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

A process for forming a cured article of consistent shape from a hydrolyzable siloxane composition of a liquid or paste viscosity, comprising:

• (A) extruding a non-self-supporting composition which is maintained at a temperature greater than 10.degree. C. and which comprises a polydiorganosiloxane having at least two silicon-bonded hydrolyzable groups per molecule, a hydrolyzable silicon crosslinker, a filler, and optionally a curing catalyst, at a constant rate through a shaping die to form a shaped extrusion having a cross-sectional area that is substantially uniform throughout the length of the shaped extrusion;
• (B) feeding the shaped extrusion in a continuous flow into a circulating aqueous curing bath maintained at a temperature of at least 20.degree. C. and having a density substantially the same as or slightly greater than the density of the shaped extrusion;
• (C) moving the shaped extrusion through the aqueous curing bath as the shaped extrusion cures into a cured article having a cross-sectional area that is substantially uniform throughout the length of the cured article;
• and
• (D) recovering the cured article from the aqueous curing bath.

A process for forming a cured article of consistent shape from a hydrolyzable siloxane composition of a liquid or paste viscosity, comprising:

• (A) extruding a non-self-supporting composition which is maintained at a temperature greater than 5.degree. C. and which comprises a hydroxyl-endblocked polydiorganosiloxane, a polyalkoxy-silicon crosslinker, a hexamethyldisilazane treated silica, a stearated calcium carbonate, and a curing catalyst, at a constant rate through a shaping die to form a shaped extrusion having a cross-sectional area that is substantially uniform throughout the length of the shaped extrusion;
• (B) feeding the shaped extrusion in a continuous flow into an aqueous curing bath maintained at a temperature of at least 20.degree. C. and having a density substantially the same as or slightly greater than the density of the shaped extrusion;
• (C) moving the shaped extrusion through the aqueous curing bath as the shaped extrusion cures into a cured article having a cross-sectional area that is substantially uniform throughout the length of the cured article;
• and
• (D) recovering the cured article from the aqueous curing bath.

A process for forming a cured article of consistent shape from a hydrolyzable siloxane composition of a liquid or paste viscosity, comprising:

• (A) extruding a non-self-supporting composition which is maintained at a temperature greater than 5.degree. C. and which is formed in two parts, the first part comprising a hydroxyl endblocked polydimethylsiloxane having a viscosity of 350 Pa.s, a hydroxyl-endblocked polydimethylsiloxane having a viscosity of 150 Pa.s, a trimethylsiloxy-endblocked polydimethylsiloxane having a viscosity of 0.1 Pa.s, a hydroxyl-endblocked polydimethylsiloxane having a silicon-bonded hydroxyl content of about 4.0 weight percent, a precipitated silica filler, having a surface treated with hexamethyldisilazane and an average particle size of about 0.3 micrometers and a surface area of about 125 m.sup.2 /g, a precipitated calcium carbonate treated with stearic acid having a surface area of about 22 m.sup.2 /g, and a ground calcium carbonate having an average particle size of 2-3 micrometers;
• and the second part comprising a tetra(n-propyl) ortho silicate, a trimethylsiloxy terminated polydimethylsiloxane having a viscosity of 1 Pa.s, a fumed silica filler, a dibutyltin diacetate, glacial acetic acid, and mineral spirits;
• at a constant rate through a shaping die to form a shaped extrusion having a cross-sectional area that is substantially uniform throughout the length of the shaped extrusion;
• (B) feeding the shaped extrusion in a continuous flow into an aqueous curing bath maintained at a temperature of at least 20.degree. C. and having a density substantially the same as or slightly greater than the density of the shaped extrusion;
• (C) moving the shaped extrusion through the aqueous curing bath as the shaped extrusion cures into a cured article having a cross-sectional area that is substantially uniform throughout the length of the cured article;
• and
• (D) recovering the cured article from the aqueous curing bath.

A process for forming a cured article of consistent shape from a hydrolyzable siloxane composition of a liquid or paste viscosity, comprising:

• (A) extruding a non-self-supporting composition which is maintained at a temperature greater than 10.degree. C. and which comprises a hydroxyl-endblocked polydiorganosiloxane, a polyalkoxy-silicon crosslinker, a hexamethyldisilazane treated silica, a stearated calcium carbonate, and a curing catalyst, at a constant rate through a shaping die to form a shaped extrusion having a cross-sectional area that is substantially uniform throughout the length of the shaped extrusion;
• (B) feeding the shaped extrusion in a continuous flow into a circulating aqueous curing bath maintained at a temperature of at least 20.degree. C. and having a density substantially the same as or slightly greater than the density of the shaped extrusion;
• (C) moving the shaped extrusion through the aqueous curing bath as the shaped extrusion cures into a cured article having a cross-sectional area that is substantially uniform throughout the length of the cured article;
• and
• (D) recovering the cured article from the aqueous curing bath.