Preparation method of pesticide microcapsule with long-term slow release effect

Abstract

The invention discloses a preparation method of a pesticide microcapsule with a long-term slow release effect, and relates to the technical field of pesticides and pharmaceutical preparations. The invention aims to solve the technical problem of poor slow-release effect of the existing pesticide slow-release microcapsule. The method comprises the following steps: preparing a capsule core suspension; preparing a urea resin prepolymer solution; preparing a microcapsule solution; and filtering, drying and sieving. According to the invention, the drug crystal particles are coated, so that the drug release speed can be controlled, the maximum sustained release time can reach more than 20 days, and the technology can greatly reduce the drug application period and reduce the labor cost of a user. The pesticide microcapsule prepared by the invention is used for crop production.

Description

Technical Field

[0001] The present invention relates to the technical field of pesticides and pharmaceutical preparations, and relates to a preparation method of pesticide microcapsules with a long-term sustained release effect. Background Art

[0002] Pesticides specifically refer to agents used in agriculture to control pests and diseases, regulate plant growth, and remove weeds. Pesticides mainly exist in liquid or solid forms. Currently, the method of preparing liquid drugs into microcapsules generally involves first preparing the original drug into a microemulsion and then coating it with a polymer material. Compared with liquid drugs, the process of preparing microcapsules for solid drugs is more complex. For example, in patent CN118266475A, isocyanate and a curing agent are crosslinked to obtain polyurethane as the capsule wall. The original drug is made into an oil phase and then added to the water phase for emulsification to obtain an O / W emulsion, which is mixed with an aqueous solution of the curing agent for an interfacial polymerization reaction to obtain an epoxy chlorantraniliprole hybrid sustained-release microcapsule. The sustained-release microcapsule obtained by this process improves the mechanical strength and thermal stability of the microcapsule and has a high drug content. The mass percentage of epoxy chlorantraniliprole is 5-20%, but the longest sustained-release time of the obtained sustained-release microcapsule is 96h, and it does not have a long-term sustained-release effect. In CN115812731A, diphenylmethane diisocyanate, isophorone diisocyanate, or toluene diisocyanate is used as the capsule wall material to coat carbosulfan. First, carbosulfan is mixed with a solvent to obtain the original drug mother liquor, and then the raw materials of the capsule wall material and the original drug mother liquor are mixed to obtain an oil phase, which is then added to the water phase for high-speed shearing. After forming an O / W emulsion, an interfacial polymerization reaction is carried out to completely react the capsule wall material and solidify it into a capsule. The microcapsule obtained by this process has high safety and can effectively improve the control effect on maize white grubs, slowing down the degradation of carbosulfan in the environment, and the effective period can be up to 60 days. However, the process is relatively complex, and the continuous effect will gradually weaken after long-term use. In CN117958257A, a polyurea structure is used as the capsule wall material to coat the pesticide composition. First, the pesticide composition and an oily capsule wall material are stirred and dissolved, and the temperature is kept until the material is in a molten state. As the oil phase, it is mixed with the water phase through high shear to obtain an O / W emulsion. Then, an aqueous solution of the aqueous capsule wall material is dropped into the above emulsion, and the emulsion is kept warm. Interfacial polymerization occurs at the oil-water interface, and the temperature is raised for curing to obtain a compound pesticide microcapsule suspension. This process improves the capsule formation efficiency and the suspension stability of the microcapsule and is suitable for large-scale production. However, the process uses more materials, and the final microcapsule does not have a sustained-release effect. In CN114794114A, triphenylmethane triisocyanate is used as the capsule shell to encapsulate tricyclazole and hexaconazole. First, the drug and the capsule shell material are mixed to prepare an oil phase, which is then added to the water phase for high-speed shearing to obtain an emulsion. Then, the interfacial polymerization is started by raising the temperature and stirring to obtain a polymerization suspension. The microcapsule suspension obtained by this process has good stability and can play a good control effect on rice diseases after application. However, it takes two applications to achieve a control effect that can last up to 17 days at most. In CN113615687A, urea-formaldehyde resin is used as the wall material to coat pyraclostrobin.First, mix urea, formaldehyde, emulsifier and water, then adjust the pH value, and then continuously heat up to 65 - 75 °C and maintain for a period of time to obtain an aqueous solution of urea-formaldehyde resin prepolymer. Mix pyraclostrobin with the core solvent to prepare an oil phase, and mix it with the prepolymer, and obtain an O / W emulsion through high shear. Finally, obtain a pyraclostrobin nano-microcapsule suspension by acidification and curing. This process is relatively simple, improves the toxicological properties of the product, and is more environmentally friendly. The maximum slow-release time is 264 h, but the pyraclostrobin nano-microcapsule suspension still has problems such as larger particle size, lower dispersibility and stability. In CN105981717A, using biological microalgae, urea, and formaldehyde as raw materials, biological microalgae microcapsule suspension is prepared by coating and adsorbing pesticides with urea-formaldehyde resin prepolymer. The bio-microcapsules prepared by this two-step method for preparing biological microalgae microcapsule suspension can achieve hierarchical and stepwise release of the core active substance, and have the characteristics of high stability and low production cost, but do not have a long-term slow-release effect. These microcapsules prepared with urea-formaldehyde resin as the wall material are all for liquid drugs or first dissolve solid drugs with organic solvents, then prepare emulsions and then coat them, and do not directly coat solid drugs. We found that the compactness of the urea-formaldehyde resin wall material prepared under different experimental conditions is different, and the compactness of the wall material has a significant impact on the drug release effect. By adjusting the experimental parameters and improving the compactness of the wall material, the urea-formaldehyde resin microcapsules prepared can achieve long-term slow-release effects. Currently, the preparation technology that can directly coat solid drug crystal particles and achieve ultra-long-term slow release has not been able to break through. The main reason is that solid particles have irregular shapes, and the sharp corners will cause poor coating effect of the capsule material, and some crystal particles cannot be coated. If the amount of wall material is increased, most crystal particles will have an overly thick coating layer, resulting in poor slow-release effect or no release at all. These problems make it difficult to directly coat solid particles. Summary of the Invention

