Reasonable selection of plastic granulation process

Electronic product shell processing factory after the formula of the filling masterbatch is determined, the granulation process is an important factor that determines the quality of the masterbatch.

(1) Heating temperature The heating temperature depends on the softening point or melting temperature of the carrier resin. The higher the softening point or melting temperature of the carrier resin, the higher the heating temperature. Generally, it should be about 5°C higher than the melting temperature of the resin. If the heating temperature is too low, the resin cannot be fully melted, and the limited carrier resin cannot completely cover the inorganic powder. The surface of the masterbatch is rough and there are cavities in the middle of the particles. The resin and inorganic powder cannot form a uniform system. If the heating temperature is too high, the additive is easy to volatilize, the screw shear force is reduced and it is not suitable for plasticization, which also affects the quality of the masterbatch. Under normal circumstances, the temperature of zone 2 should be the highest temperature for granulation. The temperature of zone 1 is about 10°C lower than that of zone 2. The temperature of zones 3 and 4 is basically the same as that of zone 2. From zone 5 to the head, it gradually decreases by 5~10°C.

(2) Main engine speed For a twin-screw extruder of a certain specification, the main engine speed is determined by the output. The higher the main engine speed, the greater the output. Practice has shown that for any twin-screw extruder, the greater the output is not necessarily better. Generally, it is appropriate to control the main engine speed at 60~70% of the maximum speed. If the speed is too high, the particles will stay in the screw for a short time, and the plasticization will naturally be poor. The main engine speed should also match the speed of the feeder and the speed of the pelletizer, otherwise there will be abnormal phenomena such as overflow or particles that are too large or too small. ——This is not a simple question of the main engine speed or the feeding speed. In a macro sense, the main engine speed reflects the speed at which the material comes out of the main engine screw, while the feeding screw speed reflects the speed at which the feeding screw transmits the material to the main engine screw. So the key here is whether the feeding screw speed matches the main engine screw speed.
1. When the feeding screw speed is too small relative to the main engine screw speed, the material in the main engine screw does not completely fill the screw gap. In the main engine screw, there is relatively little material and the load is small. At this time, the material in the screw presents a low-pressure shear, which cannot achieve a good dispersion effect. (From this, it can be seen that the dispersion of fillers is not only related to small molecule dispersants, but is actually closely related to factors such as production process and mixing process.)
2. When the feeding screw speed is too large relative to the main engine screw speed, the material transmitted by the feeding screw to the main engine screw gap is always too late to be transmitted by the main engine screw, water-cooled and pelletized, so the main engine screw gap is oversaturated, The materials that cannot be delivered in time will collide around and look for a breakthrough under the huge squeezing and compacting. At this time, they will overflow from the glass fiber port or vacuum channel, causing the glass fiber port to overflow or return, or even vacuum blockage. In general, it is appropriate to control the main engine speed at 60~70% of the maximum speed. This actually considers that the main engine speed is too high, which is the situation 1, and the main engine speed is too low, which is the situation 2. These should actually be regarded as production abnormalities. Of course, there may be some other problems involved, such as too high speed (100% of the main engine maximum speed), high load operation of the machine, which may reduce the service life of the machine.

3. Use of water pump and vacuum pump The water pump is a device used to adjust the temperature of the screw. Unless the temperature in a certain area is too high, the water valve should be closed as much as possible to save power consumption. As long as the temperature of each area is reasonably adjusted, the water pump can be used. The vacuum pump is a device used to remove low-volatile components. It is generally used for grafting reactions or the production of starch-filled masterbatches. For the production of inorganic powder-filled masterbatches, it is best not to use or use less. Vacuuming can easily remove additives from the material, affecting the dispersion or processing of the masterbatch in the matrix resin.