CN103819292B - A kind of solvent-free film-coated controlled release fertilizer and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of solvent-free film-coated controlled release fertilizer and preparation method thereof.Described film-coated controlled release fertilizer is made up of fertiliser granulates and the coating layer be coated on outside described fertiliser granulates; The mass percentage of described fertiliser granulates is 93% ~ 97%, and the mass percentage of described coating layer is 3% ~ 7%; Described coating layer is obtained by the polymerization of polyisocyanates, polyester polyol and microcrystalline wax.2 kinds of polymkeric substance are successively sprayed application to particle surface by preparation method provided by the invention respectively, solve a shared pipeline, problem that nozzle and the blocking caused make coating interrupt, make the probability that particle adhesion occurs in equipment significantly reduce simultaneously, the stability of coating process is obviously strengthened.Solve the problem that coating speed and coating homogeneity can not be taken into account, complete being uniformly distributed of rete in fast filming process.

Description

A kind of solvent-free coated controlled-release fertilizer and preparation method thereof

technical field

The invention relates to a solvent-free coated controlled-release fertilizer and a preparation method thereof.

Background technique

Under the pressure of dwindling cultivated land and growing urban population, the application of chemical fertilizers will still be an important measure for the stable and sustainable development of my country's agriculture for a long time to come. However, with the increase of fertilizer application, there has been a situation where the amount of chemical fertilizer has increased significantly but the yield per unit area of crops has remained stagnant. At the same time, a large amount of nitrogen and phosphorus loss has caused serious environmental pollution and other problems. These have become one of the fundamental issues restricting my country's food security and environmental security. For this reason, the Central Document No. 1 has promoted slow and controlled release fertilizers as an important force in agricultural science and technology for three consecutive years. Since slow and controlled release fertilizers were first included in the priority development industry in 2011, in 2012 it was required to focus on breaking through the bottleneck of agricultural technology. Significant practical technical achievements have been made in medicine and other aspects, especially in 2013, the subsidy program for slow and controlled release fertilizers was stipulated for the first time, which has brought unprecedented development opportunities and strong policy support to the promotion and application of slow and controlled release fertilizers.

In the past 10 years, the consumption of common chemical fertilizers in the world has experienced negative growth, but the consumption of slow and controlled release fertilizers has been increasing at a rate of about 4-5% per year, and the proportion of the total consumption of chemical fertilizers in the world has increased from 0.12% in 1995 to 0.45% in 2006. %. Since 2005, the application of slow and controlled release fertilizers in field crops has developed rapidly, and the production capacity of slow and controlled release fertilizers in China, Canada and the United States has also increased rapidly. my country's slow-release fertilizer industry has developed rapidly since the 1990s. The research on sulfur-coated urea and resin-coated controlled-release fertilizers has developed to a relatively high level. The technology has become increasingly mature, and the controlled-release performance of nutrients is good. At present, there are more than 30 scientific research institutions engaged in the research of slow and controlled release fertilizers in China, and more than 70 units engaged in industrial development and promotion and application, with an annual production capacity of more than 1 million tons. Slow and controlled release fertilizers have become my country's chemical fertilizers. important direction of industry development.

my country has made some progress in the research and promotion of slow and controlled release fertilizers, but there are still many problems. First of all, the price of domestic slow and controlled release fertilizers is higher than that of traditional fertilizers; secondly, the application and promotion of slow and controlled release fertilizers is slow, there is a lack of support system for slow/controlled release fertilizer application technology, and there is a lack of fertilizer application evaluation tests. The construction of dedicated laboratories, test bases and application demonstration promotion systems is relatively incomplete. The research and development of efficient and environmentally friendly slow-release fertilizers is of great significance in terms of saving resources, realizing the coordinated development of agricultural production and ecology, saving costs and increasing efficiency, and saving energy and reducing emissions. The excessive application of nitrogen fertilizer in my country and the resulting environmental problems are already very urgent, and the slow and controlled release of nitrogen fertilizer will become the main means to solve this problem in the future. The research and development of controlled-release fertilizers at home and abroad are developing in the direction of low cost and high environmental protection. Polymer coated fertilizer is the fastest growing field of slow and controlled release fertilizers in recent years. Typical technologies and products in the world mainly include the following:

1) Japan’s Chisso Company earlier developed a controlled-release fertilizer with polyolefin resin as the coating material. It used organic solvents to dissolve polyethylene, polypropylene and other materials at high temperatures, and applied it to the fertilizer particles in the coating tower through a spray device. while recovering the solvent. The main products are coated urea named after Meister and coated compound fertilizer named after Nutricote.

