CA2070077A1 - Multi-layer plastics material sheet - Google Patents
Multi-layer plastics material sheetInfo
- Publication number
- CA2070077A1 CA2070077A1 CA002070077A CA2070077A CA2070077A1 CA 2070077 A1 CA2070077 A1 CA 2070077A1 CA 002070077 A CA002070077 A CA 002070077A CA 2070077 A CA2070077 A CA 2070077A CA 2070077 A1 CA2070077 A1 CA 2070077A1
- Authority
- CA
- Canada
- Prior art keywords
- outer layers
- inner structure
- sheet material
- thermoplastic sheet
- layers
- 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.)
- Abandoned
Links
- 239000000463 material Substances 0.000 title claims abstract description 24
- 239000004033 plastic Substances 0.000 title description 4
- 229920003023 plastic Polymers 0.000 title description 4
- 229920001169 thermoplastic Polymers 0.000 claims abstract description 19
- 239000004416 thermosoftening plastic Substances 0.000 claims abstract description 19
- 238000001125 extrusion Methods 0.000 claims description 24
- 238000009826 distribution Methods 0.000 claims description 7
- -1 polyethylene Polymers 0.000 claims description 4
- 238000003475 lamination Methods 0.000 claims description 3
- 239000012815 thermoplastic material Substances 0.000 claims description 3
- 239000004698 Polyethylene Substances 0.000 claims description 2
- 229920000573 polyethylene Polymers 0.000 claims description 2
- 238000000034 method Methods 0.000 abstract description 6
- 238000003825 pressing Methods 0.000 abstract description 4
- 238000010030 laminating Methods 0.000 abstract description 2
- 238000007789 sealing Methods 0.000 description 8
- 235000013550 pizza Nutrition 0.000 description 6
- 235000013305 food Nutrition 0.000 description 5
- 238000003466 welding Methods 0.000 description 5
- 230000000750 progressive effect Effects 0.000 description 4
- 229920000114 Corrugated plastic Polymers 0.000 description 3
- 239000000123 paper Substances 0.000 description 3
- 229920000119 Coroplast Polymers 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 244000052616 bacterial pathogen Species 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000002985 plastic film Substances 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 241000894006 Bacteria Species 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 241000700605 Viruses Species 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000003670 easy-to-clean Effects 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000011087 paperboard Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form
- B32B3/26—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer
- B32B3/28—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer characterised by a layer comprising a deformed thin sheet, i.e. the layer having its entire thickness deformed out of the plane, e.g. corrugated, crumpled
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2323/00—Polyalkenes
- B32B2323/04—Polyethylene
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2439/00—Containers; Receptacles
- B32B2439/40—Closed containers
- B32B2439/62—Boxes, cartons, cases
Landscapes
- Laminated Bodies (AREA)
Abstract
ABSTRACT
Thermoplastics material corrugated sheet is provided having two outer layers sandwiching an inner structure, the mass of which is substantially evenly distributed between the outer layers. The sandwiching or laminating process is conveniently carried out from three separate extruders providing a vertical fall of layers which are laminated by the use of at least some of heat pressure, and chill rollers against the vertical layers.
On pressing the two outer layers together the inner structure crumples so that it is evenly distributed between the layers and does not form separate lumps which tend to hold the outer layers apart. When the layers have been pressed together they may be heat sealed to close channels between the layers.
POLYBOX\10APP
Thermoplastics material corrugated sheet is provided having two outer layers sandwiching an inner structure, the mass of which is substantially evenly distributed between the outer layers. The sandwiching or laminating process is conveniently carried out from three separate extruders providing a vertical fall of layers which are laminated by the use of at least some of heat pressure, and chill rollers against the vertical layers.
On pressing the two outer layers together the inner structure crumples so that it is evenly distributed between the layers and does not form separate lumps which tend to hold the outer layers apart. When the layers have been pressed together they may be heat sealed to close channels between the layers.
POLYBOX\10APP
Description
This invention relates to multi layer thermoplastics material sheet.
Corrugated liner board is a well known corrugated paper product for packing sheet having insulating and strength properties. Boxes are frequently made from this product since the two outer layers of paper or paperboard united by a corrugated paper inner layer provide a structure of increased rigidity in comparison with the component layers.