[0003] The present invention provides a preparation method of a pesticide microcapsule with a long-term slow-release effect to solve the technical problem of poor slow-release effect of current pesticide slow-release microcapsules.

[0004] The present invention provides a pesticide microcapsule that can directly coat drug crystal particles and achieve a long-term slow-release effect, which is more beneficial for the use of crops.

[0005] A preparation method of a pesticide microcapsule with a long-term slow-release effect is carried out according to the following steps:

[0006] I. Take micronized water-insoluble pesticide powder, add a surfactant and distilled water, and stir and disperse evenly to obtain a core suspension.

[0007] II. Mix an aldehyde compound with urea, add water for dissolution, and at the same time add a basic catalyst; then heat in a water bath to 45 - 75 °C and react for 1 - 4 h to obtain a urea-formaldehyde resin prepolymer solution;

[0008] III. Under mechanical stirring conditions, add the core suspension prepared in Step I into the urea-formaldehyde resin prepolymer solution prepared in Step II, control the mechanical stirring speed at 50 - 240 rpm, mix evenly, add an acidic catalyst, and stir to obtain a mixed solution;

[0009] IV. Stir the mixed solution obtained in Step III, set the initial temperature and the end temperature of the water bath heating, control the heating rate, and heat up. When the temperature reaches 30 - 40 °C, add the acidic catalyst again, and then continue the reaction until the end temperature is reached to obtain a microcapsule solution;

[0010] V. Filter the microcapsule solution obtained in Step IV, dry the filtrate, and then sieve it to obtain the pesticide microcapsules with a long-term slow-release effect, thus completing the preparation.

