In order to meet the requirements of low smoke halogen-free flame retardant, a large amount of inorganic flame retardant must be added to the wire and cable materials. During extrusion, the melt viscosity is large and the flow performance is poor, which is easy to generate friction and heat, resulting in excessive local temperature of the melt, materials are easy to decompose when staying in the fuselage for a long time, and the gas generated by decomposition is easy to form pores in the products.
Low smoke halogen free flame retardant wire and cable material extrusion processing, we should pay attention to the following points. (1)Selection of extruder.
Because there are many additives for low smoke halogen-free flame retardant wire and cable materials and the melt viscosity is large, an extruder with lower screw compression ratio should be adopted.
The common single-screw extruder has low shear rate and poor mixing capacity. The twin-screw extruder has higher mixing capacity, but it processes high-filled low-smoke halogen-free flame retardant wire and cable materials, often because of excessive shear and material decomposition, discoloration and other problems, so it is best to choose a single screw and twin screw combination of two-stage mixing extruder.
It is introduced that reciprocating single screw mixer is currently an ideal low-smoke halogen-free flame retardant wire and cable material processing equipment. (2)Selection of processing technology.
In addition to selecting a suitable extruder, the processing technology should also be reasonable.
If the temperature is too high, the auxiliary agent will be decomposed, resulting in the product with low pore temperature, which will produce poor plasticization.
The pressure of the machine body should be reduced as much as possible, and the screw speed should not be too high to properly reduce the extrusion temperature under the condition of ensuring sufficient plasticization of the material.
The processing technology should be adjusted according to different materials and different formulas. (3)
Before the material extrusion processing, it should be dried to avoid the porosity of the product section. (4)
Due to the poor fluidity of the material and the large friction resistance with the equipment, silicone can be added to improve the dispersibility of inorganic flame retardant and reduce the processing torque.
The addition of silicone can improve the flame retardant performance of wire and cable materials and is a good processing aid.
In short, low smoke halogen-free flame retardant wire and cable materials have strict requirements on processing equipment and process conditions, and appropriate extrusion equipment and process conditions must be selected according to raw material characteristics, product properties and extrusion characteristics.