Substrate Secrets

Answer:  Orange peel is a surface defect which is generally caused by a dirty casting roll.  So it would be generally seen on the chill roll surface but would be visible from both surfaces.   it creates a slightly irregular surface which then distorts the light passing through the film making it distorted.  And when examined closely has an appearance much like that of an orange peel surface hence the name.  If you have a rough film surface and then metallize it, the metal deposit will enhance the appearance of the defect when viewed through the film.  however, if you metallize the film surface opposite he orange peel and that surface is smooth you will not see the orange peel when viewing the metal surface directly, but if viewed from behind it will be visible.

If you are seeing variations in appearance with different resins of different melt flows (average viscosity level) then you are likely seeing a melt disturbance of the surface.  Because you have “orange peel” on both surfaces I assume you have a melt disturbance.  To have a melt disturbance free film you must have the skin layers a lower viscosity than the core.  Core viscosity is impacted by the core melt temperature, the MF of the virgin polymer and the percentage and MF of the reclaim added to the core.  Therefore you have to increase the MF of the skins or lower the MF of the core resin.  Typically you would want the skins to be 2MF units higher than the core, but this assumes good melt temperature levels and good quality reclaim resin.  You need to look at the viscosity of each layer to see how you need to choose your skin and core resins.  You also need to evaluate the screw performance to see what melt temperature you have for the core.  Once you know this you can engineer the coextrusion solution.