Method for producing a powder comprising at least one polymer and such a type of powder

A method for producing a powder comprising at least one polymer for use in a method for the additive manufacture of a three-dimensional object, comprising:

• mechanically treating the powder in a mixer with at least one rotating mixing blade;
• conducting at least one heat treatment, wherein the at least one heat treatment includes a TB heat treatment on the powder that heats the powder to a temperature TB and wherein the TB heat treatment is the only heat treatment that heats the powder to a temperature TB;
• wherein TB is at least 30° C. and wherein TB is below a melting point Tm of the polymer (determined according to DIN EN ISO 11357) if the polymer is a semi-crystalline polymer;
• or
• wherein TB is at least 30° C. and wherein TB is at most 50° C. above a glass transition temperature Tg of the polymer (determined according to DIN EN ISO 11357) if the polymer is a melt-amorphous polymer;
• wherein the TB heat treatment consists of a single, continuous heating phase and a holding phase,
• wherein the single, continuous heating phase is defined by raising a heating temperature, starting from an initial temperature below TB, which exists when starting mechanically treating the powder, until the heating temperature reaches the temperature TB;
• and
• wherein the holding phase is defined by maintaining the heating temperature in a range of TB±10° C. for a holding time;
• and
• cooling to a temperature of at most 35° C. after the TB heat treatment and before the powder is used in an additive manufacturing method,
• wherein TB is defined by one or more of the following conditions or methods (i) to (vii):
• (i) TB is above a heat deflection temperature HDT-A of the polymer (determined according to DIN EN ISO 75, measured in a reference measurement on a test specimen consisting only of the polymer, i.e. without any additives);
• (ii) TB is above the heat deflection temperature HDT-A of the polymer (determined according to DIN EN ISO 75, measured in a reference measurement on a test specimen consisting only of the polymer, i.e. without any additives), wherein the polymer is a semi-crystalline polymer;
• (iii) TB is at most 100° C. below the glass transition temperature Tg of the polymer (determined according to DIN EN ISO 11357);
• (iv) TB is at most 100° C. below the glass transition temperature Tg of the polymer (determined according to DIN EN ISO 11357), wherein the polymer is a semi-crystalline polymer;
• (v) TB is at most 100° C. below the glass transition temperature Tg of the polymer (determined according to DIN EN ISO 11357), wherein the polymer is a melt-amorphous polymer;
• (vi) for a polymer powder to be used, TB is at most a temperature Tmax determined in a temperature-current consumption measurement of the same polymer in a mixer with a mixing blade rotation in the range of 20 to 50 m/s during the heating process, wherein Tmax is determined in the temperature-current consumption measurement by one or both methods (a) or (b) as follows:
• (a) maximum TB is determined by a temperature-current consumption diagram, wherein one data point is recorded every minute, wherein [(gradient/min)/current consumption] considered only in the range Tg−20° C. to Tm is at least greater than 5% and at most 30%;
• or
• (b) maximum TB is determined by a temperature-current consumption diagram, wherein the current consumption of the mixer rises disproportionately strongly within a short time to an increased current consumption value Ix, which fulfils at least one condition selected from the group consisting of the conditions:
• Ix is at least 10% higher than the average value of at least 10 preceding measuring points, recorded at at least one measurement per minute, wherein only current increases in the range Tg−20° C. to Tm are considered;
• and
• Ix is at most 100% higher than the average value of at least 10 preceding measuring points, recorded at at least one measurement per minute, wherein only current increases in the range Tg−20° C. to Tm are considered;
• (vii) TB is at the temperature Tmax±10° C. or below the temperature Tmax at which a bulk density of the powder drops to a value below a bulk density of untreated powder as a result of use of the mixer, wherein the maximum Tmax is determined by a test series with different TB and otherwise the same mixing conditions.