Calcium carbonate as the largest inorganic powder material, the direct use of plastic can cause dust flying, seriously damaging the production environment. At the same time, because it is a hydrophilic material, the lipophilic resin directly added to the dispersion is not good, so for calcium carbonate powder, the general need to be processed into masterbatch beforehand to provide customers, so that you can solve the production environment and Compatibility issues. Before, Xiao Bian to introduce technology | calcium carbonate masterbatch formula design principles, here we introduce the production technology of calcium carbonate masterbatch.
01, melt mixing equipment
The choice of reciprocating single-screw extruder, symmetrical or asymmetric twin-screw extruder, continuous or double-rotor mixer, double extrusion unit can be, underwater pull, grinding face can be eager.
If the carrier material is suitable, the equipment is best to use continuous mixer, but should pay attention to:
Time - mixing time to control properly, too long can easily lead to stick pan, yellow, and even decomposition.
Exhaust - Before mixing begins at the beginning of physical caking of the aggregate, 3-5 venting to eliminate moisture or small molecule volatiles and accelerate dispersion of inorganic powders.
(1) continuous mixer
Mixer + single-screw extruder and internal mixer + twin-screw extruder, continuous mixer can be used for PE and PBS carrier. Double rotor continuous mixer exhaust effect prominent, the realization of automatic continuous dust production.
(2) double extrusion equipment
Twin-screw extruder + single-screw extruder, outstanding exhaust effect, PP carrier can only be used two-stage screw extruder.
(3) twin-screw extruder
L / D is as high as possible, the general requirements of more than 40, PP carrier can only use twin-screw extruder. Recently, an asymmetric twin-screw extruder has been developed with the double plasticization effect of shearing and extrusion.
02, melt mixing process
(1) high-speed mixer
Calcium carbonate should be added to the dehydration treatment, after the addition of other components. Add calcium carbonate mixed for about 5 minutes (expected temperature reached 60-80);
Add about 1% coupling agent surface treatment for 5 minutes (after the treatment of calcium carbonate in the glass all float above is handled);
Join PP carrier, polypropylene wax for 2 minutes;
Add lubricant and stir for 2 minutes (high speed mixer current is increased from 70A to 100A, low speed stirring and cooling at 40 ℃).
Moisture control: the temperature to reach a certain height, prolapse of water adsorbed on the surface of calcium carbonate, so that the control of less than 0.3%.
Static elimination: calcium carbonate in the mixing process is likely to cause frictional electrification, especially the obvious sheet-shaped structure of calcium carbonate, which will cause serious aggregation of particles into a group, affecting the dispersion effect. Masterbatch in use, will appear in the product white spots. The first solution is to add a small amount of antistatic agent in the formula, the second is the high-speed mixing of materials left to stand for 20 hours before use.
The filter must be set, its role is great, often overlooked. The filter can rotate the material into linear motion, the use of strong shear operation to further plasticize the material, adjust the melt pressure in the nose, filter impurities and decomposition of materials.
The filter is generally three or four layers of structure, such as 80/120/80, 100/140/100 and 100/120/140/100. Usually 1 hour for 1, disposable, do not recommend burning and then use. If the filter is too thin, it will lead to the extruder pressure increases, the current increases, reducing production.
There are two possibilities for blocking a network:
First, the larger particles of the powder, or the powder is too fine to cause reunion, leaving a large number of inorganic powder after sintering the residue of the mesh belongs to this reason;
Second, the carrier resin or small molecule additives accumulate in the filter, residence time is too long, resulting in thermal decomposition, if the plugging the yellow residue, gray, black, no residue after sintering, this is the reason.
03, product quality control
(1) moisture control
Moisture and its low molecular weight volatiles should be controlled below 0.3%, to ensure that the blown film is not leaks, no water ripples. Specific means of inspection with a magnifying glass to observe the masterbatch compact no obvious foam voids, so the product surface is very bright.
(2) Density control
Single-screw extruder mainly plays the role of uniform granulation and compacting compaction, the parent material as dense as possible, can be fully ruled out moisture or small molecules of volatile matter, so follow-up composite filler products, the more bright the surface. Density by single-screw extruder pelletizing head melt pressure increases, in particular, can reduce the melt temperature, increase feed speed and so on.