Effect of double and triple layers coating technique on controlled release properties of waterbased resin coating material

To improve the controlled release properties of water medium resin as coating material (WMRM), multi-layer coating technique that based on a bottom spraying fluid-bed coater was used to manufacture double and triple layers coating urea that were made from the WMRM as a coating layer and the additive lipid soluble resin (LSR) as the isolation layer. The double layers consisted of a coating layer as the inner one and an isolation layer as the outer one, the triple layers consisted of two isolation layers and a coating layer between them. Further more, the effects of double and triple layers coating technique on controlled release properties of coating layer with the WMRM were evaluated via the nutrient release characteristics from the multi-layer coating ureas. The results as follows, the nutrient longevity of the coated ureas by the triple layers coating technique could be extended as five times as that by double layers coating technique. By the triple layers coating technique, the thickness of the inner isolation LSR layer from 5 to 15 g/m2 could affect the longevity hardly. With the same technique, the triple layer coating urea had longevity as long as about 260 days with 50 g/m2 WMRM as the coating layer and 10 g/m2 LSR as the outer isolation layer. However, nutrient release patterns of triple layers coating ureas were affected by thickness of the inner isolation layer. When the outer isolation material applied was 10 g/m2 and more, the nutrient release curve was transformed from parabolic to sigmoid. It concluded that the triple layers coating technique which with the WMRM as the coating layer and the LSR as the isolation layer could improve the controlled release properties of the WMRM significantly. The appropriate amount of the inner isolation LSR layer is among 5 and 10 g/m2.