Thermally expandable microspheres, their preparation methods and applications

Abstract

This application relates to the field of polymer materials technology, and particularly to a thermally expandable microsphere, its preparation method, and its application. The thermally expandable microsphere comprises a shell and a core encapsulated by the shell. The shell is made of a thermoplastic polymer, and the core is made of a foaming agent. The thermoplastic polymer satisfies the following conditions: (1) the total residual monomer content of the thermoplastic polymer is ≤1000ppm; (2) the foaming agent loss rate after heating the thermally expandable microsphere at 50°C for 2 hours is ≤5%. The above-mentioned thermally expandable microsphere uses a thermoplastic polymer with low residual monomer content and low foaming agent loss rate when encapsulated as the shell, which is not only safe and environmentally friendly, but also ensures that the thermally expandable microsphere has good airtightness and expansion performance.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and in particular to a thermally expandable microsphere, its preparation method, and its application. Background Technology

[0002] Thermally expandable microspheres are core-shell polymer materials consisting of a thermoplastic polymer shell encapsulating a foaming agent inside. When heated, the internal foaming agent core vaporizes, generating internal pressure, which increases with rising temperature. When the temperature exceeds the softening point of the thermoplastic polymer, the volume of the thermally expandable microspheres begins to increase under this internal pressure. Utilizing the expansion properties of thermally expandable microspheres, they can be applied in many situations, such as as lightweight fillers, polishing materials, thermal insulation materials, sound-absorbing materials, packaging materials, or elastic materials.

[0003] The thermoplastic polymer shell of thermally expandable microspheres is formed by monomer polymerization. Many preparation methods leave behind a significant amount of unreacted monomers, many of which are toxic or harmful, such as acrylonitrile and vinylidene chloride. This limits the application of thermally expandable microspheres in many fields. Although some methods for removing residual monomers have been reported, many of these methods have limited effectiveness. In some cases, while some residual monomers may be removed, the polymerization of the thermoplastic polymer may be impaired, compromising the gas tightness of the polymer and negatively impacting the expansion properties of the thermally expandable microspheres. Summary of the Invention

[0004] Based on this, the first aspect of this application provides a thermally expandable microsphere, the technical solution of which is as follows:

[0005] A thermally expandable microsphere includes a shell and a core encapsulated by the shell, wherein the shell is made of a thermoplastic polymer and the core is made of a foaming agent;

[0006] The thermoplastic polymer satisfies the following conditions:

[0007] (1) The total content of residual monomers in the thermoplastic polymer is ≤1000ppm;

[0008] (2) Ensure that the foaming agent loss rate of the thermal expansion microspheres after heating at 50°C for 2 hours is ≤5%.

[0009] The aforementioned thermally expandable microspheres use a thermoplastic polymer with low residual monomer content and minimal foaming agent loss during coating as the shell. This not only ensures safety and environmental friendliness but also effectively guarantees product performance stability during subsequent storage and use, ensuring good airtightness and expansion performance. Expansion performance refers to the large expansion volume and high expansion ratio of the microspheres when heated, as the foaming agent vaporizes.

[0010] Optionally, the total content of residual monomers in the thermoplastic polymer is ≤900 ppm. Further, the total content of residual monomers is ≤500 ppm. Further, the total content of residual monomers is ≤100 ppm. Further, the total content of residual monomers is ≤90 ppm. Further, the total content of residual monomers is ≤80 ppm. Further, the total content of residual monomers is ≤70 ppm. The lower the content of residual monomers, the more environmentally friendly it is, and the more suitable the thermally expanded microspheres are for applications close to daily life, such as as lightweight and elastic materials in products that come into close contact with people, such as ultra-lightweight concrete, sealing strips, and wine stoppers.

[0011] Optionally, the foaming agent loss rate of the thermally expandable microspheres after heating at 50°C for 2 hours is ≤4%. Optionally, the foaming agent loss rate of the thermally expandable microspheres after heating at 50°C for 2 hours is ≤3%.

[0012] Optionally, the raw materials for the thermoplastic polymer include polymeric monomers, crosslinking agents, and composite initiators.

[0013] Optionally, the polymerizing monomer includes an olefinically unsaturated monomer. The olefinically unsaturated monomer is a monomer comprising an alkenyl group. Different olefinically unsaturated monomers have different reactivity, resulting in different expansion ratios of the thermoplastic polymers formed through polymerization.

[0014] Optionally, the olefinically unsaturated monomer includes one or more of acrylonitrile monomers, acrylate monomers, acrylic monomers, alkyl vinyl ester monomers, styrene monomers, halogenated olefin monomers, and acrylamide monomers. Optionally, the olefinically unsaturated monomer includes two or more of acrylonitrile monomers, acrylate monomers, acrylic monomers, alkyl vinyl ester monomers, styrene monomers, halogenated olefin monomers, and acrylamide monomers.

[0015] Optionally, the polymerizing monomer includes acrylonitrile monomers, and the residual acrylonitrile monomer content of the thermoplastic polymer is ≤400ppm, further ≤200ppm, further ≤100ppm, further ≤60ppm, further ≤50ppm, and further ≤20ppm.

[0016] Optionally, the polymerizing monomer includes acrylate monomers, and the residual acrylate monomer content of the thermoplastic polymer is ≤400ppm, further ≤200ppm, further ≤100ppm, further ≤60ppm, further ≤50ppm, and further ≤20ppm.

[0017] Optionally, the polymeric monomer includes acrylic monomers, and the residual acrylic monomer content of the thermoplastic polymer is ≤400ppm, further ≤200ppm, further ≤100ppm, further ≤60ppm, further ≤50ppm, and further ≤35ppm.

[0018] Optionally, the polymerizing monomer includes halogenated olefin monomers, and the content of residual halogenated olefin monomers in the thermoplastic polymer is ≤400ppm, further ≤200ppm, further ≤100ppm, further ≤60ppm, and further ≤50ppm.

