Process for the preparation of condensation products of melamine

Process for the purification of a melamine condensation product obtained by a process comprising the step of heating a starting material comprising melamine or a melamine salt in the presence of:

• (i) at least one organic or inorganic acid, or
• (ii) at least one ammonia or melamine salt of the acid, or
• (iii) a combination of (i) and (ii),
• under reaction conditions effective for the formation of a melamine condensation product, resulting in a reaction product mixture comprising melamine condensation product and the organic or inorganic acid and/or salts or other residues thereof wherein the purification process comprises the steps of
• a) making a diluted slurry of the reaction product mixture in a solution of a base in water with a pH of at least 9,
• b) keeping the diluted slurry for a period of at least 1 hour,
• c) concentrating the diluted slurry, thereby obtaining a concentrated slurry and an eluent, and
• d) washing the concentrated slurry by diluting the concentrated slurry with aqueous liquid and repeating step c,
• wherein the washing is performed by counterflow washing wherein eluents of downstream concentration steps are used to wash the slurry in upstream concentration steps.