Flame-retardant expanded microsphere and preparation method thereof

Abstract

The invention relates to the technical field of preparation of expanded microspheres, and particularly provides flame-retardant expanded microspheres and a preparation method thereof. The flame-retardant expanded microspheres are prepared from the following raw materials: styrene, a composite foaming agent, an oil-phase initiator, a water-phase initiator, a cross-linking agent, an antistatic agent, an emulsifier, a phosphazene flame retardant, a catalyst, an accelerant, deionized water, a surfactant, a dispersing agent, a reducing agent and an organic solvent. The flame-retardant expanded microsphere disclosed by the invention is good in foaming property and flame-retardant property, and can endow and improve the flame-retardant property of a base material.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of expandable microspheres, and particularly relates to an expandable microsphere for flame retardancy and a preparation method thereof. Background Art

[0002] Expandable microspheres, usually also called thermally expandable microspheres, are thermally expandable microcapsules with a core-shell structure composed of a thermoplastic polymer shell encapsulating a low-boiling solvent (such as a liquid alkane gas or other compounds), and generally have a diameter between 10 - 50 μm. At room temperature, the microsphere shell is hard; when heated, the liquid hydrocarbon gradually vaporizes, and the pressure inside the sphere increases. When the temperature rises to the glass transition temperature of the polymer shell layer, the shell layer becomes soft, and the microsphere begins to expand under the action of the internal and external pressure difference until the internal and external pressures of the sphere reach equilibrium and the expansion stops, reaching the maximum foaming state. After cooling, the microsphere can still maintain the volume at the time of expansion without shrinking back. Due to its light weight and uniformity, having a uniform foaming ratio, and the foamed microspheres having characteristics such as sound insulation, heat insulation, shock absorption, and weight reduction, it is widely used in industries such as coating printing, foam industry, leather, and automobile manufacturing.

[0003] In many application scenarios, the flame retardancy of materials is crucial. The hydrocarbons in traditional expandable microspheres are flammable substances. During the expansion process of the microspheres, as the temperature rises, the thermoplastic shell material becomes thinner accordingly, and the internal gaseous alkanes are easily volatilized, with low safety, which limits its application in some special fields with high fire safety requirements, such as construction, automotive interiors, electronic appliances, etc. Therefore, it is of great significance to improve the flame retardancy and thermal stability of thermally expandable microspheres and study an expandable microsphere for flame retardancy that meets environmental protection requirements. Summary of the Invention

[0004] In view of this, the present invention aims to provide an expandable microsphere for flame retardancy, so as to provide a product with good foaming performance and flame retardancy, and can endow and improve the flame retardancy of the substrate.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] An expandable microsphere for flame retardancy, the production raw materials of the expandable microsphere for flame retardancy include styrene, composite blowing agent, oil-phase initiator, water-phase initiator, cross-linking agent, antistatic agent, emulsifier, phosphazene flame retardant, catalyst, accelerator, deionized water, surfactant, dispersant, reducing agent, organic solvent.

[0007] Further, the production raw materials of the expandable microsphere for flame retardancy include the following in parts by weight:

[0008] 25 - 31 parts of styrene, 33 - 39 parts of composite foaming agent, 0.8 - 1.2 parts of oil - phase initiator, 0.6 - 1.2 parts of water - phase initiator, 0.5 - 1.5 parts of cross - linker, 0.8 - 1.2 parts of antistatic agent, 4.4 - 6.2 parts of emulsifier, 4 - 6 parts of phosphazene flame retardant, 0.08 - 0.12 parts of catalyst, 0.04 - 0.06 parts of accelerator, 120 - 140 parts of deionized water, 0.8 - 1.2 parts of surfactant, 3 - 5 parts of dispersant, 0.3 - 0.5 parts of reducing agent, 6 - 10 parts of organic solvent.

[0009] Further, the phosphazene flame retardant adopts hexaphenoxycyclotriphosphazene; and / or,

[0010] The catalyst adopts cobalt naphthenate; and / or,

[0011] The accelerator adopts cyclohexanone peroxide.

[0012] Further, the composite foaming agent adopts a mixture of petroleum ether and CO2; and / or,

[0013] The oil - phase initiator adopts azobisisobutyronitrile; and / or,

[0014] The water - phase initiator adopts ammonium persulfate; and / or,

[0015] The cross - linker adopts divinyl ether; and / or,

[0016] The surfactant adopts sodium dodecylbenzenesulfonate; and / or,

[0017] The dispersant adopts polyvinylpyrrolidone; and / or,

[0018] The reducing agent adopts sodium bisulfite.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] The expandable microspheres for flame retardancy of the present invention use styrene as the polymerization monomer, a mixture of petroleum ether and CO2 as the composite foaming agent, azobisisobutyronitrile as the initiator, and divinyl ether as the cross - linker, and form a polymerization system composed of hydrophobic monomers, dispersion media, water - soluble initiators, emulsifiers, phosphazene flame retardants, etc., and prepare polymer microspheres by using the free - radical polymerization principle.