Multi-layer polypropylene in which the layers are spaced apart by vertical walls is also known. Such a product is "Coroplast" T~ manufactured by porthole extrusion, i.e. a single extrusion die is actually configured to extrude a sheet having longitudinally extending, substantially square section, open ended channels.
For the sake of simplicity, multi-layer plastic sheeting have layers spaced apart by inner walls, will be referred to as "corrugated plastic sheet". This is intended as a comparison with "corrugated liner board"
rather than as a strict definition. The term is used to include structures such as Coroplast T~1 which is not strictly corrugated.
The top and bottom surfaces of the known corrugated plastic sheet tend to be not entirely flat due to differential cooling of the extrusion. Thus the top and bottom surfaces are at least usually slightly fluted along the lines of the interior walls. The surfaces are thin and comparatively fragile. It may be difficult to form coined lines for sharp bends, as for example right angled bends between walls of cartons.
With the increased emphasis on recycling, it has r~ 7 - z -been found desirable to provide a recyclable, insulating plastic corrugated sheet suitable for direct contact with food and being washable and sterilizable for reuse. The present applicant has addressed this problem.
According to the invention, there is provided a thermoplastic material sheet having internal parallel channels comprising two outer layers spaced apart by an inner structure comprising sloping walls, alternate walls sloping in opposing directions, to form the channels between opposing walls and at least one of the outer layers. The inner structure may comprise walls sloping at substantially 60 to each of the two outer layers and to each other, alternate opposing walls meeting at their edges through which they join a respective one of the outer layers.
Such a structure may be extruded by porthole extrusion, but if this technique is used, it is possible that a small amount of fluting will be present on the outer surfaces even though differential shrinkage between the layers may be minimized due to the even distribution of the mass of the inner structure between -the outer layers. It is preferred that sheet according to the invention be produced by progressive extrusion to form a laminate of two outer layers sandwiching an inner structure. The progressive extrusion may involve the extrusion of separate layers for lamination for separate extruders. These layer~
are conveniently laminated in a vertical fall utilizing any or all of heating, pressure and chill rollers~ Of course it is also possible to laminate preformed sheets or extruded layers with one or more preformed sheets.
Progressive lamination may be regarded as the simultaneous extrusion of the outer layers and the inner structure through three separate extrusion nozzles. The two outer layers and the inner structure are quickly brought into contact while the extrusion is still unset to ~q~'J
form the laminate.
The inner structure may be any suitable structure in which the mass of the structure is substantially evenly distributed between the outer layers. Suitable inner structures may comprise corrugated extrusions having ridges and troughs of V-shape, e.g. having an angle of 60, or of undulating form, e~g. of sinusoidal form.
The inner structure holds the outer layers apart and provides parallel channels between them. The channels have triangular cross section for an inner structure of V-shaped corrugation and have a curved side and a straight side for an inner structure of generally sinusoidal form.
The channels may be closed at their ends by, for example, pinching together the outer layers such that the inner structure is collapsed to an end mass of substantially even distribution between the outer layers.
If it is desired to seal the channel ends in addition to closing them, the pinched together ends may be heat sealed, e.g. by ultrasonic welding.
A somewhat similar technique may be used to provide flattened panels in a sheet of corrugated plastics sheet according to the invention, in this case, panel areas are pinched together to collapse the inner structure to a panel mass of substantially even distribution between the outer layers, and the outer layers and substantially evenly distributed panel mass are heat sealed together, e.g. by ultrasonic welding. Such panel areas are useful as "plates" in food cartons such as pizza boxes or may be used for tabs of erectable carton blanks.
Similarly, coining may be provided by pinching together the outer layers to collapse the inner structure to form a line mass of substantially even distribution between the outer layers. These coined lines may be heat 7~
sealed if desired.
