How to Use Titanate Coupling Agents (Pretreatment Method)
Fillers or pigments are first pretreated with the coupling agent and then processed and mixed with the polymer and other additives. This method has many advantages and is particularly suitable for certain engineering plastics whose polymer composition is complex or whose processing temperature is relatively high, because it prevents unwanted side reactions. After the coupling agent has been used to pretreat the filler, its decomposition point is greatly raised.
This method can be further divided into two types:
(1) Dry Mixing Method
In order to coat a small amount of titanate uniformly onto the surface of the pigments and fillers, a small quantity of diluent is generally added. When the diluent and the coupling agent are used in a 1:1 ratio, the small amount of titanate can be evenly distributed over the filler surface; without a diluent the filler cannot be coated uniformly. The diluent may be the solvent or lubricant already used in the original process formulation — for example, white oil (liquid paraffin) in the plastics industry, machine oil in the rubber industry, and No. 200 solvent naphtha or isopropanol in the coatings industry. The treatment equipment is generally a high-speed mixer: while the filler is stirred at high speed, the diluted coupling agent is sprayed in as a mist; stirring is continued for 5–15 minutes (depending on the efficiency of the mixer), after which the material is processed as usual or discharged and stored for later use (cooling is required, otherwise local overheating may discolour the filler and impair its filling performance).
(2) Wet Mixing Method
Monoalkoxy and coordinate types of coupling agents can be diluted with solvent naphtha, petroleum ether, benzene–alcohol mixtures and other solvents so that the pigments are soaked in the solution; the solvent is then removed by heating or under reduced pressure. For water-soluble chelate types, dilution and soaking are carried out with water, after which the water is removed. This method achieves more complete coupling, but in industrial production its cost is too high and it is economically unattractive.
