Compound extruder process parameters

1 The structural type of the coextrusion composite die: the quality of the coextruded composite film, and the composite die is the key. Co-extrusion composite die heads are divided into the following three, see the figure (slightly). The method of welding before the die is called feeding method; the method of welding inside the die is called multi-tube method; the method of welding outside the die is called multi-port method. The length of the straight part of the die head of the co-extrusion head is 50 to 100 mm.
2 Factors affecting the quality of coextruded composite membranes. Extruder operating conditions control; composite die structure, plastic and plastic compatibility. The thickness of each layer of the composite film is controlled by the rotation speed of the extruder, and the rotation speed is increased. The thickness of the layer is increased with other conditions being constant.
3 Whether the two plastics can be heat-sealed together depends on whether the two resins are compatible. According to the principles of structural similarity and emptyness, some plastics are compatible and others are not. In the case of two kinds of plastics that are not compatible, a co-extruded method is used to make the composite film. A third one that is compatible with both must be sandwiched between the two. This is a pair of two incompatible plastics. There are compatible plastics called adhesive resins, also known as compatibilizers. The compatibility of various resins is shown in the table (abbreviated in the table).
The ionic resins Surlyn, Bynel, and Nucrel produced by DuPont are all compatible with many resins. These resins are all compounds of ethylene and acrylic esters. Although these adhesive resins are expensive, the cost of the coextruded composite film is still the lowest due to the small amount.
4 The composite fastness of the coextruded composite film is related to the compatibility between the resin, humidity, pressure, and the straight part and length of the composite coextrusion die. The adhesive strength between various resin layers is shown in the table (abbreviated in the table). Compound humidity is high (in composite die), resin diffusion ability, strong adhesion. Therefore, the die temperature of the melt should be controlled within the range of the resin processing temperature with the highest melting point in the three composite materials.
For example, in the case of nylon compounding, nylon has the highest melting point, nylon 6 has a melting point of 223°C, PA66 has a melting point of 265°C, PA11 has a melting point of 193°C, and PA12 has a melting point of 183°C. The greater the pressure in the composite die, the more favorable the mutual penetration of the layers in the molten state and the better the composite fastness. The co-extrusion port has a long straight length and good composite fastness.