Slow-release coating film for pesticide-fertilizer particles and preparation method of slow-release coating film

Abstract

The invention discloses a slow-release coating for pesticide-fertilizer particles and a preparation method of the slow-release coating, and belongs to the technical field of biological agriculture. The coating is composed of 30-60 parts of potassium fulvate, 20-40 parts of a high polymer material, 5-15 parts of a lubricant, 5-10 parts of a binder and 1-10 parts of a performance additive, the performance additive is prepared into nanoparticles through tetraethoxysilane and 11-chlorodecanoic acid, and the nanoparticles are modified through a silane coupling agent and then crosslinked with chitosan to form a composite structure. According to the preparation method, a double-screw gradient mixing process (800-1200 rpm, 40 + / -5 DEG C) is adopted, and fluidized bed atomization spraying and three-stage drying are combined. According to the technical breakthrough, the utilization rate of zinc ions is increased to 68.2% from 41.5%, the coating crushing strength reaches 48.3 N, the 28d zinc release amount is 12.3 mg / L, and the 30d degradation rate is 14.2%. Through the synergistic effect of pH buffering of potassium fulvate and modified nanoparticles, the problems of zinc immobilization and phosphorus-zinc antagonism of high-pH soil are effectively solved, the fertilizer is suitable for corn, rice and other crops, and field tests show that the yield is increased by 18.7%.

Description

Technical Field

[0001] The present invention belongs to the technical field of bio-agriculture, and specifically relates to a slow-release coating for medicine-fertilizer granules and a preparation method thereof. Background Art

[0002] Zinc fertilizer is one of the essential trace elements for crops, and is particularly crucial for the growth and development of crops such as corn, rice, cotton, beans, and fruit trees. When crops are deficient in zinc, it will lead to chlorosis of leaves, weakened photosynthesis, shortened internodes, dwarf plants, inhibited growth, and ultimately reduced yield. For example, when fruit trees such as apples, pears, cherries, plums, and grapes are deficient in zinc, the leaves will show symptoms such as becoming smaller and yellowing, and even the so-called "little leaf disease" may occur. When corn is deficient in zinc, it may cause "white seedling disease". However, due to the small application amount of existing zinc fertilizers, only 1-2 kg, it is difficult to achieve large-scale fertilization.

[0003] Existing zinc fertilizers mainly include water-soluble acid zinc and zinc sulfate heptahydrate, but they have the following problems in application: Soil pH value affects absorption: When the soil pH value is relatively high (>6), zinc ions in zinc fertilizers are easily fixed, reducing effectiveness. It is easy to combine with calcium carbonate in the soil: resulting in the inactivation of zinc elements. Antagonistic effect with phosphate fertilizers: Excessive use of phosphate fertilizers will cause zinc deficiency symptoms. It is easy to absorb moisture and caking: It is easy to absorb moisture and cake when mixed with other chemical fertilizers, reducing fertilizer efficiency. Strong corrosiveness: It has a certain corrosive effect on equipment and the environment.

[0004] To solve the above problems, currently, the medicine-fertilizer granule technology is gradually adopted in the agricultural field. Through a specific slow-release coating technology, the medicine-fertilizer granules can slowly release nutrients in the soil, thereby improving nutrient utilization rate and prolonging fertilizer efficiency. However, the current preparation method of the slow-release coating is relatively complex and costly, and there is still room for improvement in terms of stability and environmental friendliness. Therefore, there is an urgent need to develop a new type of slow-release coating for medicine-fertilizer granules and a preparation method thereof to overcome the deficiencies of the existing technology, improve the application effect, and reduce environmental pollution. Summary of the Invention

[0005] Problems to be Solved

[0006] In view of the systematic defects existing in the existing zinc fertilizers and slow-release coating technologies, the following core technical problems to be solved are proposed: First, the environmental adaptability defect of zinc ions: the pH-sensitive inactivation mechanism. For traditional zinc fertilizers (such as zinc sulfate heptahydrate), the zinc fixation rate in soils with pH > 6 is as high as 65 - 78%, resulting in a decrease in the effective zinc concentration to 0.08 - 0.15 ppm (lower than the crop critical value of 0.2 ppm); the phosphorus-zinc antagonistic effect. The application of phosphate fertilizers leads to a 42 - 57% reduction in the soil exchangeable zinc content. The existing technologies have not solved the problem of excessive contact area between zinc and phosphorus (the measured contact area reaches 83% ± 5%). Second, the physicochemical stability defect: insufficient mechanical properties. The crushing strength of traditional coated granules is only 33.4 - 39.5 N, and the mass loss rate during fluidization treatment is > 3.0%; the problem of moisture absorption and caking. The caking rate of uncoated zinc fertilizers exceeds 30% when the humidity > 65%RH, resulting in a CV value of the fertilization uniformity > 15%. Third, the slow-release control technology defect: the mismatch of release kinetics. The initial release concentration of traditional slow-release membranes at 0 h reaches 0.18 - 0.30 mg / L, causing nutrient waste (the utilization rate is only 41.5%); the slow environmental response. The existing technologies lack pH buffering capacity (when ΔpH > 1.5, the coefficient of variation of the release rate CV > 45%). Fourth, the bottleneck of production process technology: insufficient coating uniformity. Traditional spraying processes form droplets > 50 μm, resulting in a coating porosity > 15%; low energy consumption efficiency. Traditional drying processes take 120 min to complete, and the heat consumption reaches 18.6 MJ / ton. Fifth, the ecological safety problem: non-controllable degradation. The weight loss rate of traditional coatings after 30 days is > 20%, causing soil cumulative pollution.

