5425970A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2394382B1 (en) | 1984-10-12 |
| IT7824568A0 (en) | 1978-06-14 |
| IL54861A0 (en) | 1978-08-31 |
| DE2825889A1 (en) | 1979-01-04 |
| JPS5425970A (en) | 1979-02-27 |
| SE432559B (en) | 1984-04-09 |
| NZ187437A (en) | 1982-03-16 |
| IT1095400B (en) | 1985-08-10 |
| DK259278A (en) | 1978-12-15 |
| ZA783384B (en) | 1979-06-27 |
| AU3694178A (en) | 1979-12-13 |
| CH625456A5 (en) | 1981-09-30 |
| FR2394382A1 (en) | 1979-01-12 |
| SE7806266L (en) | 1978-12-15 |
| GB1601924A (en) | 1981-11-04 |
| IL54861A (en) | 1981-05-20 |
| ES470742A1 (en) | 1979-10-01 |
| LU79804A1 (en) | 1978-12-07 |
| BE868098A (en) | 1978-10-02 |
| NL7806443A (en) | 1978-12-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |