Coated inorganic foaming agent, preparation method and application thereof, and foamed material

Abstract

The application discloses a coated inorganic foaming agent and a preparation method and application thereof, and a foaming material, relates to the technical field of inorganic foaming agents, and the preparation method of the coated inorganic foaming agent comprises the following steps: (1) dissolving an emulsifier in a solvent to obtain an oil phase; (2) dissolving or dispersing a hydrophilic foaming agent-precipitating agent material in water to obtain a first water phase; (3) dissolving a silicon dioxide precursor in water to obtain a second water phase; (4) uniformly mixing the first water phase and the oil phase, then quickly pouring into the second water phase, stirring and reacting, centrifuging or naturally settling, discarding the supernatant, and drying to obtain the coated inorganic foaming agent. Inorganic SiO2 is used as the coating material, the thermal stability and storage stability of the foaming material can be increased, meanwhile, the foaming material has uniform cell structure and higher flame retardant performance.

Description

Technical fields:

[0001] This invention relates to the field of inorganic foaming agent technology, specifically to a coated inorganic foaming agent, its preparation method and application, and foaming materials. Background technology:

[0002] By introducing gas into a polymer matrix material (such as plastics, elastomers, or natural polymers) through foaming technology, polymer foam materials with countless micropores are prepared. This process can impart properties such as light weight, sound insulation, heat insulation, shock absorption, cushioning, and flexibility while maintaining the unique properties of the matrix material. These materials are widely used in household goods, transportation, insulation materials, packaging materials, electrical appliances, sports equipment, electronic products, chemicals, and textiles. High-performance foam plastics play an important role in cutting-edge fields such as military and aerospace.

[0003] Commonly used foaming methods mainly include physical foaming and chemical foaming. Physical foaming methods include solution-based pore-forming technology, supercritical foaming technology, and expandable microsphere foaming technology. Chemical foaming technologies include reactive foaming methods, organic foaming agent decomposition methods, and inorganic foaming agent decomposition methods.

[0004] Inorganic foaming agents are generally endothermic, such as sodium bicarbonate, ammonium carbonate, and thiocyanate. When an inorganic foaming agent is added to a polymer matrix material, it decomposes under specific temperature and pressure conditions, releasing gases such as carbon dioxide, ammonia, and water vapor. During the gas escape process, numerous bubble nuclei are generated, which gradually grow to form cells. After the polymer cools or solidifies, the formed cell structure is retained within the polymer, ultimately resulting in a foamed material. Inorganic foaming agents have the advantages of good nucleation effects and readily available raw materials.

[0005] However, inorganic foaming agents have poor compatibility with polymer matrix materials, and most inorganic foaming agents exhibit moisture absorption and clumping during storage, leading to unstable performance and significant agglomeration after mixing. The foaming agent cannot be uniformly dispersed in the polymer matrix material, thus failing to obtain foamed materials with uniform cell size. Furthermore, the low decomposition temperature and wide decomposition temperature range of inorganic foaming agents are unfavorable for forming uniform and fine cells during the foaming process of materials.

[0006] Patent CN200610052961.2 discloses a composite foaming agent and its preparation method. The method involves mechanically or air-jet grinding an inorganic foaming agent, bicarbonate, and then uniformly mixing the ground bicarbonate with molecular sieves in a mixer according to a specific ratio. This results in a composite foaming agent with significantly improved flowability and dispersibility. This patent addresses the issue of foaming agent agglomeration by controlling the moisture content in the system, thus achieving uniform dispersion. However, simple mixing does not solve the problems of agglomeration when inorganic compounds are mixed with polymer matrix materials, nor the issues of long-term storage stability. Furthermore, if the amount of molecular sieve is small, the water adsorption capacity is low, leading to poor storage stability; if the amount of molecular sieve is large, more gas molecules are adsorbed during the preparation of the foaming material, affecting the foaming ratio. Summary of the Invention:

[0007] The technical problem to be solved by this invention is to provide a core-shell structured coated inorganic foaming agent, with a shell of spherical SiO2 and a core material that generates gas upon thermal decomposition. The coated inorganic foaming agent of this invention is prepared by a three-phase emulsion method. First, a hydrophilic foaming agent-precipitant material is dispersed in water to form a first aqueous phase. Then, an emulsion is formed by high-speed homogenization and stirring with an oil phase containing dissolved W / O and O / W emulsifiers. Next, a second aqueous phase containing dissolved silica precursor is added to the emulsion, and stirring is used to form a three-phase emulsion. Due to the surface tension of the oil phase acting between the first and second aqueous phases, the silica precursor in the second aqueous phase contacts the precipitant in the first aqueous phase, reacting to generate SiO2. With continued stirring, SiO2 continues to be generated along the interface of the first aqueous phase, ultimately forming spherical SiO2 coated with the inorganic foaming agent.