Embodiments of the invention will now be described by way of example with reference to the drawings, in which:
Figure 1 is a cross section of one example of prior art thermoplastics sheet;
Figure 2 is a cross section of the sheet of - 10 Figure 1 showing buckling of interior walls when outer layers are pinched together;
Figure 3 is a cross section of one sheet according to the invention;
Figure 4 is a cross section of the sheet of Figure 1 after pinching the outer layers together and sealing them;
Figure 5 is a cross section through another sheet according to the invention;
Figure 6 is a s~etch showing a sheet of the invention having a sealed end, a sealed panel and a coined line;
Figure 7 shows a pizza box formed from sheet material of the invention; and, Figure 8 shows a sketch of the sequence of process steps in one possible process of making a sheet according to the invention.
The example of prior art sheet material 10 shown in Figures 1 and 2 of the drawings may usually be formed of polypropylene and produced by porthole extrusion.
Thus, the prior art sheet 10 which has adjacent elongate channels 16 of substantially square cross section may be produced by extrusion through a single extrusion nozzle configured to have an outlet comprising a pair of elongate, horizontal, parallel slots for extruding the outer layers 12 of the sheet. The slots are connected by short, vertical, parallel slots for extruding the inner ~ 3 walls 14. The resulting extrusion shrinks as it cools so that the outer layers 12 are not entirely flat but have elongate grooves 13 extending along the line o~ each interior wall 14. Thus, the upper and lower surfaces o~
the sheet may be slightly fluted.
This prior art sheet has considerable advantages for use in place of corrugated liner board for many applications. It is, however, not very suitable for reuse applications where it has direct contact with food. The fluted surface is not so easy to clean as a flat surface, the ends of channels 16 are open to the ingress of dirt, bacteria and viruses and, importantly, the surface is quite fragile and easily penetrated by a knife or fork or other sharp edge or point. Difficulties also arise in bending this prior art material about a sharp fold line. When the layers 12 are squeezed together, walls 14 may tend to buckle each into a separate crumbled mass resisting further squeezing together of layers 12 and making sealing together of layers 12 aither difficult or impossible. Thus it may be seen that attempts to coin a fold line or to bring edges of the sheet together to close the mouths of channel 16 or squeeze the inner and outer layers together for other purposes, may result in a structure as shown in the sketch of Figure 2.
Figures 3 and 5 show cross sections of sheets according to the invention in which the inner structure is distributed over space between outer layers 32 (Figure 3) or 42 (Figure 5).
To avoid the problem presented by fluted upper and lower surfaces, sheet according to the invention may be made by progressive extrusion, i.e. two separate elongate extrusion slots are provided, each being for the extrusion of one of the upper or lower layers 32, 42. A further slot of saw tooth or waved configuration is provided for extrusion of the inner structure. Upon extrusion, the 3~
outer layers 32, 42 are contacted with ridges or troughs of walls 34, or 44 of the inner structure to bond the laminated outer layers and the inner structure together.
The inner structure may comprise walls 3~ each sloped at substantially 60 to the outer layers 32, alterna~e walls sloping in opposite directions and meeting at ridges and troughs respectively coincident with the upper and lower layers 32. In this case (Figure 3), the bulk of the walls 34 is distributed with respect to the area of layers 32. If the layers 32 are squeezed together, the walls 32 will tend -to crumple in an inner layer distributed evenly between outer layers 32. Discrete separate masses of crumpled inner walls such as described in relation to Fiyure 2 should not occur. As a result, it may be possible to squeeze layers 32 more closely together than was possible for prior art structures. The structures produced by squeezing the layers 32 closely together may approach the structure shown in Figure 4 in which collapsed walls 34 are shown as a single inner layer 38. In fact, the integral layer 38 may only be actually formed after heat sealing, e.g. by ultrasonic welding. Nevertheless, even before sealing, the close proximity of layers 32 after pinching them together, may allow the forming of coining 52 (Figure 6~ for improved folding of the shset at a sharp bend. Such coining 52 may, if desired, be additionally heat sealed.
Figure 5 shows a cross section of another embodiment of the invention. As described in relation to Figures 3 and 4, the inner structure between the outer layers 42 of the sheet of Figure 5 is distributed over the region between layers 42. In this case, however, sloping walls 44 provided by an undulating inner sheet which may be of sinusoidal form. The ridges and troughs are smoothly curved and sloping walls 44 merge the one within the other.
