A slow-release coating for medicinal fertilizer particles and its preparation method

Abstract

The present invention discloses a sustained-release coating for medicinal fertilizer granules and its preparation method, belonging to the field of bioagricultural technology. The coating is composed of potassium fulvate (30-60 parts), a polymer material (20-40 parts), a lubricant (5-15 parts), a binder (5-10 parts), and a modification agent (1-10 parts). The modification agent is prepared by combining ethyl orthosilicate and 11-chlorodecanoic acid to form nanoparticles, which are modified with a silane coupling agent and then cross-linked with chitosan to form a composite structure. The preparation method utilizes a twin-screw gradient mixing process (800-1200 rpm, 40±5°C) combined with fluidized bed atomization spraying and three-stage drying. This technology has achieved breakthroughs: zinc ion utilization has increased from 41.5% to 68.2%, the coating crushing strength has reached 48.3N, zinc release has reached 12.3 mg / L over 28 days, and degradation rate has reached 14.2% over 30 days. Through the synergistic effect of pH buffering of potassium humate and modified nanoparticles, the problems of zinc fixation and phosphorus-zinc antagonism in high pH soils are effectively solved. It is suitable for crops such as corn and rice. Field trials have shown an 18.7% increase in yield.

Description

Technical Field

[0001] The invention belongs to the technical field of biological agriculture, and in particular relates to a slow-release coating for medicinal fertilizer particles and a preparation method thereof. Background Art

[0002] Zinc fertilizer is an essential trace element for crops, especially crucial for the growth and development of crops such as corn, rice, cotton, beans, and fruit trees. Zinc deficiency in crops can lead to leaf chlorosis, reduced photosynthesis, shortened internodes, dwarfed plants, and inhibited growth, ultimately resulting in reduced yields. For example, zinc deficiency in fruit trees such as apples, pears, cherries, apricots, and grapes can cause symptoms such as smaller and yellower leaves, and even the so-called "small leaf disease." Zinc deficiency in corn can cause "white seedling disease." However, the current low application rate of zinc fertilizer, only 1-2 kilograms, makes large-scale fertilization difficult.

[0003] Existing zinc fertilizers primarily include water-soluble zinc acid and zinc sulfate heptahydrate, but these fertilizers present the following challenges: Soil pH affects absorption: When soil pH is high (>6), zinc ions in zinc fertilizers are easily immobilized, reducing their effectiveness. They readily bind to calcium carbonate in the soil, resulting in zinc inactivation. They interact antagonistically with phosphate fertilizers: Excessive use of phosphate fertilizers can cause zinc deficiency. They readily absorb moisture and form lumps: When mixed with other chemical fertilizers, they easily absorb moisture and form lumps, reducing their effectiveness. They are highly corrosive: They are somewhat corrosive to equipment and the environment.

[0004] To address these issues, the agricultural sector is increasingly adopting medicated fertilizer granules. Using a specific slow-release coating, these granules slowly release nutrients in the soil, thereby improving nutrient utilization and prolonging fertilizer effectiveness. However, current methods for preparing slow-release coatings are complex and costly, and there remains room for improvement in terms of stability and environmental friendliness. Therefore, there is an urgent need to develop a novel slow-release coating for medicated fertilizer granules and its preparation method to overcome the shortcomings of existing technologies, improve application effectiveness, and reduce environmental pollution. Summary of the Invention

[0005] Problem to be solved

[0006] This invention addresses the systemic deficiencies of existing zinc fertilizers and slow-release coating technologies, and proposes the following core technical issues to be addressed: 1. Deficiencies in zinc ion environmental adaptability: pH-sensitive inactivation mechanism. Traditional zinc fertilizers (such as zinc sulfate heptahydrate) have a zinc fixation rate of up to 65-78% in soils with a pH > 6, resulting in a drop in effective zinc concentration to 0.08-0.15 ppm (below the crop critical value of 0.2 ppm); phosphorus-zinc antagonism: phosphate fertilizer application reduces soil exchangeable zinc content by 42-57%, and existing technologies fail to address the issue of excessive zinc-phosphorus contact area (measured contact area reaches 83% ± 5%). 2. Deficiencies in physical and chemical stability: Inadequate mechanical properties: Traditional coated granules have a crushing strength of only 33.4-39.5N, and a mass loss rate >3.0% during fluidized bed processing; and hygroscopic caking: Uncoated zinc fertilizers experience a caking rate exceeding 30% at humidity > 65% RH, resulting in a fertilization uniformity CV value >15%. 3. Technical flaws in controlled release: Release kinetics are mismatched. Traditional controlled-release membranes release an initial concentration of 0.18-0.30 mg / L after 0 hours, resulting in nutrient waste (utilization rate is only 41.5%). Environmental response is sluggish, with existing technologies lacking pH buffering capacity (release rate coefficient of variation (CV) >45% when ΔpH > 1.5). 4. Production process bottlenecks: Insufficient coating uniformity. Traditional spraying processes form droplets >50 μm, resulting in a membrane porosity >15%. Energy efficiency is low, with traditional drying processes requiring 120 minutes and consuming 18.6 MJ / ton of heat. 5. Ecological safety concerns: Uncontrolled degradation. Traditional membranes experience a weight loss >20% after 30 days, causing cumulative soil contamination.

[0007] This technical solution systematically solves the key technical bottlenecks in the application of the above-mentioned zinc fertilizer through component innovation (potassium fulvate-modified nanoparticle synergistic system) and process optimization (three-stage gradient drying), thereby increasing the zinc ion utilization rate from 41.5% to 68.2%, while reducing production costs by 42%.

[0008] Technical Solution

[0009] To solve the above problems, the present invention adopts the following technical solutions.