2) Sierra Europe B.V, the Netherlands, uses cyclopentadiene and glycerol lipid copolymer as the coating material, and performs multi-layer coating on the soluble fertilizer core in the intermittent coating cylinder. During the successive spraying of the solution, drying and solvent recovery can be carried out simultaneously. The coating amount is between 10% and 20%, and its typical product is Osmocote series coated compound fertilizer.

3) The coating technology of Haifa Chemical Ltd. in Israel can be classified into the category of reaction film formation, but it is not a polymer coating. Granular fertilizers are heated on a turntable while being treated with fatty acids and metal hydroxides (such as hard fatty acids and calcium hydroxide), and the two react to form a coating layer of fatty acid metal salts (such as calcium stearate). Layers of fatty acid salts are reacted in situ on the surface of the particles, and finally a paraffin coating is applied. The main products are coated compound fertilizer, coated urea and coated potassium nitrate, all of which are named Multicote.

4) Canadian AGRIUM company adopts the new process of reactive layer coating (Reactive Layer Coating) to produce controlled-release fertilizers. The key point of this process technology is to coat the fertilizer core particles through a series of sequential in-situ polymerization reactions. The fertilizer granule core is first coated with diphenylmethane diisocyanate, which is then coated with a polyol polymer, and the two coatings react in situ to form polyurethane. The advantage of this process is that it can be coated in a coating drum or a mixing drum without the need for solvents and associated recovery equipment, so its production cost is lower than other existing polymer coating processes.

With the continuous development of agricultural production models, the society has a strong demand for controlled-release fertilizers, and the high-yield and efficient production of field crops urgently requires the application of controlled-release fertilizers. Although the coating technology continues to improve, it is still limited in terms of cost and product types, and its application in field crops cannot be widely promoted. For example, Osmocote products, which are mainly used in horticultural crops, have a high coating rate, and the cost of solvent recovery is limited. The technology of Multicote is complicated, and multi-layer and intermittent coating is not conducive to the reduction of production costs. Environmental and cost aspects are affected. AGRIUM's reaction film-forming products are the most competitive in terms of cost. Not only is the coating rate low and can be produced continuously, but there are also shortcomings such as strong technical expertise, short product release period, and easy tearing of the film layer, which needs to be further improved. Improve.

In view of the key issues in the development of my country's slow and controlled release fertilizer industry, aiming at the frontier field of fertilizer technology in the world, the development of new coating materials is an important development direction at present. The reaction film forming technology adapts to the new development trend of low cost and high environmental protection. It adopts the principle of in-situ polymerization on the particle surface to form a thin and tough film layer, which belongs to the international frontier research field. This technology no longer uses organic solvents, and is an environmentally friendly coated controlled-release fertilizer, which has a good role in promoting the international competitiveness of my country's controlled-release fertilizer industry. Many domestic units are stepping up the development of this technology, and the maturity of this technology will provide support for the development of a new generation of controlled-release fertilizers.

The US series of patents (US4711659, US4804403 and US4969947) earlier reported the coating technology of solvent-free reaction film formation, which uses isocyanate to react with the surface of urea particles to form a first layer of film, and then coats the second layer to form a polyurethane film layer. Spraying increases film thickness to control nutrient release. In order to improve the release performance of the polyurethane film layer, later patents (US7682656, US20070137274) further clarified the range of coating materials, such as using diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and polyether polyol, The polyester polyol reacts to form a polymer film layer. At the same time, the improvement of the fertilizer production equipment is also being carried out continuously. US Patent No. 7,682,656 reports the use of the relationship between the radius, rotational speed, and particle velocity of the coated drum to achieve the purpose of adjusting the release rate of the controlled-release fertilizer.

The principles of the above inventions are all based on the reaction of isocyanate and polyol to form a film. However, due to the surface tension between the polymer and the fertilizer surface, while reducing the amount of polymer, the coating effect of the particles will be significantly reduced. Therefore, The coating ratio of some polymer films can reach 8-12%, and the number of coatings can reach as many as 16-20 times, and the cost will also increase greatly. Once the number of coatings is reduced to 3-5%, the controlled release effect of nutrients will be significantly weakened, and the release will not meet the standards of controlled release fertilizers. How to make a small amount of coating material evenly distributed on all particle surfaces in a short time or a few times of coating through equipment improvement and spray optimization is the problem to be solved by the present invention.

