A kind of heat expansion microsphere and its preparation method and application

Abstract

The present invention provides a heat-expandable microsphere and a preparation method and application thereof, wherein the heat-expandable microsphere comprises an outer shell and an inner core arranged in the outer shell; the outer shell is obtained by reacting a monomer and a crosslinking agent, the monomer comprises a combination of at least two different ethylenically unsaturated monomers, the crosslinking agent comprises a combination of an acrylate crosslinking agent and an allyl crosslinking agent; the inner core comprises a foaming agent. The present invention uses the design and compounding synergistic effect of different ethylenically unsaturated monomers and crosslinking agents with different reactivity, so that each polymer component in the outer shell has a suitable crosslinking degree, the crosslinking degree of the entire heat-expandable microsphere is more uniform, the outer shell has excellent ductility, air tightness and heat resistance, so that the heat-expandable microsphere has excellent expansion performance and increases the initial expansion temperature, thereby obtaining excellent heat resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer microspheres, and in particular relates to a thermal expansion microsphere and a preparation method and application thereof. Background Art

[0002] Heat-expandable microspheres with a thermoplastic polymer as the shell and a foaming agent sealed inside are generally called heat-expandable microspheres. During the heating process, the foaming agent inside the polymer shell is vaporized, and the vapor pressure increases with the increase of temperature. When the temperature is higher than the softening point temperature of the shell, the heat-expandable microspheres begin to expand. The temperature at this time is called the starting expansion temperature (Tstart), and the temperature when the microsphere expands to the maximum volume is called the maximum expansion temperature (Tmax). Heat-expandable microspheres are generally prepared by suspension polymerization. During the suspension polymerization process, the oil phase and the water phase are generally mixed first, and polymer oil droplets are formed through high-speed dispersion shearing, and the suspension state is maintained by adding stabilizers such as magnesium hydroxide and colloidal silica, and finally polymerized into balls.

[0003] Thermal expansion microspheres are widely used in sound absorption, heat insulation, thermal insulation, lightweight and other materials due to their uniform closed pore structure, highly controllable precise foaming and good expansion ability. However, with the continuous development of aviation, aerospace, construction, automobile, energy and other fields, higher requirements are also placed on the various properties of materials. Traditional medium and low temperature thermal expansion microspheres can no longer meet current technical needs.

[0004] In order to improve the high temperature performance of heat-expandable microspheres and broaden their application range, researchers have improved the thermoplastic polymer used as the shell. For example, CN107001911A discloses a heat-expandable microsphere, which is composed of a shell containing a thermoplastic resin and a foaming agent contained in the shell and gasified by heating. The monomers for preparing the thermoplastic resin include the following three categories: a nitrile monomer (A) containing acrylonitrile and methacrylonitrile, a carboxyl-containing monomer (B), and a monomer (C) that can copolymerize with the nitrile monomer (A) and the carboxyl-containing monomer (B), wherein the monomer (C) is selected from at least one of a (meth)acrylate monomer, a (meth)acrylamide monomer, a styrene monomer, and a monomer that can react with the carboxyl group of the carboxyl monomer (B), and the proportion of acrylonitrile in the nitrile monomer (A) is 0.1-9% by weight; the heat-expandable microsphere has a high maximum expansion temperature and good heat resistance. CN101341227A discloses a heat-expandable microsphere, wherein the shell comprises a copolymer having a polymethacrylimide structure, wherein the monomers forming the copolymer having the polymethacrylimide structure comprise methacrylonitrile and methacrylic acid, and the molar ratio of the two is 1:9-9:1; the heat-expandable microsphere has high heat resistance and stable foaming behavior. CN102633936A discloses a heat-expandable thermoplastic microsphere, which is a microsphere with a core-shell structure having a thermoplastic polymer as a shell and an expandable substance as a core, wherein the thermoplastic polymer is polymerized with olefinic polymerizable monomers, specifically comprising 30-90wt% of acrylonitrile, 5-50wt% of methacrylate monomers, 1-20wt% of acrylamide monomers, 0.01-1wt% of fluorine-containing acrylate monomers, and 0-40wt% of acrylic monomers. In general, the current method for preparing high-temperature expandable microspheres is mainly to select the monomer types of thermoplastic polymers, add more monomers with high glass transition temperatures, thereby increasing the glass transition temperature of the polymer shell layer, and then allowing the microspheres to expand at higher temperatures; however, the ductility of this polymer shell layer is reduced, thereby sacrificing the foaming and expansion performance of the microspheres; in addition, some high-heat-resistant polymer shell layers have poor barrier properties to the blowing agent, resulting in the escape of the blowing agent, which reduces the expansion performance of the microspheres.

[0005] Therefore, developing heat-expandable microspheres with good expansion performance, high expansion temperature and good heat resistance is an urgent problem to be solved in this field. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a heat-expandable microsphere and a preparation method and application thereof. Through the design and compounding of different ethylenically unsaturated monomers and different cross-linking agents, the shell layer of the heat-expandable microsphere has a suitable cross-linking degree, and while having excellent expansion performance, the initial expansion temperature of the heat-expandable microsphere is effectively increased, giving it excellent heat resistance.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a heat-expandable microsphere, comprising an outer shell and an inner core arranged in the outer shell; the outer shell is obtained by reacting a monomer and a cross-linking agent, the monomer comprises a combination of at least two different ethylenically unsaturated monomers, the cross-linking agent comprises a combination of an acrylate cross-linking agent and an allyl cross-linking agent; the inner core comprises a foaming agent.

