Fertilizer coating method

Abstract

To provide a method for coating particles, and in particular to a method for coating fertilizer particles.SOLUTION: The present invention provides a method for coating fertilizer particles with a coating. The method comprises: a step of providing fertilizer particles in a coating unit; one or more steps of applying a coating layer by applying one or more coating components to the fertilizer particles in the coating unit; and a step of at least partially curing or hardening the coating layer, wherein the curing or hardening involves a chemical reaction of the one or more coating components, and discharging the coated fertilizer particles from the coating unit, optionally after a final cure or hardening step, and wherein the coating unit comprises a stationary frame and at least two movable elements.SELECTED DRAWING: None

Description

[Technical Field] 【0001】 The present invention relates to a method for coating particles, in particular fertilizer particles. [Background technology] 【0002】 Many fertilizers are used as granular materials and are water-soluble, such as urea-containing fertilizers. Controlled-release fertilizers can be used to provide sustained release of the fertilizer from the particles. The sustained release can contribute to more efficient use of the fertilizer. Such fertilizers can be produced, for example, by applying a coating to the fertilizer particles. For example, U.S. Patent Application Publication No. 2014 / 0033779 describes a method for coating a substrate in which a substrate material and a coating material are mixed and the coated mixture is cured in a separate reactor. U.S. Patent Application Publication No. '779 also notes that while methods for producing controlled-release fertilizers using a single drum or reactor (i.e., batch processing) are functional and commonly used, they are associated with several issues, such as the risk of creating lumps or balls of coated material. 【0003】 U.S. Pat. No. 5,538,531 describes a method for making controlled release granular fertilizer which involves heating fertilizer granules, agitating the granules to maintain a gentle mixture, adding a polyol, adding a polyisocyanate after the polyol component is uniformly distributed, reacting the components, and adding a wax. 【0004】 Furthermore, existing methods for coating fertilizers are relatively expensive, especially because the coating process adds a separate process step to the production of fertilizer. The coating process typically requires long processing times, large equipment, and high capital and operating costs. While higher prices can be tolerated for specialty coatings and horticulture, low cost is important for large-scale agricultural crops such as corn (maize). Therefore, methods for coating particles, especially fertilizer particles, are desirable, particularly methods for coating fertilizers at competitive prices to produce controlled release fertilizers suitable for efficient fertilization of large-scale commercial crops. [Prior art documents] [Patent documents] 【0005】 [Patent Document 1] US Patent Application Publication No. 2014 / 0033779 [Patent Document 2] U.S. Patent No. 5,538,531 Summary of the Invention [Problem to be solved by the invention] 【0006】 SUMMARY OF THE INVENTION It is an object of the present invention, in one aspect, to provide a coating method that at least partially addresses the above problems and needs. [Means for solving the problem] 【0007】 The present invention provides in a first aspect a method of coating fertilizer particles with a coating, comprising the steps of: a) providing fertilizer granules in a coating unit; b) applying a coating layer (step b), applying one or more coating components to the fertilizer particles in a coating unit to provide coated fertilizer particles comprising a coating layer and the fertilizer particles; and at least partially curing or hardening the coating layer, wherein the curing or hardening involves a chemical reaction of the one or more coating components; applying a coating layer by performing step b) one or more times to provide coated fertilizer particles; c) discharging the coated fertilizer particles from the coating unit, or performing a final curing or hardening of the coated fertilizer particles in the coating unit and then discharging the fertilizer particles from the coating unit, wherein the discharged fertilizer particles comprise the coating, and the coating preferably comprises a water-insoluble polymer; The coating unit comprises a fixed frame and at least two movable elements, the movable elements being independently movable relative to the frame, and the method comprises, at least during step b), moving the at least two movable elements relative to the frame. [Brief explanation of the drawings] 【0008】 [Figure 1] FIG. 1 shows a schematic diagram of an exemplary coating unit that can be used in the method of the present invention. [Figure 2] FIG. 1 shows experimentally obtained urea release rates of fertilizer particles prepared by a method according to the present invention using coating compositions with different reactivity time values. [Figure 3] FIG. 1 shows experimentally obtained urea release time profiles for two fertilizers coated according to the method of the present invention and two fertilizers coated according to a comparative method using a rotary drum coater. DETAILED DESCRIPTION OF THE INVENTION 【0009】 The present invention broadly provides the clever insight of combining a short residence time in a coating unit, in which the particles are constantly moving before being coated, with a coating unit comprising two moving elements and preferably also with a coating composition that has a short cure or hardening time. 【0010】 The present invention provides a method that involves carrying out a chemical reaction of one or more coating components within the coating unit while the particles continue to move to at least partially cure or harden the coating, which advantageously allows for a high throughput and high speed coating process without agglomeration of the fertilizer particles or the formation of solid deposits within the coating unit. 【0011】 The present invention relates to a method for coating fertilizer particles, which may also be referred to as granular fertilizer. The particles before and / or after coating have a particle size of, for example, 0.10 to 20 mm, e.g., 0.5 to 15 mm, or 1.5 to 5 mm. The particles have, for example, a weight-average particle size within this range, or, for example, at least 90% by weight of the particles have a particle size within this range, and the particle size refers, for example, to the minimum size. The particles are, for example, granulated or spheroidized fertilizer, or pelletized, tableted, or compacted fertilizer material. Optionally, the method includes a step of solidifying a liquid fertilizer material into fertilizer particles before coating, for example, using a prill tower, a granulation unit (e.g., with a spouted or fluidized bed), or a pelletizer, particularly when the fertilizer is a urea fertilizer or a urea-containing fertilizer. Preferably, in this solidification step, the melt (e.g., urea melt) is cooled, for example, using cooling air. Preferably, the particles are maintained at a temperature above 50°C or above 60°C between the solidifying and coating steps. 【0012】 The particles before coating comprise (or consist of) a fertilizer material. The fertilizer material may be, for example, a nitrogenous fertilizer material, e.g., containing at least 10% by weight, at least 20% by weight, or at least 30% by weight of nitrogen (based on N atoms). The fertilizer material may contain, for example, urea and / or ammonium salts such as ammonium sulfate and ammonium nitrate, and may contain, for example, less than 10% by weight, or less than 5% by weight, of components other than urea and ammonium salts. Preferably, the fertilizer material is a urea fertilizer containing urea, e.g., at least 50% by weight urea, and preferably having at least 40% by weight N or at least 46% by weight N. The fertilizer material may also contain K (potassium), Ca (calcium), P (phosphorus), and / or S (sulfur) (based on elemental composition), e.g., as sulfates and / or salts of phosphorus, optionally in combination with N, e.g., as urea and / or ammonia. Fertilizer materials are typically water-soluble, and when the fertilizer particles are applied to the land, the fertilizer elements (N, P and S, K, Ca, etc.) are provided to the crop as dissolved species, and optionally Zn and / or other micronutrients are also provided. 【0013】 The method of the present invention relates to coating fertilizer particles with a coating. Thus, the coated particles (obtained after the coating method) comprise fertilizer particles and an outer layer of coating material that partially or completely covers the fertilizer particles. 【0014】 The coating layer provides a controlled release of the fertilizer material, for example, when the fertilizer is applied to land (in soil) and comes into contact with water. The coating layer may also provide a sustained release of the fertilizer material. In such embodiments, the fertilizer material is released from the particles, for example, by hydrolysis, biodegradation, or limited solubility, or a combination thereof. Released fertilizer material refers to the release of nutrients available to plants. 