Expandable Graphite Mould
During recent years expandable graphite (EG) has been used as a flame retardant for production of graphite foils, sheets, strips, seals, gaskets, sleeves, bearings and formed piece parts. EG is multi-porous with an average pore size of 2-10 nm, allowing easy intercalation with host molecules including monomers and polymers. EG also possesses excellent mechanical properties and thermal stability and is compatible with most processing methods.
When exposed to heat, EG expands up to 600 times its original volume and the expanded carbon surface provides a large area for rapid oxidation. This oxidation removes oxygen from ambient air making the surrounding air almost inert. This inert air distinguishes the intumescent EG from other materials that can form flames and suffocate fires.
The presently known methods of employing expandable graphite for the purpose of producing intumescent mouldings involve heating the graphite in powder form to temperatures above 180deg C in moulds which are permeable to gas and largely closed. However, such a process gives rise to undesirable odours and the mouldings formed are only of low mechanical stability.
A new method of producing expandable graphite mouldings with improved mechanical stability and good resistance to water is proposed. The invention is based on the use of acid metal phosphates which are capable of expanding together with the expandable graphite when heated at above-mentioned expansion temperatures, in particular the ethanolamine salts of acid aluminium phosphates. Unlike the alkalis used previously, these acid metal phosphates do not liberate undesirable odours and have relatively low volatility at temperature above 180deg C.
