A bio-based coated controlled-release fertilizer with S-type release characteristics and its preparation method

Abstract

The present invention discloses a bio-based coated controlled-release fertilizer with an S-shaped release characteristic and a preparation method thereof. The controlled-release fertilizer of the present invention comprises fertilizer particles and a coating layer wrapped around the surface of the fertilizer particles; the coating layer is a double-layer structure, which consists of an inner coating layer and an outer coating layer; wherein the material constituting the inner coating layer is wax; the material constituting the outer coating layer is a film formed by the reaction of component A and component B; the component A includes vegetable oil polyols, lubricants, chain extenders, catalysts and cross-linking agents; the component B is isocyanate. The present invention adopts a double-layer coating process, and the nutrient release of the controlled-release fertilizer not only has excellent nutrient blocking and control functions in the initial stage, but also its nutrient release curve is a typical S-shaped curve, and the nutrient release time and amount are intelligently controlled, which can meet the dynamic nutrient needs of crops in different growth stages.

Description

Technical Field

[0001] The present invention relates to the field of fertilizers, and in particular to a bio-based coated controlled-release fertilizer with S-shaped release characteristics and a preparation method thereof. Background Art

[0002] Fertilizers, as food for crops, contribute significantly to meeting the food and fiber needs of a growing global population. It is estimated that fertilizers contribute approximately 40%-50% to increased crop yields. In recent years, the low fertilizer utilization rate, resource waste, and environmental pollution caused by inappropriate fertilizer application practices (such as application rates and methods) have gradually attracted the attention and concern of scholars, governments, and the public.

[0003] Scientific fertilization is a key safeguard for sustainable agricultural development. To improve fertilizer utilization, in addition to continuing to vigorously promote balanced fertilization and on-demand fertilization, the development of new fertilizer varieties and efficient fertilization technologies remains a hot topic and a challenge in current scientific fertilization research. The research and development of slow-release and controlled-release fertilizers offers new ideas and approaches for addressing the issue of low fertilizer utilization. Among various slow-release and controlled-release fertilizers, polymer-coated controlled-release fertilizers offer a precise, controlled release mechanism that better meets crop nutrient needs during growth. Consequently, their rapid growth in recent years has led to their rapid development.

[0004] Coated controlled-release fertilizers are categorized by their nutrient release pattern: linear release (L-type) and delayed release (S-type). Compared to the uniform nutrient release of conventional L-type controlled-release fertilizers, the nutrient release pattern of S-type controlled-release fertilizers consists of an inhibition period with extremely low nutrient dissolution and a release period with rapid nutrient release. Since most crops' nutrient requirements conform to the S-type pattern, S-type controlled-release fertilizers better align with crop absorption patterns than L-type controlled-release fertilizers, truly synchronizing nutrient release with crop absorption, thereby maximizing nutrient utilization efficiency and being environmentally friendly. Furthermore, since S-type controlled-release fertilizers release very little nutrient in the initial stage, large-scale application of this fertilizer to certain crops can be achieved by applying it directly to seeds or roots, further promoting efficient root absorption of dissolved nutrients. Its application has also revolutionized fertilization technology, such as seed-fertilizer contact fertilization.

[0005] In response to the strong demand for this type of highly effective controlled-release fertilizer, since the 1990s, several Japanese companies, including Chisso Co., Ltd., and the Beijing Academy of Agriculture and Forestry Sciences have developed and commercialized polyolefin-coated fertilizers with delayed-release characteristics (S-type). Furthermore, a number of patents for the production of S-type controlled-release fertilizers have been published, including JP 2002-234790, CN 1749220A, JP 2004-217434, JP 2000-185991, ZL201510315741.3, and ZL200810113258.7. The coating materials used in these patents are polyolefins, which are very stable and difficult to degrade. After fertilizer application, residual film can persist in the soil as microplastics for a long time, potentially having a significant adverse impact on the soil environment and microorganisms. In addition, toxic organic solvents are required in the production of controlled-release fertilizers, which can cause air pollution and pose a threat to workers' personal safety.

[0006] Polyurethane-coated controlled-release fertilizers, which form films through an in-situ reaction, are solvent-free, byproduct-free, pollution-free, low-energy-consumption, and feature thin, low-cost films. These fertilizers have become a hot topic in recent domestic and international research. Polyurethane-coated fertilizers have been the subject of extensive research and numerous patent applications, including WO2007 / 016788A1 from Agrium INC., CN10648837A from China National Chemical Corporation, CN201610369530.2 from Kingenta Ecological Engineering Group Co., Ltd., and CN201610988177.6 from Shandong Agricultural University. These patents detail the production methods for polyurethane-coated fertilizers.

