Flavor microcapsule and method for preparing the same

Abstract

The application discloses a kind of essence microcapsules and preparation method thereof, the oil phase containing essence and polyisocyanate is added to aqueous phase, and O / W emulsion is formed under the action of high-speed shearing;First chain extender is added, and polyurea capsule shell is formed at oil-water interface by reacting with polyisocyanate;Second chain extender is added, and polyurea capsule shell is reinforced and shaped by consuming unreacted polyisocyanate at oil-water interface, and then the polymerization coating of non-water-soluble essence is completed, and essence microcapsules are prepared;The first chain extender is small molecule polyamine, and the second chain extender is macromolecular polyamine.The first and second chain extenders are used in the application, which effectively avoids the problems of insufficient charge and agglomeration of polyurea capsule shell, and the prepared essence microcapsules have good appearance, smooth and full surface, approximate spherical shape, good dispersibility, and sufficient positive charge on the surface, which can be firmly combined with negatively charged fiber fabric through electrostatic effect, thereby increasing the fragrance retention capacity of essence microcapsules on fabric.

Description

Technical Field

[0001] This invention belongs to the field of fragrance microcapsules, and specifically relates to a polyurea shell fragrance microcapsule with a positively charged surface and its preparation method. Background Technology

[0002] As people's living standards improve, they begin to pursue and aspire to a healthy, comfortable, and high-quality life. Studies have shown that certain aromatic scents can not only purify the air but also please the mind and body, improving overall health. Traditional fragrances, however, are formulated with various flavorings, solvents, and other additives, resulting in complex compositions containing many volatile and chemically unstable compounds. To address these issues, fragrance microencapsulation has emerged. Microencapsulation technology is a micro-encapsulation protective technique that uses high-molecular polymer film-forming materials to encapsulate finely dispersed, reactive, sensitive, or volatile droplets, solid particles, or gases through specific physical or chemical methods, forming a thin film-encapsulated microcapsule. After microencapsulation, fragrances have less contact with the external environment, preventing excessive evaporation, reducing aroma loss, providing a certain degree of sustained release, and prolonging the fragrance's lasting effect.

[0003] Common fragrance microcapsules utilize various wall materials, such as melamine resin aromatic microcapsules and gelatin-gum arabic aromatic microcapsules. Melamine resin microcapsules use formaldehyde as the wall material reactant monomer, leaving residual formaldehyde and other harmful substances. Gelatin-gum arabic aromatic microcapsule systems often use toxic and harmful formaldehyde and glutaraldehyde as cross-linking agents. Polyurea microcapsules avoid these problems. They are prepared using interfacial polymerization, where monomers directly cross-link at the oil-water interface, forming a microcapsule shell with a cross-linked network structure. This method avoids the addition of toxic cross-linking agents like formaldehyde during preparation, thus solving the problem of residual toxic substances. However, this type of method often uses large-molecule polyamines as chain extenders to improve performance, but these large-molecule chain extenders can easily cause microcapsule aggregation, leading to poor performance.

[0004] In addition, to further extend the fragrance duration, existing technologies also employ padding methods. For example, one method for obtaining long-lasting scented fabrics generally involves: preparing a finishing agent by combining microcapsules, adhesives, penetrants, and softeners; then padding the fabric in the finishing agent and drying it to obtain the scented fabric. In summary, padding methods are relatively complex and have limited applicability. Summary of the Invention

[0005] The purpose of this invention is to provide a polyurea-shelled fragrance microcapsule with a positively charged surface and its preparation method. The microcapsule is prepared by reacting water-soluble small-molecule polyamine monomers and large-molecule polyamine monomers sequentially with isocyanate monomers. Compared with existing technologies, the fragrance microcapsules of this invention can solve the aggregation problem caused by using large-molecule polyamine monomers alone as chain extenders, while retaining the high positive charge advantage of the large-molecule polyamine monomers.

