Invented by Leslie L. Martin, Jr., Potlatch Corp
The Potlatch Corp invention works as followsA laminated Web is composed of paper substrate with a layer bonded of oriented polyethyleneterephthalate and a polyolefinic layer covering its second side. The film has an exposed surface that is heat sealable, but not to polyolefinics resins. It is possible to use the web in production of containers that have seams created by flame heat sealing. The flame activation of the surface seals allows heat sealing opposite surfaces to each other without the use of adhesive. The containers produced using this laminate show high retention of volatile oils and flavors that are commonly lost when food is stored in containers made of paper laminates.
Background for The paperboard container and laminated paperboard containers are produced by a method that uses paper.
Paperboard cartons are commonly used to package liquid food products such as fruit juices and milk. In order to create a barrier between contents and paperboard, it is common to use films, foils and resin coatings. Containers are also usually coated with an exterior resin that provides a waterproof barrier, printable surface, and improves container appearance. The exterior resin coatings help to form the overlapping seals that are required for carton manufacturing, setup and sealing.
The aluminum foil-lined paperboard cartons that are currently in use have been a first step towards developing lighter, cheaper, and more disposable paperboard packaging for liquid food which is oxygen and light sensitive. In foil cartons of this type, the material that is exposed to the product was traditionally polyethylene. The heat sealing properties, low cost, and organoleptic considerations have all led to its use. Polyethylene, on the other hand, has a tendency to absorb ethanol, and many organic chemicals. This includes flavor oils in foods such as juices. Polyethylene’s absorption ability can cause flavor loss in food products during storage, and also lower adhesion between structural layers, especially between foil and polyethylene. Even the most common juices are affected by this.
The current attempts to package wine in foil-lined cartons has resulted inconsistent seals for the required storage life of the packages. This is apparently due to the degradation of the heat seals caused by reactions caused by the alcohol content of the wine. The use of adhesive resins in between the layers can solve these adhesion issues. The use of adhesive layers can result in laminates with six or seven layers. This requires special coextrusion machinery or multiple extruders passes to manufacture. These additional layers add material costs to a product where high production volumes and low unit costs are the driving factors for the industry.
Recent attempts to reduce costs, simplify production, and circumvent organic absorption by using fewer layers, while maintaining good oxygen barrier characteristics, have resulted in a series of new paper-based laminates. No paper laminates have been developed that meet the requirements for lightness, oxygen barrier properties, ease of manufacturing, and the use of volatile components. “They require complex extrusion equipment, expensive resins and are not compatible with existing carton systems.
This disclosure describes a paper laminate that improves upon previously known laminates, including reducing the combined weight of the laminate. The weight of the carton and laminate is critical to shipping costs, but it’s even more crucial for some applications such as beverage service for commercial flights, where a reduced weight can translate into fuel savings.
There have been many proposals in the past to design such paper substrate laminations to meet the barriers requirements for products that are susceptible to degradation when stored, such as wine and fruit juices, while also accommodating existing machinery to handle such container blanks.
The U.S. Patent shows an example. No. No. The patent describes a laminate where an ethylene polymer is coated on the exterior laminate surface. The inner laminate surface is coated with a second ethylene-polymer coating, and the outer surface is coated with an olefin-polymer coating. Coextruded coatings have undergone many variations with varying degrees success. Coextruding multiple resin layers onto paperboard is difficult because it requires complex extruding and drying equipment. “Extrusion coated layers are not metallized for oxygen and light barriers.
In U.S. Pat. No. No. No. The polyethylene terephthalate is used with a layer of coextruded polymeric adhesive placed between the polyester resins and the paperboard. This attempt to use polyethylene terephthalate as a barrier in container paperboards also faces the recognized quality control issues in such complex extrusion processes. The resulting laminate is not adaptable to common flame heat sealing processes in carton blank manufacturing.
The U.S. Patent shows an additional coextruded coat. No. 4,513,036 (Thompson et al.) This teaches the coextrusion and coating of low density Polyethylene with polypropylene to create a coating that is suitable for side-sealing by direct flame systems. These containers do not provide an effective oxygen barrier, according to tests. “The sandwiching of polypropylene under polyethylene provides little improvement to flavor oil barriers beyond that of paperboard cardboard cartons with low density polyethylene interior coatings.
Another way to produce such laminates would be to laminate a layer of film on top of the paperboard, allowing the possibility to metallize the film and incorporate barrier properties similar those obtained from metal foil linings. U.S. Pat. is an example of a disclosure of a patent that teaches lamination of polyester film layers for this purpose. No. Whillock and others receive 3,972,467. The disclosure consists of a laminated polyester film coated with an extruded polyethylene coating to give the composite the required heat sealing properties. Since the contents of the carton are directly exposed to the polyethylene coating which is known to absorb a lot, the resulting cartons have marginal oxygen barrier properties.
In U.S. Pat., “A laminated-paper material that incorporates coextruded films composed of two or more layer combinations of ethylene methyl acrylate copolymer with polyester” is disclosed. No. 4,387,126. It is combined by bonding layers interposed between the barrier and substrate surface. “A polyolefin innermost film layer is used to provide heat sealing.