[0007] There are also many literatures on polyurethane-coated fertilizers. These patents and literatures focus more on the screening of raw materials (isocyanates, polyols), the physical and chemical structure of film-forming substances and the impact of their properties on the nutrient release period of ordinary controlled-release fertilizers. Agricultural production urgently needs bio-based coated controlled-release fertilizers whose nutrient release is highly consistent with crop needs and which are both nutritionally efficient and environmentally friendly. Summary of the Invention

[0008] The present invention aims to provide a bio-based coated controlled-release fertilizer with S-type release characteristics and a preparation method thereof.

[0009] The present invention first provides a controlled-release fertilizer, comprising fertilizer particles and a coating layer wrapped around the surface of the fertilizer particles; the coating layer is a double-layer structure consisting of an inner coating layer and an outer coating layer;

[0010] Wherein, the material constituting the inner envelope layer is wax;

[0011] The material constituting the outer membrane layer is a membrane formed by the reaction of component A and component B;

[0012] The component A includes vegetable oil polyol, lubricant, chain extender, catalyst and cross-linking agent;

[0013] The B component is isocyanate;

[0014] The mass of the catalyst is 0 to 0.37% of the mass of the outer membrane layer.

[0015] In the above-mentioned controlled-release fertilizer, the wax is at least one of microcrystalline wax, polyethylene wax and acetic acid wax; preferably microcrystalline wax having a melting point of 70 to 85°C;

[0016] The vegetable oil polyol is selected from at least one of castor oil, epoxy soybean oil polyol and palm oil polyol; preferably castor oil or modified soybean oil polyol;

[0017] The lubricant is selected from at least one of solid paraffin, amide wax and liquid paraffin; preferably 52# to 56# solid paraffin;

[0018] The chain extender is selected from at least one of ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 3,3-dichloro-4,4-diphenylmethanediamine and 3,5-dimethylthiophenylenediamine; preferably 1,4-butanediol;

[0019] The catalyst may be selected from at least one of triethylenediamine, stannous octoate, dibutyltin dilaurate, dibutylzinc oxide, dimethylhexadecylamine and triethanolamine; preferably stannous octoate;

[0020] The cross-linking agent is selected from at least one of glycerol, trimethylolpropane, diethanolamine, ethanolamine, triethanolamine and pentaerythritol; preferably trimethylolpropane;

[0021] The isocyanate is selected from at least one of diphenylmethane diisocyanate, toluene diisocyanate, liquefied MDI and polymethylene polyphenyl polyisocyanate; preferably polymethylene polyphenyl polyisocyanate;

[0022] The isocyanate index is 1.2 to 2.0, and specifically 1.2 to 1.6.

[0023] In the above-mentioned controlled-release fertilizer, the mass of the vegetable oil polyol is 35% to 55% of the mass of the outer film layer; specifically, it can be 40% to 51%;

[0024] The mass of the chain extender is 2% to 5.5% of the mass of the outer film layer; specifically, it can be 2.8% to 5.5%, 3.2%, 3.5%, 3.8%, 4.4% or 5.2%;

[0025] The mass of the cross-linking agent is 0.5% to 1.3% of the mass of the outer film layer; specifically, it can be 0.7% to 1.3%;

[0026] The mass of the lubricant is 1% to 5% of the mass of the outer film layer; specifically, it can be 1% to 3%;

[0027] The mass of the isocyanate is 40% to 55% of the mass of the outer film layer; specifically, it can be 40% to 51%;

[0028] The mass of the outer film layer is the sum of the masses of the A component and the B component.

[0029] In the above-mentioned controlled-release fertilizer, the mass percentage of the coating layer is 2.5% to 10% based on the total mass of the controlled-release fertilizer; specifically, 2.5% to 7%;

[0030] Based on the total mass of the coating layer, the mass percentage of the outer coating layer is 90% to 94%.

[0031] The nutrient release curve of the above-mentioned controlled-release fertilizer is an S-shaped curve; the initial release rate (24 hours) under the condition of immersion in constant temperature water at 25°C does not exceed 0.5%, and the inhibition period (nutrient cumulative release rate does not exceed 5%) is greater than or equal to 30 days.

[0032] In the above-mentioned controlled-release fertilizer, the coating rate of the controlled-release fertilizer is 2.5% to 7%;

[0033] The fertilizer particles can be selected from at least one of urea, potassium chloride, potassium sulfate, binary compound fertilizer and ternary compound fertilizer particles;

[0034] The particle size of the fertilizer particles is 2 mm to 4 mm.

[0035] In the above-mentioned controlled-release fertilizer, when the fertilizer granules are urea, the amount of the catalyst added is 0. When the fertilizer granules are potassium chloride, potassium sulfate, binary compound fertilizer, or ternary compound fertilizer granules, the amount of the catalyst added is not 0; it is preferably 0.28% to 0.37% of the mass of the outer coating layer, and specifically can be 0.28% or 0.34%.