[0007] This technical solution systematically solves the key technical bottlenecks in the application of zinc fertilizers through component innovation (the synergistic system of potassium humate - modified nanoparticles) and process optimization (three-stage gradient drying), achieving an increase in the zinc ion utilization rate from 41.5% to 68.2% and simultaneously reducing the production cost by 42%.

[0008] Technical solution

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

[0010] A slow-release coating for pharmaceutical fertilizer granules, in parts by weight, the components are as follows: potassium humate (CAS No.: 68514-28-3) 30 parts - 60 parts, polymer material 20 parts - 40 parts, lubricant 5 parts - 15 parts, binder 5 parts - 10 parts, modification aid 1 part - 10 parts; the preparation method of the modification aid is as follows: (1) Mix tetraethyl orthosilicate (CAS No.: 78-10-4) with anhydrous ethanol 2 to 6 times its mass, then add ammonia water with a mass percentage of 25% 1 to 4 times the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid (CAS No.: 1860-44-2) 0.2 to 0.6 times the mass of tetraethyl orthosilicate, stir at room temperature for 2h - 6h, centrifuge, wash, and dry at 60°C - 75°C for 6h - 12h to obtain nanoparticles; (2) Disperse the nanoparticles in anhydrous ethanol 20 to 40 times its mass, add a silane coupling agent 3 to 8 times the mass of the nanoparticles, stir at 40°C - 50°C for 2h - 4h, centrifuge, wash, and dry at 60°C - 80°C for 12h - 18h to obtain modified nanoparticles; (3) Add the modified nanoparticles to a 10% chitosan (CAS No.: 9012-76-4) solution 10 to 20 times its mass, ultrasonically disperse for 30min - 45min, add a 25% glutaraldehyde solution 0.5 to 1.5 times the mass of the modified nanoparticles, stir at 40°C - 50°C for 1h - 3h, centrifuge, wash, and dry at 40°C - 50°C for 24h to obtain the product.

[0011] The slow-release coating for pharmaceutical fertilizer granules described above, in parts by weight, the components are as follows: potassium humate 40 parts - 55 parts, polymer material 25 parts - 35 parts, lubricant 8 parts - 15 parts, binder 5 parts - 10 parts, modification aid 1 part - 7 parts; the preparation method of the modification aid is as follows: (1) Mix tetraethyl orthosilicate with anhydrous ethanol 3 to 5 times its mass, then add ammonia water with a mass percentage of 25% 1 to 4 times the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid 0.3 to 0.6 times the mass of tetraethyl orthosilicate, stir at room temperature for 2h - 6h, centrifuge, wash, and dry at 65°C - 75°C for 6h - 10h to obtain nanoparticles; (2) Disperse the nanoparticles in anhydrous ethanol 20 to 35 times its mass, add a silane coupling agent 3 to 6 times the mass of the nanoparticles, stir at 40°C - 50°C for 2h - 4h, centrifuge, wash, and dry at 65°C - 80°C for 12h - 16h to obtain modified nanoparticles; (3) Add the modified nanoparticles to a 10% chitosan solution 12 to 18 times its mass, ultrasonically disperse for 30min - 45min, add a 25% glutaraldehyde solution 0.5 to 1.2 times the mass of the modified nanoparticles, stir at 40°C - 48°C for 1h - 3h, centrifuge, wash, and dry at 42°C - 50°C for 24h to obtain the product.

[0012] The slow-release coating for the medicated fertilizer granules, by weight, consists of the following components: 48 parts of potassium humate, 30 parts of polymer material, 12 parts of lubricant, 8 parts of binder, and 5 parts of modification aid; the preparation method of the modification aid is as follows: (1) Mix tetraethyl orthosilicate with 4 times its mass of absolute ethanol, then add 3 times the mass of tetraethyl orthosilicate of 25% ammonia water by mass percentage, and add 0.5 times the mass of tetraethyl orthosilicate of 11-chlorodecanoic acid, stir at room temperature for 4 h, centrifuge, wash, and dry at 70 °C for 8 h to obtain nanoparticles; (2) Disperse the nanoparticles in 30 times its mass of absolute ethanol, add 5 times the mass of the nanoparticles of silane coupling agent, stir at 45 °C for 3 h, centrifuge, wash, and dry at 75 °C for 14 h to obtain modified nanoparticles; (3) Add the modified nanoparticles to 15 times its mass of 10% chitosan solution by mass percentage, ultrasonically disperse for 38 min, add 0.8 times the mass of the modified nanoparticles of 25% glutaraldehyde solution by mass percentage, stir at 45 °C for 2 h, centrifuge, wash, and dry at 46 °C for 24 h to obtain the product.

[0013] The slow-release coating for the medicated fertilizer granules, 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 slow-release coating for the medicated fertilizer granules, the lubricant is one or more of calcium stearate (CAS No.: 1592-23-0), magnesium stearate (CAS No.: 557-04-0), and talc powder (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 starch-based binder; the starch-based binder is hydroxypropyl starch (CAS No.: 9049-76-7).

[0015] The slow-release coating for the medicated fertilizer granules, the silane coupling agent is γ-aminopropyltriethoxysilane (CAS No.: 919-30-2) or 3-(methacryloyloxy)propyltrimethoxysilane (CAS No.: 2530-85-0).

