Transmission Efficiency of plastic Films Part 1

TRANSMISSION EFFICIENCY OF PLASTIC FILMS
the particular resins to be processed. In the other system, known as the laminar flow
(or combining adaptor) process, the separate melts are brought together in a
common manifold.
The flow passages are designed to minimize turbulence and mixing of the separate
streams is avoided. In general, the viscosities of the several polymers should be
closely matched when using a combining adaptor. It is also desirable that the
viscosities match at about the same temperature to eliminate problems associated
with maintaining different melt temperatures in the die.
The combining adaptor allows great flexibility in operation. It can extrude two or more
layers relatively easily and it can extrude a polymer in a much thinner layer than
would be possible if it were extruded as a single film. However, it is not possible to
maintain a large temperature difference between layers (which is possible in the
multiple manifold processes). There are also many combinations of materials that do
not flow together and produce a uniform product.
In the case of co extrusion (of tubular film) there is also a third process. This involves
the coextrusion of two films from separate annuli in the same die head. The separate
film are brought together below the ‘freeze line of both bubbles, Provision is made in
the die for the space between the films to be saturated with a reactive gas which
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