A coated controlled-release fertilizer suitable for trace element fertilizer particles and a preparation method thereof
By coating the surface of micronutrient fertilizer granules with microgel films and polyurethane films, the problems of micronutrient fertilizer fixation and loss in the soil are solved, achieving controlled release and efficient absorption, adapting to different climatic conditions, and conforming to the development of green agriculture.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUHAN SHENGDASHENNONG BIOLOGICAL ENG CO LTD
- Filing Date
- 2026-04-10
- Publication Date
- 2026-06-05
AI Technical Summary
Existing micronutrient fertilizers are easily fixed or lost by the soil, resulting in low utilization rates. Traditional slow-release fertilizer processes are complex and energy-intensive, making them difficult to apply in the field of micronutrients.
The surface of modified micronutrient fertilizer granules is coated with a microgel film and a polyurethane film. Controlled release is achieved by adjusting the pore size of the microgel film. Combined with bio-based polyols and cross-linking agents, a coated controlled-release fertilizer is formed.
It significantly improves the absorption efficiency of micronutrients, achieves precise release control of different soluble elements, extends the fertilizer effect period to 90 days, reduces energy consumption, adapts to different climatic conditions, and conforms to the concept of green agricultural development.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of agricultural fertilizer technology, specifically relating to a coated controlled-release fertilizer suitable for micronutrient fertilizer granules and its preparation method. Background Technology
[0002] Since the advent of modern industry, fertilizers have become an indispensable part of modern agriculture. Healthy plant growth requires not only macronutrients such as nitrogen, phosphorus, and potassium, but also micronutrients such as calcium, magnesium, sulfur, copper, iron, zinc, and boron, which play an equally irreplaceable role in plant growth. However, with modernization and increased crop yields, the deficiency of micronutrients in the soil is becoming increasingly common. Conventional micronutrient fertilizers are easily fixed or lost by the soil, resulting in low utilization rates. This not only leads to a huge waste of resources, but also leaves the core problem of plant nutrient deficiency unresolved.
[0003] CN115716764A discloses an ecological fertilizer with a trace element core encapsulated in sulfur and its preparation method. This patent first uses sulfur to encapsulate trace element particles as fertilizer cores and then granulates them together with nitrogen, phosphorus, and potassium macroelements. The sulfur used not only needs to be melted with steam, but also needs to be kept warm with steam before encapsulation. The steps are very complicated and energy-intensive, and it is not universally applicable.
[0004] CN108976018A discloses a mixture of micronutrients and a method for preparing micronutrient-encapsulated fertilizer. This patent involves adding micronutrients to liquid sulfur and coating them on the surface of macronutrients. This causes the micronutrients to be released first, which can easily lead to fixation by the soil or nutrient loss. It does not solve the problem of low efficiency in plant absorption of micronutrients.
[0005] CN114773122A discloses a sulfur-coated superphosphate containing trace elements and its preparation method. This patent uses phosphorus pentoxide and superphosphate mixed together, followed by the addition of trace elements and granulation, and then sulfur coating. Instead of coating directly on the surface of the trace element particles, although it can achieve a similar effect, the process is complex, energy consumption is high, and the slow-release effect is uncontrollable.
[0006] Therefore, from a practical perspective, inventing a controlled-release process for micronutrient fertilizers with a slow-release effect is of great significance for solving these problems. Traditional controlled-release fertilizers mainly focus on macronutrients such as nitrogen and potassium, with fewer reports on micronutrients and relatively few products actually applied. Summary of the Invention
[0007] To overcome the problems existing in the current polyurethane-coated fertilizer technology, this invention provides a coated controlled-release fertilizer suitable for micronutrient fertilizer granules and its preparation method.
