Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Patent
1997-02-24
1999-11-30
Thibodeau, Paul
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
428513, 428520, 428 349, 428 366, 428 367, 525 57, B32B 2710, B32B 2730
Patent
active
059939770
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a packaging material which has good barrier properties vis-a-vis gases and moisture. The invention further relates to a polymeric material which is used as a gastight layer in such packages, and further to multilayer products in which said polymer is used.
Liquid foodstuffs, such as juices, which are sensitive to oxidation, are in general packaged in sales packages made from laminated paperboard. Through selection of the packaging material, efforts are made to provide good chemical and mechanical protection for the product, and the material has to be sufficiently firm in shape to be easy to handle.
There is in general use a packaging material the structural part of which consists of paperboard or paper which is sufficiently firm but, nevertheless, flexible so that a package of a desired shape can be formed therefrom. To protect the structural material from liquid and other moisture, it is coated with plastic, usually polyethylene. However, the oxygen permeability of polyethylene and paperboard is high, and therefore the product would spoil very rapidly if a gas-tight layer were not also added to the package. The gas-tight layer conventionally used has been aluminum foil bonded to the paperboard. Another alternative has been a gas barrier polymer such as ethylene/vinyl alcohol copolymer (EVOH). The purpose of the gas-tight layer is to prevent the access of oxygen into the product and thus, for example, to maintain high the level of vitamin C in the product.
For some time, attempts have been made to eliminate the aluminum foil, for example for reasons of environmental protection, but also because of its poor handlability. Furthermore, the aluminum layer is easily broken.
Finnish Patent F189567 discloses a barrier structure in which ethylene/vinyl alcohol copolymer is used. Such structures, in the same way as when aluminum is used, usually contain, in addition to the carrier web (polyethylene+paperboard), at least five layers: polyethylene/paperboard/polyethylene/adhesion plastic/gas-tight EVOH polymer/adhesion plastic/polyethylene. The multilayer structure, of course, also increases the price of the package and renders its manufacture complicated. Furthermore, the gas-tight polymer in itself is expensive.
EP patent 423511 sought a solution in which lower amounts of EVOH would suffice. Therein a blend of EVOH and polyethylene is used, in which the amount of polyethlene is at maximum 80%, but preferably at maximum 40%. The EVOH/PE layer on the inside of the package mainly serves as an aroma-proof layer and, if good gas-tightness (oxygen-tightness) is also desired, a second EVOH/PE layer or some other oxygen-tight layer is added, with adhesion plastic layers on its both sides. In this case the number of layers is four in addition to the carrier web.
An object of the present invention is to provide a multilayer product by means of which the disadvantages of the prior art can be eliminated. When polymers according to the invention are used, the number of layers can be reduced from the conventional number, which is usually five in addition to the carrier web, since a separate adhesion plastic layer is not needed. It has been observed, surprisingly, that, if a blend of a commonly known gas-tight polymer, i.e. ethylene/vinyl alcohol copolymer (EVOH), and of a polar ethylene polymer is used in the gas-tight layer, this layer having good adhesion properties and being heat-sealable, the use of the adhesion plastic layer can be abandoned.
In the system according to the invention, the gas-tight layer contains a polar ethylene polymer in an amount of 5-60%, preferably 15-40%. The polar polymer may be a copolymer of ethylene and acrylic ester, such as ethylene/ethyl acrylate copolymer (E/EA), ethylene/butyl acrylate copolymer (E/BA), ethylene/methyl acrylate copolymer (E/MA), ethylene/vinyl acetate copolymer (E/VA), or a copolymer of ethylene and (met)acrylic acid (E/EA, E/MAA). The polar polymer may also be an anhydride- or acid- modified polyolefin, in which case the acid (anhydride) used may be,
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patent: 4670349 (1987-06-01), Najagawa et al.
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"Vinyl Alcohol Polymers", Encyclopedia of Polymer Science and Engineering, vol. 17, p. 186, 1985.
Koski Elina
Koskiniemi Riitta
Kuusela Seppo
Laiho Erkki
Penttinen Tapani
Borealis A/S
Tarazano D. Lawrence
Thibodeau Paul
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