【0015】 The coating preferably comprises a polymer, more preferably a water-insoluble polymer. The polymer has a solubility of less than 0.10 g / L in deionized water at 100 kPa and 20°C. The polymer is insoluble in deionized water at 20°C, as determined by the method described in D. Braun et al., "Practical Macromolecular Organic Chemistry," CRC Press, 1984, p. 73, in which 30 to 50 mg of an ultrafine particle polymer sample is placed in a small test tube containing 1 mL of liquid and allowed to stand for several hours. 【0016】 The coating material may be, for example, water impermeable or semi-permeable. Preferably, the coating material protects the fertilizer inside the coating from soil processes until it is released. 【0017】 In some embodiments, water and solutes can penetrate the coating by diffusion. The time required for diffusion can provide a desired release rate of fertilizer nutrients from the coated particles into the soil. In this way, the coating can provide controlled release. 【0018】 In some embodiments, the coating material is semi-permeable (e.g., permeable to water but impermeable to fertilizer materials such as urea) and, upon application to land, water will infiltrate through the coating due to osmosis, causing swelling of the core of the fertilizer material. This can result in cracking of the coating and / or migration of the fertilizer material through the pores of the coating. In this manner, sustained and / or delayed release of the coating material can be achieved. 【0019】 The coating material may, for example, be at least 0.0010 wt. % in total, e.g., 0.10 wt. % to 10 wt. % based on the weight of the total particle, and / or, for example, 0.2 to 5 wt. %, or 0.3 to 3.0 wt. %, or 0.3 to 1.5 wt. %, or 0.5 to 1.2 wt. % per coating layer, e.g., 1.0 to 3 wt. % per coating layer. The coating thickness may, for example, be in the range of 1.0 μm to 50 μm in total and / or per coating layer, although other thicknesses are possible. 【0020】 The coating material present in the coated particles is, for example, a polymer, and the coating composition applied to the fertilizer particles during the coating process is, for example, a resin. 【0021】 Preferably, the coating of the particles emitted from the coating unit comprises a polymer. Preferably, the polymer is crosslinked. Preferably, the polymer is thermoset or thermoplastic. 【0022】 The method involves providing fertilizer particles in a coating unit, e.g., the particles are fed into a coating unit, particularly a rotary vessel, configured to receive the fertilizer particles before coating. The coating unit may include, for example, a vessel for receiving and holding the fertilizer particles. Such a vessel preferably has a wall and an interior space capable of receiving the fertilizer particles. 【0023】 The method may include screening the fertilizer particles to a desired size range before introducing the fertilizer particles into the coating unit. 【0024】 The method may further comprise the step of preheating the fertilizer particles before they are introduced into the coating unit, for example to a temperature of at least 30°C, at least 40°C, at least 50°C or at least 60°C, and / or to a temperature at least 5°C, at least 10°C or at least 20°C above ambient temperature, typically to a temperature below 100°C or below 80°C. 【0025】 The method includes the step of applying a coating layer, which can be performed one or more times to provide coated fertilizer particles having one or more coating layers. 【0026】 The step of applying a coating layer involves providing fertilizer particles having a coating layer. The step includes applying one or more coating components to the fertilizer particles while the particles are in a coating unit. Additionally, during such a step of applying a coating layer, other compounds, such as a solvent, can be applied to the fertilizer particles, although in a preferred embodiment, no solvent is used. The method can also include an additional step of applying an additional coating layer to the particles, such as a step of applying a wax layer. In a particular step of applying a coating layer, the coating components and optional additional compounds can be applied, for example, simultaneously or subsequently. For example, at least two coating components having different compositions are applied subsequently, for example, stepwise. Each coating component can also be a mixture of compounds. The coating components are typically applied as liquids (which can include, for example, emulsions, solutions, and dispersions, as well as polymer melts), for example, by injection, such as by spraying the liquid. In this way, fertilizer particles are provided that include a coating layer and a fertilizer particle as a core. Thus, the applied one or more coating components are present as (additional) layers on the fertilizer particles. 【0027】 In preferred embodiments, at least one or all of the coating components when applied have a viscosity of less than 2000 mPa·s or less than 1000 mPa·s at 25° C., typically greater than 100 mPa·s at 25° C. Viscosity is measured, for example, according to ISO 3219:1993. 【0028】 Preferably, one or more coating components are added to a bed of fertilizer particles, which is provided by the movement of the moving elements of the coating unit, particularly by a rolling action or by particle-to-particle contact. Preferably, the bed is a suspended particle bed, and the fertilizer particles are suspended by the movement of the moving elements. The coating unit is preferably operated so that all materials within the interior space are kept in constant motion. Preferably, the coating unit is operated so that the airborne particles move continuously in multiple directions. In some embodiments, the coating process is carried out in an atmosphere other than air, e.g., an inert atmosphere such as N2. For example, the coating unit is operated so that at least some of the particles are "gasborne" particles (e.g., airborne particles), and these particles typically move continuously in multiple directions. This can help overcome the effects of gravity, negate particle size, shape, and density limitations, and achieve homogeneous mixing of the coating components with the particles in a short mixing cycle. 【0029】 The fertilizer particles are introduced into the vessel in an amount of more than 10%, or more than 20%, or more than 40%, or more than 60%, and / or less than 95%, or less than 90%, or less than 80%, for example, 60-90%, preferably 75-90%, based on the bulk density of the uncoated fertilizer particle material, all relative to the volume of the interior space of the vessel. A volume fraction based on bulk density means that the bulk bed of uncoated particles (including voids within the bed) occupies that volume fraction of the interior space. For example, for urea particles or urea-containing particles, a density of 720-820 kg / m is used. 3 , e.g., 770 kg / m 3A bulk density of 0.01 to 0.01 can be used. The packing fraction based on the true density of the fertilizer material (uncoated) is, for example, more than 10%, or more than 20%, or more than 30%, and / or less than 60%, or less than 50% of the internal space volume. This packing fraction can contribute to the formation of a floating bed and good distribution of the coating components during step b). 【0030】 Preferably, the coating composition is solvent-free, e.g., comprising less than 5 wt. % water, e.g., less than 1.0 wt. % water, and less than 5 wt. % or less than 1.0 wt. % organic solvent, e.g., an organic solvent having a boiling point less than 120°C. Preferably, less than 1.0 wt. % water and / or less than 1.0 wt. % organic solvent is applied in the entire process, based on the weight of the uncoated fertilizer particles. Water is preferably avoided because many fertilizers are water-soluble. Organic solvents are preferably avoided to avoid emissions risks and to comply with emissions standards and other regulations. 【0031】 Preferably, the coating components comprise less than 40% by weight, or less than 20% by weight, or less than 10% by weight of the components other than reactants in the chemical reaction carried out during step b). Preferably, each coating component comprises more than 50% by weight, or more than 80% by weight, of the reactants in the chemical reaction carried out for curing or hardening. Preferably, each coating component comprises less than 10% by weight of the compounds that are not included in the coated fertilizer particles when discharged. 【0032】 In embodiments in which one or more coating components comprises or is a polymer, the polymeric coating components are preferably applied as a liquid, such as a polymer melt, at a temperature sufficiently above the glass transition temperature of the polymer so that the polymer has a viscosity low enough to allow processing. 【0033】 The method further involves at least partially curing or hardening the applied coating component or components, which may be carried out in a coating unit, for example, to ensure that the final coating comprises a preferred water-insoluble coating. 【0034】 Curing or hardening involves a chemical reaction of one or more coating components. This chemical reaction occurs within the coating unit, more specifically, while at least one of the moving elements is moving. The chemical reaction results, for example, in an increase in the viscosity of the coating layer. In some embodiments, the chemical reaction involves the formation of a compound having a higher molecular weight than the reactants. The chemical reaction involves, for example, polymerization and / or crosslinking of a polymer. 