A CS-linked high-temperature thermally expandable microsphere and its preparation method

Abstract

This application provides a C-S bond crosslinked high-temperature thermal expansion microsphere and its preparation method. The high-temperature thermal expansion microsphere includes a microsphere shell and a core structure encapsulated inside the microsphere shell. The core structure includes a foaming agent. The microsphere shell is formed by copolymerization of an olefinic unsaturated monomer and a crosslinking agent. The crosslinking agent includes at least a thiol-containing crosslinking agent, which participates in the copolymerization reaction to form the C-S bond crosslinking network of the microsphere shell. This application introduces a thiol-containing crosslinking agent with good compatibility with the foaming agent to copolymerize with the monomer and participate in the formation of the microsphere shell. This significantly optimizes the foaming temperature range, sphericity, and expansion ratio of the microspheres, and significantly improves the maximum foaming temperature and expansion performance of the microspheres.

Description

Technical Field

[0001] This application relates to the field of manufacturing expandable particles, and more specifically, to a CS-linked high-temperature thermally expandable microsphere and its preparation method. Background Technology

[0002] Thermally expandable microspheres are functional polymer microcapsules with a core-shell structure. The core consists of a low-boiling-point alkane blowing agent, while the outer shell is a thermoplastic polymer. When heated above the glass transition temperature of the outer shell, the polymer shell softens, and the blowing agent in the core vaporizes, generating internal pressure that drives the microsphere to expand to several times or even tens of times its original diameter. Upon cooling, the outer shell hardens and sets again, achieving permanent foaming. Due to this unique thermal expansion property, thermally expandable microspheres are widely used as physical blowing agents and lightweight fillers in numerous fields such as coatings and printing, foamed plastics, automotive manufacturing, and aerospace.

[0003] For thermally expandable microspheres, different foaming properties are crucial. Microspheres with different foaming temperature ranges have different applications. For example, in the injection molding of thermoplastics (such as PP, PC, PA, ABS, etc.), a wide foaming range allows microspheres to expand uniformly at different processing temperatures, avoiding uneven foaming or premature expansion due to temperature fluctuations. This not only helps to form a uniform closed-cell structure and reduce material density, but also improves the surface quality of the product, reduces shrinkage deformation, and improves dimensional stability. Furthermore, in the fields of heat-sensitive devices or special applications (such as explosives and impact materials), high-temperature microspheres with a wide foaming range can provide a more flexible foaming response. For example, in scenarios requiring rapid foaming to generate strong impact force, a wide foaming range ensures that the microspheres respond quickly at high temperatures while avoiding premature activation at lower temperatures, which could affect storage stability or performance. Therefore, developing thermally expandable microspheres with a wide foaming range and high expansion ratio is a key research direction for improving their applicability in engineering plastics, impact materials, and other fields, and also a significant technological challenge for the industry.

[0004] CN102070868A discloses the effect of long-chain crosslinking agents on the foaming properties of expandable microspheres, finding that long-chain crosslinking agents appropriately broaden the foaming range. However, the above method has the disadvantage of a relatively low maximum foaming temperature. CN202410666163.7 reports that by controlling the type of foaming agent and the phase transition temperature of the shell, the foaming agent is fully vaporized before the phase transition, thereby achieving rapid expansion of the microspheres upon reaching the phase transition without shell rupture. The shortcoming of this patent is that the foaming temperature of the microspheres is too low (90-120℃), preventing its application in medium- and high-temperature research. CN201410362784.2 discloses a rapid-foaming thermoplastic expandable microsphere. This microsphere uses vinyl acetate as a modified monomer to overcome the limitation of long foaming time in the past, but the temperature difference required from the start of expansion to maximum foaming is extremely small, generally around 10℃, and it collapses rapidly after expansion. Patent CN121736362A describes a method to construct a uniform cross-linked network between polymer segments in the outer shell by controlling the decomposition activity of the initiator and the reactivity of the cross-linking agent within a specific temperature range. The resulting thermally expandable microspheres exhibit a wide expansion temperature range and good heat resistance, with stable expansion behavior and a high expansion ratio. However, the maximum expansion temperature of these microspheres is relatively low, and they are not extended to high-temperature applications. Patent CN120098321A introduces monofunctional cage-type polysilsesquioxane monomers containing double bonds to participate in polymerization and form the microsphere shell, significantly improving the foaming response speed of the microspheres. These microspheres possess a higher maximum expansion temperature and higher expansion performance. However, the foaming ratio is slightly insufficient, failing to meet the application requirements of high-foaming-ratio products. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this application is to provide a CS bond crosslinked high-temperature thermal expansion microsphere and its preparation method.