[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing a coated controlled-release fertilizer suitable for micronutrient fertilizer granules includes the following steps: S1. Weigh out micronutrient fertilizer granules and modify them to obtain modified micronutrient fertilizer granules. S2. Prepare microgel film agent, polyurethane A material and polyurethane B material respectively; S3. Coat the surface of the modified micronutrient fertilizer granules obtained in step S1 with a microgel film to obtain fertilizer granules with a microgel film layer; uniformly coat polyurethane A material on the surface of the fertilizer granules with the microgel film layer, and then continue to coat polyurethane B material. After uniform coating and mixing treatment for a period of time, repeat the coating operation of polyurethane A material and polyurethane B material multiple times to obtain a coated controlled-release fertilizer.
[0009] Furthermore, the micronutrient fertilizer granules are composed of one or more of the following micronutrient fertilizer granules: zinc fertilizer granules, boron fertilizer granules, copper fertilizer granules, calcium and magnesium fertilizer granules, etc., and the mesh size of the micronutrient fertilizer granules is 2-4 mesh.
[0010] Further, in step S1, the modification treatment of the micronutrient fertilizer granules is as follows: after preheating the micronutrient fertilizer granules, surface additives are added, and after coating, modified micronutrient fertilizer granules are obtained. The surface additive is a mixture of a base additive and an alkyl glycoside in a mass ratio of 1:1. The base additive is one or two of the following: disodium ethylenediaminetetraacetate, humic acid powder, citric acid, diethylenetriaminepentaacetic acid, and mannitol. When there are two base additives, they are mixed in a mass ratio of 1:1.
[0011] Furthermore, the temperature conditions for the preheating treatment of the micronutrient fertilizer granules are 50-60℃, and the time conditions are 5-10min.
[0012] Further, in step S2, the steps for preparing the microgel film are as follows: S21. Take 0.5 parts of acrylamide and 0.1-1 parts of pentaerythritol triacrylate, mix them evenly, and heat them to 60-80℃, preferably 70℃, under a nitrogen atmosphere; add 0.01-0.1 parts of potassium persulfate aqueous solution with a concentration of 0.01mol / L to initiate the reaction. After reacting for 3 hours, centrifuge at 8000rpm for 10 minutes to remove the supernatant and obtain the intermediate product. S22. Add 0.3 parts of nonlinear polyethylene glycol dimethacrylate, 0.3 parts of poly(N-isopropylacrylamide), 0.6 parts of methoxy polyethylene glycol methacrylate, and 0.1 parts of nanoporous silica to the intermediate product. Heat to 70-90℃ under a nitrogen atmosphere, then add 0.02 parts of azobisisobutyronitrile to initiate the reaction. After 3 hours, dry at 40-50℃ for 5-10 minutes to obtain a microgel film.
[0013] Furthermore, the nonlinear polyethylene glycol dimethacrylate has a molecular weight of 1000-3000, and the nanoporous silica has a size of 40-100 nm.
[0014] Furthermore, the polyurethane A component is composed of polypropylene glycol and castor oil in a mass ratio of 2:1, wherein the molecular weight of the polypropylene glycol is 400-800; the polyurethane B component is diphenylmethane diisocyanate.
[0015] Further, by weight, the micronutrient fertilizer granules are 100 parts, the surface additives are 1-1.5 parts, the microgel film agent is 0.5-1 part, and the polyurethane A and polyurethane B components total 1.8 parts.
[0016] The above preparation method yields a coated controlled-release fertilizer suitable for micronutrient fertilizer granules.
[0017] Furthermore, the coated controlled-release fertilizer comprises modified micronutrient fertilizer particles, a microgel membrane layer, and a polyurethane coating layer distributed sequentially from the inside out. Furthermore, by weight, the micronutrient fertilizer granules comprise 100 parts, the surface additive comprises 1-1.5 parts, the microgel film agent comprises 0.5-1 parts, and the polyurethane A component and the polyurethane B component comprise a total of 1.8 parts.
