Composite flame retardant, preparation method and application thereof, and ultraviolet light-cured coating

Abstract

The application provides a composite flame retardant, a preparation method and application thereof, and ultraviolet light curing paint, and relates to the technical field of flame retardants.The composite flame retardant provided by the application has a structure of "core-silica outer core layer-shell", wherein the first organic silane coupling agent in the core is grafted and bonded with zinc borate and aluminum hypophosphite, so that the two are uniformly dispersed;the refractive index of the silica outer core layer is between the core and the resin, thereby playing the role of a transition layer of refractive index matching, reducing light scattering at the interface, and improving transparency;the second organic silane coupling agent can form a covalent bond with the silica outer core layer, and the carbon-carbon double bond thereof can participate in the copolymerization reaction of the resin;there is no clear physical boundary between the composite flame retardant and the resin, light scattering caused by the discontinuity of the refractive index and the interface defects is reduced, and the optical transparency and the flame retardant efficiency of the coating layer formed by using the composite flame retardant provided by the application as the flame retardant of the ultraviolet light curing paint are excellent.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology, specifically to a composite flame retardant, its preparation method and application, and ultraviolet-cured coatings. Background Technology

[0002] Ultraviolet (UV) curable coatings have been widely used for decoration and protection in fields such as wooden furniture, electronic products, plastic products, and paper printing due to their outstanding advantages, including fast curing speed, high energy efficiency, low volatile organic compound (VOC) emissions, and excellent coating performance. However, the acrylic resins and reactive monomers that make up these coatings are mostly hydrocarbon organic compounds, which are inherently flammable, with limiting oxygen index (LOI) typically below 18%, posing a significant fire safety hazard. Therefore, effective flame-retardant modification of UV curable coatings is a key prerequisite for expanding their application scenarios to meet higher requirements (such as electronic appliances, public transportation interiors, and high-end building materials).

[0003] In existing technologies, additive inorganic flame retardants (such as micron-sized aluminum hydroxide and zinc borate) or reactive flame retardants (such as phosphorus-containing reactive flame retardants like acrylate phosphates and phosphorus-nitrogen synergistic acrylates, or nitrogen-containing reactive flame retardants like melamine triacrylate and melamine-formaldehyde resin modified acrylates) are the most commonly used flame retardants in UV-curable coatings. However, the introduction of these flame retardants can severely reduce the light transmittance of the resulting coating: additive inorganic flame retardants have a significant difference in refractive index compared to the UV-curable resin matrix, causing light scattering at the resin interface when light passes through the coating, leading to increased haze and decreased transparency; while reactive flame retardants, although having better compatibility, may have chromophores or polar groups in their molecular structure that affect the microscopic phase separation structure of the UV-curable resin matrix, or migrate or crystallize during later curing and use, resulting in whitening or turbidity of the coating. Therefore, there is an urgent need to develop a composite flame retardant that combines high flame retardancy with excellent optical transparency. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a composite flame retardant, its preparation method and application, and a UV-curable coating. The composite flame retardant provided by this invention, when added to a UV-curable coating, forms a coating with excellent optical transparency and flame retardant efficiency.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a composite flame retardant, comprising a composite core layer and a shell layer encapsulating the outer surface of the composite core layer; The composite core layer includes a core and a silicon dioxide outer core layer wrapped around the outer surface of the core; The core material includes a wetting and dispersing agent, a flame retardant component, and a first organosilane coupling agent grafted onto the flame retardant component; the flame retardant component is zinc borate and aluminum hypophosphite. The shell layer is made of a second organosilane coupling agent; the second organosilane coupling agent is grafted onto a silica outer core layer; The second organosilane coupling agent contains carbon-carbon double bonds.

[0006] Preferably, the wetting and dispersing agent includes one or more of BYK-163, BYK-164 and Disperbyk-2152; The first organosilane coupling agent includes one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-aminopropyltriethoxysilane and γ-ureapropyltrimethoxysilane; The second organosilane coupling agent includes one or more of γ-methacryloxypropyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, and vinyltrimethoxysilane.

[0007] Preferably, the mass ratio of zinc borate to aluminum hypophosphite is 10~18:10~18; The mass ratio of the first organosilane coupling agent to the flame retardant component is 0.5~1:100; The mass ratio of the second organosilane coupling agent to the flame retardant component is 3~5:100; The mass ratio of the wetting and dispersing agent to the flame retardant component is 0.68~1.32:100.

[0008] This invention provides a method for preparing the composite flame retardant described in the above technical solution, comprising the following steps: A wetting and dispersing agent, zinc borate, aluminum hypophosphite, and a first organosilane coupling agent are dispersed in propylene glycol methyl ether, and the zinc borate and aluminum hypophosphite are respectively grafted with the first organosilane coupling agent to obtain a first composite slurry with a core dispersed therein. The first composite slurry is separated into solid and liquid phases to obtain a first solid phase; the first solid phase and tetraethyl orthosilicate are dispersed in an aqueous ethanol solution to form a silica outer core layer on the outer surface of the core, thereby obtaining a second composite slurry with a dispersed composite core layer. The second composite slurry is separated into solid and liquid phases to obtain a second solid phase; the second solid phase, the second organosilane coupling agent, and acetic acid are dispersed in ethanol to graft the second organosilane coupling agent and the silica outer core layer to obtain a composite flame retardant.

[0009] Preferably, the zinc borate and propylene glycol methyl ether are used in the form of a propylene glycol methyl ether dispersion of zinc borate; The mass concentration of the zinc borate propylene glycol methyl ether dispersion is 10-18%; The aluminum hypophosphite and propylene glycol methyl ether are used in the form of a propylene glycol methyl ether dispersion of aluminum hypophosphite; The mass concentration of the propylene glycol methyl ether dispersion of aluminum hypophosphite is 10-18%.

[0010] Preferably, the temperature of the first grafting is 50~70℃ and the time is 2~4h.

