What You Need to Know to Get into Coextrusion

摘要

Coextrusion requires far more polymer and extrusion knowledge than monolayer extrusion,so operating personnel need to be prop-erly prepared.And there's lots to consider.First,it's necessary to select polymers that meet a host of performance requirements in the finished extrusion and will also bond to form a strong structure.Bonding is largely dependent on the respective surface energies of the polymers.If the polymers selected for the performance requirements of the finished coextrusion do not provide adequate bonding strength,then it will be necessary to use tie layers,which will require additional extruders.Among the many performance factors to consider-determined by the final use of the finished product-are flexibility,chemical resistance,permeability and ideal layer placement,to name a few.For sheet and cast film applications in particular,processors must choose between a multi-manifold die or a coextrusion feedblock.Coex feed-blocks generally provide more flexibility as well as lower initial cost and less maintenance.Both have valves of various designs to adjust the layer flow rates,but melt pumps are typically used to precisely control the output of each layer.I suggest you evaluate and select from experienced coextrusion machine builders so they can provide you all the technical information necessary for the polymer selection,structure,and equipment design for a proposed coextrusion line.However,the actual daily operation of the line depends heavily