Channels 46 have a cross section with one straight edge and a curved edge. On squeezing, pinching or pressing together, a sheet having substantially the structure of that shown in Figure 4 may be obtained.
Figure 6 shows a detail of a sheet according to the invention having an edge 56 in with the outer layers been pressed together and sealed to close the mouths of channels within the structure. A panel 54 also provided.
the panel 54 has no channels in the thickness of the sheet but may be provided by pressing together the outer layers so that the inner structure is evenly distributed between thin and heat sealing the layers of the panel.
Figure 7 shows one embodiment of an improved carton suitable for use in direct contact with food and which may be recyclable~ Suitable thermoplastics material from which the sheet and the carton 60 may be made is polyethylene but any food grade thermoplastic material may be used especially those suitable for recycling.
Carton 60 may be a pizza box formed of thermoplastics material sheet according to the invention.
The sheet should be sufficiently rigid to retain the carton shape. To an extent, the channel structure of the sheet provides rigidity to sheet of which the thickness of individual layers and inner structure might otherwise be insufficient to be self-supporting. It may be seen, therefore, that cartons may be constructed with less total bulk of plastic material then has hitherto been possible.
The reduction in mass that may be possible is envisaged to be in the region of 40% to 60%. The dagree of rigidity required is a function of the particular carton and the degree of strength and durability required is a function of the envisaged amount of reusage. These characteristics are a matter of choice within the general scope of the invention.
For a pizza box, for example, a pizza box as shown in Figure 7, it may be desirable to incorporate a 3~ ~7 panel of greater surface toughness against the e-Efects of pronged or sharp edge~ instruments. Thus panel 54 may be provided in any desirsd shape by crushing or pressing outer layers 32 of the sheet together over the desired area.
5 That area may then be subjected to heat, for example, by ultrasonic welding, to form a laminated flattened panel 54.
The inner layer of panel 54 comprises collapsed walls of the inner structure of the sheet which have, on crushing, collapsed relatively evenly between outer layers 32. These 10 collapsed walls form an integral inner layer on heat sealing. It may be that ultrasonic welding plates may also be utilized to initially press layers 12 together. The edges of the pizza box which are adjacent longitudinal walls of channels of the sheet material are sealed against 15 the ingress of dirt and germs. The edges to which section the channels must be sealed by provision of a sealing edge such as sealing edge 56.
To guard against ingress of dirt and germs into 20 channels 36, 46 the ends of the channels may be sealed.
Thus layers 32, 42, at open ends of channels 36, 46, may be pressed together and heat sealed. Such a closed, sealed edge is shown at 56 in Figure 6.
Other embodiments are possible within the spirit of the invention. In particular, it may be possible to provide a steel structure comprising more than two layers 32, 42 each pair of layers having an inner structure there between.
Figure 8 shows one example of process steps which may be used. Corrugated sheet is either preformed or extruded from extruder 62. In any event it may be allowed to fall vertically. Outer laminating sheets 64, are 35 provided either pre-formed or from extruders 66 and allowed to fall vertically to either side of sheet 60. The three sheets 64, 60, 64 may pass guide rollers 67 and then between heating rollers 68. These are of importance when ~p;~ 5~7 g pre-formed sheet is used. Then sheets then pass between pressure rollers 70 which laminate them together.
Thereafter they may pass through chill rollers 72 and possibly transport conveyor 74. Other transport rollers may additionally be used.
Corrugated liner board is a well known corrugated paper product for packing sheet having insulating and strength properties. Boxes are frequently made from this product since the two outer layers of paper or paperboard united by a corrugated paper inner layer provide a structure of increased rigidity in comparison with the component layers.
Multi-layer polypropylene in which the layers are spaced apart by vertical walls is also known. Such a product is "Coroplast" T~ manufactured by porthole extrusion, i.e. a single extrusion die is actually configured to extrude a sheet having longitudinally extending, substantially square section, open ended channels.
For the sake of simplicity, multi-layer plastic sheeting have layers spaced apart by inner walls, will be referred to as "corrugated plastic sheet". This is intended as a comparison with "corrugated liner board"
rather than as a strict definition. The term is used to include structures such as Coroplast T~1 which is not strictly corrugated.
