Solid silicones (HTV)
Solid silicones are copolymers of dimethylsiloxanes (main chain) and isolated vinylmethylsiloxanes (functional group). Due to their low intermolecular interaction, they have a soft, pasty consistency. With a viscosity of 10,000 to 50,000 Pa-s, solid silicones are easy to process at room temperature.
In the first step, the silicone is mixed with the crosslinker and other additives (such as stabilizers, color, fillers, etc.) on a roller or in a kneader. The silicone compound obtained in this manner is then cold extruded onto the conductor by means of an extruder and then crosslinked by heat input.
The amount of crosslinker and the proportion of functional (vinyl) groups determines the crosslink density and thus the final properties (such as tensile strength, tear resistance, elongation, hardness, etc.) of the silicone compound.
Peroxides (including halogen-free peroxides) or platinum-catalyzed systems are usually used as crosslinkers. By means of modern extruders or extrusion heads, several silicone layers can be applied to the conductor simultaneously in co-extrusion.