Applications of EVOH multi-layer Cast Extrusion

EVOH multi-layer coextrusion or coating extrusion Cast films are used for food and textiles packaging, flower wrapping, as photo album page protectors. 

Typically, the cast film process involves the use of coextrusion, which is a simultaneous extrusion of two or more materials from a single die to form a multi-layered film. This is because in many cases the final application of the plastic film demands a performance that cannot be achieved if the film is composed of only one material.  For example, in many instances food packaging applications require the use of films with oxygen barrier capabilities.  To meet the requirement a high oxygen barrier material like EVOH is combined with polyolefin materials in a multi-layered structure.  

Coextruded films typically contain up to seven layers; however, the use of more layers is becoming more common.  The number of layers, their position in the coextrudate and their individual thickness are all variables that change depending on the particular application of the film.

In the structures, EVOH is used to provide the oxygen barrier, the presence of PP as a skin layer facilitates the thermoformability of the film, and the PE used as a skin layer acts as a heat-sealing material.  Combining PVDC with EVOH is an effective way to address the potential loss of oxygen barrier capabilities experienced by the EVOH when exposed to moisture like in the case of meat packaging.  Nylon material is used in combination with EVOH to provide added barrier when the film is to be thermoformed and the rigidity of the EVOH limits the thickness of the EVOH layer. 
 
As seen, the specification process of these structures is not a simple task and multiple variables need to be considered.  Companies wishing to diversify their product portfolio with the inclusion of specialty films need to be aware that the high cost of added value resins and the constantly changing market are factors that demand the use of high technology process equipment that is sufficiently flexible to be effectively used in the production of both commodities and specialty films. 

Concluding Remarks

The technology of each component is complex, as is also their interaction and functional integration in the line. 

In order to prevent premature technological obsolescence of the equipment, special consideration needs to be given before purchasing your equipment. It is imperative to establish a clear understanding of what product, and its application, is to be produced on the line.  

The idea of an all-encompassing "universal" line may be attractive, but in reality no such line exists.  The more generalized a line is designed, the less optimized the product can be manufactured because the line components may not be suitable for product-specific process requirements.  In addition, industrial sized cast lines are built for long production runs that are not well suited for frequent product changes - the operation of cast lines regularly requires a significant number of process adjustments.  Production of complex and sophisticated films often consume large amount of time for fine-tuning, especially during the development of a film structure.  Many trials are typically required to achieve the targeted mechanical, physical, optical and technological parameters.

All cast line components will affect the overall performance of the complete line.  In order to get a first class line that is suitable of producing an excellent quality product, each of the individual components or systems must be of equally high quality.