“All-in-one” Thixotropic Polysiloxane Pastes for UV-Activated Room Temperature Hydrosilylation Cross-Linking in Additive Manufacturing

In search of "inks" for additive manufacturing of silicone rubber parts, three different types of "all-in-one" pastes with suitable rheological flow properties, ultraviolet (UV)-activated fast cross-linking by hydrosilylation in air at room temperature (as quick as 20-30 s), and shelf lives of over six months in the dark and 6-9 days in laboratory daylight, depending on paste composition, have been developed. The pastes are based on vinylsiloxy-functionalized, completely amorphous, linear terpolysiloxanes containing predominantly dimethylsiloxy-, DiMeS, repeat units with small amounts (typically less than 5 mol %), of diphenylsiloxy-, DiPhS, methylphenylsiloxy-, MePhS, or diethylsiloxy-, DiEtS, crystallization disruptors. The base polymers were compounded with trimethylsilylated hydrophobic silica fillers, thixotropic flow agents, hydrosilyl-functionalized oligomeric cross-linkers, and catalytic systems containing either platinum(II) acetylacetonate, Pt(AcAc)(2), or trimethyl(methylcyclopentadienyl)platinum(IV), MeCpPtMe3, and diethyl azodicarboxylate, DEAD, catalyst inhibitors. Paste preparation, steady and oscillatory shear rheology, and UV-activated cross-linking and shelf-life stabilities are described.