CA1150461A - Retortable container - Google Patents
Retortable containerInfo
- Publication number
- CA1150461A CA1150461A CA000319973A CA319973A CA1150461A CA 1150461 A CA1150461 A CA 1150461A CA 000319973 A CA000319973 A CA 000319973A CA 319973 A CA319973 A CA 319973A CA 1150461 A CA1150461 A CA 1150461A
- Authority
- CA
- Canada
- Prior art keywords
- container
- heated
- layer
- sheet
- heat
- 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
Landscapes
- Laminated Bodies (AREA)
- Packages (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A coextruded theremoplastic sheet, suitable for forming into a retortable container, comprising a heat-tolerant structural layer that remains rigid when heated to temperatures above 200°F for maintaining therigidity of said container when heated and a gas barrier layer for preventing diffusion of gases into and out of said container, whereby said container, when formed from said sheet, can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products, provides a barrier to oxygen and other gases, both incoming and outgoing, during storage of said container, and can be heated to prepare food for eating.
A coextruded theremoplastic sheet, suitable for forming into a retortable container, comprising a heat-tolerant structural layer that remains rigid when heated to temperatures above 200°F for maintaining therigidity of said container when heated and a gas barrier layer for preventing diffusion of gases into and out of said container, whereby said container, when formed from said sheet, can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products, provides a barrier to oxygen and other gases, both incoming and outgoing, during storage of said container, and can be heated to prepare food for eating.
Description
~5~
Field of the Invention This lnvention relates to plastic food containers.
Backcround of the Invention In vacuum packing foods and in pacXing some non-~cod products, it is necessary to retort, or heat, the contents.
Foods must be heated during their processing to temperatures 2p-proaching 250F to kill bacteria. Some non-food products such as wax must be heated to keep them fluid while they are poured into their packages.
Foods can also be reheated in their containers, in either conventional or microwave ovens, to temperatures in the same range as in processing or higher.
Presently, such retortable containers are made from glass or metal. Both materials provide the gaseous barrier necessary for long shelf life and can easily withstand high temp-eratures without losing their rigidity, but both are becoming increasingly expensive to manufacture. Furthermore, each has its own disadvantages. For example, metal containers cannot be reheated in microwave ovens, and glass containers are easily bro~en.
Rigid plastic containers have only heretofore been used in low-heat applications (less than about 190F), such as in hot-filled beveraye cups or the like. And these plastic containers have been sinyle-layer structures composed of, ~or example, polypropylene.
Plastics have been used in some retortable packa~es.
~or example, flexlble retortable bacs have been made bv laminatin~
iuminum and plastic.
.. , ~;
~s~
Summary of the Invention I have discovered that a less-expensive and generally more desirable retortable container can be made from multiple layers of plastic materials. A heat-tolerant structural layer (e.g., ~ a}d~350, (Arco Polymers trademark)) is co~bined with a gase~ barrier layer (e.g., a nitrile-based resin such as Barex 210, (Vistron trademark)) to give a plastic container that can be retorted and that is substantially impenetrable to oxygen or other gases, such as food aromatics, so as to prolong shelf life.
According to the present invention; there is provided a coextruded thermoplastic sheet, suitable for forming into a retortable container, comprising a heat-tolerant structural layer made of Dylark , a styrene-maleic anhydride copolymer, that remains rigid when heated to temperatures above 200F for main-taining the rigidity of said container when heated and a gaseous barrier layer for preventing diffusion of gases into and out of said container, whereby said container, when forrned from said sheet, can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products, provides a barrier to oxygen and other gases, both incomlng and outgoing, during storage of said container, and can be heated to prepare food for eating.
In another aspect, the invention provides a retortable container for packaging foods and other products heated during packaging, comprising a heat-tolerant structural layer that remains rigid when heated to temperatures above 200F for maintaining the rigidity of said container when heated and a gaseous barrier layer for preventing diffusion of gases into and out of said container, whereby said container formed can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products provides a barrier to oxygen and other * trademark 7".
6~
gases, both incoming and outgoing, during storage of said container, and can be heated to prepare food for eating.
