Patent Application
20080020104
Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.
This invention pertains to the design, construction, closure, sealing and use of novel consumer friendly paperboard package systems (e.g. boxes, cartons) formulated to include plastic coating or film of selected gas permeability as part of the wall structure for prolonging the storage life of fresh fruits, vegetables and flowers under modified atmosphere (MA) in the headspaces of the closed package systems, and retail purchase by consumers.
Due to the long distance and the time required for continental and overseas shipment of MAP preserved fruits, vegetables and flowers, we have invented a unique three-layer linerboard which can be cut, folded and formed into a consumer sized box bottom and lid which in turn can fit into a modified Euro tray (60×40 cm) which can be used for the shipment of tomatoes, grapes, peaches and nectarines. Typically, the box bottom and lid are of a size that can contain four to six peaches, which is a convenient quantity for a consumer to purchase. Thus the MA box bottom and lid, being sealed, does not have to be opened until it reaches the consumer's home, thereby preserving the produce contents. The modified Euro tray, according to the invention, is an open tray with air circulating recessed sides and ends and has strong corner supports which enables the modified Euro trays to be stacked on a pallet.
A common request from customers of packaged fruits, vegetables and flowers is a capability to view the packaged product without opening the package. A window in the package is desirable. However, since the packaged product is refrigerated and since moisture is present in the interior of the package from fruit or vegetables, the window, if there is one, usually fogs up from condensation. A problem with conventional corrugated modified atmosphere packaged fruit, vegetables or flowers is that the corrugated paperboard construction provides insulation, which retains heat. If the fruit or vegetable product in the package is warm, it requires time to cool down to acceptable modified atmosphere refrigeration levels. A window in the package is useful because it transmits respiration heat from the packaged produce, whereas linerboard inhibits heat transmission. A window also enables the produce to be cooled quickly to refrigeration temperatures if the produce is initially at room temperature.
The weight of the fruits or vegetables to be packaged can be in a range from small such as 100 g to a large package such as 5 kg (equivalent of a wholesale pack). The MA packages are adapted to include fruits, vegetables, fresh-cut flowers, meat and fish. Currently, paper companies manufacture coated paper products or laminated papers. However, the purpose or usage of such papers is mainly for water repellent or physical strength.
The three-layer linerboard blanks for the MA package, according to the invention, have sufficient physical strength that they can be constructed into boxes or bags with a clear window. The linerboard blanks can be cut with appropriate fold lines to form either a two-piece container (box base and lid) or a one-piece container with the lid flap folding over the open top of the box base. Square, rectangular and other shapes are possible. The openings between the lid and the bottom are taped or glued to seal the package completely in order to provide an MA atmosphere. The linerboard blanks can be formed so that the lid area has a window, which is created by not having a first or second layer of kraft paper obscuring the polymer film in the window area. The polymer film layer for the window should be reasonably clear and contain or be treated with an anti-fog agent. The glue used to seal the MA package must be waterproof. With the box construction, the linerboard must be of a specified weight to provide the appropriate strength. The linerboard weight can be about 100 to 140 g/m2. However, a larger range is included in the scope of the invention for wholesale and other applications.
For a larger wholesale bag application, the paper weight can be reduced but the polymer must remain approximately the same for gas transmission purposes. The thinner linerboard for bags is more pliable and can be formed on a packaging machine into paper bags without sacrificing gas permeability. The weight of the linerboard can be 140 g/m2 but broader ranges are included in the scope of the invention.
Specific embodiments of the invention will now be discussed in association with the drawings.
Storage life of fresh fruits and vegetables is dependent on storage temperature, gas composition around the produce and degree of physical abuse leading to bruises, abrasions and cuts. Storage and transportation of fruits and vegetables is facilitated by the packing of the produce in suitable package systems which provide features such as prolonging storage life, reducing physical abuse and lowering the rate of water loss of produce.
Corrugated paperboard boxes and cartons are used commercially for the storage and transportation of fresh fruits and vegetables for the following reasons:
Since corrugated paperboard has very high O2 and CO2 permeabilities, this material by itself would be unsuitable for the construction of MA package systems. By incorporating a plastic, gas-permeable membrane into the corrugated paperboard structure, suitable MA package systems with specific gas and moisture permeabilities can be constructed.