[0010] A sustained-release coating for medicinal fertilizer granules, comprising the following components in parts by weight: 30-60 parts of potassium fulvate (CAS No.: 68514-28-3), 20-40 parts of polymer material, 5-15 parts of lubricant, 5-10 parts of binder, and 1-10 parts of modification auxiliary agent; wherein the modification auxiliary agent is prepared by the following method: (1) mixing ethyl orthosilicate (CAS No.: 78-10-4) with anhydrous ethanol in an amount of 2-6 times its mass, then adding 25% ammonia water in an amount of 1-4 times its mass, and adding 11-chlorodecanoic acid (CAS No.: 1860-44-2) in an amount of 0.2-0.6 times its mass, stirring at room temperature for 2-6 hours, centrifuging, washing, and drying at 60-75°C for 6 hours. h-12h to obtain nanoparticles; (2) disperse the nanoparticles in anhydrous ethanol 20-40 times the mass of the nanoparticles, add silane coupling agent 3-8 times the mass of the nanoparticles, stir at 40℃-50℃ for 2h-4h, centrifuge, wash, and dry at 60℃-80℃ for 12h-18h to obtain modified nanoparticles; (3) add 10% chitosan (CAS No.: 9012-76-4) solution 10-20 times the mass of the modified nanoparticles, ultrasonically disperse for 30min-45min, add 25% glutaraldehyde solution 0.5-1.5 times the mass of the modified nanoparticles, stir at 40℃-50℃ for 1h-3h, centrifuge, wash, and dry at 40℃-50℃ for 24h to obtain the product.

[0011] The medicinal fertilizer granules are coated with a slow-release film, and the components thereof are as follows, in parts by weight: 40-55 parts of potassium fulvate, 25-35 parts of polymer material, 8-15 parts of lubricant, 5-10 parts of binder, and 1-7 parts of modification auxiliary agent; wherein the modification auxiliary agent is prepared by the following method: (1) mixing ethyl orthosilicate with anhydrous ethanol in an amount of 3-5 times its mass, then adding 25% ammonia water in an amount of 1-4 times its mass, and adding 11-chlorodecanoic acid in an amount of 0.3-0.6 times its mass, stirring at room temperature for 2h-6h, centrifuging, washing, and drying at 65°C-75°C for 6h-10h to obtain nanoparticles; (2) The nanoparticles are dispersed in anhydrous ethanol (20 to 35 times their mass), a silane coupling agent (3 to 6 times their mass) is added, stirred at 40°C to 50°C for 2h to 4h, centrifuged, washed, and dried at 65°C to 80°C for 12h to 16h to obtain modified nanoparticles; (3) the modified nanoparticles are added with a 10% chitosan solution (12 to 18 times their mass), ultrasonically dispersed for 30min to 45min, a 25% glutaraldehyde solution (0.5 to 1.2 times their mass) is added, stirred at 40°C to 48°C for 1h to 3h, centrifuged, washed, and dried at 42°C to 50°C for 24h to obtain the product.

[0012] The medicinal fertilizer granules are coated with a slow-release film, and the components are as follows in parts by weight: 48 parts of potassium fulvate, 30 parts of polymer material, 12 parts of lubricant, 8 parts of binder, and 5 parts of modification auxiliary agent; wherein the modification auxiliary agent is prepared by the following method: (1) mixing ethyl orthosilicate with anhydrous ethanol in an amount 4 times its mass, then adding 25% ammonia water in an amount 3 times its mass, and adding 11-chlorodecanoic acid in an amount 0.5 times its mass, stirring at room temperature for 4 hours, centrifuging, washing, and drying at 70°C for 8 hours to obtain nanoparticles. ; (2) The nanoparticles were dispersed in anhydrous ethanol 30 times the mass of the nanoparticles, silane coupling agent 5 times the mass of the nanoparticles was added, stirred at 45 ° C for 3 hours, centrifuged, washed, and dried at 75 ° C for 14 hours to obtain modified nanoparticles; (3) The modified nanoparticles were added to a 10% chitosan solution 15 times the mass of the modified nanoparticles, ultrasonically dispersed for 38 minutes, and 25% glutaraldehyde solution 0.8 times the mass of the modified nanoparticles was added, stirred at 45 ° C for 2 hours, centrifuged, washed, and dried at 46 ° C for 24 hours to obtain the product.

[0013] The medicinal fertilizer particles are coated with a slow-release film, and the polymer material is one of polylactic acid (CAS No.: 26023-30-3), polyethylene (CAS No.: 9002-88-4), polypropylene (CAS No.: 9003-07-0), and polyester (CAS No.: 25038-59-9).

[0014] The medicinal fertilizer particles are coated with a slow-release film, the lubricant is one or more of calcium stearate (CAS No.: 1592-23-0), magnesium stearate (CAS No.: 557-04-0), and talc (CAS No.: 14807-96-6); the binder is one or more of carboxymethyl cellulose (CAS No.: 9000-11-7), polyvinyl alcohol (CAS No.: 9002-89-5), and a starch-based binder; the starch-based binder is hydroxypropyl starch (CAS No.: 9049-76-7).

[0015] The medicinal fertilizer particles are coated with a slow-release coating, and the silane coupling agent is γ-aminopropyltriethoxysilane (CAS No.: 919-30-2) or 3-(methacryloyloxy)propyltrimethoxysilane (CAS No.: 2530-85-0).

[0016] The method for preparing the sustained-release coating for the medicinal fertilizer granules as described above comprises the following steps: preparing a twin-screw mixer and controlling the speed to 800-1200 rpm and the temperature to 40±5°C, then adding the components in three gradient steps: first, premixing the polymer material with one-third of the mass of the lubricant for 3 min-10 min to form a base material, then adding potassium fulvic acid to the base material and mixing with the remaining mass of the lubricant for 5 min-15 min, finally injecting the binder and the modifying agent, and continuing to mix for 8 min-10 min until the system viscosity reaches 2500±100 mPa·s; then, fluidizing , atomization and spraying treatment, wherein the fluidizing gas pressure is 0.15MPa-0.25MPa, the fluidized bed porosity is maintained at 60%-70%, wherein the atomization pressure is 0.8MPa-1.2MPa, the atomization electric field pressure is 30kV-50kV, the atomized droplet particle size is 30μm-50μm, wherein the initial 5min of spraying is maintained at 50℃-55℃, wherein the temperature is linearly increased to 70℃-75℃ within 10min-25min of spraying, wherein the temperature is reduced to 60℃-65℃ for the last 5min of spraying, and finally a three-stage drying treatment is carried out to obtain the product.

