LASER SINTERING POWDER WITH IMPROVED RECYCLING PROPERTIES, PROCESS FOR ITS PRODUCTION AND USE OF THE LASER SINTERING POWDER

摘要

The present invention relates to a sinter powder, to a process for laser sintering, and also to moldings produced from this sinter powder. The laser sintering process produces a body in the shape of a block which is composed firstly of the desired components and secondly, usually predominantly, of non- irradiated powder, which remains with the components in this block until the molding is reveale d, or its covering is removed. Depending on the nature of the powder used, the non-irradiated powder can be used in a further forming process (recycling) after sieving and addition of virgin powder. Non-irradiated sinter powder of the prior art has a tendency toward post- condensation under the conditions (temperature, and, where appropriate, residual oxygen content ) prevailing in the forming chamber of the laser sintering machine - and also in particular instances toward uncontrolled cleavage of amino end groups - and the reclaimed powder has markedly increased solution viscosity, and cannot be used, or has only very limited capability for use, in the next forming process. Inventive addition of organic carboxylic acids as regulators permits preparation of a polyamide powder with almost constant solution viscosity, capable of use repeatedly in the laser sintering process without addition of virgin powder.