[0009] The heat-expandable microspheres provided by the present invention have a core-shell structure, wherein the core contains a foaming agent, which is vaporized under heating conditions to expand the heat-expandable microspheres; the material of the shell is a thermoplastic polymer obtained by reacting a monomer and a cross-linking agent. The monomers include a combination of at least two different ethylenically unsaturated monomers, and different ethylenically unsaturated monomers have different reactivity; the cross-linking agent includes two types of acrylate cross-linking agents and allyl cross-linking agents, and the activity of acrylate cross-linking agents is higher than that of allyl cross-linking agents; the design and synergistic effect of the two types of specific cross-linking agents enable linear / mildly branched macromolecules to be bonded to each other through chemical bonds and transformed into a three-dimensional network structure, thereby improving the strength, toughness, elongation, heat resistance, solvent resistance and other properties. Specifically, during the preparation of the heat-expandable microspheres, due to the influence of the polymerization reaction rate, in the early stage of the polymerization reaction, the molecular chain is a polymer component with higher reaction activity, which constitutes the outer layer of the shell, and the highly active acrylate cross-linking agent is mainly added to the amorphous polymer component formed in the early stage of the polymerization. The ductility of this component has an important influence on the expansion performance, mainly affecting the maximum expansion ratio of the heat-expandable microspheres; in the late stage of the polymerization reaction, the polymer component formed by the monomer with lower reaction activity constructs the inner layer of the shell, and the low-activity allyl cross-linking agent is mainly added to the crystalline inner layer polymer component, which has an important influence on the yield strength of the shell. When the internal pressure of the heat-expandable microspheres is large enough, it is enough to overcome the yield strength of the polymer shell layer, so that the heat-expandable microspheres begin to expand, which determines the starting expansion temperature of the heat-expandable microspheres. The invention designs and compounds different ethylenically unsaturated monomers and cross-linking agents with different reactivity, so that each polymer component in the shell has a suitable cross-linking degree, and the cross-linking degree of the entire heat-expandable microsphere is more uniform, so that the heat-expandable microsphere has excellent expansion performance and increases the initial expansion temperature, so as to obtain excellent heat resistance.

[0010] Preferably, the monomers include a combination of at least two of acrylonitrile monomers, (meth)acrylate monomers, (meth)acrylic acid monomers, alkyl vinyl ester monomers, styrene monomers, olefin monomers, and acrylamide monomers, and more preferably include a combination of at least two of acrylonitrile monomers.

[0011] Illustratively, the acrylonitrile monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and the like.

[0012] Exemplarily, the (meth)acrylate monomers include 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, allyl methacrylate, and the like.

[0013] Illustratively, the (meth)acrylic monomer includes methacrylic acid, acrylic acid, and the like.

[0014] Illustratively, the alkyl acid vinyl ester monomers include vinyl acetate, vinyl laurate, vinyl stearate, and the like.

[0015] Illustratively, the styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, halogenated styrene, and the like.

[0016] Illustratively, the olefin monomers include vinyl halides, vinylidene halides, vinyl dihalides, and the like.

[0017] Illustratively, the acrylamide monomers include acrylamide, N-isopropylacrylamide, methacrylamide, and the like.

[0018] As a preferred technical solution of the present invention, the monomer includes a combination of at least two acrylonitrile monomers; thereby, the heat-expandable microspheres have good heat resistance and excellent film-forming properties.

[0019] Preferably, the monomer includes a combination of at least two of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile and fumaronitrile.

[0020] Preferably, the monomer includes acrylonitrile and at least one of methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile and fumaronitrile.

[0021] Preferably, the monomer comprises a combination of acrylonitrile (AN) and methacrylonitrile (MAN).

[0022] As a preferred technical solution of the present invention, the monomer includes acrylonitrile AN with lower reactivity and α-substituted acrylonitrile (such as methacrylonitrile MAN, α-chloroacrylonitrile, α-ethoxyacrylonitrile, etc., preferably MAN) with higher reactivity, which has the characteristics of easy acquisition, good heat resistance, good air tightness and good film-forming property. In the preparation process of heat-expandable microspheres, due to the influence of the polymerization reaction rate, in the early stage of the polymerization reaction, the molecular chain is a MAN-rich polymer component, which constitutes the outer layer of the polymer shell layer, and the highly active acrylate crosslinking agent is mainly added to the amorphous MAN-rich polymer component formed in the early stage of the polymerization. The ductility of the amorphous MAN-rich component has an important influence on the expansion, mainly affecting the maximum expansion ratio; while the reactivity of AN is lower than that of MAN, and the AN-rich polymer component formed in the later stage of the reaction constitutes the interior of the polymer shell layer, and the low-activity allyl crosslinking agent is mainly added to the crystalline AN-rich part, which has an important influence on the yield strength of the polymer shell layer. When the internal pressure of the microsphere is large enough to overcome the yield strength of the polymer shell layer, the heat-expandable microspheres begin to expand, which determines the initial expansion temperature of the heat-expandable microspheres. Therefore, by matching cross-linking agents with different reactivity, the methacrylonitrile-rich part and the acrylonitrile-rich part both have a suitable degree of cross-linking, so that the heat-expandable microspheres have excellent expansion performance and the initial expansion temperature of the heat-expandable microspheres is increased to obtain good heat resistance.