The top and bottom surfaces of the known corrugated plastic sheet tend to be not entirely flat due to differential cooling of the extrusion. Thus the top and bottom surfaces are at least usually slightly fluted along the lines of the interior walls. The surfaces are thin and comparatively fragile. It may be difficult to form coined lines for sharp bends, as for example right angled bends between walls of cartons.
With the increased emphasis on recycling, it has r~ 7 - z -been found desirable to provide a recyclable, insulating plastic corrugated sheet suitable for direct contact with food and being washable and sterilizable for reuse. The present applicant has addressed this problem.
According to the invention, there is provided a thermoplastic material sheet having internal parallel channels comprising two outer layers spaced apart by an inner structure comprising sloping walls, alternate walls sloping in opposing directions, to form the channels between opposing walls and at least one of the outer layers. The inner structure may comprise walls sloping at substantially 60 to each of the two outer layers and to each other, alternate opposing walls meeting at their edges through which they join a respective one of the outer layers.
Such a structure may be extruded by porthole extrusion, but if this technique is used, it is possible that a small amount of fluting will be present on the outer surfaces even though differential shrinkage between the layers may be minimized due to the even distribution of the mass of the inner structure between -the outer layers. It is preferred that sheet according to the invention be produced by progressive extrusion to form a laminate of two outer layers sandwiching an inner structure. The progressive extrusion may involve the extrusion of separate layers for lamination for separate extruders. These layer~
are conveniently laminated in a vertical fall utilizing any or all of heating, pressure and chill rollers~ Of course it is also possible to laminate preformed sheets or extruded layers with one or more preformed sheets.
Progressive lamination may be regarded as the simultaneous extrusion of the outer layers and the inner structure through three separate extrusion nozzles. The two outer layers and the inner structure are quickly brought into contact while the extrusion is still unset to ~q~'J
form the laminate.
The inner structure may be any suitable structure in which the mass of the structure is substantially evenly distributed between the outer layers. Suitable inner structures may comprise corrugated extrusions having ridges and troughs of V-shape, e.g. having an angle of 60, or of undulating form, e~g. of sinusoidal form.
The inner structure holds the outer layers apart and provides parallel channels between them. The channels have triangular cross section for an inner structure of V-shaped corrugation and have a curved side and a straight side for an inner structure of generally sinusoidal form.
The channels may be closed at their ends by, for example, pinching together the outer layers such that the inner structure is collapsed to an end mass of substantially even distribution between the outer layers.
If it is desired to seal the channel ends in addition to closing them, the pinched together ends may be heat sealed, e.g. by ultrasonic welding.
A somewhat similar technique may be used to provide flattened panels in a sheet of corrugated plastics sheet according to the invention, in this case, panel areas are pinched together to collapse the inner structure to a panel mass of substantially even distribution between the outer layers, and the outer layers and substantially evenly distributed panel mass are heat sealed together, e.g. by ultrasonic welding. Such panel areas are useful as "plates" in food cartons such as pizza boxes or may be used for tabs of erectable carton blanks.
Similarly, coining may be provided by pinching together the outer layers to collapse the inner structure to form a line mass of substantially even distribution between the outer layers. These coined lines may be heat 7~
sealed if desired.
Embodiments of the invention will now be described by way of example with reference to the drawings, in which:
Figure 1 is a cross section of one example of prior art thermoplastics sheet;
Figure 2 is a cross section of the sheet of - 10 Figure 1 showing buckling of interior walls when outer layers are pinched together;
Figure 3 is a cross section of one sheet according to the invention;
Figure 4 is a cross section of the sheet of Figure 1 after pinching the outer layers together and sealing them;
Figure 5 is a cross section through another sheet according to the invention;
Figure 6 is a s~etch showing a sheet of the invention having a sealed end, a sealed panel and a coined line;
Figure 7 shows a pizza box formed from sheet material of the invention; and, Figure 8 shows a sketch of the sequence of process steps in one possible process of making a sheet according to the invention.
The example of prior art sheet material 10 shown in Figures 1 and 2 of the drawings may usually be formed of polypropylene and produced by porthole extrusion.
