Stock material or miscellaneous articles – Hollow or container type article – Cellular material derived from plant or animal source
Reexamination Certificate
2001-01-24
2004-07-27
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Cellular material derived from plant or animal source
C428S035700, C428S036600, C428S036700, C428S035400, C428S507000
Reexamination Certificate
active
06767600
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a laminate with superior gas barrier properties, a production method therefor, and a paper container employing this laminate. More specifically, the present invention relates to a laminate with gas barrier properties that can be produced without using an organic solvent, this laminate being excellent for long-term storage, non-refrigerated transport, and aseptic packaging applications due to its superior capacity to act as an oxygen barrier. The present invention further relates to a production method for this laminate, and to a paper container employing this laminate.
This application is based on patent applications filed in Japan (Japanese Patent Application Nos. Hei 10-210080 and Hei 10-210081), the contents of which are incorporated herein by reference.
PRIOR ART
In general, a laminate having a three-layer structure consisting of polyethylene/paper board/polyethylene is employed for the laminate used in paper containers and the like for packaging liquids (polyethylene will be abbreviated as “PE” hereinafter). (Note that “PE/paper board/PE” as employed in this specification indicates that PE, paper board and PE have been laminated together in this order). A laminate of this design is formed into a box-shaped, sealed container by making use of the high rigidity of paper board and the heat sealing properties of the PE which is disposed to the outer and inner surfaces of the paper board. Containers of this design are widely used as 200 ml to 2 liter milk cartons, or as containers for refreshments or alcoholic beverages. As compared to a metal or glass container, however, containers consisting of this type of laminate using paper board and PE permit more oxygen to permeate through the container. Thus, in cases where the quality of the contents within the container could be affected by oxidation, these containers are disadvantageous in that they require chilled transport and only permit storage for a short period of time.
When a container is to be filled with sterile contents or to be transported at room temperature, a packaging material which allows minimal deterioration in contents must be employed. In this case, a paper container consisting of a laminate that has gas barrier properties is required. In addition, depending on the material held, a container may be required to retain the odor of the contents. From this perspective as well, a paper container that has gas barrier properties is needed.
Paper thinner than the paper board used for packaging liquids is employed in the case of paper containers for holding dry food products, medicines or the like. Namely, a two-layer laminated paper consisting of paper and PE layers is employed. Characteristically, a container employing this type of laminated paper is easily torn by hand, provided that the paper has some stiffness and is thin. As in the case of a paper container for packaging liquids, this type of paper container may also be required to have a gas barrier function according to its application.
Laminating aluminum foil (“Al foil” hereinafter) is a frequently employed approach for providing gas barrier properties to a paper container. In this case, when taking into consideration adhesiveness between layers and the heat sealing ability of the inner layer of the container, a PE/paper/PE/Al foil/ethylene-methacrylic acid copolymer (“EMAA” hereinafter)/PE structure, or a PE/paper/PE/Al foil/PE structure is used.
A container for holding an alcoholic beverage, for example, must have gas barrier properties, a heat-sealing capability on either surface, and have sufficient impact-resistance to prevent damage to the container if dropped. In this case, a PE/paper/PE/Al foil/PET/PE structure may be employed in which the Al foil is used as the gas barrier layer and polyethylene terephthalate (“PET” hereinafter) is used as-the impact-resistant resin layer.
A dry laminating method, extrusion laminating method, or the like may be suitably selected as the method employed to produce a laminate having Al foil in this way. Alternatively, depending on the structure of the laminate, both methods may be employed together.
In a dry laminating method, an adhesive agent such as isocyanate is dissolved in organic solvent, and the liquid material resulting is coated to one side of a base material. The solvent is evaporated in a dryer and respective base materials are adhered together using a nip roller. This method requires using a large amount of expensive adhesive agent, and thus increases production costs. In addition, the use of organic solvents has a negative impact on the work environment and results in an unpleasant odor remaining in the final product.
In contrast, the extrusion laminating method does not require an adhesive agent when adhering together the PE and the paper. However, when laminating together PE and a base material consisting of a film, such as PET film, or when laminating together PE and a base material consisting of a metal foil such as Al foil, the usual method is one in which an isocyanate or similar type adhesive agent referred to as an anchor coat agent (“AC” hereinafter) is coated in advance onto the base material in order to increase adhesion. A resin is then melt extruded onto this coated layer. However, this method not only has higher production costs as was the case of the dry laminating method above, but there is also a deterioration in the work environment due to the use of organic solvents. This method is further problematic in that an odor remains in the final product.
In order to resolve these problems, methods have been proposed which do not employ an AC agent derived from organic solvents, or which employ an aqueous AC agent derived from polyethyleneimine.
However, aqueous AC agents have the disadvantage of inferior water resistance due to the adhesive agent's intrinsic aqueous solubility.
As approaches which do not employ an AC agent, methods have been proposed in which a polar group, such as a carboxyl group or acid anhydride group, is introduced into polyolefin. Examples of this approach include the methods disclosed in Japanese Patent Application, First Publication No. (A) Sho 57-157724 (WPI Acc No. 82-95762E); Japanese Patent Application First Publication No. (A) Sho 59-75915 (WPI Acc No. 84-143564); Japanese Patent Application First Publication No. (A) Hei 8-252890 (WPI Acc No. 96-492986); Japanese Patent Application First Publication No. (A) Hei 8-258225 (WPI Acc No. 96-501588); Japanese Patent Application First Publication No. (A) Hei 8-258234 (WPI Acc No. 96-501597); Japanese Patent Application First Publication No. (A) Hei 9-66587 (WPI Acc No. 97-221082); Japanese Patent Application First Publication No. (A) Hei9-76419 (WPI Acc No. 97-240491); Japanese Patent Application First Publication No. (A) Hei 10-264342 (WPI Acc No. 98-588752), and the like. While there is an increase in the adhesive strength of the laminate obtained using these method as compared to a laminate formed using polyolefin alone, this adhesive strength is not adequate when compared to the case where an AC agent is used.
In addition, productivity is poor with methods employing dry laminate adhesive agents or extrusion laminate AC agents, making these approaches problematic as well.
For example, when producing the laminate employed in the aforementioned alcoholic beverage container, dry laminating is performed one time in order to laminate the Al foil and PET, tandem extrusion laminating and single extrusion laminating are performed one time in order to laminate the PE, and a urethane AC agent is required to laminate the PET and PE.
In other words, in order to produce a laminate of a structure consisting of Al foil and PET, a dry laminate adhesive agent and an extrusion laminate AC agent are necessary. As a result, production costs increase, a considerable amount of organic solvent is used, and there are numerous steps involved to make the laminate. For example, in the aforementioned alcoholic beverage container, dry laminating is performed one time, tandem extrusion laminating i
Japan Polyolefins Co., Ltd.
Miggins Michael C.
Pyon Harold
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