In recent years coextrusion process had gained wide recognition as an appro
ach to achieving high quality or quantity and low costs by multilayered sys
tem as well as an polymer alloy or blend. We performed a strict 3-D numeric
al simulation with viscoelastic model on the encapsulation phenomena which
is one of the problems in the coextrusion process. The effects of material
properties such as viscosity ratio, extensional viscosity and second normal
stress difference and an effect of flow rate ratios on the encapsulation p
henomena were examined. Numerical results showed that encapsulation phenome
na were affected by not only viscous properties but also elastic properties
or non-linear properties. It was found that the difference of second norma
l stress differences working on the interface between fluid I and fluid II
(we defined it as DN2) had a correlation with the interface shape.