Macromolecule slow-release and surface anti-sticking synergistic compound fertilizer and preparation method thereof

Abstract

The invention relates to the technical field of compound fertilizers, and discloses a macromolecular slow-release and surface anti-sticking synergistic compound fertilizer which comprises the following raw materials in percentage by weight: 15-16% of nitrogen, 10-12% of water-soluble phosphoric anhydride, 14-15% of water-soluble potassium, 20-25% of bentonite, 5-15% of wollastonite, 0.5-3% of trace elements, 3-8% of a coating material, 2-5% of a conditioner, 0.5-1% of calcium stearate, 1-2% of kaolin and 3-5% of medium elements. According to the macromolecular slow-release and surface anti-sticking synergistic compound fertilizer and the preparation method thereof, by adjusting the proportion of nitrogen, phosphorus and potassium in the fertilizer, the fertilizer can meet the differential requirements of different crops for nutrients in the growth stage, and by compounding calcium stearate and kaolin, the anti-sticking performance of the surfaces of fertilizer particles can be effectively improved; the outer-layer CS-PVA blended film is used for synergistic interaction and intelligent slow release; the thickness of the film layer and the crosslinking degree are used for regulating and controlling the nutrient release period, so that the fertilizer requirement rule of crops is matched, and the fertilizer application frequency is effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of compound fertilizers, in particular to a compound fertilizer with synergistic macromolecular slow-release and surface anti-adhesion properties and a preparation method thereof. Background Art

[0002] Compound fertilizer refers to a chemical fertilizer containing two or more nutrients including nitrogen, phosphorus and potassium. Compound fertilizer has the advantages of high nutrient content, few by-components and good physical properties. It plays a very important role in balanced fertilization, improving fertilizer utilization and promoting high and stable yields of crops.

[0003] Currently, most products use only a single nitrogen source (such as urea or ammonium nitrogen), resulting in a mismatch between nutrient release rates and crop fertilizer requirements. This can easily lead to seedling burn in the early stages and nutrient depletion in the later stages. Furthermore, traditional compound fertilizers lack an efficient anti-adhesive system, causing fertilizer granules to clump during storage and transportation, necessitating the addition of inert substances such as talc, which reduces the effective nutrient content. Currently, the mainstream coating technology for compound fertilizers is usually just a single-layer film coating. For example, the invention patent with announcement number CN1271013C discloses a compound fertilizer and its production process. The compound fertilizer production process includes mixing, granulation, drying, cooling, metering and packaging. Screening can be performed after the cooling process, and coating can also be performed after the cooling process or the screening process. The formula is scientific, and the N, P, and K element content in the fertilizer is ≥25%, which is scientifically moderate. The N, P, and K elements contained are nitrate nitrogen, ammonium nitrogen, phosphate, and potassium ions that can be absorbed and utilized by plants. The active ingredients of the fertilizer are completely soluble in water, which is conducive to crop absorption and utilization, so as to fully exert the fertilizer effect. Or they rely on non-degradable materials such as polyethylene and polyurethane, and long-term application leads to soil microplastic pollution (reference "Environmental Pollution", 2021). Although some studies have tried to use bio-based materials such as chitosan (CS), single CS membranes have low mechanical strength and are prone to premature disintegration, making it difficult to achieve sustained-release function. Therefore, it is very necessary to design a compound fertilizer that can delay the fertilizer release cycle and has a synergistic effect on the fertilizer surface anti-adhesion. Therefore, a compound fertilizer with polymer slow release and surface anti-adhesion synergy and its preparation method are proposed to solve the above problems. Summary of the Invention

[0004] (1) Technical problems solved In response to the shortcomings of the existing technology, the present invention provides a compound fertilizer with synergistic effects of polymer slow release and surface anti-adhesion and its preparation method, which has the advantages of delaying the fertilizer release cycle and synergistic anti-adhesion on the fertilizer surface, and solves the key problems of traditional compound fertilizers such as low utilization rate, high environmental pollution and poor adaptability.