[0006] According to a first aspect of this application, a CS-linked high-temperature thermal expansion microsphere is provided, comprising a microsphere shell and a core structure encapsulated inside the microsphere shell, the core structure comprising a foaming agent, the microsphere shell being formed by copolymerization of an olefinic unsaturated monomer and a crosslinking agent, the crosslinking agent comprising at least a thiol-containing crosslinking agent, the thiol-containing crosslinking agent participating in the copolymerization reaction to constitute a CS-linked crosslinking network of the microsphere shell.

[0007] Specifically, the raw materials for forming high-temperature thermal expansion microspheres include olefinic unsaturated monomers (i.e., olefinic unsaturated monomers), foaming agents, crosslinking agents, initiators, dispersing stabilizers, dispersing stabilizing aids, and dispersion media. Copolymerization reactions occur between monomers, between monomers and crosslinking agents, and between crosslinking agents. However, due to the small amount of crosslinking agents, the probability of reactions occurring between crosslinking agents is relatively low.

[0008] The thermal expansion microspheres in this application have a high maximum foaming temperature (generally >200℃), a wide foaming temperature range, and a high expansion capacity, exhibiting superior foaming performance at high temperatures.

[0009] Optionally, the mass percentage of the thiol-containing crosslinking agent to the microsphere shell is 0.1%-10%.

[0010] Optionally, the chemical structure of the thiol-containing crosslinking agent is any one of aliphatic, aromatic, and organic-inorganic hybrid derivatives containing 2-4 thiol groups.

[0011] Thiol-containing crosslinking agents include, but are not limited to, pentanedithiol, octanedithiol, decandithiol, polyethylene glycol dithiol, dimercaptohexaoctyl POSS, tetramercaptotetraoctyl POSS, dimercaptooctyl POSS and tetramercaptohexaoctyl POSS, naphthiophenol, tris[2-(3-mercaptopropionyloxy)ethyl isocyanurate], quinoline-3-thiol, trimethylolpropane tris(3-mercaptopropionic acid) ester, etc. They can be used alone or in combination of two or more.

[0012] Optionally, the thiol-containing crosslinking agent is a thiol crosslinking agent with good compatibility with the foaming agent (such as a mixture of isopentane and isooctane), selected from any one or more of dimercaptohexaoctyl POSS, tetramercaptotetraoctyl POSS, dimercaptooctaoctyl POSS, and tetramercaptohexaoctyl POSS. If the crosslinking agent is not compatible with the foaming agent, it may lead to uneven crosslinking density, which in turn results in poor microsphere expansion.

[0013] By employing a thiol-containing crosslinking agent with good compatibility with the foaming agent, it can directly participate in the free radical reaction of the double bond, completing the reaction in one step without the need for subsequent addition. Simultaneously, the thiol compound is uniformly dispersed within the microsphere shell, with its content adjustable from 0.1% to 10%, significantly optimizing the microsphere expansion ratio and foaming range.

[0014] Optionally, the crosslinking agent may further include crosslinking agents containing multiple tubular double bonds.

[0015] Multi-tube double-bond crosslinking agents include, but are not limited to, ethylene glycol (meth)diacrylate, diethylene glycol di(meth)acrylate, glyceryl dimethacrylate, polyethylene glycol (400) dimethacrylate, polyethylene glycol (600) dimethacrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and divinyl ether. They can be used alone or in combination of two or more.

[0016] Optionally, the mass percentage of the crosslinking agent containing multiple double bonds to the microsphere shell is 0.1%-5%.

[0017] The microsphere shell comprises the following components by weight percentage: 40%-70% acrylonitrile monomers, 10%-30% acrylic monomers, 10%-30% acrylamide monomers, 0.1%-10% mercapto-containing crosslinking agent, and 0.1%-5% multi-tube double bond-containing crosslinking agent. The sum of the weight percentages of these five components is 100%. Each component participates in polymerization to form the microsphere shell, thereby improving the foaming temperature range and maximum expansion capacity of the microspheres.