[0023] Preferably, the mass percentage of acrylonitrile in the monomer is 20-80%, for example, it can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 78%, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range, and it is further preferably 30-80%.

[0024] As a preferred technical solution of the present invention, the mass percentage of AN with low activity in the monomer is 20-80%, further preferably 25-70%, and more preferably 28-70%; thereby, the heat-expandable microspheres have excellent expansion performance, air tightness and high initial expansion temperature. If the mass percentage of AN in the monomer is too low, the air tightness of the heat-expandable microspheres will be poor, and the expansion ratio will be extremely low due to air leakage during the expansion process; if the mass percentage of AN in the monomer is too high, the rigidity of the shell of the heat-expandable microspheres will be too strong, making it difficult to achieve an ideal expansion ratio.

[0025] Preferably, the acrylate crosslinking agent includes any one of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane triethylene glycol triacrylate, 1,6-hexanediol diacrylate, and polyethylene glycol di(meth)acrylate, or a combination of at least two thereof.

[0026] Preferably, the polyethylene glycol di(meth)acrylate includes any one of PEG200 di(meth)acrylate, PEG400 di(meth)acrylate, and PEG600 di(meth)acrylate, or a combination of at least two of them.

[0027] Preferably, the allyl crosslinking agent includes any one of diallyl phthalate, diallyl carbonate, triallyl isocyanate, triallyl isocyanurate, trimethylolpropane diallyl ether, trimethallyl isocyanate, pentaerythritol triallyl ether, and 2,2-bis(allyloxymethyl)-1-butanol, or a combination of at least two thereof.

[0028] Preferably, the mass ratio of the acrylate crosslinking agent to the allyl crosslinking agent is (0.5-2):1, for example, it can be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1 or 1.9:1, and more preferably (1-1.2):1.

[0029] As a preferred technical solution of the present invention, the mass ratio of the highly active acrylate crosslinking agent to the low-active allyl crosslinking agent is (0.5-2):1, and further preferably (1-1.2):1; thus, the crosslinking agents of different activities cooperate in a specific ratio, so that the shell structure of the heat-expandable microsphere has a uniform crosslinking density as a whole, and has excellent ductility, air tightness and heat resistance, thereby showing a high expansion ratio, a high initial expansion temperature and a high maximum expansion temperature. If the ratio of the two types of crosslinking agents exceeds the above range, the amount of the acrylate crosslinking agent is too low, which will make the outer layer of the polymer shell insufficiently crosslinked, resulting in poor ductility and affecting the expansion ratio of the heat-expandable microspheres; and the amount of the allyl crosslinking agent is too low, which will affect the inner layer crosslinking degree of the polymer shell, resulting in uneven crosslinking degree of the inner and outer layers of the shell, affecting the expansion ratio and the initial expansion temperature.

[0030] Preferably, based on 100 parts by mass of the monomer, the mass of the cross-linking agent is 0.01-5 parts, for example, it can be 0.05 parts, 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 parts, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts or 4.5 parts, as well as specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively enumerates the specific points included in the range, and it is further preferably 0.1-2 parts, and even more preferably 0.2-1 parts.

[0031] In the present invention, the foaming agent is a liquid substance that can be gasified under heating conditions.

[0032] Preferably, the foaming agent is a C3-C13 alkane foaming agent, such as C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, or C13 alkane foaming agents.

[0033] The foaming agent illustratively includes but is not limited to: pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, etc. The aforementioned alkanes include all feasible isomers thereof; for example, pentane can be n-pentane, isopentane, neopentane, etc.

[0034] Preferably, the foaming agent includes any one of isopentane, neopentane, n-pentane, n-hexane, heptane, isooctane, n-octane and petroleum ether, or a combination of at least two thereof.

[0035] Preferably, the mass percentage of the foaming agent in the heat-expandable microspheres is 20-30%, for example, it can be 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28% or 29%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0036] Preferably, the inner core also includes a gas migration inhibitor; the gas migration inhibitor helps to prevent the gas coverage of the heat-expandable microspheres from decreasing during the heating process, thereby reducing the escape of the foaming agent as the inner core material through the thermoplastic shell.

[0037] The type of the gas migration inhibitor is not particularly limited, as long as the boiling point of the gas migration inhibitor is higher than the glass transition temperature of the shell material (thermoplastic polymer).

[0038] Preferably, the gas migration inhibitor comprises any one of hydrocarbon compounds, carboxylic acid compounds, ester compounds, and alcohol compounds, or a combination of at least two thereof, and hydrocarbon compounds are more preferred.

[0039] Preferably, the gas migration inhibitor comprises naphthenic oil.

[0040] Preferably, based on 100 parts by mass of the foaming agent, the mass of the gas migration inhibitor is ≤30 parts, for example, it can be 1 part, 3 parts, 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, 22 parts, 25 parts or 28 parts, as well as specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range. Of course, the mass of the gas migration inhibitor can also be 0, that is, no gas migration inhibitor is added.

[0041] Preferably, the particle size of the heat-expandable microspheres is 1-100 μm, for example, it can be 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 or 90 μm, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and it is further preferably 5-50 μm.