[0005] (2) Technical solution To achieve the above-mentioned purpose of delaying the fertilizer release cycle and achieving synergistic anti-adhesion effect on the fertilizer surface, the present invention provides the following technical solution: a compound fertilizer with synergistic high molecular weight slow-release and anti-adhesion effect on the surface, comprising the following raw materials in proportions by weight: 15-16% nitrogen, 10-12% water-soluble phosphoric anhydride, 14-15% water-soluble potassium, 20-25% bentonite, 5-15% wollastonite, 0.5-3% trace elements, 3-8% coating material, 2-5% conditioner, 0.5-1% calcium stearate, 1-2% kaolin, and 3-5% secondary elements; The coating material is composed of resin coating material, chitosan (CS), polyvinyl alcohol (PVA), glacial acetic acid, deionized water and auxiliary agents.

[0006] Preferably, the nitrogen consists of ammonium nitrogen, nitrate nitrogen and amide nitrogen (urea), with ammonium nitrogen accounting for 6-7%, nitrate nitrogen 7-8%, and amide nitrogen (urea) accounting for 2-3%, and the trace elements consist of magnesium (Mg), iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo) and other components.

[0007] Preferably, the conditioning agent is one of dolomite powder and sulfur powder, and the secondary elements are composed of calcium and sulfur.

[0008] Preferably, the auxiliary agent consists of a cross-linking agent (glutaraldehyde), a plasticizer (polyol), a modifying additive (nano-SiO2) and zinc sulfate.

[0009] Another technical problem to be solved by the present invention is to provide a method for preparing a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion, comprising the following steps: S1. Compounding: Calcium stearate and kaolin are added into a mixing device in a ratio of 1:1 to 1:4, and the stirring speed is controlled at 100 to 300 r / min for 15 to 30 minutes to obtain a compound mixture for improving the anti-sticking performance of the fertilizer; S2. Preliminary mixing: sieve nitrogen, water-soluble phosphoric anhydride, and water-soluble potassium, remove lumps or impurities, and add them to a mixing device in a ratio of 10-15:5-15:15-25 for preliminary mixing for 10-30 minutes; S3, secondary mixing: Then, add bentonite, trace elements, conditioning agents, secondary elements and the composite mixture in step S1 into the mixing equipment according to the proportion, control the stirring speed at 200-400 r / min, and continue mixing for 10-20 minutes; S4, granulation: the mixed material in step S3 is fed into a rotary drum granulator. Under the rotation of the drum, the raw materials interact with the added medium such as water or steam to form granules. The speed of the drum is generally 5-10 r / min, and the granulation time is 10-20 min. S4.1, Particle screening: The granulated fertilizer particles are separated into qualified particles (2-4mm) by a vibrating screening machine and returned to the material; S5. Drying: The granulated compound fertilizer particles are sent to the drying equipment for drying to remove moisture from the particles. The drying temperature is generally controlled at 80~120℃. The drying time is determined according to the particle size and initial moisture content, and is generally 15~30 minutes. S5.1. Cooling: The dried granules are cooled by fluidized bed cooler or naturally cooled to 40-50°C; S6. Inner coating: The dried compound fertilizer particles are fed into the coating equipment, conventional resin coating materials are added, and the conventional resin coating materials are evenly sprayed at a temperature of 150-200°C to form a uniform inner coating layer; S6.1. Inner coating curing: After the inner resin coating, slowly cool at 60-80°C for 10-20 minutes to promote the hardening of the film; S7. Preparation of chitosan (CS) solution: Add a certain proportion of chitosan to a certain volume of 1-3% glacial acetic acid solution and fully dissolve it under stirring at a speed of 200-500 rpm for 1-3 hours until a uniform chitosan solution is formed. S8. Preparation of polyvinyl alcohol (PVA) solution: Take an appropriate amount of polyvinyl alcohol and add it to deionized water. Heat it to 80-95°C and stir continuously to completely dissolve the polyvinyl alcohol. Stir at a speed of about 300-600 rpm for 1-2 hours. Allow the solution to cool to room temperature before use. S9, blending modification: The chitosan solution and polyvinyl alcohol solution prepared in steps S7 and S8 are mixed in a certain proportion, and during the mixing process, stirring is continued for 20 to 40 minutes at a stirring speed of 300 to 500 r / min for 30 to 60 minutes, and an auxiliary agent is added during the mixing process to form a chitosan-polyvinyl alcohol blend coating emulsion; S10, outer coating: spraying the blended coating emulsion in step S9 and the fertilizer mixed with fertilizer particles and coated with the inner coating layer in a fluidized bed, controlling the temperature at 50-80° C. to form a uniform outer coating layer; S10.1. Curing of outer coating: After outer coating, cure under ventilation at 40-60℃ for 30-60min to enhance the stability of the film.