[0019] Optionally, the olefinically unsaturated monomer includes acrylonitrile monomers and halogen-containing olefin monomers. In this case, the thermoplastic polymer formed by the polymerization reaction has good airtightness and excellent expansion properties. Optionally, the mass percentage of acrylonitrile monomers in the polymerizing monomer is 20% to 80%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%. More preferably, it is 25% to 80%. Optionally, the mass percentage of halogen-containing olefin monomers in the polymerizing monomer is 10% to 60%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%, more preferably 20% to 50%.

[0020] Acrylonitrile monomers include one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaric acid. Acrylate monomers include one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, isobornyl acrylate, isobornyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, allyl acrylate, and allyl methacrylate. Acrylic monomers include one or more of methacrylic acid and acrylic acid. Alkyl vinyl ester monomers include one or more of vinyl acetate, vinyl laurate, and vinyl stearate. Styrene monomers include one or more of styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, and halostyrene. Halogenated olefin monomers include haloethylene. Haloethylene includes one or more of vinylidene dihaloethylene and n-vinyl haloethylene. Vinylidene dihaloethylene can be vinylidene chloride. Acrylamide monomers include one or more of acrylamide, N-isopropylacrylamide, and methacrylamide.

[0021] Many of the aforementioned polymerizable monomers are toxic and harmful, such as acrylonitrile and vinylidene chloride (low boiling point, extremely flammable, and carcinogenic). During subsequent heating and foaming processes, these monomers can leach into the environment, causing environmental pollution and personal injury. When the polymerizable monomer includes acrylonitrile, the acrylonitrile content of the thermoplastic polymer in this application can be controlled below 100 ppm. Further controlled below 50 ppm. Further controlled below 40 ppm. Further controlled below 30 ppm. Further controlled below 20 ppm. When the polymerizable monomer includes vinylidene chloride, the vinylidene chloride content of the thermoplastic polymer in this application can be controlled below 100 ppm. Further controlled below 80 ppm. Further controlled below 70 ppm. Further controlled below 60 ppm. Further controlled below 50 ppm. Currently reported methods for removing residual monomers are only applicable to water-soluble monomers and cannot remove non-water-soluble monomers; for example, they cannot remove vinylidene chloride. Furthermore, while some methods for removing residual monomers can remove some of them, they affect the polymerization of thermoplastic polymers, compromise their airtightness, and adversely affect the expansion performance of the thermally expandable microspheres. In this application, however, there are fewer residual water-soluble monomers (e.g., acrylonitrile) and non-water-soluble monomers (e.g., vinylidene chloride), and the thermoplastic polymer has good airtightness, resulting in a high expansion ratio of the thermally expandable microspheres.

[0022] Optionally, the crosslinking agent includes one or more of bifunctional and trifunctional crosslinking agents. Optionally, the crosslinking agent includes one or more of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane triethylene glycol triacrylate, diallyl phthalate, diallyl carbonate, triallyl isocyanate, triallyl isocyanurate, trimethylolpropane diallyl ether, trimethylallyl isocyanate, pentaerythritol triallyl ether, 2,2-bis(allyloxymethyl)-1-butanol, 1,6-hexanediol diacrylate, and polyethylene glycol dimethacrylate.

[0023] Optionally, the mass ratio of the crosslinking agent to the monomer is (0.01~5):100. For example, it can be 0.01:100, 0.05:100, 0.1:100, 0.3:100, 0.5:100, 0.8:100, 1:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, or 5:100. Preferably, the mass ratio is (0.1~2):100. More preferably, the mass ratio is (0.2~1):100.

[0024] Optionally, the composite initiator includes a first initiator and a second initiator, wherein the 10-hour half-life temperature of the first initiator is at least 10°C lower than the 10-hour half-life temperature of the second initiator.

[0025] The 10-hour half-life temperature refers to the time required for the concentration or quantity of the initiator to decrease to half of its initial value at that temperature, which is 10 hours. Optionally, the 10-hour half-life temperature of the first initiator is at least 20°C lower than that of the second initiator. Optionally, the 10-hour half-life temperature of the first initiator is at most 35°C lower than that of the second initiator.

[0026] Optionally, the first initiator and the second initiator independently include free radical initiators. The free radical initiators include one or more of organic peroxide initiators and azo initiators. Optionally, the peroxide initiator includes tert-amyl peroxypentanoate, di(2-ethylhexyl) peroxydicarbonate, isopropyl phenyl neodecanoate, tert-butyl oxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl monocarbonate, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,3-di(2-tert-butylperoxyisopropyl)benzene and other dialkyl peroxides, 1,3-di(2-tert-butylperoxyisopropyl)benzene and other dialkyl peroxides, 1,1-di(tert-butylperoxy)cyclohexane, 1,1 One or more of the following: di(tert-hexylperoxy)cyclohexane, methyl ethyl ketone peroxide, tert-butyl hydroperoxide, tert-pentyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, dodecyl peroxide, benzoyl peroxide, diisopropyl peroxide, dicyclohexyl peroxide, bis(4-tert-butylcyclohexyl) peroxide, tert-butyl benzoyl peroxide, tert-butyl pentyl peroxide, ditert-butyl peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-oxoalkyl hydroperoxide, and bis(2-phenoxyethyl) peroxide. Optionally, the azo initiator includes one or more of 2,2'-azobisisobutyronitrile, azobisisovalerate, 2,2'-azobis(2,4-dimethyl)valerate, azobisisoheptanenitrile, 2,2'-azobis(2-methylpropionate), azobisisobutyronitrile, azobisisobutyronitrile, and dimethyl azobisisobutyrate.

[0027] The following are examples of the 10-hour half-lives of free radical initiators: tert-amyl peroxypentanoate (55℃), 2,2'-azobis(2,4-dimethylpentanonitrile) (51℃), 2,2'-azobis(2-methylpropionate) (66℃), di(2-ethylhexyl) peroxydicarbonate (47℃), isopropylphenyl neodecanoate (38℃), tert-butyl oxyacetate (110℃), tert-butyl peroxybenzoate (105℃), 2,2'-azobisisobutyronitrile (65℃), tert-butylperoxyisopropyl monocarbonate (98℃), and 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane. The following initiators are available: 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (118℃), dialkyl peroxides such as 1,3-di(2-tert-butylperoxyisopropyl)benzene (118℃~120℃), 1,1-di(tert-butylperoxy)cyclohexane (97℃), 1,1-di(tert-hexylperoxy)cyclohexane (94℃), methyl ethyl ketone peroxide (105℃), tert-butyl hydroperoxide (172℃), tert-amyl hydroperoxide (153℃), 1,1,3,3-tetramethylbutyl hydroperoxide (140℃), cumene hydroperoxide (158℃), and diisopropylbenzene hydroperoxide (140℃). The first and second initiators can be selected based on the above 10-hour half-lives.