[0011] Further, the surfactant described in Step I is one or a combination of several of Tween 20, Tween 40, Tween 60, Tween 80, Span 85, Span 80, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, benzyl ether-721, polyethylene glycol, polyoxyethylene monostearate, and polyoxyethylene lauryl ether.

[0012] Further, the mass ratio of the pesticide powder to the surfactant in Step I is 1:(0.01 - 0.5); the mass ratio of the pesticide powder to distilled water is 1:(1 - 50).

[0013] Further, the mass percentage content of the core in the core suspension obtained in Step I is 2% - 50%.

[0014] Further, the mass ratio of the aldehyde compound to urea in Step II is (0.05 - 1):1; the aldehyde compound is one or a combination of several of formaldehyde, paraformaldehyde, acetaldehyde, n-propionaldehyde, isopropyl aldehyde, butyraldehyde, succinaldehyde, valeraldehyde, and glutaraldehyde.

[0015] Further, the basic catalyst described in Step II is one or a mixture of several of sodium hydroxide, potassium hydroxide, triethanolamine, triethylamine, dipotassium hydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, and potassium carbonate.

[0016] Further, the acidic catalysts added in Step III and Step IV are both one or a mixture of several of citric acid, potassium dihydrogen phosphate, sodium dihydrogen phosphate, glacial acetic acid, malic acid, dilute hydrochloric acid, phosphoric acid, and dilute sulfuric acid.

[0017] Further, the core-to-wall ratio in the mixed solution of Step III is 1:(1 - 20).

[0018] Further, the initial temperature set in Step 4 is ≥10°C, the final temperature is ≤80°C, and the heating rate is controlled at 0.1 - 1.5°C / min.

[0019] Further, the sustained release duration of the pesticide microcapsules with long-term sustained release effect obtained in Step 5 is 1 - 30 days.

[0020] Advantages of the present invention: By coating the drug crystal particles, the release rate of the drug can be controlled, and the maximum continuous release time can reach more than 20 days. This technology can greatly reduce the application cycle and the labor cost of users. By using these microcapsules, the risks of inhalation or transdermal absorption during application can also be reduced. After application, due to the long-term continuous release of the pesticide microcapsules, the drug concentration will not be too high while maintaining above the effective herbicidal concentration. On the one hand, it can reduce the occurrence of phytotoxicity, and at the same time, due to the low drug concentration, it can reduce the pesticide residues in agricultural products while achieving good herbicidal effects.

[0021] The pesticide microcapsules prepared by the present invention are used in crop production. Description of the Drawings

[0022] Figure 1 Scanning electron micrograph of the mesotrione microcapsule powder prepared in Example 1;

[0023] Figure 2 Scanning electron micrograph of the cross-section of the mesotrione microcapsule empty capsule shell prepared in Example 1;

[0024] Figure 3 Release curve of the mesotrione microcapsule powder prepared in Example 1 in water. Detailed Embodiments

[0025] Detailed Embodiment 1: A preparation method of pesticide microcapsules with long-term sustained release effect is carried out according to the following steps:

[0026] I. Take the micronized water-insoluble pesticide powder, add a surfactant and distilled water, and stir to disperse evenly to obtain a core suspension;

[0027] II. Mix an aldehyde compound with urea, add water for dissolution, and at the same time add a basic catalyst; then heat in a water bath to 45 - 75°C and react for 1 - 4 h to obtain a urea-formaldehyde resin prepolymer solution;

[0028] III. Under mechanical stirring conditions, add the core suspension prepared in Step I to the urea-formaldehyde resin prepolymer solution prepared in Step II, control the mechanical stirring speed at 50 - 240 rpm, disperse evenly, add an acidic catalyst, and stir to obtain a mixed solution;

[0029] IV. Stir the mixed solution obtained in Step III, set the initial temperature and the end temperature of the water bath heating, control the heating rate, and heat up. When the temperature reaches 30-40 °C, add the acidic catalyst again, and then continue the reaction until the end temperature is reached to obtain the microcapsule solution;

[0030] V. Filter the microcapsule solution obtained in Step IV, dry the filtrate, and then sieve it to obtain the pesticide microcapsules with long-term slow-release effect, thus completing the preparation.