[0018] Crosslinking agents are compounds possessing two or more polymerizable sites. Crosslinking agents include multi-tube double-bond crosslinking agents and, for the first time in this application, thiol-containing crosslinking agents. Multi-tube double-bond crosslinking agents primarily function as crosslinking agents, maintaining a certain mechanical strength of the shell and preventing rapid collapse of the microspheres after expansion. The two types of crosslinking agents work together to maintain crosslinking density while introducing a CS bond crosslinking network and improving the flexible tensile properties of the CS bonds.

[0019] The type and content of crosslinking agents affect the expansion ratio and temperature of microspheres. A low crosslinking agent content results in poor foam stability, poor heat resistance, and rapid shrinkage after expansion. A high crosslinking agent content leads to denser crosslinking, which, while moderately improving heat resistance, reduces the expansion effect. Generally, trifunctional crosslinking agents have a higher degree of crosslinking than difunctional crosslinking agents.

[0020] Optionally, when the crosslinking agent is a trifunctional compound, the mass percentage of the crosslinking agent to the olefin unsaturated monomer is 0.1 to 3 wt%.

[0021] Optionally, when the crosslinking agent is a difunctional compound, the mass percentage of the crosslinking agent to the olefin unsaturated monomer is 0.1 to 5 wt%.

[0022] The foaming agent typically accounts for 24% of the microsphere shell as the core, while the initiator accounts for about 1.1% of the microsphere shell.

[0023] The foaming agent is a liquid with a boiling point temperature not higher than the softening temperature of the thermoplastic polymer shell. Optionally, 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.

[0024] 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.

[0025] Preferably, the volume average particle size of the high-temperature thermally expandable microspheres (i.e., thermally expandable microcapsules) in this application is 10 to 50 μm. More preferably, the volume average particle size is 15 to 35 μm.

[0026] It should be noted that if the volume average particle size of the microspheres is less than 10 μm, the resulting foamed body will have excessively small bubbles when using thermally expandable microcapsules for foaming, sometimes resulting in insufficient weight reduction. If the volume average particle size exceeds 50 μm, the resulting foamed body will have excessively large bubbles when using thermally expandable microcapsules for foaming, sometimes causing problems in terms of strength, etc.

[0027] According to a second aspect of this application, a method for preparing the CS-bonded cross-linked high-temperature thermal expansion microspheres is provided, comprising: An oil phase for suspension polymerization is obtained by mixing an olefinic unsaturated monomer, a crosslinking agent, an initiator, and a foaming agent. The dispersant stabilizer, the dispersant stabilizing aid, and the dispersion medium are mixed to obtain an aqueous phase for suspension polymerization; 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, resulting in slurry-like high-temperature thermal expansion microspheres.

[0028] The method for preparing thermally expandable microspheres provided in this application 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 (around 110°C), and then encapsulating the shell with a foaming agent to obtain thermally foamable microspheres.

[0029] 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 0.1-10% 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.

[0030] 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.

[0031] 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 salts of methacrylic acid, etc. Exemplary examples of carboxyl metal salt-containing methacrylic acid monomers (metal salts of methacrylic acid) 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.

[0032] 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.

[0033] 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.

[0034] Optionally, the dispersion medium is deionized water, or ionized water containing hydrophilic organic solvents such as alcohols.

[0035] 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.

[0036] Depending on the selection of the dispersant stabilizer, the pH value of the dispersion medium is controlled. For example, 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, with the pH value controlled between 5 and 12, preferably 6 to 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, thus affecting 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 droplets), thereby affecting the final microsphere particle size and dispersion uniformity (CV value). Furthermore, high viscosity - high thixotropy affects workability; under high viscosity conditions, the stirring power is higher, resulting in higher energy consumption. Preferably, the pH value of the dispersion medium is 3 to 5.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Optionally, the suspension polymerization reaction temperature is 40~100℃, preferably 45~90℃; more preferably 60~75℃.

[0047] Optionally, the suspension polymerization reaction pressure is 0~5.0 MPa, preferably 0.1~0.3 MPa; more preferably 0.2~2.0 MPa.

[0048] Optionally, the suspension polymerization reaction time is 18 to 22 hours.

[0049] Optionally, to control the pH of the aqueous phase, a weak acid needs to be added. The weak acid can be 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.

