As the first largest inorganic powder material, calcium carbonate, used directly in plastic, will cause dust to fly and severely damage the production environment.Meanwhile, because of its hydrophilicity, the dispersibility is not very good when it is directly added into the lipophilic resin.Therefore, For calcium carbonate powder, the general need to be processed into masterbatch beforehand to provide customers, so you can solve the production environment and compatibility issues.In this paper, calcium carbonate masterbatch production technology are introduced.
Calcium carbonate masterbatch production technology
◆ 1, 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 - When mixing, expelled 3-5 times prior to physical start of agglomeration to exclude moisture or small molecule volatiles and accelerate dispersal 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, dual-rotor continuous mixer has excellent exhaust effect, and automatic dust continuous 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
The higher the L / D, the better, generally greater than 40, and the PP carrier can only use twin-screw extruders. An asymmetric twin-screw extruder has recently been developed with double plasticizing effects of shear and extrusion.
◆ 2, melt mixing process
(1) high-speed mixer
Addition order: Calcium carbonate should be added to dehydration treatment, after the addition of other components. Calcium carbonate added to the mixing for about 5 minutes (feed temperature reached 60-80); Add about 1% coupling agent surface treatment for 5 minutes ( After the treatment, calcium carbonate is added to the glass and floats all above, which is treated well); adding PP carrier and polypropylene wax for 2 minutes; adding lubricant for 2 minutes (when the high-speed mixer current is increased from 70A to 100A, the low- ℃).
● Moisture control: the temperature to reach a certain height, prolapse of water adsorbed on the surface of calcium carbonate, so that it is controlled below 0.3%.
● Static Elimination: Calcium carbonate is easy to cause frictional electrification in the mixing process, especially calcium carbonate with flaky structure, which will cause the particles to agglomerate agglomerate and affect the dispersion effect. When the masterbatch is used, it will appear on the product White spots. The first solution is to add a small amount of antistatic agent in the formula, and second, high-speed mixing of materials to be allowed to stand for 20 hours before use.
(2) filter
The filter must be set, although its function is very big, but it is often neglected.The filter can change the material of the rotary movement into the linear movement, use the strong shear to further plasticize the material and adjust the melt in the head Pressure, filter impurities and decomposition materials.
The filter is generally three or four layers of structure, such as 80/120/80, 100/140/100, 100/120/140/100, etc. Usually 1 hour for 1 time, disposable, not recommended after burning If the filter is too thin, it will lead to the extruder pressure increases, the current increases, the output decreases.
There are two possible plugging: First, larger particles of the powder, or the powder is too fine to cause reunion, leaving a large number of inorganic powder after sintering block residue for this reason; Second, the carrier resin or small molecule additives Accumulation in the filter, the residence time is too long, leading to its decomposition of heat, if the plugging yellow residue, gray or black, no residue after sintering, belongs to this reason.
◆ 3, product quality control
(1) moisture control
Moisture and low molecular weight volatile matter should be controlled below 0.3%, to ensure that the blown film is not leaky, no water ripples. Specific inspection methods using a magnifying glass to observe the masterbatch, if the dense no obvious foaming voids, the surface of such products Very bright.
(2) Density control
The single-screw extruder mainly plays the role of uniform granulation and compacting, the denser the masterbatch is, the more water or small molecule volatiles can be completely eliminated, so the surface of the subsequent composite filled product is brighter. Screw extruder granulator head melt pressure to achieve, in particular, can reduce the melt temperature, increase feeding speed, and so on.