Contents of the invention

The purpose of the present invention is to provide a solvent-free coated controlled-release fertilizer and its preparation method. The present invention mainly sprays the coating solution on the moving particles in proportion to obtain the fertilizer described in the present invention through a double nozzle process and equipment. The controlled-release fertilizer, the invention solves the problem of uneven distribution of the coating liquid on the particles during the solvent-free coating process.

A solvent-free coated controlled-release fertilizer provided by the present invention is composed of fertilizer granules and a coating layer coated outside the fertilizer granules;

The mass percentage of the fertilizer granules is 93% to 97%, and the mass percentage of the coating layer is 3% to 7%;

The coating layer is obtained by polymerizing polyisocyanate, polyester polyol and microcrystalline paraffin.

For the above-mentioned solvent-free coated controlled-release fertilizer, the mass percentage of the fertilizer granules may specifically be 93.5% to 94.0%, 93.5%, 93.7% or 94.0%, and the mass percentage of the coating layer may specifically be 6.0% to 6.5%, 6.0%, 6.3% or 6.5%.

For the above-mentioned solvent-free coated controlled-release fertilizer, the particle size of the fertilizer particles can be 2 mm to 4 mm, and can be large-grain urea or compound fertilizer;

The isocyanate is diphenylmethane polyisocyanate (PAPI);

The polyester polyol is phthalic anhydride polyester diol, such as polyester type SKR-T4 (Sikerui Company);

The melting point of the microcrystalline paraffin may be 60°C to 75°C.

In the above-mentioned solvent-free coated controlled-release fertilizer, in the coating layer, the mass percentage of the isocyanate can be 37.9-45.3%;

The mass percentage of the polyester polyol can be 47.7-57.6%;

The mass percent content of the microcrystalline paraffin can be 4.42-8.54%.

The above-mentioned solvent-free coated controlled-release fertilizer, catalyst and surfactant are also added in the polymerization process;

The catalyst can be stannous octoate or zinc isooctanoate;

The surfactant can be polysiloxane or polyester-modified polysiloxane (D5500, Deqian Company).

For the above-mentioned solvent-free coated controlled-release fertilizer, in the coating layer, the mass percentage of the isocyanate can specifically be 38.7% to 43.1%, 38.7%, 42.8% or 43.1%;

The mass percentage of the polyester polyol can specifically be 48.2% to 55.2%, 48.2%, 50.4% or 55.2%;

The mass percentage of the microcrystalline paraffin can specifically be 5.2% to 7.12%, 5.2%, 6.0% or 7.12%;

The mass percentage of the catalyst can specifically be 0.42% to 0.99%, 0.66% to 0.86%, 0.66%, 0.72% or 0.86%;

The mass percentage of the surfactant may specifically be 0.11%-0.25%, 0.13%-0.18%, 0.13%, 0.16% or 0.18%.

In the above-mentioned solvent-free coated controlled-release fertilizer, the coating layer is obtained by polymerizing the isocyanate, the polyester polyol and the microcrystalline paraffin in the presence of the catalyst and the surfactant, the The mass ratio of the isocyanate, the polyester polyol, the microcrystalline paraffin, the catalyst and the surfactant in the coating layer is specifically as any of the following 1)-3):

1) 43.1:48.2:7.12:0.76:0.16;

2) 42.8:50.4:6.0:0.66:0.13;

3) 38.7:55.2:5.2:0.72:0.18.

The present invention further provides a method for preparing the coated controlled-release fertilizer, comprising the steps of:

(1) Heating the fertilizer granules to 75-80°C and making them reciprocate under the action of air blast;

(2) Heating the polyisocyanate or the mixture of the polyisocyanate and the surfactant in the mass ratio to 75-85°C, and coating it on the reciprocating fertilizer particles; then The mixture of the polyester polyol and the microcrystalline paraffin or the mixture of the polyester polyol, the microcrystalline paraffin and the catalyst is heated to 85-95°C, and applied to the reciprocating fertilizer On the particles, the polyisocyanate, the polyester polyol and the microcrystalline paraffin or the polyisocyanate, the polyester polyol, the microcrystalline paraffin, the surfactant and the microcrystalline paraffin coated successively The catalyst is polymerized on the surface of the fertilizer particles to obtain the coated controlled-release fertilizer.