【0035】 In the case of partial curing or hardening in step b), a final curing or hardening is subsequently carried out before and / or after the discharge of the coated fertilizer particles from the coating unit, for example in the coating unit used for step b). 【0036】 Hardening and curing can involve the solidification of one or more liquid coating components added to the fertilizer particles into a solid coating material through a chemical reaction of one or more coating components. In the case of curing, the chemical reaction involves, for example, a cross-linking reaction to obtain a thermoset polymer. In the case of hardening, the chemical reaction typically does not involve cross-linking; the chemical reaction typically produces a thermoplastic polymer. In embodiments where only one coating component is applied, this component can react with itself, for example, in a polymerization reaction. 【0037】 From a reactive curing or hardening perspective, one or more coating components include an initiator and / or catalyst, such as, for example, a polymerization initiator (e.g., a free radical initiator or a cationic initiator) and a polymerization catalyst. 【0038】 The coated fertilizer particles and / or coating material may contain additional components, such as one or more selected from the group consisting of wetting agents, surfactants, biocides, herbicides, insecticides, fungicides, antistatic agents, and micronutrients, such as Fe, Mn, Zn, Cu, Mo, Ni, Cl, Mg, and B. 【0039】 Such additional components may be applied, for example, during one or more steps of applying the coating layer, e.g., as part of one or more coating components or as additional components added during step b) and / or step c). 【0040】 The coating may comprise a wax, for example, applied as a layer between the coating layers cured or hardened during step b) and / or as a final layer. The wax may be, for example, an olefin wax, more preferably an α-olefin wax, such as one having at least 20 or at least 30 carbon atoms, or a hydrocarbon (such as an alkane) having, for example, 20 to 40 carbon atoms. The wax may be, for example, a paraffin wax, a petrolatum wax, or a polyamide wax, and / or may be, for example, a microcrystalline wax. 【0041】 The method further includes discharging the coated fertilizer particles from the coating unit, optionally after a final curing or hardening step. The final curing step may include, for example, evaporation of unreacted monomers, or cooling, and / or a final hardening chemical reaction step. The optional final curing step may include further reacting coating components present in the applied coating layer. The final curing step may involve crosslinking of the polymeric coating material. The discharged fertilizer particles include the coating and the coating material. The optional final hardening step is applied to bring the particles to a dischargeable state, particularly a non-sticky state, and to provide sufficient mechanical / crushing strength for handling, packaging, and storage. 【0042】 The method optionally includes one or more steps after release of the coated fertilizer particles, such as cooling, packaging, weighing, and / or storing. The cooling step may use, for example, chilled air. The coated fertilizer particles may be suspended in, for example, chilled air. The packaging step may include, for example, packaging the fertilizer particles in bags or containers. The weighing step may involve dividing the successive coated fertilizer particles into measured-amount batches, which may be transported, for example, to a vehicle or ship, with or without packaging. 【0043】 The coating method may be carried out, for example, as a batch process or a continuous process. The method may be, for example, a batch process resulting in multiple coating layers, where two or more steps of applying the coating layers are carried out in the same coating unit (e.g., the same vessel). Also, with respect to a batch process, one or more components may be added continuously, for example, over at least 10 seconds or at least 30 seconds. In an exemplary process, two or more batch coating units are operated in parallel, with the parallel coating units performing different steps at each time. In such an embodiment, the method is carried out in a so-called batch continuous mode or semi-continuous mode. For example, the method may involve loading fertilizer particles into a first coating unit, while a second coating unit performs a different step of the method than loading. In this manner, two or more coating units may be used in parallel, with a continuous supply of fertilizer particles being processed at any one time by at least one of the parallel coating units receiving uncoated fertilizer particles. In such an embodiment, the method may involve, for example, applying the total number of coating layers to be applied to the fertilizer particles (e.g., one, two, three, or more layers) in each of the parallel coating units. 【0044】 In exemplary embodiments in which the method is carried out as a continuous process, two or more coating layers are applied to different coating units described herein arranged in series, each coating unit having, for example, a container and a rotor, and the method includes transporting fertilizer particles from a first coating unit for applying a first coating layer to a second coating unit for applying a second coating layer. Such transport can be carried out, for example, using a moving belt, or, for example, the coating units can be arranged one above the other and transport carried out by gravity. A continuous process can involve continuously feeding fertilizer particles to a first coating unit, transporting the fertilizer particles with the coating layer from the first coating unit to a downstream second coating unit, and recovering the fertilizer particles with the additional coating layer from the second coating unit. In some further embodiments, two or more coating units as described are used in series, different coating layers are applied in stages to different coating units, and transporting involves transporting a batch of coated fertilizer particles from at least the first coating unit to the downstream second coating unit. 【0045】 The coating unit comprises a stationary frame and at least two movable elements, including first and second movable elements. The coating unit is capable of receiving fertilizer particles before they are (further) coated. The movable elements are configured to move the fertilizer particles during the coating process. The first and second movable elements are each movable relative to the frame, typically in an independent manner relative to the frame. The method includes moving the at least two movable elements relative to the frame at least during step b), preferably while in contact with the fertilizer particles. Preferably, the first and second movable elements also move relative to each other. The first and second movable elements move independently, for example, independently of each other and by rotation and / or reciprocation. 【0046】 The movement of the moving elements can result in movement of the fertilizer particles during step b), which can improve mixing of the added one or more coating components with each other and with the fertilizer particles. Operating the moving elements can also avoid or prevent the formation of agglomerates during the coating process, such as clumps of coating material and fertilizer particles. 【0047】 The stationary frame is used to mount a moving element, for example an actuator such as a motor, and may include a static case. 【0048】 Preferably, the first movable element includes or is a container. The container has a wall and an internal space. The wall has, for example, a bottom and one or more sides. The wall can have, for example, a closable outlet opening at the bottom for discharging the coated fertilizer particles. The container is closed at the top by, for example, a cover plate that is part of the coating unit. The cover plate can have an inlet opening for the fertilizer particles, for example, provided with one or more spray nozzles for one or more coating components. The inlet opening can also be provided by an open pipe. The open pipe is used, for example, to drip the coating components onto the particle bed. The internal space is used in a method for containing particles, for example, by receiving and holding the fertilizer particles within the free space of the internal space. During this method, the container, for example, rotates and / or reciprocates, and involves a rotational or reciprocating movement (e.g., horizontally or vertically). The method can, for example, involve spinning the container around a rotation axis while the container, in particular, holds the fertilizer particles in the internal space. Preferably, at least step b) is performed during this spinning. The container is spun, for example, to cause the fertilizer particles to tumble during step b). Preferably, the particles are kept in continuous movement within the container until they are discharged, such as by rotating the container. 【0049】 The container may be, for example, cylindrical, e.g., a pan. The container may have, for example, a circular cross section in a plane perpendicular to the axis of rotation. The container may be connected to a first actuator, e.g., a motor. The first actuator may be, for example, mounted within a frame and configured for movement of the container relative to the frame. 