[0006] A method for preparing fragrance microcapsules involves adding an oil phase containing fragrance and polyisocyanate to an aqueous phase, forming an O / W emulsion under high-speed shearing; adding a first chain extender, which reacts with the polyisocyanate at the oil-water interface to form an initial polyurea shell; then adding a second chain extender, which consumes unreacted polyisocyanate at the oil-water interface to strengthen the polyurea shell, thereby completing the polymerization and encapsulation of non-water-soluble fragrance to obtain fragrance microcapsules; the first chain extender is a small molecule polyamine (molecular weight less than 1000), and the second chain extender is a large molecule polyamine (molecular weight greater than 1000).

[0007] Preferably, the preparation method includes the following steps:

[0008] (1) The oil phase containing fragrance and polyfunctional isocyanate is added dropwise to the aqueous phase containing emulsifier and alkali metal salt, and the mixture is subjected to high-speed shearing in a homogenizer to obtain an O / W emulsion;

[0009] (2) Add small molecule polyamine solution dropwise to O / W emulsion and stir at 35±5℃ for 30-60 min; then add large molecule polyamine solution dropwise and stir at 35±5℃ for 30-60 min.

[0010] (3) Heat to 55±5℃ and continue the reaction for 2±1h; filter and wash the resulting emulsion until the pH value is neutral, then remove the water to obtain the fragrance microcapsules.

[0011] Preferably, the raw material additions, by mass percentage, are: 1-35% fragrance, 1-20% polyfunctional isocyanate, 0.01-15% small molecule polyamine, 0.01-10% large molecule polyamine, 0.01-10% emulsifier, 0.01-15% alkali metal salt, and the balance being water.

[0012] Preferably, the macromolecular polyamine is 0.01-65% of the small molecule polyamine.

[0013] Preferably, the macromolecular polyamine is 1-40% of the small molecule polyamine.

[0014] Preferably, the high-speed shearing speed in step (1) is 1000-8000 rpm.

[0015] Preferably, the macromolecular polyamine is branched polyethyleneimine; the small molecule polyamine is one or more of aromatic amines and aliphatic amines.

[0016] The small molecule polyamine is one or more of the following: hexamethylenediamine, pentamethylenediamine, hexamethylenediamine, tetramethylenediamine, dicyclohexylmethanediamine, methylcyclohexanediamine, 1,3-cyclohexanedimethylenediamine, ethylenediamine, 1,3-diaminopropane, 1,2-diaminopropane, 1,4-diaminobutane, diethylenetriamine, pentaethylenehexamine, 5-amino-1,3,3-trimethylcyclohexylmethylamine, triethylamine, diethylenetriamine, tetramethylethylenediamine, 2,2-dimethyl-1,3-propanediamine, tris(2-aminoethyl)amine, and hexamethylenetetramine.

[0017] Polyisocyanates are defined as containing at least two isocyanate (-NCO) groups. These isocyanates can be aliphatic, aromatic, branched, linear, or cyclic. In some embodiments, aliphatic isocyanates are more preferred polyisocyanates used in this invention. Examples include: 4,4'-dicyclohexylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), hydrogenated diphenylmethylene diisocyanate (HXDI), cyclohexane-1,4-diisocyanate (CHDI), norbornene diisocyanate (NBDI), hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI), trimethyl-1,6-hexamethylene diisocyanate (TMDI), and methylcyclohexyl diisocyanate (HTDI). Lysine diisocyanate (LDI), hexamethylene diisocyanate dimer, hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, pentamethylene diisocyanate trimer, hexamethylene diisocyanate biuret, isophorone diisocyanate biuret, hexamethylene diisocyanate adduct, hexamethylene diisocyanate urea formate, isophorone diisocyanate (IPDI) adduct, hexamethylene diisocyanate prepolymer, or a mixture thereof.

[0018] Preferably, the alkali metal salt includes one or more of sodium carbonate, sodium chloride, calcium chloride, sodium sulfate, potassium sulfite, bisulfite, sodium bicarbonate, and potassium chloride.