[0016] The preparation method of the slow-release coating for the medicine-fertilizer granules described above includes the following steps: Prepare a twin-screw mixer and control the rotation speed at 800 - 1200 rpm and the temperature at 40 ± 5 °C. Then add the components in three gradients: First, premix the polymer material with one-third of the mass of the lubricant for 3 min - 10 min to form a base material. Subsequently, add potassium fulvate and the remaining mass of the lubricant to the base material and mix for 5 min - 15 min. Finally, inject the binder and the modification aid and continuously mix for 8 min - 10 min until the system viscosity reaches 2500 ± 100 mPa·s. Then, perform fluidization, atomization, and spraying treatments. Among them, the fluidization air pressure is 0.15 MPa - 0.25 MPa, and the void fraction of the fluidized bed layer is maintained at 60% - 70%. Among them, the atomization pressure is 0.8 MPa - 1.2 MPa, the atomization electric field pressure is 30 kV - 50 kV, and the atomized droplet diameter is 30 μm - 50 μm. Among them, the initial 5 min of spraying is maintained at 50 °C - 55 °C. Among them, the temperature is linearly increased to 70 °C - 75 °C within 10 min - 25 min of spraying. Among them, the temperature is decreased to 60 °C - 65 °C in the last 5 min of spraying. Finally, perform a three-stage drying treatment to obtain the product.

[0017] The equipment selection is as follows: Twin-screw mixer (for homogenizing the mixed slurry), manufacturer: DAHAN Vibration Machinery, equipment model: Twin Screw Mixer. Equipment for fluidization, atomization, and spraying treatment, manufacturer: Senieer, equipment model: FBM series Fluidized Bed Processor. Drying equipment, recommended manufacturer: Prism Pharma Machinery, equipment model: Multi-stage Fluid Bed Dryer.

[0018] The preparation method of the slow-release coating for the medicine-fertilizer granules described above, in which within 10 min - 25 min of spraying, high-pressure spraying at 1.5 MPa for 5 s - 10 s is carried out every 1 min.

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

[0020] Beneficial effects

[0021] The slow-release coating technology solution for the medicated fertilizer granules provided by the present invention has the following beneficial effects in multiple dimensions compared with the prior art. Precise slow-release control and efficient nutrient utilization are achieved through the synergistic effect of modified nanoparticles (ethyl orthosilicate-based chitosan composite system) and potassium fulvate, realizing a high coupling between the zinc ion release rate and the crop demand curve. The pH buffering property of potassium fulvate (pH 4.5 - 6.5) enables the coating to maintain zinc effectiveness in high-pH soils, solving the fixation problem of traditional zinc fertilizers when pH > 6; Anti-antagonism design: The physical isolation of the coating reduces the contact area between zinc and phosphate fertilizers by 70%. Breakthrough improvement in mechanical properties: The single-particle crushing strength reaches 44.5 - 48.3 N (Examples), which is 25% - 45% higher than that of the comparative example (33.4 - 39.5 N), and the mass loss rate in the abrasion test is only 1.7% - 2.1% (Examples), which is 40% - 57% lower than that of the traditional process (3.0% - 4.0%). Comprehensive application benefits: The agronomic performance is improved. Early maize field trials showed that the zinc utilization rate reached 68.2% (41.5% for traditional zinc fertilizers), and the incidence of apple leaflet disease decreased from 23% to 6% (three-year tracking data). By constructing a three-level regulation system of carrier-interface-structure, this technology breaks through the technical bottlenecks of traditional coating technologies such as disordered nutrient release, insufficient mechanical strength, and slow environmental response, providing an innovative solution for the development of intelligent fertilizers. After third-party testing (SGS report No. SH2025 - 036), the product meets the ISO 18645:2024 international standard for slow-release fertilizers and has been successfully applied to a rice planting demonstration project in the Northeast black soil area (pH 7.2 - 8.1), achieving a significant yield increase of 18.7%. Description of the Drawings

[0022] Figure 1 It is a scanning electron micrograph of the slow-release coating prepared in Example 5. Detailed Embodiments

[0023] The present invention will be further described below in conjunction with specific embodiments.

[0024] Unless otherwise defined, the technical and scientific terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. In actual application, the parts by weight involved in the present invention can be set to kilograms.

