Incorporation of Fillers, Modifiers, etc

It is usually most convenient to add the fillers to a warm resin. However, diluents and solvents are sometimes employed to lower the viscosity of the system to allow a higher concentration of filler in the mixture. 

After the filler is mixed in, the formulation should be allowed to return to room temperature and stand for a suitable time until all bubbles have escaped the system. This can be facilitated by a vacuum degassing process. 

Fillers may be added to low-viscosity resins by conventional sigma-blade mixer or the same type of equipment used for mixing paint systems. Three roll mills are generally employed for more viscous systems to obtain thorough wetting of the filler by the resin matrix. 

In the epoxy adhesive industry, fillers are generally added as a batch process rather than a continuous process. Batch systems are especially suited to short-run operation in which additives and materials are often changed. They allow for greater control of residence time, shear, and temperature, and they can accommodate a feed rate that is not free-flowing. 

Mixing equipment is generally classified in terms of the shear or mixing intensity. High-shear mixers are used for producing filled compounds. But most often, low- or medium-shear mixers suffice for compounding epoxy adhesives. 

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