Preparation And Characterization Of Silicone Rubber Used For Encapsulation

Silicone rubbers were of excellent electric and mechanical properties; chemical stabilization; excellent resistance of water, ozone and weather, flame retarded and no harmful gas while vulcanizing during a wide service temperature range ( -60℃-200 ℃ ). When the electronic devices were encapsulated with silicone rubbers, the former had the advantages, such as, resistance of moisture, corrosion, shock and dust, and their service performance and steadiness parameter were improved. In this thesis, two styles of Room Temperature Vulcanizing ( RTV ) silicone rubbers were prepared, the effects of the technical factors of addition RTV silicone rubbers were emphatically studied. The addition RTV silicone rubber with excellent electric properties and the tensile strength (TS) above 5 MPa was obtained.In Chapter one the research development of silicone rubber encapsulation materials was reviewed. The styles and development tendency of encapsulation were summarized. The vulcanizing mechanism, main components and their style and preparation method of RTV silicone rubber were summed up according to vulcanizing style. Additionally, the style of reinforcement filler and semi-reinforcement filler, surface treatment method and reinforcement mechanism of silica were presented. The effects of cross link agent and filler on addition RTV silicone rubber were also discussed.In Chapter two the experimental and measurement methods were described. The base component and concentrated cross-linking agent were prepared by ion polymerization and the cross-linking agent was prepared by cation polymerization. Three kinds of addition platinum complex catalyst, such as platinum complex with i-PrOH, or THF, or divinyl tetramethyl disiloxane, and the condensation titanium chelate complex catalyst were synthesized. All components vulcanized at room temperature so that the RTV silicone rubber were obtained. The following characterization, i.e. viscosity and vinyl content of polydimethylsiloxane, mechanical properties such as tear strength, elongation at break (E_b) and tear strength (T_s), and electric properties such as volume resistivity and dielectric constant were measuredand analyzed.In Chapter three the influencing factors of base component and properties of condensation RTV silicone rubber were examined. The results showed that the viscosity-of polydimethylsiloxane was greater using KOH as catalyst than that using LiOH, and that the viscosity was increased as the reaction time. The viscosity of product would be lower using less end capped reactant. The properties of silicone rubber were excellent while using dibutyl tin dilaurate as catalyst. The mechanical and electric properties of silicone rubber appeared optimum values as the catalyst amount was increased. The mechanical properties decreased as the viscosity of base component was increased. The mechanical properties were improved, but the electric properties were reduced while the filler amount was increased.In Chapter four the technical factors of addition RTV silicone rubber were analyzed, and the RTV silicone rubber with high tensile strength was prepared by orthogonal design. The platinum complex of divinyl teramethyl disiloxane had the highest activity. The results showed that the dielectric properties of silicone rubber were almost invariable when the filler amount was constant. The mechanical properties were reduced as catalyst amount was increased. The integrative properties were excellent when the viscosity of base component was 5 Pa·s. Though the mechanical properties of silicone rubber were increased as the filler amount was increased, too much filler would block the cross linking, so that the mechanical properties were decreased. The optimum electric properties were obtained while the A( mole ratio of SiH/SiVi) value was approximate 1, and the mechanical properties were excellent when A value was above 1. The addition RTV silicone rubber had stable dielectric constant and low dissipation factor. The high tensile strength was obtained by concentrated crosslinking. The elongation at break of condensation RTV silicone rubber was better than that of addition RTV silicone rubber.In Chapter five the research work of this thesis was summed up, and the conclusion was brought forward.