[0011] Preferably, the tetraethyl orthosilicate is used in the form of an ethanol solution of tetraethyl orthosilicate; The mass ratio of tetraethyl orthosilicate to ethanol in the ethanol solution is 1:1.8~2.5; The mass ratio of the tetraethyl orthosilicate to the flame retardant component is 4~4.5:100; The silicon dioxide outer core layer is formed at a temperature of 40~60℃ for 6~12 hours.

[0012] Preferably, the temperature of the second grafting is 70~80℃, and the time is 4~8h; The second grafting was performed under reflux conditions.

[0013] This invention provides the application of the composite flame retardant described in the above technical solution or the composite flame retardant prepared by the above technical solution in ultraviolet curable coatings.

[0014] The present invention also provides a UV-curable coating, comprising, by weight parts: 59-61 parts of UV-curable resin, 34-36 parts of acrylate reactive diluent, 4.9-5.1 parts of free radical photoinitiator, 0.19-0.21 parts of silicone leveling agent, 0.09-0.11 parts of silicone-free defoamer, and 5-5.04 parts of flame retardant; The flame retardant is the composite flame retardant described in the above technical solution or the composite flame retardant prepared by the preparation method described in the above technical solution.

[0015] This invention provides a composite flame retardant, comprising a composite core layer and a shell layer encapsulating the outer surface of the composite core layer; the composite core layer comprises a core and a silica outer core layer encapsulating the outer surface of the core; the core is made of a wetting and dispersing agent, a flame retardant component, and a first organosilane coupling agent grafted onto the flame retardant component; the flame retardant component is zinc borate and aluminum hypophosphite; the shell layer is made of a second organosilane coupling agent; the second organosilane coupling agent is grafted onto the silica outer core layer; the second organosilane coupling agent contains carbon-carbon double bonds. The composite flame retardant provided by this invention has a structure of "core-silica outer core-shell". In the core, a first organosilane coupling agent acts as a bridging agent, grafting and bonding the hydroxyl groups on the surfaces of zinc borate and aluminum hypophosphite to the first organosilane coupling agent. This masks the originally polar Zn-OH and Al-OH / P-OH groups within the inner layer, while the outermost layer is exposed with a large number of epoxy groups and ether chains with almost identical properties. Therefore, the grafted zinc borate and aluminum hypophosphite possess similar moderate polarity and hydrophobic surface characteristics, resulting in uniform dispersion, improved flame retardant effect, reduced light scattering caused by agglomeration, and increased transparency. The outer core layer is silica, with a refractive index (approximately 1.46) between that of the core and the UV-curable resin. The outer core layer acts as a transition layer for refractive index matching, significantly reducing light scattering at the interface between the composite flame retardant and the resin, thus further improving transparency. The second organosilane coupling agent in the shell layer forms strong Si-O-Si covalent bonds with silica. Simultaneously, the second organosilane coupling agent contains C=C double bonds, allowing it to participate in the copolymerization reaction of the resin, making the flame retardant component an organic part of the entire three-dimensional cross-linked polymer network. There is no clear physical boundary between the composite flame retardant and the resin, thereby minimizing light scattering caused by refractive index discontinuities and interface defects. Using the composite flame retardant provided by this invention as a flame retardant in UV-curable coatings results in coatings with excellent optical transparency and flame retardant efficiency. Furthermore, the silica in the outer core layer lowers surface energy and is rich in silanol groups, providing uniform reaction sites for the subsequent grafting of the second organosilane coupling agent, further improving the dispersion stability and interfacial compatibility of the composite flame retardant in the resin, thereby enhancing the optical transparency and flame retardant efficiency of the formed coating. Detailed Implementation

[0016] The present invention provides a composite flame retardant, comprising a composite core layer and a shell layer encapsulating the outer surface of the composite core layer; The composite core layer includes a core and a silicon dioxide outer core layer wrapped around the outer surface of the core; The core material includes a wetting and dispersing agent, a flame retardant component, and a first organosilane coupling agent grafted onto the flame retardant component; the flame retardant component is zinc borate and aluminum hypophosphite. The shell layer is made of a second organosilane coupling agent; the second organosilane coupling agent is grafted onto a silica outer core layer; The second organosilane coupling agent contains carbon-carbon double bonds.

[0017] In this invention, the mass ratio of zinc borate to aluminum hypophosphite can be 10~18:10~18, specifically 10:18, 10:15, 10:12, 10:10, 12:10, 15:10, or 18:10. In this invention, the median particle size (D) of the zinc borate and aluminum hypophosphite... 50 The particle size distribution can be independently <50nm, the particle size distribution can be independently ≤0.25, the crystal morphology can be independently near-spherical, and the purity can be independently ≥98%; the pH value of the zinc borate can be 6.5~8.5 (based on a 10% aqueous solution); the pH value of the aluminum hypophosphite can be 4.5~6.5 (based on a 10% aqueous solution).

[0018] In this invention, the wetting and dispersing agent may include one or more of BYK-163, BYK-164, and Disperbyk-2152; the mass ratio of the wetting and dispersing agent to the total mass of zinc borate and aluminum hypophosphite may be 0.68~1.32:100, specifically 0.7:100, 1.01:100, and 1.22:100. This invention uses BYK-163 as the wetting and dispersing agent, which has high steric hindrance, allowing it to stabilize the flame-retardant components and prevent agglomeration during storage and subsequent processing.

[0019] In this invention, the first organosilane coupling agent may include one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), γ-aminopropyltriethoxysilane, and γ-ureapropyltrimethoxysilane. In this invention, the mass ratio of the first organosilane coupling agent to the flame-retardant component may be 0.5 to 1:100, specifically 0.6:100, 0.7:100, 0.8:100, or 0.9:100.