The above-mentioned preparation method can be carried out in a double-nozzle coating machine, the double-nozzle coating machine includes a spouted bed, the side wall of the spouted bed is provided with a feed port, and the bottom of the spouted bed is connected to A discharge pipeline; the discharge pipeline is provided with a high-pressure airless nozzle I and a high-pressure airless nozzle II, and the high-pressure airless nozzle I and high-pressure airless nozzle II are respectively connected to the spouted bed The high-pressure pump I and the high-pressure pump II are connected; the outlets of the high-pressure airless nozzle I and the high-pressure airless nozzle II are set towards the bottom of the spouted bed; the specific steps are as follows:

The fertilizer particles reciprocate in the spouted bed under the action of air blast;

The polyisocyanate or the mixture of the polyisocyanate and the surfactant in the mass ratio is applied to the reciprocating fertilizer particles through the high-pressure pump I and the high-pressure airless nozzle I;

The mixture of the polyester polyol and the microcrystalline paraffin or the mixture of the polyester polyol, the microcrystalline paraffin and the catalyst is applied to the The reciprocating motion of the fertilizer granules.

In the above preparation method, the coating solution is divided into two different paths into the spouted bed through the high-pressure airless nozzle I and the high-pressure airless nozzle II, which avoids the viscosity of the two polymers caused by the reaction in the same pipeline. The problem of increased height, poor dispersion and eventually increased film layer inhomogeneity. At the same time, it can reduce the blockage of the nozzle and the poor pipeline caused by the residual solidification of the polymer in the pipeline after the coating is completed.

In the above preparation method, the shape of the reciprocating motion may be an ellipse, and the major axis of the ellipse is arranged along the vertical direction.

In the above preparation method, the distance between the high-pressure airless nozzle I and the high-pressure airless nozzle II and the lowest point of the reciprocating motion can be 10-15 cm;

The control pressure of the high-pressure pump I and the high-pressure pump II may be 3-5 MPa.

In the above preparation method, step (2) is repeated 3 times, and the interval time between each time can be 2-3 minutes, so as to construct the waterproof structure of the film layer from the inside to the outside.

The present invention has the following advantages:

(1) The two polymers are sprayed on the surface of the particles successively, which solves the problem of interruption of coating due to blockage caused by sharing a pipeline and nozzle, and at the same time significantly reduces the probability of particle adhesion in the equipment, making the coating The stability of the process is significantly enhanced. It solves the problem that the coating speed and coating uniformity cannot be balanced, and completes the uniform distribution of the film layer in the rapid film formation process.

(2) Through the high-pressure airless liquid spray control system, the dispersibility of the coating solution is significantly enhanced, the uniform distribution of the liquid on the particles is significantly improved, and the coating dosage is reduced on the basis of ensuring the controlled release performance.

(3) According to the waterproof structure of the film layer, the coating formula and polymerization time of each spraying are constructed from the inside to the outside, and the product quality control is completed through three times of coating.

(4) There is no solvent recovery link in the coating process, which is safe and environmentally friendly, and the rapid reaction film formation shortens the coating time, so that the output per unit time is significantly improved, which is conducive to industrial production.

Description of drawings

Fig. 1 is a schematic structural view of a double-nozzle coating machine used in the preparation method of coated controlled-release fertilizer of the present invention.

The labels in Figure 1 are as follows:

1 Feed inlet, 2 Spouted bed, 3 Heating liquid reservoir Ⅱ, 4 High pressure pump Ⅱ, 5 High pressure airless nozzle Ⅱ, 6 High pressure airless nozzle Ⅰ, 7 High pressure pump Ⅰ, 8 Heating liquid reservoir Ⅰ, 9 Dust removal device, 10 discharge pipelines.

In Figure 1, the substances placed in the heating reservoir I are isocyanate (B) and surfactant (E); the substances placed in the heating reservoir II are polyester polyol (A), microcrystalline paraffin (C) and Catalyst (D).

Detailed ways

The experimental methods used in the following examples are conventional methods unless otherwise specified.