【0050】 The coating unit may, for example, include a scraper that is fixed relative to the frame, or can remain fixed relative to the frame, for example, while the container is spinning. The scraper can be used to scrape solid material from the wall of the rotating container. The scraper can also agitate particles during operation. The scraper is positioned near the wall and / or bottom of the container (e.g., at a gap of 1 to 10 mm, such as 1 to 5 mm), preferably above the preferred slope of the container. The scraper is movable relative to the wall of the container. In a preferred embodiment, the container has a bottom and side walls, and the coating unit further includes a scraper, which is fixed relative to the frame at least during step b), and which is positioned to scrape material from the side walls and / or bottom of the container. 【0051】 In preferred embodiments, the second movable element is or comprises a stirring member. The stirring member is disposed in the interior space of the vessel and is configured, for example, to rotate and / or reciprocate within the interior space. The method preferably includes operating the stirring member simultaneously with spinning the vessel during at least step b), more preferably continuously during step b). In this manner, the stirring member contacts the fertilizer particles during step b) when the particles are provided with one or more coating components. The stirring member is, for example, a mixing tool. The movement of the stirring member can help prevent mixing of the particles and / or the formation of agglomerates. In some embodiments, the stirring member is arranged, for example, to keep most (e.g., more than 30% by number) or most of the particles suspended in air (without contacting the vessel) at any given time during step b). Individual particles bounce, for example, between the vessel wall and the stirring member during step b). 【0052】 The agitating member is connected to an actuator, e.g., a second actuator provided within the frame, for movement of the agitating member relative to the frame, which movement may be rotational. The speed and movement of the agitating member may preferably be controlled separately from the speed and movement of the vessel. 【0053】 More preferably, the stirring member is a rotor. The rotor comprises, for example, a shaft and one or more blades. The blades can be provided as paddles. The blades or paddles are preferably evenly spaced angularly around the shaft. The method can, for example, include spinning the container during at least step b) while simultaneously rotating the rotor around its rotation axis. One or more rotors can be provided for one container. The rotor preferably rotates around a shaft. The rotor's rotation axis is, for example, substantially parallel (including parallel) to the container's rotation axis. The rotor's rotation axis has, for example, an included angle of less than 30°, less than 20°, or less than 5°, e.g., 0°, with respect to the container's rotation axis. The shaft can extend through a hole in the container's cover plate. For example, the rotor is mounted above the container in a frame and secured within the container. 【0054】 The vessel and rotor can rotate (at any given time) in the same or opposite rotational directions, particularly if the shaft and axis of rotation are substantially parallel. Opposite rotation is preferred. For example, when viewed from above relative to gravity, the vessel may rotate in a clockwise direction and the rotor in a counterclockwise direction, or vice versa. 【0055】 The vessel is rotated, for example, at a speed of at least 1 rpm (revolutions per minute), typically less than 500 rpm, preferably 5 to 100 rpm, for example, 10 to 60 rpm. The rotor is rotated, for example, at a speed of at least 1 rpm (revolutions per minute), typically less than 500 rpm, preferably 5 to 100 rpm, for example, 10 to 60 rpm. The tip speed of the vessel is, for example, 0.10 to 1 m / s, preferably 0.2 to 2.0 m / s or 0.5 to 2.0 m / s. The tip speed of the rotor is, for example, 0.2 to 10 m / s, preferably 0.5 to 5.0 m / s or 1.0 to 2.5 m / s. The tip speed of the rotor is preferably faster than the tip speed of the vessel. These preferred speeds apply particularly to step b). 【0056】 The rotor's rotation axis is preferably spaced apart from the container's rotation axis (at least in a plane perpendicular to the container's rotation axis), thereby eccentrically mounting the rotor within the container's interior space; in particular embodiments, the rotor's rotation axis is, for example, substantially parallel (including parallel) to the container's rotation axis. The spacing is, for example, at least 2% or at least 5% of the diameter of the container's interior space within a plane perpendicular to the container's rotation axis. In some embodiments, a single container can optionally be provided with multiple rotors. The rotor axes of the multiple rotors are, for example, at the same or different radial distances from the container's rotation axis. 【0057】 In a preferred embodiment, the rotor comprises a shaft and one or more blades. The shaft has a first longitudinal end and a second longitudinal end, the first end being disposed within the interior space of the vessel. The blades are also disposed within the interior space. The second end is connected to an actuator, e.g., a second actuator, e.g., a second motor. The blades are connected to the shaft and extend from the shaft within the interior space of the vessel in a direction perpendicular to the entire length of the shaft. For example, the blades have a length perpendicular to the shaft of at least 2% or at least 5% of the radius of the vessel in a cross section perpendicular to the vessel's rotation axis. 【0058】 Preferably, the rotation axis of the container is inclined relative to the vertical direction, the vertical direction being defined relative to gravity. Preferably, the rotation axis has an angle of at least 5° or at least 10°, typically less than 30°, relative to the vertical direction. The rotation axis may also be perpendicular to gravity. A vertical or slightly inclined orientation can result in a more homogeneous distribution of particles in the container (substantially angularly symmetric about the rotation axis) compared to an embodiment in which the rotation axis is horizontal or nearly horizontal. In the case of an inclined rotation axis, the frame comprises a casing in which the container is placed on a support element such that the rotating container is inclined relative to a horizontal plane parallel to the bottom of the support element. Preferably, the container has a bottom wall provided by a flat plate, e.g., a cylindrical plate. Preferably, the bottom wall is mounted in the frame at an angle of at least 5° or at least 10° relative to the horizontal plane. For example, the cylindrical bottom wall can have a lowest point when stationary (not rotating). An outlet duct for discharging the coated fertilizer particles is provided, for example, at the lowest point or, for example, in the center of the bottom wall. Inclined rotation also allows for better mixing of the fertilizer and one or more added coating ingredients. 【0059】 In some embodiments, the coating unit comprises multiple coating devices arranged in series or in parallel, each coating device comprising a container and at least one rotor. For example, the coating unit comprises multiple coating devices arranged in series and connected to a transport line (such as a moving belt or duct) for the coated fertilizer particles, each coating device having one container. Each container has, for example, an inlet and an outlet for the (coated) fertilizer particles. Such a coating unit can be used, for example, in a method in which step b) is performed two or more times. Each coating layer is applied, for example, in a different coating device (and in a different container), and in each container, for example, one or less coating layers are applied. The fertilizer particles are fed to the most upstream coating device and discharged from the most downstream coating device. The last coating device is used, for example, to perform final curing rather than apply a coating layer. In another embodiment, the coating system is used with multiple coating units in parallel and with a common cooling stage downstream of the coating units. 【0060】 According to the invention, the coating unit is, for example, an Eirich mixer, such as an Eirich Intensive Mixer Type R, or a plurality of such mixers, for example arranged in parallel or in series. According to the invention, the coating unit is, for example, a mixing device as described in U.S. Patent Application Publication No. 4,854,715 or as described in U.S. Patent Application Publication No. 9,295,109. 【0061】 The coating unit may be, for example, a horizontal mixing system available from Loedige, or, for example, an Eirich Plow Blender. The coating unit is, for example, a mixing device with a horizontal cylindrical tank and a solid horizontal shaft, on which a wedge-shaped plow or angled paddle is attached, such as an Eirich Plow Blender. 