[0020] This invention uses KH-560 as a bridging agent to graft the hydroxyl groups on the surfaces of zinc borate and aluminum hypophosphite with a first organosilane coupling agent. This masks the originally polar Zn-OH and Al-OH / P-OH groups within the inner layer, while the outermost layer is exposed with a large number of epoxy groups and ether chains with almost identical properties. Therefore, the grafted zinc borate and aluminum hypophosphite possess similar moderate polarity and hydrophobic surface characteristics, resulting in uniform dispersion, improved flame retardant effect, reduced light scattering caused by agglomeration, and increased transparency. Furthermore, the use of the first organosilane coupling agent improves the compatibility between the flame retardant component and propylene glycol methyl ether during preparation, achieving uniform dispersion of the flame retardant component. The Si-O-Si or unreacted Si-OH groups in the middle of the KH-560 molecule become nucleation sites for SiO2 coating, ensuring that the SiO2 shell can uniformly coat the already bridged core as a whole, rather than coating individual particles separately.

[0021] In this invention, the second organosilane coupling agent may include one or more of γ-methacryloxypropyltrimethoxysilane (KH-570), γ-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane; the mass ratio of the second organosilane coupling agent to the flame retardant component may be 3~5:100; specifically, it may be 3.5:100, 4:100, or 4.5:100. This invention uses the second organosilane coupling agent as the shell material, which can form strong Si-O-Si covalent bonds with the silica of the outer core layer. Simultaneously, in the methacryloxy group of the second organosilane coupling agent, due to the influence of adjacent strong electron-withdrawing groups, its C=C double bond exhibits high reactivity in free radical polymerization reactions and can participate in the copolymerization reaction of the resin, making the flame retardant component an organic component of the entire three-dimensional cross-linked polymer network. There is no clear physical boundary between the composite flame retardant and the resin, thereby minimizing light scattering caused by refractive index discontinuities and interface defects.

[0022] This invention provides a method for preparing the composite flame retardant described in the above technical solution, comprising the following steps: A wetting and dispersing agent, zinc borate, aluminum hypophosphite, and a first organosilane coupling agent are dispersed in propylene glycol methyl ether, and the zinc borate and aluminum hypophosphite are respectively grafted with the first organosilane coupling agent to obtain a first composite slurry with a core dispersed therein. The first composite slurry is separated into solid and liquid phases to obtain a first solid phase; the first solid phase and tetraethyl orthosilicate are dispersed in an aqueous ethanol solution to form a silica outer core layer on the outer surface of the core, thereby obtaining a second composite slurry with a dispersed composite core layer. The second composite slurry is separated into solid and liquid phases to obtain a second solid phase; the second solid phase, the second organosilane coupling agent, and acetic acid are dispersed in ethanol to graft the second organosilane coupling agent and the silica outer core layer to obtain a composite flame retardant.

[0023] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0024] This invention disperses a wetting and dispersing agent, zinc borate, aluminum hypophosphite, and a first organosilane coupling agent in propylene glycol methyl ether, allowing the zinc borate and aluminum hypophosphite to be grafted onto the first organosilane coupling agent, respectively, to obtain a first composite slurry with a dispersed core. This invention wets the zinc borate and aluminum hypophosphite with propylene glycol methyl ether while simultaneously stabilizing the first organosilane coupling agent, controlling its hydrolysis rate, and ensuring a uniform grafting reaction.

[0025] In this invention, the zinc borate and propylene glycol methyl ether can be used in the form of a propylene glycol methyl ether dispersion of zinc borate; the mass concentration of the propylene glycol methyl ether dispersion of zinc borate can be 10-18%, specifically 12%, 14%, 15%, 16%, or 17%. In this invention, the zinc borate is further dried before use; the drying can include vacuum drying; the vacuum drying temperature can be 60-80°C, specifically 65°C, 70°C, or 75°C; the vacuum drying time can be 4-6 hours, specifically 4.5 hours, 5 hours, or 5.5 hours. This invention reduces the moisture content of zinc borate to below 0.3% through vacuum drying.

[0026] In this invention, the aluminum hypophosphite and propylene glycol methyl ether can be used in the form of a propylene glycol methyl ether dispersion of aluminum hypophosphite; the mass concentration of the propylene glycol methyl ether dispersion of aluminum hypophosphite can be 10-18%, specifically 11%, 12%, 13%, 15%, or 17%. In this invention, the aluminum hypophosphite is further dried before use; the drying can include vacuum drying; the vacuum drying temperature can be 60-80°C, specifically 65°C, 70°C, or 75°C; the vacuum drying time can be 4-6 hours, specifically 4.5 hours, 5 hours, or 5.5 hours. This invention reduces the moisture content of aluminum hypophosphite to below 0.3% through vacuum drying. Since aluminum hypophosphite has a slightly lower density (2.1) than zinc borate (2.8), and nano-sized aluminum hypophosphite is generally more hygroscopic, has a higher surface energy, and is more difficult to disperse, the aluminum hypophosphite content in the propylene glycol methyl ether dispersion of aluminum hypophosphite is slightly lower than the zinc borate content in the propylene glycol methyl ether dispersion of zinc borate. This ensures that it achieves a viscosity and dispersion stability similar to that of the propylene glycol methyl ether dispersion of zinc borate, facilitating uniform mixing of the two dispersions.

[0027] In this invention, the mass ratio of the zinc borate propylene glycol methyl ether dispersion and the aluminum hypophosphite propylene glycol methyl ether dispersion can be 1:0.8~1.2, specifically 1:0.9, 1:1 or 1:1.1.

[0028] In this invention, dispersing the wetting and dispersing agent, zinc borate, aluminum hypophosphite, and the first organosilane coupling agent in propylene glycol methyl ether may include the following steps: Zinc borate, a wetting and dispersing agent (referred to as the first wetting and dispersing agent), and propylene glycol methyl ether are mixed to obtain a propylene glycol methyl ether dispersion of zinc borate. Aluminum hypophosphite, wetting and dispersing agent (referred to as the second wetting and dispersing agent), and propylene glycol methyl ether second are mixed to obtain a propylene glycol methyl ether dispersion of aluminum hypophosphite; The zinc borate propylene glycol methyl ether dispersion and the aluminum hypophosphite propylene glycol methyl ether dispersion are mixed for the third time to obtain a mixed slurry; The mixed slurry is mixed with the first organosilane coupling agent.