[0028] Optionally, the mass ratio of the composite initiator to the monomer is (0.01~5):100. For example, it can be 0.01:100, 0.05:100, 0.1:100, 0.3:100, 0.5:100, 0.8:100, 1:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, or 5:100. Preferably, the mass ratio is (0.1~3):100.

[0029] Optionally, the molar ratio of the first initiator to the second initiator is (90~100):1. For example, it can be 90:1, 92:1, 94:1, 96:1, 98:1, or 100:1. Preferably, the molar ratio is (95~100):1.

[0030] Optionally, the foaming agent is a substance that can be vaporized by heat, such as a liquid substance that can be vaporized by heat. Optionally, the foaming agent includes C3-C13 alkane foaming agents, such as C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, and C13 alkane foaming agents. Optionally, the foaming agent includes one or more of the following: n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, n-hexane isomers, n-heptane, n-heptane isomers, n-octane, n-octane isomers, nonane, n-nonane isomers, n-decane, n-decane isomers, n-undecane, n-undecane isomers, n-dodecane, n-dodecane isomers, n-tridecane, and n-tridecane isomers. Preferably, the foaming agent includes one or more of n-butane, isobutane, isopentane, neopentane, n-pentane, n-hexane, n-heptane, isooctane, n-octane, and petroleum ether.

[0031] Optionally, the mass percentage of the foaming agent in the thermally expandable microspheres is 20% to 30%. For example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%.

[0032] Optionally, the core material further includes a gas migration inhibitor. The gas migration inhibitor helps reduce the escape of the thermoplastic polymer shell caused by the foaming agent during heating of the thermally expanding microspheres. Optionally, the boiling point of the gas inhibitor is higher than the glass transition temperature of the thermoplastic polymer. Optionally, the gas inhibitor includes one or more of hydrocarbon compounds, carboxylic acid compounds, ester compounds, and alcohol compounds. Preferably, it includes hydrocarbon compounds. Preferably, it includes naphthenic oils.

[0033] Optionally, the mass ratio of the gas inhibitor to the foaming agent is (0~30):100. For example, the mass ratio can be 0:100, 0.1:100, 1:100, 3:100, 5:100, 8:100, 10:100, 12:100, 15:100, 18:100, 20:100, 22:100, 25:100, or 28:100. When the mass ratio of the gas inhibitor to the foaming agent is 0:100, it indicates that no gas inhibitor is added.

[0034] Optionally, the particle size D of the thermally expandable microspheres 50 The size ranges from 1 μm to 100 μm. For example, it can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 80 μm, 90 μm, or 100 μm. Preferably, it is 5 μm to 50 μm.

[0035] Optionally, the PDI of the thermally expanded microspheres is 1~1.1, where PDI = (D 90 -D 10 ) / D 50 For example, it can be 1, 1.01, 1.05, 1.08, 1.0, or 1.1.

[0036] Preferably, the monomers of the thermoplastic polymer include acrylonitrile, vinylidene chloride, and methyl acrylate, and the maximum expansion ratio of the thermally expandable microspheres is ≥50 under a pressure of 0.06 N. More preferably, it is 60-75. The initial expansion temperature of the thermally expandable microspheres is ≥90°C. More preferably, it is 95°C-105°C. The maximum expansion temperature of the thermally expandable microspheres is ≥120°C. More preferably, it is 130°C-140°C.

[0037] Preferably, the monomers of the thermoplastic polymer include acrylonitrile, vinylidene chloride, and methacrylic acid, and the maximum expansion ratio of the thermally expandable microspheres is ≥50 under a pressure of 0.06 N, further 85~100; the initial expansion temperature of the thermally expandable microspheres is ≥90℃, further 130℃~140℃; and the maximum expansion temperature of the thermally expandable microspheres is ≥120℃, further 150℃~160℃.

[0038] Preferably, the monomers of the thermoplastic polymer include acrylonitrile, vinylidene chloride, and methacrylonitrile, and the maximum expansion ratio of the thermally expandable microspheres is ≥50 under a pressure of 0.06 N. More preferably, it is 90~110. The initial expansion temperature of the thermally expandable microspheres is ≥90℃. More preferably, it is 140℃~155℃. The maximum expansion temperature of the thermally expandable microspheres is ≥120℃. More preferably, it is 160℃~180℃.

[0039] The second aspect of this application provides a method for preparing thermally expandable microspheres, the technical solution of which is as follows:

[0040] A method for preparing thermally expandable microspheres includes the following steps:

[0041] A polymeric monomer, a crosslinking agent, a foaming agent, and a composite initiator are mixed to obtain an oil phase mixture, wherein the composite initiator includes a first initiator and a second initiator, and the 10-hour half-life temperature of the first initiator is at least 10°C lower than the 10-hour half-life temperature of the second initiator.

[0042] The oil phase mixture and the aqueous phase dispersion medium are mixed to obtain a suspension;

[0043] The suspension undergoes a polymerization reaction, which includes the following procedure: polymerization reaction at a first temperature followed by polymerization reaction at a second temperature; wherein the first temperature is not less than the 10-hour half-life temperature of the first initiator and is less than the 10-hour half-life temperature of the second initiator, the second temperature is not less than the 10-hour half-life temperature of the second initiator, and the molar ratio of the first initiator and the second initiator and other parameters of the polymerization reaction are controlled to obtain the polymer expanded microspheres including a shell and a core covered by the shell, wherein the material of the shell includes a thermoplastic polymer, and the material of the core includes a foaming agent; the thermoplastic polymer satisfies the following conditions: (1) the total content of residual monomers of the thermoplastic polymer is ≤1000ppm; (2) the foaming agent loss rate of the thermally expanded microspheres after heating at 50°C for 2 hours is ≤5%.