In preferred embodiments, the container is thermoformed from a three-layer coextruded sheet consisting of a Dylark 350 inner layer, a Barex 210 outer layer and an intermediate tie layer that is a mixture of two DuPont commercial resins:
CXA 1025 and Eva 3135X, both of which are ethylene vinyl acetates;
the container has either a heat-sealed lid composed of the same three layers or a mechanically sealed metal lid.
Preferred Embodiment I turn now to description of the structure, manu-facturing and use of a preferred embodiment of the invention, after first briefly describing the drawings.
FIGURE 1 is an elevation, partially cross-sectional, view of said preferred container embodiment, with the lid shown raised above its installed position.
FIGURE 2 is a cross-sectional view at 2-2 of Figure 1, showing the multilayer structure of the container walls.
FIGURE 3 is a diagrammatic view of the manufacturing process for forming the container.
Turning to the Figures, there is shown container 10 in which food (e.g., a ready-prepared stew) has been packed. The container consists of bowl 14 and lid 16.
Both the lid and bowl are made from multilayer sheets that are formed by coextrusion casting. Bowl 14 is thermoformed from such sheets, as depicted in Figure 3. ~id 16 is cut from a similar sheet and heat sealed to rim 20 of the bowl.
- 2a -"
~ 5~4~
As shown in Figure 2 the finished bowl and lid have three layers: an inner structural layer 22 of Dylark* 350 (product of Arco Polymers) that remains rigid at temperatures up to about 250F; an outer layer 24 of Barex* 210, (product of Vistron), a nitrile-based resin that acts as a barrier to incom-ing oxygen to prevent food spoilage; and an intermediate tie layer 26 that is a mixture of two DuPont commercial resins--25%
CXA 1025, an ethylene vinyl acetate and Eva 3135X, a second ethylene vinyl acetate.
The resin combination adheres well to nitrile layer 24 and to Dylark Layer 22, and it provides a good moisture bar-rier, a property not adequately present in either of layers 22and 24.
The C~A 1025 (vinyl acetate) provides the necessary adhesive qualities. The Eva 3135X dilutes the adhesive to allow a thicker layer to be used. An undiluted CXA 1025 layer of the desired tie layer thickness would tend to be pushed to the lateral edges of the sheet during extrusion and to there emerge from the sheet and stick to the rolls causing the sheet to bind. The combination thereby solves the roll sticking problem.
Turning to Figure 3, the coextrusion process for forming the three-layer sheet material is shown.
Three heated containers 30, 32 and 34 serve as sources of the Dylark 350, the mixture of DuPont resins, and Barex 210, respectively. The DuPont resin mixture is heated in container 32 to about 390F. The Dylark 350 and Barex* 210 are heated in containers 30 and 34 to about 400F.
*Trademark Three conduits 36, 38 and 40 supply the heated materials to coextrusion block 42. There the materials merge together to form under pressure a unitary, three-layer, thick stream 44 of generall~ circular cross-section. Stream 44 passes into extrusion die 46 (Welex standard 54 inch flex-lip die), while maintained at a temperature of about 400F, or slightly in excess thereof, for extrusion into continuous sheet 48 about 36 mils ~5~46~
thic~ (Dylark 23 mils; tie layer 4 mils; and Barex 210, g milJ~.
Sheet 48 then passes through a series of chill rolls 37.
The sheet may then be processed into containers or wour.d into spools for storage (not shown).
To process sheet 48 into containers, the sheet is passed through conventional thermoEorming apparatus 50 which impresses the bowl shape and in doing so reduces the wall thickness by about 503 on the average, making the finished container wall about 18 mils thick. The individual layer thic~nesses are also each reduced by about 50% during thermoforming, maXing the ~inished thickness about 12 mils of Dylark 350, about 2 mils of tie layer, and about 5 mils of Barex 210.
After thermoforming, the shaped sheet 52 passes throug~
trim press 54, in which the individual bowls 14 for the containers are separated. Thereafter, each bowl is given curled rim 20 (Fig. 1) by a conventional curling machine (not shown).
Lids 16 are separately cut from sheet 48 and heat-sealed to curled rim 2Q by conventional heat-sealing techniques.