[0021] In terms of the flame retardancy of the expandable microspheres for flame retardancy of the present invention, a halogen-free phosphazene flame retardant is used to coat the expandable microspheres, and cobalt naphthenate and cyclohexanone peroxide are used to improve the bonding force and coating rate between the phosphazene flame retardant and the expandable microspheres, thereby significantly improving the flame retardancy efficiency and flame retardancy stability of the expandable microspheres. In addition, cobalt naphthenate and cyclohexanone peroxide added to the expandable microspheres for flame retardancy of the present invention can also promote the rapid degradation of the phosphazene flame retardant during a fire, thereby rapidly forming a dense carbon layer on the surface of the expandable microspheres, playing a good role in flame retardancy and ablation resistance, so that the expandable microspheres for flame retardancy of the present invention have both good foaming properties and flame retardancy properties.

[0022] Meanwhile, the present invention also provides a preparation method of expandable microspheres for flame retardancy, and the preparation method includes:

[0023] Mix styrene, a composite foaming agent, an antistatic agent, an emulsifier, an oil-phase initiator and an organic solvent, and stir under a first preset stirring condition to obtain an oil-phase solution;

[0024] Mix deionized water, a surfactant, a dispersant, a reducing agent and an aqueous-phase initiator dissolved in an organic solvent, stir under a second preset stirring condition and perform ultrasonic treatment to obtain an aqueous-phase solution;

[0025] Mix the oil-phase solution and the aqueous-phase solution, and perform homogenization treatment to obtain a uniform emulsion;

[0026] Add the uniform emulsion into a reaction vessel, and perform a polymerization reaction under a nitrogen condition to obtain an intermediate product;

[0027] Add a phosphazene flame retardant, a catalyst and a promoter to the intermediate product, stir and react to form a dense flame retardant layer, and then perform separation, washing and drying to obtain expandable microspheres for flame retardancy.

[0028] Further, the first preset stirring condition includes that the stirring temperature is controlled between 80°C and 100°C, the stirring rate is controlled between 700 rpm and 900 rpm, and the stirring time is controlled between 60 min and 90 min; and / or,

[0029] The second preset stirring condition includes that the stirring speed is controlled between 400 rpm and 600 rpm.

[0030] Further, the homogenization treatment includes: treating the mixed oil-phase solution and aqueous-phase solution at a rotation speed of 11000 rpm to 13000 rpm for 8 min to 12 min, and controlling the temperature during the treatment to be ≤30°C.

[0031] Further, the reaction temperature of the polymerization reaction is between 85°C and 95°C, the stirring rate is between 250 rpm and 350 rpm, and the reaction time is between 280 min and 320 min.

[0032] Further, the formation of the dense flame-retardant layer by stirring and reacting includes:

[0033] The intermediate product added with the phosphazene flame retardant, the catalyst and the promoter is stirred at 35°C - 45°C and 250 rpm - 350 rpm for 25 min - 35 min, and then heated to 55°C - 65°C and reacted for 1.5 h - 2.5 h to form the dense flame-retardant layer on the intermediate product.

[0034] Further, the drying conditions include vacuum drying at 55°C - 65°C for 10 h - 14 h.

[0035] Further, after forming the dense flame-retardant layer, the drying in the separation, washing and drying is to control the moisture content ω of the expandable microspheres so that ω ≤ 0.5%.

[0036] The preparation method of the expandable microspheres for flame retardancy of the present invention is emulsion polymerization and suspension polymerization. Styrene polymerization monomers are selected. By restricting the diffusion of gas in the foaming agent, the production energy consumption is reduced, the safety in the production operation process is improved, it is environmentally friendly, safe and controllable, and the foaming performance is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0038] Figure 1 is a flowchart of the preparation method of the expandable microspheres for flame retardancy according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0040] For those conditions not specified in the present invention, they can be carried out according to conventional conditions or the conditions recommended by the manufacturer of the equipment used. For the reagents or instruments whose manufacturers are not specified, they are all conventional products obtained through commercial purchase. For the technical means or process methods involved, if the specific conditions are not written, they are carried out according to the existing methods in the field.

[0041] This embodiment relates to an expandable microsphere for flame retardancy, which can provide a product with good foaming performance and flame retardancy performance, and can endow and improve the flame retardancy performance of the substrate.

