Wire and cable materials to achieve the requirements of the low smoke zero halogen flame retardant, must add a large amount of inorganic flame retardants, extrusion, melt viscosity, flow performance is poor, easy to produce friction heat production, resulting in the melt temperature is too high, long residence time is easy to decompose the fuselage materials, decomposition of gas formation porosity in products easily.
Low smoke halogen-free flame retardant wire and cable material extrusion processing, should pay attention to the following points.
(1) Selection of extruder.Because of the low smoke halogen-free flame retardant wire and cable material additives, melt viscosity is large, should use screw compression lower extruder.The shear rate of ordinary single screw extruder is low and the mixing capacity is poor.Twin-screw extruder has a high mixing capacity, but processing high-filled low-smoke halogen-free flame retardant wire and cable materials, often due to excessive shear material decomposition, discoloration and other problems, so it is best to choose the combination of single-screw and twin-screw double order mixing extruder.It is introduced that reciprocating single screw mixer is an ideal low smoke halogen-free flame retardant wire and cable material processing equipment at present.
(2) Selection of processing technology.In addition to the selection of appropriate extruder, processing technology should also be reasonable.If the temperature is too high will make the assistant decomposition, resulting in a product with air holes;Too low temperature, will produce poor plasticization.The pressure of the machine body should be reduced as far as possible. The screw speed should not be too high. Under the condition that the material is fully plasticized, the extrusion temperature should be reduced appropriately.The processing technology should be adjusted according to different materials and different formulations.
(3) Before material extrusion processing, it is necessary to carry out drying treatment, so as to avoid stomata in product section.
(4) Due to the poor fluidity of materials and great friction resistance with equipment, organic silicon can be added to improve the dispersability of inorganic flame retardants and reduce the processing torque.
The addition of organosilicone can improve the flame retardant property of wire and cable materials, and it is a good processing aid.
In a word, low smoke halogen-free flame-retardant wire and cable materials have strict requirements on processing equipment and process conditions, etc., so it is necessary to select appropriate extrusion equipment and process conditions according to the characteristics of raw materials, product performance and extrusion characteristics.