Composite shell fire extinguishing microcapsule and preparation method thereof

Abstract

The invention discloses a composite shell layer fire extinguishing microcapsule and a preparation method thereof, and belongs to the field of fire extinguishing agent preparation, the first shell layer of the composite shell layer fire extinguishing microcapsule is polyurethane resin, the shell layer can be preliminarily formed at the temperature of 0-10 DEG C, and then the temperature is gradually increased to improve the compactness of the shell layer, so that core material escape caused by temperature rise can be reduced; therefore, the yield of the microcapsules is improved, and the quality of the microcapsules can be ensured; the second shell layer adopts gelatin, chitosan, sodium alginate and other natural polymers as raw materials, glutaraldehyde, triethylamine, calcium chloride and other curing agents are correspondingly used, a compact film is formed outside the first shell layer, the compactness of the overall shell layer of the fire extinguishing microcapsule is further improved, the application performance of the fire extinguishing microcapsule is guaranteed, and the fire extinguishing microcapsule has the advantages of being safe, environmentally friendly and excellent in fire extinguishing performance on the whole.

Description

Technical Field

[0001] The present invention relates to the technical field of fire extinguishing agents, and more specifically, to a composite shell fire extinguishing microcapsule and a preparation method thereof. Background Art

[0002] When items such as vehicle-mounted batteries, household appliances, and distribution cabinets catch fire, the fire situation is sudden, hidden, scattered, and develops rapidly. Traditional dry powder fire extinguishers require operators to make correct disposals quickly within a certain time, making it difficult to extinguish the fire immediately and causing greater disasters. By compounding fire extinguishing microcapsules into the coatings of the above items, when a fire occurs, the coating can extinguish the fire quickly autonomously, which can protect the safety of personnel and property to the greatest extent.

[0003] Fire extinguishing microcapsules are solid microcapsules formed by coating fire extinguishing agents with a dense shell layer through physical or chemical methods, with a particle size ranging from a dozen micrometers to several hundred micrometers. At room temperature, the fire extinguishing microcapsules exist stably, and the core material is tightly encapsulated inside the shell layer and will not escape. When the environmental temperature of the microcapsules reaches the warning value, the shell layer gradually softens and undergoes a phase change, while the internal core material is heated and vaporized. Finally, the fire extinguishing agent breaks through the shell layer and is released, cutting off the combustion path through physical cooling and chemical reactions, etc., to achieve fire extinguishing.

[0004] The prior art also involves related fire extinguishing agent technologies. For example, US Patent US9968813, Chinese Patents CN109453491 and CN113230577A introduce the use of urea-formaldehyde or melamine resin as the shell material of fire extinguishing microcapsules. However, the preparation of urea-formaldehyde and melamine resin requires the use of a large amount of formaldehyde as a cross-linking agent, which not only endangers personal safety during the production process but also causes a part of formaldehyde to remain in the shell material, resulting in continuous health hazards. Another example is that Patents RU2162520 and RU2015133303A introduce the preparation technology of using gelatin material as the shell of fire extinguishing microcapsules. However, during the preparation process by complex coacervation method, it is necessary to raise the temperature to a relatively high temperature, which is extremely likely to cause the escape of the core material and reduce the yield.

[0005] Therefore, it is of great significance to develop a composite shell technology to effectively solve the problems of safe production and improve the yield. Summary of the Invention

[0006] Based on this, in order to solve the problem that fire extinguishing microcapsules with urea-formaldehyde and melamine resin as the shell material in the prior art need to use a large amount of formaldehyde, which causes great harm to human health; while fire extinguishing microcapsules with gelatin as the shell material by complex coacervation method have the defects of low yield and dark color, the present invention provides a composite shell fire extinguishing microcapsule and a preparation method thereof. The specific technical solutions are as follows:

[0007] A composite shell fire-extinguishing microcapsule, the composite shell fire-extinguishing microcapsule is a multi-layer structure, and the multi-layer structure includes a core material, a first shell layer covering the core material, and a second shell layer covering the first shell layer;

[0008] Among them, the raw materials for preparing the core material are at least one of perfluoromethyl hexanone, perfluoroheptane, 1,2-tetrafluorodibromoethane, perfluorotriethylamine, and methyl nonafluorobutyl ether;

[0009] The first shell layer is polyurethane resin;

[0010] The raw materials for preparing the second shell layer include at least one of gelatin, sodium alginate, gum arabic, montmorillonite, and chitosan.