[0029] In this invention, the mass ratio of the first wetting and dispersing agent to zinc borate can be 0.5 to 1:100, specifically 0.6:100, 0.7:100, 0.8:100 or 0.9:100; the mass ratio of the second wetting and dispersing agent to aluminum hypophosphite can be 1 to 1.5:100, specifically 1.1:100, 1.2:100, 1.3:100 or 1.4:100.

[0030] In this invention, the first mixing may include sequential dispersion and ultrasonic treatment; the dispersion treatment may include dispersion using a high-speed disperser. In this invention, the dispersion rotation speed may be 3000~3500 rpm, specifically 3100 rpm, 3200 rpm, 3300 rpm, or 3400 rpm; the dispersion treatment time may be 15~20 min, specifically 16 min, 17 min, 18 min, or 19 min. In this invention, the ultrasonic treatment temperature may be ≤30℃, specifically 0℃, 5℃, 10℃, 15℃, 20℃, or 25℃; the ultrasonic treatment may be performed under ice bath conditions; the ultrasonic treatment may include probe ultrasonic treatment; the ultrasonic treatment time may be 3~5 min, specifically 3.5 min, 4 min, or 4.5 min. This invention, through dispersion and ultrasonic treatment, uniformly disperses zinc borate in propylene glycol methyl ether.

[0031] In this invention, the conditions for the second mixing can be the same as those for the first mixing, and will not be repeated here.

[0032] In this invention, the third mixing may include sequentially performing stirring and mixing, shear dispersion treatment, and ultrasonic treatment; in this invention, the stirring and mixing speed may be 600~800 rpm, specifically 650 rpm, 700 rpm, or 750 rpm; the shear dispersion treatment speed may be 4000~5000 rpm, specifically 4200 rpm, 4400 rpm, 4600 rpm, or 4800 rpm; the shear dispersion treatment time may be 20~30 min, specifically 22 min, 24 min, 26 min, or 28 min; the ultrasonic treatment temperature may be ≤30℃, specifically 0℃, 5℃, 10℃, 15℃, 20℃, or 25℃; the ultrasonic treatment may be performed under ice bath conditions; the ultrasonic treatment may include probe ultrasonic treatment; the ultrasonic treatment time may be 10~20 min, specifically 12 min, 14 min, 16 min, or 18 min. This invention utilizes probe ultrasonic treatment under ice bath conditions, which has an energy density 10 to 100 times higher than that of ordinary ultrasound. This provides sufficient energy to break the strong van der Waals forces between nanoparticles, forcing the two types of nanoparticles to interpenetrate in the liquid phase, achieving uniform mixing at the nanoscale, and further breaking down any residual agglomerates.

[0033] In this invention, the fourth mixing may include stirring; the stirring speed may be 150~300 rpm, specifically 180 rpm, 200 rpm, 250 rpm or 280 rpm.

[0034] In this invention, the temperature of the first grafting can be 50~70℃, specifically 55℃, 60℃ or 65℃; the first grafting can be carried out under water bath conditions; the time of the first grafting can be 2~4h, specifically 2.5h, 3h or 3.5h.

[0035] After obtaining the first composite slurry, the present invention performs solid-liquid separation of the first composite slurry to obtain a first solid phase; disperses the first solid phase and tetraethyl orthosilicate in an aqueous ethanol solution to form an outer core layer on the outer surface of the core, thereby obtaining a second composite slurry with a dispersed composite core layer.

[0036] In this invention, the solid-liquid separation may include centrifugal separation. After completing the solid-liquid separation, the invention may further include washing the solid obtained from the solid-liquid separation to obtain a first solid phase. In this invention, the washing may be alcohol washing, specifically ethanol washing; the ethanol used for ethanol washing may specifically be anhydrous ethanol; the number of ethanol washings may be 2 to 3 times. This invention does not have a special limitation on the amount of ethanol used, as long as it is sufficient to obtain a clear supernatant after 2 to 3 ethanol washings.

[0037] In this invention, the tetraethyl orthosilicate can be used in the form of an ethanol solution of tetraethyl orthosilicate; the mass ratio of tetraethyl orthosilicate to ethanol in the ethanol solution of tetraethyl orthosilicate can be 1:1.8~2.5, specifically 1:1.9, 1:2, 1:2.2 or 1:2.4; the mass ratio of tetraethyl orthosilicate to the flame retardant component can be 4~4.5:100, specifically 4.1:100, 4.2:100, 4.3:100 or 4.4:100.

[0038] In this invention, dispersing the first solid phase and tetraethyl orthosilicate in an aqueous ethanol solution may include the following steps: The first solid phase and the ethanol-water solution (denoted as the first ethanol-water solution) are mixed to obtain the first solid phase dispersion; The first solid dispersion and the ethanol solution of tetraethyl orthosilicate were mixed together.

[0039] In this invention, the mass ratio of ethanol to water in the first ethanol-water solution is 8.5~9.5:0.5~1.5, specifically 8.5:1.5, 8.5:1, 8.5:0.5, 9:0.5, or 9.5:0.5. In this invention, the pH value of the first solid-phase dispersion can be 9~10, specifically 9.2, 9.4, 9.6, or 9.8; the reagent for adjusting the pH value of the first solid-phase dispersion can be ammonia; the concentration of the ammonia can be 5~10 wt%, specifically 6 wt%, 7 wt%, 8 wt%, or 9 wt%. In this invention, the amount of water in the first ethanol-water solution is much smaller than the amount of ethanol. With less water, the hydrolysis rate of tetraethyl orthosilicate is slow, and the condensation reaction dominates, which is beneficial for the uniform and slow deposition of silica on the outer surface of the core, forming a dense, thin coating layer (outer core layer).

