Powder of spherical crosslinkable polyamide particles, preparation process and use with the selective laser sintering technique

A process for the preparation of a powder of particles of crosslinkable polyamide (I) functionalized by crosslinking functions Rt rendering it crosslinkable, characterized in that said crosslinking functions Rt are present at the surface and in the mass of said particles and in that said particles of crosslinkable polyamide (I) have a mean diameter d50 in the range 20 μm to 100 μm and said powder is obtained by the process comprising the following steps:

• a) providing a powder of spherical particles of a polyamide (II), said particles having a mean diameter d50 in the range 20 μm to 100 μm;
• b) providing a crosslinking agent (III) comprising both at least one crosslinking function Rt and also at least one grafting function Rg that is capable of reacting with the amine and/or carboxyl and/or amide functions of the polyamide (II), termed reactive functions Rr;
• c) mixing the powder of spherical particles of polyamide (II) with the crosslinking agent (III) in order to obtain a mixture (II+III);
• d) heating the mixture (II+III) obtained from step c) to a temperature T1 that is in the range from the glass transition temperature of the polyamide (II) Tg(II)+5° C. to the glass transition temperature of the polyamide (II) Tg(II)+70° C. if Tg(II)+70° C.≤to the crystallization temperature of the polyamide (II) Tcryst(II)−35° C., or in the range from Tg(II)+5° C. to the crystallization temperature of the polyamide (II) Tcryst(II)−35° C. if Tg(II)+70° C.>Tcryst(II)−35° C., in order to obtain a powder of spherical particles of polyamide impregnated with crosslinking agent (IV);
• and
• e) heating the polyamide powder impregnated with crosslinking agent (IV) to a temperature T2 that is higher than T1 and lower than the crystallization temperature Tcryst(II) of the polyamide (II), in order to obtain a powder of crosslinkable polyamide (I).