[0011] In addition, the present application also provides a preparation method of a composite shell fire-extinguishing microcapsule, and the preparation method includes the following steps:

[0012] Compound the oil-soluble monomer of polyurethane resin with the raw materials for preparing the core material to obtain a uniform solution A;

[0013] Add an emulsifier to water to form solution B;

[0014] Add solution A to solution B, stir and emulsify to obtain solution C;

[0015] Add curing agent A to the solution C, and slowly raise the temperature. After the first reaction treatment, filter the microcapsules and wash them with water multiple times to obtain the microcapsules forming the first shell layer;

[0016] Disperse the microcapsules forming the first shell layer in an aqueous solution containing the raw materials for preparing the second shell layer, slowly add curing agent B while stirring, and after the second reaction treatment, filter out the product, wash it thoroughly, and dry it thoroughly to obtain the microcapsules forming the second shell layer, that is, the composite shell fire-extinguishing microcapsule.

[0017] Furthermore, the oil-soluble monomer of the polyurethane resin is at least one of isophorone diisocyanate, isophorone diisocyanate trimer, toluene diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate.

[0018] Furthermore, the mass of the oil-soluble monomer of the polyurethane resin accounts for 2% to 20% of the mass of the core material.

[0019] Furthermore, the emulsifier is at least one of gum arabic, polystyrene maleic anhydride, polyvinyl alcohol, and sodium dodecylbenzenesulfonate.

[0020] Furthermore, the mass of the emulsifier accounts for 2% to 6% of the mass of the core material.

[0021] Further, the conditions for stirring and emulsifying treatment are as follows: the temperature is 0 - 10°C, the time is 10 - 30 min, and the rotation speed is 300 - 800 r / min.

[0022] Further, the curing agent A is at least one of diethylenetriamine, polyethyleneimine, and melamine;

[0023] The mass of the curing agent A accounts for 2% - 10% of the mass of the core material.

[0024] Further, the curing agent B is at least one of calcium chloride, glutaraldehyde, tannic acid, triethylamine, and sodium hydroxide.

[0025] Further, the mass of the second shell layer accounts for 15% - 30% of the mass of the core material.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] 1. For the composite shell fire - extinguishing microcapsules of the present invention, the first shell layer is polyurethane resin, which can be initially formed at 0 - 10°C and then gradually heated to increase the density of the shell layer, reducing the escape of the core material caused by temperature rise, thereby improving the yield of the microcapsules and ensuring their quality.

[0028] 2. For the composite shell fire - extinguishing microcapsules of the present invention, the second shell layer uses natural polymers such as gelatin, chitosan, and sodium alginate as raw materials, and corresponding curing agents such as glutaraldehyde, triethylamine, and calcium chloride are used to form a dense film outside the first shell layer, further improving the density of the overall shell layer of the fire - extinguishing microcapsules and ensuring their application performance.

[0029] 3. For the composite shell fire - extinguishing microcapsules of the present invention, no volatile and highly toxic reagents are used in the entire preparation process, and no organic pollutants are generated during thermal decomposition. It is very safe and environmentally friendly. The entire preparation process is in a low - temperature state, and the core material can be largely coated by the shell material. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the electron microscope scan of the composite shell fire - extinguishing microcapsules prepared in Example 1. Detailed Embodiments

[0031] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with its embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the protection scope of the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of this invention are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0033] A composite shell fire-extinguishing microcapsule in an embodiment of the present invention, the composite shell fire-extinguishing microcapsule is a multi-layer structure, and the multi-layer structure includes a core material, a first shell layer covering the core material, and a second shell layer covering the first shell layer;

[0034] Among them, the raw materials for preparing the core material are at least one of perfluoropentanone, perfluoroheptane, 1,2-tetrafluorodibromoethane, perfluorotriethylamine, and methyl nonafluorobutyl ether;

[0035] The first shell layer is polyurethane resin;

[0036] The raw materials for preparing the second shell layer include at least one of gelatin, sodium alginate, gum arabic, montmorillonite, and chitosan.