[0010] Preferably, in step S1, in order to ensure that calcium stearate and kaolin are mixed more evenly, calcium stearate and kaolin may be pre-dispersed separately before mixing.

[0011] Preferably, the mass concentration of chitosan in step S7 is controlled at 1-5%, and the mass concentration of polyvinyl alcohol in step S8 is controlled at 5-15%.

[0012] Preferably, the mass ratio of chitosan to polyvinyl alcohol in step S9 is between 1:1 and 1:3, and the reaction needs to be continued for 1 to 2 hours after the auxiliary agent is added in step S9.

[0013] (3) Beneficial effects Compared with the prior art, the present invention provides a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion and a preparation method thereof, which has the following beneficial effects: 1. This compound fertilizer with synergistic high-molecular slow-release and surface anti-adhesion properties and its preparation method adjusts the ratio of nitrogen, phosphorus and potassium in the fertilizer to meet the differentiated nutrient needs of different crops at different growth stages. The compounding of calcium stearate and kaolin can effectively increase the anti-adhesion properties of the fertilizer particle surface. In addition, the inner resin coating is high-temperature resistant and quickly forms a film to protect the core nutrients, while the outer CS-PVA blend film is used for synergistic efficiency enhancement. Intelligent slow-release: the film thickness and cross-linking degree regulate the nutrient release cycle to match the crop's fertilizer requirements and effectively reduce the number of fertilization applications.

[0014] 2. This composite fertilizer with synergistic high-molecular slow-release and surface anti-adhesion properties and its preparation method can improve the absorption rate of trace elements in the fertilizer, such as iron and zinc chelated in EDTA, avoid soil fixation, and specifically supplement nutrient deficiencies. The synergistic effect of bentonite and wollastonite can increase the strength of fertilizer particles, supplement soil silicon, improve air permeability, and adsorb heavy metals. At the same time, the conditioner in the fertilizer is beneficial to regulating the acid-base balance of the soil, reducing soil damage, and improving the hand-washing effect of crop fertilizers.

[0015] 3. This composite fertilizer with synergistic high-molecular-weight slow-release and surface anti-stick properties and its preparation method uses a vibrating screening machine to separate qualified particles of 2 to 4 mm, and the returned materials (oversized / undersized particles) are crushed and re-granulated, thereby improving raw material utilization and reducing waste. In the fertilizer particle coating stage, the fertilizer particles are quickly cooled to 40 to 50°C to avoid denaturation of the coating material caused by high-temperature particles, while reducing cooling time and improving the fertilizer particle coating effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Example 1: A composite fertilizer with a synergistic effect of high molecular weight slow release and surface anti-sticking, comprising the following raw materials in the following proportions by weight: 15% nitrogen, 11% water-soluble phosphoric anhydride, 14% water-soluble potassium, 23% bentonite, 10% wollastonite, 1.5% trace elements, 5% coating material, 3% conditioner, 0.8% calcium stearate, 1.2% kaolin, and 4% secondary elements; The coating material is composed of resin coating material, chitosan (CS), polyvinyl alcohol (PVA), glacial acetic acid, deionized water and auxiliary agents, wherein the inner layer resin is 3% and the outer layer CS-PVA is 2%.

[0019] Among them, the nitrogen is composed of ammonium nitrogen, nitrate nitrogen and amide nitrogen (urea), and ammonium nitrogen accounts for 6%, nitrate nitrogen accounts for 7%, and amide nitrogen (urea) accounts for 2%. The trace elements are composed of magnesium (Mg), iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo) and other components.

[0020] It should be noted that the conditioning agent is one of dolomite powder and sulfur powder, the secondary elements are composed of calcium and sulfur, wherein calcium 2% + sulfur 2%; the auxiliary agent is composed of a cross-linking agent (glutaraldehyde), a plasticizer (polyol), a modifying additive (nano-SiO2) and zinc sulfate.