[0017] The equipment selected is as follows: Twin-screw mixer (mixing slurry homogenization), manufacturer: DAHAN Vibration Machinery, equipment model: Twin Screw Mixer. Fluidized atomization spray equipment, manufacturer: Senieer (Sener Technology), equipment model: FBM series Fluidized Bed Processor. Drying equipment, recommended manufacturer: Prism Pharma Machinery, equipment model: Multi-stage Fluid Bed Dryer.

[0018] The method for preparing the sustained-release coating for the medicinal fertilizer particles comprises the following steps: spraying at a high pressure of 1.5 MPa for 5 seconds to 10 seconds at intervals of 1 minute within 10 minutes to 25 minutes of spraying.

[0019] The preparation method of the sustained-release coating for the medicinal fertilizer granules, the three-stage drying treatment is as follows: the initial drying stage adopts air drying at 60°C-65°C for 15 minutes, and the air drying wind speed is 8m / s-10m / s; the curing stage adopts hot air treatment at 80°C-90°C for 30 minutes, the pulsation frequency of the hot air is 2Hz, and the relative humidity is reduced to 30%; the aging stage adopts air drying at 45°C-50°C for 15 minutes, and the air drying wind speed is 2m / s-8m / s, and nitrogen protection is carried out simultaneously.

[0020] Beneficial effects

[0021] The slow-release coating technology for pesticide-fertilizer granules provided by this invention offers the following multi-faceted benefits compared to existing technologies. Precise slow-release control and efficient nutrient utilization are achieved through the synergistic effect of modified nanoparticles (ethyl orthosilicate-chitosan composite system) and potassium fulvate, achieving a close coupling between the zinc ion release rate and crop demand curve. The pH buffering properties of potassium fulvate (pH 4.5-6.5) ensure that the coating maintains zinc availability in high-pH soils, resolving the fixation issue of traditional zinc fertilizers at pH > 6. Furthermore, the coating's anti-antagonistic design physically isolates zinc from phosphate fertilizers by 70%. Mechanical properties are significantly improved: the single-particle crushing strength reaches 44.5-48.3N (Example), a 25%-45% increase over the comparative example (33.4-39.5N). The mass loss rate in abrasion resistance testing is only 1.7%-2.1% (Example), a 40%-57% reduction over the conventional process (3.0%-4.0%). Comprehensive application benefits: Agronomic performance has been improved. Early field trials in corn have shown a zinc utilization rate of 68.2% (compared to 41.5% for conventional zinc fertilizers), and the incidence of apple leaflet disease has been reduced from 23% to 6% (three-year follow-up data). This technology, by constructing a three-level regulatory system (carrier-interface-structure), overcomes technical bottlenecks such as disordered nutrient release, insufficient mechanical strength, and slow environmental response associated with traditional coating technologies, providing an innovative solution for smart fertilizer development. Third-party testing (SGS report No. SH2025-036) confirms that the product complies with the ISO 18645:2024 international standard for slow-release fertilizers. It has been successfully applied in a rice cultivation demonstration project in the black soil region of Northeast China (pH 7.2-8.1), achieving a significant 18.7% yield increase. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a scanning electron micrograph of the sustained-release coating prepared in Example 5. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to specific embodiments.

[0024] Unless otherwise defined, the technical and scientific terms used in the following examples have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. In practical application, the weight parts referred to in the present invention can be set as the unit kilogram.

[0025] Example 1

[0026] The medicinal fertilizer granules are coated with a slow-release film, and the components are as follows, in parts by weight: 30 parts of potassium fulvate, 40 parts of polymer materials, 5 parts of lubricants, 10 parts of binders, and 1 part of modification aids; wherein the modification aids are prepared as follows: (1) ethyl orthosilicate is mixed with anhydrous ethanol twice its mass, and then 25% ammonia water of 4 times the mass of ethyl orthosilicate is added, and 11-chlorodecanoic acid of 0.2 times the mass of ethyl orthosilicate is added, and the mixture is stirred at room temperature for 6 hours, centrifuged, washed, and dried at 60°C for 12 hours to obtain nanoparticles; (2) The nanoparticles were dispersed in anhydrous ethanol (20 times their mass), a silane coupling agent (8 times their mass) was added, the mixture was stirred at 40°C for 4 hours, centrifuged, washed, and dried at 60°C for 18 hours to obtain modified nanoparticles; (3) The modified nanoparticles were added to a 10% chitosan solution (10 times their mass), ultrasonically dispersed for 45 minutes, a 25% glutaraldehyde solution (0.5 times their mass) was added, the mixture was stirred at 50°C for 1 hour, centrifuged, washed, and dried at 50°C for 24 hours to obtain the product. The medicinal fertilizer particles were coated with a sustained-release film, and the polymer material was polylactic acid. The medicinal fertilizer particles were coated with a sustained-release film, and the lubricant was calcium stearate; the binder was carboxymethyl cellulose. The medicinal fertilizer particles were coated with a sustained-release film, and the silane coupling agent was γ-aminopropyltriethoxysilane.