[0008] The technical problem to be solved by this invention is achieved by the following technical solution:

[0009] One objective of this invention is to provide a method for preparing a coated inorganic foaming agent, the method comprising the following steps:

[0010] (1) Dissolve the emulsifier in a solvent to obtain the oil phase;

[0011] (2) Dissolve or disperse the hydrophilic foaming agent-precipitant material in water to obtain the first aqueous phase;

[0012] (3) Dissolve the silica precursor in water to obtain the second aqueous phase;

[0013] (4) After mixing the first aqueous phase and the oil phase evenly, quickly pour the mixture into the second aqueous phase, stir to react, centrifuge or allow to settle naturally, discard the supernatant, and dry to obtain the coated inorganic foaming agent.

[0014] The second objective of this invention is to provide a coated inorganic foaming agent obtained by the aforementioned preparation method.

[0015] A third objective of this invention is to provide the application of the aforementioned coated inorganic foaming agent in foamed materials.

[0016] The fourth objective of this invention is to provide a foaming material, comprising a polymer matrix and a foaming agent, wherein the foaming agent is the aforementioned coated inorganic foaming agent.

[0017] The beneficial effects of this invention are:

[0018] (1) The preparation method of the coating inorganic foaming agent provided by the present invention does not allow the SiO2 shell material to precipitate independently, and has a higher coating efficiency compared with other coating methods such as sol-gel method; and the use of inorganic SiO2 as coating material has higher flame retardant performance compared with other organic coating materials that release heat during decomposition.

[0019] (2) The foaming agent-precipitant material used in the preparation method of the coated inorganic foaming agent provided by the present invention is both the main material of the coated foaming agent and the precipitant of the SiO2 precursor, thus avoiding the complexity of the preparation process.

[0020] (3) The coated inorganic foaming agent prepared by the present invention is spherical, which can more effectively block the contact between foaming material particles, prevent particle aggregation and moisture absorption, and effectively improve the storage stability of foaming material.

[0021] (4) The particle size distribution of the coated inorganic foaming agent prepared by the present invention is relatively uniform. Due to the barrier and sealing effect of the coating layer, its decomposition temperature range is narrowed. The foaming material prepared by the coated inorganic foaming agent has a uniform cell structure. Attached image description:

[0022] Figure 1-4 The images shown are scanning electron microscope (SEM) images of the coated inorganic foaming agents obtained in Examples 1-4, respectively.

[0023] Figure 5 , 7 Images 9 and 11 are internal micrographs of foamed materials prepared by adding the coated inorganic foaming agents obtained in Examples 1-4, respectively.

[0024] Figure 6 , 8 10 and 12 are internal images of the foamed materials prepared by adding the coated inorganic foaming agents obtained from Comparative Examples 1-4 (the images were taken directly with a camera because the pores are large and uneven).

[0025] Figure 13Thermogravimetric analysis (TGA) curves of SiO2@NaHCO3 obtained in Example 2 are shown.

[0026] Figure 14 A diagram illustrating the microscopic mechanism of SiO2-coated inorganic foaming agent preparation using the three-phase emulsion method. Detailed implementation method:

[0027] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments and illustrations.

[0028] This invention provides a method for preparing a coated inorganic foaming agent, the method comprising the following steps:

[0029] (1) Dissolve the emulsifier in a solvent to obtain the oil phase;

[0030] (2) Dissolve or disperse the hydrophilic foaming agent-precipitant material in water to obtain the first aqueous phase;

[0031] (3) Dissolve the silica precursor in water to obtain the second aqueous phase;

[0032] (4) After mixing the first aqueous phase and the oil phase evenly, quickly pour the mixture into the second aqueous phase, stir to react, centrifuge or allow to settle naturally, discard the supernatant, and dry to obtain the coated inorganic foaming agent.

[0033] In this invention, the emulsifier includes W / O type emulsifier and O / W type emulsifier.

