Microencapsules for technical applications

Microencapsulation is used to protect either the active substance against the environment or vice versa. Additives such as fragrances, colorants or protective agents are often not sufficiently stable to be incorporated directly into polymeric materials, paints or coatings. They are therefore encapsulated in polymer materials. Beside the protection of the active substance or the surrounding area the controlled release of active substances is of major interest. By the use of depot systems those active substances can be released in controllable amounts over a certain period of time. Microcapsules consist of a solid, liquid or gaseous nucleus of active substance and a polymer shell of varying permeability or density. Matrix particles are solid spheres of one or more polymers. The physical structure of matrix particles can range from dense to highly porous. We vary the molecular and macroscopic properties of the particles to tailor the geometric and morphological structure and functionality to specific requirements. Recently the technical application of microcapsules as functional materials or smart systems has been developed. Intelligent sealants contain microcapsules with watersoluble shells - the insoluble core material swells to a multiple of the original volume. Screws agglutinate during tightening if the threads are coated with microcapsules which contain adhesives. By microencapsulation materials with apparently controversial properties can be produced. An example for this can be watersoluble fertilisers or insectizides which resist heavy showers but are active during the whole season. Proven applications include: controlled-release systems, - compatibilization of plastics additives, - microparticles with sensor functionalities, - microparticles for applications in electroplating. Fields of application are for example: - plastics industry (incorporation of active substances ot fillers), - electroplating (integration of lubricants or anticorrosives), - construction industry (heat accumulators, pest control), - paint industrie (pigments, antifouling agents), - textile industry or- paper industry. For the preparation of microcapsules several reactive and nonreactive techniques are applied. For the production of technically relevant materials mostly reactive encapsulation techniques are used, like interfacial polycondensation or polyaddition techniques. Preferred wall materials are amino resins or polyureas. Core materials can be dyes or pigments, mineral oils, adhesives, metal flakes, lubricants, sulphur or phosphorus, e.g.