[0037] In addition, the present application also provides a method for preparing a composite shell fire-extinguishing microcapsule, and the preparation method includes the following steps:

[0038] Compound the oil-soluble monomer of polyurethane resin with the raw materials for preparing the core material to obtain a uniform solution A;

[0039] Add an emulsifier to water to form solution B;

[0040] Add solution A to solution B, stir and emulsify to obtain solution C;

[0041] Add curing agent A to the solution C, slowly raise the temperature, perform the first reaction treatment, filter the microcapsules, and wash them with water multiple times to obtain the microcapsules forming the first shell layer;

[0042] Disperse the microcapsules forming the first shell layer in an aqueous solution containing the raw materials for preparing the second shell layer, slowly add curing agent B while stirring, perform the second reaction treatment, filter out the product, wash it thoroughly, and dry it thoroughly to obtain the microcapsules forming the second shell layer, that is, the composite shell fire-extinguishing microcapsule.

[0043] In one of the embodiments, the oil-soluble monomer of the polyurethane resin is at least one of isophorone diisocyanate, isophorone diisocyanate trimer, toluene diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate.

[0044] In one embodiment, the mass of the oil-soluble monomer of the polyurethane resin accounts for 2% to 20% of the mass of the core material.

[0045] In one embodiment, the emulsifier is at least one of gum arabic, polystyrene maleic anhydride, polyvinyl alcohol, and sodium dodecylbenzenesulfonate.

[0046] In one embodiment, the mass of the emulsifier accounts for 2% to 6% of the mass of the core material.

[0047] In one embodiment, the conditions for the stirring and emulsifying treatment are as follows: the temperature is 0 to 10 °C, the time is 10 to 30 min, and the rotation speed is 300 to 800 r / min.

[0048] In one embodiment, the curing agent A is at least one of diethylenetriamine, polyethyleneimine, and melamine;

[0049] The mass of the curing agent A accounts for 2% to 10% of the mass of the core material.

[0050] In one embodiment, the molecular weight of the polyethyleneimine is 600.

[0051] In one embodiment, the first reaction treatment uses programmed temperature rise, and the temperature range is 0 to 30 °C.

[0052] In one embodiment, in the first reaction treatment, the heating rate of the programmed temperature rise is 1 °C / min to 3 °C / min.

[0053] In one embodiment, the curing agent B is at least one of calcium chloride, glutaraldehyde, tannic acid, triethylamine, and sodium hydroxide.

[0054] In one embodiment, the mass of the second shell layer accounts for 15% to 30% of the mass of the core material.

[0055] In one embodiment, the average particle size of the composite shell layer fire-extinguishing microcapsules is 50 μm to 150 μm.

[0056] The composite shell layer fire-extinguishing microcapsules prepared by the above scheme have excellent environmental protection performance, and the active ingredients are not easily escaped, ensuring their application performance, high yield, and can ensure their large-scale production and application.

[0057] The embodiments of the present invention will be described in detail below in conjunction with specific embodiments.

[0058] Example 1:

[0059] A method for preparing a composite shell layer fire-extinguishing microcapsule, comprising the following steps:

[0060] 10 g of perfluoromethylcyclohexanone, 10 g of methyl nonafluorobutyl ether, 0.02 g of dibutyltin dilaurate, and 0.4 g of isophorone diisocyanate were ultrasonically treated for 5 min at room temperature to obtain a homogeneous solution A;

[0061] 0.6 g of polyvinyl alcohol was dissolved in 100 mL of water by heating at 80 °C until completely dissolved, and then cooled to 8 °C to form solution B;

[0062] Solution A was added to solution B, and 0.1 g of n-butanol was added. The system was emulsified at 5 °C at a speed of 400 r / min for 10 min to obtain solution C;

[0063] 0.6 g of diethylenetriamine was added to the solution C, and the temperature was increased at a rate of 1 °C / min using a programmed temperature increase. The system was reacted at 0 - 10 °C for 1 h, then the temperature was raised to room temperature and reacted for 2 h. The microcapsules were filtered and washed with water multiple times to obtain microcapsules with a first shell layer formed;