[0040] In this invention, the fifth mixing may include stirring; the stirring speed may be 100~200 rpm, specifically 120 rpm, 140 rpm, 160 rpm or 180 rpm; the sixth mixing may include stirring; the stirring speed may be 150~300 rpm, specifically 180 rpm, 200 rpm, 230 rpm, 250 rpm or 280 rpm.

[0041] In this invention, the temperature at which the silica outer core layer is formed can be 40~60℃, specifically 45℃, 50℃, or 55℃; the formation time of the silica outer core layer can be 6~12h, specifically 7h, 8h, 9h, 10h, or 11h. This invention utilizes a hydrolysis-condensation reaction of tetraethyl orthosilicate, causing the tetraethyl orthosilicate to hydrolyze and condense with a first organosilane coupling agent, or to condense itself (sol-gel condensation), forming a Si-O-Si network to obtain a silica outer core layer, thus forming a composite core layer.

[0042] After obtaining the second composite slurry, the present invention performs solid-liquid separation of the second composite slurry to obtain a second solid phase; the second solid phase, the second organosilane coupling agent and acetic acid are dispersed in ethanol, so that the second organosilane coupling agent and the silica outer core layer are second grafted to obtain a composite flame retardant.

[0043] In this invention, the solid-liquid separation may include centrifugal separation. After completing the solid-liquid separation, the invention may further include washing the solid obtained from the solid-liquid separation to obtain a second solid phase.

[0044] In this invention, the mass ratio of acetic acid to the second organosilane coupling agent can be 1~2:100, specifically 1.2:100, 1.4:100, 1.6:100, or 1.8:100. This invention achieves efficient and uniform grafting of polymerizable functional layers by adding acetic acid to catalyze the hydrolysis and condensation of the second organosilane coupling agent. The addition of glacial acetic acid accelerates the reaction of the second organosilane coupling agent while suppressing side reactions, ensuring maximum retention of active double bonds.

[0045] In this invention, dispersing the second solid phase, the second organosilane coupling agent, and acetic acid in ethanol may include the following steps: The second solid phase and ethanol were mixed to obtain a second solid phase dispersion; The second solid dispersion, the second organosilane coupling agent, and acetic acid 8 are mixed.

[0046] In this invention, the eighth mixing may include stirring; the stirring speed may be 150~300 rpm, specifically 180 rpm, 200 rpm, 230 rpm, 250 rpm or 280 rpm.

[0047] In this invention, the temperature of the second grafting can be 70~80℃, specifically 72, 74, 76 or 78℃; the time of the second grafting can be 4~8h, specifically 5h, 6h or 7h; the second grafting can be carried out under reflux conditions.

[0048] After completing the second grafting, the present invention may further include solid-liquid separation of the reaction liquid obtained from the second grafting, and drying the obtained solid phase after alcohol washing to obtain a composite flame retardant.

[0049] In this invention, the solid-liquid separation may include centrifugation; the alcohol washing may include ethanol washing; and the number of ethanol washings may be 2 to 3. This invention removes unreacted substances by washing the solid phase with ethanol.

[0050] In this invention, the drying may include vacuum drying; the temperature of the vacuum drying may be <60°C.

[0051] This invention provides the application of the composite flame retardant described in the above-described technical solution or the composite flame retardant prepared by the above-described technical solution in ultraviolet-curable coatings. When the composite flame retardant provided by this invention is applied to ultraviolet-curable coatings, the resulting coating exhibits excellent optical transparency and flame retardant efficiency.

[0052] The present invention also provides a UV-curable coating, comprising, by weight parts: 59-61 parts of UV-curable resin, 34-36 parts of acrylate reactive diluent, 4.9-5.1 parts of free radical photoinitiator, 0.19-0.21 parts of silicone leveling agent, 0.09-0.11 parts of silicone-free defoamer, and 5-5.04 parts of flame retardant; The flame retardant is the composite flame retardant described in the above technical solution or the composite flame retardant prepared by the preparation method described in the above technical solution.

[0053] In this invention, the UV-curable resin may include Changxing Chemical 6130B UV-curable resin; the acrylate reactive diluent may include isobornyl acrylate and tripropylene glycol diacrylate; the mass ratio of isobornyl acrylate to tripropylene glycol diacrylate may be 23~25:10, specifically 23.5:10, 24:10 or 24.5:10; the photoinitiator may include TPO solid photoinitiator and 819 solid photoinitiator; the mass ratio of TPO solid photoinitiator to 819 solid photoinitiator may be 3:2; the silicone leveling agent may include BYK-333 leveling agent; the silicone-free defoamer may include BYK-055 defoamer.

[0054] In this invention, the UV-curable coating may specifically include, by weight parts: 60 parts UV-curable resin, 35 parts acrylate reactive diluent, 5 parts free radical photoinitiator, 0.2 parts silicone leveling agent, 0.1 parts silicone-free defoamer, and 5.02 parts flame retardant.

[0055] To further illustrate the present invention, the solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] In all embodiments of the present invention, the D of zinc borate and aluminum hypophosphite 50 <50nm, particle size distribution PDI≤0.25, near-spherical crystal morphology, purity≥98%, zinc borate has a pH value of 6.5~8.5 in a 10% aqueous solution, and aluminum hypophosphite has a pH value of 4.5~6.5 in a 10% aqueous solution.

[0057] Example 1 D 50 Zinc borate with a mass of 42 nm was vacuum dried at 60 °C for 6 h to reduce its moisture content to 0.23%. The dried zinc borate was then dispersed in propylene glycol methyl ether, and 0.5% (by mass) of BYK-163 polymeric dispersant was added. The dispersion was carried out using a high-speed disperser for 15 min at a dispersion disc speed of 2000 rpm. The dispersion was then subjected to ultrasonic treatment with a probe under an ice bath for 3 min to obtain a propylene glycol methyl ether dispersion of zinc borate with a mass concentration of 15%.