[0019] Preferably, the emulsifier comprises ionic and nonionic emulsifiers. The ionic emulsifiers include cationic emulsifiers such as dodecyltrimethylamine oxide, dodecyl dimethylamine oxide, cocamidopropylamine oxide, polyacrylamide, polyguanidine carbonate, and quaternary ammonium salts; and anionic emulsifiers such as sodium α-alkenyl sulfonate, potassium lauryl phosphate, potassium lauryl ether-3 phosphate, fatty acid soap, sodium ethoxylated alkyl sulfate, disodium lauryl sulfosuccinate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, phosphates, sodium polyacrylate, and FES61. The nonionic emulsifiers include one or more of lauryl ether-4, polyvinylpyrrolidone, polyvinyl alcohol, Tween series, hydroxyethyl cellulose, isotridecyl alcohol polyoxyethylene ether (6EO), isotridecyl alcohol polyoxyethylene ether (9EO), and A3065.

[0020] Preferably, the oil phase further contains 0.1-15% of an oil phase regulator, wherein the oil phase regulator is one or a mixture of isopropyl palmitate, isopropyl myristate, caprylic triglyceride, caprylic triglyceride, benzyl benzoate, C5-C50, triglycerides, silicone oil, isoparaffin hydrocarbons, dioctyl adipate, triethyl citrate, C3-C40, methyl rosinate, benzyl salicylate, mineral oil, and D-limonene.

[0021] Preferably, the fragrance can be a single flavoring or seasoning ingredient, or a combination thereof. These combinations can be found in literature such as "Practical Fragrance Formulations," "Fragrance Formulation Handbook," and numerous other fragrance industry-related documents, books, patents, etc., but are not limited thereto. These are ingredients well-known to those skilled in the art of flavoring and seasoning consumer products, such as: lavender fragrance, Tide fragrance, floral fragrance, lotus fragrance, Hawaiian fragrance, fresh ocean fragrance, pink gold fragrance, blue gold fragrance, natural fresh fragrance, bluebell fragrance, gardenia fragrance, comfort fabric fragrance, Tide fragrance, Omo fragrance, or a mixture thereof.

[0022] This invention employs interfacial polymerization, utilizing a insufficient amount of small-molecule polyamine and a small amount of large-molecule polyamine to react sequentially with isocyanate at the oil-water interface to form a polyurea shell. The remaining unreacted amine groups are protonated, becoming positively charged, thus giving the microcapsule shell a positive charge. Traditional polyurea microcapsules use large-molecule polyamine monomers alone as chain extenders. Due to their high reactivity and long molecular chains, these chain extenders have a chance to react with multiple adjacent oil phase droplets during polymerization, causing microcapsule aggregation. Aggregated microcapsules, due to their large size, are not conducive to entering the fabric interior and can only be adsorbed on the fabric surface, resulting in poor wash fastness. Alternatively, using small-molecule polyamine monomers alone as chain extenders results in a small amount of protonated amine groups, leading to weak electrostatic adsorption on the fabric and easy detachment during washing. This invention first introduces a insufficient amount of small-molecule polyamine monomer into an O / W emulsion to react with isocyanate to form an initial polyurea shell. Then, a small amount of large-molecule polyamine monomer is introduced to consume the remaining unreacted isocyanate, thus strengthening the polyurea shell. The small-molecule polyamine is the primary component, while the large-molecule polyamine is secondary; the two work synergistically to compensate for the insufficient charge on the shell when using small-molecule polyamine alone as a chain extender. It also compensates for the problem of microcapsule aggregation caused by excessive use of large-molecule polyamine alone as a chain extender.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention uses small molecule polyamines and large molecule polyamines as the first and second chain extenders, which effectively avoids the problem of insufficient charge and aggregation of the capsule shell. The prepared fragrance microcapsules have good morphology, smooth and full surface, and are approximately spherical. They have good dispersibility and sufficient positive charge on the surface, which can firmly bind with negatively charged fiber fabrics through electrostatic effect, thereby increasing the fragrance retention ability of the fragrance microcapsules on the fabric.