[0050] 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.

[0051] 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.

[0052] This application provides a high-temperature thermally expandable microsphere with a wide temperature range. Its preparation method includes the following steps: aqueous phase preparation, oil phase preparation, and suspension polymerization. It has a structure in which a foaming agent is encapsulated within a polymer-formed shell. The olefinic unsaturated monomer participates in the formation of the microsphere shell, resulting in better foaming performance. The microspheres are synthesized using a one-pot copolymerization-suspension polymerization method. The thermally expandable 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.

[0053] The CS-linked high-temperature thermal expansion microspheres provided in this application introduce a mercapto-containing crosslinking agent with good compatibility with the foaming agent to copolymerize with the monomer and participate in the formation of the microsphere shell. This can significantly optimize the foaming temperature range, sphericity and expansion ratio of the microspheres, and significantly improve the maximum foaming temperature (>200 ℃) and expansion performance of the microspheres.

[0054] This application 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 can be controlled between 10 and 50 micrometers.

[0055] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0056] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating a method for preparing CS-linked high-temperature thermally expandable microspheres according to an exemplary embodiment; Figure 2The images shown are schematic diagrams (a, b) of the microsphere morphology prepared using acrylate crosslinking agents in Comparative Example 10 and (c, d) of the microsphere morphology prepared using mercapto crosslinking agents in Example 1, where a and c are images magnified 200 times, and b and d are images magnified 500 times. Figure 3 The images shown are schematic diagrams (e, f) of the microsphere morphology prepared in Example 2 and (g, h) of the microsphere morphology prepared in Example 3, where e and g are images magnified 200 times, and f and h are images magnified 500 times. Detailed Implementation

[0057] The present application will now be described in detail with reference to specific embodiments / comparative examples. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.

[0058] Example 1 Reference Figure 1 As shown, the preparation method of CS bond crosslinked high-temperature thermal expansion microspheres in this embodiment includes the following steps: S1. 90 g acrylonitrile, 30 g methacrylic acid, 30 g N,N-dimethylacrylamide, 2 g decanethiol, 1 g ethylene glycol dimethacrylate, 15 g ethanol, 15 g isopentane, 35 g isooctane, and 1.6 g AIBN were added sequentially to obtain the oil phase for suspension polymerization.

[0059] S2. 300 g of deionized water, 72 g of sodium chloride, 50.4 g of silica sol, 1.6 g of citric acid, 0.1 g of sodium nitrite, and 4 g of dispersant (adipic acid-diethanolamine polymer) were added sequentially to obtain an aqueous phase for suspension polymerization.

[0060] 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 purged 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.

[0061] Other embodiments and comparative examples Reference Figure 1As shown, the preparation methods of high-temperature thermal expansion microspheres in other embodiments and comparative examples, and the specific process parameters such as the adjustment of crosslinking agent dosage are shown in Tables 1 and 2.

[0062] The performance of the high-temperature thermal expansion microspheres in the above embodiments and comparative examples was tested, as follows: 1. Particle size distribution characteristics For microsphere particle size testing, take approximately 1-2 g of washed and dried sample, add 20-30 ml 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 particle size distribution curves.

[0063] The formula for calculating particle size distribution is: CV value = (standard deviation / average diameter) × 100%.

[0064] 2. Microsphere foaming performance test 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 Foaming ratio and foam stability.

[0065] The performance test results are shown in Tables 1 and 2.

[0066] Table 1. Process parameters and performance test results of the high-temperature thermal expansion microspheres in each embodiment. Table 2. Process parameters and performance test results of high-temperature thermal expansion microspheres in each comparative example. In the table, crosslinker 1 is an acrylate crosslinker, and crosslinker 2 is a mercapto crosslinker. AN: Acrylonitrile, MAA: Methacrylic acid, DMAA: N,N-dimethylacrylamide, EDGMA: Ethylene glycol dimethacrylate, TMPTA: Trimethylolpropane triacrylate, GDMP: Di(3-mercaptopropionic acid)ethylene glycol, PETMP: Pentaerythritol tetrakis(3-mercaptopropionic acid) ester.

[0067] Regarding the foaming situation, the size of the microspheres before and after expansion is compared based on the microscopic foaming images. Expansion of more than 4 times is excellent, 3-4 times is good, 2-3 times is average, and less than 2 times is poor.