【0062】 In a preferred embodiment, in step b), the coating layer is applied in an amount of 0.10 to 6.0 wt %, more preferably 0.50 to 4.0 wt %, and even more preferably 0.5 to 1.5 wt %, based on the weight of the uncoated fertilizer particles before coating. When step b) is performed two or more times, for example, to obtain coating layers with different compositions, these amounts and times refer to a single instance of step b). For example, the total coating is 1.0 to 25 wt %, or 1.0 to 15 wt %, or for example 1.5 to 10 wt %, preferably 1.5 to 7.5 wt %, based on the weight of the uncoated fertilizer particles before coating. 【0063】 Preferably, step b) is carried out (and completed) in 10 to 600 seconds, preferably 30 to 240 seconds, or 10 to 120 seconds, or 30 to 120 seconds, or 10 to 60 seconds, or 10 to 30 seconds, or 30 to 90 seconds, particularly for such amounts of coating material. In some embodiments, the coating components are added to the container in 0.5 to 30 seconds, or 1 to 10 seconds, or 1 to 5 seconds, preferably the entire amount of such coating components, preferably each coating component, is added in such a period. In some embodiments, the components are distributed onto (i.e., mixed with) the fertilizer particles in 10 to 45 seconds, or 10 to 30 seconds. Such fast mixing times are achieved, for example, by the movement of the container and rotor, if used. 【0064】 When step b) is performed two or more times, for example, to obtain coating layers with different compositions, these times refer to a single instance of step b). Preferably, the final curing of step c), if performed, is performed (and completed) in 60 seconds to 15 minutes, more preferably 2 to 10 minutes. Preferably, step b) involves applying two or more coating components to the fertilizer particles in succession, stepwise fashion, while both the container and the rotor are rotating. Preferably, the coating component added first to the particles has a higher molecular weight (e.g., number average molecular weight) and / or a higher viscosity than the second coating component. Preferably, the first (initial) coating component is added to the particles and mixed for 2 to 120 seconds, such as 10 to 60 seconds, before the second coating component is added. Preferably, the first coating component is mixed to homogeneously distribute the coating component on the particles at the end of the mixing period and before the second coating component is added. Preferably, both coating components are injected as liquids (which may include dripping and spraying), preferably into a bed of suspended particles. In a preferred embodiment, the bed of suspended particles includes a zone where the particles are moving fastest (e.g., near the rotor) and where the coating components are added. This allows for a fast and uniform distribution of the coating components on the particles. In some embodiments, the first two coating components added are reactive with each other. After one or more reactive coating components are applied, the method can involve allowing the coating components to react with each other while the particles continue to move, for example, for 10 to 300 seconds, such as 10 to 120 seconds. An advantage of the present invention is that this reaction carried out in the coating unit can provide curing or hardening of the particles without agglomeration of the coated particles. 【0065】 It has been found that carrying out the reaction in a coating unit, preferably in a rotating vessel equipped with a rotor, provides rapid and complete distribution of the coating components. The distribution also provides complete encapsulation of the fertilizer particles with the coating layer. Rapid distribution also allows the use of coating components at a faster reaction rate. At the same time, a faster reaction rate is important for achieving high-quality coatings in such coating units. In particular, both too fast and too slow a reaction rate can result in too fast a release rate of nutrients from the coated fertilizer particles. Furthermore, it has been found that the formation of agglomerates in the coating unit is avoided by the movement of moving elements (e.g., vessel and rotor). 【0066】 After such a reaction time, one or more additional coating components can be added, such as wax, preferably liquid wax, which is injected into the fertilizer bed. Preferably, wax is applied between coating layers. These steps are optionally repeated one or more times in the same vessel or in additional vessels in series to obtain multiple coating layers, optionally followed by a final curing step. The final curing step is carried out (and completed) for, for example, 60 seconds to 15 minutes, e.g., 2 to 10 minutes, preferably 2 to 5 minutes, to ensure complete hardening or curing of the coating layers. Optionally, a final additional coating layer, such as a wax layer, is applied. The final curing can be carried out in the same rotating vessel or in a different part of the coating unit. The final curing is typically stopped by discharging the coated fertilizer particles. 【0067】 Preferably, steps a) and b) are carried out at a temperature of at least 10°C, 30°C, at least 40°C, at least 50°C, at least 55°C, or at least 60°C, typically less than 120°C or less than 80°C, e.g., 40-120°C or 50-100°C, more preferably 55-80°C. Preferably, the fertilizer particles are maintained at such a temperature during their entire residence time in the coating unit. Preferably, the particles are at least 50°C or at least 60°C when discharged from the coating unit. The method may involve cooling the discharged particles from a temperature of at least 50°C or at least 60°C to a lower temperature, e.g., less than 30°C. In some embodiments, the method includes a preheating step of the solid fertilizer particles. In some other embodiments, the method involves obtaining fertilizer particles (e.g., formed during granulation or prilling) formed by solidification at such a temperature and transporting the urea particles from the solidification unit to the coating unit at such a temperature (e.g., above 50°C). Maintaining the particles in the coating unit at temperatures above 50°C or above 60°C, especially throughout the residence time, can contribute to faster reactive curing or reactive hardening of the coating components, for example, when a polyurethane coating is used. Other coating components may already react sufficiently quickly at lower temperatures, such as 10-50°C. Furthermore, maintaining the particles below 80°C, or even below 60°C or below 50°C, can be beneficial when the coating contains additional components that are prone to decomposition or undesirable side reactions at elevated temperatures. The coating unit preferably operates at a pressure of 0.010 to 10 bar absolute, for example, below 0.5-2.0 or 0.5-1.0 bar absolute (slight vacuum). 【0068】 In a preferred embodiment, the coating is a polyurethane coating. Preferably, the coating components include a polyisocyanate and a polyol. Preferably, the polyisocyanate has two or more isocyanate groups per molecule. The polyisocyanate may be, for example, aliphatic or aromatic, preferably aromatic. The polyisocyanate may be, for example, a diisocyanate having exactly two isocyanate groups. A particularly useful polyisocyanate is methylene diphenyl diisocyanate (MDI), such as 4,4'MDI; another example is toluene diisocyanate (TDI). Aromatic polyisocyanates are used, for example, as blends of polymeric isomers and diisomers of isocyanates. 【0069】 The polyol has at least two hydroxyl groups per molecule, preferably two to five hydroxyl groups, and even more preferably three or four hydroxyl groups. The polyol is, for example, based on polyether, polyester, or natural oil, preferably polyether. The polyol has, for example, a hydroxyl number of 150 to 700 and an average functionality (number of isocyanate-reactive sites per molecule) of, for example, 3. 【0070】 For example, polypropylene or polyethylene polyols having a hydroxyl number of 150 to 700 and a functionality of 3 or 4 are used because they provide a relatively short chain length (e.g., a molecular weight of 300 to 700 Da), which can contribute to a low viscosity of the polyol. 【0071】 In preferred embodiments, the polyol has a viscosity of less than 2000 mPa·s or less than 1000 mPa·s at 25° C., and typically greater than 100 mPa·s at 25° C. The hydroxyl number is measured, for example, according to ASTM D4274-99 or ISO 14900:2017. The viscosity is measured, for example, according to ASTM D4878-15 (preferably Method A) or ISO 3219:1993. 【0072】 The polyol may be, for example, an aliphatic polyether polyol, such as one formed from an initiator and multiple alkylene oxide units. The polyol may be initiated with a compound having three hydroxyl groups, such as glycerol, or may be initiated with an amine, or a combination thereof. The polyol may be, for example, polyethylene oxide or polypropylene oxide polyol, or other polyether polyol. Polyester polyols may also be used. The ratio of NCO to OH groups ranges, for example, from 0.8:10 to 1.2:10. However, many polyurethane coatings can be used. 【0073】 The coating ingredients include a polymerization catalyst, such as an organometallic catalyst, a tertiary amine, an organic or inorganic base. 【0074】 Preferably, the polyol and polyisocyanate cure in less than 2 minutes at 25° C., 70° C., and / or the temperature at which the coating is applied, allowing subsequent applications at intervals of less than 2 minutes. The amount and type of catalyst can be adjusted accordingly to accommodate such cure times. 