[0021] A method for preparing a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion, comprising the following steps: S1. Compounding: Calcium stearate and kaolin are added into a mixing device in a ratio of 1:1 and mixed at a stirring speed of 100 r / min for 15 minutes to obtain a compound mixture with improved anti-stick properties of the fertilizer. To ensure that the calcium stearate and kaolin are mixed more evenly, the calcium stearate and kaolin can be pre-dispersed separately before mixing. S2. Preliminary mixing: Nitrogen, water-soluble phosphoric anhydride, and water-soluble potassium are sieved, and after removing lumps or impurities, they are added to a mixing device in a ratio of 15:11:14 for preliminary mixing. During the mixing process, ensure that the raw materials are fully and evenly mixed. Use equipment such as a horizontal mixer and a rotary drum mixer and mix for 10 minutes; S3, secondary mixing: Then, the bentonite, trace elements, conditioning agent, secondary elements and the composite mixture in step S1 are added to the mixing equipment according to the proportion, the stirring speed is controlled at 200 r / min, and the mixing is continued for 10 minutes to fully mix all the raw materials to obtain a mixture; S4, granulation: the mixed material in step S3 is fed into a rotary drum granulator. Under the rotation of the drum, the raw materials interact with the added medium such as water or steam to form granules. The speed of the drum is generally 8 r / min, and the granulation time is 10 min. S4.1. Particle screening: The granulated fertilizer particles are separated into qualified particles (3mm) by a vibrating screening machine and returned (oversized particles are crushed and reused, and undersized particles are returned for further granulation); S5. Drying: The granulated compound fertilizer particles are sent to the drying equipment for drying to remove moisture from the particles and improve the stability and storage performance of the fertilizer. The drying temperature is generally controlled at 100°C. The drying time is determined according to the particle size and initial moisture content, and is generally 20 minutes. S5.1. Cooling: The dried granules are cooled by fluidized bed cooler or naturally cooled to 40°C; S6. Inner coating: The dried compound fertilizer particles are fed into the coating equipment, conventional resin coating material is added, and the conventional resin coating material is evenly sprayed at a temperature of 180°C to form a uniform inner coating layer; S6.1. Inner coating curing: After the inner resin coating, slowly cool at 60°C for 10 minutes to promote film hardening; S7. Preparation of chitosan (CS) solution: Take a certain proportion of chitosan, with the mass concentration of chitosan controlled at 1%, add it to a certain volume of 1% glacial acetic acid solution, and fully dissolve it under stirring conditions at a speed of 200 r / min for 1 hour until a uniform chitosan solution is formed; S8. Preparation of polyvinyl alcohol (PVA) solution: Take an appropriate amount of polyvinyl alcohol (PVA) with a mass concentration of 5% and add it to deionized water. Heat to 80°C and stir continuously to completely dissolve the PVA. Stir at a speed of about 300 r / min for 1 hour. Allow the solution to cool to room temperature before use. S9, blending modification: The chitosan solution and polyvinyl alcohol solution prepared in steps S7 and S8 are mixed in a certain ratio, with a mass ratio of chitosan to polyvinyl alcohol between 1:1. During the mixing process, stirring is continued for 20 minutes at a stirring speed of 300 r / min and a stirring time of 30 minutes to fully mix the two. An auxiliary agent is added during the mixing process, and the reaction is continued for 1 hour after the addition of the auxiliary agent to form a chitosan-polyvinyl alcohol blend coating emulsion; S10, outer coating: spraying the blended coating emulsion in step S9 and the fertilizer mixed with fertilizer particles and coated with the inner coating layer in a fluidized bed at a controlled temperature of 50° C. to form a uniform outer coating layer; S10.1. Curing of outer coating: After outer coating, cure under ventilation at 40℃ for 30 minutes to enhance the stability of the film.

[0022] In this embodiment, in the early stage (seedling stage): nitrate nitrogen takes effect quickly, promotes root development, and improves the emergence rate; in the middle stage (jointing stage): ammonium nitrogen and urea are continuously released, supporting stem and leaf growth, and increasing stem thickness; in the late stage (filling stage): potassium promotes full grains, significantly increases yield, has a long number of days for slow-release of nutrients, and effectively reduces the number of times of topdressing.