[0036] The present invention also provides a method for preparing the above-mentioned controlled-release fertilizer, comprising the following steps:

[0037] (1) melting the material of the inner coating layer and spraying it onto the surface of the fertilizer particles to form a film;

[0038] (2) Spraying the mixed component A and component B onto the surface of the fertilizer particles obtained in step (1) to obtain the controlled-release fertilizer.

[0039] In the above preparation method, the mixed spraying of component A and component B adopts the spraying device described in ZL201820542268.1.

[0040] In the above preparation method, the fertilizer is preheated to 65°C;

[0041] The inner envelope layer material is melted at 100° C. and then sprayed;

[0042] The A component is heated to 60°C;

[0043] The B component is heated to 30°C (no need to heat when the air temperature is higher than 30°C).

[0044] In the above preparation method, in step (2), the spray rate of the mixed liquid when the components A and B are mixed and sprayed is 750 to 1000 g / min.

[0045] The present invention has the following beneficial effects:

[0046] The controlled-release fertilizer provided by this invention uses a bio-based polyol as the primary coating material and utilizes a double-layer coating process. This controlled-release fertilizer not only exhibits excellent nutrient barrier control in the initial stage, but also exhibits a typical S-shaped nutrient release curve. This intelligently controls the timing and quantity of nutrient release, meeting the dynamic nutrient needs of crops at different growth stages, such as seedling contact fertilization and one-time seed fertilizer contact fertilization. Furthermore, the bio-based coating material degrades rapidly in soil, minimizing negative environmental impact.

[0047] The method for preparing a controlled-release fertilizer provided by the present invention uses coating materials that are widely available on the market. The used materials are low in cost, easily degradable, and easy to operate. A rotary drum coating machine is used to coat the fertilizer particles. An independently developed high-efficiency internal mixing spray coating is adopted, and parameters such as temperature, rotation speed, air volume, and spray flow rate are set to ensure that the coating is more uniform and dense, and the surface is smooth and consistent.

[0048] The controlled-release fertilizer provided by the present invention can greatly improve the utilization efficiency of nitrogen fertilizer and reduce the loss of nitrogen nutrients into the environment because it can give full play to the synchronization of nutrient supply and crop nutrient absorption. It is of great significance for preventing and controlling microplastics and farmland non-point source pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The nutrient release curves of the bio-based coated controlled-release fertilizers prepared in Examples and Comparative Examples are shown.

[0050] Figure 2 Schematic diagram of spraying the outer coating liquid of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below in conjunction with specific embodiments. The examples given are only for illustrating the present invention, not for limiting the scope of the present invention.

[0052] The experimental methods in the following examples are conventional methods unless otherwise specified.

[0053] The quantitative tests in the following examples were all repeated three times, and the results were averaged.

[0054] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0055] In order to solve the problem that ordinary controlled-release fertilizers release more nutrients than crops need in the early stage and there is insufficient fertilizer supply in the later stage, the inventors of the present invention have done a lot of screening and matching work on coating materials. Combining the coating liquid spraying process and equipment independently developed, they found a formula mainly composed of bio-based polyols and isocyanates and adopted a double-layer coating process. The coating not only promotes the close bonding of the film layer to the particle surface, but also has excellent nutrient barrier function and an S-shaped nutrient release curve.

[0056] Unless otherwise specified, the percentages in the following examples are by mass.

[0057] The controlled-release properties of the controlled-release fertilizers in the following examples were tested using a 25°C constant-temperature water immersion method, as follows:

[0058] Weigh 10g of controlled-release fertilizer and place it in a 100-mesh nylon mesh bag. After sealing, place the bag in a plastic container filled with 250mL of distilled water and place it in a constant temperature incubator at 25℃. Take samples regularly and determine the nitrogen dissolution data using spectrophotometry or Kjeldahl method.

[0059] The nutrient release period refers to the number of days required for the cumulative release rate of nitrogen in the coated controlled-release fertilizer to reach 80% in water at 25°C.

[0060] Example 1

[0061] (1) Weigh 50 kg of urea granules with a diameter of 2-4 mm (nitrogen content of 46%, Shandong Hualu Hengsheng Group Co., Ltd.) and place them in a 1000 mm diameter water chestnut-type coating machine (Shandong Jingcheng Pharmaceutical Equipment Manufacturing Co., Ltd.). Turn on the machine and adjust the speed to 50 rpm. Start the heating fan and heat the urea granules to 65°C with hot air and maintain it.

[0062] Microcrystalline wax (melting point 70° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.) was heated to 100° C. and maintained at 100° C. 150 g of melted microcrystalline wax was sprayed onto the surface of the urea granules to form a film, forming an inner coating layer.

