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 section of compound rubber (usually called masterbatch), and then cool down for a period of time (generally above 16h). In order to better disperse carbon black in rubber and improve production efficiency, a fast (more than 40r / min) mixer is usually used to prepare a section of masterbatch, and sometimes the preparation process of masterbatch is combined with the plasticizing process And get up. The subsequent two-stage mixing is based on the one-stage mixing, and the remaining compounding agents such as vulcanizing agents and accelerators are added for supplementary mixing. The two-stage mixing can be performed on an internal mixer or an open mixer. A slow mixer or kneader is usually used for two-stage mixing, so that the vulcanizing agent and accelerator are added at a lower temperature, and it has higher production efficiency. The two-stage mixing time in the internal mixer is generally 2-4 minutes.
The two-stage mixing always makes the carbon black of the fine particles have better dispersibility. For some compounds containing a large amount of this carbon black, it may be divided into two regardless of the type of mixer. Join even more times as well.
Process of two-stage mixing method:
The first mixing process:
The same as the one-stage mixing method, except that the active catalyst and sulfur are not added during the discharge.
The second mixing process:
Adding sulfur and active catalyst after a period of compounding rubber discharge for supplementary mixing (using a slow mixer or kneader) → the top pin drops to start the mixing → the end of the mixing → unloading to the open mixing Machine or tablet press → tablet cooling (hanging cooling device cooling or cooling water cooling) → slicing standby
Advantages of two-stage mixing: better wettability and dispersibility, such as extruded sealant compounds; compounds containing fast curing agents or blowing agents. If the temperature in the mixer is very high at the end of the mixing, a two-stage mixing method can be adopted, that is, the one-stage compound is cooled down, parked, and then put into the mixer again, and the vulcanizing agent is added in the second stage. Mixing. For some low-viscosity soft rubbers, the viscosity of the rubber compound becomes lower due to the rise in temperature in the late mixing stage, and the shear force generated during mixing is too small to open the carbon black aggregates or some agglomerated compounding agents. Particles, which are mixed in two stages, can improve the dispersibility of these low-viscosity soft compounds.
Adopting the two-stage mixing method has a good effect on improving the quality of the rubber compound and improving the technical performance of the rubber compound; it can significantly improve the dispersion uniformity of the rubber compound and the physical and mechanical properties of the vulcanizate; it can reduce the scorch tendency caused by continuous high temperature . It is suitable for high-reinforcing fillers (high-reinforcing carbon black, white carbon black) and compounds with high heat generation, such as tire tread rubber.
When performing two-stage mixing in an internal mixer, pay attention to:
1. The initial mixing temperature of adding sulfur and accelerator should be lower than 90 degrees, and the discharge temperature should not exceed 110 degrees. The mixing time should generally not exceed 2 minutes to prevent scorch.
2. Adding hygroscopic calcium oxide generally can not be mixed for a long time under the condition of more than 120 degrees, otherwise it should be added by mixing.