[0025] (2) The fragrance microcapsules prepared by this invention have a high utilization rate because there is no aggregation between the microcapsules. When used in fabric care products, such as fabric softeners, liquid laundry detergents, fragrance beads, and laundry gel beads, the fragrance microcapsules are adsorbed onto the fabric by electrostatic attraction during the washing process. They can achieve a good fragrance retention effect without the need for padding. The natural fragrance retention time is more than 15 days. Moreover, after the fabric is rubbed and air-dried, the polyurea capsule shells rupture, resulting in a burst of fragrance. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the preparation principle of flavor microcapsules according to the present invention.

[0027] Figure 2 This is a scanning electron microscope image of the flavor microcapsules of Embodiment 1 of the present invention.

[0028] Figure 3This is a scanning electron microscope image of the flavor microcapsules of Comparative Example 1 of the present invention.

[0029] Figure 4 This is a scanning electron microscope image of the flavor microcapsules of Comparative Example 2 of the present invention.

[0030] Figure 5 This is a scanning electron microscope image of the flavor microcapsules of Comparative Example 3 of the present invention.

[0031] Figure 6 These are the Zeta potential diagram (a) and phase diagram (b) of Embodiment 1 of the present invention.

[0032] Figure 7 These are the Zeta potential diagram (a) and phase diagram (b) of Embodiment 2 of the present invention.

[0033] Figure 8 These are the Zeta potential diagram (a) and phase diagram (b) of Embodiment 3 of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0035] Example 1

[0036] The raw materials used in this embodiment are as follows:

[0037] The oily fragrance is lavender fragrance, produced by Guangzhou Xinyu Fragrance Co., Ltd.

[0038] The aliphatic isocyanate is isophorone diisocyanate with an NCO mass fraction ≥37.5%, manufactured by Wanhua Chemical Group Co., Ltd.

[0039] The oil phase conditioner is isopropyl palmitate, manufactured by Guangzhou Zhengli Chemical Co., Ltd.

[0040] The emulsifier is polyvinyl alcohol and sodium dodecyl sulfate, wherein 1.5 parts of polyvinyl alcohol with a degree of alcoholysis of 88% are from Kuraray Corporation, and 1 part of sodium dodecyl sulfate is from China National Light Industry Chemical Co., Ltd.

[0041] The macromolecular polyamine is polyethyleneimine with a molecular weight of 1500, manufactured by Shanghai Youen Chemical Co., Ltd.

[0042] The small molecule polyamine is ethylenediamine, manufactured by Chengdu Kelong Chemical Co., Ltd.

[0043] The alkali metal salt is sodium chloride, manufactured by Tianjin Dingshengxin Chemical Co., Ltd.

[0044] A polyurea fragrance microcapsule with a positively charged surface comprises the following raw materials in parts by mass, with the total parts by mass of all components being 100 parts: 12 parts oily fragrance, 5 parts aliphatic diisocyanate, 1.5 parts oil phase modifier, 2.5 parts emulsifier, 0.2 parts macromolecular polyamine, 3 parts small molecule polyamine, 2.5 parts alkali metal salt, and 73.3 parts deionized water.

[0045] The preparation method of polyurea flavor microcapsules includes the following steps:

[0046] S1. Prepare the aqueous phase: Add the emulsifier and alkali metal salt to a round-mouthed beaker according to the weight ratio, then add 53.3 parts of deionized water, stir for 15 minutes to completely dissolve and mix the emulsifier, and set aside.

[0047] S2. Prepare the oil phase: Add the oily fragrance, aliphatic isocyanate and oil phase modifier to a round-mouthed beaker according to the weight ratio, stir for 10 minutes to make the oil phase uniform, and set aside.

