Plastic Industry Today

A new development from the two companies, namely Kaupert and Winkler, and Dunnebier SuBwarenmaschinen (WDS) enables the casting of hard sugar candies into plastic moulds, allowing candy to be produced in various shapes. The MultiSweet technology provides plastic moulds offering a wide variety of shapes and designs for all sugar and sugar-free candy recipes.

The present invention relates to plastic moulded bodies, processes for their production and their use. In particular, the present invention relates to plastic moulded bodies exhibiting a barrier layer of polyvinyl alcohol and a cover layer which his highly suitable for storing liquids containing carbon dioxide and/or sensitive to oxidation.

The use of weight-reducing packaging, particularly in the field of beverage packaging, is increasing continually and the substitution of glass by plastics, in particular by polyethylene terephthalate (PET) containers, is progressing steadily. However, in order to achieve the properties of glass especially with regard to the gas barrier properties polyethylene terephthalate is satisfactory only if the bottles are correspondingly thick-walled. However, this requires a larger amount of material to be used than would be necessary for static reasons. Apart from involving higher material costs, this has a particularly negative effect at the expense of the desired weight reduction.

For this reason, the use of polyethylene terephthalate containers provided with barrier layers has been suggested in the literature which are to be produced e.g. by means of coextrusion, in the case of which, in the simplest case, a multiple layer sequence, e.g. polyethylene terephthalate (PET)/barrier layer/polyethylene terephthalate (PET) is produced, or by means of plasma-enhanced vapour deposition processes, preferably with aluminium and/or its oxides, silicon and/or its oxides or carbon as primary layer material.

Although the gas barrier properties of the containers can in this way, basically, be improved, both procedures are poorly suited for practical application because they are, on the one hand, highly cost-intensive and time-consumung as a result of the high cost price of the required machinery, the limited useful life of the machinery and the high sensitivity of the machinery.

Moreover, the mechanical properties of the containers which are achievable in this way are insufficient for day-to-day use. The high mechanical stresses to which the coated containers are subject even during a normal filling and packaging process and even more so during subsequent distribution and in use, frequently lead to impairment of the surface of the barrier layer which in turn drastically reduces the gas barrier effect of the barrier layer.

A first approach to solve these problems is described in the printed document GB 2 337 470 A which proposes reducing the gas permeability of a substrate, such as e.g. a PET bottle, by applying a barrier layer of a first polymer, such as e.g. polyvinyl alcohol, onto the substrate and then protecting the barrier layer against the environment by applying a protective layer of a second polymer with a molecular weight in the region of 5,000 to 50,000 g/mole. As possible materials for the protective layer, polyethylene terephthalate, polyester, polyester copolymers, polycarbonates, polyolefins, PEN, polyvinyl chloride, polyamides, polypropylene, polystyrene, aliphatic polyketones and/or polyethylene are mentioned.

An advantage of this solution is the use of polyvinyl alcohol as barrier polymer since, on the one hand, exhibits excellent gas barrier properties, in particular vis-a-vis carbon dioxide and oxygen. At the same time, polyvinyl alcohol is classified as an environmentally friendly raw material safe for health which can be used for food packaging without reservations. However, it is a disadvantage that the coated PET bottles obtainable according to GB 2 337 470 are still not able to withstand the strong mechanical stresses during the normal filling and packaging process and later during distribution and in use. On the contrary, cracks in the protective layer are frequently observed after only a short time, which cracks lead to either the protective layer, in some cases even including the barrier layer, peeling off partly or completely and/or the barrier layer becoming detached by contact with water such as e.g. water of condensation, water vapour etc., as a result of which the desired barrier effect is almost completely lost.

In view of this state of the art, it was thus the task of the present invention to provide plastic moulded bodies with as low a gas permeability, in particular to oxygen and carbon dioxide, as possible, which moulded bodies simultaneously exhibit as high a mechanical stability and durability as possible such that they withstand the strong mechanical stresses during the normal filling and packaging process and later during distribution and use. In particular, the plastic moulded bodies should exhibit gas barrier properties which are almost unchanged even after prolonged use.