[0025] Example 1

[0026] Slow-release coating for pharmaceutical and fertilizer granules, by weight, the components are as follows: potassium humate 30 parts, polymer material 40 parts, lubricant 5 parts, binder 10 parts, modified additive 1 part; the preparation method of the modified additive is as follows: (1) Mix tetraethyl orthosilicate with anhydrous ethanol twice its mass, then add ammonia water with a mass percentage of 25% four times the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid 0.2 times the mass of tetraethyl orthosilicate, stir at room temperature for 6 h, centrifuge, wash, and dry at 60 °C for 12 h to obtain nanoparticles; (2) Disperse the nanoparticles in anhydrous ethanol 20 times its mass, add silane coupling agent 8 times the mass of the nanoparticles, stir at 40 °C for 4 h, centrifuge, wash, and dry at 60 °C for 18 h to obtain modified nanoparticles; (3) Add the modified nanoparticles to a chitosan solution with a mass percentage of 10% ten times its mass, ultrasonically disperse for 45 min, add a glutaraldehyde solution with a mass percentage of 25% 0.5 times the mass of the modified nanoparticles, stir at 50 °C for 1 h, centrifuge, wash, and dry at 50 °C for 24 h to obtain the product. For the slow-release coating for pharmaceutical and fertilizer granules, the polymer material is polylactic acid. For the slow-release coating for pharmaceutical and fertilizer granules, the lubricant is calcium stearate; the binder is carboxymethyl cellulose. For the slow-release coating for pharmaceutical and fertilizer granules, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0027] Preparation method of slow-release coating for pharmaceutical and fertilizer granules, including the following steps: Prepare a twin-screw mixer and control the rotation speed at 800 rpm and the temperature at 40 ± 5 °C, then add the components in three gradients: First, premix the polymer material with one-third of the mass of the lubricant for 3 min to form a base material, then add potassium humate and the remaining mass of the lubricant to the base material and mix for 15 min, and finally inject the binder and the modified additive, and continuously mix for 8 min until the system viscosity reaches 2500 ± 100 mPa·s; then, perform fluidization, atomization, and spraying treatments, where the fluidization air pressure is 0.25 MPa, the void fraction of the fluidized bed layer is maintained at 60%, the atomization pressure is 1.2 MPa, the atomization electric field pressure is 30 kV, the atomized droplet diameter is 50 μm, the initial 5 min of spraying is maintained at 50 °C, the temperature is linearly increased to 70 °C within 25 min of spraying, the temperature is decreased to 65 °C in the last 5 min of spraying, and finally, perform a three-stage drying treatment to obtain the product. Among them, within 10 min of spraying, high-pressure spraying at 1.5 MPa is carried out for 10 s every 1 min. The three-stage drying treatment is as follows: In the initial drying stage, air drying at 60 °C is carried out for 15 min, and the air drying speed is 10 m / s; in the curing stage, hot air treatment at 80 °C is carried out for 30 min, the pulsation frequency of the hot air is 2 Hz, and the relative humidity is reduced to 30%; in the aging stage, air drying at 50 °C is carried out for 15 min, and the air drying speed is 2 m / s, and nitrogen protection is carried out synchronously.

[0028] Example 2

[0029] Slow-release coating for pharmaceutical and fertilizer granules, by weight, the components are as follows: 60 parts of potassium humate, 20 parts of polymer material, 15 parts of lubricant, 5 parts of binder, 10 parts of modified additive; the preparation method of the modified additive is as follows: (1) Mix tetraethyl orthosilicate with anhydrous ethanol 6 times its mass, then add ammonia water with a mass percentage of 25% 1 time the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid 0.6 times the mass of tetraethyl orthosilicate, stir at room temperature for 2 h, centrifuge, wash, and dry at 75 °C for 6 h to obtain nanoparticles; (2) Disperse the nanoparticles in anhydrous ethanol 40 times its mass, add a silane coupling agent 3 times the mass of the nanoparticles, stir at 50 °C for 2 h, centrifuge, wash, and dry at 80 °C for 12 h to obtain modified nanoparticles; (3) Add the modified nanoparticles to a chitosan solution with a mass percentage of 10% 20 times its mass, ultrasonically disperse for 30 min, add a glutaraldehyde solution with a mass percentage of 25% 1.5 times the mass of the modified nanoparticles, stir at 40 °C for 3 h, centrifuge, wash, and dry at 40 °C for 24 h to obtain the product. For the slow-release coating for pharmaceutical and fertilizer granules, the polymer material is polyethylene. For the slow-release coating for pharmaceutical and fertilizer granules, the lubricant is magnesium stearate; the binder is polyvinyl alcohol. For the slow-release coating for pharmaceutical and fertilizer granules, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0030] Preparation method of slow-release coating for pharmaceutical and fertilizer granules, including the following steps: Prepare a twin-screw mixer and control the rotation speed at 1200 rpm and the temperature at 40 ± 5 °C, then add the components in three gradients: First, premix the polymer material with one-third of the mass of the lubricant for 10 min to form a base material, then add potassium humate and the remaining mass of the lubricant to the base material and mix for 5 min, and finally inject the binder and the modified additive, and continue to mix for 10 min until the system viscosity reaches 2500 ± 100 mPa·s; then, perform fluidization, atomization and spraying treatments, where the fluidization air pressure is 0.25 MPa, the void fraction of the fluidized bed layer is maintained at 70%, where the atomization pressure is 0.8 MPa, the atomization electric field pressure is 50 kV, the atomization droplet diameter is 30 μm, where the initial 5 min of spraying is maintained at 55 °C, where the temperature is linearly increased to 75 °C within 10 min of spraying, where the temperature is decreased to 60 °C in the last 5 min of spraying, and finally perform a three-stage drying treatment to obtain the product. Among them, within 25 min of spraying, high-pressure spraying at 1.5 MPa for 5 s is performed every 1 min. The three-stage drying treatment is as follows: The initial drying stage uses air drying at 65 °C for 15 min, and the air drying speed is 8 m / s; the curing stage uses hot air at 90 °C for 30 min, the pulsation frequency of the hot air is 2 Hz, and the relative humidity is reduced to 30%; the aging stage uses air drying at 45 °C for 15 min, and the air drying speed is 8 m / s, and nitrogen protection is carried out synchronously.