[0063] (2) 615 g of castor oil (hydroxyl value 263, functionality 2.7, Jinan Sunny Chemical Technology Co., Ltd.), 66 g of 1,4-butanediol (industrial grade), 16.5 g of trimethylolpropane (industrial grade), and 45 g of paraffin wax (52# refined wax, Shandong Chuangda Chemical Co., Ltd.) were mixed and heated to 60°C and stirred to mix evenly. This mixture was used as component A of the outer film layer. 758 g of polymethylene polyphenyl polyisocyanate (PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film layer. The isocyanate index was set to 1.56.

[0064] A special spraying device (ZL201820542268.1) was used to spray the outer coating layer A and B components onto the surface of the fertilizer with the inner coating layer obtained in (1). The coating liquid formed a film on the surface of the urea particles after a wetting-adhesion-dispersion-drying process. The coating liquid mixed spray rate was 857 g / min (the outer coating layer A component and the outer coating layer B component were 424 g / min and 433 g / min, respectively), the spraying time was 35 s, and the coating liquid (A component and B component) spraying amount was 500 g.

[0065] Repeat the above steps twice for the outer coating layer until the coating layer mass reaches 3.3% of the mass of the urea granules. The actual fertilizer coating rate is 2.84%.

[0066] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 The results show that the coated controlled-release urea prepared above had an initial release rate of 0.08%, a release period of 61 days, an inhibition period of 30 days (the number of days required for cumulative nutrient dissolution to reach 5%. Since 5% cannot be accurately determined during actual nutrient dissolution measurements, the inhibition period is represented by the result closest to 5%), and a ratio of the inhibition period to the dissolution period (the number of days from the end of the inhibition period to the time when nutrient dissolution reaches 80%) of 0.96.

[0067] Example 2

[0068] (1) The same as Example 1, except that 150 g of microcrystalline wax (melting point 70° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.) in Example 1 was replaced by 200 g of microcrystalline wax (melting point 75° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.).

[0069] (2) 960 g of modified soybean oil polyol (hydroxyl value 200, functionality 3.8, Zhangjiagang Feihang Technology Co., Ltd.), 76 g of 1,4-butanediol (industrial grade), 18 g of trimethylolpropane (industrial grade), and 40 g of paraffin wax (52# refined wax) were mixed and heated to 60°C and stirred to mix evenly. This mixture was used as component A of the outer film layer. 906 g of polymethylene polyphenyl polyisocyanate (PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film layer. The isocyanate index was set to 1.22.

[0070] A special spraying device (ZL201820542268.1) was used to spray the outer coating layer A and B components onto the surface of the fertilizer with the inner coating layer obtained in (1). The coating liquid formed a film on the surface of the urea particles after a wetting-adhesion-dispersion-drying process. The coating liquid mixed spray rate was 857 g / min (the outer coating layer A component and the outer coating layer B component were 469 g / min and 388 g / min, respectively), the spraying time was 35 s, and the coating liquid (A component and B component) spraying amount was 500 g.

[0071] The above steps were repeated three times for the outer coating layer until the coating layer mass reached 4.4% of the mass of the urea granules. The fertilizer coating rate was measured to be 3.92%.

[0072] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 The results show that the coated controlled-release urea prepared above had an initial release rate of 0.06%, a release period of 99 days, an inhibition period of 42 days (the number of days required for cumulative nutrient dissolution to reach 5%. Since 5% cannot be accurately determined during actual nutrient dissolution measurements, the inhibition period is represented by the result closest to 5%), and a ratio of the inhibition period to the dissolution period (the number of days from the end of the inhibition period to the time when nutrient dissolution reaches 80%) of 0.73.

[0073] Example 3

[0074] (1) The same as Example 1, except that 150 g of microcrystalline wax (melting point 70° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.) in Example 1 was replaced by 250 g of microcrystalline wax (melting point 80° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.).

[0075] (2) 1250 g of castor oil (hydroxyl value 263, functionality 2.7, Jinan Sunny Chemical Technology Co., Ltd.), 87.5 g of 1,4-butanediol (industrial grade), 20 g of trimethylolpropane (industrial grade), and 75 g of paraffin wax (52# refined wax, Shandong Chuangda Chemical Co., Ltd.) were mixed and heated to 60°C and stirred to mix evenly. This mixture was used as component A of the outer film layer. 1068 g of polymethylene polyphenyl polyisocyanate (PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film layer. The isocyanate index was set to 1.32.

[0076] A special spraying device (ZL201820542268.1) was used to spray the outer coating layer A and B components onto the surface of the fertilizer with the inner coating layer obtained in (1). The coating liquid formed a film on the surface of the urea particles after a wetting-adhesion-dispersion-drying process. The coating liquid mixed spray rate was 750 g / min (the outer coating layer A component and the outer coating layer B component were 430 g / min and 320 g / min, respectively), the spraying time was 35 s, and the coating liquid (component A and component B) spraying amount was 500 g.