【0075】 The coating components preferably have a reactivity of 25 to 125 seconds (the time required for at least 50% cure) at room temperature, preferably 10 to 45 seconds at the operating temperature of the coating unit and / or 55°C. Preferably, the reactivity at room temperature is measured as described in Procedure A below ("Procedure for Determining Reactivity Parameters (at 25°C) - Cup Reactivity"). Preferably, the reactivity at operating temperature is measured as described in Procedure B below ("Procedure for Determining Reactivity Parameters at Desired Cure Temperature - Hotplate Reactivity"). 【0076】 In some embodiments, the coating is a polyester coating, more preferably a thermosetting polyester coating. The coating components may include an unsaturated polyester (containing a carbon-carbon double bond) and a vinyl monomer. The curing reaction in step b) may involve copolymerization of the vinyl monomer with the unsaturated polyester. The unsaturated polymer may be, for example, the reaction product of a saturated dicarboxylic acid (or anhydride), an unsaturated dicarboxylic acid (or anhydride), and a polyol, such as a diol (glycol). The glycol may be, for example, ethylene glycol, propylene glycol, 1,3-butylene glycol, or hydrogenated bisphenol A. The glycol may be, for example, cyclic or acyclic, and may be, for example, aliphatic or aromatic. The glycol may have, for example, 2 to 30 carbon atoms. The vinyl monomer may be, for example, styrene. The reaction in step b) may involve copolymerization of the unsaturated polyester and the vinyl monomer, for example, in the presence of a free-radical initiator and a catalyst. The unsaturated polyester may be, for example, injected as a liquid mixture with the vinyl monomer, which also serves as a solvent for the polyester. 【0077】 In a further embodiment, the coating is a polyurea coating and the coating components include a polyisocyanate having two or more isocyanate groups per molecule and a polyamine having two or more amine groups per molecule, preferably 2 to 5 amine groups, more preferably 3 or 4 amine groups. 【0078】 In a further embodiment, the coating composition is a phenolic resin coating and the coating components include phenol and formaldehyde. The phenolic and formaldehyde components can react in the coating unit to form a thermoset polymer. 【0079】 In a further embodiment, the coating composition is an epoxy coating, and the coating components include an epoxy component (having epoxide groups) and, optionally, a co-reactant having reactive groups such as amines, acids and anhydrides, phenols, alcohols, and thiols. The co-reactant typically has two or more such reactive groups per molecule to provide for the formation of a thermoset polymer. The epoxy component can be crosslinked by homopolymerization in step b) or by reaction with an optional co-reactant. 【0080】 The described coating unit operation advantageously avoids particle crushing during coating while significantly improving the degree of mixing compared to, for example, rotary drum coaters. The coating unit allows for faster reaction times (e.g., between polyol and polyisocyanate) and substantially shorter batch cycle times than prior art. For example, the overall batch time for a three-layer process may be 5-6 minutes, whereas a rotary drum may require 6-8 minutes per layer. The high-intensity mixing and faster reaction times of the present method allow for the production of coated fertilizer particles without particle agglomeration. Furthermore, the reaction rate can be used to optimize the fertilizer release rate by adjusting the type and amount of catalyst used. The coating method is particularly suitable for producing coated fertilizer for large-scale crops such as corn (maize). 【0081】 The one or more coating components preferably have a reaction time of preferably 30 to 250 seconds at 25°C, the reaction time being the time required for hardening (optionally measured as Procedure A - "Cup Reactivity" described herein). 【0082】 The one or more coating components preferably have a reaction time at the coating temperature (such as 70°C) of preferably 10 to 120 seconds, more preferably 10 to 60 seconds, the reaction time being the time required for hardening (optionally measured as "hotplate reactivity" as described herein). 【0083】 The reaction time can be achieved or adjusted by varying the amount and type of catalyst used for curing or hardening. 【0084】 In a preferred, non-limiting embodiment, the coating unit comprises a container and a rotor, the coating is a polyurethane coating, and step b) is followed (after each other, but optionally before, between, and / or after further steps): B1) injecting a polyol into the bed of fertilizer particles in the vessel, preferably the particles in the bed are suspended by the movement of the vessel and rotor, preferably the injection is carried out using an open pipe or a spray nozzle; B2) mixing the polyol with the fertilizer particles for 5 to 120 seconds, preferably 10 to 60 seconds; B3) injecting a polyisocyanate component into the bed of fertilizer particles in the vessel, preferably by means of an open pipe or a spray nozzle; B4) rolling the fertilizer particles in the container for at least 10 to 300 seconds, preferably 20 to 180 seconds, to react the polyol and polyisocyanate components with each other and at least partially cure the coating layer while simultaneously rotating the rotor; B5) optionally injecting liquid wax into the fertilizer bed; and optionally repeating steps B1 to B5. B6) Optionally, tumbling the fertilizer in the container for at least 10 seconds to further harden the coating. 【0085】 In a variant, step B3 is performed before steps B1 and B2 so that the polyisocyanate is injected first. However, it is preferred that the polyol be injected first, especially when the polyol is a polymeric compound. In some embodiments, step B5, which injects the wax, is omitted, for example, in at least some of the optional repetitions of steps B1 to B5. In some embodiments, steps B1 to B6 are performed using coating components other than the polyisocyanate and polyol to obtain different types of coating layers. In steps B1 to B6, the fertilizer can be tumbled by rotating the container and rotor. This preferred embodiment has been found to provide particularly good coating results with a desirable release rate of the fertilizer when immersed in water. 【0086】 The present invention also relates to a urea finishing plant comprising a urea finishing unit, such as a granulation unit or a prill tower, having an inlet for a urea melt and an outlet for warm urea particles, and a coating unit having an inlet for the urea particles, preferably warm urea particles, connected to said outlet, the coating unit being as described and comprising a frame and at least two movable elements, the movable elements being independently movable relative to the frame. In this specification, "warm urea particles" refers to particles having a temperature above ambient temperature at the inlet of the coating unit, for example, a temperature of 30 to 95°C, preferably 50 to 85°C, more preferably 55 to 75°C. The connection between the inlet of the coating unit and the outlet of the finishing unit preferably does not include a cooling unit between the urea finishing unit and the inlet of the coating unit, in particular a cooling unit using cooled air, for example, a cooling unit including a blower or fan for cooled air. 【0087】 The moving elements are preferably the container and stirring member described above, more preferably a container having walls and an internal space for accommodating the fertilizer particles before coating, and preferably a stirring member disposed in the internal space of the container. The stirring member is preferably a rotor as described above. The coating unit further comprises an outlet for the coated urea particles. The plant also comprises a cooling unit. The cooling unit has an inlet connected to the outlet for the coated urea particles and an outlet for the cooled, coated urea particles, and preferably further has an inlet for cooling air and an outlet for exhaust air. The plant can be used to carry out the method of the present invention. The method of the present invention can also be carried out by obtaining the fertilizer particles from a storage unit and, for example, preheating them if necessary. 【0088】 The present invention also relates to fertilizer particles obtainable by the method of the present invention. These fertilizer particles exhibit advantageous release rates. An example of advantageous release rates is shown in Example 3. Fertilizer particles obtainable by the described method contain urea, such as at least 50% by weight of urea, based on the total weight of the coated fertilizer particles. The particle coating is, for example, a polyurethane coating. Preferably, the fertilizer particles obtainable by the described method have a release rate of less than 40% after 20 days of immersion in water, as measured according to Procedure C described herein. Preferably, the release rate is even less than 20% by weight after 7 days of immersion. The preferred use of a water-insoluble polymer can advantageously contribute to achieving such release rates. The total coating amount is, for example, 5 to 25% by weight or 10 to 20% by weight, based on the weight of the uncoated fertilizer particles before coating. The number of coating layers is, for example, 1 to 12 layers, such as 4 to 8 layers, with the wax layer being counted as a separate layer. The particles may, for example, comprise three polyurethane layers and three wax layers (six layers in total). For example, the coating may comprise two to six polyurethane layers, which may be separated from one another by, for example, wax layers. 