[0034] In a further technical solution, the W / O type emulsifier is a surfactant with an HLB value of 3 to 6, including but not limited to glyceryl monostearate, propylene glycol fatty acid ester, diethylene glycol fatty acid ester, polyoxyethylene sorbitan beeswax derivative, propylene glycol monostearate, propylene glycol monolaurate, sorbitan sesquioleate, sorbitan monostearate, sorbitan monooleate, diethylene glycol monostearate, diethylene glycol monooleate, methyl glucoside sesquistearate, oleyl alcohol polyoxyethylene ether, hydroxylated lanolin, and ethylene glycol fatty acid ester, one or more of these.

[0035] In a further technical solution, the O / W type emulsifier is a surfactant with an HLB value of 8 to 18, including but not limited to polyoxyethylene monostearate, polyoxyethylene monolaurate, polyoxyethylene sorbitan lanolin derivative, polyoxyethylene dehydrated sorbitan monolaurate, polyoxyethylene oil-based ether, polyoxyethylene lauryl ether, polyoxyethylene esters of mixed fatty acids and resin acids, polyoxypropylene lanolin ether, polyoxyethylene acetylated lanolin derivative, polyoxyethylene lanolin ether, polyoxyethylene methyl glucoside sesquioleate, polyoxyethylene dehydrated sorbitan monostearate, and polyoxyethylene... Sorbitol monooleate, polyoxyethylene sorbitol monolaurate, polyoxyethylene sorbitol monopalmitate, polyoxyethylene oleyl alcohol ether, polyoxyethylene cholesterol ether, polyoxyethylene lanolin alcohol ether, polyoxyethylene sorbitol monolaurate, polyoxyethylene acetylated lanolin derivative, polyoxyethylene castor oil, polyoxyethylene monooleate, polyoxyethylene octadecyl alcohol, polyoxyethylene hexadecyl alcohol, polyoxyethylene alkyl aryl ether, polyoxyethylene oxypropylene stearate, polyoxyethylene oleyl alcohol, polyoxyethylene fatty alcohol, polyoxyethylene vegetable oil, and polyethylene glycol monopalmitate are among one or more of these.

[0036] In this invention, the solvent is an organic solvent that is insoluble in water, including but not limited to alkanes such as cyclohexane, n-heptane, n-hexane, isooctane, and pentane; aromatic hydrocarbons such as benzene, toluene, and xylene; haloalkanes such as carbon tetrachloride, chloroform, dichloroethane, dichloromethane, and trichloroethane; esters such as ethyl acetate and methyl acetate; and one or more ethers such as diethyl ether, petroleum ether, diisopropyl ether, and tert-butyl methyl ether.

[0037] In a further technical solution, the ratio of W / O type emulsifier, O / W type emulsifier to solvent in the oil phase is (0.1-3g):(0.1-3g):100mL. Preferably, the ratio of W / O type emulsifier, O / W type emulsifier to solvent in the oil phase is (1-2g):(1-2g):100mL.

[0038] In this invention, the hydrophilic foaming agent-precipitant material includes, but is not limited to, one or more of (NH4)2CO3, NH4HCO3, (NH4)2HPO4, NaHCO3, and KHCO3.

[0039] In a further technical solution, the ratio of hydrophilic foaming agent-precipitant material to water in the first aqueous phase is (20-100g):100mL. Preferably, the ratio of hydrophilic foaming agent-precipitant material to water in the first aqueous phase is (50-80g):100mL.

[0040] In this invention, the silica precursor includes, but is not limited to, one or more of sodium silicate, potassium silicate, and silica sol.

[0041] The chemical reaction principle of this invention is as follows:

[0042] M2SiO3+2NH4 + →SiO2↓+H2O+2NH3↑+2M +

[0043] or

[0044] M2SiO3 + 2HCO3 - →M2CO3 + H2O + SiO2↓ + 2OH -

[0045] M is one of H, Na, and K.

[0046] In a further technical solution, the ratio of silica precursor to water in the second aqueous phase is (1-50g):100mL. Preferably, the ratio of silica precursor to water in the second aqueous phase is (10-20g):100mL.

[0047] In a further technical solution, the volume ratio of the first aqueous phase, the oil phase, and the second aqueous phase is 1:(1-3):(5-15). Preferably, the volume ratio of the first aqueous phase, the oil phase, and the second aqueous phase is 1:(1.5-2.5):(7-10).

