Coated granular fertilizer and method for producing same

Abstract

The invention relates to a coated granular fertilizer having a film covering fertilizer granules. This film comprises a polyurethane resin prepared by a method comprising the steps of (a) reacting an aromatic polyisocyanate with a first polyol component (i.e., castor oil or a castor oil derivative), thereby to obtain a prepolymer having terminal isocyanate groups in the molecule; and (b) reacting the prepolymer with a second polyol component (i.e., castor oil or a castor oil derivative) and a third polyol component which is an amine having at least two hydroxyl groups in the molecule, thereby to cure the prepolymer and thus to prepare the polyurethane resin. The invention relates to another coated granular fertilizer having a film covering fertilizer granules. This film comprises a urethane resin and aqueous-fluid-absorbing particles having a particle diameter of from 1 to 200 μm. This urethane resin may be the above polyurethane resin. This coated granular fertilizer can be produced by a method comprising the steps of (a) applying an aromatic polyisocyanate, a polyol component (i.e., castor oil or a castor oil derivative), an amine, and the aqueous-fluid-absorbing particles, at the same time or separately in no special order, while the fertilizer granules are kept fluidized or rolled, thereby to form a precursory film on the fertilizer granules; and (b) curing the precursory film into the film. Each coated granular fertilizer is substantially superior in regulation of the release of plant nutrient elements therefrom.

Dependencies are inferred from the claim text.