EVOH as a barrier layer of the composite film , It will be normally used in flexible packaging plant during production . This article focuses on the characteristics of its processing methods and different types of EVOH film.
There are three processing methods EVOH
( 1 ) co-extruded EVOH with polyolefin or polyamide co-extruded composite .
(2) EVOH film lamination to other substrates , or other materials for the coating.
( 3 ) with the EVOH resin for coating various substrates or a single container . No special change , EVOH can be processed on conventional processing equipment.
EVOH biaxially stretched film characteristics
Between EVOH resin molecules and high molecular cohesive energy inside , not easy to draw . Therefore, biaxially stretched EVOH grade chosen higher ethylene content grades , and other resins such as EP-G115 ( ethylene mole fraction of 48% ) .
Biaxially stretched EVOH film high tensile strength, impact strength, puncture resistance , and can be comparable with nylon film ; and an elastic modulus comparable with BOPET ; gas and oxygen permeability of EVOH stretch is only 1/10 compared to the original , it is a strength and rigidity both high barrier substrate.
Features EVOH barrier coextruded film
1 ) co-extruded film is no organic solvent residue on food packaging more in line with health requirements , and more secure.
2 ) between the components EVOH coextruded film has good inter- layer combination of integration from the co-extrusion die lip out , improved packaging film ( sheet ) mechanical properties, especially after repeated twists and turns still maintain the original barrier properties , while the polyester – aluminum foil composite film after bending curved portion susceptible to damage , directly reduce the barrier properties.
3 ) one-time continuous formed into a film ( sheet ) , simplifying the process , in favor of industrial production , reducing costs.
Common EVOH coextruded film structure
Structure commonly used EVOH coextruded film , there are three , five, seven , nine-layers structure . Advantages of the multilayer structure are as following : barrier layer can be made very thin , reducing the cost ; humidity of EVOH barrier layer as an intermediate layer , EVOH effectively prevent moisture and improve the efficiency of its use ; having two outer have chosen hot performance resin for sealing the bag provides a convenient ; printed symmetry structure , the film without the volume trend , good flatness.
( 1 ) three-component (ABCAB) symmetrical structure.
The typical structure of LDPE or LDPE / adhesive layer / EVOH / adhesive layer or LLDPE. If using the LLDPE has good heat sealing, and mechanical properties are also superior to LDPE, but also has good printability and smoothness .
In addition , widely used microwave ovens also contributed to the growth of co-extruded sheet of such a structure . In a microwave oven , co-extruded sheet of container products to be subjected to ≧ 150 ℃ heated environment by opening up to PP, PC for the surface layer barrier sheet , such as PP / adhesive layer / PP, CP / adhesive layer / EVOH / adhesive layer / CP.
( 2 ) four-component (ABCBD) structure .
This structure can also be placed in the middle layer of the barrier layer and the inner layer may be a material good hot properties , high mechanical properties of the outer layer can use a material or materials with good opening performance , after support film ( sheet ) applies tell automatic packaging line . Such as PC / adhesive layer / EVOH / adhesive layer / PE, PS / adhesive layer / EVOH / adhesive layer / PE and so on .
( 3 ) five -component structure .
This structure has a greater combination of flexibility , in order to achieve more and higher requirements. The copolymer PA / EVOH / PA / adhesive layer / LLDPE or ionomer . It has better viscosity and better polyolefin compatibility .