High-temperature thermal expansion microsphere

Abstract

The invention provides a high-temperature thermal expansion microsphere which comprises an olefinic unsaturated monomer, a foaming agent, a cross-linking agent, an initiator, a dispersion stabilizer, a dispersion stabilizing additive and a dispersion medium, wherein the olefinic unsaturated monomer is prepared from the following components in percentage by weight: 40 to 70 percent of acrylonitrile monomer, 10 to 30 percent of acrylic acid monomer, 10 to 30 percent of acrylamide monomer, 0 to 30 percent of acrylate monomer and 5 to 30 percent of silicon-containing acrylate monomer. The foam breaking temperature, the durability and the foam stabilizing performance of the microspheres can be remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of manufacturing expandable particles, and more specifically, to a high-temperature thermally expandable microsphere. Background Technology

[0002] Thermally expandable microspheres, which have a structure consisting of a thermoplastic resin shell and a foaming agent encapsulated inside, are commonly referred to as thermally expandable microcapsules. Common thermoplastic resins used are vinylidene chloride copolymers, acrylonitrile copolymers, and acrylate copolymers. Additionally, alkanes such as isooctane or isopentane are primarily used as foaming agents.

[0003] Methods for preparing various thermally expandable microspheres have been disclosed in patents such as WO2007 / 142593A1, EP1149628A1, EP1811007A1, EP1302239A1, EP0486080, EP112807B1, EP0348372A2, WO2004 / 0566549A1, US4287308, and EP1592733B1.

[0004] For thermally expandable microspheres, different initial foaming temperatures are crucial. Microspheres with different initial foaming temperatures have different applications. High-temperature expandable microspheres, typically with a high initial foaming temperature of 150-180℃, can be used in the injection molding of thermoplastic materials such as PP, PC, PA, and ABS. During injection molding, the microspheres expand due to heat, achieving controlled foaming and helping various thermoplastic materials form a uniform closed-cell structure. This reduces density while improving surface structure and enhancing finished product stability. However, premature bubble breakage often occurs during hot injection molding applications. Therefore, improving the bubble breakage temperature and heat resistance of microspheres remains an important issue for the industry.

[0005] To improve the heat resistance and foaming temperature of thermally expandable microspheres, in addition to selecting monomers with high glass transition temperatures and increasing the degree of cross-linking of the shell, research has found that modifying thermally expandable microspheres with organosilicon monomers can improve their adhesion, heat resistance, and solvent resistance. Patents CN100436562C, CN115895019A, and CN109705392A disclose methods for modifying thermally expandable microspheres with organosilicon compounds, improving the degree of shell cross-linking through silane modification and surface adsorption modification. However, these patents all use a post-addition method of silane, the purpose of which is to prevent the premature hydrolysis of highly reactive functional groups such as methoxy and ethoxy groups of silane, which would make the reaction uncontrollable. The post-addition method has problems such as multiple reaction steps, long reaction time, relatively small addition amount, low organosilicon content, and distribution only on the outer surface of the shell, limiting the aging resistance and heat resistance of organosilicon. Patent CN107915799A discloses a method for modifying thermally expandable microspheres by copolymerizing with organosilicon monomers, which improves the aging resistance and UV resistance of the microspheres. CN117069996B discloses a method for synthesizing organosilicon-modified epoxy resin and introducing this resin into expandable microspheres, improving the high-temperature durability of the microspheres. However, neither of these methods addresses a method to further increase the foaming temperature of the microspheres. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the purpose of this invention is to provide a high-temperature thermal expansion microsphere that is halogen-free and has a high maximum foaming temperature (generally >180°C) and a high expansion capacity.

[0007] This invention provides high-temperature thermal expansion microspheres, comprising an olefinic unsaturated monomer (i.e., an olefinic unsaturated monomer), a foaming agent, a crosslinking agent, an initiator, a dispersing stabilizer, a dispersing stabilizing aid, and a dispersion medium, wherein:

[0008] The olefinic unsaturated monomer comprises, by weight percentage: 40-70% acrylonitrile monomers, 10-30% acrylic acid monomers, 10-30% acrylamide monomers, 0-30% acrylate monomers, and 5-30% silicone-containing acrylate monomers. The silicone-containing acrylate monomers participate in the polymerization, forming the microsphere shell and improving the microsphere's rupture temperature, foam stabilization ability, and heat resistance.