[0031] Example 3

[0032] The slow-release coating for medicated fertilizer granules, by weight, consists of the following components: 40 parts of potassium humate, 35 parts of polymer material, 15 parts of lubricant, 5 parts of binder, and 7 parts of modification aid; the preparation method of the modification aid is as follows: (1) Mix tetraethyl orthosilicate with anhydrous ethanol three times its mass, then add ammonia water with a mass percentage of 25% four times the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid 0.3 times the mass of tetraethyl orthosilicate, stir at room temperature for 6 h, centrifuge, wash, and dry at 65 °C for 10 h to obtain nanoparticles; (2) Disperse the nanoparticles in anhydrous ethanol 20 times its mass, add a silane coupling agent six times the mass of the nanoparticles, stir at 40 °C for 4 h, centrifuge, wash, and dry at 65 °C for 16 h to obtain modified nanoparticles; (3) Add the modified nanoparticles to a chitosan solution with a mass percentage of 10% twelve times its mass, ultrasonically disperse for 45 min, add a glutaraldehyde solution with a mass percentage of 25% 0.5 times the mass of the modified nanoparticles, stir at 48 °C for 1 h, centrifuge, wash, and dry at 50 °C for 24 h to obtain the product. For the slow-release coating for medicated fertilizer granules, the polymer material is polyethylene. For the slow-release coating for medicated fertilizer granules, the lubricant is talcum powder; the binder is a starch-based binder; the starch-based binder is hydroxypropyl starch. For the slow-release coating for medicated fertilizer granules, the silane coupling agent is 3-(methacryloyloxy)propyltrimethoxysilane.

[0033] The preparation method of the slow-release coating for medicated fertilizer granules includes the following steps: Prepare a twin-screw mixer and control the rotation speed at 900 rpm and the temperature at 40 ± 5 °C, then add the components in three gradients: First, premix the polymer material with one-third of the mass of the lubricant for 8 min to form a base material, then add potassium humate and the remaining mass of the lubricant to the base material and mix for 7 min, and finally inject the binder and the modification aid, and continuously mix for 10 min until the system viscosity reaches 2500 ± 100 mPa·s; then, perform fluidization, atomization, and spraying treatments, where the fluidization air pressure is 0.15 MPa, the void fraction of the fluidized bed layer is maintained at 68%, where the atomization pressure is 0.8 MPa, the atomization electric field pressure is 45 kV, the atomization droplet diameter is 35 m, where the initial 5 min of spraying is maintained at 55 °C, where the temperature is linearly increased to 75 °C within 15 min of spraying, where the temperature is decreased to 60 °C in the last 5 min of spraying, and finally perform a three-stage drying treatment to obtain the product. Among them, within 25 min of spraying, high-pressure spraying at 1.5 MPa for 5 s is performed every 1 min. The three-stage drying treatment is as follows: In the initial drying stage, air drying is performed at 65 °C for 15 min, and the air drying speed is 8 m / s; in the curing stage, hot air treatment is performed at 90 °C for 30 min, the pulsation frequency of the hot air is 2 Hz, and the relative humidity is reduced to 30%; in the aging stage, air drying is performed at 45 °C for 15 min, and the air drying speed is 8 m / s, and nitrogen protection is carried out synchronously.

[0034] Example 4

[0035] The slow-release coating for the medicated fertilizer granules, by weight, has the following components: 55 parts of potassium fulvate, 25 parts of polymer material, 15 parts of lubricant, 5 parts of binder, and 7 parts of modification additive; the preparation method of the modification additive is as follows: (1) Mix tetraethyl orthosilicate with anhydrous ethanol five times its mass, then add ammonia water with a mass percentage of 25% that is one time the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid that is 0.6 times the mass of tetraethyl orthosilicate, stir at room temperature for 2 h, centrifuge, wash, and dry at 75 °C for 6 h to obtain nanoparticles; (2) Disperse the nanoparticles in anhydrous ethanol 35 times its mass, add a silane coupling agent six times the mass of the nanoparticles, stir at 40 °C for 4 h, centrifuge, wash, and dry at 65 °C for 16 h to obtain modified nanoparticles; (3) Add the modified nanoparticles to a chitosan solution with a mass percentage of 10% that is 18 times its mass, ultrasonically disperse for 30 min, add a glutaraldehyde solution with a mass percentage of 25% that is 1.2 times the mass of the modified nanoparticles, stir at 40 °C for 1 h, centrifuge, wash, and dry at 42 °C for 24 h to obtain the product. For the slow-release coating for the medicated fertilizer granules, the polymer material is polyester. For the slow-release coating for the medicated fertilizer granules, the lubricant is magnesium stearate; the binder is polyvinyl alcohol. For the slow-release coating for the medicated fertilizer granules, the silane coupling agent is 3-(methacryloyloxy)propyltrimethoxysilane.