The materials and reagents used in the following examples can be obtained from commercial sources unless otherwise specified.

The structural representation of the double-nozzle coating machine used in the following examples is shown in Figure 1, the double-nozzle coating machine comprises a spouted bed 2, and the side wall of the spouted bed 2 is provided with a feed port 1 , the bottom of the spouted bed 2 is connected to a discharge pipeline 10 . A dust collector 9 is connected to the top of the spouted bed 2 . The discharge pipeline 10 is provided with a high-pressure airless nozzle I6 and a high-pressure airless nozzle II5, wherein the high-pressure airless nozzle I6 communicates with the high-pressure pump I7 located outside the spouted bed 2, and the high-pressure airless nozzle II5 communicates with the high-pressure airless nozzle II5. The high-pressure pump II located outside the spouted bed 2 is connected to 4 to provide power for spraying the coating solution. The outlets of the high-pressure airless nozzle I6 and the high-pressure airless nozzle II5 are both set towards the bottom of the spouted bed 2 .

The modified polysiloxane used in the following examples is the polysiloxane of model D5500 provided by Deqian Company.

Embodiment 1, preparation coated controlled-release fertilizer

The formula table of this embodiment is shown in Table 1.

Table 1 Coating polymer formula table

(1) Weigh 3kg of 2-3mm large grain urea for later use. Weigh 31.2 grams of diphenylmethane polyisocyanate (PAPI, Bayer company), put it in the heating liquid reservoir I8 and raise the temperature to 75 ° C, drop in 0.11 g of surfactant, stir well and keep warm at 75 ° C; at the same time, weigh the polyester Put 33.8g of polyol in another heating reservoir Ⅱ3, weigh 3.15g of microcrystalline paraffin wax (melting point 70°C, commercially available), put it into the heating reservoir Ⅱ3 and raise the temperature to 85°C, keep warm and stir, The microcrystalline paraffin wax is evenly dispersed in the polyol solution, and finally 0.6 g of the catalyst is added dropwise and continued to stir evenly.

(2) While the temperature of the two solutions is rising, continue to prepare the coating solution for the second spraying according to the above steps, weigh 30.1g of PAPI and 0.12g of surfactant respectively, heat and stir and keep warm at 75°C for later use, and weigh them respectively 33.6g of polyol, 5.94g of microcrystalline paraffin and 0.6g of catalyst, heated and stirred and kept at 85°C for use; the third spraying solution was 30.4g of PAPI and 0.12g of surfactant, heated and stirred at 75°C for use, Weigh 33.9g of polyol, 5.88g of microcrystalline wax and 0.6g of catalyst respectively, heat and stir and keep warm at 85°C for later use.

(3) While the coating solution is being heated and kept warm, add urea granules to the spouted bed 2 of the double-nozzle coating machine shown in Figure 1, and turn on the hot air blower to start the circulation of the granules and raise the temperature to 75°C. The path of particle circulation is an ellipse with the major axis vertically arranged. Turn on the high-pressure pump Ⅰ7 to increase the pressure to 3MPa, and start spraying. The high-pressure pump Ⅰ7 will suck the prepared isocyanate coating mixture into the pump body and spray it evenly on the reciprocating urea particles. Control the high-pressure airless nozzle Ⅰ6 and the movement of urea particles. The distance of the lowest point is 15cm. After the coating liquid in the heating reservoir I8 is used up, the high-pressure pump I7 is turned off, and the material continues to reciprocate in the spouted bed 2 for 1 minute. Turn on the high-pressure pump Ⅱ4, spray the polyol mixed coating solution installed in the heating reservoir Ⅱ3 on the reciprocating urea particles, control the distance between the high-pressure airless nozzle Ⅱ5 and the lowest point of the urea particle movement to be 15cm, spray the solution After completion, the urea granules continue to heat preservation cycle, so that the two coating liquids solidify and form a film on the surface of the granules. After 2 minutes, start the second coating, and apply the coating solution prepared for the second time to form a film according to the method of the first spraying. After 3 minutes, spray for the third time. After spraying, keep warm for 3 minutes, turn off the heat source, continue blowing, cool the material for 2 minutes, stop blowing, and unload the material, which is the finished product of coated controlled-release fertilizer.