[0009] Optionally, the acrylonitrile monomer is any one or more selected from acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaric acid, and crotonitrile. Preferably, it is one or a mixture of acrylonitrile and methacrylonitrile.

[0010] Optionally, the acrylic monomer is a carboxyl-containing methacrylic acid monomer, including carboxyl-containing methacrylic acid monomers and / or carboxyl metal salts of methacrylic acid monomers. The aforementioned carboxyl-containing methacrylic acid monomers are not particularly limited; exemplary examples include methacrylic acid, metal methacrylic acid salts, etc. Exemplary examples of the aforementioned carboxyl metal salt-containing methacrylic acid monomers (metal methacrylic acid salts) include magnesium methacrylate, calcium methacrylate, zinc methacrylate, etc. These carboxyl-containing methacrylic acid monomers can be used alone or in combination of two or more.

[0011] Optionally, the acrylamide monomer is any one or more of N-isopropylacrylamide, N-hydroxymethylacrylamide, N-methoxymethylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, and acryloylmorpholine. Preferably, it is N,N-dimethylacrylamide.

[0012] Optionally, the acrylate monomers are C1-C5 (meth)acrylate monomers. Specifically, they include ethyl methacrylate, butyl acrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl acrylate, methyl acrylate, etc., but are not limited to these, and can be used alone or in combination of two or more.

[0013] The thermally expandable microsphere composition with foaming properties at high temperatures provided by the present invention includes an olefinic unsaturated monomer and a foaming agent, etc. Optionally, the silicon-containing acrylate monomer is an organosilicon acrylate monomer, preferably a alkyl silyl (meth)acrylate, with the following structural formula:

[0014]

[0015] In the formula, R1 = H, methyl, R2 = C n H 2n ,n≥0,R3,R4,R5=alkyl groups and their siloxane-containing alkyl derivatives, etc.

[0016] Optionally, the alkyl silyl acrylate is any one or more of trimethylsilyl acrylate, trimethylsilyl methacrylate, triisopropylsilyl methacrylate, triisopropylsilyl acrylate, methacryloxypropyltris(trimethylsiloxane), trimethylsilyl methacrylate, (phenyldimethylsilyl)methyl methacrylate, and 2-methyl-2-acrylate tributylsilyl acrylate. Preferably, it is any one or more of triisopropylsilyl methacrylate, triisopropylsilyl acrylate, and methacryloxypropyltris(trimethylsiloxane).

[0017] This invention utilizes organosilicon monomers containing acrylate functional groups, which are miscible with other acrylate and acrylonitrile monomers and directly participate in the free radical reaction of double bonds, completing the reaction in one step without the need for subsequent additions. Simultaneously, the silicon-containing monomers are uniformly dispersed within the microsphere shell, and their content can be adjusted arbitrarily. As the content increases, the inorganic silicon content increases, significantly improving the heat resistance of the microspheres and thus increasing the bubble-breaking temperature.

[0018] Optionally, by weight percentage, the olefinic unsaturated monomer accounts for 50-70% of the oil phase, the foaming agent accounts for 20-30% of the oil phase, the crosslinking agent accounts for 0.1-0.6% of the oil phase, and the initiator accounts for 0.6-1% of the oil phase. The dispersing stabilizer accounts for 8-15% of the aqueous phase, the dispersing stabilizing aid accounts for 0.5-2% of the aqueous phase, and the dispersion medium accounts for 60-80% of the aqueous phase.

[0019] Optionally, the foaming agent is a liquid with a boiling point temperature not higher than the softening temperature of the thermoplastic polymer shell. The foaming agent is a hydrocarbon or halogenated hydrocarbon compound with 5 to 8 carbon atoms, specifically including any one or more of n-pentane, isopentane, n-hexane, isohexane, n-octane, and isooctane. The boiling point of the foaming agent is 25 to 127°C, preferably 70 to 100°C.