[0018] Compared with the prior art, the present invention has significant advantages and beneficial effects, specifically reflected in the following aspects: (1) The coated controlled-release fertilizer of the present invention achieves controlled release of micronutrients by sequentially coating the surface of fertilizer particles with a microgel membrane layer and a polyurethane membrane layer, effectively reducing the fixation and loss of nutrients in the soil and significantly improving the absorption efficiency of micronutrients by plants. (2) The coated release control fertilizer of the present invention can adjust the size of the gel pores by adjusting the amount of pentaerythritol triacrylate and potassium persulfate aqueous solution in the microgel membrane layer, thereby achieving precise control of the release rate of micronutrient fertilizers with different solubility (such as easily soluble or poorly soluble), and extending the fertilizer effect period to a maximum of 90 days. (3) The coated controlled-release fertilizer of the present invention uses surface additives to modify fertilizer particles, reduce particle surface energy, enhance the bonding force between microgel film layer and fertilizer particles, and improve the uniformity and stability of coating. (4) The coating-controlled fertilizer of the present invention has a microgel membrane layer that not only fills the unevenness on the surface of the particles and improves the quality of subsequent polyurethane coating, but also has multiple functions such as water retention, temperature-sensitive shrinkage and ion adsorption, adapting to different climatic conditions and enhancing the environmental response capability of the fertilizer. (5) The coated controlled-release fertilizer of the present invention uses bio-based polyols (such as castor oil) and bio-based crosslinking agents to reduce dependence on petroleum-based raw materials, which is in line with the concept of green agricultural development; no high-temperature melting equipment is required in the preparation process, resulting in low energy consumption and environmental friendliness; (6) The coated controlled-release fertilizer of the present invention, through comparative experiments of examples and comparative examples, shows that the coated controlled-release fertilizer prepared by the present invention exhibits good controlled-release performance at 3 days, 5 days, 10 days, 30 days, 60 days and 90 days, which is better than the control sample without coating or with incomplete coating, proving that its controlled-release effect is significant. (7) The preparation method described in this invention is simple and reliable. It adopts in-situ film formation technology, requires no complex equipment, and has good universality and industrialization prospects. Detailed Implementation
[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail. Furthermore, the above embodiments and features described herein can be combined with each other unless otherwise specified.
[0020] The first aspect of this invention is to protect a method for preparing a coated, controlled-release fertilizer suitable for micronutrient fertilizer granules, comprising the following steps: S1. Weigh out micronutrient fertilizer granules and modify them to obtain modified micronutrient fertilizer granules.
[0021] In this invention, the micronutrient fertilizer granules are composed of one or more of the following: zinc fertilizer granules, boron fertilizer granules, copper fertilizer granules, calcium and magnesium fertilizer granules, etc., and the mesh size of the micronutrient fertilizer granules is 2-4 mesh. Preferably, zinc chloride granules are preferred as the micronutrient fertilizer granules of this invention.
[0022] The specific steps of the modification treatment are as follows: place the micronutrient fertilizer granules in a coating machine, heat to 50-60℃, preferably 55℃, for 5-10 minutes; adjust the coating machine speed to 20 rpm / min, apply 1-1.5 parts of pre-mixed surface additive to the surface of the fertilizer granules in the coating machine, and grind at a uniform speed for 30 minutes to obtain modified micronutrient fertilizer granules. Preferably, the surface additive is 1 part.
[0023] In this invention, the surface additive is a mixture of a basic additive and an alkyl glycoside in a mass ratio of 1:1. The basic additive is one or two of the following: disodium ethylenediaminetetraacetate, humic acid powder, citric acid, diethylenetriaminepentaacetic acid, and mannitol. When there are two basic additives, they are mixed in a mass ratio of 1:1.
[0024] In this invention, the surface of micronutrient fertilizer particles is modified using basic adjuvants and alkyl glycosides. Alkyl glycosides, as nonionic surfactants, significantly reduce the surface energy of the fertilizer, facilitating subsequent film formation. As an embodiment of this invention, the basic adjuvant is either a chelating agent such as humic acid powder, or a solubilizing agent such as citric acid solution; the choice can be flexible depending on the specific fertilizer core.
