Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2000-11-28
2003-10-14
Zacharia, Ramsey (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S411100, C428S426000, C428S457000, C428S480000, C428S523000, C428S688000
Reexamination Certificate
active
06632519
ABSTRACT:
The invention relates to a composite material comprising a substrate and at least one layer applied to the substrate. The invention relates in particular to an composite material comprising a substrate and a layer having permeability barrier properties on the substrate. The invention also relates to a process for the manufacture of a composite material comprising a substrate and a barrier layer applied to the substrate using vapour deposition.
A composite material comprising a substrate and a layer on the substrate was disclosed in U.S. Pat. No. 3,442,686. This patent describes a composite film that includes an organic base sheet, a heat sealable top coating, and an intermediate barrier layer of an inorganic material. The disclosed barrier layer, preferably comprising an inorganic oxide or salt, is typically vapour deposited on the base sheet and then covered by an extruded top coating. The barrier layer, generally at least 0.02 &mgr;m thick, and more typically 0.06-0.6 &mgr;m thick, is provided to reduce the permeability of the composite film to gases and water vapour.
However, despite the use of “glassy state” inorganic materials, preferred over more crystalline materials, to form the layer, the disclosed inorganic barrier layers remain relatively brittle. This brittleness remained a drawback that allowed cracks to form in the barrier layer when the film was deformed. This cracking seriously degrades the barrier layer performance, allowing gases and water vapor to permeate the film. Another drawback associated with the disclosed inorganic layers are the high temperatures developed in the film during the vaccuum deposition process, usually above 100° C. These high temperatures seriously limit the use of the disclosed inorganic layers on temperature-sensitive substrates such as polymers with a low glass transition temperature. Moreover, further drawbacks associated with the disclosed films are their high cost, reduced optical clarity, and discoloration such as yellow (silicon oxide) or yellow-red (iron oxides).
The applicant has developed an improved composite material comprising a substrate and a triazine compound barrier layer that overcomes some of the deficiencies associated with inorganic barrier layers. In addition, the applicant has developed a process for manufacturing the improved composite material in which the triazine barrier layer may be vapour deposited on heat-sensitive substrate materials.
The composite material according to the invention was found to provide a surprizingly durable barrier to gases, in particular oxygen, using a barrier layer comprising a triazine compound. Surprizingly, it was also found that composite materials according the present invention exhibits excellent sealability and further provides good paintability, printability and scratch resistance.
The composition material according to the present invention, utilizing a triazine compound barrier layer rather than an inorganic barrier layer such as silicon oxide, also exhibits improved resistance to mechanical damage. This means that materials prepared according to the present invention are better able to maintain their barrier properties after being subjected to deformation and increasing their utility as packaging materials.
A further advantage is derived from the lower temperatures required for applying the triazine compound layer to the substrate material. These lower temperatures allow a triazine compound layer to be applied to temperature-sensitive materials such as polyethylene that would not tolerate the temperatures necessary for application of an inorganic barrier layer.
In addition, the production costs of composite materials with a triazine compound barrier layer are lower than those associated with the production of equivalent composite materials using an inorganic barrier layer. Moreover, it has been found that composite materials incorporating a triazine compound barrier layer, even at thickness of 1 &mgr;m and more, maintains satisfactory transparency.
Examples of triazine compounds that can be used according to the invention are 1,3,5-triazines such as melamine, ammeline, ammelide, cyanuric acid, 2-ureidomelamine, melam, melem, melon, melamine salts such as for instance melamine cyanurate, melamine phosphate, dimelamine pyrophosphate or melamine polyphosphate and functionalized melamines, such as for instance hexamethoxymethyl melamine or acrylate-functionalized melamine. However, the invention is not limited to these triazine compounds. The preferred triazine compounds are melamine, melam, melem, melon, or a combination thereof, melamine being particularly preferred. The temperature at which melamine or other triazine compounds can be vapour deposited is lower than 600° C., preferably lower than 400° C.
The invention can be applied with the layer comprising only one triazine compound, but it is also possible for the layer to comprise a combination of two or more triazine compounds. It is also possible for several distinct layers of one or more triazine compounds to be used, for example a melamine layer as well as a melam or melem layer, to form the barrier layer. The advantage of this procedure is that it allows the specific properties of the different triazine compounds to be combined.
According to the invention it is also possible for the barrier layer to contain compounds in addition the described triazine compounds. Preferably, a triazine compound, or a combination of triazine compounds, comprises the majority of the barrier layer in composite materials according to the invention. In particular, the barrier layer preferably contains at least 75 wt. %, and more preferably at least 90 wt. %, of the trizazine compound(s). In composite materials according to the invention, barrier layer thickness is preferably less than 50 &mgr;m, more preferably less than 10 &mgr;m, and most preferably less than 5 &mgr;m. The minimum barrier layer thickness, however, would provide a continuous monomolecular layer of the triazine, and more preferably, would have a thickness of at least 5 nm.
Suitable substrates for application of the triazine barrier layer according to the invention include, but are not limited to, polymers, glass, paper and preferably precoated paper, cardboard and preferably precoated cardboard, and metal. The type of substrate selected, as well as the shape and thickness of the substrate, will depend largely on the application intended for the final product and do not, therefore, act to limit the scope of the invention. Examples of polymers that may be utilized as a substrate include polyethylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, polyamide, polycarbonate, but the invention is not limited to these polymers either.
In particular, the applicant has developed a composite material comprising a substrate and a barrier layer, the barrier layer comprising a triazine compound. As used herein, a barrier layer refers to a layer that, when applied to a substrate, produces a composite material that exhibits greatly reduced gas permeability, particularly reduced oxygen permeability, when compared with an uncoated substrate.
The applicants have found that triazine compounds are particularly suitable for application to a wide variety of substrate materials to form a barrier layer. Further, it is preferred that all, or at least a portion, of the triazine compound used in the barrier layer has a crystalline structure. Without committing itself to any scientific theory, the applicant speculates that the preferred triazine compounds are able to form crystalline structures comprising a plurality of triazine ring interconnected by hydrogen bonds. The advantage of such a crystalline structure is reported by M. Salame; Journal of Plastic Films &mgr;Sheeting; vol. 2; October 1986.
The gas barrier performance of the composite material according to the present invention provides advantages for foodstuff packaging applications. In foodstuff packaging applications, the composite material according to the invention can be provided as a composite fil
Aagaard Olav M
Houben Jan M
Jahromi Shahab
Raemaekers Karel G. H.
DSM N.V.
Zacharia Ramsey
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