Determination of the nitrogen release effect of the coated controlled-release fertilizer prepared in this example, using the constant temperature water immersion method to test the nitrogen dissolution rate of the coated controlled-release fertilizer at different times, the specific steps are as follows:

Weigh 10.00 g of the above-mentioned controlled-release urea, put it into a nylon mesh bag, place the bag in a plastic bottle, then add 250 ml of distilled water, cover the bottle cap, and put it in a thermostat at 25°C. Set up 3 repetitions. Pre-sampling was carried out at intervals of days 1, 3, 7, 14, 21, and 28. When sampling each time, the nylon mesh bag was taken out and placed in a new plastic bottle with distilled water added in advance to continue soaking. The soaked controlled-release urea Shake the extract in the plastic bottle and take a sample to measure the urea content, and calculate the dissolution ratio of N. Late sampling with a longer release period determines the sampling time according to the release rate. Urea was determined by p-dimethylaminoformaldehyde-spectrophotometric method, and compound fertilizer nitrogen was determined by semi-micro Kjeldahl method.

For the determination of the coating rate, set 3 repetitions, accurately weigh 5.00g of the coated fertilizer, put it into a mortar, crush it, grind it, add water to dissolve and filter, air-dry the obtained film layer, weigh it, and calculate the percentage of the film layer in the coated fertilizer. is the coating rate.

It was determined that the coating rate of this embodiment was 5.3%, and the dissolved nitrogen accounted for 82% of the total nitrogen mass on the 51st day.

Embodiment 2, preparation coated controlled-release fertilizer

The formula table of this embodiment is shown in Table 2.

Table 2 Coating polymer formula table

(1) Weigh 3kg of 3-4mm large grain urea for use. Weigh 30.9 grams of polyisocyanate (PAPI, Bayer company), place it in the heating reservoir I8 and raise the temperature to 80°C, drop in 0.12g of surfactant, stir evenly and keep warm at 80°C; at the same time, weigh 34.8g of polyester polyol , put it in the heating reservoir Ⅱ3, weigh 3.81g of microcrystalline paraffin wax (melting point 75°C, commercially available), put it into the heating reservoir Ⅱ3 and raise the temperature to 95°C, keep warm and stir to make the microcrystalline paraffin evenly Disperse in the polyol solution, and finally add 0.45 g of the catalyst dropwise and continue to stir evenly.

(2) While the temperature of the two solutions is rising, continue to prepare the coating solution for the second spraying according to the above steps, weigh 32.0g of PAPI and 0.09g of surfactant respectively, heat and stir and keep warm at 80°C for later use, and weigh 33.8g of polyol, 4.84g of microcrystalline paraffin and 0.3g of catalyst, heated and stirred and kept at 95°C for use; the third spraying solution was 24.1g of PAPI and 0.06g of surfactant, heated and stirred at 80°C for use, Weigh 33.7g of polyol, 3.48g of microcrystalline wax and 0.6g of catalyst respectively, heat and stir and keep warm at 95°C for use.

(3) While the coating solution is being heated and kept warm, add urea granules to the spouted bed 2 of the double-nozzle coating machine shown in Figure 1, and turn on the hot air blower to start the circulation of the granules and raise the temperature to 80°C. Turn on the high-pressure pump Ⅰ7 to increase the pressure to 4MPa, and start spraying. The high-pressure pump Ⅰ7 will suck the prepared isocyanate coating mixture into the pump body and spray it evenly on the reciprocating urea particles, and control the high-pressure airless nozzle Ⅰ6 and the movement of urea particles. The distance from the lowest point is 10cm. After the coating liquid in the heating reservoir I8 is used up, the high-pressure pump I7 is turned off, and the material continues to circulate in the spouted bed for 1 minute. Turn on the high-pressure pump Ⅱ4, spray the polyol mixed coating solution installed in the heating reservoir Ⅱ3 on the reciprocating urea particles, control the distance between the high-pressure airless nozzle Ⅱ5 and the lowest point of the urea particle movement to be 10cm, spray the solution After completion, the urea granules continue to heat preservation cycle, so that the two coating liquids solidify and form a film on the surface of the granules. After 2 minutes, start the second coating, and apply the coating solution prepared for the second time to form a film according to the method of the first spraying. After 3 minutes, spray for the third time. After spraying, keep warm for 3 minutes, turn off the heat source, continue blowing, cool the material for 3 minutes, stop blowing, and unload the material, which is the finished product of coated controlled-release fertilizer.