[0048] S3. Prepare the first chain extender solution by mixing the small molecule polyamine with 10 parts of deionized water for 5 minutes. After mixing, transfer the first chain extender solution to a constant pressure funnel for later use.

[0049] S4. Prepare the second chain extender solution by mixing the macromolecular polyamine with 10 parts of deionized water for 5 minutes. After mixing, transfer the second chain extender solution to a constant pressure funnel for later use.

[0050] S5. Add the oil phase dropwise to the aqueous phase and shear homogenize it at 2500 rpm for 10 min using a shear mill to obtain the O / W emulsion.

[0051] S6. Place the O / W emulsion in an oil bath, stir at 350 rpm, and set the temperature to 35°C.

[0052] S7. Add the first chain extender to the emulsion dropwise and react for 40 min at a reaction temperature of 35℃. After reacting for 40 min with the first chain extender, add the second chain extender to the emulsion dropwise at a titration rate of 5-10 drops / min and react for 40 min at a reaction temperature of 35℃.

[0053] S8. After adding the second chain extender and reacting for 40 minutes, the oil bath is heated to 55°C and reacted for 2 hours.

[0054] S9. After reacting for 2 hours, stop the reaction. Filter the emulsion, wash until the pH value is neutral, then dry the mixture. The remaining components are the fragrance microcapsules.

[0055] Example 2

[0056] The difference from Example 1 is that the molecular weight of polyethyleneimine in Example 2 is 3000.

[0057] Example 3

[0058] The difference from Example 1 is that the molecular weight of polyethyleneimine in Example 3 is 5000.

[0059] Example 4

[0060] The difference from Example 1 is that the emulsifier selected isotridecyl alcohol polyoxyethylene ether (6EO) from Shanghai Sokai Industrial Co., Ltd., and disodium lauryl sulfosuccinate from Guangzhou Huayu Fine Chemical Co., Ltd., wherein 1.5 parts of isotridecyl alcohol polyoxyethylene ether (6EO) and 1 part of disodium lauryl sulfosuccinate are used.

[0061] Example 5

[0062] The difference between this invention and Example 1 is that: the emulsifier selected isotridecyl alcohol polyoxyethylene ether (9EO) from Shanghai Sokai Industrial Co., Ltd., and dodecyltrimethylamine oxide from Shandong Anmi Chemical Technology Co., Ltd., wherein isotridecyl alcohol polyoxyethylene ether (9EO) is 1.5 parts and dodecyltrimethylamine oxide is 1 part; the aliphatic diisocyanate selected is hexamethylene diisocyanate with an NCO mass fraction of 21.5-22.1% from Wanhua Chemical Group Co., Ltd., and the quantity is 5 parts.

[0063] Comparative Example 1

[0064] The difference between this invention and Example 1 is that only the first chain extender, ethylenediamine, is added for chain extension, and the amount added is 3.2 parts.

[0065] Comparative Example 2

[0066] The difference between this invention and Example 1 is that only the second chain extender, polyethyleneimine 1500, is added for chain extension, and the amount added is 3.2 parts.

[0067] Comparative Example 3

[0068] The difference between this invention and Example 1 is that: 3 parts of the first chain extender ethylenediamine and 0.2 parts of the second chain extender polyethyleneimine 1500 are taken, the two chain extenders are mixed, 20 parts of deionized water are added and stirred, and after stirring for 5 minutes, the mixture is added dropwise to the emulsion. The reaction temperature is 35°C and the reaction time is 90 minutes.