[0020] The foaming agent is encapsulated inside the microspheres; it is liquid at room temperature, forming a core structure. As the temperature rises, the liquid begins to evaporate, and the internal pressure within the sealed shell gradually increases. Upon reaching a certain pressure, the microspheres begin to expand. Generally, the higher the boiling point of the foaming agent, the higher the foaming temperature of the microspheres. However, the expansion effect (expansion rate) of the microspheres also depends on whether the composition of the microsphere shell matches the type and content of the foaming agent, and is also affected by the pressure difference between the inside and outside of the microspheres at a specific temperature. Using the above-mentioned substance as a foaming agent allows for the expansion of microspheres at high temperatures while maintaining an excellent expansion rate.

[0021] Crosslinking agents are crosslinking monomers having two or more polymerizable double bonds. These monomers crosslink linear copolymers containing the monomers mentioned above to extend the elastic range of the copolymer and impart thermal stability. These monomers include, but are not limited to, ethylene glycol (meth) diacrylate, diethylene glycol di(meth) acrylate, dipropylene glycol di(meth) acrylate, 1,4-butanediol di(meth) acrylate, 1,6-hexanediol diacrylate, neopentyl glycol di(meth) acrylate, glyceryl dimethacrylate, polyethylene glycol (200) dimethacrylate, polyethylene glycol (400) dimethacrylate, polyethylene glycol (600) dimethacrylate, trimethylolpropane tri(meth) acrylate, trimethylolpropane tri(meth) acrylate, divinyl ether, triethylene glycol divinyl ether, butanediol divinyl ether, etc. They can be used alone or in combination of two or more.

[0022] Preferably, the crosslinking agent is any one or more of polyethylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol (400) dimethacrylate, polyethylene glycol (600) dimethacrylate, and trimethylolpropane tri(meth)acrylate.

[0023] The type and content of crosslinking agents affect the expansion ratio and temperature of microspheres. Low crosslinking agent content results in poor foam stability, poor heat resistance, and rapid shrinkage after expansion. High crosslinking agent content leads to denser crosslinking, which, while moderately improving heat resistance, degrades the expansion effect. Generally, trifunctional crosslinking agents have a higher degree of crosslinking than difunctional crosslinking agents. If the crosslinking agent is a trifunctional compound, its dosage is 0.01–2 wt% of the olefin unsaturated monomer.

[0024] If the crosslinking agent is a difunctional compound, the amount of the crosslinking agent is 0.1 to 3 wt% of the olefin unsaturated monomer.

[0025] Optionally, the initiator is an oil-soluble, cracking-type thermal initiator, such as benzoyl peroxide, dibenzoic acid peroxide, lauroyl peroxide, dilauric acid peroxide, tert-butyl perlaurate, 2,2'-azobisisobutyronitrile, 2,2'-azobis((2,4-dimethylpentanonitrile)), etc., but is not limited to this, and can be used alone or in combination of two or more.

[0026] Optionally, the dispersion medium is deionized water, or ionized water containing hydrophilic organic solvents such as alcohols.

[0027] Optionally, the dispersant stabilizer is an insoluble salt, oxide, or hydroxide of metals such as calcium, magnesium, barium, iron, zinc, nickel, or manganese; it can also be a polymeric dispersant stabilizer, including the condensation product of diethanolamine and aliphatic dicarboxylic acids, polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol, methylcellulose, agar powder, hydroxypropyl methylcellulose, carboxymethyl cellulose, silica sol, colloidal clay, etc., but is not limited thereto. They can be used alone or in combination of two or more.