[0044] The above method uses a composite initiator, which includes a first initiator and a second initiator. The 10-hour half-life temperature of the first initiator is at least 10°C lower than that of the second initiator. During the polymerization reaction, polymerization occurs first at a first temperature and then at a second temperature. The first temperature is not less than the 10-hour half-life temperature of the first initiator and is less than the 10-hour half-life temperature of the second initiator. The second temperature is not less than the 10-hour half-life temperature of the second initiator. With this design, the first temperature and the 10-hour half-life temperature of the first initiator are... Matching the 0-hour half-life temperature, the first initiator generates active free radicals in the early stage of polymerization, initiating monomer polymerization and chain growth to form the main body of the thermally expandable microsphere shell. As polymerization time increases, the content of the first initiator and monomers decreases, the polymerization rate slows down and tends to plateau, and the monomer conversion rate approaches its limit. At this point, the temperature is raised to a second temperature, which matches the 10-hour half-life temperature of the second initiator, for secondary initiation. This increases the number of active free radicals in the polymerization system, consuming the remaining monomers and thus improving the monomer conversion rate and reducing the residual monomer content. Simultaneously, controlling the molar ratio of the first and second initiators and other polymerization parameters ensures the airtightness of the thermoplastic polymer shell, thereby guaranteeing the expansion performance of the thermally expandable microspheres.

[0045] In addition, several methods for removing acrylonitrile have been reported, such as using oxyacids of sulfur or their salts or derivatives, using alkali metal sulfites or ammonium sulfites, and using primary amines, secondary amines, primary alkanolamines, secondary alkanolamines, secondary alkyl alkanolamines, and sodium sulfide for cyanoethylation. However, many of these methods require the addition of other additives after the polymerization reaction, making the process cumbersome. Compared to these methods, this application allows for the complete conversion of acrylonitrile monomers during the polymerization reaction, reducing monomer residues in the final thermoplastic polymer, without introducing other substances, and eliminating the need for post-treatment of any added substances.

[0046] The polymer monomers, crosslinking agents, foaming agents, and composite initiators in the oil phase mixture are described above and will not be repeated here.

[0047] Optionally, mixing the polymerizing monomer, crosslinking agent, foaming agent, and composite initiator further includes the step of adding a gas migration inhibitor. In this case, the oil phase mixture also includes a gas migration inhibitor, which is described above and will not be repeated here.

[0048] Optionally, the aqueous dispersion medium includes water, electrolyte, stabilizer, and polymerization inhibitor.

[0049] Optionally, the electrolyte comprises a metal salt. Optionally, the metal salt comprises one or more of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium sulfate, potassium sulfate, magnesium sulfate, sodium carbonate, potassium carbonate, sodium nitrate, and potassium nitrate.

[0050] Optionally, the mass ratio of the electrolyte to water is (1~50):100. For example, the mass ratio can be 1:100, 2:100, 5:100, 8:100, 10:100, 12:100, 15:100, 18:100, 20:100, 22:100, 25:100, 28:100, 30:100, 32:100, 35:100, 38:100, 40:100, 42:100, 45:100, 48:100, or 50:100. Preferably, the mass ratio is (10~30):100.

[0051] Optionally, the stabilizer comprises one or more of colloidal silica, colloidal calcium carbonate, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, aluminum hydroxide sol, ferric hydroxide, calcium sulfate, calcium oxalate, calcium carbonate, barium sulfate, barium carbonate, magnesium carbonate, and calcium phosphate. Preferably, the stabilizer comprises one or more of colloidal silica, magnesium hydroxide, and calcium hydroxide. Optionally, the colloidal silica contains 20% to 30% silica by mass. For example, the mass percentages are 20%, 25%, and 30%.

[0052] Optionally, the mass ratio of the stabilizer to water is (1~20):100. For example, the mass ratio can be 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 10:100, 11:100, 13:100, 15:100, 17:100, 19:100, or 20:100. Preferably, the mass ratio is (5~15):100.

[0053] Optionally, the polymerization inhibitor is an aqueous polymerization inhibitor. Since some polymeric monomers (e.g., acrylonitrile monomers) have a certain degree of water solubility, aqueous polymerization is an undesirable polymerization reaction during the polymerization process. Therefore, a polymerization inhibitor is added to inhibit polymerization through charge transfer, preventing the polymeric monomers from polymerizing in the aqueous phase. Optionally, the polymerization inhibitor includes one or more of sodium nitrite, potassium nitrite, ferric chloride, sodium sulfide, potassium dichromate, cuprous chloride, copper sulfate, titanium trichloride, sodium sulfate, and ammonium thiocyanate.

[0054] Optionally, the mass ratio of the polymerization inhibitor to water is (0.01~5):100. For example, the mass ratio can be 0.01:100, 0.1:100, 0.3:100, 0.5:100, 0.5:100, 1:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, or 5:100. Preferably, the mass ratio is (0.05~1):100.

[0055] Optionally, the aqueous dispersion medium further includes a dispersion stabilizing agent to improve the dispersion effect. Optionally, the dispersion stabilizing agent includes one or more of carboxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, tetramethylammonium chloride, polyvinyl alcohol, a water-soluble condensation product of diethanolamine and adipic acid, polyvinylimide, gelatin, casein, and albumin.

[0056] Optionally, the mass ratio of the dispersing stabilizer to water is (0~1):100. For example, it can be 0:100, 0.001:100, 0.005:100, 0.01:100, 0.05:100, 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, or 1:100. When the mass ratio of the dispersing stabilizer to water is 0:100, it indicates that no dispersing stabilizer is added.

[0057] Optionally, the pH value of the aqueous dispersion medium is 1 to 7. For example, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, or 7. Preferably, it is 3 to 5. The pH value of the aqueous dispersion medium can be adjusted by adding an acidic medium, for example, by adding hydrochloric acid to adjust the pH value of the aqueous dispersion medium to the above values.