[0064] The microcapsules with a first shell layer formed were dispersed in 100 mL of an aqueous solution of gelatin with a concentration of 40 g / L. While stirring, a curing agent B and 30 mL of a montmorillonite dispersion with a concentration of 1 g / L were slowly added. Then, it was stirred at room temperature for 5 min, 0.3 g of sodium poly metaphosphate was added, and the temperature was raised to 35 °C at a rate of 2 °C / min and stirred for 15 min. Then, the pH was adjusted to 4 and reacted for 30 min. The system was cooled to 0 - 10 °C, maintained for 1 h, 1 mL of glutaraldehyde was added, stirred for 30 min, the pH was adjusted to 9, and then slowly heated to 35 °C. The microcapsules were filtered out, washed thoroughly, and dried thoroughly at room temperature to obtain composite shell fire-extinguishing microcapsules.

[0065] Example 2:

[0066] A method for preparing composite shell fire-extinguishing microcapsules, comprising the following steps:

[0067] 20 g of perfluorotriethylamine, 0.02 g of dibutyltin dilaurate, and 0.4 g of isophorone diisocyanate trimer were ultrasonically treated for 5 min at room temperature to obtain a homogeneous solution A;

[0068] 0.6 g of polystyrene maleic anhydride was dissolved in 100 mL of water, the pH was adjusted to 10, and it was heated at 80 °C until completely dissolved, and then cooled to 8 °C to form solution B;

[0069] Solution A was added to solution B, and 0.1 g of n-butanol was added. The system was emulsified at 7 °C at a speed of 400 r / min for 10 min to obtain solution C;

[0070] Add 1 g of polyethyleneimine (M = 600) to the solution C, and slowly raise the temperature at a heating rate of 1 °C / min. The system reacts at 0 - 10 °C for 1 h, then raises the temperature to room temperature and reacts for 2 h. Filter the microcapsules and wash them with water multiple times to obtain the microcapsules with the first shell layer formed.

[0071] Disperse the microcapsules with the first shell layer formed in 30 mL of an aqueous solution containing the raw materials for preparing the second shell layer (add 1 g of chitosan and 1 g of montmorillonite to 100 mL of water, fully dissolve, and then ultrasonically treat for 90 min). While stirring, slowly add 100 mL of n-hexane, stir rapidly, mechanically add 3 mL of triethylamine, stir at room temperature for 30 min, filter out the product, wash it thoroughly, and dry it thoroughly at room temperature to obtain the composite shell fire-extinguishing microcapsules.

[0072] Example 3:

[0073] A preparation method of composite shell fire-extinguishing microcapsules, comprising the following steps:

[0074] Add 10 g of perfluorotriethylamine, 10 g of perfluoroheptane, 0.02 g of dibutyltin dilaurate, and 0.4 g of diphenylmethane diisocyanate, and ultrasonically treat for 5 min at room temperature to obtain a uniform solution A;

[0075] Add 0.6 g of sodium dodecylbenzenesulfonate to 100 mL of water, then add 0.1 g of n-butanol, and cool to 7 °C to form solution B;

[0076] Add solution A to solution B, and emulsify the system at 8 °C at a rotation speed of 400 r / min for 10 min to obtain solution C;

[0077] Add 1 g of polyethyleneimine (M = 600) to the solution C, and slowly raise the temperature at a heating rate of 1 °C / min. React at 0 - 10 °C for 1 h, then raise the temperature to room temperature and react for 2 h. Filter the microcapsules and wash them with water multiple times to obtain the microcapsules with the first shell layer formed.

[0078] Disperse the microcapsules with the first shell layer formed in 30 mL of an aqueous solution containing the raw materials for preparing the second shell layer (add 1 g of sodium alginate, 1 g of gelatin, and 1 g of montmorillonite to 100 mL of water, fully dissolve, and then ultrasonically treat for 90 min). While stirring, slowly add 100 mL of ethyl acetate, stir rapidly, add 0.3 g of glutaraldehyde and 1 mL of triethylamine to the system, stir at room temperature for 120 min, filter out the microcapsules, immerse them in 1 mol / L calcium chloride solution, stir for 1 h, filter out the product, wash it thoroughly, and dry it thoroughly at room temperature to obtain the composite shell fire-extinguishing microcapsules.