[0025] S2. Preparation of microgel film agent, the specific method is as follows: S21. Take 0.5 parts of acrylamide and 0.1-1 parts of pentaerythritol triacrylate, mix them evenly, and heat them to 60-80℃, preferably 70℃, under a nitrogen atmosphere; add 0.01-0.1 parts of potassium persulfate aqueous solution with a concentration of 0.01mol / L to initiate the reaction. After reacting for 3 hours, centrifuge at 8000rpm for 10 minutes to remove the supernatant and obtain the intermediate product. S22. Add 0.3 parts of nonlinear polyethylene glycol dimethacrylate, 0.3 parts of poly(N-isopropylacrylamide), 0.6 parts of methoxy polyethylene glycol methacrylate, and 0.1 parts of nanoporous silica to the intermediate product. Heat to 70-90°C under a nitrogen atmosphere, then add 0.02 parts of azobisisobutyronitrile to initiate the reaction. After 3 hours, dry at 40-50°C for 5-10 minutes. Preferably, the drying temperature is 50°C and the drying time is 10 minutes to obtain a microgel film.
[0026] In this invention, the molecular weight of nonlinear polyethylene glycol dimethacrylate is 1000-3000, the amount of pentaerythritol triacrylate is 0.1-1 part, preferably 1 part; the amount of potassium persulfate aqueous solution is 0.01-0.1 part, preferably 0.1 part; and the mass ratio of pentaerythritol triacrylate to potassium persulfate aqueous solution is 10:1, the size of nanoporous silica is 40-100 nm, preferably, the average size is 80 nm.
[0027] This invention involves coating a gel obtained by reacting acrylamide with pentaerythritol triacrylate onto the surface of fertilizer. This not only effectively fills the unevenness in the fertilizer granule coating, facilitating subsequent polyurethane film formation, but also possesses strong water retention, acting as a water absorber during the rainy season. Nonlinear polyethylene glycol dimethacrylate, poly(N-isopropylacrylamide), and nanoporous silica are used to modify the gel, forming an interpenetrating network. This nonlinear polyethylene glycol dimethacrylate has a hyperbranched structure, which acts as the framework of the microgel membrane, preventing gel collapse. Furthermore, poly(N-isopropylacrylamide) imparts temperature-sensitive properties to the microgel layer; its high-temperature shrinkage allows the gel layer to effectively release nutrients and water during the dry season. The addition of mesoporous nano-silica effectively adsorbs ionic nutrients, mitigating burst release and increasing the solubility of insoluble nutrients.
[0028] The microgel film agent of the present invention can also effectively prevent the explosive release of easily soluble micronutrient fertilizers after dissolution. By adjusting the amount of crosslinking agent in the reaction, the pore size of the gel can be effectively adjusted. For easily soluble element fertilizers, the amount of pentaerythritol triacrylate and potassium persulfate aqueous solution can be appropriately increased, while for sparingly soluble elements, the amount of pentaerythritol triacrylate and potassium persulfate aqueous solution can be appropriately reduced to increase the pore size.
[0029] S3. Weigh out polyurethane component A and polyurethane component B, and set aside. The mass ratio of polyurethane component A to polyurethane component B is 2:1. Polyurethane component A is composed of polypropylene glycol and castor oil in a mass ratio of 2:1, wherein the molecular weight of polypropylene glycol is 400-800, preferably 600. Polyurethane component B is diphenylmethane diisocyanate.
[0030] In this invention, by compounding polypropylene glycol with castor oil, and using low molecular weight polypropylene glycol, the resulting polyurethane membrane will form a moderately porous structure, making it difficult for water to penetrate in the early stage without affecting water penetration in the middle and later stages. Castor oil has long-chain hydrophobic fatty chains and a regular structure, which can form a good microphase separation zone with the polyurethane after reacting with MDI, which is crucial for controlling the release rate of fertilizer in the early stage.
[0031] S4. Preparation of coated controlled-release fertilizer, the specific method is as follows: In step S1, 0.5-1 parts of a microgel film agent are coated onto the surface of the modified micro-element fertilizer granules to obtain fertilizer granules with a microgel film layer. Polyurethane A is uniformly coated onto the surface of the fertilizer granules with the microgel film layer, and then polyurethane B is coated. After the coating is uniform, the coating speed is reduced to 10 rpm / min, and the reaction is allowed to proceed for 8-15 minutes. After observing that the granules are loose and do not agglomerate, the coating speed is adjusted to 20 rpm / min, and the coating is repeated 3 times. Each time, the amount of polyurethane A coating is 0.4 parts and the amount of polyurethane B coating is 0.2 parts, to obtain a coated controlled-release fertilizer.