The tri-layer linerboard comprising polymer film 30, and paper layers 28 and 32 (see
The tri-layer liner with the polymeric plastic film membrane 30 as the middle layer will prevent water movement from the inside cavity, filled with a fruit or vegetable, with the benefit of the retention of the original wall strength. A gas-permeable, flexible polymeric plastic film with specific gas and moisture permeabilities is suitable for placement between two sheets 28 and 32 of kraft paper to form a tri-layer complex with specific O2 and CO2 and moisture permeabilities. The tri-layer liner may be manufactured by any of the following production methods:
This is a process whereby a molten polymer is extruded through a slit die and applied as a laminant to combine the two kraft paper substrates. By employing extrusion lamination, it is possible to produce very thin calliper films thereby producing a material with high permeability characteristics. Such thin polymer films would not be practical if produced as separate film liners or bag-in-box. By laminating to kraft paper, physical support is provided to protect the thin polymer film.
This is a process whereby a molten polymer film is extruded through a slit die onto one kraft paper substrate and in a second operation, adhesive lamination is employed to combine the second kraft liner.
This is a process whereby a pre-made polymer film, produced by slit die extrusion or annular die film blowing, is adhesive laminated to the two kraft substrates, either simultaneously or in sequence.
The gas permeable polymeric layer can be homopolymers or copolymers produced as a monolayer or coextruded layers with specific formulation and caliper selected to produce the required oxygen (O2) and carbon dioxide (CO2) permeabilities. Polymers would likely be selected from the polyolefin family, typically Low Density Polyethylene (LDPE), linear low density polyethylene (LLDPE), medium and high density polyethylene (MDPE and HDPE), polypropylene (PP). Additional polymers such as ethylenevinylacetate (EVA), ethyl butyl acetate (EBA), ionomer resins (cross-linked), cast polyester (PET), nylon (polyamide) and polycarbonate (PC) may also be considered.
Coextrusions combining low density polyethylene with ethylenevinylacetate or ethylbutylacetate have been found to be particularly effective in lowering gas barrier to produce a highly permeable film. Percentages of ethylenevinylacetate or ethylbutylacetate are at the range of 5% to 30%.
A further unique embodiment of this invention is the ability of the box to maintain its internal equilibrium volume under varying gas compositions in the headspace. The gas permeability of the box prevents a vacuum condition developing which can occur in conventional MAP systems if the package produce starts to absorb carbon dioxide. If such conditions were to develop in the permeable box, the controlled influx of gases through the gas permeable film would not allow a vacuum to develop.
For specific product applications, the rate of gas exchange within the box may be achieved by a combination of polymer barrier and controlled film porosity. Porosity may also be achieved by piercing holes through the polymer containing inner liner either at the corrugating stage, die cutting operation, box forming stage, or in the completed box. Hole size, either single or multiple, may vary depending on the required gas exchange rate but typical diameter would be in the range of 0.25 to 2.00 mm. Hole positions on the box will vary depending on the optimum location for each product and the gas flow dynamics within the box.
It has been established that oxygen (O2) and carbon dioxide (CO2) gas exchange rates through the tri-layer paperboard of the invention fall within the range 50-100,000 cc3/m2 24 hr. 1 atm.
It has also been found that the following additional factors must be critically controlled if consistent polymer characteristics are to be achieved:
In this invention, the plastic film membrane 30 is sandwiched between two sheets 28 and 32 of kraft paper to form a tri-layer complex as the inner liner of a paperboard MA package system. The film membrane 30 may be a gas-permeable plastic film or a plastic coating applied to one of the sheets of kraft paper, and then sealed between the two sheets. The membrane is bonded to both of the kraft paper sheets when the plastic is in semi-molten state and the two paper sheets are pressed together.
When 25 g/m2 low density polyethylene was used, extrusion laminated on 40 g/m2 and 125 g/m2 MG kraft, the O2 and CO2 permeability were 1300 and 2200 cc/m2 24 hr. 1 atm. respectively. When a 35 g/m2 coating of 17% EBA and LDPE was extrusion laminated, the O2 and CO2 permeability were 2300 and 4700 cc/m2 24 hr. 1 atm. respectively.