[0023] Example 2: A composite fertilizer with synergistic high-molecular-weight slow-release and surface anti-adhesion properties, comprising the following raw materials in the following proportions by weight: 15.5% nitrogen, 10% water-soluble phosphoric anhydride, 15% water-soluble potassium, 20% bentonite, 5% wollastonite, 2% trace elements, 7% coating material, 2% conditioner, 0.6% calcium stearate, 1.4% kaolin, and 4.5% secondary elements; The coating material is composed of resin coating material, chitosan (CS), polyvinyl alcohol (PVA), glacial acetic acid, deionized water and auxiliary agents, wherein the inner layer resin is 4% and the outer layer CS-PVA is 3%.

[0024] Among them, the nitrogen is composed of ammonium nitrogen, nitrate nitrogen and amide nitrogen (urea), and ammonium nitrogen accounts for 6.5%, nitrate nitrogen accounts for 7.5%, and amide nitrogen (urea) accounts for 1.5%. The trace elements are composed of magnesium (Mg), iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo) and other components, among which Zn 0.8% + B 0.5% + others 0.7%.

[0025] It should be noted that the conditioning agent is one of dolomite powder and sulfur powder, the secondary elements are composed of calcium and sulfur, wherein calcium 2.5% + sulfur 2%; the auxiliary agent is composed of a cross-linking agent (glutaraldehyde), a plasticizer (polyol), a modifying additive (nano-SiO2) and zinc sulfate.

[0026] A method for preparing a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion, comprising the following steps: S1. Compounding: Calcium stearate and kaolin are added into a mixing device in a ratio of 1:3 and mixed at a stirring speed of 200 r / min for 26 minutes to obtain a compound mixture with improved anti-stick properties of the fertilizer. To ensure that the calcium stearate and kaolin are mixed more evenly, the calcium stearate and kaolin can be pre-dispersed separately before mixing. S2. Preliminary mixing: Nitrogen, water-soluble phosphoric anhydride, and water-soluble potassium are sieved, and after removing lumps or impurities, they are added to a mixing device in a ratio of 15:10:15 for preliminary mixing. During the mixing process, ensure that the raw materials are fully and evenly mixed. Use equipment such as a horizontal mixer and a drum mixer and mix for 20 minutes; S3, secondary mixing: Then, the bentonite, trace elements, conditioning agent, secondary elements and the composite mixture in step S1 are added to the mixing equipment according to the proportion, the stirring speed is controlled at 300 r / min, and the mixing is continued for 15 minutes to fully mix all the raw materials to obtain a mixture; S4, granulation: the mixed material in step S3 is fed into a rotary drum granulator. Under the rotation of the drum, the raw materials interact with the added medium such as water or steam to form granules. The speed of the drum is generally 7 r / min, and the granulation time is 15 min. S4.1. Particle screening: The granulated fertilizer particles are separated into qualified particles (3.5mm) by a vibrating screening machine and returned (oversized particles are crushed and reused, and undersized particles are returned for further granulation); S5. Drying: The granulated compound fertilizer particles are sent to the drying equipment for drying to remove moisture from the particles and improve the stability and storage performance of the fertilizer. The drying temperature is generally controlled at 90°C. The drying time is determined according to the particle size and initial moisture content, and is generally 25 minutes. S5.1. Cooling: The dried granules are cooled by fluidized bed cooler or naturally cooled to 45°C; S6. Inner coating: The dried compound fertilizer particles are fed into the coating equipment, conventional resin coating material is added, and the conventional resin coating material is evenly sprayed at a temperature of 175°C to form a uniform inner coating layer; S6.1. Inner coating curing: After the inner resin coating, slowly cool at 70°C for 15 minutes to promote film hardening; S7. Preparation of chitosan (CS) solution: Take a certain proportion of chitosan, with the mass concentration of chitosan controlled at 3%, add it to a certain volume of 2% glacial acetic acid solution, and fully dissolve it under stirring conditions at a stirring speed of 350 r / min for 2 hours until a uniform chitosan solution is formed; S8. Preparation of polyvinyl alcohol (PVA) solution: Take an appropriate amount of polyvinyl alcohol (PVA) with a mass concentration of 10%, add it to deionized water, heat it to 87°C, and stir continuously to completely dissolve the PVA. Stir at a speed of about 450 rpm for 2 hours. Allow the solution to cool to room temperature before use. S9, blending modification: The chitosan solution and polyvinyl alcohol solution prepared in steps S7 and S8 are mixed in a certain ratio, with a mass ratio of chitosan to polyvinyl alcohol between 1:2. During the mixing process, stirring is continued for 30 minutes at a stirring speed of 400 r / min and a stirring time of 45 minutes to fully mix the two. An auxiliary agent is added during the mixing process, and the reaction is continued for 2 hours after the addition of the auxiliary agent to form a chitosan-polyvinyl alcohol blend coating emulsion; S10, outer coating: spraying the blended coating emulsion in step S9 and the fertilizer mixed with fertilizer particles and coated with the inner coating layer in a fluidized bed at a controlled temperature of 65° C. to form a uniform outer coating layer; S10.1. Curing of outer coating: After outer coating, cure at 50℃ with ventilation for 45 minutes to enhance the stability of the film.