[0042] Preferably, the initial expansion temperature of the heat-expandable microspheres is ≥155°C, more preferably ≥160°C, further preferably ≥165°C, and can be 165-174°C.

[0043] Preferably, the maximum expansion temperature of the heat-expandable microspheres is ≥180°C, more preferably ≥185°C, further preferably ≥188°C, and can be 188-196°C.

[0044] Preferably, the expansion ratio of the heat-expandable microspheres is ≥100, more preferably ≥130, further preferably ≥133, and can be 133-149.

[0045] In a second aspect, the present invention provides a method for preparing the heat-expandable microspheres as described in the first aspect, the preparation method comprising:

[0046] Mixing monomers, cross-linking agents, blowing agents and initiators to obtain an oil phase mixture;

[0047] dispersing the oil phase mixture in an aqueous dispersion medium to obtain a suspension;

[0048] The suspension is polymerized to obtain the heat-expandable microspheres.

[0049] Preferably, the initiator is a free radical initiator, including an organic peroxide initiator and / or an azo initiator.

[0050] Exemplarily, the organic peroxide initiator includes peroxycarboxylates such as tert-butyl peroxyacetate, tert-amyl peroxypivalate, tert-butyl peroxybenzoate, di-tert-butyl peroxyisophthalate, and di-tert-butyl peroxyisophthalate; peroxycarbonates such as tert-butyl peroxyisopropyl monocarbonate, tert-butyl peroxyisopropyl carbonate, tert-amyl peroxyisopropyl carbonate, and 1,6-bis(tert-butylperoxycarbonyloxy)hexane; dialkyl peroxides such as 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,3-di(2-tert-butylperoxyisopropyl)benzene; 2,2-di(tert-butylperoxy)butane, 1,1-di(tert-butylperoxy)cyclohexane, and 3,3-di(tert-butylperoxy)butane. The invention relates to a peroxide initiator comprising: a peroxide ketal such as ethyl ester, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-hexylperoxy)cyclohexane, n-butyl 4,4-di(tert-butylperoxy)valerate, 1,1-di(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, 2,2-di(4,4-di-tert-butylperoxycyclohexyl)propane; a ketone peroxide such as methyl ethyl ketone peroxide; a hydroperoxide such as tert-butyl hydroperoxide, tert-amyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, tert-butyl peroxyallyl monocarbonate, diisopropylbenzene hydroperoxide, 3,3',4,4'-tetra(tert-butylperoxycarbonyl)benzophenone; and the organic peroxide initiator comprises any one of the aforementioned peroxides or a combination of at least two thereof.

[0051] Illustratively, the azo initiator includes any one of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methylbutyronitrile), or a combination of at least two thereof.

[0052] Preferably, based on 100 parts by mass of the monomer, the mass of the initiator is 0.01-5 parts, for example, it can be 0.05 parts, 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 parts, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts or 4.5 parts, as well as specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range, and 0.1-3 parts is further preferred.

[0053] Preferably, the mass percentage of the foaming agent in the oil phase mixture is 20-30%, for example, it can be 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28% or 29%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0054] Preferably, the oil phase mixture also includes a gas migration inhibitor.

[0055] Preferably, the aqueous dispersion medium comprises a combination of water, a stabilizer, an electrolyte and an inhibitor.

[0056] Preferably, the stabilizer includes any one or a combination of at least two of colloidal silicon dioxide, 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, and further preferably includes any one or a combination of at least two of colloidal silicon dioxide, magnesium hydroxide, and calcium hydroxide.

[0057] Preferably, based on 100 parts by mass of the water, the mass of the stabilizer is 1-20 parts, for example, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 10 parts, 11 parts, 13 parts, 15 parts, 17 parts or 19 parts, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and 5-15 parts are further preferred.

[0058] Preferably, the aqueous dispersion medium also includes a dispersion stabilization aid to improve the dispersion effect.

[0059] Preferably, the dispersion stabilization aid includes any one of carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl pyrrolidone, tetramethyl ammonium chloride, polyvinyl alcohol, a water-soluble condensation product of diethanolamine and adipic acid, polyethylene imine, gelatin, glue, casein, albumin, or a combination of at least two thereof.

[0060] Preferably, based on 100 parts of the mass of the water, the mass of the dispersion and stabilization aid is 0.001-1 part, for example, it can be 0.005 parts, 0.01 parts, 0.05 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts or 0.9 parts, and specific point values ​​between the above point values. Due to space limitations and for simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range. Of course, the mass of the dispersion and stabilization aid can also be 0, that is, no dispersion and stabilization aid is added.

[0061] Preferably, the electrolyte is a metal salt, and further preferably includes any one or a combination of at least two of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium sulfate, potassium sulfate, magnesium sulfate, sodium carbonate, potassium carbonate, sodium nitrate, and potassium nitrate.

[0062] Preferably, based on 100 parts by mass of the water, the mass of the electrolyte is 1-50 parts, for example, it can be 2 parts, 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, 42 parts, 45 parts or 48 parts, as well as specific point values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and 10-30 parts is further preferred.