[0077] The above steps were repeated 4 times for the outer coating layer until the coating layer mass reached 5.5% of the mass of the urea granules. The fertilizer coating rate was measured to be 4.88%.

[0078] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 The results show that the coated controlled-release urea prepared above had an initial release rate of 0.02%, a release period of 140 days, an inhibition period of 82 days (the number of days required for cumulative nutrient dissolution to reach 5%. Since 5% cannot be accurately determined during actual nutrient dissolution measurements, the inhibition period is represented by the result closest to 5%), and a ratio of the inhibition period to the dissolution period (the number of days from the end of the inhibition period to the time when nutrient dissolution reaches 80%) of 1.41.

[0079] Example 4

[0080] (1) Weigh 50 kg of granular compound fertilizer (15-11-23+TE, Sichuan Haoshiji Chemical Co., Ltd.) with a diameter of 2-4 mm and place it in a 1000 mm diameter water chestnut-type coating machine. Turn on the machine and adjust the speed to 50 rpm. Start the heating fan to heat the fertilizer granules with hot air to 65°C and maintain the temperature.

[0081] Microcrystalline wax (melting point 75° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.) was heated to 100° C. and maintained at 100° C. 150 g of melted microcrystalline wax was sprayed onto the surface of the compound fertilizer particles to form a film, forming an inner coating layer.

[0082] (2) 1020 g of castor oil (hydroxyl value 263, functionality 2.7, Jinan Qingtian Chemical Technology Co., Ltd.), 64 g of 1,4-butanediol (industrial grade), 14 g of trimethylolpropane (industrial grade), 20 g of paraffin wax (52# refined wax, Shandong Chuangda Chemical Co., Ltd.), and 5.6 g of stannous octoate (Guangdong Wengjiang Chemical Reagent Co., Ltd.) were mixed and heated to 60°C and stirred to mix evenly. This mixture was used as component A of the outer film layer. 882 g of polymethylene polyphenyl polyisocyanate (PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film layer. The isocyanate index was set to 1.40.

[0083] A special spraying device (ZL201820542268.1) was used to spray the outer coating layer A and B components onto the surface of the fertilizer with an inner coating layer obtained in (1). The coating liquid formed a film on the surface of the compound fertilizer particles after a wetting-adhesion-dispersion-drying process. The coating liquid mixed spray rate was 750 g / min (the outer coating layer A component and the outer coating layer B component were 420 g / min and 330 g / min, respectively), the spraying time was 35 s, and the coating liquid (A component and B component) spraying amount was 500 g.

[0084] The above steps were repeated three times for the outer coating layer until the coating layer mass reached 4.3% of the mass of the compound fertilizer particles. The fertilizer coating rate was measured to be 3.88%.

[0085] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 (Cumulative nutrient release curve). The results show that the coated controlled-release compound fertilizer prepared above had an initial release rate of 0.06%, a release period of 93 days, an inhibition period of 47 days (the number of days for cumulative nutrient dissolution to reach 5%. The actual nutrient dissolution measurement cannot accurately obtain 5%, so the measurement result closest to 5% is used to represent the inhibition period). The ratio of the inhibition period to the dissolution period (the number of days from the end of the inhibition period to the nutrient dissolution reaching 80%) is 1.02.

[0086] Example 5

[0087] (1) Weigh 50 kg of granular compound fertilizer (15-15-15+TE, Sichuan Haoshiji Chemical Co., Ltd.) with a diameter of 2-4 mm and place it in a 1000 mm diameter water chestnut-type coating machine. Turn on the machine and adjust the speed to 50 rpm. Start the heating fan to heat the compound fertilizer granules with hot air and heat to 65°C and maintain it.

[0088] Microcrystalline wax (melting point 75° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.) was heated to 100° C. and maintained at 100° C. 200 g of melted microcrystalline wax was sprayed onto the surface of the compound fertilizer particles to form a film, forming an inner coating layer.

[0089] (2) 1253 g of modified soybean oil polyol (hydroxyl value 200, functionality 3.8, Zhangjiagang Feihang Technology Co., Ltd.), 156 g of 1,4-butanediol (industrial grade), 39 g of trimethylolpropane (industrial grade), 10.3 g of stannous octoate (Guangdong Wengjiang Chemical Reagent Co., Ltd.), and 30 g of paraffin wax (56# refined wax) were mixed and heated to 60°C and stirred to mix evenly. This mixture was used as component A of the outer film layer. 1523 g of polymethylene polyphenyl polyisocyanate (brand name PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film layer. The isocyanate index was set to 1.29.

