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ASK Chemicals offers a 2K PU resin system for the production of polymer coated controlled release fertilizers based on all kind of granules.
The patented coating system consists of two components, a polyol and an isocyanate. The polyol is a modified solvent-free phenolic resin formulation containing more than 60 % renewable raw materials. The isocyanate component is a modified isocyanate formulation including a bench life extender to achieve a controllable reaction in the mixing equipment. Both components are solvent-free and contain only reactive ingredients to prevent leach out of coating chemicals into the soil.
The fertilizer granules are coated at ambient to moderate temperatures in a drum mixer. Therefore, also granules with lower melting points like urea, can be coated with this technology. The resin system shows a homogeneous distribution without any defects on all kind of granules. The curing reaction takes place by a polyaddition reaction and is catalyzed by addition of a gaseous or liquid amine to the resin system. Using a liquid amine with high flash points prevents the use of ATEX equipment. A spray curing process secures optimal catalyst distribution. The coatings process is very fast and efficient, the typical curing time for one layer is below two minutes to be tack free.
The ASKOCOAT system is especially designed for fertilizer coatings to achieve excellent adjustable release properties. Water is able to slowly penetrate through the coating layers into the granule and dissolves the nutrients of the fertilizer granule. The nutrients are released due to osmosis. The release time of nutrients is controlled by coating thickness and temperature. Thinner coatings f. ex. and warmer temperatures result in faster release. The release time can be adjusted from 2 to 24 months depending on the quantity of coating material. The patented phenolic PU coating increases the stability and elasticity of the coated fertilizer and prevents salt stress caused by uncontrolled release of nutrients.