[0031] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the surfactant described in Step I is one or a combination of several of Tween 20, Tween 40, Tween 60, Tween 80, Span 85, Span 80, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, benzyl alcohol-721, polyethylene glycol, polyoxyethylene monostearate, and polyoxyethylene lauryl ether. Others are the same as Specific Embodiment 1.

[0032] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: the mass ratio of the pesticide powder to the surfactant in Step I is 1:(0.01-0.5); the mass ratio of the pesticide powder to distilled water is 1:(1-50). Others are the same as Specific Embodiment 1 or 2.

[0033] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: the mass percentage content of the core in the core suspension obtained in Step I is 2%-50%. Others are the same as any one of Specific Embodiments 1 to 3.

[0034] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that: the mass ratio of the aldehyde compound to urea in Step II is (0.05-1):1; the aldehyde compound is one or a combination of several of formaldehyde, paraformaldehyde, acetaldehyde, n-propionaldehyde, isopropyl aldehyde, butyraldehyde, succinaldehyde, valeraldehyde, and glutaraldehyde. Others are the same as any one of Specific Embodiments 1 to 4.

[0035] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that: the basic catalyst described in Step II is one or a mixture of several of sodium hydroxide, potassium hydroxide, triethanolamine, triethylamine, dipotassium hydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, and potassium carbonate. Others are the same as any one of Specific Embodiments 1 to 5.

[0036] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that: the acidic catalysts added in Step III and Step IV are both one or a mixture of several of citric acid, potassium dihydrogen phosphate, sodium dihydrogen phosphate, glacial acetic acid, malic acid, dilute hydrochloric acid, phosphoric acid, and dilute sulfuric acid. Others are the same as any one of Specific Embodiments 1 to 6.

[0037] Embodiment VIII in detail: The difference between this embodiment and any one of Embodiments I - VII is that in step three, the ratio of the core to the wall in the mixed solution is 1:(1 - 20). Others are the same as any one of Embodiments I - VII.

[0038] Embodiment IX in detail: The difference between this embodiment and any one of Embodiments I - VIII is that in step four, the set initial temperature ≥ 10°C, the end temperature ≤ 80°C, and the heating rate is controlled at 0.1 - 1.5°C / min. Others are the same as any one of Embodiments I - VIII.

[0039] Embodiment X in detail: The difference between this embodiment and any one of Embodiments I - IX is that in step five, the slow - release duration of the pesticide microcapsules with long - term slow - release effect is 1 - 30 days. Others are the same as any one of Embodiments I - IX.

[0040] The content of the present invention is not limited to the content of the above - mentioned embodiments. The combination of one or several of the specific embodiments can also achieve the purpose of the invention.

[0041] Example 1:

[0042] The preparation method of a kind of pesticide microcapsules with long - term slow - release effect in this example is carried out according to the following steps:

[0043] 1. Take 10 g of micronized mesotrione powder, add 1.2 g of sodium dodecyl sulfate and 50 g of distilled water, stir and disperse evenly to obtain a core suspension.

[0044] 2. Mix 10 g of paraformaldehyde and 10 g of urea, add 50 g of distilled water for dissolution, and at the same time add 0.08 g of alkaline catalyst triethylamine; then heat in a water bath to 45 - 75°C and react for 1.5 h to obtain a urea - formaldehyde resin prepolymer solution.

[0045] 3. Under mechanical stirring conditions, add the core suspension prepared in step 1 into the urea - formaldehyde resin prepolymer solution prepared in step 2, control the mechanical stirring speed at 80 - 240 rpm, suspend evenly, add 1.2 g of 20% hydrochloric acid by mass concentration, stir, and make the urea - formaldehyde resin generated by the reaction precipitate and adhere to the surface of the crystal particles to obtain a mixed solution.