[0028] Depending on the selection of the dispersant stabilizer, the pH value of the dispersion medium is controlled. For example, if the dispersant stabilizer is selected from one or more of the insoluble salts, oxides, or hydroxides of metals such as calcium, magnesium, barium, iron, zinc, nickel, or manganese, such as calcium phosphate, calcium carbonate, magnesium hydroxide, magnesium oxide, calcium oxalate, and hydroxides of zinc, nickel, or manganese, the pH value is controlled between 5 and 12, preferably between 6 and 10. If the dispersant stabilizer is selected from polymeric dispersants such as methylcellulose, agar powder, hydroxypropyl methylcellulose, carboxymethylcellulose, silica sol, or colloidal clay, the pH value is selected between 1 and 6. The pH value of the dispersion medium affects the viscosity and thixotropy of the suspension, and thus affects the dispersion stability of the suspension, i.e., the uniformity of oil droplets, and the collision rate between oil droplets during the reaction process (low viscosity - low thixotropy, oil droplets easily merge to form large oil droplets), thereby affecting the final microsphere particle size and dispersion uniformity (CV value). In addition, high viscosity - high thixotropy will affect workability. Under high viscosity conditions, the stirring power is higher and the energy consumption is higher. Preferably, the pH value of the dispersion medium is 3 to 5.

[0029] Optionally, the auxiliary stabilizer may be selected from the following substances: condensation products of diethanolamine and aliphatic dicarboxylic acids, condensation products of urea and formaldehyde, water-soluble nitrogen-containing compounds, polyethylene oxide, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, various emulsifiers, etc.

[0030] The aforementioned water-soluble nitrogen-containing compound can be, for example, polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polyacrylamide, polycationic acrylamide, polyurethane, polyallylamine, etc.; or it can be polydialkylaminoethyl methacrylate, polydialkylaminoalkyl(meth)acrylate, polydimethylaminopropylacrylamide, polydimethylaminopropyl methacrylamide, etc. Preferably, the water-soluble nitrogen-containing compound is polyvinylpyrrolidone.

[0031] When the above-mentioned auxiliary stabilizer is added to the above-mentioned aqueous dispersion medium, the amount of the auxiliary stabilizer added can be appropriately determined according to the average particle size of the target thermally expandable microcapsules.

[0032] For example, when the above-mentioned condensation product or the above-mentioned water-soluble nitrogen-containing compound is used as the above-mentioned auxiliary stabilizer, the preferred lower limit of the amount of the above-mentioned auxiliary stabilizer added relative to 100 parts by weight of all monomer components in the above-mentioned monomer mixture is 0.05 parts by weight, and the preferred upper limit is 2 parts by weight.

[0033] The combination of the aforementioned dispersant stabilizer and the aforementioned auxiliary stabilizer is not particularly limited. For example, combinations of colloidal silica and condensation products, combinations of colloidal silica and water-soluble nitrogen-containing compounds, and combinations of magnesium hydroxide or calcium phosphate and emulsifiers are possible. Among these, the combination of colloidal silica and condensation products is preferred. As for the condensation product, the condensation product is preferably a condensation product of diethanolamine and aliphatic dicarboxylic acid, and particularly preferably a condensation product of diethanolamine and adipic acid, or a condensation product of diethanolamine and itaconic acid.

[0034] The high-temperature thermal expansion microspheres of the present invention are prepared by a method comprising:

[0035] S1. Mix olefinic unsaturated monomers, crosslinking agents, initiators and foaming agents to prepare an oil phase for suspension polymerization;

[0036] S. Mix the dispersant stabilizer, the dispersant stabilizing aid, and the dispersion medium to prepare an aqueous phase for suspension polymerization;

[0037] S3. After emulsifying the aqueous phase and the oil phase into a suspension, the mixture is stirred in a high-pressure reactor to carry out a suspension polymerization reaction, thereby obtaining slurry-like high-temperature thermal expansion microspheres.

[0038] Furthermore, the aqueous phase also includes an electrolyte selected from sodium chloride, potassium chloride, lithium chloride, magnesium chloride, sodium bicarbonate, lithium sulfate, sodium sulfate, potassium sulfate, ammonium sulfate, sodium carbonate, or benzoic acid; the amount of electrolyte used is 0.1 to 50 parts by weight relative to 100 parts by weight of dispersion medium. The electrolyte effectively reduces the solubility of polar monomers in the aqueous phase, decreases the probability of nucleation and polymerization in the aqueous phase, effectively improves particle size uniformity, ensures efficient participation of polar monomers in the formation of shell-wall polymers, enhances the interaction between shell-wall polymers, and improves the heat resistance of microspheres, thereby improving the high-temperature foam stability of the microspheres.