[0063] Preferably, the polymerization inhibitor is a water-phase polymerization inhibitor. Since the monomer (acrylonitrile monomer) has a certain water solubility, water-phase polymerization is an undesirable polymerization reaction during the polymerization process. Therefore, the polymerization inhibitor is added to inhibit the polymerization through charge transfer, thereby preventing the monomer from polymerizing in the water phase.

[0064] Preferably, the inhibitor includes any one of sodium nitrite, potassium nitrite, ferric chloride, sodium sulfide, potassium dichromate, cuprous chloride, cupric sulfate, titanium trichloride, sodium sulfate, and ammonium thiocyanate, or a combination of at least two thereof.

[0065] Preferably, based on 100 parts by mass of the water, the mass of the inhibitor is 0.01-5 parts, for example, it can be 0.05 parts, 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 parts, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts or 4.5 parts, as well as specific point values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and 0.05-1 parts is further preferred.

[0066] Preferably, the aqueous dispersion medium is an acidic medium, and its pH value is adjusted to acidic by hydrochloric acid after preparation.

[0067] Preferably, the pH value of the aqueous dispersion medium is 1-7, for example, it can be 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 or 6.5, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and it is further preferably 3-5.

[0068] Preferably, the sum of the masses of the aqueous dispersion medium and the oil phase mixture is 100%, and the mass of the oil phase mixture is 15-30%, for example, it can be 16%, 18%, 20%, 21%, 23%, 25%, 27% or 29%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and 18-25% is further preferred.

[0069] Preferably, the oil phase mixture is dispersed in an aqueous dispersion medium by high-speed shearing to obtain a suspension.

[0070] Preferably, the dispersion rotation speed is 500-8000rpm, for example, it can be 1000rpm, 1500rpm, 2000rpm, 2500rpm, 3000rpm, 3500rpm, 4000rpm, 4500rpm, 5000rpm, 6000rpm or 7000rpm, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0071] Preferably, the polymerization reaction is carried out in an inert atmosphere.

[0072] Preferably, the inert atmosphere includes at least one of a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere.

[0073] Preferably, the polymerization reaction is carried out under stirring conditions.

[0074] Preferably, the polymerization reaction pressure is 0.3-0.8 MPa, for example, it can be 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, 0.55 MPa, 0.6 MPa, 0.65 MPa, 0.7 MPa or 0.75 MPa, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0075] Preferably, the polymerization reaction temperature is 50-80°C, for example, it can be 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C or 78°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0076] Preferably, the polymerization reaction time is 15-25h, for example, it can be 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0077] In the present invention, the heat-expandable microspheres are prepared by suspension polymerization, preferably by high-speed shearing, the oil phase mixture is dispersed into fine droplets in an aqueous dispersion medium, each fine droplet is coated with a stabilizer to prevent it from aggregating. The suspension is subjected to polymerization reaction under stirring and heating conditions, and as the initiator decomposes, the polymerization reaction starts quickly, as the monomers gradually polymerize into polymers, phase separation is formed with the foaming agent and accumulated in the outer layer of the droplets, gradually forming a core-shell structure in which the polymer wraps the foaming agent. In this process, the polymer segments formed by the monomers with high reaction activity precipitate earlier to form the outer layer of the polymer shell (shell), and the polymer segments formed by the monomers with low activity precipitate later to form the inner layer of the polymer shell (shell). The present invention introduces an acrylate crosslinking agent and an allyl crosslinking agent with different activities, so that the polymer segments formed by the monomers with different activities have a certain degree of crosslinking during the precipitation process, and the crosslinking degree of the entire heat-expandable microspheres is more uniform. While the heat-expandable microspheres have excellent thermal expansion properties, the initial expansion temperature is also effectively improved, and the heat resistance is better.

[0078] Preferably, after the polymerization reaction is completed, a post-treatment step is also included.

[0079] Preferably, the post-treatment comprises filtration and drying.

[0080] In a third aspect, the present invention provides a use of the heat-expandable microspheres as described in the first aspect in printing and dyeing, coatings, inks, polyurethane polishing materials, shoe soles, sound-absorbing materials or thermal insulation materials.

[0081] Compared with the prior art, the present invention has the following beneficial effects:

[0082] (1) In the heat-expandable microspheres provided by the present invention, through the design and compounding synergistic effect of different ethylenically unsaturated monomers and cross-linking agents with different reactivity, each polymer component in the shell has an appropriate cross-linking degree, the cross-linking degree of the entire heat-expandable microsphere is more uniform, and the shell has excellent ductility, air tightness and heat resistance. The heat-expandable microspheres have excellent expansion performance and an increased initial expansion temperature, thereby obtaining excellent heat resistance.

[0083] (2) The present invention further optimizes the types / ratios of monomers and cross-linking agents, so that the initial expansion temperature of the heat-expandable microspheres is ≥165°C, the maximum expansion temperature is ≥188°C, and the expansion ratio is ≥133. The present invention has a high expansion ratio, a high initial expansion temperature, and a high maximum expansion temperature, and has excellent comprehensive performance in expansion performance and heat resistance. DETAILED DESCRIPTION

[0084] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0085] As used herein, the terms "comprises," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0086] "Optionally" or "either" means that the subsequently described matter or event can or cannot occur, and that the description includes instances where the event occurs and instances where it does not.