[0046] 4. Stir the mixed solution obtained in step 3, set the initial temperature of the water - bath heating at 15°C, the end temperature at 75°C, control the heating rate at 1.0°C / min, and carry out heating and temperature - rising. When the temperature reaches 35°C, add 1.2 g of 20% hydrochloric acid by mass concentration again, and then continue the reaction until the end temperature is reached to obtain a microcapsule solution.

[0047] V. Filter the microcapsule solution obtained in Step IV, dry the filtrate, and then pass it through a 325-mesh sieve to obtain the mesotrione microcapsule powder with long-term sustained release effect, thus completing the preparation.

[0048] The mesotrione microcapsule powder prepared in this example is a white spherical solid, the microcapsule encapsulation efficiency is 77%, and the release rate reaches 80.7% on the 20th day. The scanning electron micrograph of the mesotrione microcapsule powder prepared in this example is as shown in Figure 1 Figure [omitted], from which it can be seen that a continuous and uniform wall material is coated on the surface of the drug crystal to form microcapsules.

[0049] The scanning electron micrograph of the cross-section of the empty mesotrione microcapsule shell prepared in this example is as shown in Figure 2 Figure [omitted], from which it can be seen that the film formed by the wall material is uniform and dense, and the thickness of the film is about 0.5 μm.

[0050] The release curve of the mesotrione microcapsule powder prepared in this example in water is shown in Figure 3 Figure [omitted], and it can be seen from the figure that the maximum continuous release time can reach more than 20 days.

[0051] Example 2:

[0052] The preparation method of a pesticide microcapsule with long-term sustained release effect in this example is carried out according to the following steps:

[0053] I. Take 10 g of micronized pyrithiobac-sodium powder, add 1.2 g of sodium dodecyl sulfate and 40 g of distilled water, stir and disperse evenly to obtain a core suspension.

[0054] II. Mix 10 g of paraformaldehyde and 10 g of urea, add 45 g of distilled water for dissolution, and at the same time add 0.08 g of the alkaline catalyst triethylamine; then heat in a water bath to 45 - 75 °C and react for 1.5 h to obtain a urea-formaldehyde resin prepolymer solution.

[0055] III. Under mechanical stirring conditions, add the core suspension prepared in Step I to the urea-formaldehyde resin prepolymer solution prepared in Step II, control the mechanical stirring speed to 80 - 240 rpm, suspend evenly, add 0.8 g of hydrochloric acid with a mass concentration of 20%, stir, and make the urea-formaldehyde resin generated by the reaction precipitate and adhere to the surface of the crystal particles to obtain a mixed solution.

[0056] IV. Stir the mixed solution obtained in Step III, set the initial temperature of the water bath heating to 22 °C, the end temperature to 75 °C, control the heating rate to 1.1 °C / min, carry out heating and temperature rising, when the temperature reaches 30 °C, add another 0.8 g of hydrochloric acid with a mass concentration of 20%, and then continue to react until the end temperature is reached to obtain a microcapsule solution.

[0057] V. Filter the microcapsule solution obtained in Step 4, dry the filtrate, and then pass it through a 325-mesh sieve to obtain the pyrazoxyfen microcapsule powder with long-term sustained release effect, thus completing the preparation.

[0058] The microcapsule encapsulation efficiency of the pyrazoxyfen microcapsule powder prepared in this example is 74%, and the release rate reaches 83% on the 20th day.

[0059] Example 3:

[0060] The preparation method of a pesticide microcapsule with long-term sustained release effect in this example is carried out according to the following steps:

[0061] I. Take 10 g of micronized mesotrione powder, add 1.2 g of sodium dodecyl sulfate and 40 g of distilled water, and stir to disperse evenly to obtain a core suspension.

[0062] II. Mix 10 g of paraformaldehyde and 10 g of urea, add 40 g of distilled water for dissolution, and at the same time add 0.06 g of the alkaline catalyst triethylamine; then heat in a water bath to 45 - 75 °C and react for 1.5 h to obtain a urea-formaldehyde resin prepolymer solution.

