Packaging laminate with gas and aroma barrier properties

Details Packaging laminate with gas and aroma barrier properties Packaging laminate with gas and aroma barrier properties

2000-04-07

2002-01-15

Dawson, Robert (Department: 1712)

Coating processes

With stretching or tensioning

C427S173000, C427S179000, C427S209000, C427S255270, C427S255310, C427S275000, C427S296000, C427S452000, C427S294000

Reexamination Certificate

active

06338870

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method for manufacturing of a packaging laminate having a thin silicone oxide coating formed on each side of a substrate plastics film, a packaging laminate manufactured by the method and a packaging container, as well as a packaging material blank, manufactured from such a packaging laminate.
BACKGROUND ART
Laminated packaging materials having flexibility have been used for packaging liquid food products for many years. For example, milk has been packaged in cartons made from a laminate composed of paperboard substrate with thermoplastic coatings on both surfaces. The surfaces of the carton are heatsealed together so as to form a package carton of desired shape.
Some food products, such as orange juice, packaged in such cartons, lose their nutritional values due to the permeation of oxygen through the carton walls. It has therefore been common to include an aluminum foil layer with the laminate material, in order to reduce the permeation of oxygen through the walls and to minimize the degradation of the nutrients such as vitamin C. Although aluminum foil is highly effective as a barrier material, its use in cartons may in some cases raise concern from environmental and recycling points of view and it may be deemed appropriate to replace aluminium foil by other barrier materials. Various attempts have been made to develop practical alternatives to aluminum foil. Such alternatives should have excellent oxygen, gas and aroma barrier properties, and be easily disposable after use.
Another problem in the packaging of liquid food products in cartons arises from the structure of the carton. The carton is fabricated from a carton blank or a carton web (composed of a laminate such as the ones discussed above) that is folded along one or more crease lines for formation into the desired shape. In general, portions of the blank are overlapped for sealing which may be accomplished by the application of suitable adhesive or by heat-sealing the thermoplastic layers together. The creasing of the laminate material as mentioned above imposes stresses to the laminated material. These stresses may cause leakage or, at least weaken the laminate material so that subsequent handling of the carton may lead to leakage.
New oxygen barrier materials have emerged from recent developments in plasma deposition technology for plastics films. The food and pharmaceutical packaging industries have shown tremendous interest in substrate films, usually of thermoplastic polyester, coated with a thin silicon oxide layer. These materials show excellent barrier properties as well as tolerance to the thermomechanical stress encountered during the various converting processes in the manufacture of laminated packaging materials.
U.S. Pat. No. 4,888,199 describes the process of depositing a thin film of a silicon oxide on a surface with the use of plasma under controlled conditions. The plasma is formed in a closed reaction chamber, in which the substrate is positioned. The above-mentioned substrate can be formed from metal, glass or certain plastics. The air is pumped out of the chamber until a high degree of vacuum is achieved.
For example, the organic silicon compound such as hexamethyl disiloxane is introduced into the chamber together with oxygen and helium, so the silicon molecules and oxygen molecules are deposited on the surface of the substrate. The resulting film is described as being a thin film that is very hard, scratch-resistant, optically clear and adheres well to a flexible substrate. The disclosure of the patent is hereby incorporated into this specification by reference.
An improved plasma enhanced chamical vapour deposition (PECVD) method process is described in U.S. Pat. No. 5,224,441, which is also incorporated into this specification. In the process mentioned in the patent, the substrate deposited with the silicon oxide is maintained at a temperature of about 10-35° C., preferably 15-25° C. and the substrate may be formed from polyethylene terephthalate (PET) or polycarbonate resin. In this specification, the thickness of the silicon oxide film when used for food packaging, is about 100 Å (Angstrom)-400 Å and the thickness of the substrate is 1.5 microns −250 microns.
However, during these processes, a major concern is the durability of the barrier layer in that it must not crack or delaminate (detach) from the substrate film. Tendency to cracking is controlled by the cohesion of the oxide material to itself, whereas delamination is controlled by the interfacial adhesion between the oxide layer and the substrate film. Thus there remains a need for a silicon oxide coated substrate that is resistant to cracking and delamination, for providing packages having improved gas barrier and durability properties.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the deficiencies of conventional barrier laminate materials such as presented above, it is an object of this invention to provide a packaging laminate material having improved barrier and durability properties.
It is a further object of this invention to provide a laminated packaging material that is flexible, and readily capable of being formed into packages, filled and sealed, using conventional packaging machines, thus resulting in packages having improved barrier properties.
Furthermore, it is an object to provide a laminated packaging material that may be readily disposed or recycled without or with reduced detriment to the environment.
Moreover, it is further an object of the invention to provide a laminated barrier packaging material having improved durability to thermomechanical stresses encountered during various converting processes in the manufacturing of laminated packaging materials and of packaging containers.
These objects are accomplished by a packaging laminate including a substrate plastics film having a silicon oxide coating formed on each side thereof, being manufactured by a method which comprises a step for obtaining said silicone oxide coatings by means of vapour-depositing a silicon oxide coating onto each side of the substrate film by a plasma method chemical vapour deposition method (PECVD) while straining the film within a range between an upper limit of an intial plastic deformation, determined by the Young modulus of the substrate, and a lower limit of any improvement of a cohesion force in the oxide coating and an adhesion force, i.e. interfacial shear strength, between the oxide coating and the substrate film.
According to preferred and advantageous embodiments of the invention, a method and a packaging laminate as set out in claims
2
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7
and claims
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12
, respectively is provided.
According to a further aspect of the invention, a packaging container manufactured from the packaging laminate of the invention is provided, as set out in claims
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19
. Furthermore, a package blank comprising the packaging laminate of the invention is provided as defined in claims
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and
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.
The silicon oxide coatings, vapor-deposited by a plasma CVD method, are preferably carbon-containing silicone oxide coatings. The preferred carbon-containing silicone oxide has the following general formula;
SiOxCy in which x is within the range of preferably 1.5-2.2, y is within the range of 0.15-0.80, more preferably x is within the range of 1.7-2.1, y is within the range of 0.39-0.47.
The oxide coating may not be limited to these three elements due to impurities occurring throughout the manufacturing process of the laminate. The silicon oxide coating may also contain hydrogen atoms in varying amounts, depending on the precursor compounds employed.
The silicon oxide is usually formed by means of plasma discharge containing a gas mixture of oxygen, helium and organic silicon compounds (silicon precursor compounds that contain carbon). The organic silicon compounds may contain a lot of carbon atoms that participate in the plasma discharge. Some of the carbon atoms may be incorporated in the deposited layer, while the remaining carbon atoms are exhausted from the system in th

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