[0027] The method for preparing a sustained-release coating for medicinal fertilizer particles comprises the following steps: preparing a twin-screw mixer and controlling the speed to 800 rpm and the temperature to 40±5°C; then adding components in three gradient steps: first, premixing a polymer material with one-third of a lubricant by weight for 3 minutes to form a base material; then adding potassium fulvic acid and the remaining lubricant by weight to the base material and mixing for 15 minutes; finally, injecting a binder and a modification auxiliary agent; and continuously mixing for 8 minutes until the system viscosity reaches 2500±100 mPa·s; then, performing fluidization, atomization and spraying treatments, wherein the fluidization air pressure is 0.25 MPa, the fluidized bed porosity is maintained at 60%, the atomization pressure is 1.2 MPa, the atomization electric field pressure is 30 kV, the atomized droplet particle size is 50 μm, wherein the spraying temperature is maintained at 50°C for the initial 5 minutes, wherein the temperature is linearly increased to 70°C within 25 minutes of the spraying, wherein the temperature is reduced to 65°C for the last 5 minutes of the spraying; and finally, performing a three-stage drying treatment to obtain a product. The three-stage drying process is as follows: the initial drying stage uses air drying at 60°C for 15 minutes at a wind speed of 10 m / s; the curing stage uses hot air at 80°C for 30 minutes at a pulsation frequency of 2 Hz and a relative humidity of 30%; and the aging stage uses air drying at 50°C for 15 minutes at a wind speed of 2 m / s, with nitrogen protection simultaneously applied.

[0028] Example 2

[0029] The medicinal fertilizer granules are coated with a slow-release film, and the components are as follows, in parts by weight: 60 parts of potassium fulvate, 20 parts of polymer material, 15 parts of lubricant, 5 parts of binder, and 10 parts of modification auxiliary agent; wherein the modification auxiliary agent is prepared as follows: (1) ethyl orthosilicate is mixed with anhydrous ethanol in an amount of 6 times its mass, and then 25% ammonia water in an amount of 1 times the mass of ethyl orthosilicate is added, and 11-chlorodecanoic acid in an amount of 0.6 times the mass of ethyl orthosilicate is added, and the mixture is stirred at room temperature for 2 hours, centrifuged, washed, and dried at 75°C for 6 hours to obtain nanoparticles; (2) The nanoparticles are dispersed in anhydrous ethanol 40 times their mass, a silane coupling agent 3 times their mass is added, the mixture is stirred at 50°C for 2 hours, centrifuged, washed, and dried at 80°C for 12 hours to obtain modified nanoparticles; (3) The modified nanoparticles are added to a 10% chitosan solution 20 times their mass, ultrasonically dispersed for 30 minutes, a 25% glutaraldehyde solution 1.5 times their mass is added, the mixture is stirred at 40°C for 3 hours, centrifuged, washed, and dried at 40°C for 24 hours to obtain the product. The medicinal fertilizer particles are coated with a sustained-release film, and the polymer material is polyethylene. The medicinal fertilizer particles are coated with a sustained-release film, and the lubricant is magnesium stearate; the binder is polyvinyl alcohol. The medicinal fertilizer particles are coated with a sustained-release film, and the silane coupling agent is γ-aminopropyltriethoxysilane.

[0030] The method for preparing a sustained-release coating for medicinal fertilizer particles comprises the following steps: preparing a twin-screw mixer and controlling the speed to 1200 rpm and the temperature to 40±5°C; then adding components in three gradient steps: first, premixing a polymer material with one-third of a lubricant by weight for 10 minutes to form a base material; then adding potassium fulvic acid and the remaining lubricant by weight to the base material and mixing for 5 minutes; finally, injecting a binder and a modification auxiliary agent; and continuously mixing for 10 minutes until the system viscosity reaches 2500±100 mPa·s; then, performing fluidization, atomization and spraying treatments, wherein the fluidization air pressure is 0.25 MPa, the fluidized bed porosity is maintained at 70%, the atomization pressure is 0.8 MPa, the atomization electric field pressure is 50 kV, the atomized droplet particle size is 30 μm, wherein the initial 5 minutes of spraying are maintained at 55°C, wherein the temperature is linearly increased to 75°C within 10 minutes of spraying, wherein the temperature is reduced to 60°C during the last 5 minutes of spraying; and finally, performing a three-stage drying treatment to obtain a product. During the 25-minute spraying period, high-pressure spraying at 1.5 MPa was applied for 5 seconds every 1 minute. The three-stage drying process was as follows: the initial drying stage employed air drying at 65°C for 15 minutes at a wind speed of 8 m / s; the curing stage employed hot air at 90°C for 30 minutes at a pulsation frequency of 2 Hz, with relative humidity reduced to 30%; and the aging stage employed air drying at 45°C for 15 minutes at a wind speed of 8 m / s, with nitrogen protection applied simultaneously.

[0031] Example 3

[0032] The medicinal fertilizer granules are coated with a slow-release film, and the components are as follows in parts by weight: 40 parts of potassium fulvate, 35 parts of polymer material, 15 parts of lubricant, 5 parts of binder, and 7 parts of modification auxiliary agent; wherein the modification auxiliary agent is prepared by the following method: (1) mixing ethyl orthosilicate with anhydrous ethanol in an amount 3 times its mass, then adding 25% ammonia water in an amount 4 times its mass, and adding 11-chlorodecanoic acid in an amount 0.3 times its mass, stirring at room temperature for 6 hours, centrifuging, washing, and drying at 65°C for 10 hours to obtain nanoparticles. (2) The nanoparticles are dispersed in anhydrous ethanol (20 times their mass), a silane coupling agent (6 times their mass) is added, the mixture is stirred at 40°C for 4 hours, centrifuged, washed, and dried at 65°C for 16 hours to obtain modified nanoparticles; (3) The modified nanoparticles are added to a 10% chitosan solution (12 times their mass), ultrasonically dispersed for 45 minutes, a 25% glutaraldehyde solution (0.5 times their mass) is added, the mixture is stirred at 48°C for 1 hour, centrifuged, washed, and dried at 50°C for 24 hours to obtain the product. The medicinal fertilizer particles are coated with a sustained-release film, and the polymer material is polyethylene. The medicinal fertilizer particles are coated with a sustained-release film, and the lubricant is talc; the binder is a starch-based binder; wherein the starch-based binder is hydroxypropyl starch. The medicinal fertilizer particles are coated with a sustained-release film, and the silane coupling agent is 3-(methacryloyloxy)propyltrimethoxysilane.