To measure the nitrogen release effect of the coated controlled-release fertilizer prepared in this example, the constant temperature water immersion method in Example 1 was used to measure nitrogen dissolution.

It was determined that the coating rate of the coated controlled-release fertilizer prepared in this example was 5.03%, and the dissolved nitrogen accounted for 80% of the total nitrogen mass on the 45th day.

Embodiment 3, preparation coated controlled-release fertilizer

The formula table of this embodiment is shown in Table 3.

Table 3 Coating polymer formula table

(1) Weigh 5kg of 2-3mm compound fertilizer (N:P ₂ O ₅ :K ₂ O=15:15:15, mass ratio) for later use. The first spraying solution is 40.0g of PAPI, 0.2g of surfactant is added to the heating reservoir Ⅰ8, stirred and heated to 85°C, 60.8g of polyol, 4.67g of microcrystalline paraffin wax 70# (melting point 70°C) and 0.67g of catalyst , added to the heating reservoir II3, stirred and heated to 90°C for later use. According to the formula shown in Table 3, add the 2 materials required for secondary spraying into the heating reservoir I8, stir and heat to 80°C, add the corresponding 3 materials in Table 3 into the heating reservoir II3, stir and heat To 90°C, according to the above method, weigh the materials required for the third time in Table 3 and add them to the corresponding heating container, stir and raise the temperature to the stated temperature and keep it warm for later use.

(2) While the coating solution is being heated and kept warm, add the compound fertilizer particles into the spouted bed 2 of the double-nozzle coating machine shown in Figure 1, and turn on the hot air blower to start the circulation of the particles and raise the temperature to 80°C. Turn on the high-pressure pump Ⅰ7 to increase the pressure to 5MPa, and start spraying. The high-pressure pump Ⅰ7 sucks the prepared isocyanate coating mixture into the pump body and sprays it evenly on the reciprocating fertilizer particles. Control the high-pressure airless nozzle Ⅰ6 and the movement of fertilizer particles. The distance from the lowest point is 12cm. After the coating liquid in the container is used up, turn off the high-pressure pump I7, and the material continues to reciprocate in the spouted bed for 1 minute. Turn on the high-pressure pump Ⅱ4, spray the polyol mixed coating solution installed in the heating reservoir Ⅱ3 on the circulating fertilizer particles, control the distance between the high-pressure airless nozzle Ⅱ5 and the lowest point of the fertilizer particle movement to be 12cm, and spray the solution Afterwards, the particles continue the heat preservation cycle, so that the two coating liquids solidify and form a film on the surface of the particles. After 2 minutes, start the second coating, and apply the coating solution prepared for the second time to form a film according to the method of the first spraying. After 3 minutes, spray for the third time. After spraying, keep warm for 3 minutes, turn off the heat source, continue blowing, cool the material for 3 minutes, stop blowing, and unload the material, which is the finished product of coated controlled-release fertilizer.

To measure the nitrogen release effect of the coated controlled-release fertilizer prepared in this example, the constant temperature water immersion method in Example 1 was used to measure nitrogen dissolution.

It was determined that the coating ratio of the coated controlled-release fertilizer prepared in this example was 4.7%, and the dissolved nitrogen accounted for 83% of the total nitrogen mass on the 43rd day.

Claims (3)