[0032] In this invention, the microgel film agent is preferably 1 part.
[0033] The preparation method of this invention is simple and reliable, adaptable to different fertilizer particles, and effectively solves the problems of high surface energy, roughness, easy water absorption, and uneven release of different inorganic salt fertilizer particles. Compared with the prior art, this process does not require high-temperature melting equipment, and can achieve controlled release of micronutrient fertilizers by coating them with a simple in-situ film-forming technique, with a controlled release period of up to 90 days.
[0034] The second aspect of this invention is to protect the coated controlled-release fertilizer obtained by the above preparation method. The coated controlled-release fertilizer comprises modified micronutrient fertilizer particles, a microgel film layer, and a polyurethane coating layer, distributed sequentially from the inside out. Specifically, by weight, the micronutrient fertilizer particles comprise 100 parts, the surface additive comprises 1-1.5 parts, the microgel film agent comprises 0.5-1 part, and the polyurethane A component and the polyurethane B component comprise a total of 1.8 parts.
[0035] <Example 1> A method for preparing a coated controlled-release fertilizer suitable for micronutrient fertilizer granules includes the following steps: S1. Weigh 100 parts of zinc sulfate granules (mesh size 2-4 mesh), place the zinc sulfate granules in a coating machine, heat to 55℃, and treat for 10 min; adjust the speed of the coating machine to 20 rpm / min; mix alkyl glycoside and disodium ethylenediaminetetraacetate at a mass ratio of 1:1 to obtain a surface additive; coat 1 part of the surface additive onto the surface of the zinc sulfate granules in the coating machine, and grind at a uniform speed for 30 min to obtain modified micronutrient fertilizer granules.
[0036] S2. Preparation of microgel film agent, the specific method is as follows: S21. Take 0.5 parts of acrylamide and 1 part of pentaerythritol triacrylate, mix them evenly, and heat them to 70°C under a nitrogen atmosphere; add 0.1 parts of potassium persulfate aqueous solution with a concentration of 0.01 mol / L to initiate the reaction. After reacting for 3 hours, centrifuge at 8000 rpm for 10 minutes to remove the supernatant and obtain the intermediate product. S22. Add 0.3 parts of nonlinear polyethylene glycol dimethacrylate, 0.3 parts of poly(N-isopropylacrylamide), 0.6 parts of methoxy polyethylene glycol methacrylate, and 0.1 parts of nanoporous silica to the intermediate product. Heat to 70-90°C under a nitrogen atmosphere, then add 0.02 parts of azobisisobutyronitrile to initiate the reaction. After 3 hours, dry at 50°C for 10 minutes. Preferably, the drying temperature is 50°C and the drying time is 10 minutes to obtain a microgel film.
[0037] S3. Weigh out polyurethane component A and polyurethane component B for later use. Polyurethane component A is composed of polypropylene glycol and castor oil in a mass ratio of 2:1, with polypropylene glycol having a molecular weight of 600. Polyurethane component B is diphenylmethane diisocyanate.
[0038] S4. Coat the surface of the modified micronutrient fertilizer granules obtained in step S1 with 1 part of microgel film agent to obtain fertilizer granules with microgel film layer; uniformly coat polyurethane A material on the surface of the above-mentioned fertilizer granules with microgel film layer, and then continue to coat polyurethane B material. After the coating is uniform, reduce the coating speed to 10 rpm / min and react for 8-15 min. After observing that the granules are loose and do not agglomerate, adjust the coating speed to 20 rpm / min and repeat the coating 3 times. Each time, the coating amount of polyurethane A material is 0.4 parts and the coating amount of polyurethane B material is 0.2 parts to obtain coated controlled-release fertilizer.