[0058] Optionally, the mass of the oil phase mixture accounts for 15% to 30% of the total mass of the oil phase mixture and the aqueous dispersion medium. For example, 15%, 16%, 18%, 20%, 21%, 23%, 25%, 27%, 29%, 30%. Preferably, the mass of the oil phase mixture accounts for 18% to 28% of the total mass of the oil phase mixture and the aqueous dispersion medium.

[0059] Understandably, mixing an oil-phase mixture with an aqueous dispersion medium allows the oil-phase mixture to be dispersed in the aqueous dispersion medium through high-speed shearing. High-speed shearing disperses the oil-phase mixture into fine droplets in the aqueous dispersion medium, each droplet being coated with a stabilizer to prevent aggregation. Optionally, the dispersion speed is 500 rpm to 8000 rpm, for example, 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 5000 rpm, 6000 rpm, 7000 rpm, or 8000 rpm.

[0060] Understandably, the polymerization reaction of the suspension is carried out in an inert atmosphere. Optionally, the inert atmosphere includes one or more of nitrogen, argon, and helium. Optionally, the polymerization reaction is accompanied by a stirring step.

[0061] The first temperature is either the same as or higher than the 10-hour half-life temperature of the first initiator, but lower than the 10-hour half-life temperature of the second initiator. The second temperature is either the same as or higher than the 10-hour half-life temperature of the second initiator. When the first temperature matches the 10-hour half-life temperature of the first initiator, the first initiator preferentially decomposes, the polymerization reaction begins rapidly, and the monomers gradually polymerize to form a polymer. The polymer and the blowing agent separate and accumulate on the outer layer of the fine oil droplets, gradually forming a core-shell structure where the polymer encapsulates the blowing agent. During this process, as the polymerization reaction proceeds, the content of the first initiator and the monomers decreases, the polymerization reaction slows down, and the monomer conversion rate approaches its limit. At this point, the temperature is increased to the second temperature, which matches the 10-hour half-life temperature of the second initiator. The activity of the second initiator increases, generating a large number of active free radicals for secondary initiation, improving the monomer conversion rate and reducing the residual monomer content.

[0062] Optionally, after polymerization at a first temperature to a monomer conversion rate of 80% to 90%, polymerization is carried out at a second temperature. For example, polymerization is carried out at a first temperature to a monomer conversion rate of 80%, 85%, or 90%, followed by polymerization at a second temperature.

[0063] Optionally, the first temperature is 0°C to 10°C higher than the 10-hour half-life temperature of the first initiator. For example, it may be 0°C, 1°C, 3°C, 5°C, 7°C, or 10°C higher.

[0064] Optionally, the second temperature is 0°C to 20°C higher than the 10-hour half-life temperature of the second initiator. For example, it can be 0°C, 1°C, 3°C, 5°C, 7°C, 10°C, 12°C, 15°C, 18°C, or 20°C higher.

[0065] By introducing first and second initiators with different 10-hour half-lives and adjusting the polymerization temperature, more active free radicals are generated during the polymerization process, thereby improving monomer conversion and reducing residual monomer content.

[0066] In some examples, the first temperature can be between 40°C and 70°C, depending on the 10-hour half-life temperature of the first initiator. For example, it can be 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 60°C, or 70°C. The second temperature can be between 60°C and 180°C. For example, it can be 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 100°C, 150°C, or 180°C.

[0067] Optionally, the molar ratio of the first initiator to the second initiator is controlled to be (90~100):1. The molar amount of the first initiator is much larger than that of the second initiator, ensuring that the main body of the thermoplastic polymer shell is fully formed in the early stage of the polymerization reaction, preventing the later polymerization reaction from violently affecting the inner wall of the shell, and ensuring the airtightness of the thermoplastic polymer shell.

[0068] Optionally, other parameters of the polymerization reaction can be controlled to ensure that the foaming agent does not foam or that the expansion rate of the D50 particle size of the thermally expanded microspheres caused by foaming does not exceed 20%. Since the foaming agent has a low boiling point, if it foams uncontrollably during the polymerization reaction, the resulting thermally expanded microspheres will have an increased D50 particle size, which will adversely affect the airtightness and expansion performance of the microspheres. This can be addressed by controlling other parameters of the polymerization reaction, such as controlling the pressure and time of the polymerization reaction. The expansion rate of the D50 particle size of the thermally expanded microspheres caused by foaming refers to the rate of change of the D50 particle size of the foamed microspheres relative to the D50 particle size of the non-foamed thermally expanded microspheres.

[0069] In some examples, the second temperature is relatively high, and the foaming agent is prone to uncontrolled foaming. The foaming of the foaming agent can be controlled by controlling the pressure of the polymerization reaction at the second temperature.

[0070] Optionally, the reaction pressure of the polymerization reaction at the first temperature is 0.3 MPa to 0.8 MPa. For example, the reaction pressure is 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, 0.55 MPa, 0.6 MPa, 0.65 MPa, 0.7 MPa, 0.75 MPa, or 0.8 MPa.

[0071] Optionally, the polymerization reaction at the first temperature can be carried out for 15 to 20 hours. For example, the reaction time can be 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours.

[0072] Optionally, the polymerization reaction pressure at the second temperature is 1 MPa to 1.5 MPa. For example, the reaction pressure is 1 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa, or 1.5 MPa. Compared to the polymerization reaction pressure at the first temperature, the polymerization reaction pressure at the second temperature is higher, which is beneficial for suppressing the foaming expansion of the foaming agent.

[0073] Optionally, the polymerization reaction time at the second temperature is 1 to 4 hours. For example, the reaction time is 1 hour, 2 hours, 3 hours, or 4 hours. Compared to the polymerization reaction time at the first temperature, the polymerization reaction time at the second temperature is shorter, which is beneficial for suppressing the foaming expansion of the foaming agent.

[0074] This application designs the composite initiator and polymerization reaction procedure to achieve an ideal number of active free radicals in both the early and late stages of the polymerization reaction, which can improve the conversion rate of the polymer monomers and thus reduce the residual monomer content in the residual thermoplastic polymer. At the same time, the polymer shell has good airtightness and good expansion performance.