[0027] In this embodiment, during the fruit-setting period, high potassium promotes fruit enlargement, increases single fruit weight, and reduces the rate of deformed fruit. During the color change period, potassium and boron synergistically promote sugar accumulation in the crop. Chitosan coating enhances plant disease resistance, reduces the incidence of late blight, and reduces the incidence of grape powdery mildew by 30%. The nutrient release curve matches the crop's fertilizer requirements, releasing 30% of nutrients in the early stage, 40% in the middle stage, and 30% in the late stage, thereby reducing the rate of fruit cracking.

[0028] Example 3: A composite fertilizer with a synergistic effect of high molecular weight slow release and surface anti-adhesion, comprising the following raw materials in the following proportions by weight: 16% nitrogen, 10% water-soluble phosphoric anhydride, 14% water-soluble potassium, 25% bentonite, 5% wollastonite, 0.5% trace elements, 3% coating material, 5% conditioner, 0.5% calcium stearate, 1% kaolin, and 3% secondary elements; The coating material is composed of resin coating material, chitosan (CS), polyvinyl alcohol (PVA), glacial acetic acid, deionized water and auxiliary agents, wherein the inner layer resin is 1.5% + the outer layer CS-PVA is 1.5%.

[0029] Among them, the nitrogen is composed of ammonium nitrogen, nitrate nitrogen and amide nitrogen (urea), and ammonium nitrogen accounts for 7%, nitrate nitrogen accounts for 7%, and amide nitrogen (urea) accounts for 2%. The trace elements are composed of magnesium (Mg), iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo) and other components, among which Fe 0.2% + Mn 0.1% + B / Zn 0.2%.

[0030] It should be noted that the conditioning agent is one of dolomite powder and sulfur powder, the secondary elements are composed of calcium and sulfur, wherein calcium is 1.5% + sulfur is 1.5%; the auxiliary agent is composed of a cross-linking agent (glutaraldehyde), a plasticizer (polyol), a modifying additive (nano-SiO2) and zinc sulfate.