[0079] Example 4:

[0080] A preparation method of a composite shell fire-extinguishing microcapsule, comprising the following steps:

[0081] Ultrasonicate 5 g of perfluoromethylcyclohexanone, 15 g of 1,2-dibromo-1,1,2,2-tetrafluoroethane, 0.02 g of dibutyltin dilaurate and 0.6 g of isophorone diisocyanate at room temperature for 5 min to obtain a uniform solution A;

[0082] Add 0.6 g of sodium dodecylbenzenesulfonate to 100 mL of water, then add 0.1 g of n-butanol, and cool to 5 °C to form solution B;

[0083] Add solution A to solution B, and emulsify at 9 °C at a rotation speed of 400 r / min for 10 min to obtain solution C;

[0084] Add 1 g of polyethyleneimine (M = 1800) to the said solution C, and at a heating rate of 1 °C / min, react the system at 0-10 °C for 1 h, then raise the temperature to room temperature and react for 2 h, filter the microcapsules, and wash them with water multiple times to obtain microcapsules forming the first shell;

[0085] Disperse the microcapsules forming the first shell in 100 mL of an aqueous solution (gelatin with a concentration of 40 g / L) containing the preparation raw materials of the second shell, then add 30 mL of a montmorillonite dispersion with a concentration of 1 g / L, then stir at room temperature for 5 min, then add 0.3 g of sodium polyphosphate, raise the temperature to 35 °C and stir for 15 min, then adjust the pH to 4 and react for 30 min. Cool the system to 8 °C, keep it for 1 h, then add 1 mL of glutaraldehyde, stir for 30 min, adjust the pH to 9, then slowly raise the temperature to 35 °C, filter out the product, wash it thoroughly, and dry it thoroughly to obtain the composite shell fire-extinguishing microcapsule.

[0086] Comparative Example 1:

[0087] A preparation method of a fire-extinguishing capsule, comprising the following steps:

[0088] (1) Compound of core material and first shell monomer: Take 10 g of perfluoromethylcyclohexanone, 10 g of methyl nonafluorobutyl ether, 0.02 g of dibutyltin dilaurate and 0.4 g of isophorone diisocyanate, and ultrasonicate at room temperature for 5 min to obtain a uniform solution A;

[0089] (2) Preparation of emulsifier: Take 0.6 g of polystyrene maleic anhydride in 100 mL of water, adjust the pH = 10, heat at 80 °C until completely dissolved, and cool to 5 °C to obtain solution B;

[0090] (3) Emulsification: Add solution A to solution B, add 0.1 g of n-butanol, and emulsify the system at 5 °C at a rotation speed of 400 r / min for 10 min to obtain solution C;

[0091] (4) Formation of the first shell layer: Add 1 g of polyethyleneimine (M = 600) to Solution C. The system reacts at 8 °C for 1 h, then the temperature is raised to room temperature and reacts for 2 h. The microcapsules are filtered out, washed with water multiple times, and dried at room temperature to obtain the fire-extinguishing capsules.

[0092] Comparative Example 2:

[0093] A method for preparing fire-extinguishing capsules, comprising the following steps:

[0094] (1) Take 10 g of perfluoromethylcyclohexanone and 10 g of methyl nonafluorobutyl ether, and ultrasonicate for 5 min at room temperature to obtain a uniform solution;

[0095] (2) Disperse the solution in step (1) into 100 mL of an aqueous solution of gelatin with a concentration of 40 g / L, then add 30 mL of a montmorillonite dispersion with a concentration of 1 g / L, and then stir at room temperature for 5 min. Then add 0.3 g of sodium polyphosphate, raise the temperature to 35 °C and stir for 15 min, then adjust the pH to 4 and react for 30 min. The system is cooled to 0 - 10 °C, kept for 1 h, then add 1 mL of glutaraldehyde, stir for 30 min, adjust the pH to 9, and then slowly raise the temperature to 35 °C. The microcapsules are filtered out, washed thoroughly, and dried thoroughly at room temperature.

[0096] Record the yields of Examples 1 - 4 and Comparative Examples 1 - 2, and the results are shown in Table 1 below.