[0039] Optionally, the emulsification method for the oil phase and the aqueous phase is selected from dispersion methods such as stirring by a homogenizer or homogenizing disperser, static dispersion by a static mixer or static dispersant, membrane emulsification, ultrasonic dispersion or microchannel dispersion.

[0040] The suspension polymerization method refers to using water as a medium, dispersing monomers into fine particles suspended in water through mechanical stirring, and then thermally initiating polymerization.

[0041] The suspension polymerization reaction temperature is determined based on the initiation temperature of the initiator. Excessive temperature accelerates the reaction rate, increases the molecular weight of the polymer in the microsphere shell, and negatively impacts foaming performance. Furthermore, temperature also affects the properties and morphology of the microspheres. Pressure influences the gas-liquid balance between the monomer and the blowing agent; appropriate pressure ensures a certain amount of blowing agent is encapsulated within the microspheres. The reaction time is determined based on the half-life of the initiator at a given temperature to ensure complete monomer conversion.

[0042] Optionally, the suspension polymerization reaction temperature is 40–100°C, preferably 45–90°C, and more preferably 50–80°C.

[0043] Optionally, the suspension polymerization reaction pressure is 0–5.0 MPa, preferably 0.1–0.3 MPa; more preferably 0.2–2.0 MPa.

[0044] Optionally, the suspension polymerization reaction time is 18 to 22 hours.

[0045] Optionally, to control the pH value of the aqueous phase, the acid mentioned in step 4) is an organic acid or an inorganic acid. For example, organic acids are selected from oxalic acid, tartaric acid, malic acid, citric acid, ascorbic acid (i.e., vitamin C), etc., and aromatic organic acids such as benzoic acid, salicylic acid, caffeic acid, etc. Inorganic acids are selected from sulfuric acid, hydrochloric acid, phosphoric acid, etc., but are not limited to these. They can be used alone or in combination of two or more.

[0046] Furthermore, the preparation method also includes dehydrating the slurry-like high-temperature thermally expandable microspheres to obtain wet filter cake-like thermally expandable microspheres; or washing, dehydrating and drying to obtain dispersed thermally expandable microspheres.

[0047] The dehydration methods include bed filtration, pressure filtration, liquid filtration, rotary filtration, vacuum filtration, or centrifugal separation; the drying methods include spray drying, support drying, tunnel drying, rotary drying, drum drying, ventilation drying, turbine support drying, disc drying, or fluidized bed drying.

[0048] The method for preparing thermally expandable microspheres provided by the present invention involves suspending a mixture of olefinic unsaturated monomers in an aqueous dispersion medium containing a dispersing stabilizer in the presence of a foaming agent to prepare a shell of a thermoplastic copolymer with a high glass transition temperature, and then encapsulating the shell with a foaming agent to obtain thermally foamable microspheres.

[0049] In this invention, the volume average particle size of the high-temperature thermally expandable microspheres (i.e., thermally expandable microcapsules) preferably has a lower limit of 10 μm and a higher limit of 50 μm; more preferably, the lower limit is 15 μm and the upper limit is 35 μm. When the volume average particle size is less than 10 μm, for example, when the thermally expandable microcapsules are used for foaming, the bubbles in the resulting foamed body are too small, sometimes resulting in insufficient weight reduction. When the volume average particle size exceeds 50 μm, for example, when the thermally expandable microcapsules are used for foaming, the bubbles in the resulting foamed body become too large, sometimes causing problems in terms of strength, etc.

[0050] This invention provides high-temperature thermal expansion microspheres with excellent durability. The preparation method includes the following steps: aqueous phase preparation, oil phase preparation, and suspension polymerization. These microspheres have a structure in which a foaming agent is encapsulated within a polymer-formed shell. Silicone-containing acrylate monomers participate in the formation of the microsphere shell, resulting in better durability and foam stability. The microspheres are synthesized using a one-pot copolymerization-suspension polymerization method. The thermal expansion microspheres have a smooth surface and a well-developed core-shell structure. The microsphere particle size is uniformly controlled, ranging from 10 to 50 micrometers.