[0031] A method for preparing a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion, comprising the following steps: S1. Compounding: Calcium stearate and kaolin are added into a mixing device in a ratio of 1:4 and mixed at a stirring speed of 300 r / min for 30 min to obtain a compound mixture with improved anti-stick properties of the fertilizer. To ensure that calcium stearate and kaolin are mixed more evenly, calcium stearate and kaolin can be pre-dispersed separately before mixing. S2. Preliminary mixing: Nitrogen, water-soluble phosphoric anhydride, and water-soluble potassium are sieved, and after removing lumps or impurities, they are added to a mixing device in a ratio of 16:10:14 for preliminary mixing. During the mixing process, ensure that the raw materials are fully and evenly mixed. Use equipment such as a horizontal mixer and a drum mixer and mix for 30 minutes; S3, secondary mixing: Then, the bentonite, trace elements, conditioning agent, secondary elements and the composite mixture in step S1 are added to the mixing equipment according to the proportion, the stirring speed is controlled at 400 r / min, and the mixing is continued for 20 minutes to fully mix all the raw materials to obtain a mixture; S4, granulation: the mixed material in step S3 is fed into a rotary drum granulator. Under the rotation of the drum, the raw materials interact with the added medium such as water or steam to form granules. The speed of the drum is generally 10 r / min, and the granulation time is 20 min. S4.1. Particle screening: The granulated fertilizer particles are separated into qualified particles (4mm) by a vibrating screening machine and returned (oversized particles are crushed and reused, and undersized particles are returned for further granulation); S5. Drying: The granulated compound fertilizer particles are sent to the drying equipment for drying to remove moisture from the particles and improve the stability and storage performance of the fertilizer. The drying temperature is generally controlled at 110°C. The drying time is determined according to the particle size and initial moisture content, and is generally 15 minutes. S5.1. Cooling: The dried granules are cooled by fluidized bed cooler or naturally cooled to 50°C; S6. Inner coating: The dried compound fertilizer particles are fed into the coating equipment, conventional resin coating material is added, and the conventional resin coating material is evenly sprayed at a temperature of 200°C to form a uniform inner coating layer; S6.1. Inner coating curing: After the inner resin coating, slowly cool at 80°C for 20 minutes to promote film hardening; S7. Preparation of chitosan (CS) solution: Take a certain proportion of chitosan, with the mass concentration of chitosan controlled at 5%, add it to a certain volume of 3% glacial acetic acid solution, and fully dissolve it under stirring conditions at a stirring speed of 500 r / min for 3 hours until a uniform chitosan solution is formed; S8. Preparation of polyvinyl alcohol (PVA) solution: Take an appropriate amount of polyvinyl alcohol (PVA) with a mass concentration of 15%, add it to deionized water, heat it to 95°C, and stir continuously to completely dissolve the PVA. Stir at a speed of about 600 rpm for 2 hours. Allow the solution to cool to room temperature before use. S9, blending modification: The chitosan solution and polyvinyl alcohol solution prepared in steps S7 and S8 are mixed in a certain ratio, the mass ratio of chitosan to polyvinyl alcohol is between 1:3, and during the mixing process, stirring is continued for 40 minutes, the stirring speed is 500r / min, and the stirring time is 60 minutes to fully mix the two. An auxiliary agent is added during the mixing process, and the reaction is continued for 2 hours after the addition of the auxiliary agent to form a chitosan-polyvinyl alcohol blend coating emulsion; S10, outer coating: spraying the blended coating emulsion in step S9 and the fertilizer mixed with fertilizer particles and coated with the inner coating layer in a fluidized bed at a controlled temperature of 80° C. to form a uniform outer coating layer; S10.1. Curing of outer coating: After outer coating, cure at 60℃ with ventilation for 60 minutes to enhance the stability of the film.

[0032] In this embodiment, the number of leaves, leaf width and yield of vegetable crops can be effectively increased; nitrate nitrogen takes effect quickly, shortens the seedling acclimatization period, and improves the freshness and greenness of leaves (SPAD value increases by 10-15); compared with conventional compound fertilizers, the raw material cost is reduced and the coating cost is reduced (by reducing the amount of coating material); the particle strength is ≥12N / particle, and the initial dissolution rate (24h) is ≤25%, which meets the short-term fertilizer needs of leafy vegetables.

[0033] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion, characterized in that: The invention comprises the following raw materials in proportion by weight: 15-16% nitrogen, 10-12% water-soluble phosphoric anhydride, 14-15% water-soluble potassium, 20-25% bentonite, 5-15% wollastonite, 0.5-3% trace elements, 3-8% coating material, 2-5% conditioning agent, 0.5-1% calcium stearate, 1-2% kaolin and 3-5% secondary elements; The coating material is composed of resin coating material, chitosan (CS), polyvinyl alcohol (PVA), glacial acetic acid, deionized water and auxiliary agents.

2. The composite fertilizer with polymer slow-release and surface anti-adhesion synergy according to claim 1, characterized in that: The nitrogen is composed of ammonium nitrogen, nitrate nitrogen and amide nitrogen (urea), with ammonium nitrogen accounting for 6-7%, nitrate nitrogen 7-8%, and amide nitrogen (urea) accounting for 2-3%. The trace elements are composed of magnesium (Mg), iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo) and other components.

3. The composite fertilizer with polymer slow-release and surface anti-adhesion synergy according to claim 1, characterized in that: The conditioning agent is one of dolomite powder and sulfur powder, and the secondary elements are composed of calcium and sulfur.

4. The composite fertilizer with polymer slow-release and surface anti-adhesion synergy according to claim 1, characterized in that: The auxiliary agent consists of a cross-linking agent (glutaraldehyde), a plasticizer (polyol), a modification additive (nano SiO2) and zinc sulfate.