[0069] Fragrance microcapsule washing test procedure: Weigh 6g of laundry detergent sample combination and place it in a small drum washing machine with the same washing capacity. Add 50g of 30*30cm woven pure cotton towel and wash according to the mixed program, circulating and washing 3 times, with a water volume of 1kg each time. Prepare compound laundry detergent with a total mass of 6g for Examples 1-5 and Comparative Examples 1-3. The compound laundry detergent formula is shown in Table 1. Wash according to the program, and hang the washed fabric on the laboratory clothes rack. The towel should not touch to avoid cross-contamination. Keep the laboratory clean, with fresh air and no odor. Start timing after drying, and check the fragrance at 0h, 4h, 12h, 24h, 2d, 3d, 4d, 5d, 7d, 10d, and 15d. Fragrance evaluation is carried out by a sensory evaluation group of 5 people. They rub the towel and test the gas release. In all tests, including rubbing force, time, and number of times, the rubbing force, time, and number of times should be consistent. Calculate the average score of the 5 people, as shown in Table 2.

[0070] Table 1 Compound Laundry Detergent Formulation

[0071]

[0072] Table 2 Fragrance retention test records

[0073]

[0074]

[0075] As shown in Table 2, under the same testing standards, compared with the blank control group, the blank control group, without encapsulation, released its fragrance completely immediately after washing, resulting in a stronger aroma. However, by the second day, the fabric had no fragrance characteristic. In contrast, the fabric in Example 1 retained its fragrance characteristic on the third day due to the encapsulation protection, indicating that the microcapsules effectively slowed down fragrance evaporation and possessed a sustained-release function. Comparing Example 1 with Comparative Examples 1-3, the difference in fragrance characteristics between the two within 24 hours was not significant. Starting from 2 days, the difference began to widen, with the latter showing a greater decrease in fragrance characteristic compared to the former. After 10 days, the latter had no fragrance characteristic, while the former still retained a faint fragrance characteristic. This difference is due to the microcapsules formed by interfacial polymerization using the first and second chain extenders, which possess both high positive charge and good dispersibility, allowing them to firmly adhere to the fabric during washing and release fragrance after rubbing. Comparative Examples 1-3, constrained by aggregation and insufficient charge, exhibited less fragrance retention on the fabric. Comparing Examples 1 and 2-3, the increased molecular weight of the second chain extender leads to a higher positive charge on the capsule shell. This enhances the electrostatic adsorption of the microcapsules onto the fabric during washing, resulting in greater retention of the fragrance on the fabric after washing. Consequently, the fragrance retention time and aroma enhancement on the fabric are improved. This can be seen from the scores in Table 2. Figure 6-8The Zeta potential diagram illustrates this. Comparing Examples 1 and 4, changing the emulsifier combination slightly improved the fragrance retention of the fabric, but the difference in fragrance retention over 0-15 days was not significant. Comparing Examples 1 and 5, changing the emulsifier combination and polyisocyanate slightly increased the fragrance retention of the fabric over 0-15 days. This may be because using hexamethylene diisocyanate monomer as part of the synthetic polyurea shell, due to its stronger reactivity than isophorone diisocyanate, resulted in a more complete reaction with amine monomers under the same reaction conditions. Therefore, the synthesized polyurea shell was denser and stronger, reducing the probability of fragrance microcapsule rupture during washing. Thus, the fragrance retention of the fabric was slightly improved after washing.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing flavor microcapsules, characterized in that, An oil phase containing fragrance and polyisocyanate is added to an aqueous phase, forming an O / W emulsion under high-speed shearing. A first chain extender is added, reacting with the polyisocyanate at the oil-water interface to form an initial polyurea shell. A second chain extender is then added, consuming unreacted polyisocyanate at the oil-water interface to strengthen the polyurea shell, thereby completing the polymerization and encapsulation of the non-water-soluble fragrance to obtain fragrance microcapsules. The first chain extender is a small molecule polyamine with a molecular weight of less than 1000, and the second chain extender is a large molecule polyamine with a molecular weight of more than 1000. The high-speed shearing speed is 1000-8000 rpm.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: (1) The oil phase containing fragrance and polyfunctional isocyanate is added dropwise to the aqueous phase containing emulsifier and alkali metal salt, and the mixture is subjected to high-speed shearing in a homogenizer to obtain an O / W emulsion; (2) Add small molecule polyamine solution dropwise to O / W emulsion and stir at 35±5℃ for 30-60 min; then add large molecule polyamine solution dropwise and stir at 35±5℃ for 30-60 min. (3) Heat to 55±5℃ and continue the reaction for 2±1h; filter and wash the resulting emulsion until the pH value is neutral, then remove the water to obtain the fragrance microcapsules.