In use, food is packed in bowl 14, the bowl and food are retorted, and lid 16 is heat-sealed to rim 20. The consumer can reheat the container in an oven (conventional or microwave), making sure that temperatures do not exceed about 250F.
trc~Qe ,'~ `k ~L~4~3~
_her Embodiments Other embodiments of the invention will occur to those skilled in the art. For example, a metal lid could be substituted for the plastic one and could be mechanically sealed to rim 20. Such a lid could then be opened with a conventional can opener, but reheating would have to be in a conventional oven and not a microwave oven unless the metal lid were first removed. Other heat-tolerant structural layers could be substituted, e.g., polycarbonates or filled poly-propylene could be used. And similarly other gaseous barrierlayers could be used, e.g., Nylon 6 or hydrolyzed polyvinyl alcohol such as Eval , with suitable tie layers.
* trademark
Field of the Invention This lnvention relates to plastic food containers.
Backcround of the Invention In vacuum packing foods and in pacXing some non-~cod products, it is necessary to retort, or heat, the contents.
Foods must be heated during their processing to temperatures 2p-proaching 250F to kill bacteria. Some non-food products such as wax must be heated to keep them fluid while they are poured into their packages.
Foods can also be reheated in their containers, in either conventional or microwave ovens, to temperatures in the same range as in processing or higher.
Presently, such retortable containers are made from glass or metal. Both materials provide the gaseous barrier necessary for long shelf life and can easily withstand high temp-eratures without losing their rigidity, but both are becoming increasingly expensive to manufacture. Furthermore, each has its own disadvantages. For example, metal containers cannot be reheated in microwave ovens, and glass containers are easily bro~en.
Rigid plastic containers have only heretofore been used in low-heat applications (less than about 190F), such as in hot-filled beveraye cups or the like. And these plastic containers have been sinyle-layer structures composed of, ~or example, polypropylene.
Plastics have been used in some retortable packa~es.
~or example, flexlble retortable bacs have been made bv laminatin~
iuminum and plastic.
.. , ~;
~s~
Summary of the Invention I have discovered that a less-expensive and generally more desirable retortable container can be made from multiple layers of plastic materials. A heat-tolerant structural layer (e.g., ~ a}d~350, (Arco Polymers trademark)) is co~bined with a gase~ barrier layer (e.g., a nitrile-based resin such as Barex 210, (Vistron trademark)) to give a plastic container that can be retorted and that is substantially impenetrable to oxygen or other gases, such as food aromatics, so as to prolong shelf life.
According to the present invention; there is provided a coextruded thermoplastic sheet, suitable for forming into a retortable container, comprising a heat-tolerant structural layer made of Dylark , a styrene-maleic anhydride copolymer, that remains rigid when heated to temperatures above 200F for main-taining the rigidity of said container when heated and a gaseous barrier layer for preventing diffusion of gases into and out of said container, whereby said container, when forrned from said sheet, can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products, provides a barrier to oxygen and other gases, both incomlng and outgoing, during storage of said container, and can be heated to prepare food for eating.
In another aspect, the invention provides a retortable container for packaging foods and other products heated during packaging, comprising a heat-tolerant structural layer that remains rigid when heated to temperatures above 200F for maintaining the rigidity of said container when heated and a gaseous barrier layer for preventing diffusion of gases into and out of said container, whereby said container formed can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products provides a barrier to oxygen and other * trademark 7".
6~
gases, both incoming and outgoing, during storage of said container, and can be heated to prepare food for eating.
In preferred embodiments, the container is thermoformed from a three-layer coextruded sheet consisting of a Dylark 350 inner layer, a Barex 210 outer layer and an intermediate tie layer that is a mixture of two DuPont commercial resins:
CXA 1025 and Eva 3135X, both of which are ethylene vinyl acetates;
the container has either a heat-sealed lid composed of the same three layers or a mechanically sealed metal lid.
Preferred Embodiment I turn now to description of the structure, manu-facturing and use of a preferred embodiment of the invention, after first briefly describing the drawings.
FIGURE 1 is an elevation, partially cross-sectional, view of said preferred container embodiment, with the lid shown raised above its installed position.
FIGURE 2 is a cross-sectional view at 2-2 of Figure 1, showing the multilayer structure of the container walls.
FIGURE 3 is a diagrammatic view of the manufacturing process for forming the container.