[0090] A special spraying device (ZL201820542268.1) was used to spray the outer coating layer A and B components on the surface of the fertilizer with an inner coating layer obtained in (1). The coating liquid formed a film on the surface of the compound fertilizer particles after a wetting-adhesion-dispersion-drying process. The coating liquid mixed spray rate was 1000 g / min (the outer coating layer A component and the outer coating layer B component were 493 g / min and 507 g / min, respectively), the spraying time was 45 s, and the coating liquid (A component and B component) spraying amount was 750 g.

[0091] Repeat the above steps for the outer coating layer three times until the coating layer mass reaches 6.4% of the compound fertilizer particle mass. The fertilizer coating rate is measured to be 5.78%.

[0092] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 (Cumulative nutrient release curve). The results show that the coated controlled-release compound fertilizer prepared above had an initial release rate of 0.23%, a release period of 184 days, an inhibition period of 80 days (the number of days until the cumulative nutrient dissolution reached 5%. The actual nutrient dissolution measurement cannot accurately obtain 5%, so the measurement result closest to 5% is used to represent the inhibition period). The ratio of the inhibition period to the dissolution period (the number of days from the end of the inhibition period to the nutrient dissolution reaching 80%) was 0.77.

[0093] Comparative Example 1

[0094] The preparation method is the same as that of Example 1, except that the inner coating layer of microcrystalline wax is not sprayed, and the outer coating layer spraying step is repeated twice until the coating layer mass reaches 3.0% of the mass of the urea particles. The fertilizer coating rate is measured to be 2.67%.

[0095] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1The results show that the coated controlled-release urea prepared above had an initial release rate of 0.36%, a release period of 52 days, an inhibition period of 16 days (the number of days required for cumulative nutrient dissolution to reach 5%. Since the actual nutrient dissolution measurement cannot accurately obtain 5%, the measurement result closest to 5% is used to represent the inhibition period). The ratio of the inhibition period to the dissolution period (the number of days from the end of the inhibition period to the time when nutrient dissolution reaches 80%) is 0.41.

[0096] Comparative Example 2

[0097] The preparation method was the same as that of Example 2, except that 274 g of the outer coating layer component A and 226 g of the outer coating layer component B were alternately sprayed onto the surface of the fertilizer having the inner coating layer obtained in (1) and reacted. The spraying rates of the outer coating layer component A and the outer coating layer component B were 469 g / min and 388 g / min, respectively. The coating liquid formed a film on the surface of the urea granules through a wetting-adhesion-dispersion-drying process.

[0098] Repeat the above steps for the outer coating layer three times until the coating layer mass reaches 4.4% of the mass of the urea granules. The fertilizer coating rate is measured to be 3.74%.

[0099] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 The results show that the initial release rate of the coated controlled-release urea prepared above is 1.23%, the release period is 78 days, and the nutrient release curve is linear.

[0100] Comparative Example 3

[0101] (1) Weigh 50 kg of granular compound fertilizer (15-11-23+TE, Sichuan Haoshiji Chemical Co., Ltd.) with a diameter of 2-4 mm and place it in a 1000 mm diameter water chestnut-type coating machine. Turn on the machine and adjust the speed to 50 rpm. Start the heating fan to heat the fertilizer granules with hot air to 65°C and maintain the temperature.

[0102] Microcrystalline wax (melting point 75° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.) was heated to 100° C. and maintained at 100° C. 150 g of melted microcrystalline wax was sprayed onto the surface of the compound fertilizer particles to form a film, forming an inner coating layer.

[0103] (2) 1200 g of castor oil (hydroxyl value 263, functionality 2.7, Jinan Qingtian Chemical Technology Co., Ltd.), 56 g of 1,4-butanediol (industrial grade), 2 g of trimethylolpropane (industrial grade), 20 g of paraffin wax (52# refined wax, Shandong Chuangda Chemical Co., Ltd.), and 6.4 g of stannous octoate (Guangdong Wengjiang Chemical Reagent Co., Ltd.) were mixed and heated to 60°C and stirred to mix evenly. This mixture was used as component A of the outer film layer. 722 g of polymethylene polyphenyl polyisocyanate (PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film layer. The isocyanate index was set to 1.12.

[0104] 320g of component A and 180g of component B were alternately sprayed onto the fertilizer surface and allowed to react at spray rates of 479g / min and 271g / min, respectively. The coating liquid formed a film on the surface of the compound fertilizer particles through a process of wetting, adhesion, dispersion, and drying.

[0105] Repeat the above steps for the outer coating layer three times until the coating layer mass reaches 4.3% of the mass of the compound fertilizer particles. The fertilizer coating rate is measured to be 3.75%.

[0106] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 (Nutrient cumulative release curve) The results show that the initial release rate of the coated controlled-release compound fertilizer prepared above is 0.15%, the release period is 74 days, and the nutrient release curve is linear.