[0033] The method for preparing a sustained-release coating for medicinal fertilizer particles comprises the following steps: preparing a twin-screw mixer and controlling the speed to 900 rpm and the temperature to 40±5°C; then adding components in three gradient steps: first, premixing a polymer material with one-third of a lubricant by weight for 8 minutes to form a base material; then adding potassium fulvic acid and the remaining lubricant by weight to the base material and mixing for 7 minutes; finally, injecting a binder and a modification auxiliary agent; and continuously mixing for 10 minutes until the system viscosity reaches 2500±100 mPa·s; then, performing fluidization, atomization and spraying treatments, wherein the fluidization air pressure is 0.15 MPa, the fluidized bed porosity is maintained at 68%, the atomization pressure is 0.8 MPa, the atomization electric field pressure is 45 kV, the atomized droplet size is 35 μm, wherein the initial 5 minutes of spraying are maintained at 55°C, wherein the temperature is linearly increased to 75°C within 15 minutes of spraying, wherein the temperature is reduced to 60°C during the last 5 minutes of spraying; and finally, performing a three-stage drying treatment to obtain a product. During the 25-minute spraying period, high-pressure spraying at 1.5 MPa was applied for 5 seconds every 1 minute. The three-stage drying process was as follows: the initial drying stage employed air drying at 65°C for 15 minutes at a wind speed of 8 m / s; the curing stage employed hot air at 90°C for 30 minutes at a pulsation frequency of 2 Hz, with relative humidity reduced to 30%; and the aging stage employed air drying at 45°C for 15 minutes at a wind speed of 8 m / s, with nitrogen protection applied simultaneously.

[0034] Example 4

[0035] The medicinal fertilizer granules are coated with a slow-release film, and the components are as follows in parts by weight: 55 parts of potassium fulvate, 25 parts of polymer material, 15 parts of lubricant, 5 parts of binder, and 7 parts of modification auxiliary agent; wherein the modification auxiliary agent is prepared by the following method: (1) mixing ethyl orthosilicate with anhydrous ethanol 5 times its mass, then adding 25% ammonia water 1 times the mass of ethyl orthosilicate, and adding 11-chlorodecanoic acid 0.6 times the mass of ethyl orthosilicate, stirring at room temperature for 2 hours, centrifuging, washing, and drying at 75°C for 6 hours to obtain nanoparticles. (2) The nanoparticles were dispersed in anhydrous ethanol (35 times their mass), a silane coupling agent (6 times their mass) was added, the mixture was stirred at 40°C for 4 hours, centrifuged, washed, and dried at 65°C for 16 hours to obtain modified nanoparticles; (3) The modified nanoparticles were added to a 10% chitosan solution (18 times their mass), ultrasonically dispersed for 30 minutes, a 25% glutaraldehyde solution (1.2 times their mass) was added, the mixture was stirred at 40°C for 1 hour, centrifuged, washed, and dried at 42°C for 24 hours to obtain the product. The medicinal fertilizer particles were coated with a sustained-release film, and the polymer material was polyester. The medicinal fertilizer particles were coated with a sustained-release film, and the lubricant was magnesium stearate; the binder was polyvinyl alcohol. The medicinal fertilizer particles were coated with a sustained-release film, and the silane coupling agent was 3-(methacryloyloxy)propyltrimethoxysilane.

[0036] The method for preparing a sustained-release coating for medicinal fertilizer particles comprises the following steps: preparing a twin-screw mixer and controlling the speed to 1100 rpm and the temperature to 40±5°C; then adding components in three gradient steps: first, premixing a polymer material with one-third of a lubricant by weight for 7 minutes to form a base material; then adding potassium fulvic acid and the remaining lubricant by weight to the base material and mixing for 13 minutes; finally, injecting a binder and a modification auxiliary agent; and continuously mixing for 8 minutes until the system viscosity reaches 2500±100 mPa·s; then, performing fluidization, atomization and spraying treatments, wherein the fluidization air pressure is 0.22 MPa, the fluidized bed porosity is maintained at 63%, the atomization pressure is 1.2 MPa, the atomization electric field pressure is 35 kV, the atomized droplet particle size is 45 μm, wherein the spraying is maintained at 50°C for the initial 5 minutes, wherein the temperature is linearly increased to 70°C within 15 minutes of the spraying, wherein the temperature is reduced to 65°C for the last 5 minutes of the spraying; and finally, performing a three-stage drying treatment to obtain a product. The three-stage drying process is as follows: the initial drying stage uses air drying at 60°C for 15 minutes at a wind speed of 10 m / s; the curing stage uses hot air at 80°C for 30 minutes at a pulsation frequency of 2 Hz and a relative humidity of 30%; and the aging stage uses air drying at 50°C for 15 minutes at a wind speed of 2 m / s, with nitrogen protection simultaneously applied.

[0037] Example 5

[0038] The medicinal fertilizer granules are coated with a slow-release film, and the components are as follows in parts by weight: 48 parts of potassium fulvate, 30 parts of polymer material, 12 parts of lubricant, 8 parts of binder, and 5 parts of modification auxiliary agent; wherein the modification auxiliary agent is prepared by the following method: (1) mixing ethyl orthosilicate with anhydrous ethanol in an amount 4 times its mass, then adding 25% ammonia water in an amount 3 times its mass, and adding 11-chlorodecanoic acid in an amount 0.5 times its mass, stirring at room temperature for 4 hours, centrifuging, washing, and drying at 70°C for 8 hours to obtain nanoparticles. (2) The nanoparticles were dispersed in anhydrous ethanol 30 times their mass, a silane coupling agent 5 times their mass was added, stirred at 45°C for 3 hours, centrifuged, washed, and dried at 75°C for 14 hours to obtain modified nanoparticles; (3) The modified nanoparticles were added to a 10% chitosan solution 15 times their mass, ultrasonically dispersed for 38 minutes, and a 25% glutaraldehyde solution 0.8 times their mass was added, stirred at 45°C for 2 hours, centrifuged, washed, and dried at 46°C for 24 hours to obtain the product. The medicinal fertilizer particles were coated with a sustained-release film, and the polymer material was polylactic acid. The medicinal fertilizer particles were coated with a sustained-release film, and the lubricant was talc; the binder was a starch-based binder; wherein the starch-based binder was hydroxypropyl starch. The medicinal fertilizer particles were coated with a sustained-release film, and the silane coupling agent was γ-aminopropyltriethoxysilane.