[0048] In a further technical solution, the first aqueous phase and the oil phase can be homogenized after being mixed evenly and before the second aqueous phase is poured in, with a rotation speed of 5000-15000 rpm and a time of 1-10 min.

[0049] In this invention, the drying process is low-temperature atmospheric pressure drying, reduced pressure drying, or freeze drying.

[0050] This invention provides a coated inorganic foaming agent obtained by the aforementioned preparation method.

[0051] The present invention can also use silane coupling agents or titanate coupling agents to perform surface modification on the aforementioned coated inorganic foaming agents by wet or dry methods, thereby further improving the dispersibility of the inorganic foaming agents in the polymer matrix.

[0052] The present invention also provides the application of the aforementioned coated inorganic foaming agent in foamed materials.

[0053] The present invention also provides a foaming material, comprising a polymer matrix and a foaming agent, wherein the foaming agent is the aforementioned coated inorganic foaming agent.

[0054] In this invention, the polymer matrix is ​​a thermoplastic, a thermosetting plastic, or a rubber.

[0055] In further technical solutions, the thermoplastic plastic includes, but is not limited to, one or more of low-density polyethylene, high-density polyethylene, polypropylene, polyvinyl chloride, poly-1-butene, polycarbonate, ethylene-vinyl acetate copolymer, polyester, polystyrene, TPE, and TPR.

[0056] In further technical solutions, the thermosetting plastic includes, but is not limited to, one or more of phenolic resin, epoxy resin, and unsaturated polyester resin.

[0057] In a further technical solution, the rubber is natural rubber and / or synthetic rubber.

[0058] The coated inorganic foaming agent of the present invention is mixed with a polymer matrix material under conditions below the decomposition temperature of the foaming agent using equipment such as an open mill or internal mixer, and then foamed. The foaming method is extrusion foaming, calendering foaming or molding foaming. The shape is fixed by cooling after foaming or by cross-linking reaction during foaming, and a foamed material of a specific shape is produced.

[0059] In a further technical solution, the foaming material also includes functional fillers, which are flame-retardant fillers and / or ceramic fillers.

[0060] Preferably, the flame-retardant filler includes, but is not limited to, one or more of magnesium hydroxide, aluminum hydroxide, basic magnesium carbonate, ammonium polyphosphate, microencapsulated composite flame retardant, and synergistic flame retardant.

[0061] Preferably, the ceramic filler includes, but is not limited to, one or more of the following: low melting point glass powder, zinc oxide, calcium oxide, zinc borate, calcium borate, mica powder, wollastonite powder, and palygorskite powder.

[0062] By combining the coated inorganic foaming agent and functional filler described in this invention in a polymer matrix, higher performance foaming materials (such as flame retardancy, ceramic properties, etc.) can be obtained.

[0063] Example 1

[0064] Preparation of coated inorganic foaming agents:

[0065] (1) Add 0.8g of propylene glycol monolaurate and 0.8g of polyoxyethylene sorbitan monooleate to 70mL of n-hexane and stir until completely dissolved to obtain the oil phase.

[0066] (2) Add 15g NH4HCO3 to 25mL of water and add zirconium beads. Use a planetary ball mill to ball mill at 500rpm for 2h. Filter out the zirconium beads with a sieve to obtain the first aqueous phase.

[0067] (3) Add 30g of sodium silicate with a modulus of 1.5 to 250mL of water and stir until completely dissolved to obtain the second aqueous phase.

[0068] (4) The first aqueous phase and the oil phase were stirred and mixed evenly, and then homogenized at 9000 rpm for 2 min using a high-speed homogenizer to prepare an O / W type emulsion. The emulsion was then quickly poured into the second aqueous phase and stirred for 5 h. After centrifugation, the supernatant was discarded and the mixture was freeze-dried to obtain the SiO2-coated inorganic foaming agent.

[0069] Applications of coated inorganic foaming agents:

[0070] By mass, 100 parts of vinyl silicone oil (vinyl content 0.16%), 30 parts of fumed silica, 20 parts of aluminum hydroxide, 30 parts of calcium silicate, 10 parts of zinc borate (2ZnO·3B2O3·3.5H2O), 4 parts of the SiO2-coated inorganic foaming agent prepared in this embodiment, 0.5 parts of caster platinum catalyst (platinum content 1000ppm), 1 part of hydrogen-containing silicone oil (hydrogen content 1%), and 0.06 parts of alkynyl alcohol inhibitor (ethynylcyclohexanol) were kneaded evenly using a kneader, then calendered to a thickness of 2mm using a calender, and then placed in an 80℃ oven for foaming-vulcanization for 10 minutes. Finally, it was placed in a 150℃ oven for secondary vulcanization for 2 hours to obtain foamed silicone rubber material.

