At present, there are two processes for filler masterbatch production: premix and split-feed.When choosing the suitable process for manufacturing filler masterbatch,it mainly depends on the percentage of additives in the formulation.
Generally,When the amount above 4%, the premix is efficient for high output.When the content of additives is less than 4%, the additives cannot cover all calcium carbonate powder in a high speed mixer, and the calcium powder cannot be dispersed efficiently.Based on the compatibility principle of activated calcium carbonate with plastics, calcium carbonate powder is fed seperately through loss-in-weight feeder along the twin screw extruder to ensure uniform dispersion of the calcium powder.
The pre-mix process can effectively mix calcium carbonate powder, solve the feeding problem, improve productivity.Currently,a majority of filler materbatches in the market are manufactured through this process and enjoy a intense competition. Compared to pre-mix process,the masterbatch through split-feed process is more competitive with high quality however the initial investment will be higher.
Compounding the martix on twin screw extruder
The co-rotating twin-screw extruder
has long been the equipment of choice for filler masterbatch compounding.The high compounding capacity of twin screw extruder will make up for the unsufficient surface modificaiton and adhesion of matrix/filler.
There are two main process tasks for the twin screw extruder:
1.Be able to intake a large amount of calcium carbonate powder to the extruder.
2.Be able to highly disperse and mix the filler with the polymer carrier
It involves five steps in the compounding process:
1.Melting of polymer matrix.
2.Wetting of the filler by the melt of polymer matrix.
3.Dispersion of agglomerates and clusters (dispersive mixing).
4.Uniform distribution of filler in the polymer matrix.
5.Degassing and homogenization of the melt.
The extruder should have as much free space as possible to allow the intaking of the high loading level of filler. The screw should have a higher torque, the barrel should have efficient heating and cooling system, and the barrel&screw design of the processing section should be reasonable to meet the process requirements. This should achieve excellent dispersion and distribution effects while ensuring high production, safe and reliable equipment operation, and efficient energy savings.