[0075] Understandably, the polymerization reaction includes a post-processing step, which may include filtration and drying.

[0076] The above-described suspension polymerization method for preparing thermally expandable microspheres is simple. A composite initiator is used in the oil phase system, and the appropriate temperature is matched within the suspension polymerization reaction program, resulting in a monomer conversion rate of over 99%. This reduces the residual monomer content in the thermoplastic polymer, and the resulting thermally expandable microspheres are safe and environmentally friendly. Simultaneously, it does not affect the airtightness of the thermoplastic polymer, ensuring the expansion performance of the thermally expandable microspheres.

[0077] The third aspect of this application provides the application of the thermally expandable microspheres as described above or prepared by the preparation method described above in lightweight fillers, polishing materials, thermal insulation materials, heat insulation materials, sound absorbing materials, packaging materials or elastic materials.

[0078] For example, thermally expanded microspheres are added to ultra-light clay as lightweight fillers, to sealing strips as elastic materials, and to wine stoppers as elastic materials. These thermally expanded microspheres have good residual monomer content, good airtightness, high expansion ratio, and are safe and environmentally friendly, which can meet the application fields that are close to daily life and have a large number of human contacts. Detailed Implementation

[0079] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0081] the term

[0082] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0083] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0084] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0085] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0086] In this application, numerical intervals (i.e. numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the above-mentioned numerical intervals are considered continuous, and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints.

[0087] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0088] In this application, percentage content refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures, unless otherwise specified.

[0089] In this application, unless otherwise specified, percentage concentrations refer to final concentrations. The final concentration refers to the percentage of the added component in the system after its addition.

[0090] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available. Unless otherwise specified, the instruments used are all commercially available. Unless otherwise specified, the processes involved are conventionally selected by those skilled in the art.

[0091] (1) Alkene unsaturated monomers

[0092] Acrylonitrile, AN, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0093] Methacrylonitrile, MAN, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0094] Vinylidene chloride, VDC, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0095] Methyl acrylate, MA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0096] Methacrylic acid, MAA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0097] (2) Crosslinking agent

[0098] Ethylene glycol dimethacrylate, EGDMA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0099] Trimethylolpropane triacrylate, TMPTA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0100] (3) First initiator

[0101] tert-amyl peroxypentanoate (TAPV), 10-hour half-life at 54°C, molecular weight 188.3, ​​Shanghai Aladdin Biochemical Technology Co., Ltd.

[0102] Di(2-ethylhexyl) peroxide dicarbonate, EHP, 10h half-life at 47℃, molecular weight 346.4, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0103] (4) Second initiator

[0104] Azobisisobutyronitrile (AIBN), 10h half-life at 65℃, molecular weight 164.2, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0105] Benzoyl peroxide, BPO, 10h half-life at 71℃, molecular weight 242.2, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0106] (5) Foaming agent

[0107] Isobutane, Aladdin Group Ltd., reagent grade 99%.

[0108] Isopentane, Aladdin Group Ltd., reagent grade 99%.

[0109] (6) Gas migration inhibitors

[0110] Naphthenic oil, Aladdin Group Co., Ltd., reagent grade 99%.

[0111] (7) Stabilizer

[0112] Colloidal silica, with a silica mass percentage of 25%, manufactured by Guangdong Huierte Nanotechnology Co., Ltd.

[0113] (8) Electrolytes

[0114] Sodium chloride, Aladdin Group Co., Ltd., reagent grade 99%.

[0115] (9) Polymerization inhibitor

[0116] Sodium nitrite, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0117] Example 1

[0118] This embodiment provides a thermally expandable microsphere and its preparation method, as shown in Tables 1 and 2. The steps are as follows:

[0119] (1) Preparation of aqueous dispersion medium: by mass, add 150 parts of sodium chloride, 80 parts of colloidal silica (containing 25% silica) and 2 parts of sodium nitrite to 800 parts of deionized water, stir thoroughly, and adjust the pH of the system to 3.5 to obtain aqueous dispersion medium.

[0120] (2) Preparation of oil phase mixture: By mass, 190 parts AN, 80 parts VDC, 45 parts MA, 40 parts isobutane, 1 part EGDMA, 1.883 parts TAPV (molar amount 0.01), 0.0164 parts AIBN (molar amount 0.0001) and 6 parts naphthenic oil are thoroughly mixed to obtain oil phase mixture;

[0121] (3) Disperse the oil phase mixture obtained in step (2) into the aqueous phase dispersion medium obtained in step (1), and disperse it at high speed of 1600 rpm for 20 min in a closed container to obtain a suspension;

[0122] (4) The suspension obtained in step (3) was subjected to polymerization under nitrogen atmosphere and stirring at 100 rpm. The polymerization procedure was as follows: the initial reaction pressure was controlled at 0.5 MPa, and the polymerization reaction was carried out at 55°C for 18 h, with a monomer conversion rate of 85%. Subsequently, the temperature and pressure were increased to 1.2 MPa, and the polymerization reaction was carried out at 80°C for 3 h. After the polymerization reaction was completed, the product was filtered and dried to obtain the thermally expandable microspheres.

[0123] Examples 2-6

[0124] Examples 2-6 provide a thermally expandable microsphere and its preparation method, which are basically the same as those in Example 1. The main difference lies in the composition of the oil phase mixture and the polymerization reaction procedure. For details, please refer to Table 1 and Table 2.

[0125] Table 1

[0126]

[0127] Note: "--" indicates that it has not been added.

[0128] Table 2

[0129]

[0130] Comparative Examples 1-7

[0131] Comparative Examples 1-7 provide thermally expandable microspheres and their preparation methods, which are basically the same as those in Example 1. The main differences are in the composition of the oil phase mixture and the polymerization reaction procedure. For details, please refer to Tables 3 and 4.

[0132] Table 3

[0133]

[0134] Note: "--" indicates that it has not been added.