Turning to the Figures, there is shown container 10 in which food (e.g., a ready-prepared stew) has been packed. The container consists of bowl 14 and lid 16.
Both the lid and bowl are made from multilayer sheets that are formed by coextrusion casting. Bowl 14 is thermoformed from such sheets, as depicted in Figure 3. ~id 16 is cut from a similar sheet and heat sealed to rim 20 of the bowl.
- 2a -"
~ 5~4~
As shown in Figure 2 the finished bowl and lid have three layers: an inner structural layer 22 of Dylark* 350 (product of Arco Polymers) that remains rigid at temperatures up to about 250F; an outer layer 24 of Barex* 210, (product of Vistron), a nitrile-based resin that acts as a barrier to incom-ing oxygen to prevent food spoilage; and an intermediate tie layer 26 that is a mixture of two DuPont commercial resins--25%
CXA 1025, an ethylene vinyl acetate and Eva 3135X, a second ethylene vinyl acetate.
The resin combination adheres well to nitrile layer 24 and to Dylark Layer 22, and it provides a good moisture bar-rier, a property not adequately present in either of layers 22and 24.
The C~A 1025 (vinyl acetate) provides the necessary adhesive qualities. The Eva 3135X dilutes the adhesive to allow a thicker layer to be used. An undiluted CXA 1025 layer of the desired tie layer thickness would tend to be pushed to the lateral edges of the sheet during extrusion and to there emerge from the sheet and stick to the rolls causing the sheet to bind. The combination thereby solves the roll sticking problem.
Turning to Figure 3, the coextrusion process for forming the three-layer sheet material is shown.
Three heated containers 30, 32 and 34 serve as sources of the Dylark 350, the mixture of DuPont resins, and Barex 210, respectively. The DuPont resin mixture is heated in container 32 to about 390F. The Dylark 350 and Barex* 210 are heated in containers 30 and 34 to about 400F.
*Trademark Three conduits 36, 38 and 40 supply the heated materials to coextrusion block 42. There the materials merge together to form under pressure a unitary, three-layer, thick stream 44 of generall~ circular cross-section. Stream 44 passes into extrusion die 46 (Welex standard 54 inch flex-lip die), while maintained at a temperature of about 400F, or slightly in excess thereof, for extrusion into continuous sheet 48 about 36 mils ~5~46~
thic~ (Dylark 23 mils; tie layer 4 mils; and Barex 210, g milJ~.
Sheet 48 then passes through a series of chill rolls 37.
The sheet may then be processed into containers or wour.d into spools for storage (not shown).
To process sheet 48 into containers, the sheet is passed through conventional thermoEorming apparatus 50 which impresses the bowl shape and in doing so reduces the wall thickness by about 503 on the average, making the finished container wall about 18 mils thick. The individual layer thic~nesses are also each reduced by about 50% during thermoforming, maXing the ~inished thickness about 12 mils of Dylark 350, about 2 mils of tie layer, and about 5 mils of Barex 210.
After thermoforming, the shaped sheet 52 passes throug~
trim press 54, in which the individual bowls 14 for the containers are separated. Thereafter, each bowl is given curled rim 20 (Fig. 1) by a conventional curling machine (not shown).
Lids 16 are separately cut from sheet 48 and heat-sealed to curled rim 2Q by conventional heat-sealing techniques.
In use, food is packed in bowl 14, the bowl and food are retorted, and lid 16 is heat-sealed to rim 20. The consumer can reheat the container in an oven (conventional or microwave), making sure that temperatures do not exceed about 250F.
trc~Qe ,'~ `k ~L~4~3~
_her Embodiments Other embodiments of the invention will occur to those skilled in the art. For example, a metal lid could be substituted for the plastic one and could be mechanically sealed to rim 20. Such a lid could then be opened with a conventional can opener, but reheating would have to be in a conventional oven and not a microwave oven unless the metal lid were first removed. Other heat-tolerant structural layers could be substituted, e.g., polycarbonates or filled poly-propylene could be used. And similarly other gaseous barrierlayers could be used, e.g., Nylon 6 or hydrolyzed polyvinyl alcohol such as Eval , with suitable tie layers.