[0071] Example 2

[0072] Preparation of coated inorganic foaming agents:

[0073] (1) Add 1g of dehydrated sorbitan monooleate and 1g of polyoxyethylene monolaurate to 70mL of ethyl acetate and stir until completely dissolved to obtain the oil phase.

[0074] (2) Add 20g NaHCO3 to 30mL of water and add zirconium beads. Use a planetary ball mill to ball mill at 500rpm for 2h. Filter out the zirconium beads with a sieve to obtain the first aqueous phase.

[0075] (3) Add 40g of sodium silicate with a modulus of 1.5 to 300mL of water and stir until completely dissolved to obtain the second aqueous phase.

[0076] (4) The first aqueous phase and the oil phase were stirred and mixed evenly, and then homogenized at 12,000 rpm for 5 min using a high-speed homogenizer to prepare an O / W type emulsion. The emulsion was then quickly poured into the second aqueous phase and stirred for 3 h. After centrifugation, the supernatant was discarded and the mixture was dried under reduced pressure to obtain the SiO2-coated inorganic foaming agent.

[0077] Applications of coated inorganic foaming agents:

[0078] By weight, 100 parts of bisphenol A diglycidyl ether were preheated at 60°C for 0.5 h, and 15 parts of microencapsulated composite flame retardant (Anhui Yishitong Materials Technology Co., Ltd., VMFAPP) were added. The mixture was stirred at 500 rpm, and then 27.5 parts of curing agent DDS were added. The mixture was pre-cured for 10 min, and then 5 parts of the SiO2-coated inorganic foaming agent prepared in this example were added. The mixture was stirred for 10 min. The pre-cured epoxy resin was cast into an aluminum mold and finally transferred to an oven at 185°C for foaming and curing for 4 h to obtain the foamed epoxy resin material.

[0079] Example 3

[0080] Preparation of coated inorganic foaming agents:

[0081] (1) Add 1g of diethylene glycol monostearate and 1g of polyoxyethylene monostearate to 70mL of n-heptane and stir until completely dissolved to obtain the oil phase.

[0082] (2) Add 15g(NH4)2HPO4 to 25mL of water and stir until completely dissolved to obtain the first aqueous phase.

[0083] (3) Add 50g of 30% silica sol to 350mL of water and stir until completely dissolved to obtain the second aqueous phase.

[0084] (4) The first aqueous phase and the oil phase were stirred and mixed evenly, and then homogenized at 6000 rpm for 8 min using a high-speed homogenizer to prepare an O / W type emulsion. The emulsion was then quickly poured into the second aqueous phase and stirred for 8 h. After natural sedimentation, the supernatant was discarded and dried at normal pressure to obtain the SiO2-coated inorganic foaming agent.

[0085] Applications of coated inorganic foaming agents:

[0086] By weight, 100 parts of LDPE (general grade) were added to a two-roll plasticizer (roll temperature 100℃). After melting, 30 parts of EVA (vinyl acetate content 28.0wt%), 10 parts of EPDM rubber (vinyl content 69wt%, ENB content 2.8wt%), and 100 parts of nano CaCO3 (average particle size = 60nm) were added. Then, 0.5 parts of dicumyl peroxide and 7 parts of the SiO2-coated inorganic foaming agent prepared in this example were added. After mixing for 10 minutes, the mixture was sheeted out and then placed on a flat vulcanizing machine for compression molding. The pressing temperature was 170℃, the time was 10 minutes, and the pressure was 10MPa. After depressurization and cooling, foamed LDPE / EVA material was obtained.

[0087] Example 4

[0088] Preparation of coated inorganic foaming agents:

[0089] (1) Add 1.2g of methyl glucoside sesquistearate and 1.2g of polyoxyethylene hexadecyl alcohol to 70mL of tert-butyl methyl ether and stir until completely dissolved to obtain the oil phase.