[0107] Comparative Example 4

[0108] Weigh 50 kg of 2-4 mm diameter granular compound fertilizer (15-11-23+TE, Sichuan Haoshiji Chemical Co., Ltd.) and place it in a 1000 mm diameter water chestnut coating machine. Turn on the machine and adjust the speed to 50 rpm. Start the heating fan to heat the fertilizer granules with hot air to 65°C and maintain the temperature.

[0109] 1302g of polyethylene glycol (PEG-2000, hydroxyl value 63, functionality 2, Guangzhou Zhongshan Chemical Co., Ltd.), 64g of 1,4-butanediol (industrial grade), 14g of trimethylolpropane (industrial grade), 20g of paraffin wax (52# refined wax, Shandong Chuangda Chemical Co., Ltd.), and 7g of stannous octoate (Guangdong Wengjiang Chemical Reagent Co., Ltd.) were mixed and heated to 60°C and stirred until uniformly mixed. This mixture served as component A of the outer film. 600g of polymethylene polyphenyl polyisocyanate (PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film. The isocyanate index was set to 1.40.

[0110] 350g of component A and 150g of component B were alternately sprayed onto the fertilizer surface and allowed to react. The spraying rates of component A and component B were 525g / min and 225g / min, respectively. The coating liquid formed a film on the surface of the compound fertilizer particles after a process of wetting, adhesion, dispersion, and drying.

[0111] Repeat the above steps for the outer coating layer three times until the coating layer mass reaches 4.0% of the mass of the compound fertilizer particles. The fertilizer coating rate is measured to be 3.54%.

[0112] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 (Nutrient cumulative release curve) The results show that the initial release rate of the coated controlled-release urea prepared above is 0.89%, the release period is 65 days, and the nutrient release curve is linear.

[0113] Comparative Example 5

[0114] (1) Weigh 50 kg of urea granules with a diameter of 2-4 mm (nitrogen content of 46%, Shandong Hualu Hengsheng Group Co., Ltd.) and place them in a 1000 mm diameter water chestnut-type coating machine. Turn on the machine and adjust the speed to 50 rpm. Start the heating fan to heat the urea granules with hot air until the temperature reaches 65°C and maintain it.

[0115] Microcrystalline wax (melting point 80° C., Fanmei Wax Industry (Shenzhen) Co., Ltd.) was heated to 100° C. and maintained at 100° C. 250 g of the melted microcrystalline wax was sprayed onto the surface of the urea granules to form a film, forming an inner coating layer.

[0116] (2) 1580 g of polyethylene glycol (PEG-2000, hydroxyl value 63, functionality 2, Guangzhou Zhongshan Chemical Co., Ltd.), 87.5 g of 1,4-butanediol (industrial grade), 20 g of trimethylolpropane (industrial grade), and 75 g of paraffin wax (52# refined wax, Shandong Chuangda Chemical Co., Ltd.) were mixed and heated to 60°C and stirred to mix evenly. This mixture was used as component A of the outer film layer. 738 g of polymethylene polyphenyl polyisocyanate (PM200, Wanhua Chemical Group Co., Ltd.) was preheated to 30°C and used as component B of the outer film layer. The isocyanate index was set to 1.32.

[0117] A special sprayer (ZL201820542268.1) was used to spray the outer coating layer A and B components onto the surface of the fertilizer with the inner coating layer obtained in (1). The coating liquid formed a film on the surface of the urea particles after a wetting-adhesion-dispersion-drying process. The coating liquid mixed spray rate was 750 g / min (the outer coating layer A component and the outer coating layer B component were 529 g / min and 221 g / min, respectively), the spraying time was 35 s, and the coating liquid (A component and B component) spraying amount was 500 g.

[0118] The above steps were repeated 4 times for the outer coating layer until the coating layer mass reached 5.5% of the mass of the urea granules. The fertilizer coating rate was measured to be 4.94%.

[0119] The results of the 25°C constant temperature water immersion test are shown in Table 1 and Figure 1 (Nutrient cumulative release curve) The results show that the initial release rate of the coated controlled-release urea prepared above is 0.52%, the release period is 96 days, and the nutrient release curve is linear.

[0120] Table 1 Nutrient release test results of coated controlled-release fertilizer

[0121]

[0122] Note: Inhibition period: the time required for the cumulative dissolution of nutrients in controlled-release fertilizer to reach 5%; Dissolution period: the time required from the end of the inhibition period to the time when the nutrient dissolution reaches 80%.

[0123] As can be seen from Table 1, the fertilizer release curves of the examples of the present invention are all typical S-shaped curves, simultaneously meeting the requirements of an initial release rate of no more than 0.5% and an inhibition period (cumulative nutrient release ≤ 5%) of 30 days or longer. This allows for contact fertilization of seed and fertilizer in agricultural production, such as rice and vegetable seedling cultivation, without causing seedling burns or root damage, significantly improving fertilizer utilization while simplifying the process. In comparison, the fertilizer release curves of the comparative examples are mostly linear release types. Even with S-shaped curves, the inhibition and release periods are relatively short, failing to meet the stringent requirements of contact fertilization for controlled nutrient release in the early stages.