[0058] D 50 Aluminum hypophosphite with a mass of 45 nm was vacuum dried at 60 °C for 6 h to reduce its moisture content to 0.27%. The dried aluminum hypophosphite was then dispersed in propylene glycol methyl ether, and 1% (by mass) of BYK-163 polymeric dispersant was added. The dispersion was carried out using a high-speed disperser for 15 min at a dispersion disc speed of 2000 rpm. The dispersion was then subjected to ultrasonic treatment under an ice bath for 3 min to obtain a propylene glycol methyl ether dispersion with a mass concentration of 10% aluminum hypophosphite.

[0059] The zinc borate propylene glycol methyl ether dispersion and the aluminum hypophosphite propylene glycol methyl ether dispersion were stirred at a mass ratio of 1:1 at a stirring speed of 600 rpm. After mixing, the mixture was immediately sheared and dispersed at a speed of 4000 rpm for 20 min, and then subjected to ultrasonic treatment with a probe under ice bath conditions for 10 min to obtain a mixed slurry.

[0060] At a stirring speed of 150 rpm, 0.5% KH-560 (based on the total mass of zinc borate and aluminum hypophosphite) was added to the obtained mixed slurry. The mixture was heated in a water bath to maintain the temperature of the mixed solution at 50°C. The reaction was continued for 2 hours to obtain the first composite slurry.

[0061] The first composite slurry was centrifuged, and the resulting solid was washed and redispersed. The solvent was replaced with an aqueous ethanol solution (ethanol to water mass ratio of 9:1), and the pH was adjusted to 9.3 to obtain a first solid-phase dispersion. An ethanol solution of tetraethyl orthosilicate was added dropwise to the first solid-phase dispersion at a stirring speed of 150 rpm. After the addition was complete, the mixture was reacted at 40°C for 12 h to obtain a second composite slurry. The mass ratio of tetraethyl orthosilicate to ethanol was 1:2, and the mass of tetraethyl orthosilicate accounted for 4% of the total mass of zinc borate and aluminum hypophosphite.

[0062] The obtained second composite slurry was centrifuged, and the resulting solid was washed and redispersed. The solvent was replaced with anhydrous ethanol to obtain a second solid-phase dispersion. KH-570 (4% by mass of zinc borate and aluminum hypophosphite) was added to the obtained second solid-phase dispersion at a stirring speed of 150 rpm, and acetic acid (1% by mass of KH-570) was added for catalysis. The reaction was carried out at 70°C under reflux for 8 hours. After the reaction was completed, the resulting reaction mixture was centrifuged, and the obtained solid phase was washed three times with ethanol and vacuum dried at 50°C to obtain the composite flame retardant.

[0063] Example 2 D 50 Zinc borate with a concentration of 40 nm was vacuum dried at 70 °C for 5 h to reduce its moisture content to 0.22%. The dried zinc borate was then dispersed in propylene glycol methyl ether, and 0.8% (by mass) of BYK-163 polymeric dispersant was added. The dispersion was carried out using a high-speed disperser for 18 min at a dispersion disc speed of 3000 rpm. The dispersion was then subjected to ultrasonic treatment with a probe under an ice bath for 4 min to obtain a propylene glycol methyl ether dispersion of zinc borate with a mass concentration of 17%.

[0064] D 50 Aluminum hypophosphite with a mass of 43 nm was vacuum dried at 70 °C for 5 h to reduce its moisture content to 0.25%. The dried aluminum hypophosphite was then dispersed in propylene glycol methyl ether, and 1.3% (by mass) of BYK-163 polymeric dispersant was added. The dispersion was carried out using a high-speed disperser for 18 min at a dispersion disc speed of 3000 rpm. The dispersion was then subjected to ultrasonic treatment with a probe under an ice bath for 4 min to obtain an aluminum hypophosphite dispersion with a mass concentration of 12% in propylene glycol methyl ether.

[0065] The zinc borate propylene glycol methyl ether dispersion and the aluminum hypophosphite propylene glycol methyl ether dispersion were stirred at a stirring speed of 700 rpm at a mass ratio of 1:1. After mixing, the mixture was immediately sheared and dispersed at a speed of 4500 rpm for 25 min, and then subjected to ultrasonic treatment with a probe under ice bath conditions for 15 min to obtain a mixed slurry.

[0066] At a stirring speed of 200 rpm, 0.7% KH-560 (based on the total mass of zinc borate and aluminum hypophosphite) was added to the obtained mixed slurry. The mixture was heated in a water bath to maintain the temperature of the mixed solution at 60°C. The reaction was continued for 3 hours to obtain the first composite slurry.

[0067] The first composite slurry was centrifuged, and the resulting solid was washed and redispersed. The solvent was replaced with an aqueous ethanol solution (ethanol to water mass ratio of 9:1), and the pH was adjusted to 9.5 to obtain a first solid-phase dispersion. An ethanol solution of tetraethyl orthosilicate was added dropwise to the first solid-phase dispersion at a stirring speed of 200 rpm. After the addition was complete, the mixture was reacted at 50°C for 8 hours to obtain a second composite slurry. The mass ratio of tetraethyl orthosilicate to ethanol was 1:2, and the mass of tetraethyl orthosilicate accounted for 4.2% of the total mass of zinc borate and aluminum hypophosphite.

[0068] The obtained second composite slurry was centrifuged, and the resulting solid was washed and redispersed. The solvent was replaced with anhydrous ethanol to obtain a second solid-phase dispersion. KH-570 (4% by mass of zinc borate and aluminum hypophosphite) was added to the obtained second solid-phase dispersion at a stirring speed of 200 rpm, along with acetic acid (1.5% by mass of KH-570) for catalysis. The reaction was carried out at 75°C under reflux for 6 hours. After the reaction was completed, the resulting reaction mixture was centrifuged, and the obtained solid phase was washed three times with ethanol and vacuum dried at 50°C to obtain the composite flame retardant.