[0087] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0088] In the following specific embodiments of the present invention, the raw materials used are described as follows:

[0089] (1) Ethylenically unsaturated monomers

[0090] Methacrylonitrile, MAN;

[0091] Acrylonitrile, AN, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%;

[0092] Methyl methacrylate, MMA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%;

[0093] Methyl acrylate, MA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0094] (2) Acrylate crosslinking agent

[0095] Ethylene glycol dimethacrylate, EGDMA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%;

[0096] Trimethylolpropane triacrylate, TMPTA, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0097] (3) Allyl crosslinking agent

[0098] Diallyl carbonate, DAC, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%;

[0099] Pentaerythritol triallyl ether, APE, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0100] (4) Initiator

[0101] Azobisisobutyronitrile, AIBN, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0102] (5) Foaming agent

[0103] Isopentane, Aladdin Group Co., Ltd., reagent grade 99%;

[0104] Isooctane, Aladdin Group Ltd., reagent grade 99%.

[0105] (6) Gas migration inhibitors

[0106] Naphthenic oil, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0107] (7) Stabilizer

[0108] Colloidal silicon dioxide, containing 25% by mass of silicon dioxide as an active ingredient, Shandong Kehan ​​Silicon Products Co., Ltd.

[0109] (8) Electrolytes

[0110] Sodium chloride, Shenghai Chemical Co., Ltd., industrial grade 99%.

[0111] (9) Inhibitor

[0112] Sodium nitrite, Shanghai Aladdin Biochemical Technology Co., Ltd., reagent grade 99%.

[0113] In the following specific embodiments of the present invention, unless otherwise specified, "parts" and "%" are based on mass.

[0114] Example 1

[0115] A heat-expandable microsphere and a preparation method thereof. The heat-expandable microsphere comprises an outer shell and an inner core arranged in the outer shell. The outer shell is made of a thermoplastic polymer obtained by reacting monomers (methacrylonitrile MAN and acrylonitrile AN) and crosslinking agents (ethylene glycol dimethacrylate EGDMA and diallyl carbonate DAC); and the inner core comprises a foaming agent (isopentane and isooctane) and a gas migration inhibitor.

[0116] The preparation method of the heat-expandable microspheres comprises the following steps:

[0117] (1) preparing an aqueous dispersion medium: adding 150 parts of sodium chloride, 80 parts of colloidal silicon dioxide (containing 25% by mass of silicon dioxide) and 2 parts of sodium nitrite (prepared as a 3% aqueous solution) to 800 parts of deionized water, stirring thoroughly, and adjusting the pH value of the system to 3.5 to obtain an aqueous dispersion medium;

[0118] Prepare an oil phase mixture: fully mix 190 parts of AN, 80 parts of MAN, 25 parts of isopentane, 65 parts of isooctane, 1 part of EGDMA, 1 part of DAC, 9 parts of naphthenic oil, and 1.5 parts of AIBN to obtain an oil phase mixture;

[0119] (2) mixing the aqueous dispersion medium obtained in step (1) with the oil phase mixture, and dispersing at a high speed of 1500 rpm for 15 min in a closed container to obtain a suspension;

[0120] (3) Purging with nitrogen, subjecting the suspension obtained in step (2) to a polymerization reaction, wherein the polymerization reaction is carried out in a nitrogen atmosphere and under stirring at 80 rpm, the initial reaction pressure is controlled at 0.5 MPa, and the polymerization reaction is carried out at 70° C. for 20 h; after the polymerization reaction is completed, filtering and drying the product to obtain the heat-expandable microspheres.

[0121] Examples 2-9, Comparative Examples 1-6

[0122] A heat-expandable microsphere and a preparation method thereof, the heat-expandable microsphere comprising an outer shell and an inner core arranged in the outer shell, the difference between the heat-expandable microsphere and Example 1 is that the monomer and / or the cross-linking agent are different, which are specifically shown in Table 1 and Table 2; the preparation method of the heat-expandable microsphere is the same as that of Example 1 (the components / parameters not shown in Table 1 and Table 2 are exactly the same as those in Example 1); in Table 1 and Table 2, the mass of each component is measured in "parts", and "--" means that the component is not added.

[0123] Table 1

[0124]

[0125]

[0126] Table 2

[0127]

[0128]

[0129] The performance test of the heat-expandable microspheres provided in Examples 1-9 and Comparative Examples 1-6 was carried out, and the specific method included:

[0130] (1) Particle size test

[0131] The particle size of the heat-expandable microspheres was tested by a laser particle size analyzer (Bettersize 2600) using a wet method, a shading rate of 5-20%, and water as the test medium. The median particle size D 50 , and D 90 and D 10 , particle size distribution PDI = (D 90 -D 10 ) / D 50 ;

[0132] (2) Expansion performance test

[0133] The test was performed using a static thermomechanical analyzer (TMA, Mettler TMA / SDTA2+) with a heating rate of 15°C / min. The specific test steps are as follows:

[0134] 1 mg of heat-expandable microspheres to be tested was added to a 150 μL ceramic crucible, and a gasket of matching diameter was added on top of the microsphere layer to prepare a sample; the sample height was measured while a force of 0.06 N was applied to the sample from above using a pressurizer; the temperature was raised from 20°C to 300°C at a heating rate of 15°C / min while a force of 0.06 N was applied using a pressurizer, and the displacement of the pressurizer in the vertical direction was measured; the temperature at which the displacement in the positive direction started was recorded as the starting expansion temperature (Tstart), the temperature at which the maximum displacement was displayed was recorded as the maximum expansion temperature (Tmax), and the ratio of the maximum height of the expansion process to the initial sample height was the expansion ratio.