[0042] In terms of the overall design, the raw materials for manufacturing the expandable microspheres for flame retardancy in this embodiment include styrene, composite foaming agent, oil-phase initiator, water-phase initiator, crosslinking agent, antistatic agent, emulsifier, phosphazene flame retardant, catalyst, accelerator, deionized water, surfactant, dispersant, reducing agent, and organic solvent.

[0043] Specifically, styrene in the above raw materials forms polystyrene through a polymerization reaction. Polystyrene has good rigidity, hardness, and chemical stability, which can provide a certain strength and shape retention ability for the microspheres, making them not easily break or deform during subsequent processing and use. At the same time, styrene monomer and its polymer play a role in stabilizing the foaming agent during the foaming process of the expandable microspheres. The foaming agent decomposes to generate gas when heated, causing the microspheres to expand. The polystyrene shell can withstand the pressure generated by the foaming agent and prevent premature gas leakage, thus ensuring the smooth progress of the foaming process and enabling the microspheres to expand evenly to the required size.

[0044] The composite foaming agent in the above raw materials is preferably, for example, a mixture of petroleum ether and CO2. Petroleum ether has a low boiling point and a high vapor pressure, and can quickly vaporize under heating or reduced pressure conditions to generate a large amount of gas, providing an initial gas source for foaming. CO2 is a gas under normal temperature and pressure, and can dissolve in the polymer matrix under a certain pressure. When the pressure decreases, CO2 will form a large number of tiny bubble nuclei, acting as a nucleating agent to promote the formation of foam. The combination of the two can play a synergistic role, making the foaming process more efficient, the formed foam structure more uniform and delicate, and the pore size distribution narrower.

[0045] The oil-phase initiator in the above raw materials is preferably, for example, azobisisobutyronitrile. Azobisisobutyronitrile can quickly decompose under heating or light conditions to generate two highly active isobutyronitrile free radicals, which initiate the polymerization reaction of monomers in the oil phase. The initiation efficiency is relatively high, and it can effectively control the rate and molecular weight of the polymerization reaction.

[0046] The water-phase initiator in the above raw materials is preferably, for example, ammonium persulfate. Ammonium persulfate can dissolve well in the water phase and decompose when heated in the water phase to generate sulfate radicals. Sulfate radicals have high activity and can effectively initiate the free radical polymerization reaction of monomer molecules, shortening the reaction time and improving production efficiency.

[0047] The crosslinking agent in the above raw materials is preferably, for example, divinyl ether. As a crosslinking agent, divinyl ether mainly realizes the crosslinking reaction through the addition reaction of its vinyl group with other compounds containing active hydrogen or double bonds.

[0048] The antistatic agent in the above raw materials is preferably, for example, methacrylic acid. Methacrylic acid itself does not have good antistatic properties, but it can generate polymethacrylic acid through polymerization reaction or copolymerize with styrene. In these polymers, by introducing some hydrophilic or ionic groups, such as carboxyl group, sulfonic acid group, quaternary ammonium salt, etc., they can be made to have antistatic properties. These groups can absorb moisture in the air and form a thin water film on the material surface, thereby improving the conductivity of the material surface and enabling static charges to be quickly conducted and dissipated, achieving the purpose of antistatic.

[0049] The emulsifier in the above raw materials is preferably, for example, tert-dodecyl mercaptan.

[0050] The phosphazene flame retardant in the above raw materials is preferably, for example, hexaphenoxycyclotriphosphazene. The flame retardant principle of hexaphenoxycyclotriphosphazene belongs to the phosphorus-nitrogen synergistic flame retardant system. During combustion, phosphides and nitrides form an intumescent coke layer at high temperature, which acts as a heat-insulating and oxygen-barrier protective layer. The nitrogen-containing compounds act as foaming agents and coke strengtheners, which can promote the decomposition of esters at lower temperatures to form coke and water and increase the amount of coke residues generated, thereby improving the flame retardant efficiency. And hexaphenoxycyclotriphosphazene does not emit toxic and corrosive gases during combustion, meeting the requirements of environmental protection.

[0051] The catalyst in the above raw materials is preferably, for example, cobalt naphthenate. Cobalt naphthenate has moderate catalytic activity and can effectively promote chemical reactions without requiring harsh reaction conditions. It will neither make the reaction too violent to control nor cause the reaction rate to be too slow.

[0052] The accelerator in the above raw materials is preferably, for example, cyclohexanone peroxide. The peroxy bond (-O-O-) in the cyclohexanone peroxide molecule will undergo homolytic cleavage under certain conditions to generate free radicals. These free radicals can initiate the polymerization reaction of monomer molecules.