[0039] The method for preparing a sustained-release coating for medicinal fertilizer particles comprises the following steps: preparing a twin-screw mixer and controlling the speed to 1000 rpm and the temperature to 40±5°C; then adding components in three gradient steps: first, premixing a polymer material with one-third of a lubricant by weight for 7 minutes to form a base material; then adding potassium fulvic acid and the remaining lubricant by weight to the base material and mixing for 10 minutes; finally, injecting a binder and a modification auxiliary agent; and continuously mixing for 9 minutes until the system viscosity reaches 2500±100 mPa·s; then, performing fluidization, atomization and spraying treatments, wherein the fluidization air pressure is 0.20 MPa, the fluidized bed porosity is maintained at 65%, the atomization pressure is 1.0 MPa, the atomization electric field pressure is 40 kV, the atomized droplet particle size is 40 μm, wherein the spraying temperature is maintained at 53°C for the initial 5 minutes, wherein the temperature is linearly increased to 73°C within 18 minutes of the spraying, wherein the temperature is reduced to 63°C for the last 5 minutes of the spraying; and finally, performing a three-stage drying treatment to obtain a product. The spraying process involved applying a high-pressure spray of 1.5 MPa for 8 seconds at intervals of 1 minute within the 17-minute spraying period. The three-stage drying process was as follows: the initial drying stage involved air drying at 63°C for 15 minutes at a wind speed of 9 m / s; the curing stage involved hot air treatment at 85°C for 30 minutes at a pulsation frequency of 2 Hz, with relative humidity reduced to 30%; and the aging stage involved air drying at 48°C for 15 minutes at a wind speed of 5 m / s, with nitrogen protection applied simultaneously.

[0040] Comparative Example 1

[0041] Same as Example 5, except that the modifying agent is removed.

[0042] Comparative Example 2

[0043] The same as Example 5, the preparation of the modification auxiliary agent was adjusted: in step (1), the addition of 11-chlorodecanoic acid was eliminated, and in step (3), sodium alginate was used instead of chitosan.

[0044] Comparative Example 3

[0045] Same as Example 5, with the modification aid preparation adjusted as follows: in step (1), sodium metasilicate was used instead of ethyl orthosilicate.

[0046] Comparative Example 4

[0047] Same as Example 5, with the modification aid preparation adjusted as follows: in step (3), the addition of chitosan is eliminated.

[0048] Comparative Example 5

[0049] Same as Example 5, except that ethyl orthosilicate was used instead of the modification aid.

[0050] Test method: Nutrient release characteristics test: Take 5.0g of coated fertilizer granules (1g of granular zinc is wrapped in every 2g of slow-release film, Shengyuan Agricultural Materials Lvlong-granular zinc, zinc content is 33.5%, Shandong Lvlong Biotechnology Co., Ltd.), place it in 100mL of deionized water, oscillate at a constant temperature of 25℃ (120rpm), take samples at 0h and 28d respectively, and use colorimetry to determine the zinc ion concentration. Coating mechanical property test: Use TA.XT Plus texture analyzer to determine the single particle crushing strength, loading rate 1.0mm / s, and record the maximum pressure value at the moment of rupture. Referring to ASTM D4058 standard, 100g of sample was placed on a drum tester (rotation speed 30rpm) for 1h, and the mass loss rate was calculated. Microstructural characterization: A field emission scanning electron microscope (S4800, Hitachi) was used to observe the cross-sectional morphology of the coating, with an acceleration voltage of 5kV and a working distance of 8mm. The results are as follows Figure 1 Degradation performance test: Weigh 10g of the coating material and bury it in potting soil (humidity 30%, 25℃), and measure the weight loss rate every 10 days.

[0051] Table 1 Test results

[0052]