Thus, the prior art sheet 10 which has adjacent elongate channels 16 of substantially square cross section may be produced by extrusion through a single extrusion nozzle configured to have an outlet comprising a pair of elongate, horizontal, parallel slots for extruding the outer layers 12 of the sheet. The slots are connected by short, vertical, parallel slots for extruding the inner ~ 3 walls 14. The resulting extrusion shrinks as it cools so that the outer layers 12 are not entirely flat but have elongate grooves 13 extending along the line o~ each interior wall 14. Thus, the upper and lower surfaces o~
the sheet may be slightly fluted.
This prior art sheet has considerable advantages for use in place of corrugated liner board for many applications. It is, however, not very suitable for reuse applications where it has direct contact with food. The fluted surface is not so easy to clean as a flat surface, the ends of channels 16 are open to the ingress of dirt, bacteria and viruses and, importantly, the surface is quite fragile and easily penetrated by a knife or fork or other sharp edge or point. Difficulties also arise in bending this prior art material about a sharp fold line. When the layers 12 are squeezed together, walls 14 may tend to buckle each into a separate crumbled mass resisting further squeezing together of layers 12 and making sealing together of layers 12 aither difficult or impossible. Thus it may be seen that attempts to coin a fold line or to bring edges of the sheet together to close the mouths of channel 16 or squeeze the inner and outer layers together for other purposes, may result in a structure as shown in the sketch of Figure 2.
Figures 3 and 5 show cross sections of sheets according to the invention in which the inner structure is distributed over space between outer layers 32 (Figure 3) or 42 (Figure 5).
To avoid the problem presented by fluted upper and lower surfaces, sheet according to the invention may be made by progressive extrusion, i.e. two separate elongate extrusion slots are provided, each being for the extrusion of one of the upper or lower layers 32, 42. A further slot of saw tooth or waved configuration is provided for extrusion of the inner structure. Upon extrusion, the 3~
outer layers 32, 42 are contacted with ridges or troughs of walls 34, or 44 of the inner structure to bond the laminated outer layers and the inner structure together.
The inner structure may comprise walls 3~ each sloped at substantially 60 to the outer layers 32, alterna~e walls sloping in opposite directions and meeting at ridges and troughs respectively coincident with the upper and lower layers 32. In this case (Figure 3), the bulk of the walls 34 is distributed with respect to the area of layers 32. If the layers 32 are squeezed together, the walls 32 will tend -to crumple in an inner layer distributed evenly between outer layers 32. Discrete separate masses of crumpled inner walls such as described in relation to Fiyure 2 should not occur. As a result, it may be possible to squeeze layers 32 more closely together than was possible for prior art structures. The structures produced by squeezing the layers 32 closely together may approach the structure shown in Figure 4 in which collapsed walls 34 are shown as a single inner layer 38. In fact, the integral layer 38 may only be actually formed after heat sealing, e.g. by ultrasonic welding. Nevertheless, even before sealing, the close proximity of layers 32 after pinching them together, may allow the forming of coining 52 (Figure 6~ for improved folding of the shset at a sharp bend. Such coining 52 may, if desired, be additionally heat sealed.
Figure 5 shows a cross section of another embodiment of the invention. As described in relation to Figures 3 and 4, the inner structure between the outer layers 42 of the sheet of Figure 5 is distributed over the region between layers 42. In this case, however, sloping walls 44 provided by an undulating inner sheet which may be of sinusoidal form. The ridges and troughs are smoothly curved and sloping walls 44 merge the one within the other.
Channels 46 have a cross section with one straight edge and a curved edge. On squeezing, pinching or pressing together, a sheet having substantially the structure of that shown in Figure 4 may be obtained.
Figure 6 shows a detail of a sheet according to the invention having an edge 56 in with the outer layers been pressed together and sealed to close the mouths of channels within the structure. A panel 54 also provided.
the panel 54 has no channels in the thickness of the sheet but may be provided by pressing together the outer layers so that the inner structure is evenly distributed between thin and heat sealing the layers of the panel.
Figure 7 shows one embodiment of an improved carton suitable for use in direct contact with food and which may be recyclable~ Suitable thermoplastics material from which the sheet and the carton 60 may be made is polyethylene but any food grade thermoplastic material may be used especially those suitable for recycling.