[0063] III. Under mechanical stirring conditions, add the core suspension prepared in Step I to the urea-formaldehyde resin prepolymer solution prepared in Step II, control the mechanical stirring speed to 80 - 240 rpm, suspend evenly, add 1.0 g of 10% phosphoric acid by mass concentration, stir, and make the urea-formaldehyde resin precipitated by the reaction attach to the surface of the crystal particles to obtain a mixed solution.

[0064] IV. Stir the mixed solution obtained in Step III, set the initial temperature of the water bath heating to 18 °C, the end temperature to 70 °C, control the heating rate to 0.9 °C / min, and carry out heating and temperature rising. When the temperature reaches 30 °C, add 1.0 g of 10% phosphoric acid by mass concentration again, and then continue to react until the end temperature is reached to obtain a microcapsule solution.

[0065] V. Filter the microcapsule solution obtained in Step IV, dry the filtrate, and then pass it through a 325-mesh sieve to obtain the mesotrione microcapsule powder with long-term sustained release effect, thus completing the preparation.

[0066] The microcapsule encapsulation efficiency of the mesotrione microcapsule powder prepared in this example is 72%, and the release rate reaches 87% on the 20th day.

[0067] Example 4

[0068] The preparation method of a pesticide microcapsule with long-term sustained release effect in this example is carried out according to the following steps:

[0069] I. Take 20 g of micronized pyrazoxyfen powder, add 1.8 g of sodium dodecyl sulfate and 60 g of distilled water, and stir to disperse evenly to obtain a core suspension.

[0070] II. Mix 20 g of paraformaldehyde and 20 g of urea, add 70 g of distilled water for dissolution, and simultaneously add 0.16 g of the basic catalyst triethylamine; then heat in a water bath to 45 - 75 °C and react for 2 h to obtain a urea - formaldehyde resin prepolymer solution;

[0071] III. Under mechanical stirring conditions, add the core suspension prepared in Step I to the urea - formaldehyde resin prepolymer solution prepared in Step II, control the mechanical stirring speed at 80 - 240 rpm, mix evenly, add 2 g of phosphoric acid with a mass concentration of 20%, stir, and make the urea - formaldehyde resin generated by the reaction precipitate and adhere to the surface of the crystal particles to obtain a mixed solution;

[0072] IV. Stir the mixed solution obtained in Step III, set the initial temperature of the water - bath heating at 25 °C and the end - point temperature at 75 °C, control the heating rate at 1.1 °C / min for heating and raising the temperature. When the temperature reaches 30 °C, add another 2 g of phosphoric acid with a mass concentration of 20%, and then continue the reaction until the end - point temperature is reached to obtain a microcapsule solution;

[0073] V. Filter the microcapsule solution obtained in Step IV, dry the filtrate, and then pass through a 325 - mesh sieve to obtain the pyrazolate microcapsule powder with a long - term sustained - release effect, thus completing the preparation.

[0074] The microcapsule encapsulation rate of the pyrazolate microcapsule powder prepared in this example is 77%, and the release rate reaches 82% on the 20th day.

[0075] Example 5:

[0076] A preparation method of a pesticide microcapsule with a long - term sustained - release effect in this example is carried out according to the following steps:

[0077] I. Take 20 g of micronized pyrazolate powder, add 2.0 g of sodium dodecyl sulfate and 25 g of distilled water, stir and disperse evenly to obtain a core suspension;

[0078] II. Mix 25 g of paraformaldehyde and 25 g of urea, add 80 g of distilled water for dissolution, and simultaneously add 0.18 g of the basic catalyst triethylamine; then heat in a water bath to 45 - 75 °C and react for 1.5 h to obtain a urea - formaldehyde resin prepolymer solution;