[0135] The test results are shown in Table 3:

[0136] Table 3

[0137]

[0138] According to the test data in Table 3, the present invention, through the design and synergy of different ethylenically unsaturated monomers and cross-linking agents with different reactivity, makes each polymer component in the shell of the heat-expandable microsphere have a suitable and uniform degree of cross-linking, so that the heat-expandable microsphere has excellent expansion performance and improves the initial expansion temperature to obtain excellent heat resistance. In Examples 1-5, through the design of monomer types, the good types of cross-linking agents and the further optimization of the ratio, the initial expansion temperature of the heat-expandable microsphere is 165-174°C, the maximum expansion temperature is 188-196°C, and the expansion ratio is 133-149, which has excellent comprehensive performance in terms of expansion performance and heat resistance. Compared with Example 1, the monomers used to prepare the polymer shell in Examples 6 and 8 do not contain methacrylonitrile, but acrylonitrile and methyl (meth)acrylate are polymerized to reduce the initial expansion temperature and expansion ratio of the heat-expandable microspheres; the ratio of the acrylate crosslinking agent to the allyl crosslinking agent in Examples 7 and 9 exceeds the preferred range of the present invention, which affects the uniformity of the crosslinking degree of the inner and outer layers of the polymer shell, resulting in a decrease in the heat resistance and expansion performance of the heat-expandable microspheres.

[0139] In the present invention, cross-linking agents of different activities are matched, and ethylenically unsaturated monomers of different activities are coordinated to make the polymer shell structure have uniform cross-linking density, thereby having excellent ductility, air tightness and heat resistance, showing high expansion ratio, high initial expansion temperature and high maximum expansion temperature. A single type of cross-linking agent is used in Comparative Examples 1-4, resulting in poor cross-linking uniformity of the polymer shell layer, making the initial expansion temperature of the heat-expandable microspheres lower, and the expansion ratio is also reduced. Two different acrylate cross-linking agents are used in Comparative Example 5, and the cross-linking degree inside and outside the polymer shell layer is uneven, and the outer layer cross-linking degree is higher. Although good expansion performance is shown, good air tightness cannot be maintained in the expansion rear section, so the maximum expansion temperature is lower. Two different allyl cross-linking agents are used in Comparative Example 6, and the cross-linking degree inside and outside the polymer shell layer is uneven, and the cross-linking degree of the inner polymer layer is higher, showing good heat resistance, so it has a higher initial expansion temperature and maximum expansion temperature, but the expansion ratio is deteriorated.

[0140] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the heat-expandable microspheres and the preparation method and application thereof, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A heat-expandable microsphere, characterized in that: The heat-expandable microspheres include an outer shell and an inner core disposed in the outer shell; The shell is obtained by reacting a monomer and a cross-linking agent, wherein the monomer comprises a combination of at least two different ethylenically unsaturated monomers, and the cross-linking agent comprises a combination of an acrylate cross-linking agent and an allyl cross-linking agent; The inner core includes a foaming agent; The monomer includes acrylonitrile and at least one of methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile and fumaronitrile; The mass percentage of acrylonitrile in the monomer is 20-80%; The mass ratio of the acrylate crosslinking agent to the allyl crosslinking agent is (0.5-2):

1.

2. The heat-expandable microspheres according to claim 1, characterized in that: The mass percentage of acrylonitrile in the monomer is 30-80%.

3. The heat-expandable microspheres according to claim 1, characterized in that: The acrylate crosslinking agent includes any one of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane triethylene glycol triacrylate, 1,6-hexanediol diacrylate, and polyethylene glycol di(meth)acrylate, or a combination of at least two thereof.

4. The heat-expandable microspheres according to claim 1, characterized in that: The allyl crosslinking agent includes any one of diallyl phthalate, diallyl carbonate, triallyl isocyanate, triallyl isocyanurate, trimethylolpropane diallyl ether, trimethallyl isocyanate, pentaerythritol triallyl ether, and 2,2-bis(allyloxymethyl)-1-butanol, or a combination of at least two thereof.

5. The heat-expandable microspheres according to claim 1, characterized in that: The mass ratio of the acrylate crosslinking agent to the allyl crosslinking agent is (1-1.2):

1.

6. The heat-expandable microspheres according to claim 1, characterized in that: Based on 100 parts by weight of the monomer, the weight of the cross-linking agent is 0.01-5 parts by weight.

7. The heat-expandable microspheres according to claim 6, characterized in that: Based on 100 parts by weight of the monomer, the weight of the cross-linking agent is 0.1-2 parts by weight.

8. The heat-expandable microspheres according to claim 1, characterized in that: The foaming agent is a C3-C13 alkane foaming agent.

9. The heat-expandable microspheres according to claim 8, characterized in that: The foaming agent is any one of isopentane, neopentane, normal pentane, normal hexane, heptane, isooctane, normal octane and petroleum ether, or a combination of at least two of them.

10. The heat-expandable microspheres according to claim 1, characterized in that: The mass percentage of the foaming agent in the heat-expandable microspheres is 20-30%.