Many researchers and manufacturers of paperboard containers have tried to incorporate polyethylene terephthalate into laminates to be used in such containers. This is because the industry has recognized that PET can provide a barrier for volatile or degradable foods. A commercially available laminate with an outer coating of low-density polyethylene and an interior coating of low-density polyethylene sandwiched in between paperboard and a modified extruded polyethylene terephthalate layer that can be heat sealed is of particular interest. The modification of polyethylene terephthalate can cause high stress cracking, and it has also been shown to lose a lot of its moisture barrier property. This requires the use of the low density polyethylene coating underneath. Modifying PET to heat seal it also seems to reduce its flavor barrier. The polyethylene terephthalate, which is extrusion-coated, cannot be metallized in order to provide an effective oxygen and light barrier inside the containers. This laminate is produced using a multiple extrusion method that requires complex extrusion equipment, and handling of molten polyethyleneterephthalate. This resin is known to be difficult to extrude. This laminate also has inconsistent heat sealing properties due to the unusual difficulties of coating paperboard with resin.
Heat-sealed pouches with flexible polyester film are used to package materials including food. These pouches are usually formed and sealed using heated irons to press the inner surfaces against each other. The seals are formed between the inner surfaces that touch. In order to meet these packaging requirements, producers of these films have developed coated or coextruded film with different properties on their outer and interior surfaces.
While such films are commonly used to produce flexible bags and pouches they were not found to be easily adaptable to conventional paperboard container conversion equipment. Paperboard container blanks can be produced at high temperatures using flame seam sealers. These machines produce the lap side seams that join inner and outer surfaces. “The temperatures, seaming forces and speeds encountered by such machinery has posed serious challenges in adapting high-barrier films, such polyethylene terephthalate to the needs for paperboard container manufacturing operations.
The present invention was discovered accidentally during tests to use a coextruded, oriented PET as a vapor-barrier within a paperboard box. The discovery was in direct contradiction to published information about the film which stated unequivocally that the heat-sealable surface would heat seal to many different materials including the film itself but not polyolefins.
The present discovery was made during the testing of luminations on flat paperboard blanks with dual-surface coextruded polyethylene terephthalate films bonded to their both surfaces. The “self-sealable” film layers of flat paperboards made from this laminate did not heat seal together when exposed to direct flames. In an effort to overcome this problem, a number of adhesives were applied on the outer surfaces of the blanks. “Some did improve the lapping seams but they were either prohibitively expensive or had problems.
By chance, we tested laminates that included the film, and a low density polyethylene exterior surface coated on paperboard, using the same flame activation techniques followed by heat seal. These blanks produced a successful seam. The present invention was developed as a result of this discovery. The tests revealed that the high-level flame exposure was responsible for the oxidation of the polyethylene terephthalate surfaces that were activated. This exposure is higher than the flame priming that exposes the surface of the film to an open flame. After such priming, the heat sealable polyester is still bonded to itself rather than polyethylene. It appears that oxidation is what facilitates the heat sealing of a polyethylene terephthalate outer surface to a resin polyolefinic, such as polyethylene. The flame exposure must “activate” the polyethylene and polyethylene surfaces in order to bond them when they are exposed to a seam sealer. For those who are familiar with the process, activation occurs when the resin surfaces appear slightly roughened, but not discolored. The activation can be followed quickly by flame heat sealer as in a lap seam sealer or it may take place separately, followed by non flame heat sealing.
The products and processes described in this document provide a paper-plastic laminate that offers better oxygen protection and volatile oil retention for a cost significantly lower than the costs required to manufacture foil lined cartons. The laminate, when the film is metallized offers moisture, oxygen and light protection similar to foil-lined cartons. It also retains volatile flavor oils much better at a lower cost than foil-lined cartons. The laminate is a high-barrier liquid packaging structure that can be manufactured in one pass by any tandem extruder with a laminating unit. The extruder only needs to be capable of running the most common thermoplastics (usually low density polyethylene), without additional equipment such as dryers. The laminate offers the opportunity to develop a liquid container for wine and other oxygen sensitive products with substantial weight savings compared to glass bottles, and even up 15 percent if compared with the foil-lined cartons that are currently used. Based on the properties of the resins in this new laminate, the package should exhibit better wine flavor retention.
The following disclosure of the patent law is in accordance with the purpose of the Patent Laws, which is to “promote the progress of science and useful art” (Article 1 Section 8).
This disclosure will refer to a number of terms that are commonly used to describe seaming systems in the packaging industry. “Heat sealing” is a term that includes all seaming systems in which the application of pressure and heat to resin surfaces creates a structural bond. This broad definition includes “flame heat seal” systems where the resin seaming surfaces are directly exposed and “activated”, during or before heat sealing. It also includes “non-flame heating sealing” system where the surfaces are primed but not activated”, and then heat and pressure are applied by hot air or heated irons or microwave energy. “Priming” refers to any surface preparation method that facilitates non-flame heat seal, such as exposure to corona, flame heat, chemical treatment or other methods. However, it does not include ‘activation”. “Activation” of the surface of resin is achieved by exposing the resin to direct flames to the extent of causing surface oxidation, and degradation of the exposed surfaces.
As an example of a possible end-use application, FIG. The 1 illustrates a paperboard carton with a laminated construction that is widely used to package liquid food products such as milk and fruit juices. The interior surfaces of the paperboard substrate or stock are coated to provide a barrier that separates the contents from the structural paperboard. The exterior coating enhances the appearance of the carton, and it is also a part of a heat seal that’s required for its production, setup and sealing.Click here to view the patent on Google Patents.