Black Masterbatch Production Process
Posted by Andy
The black masterbatch is widely used in the plastic processing industry, such as injection molding, extrusion molding, and blow molding process with its performance conductive properties and UV resistance. But no matter which product you make, the dispersion of carbon black is the main problem you should solve.
As the most important filler material, carbon black is one kind of ultrafine powder that fluffy and lighter than air. It’s easy to dirty machines and workers and the working environment. However, the most difficult is that the finer the carbon black powder, the more contact points between the carbon black aggregates and, as a result, the stronger the cohesion between them. If the carbon black is to be evenly distributed, the work to be done on the dispersion will be large. But sometimes we must do like this. For example, the density of carbon black particles is greater, the better the electrical conductivity; the smaller the carbon black, the higher the degree of light absorption.
The following is the research of carbon black dispersing in PE, reported by (Chue-Kwok J. KeungDonald E. Rathgeber )
Normally there are two ways to produce the black masterbatch:
- High-speed mixer + Double stage compounding extruder (twin screw extruder + single screw extruder) + Pelletizing system (water-ring cutting system, underwater cutting system etc.)
- Kneader mixer + Conical force feeder + Double stage compounding extruder (twin screw extruder + single screw extruder) + Pelletizing system (water-ring cutting system, underwater cutting system etc.)
1. The high-speed mixer can only simple mix LDPE/HDPE/PP, carbon black, additives, powder to powder. So the carbon black dispersion and compounding is mainly finished by the twin screw extruder. For different filling rate carbon black, the difference is just the twin screw extruder screw L/D ratio (a longer mixing time), like L/D=44:1, L/D=48:1, L/D=52:1.
But in this way, it also has its disadvantage. 1. All of the carbon black dispersion finished only by the twin screw extruder, so the quality of black masterbatch is not good then made by kneader unit. 2. This way cannot work with the high filling rate black masterbatch, normally we suggest using for carbon black < 35%.
2. The kneader mixer can excellent mix the plastic & carbon black very well (the material likes dough after kneader machine). And then feeding into twin screw extruder for the second time compounding to get the best dispersion of carbon black.
This design can work with carbon black filling rate up to 50% or even more and meantime with best dispersion ability. It is the best choice for high filling and high-quality black masterbatch. Its disadvantage is the high investment cost and high energy consumption.
Q: Can we use only single stage twin screw extruder to produce black masterbatch?
A: No, it can’t. It’s hard to cut the melted carbon black compounds directly with twin screw extruder, due to its high rotary speed. And also the carbon black is very hard, the pressure of die-head will be very higher. So we need to add one low rotary speed single screw extruder for pelletizing. But if you use LDPE+Black masterbatch(high filling) to produce low filling black masterbatch(1-5% carbon black), we can use only twin screw extruder to produce.
Q: Can we use Kneader + Single screw extruder to produce black masterbatch?
A: Yes, it can, but the quality of black masterbatch is also not so good. Because it has only one kneader mixing process. And you cannot save a lot of money if only cut down the twin screw extruder. If the carbon black filling rate is not too high, you can use the double stage design to save cost.
Q: Can we avoid the pollution of carbon black?
A: Say honestly, No. Because the carbon black is so light floating in the air. The best way is setting a separate room for carbon black feeding and using Non-woven dust bag.
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