Claims

1. A controlled-release fertilizer comprising fertilizer particles and a coating layer wrapped around the surface of the fertilizer particles; characterized in that: The envelope layer is a double-layer structure, which consists of an inner envelope layer and an outer envelope layer; Wherein, the material constituting the inner envelope layer is wax; The wax is at least one of microcrystalline wax, polyethylene wax and acetate wax; The material constituting the outer membrane layer is a membrane formed by the reaction of component A and component B; The component A includes vegetable oil polyol, lubricant, chain extender, catalyst and cross-linking agent; The B component is isocyanate; The vegetable oil polyol is castor oil or modified soybean oil polyol; The mass of the catalyst is 0-0.37% of the mass of the outer membrane layer; The mass of the vegetable oil polyol is 35% to 55% of the mass of the outer film layer; The mass of the chain extender is 2% to 5.5% of the mass of the outer film layer; The mass of the cross-linking agent is 0.5% to 1.3% of the mass of the outer film layer; The mass of the lubricant is 1% to 5% of the mass of the outer film layer; The mass of the isocyanate is 40% to 55% of the mass of the outer film layer; The mass of the outer film layer is the sum of the masses of the A component and the B component; The lubricant is selected from at least one of solid paraffin, amide wax and liquid paraffin; The chain extender is selected from at least one of ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 3,3-dichloro-4,4-diphenylmethanediamine and 3,5-dimethylthiophenylenediamine; The catalyst is selected from at least one of triethylenediamine, stannous octoate, dibutyltin dilaurate, dibutylzinc oxide, dimethylhexadecylamine and triethanolamine; The cross-linking agent is selected from at least one of glycerol, trimethylolpropane, diethanolamine, ethanolamine, triethanolamine and pentaerythritol; The isocyanate is selected from at least one of diphenylmethane diisocyanate, toluene diisocyanate, liquefied MDI and polymethylene polyphenyl polyisocyanate; The isocyanate index is 1.2 to 2.0; The preparation method of the controlled-release fertilizer comprises the following steps: (1) Melting the material of the inner coating layer and spraying it onto the surface of the fertilizer particles to form a film; (2) The components A and B are mixed and sprayed onto the surface of the fertilizer particles obtained in step (1) to obtain the controlled-release fertilizer.

2. The controlled-release fertilizer according to claim 1, wherein: The isocyanate index is 1.2 to 1.

6.

3. The controlled-release fertilizer according to claim 1, wherein: The wax is a microcrystalline wax with a melting point of 70-85°C; The lubricant is 52#~56# solid paraffin; The chain extender is 1,4-butanediol; The catalyst is stannous octoate; The cross-linking agent is trimethylolpropane; The isocyanate is polymethylene polyphenyl polyisocyanate.

4. The controlled-release fertilizer according to any one of claims 1 to 3, characterized in that: The mass of the vegetable oil polyol is 40% to 51% of the mass of the outer film layer; The mass of the chain extender is 2.8% to 5.5% of the mass of the outer film layer; The mass of the cross-linking agent is 0.7% to 1.3% of the mass of the outer film layer; The mass of the lubricant is 1% to 3% of the mass of the outer film layer; The mass of the isocyanate is 40-51% of the mass of the outer film layer; The mass of the outer film layer is the sum of the masses of the A component and the B component.

5. The controlled-release fertilizer according to any one of claims 1 to 3, characterized in that: Based on the total mass of the controlled-release fertilizer, the mass percentage of the coating layer is 2.5% to 10%; Based on the total mass of the coating layer, the mass percentage of the outer coating layer is 90% to 94%.

6. The controlled-release fertilizer according to claim 5, wherein: Based on the total mass of the controlled-release fertilizer, the mass percentage of the coating layer is 2.5% to 7%.

7. The controlled-release fertilizer according to any one of claims 1 to 3, characterized in that: The nutrient release curve of the controlled-release fertilizer is an S-shaped curve, and the initial release rate does not exceed 0.5%, and the inhibition period is greater than or equal to 30 days; The inhibition period refers to the cumulative nutrient release ≤ 5%.

8. The method for preparing the controlled-release fertilizer according to any one of claims 1 to 7, comprising the steps of: (1) Melting the material of the inner coating layer and spraying it onto the surface of the fertilizer particles to form a film; (2) The components A and B are mixed and sprayed onto the surface of the fertilizer particles obtained in step (1) to obtain the controlled-release fertilizer.

9. The preparation method according to claim 8, characterized in that: The fertilizer is preheated to 65°C; The inner envelope layer is melted at 100° C. and then sprayed; The A component is heated to 60°C; The B component was heated to 30°C.

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