Encapsulated pigments and fillers

Encapsulation is the process of obtaining small solid nanoparticles, liquid nanodroplets or gas nanobubbles with a polymeric coating. We will give a historic account of some of the early work on encapsulating inorganic pigments and fillers with a polymer through (mini)emulsion polymerization. 

The encapsulation of pigment and filler particles is an important area of research, both in the academic world and in industrial laboratories. At present, emphasis is given to the incorporation of clay in polymeric materials, including polymeric nanoparticles. Such systems are expected to exhibit properties other than the sum of the properties of the individual components. In general, several benefits from this encapsulation step can be expected when the obtained particles will be applied in a polymeric matrix (e.g., plastics or emulsion paints) as compared to physical blends ... 

Besides inorganic pigment and filler partieles, there is also early work (from 1978) on encapsulation of organic pigments, e.g. eopper-phtaloeyanine and azo pigments [43]. For further reading on encapsulation of different materials see [44]. 

Table 4.2 Common pigments and fillers involved in encapsulation reactions. Isolectric pH values, particles dimensions and fields of application.

For the protection of the light sensitive IC devices, pigments are usually incorporated into the RTV encapsulant (such as low level of the carbon black and titanium dioxide). The main parameter that affects the RTV rheology may be filler incorporation and filler activity. Through the RTV silicone study, we have learned that the rheology of the RTV silicone is closely related to its coating performance. 

The applications of these encapsulated particles can be found in filled plastics, paints, inks, paper coatings etc. In solid polymeric materials and films, the interaction between filler or pigment and polymer is very important for mechanical properties like fracture toughness [34, 35]. 

The PVC Emulsion types (containing up to 2.5% emulsifier) and those containing filler require a higher pigment loading because of their opacity. Since the emulsifiers are mostly alkaline, it is recommended to use silica-encapsulated metallic pigments to ensure consistent quality of the final product. 

Several additives are susceptible to microorganisms, notably certain PVC plasticisers, especially the epoxy oils and esters, polyesters and sebacates. Most aryl plasticisers are more resistant than their alkyl equivalents. Natural fillers such as starch and wood flour are also attacked, although if the particles are fully encapsulated by resin they will have considerable protection. This is important for wood-plastics composites, currently being promoted as potential substitutes for wood, MDF and even UPVC. It is possible for microorganisms to attack certain lubricants such as polyethylene waxes and pigments. 

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