[0090] (2) Add 15g KHCO3 to 25mL of water and add zirconium beads. Use a planetary ball mill to ball mill at 500rpm for 2h. Filter out the zirconium beads with a sieve to obtain the first aqueous phase.

[0091] (3) Add 35g of potassium silicate to 250mL of water and stir until completely dissolved to obtain the second aqueous phase.

[0092] (4) The first aqueous phase and the oil phase were stirred and mixed evenly, and then homogenized at 9000 rpm for 2 min using a high-speed homogenizer to prepare an O / W type emulsion. The emulsion was then quickly poured into the second aqueous phase and stirred for 5 h. After natural sedimentation, the supernatant was discarded and the mixture was dried under reduced pressure to obtain the SiO2-coated inorganic foaming agent.

[0093] Applications of coated inorganic foaming agents:

[0094] By mass, 100 parts of vinyl silicone rubber (vinyl content 0.18%), 30 parts of precipitated silica, 20 parts of basic magnesium carbonate, 30 parts of mica powder, 10 parts of low melting point glass powder (melting point 450℃), 6 parts of SiO2-coated inorganic foaming agent prepared in this embodiment, 0.5 parts of caster platinum catalyst (platinum content 1000ppm), 1 part of hydrogen-containing silicone oil (hydrogen content 1%), and 0.06 parts of alkynyl alcohol inhibitor (ethynylcyclohexanol) were kneaded evenly using a kneader, calendered to a thickness of 2mm using a calender, and then placed in a 150℃ oven for foaming-vulcanization for 10 minutes. Finally, it was placed in a 200℃ oven for secondary vulcanization for 2 hours to obtain foamed silicone rubber material.

[0095] Comparative Example 1

[0096] The method for preparing foamed silicone rubber material in this comparative example is the same as in Example 1, except that the same mass of NH4HCO3 is used instead of the SiO2-coated inorganic foaming agent prepared in Example 1.

[0097] Comparative Example 2

[0098] The method for preparing foamed epoxy resin material in this comparative example is the same as in Example 2, except that NaHCO3 of the same mass is used instead of the SiO2-coated inorganic foaming agent prepared in Example 2.

[0099] Comparative Example 3

[0100] The method for preparing foamed LDPE / EVA materials in this comparative example is the same as in Example 3, except that the same mass fraction of (NH4)2HPO4 is used instead of the SiO2-coated inorganic foaming agent prepared in Example 3.

[0101] Comparative Example 4

[0102] The method for preparing foamed silicone rubber material in this comparative example is the same as in Example 4, except that the same mass of KHCO3 is used instead of the SiO2-coated inorganic foaming agent prepared in Example 4.

[0103] Figure 1-4 The images shown are scanning electron microscope (SEM) images of the coated inorganic foaming agents obtained in Examples 1-4, respectively. Figure 1-4 It can be seen that the coated inorganic foaming agent obtained by the preparation method provided by the present invention has a spherical structure, uniform particle size distribution, no crystalline particles, and high coating efficiency.

[0104] Figure 5 , 7 Images 9 and 11 are internal micrographs of foamed materials prepared by adding the coated inorganic foaming agents obtained in Examples 1-4, respectively. Figure 6 , 8 Images 10 and 12 are internal cross-sectional views of the foamed materials prepared by adding the coated inorganic foaming agents obtained in Comparative Examples 1-4. Figure 5-12 It can be seen that, compared with conventional inorganic foaming agents, the coated inorganic foaming agent prepared by the present invention can be uniformly dispersed in the polymer matrix, so that the foamed material has a uniform and delicate cell structure.

[0105] Figure 13 TGA images of sodium bicarbonate and silica-coated sodium bicarbonate obtained in Example 2. Figure 13 It can be seen that the decomposition temperature range of sodium bicarbonate is 135-178℃, while the decomposition temperature range of silica-coated sodium bicarbonate is 156-172℃, indicating a narrower decomposition temperature range.

[0106] Figure 14 This diagram illustrates the microscopic mechanism of SiO2-coated inorganic foaming agent preparation via a three-phase emulsion method. A W / O / W three-phase emulsion is formed through high-speed dispersion and stirring. Due to the surface tension of the OP phase, the emulsion is slowly removed between the 1stWP and 2ndWP phases. The silica precursor of the 2ndWP phase and the precipitant of the 1stWP phase come into contact and react to generate SiO2. Continued stirring results in the continuous generation of SiO2 along the interface of the 1stWP phase, ultimately forming spherical SiO2 particles coated with the inorganic foaming agent.