[0039] <Example 2> The difference between this embodiment and Embodiment 1 is that in step S4, the amount of microgel film agent applied is 0.5 parts.
[0040] <Example 3> The difference between this embodiment and Embodiment 1 is that, in step S2, the amounts of pentaerythritol triacrylate and potassium persulfate aqueous solution are 0.1 parts and 0.01 parts, respectively.
[0041] <Example 4> The difference between this embodiment and Embodiment 1 is that, in step S2, the amounts of pentaerythritol triacrylate and potassium persulfate aqueous solution are 0.1 parts and 0.01 parts, respectively. In step S4, the amount of microgel film agent applied is 0.5 parts.
[0042] <Comparative Example 1> The difference between this comparative example and Example 1 is that no surface additive is added in step S1.
[0043] <Comparative Example 2> The difference between this comparative example and Example 1 is that the specific steps of step S4 are as follows: Polyurethane A material is uniformly coated on the surface of the modified micronutrient fertilizer granules obtained in step S1, and then polyurethane B material is coated. After the coating is uniform, the coating speed is reduced to 10 rpm / min, and the reaction is allowed to proceed for 8-15 minutes. After observing that the granules are loose and do not agglomerate, the coating speed is adjusted to 20 rpm / min, and the coating is repeated 3 times. Each time, the amount of polyurethane A material coated is 0.4 parts, and the amount of polyurethane B material coated is 0.2 parts, to obtain the coated controlled-release fertilizer.
[0044] <Comparative Example 3> The difference between this comparative example and Example 1 is that the specific steps of step S4 are as follows: S4, coat the surface of the modified micronutrient fertilizer particles obtained in step S1 with one part of microgel film agent to obtain fertilizer particles with microgel film layer; uniformly coat polyurethane A material on the surface of the above-mentioned fertilizer particles with microgel film layer to obtain coated controlled-release fertilizer.
[0045] The coated controlled-release fertilizers obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to a 25°C water immersion experiment, with blank Example 1 (untreated zinc sulfate granules) added simultaneously. The different release cycles obtained are shown in the table below: Table 1
[0046] As shown in Table 1, the comparison of the results of Examples 1 and 4 reveals that increasing the amount of pentaerythritol triacrylate and potassium persulfate aqueous solution significantly improved the zinc ion release rate of the coated controlled-release fertilizer prepared in Example 1, resulting in a marked decrease in the release rate. This is attributed to the reduced pore size of the gel layer. In Comparative Example 1, the zinc ion release rate was faster than in Example 1, but the surface additives did not affect the zinc ion release efficiency. This is because the absence of alkyl glycosides reduced the film-forming properties of the microgel on the fertilizer particle surface, thus affecting the subsequent polyurethane film formation and leading to faster release. Other examples and comparative examples also demonstrate the effectiveness of Example 1.
[0047] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.
Claims
1. A method for preparing a coated controlled-release fertilizer suitable for micronutrient fertilizer granules, characterized in that, Includes the following steps: S1. Weigh out micronutrient fertilizer granules and modify them to obtain modified micronutrient fertilizer granules. S2. Prepare microgel film agent, polyurethane A material and polyurethane B material respectively; S3. Coat the surface of the modified micronutrient fertilizer granules obtained in step S1 with a microgel film to obtain fertilizer granules with a microgel film layer; uniformly coat polyurethane A material on the surface of the above-mentioned fertilizer granules with a microgel film layer, and then continue to coat polyurethane B material. After uniform coating and mixing treatment for a period of time, repeat the coating operation of polyurethane A material and polyurethane B material multiple times to obtain a coated controlled-release fertilizer. The micronutrient fertilizer granules comprise 100 parts by weight, the surface additive comprises 1-1.5 parts, the microgel film agent comprises 0.5-1 parts, and the polyurethane A and polyurethane B comprise a total of 1.8 parts by weight, with a polyurethane A: polyurethane B ratio of 2:1 by weight.