[0097] Table 1: Yield

[0098]

[0099] From the data analysis in Table 1, it can be seen that the composite-shell fire-extinguishing microcapsules prepared in this application can significantly improve their yield while ensuring the core material content, that is, ensuring their effective application performance. The results of Example 1 and Comparative Examples 1 and 2 show that under the single-shell polyurethane and single-shell gelatin, the yield and core material content of the microcapsules are lower than those of the composite shell. When preparing the polyurethane resin shell layer by interfacial polymerization, its oil-soluble monomers are difficult to be effectively miscible with the core material, so the amount of shell material used is too small, resulting in a too thin shell material and unable to prevent the escape of the core material. When using the complex coacervation method alone to prepare the gelatin shell layer, due to the relatively high reaction temperature, the core material escapes before the shell material is cured and formed, resulting in a decrease in yield.

[0100] Figure 1 Figure for the SEM of the composite-shell fire-extinguishing microcapsules prepared in Example 1. From Figure 1 it can be known that the average particle size of the composite-shell fire-extinguishing microcapsules prepared in this application is between 50 μm and 150 μm, and it has excellent application performance. Examples 2 - 4 are similar to Example 1 and will not be elaborated here.

[0101] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0102] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A composite shell fire-extinguishing microcapsule, characterized in that, The composite shell fire-extinguishing microcapsule has a multi-layer structure, and the multi-layer structure includes a core material, a first shell layer covering the core material, and a second shell layer covering the first shell layer; Among them, the raw materials for preparing the core material are at least one of perfluoromethyl hexanone, perfluoroheptane, 1,2-tetrafluorodibromoethane, perfluorotriethylamine, and methyl nonafluorobutyl ether; The first shell layer is a polyurethane resin; The raw materials for preparing the second shell layer include at least one of gelatin, sodium alginate, gum arabic, montmorillonite, and chitosan.

2. A preparation method of a composite shell fire-extinguishing microcapsule, characterized in that, The preparation method is used to prepare the composite shell fire-extinguishing microcapsule as described in claim 1, and the preparation method includes the following steps: Compound the oil-soluble monomer of the polyurethane resin with the raw materials for preparing the core material to obtain a uniform solution A; Add an emulsifier to water to form solution B; Add solution A to solution B, stir and emulsify to obtain solution C; Add curing agent A to solution C, slowly raise the temperature, perform the first reaction treatment, filter the microcapsules, and wash them with water multiple times to obtain microcapsules with the first shell layer formed; Disperse the microcapsules with the first shell layer formed in an aqueous solution containing the raw materials for preparing the second shell layer, slowly add curing agent B while stirring, perform the second reaction treatment, filter out the product, wash it thoroughly, and dry it thoroughly to obtain microcapsules with the second shell layer formed, that is, the composite shell fire-extinguishing microcapsule.

3. The preparation method according to claim 2, characterized in that, The oil-soluble monomer of the polyurethane resin is at least one of isophorone diisocyanate, isophorone diisocyanate trimer, toluene diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate.

4. The preparation method according to claim 3, wherein The mass of the oil-soluble monomer of the polyurethane resin accounts for 2% - 20% of the mass of the core material.

5. The preparation method according to claim 2, characterized in that, The emulsifier is at least one of gum arabic, polystyrene maleic anhydride, polyvinyl alcohol, and sodium dodecylbenzenesulfonate.

6. The preparation method according to claim 2, wherein The mass of the emulsifier accounts for 2% - 6% of the mass of the core material.

7. The preparation method according to claim 2, wherein, The conditions for the stirring and emulsifying treatment are: the temperature is 0 - 10°C, the time is 10 - 30 min, and the rotation speed is 300 - 800 r / min.

8. The preparation method according to claim 2, wherein The curing agent A is at least one of diethylenetriamine, polyethyleneimine, and melamine; The mass of the curing agent A accounts for 2% - 10% of the mass of the core material.

9. The preparation method according to claim 2, wherein The curing agent B is at least one of calcium chloride, glutaraldehyde, tannic acid, triethylamine, and sodium hydroxide.

10. The preparation method according to claim 2, characterized in that, The mass of the second shell layer accounts for 15% - 30% of the mass of the core material.

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