[0036] The preparation method of the slow-release coating for the medicated fertilizer granules includes the following steps: Prepare a twin-screw mixer and control the rotation speed at 1100 rpm and the temperature at 40 ± 5 °C, and then add the components in three gradients: First, premix the polymer material with one-third of the mass of the lubricant for 7 min to form a base material, then add potassium fulvate and the remaining mass of the lubricant to the base material and mix for 13 min, and finally inject the binder and the modification additive, and continue to mix for 8 min until the system viscosity reaches 2500 ± 100 mPa·s; then, perform fluidization, atomization, and spraying treatments, where the fluidization air pressure is 0.22 MPa, the void fraction of the fluidized bed layer is maintained at 63%, where the atomization pressure is 1.2 MPa, the atomization electric field pressure is 35 kV, the atomization droplet diameter is 45 μm, where the initial 5 min of spraying is maintained at 50 °C, where the temperature is linearly increased to 70 °C within 15 min of spraying, where the temperature is decreased to 65 °C in the last 5 min of spraying, and finally perform a three-stage drying treatment to obtain the product. Among them, within 10 min of spraying, high-pressure spraying at 1.5 MPa is carried out for 10 s every 1 min. The three-stage drying treatment is as follows: In the initial drying stage, air drying at 60 °C is carried out for 15 min, and the air drying speed is 10 m / s; in the curing stage, hot air treatment at 80 °C is carried out for 30 min, the pulsation frequency of the hot air is 2 Hz, and the relative humidity is reduced to 30%; in the aging stage, air drying at 50 °C is carried out for 15 min, and the air drying speed is 2 m / s, and nitrogen protection is carried out synchronously.

[0037] Example 5

[0038] The slow-release coating for the medicated fertilizer granules, by weight, consists of the following components: 48 parts of potassium fulvate, 30 parts of polymer material, 12 parts of lubricant, 8 parts of binder, and 5 parts of modification aid; the preparation method of the modification aid is as follows: (1) Mix tetraethyl orthosilicate with anhydrous ethanol four times its mass, then add ammonia water with a mass percentage of 25% three times the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid 0.5 times the mass of tetraethyl orthosilicate, stir at room temperature for 4 h, centrifuge, wash, and dry at 70 °C for 8 h to obtain nanoparticles; (2) Disperse the nanoparticles in anhydrous ethanol 30 times its mass, add a silane coupling agent 5 times the mass of the nanoparticles, stir at 45 °C for 3 h, centrifuge, wash, and dry at 75 °C for 14 h to obtain modified nanoparticles; (3) Add the modified nanoparticles to a chitosan solution with a mass percentage of 10% 15 times its mass, ultrasonically disperse for 38 min, add a glutaraldehyde solution with a mass percentage of 25% 0.8 times the mass of the modified nanoparticles, stir at 45 °C for 2 h, centrifuge, wash, and dry at 46 °C for 24 h to obtain the product. For the slow-release coating for the medicated fertilizer granules, the polymer material is polylactic acid. For the slow-release coating for the medicated fertilizer granules, the lubricant is talcum powder; the binder is a starch-based binder; among them, the starch-based binder is hydroxypropyl starch. For the slow-release coating for the medicated fertilizer granules, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0039] The preparation method of the slow-release coating for the medicated fertilizer granules includes the following steps: Prepare a twin-screw mixer and control the rotation speed at 1000 rpm and the temperature at 40 ± 5 °C, and then add the components in three gradients: First, premix the polymer material with one-third of the mass of the lubricant for 7 min to form a base material, then add potassium fulvate and the remaining mass of the lubricant to the base material and mix for 10 min, and finally inject the binder and the modification aid, and continuously mix for 9 min until the system viscosity reaches 2500 ± 100 mPa·s; then, perform fluidization, atomization, and spraying treatments, where the fluidization air pressure is 0.20 MPa, the void fraction of the fluidized bed layer is maintained at 65%, where the atomization pressure is 1.0 MPa, the atomization electric field pressure is 40 kV, the atomization droplet diameter is 40 μm, where the initial 5 min of spraying is maintained at 53 °C, where the temperature is linearly increased to 73 °C within 18 min of spraying, where the temperature is decreased to 63 °C in the last 5 min of spraying, and finally perform a three-stage drying treatment to obtain the product. Among them, within 17 min of spraying, high-pressure spraying at 1.5 MPa is performed for 8 s every 1 min. The three-stage drying treatment is as follows: In the initial drying stage, air drying is performed at 63 °C for 15 min, and the air drying speed is 9 m / s; in the curing stage, hot air treatment is performed at 85 °C for 30 min, the pulsation frequency of the hot air is 2 Hz, and the relative humidity is reduced to 30%; in the aging stage, air drying is performed at 48 °C for 15 min, and the air drying speed is 5 m / s, and nitrogen protection is carried out synchronously.

[0040] Comparative Example 1

[0041] Same as Example 5, removing the modification additive.

[0042] Comparative Example 2

[0043] Same as Example 5, with adjustment in the preparation of the modification additive: In step (1), the addition of 11-chlorodecanoic acid is cancelled, and in step (3), sodium alginate is used to replace chitosan.

[0044] Comparative Example 3

[0045] Same as Example 5, with adjustment in the preparation of the modification additive: In step (1), sodium metasilicate is used to replace tetraethyl orthosilicate.

[0046] Comparative Example 4

[0047] Same as Example 5, with adjustment in the preparation of the modification additive: In step (3), the addition of chitosan is cancelled.

[0048] Comparative Example 5

[0049] Same as Example 5, using tetraethyl orthosilicate to replace the modification additive.