Carton 60 may be a pizza box formed of thermoplastics material sheet according to the invention.
The sheet should be sufficiently rigid to retain the carton shape. To an extent, the channel structure of the sheet provides rigidity to sheet of which the thickness of individual layers and inner structure might otherwise be insufficient to be self-supporting. It may be seen, therefore, that cartons may be constructed with less total bulk of plastic material then has hitherto been possible.
The reduction in mass that may be possible is envisaged to be in the region of 40% to 60%. The dagree of rigidity required is a function of the particular carton and the degree of strength and durability required is a function of the envisaged amount of reusage. These characteristics are a matter of choice within the general scope of the invention.
For a pizza box, for example, a pizza box as shown in Figure 7, it may be desirable to incorporate a 3~ ~7 panel of greater surface toughness against the e-Efects of pronged or sharp edge~ instruments. Thus panel 54 may be provided in any desirsd shape by crushing or pressing outer layers 32 of the sheet together over the desired area.
5 That area may then be subjected to heat, for example, by ultrasonic welding, to form a laminated flattened panel 54.
The inner layer of panel 54 comprises collapsed walls of the inner structure of the sheet which have, on crushing, collapsed relatively evenly between outer layers 32. These 10 collapsed walls form an integral inner layer on heat sealing. It may be that ultrasonic welding plates may also be utilized to initially press layers 12 together. The edges of the pizza box which are adjacent longitudinal walls of channels of the sheet material are sealed against 15 the ingress of dirt and germs. The edges to which section the channels must be sealed by provision of a sealing edge such as sealing edge 56.
To guard against ingress of dirt and germs into 20 channels 36, 46 the ends of the channels may be sealed.
Thus layers 32, 42, at open ends of channels 36, 46, may be pressed together and heat sealed. Such a closed, sealed edge is shown at 56 in Figure 6.
Other embodiments are possible within the spirit of the invention. In particular, it may be possible to provide a steel structure comprising more than two layers 32, 42 each pair of layers having an inner structure there between.
Figure 8 shows one example of process steps which may be used. Corrugated sheet is either preformed or extruded from extruder 62. In any event it may be allowed to fall vertically. Outer laminating sheets 64, are 35 provided either pre-formed or from extruders 66 and allowed to fall vertically to either side of sheet 60. The three sheets 64, 60, 64 may pass guide rollers 67 and then between heating rollers 68. These are of importance when ~p;~ 5~7 g pre-formed sheet is used. Then sheets then pass between pressure rollers 70 which laminate them together.
Thereafter they may pass through chill rollers 72 and possibly transport conveyor 74. Other transport rollers may additionally be used.
Claims (14)
1. Thermoplastics material sheet having a longitudinal dimension and a transverse direction and formed by having internal extending in a longitudinal direction comprising two parallel outer layers spaced apart by an inner structure comprising elongate sloping walls extending in the longitudinal direction of the sheet, alternate elongate walls sloping in opposing directions to form elongate channels between opposing elongate walls and at least one of the outer layers.
2. Thermoplastic sheet material as claimed in Claim 1 in which the inner structure comprises walls sloping at substantially 60° to each of the two outer layers, alternate opposing walls meeting at their edges through which they join a respective one of the outer layers.
3. Thermoplastic sheet material as claimed in Claim 1 comprising a laminate of two outer layers sandwiching the inner structure.
4. Thermoplastic sheet material as claimed in Claim 3 in which the laminate if formed by lamination of unset extrusions of the outer layers and inner structure.
5. Thermoplastic sheet material as claimed in Claim 4 in which the inner structure comprises a corrugated extrusion having ridges and troughs of V-shape.
6. Thermoplastic sheet material as claimed in Claim 5 in which the angle of each V-shaped ridge and trough is substantially 60°.
7. Thermoplastic sheet material as claimed n Claim 4 in which the inner structure comprises a corrugated extrusion having undulating ridges and troughs.
8. Thermoplastic sheet material as claimed in Claim 7 in which the undulating corrugated extrusion is of sinusoidal form.
