Hydrophobization as a factor in the stability of sealing materials

V. D. Mushenko, PhD.

One of the most technically demanded and technologically complex multi-operational processes associated with the production of products, devices and systems, as well as their components, units and parts is high-voltage sealing, carried out in most cases at the final stages of the production cycle. Its main tasks are to ensure operability and reliability during operation of radioelectronic equipment (REA), electronic equipment (EEE), communication equipment (EE), devices and units of special technical application and transportation. The solution of sealing problems is always inseparably connected with the solution of two complex problems: the development of operations combined in a technological chain, as well as the selection, directed modification or development of a new composite material that meets the technical requirements for the sealing object and the conditions of technological operations. This points to the special role of the choice of polymer functional composite materials (PFKM) applied: sealants and compounds.

When developing sealants and compounds on a polymeric basis it is necessary to take into account that fine fillers included in their composition form interphase layers at the interface with polymeric binders. Meanwhile, successful sealing can only be achieved if the applied material is stable and isotropic in all volumes of the sealing shells and layers. The performance properties of sealants and compounds fundamentally depend on the correct quantitative and qualitative combination of polymeric binder and filler, their mutual compatibility and basic initial properties. These performance properties include, first of all, the initial working viscosity of heterogeneous systems as well as the probable dynamics of changing the viscosity of the systems when they are combined with a liquid-phase curing system (curing agent, "catalyst", various curing gas pedals). Both qualitative and quantitative composition of sealants and compounds determines the intensity of their curing as well as the time of its completion with the formation of final solid or elastic complex polymer products. With proper selection of the initial composition of the sealing material and the conditions of its application, the result depends on the presence of a number of certain properties of the fillers included in the composite material system. They include stability of mechanical characteristics (strength, hardness, resistance to abrasion, resistance to impact), ability to formation and destruction of conglomerates and agglomerates, resistance to external mechanical pressure, chemical inertness and fire resistance of fillers, good selective ability to wetting by liquid media, thermal stability, selective thermal conductivity. Low cost and availability of components should be attributed to the economic requirements for the components of sealants and compounds. The domestic origin of fillers and chemical components for their technological preparation, minimal toxicity of the filler and minimal toxicity of combustion products are very important. The most important factors in selection of fillers is their good wettability by liquid or viscous-fluid components of polymer base, physical and chemical compatibility with polymers necessary for complete dispersion and formation of isotropic compositions. Of no less importance is the stability of the properties in storage conditions, which can be caused both by the physical and chemical properties of the filler particles, the properties of their labile agglomerates and conglomerates and the results of chemical pretreatment of the particles, such as by directed hydrophobization and mechanochemical processing.

Our experience in creating sealants and compounds based on silicone, epoxy, polyurethane and polyester composites allows to develop materials with both required general technical and directional selective properties (thermal conductivity, heat insulation, heat-absorbing, antistatic, conductive, dielectric properties). In addition to the development of new sealants and compounds with directed functional properties, the task of targeted modification of the properties of serially produced materials in order to change the quantitative level of their technological and operational characteristics remains relevant. Wide possibilities for this are provided by the use of production facilities of "Functional Materials" where up-to-date and perspective methods of preliminary preparation of fillers, mechanochemical activation, their hydrofobization, combined milling and temperature treatment of solid mixtures with different qualitative and quantitative composition are mastered. Wide prospects are opening up for the application of such traditional fillers as ok