Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-05-04
2001-02-27
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S244230, C156S324000
Reexamination Certificate
active
06193827
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to paperboard laminates, and more particularly to a non-foil paperboard laminate useful for making containers for products such as fruit and citrus juices, beverages and the like as well as non-liquid dry products, wherein the laminate has wood oxygen barrier characteristics as well as the ability to protect the products packaged therein against the loss of essential oils, flavor and vitamins.
Paperboard coated with low-density polyethylene (LDPE) has been used to make beverage containers, but falls short in providing an acceptable container. In particular, paperboard coated with LDPE has a relatively high permeability to oxygen which may lead to loss of flavor components and vitamins through oxidation. Flavor loss can also occur as a result of migration or uptake of flavor components into the LDPE layer, a process referred to as “scalping.” Additional barrier materials have therefore been investigated to achieve the desired goal.
The oxidative loss of the vitamin C can be substantially reduced by the use of a laminate containing a metal foil as a liner along the interior of the container. However, the economics involved in using a metal foil preclude this solution from being a viable alternative. A search for economical alternatives to foil has resulted in the development of laminate structures utilizing coextruded polymer materials such as polypropylene, polyvinylidene chloride (PVdC) and ethylene vinyl alcohol copolymer (EVOH) as the barrier material. See, for example the Tanner U.S. Pat. No. 4,988,546, the Gibbons et al. U.S. Pat. Nos. 4,789,575 and 4,701,360, the Thompson et al. U.S. Pat. No. 4,513,036, and the Huffman U.S. Pat. No. 5,059,459.
In addition to being less expensive than foil-containing structures, paperboard laminates containing such barrier materials may exhibit superior flavor loss properties due to the use of lower levels of LDPE as the product contact layer. Many conventional commercial structures for a paperboard carton for juice and similar products now utilize a laminate containing ethylene vinyl alcohol copolymer as a barrier to oxygen and flavor oils.
Nylon has also been proposed and used commercially as a barrier polymer in plastic bottles (see
Plastics World,
February 1986, pp. 36-38), as a plastic packaging material (
Aseptipak
84, pp. 119-148), and as a replacement for cellophane (
Plastics World,
July 1984, pp. 42-47). The properties of a barrier material used in plastic bottles or for packaging, however, are quite different from those required for a paperboard container and barrier materials useful in plastic bottles or wrapping material may not be useful for a barrier in a paperboard container. For a paperboard container, the Whillock et al. U.S. Pat. No. 3,972,467 discloses a nylon film laminated to a paperboard substrate by a low density polyethylene layer and having a low density polyethylene product contact layer. In this case, the nylon film is specified as having a tensile strength at the yield point of more than 4000 psi and an elongation at fracture of greater than about 200%. Such laminated film structures are expensive and require complex laminating equipment and the use of such high strength materials causes difficulty in the cutting of container blanks from a web of barrier board material and in the forming of the container.
The Thompson et al. U.S. Pat. No. 4,777,088 discloses a barrier board structure for flavor oil and oxygen retention in a juice carton wherein an extruded nylon layer of unspecified composition and physical properties is combined with a layer of a special ionic copolymer material sold by duPont tinder the trade name Surlyn on one or both sides. As described in U.S. Pat. No. 4,777,088, Surlyn is a necessary constituent of the described nylon barrier board laminate structure.
The Brown et al. U.S. Pat. No. 4,753,832 discloses a barrier based structure which has a product contact barrier layer of glycol modified polyethylene terephthalate (PET-G) and may also have a nylon oxygen barrier layer, but that patent does not disclose any specific type of nylon or specify desirable properties of the nylon material. As described in U.S. Pat. No. 4,753,832, PETG is a necessary constituent of the described barrier board laminate structure.
The Gibbons et al. U.S. Pat. No. 4,921,733 discloses various Nylon 6, Nylon 11 and Nylon 12 polymers, which are crystalline materials, having tensile strength of 10,000 psi or more, as abuse-resistent layers for use in combination with a caulking polymer such as a Surlyn ionomer resin and an oxygen barrier such as aluminum foil for paperboard containers.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved, heat-sealable laminate material for a juice carton which does not transmit flavor/odor ingredients of citrus and other juices, exhibits a substantial barrier to the loss of vitamin C, and has performance equal to or better than that of conventionally used polymer barrier laminates and reduces or eliminates manufacturing difficulties without detrimental economics.
In accordance with the present invention, improved heat-sealable, non-foil laminates for fruit or citrus juices, beverages and the like, as well as non-liquid dry products, which are easy to manufacture and which provide reliable performance in the field, include a multilayer polymer sandwich structure containing an amorphous nylon polymer barrier layer applied to the inner surface of a paperboard substrate.
Amorphous nylon is a relatively low strength polymer material different in physical characteristics from the high-strength crystalline nylon materials, such as the Nylon 6 materials heretofore used in barrier board laminates but having equivalent oxygen barrier characteristics. Surprisingly, it has been found that such low-strength amorphous nylon can be used as the barrier material in a paperboard substrate without requiring an additional high strength polymer or an additional oxygen barrier layer.
Thus, in one embodiment of the present invention a paperboard coated with an outer heat sealable polyolefin layer, preferably low-density polyethylene, is provided as the base material and a five-layer sandwich structure comprising polyolefin/tie layer/amorphous nylon/tie layer/polyolefin is coextruded onto the inner paperboard surface to produce a laminate comprising, from the outside of the container to the interior of the container, the following layers: polyolefin/board/polyolefin/tie layer/amorphous nylon/tie layer/polyolefin.
The polyolefin used in the sandwich layer is preferably low density polyethylene. If desired, to provide greater thickness to increase product stiffness, a further heat sealable polyolefin product contact layer, preferably low-density polyethylene, may be extrusion coated onto the inner surface of the coextruded sandwich layer. The entire structure can be fabricated in line in a single pass by coating one side of a flame treated paperboard with polyolefin prior to application of the coextruded sandwich to the opposite side of the paperboard. The final structure provides a barrier board laminate having a heat sealable polyolefin, preferably polyethylene, on its inner and outer surfaces to provide the most desirable heat-sealable characteristics while providing equivalent barrier characteristics and being easier to form into container blanks and containers than prior art structures.
In another embodiment of the present invention, a laminate structure for paperboard cartons or containers comprises paperboard which is coated with an outer layer of polyolefin, preferably LDPE, to provide the outer heat sealable layer of the carton. Subsequently, in a single manufacturing step, a three-layer barrier sandwich structure comprising tie layer/amorphous nylon/tie layer is coextruded onto the inner surface of the paperboard, after which a layer of polyolefin is extruded onto the exposed tie layer to form a product contact layer. Preferably, the polyolefin used as the product contact layer is low density polyethylene
Massouda Debora F.
Parks Christopher J.
Baker & Botts L.L.P.
Sells James
Westvaco Corporation
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