[0053] The surfactant in the above raw materials is preferably, for example, sodium dodecylbenzenesulfonate. The molecular structure of sodium dodecylbenzenesulfonate consists of two parts: a hydrophilic sulfonic acid group and a hydrophobic dodecylbenzene hydrocarbon group. This unique structure enables it to orientate at the interface of water and oil, thereby reducing the interfacial tension.

[0054] The dispersant in the above raw materials is preferably, for example, polyvinylpyrrolidone. Polyvinylpyrrolidone can adsorb on the particle surface to form a polymer protective film, and form a steric hindrance around the particles through its long-chain structure to prevent the particles from approaching and aggregating with each other, so that the particles are evenly dispersed in the medium. In addition, polyvinylpyrrolidone can also interact with the particle surface through ionic bonds or hydrogen bonds, making the particle surface carry a certain charge, thereby generating an electrostatic repulsive force between the particles and further enhancing the stability of the dispersion system.

[0055] The reducing agent in the above raw materials is preferably, for example, sodium bisulfite. The sulfur element in sodium bisulfite is in the +4 valence state, which is in an intermediate valence state and has strong reducibility. Therefore, it is selected as the reducing agent in this embodiment.

[0056] From the above introduction of each raw material, it can be seen that the expandable microspheres for flame retardancy in this embodiment use styrene as the polymerization monomer, petroleum ether and CO2 as the composite blowing agent, azobisisobutyronitrile as the initiator, and divinyl ether as the crosslinking agent. A polymerization system is composed of hydrophobic monomers, dispersion media, water-soluble initiators, emulsifiers, phosphazene flame retardants, etc., and polymer microspheres are prepared using the principle of free radical polymerization.

[0057] In terms of flame retardancy performance, for the thermally expandable expandable microspheres, a halogen-free phosphazene flame retardant is used to coat the expandable microspheres, and cobalt naphthenate and cyclohexanone peroxide are used to improve the binding force and coating rate between the phosphazene flame retardant and the expandable microspheres, thereby significantly improving the flame retardancy efficiency and flame retardancy stability of the expandable microspheres. In addition, the cobalt naphthenate and cyclohexanone peroxide added in this embodiment can also promote the rapid degradation of the phosphazene flame retardant during a fire, so as to quickly form a dense carbon layer on the surface of the expandable microspheres, playing a good role in flame retardancy and ablation resistance, so that the expandable microspheres have both good foaming performance and flame retardancy performance.

[0058] It should be noted that based on the above raw material composition, further, in specific implementation, the amounts of the raw materials for the expandable microspheres for flame retardancy in this embodiment are as follows by parts:

[0059] Styrene 25 - 31 parts, composite blowing agent 33 - 39 parts, oil-phase initiator 0.8 - 1.2 parts, water-phase initiator 0.6 - 1.2 parts, crosslinking agent 0.5 - 1.5 parts, antistatic agent 0.8 - 1.2 parts, emulsifier 4.4 - 6.2 parts, phosphazene flame retardant 4 - 6 parts, catalyst 0.08 - 0.12 parts, accelerator 0.04 - 0.06 parts, deionized water 120 - 140 parts, surfactant 0.8 - 1.2 parts, dispersant 3 - 5 parts, reducing agent 0.3 - 0.5 parts, organic solvent 6 - 10 parts.

[0060] This embodiment also relates to a preparation method of expandable microspheres for flame retardancy, combined with Figure 1As shown, it specifically includes the following steps:

[0061] Step S1: Mix styrene, composite blowing agent, antistatic agent, emulsifier, oil-phase initiator and organic solvent, and stir under the first preset stirring conditions to obtain an oil-phase solution.

[0062] The first preset stirring conditions in the above step S1, as a preferred implementation form, for example, may include that the stirring temperature is controlled between 80°C and 100°C, the stirring rate is controlled between 700 rpm and 900 rpm, and the stirring time is controlled between 60 min and 90 min.

[0063] Step S2: Mix deionized water, surfactant, dispersant, reducing agent and water-phase initiator dissolved in organic solvent, and stir and ultrasonically treat under the second preset stirring conditions to obtain a water-phase solution.

[0064] The second preset stirring conditions in the above step S2, as a preferred implementation form, for example, may include that the stirring speed is controlled between 400 rpm and 600 rpm.

[0065] Step S3: Mix the oil-phase solution and the water-phase solution, and perform homogenization treatment to obtain a uniform emulsion.

