Stock material or miscellaneous articles – Hollow or container type article – Paper containing
Reexamination Certificate
2000-11-13
2004-02-17
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Paper containing
C428S034300, C428S035400, C428S036600, C428S036700, C428S533000, C428S534000, C428S536000
Reexamination Certificate
active
06692801
ABSTRACT:
The present invention relates to laminated packaging materials including a gas barrier, layer, which comprises starch or a starch derivative, and to methods of making such laminates.
The invention also relates to packaging containers and packages manufactured from the laminated packaging materials of the invention.
In the packaging industry, use is often made of packages of the single-use type for packaging and transporting of various products, such as, for example, liquid food products. In order to benefit from respective advantageous properties of various materials, such different materials are often laminated together into a packaging laminate. Depending on circumstances, the aim is often to provide the best possible protection to the product to be packed, at the same time as the package must be sufficiently mechanically strong to allow for convenient handling.
For packaging of liquid food products during prolonged transport and storage, it may be important that the packaging laminate provides barrier properties towards gases, such as oxygen as well as towards liquids and moisture. Usually, the package is also required to be dimensionally stable in order to provide easy handling at transport and distribution as well as in use.
Liquid barrier properties are usually provided in a laminated packaging material by means of outer layers of plastics. Such outer layers of plastics are usually also sealable to each other by means of melt fusion, in order to provide liquid tight seals of the package in a cost efficient and reliable manner. Normally thermoplastics, such as polyolefins are employed for this purpose, and polyethylenes, such as preferably low density polyethylenes (LDPE), are most often used.
Mechanical strength and configuration stability may be obtained by the incorporation of a more rigid, core layer in the packaging laminate, usually a dimensionally stable but foldable paper or paperboard. This is usually an intermediate layer but the term “core layer” used herein includes such layers even when they form one external face of the laminate.
Barrier properties towards oxygen gas are obtained by incorporation of a layer of one of a number of barrier materials known in the art. Examples of such known oxygen barrier materials are metals and metal oxides such as aluminium foil (Al foil), silicon oxide and siloxane coatings (SiOx) on to a polymer substrate layer as well as polymer materials having gas barrier properties, such as polyamides (PA), polyvinyl alcohol (PVOH), ethylene vinyl alcohol polymers (EVOH) and polyethyleneterephthalate (PET). In addition to such synthetic materials, the possibility of using natural and biodegradable polymers (biopolymers) such as starch and starch derivatives, as gas barrier materials has been investigated.
The use of PVOA as a barrier material applied over a polymer layer on a paperboard core layer, so preventing crack formation and smoothing the board surface was disclosed in PCT/SE96/01237.
It is previously known that starch possesses some gas barrier properties when employed in relatively thick layers, such as in films having a thickness of about 20 to 30 &mgr;m. Such thick layers of starch material are not suitable for use in packaging laminates however, since they become brittle and are prone to cracking and breaking upon handling, for example in the lamination process and when fold forming of the laminate into packages. Besides not being flexible in handling at manufacturing and distribution, laminates including such thick layers of starch would also be capable of absorbing more moisture, which would influence the gas barrier properties negatively.
From W097/16312 it is known that very thin layers of starch applied on to a core layer may provide gas barrier properties, at least when employed together with an adjacent layer of plastics, which has been united with the starch barrier layer by extrusion coating of the plastics material. Two very thin layers of starch, applied in a quantity of 0.5 and 1 g/m
2
respectively, dry weight, on to opposite sides of a core layer of paperboard and each extrusion coated with a layer of plastics, provided an oxygen gas barrier of 289 cm
3
/m
2
, per 24 h at 1 atm. Similarly, two layers of starch, applied in a quantity of 1 and 1.5 g/m
2
respectively, provided an oxygen gas barrier of 141 cm
3
/m
2
, per 24 h at 1 atm. The results obtained were thus, comparable with the gas barrier properties of, for example, a 12 &mgr;m thick film of oriented PET, thus representing a “medium performance barrier” material.
The packaging laminate W097/16312 is, however, merely a medium performance gas barrier material. This means that it may only be used for packaging of liquid food products during short time periods of cool storage. It is not hitherto known in the prior art to produce packaging laminates having high performance gas barrier properties from starch or starch derivative barrier materials. It would be much more desirable to be able to provide a packaging material having sufficient gas barrier properties for long time storage of liquid food products, i.e. for extended shelf life (ESL) at cool storage or even for aseptic storage. Such desirable high performance lip oxygen gas barrier properties are in the order of about 50 cm
3
/m
2
at 24 h, 1 atm (23° C., 50% RH) or better, e.g. up to 30 cm
2
/m
2
at 24 h 1 atm, i.e. oxygen gas barrier properties comparable to those of, for example, PVOH, EVOH (ethylene vinylalcohol copolymer) or polyamides (PA) when employed at a thickness of the order of about 5 &mgr;m.
We have now established that it is possible in a packaging laminate to obtain high performance oxygen barrier properties from the use of starch and similar materials.
Accordingly the present invention now provides a packaging laminate having core of paper or paperboard and one or more gas barrier layers of starch or a starch derivative providing an oxygen gas barrier property of 50 cm
3
/m
2
at 24 h, 1 atm (23° C., 50% RH) or better, said gas barrier layer or layers having a dry coating weight or aggregate coating weight no more than 7 gm
−2
and being deposited on a plastics layer carried by said core layer, and/or having a plastics layer laminated at high temperature thereon. Preferably, oxygen barrier property provided by the starch or starch derivative layer is 40 cm
3
/m
3
at 24 h, 1 atm (23° C., 50% RH) or better. More preferably the oxygen barrier property is up to 30 cm
3
/m
2
at 24 h, 1 atm (23° C., 50% RH), e.g. 10 cm
3
/m
2
at 24 h, 1 atm (23° C., 50% RH) or below.
Preferably, the packaging laminate comprises a layer of plastics polymer, preferably a thermoplastics, e.g. polyethylene, laminated directly over the said gas barrier layer. Most preferably, said polymer is LDPE. Other thermoplastics that may be employed include all other kinds of polyethylene (including LLDPE, ULDPE, VLDPE, M-PE and HDPE), polyproplylene, and polyethyleneterephthalate.
The gas barrier layer is applied at a dry coating weight of up to 7 gm
−2
, e.g. from 0.5 to 5 gm
−2
, more preferably 0.5 to 3 gm
−2
, e.g. from 1.5 to 2 gm
−2
.
We prefer that the gas barrier layer be made entirely from natural materials but it is acceptable to include minor amounts of other polymeric materials which do not interfere with the desired properties. For instance the gas barrier layer may further comprise a minor amount of water soluble or water dispersible polymers having functional hydroxyl groups, e.g. polyvinyl alcohol, and carboxyl group containing polyolefins such as ethylene acrylic acid, or a mixture thereof. The amount of such materials may be from 0 to 30%, e.g. 0 to 20% or 0 to 10% by weight.
We have observed that when polyethylene is applied to a layer of starch at a high temperature, e.g. over 200° C., the gas barrier properties of the starch are improved and that under appropriate conditions can be made to reach or move further into a high performance level.
The invention includes a method for producing a packaging laminate having gas barrier properties, which process comprises apply
Bentmar Mats
Berlin Mikael
Leth Ib
Nolan Sandra M.
Tetra Laval Holdings & Finance S.A.
LandOfFree
Starch based gas barrier laminate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Starch based gas barrier laminate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Starch based gas barrier laminate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3282586