[0069] Example 3 D 50 Zinc borate with a concentration of 40 nm was vacuum dried at 80 °C for 4 h to reduce its moisture content to 0.21%. The dried zinc borate was then dispersed in propylene glycol methyl ether, and 1% (by mass) of BYK-163 polymeric dispersant was added. The dispersion was carried out using a high-speed disperser for 20 min at a dispersion disc speed of 3500 rpm. The dispersion was then subjected to ultrasonic treatment with a probe under an ice bath for 5 min to obtain a zinc borate dispersion with a mass concentration of 18% in propylene glycol methyl ether.

[0070] D 50 Aluminum hypophosphite with a mass of 41 nm was vacuum dried at 80 °C for 4 h to reduce its moisture content to 0.23%. The dried aluminum hypophosphite was then dispersed in propylene glycol methyl ether, and 1.5% (by mass) of BYK-163 polymeric dispersant was added. The dispersion was carried out using a high-speed disperser for 20 min at a dispersion disc speed of 3500 rpm. The dispersion was then subjected to ultrasonic treatment under an ice bath for 5 min to obtain an aluminum hypophosphite dispersion with a mass concentration of 14% in propylene glycol methyl ether.

[0071] The zinc borate propylene glycol methyl ether dispersion and the aluminum hypophosphite propylene glycol methyl ether dispersion were stirred at a mass ratio of 1:1 at a stirring speed of 800 rpm. After mixing, the mixture was immediately sheared and dispersed at a speed of 5000 rpm for 30 min, and then subjected to ultrasonic treatment with a probe under ice bath conditions for 20 min to obtain a mixed slurry.

[0072] At a stirring speed of 300 rpm, 1% KH-560 (based on the total mass of zinc borate and aluminum hypophosphite) was added to the obtained mixed slurry. The mixture was heated in a water bath to maintain the temperature of the mixed solution at 70°C. The reaction was continued for 4 hours to obtain the first composite slurry.

[0073] The first composite slurry was centrifuged, and the resulting solid was washed and redispersed. The solvent was replaced with an aqueous ethanol solution (ethanol to water mass ratio of 9:1), and the pH was adjusted to 9.6 to obtain a first solid-phase dispersion. An ethanol solution of tetraethyl orthosilicate was added dropwise to the first solid-phase dispersion at a stirring speed of 300 rpm. After the addition was complete, the mixture was reacted at 60°C for 6 hours to obtain a second composite slurry. The mass ratio of tetraethyl orthosilicate to ethanol was 1:2, and the mass of tetraethyl orthosilicate accounted for 4.5% of the total mass of zinc borate and aluminum hypophosphite.

[0074] The obtained second composite slurry was centrifuged, and the resulting solid was washed and redispersed. The solvent was replaced with anhydrous ethanol to obtain a second solid-phase dispersion. KH-570 (5% by mass of zinc borate and aluminum hypophosphite) was added to the obtained second solid-phase dispersion at a stirring speed of 300 rpm, and acetic acid (2% by mass of KH-570) was added for catalysis. The reaction was carried out at 80°C under reflux for 4 hours. After the reaction was completed, the resulting reaction mixture was centrifuged, and the obtained solid phase was washed three times with ethanol and vacuum dried at 50°C to obtain the composite flame retardant.

[0075] Test Example 1 The performance of the composite flame retardants prepared in Examples 1-3 was compared with that of conventional flame retardants in the art: nano aluminum hydroxide, nano zinc borate, nano aluminum hypophosphite, and nano mixtures (nano mixtures formed by mixing nano zinc borate and nano aluminum hypophosphite in a mass ratio of 1:1). The results are shown in Table 1.

[0076] Table 1. Test results of performance indicators of different flame retardants

[0077] As shown in Table 1, the composite flame retardants prepared in Examples 1-3 achieved uniform nanoscale dispersion (D 50With a particle size ≤78nm, PDI≤0.23 and extremely low water content (≤0.19%), and moderate oil absorption (42~43mL / 100g) and whiteness (81.9~82.3%) significantly lower than that of individual raw materials and simple physical mixtures, this invention fully demonstrates that the preparation method provided by the present invention can effectively suppress heterogeneous agglomeration, reduce particle surface polarity, and fundamentally change the light scattering characteristics of composite flame retardant powder, laying a solid foundation for achieving high transparency in UV coatings.

[0078] Test Example 2 The raw materials for preparing the UV-curable base varnish, by weight, are: 60 parts of Changxing Chemical 6130B UV-curable resin, 25 parts of isobornyl acrylate IBOA, 10 parts of tripropylene glycol diacrylate TPGDA, 3 parts of TPO solid photoinitiator, 2 parts of 819 solid photoinitiator, 0.2 parts of BYK-333 leveling agent, and 0.1 parts of BYK-055 defoamer.

[0079] The above-mentioned raw materials are mixed evenly in the dark according to the mass ratio until the TPO solid photoinitiator and 819 solid photoinitiator are completely dissolved to obtain the UV-curable base varnish for later use.

[0080] The flame retardants in Test Example 1 (the composite flame retardants prepared in Examples 1-3 and conventional flame retardants in the art: nano aluminum hydroxide, nano zinc borate, nano aluminum hypophosphite, nano zinc borate and nano mixtures) were added to the UV-curable base varnish respectively. The amount added was 5% of the total mass of the UV-curable base varnish. The mixture was first pre-wetted at a speed of 400-600 rpm and then dispersed at a speed of 1500 rpm for 20 min to obtain the UV-curable coating.

[0081] The obtained UV-curable coating was applied to a clean polyester film and a low-haze glass plate using a 100μm wire rod coater, respectively. The coatings were then leveled in an 80℃ oven for 2 minutes. Under nitrogen protection, the coatings were then cured under a UV lamp (395nm LED, 500mW / cm²). 2 The coating is cured by irradiation with an energy of 300 mJ / cm to obtain a UV-cured coating.