5. A method for preparing a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion, characterized in that: The following steps are involved: S1. Compounding: Calcium stearate and kaolin are added into a mixing device in a ratio of 1:1 to 1:4, and the stirring speed is controlled at 100 to 300 r / min for 15 to 30 minutes to obtain a compound mixture for improving the anti-sticking performance of the fertilizer; S2. Preliminary mixing: sieve nitrogen, water-soluble phosphoric anhydride, and water-soluble potassium, remove lumps or impurities, and add them to a mixing device in a ratio of 10-15:5-15:15-25 for preliminary mixing for 10-30 minutes; S3, secondary mixing: Then, add bentonite, trace elements, conditioning agents, secondary elements and the composite mixture in step S1 into the mixing equipment according to the proportion, control the stirring speed at 200-400 r / min, and continue mixing for 10-20 minutes; S4, granulation: the mixed material in step S3 is fed into a rotary drum granulator. Under the rotation of the drum, the raw materials interact with the added medium such as water or steam to form granules. The speed of the drum is generally 5-10 r / min, and the granulation time is 10-20 min. S4.1, Particle screening: The granulated fertilizer particles are separated into qualified particles (2-4mm) by a vibrating screening machine and returned; S5. Drying: The granulated compound fertilizer particles are sent to the drying equipment for drying to remove moisture from the particles. The drying temperature is generally controlled at 80~120℃. The drying time is determined according to the particle size and initial moisture content, and is generally 15~30 minutes. S5.

1. Cooling: The dried granules are cooled by fluidized bed cooler or naturally cooled to 40-50°C; S6. Inner coating: The dried compound fertilizer particles are fed into the coating equipment, conventional resin coating materials are added, and the conventional resin coating materials are evenly sprayed at a temperature of 150-200°C to form a uniform inner coating layer; S6.

1. Inner coating curing: After the inner resin coating, slowly cool at 60-80°C for 10-20 minutes to promote the hardening of the film; S7. Preparation of chitosan (CS) solution: Add a certain proportion of chitosan to a certain volume of 1-3% glacial acetic acid solution and fully dissolve it under stirring at a speed of 200-500 rpm for 1-3 hours until a uniform chitosan solution is formed. S8. Preparation of polyvinyl alcohol (PVA) solution: Take an appropriate amount of polyvinyl alcohol and add it to deionized water. Heat it to 80-95°C and stir continuously to completely dissolve the polyvinyl alcohol. Stir at a speed of about 300-600 rpm for 1-2 hours. Allow the solution to cool to room temperature before use. S9, blending modification: The chitosan solution and polyvinyl alcohol solution prepared in steps S7 and S8 are mixed in a certain proportion, and during the mixing process, stirring is continued for 20 to 40 minutes at a stirring speed of 300 to 500 r / min for 30 to 60 minutes, and an auxiliary agent is added during the mixing process to form a chitosan-polyvinyl alcohol blend coating emulsion; S10, outer coating: spraying the blended coating emulsion in step S9 and the fertilizer mixed with fertilizer particles and coated with the inner coating layer in a fluidized bed, controlling the temperature at 50-80° C. to form a uniform outer coating layer; S10.

1. Curing of outer coating: After outer coating, cure under ventilation at 40-60℃ for 30-60min to enhance the stability of the film.

6. The method for preparing a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion according to claim 5, characterized in that: In step S1, in order to ensure that calcium stearate and kaolin are mixed more evenly, calcium stearate and kaolin can be pre-dispersed separately before mixing.

7. The method for preparing a composite fertilizer with synergistic effects of polymer slow release and surface anti-adhesion according to claim 5, characterized in that: The mass concentration of chitosan in step S7 is controlled to be 1-5%, and the mass concentration of polyvinyl alcohol in step S8 is controlled to be 5-15%.

8. The method for preparing a composite fertilizer with synergistic effects of polymer slow-release and surface anti-adhesion according to claim 5, characterized in that: The mass ratio of chitosan to polyvinyl alcohol in step S9 is between 1:1 and 1:3, and the reaction needs to be continued for 1 to 2 hours after the auxiliary agent is added in step S9.

Images