Plastic laminate

Details Plastic laminate Plastic laminate

1999-05-06

2001-11-27

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Composite

Of polyamide

C428S479300, C428S479600, C428S480000, C428S481000, C428S532000, C428S533000, C428S537500

Reexamination Certificate

active

06322899

ABSTRACT:

Plastic laminates are manufactured particularly for the needs of the packaging industry. Food stuff packaging containers in particular require laminates with two or more plastic layers, one of which can have good barrier properties against substance migration while another layer is acting as a layer preventing adherence of different layers to each other, and the third has suitable surface properties for heatsealing or is compatible to the food stuff to be in contact with it, etc. Furthermore, the superimposed plastic layers can be placed on top of a cellulose-based basic layer providing the required strength to the material, and this layer can be paper or board, for example paper with suitable outer surface properties for printing, greaseproof paper or liquid packaging board, folding boxboard or sack paper.
With the growing refuse problems, the biodegradability of packaging materials has become an important issue. The problem with biodegradable plastics is, however, that as such they are often unsuitable for use as packaging materials, which are required strength and specific properties. Various multilayer structures have been developed mainly based on polyhydroxyalkanoates. For example, the European application publication 603876 (Buck Werke GmbH & Co) presents a biodegradable packaging material with a core layer of polyvinyl alcohol acting as an oxygen barrier, and on both sides of the core layer polyhydroxybutyrate and/or polyhydroxyvalerate or their copolymer (HB/HV) acting as a water vapour barrier. This three-layer structure is further coated on both sides with a layer of cellulose derivative or paper, for example with a cellulose derivative on the side in contact with aqueous food stuff, and with paper on the outmost outer surface. The purpose of the layers of polyhydroxyalkanoates (polyhydroxybutyrate, polyhydroxyvalerate or HB/HV copolymer) on both sides of the layer of polyvinyl alcohol with poor water resistance is to protect this oxygen barrier layer from the damaging effect of water. Similar compositions are presented in other publications as well.
Laminate structures containing compatible plastics and being biodegradable are few, and their industrial manufacture is often impaired by the poor strength and difficult processability of biodegradable plastics.
The purpose of the present invention is to add the number of alternatives available.
It has now been observed that a biodegradable polyester amide or a starch derivative is well compatible with one or several layers of polyhydroxyalkanoate. In a plastic laminate the polyester amide can act, for example, as a layer connecting the various polyhydroxyalkanoate layers, or as a heatsealable surface layer. A starch derivative which possesses the properties of a thermoplastic can act in the same respect, and can futhermore be used as an adhesive plastic between a fibrous basic layer and other plastic layers.
In the used compositions, the polyhydroxyalkanoate provides good barrier properties and the polyester amide or the starch derivative can be used as a supporting plastic, and they have good runability in coextrusion.
The compositions in question can be used as such or preferably on top of a biodegradable cellulose-based basic layer. This layer can be paper, greaseproof paper or board. It is also possible that the laminate has several cellulose-based layers, for example a board and a paper layer.
Biodegradable polyester amide refers to a polyester amide of thermoplastic type which in its properties resembles polyolefins and which can be worked in a molten condition, for example mould it into thin films using methods of plastic technology. This is a so called statistically constructed polyester amide with sequential ester and amide segments. A typical example is, for example, a polyester amide in which the ester segments consist of chains formed by adipic acid and butane diol, while the amide segments consist of polyamide chains formed by aminocapronic acid. The chains are connected to each other with ester and amide bonds. The proportion in weight of the ester chains can be 30-70 w-% and the corresponding proportion in weight of the amide chains 70-30 w-%. The melting point of the material is above 100° C., and the material is therefore suitable for melt working in temperatures between 100° C.-200° C. This polyester amide which can be worked like polyolefins is described, among others, in the European application publication 641817 (Bayer AG).
Biodegradable starch derivatives have similar melt working properties. As an example, the extrusion coating sorts sold under the trade name “COHPOL” by Primalco Oy can be mentioned. Biodegradable starch derivatives are produced by esterifying the glucose units of the polymer chain of starch, and such starch esters and their use is described , among others, in the international publication WO94/22919, the European application publication 638609 and the U.S. Pat. No. 5,498,706.


REFERENCES:
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patent: 5512378 (1996-04-01), Bastioli et al.
patent: 5679421 (1997-10-01), Brinton, Jr. et al.
patent: 5756194 (1998-05-01), Shogren et al.
patent: 6033747 (2000-03-01), Shiotani

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