Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Weight per unit area specified
Patent
1998-03-05
2000-06-27
Thibodeau, Paul
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Weight per unit area specified
428480, 428481, 15624411, 15624422, 15624427, B32B 2710, B32B 2736, B29C 4706
Patent
active
060804785
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a layer material.
BACKGROUND OF THE INVENTION
It is known to make packaging laminates by combining a cellulose-based, naturally decomposing basic layer with layers of biodegradable plastic which improve the tightness of the basic layer. This way total compostability of the material in the waste management of the packaging material can be achieved.
From the European application publication 534471, for example, a biodegradable laminate used as packaging material is known. This laminate consists of polyhydroxybutyrate-based copolymer, more precisely hydroxybutyric-hydroxyvaleric copolyester (HB/HV) coextruded together with a polyethylene film on a cellulose-based sheet. The polyethylene film is used as an auxiliary film in the coextrusion process, and after the process it is pulled of the laminate leaving the hydroxybutyric/hydroxyvaleric film attached to the sheet.
The biodegradable polymer in question has good barrier properties (barrier layer properties) in itself and is therefore a popular laminating agent, and it can be used to increase the tightness of cellulose-based basic materials noticeably.
In addition, the European application publication 603876 introduces the use of hydroxybutiric/hydroxyvaleric copolymer layers as water vapor barrier on both sides of an oxygen barrier layer of polyvinyl alcohol. The layers are laminated either on one side or both with a layer of cellulosic derivative or paper.
The multi layer structure in question does not provide satisfactory properties. Polyvinyl alcohol tends to dissolve in water which makes it difficult to be used under conditions of considerable humidity. Furthermore, the coextrusion of these materials is in practice difficult. And finally, polyvinyl alcohol is poorly compostible, in other words it is not biodegradable in the strict sense of the word.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a layer material which exhibits improvements to the aforementioned properties and which can be used as airtight and biodegradable packaging materials. To achieve this purpose, the layer material is primarily characterized below.
The invention combines the excellent properties of polyhydroxyalkanoate and polylactide.
By using two separate polyhydroxyalkanoate layers, such as polyhydroxybutyric-based layers, particularly hydroxybutyric-hydroxyvaleric copolymer layers, good barrier properties can be achieved with layers of great thinness, even of only micrometers thick, when they are combined with polylactic acid, i.e. polylactide (PLA) which improves the processability of the material. Polylactide exhibits good adhesion properties and it does not stick to the surface of the chill roll in coextrusion which means that also the coextrusion chances of the hydroxybutyric/hydroxyvaleric copolymers are improved, among other things edge weaving is reduced and the nucleant can be omitted.
The use of two separate polyhydroxyalkanoate layers ensures that the microscopic pinholes which may develop to the layers are not formed at the same spot, which improves barrier properties.
Because of the plastic layer structure described, the gas and grease tightness are improved, and better resistance to folding and creasing can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in more detail in the following with reference to the accompanying drawings in which
FIG. 1 shows a schematic view of the layer material according to the invention, and
FIG. 2 shows the process for manufacturing the material.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 includes a cellulose-based and naturally decomposing basic layer 1, which gives the product its strength, the basis weight of which may vary within the known values for paper and cardboard. Laminated on top of the basic layer 1 by coextrusion, are the following layers starting from the basic layer 1: A polylactide layer 2 (PLA) which attaches the other plastic layers to the basic layer by adhesion, a hydroxybutyric/hydroxyvaleric copolym
REFERENCES:
patent: 5444113 (1995-08-01), Sinclair et al.
patent: 5502158 (1996-03-01), Sinclair et al.
Derwent Accession No. 96-236165, Toyobo KK--Biodegradable polyester adhesives having stable quality and good water resistance-contains biodegradable polyester contg. lactic acid residue and caprolactone residue, JP,A,8092359, 960409, DW9624.
Derwent Accession No. 94-114861, Toppan Printing Co. Ltd--Biodegradable paper container-comprises paper laminate with biodegradable plastic layer, JP,A,6064111, 940308, DW9414.
Thibodeau Paul
UPM Kymmene Corporation
Zacharia Ramsey
LandOfFree
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