【0089】 The present invention also relates to coated fertilizer particles, preferably comprising urea, more preferably at least 50% by weight of urea, based on the weight of the coated fertilizer particle, and having a release rate, as measured according to Procedure C ("Procedure for Determining Nutrient Release Rates from Controlled-Release Fertilizers") described herein, of less than 40% after 20 days of immersion in water. Preferably, the release rate is also less than 20% by weight after 7 days of immersion. The coating of the coated fertilizer particles is, for example, a polyurethane coating. The particles have, for example, the amount and number of layers of coating as described above. 【0090】 Without wishing to be bound by theory, the coating method of the present invention can provide a uniform coating layer with high or complete coverage of the fertilizer particles. 【0091】 FIG. 1 shows a schematic diagram of an exemplary coating unit that can be used in the method of the present invention. Coating unit 1 includes a casing frame 2, a container 3, and a rotor 4. Rotor 4 is connected to a motor 5 for driving rotor 4. Rotor 4 includes a shaft 6 with blades 7. Container 3 includes a further motor 8 and has a rotation axis 9. Rotation axis 9 is parallel to and spaced apart from the shaft 6 (its midline). Container 3 also includes a scraper 10 near the container wall, which may remain stationary while container 3 spins around axis 9. Container 3 includes a cover plate 14, through which shaft 6 extends. The container also includes an inlet 11 for fertilizer particles and one or more inlets 12 for coating components. Inlet 12 may be implemented, for example, as an open pipe or as one or more spray nozzles, each having a connection to a supply line for a particular coating component, for example. The container 3 also has an outlet 13 for the coated fertilizer particles, for example implemented as a closable opening 13 in the bottom of the container. 【0092】 The present invention will now be further illustrated by the following examples, which are not intended to limit the invention or claimed subject matter. [Example] 【0093】 Example 1 The described mixer (with rotating container and rotating rotor) was preheated to approximately 75°C, 4.08 kg of urea fertilizer granules were added, and agitation was initiated. After the urea was confirmed to be approximately 75°C, the first of three polyol doses of 14.0 g was added and mixed for 30 seconds, followed by the first of three isocyanate doses of 21.3 g. After mixing for 60 seconds, the first of two wax doses of 10.2 g was added. The materials were mixed for an additional 30 seconds. The polyol, isocyanate, and wax addition steps and mixing times were repeated. Finally, the third polyol and isocyanate doses were added with the appropriate mixing time. 【0094】 Unlike the previous two coating layers, the addition of the wax layer was omitted after the third charge of urethane components (polyol charge and isocyanate charge). Optionally, a wax layer could be applied over the third polyurethane coating layer. Free-flowing, lump- or clump-free urea was dispensed from the mixer and cooled. The total batch time for this three-layer process was 5.5 minutes (a significant reduction from the most recent reported batch times, which generally require 6-8 minutes per layer). The coating was 3% by weight, with a final weight of 4.21 kg, of which 126 g was coated. Only two layers of wax were applied at 0.5%, and three coating steps were used. The fertilizer particles were completely coated based on visual inspection. 【0095】 Example 2 As shown in Table 1, polyol formulations A through G were prepared by adding increasing amounts of an organometallic catalyst or a tertiary amine catalyst to a polyether polyol. 【0096】 Table 1 shows the room temperature and high temperature reactivity of each of the polyol blends when compounded with an MDI-based polyfunctional aromatic isocyanate. The samples were compounded to have reactivities ranging from a fast reactivity time of 8 seconds to a very slow reactivity time of more than 5 minutes. At processing temperatures of about 75°C, the reaction times were significantly faster. When an entry of N / A is recorded, it means that the sample reacted during the 20 second mixing period or essentially immediately after being added to the hot plate. 【0097】 The polyol was added to preheated urea granules stirred in a mixer as described in Example 1. The reaction parameters were a process temperature of 71°C (160°F), 3% total urethane coating weight (added in three separate layers of 1% each, with the polyol added first, followed by the isocyanate), and 0.5% total wax added in two separate layers after the first and second urethane coating layers. [Table 1] 【0098】 Figure 2 shows the % release of urea (0-100%, Y-axis; measured according to procedure C) for 2 hours, 1, 3, and 7 days of immersion for the different polyol blends in Table 1 (polyol blends on the X-axis according to reactivity time (seconds) at room temperature). The desired slower release is achieved for polyol blends D, C, and B, and best for blends C and D. The release rate depends on the reactivity of the polyol blends, which are modified by using different amounts and types of catalysts. 【0099】 Example 3 In addition, polyol blends C and D were also applied to the fertilizer granules using the comparative rotary drum mixer following the same addition order and mixing time, but with reduced material loading, reflecting the reduced loading of the fertilizer granules. Release rates were determined according to Procedure C. 【0100】 Figure 3 shows the % urea release (y-axis) at 2 hours and 1, 3, 7, 14, and 21 days (x-axis, days) of immersion for blends C and D applied using the coating units (C1, D1) and comparative rotary drums (C2, D2) described above. The release rates from the mixers of the present invention are substantially better (slower) than those from the rotary drum mixer. For C2 and D2, more than 60% of the urea was released in less than 3 days of immersion. For C1 and D1, less than 40% of the urea was released in 21 days of immersion. This indicates that faster reactivity, while not beneficial for the comparative coated fertilizer produced with the comparative rotary drum mixer method, is highly advantageous for the method and urea granules of the present invention. 【0101】 Experimental procedure In Example 2, the following procedure was used: 【0102】 Procedure A: Procedure for Determining Reactivity Parameters (at 25°C) - Cup Reactivity Add the required weight of fully blended ingredients to achieve 150 in a small cup. Immediately and simultaneously start the timer and begin mixing the compound. Continue mixing for 20 seconds, or until the material solidifies if less than 20 seconds. 【0103】 To check the reaction time, periodically lightly touch the surface of the material with a stainless steel spatula (or alternatively, a wooden tongue depressor). The reaction time is considered to be when the spatula hits a hard or cured spot on the surface of the material. For Example 2, the fully formulated isocyanate component (Part A) and the fully formulated polyol component (Part B), including any optional additives, needed to achieve 150 g were added to a small cup. All chemical components and equipment are initially at 25° C. Component B is weighed into a mixing vessel first, followed by Component A, at the appropriate weight ratio of the components. 【0104】 Procedure B: Procedure for determining reactivity parameters at desired cure temperature - Hotplate reactivity Place a small mold capable of holding 2 mL of mixed material in a 1 / 8-deep cavity on a hot plate and preheat the mold to the desired temperature. Once the desired temperature is confirmed, follow the mixing procedure described as "Procedure A - Cup Reactivity," but as soon as the sample is completely mixed, pour 2 mL of the reaction mixture into the preheated mold cavity. Start a timer immediately after adding the resin to the mold. Use a spatula to periodically touch the surface of the material. The reaction time is the time it takes for the resin on this surface to solidify into a hard material. 【0105】 Procedure C: Procedure for determining nutrient release rates from controlled-release fertilizers Nutrient solutions are prepared by dissolving various known concentrations of nutrients in distilled water. The refractive index of the known concentrations is measured with a refractometer so that a calibration curve of refractive index versus concentration can be constructed. 10 g of coated fertilizer particles are then accurately weighed into a small, wide-mouth jar and 90 g of water is added. The sample is gently stirred and allowed to stand until the required measurement time. Before each new measurement, the sample is gently stirred to ensure homogeneity. A small sample of the solution is placed in the refractometer and the measurement is recorded. Comparison with the calibration curve provides the nutrient concentration in the solution. The percentage of nutrients released from the coated fertilizer particles is calculated. Experiments were performed at ambient temperature, e.g., 20°C.