[0051] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0052] The thermally expandable microspheres provided by this invention introduce silicon-containing acrylate monomers and other monomers through a copolymerization reaction to participate in the formation of the microsphere shell, which can significantly improve the maximum foaming temperature, durability and foam stability of the microspheres. The microspheres have a high maximum foaming temperature (180-220℃) and high expansion performance.

[0053] This invention uses a one-pot copolymerization-suspension polymerization method to synthesize microspheres. The prepared thermally expandable microspheres have smooth surfaces and perfect core-shell structures. The microsphere particle size is uniformly controlled, and the particle size can be controlled between 10-50 micrometers. Attached Figure Description

[0054] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0055] Figure 1 This is a schematic flowchart of the preparation method of high-temperature thermal expansion microspheres in an embodiment of the present invention. Detailed Implementation

[0056] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0057] Example 1

[0058] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0059] S1. 90g acrylonitrile, 30g methacrylic acid, 15g N,N-dimethylacrylamide, 15g triisopropylsilyl methacrylate, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase for suspension polymerization.

[0060] S2. Add 300g deionized water, 72g sodium chloride, 50.4g silica sol, 1.6g citric acid, 0.1g sodium nitrite, and 4g dispersant (adipic acid-diethanolamine polymer) sequentially to obtain the aqueous phase of suspension polymerization.

[0061] S3. The oil and aqueous phases are mixed and homogenized at 10,000 rpm for 5 minutes to emulsify and disperse the mixture, thus preparing a suspension. The suspension is injected into a 1.0 L high-pressure reactor, the air is replaced with nitrogen, and the reactor is pressurized to an initial pressure of 0.3 MPa. Then, the reaction is carried out at 62 °C for 20 hours, followed by cooling and depressurization. The mixture is then washed, filtered, and dried in an oven at 50 °C to obtain white or slightly yellow thermoplastic microspheres.

[0062] Example 2

[0063] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0064] S1. 75g acrylonitrile, 30g methacrylic acid, 15g N,N-dimethylacrylamide, 30g triisopropylsilyl methacrylate, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase of suspension polymerization.

[0065] Steps S2 and S3 are the same as in Example 1.

[0066] Example 3

[0067] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0068] S1. 90g acrylonitrile, 30g methacrylic acid, 15g N,N-dimethylacrylamide, 15g triisopropylsilyl acrylate, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase of suspension polymerization.

[0069] Steps S2 and S3 are the same as in Example 1.

[0070] Example 4

[0071] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0072] S1. 75g acrylonitrile, 30g methacrylic acid, 15g N,N-dimethylacrylamide, 30g triisopropylsilyl acrylate, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase of suspension polymerization.

[0073] Steps S2 and S3 are the same as in Example 1.

[0074] Example 5

[0075] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0076] S1. 90g acrylonitrile, 30g methacrylic acid, 15g N,N-dimethylacrylamide, 15g methacryloyloxypropyltris(trimethylsiloxane)silane, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase for suspension polymerization.

[0077] Steps S2 and S3 are the same as in Example 1.

[0078] Comparative Example 1

[0079] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0080] S1. 90g acrylonitrile, 30g methacrylic acid, 30g N,N-dimethylacrylamide, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase of suspension polymerization.

[0081] Steps S2 and S3 are the same as in Example 1.

[0082] Comparative Example 2

[0083] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0084] S1. 90g acrylonitrile, 30g methyl methacrylate, 30g N,N-dimethylacrylamide, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase of suspension polymerization.

[0085] Steps S2 and S3 are the same as in Example 1.

[0086] Comparative Example 3

[0087] Reference Figure 1 As shown, the preparation method of high-temperature thermal expansion microspheres in this embodiment includes the following steps:

[0088] S1. 75g acrylonitrile, 45g methacrylic acid, 30g N,N-dimethylacrylamide, 15g ethanol, 0.8g ethylene glycol dimethacrylate, 15g isopentane, 35g isooctane, and 1.6g AIBN were added sequentially to obtain the oil phase of suspension polymerization.

[0089] Steps S2 and S3 are the same as in Example 1.