Studies have been carried out on the MAP of fruits and vegetables with sealed polymeric, plastic film bags in a corrugated paperboard box (Prince, 1989). However, several disadvantages of using a bag-in-box are evident:
The single-piece and three-piece types of MA package systems are to be constructed in such a manner that upon gluing, folding and pressing at glue points, the following requirements are met:
The single-piece type MA package system is intended to be used on a continuous-flow or a batch-type operation consisting of:
The single-piece type MA package system may have gas inlet and gas outlet apertures in the two end panels for gasification of the produce headspace in a completely closed MA package system (including glued, sealed flaps).
A further benefit of injecting gas into an hermetically sealed box is that it is possible to include a trace gas, typically helium or sulphur hexafluoride as a leak detection method. Provided the box is relying on gas permeability and not porosity, it is possible to sense gas escape through cracks, unwanted pinholes or faulty glue seals.
Upon the insertion of a gas nozzle into the inlet aperture and upon the flow of the pressurized gas mixture through the headspace of the package system, plugs with vent pinholes or styrofoam plugs would be used for produce with high respiration rates and gas-impermeable plastic plugs may be used for low respiration rate produce.
Also, the two-piece type MA package system is intended to be used on a continuous-flow or a batch-type operation consisting of:
The three-piece type package system may have gas inlet and gas outlet apertures in the two end panels for gasification of the produce headspace in a completely closed MA package system. Upon the insertion of a gas nozzle into the inlet aperture and upon the flow of a pressurized gas mixture through the headspace of the package system, plugs with vent pinholes or styrofoam plugs are to be inserted. Styrofoam plugs would be used for produce with high respiration rate produce, and gas-impermeable plastic plugs or gas-impermeable tape may be used for low respiration rate produce.
The selection of either the single-piece type or the three-piece type will depend upon:
In the applicant's research, barrier materials were manufactured according to the following procedures:
The tri-layer samples were constructed using 40 g/m2 MG kraft+Polymer+125 g/m2 MG kraft liner. Two kinds of kraft paper were used: 125 g/m2 and 40 g/m2. The smoothness (roughness) measurements of both sides were as follows:
Three polymer materials, low density polyethylene (LDPE), and high density polyethylene (HDPE), a copolymer of LDPE and ethylene butyl acetate (EBA) at 10 g, 15 g, 25 g, 35 g and 45 g per square meter were used.
At fixed process conditions, extrusion polymer melting temperature was 315° C. and the air gap (or nip height) was 200 mm.
Using the smooth or rough side of the kraft paper, the relative permeabilities and pinhole numbers on the flat sheet, or the folding lines are tabulated below in Table 1.
A number of conclusions can be drawn from the results in Table 1:
When extrusion lamination process conditions were changed, but the kinds and amounts of polymer and kraft liner stayed the same (as in Example 1) it was found that the gas permeability of the barrier materials manufactured under various process conditions were tabulated in Table 2.
The above results lead to the following conclusions:
Although by using different polymers and process conditions, barrier materials of various permeabilities can be achieved, for very high respiring produce, high permeability materials need to be developed. In order to precisely control the permeability to match the need of certain specific produce, and box configurations (volume/surface area ratio), the permeability of a barrier material can be achieved by making controlled pinholes.
For specific product applications, the rate of gas exchange within the box may be achieved by a combination of polymer barrier and Controlled film porosity. Porosity may be achieved by piercing holes through the polymer containing inner liner either at the corrugating stage, die cutting operation, or box forming stage. Hole size, either single or multiple, may vary depending on the required gas exchange rate but typically would be in the range of 0.25 to 2.00 mm diameter. Hole positions on the box will vary depending on the optimum location for each product and the gas flow dynamics within the box.
The pinhole size and pinhole numbers will affect the resulting final gas permeability. Table 3 below gives examples of using different sizes of pinholes to achieve same open areas and relative permeabilities.
A box (dimension 56×39×19 cm) made of paperboard and tri-layer barrier liner G was filled with 20-21 lb. fresh broccoli crowns. The permeability of this MAP package was found to be very close to the broccoli produce's need but not exactly right. Therefore the controlled pinhole method was used to improve the gas permeability packaging condition. The gas composition in the headspace and the quality of the broccoli product are presented in the following table.
The following table provides dimensions for the blanks of typical two-piece and one-piece MA packages that come within the scope of the invention:
While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.