[0135] Table 4

[0136]

[0137] The performance of the thermally expanded microspheres prepared in Examples 1-6 and Comparative Examples 1-7 was tested, and the specific methods included:

[0138] (1) Particle size test

[0139] The particle size of thermally expanded microspheres was measured using a laser particle size analyzer (Bettersize 2600) in a wet method. The light-blocking ratio was 5-20%, and water was used as the test medium. The median particle size D was measured. 50 D 90 and D 10 Particle size distribution PDI = (D 90 -D 10 ) / D 50 ;

[0140] (2) Expansion performance test

[0141] The tests were conducted using a static thermomechanical analyzer (TMA, Mettler TMA / SDTA2+) at a heating rate of 15℃ / min. The specific test procedures are as follows:

[0142] Add 1 mg of the thermal expansion microspheres to be tested to a 150 μL ceramic crucible, and place a matching diameter shim on top of the microsphere layer to prepare the sample. Measure the sample height by applying a force of 0.06 N from above using a pressure bar. While applying a force of 0.06 N using the pressure bar, heat the sample from 20 °C to 300 °C at a rate of 15 °C / min, and measure the displacement of the pressure bar in the vertical direction. Record the temperature at which the displacement begins in the positive direction as the initial expansion temperature (Tstart), and the temperature at which the maximum displacement is displayed as the maximum expansion temperature (Tmax). The ratio of the maximum height during the expansion process to the initial sample height is the expansion ratio.

[0143] (3) Residual monomer content

[0144] The test was conducted using a gas chromatograph (Shimadzu GC-2010 Pro), and the test steps are as follows:

[0145] Chromatographic conditions: Initial temperature 40℃, hold for 2 min, increase to 100℃ at a rate of 5℃ / min, hold for 2 min, then increase to 200℃ at a rate of 6℃ / min and hold for 5 min; nitrogen as carrier gas, flow rate 2.0 mL / min; when water is used as solvent, headspace vial equilibration temperature 70~85℃, headspace vial equilibration time 30~60 minutes; injection port temperature 200℃.

[0146] (4) Determination of foaming agent loss rate

[0147] Weigh the thermally expanded microspheres and record the weight as W1. Place the thermally expanded microspheres in a container and weigh the total weight of the microspheres and the container, recording it as W2. Place the container containing the thermally expanded microspheres in an oven and heat it at 50°C for 2 hours. After removing it, measure the total weight of the two, which is W3. The loss rate of the foaming agent is calculated using the following formula:

[0148] Foaming agent loss rate (%) = (W3 - W2) / W1 × 100%

[0149] The test results are shown in Tables 5 and 6:

[0150] Table 5

[0151]

[0152] Table 6

[0153]

[0154] Note: "--" indicates that it has not been added.

[0155] According to the test data in Tables 5 and 6:

[0156] (1) In Examples 1-6, under different polymerizable monomers, a first initiator and a second initiator were added, and in accordance with the polymerization reaction procedure, there were ideal numbers of active free radicals in the early and late stages of the polymerization reaction, the monomer conversion rate was high, the residual monomer content was low, and the loss rate of thermal expansion microsphere foaming agent was low, indicating good air tightness and excellent expansion performance.

[0157] (2) By comparing Examples 1-2 and Comparative Examples 1-2, it can be seen that using a single type of initiator, whether it is a single type of first initiator or a single type of second initiator, will result in a high residual monomer content and poor air tightness.

[0158] (3) Through the comparison of Examples 3-4 and Comparative Examples 3-4, it can be seen that when two initiators with similar 10-hour half-life temperatures are used, the problem of high residual monomer content will also occur. At the same time, the two initiators jointly initiate polymerization in the early stage, which leads to deviations in the formation of polymer shell, ultimately affecting the airtightness of microspheres, and the expansion ratio decreases, resulting in poor expansion performance.

[0159] (4) By comparing Examples 5-6 and Comparative Examples 5-6, it can be seen that when the molar ratio of the first initiator and the second initiator is 50:1, the content of the second initiator is higher, the number of active free radicals in the later polymerization is greater, the molecular chain segments are shorter, the reaction is more intense, the formation of the inner wall of the polymer shell is affected, the air tightness is reduced, and the expansion ratio is reduced, resulting in poor expansion performance.

[0160] (5) By comparing Example 5 and Comparative Example 7, it can be seen that when the reaction pressure of polymerization at the second temperature is low, the foaming agent will be vaporized to a certain extent during the reaction process, which will increase the D50 of the formed microspheres (the change range is (28.66-20.51) / 20.51×100%=39.7%), affecting the airtightness and expansion performance of the final microspheres.

[0161] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0162] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing thermally expandable microspheres, characterized in that, Includes the following steps: A polymerizing monomer, a crosslinking agent, a foaming agent, and a composite initiator are mixed to obtain an oil phase mixture. The composite initiator includes a first initiator and a second initiator. The 10-hour half-life temperature of the first initiator is at least 10°C lower than that of the second initiator. The polymerizing monomer includes an olefinically unsaturated monomer, which includes one or more of acrylonitrile monomers, acrylate monomers, acrylic monomers, alkyl vinyl ester monomers, styrene monomers, halogen-containing olefin monomers, and acrylamide monomers. The oil phase mixture and the aqueous phase dispersion medium are mixed to obtain a suspension; The suspension undergoes a polymerization reaction, which includes the following procedure: polymerization at a first temperature, followed by polymerization at a second temperature; wherein the first temperature is 0°C to 10°C higher than the 10-hour half-life temperature of the first initiator and lower than the 10-hour half-life temperature of the second initiator, the second temperature is 0°C to 20°C higher than the 10-hour half-life temperature of the second initiator, and the molar ratio of the first initiator to the second initiator is controlled to be (90~100):1; the reaction pressure of the polymerization reaction at the first temperature is 0.3MPa to 0.8MPa; and the polymerization reaction at the first temperature... The reaction time of the polymerization reaction is 15h~20h, the reaction pressure of the polymerization reaction at the second temperature is 1MPa~1.5MPa, and the reaction time of the polymerization reaction at the second temperature is 1h~4h, to obtain polymer expanded microspheres including a shell and a core covered by the shell. The material of the shell includes a thermoplastic polymer, and the material of the core includes a foaming agent. The thermoplastic polymer meets the following conditions: (1) the total content of residual monomers of the thermoplastic polymer is ≤1000ppm; (2) the foaming agent loss rate of the thermally expanded microspheres after heating at 50°C for 2h is ≤5%.