2. The method for preparing coated controlled-release fertilizer suitable for micronutrient fertilizer granules according to claim 1, characterized in that, Micronutrient fertilizer granules are composed of one or more of the following: zinc fertilizer granules, boron fertilizer granules, copper fertilizer granules, calcium and magnesium fertilizer granules, etc., and the mesh size of the micronutrient fertilizer granules is 2-4 mesh.
3. The method for preparing coated controlled-release fertilizer suitable for micronutrient fertilizer granules according to claim 2, characterized in that, In step S1, the modification treatment of the micronutrient fertilizer granules is as follows: after preheating the micronutrient fertilizer granules, surface additives are added, and after coating, modified micronutrient fertilizer granules are obtained. The surface additive is a mixture of a base additive and an alkyl glycoside in a mass ratio of 1:
1. The base additive is one or two of the following: disodium ethylenediaminetetraacetate, humic acid powder, citric acid, diethylenetriaminepentaacetic acid, and mannitol. When there are two base additives, they are mixed in a mass ratio of 1:
1.
4. The method for preparing coated controlled-release fertilizer suitable for micronutrient fertilizer granules according to claim 3, characterized in that, The temperature conditions for the preheating treatment of the micronutrient fertilizer granules are 50-60℃, and the time conditions are 5-10min.
5. The method for preparing a coated controlled-release fertilizer suitable for micronutrient fertilizer granules according to claim 1, characterized in that, In step S2, the steps for preparing the microgel film are as follows: S21. Take 0.5 parts of acrylamide and 0.1-1 parts of pentaerythritol triacrylate, mix them evenly, and heat them to 60-80℃, preferably 70℃, under a nitrogen atmosphere; add 0.01-0.1 parts of potassium persulfate aqueous solution with a concentration of 0.01mol / L to initiate the reaction. After reacting for 3 hours, centrifuge at 8000rpm for 10 minutes to remove the supernatant and obtain the intermediate product. S22. Add 0.3 parts of nonlinear polyethylene glycol dimethacrylate, 0.3 parts of poly(N-isopropylacrylamide), 0.6 parts of methoxy polyethylene glycol methacrylate, and 0.1 parts of nanoporous silica to the intermediate product. Heat to 70-90℃ under a nitrogen atmosphere, then add 0.02 parts of azobisisobutyronitrile to initiate the reaction. After 3 hours, dry at 40-50℃ for 5-10 minutes to obtain a microgel film.
6. The method for preparing coated controlled-release fertilizer suitable for micronutrient fertilizer granules according to claim 5, characterized in that, The nonlinear polyethylene glycol dimethacrylate has a molecular weight of 1000-3000, and the nanoporous silica has a size of 40-100 nm.
7. The method for preparing coated controlled-release fertilizer suitable for micronutrient fertilizer granules according to claim 5, characterized in that, The polyurethane A component is composed of polypropylene glycol and castor oil in a mass ratio of 2:1, wherein the molecular weight of polypropylene glycol is 400-800; the polyurethane B component is diphenylmethane diisocyanate.
8. The method for preparing coated controlled-release fertilizer suitable for micronutrient fertilizer granules according to claim 5, characterized in that, By weight, the micronutrient fertilizer granules are 100 parts, the surface additives are 1-1.5 parts, the microgel film agent is 0.5-1 parts, and the polyurethane A and polyurethane B components total 1.8 parts.
9. The coated controlled-release fertilizer suitable for micronutrient fertilizer granules obtained by the preparation method according to claims 1-8.
10. The coated controlled-release fertilizer for micronutrient fertilizer granules according to claim 9, characterized in that, The coated controlled-release fertilizer comprises modified micronutrient fertilizer particles, a microgel membrane layer, and a polyurethane coating layer, which are distributed sequentially from the inside out. Furthermore, by weight, the micronutrient fertilizer granules comprise 100 parts, the surface additive comprises 1-1.5 parts, the microgel film agent comprises 0.5-1 parts, and the polyurethane A component and the polyurethane B component comprise a total of 1.8 parts, with a mass ratio of polyurethane A component: polyurethane B component = 2:1.