9. Thermoplastic sheet material as claimed in Claim 1 in which ends of the channels are closed.
10. Thermoplastic sheet material as claimed in Claim 9 in which ends of the channels are pinched together such that the inner structure is collapsed to an end mass of substantially even distribution between the outer layers.
11. Thermoplastic sheet material as claimed in Claim 10 in which the outer layers and substantially distributed collapsed inner structure are sealed together.
12. Thermoplastic sheet material as claimed in Claim 1 in which panels comprise areas in which the inner structure is collapsed to a panel mass of substantially even distribution between the outer layers, and the outer layers and substantially evenly distributed panel mass are sealed together.
13. Thermoplastic sheet material as claimed in Claim 1 having coined lines along which the sheet is bendable, the coined lines comprising lines along which the inner structure is collapsed to form a line mass of substantially even distribution between the outer layers.
14. Thermoplastic sheet material as claimed in Claim 1 in which the thermoplastic material is polyethylene.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US70822391A | 1991-05-31 | 1991-05-31 | |
| US708,223 | 1991-05-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2070077A1 true CA2070077A1 (en) | 1992-12-01 |
Family
ID=24844899
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002070077A Abandoned CA2070077A1 (en) | 1991-05-31 | 1992-05-29 | Multi-layer plastics material sheet |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2070077A1 (en) |
| WO (1) | WO1994005489A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE514747C2 (en) | 1999-08-02 | 2001-04-09 | Wellplast Ab | Method and apparatus for the manufacture of corrugated plastic material |
| GB0114691D0 (en) | 2001-06-15 | 2001-08-08 | Rasmussen O B | Laminates of films and methods and apparatus for their manufacture |
| AU2007200996B2 (en) * | 2001-06-15 | 2009-02-05 | Ole-Bendt Rasmussen | Laminates of Films and Methods and Apparatus for their Manufacture |
| CA2398033C (en) * | 2002-03-19 | 2005-06-14 | Carlo Fascio | Corrugated packaging and insulation material |
| US20150037542A1 (en) * | 2012-03-29 | 2015-02-05 | Microgreen Polymers Inc. | Composite Material That Includes Microcellular Plastic, and Related Systems and Methods |
| CA2854735C (en) * | 2013-06-20 | 2022-07-26 | Alpha Marathon Film Extrusion Technologies Inc. | Corrugated plastic board |
| EP3307536B1 (en) * | 2015-06-11 | 2021-08-04 | COLINES S.p.A. | Honeycomb sandwich sheet or panel, based on polypropylene, with a central thermoformed film |
| CN113771368B (en) * | 2021-10-15 | 2023-03-24 | 大连塑研塑料科技开发有限公司 | Automobile net-shaped splash guard forming process and device |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4829768B1 (en) * | 1970-03-16 | 1973-09-13 | ||
| US3723222A (en) * | 1970-05-01 | 1973-03-27 | Mitsui Petrochemical Ind | Process for manufacturing corrugated thermoplastic synthetic resin cardboard sheet |
| US3900356A (en) * | 1973-03-28 | 1975-08-19 | Fmc Corp | Method for making a cellular cushioning structure |
| US4132581A (en) * | 1976-12-27 | 1979-01-02 | Standard Oil Company (Indiana) | Method for the fabrication of plasticboard |
| IT7922899U1 (en) * | 1979-10-17 | 1981-04-17 | Montedison Spa | DOUBLE-WALL CELLULAR SHEET, WITH HIGH INSULATION EFFECT. |
| JPS5746743A (en) * | 1980-08-29 | 1982-03-17 | Mitsui Petrochemical Ind | Corrugated cardboard sheet in synthetic resin |
| DE8202094U1 (en) * | 1982-01-28 | 1982-07-01 | AOE Plastic GmbH, 8000 München | Insulating container, in particular insulating bag or insulating bag |
-
1992
- 1992-05-29 CA CA002070077A patent/CA2070077A1/en not_active Abandoned
- 1992-09-08 WO PCT/CA1992/000385 patent/WO1994005489A1/en active Application Filing
Also Published As
| Publication number | Publication date |
|---|---|
| WO1994005489A1 (en) | 1994-03-17 |
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