[0090] The performance of the high-temperature thermal expansion microspheres in the above embodiments and comparative examples was tested, as follows:

[0091] 1. Particle size distribution characteristics

[0092] For microsphere particle size testing, take approximately 1-2g of washed and dried sample, add 20-30ml of deionized water, stir well, and sonicate for 2 minutes. Turn on the laser particle size analyzer and the analysis software on the computer, and then pour in the sonicated sample. Using the analyzer and software together, you can obtain the average particle size, the percentage of particles within each size range, and the particle size distribution curve.

[0093] The formula for calculating particle size distribution is: CV value = (standard deviation / average diameter) × 100%.

[0094] 2. Microsphere foaming performance test

[0095] The experiment was conducted using a microscope and a temperature control system. A small amount of the product was placed on a glass slide and placed on a heated stage. Different objectives and eyepieces were used for observation based on the particle size (objectives x4, x10, x40, x80; eyepiece x10). A camera was connected to the microscope, and an appropriate heating rate was selected to observe and record the foaming process of the thermally expanded microspheres, capturing images of different stages of foaming. Simultaneously, the initial foaming temperature T was accurately recorded based on the readings on the temperature control system. start Maximum foaming temperature T max Bubble breaking temperature T break Foaming ratio and foam stability.

[0096] 3. Durability Testing

[0097] The prepared microspheres (0.4-0.5 g each) were placed in an oven at 190℃, and the foaming start time, concentrated foaming time, foam rupture time, and foam stabilization were recorded. The time required for the microspheres to begin rupturing after being placed in the oven is defined as the durability time.

[0098] The performance test results are shown in Table 1.

[0099] Table 1 Performance test results of high-temperature thermal expansion microspheres

[0100]

[0101] In Table 1, AN: acrylonitrile, MMA: methyl methacrylate, MAA: methacrylic acid, DMAA: N,N-dimethylacrylamide, TISMA: triisopropylsilyl methacrylate, TISA: triisopropylsilyl methacrylate, 3-T(ts)SPMA: methacryloyloxypropyltris(trimethylsiloxane)silane

[0102] In Examples 1-5 above, Si-containing acrylate monomers were introduced into the polymerization process, while the comparative examples did not. Based on the durability and defoaming temperature results in Table 1, the use of Si-containing acrylate monomers in the polymerization of the microsphere shells improved the maximum foaming temperature, heat resistance, and defoaming temperature of the microspheres. Therefore, the microspheres in these embodiments exhibit excellent expansion and foam stabilization properties.

[0103] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A high-temperature thermal expansion microsphere, characterized in that, It includes olefinic unsaturated monomers, foaming agents, crosslinking agents, initiators, dispersing stabilizers, dispersing stabilizing aids, and dispersion media, wherein: The olefinic unsaturated monomer comprises, by weight percentage, the following components: 40-70% acrylonitrile monomers, 10-30% acrylic acid monomers, 10-30% acrylamide monomers, 0-30% acrylate monomers, and 5-30% silicone-containing acrylate monomers.

2. The high-temperature thermal expansion microspheres according to claim 1, characterized in that, The silicon-containing acrylate monomer is a silyl (meth)acrylate alkyl ester, and its structural formula is as follows: In the formula, R1 = H, methyl, R2 = C n H 2n ,n≥0,R3,R4,R5=alkyl groups and their siloxane-containing alkyl derivatives.

3. The high-temperature thermal expansion microspheres according to claim 2, characterized in that, The alkyl silyl (meth)acrylate is any one or more of trimethylsilyl acrylate, trimethylsilyl methacrylate, triisopropylsilyl methacrylate, triisopropylsilyl acrylate, methacryloxypropyltris(trimethylsiloxane), trimethylsilyl methacrylate, (phenyldimethylsilyl)methyl methacrylate, and 2-methyl-2-acrylate tributylsilyl acrylate.

4. The high-temperature thermal expansion microspheres according to claim 2, characterized in that, The alkyl silyl (meth)acrylate is selected from any one or more of triisopropylsilyl methacrylate, triisopropylsilyl acrylate, and methacryloyloxypropyltris(trimethylsiloxane)silane.

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