11. The heat-expandable microspheres according to claim 1, characterized in that: A gas migration inhibitor is also included in the inner core.

12. The heat-expandable microspheres according to claim 11, characterized in that: The gas migration inhibitor includes any one of hydrocarbon compounds, carboxylic acid compounds, ester compounds, and alcohol compounds, or a combination of at least two of them.

13. The heat-expandable microspheres according to claim 11, characterized in that: Based on 100 parts by weight of the foaming agent, the weight of the gas migration inhibitor is ≤30 parts.

14. The heat-expandable microspheres according to claim 1, characterized in that: The particle size of the heat-expandable microspheres is 1-100 μm.

15. The heat-expandable microspheres according to claim 14, characterized in that: The particle size of the heat-expandable microspheres is 5-50 μm.

16. The heat-expandable microspheres according to claim 1, characterized in that: The initial expansion temperature of the heat-expandable microspheres is ≥155°C.

17. The heat-expandable microspheres according to claim 1, characterized in that: The initial expansion temperature of the heat-expandable microspheres is ≥160°C.

18. The heat-expandable microspheres according to claim 1, characterized in that: The maximum expansion temperature of the heat-expandable microspheres is ≥180°C.

19. A method for preparing heat-expandable microspheres according to any one of claims 1 to 18, characterized in that: The preparation method comprises: Mixing monomers, cross-linking agents, blowing agents and initiators to obtain an oil phase mixture; dispersing the oil phase mixture in an aqueous dispersion medium to obtain a suspension; The suspension is polymerized to obtain the heat-expandable microspheres.

20. The preparation method according to claim 19, characterized in that: The initiator includes an organic peroxide initiator and / or an azo initiator.

21. The preparation method according to claim 19, characterized in that: Based on 100 parts by weight of the monomer, the weight of the initiator is 0.01-5 parts by weight.

22. The preparation method according to claim 21, characterized in that: Based on 100 parts by weight of the monomer, the weight of the initiator is 0.1-3 parts by weight.

23. The preparation method according to claim 19, characterized in that: The mass percentage of the foaming agent in the oil phase mixture is 20-30%.

24. The preparation method according to claim 19, characterized in that: The oil phase mixture also includes a gas migration inhibitor.

25. The preparation method according to claim 19, characterized in that: The aqueous dispersion medium includes a combination of water, a stabilizer, an electrolyte and an inhibitor.

26. The preparation method according to claim 25, characterized in that: The stabilizer includes any one of colloidal silicon dioxide, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, iron hydroxide, calcium sulfate, calcium oxalate, calcium carbonate, barium sulfate, barium carbonate, magnesium carbonate, and calcium phosphate, or a combination of at least two thereof.

27. The preparation method according to claim 26, characterized in that: The calcium carbonate is colloidal calcium carbonate, and the aluminum hydroxide is aluminum hydroxide sol.

28. The preparation method according to claim 25, characterized in that: Based on 100 parts by mass of the water, the mass of the stabilizer is 1-20 parts.

29. The preparation method according to claim 25, characterized in that: The electrolyte is a metal salt.

30. The preparation method according to claim 29, characterized in that: The metal salt includes any one of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium sulfate, potassium sulfate, magnesium sulfate, sodium carbonate, potassium carbonate, sodium nitrate, and potassium nitrate, or a combination of at least two thereof.

31. The preparation method according to claim 25, characterized in that: Based on 100 parts by mass of the water, the mass of the electrolyte is 1-50 parts.

32. The preparation method according to claim 25, characterized in that: The inhibitor includes any one of sodium nitrite, potassium nitrite, ferric chloride, sodium sulfide, potassium dichromate, cuprous chloride, cupric sulfate, titanium trichloride, sodium sulfate, and ammonium thiocyanate, or a combination of at least two thereof.

33. The preparation method according to claim 25, characterized in that: Based on 100 parts by weight of the water, the weight of the inhibitor is 0.01-5 parts by weight.

34. The preparation method according to claim 19, characterized in that: The pH value of the aqueous dispersion medium is 1-7.

35. The preparation method according to claim 34, characterized in that: The pH value of the aqueous dispersion medium is 3-5.

36. The preparation method according to claim 19, characterized in that: If the sum of the mass of the aqueous dispersion medium and the oil phase mixture is 100%, the mass of the oil phase mixture is 15-30%.

37. The preparation method according to claim 36, characterized in that: If the sum of the mass of the aqueous phase dispersion medium and the oil phase mixture is 100%, the mass of the oil phase mixture is 18-25%.

38. The preparation method according to claim 19, characterized in that: The polymerization reaction is carried out in an inert atmosphere.

39. The preparation method according to claim 19, characterized in that: The polymerization reaction pressure is 0.3-0.8 MPa.

40. The preparation method according to claim 19, characterized in that: The polymerization temperature is 50-80°C.

41. The preparation method according to claim 19, characterized in that The polymerization reaction time is 15-25h.

42. The preparation method according to claim 19, characterized in that After the polymerization reaction is completed, a post-treatment step is also included.

43. The preparation method according to claim 42, characterized in that: The post-treatment includes filtration and drying.

44. Use of the heat-expandable microspheres according to any one of claims 1 to 18 in printing and dyeing, coatings, inks, polyurethane polishing materials, shoe soles, sound-absorbing materials or thermal insulation materials.

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