[0068] In Examples 1-10, thiol-containing crosslinking agents with good compatibility with the foaming agent were introduced to participate in the polymerization. In the comparative examples, thiol crosslinking agents or acrylate crosslinking agents with poor compatibility with the foaming agent were introduced. Based on the foaming conditions and temperature ranges in Tables 1 and 2, thiol compounds with good compatibility, as crosslinking agents, participated in the polymerization of the microsphere shells, improving the foaming temperature range and foaming ratio of the microspheres. According to Examples 5 and 9-12, POSS-type and polyethylene glycol dithiol are thiol crosslinking agents with good compatibility; therefore, they can be used alone to achieve the preparation of high-temperature thermal expansion microspheres with good performance. Figure 2 The differences in morphology between microspheres prepared by acrylate crosslinking agents and mercapto crosslinking agents are shown. Among them, a and b are microspheres prepared by crosslinking agents containing multiple tube double bonds in Comparative Example 10, and c and d are microspheres prepared by mercapto crosslinking agents in Example 1. Figure 3 The morphology of the microspheres in Examples 2 and 3 is shown, and other examples also have similar morphologies. The microspheres in all the above examples of this application have excellent expansion properties, bubble stabilization properties, and sphericity.

[0069] The foregoing has described some specific embodiments of this application. It should be understood that this application 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 substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. A type of high-temperature thermally expandable microspheres cross-linked by CS bonds, characterized in that, The microsphere shell includes a microsphere shell and a core structure encapsulated inside the microsphere shell. The core structure includes a foaming agent. The microsphere shell is formed by copolymerization of an olefinic unsaturated monomer and a crosslinking agent. The crosslinking agent includes at least a thiol-containing crosslinking agent, which participates in the copolymerization reaction to form a CS bond crosslinking network of the microsphere shell.

2. The CS-linked high-temperature thermal expansion microspheres according to claim 1, characterized in that, The mass percentage of the thiol-containing crosslinking agent to the microsphere shell is 0.1%-10%.

3. The high-temperature thermal expansion microspheres cross-linked by CS bonds according to claim 1, characterized in that, The chemical structure of the thiol-containing crosslinking agent is any one of aliphatic, aromatic, and organic-inorganic hybrid derivatives containing 2-4 thiol groups.

4. The high-temperature thermal expansion microspheres cross-linked by CS bonds according to claim 1, characterized in that, The thiol-containing crosslinking agent is selected from any one or more of octanedithiol, decandithiol, polyethylene glycol dithiol, dithiohexoctyl POSS, tetrathiotetraoctyl POSS, dithiooctaoctyl POSS, and tetrathiohexoctyl POSS.

5. The CS-linked high-temperature thermal expansion microspheres according to claim 1, characterized in that, The thiol-containing crosslinking agent is selected from any one or more of dimercaptohexaoctyl POSS, tetramercaptotetraoctyl POSS, dimercaptooctyl POSS, and tetramercaptohexaoctyl POSS.

6. The CS-linked high-temperature thermal expansion microspheres according to claim 1, characterized in that, The crosslinking agent also includes crosslinking agents containing multiple double bonds.

7. The CS-linked high-temperature thermal expansion microspheres according to claim 6, characterized in that, The mass percentage of the crosslinking agent containing multiple double bonds to the microsphere shell is 0.1%-5%.

8. The high-temperature thermal expansion microspheres cross-linked by CS bonds according to claim 1, characterized in that, The foaming agent is a hydrocarbon or halogenated hydrocarbon compound with 5 to 8 carbon atoms and a boiling point of 25 to 127°C.

9. The CS-linked high-temperature thermal expansion microspheres according to claim 1, characterized in that, The microspheres have a volume average particle size of 10 to 50 μm.

10. A method for preparing high-temperature thermally expandable microspheres cross-linked by CS bonds according to any one of claims 1-9, characterized in that, include: An oil phase for suspension polymerization is obtained by mixing an olefinic unsaturated monomer, a crosslinking agent, an initiator, and a foaming agent. The dispersant, the dispersant stabilizing agent, and the dispersion medium are mixed to obtain an aqueous phase for suspension polymerization. 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, resulting in slurry-like high-temperature thermal expansion microspheres.

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