Process for forming a cured article of consistent shape from an extruded hydrolyzable siloxane composition.

摘要

Forming a cured article (I) of consistent shape from a hydrolysable siloxane compsn. (II) of a liq. or paste viscosity is by: (A) extruding, at a constant rate, a non-self-supporting compsn. maintained at more than 5[deg]C through a shaping die to form an extrusion with a uniform cross-sectional area throughout its length. The compsn. comprises a polydiorganosiloxane having at least two Si bonded hydrolysable gps. per molecule, a hydrolysable silicone crosslinker, a filler and opt. a curing catalyst; (B) feeding the extrusion in a continuous flow into an aq. curing bath maintained at least 20[deg]C. and having a density the same as the extrusion; (C) moving the extrusion through the bath to form (I); and (D) recovering (I) from the bath. Also claimed are: (E) a process as described in steps (A)-(D) where the extruded non self-supporting compsn. in (A) is maintained at more than 10[deg]C, (F) a process as described in steps (A)-(D) where in step (A) the extruded non self-supporting compsn. ( III) comprises a hydroxyl end-blocked polydiorganosiloxane (IV), a polyalkoxy-silicon crosslinker (V), a hexamethyldisilazane treated silica (VI), a stearated CaCO3 (VII) and a cursing catalyst (VIII); (G) a process as described in steps (A)-(D) where in step (A) the extruded non self-supporting compsn. is formed in 2 parts. The first part comprises a hydroxyl end-blocked polydimethylsiloxane (viscosity = 350 Pa.s), a hydroxyl end-blocked polydimethylsiloxane (viscosity = 150 Pa.s,) a trimethylsiloxy end-blocked polydimethylsiloxane (viscosity = 0.1 Pa.s), a hydroxyl end-blocked polydimethylsiloxane having a Si bonded hydroxyl contg. of 4.0 wt.% a precipitated hexamethylsilazane surface treated silica filler (average particle size = 2-3mu m). The second part comprises a tetra(n-propyl) orthosilicate, a trimethylsiloxy end-blocked polydimethylsiloxane (viscosity - 1.0 Pa.s.) a fumed silica filler, a dibutyl tin diacetate, glacial acetic acid and mineral spirits; and (H) a process as described in step (F) where the extruded non self-supporting compsn. is maintained at more than 10[deg]C.