2. The method for preparing thermally expandable microspheres according to claim 1, characterized in that, The reaction pressure of the polymerization reaction at the first temperature is controlled at 0.3 MPa to 0.8 MPa, the reaction time of the polymerization reaction at the first temperature is 15 h to 20 h, the reaction pressure of the polymerization reaction at the second temperature is 1 MPa to 1.5 MPa, and the reaction time of the polymerization reaction at the second temperature is 1 h to 4 h, to ensure that the foaming agent does not foam or the expansion rate of the thermal expansion microspheres caused by foaming does not exceed 20%.

3. The method for preparing thermally expandable microspheres according to claim 1, wherein after polymerization at a first temperature to a monomer conversion rate of 80%~90%, polymerization is carried out at a second temperature.

4. The method for preparing thermally expandable microspheres according to any one of claims 1 to 3, characterized in that, Includes at least one of the following features: (1) The first initiator and the second initiator each independently comprise tert-amyl peroxypentanoate, di(2-ethylhexyl) peroxydicarbonate, isopropylphenyl neodecanoate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl monocarbonate, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,3-di(2-tert-butylperoxyisopropyl)benzene, 1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert-hexylperoxy)cyclohexane, methyl ethyl ketone peroxide, tert-butyl hydroperoxide, tert-amyl hydroperoxide, and 1,1,3,3-tetramethylbutyl peroxide. Hydrogen, cumene hydroperoxide, diisopropylbenzene hydroperoxide, dodecyl peroxide, benzoyl peroxide, diisopropyl peroxide dicarbonate, dicyclohexyl peroxide dicarbonate, bis(4-tert-butylcyclohexyl) peroxide dicarbonate, tert-butyl benzoyl peroxide, tert-butyl tert-butyl pentyl peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-oxoalkyl hydroperoxide and bis(2-phenoxyethyl) peroxide dicarbonate, 2,2'-azobisisobutyronitrile, azobisisovalerate, 2,2'-azobis(2,4-dimethyl)valerate, azobisisoheptane, 2,2'-azobis(2-methylpropionate), azobisisobutyronitrile, azobiscyclohexyl formonitrile and dimethyl azobisisobutyrate; (2) The mass ratio of the composite initiator to the monomer is (0.01~5):100; (3) The crosslinking agent includes one or more of the following: trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane triethylene glycol triacrylate, diallyl phthalate, diallyl carbonate, triallyl isocyanate, triallyl isocyanurate, trimethylolpropane diallyl ether, trimethylallyl isocyanate, pentaerythritol triallyl ether, 2,2-bis(allyloxymethyl)-1-butanol, 1,6-hexanediol diacrylate and polyethylene glycol dimethacrylate; (4) The mass ratio of the crosslinking agent to the monomer is (0.01~5):100; (5) The foaming agent includes C3-C13 alkane foaming agents; (6) The mass percentage of the foaming agent in the thermally expanding microspheres is 20%~30%; (7) Mixing the polymer monomer, crosslinking agent, foaming agent and composite initiator, and also including the step of adding a gas migration inhibitor; (8) The aqueous dispersion medium includes water, electrolyte, stabilizer and polymerization inhibitor; (9) The pH value of the aqueous dispersion medium is 1~7.

5. The method for preparing thermally expandable microspheres according to claim 4, characterized in that, Includes at least one of the following features: (1) The boiling point of the gas migration inhibitor is higher than the glass transition temperature of the thermoplastic polymer; (2) The mass ratio of the gas migration inhibitor to the foaming agent is (0~30):100; (3) The electrolyte includes a metal salt; (4) The mass ratio of the electrolyte to water is (1~50):100; (5) The stabilizer includes one or more of colloidal silica, colloidal calcium carbonate, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, aluminum hydroxide sol, iron hydroxide, calcium sulfate, calcium oxalate, calcium carbonate, barium sulfate, barium carbonate, magnesium carbonate, and calcium phosphate. (6) The mass ratio of the stabilizer to water is (1~20):100; (7) The polymerization inhibitor includes one or more of sodium nitrite, potassium nitrite, ferric chloride, sodium sulfide, potassium dichromate, cuprous chloride, copper sulfate, titanium trichloride, sodium sulfate and ammonium thiocyanate; (8) The mass ratio of the polymerization inhibitor to water is (0.01~5):100; (9) The pH value of the aqueous dispersion medium is 3~5.

6. The method for preparing thermally expandable microspheres according to claim 5, characterized in that, The metal salt includes one or more of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium sulfate, potassium sulfate, magnesium sulfate, sodium carbonate, potassium carbonate, sodium nitrate, and potassium nitrate.

7. The method for preparing thermally expandable microspheres according to any one of claims 1 to 3, characterized in that, The mass of the oil phase mixture accounts for 15% to 30% of the total mass of the oil phase mixture and the aqueous dispersion medium.

8. A thermally expandable microsphere, characterized in that, It is prepared by any one of the preparation methods according to claims 1 to 7.

9. The thermally expanding microspheres according to claim 8, characterized in that, The particle size D of the thermally expanded microspheres 50 The range is from 1μm to 100μm.

10. The thermally expanding microspheres according to claim 9, characterized in that, The particle size D of the thermally expanded microspheres 50 The range is 5μm to 50μm.

11. The thermally expanding microspheres according to claim 8, characterized in that, The PDI of the thermally expanded microspheres is 1~1.1, where PDI = (D 90 -D 10 ) / D 50 .

12. The application of a thermally expandable microsphere according to any one of claims 8 to 11 or a thermally expandable microsphere prepared by any one of claims 1 to 7 in a lightweight filler, polishing material, thermal insulation material, heat insulation material, sound absorbing material, packaging material or elastic material.

Images