[0050] Testing method: Nutrient release characteristic test: Take 5.0 g of coated fertilizer granules (each 2 g of slow-release film wraps 1 g of granular zinc, Shengyuan Agricultural Resources - Granular Zinc, with zinc content of 33.5%, Shandong Greenlong Biotechnology Co., Ltd.), place them in 100 mL of deionized water, and oscillate at a constant temperature of 25 °C (120 rpm). Samples are taken at 0 h and 28 d respectively, and the zinc ion concentration is measured by colorimetry. Coating mechanical property test: Use a TA.XT Plus texture analyzer to measure the crushing strength of a single particle, with a loading rate of 1.0 mm / s, and record the maximum pressure value at the moment of rupture. Referring to the ASTM D4058 standard, place 100 g of the sample in a roller tester (rotation speed 30 rpm) and run for 1 h, and calculate the mass loss rate. Microstructural characterization: Observe the cross-sectional morphology of the coating using a field emission scanning electron microscope (S4800, Hitachi), with an acceleration voltage of 5 kV and a working distance of 8 mm. The results are as Figure 1 shown. Degradation property test: Weigh 10 g of the coating material and bury it in potted soil (humidity 30%, 25 °C), and take samples every 10 d to measure the weight loss rate.

[0051] Table 1 Test Results

[0052]

[0053] The present invention discloses a slow-release coating for pharmaceutical fertilizer granules and its preparation method. Through unique component design and optimized processes, a number of remarkable technical effects are achieved, providing technical support for efficient and sustainable agricultural production. Excellent nutrient slow-release performance: This slow-release coating can effectively control the release rate of nutrients in pharmaceutical fertilizer granules, significantly reducing the initial release amount and achieving long-term continuous release. The test results show that the zinc ion release concentration of Example 5 at 0 h is only 0.11 mg / L, and at 28 d is 12.3 mg / L, showing obvious improvement compared with 0.25 mg / L (0 h) and 20.1 mg / L (28 d) of Comparative Example 1 (without modification additives). This indicates that the present invention effectively inhibits the initial burst release of nutrients and realizes a stable nutrient supply, thereby: Improving nutrient utilization efficiency: Reducing nutrient loss and ensuring continuous nutritional support for crops during the growth cycle. Reducing environmental impact: Reducing the amount of nutrients infiltrating into groundwater or soil, meeting the requirements of green agriculture. Enhanced mechanical strength and durability: The slow-release coating of the present invention significantly improves the mechanical properties and abrasion resistance of the granules. The test data shows that the single-particle crushing strength of Example 5 reaches 48.3 N, much higher than 35.6 N of Comparative Example 1; the mass loss rate (abrasion resistance index) is only 1.7%, while that of Comparative Example 1 is 3.5%. These improvements are due to: The strengthening effect of modification additives: The nanoparticles prepared by tetraethyl orthosilicate are modified by silane coupling agent and chitosan, enhancing the structural strength of the coating. Optimization of the preparation process: High-pressure spraying and three-stage drying ensure that the coating is uniform and dense, reducing breakage under mechanical stress. Its technical effects include: Improving robustness: During transportation, storage and application, the coating is not easily broken or peeled off, ensuring the controllability of nutrient release. Extending service life: Enhanced durability reduces the premature failure of the coating in the soil. Controllable degradation performance: Through component and process design, the present invention effectively controls the degradation rate of the coating in the soil. The weight loss rate of Example 5 after 30 d is 14.2%, significantly lower than 22.1% of Comparative Example 1. This characteristic is due to: The biodegradability of chitosan: As an important component of the coating, chitosan can decompose slowly. Three-stage drying process: The curing and aging stages optimize the cross-linked structure of the coating, delaying the degradation rate. Its technical effects are: Extending the nutrient release period: Matching the growth requirements 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 microscope observation shows 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, avoiding defects such as cracks or bubbles. Its technical effects include: Enhancing the barrier performance: The uniform structure enhances the ability to encapsulate nutrients and further optimizes the release control.Improve stability: The dense coating enhances the resistance of the coating film to environmental factors such as humidity and temperature. Environmental friendliness: The components and process design adopted in the present invention fully consider the environmental impact: Biodegradable materials: Components such as chitosan can be gradually decomposed in the natural environment, reducing soil pollution. Non-toxic process: No toxic or harmful substances are used in the preparation process, and the product is safe for crops and the ecosystem. Its technical effects are: Support sustainable development: Reduce chemical residues, meeting the environmental protection requirements of modern agriculture. Reduce ecological risks: Even if it contains nanoparticles, they are encapsulated in the coating film, and the release after degradation is controllable, not easily directly affecting the environment. Optimized preparation process: The preparation method of the present invention ensures the efficient production and excellent performance of the coating film through twin-screw mixing, fluidized atomization spraying, and three-stage drying processes: Twin-screw mixing: Add components step by step and control the viscosity to 2500 ± 100 mPa·s, ensuring the uniformity of the materials. Fluidized spraying: The fluidization air pressure is 0.15 - 0.25 MPa and the atomization pressure is 0.8 - 1.2 MPa. Combined with high-pressure spraying, a high-quality coating is formed. Three-stage drying: Initial drying (60 - 65 °C), curing (80 - 90 °C hot air pulsation), and aging (45 - 50 °C nitrogen protection) ensure the perfect curing of the coating. Its technical effects include: The process is simple and controllable: Using standard industrial equipment such as twin-screw mixers and fluidized bed processors, facilitating large-scale production. Cost-effectiveness improvement: Compared with traditional complex processes, this method simplifies the steps and reduces the production cost. For the problems in zinc fertilizer application such as the influence of soil pH, antagonism with other fertilizers, and corrosiveness, the present invention provides solutions: Mitigate the influence of soil pH: The slow-release characteristics enable zinc ions to be gradually released under different pH conditions, improving the absorption efficiency. Reduce fertilizer antagonism: The coating film isolates the direct contact between zinc fertilizer and other fertilizers, reducing the antagonistic effect. Reduce corrosiveness: Encapsulate zinc fertilizer particles, reducing their corrosion to equipment and the environment. Its technical effects are: Improve the application effect: Overcome the limitations of traditional zinc fertilizers, especially suitable for zinc-deficient sensitive crops such as corn and rice. Enhance compatibility: Facilitate mixing with other fertilizers, improving the flexibility of fertilization.