[0079] III. Under mechanical stirring conditions, add the core suspension prepared in Step I to the urea - formaldehyde resin prepolymer solution prepared in Step II, control the mechanical stirring speed at 80 - 240 rpm, mix evenly, add 2.2 g of phosphoric acid with a mass concentration of 15%, stir, and make the urea - formaldehyde resin generated by the reaction precipitate and adhere to the surface of the crystal particles to obtain a mixed solution;

[0080] IV. Stir the mixed solution obtained in Step III, set the initial temperature of water bath heating at 20°C and the end temperature at 70°C, control the heating rate at 1.0°C / min, and heat up. When the temperature reaches 35°C, add 2.3 g of phosphoric acid with a mass concentration of 15% again, and then continue the reaction until the end temperature is reached to obtain the microcapsule solution;

[0081] V. Filter the microcapsule solution obtained in Step IV, dry the filtrate, and then pass it through a 325-mesh sieve to obtain the pyrazoxyfen microcapsule powder with long-term slow-release effect, thus completing the preparation.

[0082] The microcapsule encapsulation rate of the pyrazoxyfen microcapsule powder prepared in this example is 75%, and the release rate reaches 86% on the 20th day.

[0083] Example 6:

[0084] The preparation method of a pesticide microcapsule with long-term slow-release effect in this example is carried out according to the following steps:

[0085] I. Take 20 g of micronized mesotrione powder, add 2.0 g of Tween 80 and 20 g of distilled water, stir and disperse evenly to obtain the core suspension;

[0086] II. Mix 10 g of paraformaldehyde and 10 g of urea, add 60 g of distilled water for dissolution, and at the same time add 0.14 g of the alkaline catalyst triethylamine; then heat in a water bath to 45 - 75°C and react for 1.5 h to obtain the urea-formaldehyde resin prepolymer solution;

[0087] III. Under mechanical stirring conditions, add the core suspension prepared in Step I to the urea-formaldehyde resin prepolymer solution prepared in Step II, control the mechanical stirring speed at 80 - 240 rpm, suspend evenly, add 1.8 g of hydrochloric acid with a mass concentration of 20%, stir, and make the urea-formaldehyde resin precipitated by the reaction adhere to the surface of the crystal particles to obtain the mixed solution;

[0088] IV. Stir the mixed solution obtained in Step III, set the initial temperature of water bath heating at 18°C and the end temperature at 70°C, control the heating rate at 1.0°C / min, and heat up. When the temperature reaches 30°C, add 1.7 g of hydrochloric acid with a mass concentration of 20% again, and then continue the reaction until the end temperature is reached to obtain the microcapsule solution;

[0089] V. Filter the microcapsule solution obtained in Step IV, dry the filtrate, and then pass it through a 325-mesh sieve to obtain the mesotrione microcapsule powder with long-term slow-release effect, thus completing the preparation.

[0090] The microcapsule encapsulation rate of the mesotrione microcapsule powder prepared in this example is 72%, and the release rate reaches 87% on the 20th day.

[0091] Example 7:

[0092] A preparation method of a pesticide microcapsule with a long-term sustained release effect in this embodiment is carried out according to the following steps:

[0093] I. Take 10 g of micronized mesotrione powder, add 1.2 g of sodium dodecyl sulfate and 30 g of distilled water, stir and disperse evenly to obtain a core suspension;

[0094] II. Mix 10 g of paraformaldehyde and 10 g of urea, add 30 g of distilled water for dissolution, and simultaneously add 0.09 g of the alkaline catalyst triethylamine; then heat in a water bath to 45 - 75 °C and react for 1.0 h to obtain a urea-formaldehyde resin prepolymer solution;

[0095] III. Under mechanical stirring conditions, add the core suspension prepared in step I into the urea-formaldehyde resin prepolymer solution prepared in step II, control the mechanical stirring speed at 80 - 240 rpm, suspend evenly, add 1.1 g of 20% phosphoric acid by mass concentration, stir, and make the urea-formaldehyde resin generated by the reaction precipitate and adhere to the surface of the crystal particles to obtain a mixed solution;

[0096] IV. Stir the mixed solution obtained in step III, set the initial temperature of the water bath heating to 20 °C and the end temperature to 65 °C, control the heating rate at 0.8 °C / min, and carry out heating and temperature rising. When the temperature reaches 30 °C, add 1.1 g of 20% phosphoric acid by mass concentration again, and then continue to react until the end temperature is reached to obtain a microcapsule solution;

[0097] V. Filter the microcapsule solution obtained in step IV, dry the filtrate, and then pass through a 325-mesh sieve to obtain mesotrione microcapsule powder with a long-term sustained release effect, thus completing the preparation.

