| 摘要 |
<p>An improved method for producing coating agents in powder form by the precipitation process is described. The powdered coating agents have a polyamide base having at least 10 aliphatically combined carbon atoms per carbonamide group, or co-polyamides, or mixtures of homo- and co-polyamides, containing at least 70% of the said components. The method is characterised in that polyamides having a relative viscosity of between 1.4 and 1.8 (measured in a 0.5% m-cresol solution at 25.degree.C) are mixed with at least twice the amount by weight of ethanol, the said mixture being converted by mechanical movement, at temperature of between 130 and 150.degree.C, into a solution, this solution being then adjusted to the precipitation temperature of between 100 and 125.degree.C, with no local undercooling, the solution being then stirred, at low r.p.m., in an inert gas atmosphere in order to prevent boiling, without further addition of heat, in order to produce powders having a grain-size distribution of at least 95% between 40 and 250 .mu.m, or being stirred at higher r.p.m., in order to produce powders having a grain-size distribution of 100% less than 100 .mu.m, until particle-forming comes to an end, the suspension thus formed being finally cooled to at least 70.degree.C and, if necessary, after partial mechanical removal of the ethanol, being then dried, initially at a reduced pressure, at walltemperatures of 100.degree.C at the most, with gentle mechanical motion and, as soon as it is capable of flowing, at wall-temperatures of up to 150.degree.C and with more forceful mechanical motion.</p> |