[0082] The optical transparency, flame retardant efficiency, dispersion stability, effect on curing speed, and film adhesion of the obtained UV-cured coating were tested using the following methods: Optical transparency: Haze (%), film thickness 100μm, GB / T 1721-2008; Flame retardancy efficiency: Limiting oxygen index (LOI, %), GB / T 2408-2021; Dispersion stability: Settling condition after 7 days of standing was tested using the ASTM D869 standard test method for coating settling properties. Effect on curing speed: drying time (s), GB / T 1728-2020; Paint film adhesion: cross-cut test (0~5 grade), GB / T 9286-2021.

[0083] Table 2. Test results of performance indicators of different UV-curable coatings

[0084] Table 2 shows the test results of the performance indicators of different UV-curable coatings. As can be seen from Table 2, compared with traditional flame retardants in the field, the composite flame retardants provided in Examples 1-3, when applied to UV-curable coatings, significantly improve the optical transparency, flame retardant efficiency, dispersion stability, influence on curing speed, and adhesion of the UV-curable coating, fully meeting the performance requirements of transparent flame-retardant UV-curable coatings.

[0085] In summary, the composite flame retardant provided by this invention has excellent flame retardant effect, and can meet the flame retardant requirements with a low addition amount (<8%). It has excellent flame retardant performance (UL94 V-0 level) and good film transparency (haze increase value ≤4%), which fully meets the product requirements of flame retardant UV curing coatings.

[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite flame retardant, characterized in that, It includes a composite core layer and a shell layer that wraps around the outer surface of the composite core layer; The composite core layer includes a core and a silicon dioxide outer core layer that wraps around the outer surface of the core; The core material includes a wetting and dispersing agent, a flame retardant component, and a first organosilane coupling agent grafted onto the flame retardant component; the flame retardant component is zinc borate and aluminum hypophosphite. The shell layer is made of a second organosilane coupling agent; the second organosilane coupling agent is grafted onto a silica outer core layer; The second organosilane coupling agent contains carbon-carbon double bonds.

2. The composite flame retardant according to claim 1, characterized in that, The wetting and dispersing agent includes one or more of BYK-163, BYK-164 and Disperbyk-2152; The first organosilane coupling agent includes one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-aminopropyltriethoxysilane and γ-ureapropyltrimethoxysilane; The second organosilane coupling agent includes one or more of γ-methacryloxypropyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, and vinyltrimethoxysilane.

3. The composite flame retardant according to claim 1 or 2, characterized in that, The mass ratio of zinc borate to aluminum hypophosphite is 10~18:10~18; The mass ratio of the first organosilane coupling agent to the flame retardant component is 0.5~1:100; The mass ratio of the second organosilane coupling agent to the flame retardant component is 3~5:100; The mass ratio of the wetting and dispersing agent to the flame retardant component is 0.68~1.32:

100.

4. The method for preparing the composite flame retardant according to any one of claims 1 to 3, characterized in that, Includes the following steps: Wetting and dispersing agent, zinc borate, aluminum hypophosphite, and a first organosilane coupling agent are dispersed in propylene glycol methyl ether, and the zinc borate and aluminum hypophosphite are respectively grafted with the first organosilane coupling agent to obtain a first composite slurry with a core dispersed therein. The first composite slurry is separated into solid and liquid phases to obtain a first solid phase; the first solid phase and tetraethyl orthosilicate are dispersed in an aqueous ethanol solution to form a silica outer core layer on the outer surface of the core, thereby obtaining a second composite slurry with a dispersed composite core layer. The second composite slurry is separated into solid and liquid phases to obtain a second solid phase; the second solid phase, the second organosilane coupling agent, and acetic acid are dispersed in ethanol to graft the second organosilane coupling agent and the silica outer core layer to obtain a composite flame retardant.

5. The preparation method according to claim 4, characterized in that, The zinc borate and propylene glycol methyl ether are used in the form of a propylene glycol methyl ether dispersion of zinc borate; The mass concentration of the zinc borate propylene glycol methyl ether dispersion is 10-18%; The aluminum hypophosphite and propylene glycol methyl ether are used in the form of a propylene glycol methyl ether dispersion of aluminum hypophosphite; The mass concentration of the propylene glycol methyl ether dispersion of aluminum hypophosphite is 10-18%.

6. The preparation method according to claim 4 or 5, characterized in that, The temperature of the first graft is 50~70℃, and the time is 2~4h.

7. The preparation method according to claim 4, characterized in that, The tetraethyl orthosilicate is used in the form of an ethanol solution of tetraethyl orthosilicate; The mass ratio of tetraethyl orthosilicate to ethanol in the ethanol solution is 1:1.8~2.5; The mass ratio of the tetraethyl orthosilicate to the flame retardant component is 4~4.5:100; The silicon dioxide outer core layer is formed at a temperature of 40~60℃ for 6~12 hours.

8. The preparation method according to claim 4, characterized in that, The temperature for the second grafting is 70~80℃, and the time is 4~8 hours; The second grafting was performed under reflux conditions.

9. The application of the composite flame retardant according to any one of claims 1 to 3 or the composite flame retardant prepared by the preparation method according to any one of claims 4 to 8 in ultraviolet curable coatings.

10. A UV-curable coating, characterized in that, By weight, it includes: 59-61 parts of UV-curable resin, 34-36 parts of acrylate reactive diluent, 4.9-5.1 parts of free radical photoinitiator, 0.19-0.21 parts of silicone leveling agent, 0.09-0.11 parts of silicone-free defoamer, and 5-5.04 parts of flame retardant; The flame retardant is the composite flame retardant according to any one of claims 1 to 3 or the composite flame retardant prepared by the preparation method according to any one of claims 4 to 8.

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