[0107] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a coated inorganic foaming agent, characterized in that, The preparation method includes the following steps: (1) Dissolve the emulsifier in a solvent to obtain the oil phase; (2) Dissolve or disperse the hydrophilic foaming agent-precipitant material in water to obtain the first aqueous phase; (3) Dissolve the silica precursor in water to obtain the second aqueous phase; (4) After mixing the first aqueous phase and the oil phase evenly, quickly pour the mixture into the second aqueous phase, stir to react, centrifuge or allow to settle naturally, discard the supernatant, and dry to obtain the coated inorganic foaming agent. The emulsifier includes W / O type emulsifiers and O / W type emulsifiers; The W / O type emulsifier is a surfactant with an HLB value of 3 to 6; The O / W type emulsifier is a surfactant with an HLB value of 8 to 18; The ratio of W / O type emulsifier and O / W type emulsifier to solvent in the oil phase is (0.1~3g): (0.1~3g): 100mL; The hydrophilic foaming agent-precipitant material is selected from one or more of (NH4)2CO3, NH4HCO3, (NH4)2HPO4, NaHCO3, and KHCO3; The ratio of hydrophilic foaming agent-precipitant material to water in the first aqueous phase is (20~100g): 100mL; The ratio of silica precursor to water in the second aqueous phase is (1~50g): 100mL; The volume ratio of the first aqueous phase, the oil phase, and the second aqueous phase is 1 : (1~3) : (5~15).

2. The preparation method according to claim 1, characterized in that: The solvent is an organic solvent that is insoluble in water.

3. The preparation method according to claim 1, characterized in that: The ratio of W / O type emulsifier and O / W type emulsifier to solvent in the oil phase is (1~2g): (1~2g): 100mL.

4. The preparation method according to claim 1, characterized in that: The ratio of hydrophilic foaming agent-precipitant material to water in the first aqueous phase is (50~80g): 100mL.

5. The preparation method according to claim 1, characterized in that: The silica precursor is selected from one or more of sodium silicate, potassium silicate, and silica sol.

6. The preparation method according to claim 1, characterized in that: The ratio of silica precursor to water in the second aqueous phase is (10~20g): 100mL.

7. The preparation method according to claim 1, characterized in that: The volume ratio of the first aqueous phase, the oil phase, and the second aqueous phase is 1 : (1.5~2.5) : (7~10).

8. A coated inorganic foaming agent obtained by the preparation method according to any one of claims 1-7.

9. The surface organic treatment method for the coated inorganic foaming agent according to claim 8, characterized in that: Surface modification of coated inorganic foaming agents is carried out by using silane coupling agents or titanate coupling agents through wet or dry methods.

10. The application of the coated inorganic foaming agent of claim 8 or the coated inorganic foaming agent obtained by the surface organic treatment method of claim 9 in foamed materials.

11. A foaming material comprising a polymer matrix and a foaming agent, wherein the foaming agent is the encapsulated inorganic foaming agent as described in claim 8.

12. The foamed material according to claim 11, characterized in that: The polymer matrix is ​​a thermoplastic, thermosetting, or rubber. The foaming material also includes functional fillers, which are flame-retardant fillers and / or ceramic fillers.

13. The foamed material according to claim 12, characterized in that: The thermoplastic is selected from one or more of low-density polyethylene, high-density polyethylene, polypropylene, polyvinyl chloride, poly-1-butene, polycarbonate, ethylene-vinyl acetate copolymer, polyester, polystyrene, TPE, and TPR.

14. The foamed material according to claim 12, characterized in that: The thermosetting plastic is selected from one or more of phenolic resin, epoxy resin, and unsaturated polyester resin.

15. The foamed material according to claim 12, characterized in that: The rubber is natural rubber and / or synthetic rubber.

16. The foamed material according to claim 12, characterized in that: The flame-retardant filler is selected from one or more of magnesium hydroxide, aluminum hydroxide, basic magnesium carbonate, ammonium polyphosphate, microencapsulated composite flame retardant, and synergistic flame retardant.

17. The foamed material according to claim 12, characterized in that: The ceramic filler is selected from one or more of the following: low melting point glass powder, zinc oxide, calcium oxide, zinc borate, calcium borate, mica powder, wollastonite powder, and palygorskite powder.

Images