[0053] This invention discloses a slow-release coating for medicinal fertilizer granules and its preparation method. Through unique component design and optimized processes, it achieves multiple significant technical benefits, providing technical support for efficient and sustainable agricultural production. Excellent nutrient slow-release performance: The slow-release coating effectively controls the nutrient release rate from the medicinal fertilizer granules, significantly reducing initial release and enabling long-term sustained release. Test results show that the zinc ion release concentration of Example 5 was only 0.11 mg / L at 0 h and 12.3 mg / L at 28 d, a significant improvement over the 0.25 mg / L (0 h) and 20.1 mg / L (28 d) values ​​of Comparative Example 1 (without a modifying adjuvant). This demonstrates that the invention effectively suppresses the initial burst of nutrient release, ensuring a steady nutrient supply. This improves nutrient utilization efficiency, reduces nutrient loss, and ensures continuous nutritional support for crops throughout their growth cycle. It also reduces environmental impact: nutrient infiltration into groundwater or soil is reduced, meeting the requirements of green agriculture. Enhanced Mechanical Strength and Durability: The sustained-release coating of this invention significantly improves the mechanical properties and wear resistance of the particles. Test data showed that the single-particle crushing strength of Example 5 reached 48.3N, significantly higher than the 35.6N of Comparative Example 1. The mass loss rate (a wear resistance indicator) was only 1.7%, compared to 3.5% in Comparative Example 1. These improvements are attributed to: the strengthening effect of the modification additive: the nanoparticles prepared using ethyl orthosilicate, modified with a silane coupling agent and chitosan, enhance the structural strength of the coating. An optimized preparation process: high-pressure spraying and three-stage drying ensure a uniform and dense coating, reducing breakage under mechanical stress. Technical benefits include: improved robustness: the coating is less susceptible to cracking or flaking during transportation, storage, and application, ensuring controllable nutrient release. Extended service life: enhanced durability reduces premature failure of the coating in soil. Controllable degradation: through component and process design, the present invention effectively controls the degradation rate of the coating in soil. The weight loss rate of Example 5 after 30 days is 14.2%, which is significantly lower than the 22.1% of Comparative Example 1. This feature is due to: the biodegradability of chitosan: as an important component of the coating, chitosan can slowly decompose. Three-stage drying process: the curing and aging stages optimize the cross-linking structure of the coating and slow down the degradation rate. Its technical effects are: extending the nutrient release cycle: matching the growth needs of crops and reducing the need for frequent fertilization. Reducing environmental residues: slow degradation reduces the risk of long-term accumulation. Uniform and dense microstructure: Scanning electron microscopy observations show that the slow-release coating of the present invention has a uniform and dense microstructure (taking Example 5 as an example). This structure comes from: high-pressure spraying technology: high-pressure spraying during the spraying process ensures uniform distribution of the coating. Three-stage drying process: the initial drying, curing and aging stages gradually stabilize the coating to avoid defects such as cracks or bubbles. Its technical effects include: improving barrier properties: the uniform structure enhances the encapsulation ability of nutrients and further optimizes release control.Improved stability: The dense coating enhances the film's resistance to environmental factors (such as humidity and temperature). Environmental friendliness: The components and process design employed in this invention fully consider environmental impacts. Biodegradable materials: Ingredients such as chitosan gradually decompose in the natural environment, reducing soil contamination. Non-toxic process: No toxic or hazardous substances are used in the preparation process, making the product safe for crops and ecosystems. Its technical benefits include: Supporting sustainable development: Reducing chemical residues and meeting the environmental protection requirements of modern agriculture. Reducing ecological risks: Even if nanoparticles are present, they are encapsulated in the film and their release after degradation is controllable, minimizing direct environmental impact. Optimized preparation process: The preparation method of this invention utilizes twin-screw mixing, fluidized atomization spraying, and a three-stage drying process to ensure efficient production and excellent performance of the film. Twin-screw mixing: Components are added stepwise and the viscosity is controlled to 2500±100 mPa·s to ensure material uniformity. Fluidized spraying: Fluidizing air pressure of 0.15-0.25 MPa and atomization pressure of 0.8-1.2 MPa, combined with high-pressure spraying, form a high-quality coating. A three-stage drying process: primary drying (60-65°C), curing (80-90°C with hot air pulsation), and aging (45-50°C with nitrogen protection) ensures a perfect coating cure. Its technical benefits include: A simple and controllable process: Standard industrial equipment (such as twin-screw mixers and fluidized bed processors) is used, facilitating large-scale production. Improved cost-effectiveness: Compared with traditional, complex processes, this method simplifies the steps and reduces production costs. This invention provides solutions to challenges in zinc fertilizer application (such as soil pH effects, antagonism with other fertilizers, and corrosiveness). It also mitigates soil pH effects: Its slow-release properties allow zinc ions to be gradually released under varying pH conditions, improving absorption efficiency. It also reduces fertilizer antagonism: The coating isolates the zinc fertilizer from direct contact with other fertilizers, minimizing antagonistic effects. It also reduces corrosion: The encapsulated zinc fertilizer particles reduce corrosion to equipment and the environment. Its technical benefits include: Improved application efficiency: It overcomes the limitations of traditional zinc fertilizers and is particularly suitable for zinc-deficiency-sensitive crops such as corn and rice. It also enhances compatibility: It facilitates mixing with other fertilizers, increasing fertilization flexibility.

[0054] In summary, the slow-release coating for the medicinal fertilizer granules of the present invention achieves the following technical effects through the scientific proportions of potassium fulvic acid, polymer materials, lubricants, binders and modification additives, as well as the optimized processes of twin-screw mixing, fluidized bed spraying and three-stage drying: precise control of nutrient release, improved utilization efficiency and reduced environmental pollution; significant enhancement of the mechanical strength and durability of the coating, ensuring reliability of use; controllable degradation, prolonged fertilizer effect and improved environmental friendliness; formation of a uniform and dense microstructure, improved performance stability; provision of a simple and efficient preparation method, and potential for industrialization. These technical effects not only solve the problems in existing zinc fertilizer applications, but also provide an innovative slow-release coating solution for the field of bio-agricultural technology, with significant economic and ecological benefits.

[0055] The above content is a further detailed description of the present invention in conjunction with specific implementation methods. It cannot be considered that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the field of bio-agricultural technology to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as falling within the scope of protection determined by the claims submitted by the present invention.

Claims

1. A slow-release coating for medicinal fertilizer granules, characterized in that: The components are as follows in parts by weight: 30-60 parts of potassium fulvic acid, 20-40 parts of polymer material, 5-15 parts of lubricant, 5-10 parts of binder, and 1-10 parts of modification aid; wherein the preparation method of the modification aid is as follows: (1) mixing ethyl orthosilicate with anhydrous ethanol in an amount of 2-6 times its mass, then adding 25% ammonia water in an amount of 1-4 times its mass, and adding 11-chlorodecanoic acid in an amount of 0.2-0.6 times its mass, stirring at room temperature for 2h-6h, centrifuging, washing, and drying at 60℃-75℃ for 6h-12h to obtain nanoparticles; (2) separating the nanoparticles into the nanoparticles; Disperse in anhydrous ethanol 20 to 40 times its mass, add silane coupling agent 3 to 8 times the mass of the nanoparticles, stir at 40°C to 50°C for 2h to 4h, centrifuge, wash, and dry at 60°C to 80°C for 12h to 18h to obtain modified nanoparticles; (3) add 10% chitosan solution 10 to 20 times its mass, ultrasonically disperse for 30min to 45min, add 25% glutaraldehyde solution 0.5 to 1.5 times the mass of the modified nanoparticles, stir at 40°C to 50°C for 1h to 3h, centrifuge, wash, and dry at 40°C to 50°C for 24h to obtain the product.

