In the food or medical packaging industry, using multi-layer coextrusion plastic film is a key component to ensuring the safety of the product. In addition, using packaging material that prolongs a products shelf life can drastically cut down on waste of perishable products, and creates a longer window for grocery stores to stock product before it reaches the hands of the consumer. A great way to achieve this is by using a packaging material that reduces the amount of oxygen that permeates the plastic, such as EVOH, incorporating the material into multi-layer coextrusion structure.
While traditional thermoplastic resin materials, such as polypropylene, polyethylene and HIPS, all have a certain degree of inherent barrier properties, they are not typically seen as “barrier” materials. Polypropylene, for example, is naturally an excellent moisture barrier but does not perform as well when it comes to oxygen permeability. In order to protect the contents of the packaging from both oxygen and moisture, a barrier material must be incorporated into the composition of the sheet – and this is where materials such as EVOH come in.
So, what is EVOH film and how does it contribute to increasing the shelf life of packaged food products?
EVOH stands for Ethylene-vinyl alcohol copolymer and is a flexible, crystal clear, glossy thermoplastic copolymer. This material has excellent flex-crack resistance, and exhibits a high resistance to hydrocarbons, oils and organic solvents. EVOH is known for having some of the best barrier resistance to gases such as oxygen, nitrogen, and carbon dioxide which makes it particularly suited for packaging food, drugs, cosmetics, and other perishable products. When compared to other common films, EVOH is considered to have superior barrier properties. However, when exposed to moisture, EVOH loses its good gas barrier properties. For this reason, EVOH is often used in a multilayer co-extruded film structure with materials such as HDPE, PP and PET, all of which have superior moisture barrier properties.
Current GWELL Capabilities at EVOH multi-layer coextrusion.
Currently GWELL can incorporate EVOH into 7-, 9-, or 11-layers structures through the process of multi-layer coextrusion.
Multi-layer coextrusion is a process in which two or more plastic materials are extruded as one. In a standard monolayer sheet extrusion process, one material is fed and extruded through a die. The coextrusion process involves multiple extruders and multiple materials (depending on the structure), and the molten material is channeled through the melt pipes to create a laminar flow for the coextrusion feed block and die technology to weld the extrudates into a one-piece structure. When multiple material layers are combined, the end result yields in a multi-layer structure deriving distinct properties from each material used in the structure. During the extrusion of these plastics materials, the required cooling is achieved by feeding the material through the cooling rolls, also known as the stack rolls or chill rolls. These rolls deliver the required cooling in addition to determining the sheet thickness and the surface texture using specialty surface finish rolls like matte, sand matte, hair cell, etc.