Coextrusion systems
Flat film extrusion: cast film

Coextrusion of several polymers is very common in cast film technology. There are two main ways of producing a multilayer cast film:

• use a single-layer die downstream of a coextrusion box (known as a feed block or black box);

• use a multi-layer die (multimanifold).

The combination of feed block and single-layer die remains the most frequently used system. Here we describe the principles, advantages and disadvantages of each of these systems.

A single-layer die (called a single-manifold) can be used downstream of a coextrusion box (usually called a feed-block), as shown in figure 5.