2. The sustained-release coating for medicinal fertilizer granules according to claim 1, characterized in that: The components are as follows in parts by weight: 40-55 parts of potassium fulvate, 25-35 parts of polymer material, 8-15 parts of lubricant, 5-10 parts of binder, and 1-7 parts of modification aid; wherein the preparation method of the modification aid is as follows: (1) mixing ethyl orthosilicate with anhydrous ethanol in an amount of 3-5 times its mass, then adding 25% ammonia water in an amount of 1-4 times its mass, and adding 11-chlorodecanoic acid in an amount of 0.3-0.6 times its mass, stirring at room temperature for 2h-6h, centrifuging, washing, and drying at 65℃-75℃ for 6h-10h to obtain nanoparticles; (2) dispersing the nanoparticles Add 3 to 6 times the mass of the nanoparticles to anhydrous ethanol at a concentration of 20 to 35 times the mass of the nanoparticles, stir at 40 to 50°C for 2 to 4 hours, centrifuge, wash, and dry at 65 to 80°C for 12 to 16 hours to obtain modified nanoparticles; (3) add 10% chitosan solution at a concentration of 12 to 18 times the mass of the modified nanoparticles, ultrasonically disperse for 30 to 45 minutes, add 25% glutaraldehyde solution at a concentration of 0.5 to 1.2 times the mass of the modified nanoparticles, stir at 40 to 48°C for 1 to 3 hours, centrifuge, wash, and dry at 42 to 50°C for 24 hours to obtain the product.

3. The sustained-release coating for the medicinal fertilizer granules according to claim 2, characterized in that: The components are as follows in parts by weight: 48 parts of potassium fulvic acid, 30 parts of polymer material, 12 parts of lubricant, 8 parts of binder, and 5 parts of modification aid; wherein the preparation method of the modification aid is as follows: (1) tetraethyl orthosilicate is mixed with anhydrous ethanol of 4 times its mass, and then 25% ammonia water of 3 times the mass of tetraethyl orthosilicate is added, and 11-chlorodecanoic acid of 0.5 times the mass of tetraethyl orthosilicate is added, stirred at room temperature for 4 hours, centrifuged, washed, and dried at 70°C for 8 hours to obtain nanoparticles; (2) the nanoparticles are mixed with anhydrous ethanol of 4 times its mass, and then 25% ammonia water of 3 times the mass of tetraethyl orthosilicate is added, and 11-chlorodecanoic acid of 0.5 times the mass of tetraethyl orthosilicate is added, stirred at room temperature for 4 hours, centrifuged, washed, and dried at 70°C for 8 hours to obtain nanoparticles; (3) the nanoparticles are mixed with anhydrous ethanol of 4 times its mass, and then 25% ammonia water of 3 times the mass of tetraethyl orthosilicate is added, and 11-chlorodecanoic acid of 0.5 times the mass of tetraethyl orthosilicate is added, stirred at room temperature for 4 hours, centrifuged, washed, and dried at 70°C for 8 hours to obtain nanoparticles. The particles were dispersed in anhydrous ethanol (30 times their mass), and a silane coupling agent (5 times their mass) was added. The mixture was stirred at 45°C for 3 h, centrifuged, washed, and dried at 75°C for 14 h to obtain modified nanoparticles. (3) The modified nanoparticles were added to a 10% chitosan solution (15 times their mass), ultrasonically dispersed for 38 min, and a 25% glutaraldehyde solution (0.8 times their mass) was added. The mixture was stirred at 45°C for 2 h, centrifuged, washed, and dried at 46°C for 24 h to obtain the product.

4. The sustained-release coating for medicinal fertilizer granules according to claim 1, characterized in that: The polymer material is one of polylactic acid, polyethylene, polypropylene and polyester.

5. The sustained-release coating for medicinal fertilizer granules according to claim 1, characterized in that: The lubricant is one or more of calcium stearate, magnesium stearate, and talc; the binder is one or more of carboxymethyl cellulose, polyvinyl alcohol, and a starch-based binder; wherein the starch-based binder is hydroxypropyl starch.

6. The sustained-release coating for medicinal fertilizer granules according to claim 1, characterized in that: The silane coupling agent is γ-aminopropyltriethoxysilane or 3-(methacryloyloxy)propyltrimethoxysilane.

7. The method for preparing the sustained-release coating for the medicinal fertilizer granules according to claim 1, wherein: The following steps are involved: Prepare a twin-screw mixer and control the speed to 800-1200rpm and the temperature to 40±5℃. Then, add the components in three steps: first, pre-mix the polymer material with one-third of the mass of the lubricant for 3min-10min to form a base material. Then, add potassium fulvic acid and the remaining mass of the lubricant to the base material and mix for 5min-15min. Finally, inject the binder and the modifying agent and continue mixing for 8min-10min until the system viscosity reaches 2500±100mPa·s. Then, perform fluidization, atomization and spraying. The air pressure is 0.15MPa-0.25MPa, the porosity of the fluidized bed is maintained at 60%-70%, the atomization pressure is 0.8MPa-1.2MPa, the atomization electric field pressure is 30kV-50kV, the atomized droplet size is 30μm-50μm, the initial 5min of spraying is maintained at 50℃-55℃, the temperature is linearly increased to 70℃-75℃ within 10min-25min of spraying, the temperature is cooled to 60℃-65℃ in the last 5min of spraying, and finally a three-stage drying treatment is carried out to obtain the product.

8. The method for preparing the sustained-release coating for the medicinal fertilizer granules according to claim 7, wherein: The high-pressure spraying of 1.5 MPa is carried out for 5 seconds to 10 seconds at intervals of 1 minute within 10 minutes to 25 minutes of spraying.

9. The method for preparing the sustained-release coating for the medicinal fertilizer granules according to claim 8, wherein: The three-stage drying process is as follows: in the initial drying stage, air drying is performed at 60°C-65°C for 15 minutes, with a wind speed of 8m / s-10m / s; in the curing stage, hot air is applied at 80°C-90°C for 30 minutes, with a pulsation frequency of 2Hz and a relative humidity reduced to 30%; in the aging stage, air drying is performed at 45°C-50°C for 15 minutes, with a wind speed of 2m / s-8m / s, and nitrogen protection is performed simultaneously.

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