[0066] The homogenization treatment in the above step S3, as an exemplary implementation form, for example, may be to treat the mixed oil-phase solution and water-phase solution at a rotation speed of 11000 rpm to 13000 rpm for 8 min to 12 min, and the temperature during the treatment is controlled at ≤30°C.

[0067] Step S4: Add the uniform emulsion into a reaction vessel, and carry out a polymerization reaction under nitrogen conditions to obtain an intermediate product.

[0068] The polymerization reaction in the above step S4, as a preferred implementation form, for example, may be that the reaction temperature is between 85°C and 95°C, the stirring rate is between 250 rpm and 350 rpm, and the reaction time is between 280 min and 320 min.

[0069] Step S5: Add the phosphazene flame retardant, the catalyst and the promoter to the intermediate product, stir and react to form a dense flame retardant layer, and then separate, wash and dry to obtain the expanded microspheres for flame retardancy.

[0070] In the above step S5, a dense flame retardant layer is formed through stirring and reaction. As an exemplary implementation form, for example, the intermediate product added with phosphazene flame retardant, catalyst and promoter can be stirred at 35°C to 45°C and 250 rpm to 350 rpm for 25 min to 35 min, and then heated to 55°C to 65°C for reaction for 1.5 h to 2.5 h to form a dense flame retardant layer on the intermediate product.

[0071] Meanwhile, the drying conditions in the above step S5 are preferably, for example, vacuum drying at 55°C to 65°C for 10 h to 14 h. Then the water content ω of the obtained expanded microspheres after drying is preferably, for example, controlled to ω ≤ 0.5%.

[0072] From the above introduction of the preparation method, the preparation method of the expanded microspheres for flame retardancy in this embodiment adopts emulsion polymerization and suspension polymerization, selects styrene as the polymerization monomer, reduces the production energy consumption and improves the safety in the production operation process by restricting the diffusion of gas in the foaming agent. This preparation process is environmentally friendly, safe and controllable, and the expanded microspheres produced have good foaming performance.

[0073] Based on the above introduction, for the expanded microspheres for flame retardancy and their preparation method of the present invention, further, in specific implementation, the following preparation examples can be referred to.

[0074] Example 1

[0075] This Example 1 is for preparing the above-mentioned expanded microspheres for flame retardancy, and its specific raw material ratio and preparation steps are as follows:

[0076] Raw material ratio:

[0077] 25 parts of styrene, 33 parts of composite foaming agent (mixture of petroleum ether and CO2), 0.8 part of oil-phase initiator (ammonium persulfate), 0.6 part of water-phase initiator (azobisisobutyronitrile), 0.5 part of cross-linking agent (divinyl ether), 0.8 part of antistatic agent (methacrylic acid), 4.4 parts of emulsifier (tert-dodecyl mercaptan), 4 parts of phosphazene flame retardant (hexaphenoxycyclotriphosphazene), 0.08 part of catalyst (cobalt naphthenate), 0.04 part of promoter (cyclohexanone peroxide), 120 parts of deionized water, 0.8 part of surfactant (sodium dodecylbenzenesulfonate), 3 parts of dispersant (polyvinylpyrrolidone), 0.3 part of reducing agent (sodium bisulfite), 6 parts of organic solvent (methanol).

[0078] Specific preparation steps:

[0079] S1. Add 25 parts of styrene, 33 parts of the mixture of petroleum ether and CO2, 0.8 part of methacrylic acid, 4.4 parts of tert-dodecyl mercaptan, 0.8 part of ammonium persulfate and 6 parts of methanol into the reaction vessel, and stir at 80°C and 700 rpm for 60 min to obtain a homogeneous thickened oil-phase solution.

[0080] S2. Mix 120 parts of deionized water, 0.8 part of sodium dodecylbenzenesulfonate, 3 parts of polyvinylpyrrolidone, 0.3 part of sodium bisulfite and a methanol solution of 0.6 part of azobisisobutyronitrile pre-dissolved therein. First, stir at 400 rpm and simultaneously apply ultrasonic treatment at 30 kHz for 15 min to obtain a transparent aqueous solution.

[0081] S3. Slowly add the oil-phase solution to the aqueous solution, and treat it at 11000 rpm in a homogenizer for 8 min, controlling the temperature ≤ 30 °C to obtain a uniform and stable emulsion.

[0082] S4. Transfer the emulsion to a reaction kettle. After displacing the air, react at 85 °C and 250 rpm for 280 min to obtain an intermediate product.