Claims

[Claim 1] A method of coating fertilizer particles with a coating, a) A step of preparing fertilizer particles inside the coating unit, b) - Applying one or more coating components to the suspended particle bed of fertilizer particles brought about by the movement of the movable elements of the coating unit, thereby applying one or more coating components to the fertilizer particles within the coating unit, and preparing coated fertilizer particles including a coating layer and the fertilizer particles (wherein the coating components are liquid coating components, and the liquid coating components are applied to the fertilizer particle bed by spraying), and, —The coating layer is hardened or cured at least partially, wherein the hardening or curing involves a chemical reaction of one or more coating components. A step of applying a coating layer including, Step b) is performed one or more times to prepare coated fertilizer particles, and the process of applying the coating layer is performed. c) A step of discharging the coated fertilizer particles from the coating unit, or A step of performing the final hardening or curing of the coated fertilizer particles within the coating unit, and then releasing the fertilizer particles from the coating unit. And, The process includes: the discharged fertilizer particles containing the coating, and the coating containing a polymer; Includes, The coating unit comprises a fixed frame and at least two movable elements, The movable element is capable of operating independently of the fixed frame. The method comprises, at least during step b), moving the at least two movable elements relative to the fixed frame, — The first movable element of the movable element is a container having walls and an internal space for containing fertilizer particles, and the method includes rotating the container around a pivot axis while the container holds the fertilizer particles during at least step b), — The second movable element of the movable element is a rotor, and the method includes rotating the container and simultaneously rotating the rotor around its axis of rotation during at least step b), method. [Claim 2] The method according to claim 1, wherein the floor specified in step b) is a suspended particle floor in which fertilizer particles are suspended by the movement of a movable element. [Claim 3] The method according to claim 1 or 2, wherein the rotation axis of the rotor and the rotation axis of the container are parallel to each other or have an angle of less than 30° between them, and the rotation axis of the rotor and the rotation axis of the container are spaced apart from each other, thereby mounting the rotor eccentrically within the internal space of the container. [Claim 4] The rotor comprises a shaft and one or more blades, The shaft has a first end and a second end, the first end is positioned in the internal space of the container, and the second end is connected to an actuator. The method according to claim 3, wherein the blade is connected to the shaft and extends from the shaft in the internal space of the container in a direction perpendicular to the entire length of the shaft. [Claim 5] The method according to any one of claims 1 to 4, wherein the rotation axis of the container is inclined with respect to a vertical axis, and the vertical axis is defined with respect to gravity. [Claim 6] The container has a bottom and walls, The coating unit further includes a scraper, the scraper being fixed to the fixed frame at least during step b), The method according to any one of claims 1 to 5, wherein the scraper is positioned to scrape material from the walls and / or bottom of the container. [Claim 7] The method according to any one of claims 1 to 6, wherein the coating of the discharged particles comprises a crosslinked polymer or a thermosetting polymer. [Claim 8] In step b), the coating layer is applied in an amount of 0.50 to 4.0% by weight based on the weight of the fertilizer particles before coating and without the coating. Step b) is performed for 10 to 600 seconds, preferably 30 to 240 seconds. The method according to claim 7, wherein if the final curing in step c) is performed, it is performed for 60 seconds to 15 minutes. [Claim 9] Steps a) and b) are carried out at a temperature of at least 50°C, The method according to any one of claims 1 to 8, wherein step c) includes cooling the discharged particles to a temperature lower than at least 50°C. [Claim 10] The method according to any one of claims 1 to 9, wherein the container rotates at 10 to 60 rpm and the rotor rotates at 10 to 60 rpm. [Claim 11] The coating is a polyurethane coating, The method according to any one of claims 7 to 9, wherein the coating component comprises a polyisocyanate component and a polyol. [Claim 12] The coating is a polyurethane coating, Step b) then: B1) A step of injecting the polyol into the bed of fertilizer particles in the container, B2) A step of mixing the polyol with the fertilizer particles for 5 to 120 seconds, B3) A step of injecting the polyisocyanate component into the bed of fertilizer particles in the container, B4) A step of rotating the rotor while the fertilizer particles are rolled in the container for at least 10 to 300 seconds, thereby causing the polyol and the polyisocyanate components to react with each other. B5) A step of injecting liquid wax into the fertilizer bed, Optionally, a process that repeats steps B1 to B5, B6) Optionally, a step of further hardening the coating by rolling the fertilizer in the container for at least 10 seconds, The method according to any one of claims 1 to 3, including [Claim 13] The method according to any one of claims 1 to 12, wherein the coating comprises a water-insoluble polymer. [Claim 14] - A urea finishing unit such as a granulation unit or prill tower having an inlet for urea molten material and an outlet for warm urea particles, - A coating unit having an inlet connected to the outlet for warm urea particles, It includes a fixed frame and at least two movable elements, wherein the movable elements are operable independently of the fixed frame. The first movable element of the movable element is a container having walls and an internal space for containing fertilizer particles before coating, The second movable element is a stirring member positioned in the internal space of the container, The coating unit further includes an outlet for coated urea particles. Coating unit and - A cooling unit having an inlet connected to the outlet for coated urea particles, further having an outlet for cooled and coated urea particles, preferably further having an inlet for cooling air and an outlet for exhaust air, A urea finishing plant equipped with, A urea finishing plant in which the coating unit is the coating unit defined in claim 1.

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