[0098] The microcapsule encapsulation rate of the mesotrione microcapsule powder prepared in this embodiment is 82%, and the release rate reaches 81% on the 20th day.

Claims

1. A preparation method of a pesticide microcapsule with a long-term sustained release effect, characterized in that The method is carried out according to the following steps: First, take the micronized water-insoluble pesticide powder, add a surfactant and distilled water, stir and disperse evenly to obtain the core suspension; Second, mix the aldehyde compound and urea, add water for dissolution, and at the same time add an alkaline catalyst; then heat in a water bath to 45-75 °C and react for 1-4 h to obtain the urea-formaldehyde resin prepolymer solution; Third, under mechanical stirring conditions, add the core suspension prepared in the first step to the urea-formaldehyde resin prepolymer solution prepared in the second step, control the mechanical stirring speed at 50-240 rpm, suspend evenly, add an acidic catalyst, and stir to obtain a mixed solution; Fourth, stir the mixed solution obtained in the third step, set the initial temperature and the end temperature of the water bath heating, control the heating rate, and heat up. When the temperature reaches 30-40 °C, add an acidic catalyst again, and then continue to react until the end temperature is reached to obtain the microcapsule solution; Fifth, filter the microcapsule solution obtained in the fourth step, dry the filtrate, and then sieve it to obtain the pesticide microcapsules with a long-term slow-release effect, thus completing the preparation.

2. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, characterized in that The surfactant described in the first step is one or a combination of several of Tween 20, Tween 40, Tween 60, Tween 80, Span 85, Span 80, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, benzyl alcohol-721, polyethylene glycol, polyoxyethylene monostearate, and polyoxyethylene lauryl ether.

3. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, characterized in that The mass ratio of the pesticide powder to the surfactant in the first step is 1:(0.01-0.5); the mass ratio of the pesticide powder to the distilled water is 1:(1-50).

4. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, wherein The mass percentage content of the core in the core suspension obtained in the first step is 2%-50%.

5. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, characterized in that The mass ratio of the aldehyde compound to urea in the second step is (0.05-1):1; the aldehyde compound is one or a combination of several of formaldehyde, paraformaldehyde, acetaldehyde, n-propionaldehyde, isopropyl aldehyde, butyraldehyde, succinaldehyde, valeraldehyde, and glutaraldehyde.

6. The preparation method of a pesticide microcapsule with a long-term slow-release effect according to claim 1, characterized in that The alkaline catalyst described in the second step is one or a mixture of several of sodium hydroxide, potassium hydroxide, triethanolamine, triethylamine, dipotassium hydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, and potassium carbonate.

7. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, characterized in that The acidic catalysts added in the third and fourth steps are both one or a mixture of several of citric acid, potassium dihydrogen phosphate, sodium dihydrogen phosphate, glacial acetic acid, malic acid, dilute hydrochloric acid, phosphoric acid, and dilute sulfuric acid.

8. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, characterized in that The ratio of the core to the wall in the mixed solution in the third step is 1:(1-20).

9. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, characterized in that The initial temperature set in the fourth step is ≥10 °C, the end temperature is ≤80 °C, and the heating rate is controlled at 0.1-1.5 °C / min.

10. The preparation method of a pesticide microcapsule with a long-term sustained release effect according to claim 1, characterized in that The slow-release duration of the pesticide microcapsules with a long-term slow-release effect obtained in the fifth step is 1-30 days.

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