[0083] S5. Add 4 parts of hexaphenoxycyclotriphosphazene, 0.08 part of cobalt naphthenate and 0.04 part of cyclohexanone peroxide to the intermediate product. First, stir at 35 °C and 250 rpm for 25 min, and then raise the temperature to 55 °C and react for 1.5 h. After the reaction is completed, separate, wash, and dry under vacuum at 55 °C for 10 h, controlling the moisture content ≤ 0.5% to obtain the finished expandable microspheres for flame retardancy.

[0084] Example 2

[0085] This Example 2 is for preparing the above expandable microspheres for flame retardancy, and its specific raw material ratio and preparation steps are as follows:

[0086] Raw material ratio:

[0087] 28 parts of styrene, 36 parts of composite blowing agent (mixture of petroleum ether and CO2), 1.0 part of oil-phase initiator (ammonium persulfate), 0.9 part of water-phase initiator (azobisisobutyronitrile), 1.0 part of crosslinking agent (divinyl ether), 1.0 part of antistatic agent (methacrylic acid), 5.3 parts of emulsifier (tert-dodecyl mercaptan), 5 parts of phosphazene flame retardant (hexaphenoxycyclotriphosphazene), 0.10 part of catalyst (cobalt naphthenate), 0.05 part of accelerator (cyclohexanone peroxide), 130 parts of deionized water, 1.0 part of surfactant (sodium dodecylbenzenesulfonate), 4 parts of dispersant (polyvinylpyrrolidone), 0.4 part of reducing agent (sodium bisulfite), 8 parts of organic solvent (methanol).

[0088] Specific preparation steps:

[0089] S1. Add 28 parts of styrene, 36 parts of the mixture of petroleum ether and CO2, 1.0 part of methacrylic acid, 5.3 parts of tert-dodecyl mercaptan, 1.0 part of ammonium persulfate and 8 parts of methanol to a reaction vessel, and stir at 90 °C and 800 rpm for 75 min to obtain a homogeneous and thickened oil-phase solution.

[0090] S2. Mix 130 parts of deionized water, 1.0 part of sodium dodecylbenzenesulfonate, 4 parts of polyvinylpyrrolidone, 0.4 part of sodium bisulfite, and a methanol solution of 0.9 part of azobisisobutyronitrile pre-dissolved. First, stir at 400 rpm while applying ultrasonic treatment at 50 kHz for 20 min to obtain a transparent aqueous solution.

[0091] S3. Slowly add the oil-phase solution to the aqueous solution and process it at 12,000 rpm in a homogenizer for 10 min, controlling the temperature ≤ 30 °C to obtain a uniform and stable emulsion.

[0092] S4. Transfer the emulsion to a reaction kettle. After displacing the air, react at 90 °C and 300 rpm for 300 min to obtain an intermediate product.

[0093] S5. Add 5 parts of hexaphenoxycyclotriphosphazene, 0.10 part of cobalt naphthenate, and 0.05 part of cyclohexanone peroxide to the intermediate product. First, stir at 40 °C and 300 rpm for 30 min, then raise the temperature to 60 °C and react for 2 h. After the reaction, separate, wash, and dry at 60 °C for 12 h to obtain the finished flame-retardant expandable microspheres.

[0094] Example 3

[0095] This Example 3 is for preparing the above-mentioned flame-retardant expandable microspheres, and its specific raw material ratio and preparation steps are as follows:

[0096] Raw material ratio:

[0097] 31 parts of styrene, 39 parts of composite blowing agent (a mixture of petroleum ether and CO2), 1.2 parts of oil-phase initiator (ammonium persulfate), 1.2 parts of water-phase initiator (azobisisobutyronitrile), 1.5 parts of cross-linking agent (divinyl ether), 1.2 parts of antistatic agent (methacrylic acid), 6.2 parts of emulsifier (tert-dodecyl mercaptan), 6 parts of phosphazene flame retardant (hexaphenoxycyclotriphosphazene), 0.12 part of catalyst (cobalt naphthenate), 0.06 part of accelerator (cyclohexanone peroxide), 140 parts of deionized water, 1.2 parts of surfactant (sodium dodecylbenzenesulfonate), 5 parts of dispersant (polyvinylpyrrolidone), 0.5 part of reducing agent (sodium bisulfite), 10 parts of organic solvent (methanol).

[0098] Specific preparation steps:

[0099] S1. Add 31 parts of styrene, 39 parts of the mixture of petroleum ether and CO2, 1.2 parts of methacrylic acid, 6.2 parts of tert-dodecyl mercaptan, 1.2 parts of ammonium persulfate, and 10 parts of methanol to a reaction vessel and stir at 100 °C and 900 rpm for 90 min to obtain a homogeneous and thickened oil-phase solution.