* trademark
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A coextruded thermoplastic sheet, suitable for forming into a retortable container, comprising a heat-tolerant structural layer made of Dylark*, a styrene-maleic anhydride copolymer, that remains rigid when heated to temperatures above 200°F for maintaining the rigidity of said container when heated and a gas barrier layer for preventing diffusion of gases into and out of said container, whereby said container, when formed from said sheet, can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products, provides a barrier to oxygen and other gases, both incoming and outgoing, during storage of said container, and can be heated to prepare food for eating.
2. A retortable container vacuum thermoformed from a coextruded sheet made by supplying heated materials to a coextrusion block to form a multilayer stream and flattening the multilayer stream in an extrusion die to form said sheet, said container comprising an outer heat-tolerant structural layer that remains rigid when heated to temperatures above 200°F for maintaining the rigidity of said container when heated, a gas barrier layer for preventing diffusion of gases into and out of said container, and an intermediate tie layer bonding said heat-tolerant structural layer to said gas barrier layer, whereby said container 50 formed can be heated to sterilize vacuum-packed foods and to pack in a fluid state other products, provides a barrier to oxygen and other gases, both incoming and outgoing, during storage of said container, and can be heated to prepare food for eating.
3. A method for making a thermoplastic structure comprising separately heating a first material that remains rigid at 200°F, a second material with gas barrier properties, and a third material to serve as an adhesive tie layer between layers of said first and second materials, supplying said heated material to a coextrusion block to form a multilayer stream with a layer of said first material, a layer of said second material, and an intermediate layer of said third material; and, flattening the multilayer stream in a coextrusion die to produce a multilayer sheet.
4. The method of claim 3 further comprising the step of thermoforming a container from said coextruded multilayer sheet.
5. The structure of claim 2 wherein said heat-tolerant layer is Dylark*, a styrene-maleic anhydride copolymer.
6. The structure of claim 1 or 2 wherein said gas barrier layer is a nitrile-based resin that is a barrier to oxygen.
7. The structure of claim 1 or 2 wherein said gas barrier layer is Barex* 210, an acrylonitrile-methyl acrylate copolymer, that is a barrier to oxygen.
8. The structure of claim 2 wherein said container comprises a bowl portion with a rim and a lid for being heat-sealed to the rim, both said bowl portion and lid being formed of said structural and barrier layers.
* Trademark
* Trademark
9. The structure of claim 1 or 2 wherein the total thick-ness of said structural and barrier layers exceeds 5 mils.
10. The method of claim 3 wherein said first material is filled polypropylene.
11. The method of claim 3 wherein said first material is filled polypropylene or styrene-maleic anhydride copolymer, and said second material is a material selected from the group consisting of acrylonitrile-methyl acrylate copolymer and hydrolysed polyvinyl alcohol.
12. The method of claim 3 wherein said first material is filled polypropylene or styrene-maleic anhydride copolymer, and said second material is a material selected from the group consisting of acrylonitrile-methyl acrylate copolymer and hydrolysed polyvinyl alcohol and said third material layer is ethylene-vinyl acetate copolymer.
13. The structure of claim 2 wherein the heat tolerant structural layer is a filled polypropylene.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000319973A CA1150461A (en) | 1979-01-19 | 1979-01-19 | Retortable container |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000319973A CA1150461A (en) | 1979-01-19 | 1979-01-19 | Retortable container |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1150461A true CA1150461A (en) | 1983-07-26 |
Family
ID=4113369
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000319973A Expired CA1150461A (en) | 1979-01-19 | 1979-01-19 | Retortable container |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1150461A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0755778A1 (en) | 1995-07-28 | 1997-01-29 | Wolff Walsrode Ag | Sterilisable barrier film based on polyamides and polyolefins |
| EP0993943A3 (en) * | 1998-10-16 | 2000-08-09 | Premark RWP Holdings, Inc. | Laminate employing liquid resistant film |
-
1979
- 1979-01-19 CA CA000319973A patent/CA1150461A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0755778A1 (en) | 1995-07-28 | 1997-01-29 | Wolff Walsrode Ag | Sterilisable barrier film based on polyamides and polyolefins |
| EP0993943A3 (en) * | 1998-10-16 | 2000-08-09 | Premark RWP Holdings, Inc. | Laminate employing liquid resistant film |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |