| 摘要 |
The present invention relates to a process for producing polyurethane coated fertilizer granules comprising core granules in a rotating drum, wherein the drum comprises an inlet and an outlet and n application zones arranged along the longitudinal direction of the drum between the inlet and the outlet, n being an integer of at least 2 and wherein each of the application zones is followed by a curing zone. The curing zone after each application zone is arranged to allow an interval of 2-15 minutes, preferably 3-5 minutes, before the application in the successive application zone, wherein the polyol and the isocyanate are applied in the first application zone at a ratio of 0.5-4 wt%, preferably 1 -3 wt% of the core granules. The process comprises the steps of: A) continuously feeding the core granules to the inlet of the rotating drum, thereby providing a flow of the core granules in the direction from the inlet to the outlet, B1 ) applying a polyol and an isocyanate to the core granules in each of the n application zones, the ratio of hydroxyl groups in the polyol to NCO groups in the isocyanate at the end of each of the application zones being in the range from about 0.9 to about 1.3, B2) reacting the polyol and the isocyanate to form a tack-free polyurethane layer in each of the n curing zones and C) continuously collecting the polyurethane coated fertilizer granules from the outlet. |