[0100] S2. Mix 140 parts of deionized water, 1.2 parts of sodium dodecylbenzenesulfonate, 5 parts of polyvinylpyrrolidone, 0.5 part of sodium bisulfite, and a methanol solution of 1.2 parts of azobisisobutyronitrile that has been pre-dissolved. First, stir at 400 rpm while applying ultrasonic treatment at 50 kHz for 25 min to obtain a transparent aqueous solution.

[0101] S3. Slowly add the oil-phase solution to the aqueous solution and treat it at 13,000 rpm in a homogenizer for 12 min, controlling the temperature ≤ 30 °C to obtain a uniform and stable emulsion.

[0102] S4. Transfer the emulsion to a reaction kettle. After displacing the air, react at 95 °C and 350 rpm for 320 min to obtain an intermediate product.

[0103] S5. Add 6 parts of hexaphenoxycyclotriphosphazene, 0.12 part of cobalt naphthenate, and 0.06 part of cyclohexanone peroxide to the intermediate product. First, stir at 45 °C and 350 rpm for 35 min, then raise the temperature to 65 °C and react for 2.5 h. After the reaction ends, separate, wash, and dry at 65 °C for 14 h to obtain the finished product of expandable microspheres for flame retardancy.

[0104] The performance comparison results of the expandable microspheres for flame retardancy prepared in Examples 1 to 3 and the existing expandable microsphere Weiyi JUZ-8019 are shown in Table 1 below:

[0105] Table 1: Comparison of the expandable microspheres for flame retardancy prepared in the examples and Weiyi JUZ-8019

[0106]

[0107]

[0108] The following are the explanations of each character in the table:

[0109] Flame retardancy efficiency: The ability of a material to inhibit combustion, expressed as a percentage. The higher the value, the stronger the flame retardancy performance.

[0110] High grade: ≥ 98%.

[0111] Medium grade: ≥ 95%.

[0112] Basic grade: ≥ 90%.

[0113] Low grade: ≤ 80%.

[0114] Expansion ratio: The multiple by which the volume of the microspheres expands during the foaming process, reflecting the ability of the foaming agent to release gas and the structural stability. The higher the ratio, the more significant the lightweight effect.

[0115] High ratio: 50 times.

[0116] Medium magnification: 40 times.

[0117] Basic magnification: 30 times.

[0118] Low magnification: 15 - 25 times.

[0119] Cell uniformity: Refers to the size consistency and distribution uniformity of the cells inside the expandable microspheres. A uniform cell structure can significantly improve the thermal insulation performance, mechanical stability, and processing suitability of the material. Due to the backward preparation process in the prior art, there are significant differences in cell size (pore size distribution range > 50μm), resulting in fluctuations in material properties. In the present invention, by optimizing the emulsification and polymerization processes, cell uniformity is achieved (pore size distribution range ≤ 15μm), improving product consistency.

[0120] Mechanical strength (compressive strength): Measured by compressive strength (MPa), it refers to the ability of the microspheres to resist damage under compressive loads. Due to defects in the cell structure and uneven dispersion of flame retardants in the prior art, the compressive strength is generally ≤ 50MPa, making it difficult to meet the requirements of high - end fields. In the present invention, by optimizing the cross - linker dosage and densifying the flame - retardant coating, the compressive strength is increased to 60 - 80MPa, significantly enhancing the load - bearing capacity and durability of the material.

[0121] Through the result analysis of Table 1 above, it can be seen that the environmentally friendly flame - retardant expandable microspheres prepared in this example are significantly superior to the existing expandable microspheres Weiyi JUZ - 8019 in terms of multiple key properties, and the flame - retardant efficiency has been greatly improved. The flame - retardant efficiencies of the expandable microspheres for flame retardancy prepared in Example 1, Example 2, and Example 3 reach ≥ 95% (UL94V - 0 grade) and ≥ 98% (UL94V - 0 grade) respectively, which are superior to ≤ 80% (UL94HB grade) of the prior art.

[0122] At the same time, the expansion ratios of the expandable microspheres for flame retardancy prepared in Example 1, Example 2, and Example 3 are increased from 15 - 25 times of the prior art to 40 - 50 times, with better foaming stability, the mechanical strength (compressive strength) is increased from ≤ 50MPa to 60 - 80MPa, and the cell uniformity is also significantly optimized.

[0123] In summary, the expandable microspheres for flame retardancy prepared in this example have better foaming performance and flame - retardant performance, can provide a product with good foaming performance and can improve the flame - retardant performance of the substrate, and its preparation method is environmentally friendly, safe, and controllable.

