The quality of PVC mixture preparation directly affects the extrusion speed of the extruder, process parameters and the quality of the product profile, so the process should be strictly controlled. Kneading of the mix is done in a high speed or low speed kneader.
What are the factors that affect the preparation of pvc mixture
1) temperature control High-speed kneading machine speed is usually between 900-2000r / min, the material in the machine high-speed friction heat, the mixing process, the temperature control is very important, the general temperature control to do the following:
① must ensure that the cooling water temperature below 15 ℃;
② PVC resin and additives into the mixer immediately after mixing, using its friction heating, when the temperature reaches about 120 ℃ can be discharged to the cold mixer;
③ hot mix in the cold mixer for a certain period of time, when the material temperature is below 45 ℃ open the cold mixer gate discharge.
2) Mixing time The process of density change, homogenization and partial gelation of the material during the mixing process takes a certain amount of time to complete. Mixing time is too short, will make the extrusion process becomes difficult, material melting time becomes longer, the quality of the product worse. But the time is too long, the temperature will rise too high, easily lead to the decomposition of materials discoloration, but also consume more energy, low productivity.
3) feeding order more components of hard PVC formulations, choose a reasonable order of feeding is very important. The choice of feeding sequence should be conducive to the role of additives to play, to avoid the adverse synergies auxiliaries, but also help to improve the dispersion rate.
If the external lubricant is added too early, it will cover the outer PVC particles, hinder the re-combination of PVC particles, thereby reducing the degree of density, degree of homogenization and gelation rate, so the external lubricant is usually added in the late mixed; There are processing aids ACR adsorption stabilizer and liquid additives, affecting its stability and plasticizing effect, it should also be added after the stabilizer.
Typical hot and cold mixing process is as follows:
A. The PVC resin in the high-speed kneader stirring first heated to 60 ℃;
B. Put stabilizer, continue stirring heated to 90 ℃;
C. Input internal lubricants, processing aids, impact agents, fillers, colorants;
D. Input external lubricant;
E continue stirring, heating to 115-120 ℃;
F. At low speed the material discharged into the rotating cooling water mixer;
G. Cold mixed to 40-45 ℃ following the material, sieved, bagging.