3. The preparation method according to claim 2, characterized in that, The raw materials added, by mass percentage, are: 1-35% fragrance, 1-20% polyfunctional isocyanate, 0.01-15% small molecule polyamine, 0.01-10% large molecule polyamine, 0.01-10% emulsifier, 0.01-15% alkali metal salt, and the balance is water.

4. The preparation method according to claim 3, characterized in that, The macromolecular polyamine is 0.01-65% of the small molecule polyamine.

5. The preparation method according to claim 4, characterized in that, The macromolecular polyamine is 1-40% of the small molecule polyamine.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The macromolecular polyamine is branched polyethyleneimine; the small molecule polyamine is one or both of aromatic amines and aliphatic amines; the polyisocyanate is an aliphatic isocyanate.

7. The preparation method according to claim 6, characterized in that, The small molecule polyamine is one or more of the following: hexamethylenediamine, pentamethylenediamine, hexamethylenediamine, tetramethylenediamine, dicyclohexylmethanediamine, methylcyclohexanediamine, 1,3-cyclohexanedimethylenediamine, ethylenediamine, 1,3-diaminopropane, 1,2-diaminopropane, 1,4-diaminobutane, pentaethylhexamine, 5-amino-1,3,3-trimethylcyclohexylmethylamine, triethylamine, diethylenetriamine, tetramethylethylenediamine, 2,2-dimethyl-1,3-propanediamine, tris(2-aminoethyl)amine, and hexamethylenetetramine.

8. The preparation method according to claim 6, characterized in that, The polyisocyanate is one or a mixture of 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, hydrogenated phenyl diisocyanate, cyclohexane-1,4-diisocyanate, norbornene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, methylcyclohexyl diisocyanate, lysine diisocyanate, a dimer of hexamethylene diisocyanate, a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, a trimer of pentamethylene diisocyanate, a biuret of hexamethylene diisocyanate, a biuret of isophorone diisocyanate, an adduct of hexamethylene diisocyanate, a urethane of hexamethylene diisocyanate, an adduct of isophorone diisocyanate, and a prepolymer of hexamethylene diisocyanate.

9. The preparation method according to any one of claims 2 to 5, characterized in that, The alkali metal salt includes one or more of sodium carbonate, sodium chloride, calcium chloride, sodium sulfate, potassium sulfite, bisulfite, sodium bicarbonate, and potassium chloride. The emulsifier comprises one or more of the following: dodecyltrimethylamine oxide, dodecyldimethylamine oxide, cocamidopropylamine oxide, polyacrylamide, polyguanidine carbonate, sodium α-alkenyl sulfonate, potassium lauryl phosphate, potassium laureth-3 phosphate, fatty acid soap, sodium ethoxylated alkyl sulfate, disodium lauryl sulfosuccinate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, phosphate, sodium polyacrylate, laureth-4, polyvinylpyrrolidone, polyvinyl alcohol, Tween series, hydroxyethyl cellulose, and isotridecyl alcohol polyoxyethylene ether.

10. The preparation method according to any one of claims 1 to 5, characterized in that, The oil phase also contains 0.1-15% oil phase regulator, which is one or a mixture of isopropyl palmitate, isopropyl myristate, caprylic triglyceride, caprylic triglyceride, benzyl benzoate, silicone oil, isoparaffin hydrocarbon, dioctyl adipate, triethyl citrate, methyl rosinate, benzyl salicylate, and D-limonene.

11. Flavor microcapsules prepared by the method according to any one of claims 1 to 10.

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