[0124] The above - mentioned are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An expandable microsphere for flame retardancy, characterized in that: The raw materials for making the expandable microsphere for flame retardancy include styrene, composite foaming agent, oil-phase initiator, water-phase initiator, crosslinking agent, antistatic agent, emulsifier, phosphazene flame retardant, catalyst, accelerator, deionized water, surfactant, dispersant, reducing agent, and organic solvent.

2. The expandable microspheres for flame retardancy according to claim 1, wherein The raw materials for making the expandable microsphere for flame retardancy by parts include: 25 - 31 parts of styrene, 33 - 39 parts of composite foaming agent, 0.8 - 1.2 parts of oil-phase initiator, 0.6 - 1.2 parts of water-phase initiator, 0.5 - 1.5 parts of crosslinking agent, 0.8 - 1.2 parts of antistatic agent, 4.4 - 6.2 parts of emulsifier, 4 - 6 parts of phosphazene flame retardant, 0.08 - 0.12 parts of catalyst, 0.04 - 0.06 parts of accelerator, 120 - 140 parts of deionized water, 0.8 - 1.2 parts of surfactant, 3 - 5 parts of dispersant, 0.3 - 0.5 parts of reducing agent, and 6 - 10 parts of organic solvent.

3. The expandable microsphere for flame retardancy according to claim 2, characterized in that: The phosphazene flame retardant uses hexaphenoxycyclotriphosphazene; and / or, The catalyst uses cobalt naphthenate; and / or, The accelerator uses cyclohexanone peroxide.

4. The expandable microsphere for flame retardancy according to any one of claims 1 to 3, characterized in that: The composite foaming agent uses a mixture of petroleum ether and CO2; and / or, The oil-phase initiator uses azobisisobutyronitrile; and / or, The water-phase initiator uses ammonium persulfate; and / or, The crosslinking agent uses divinyl ether; and / or, The surfactant uses sodium dodecylbenzenesulfonate; and / or, The dispersant uses polyvinylpyrrolidone; and / or, The reducing agent uses sodium bisulfite.

5. A preparation method of expandable microspheres for flame retardancy, characterized in that, The preparation method includes: Mix styrene, composite foaming agent, antistatic agent, emulsifier, oil-phase initiator and organic solvent, and stir under the first preset stirring conditions to obtain an oil-phase solution; Mix deionized water, surfactant, dispersant, reducing agent and water-phase initiator dissolved in organic solvent, stir and perform ultrasonic treatment under the second preset stirring conditions to obtain a water-phase solution; Mix the oil-phase solution and the water-phase solution, and perform homogenization treatment to obtain a uniform emulsion; Add the uniform emulsion into a reaction vessel, and carry out a polymerization reaction under nitrogen conditions to obtain an intermediate product; Add phosphazene flame retardant, catalyst and accelerator to the intermediate product, stir and react to form a dense flame retardant layer, and then perform separation, washing and drying to obtain the expandable microsphere for flame retardancy.

6. The preparation method of the expandable microsphere for flame retardancy according to claim 5, characterized in that: The first preset stirring conditions include that the stirring temperature is controlled between 80°C and 100°C, the stirring rate is controlled between 700 rpm and 900 rpm, and the stirring time is controlled between 60 min and 90 min; and / or, The second preset stirring conditions include that the stirring speed is controlled between 400 rpm and 600 rpm.

7. The preparation method of the expandable microspheres for flame retardancy according to claim 5, characterized in that, The homogenization treatment includes: The mixed oil-phase solution and the water-phase solution are processed at a rotation speed of 11,000 rpm to 13,000 rpm for 8 min to 12 min, and the temperature during the processing is controlled at ≤30 °C; and / or, The reaction temperature of the polymerization reaction is between 85 °C and 95 °C, the stirring rate is between 250 rpm and 350 rpm, and the reaction time is between 280 min and 320 min.

8. The preparation method of the expandable microspheres for flame retardancy according to claim 5, wherein, The formation of the dense flame retardant layer by stirring and reacting includes: After the intermediate product added with the phosphazene flame retardant, the catalyst and the promoter is stirred at 35 °C to 45 °C and 250 rpm to 350 rpm for 25 min to 35 min, and then heated to 55 °C to 65 °C and reacted for 1.5 h to 2.5 h, the dense flame retardant layer is formed on the intermediate product.

9. The method for preparing the expandable microspheres for flame retardancy according to claim 5, wherein: The drying conditions include vacuum drying at 55 °C to 65 °C for 10 h to 14 h.

10. The method for preparing the expandable microspheres for flame retardancy according to claim 5, wherein: After the dense flame retardant layer is formed, the drying in the separation, washing and drying is to control the water content ω of the expandable microspheres at ω ≤ 0.5%.

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