The Two-stage Mixing Method
The two-stage mixing method is basically the same as the one-stage mixing method, except that it does not contain a vulcanizing agent and a highly active accelerator. First make a piece of rubber (usually called masterbatch), then cool the plate for a while (usually more than 16h). In order to make the carbon black disperse better and improve the production efficiency, a quick (40r/min or more) Internal Mixer is usually used to make a master batch, and sometimes the preparation process of the masterbatch is combined with the mastication process. The subsequent two-stage mixing is based on a batch of mixning, and then a residual compounding agent,such as a vulcanizing agent or a promoter is added for supplementary mixing. The two-stage mixing can be carried out on an internal mixer or on an Two Roll Mill,added a vulcanizing agent and a promoter at a lower temperature with high production efficiency about 2-4 min.
The two-stage mixing always makes the carbon black more dispersible. For some rubbers containing a large amount of such carbon black, it may be divided into kinds of Dispersion Kneader more than two times.
Advantages of two-stage mixing: Such as extruded sealing strip compound and compounds containing rapid vulcanizing agent or blowing agent will be better wettability and dispersibility. If the temperature in the dispersion kneader is very high, a two-stage mixing method can be used, that is, a piece of the compounded rubber is cooled down, parked, and then put into the dispersion kneader again for the second stage of mixing vulcanizing agent. For some low-viscosity soft rubbers, the viscosity of the rubber compound becomes lower due to the increase of the temperature in the late stage of mixing, and the shearing force generated during the mixing is too small to open the carbon black aggregate or some agglomerate compounding agent,but two-stage mixing method is adopted, which can improve the dispersion of these low-viscosity soft compounds.
The two-stage mixing method has a good effect on improving the quality of the rubber compound and the process performance of the rubber compound; it can significantly improve the dispersion uniformity of the rubber compound and the physical properties of the vulcanized rubber; and can reduce the tendency of scorch caused by continuous high temperature.
One of the main advantages of ethylene-propylene rubber is that most of its compounds can be prepared by a one-stage mixing process!