The deck reduces the flow and equalizes the pressure within the back of the die. As the pressure increases behind the deck, the plastic is forced over the deck and out through the die slit. This reduces the pressure at the ends and increases the amount of residence time the plastics is in the die feed channel. This construction equalizes the distance that the plastic melt must travel along the entire length of the die slit. With a properly designed coat hanger die all plastics experience the same residence time and the same pressure drop.
Sheet extrudate can be double or triple layers.
The thickness of the three plastics can be controlled by the die. Typical coextruded products are butter containers and tooth paste tube because both butter contains and toothpaste tubes require the layering of several plastics onto each other. Three extruders and two coextruders lay seven layers of plastics in a flat sheet. The sheet is then rolled into a tube and sealed by downstream equipment. The tube then receives an injection molded head that is heat sealed to one end of the sleeve.