1. A solvent-free coated controlled-release fertilizer, which is composed of fertilizer granules and a coating layer coated outside the fertilizer granules; The mass percentage of the fertilizer granules is 93% to 97%, and the mass percentage of the coating layer is 3% to 7%; The coating layer is obtained by polymerizing polyisocyanate, polyester polyol and microcrystalline paraffin; The particle size of the fertilizer granules is 2 mm to 4 mm; Described polyisocyanate is diphenylmethane polyisocyanate; Described polyester polyol is phthalic anhydride polyester diol; The melting point of the microcrystalline paraffin is 60°C to 75°C; In the coating layer, the mass percentage of the polyisocyanate is 37.9-45.3%; The mass percentage of the polyester polyol is 47.7-57.6%; The mass percent content of the microcrystalline paraffin is 4.42% to 8.54%; Catalyst and surfactant are also added in the polymerization process; The catalyst is stannous octoate or zinc isooctanoate; The surfactant is polysiloxane or polyester-based modified polysiloxane; In the coating layer, the mass percentage of the catalyst is 0.42% to 0.99%; The mass percentage of the surfactant is 0.11% to 0.25%; The preparation method of the coated controlled-release fertilizer comprises the steps of: (1) heating the fertilizer granules to 75-80°C, and making them reciprocate under the action of blast; (2) Heating the mixture of the polyisocyanate and the surfactant to 75-85°C, and coating it on the reciprocating fertilizer particles; then the polyester polyol, the microcrystalline paraffin The mixture with the catalyst is heated to 85-95°C and coated on the reciprocating fertilizer particles, then the polyisocyanate, the polyester polyol, the microcrystalline paraffin, and the The surfactant and the catalyst are polymerized on the surface of the fertilizer particles to obtain the coated controlled-release fertilizer; The preparation method is carried out in a coating machine with double nozzles, the coating machine with double nozzles comprises a spouted bed, the side wall of the spouted bed is provided with a feed port, and the bottom of the spouted bed is connected to a A discharge pipeline; the discharge pipeline is provided with a high-pressure airless nozzle I and a high-pressure airless nozzle II, and the high-pressure airless nozzle I and the high-pressure airless nozzle II are respectively connected to the spouted bed. The high-pressure pump I and the high-pressure pump II are connected; the outlets of the high-pressure airless nozzle I and the high-pressure airless nozzle II are set towards the bottom of the spouted bed; the specific steps are as follows: The fertilizer particles reciprocate in the spouted bed under the action of air blast; Applying the mixture of the polyisocyanate and the surfactant to the reciprocating fertilizer particles through the high-pressure pump I and the high-pressure airless nozzle I; coating the mixture of the polyester polyol, the microcrystalline paraffin and the catalyst on the reciprocating fertilizer particles through the high-pressure pump II and the high-pressure airless nozzle II; The distance between the high-pressure airless nozzle I and the high-pressure airless nozzle II and the lowest point of the reciprocating motion is 10-15cm; Controlling the pressure of the high-pressure pump I and the high-pressure pump II to be 3-5 MPa; Step (2) is repeated 3 times with an interval of 2 to 3 minutes each time. 2. the preparation method of the described coating controlled-release fertilizer of claim 1, comprises the steps: (1) heating the fertilizer granules to 75-80°C, and making them reciprocate under the action of blast; (2) Heating the mixture of the polyisocyanate and the surfactant to 75-85°C, and coating it on the reciprocating fertilizer particles; then the polyester polyol, the microcrystalline paraffin The mixture with the catalyst is heated to 85-95°C and coated on the reciprocating fertilizer particles, then the polyisocyanate, the polyester polyol, the microcrystalline paraffin, and the The surfactant and the catalyst are polymerized on the surface of the fertilizer particles to obtain the coated controlled-release fertilizer; The preparation method is carried out in a coating machine with double nozzles, the coating machine with double nozzles comprises a spouted bed, the side wall of the spouted bed is provided with a feed port, and the bottom of the spouted bed is connected to a Discharge pipeline; the discharge pipeline is provided with a high-pressure airless nozzle I and a high-pressure airless nozzle II, and the high-pressure airless nozzle I and high-pressure airless nozzle II are respectively connected to the spouted bed. The high-pressure pump I and the high-pressure pump II are connected; the outlets of the high-pressure airless nozzle I and the high-pressure airless nozzle II are set towards the bottom of the spouted bed; the specific steps are as follows: The fertilizer particles reciprocate in the spouted bed under the action of air blast; Applying the mixture of the polyisocyanate and the surfactant to the reciprocating fertilizer particles through the high-pressure pump I and the high-pressure airless nozzle I; coating the mixture of the polyester polyol, the microcrystalline paraffin and the catalyst on the reciprocating fertilizer particles through the high-pressure pump II and the high-pressure airless nozzle II; The distance between the high-pressure airless nozzle I and the high-pressure airless nozzle II and the lowest point of the reciprocating motion is 10-15cm; Controlling the pressure of the high-pressure pump I and the high-pressure pump II to be 3-5 MPa; Step (2) is repeated 3 times with an interval of 2 to 3 minutes each time. 3. The preparation method according to claim 2, characterized in that: the shape of the reciprocating motion is an ellipse, and the major axis of the ellipse is set along the vertical direction.