[0054] In summary, the slow-release coating film for the medicine-fertilizer particles of the present invention, through the scientific ratio of potassium humate, polymer materials, lubricants, binders, and modified additives, and the optimized processes of twin-screw mixing, fluidized spraying, and three-stage drying, achieves the following technical effects: precisely control the nutrient release, improve the utilization efficiency and reduce environmental pollution; significantly enhance the mechanical strength and durability of the coating film, ensuring the reliability of use; achieve controllable degradation, extend the fertilizer efficiency and enhance environmental friendliness; form a uniform and dense microstructure, improving the performance stability; provide a simple and efficient preparation method with industrialization potential. These technical effects not only solve the problems in the existing zinc fertilizer application, but also provide an innovative slow-release coating film solution for the field of biological agriculture technology, with significant economic and ecological benefits

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

Claims

1. A sustained-release coating for medicinal fertilizer particles, characterized in that: The components are as follows, in parts by weight: 30-60 parts of potassium humate, 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 tetraethyl orthosilicate with anhydrous ethanol in an amount of 2 to 6 times its mass, then adding 25% ammonia water in an amount of 1 to 4 times the mass of tetraethyl orthosilicate, and adding 11-chlorodecanoic acid in an amount of 0.2 to 0.6 times the mass of tetraethyl orthosilicate, stirring at room temperature for 2 hours to 6 hours, centrifuging, washing, and drying at 60°C to 75°C for 6 hours to obtain nanoparticles; (2) separating the nanoparticles; and Disperse in anhydrous ethanol at a mass of 20 to 40 times the mass of the nanoparticles, add a silane coupling agent at a mass of 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 a 10% chitosan solution at a mass percentage of 10 times the mass of the modified nanoparticles, ultrasonically disperse for 30min to 45min, add a 25% glutaraldehyde solution at a mass percentage of 0.5 times 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 the medicinal fertilizer granules according to claim 1, characterized in that: The components are as follows, in parts by weight: 40-55 parts of potassium humate, 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) mix tetraethyl orthosilicate with anhydrous ethanol in an amount of 3-5 times its mass, then add 25% ammonia water in an amount of 1-4 times the mass of tetraethyl orthosilicate, and add 11-chlorodecanoic acid in an amount of 0.3-0.6 times the mass of tetraethyl orthosilicate, stir at room temperature for 2h-6h, centrifuge, wash, and dry at 65°C-75°C for 6h-10h to obtain nanoparticles; (2) disperse the nanoparticles Add 3 to 6 times the mass of the nanoparticles of silane coupling agent to anhydrous ethanol at a concentration of 20 to 35 times the mass of the nanoparticles, stir at 40 to 50°C for 2 h to 4 h, centrifuge, wash, and dry at 65 to 80°C for 12 h to 16 h 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 min to 45 min, 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 h to 3 h, centrifuge, wash, and dry at 42 to 50°C for 24 h 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 humate, 30 parts of polymer material, 12 parts of lubricant, 8 parts of binder, and 5 parts of modification aid. The preparation method of the modification aid is as follows: (1) tetraethyl orthosilicate is mixed with anhydrous ethanol in an amount of 4 times its mass, and then 25% ammonia water in an amount of 3 times the mass of tetraethyl orthosilicate is added, and 11-chlorodecanoic acid in an amount of 0.5 times the mass of tetraethyl orthosilicate is added, and the mixture is 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 in an amount of 4 times its mass, and then 25% ammonia water in an amount of 3 times the mass of tetraethyl orthosilicate is added, and 11-chlorodecanoic acid in an amount of 0.5 times the mass of tetraethyl orthosilicate is added. The mixture is 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 with a 10% chitosan solution (15 times their mass), and ultrasonically dispersed for 38 min. 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 the 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 the 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 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, characterized in that: 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, premix the polymer material with one-third of the mass of the lubricant for 3min-10min to form a base material, then add potassium humate to the base material and mix with the remaining mass of the lubricant 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, wherein the fluidization The air pressure is 0.15MPa-0.25MPa, and the porosity of the fluidized bed is maintained at 60%-70%, wherein the atomization pressure is 0.8MPa-1.2MPa, the atomization electric field pressure is 30kV-50kV, and the atomized droplet size is 30μm-50μm. 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.

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

9. The method for preparing the sustained-release coating for the medicinal fertilizer granules according to claim 8, characterized in that: The three-stage drying treatment is as follows: the initial drying stage adopts 60℃-65℃ air drying treatment for 15min, and the air drying wind speed is 8m / s-10m / s; the curing stage adopts 80℃-90℃ hot air treatment for 30min, the pulsation frequency of the hot air is 2Hz, and the relative humidity is reduced to 30%; the aging stage adopts 45℃-50℃ air drying treatment for 15min, the air drying wind speed is 2m / s-8m / s, and nitrogen protection is carried out simultaneously.

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