Environment-friendly flame-retardant vinyl resin and preparation method thereof

Abstract

This invention discloses an environmentally friendly flame-retardant vinyl resin and its preparation method. The steps include: introducing phosphorus element by ring-opening modification of epoxy resin with phosphoric acid; adding a silane coupling agent to graft double bonds and constructing a Si-O-Si inorganic network in situ; and completely replacing styrene with a self-made reactive phosphorus-silicon synergistic flame-retardant diluent. This application constructs a phosphorus-silicon inherently flame-retardant system through molecular structure design, forming an organic-inorganic interpenetrating network structure. Without adding halogen flame retardants or emitting volatile organic compounds, the flame-retardant properties, mechanical strength, and thermal stability of the resin are improved. The phosphorus element and the inorganic network produce a gas-condensate synergistic effect, giving the cured product a high heat distortion temperature and low smoke emission, meeting the needs of high-end applications.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically an environmentally friendly flame-retardant vinyl resin and its preparation method. Background Technology

[0002] Vinyl epoxy resin is a special type of epoxy resin whose molecular structure contains both epoxy groups and vinyl unsaturated double bonds. It combines the high adhesion, chemical corrosion resistance, and excellent mechanical properties of epoxy resin with the free radical curing and flexible molding process of vinyl resin. It is widely used in high-performance composite materials, anti-corrosion coatings, electronic packaging and other fields.

[0003] Traditional vinyl ester resins suffer from insufficient flame retardancy, easily igniting and releasing smoke under high temperatures or open flame conditions, limiting their application in construction, rail transportation, electronics, and other fields. Furthermore, to reduce resin viscosity and improve workability, styrene is typically added as a diluent. However, styrene has a pungent odor and is highly volatile, which does not meet current environmental policies requiring low-VOC (volatile organic compound) materials.

[0004] Meanwhile, in existing flame retardant modification technologies, additive flame retardants often lead to a decrease in the mechanical properties of the resin, while reactive flame retardant modification can improve flame retardancy, but there is still room for optimization in terms of simultaneously addressing VOC emissions, improving heat resistance and interfacial bonding.

[0005] Patent CN103304745B discloses a polymerizable flame-retardant resin, which, based on various epoxy resin compositions, adds low-molecular-weight phosphate-modified unsaturated polyester resin. Through curing, an interpenetrating polymer network is formed, thereby improving high-voltage insulation performance and flame retardancy. While this technical solution enhances inherent flame retardancy through the introduction of phosphorus, further improvements are needed in systematically removing volatile diluents such as styrene to achieve a fully environmentally friendly solution.

[0006] Patent CN1621443A discloses a flame-retardant epoxy resin and a flame-retardant epoxy resin composition, which utilizes a reactive phosphorus-containing compound to react with an epoxy resin having a polycyclic structure, and combines it with a specific hardener to obtain flame-retardant properties. This technical solution achieves the introduction of flame-retardant elements through chemical bonding, but it fails to meet the current market's urgent needs in balancing resin processing viscosity and environmental requirements. Summary of the Invention

[0007] This invention provides an environmentally friendly flame-retardant vinyl resin and its preparation method. The aim is to introduce phosphorus into the main chain segment of the resin through molecular structure design, and to completely replace the traditional styrene diluent with a self-made reactive phosphorus-silicon synergistic flame-retardant diluent. At the same time, a silane coupling agent is used to construct a Si-O-Si inorganic network in situ during the reaction process to form an organic-inorganic interpenetrating structure. Thus, without adding halogen flame retardants and without emitting volatile organic compounds, the flame-retardant properties, mechanical strength and heat resistance stability of the resin are improved.

[0008] In a first aspect, this application provides a method for preparing an environmentally friendly flame-retardant vinyl resin, comprising the following steps:

[0009] S10: Epoxy-based phosphoric acid flame retardant modification: Add 100 parts of epoxy resin to the reactor, turn on the heating device to raise the temperature to 110~120℃, and after the epoxy resin is completely melted, turn on the stirring device. Under the condition of stirring speed of 200~500 rpm, slowly add 10~50 parts of phosphoric acid through the dropping device, controlling the dropping rate to 2~5 parts per minute. After the dropping is completed, keep the reaction at 110~120℃ for 2~3 hours. During this process, the hydroxyl groups of phosphoric acid molecules undergo ring-opening addition reaction with the epoxy groups at the end of the epoxy resin molecular chain or the side chain, and the phosphate groups are covalently bonded to the epoxy resin backbone to form a phosphorus-containing epoxy intermediate.

[0010] S20: Double bond grafting and vacuum dehydration: The above reaction system is further heated to 140~150℃, 5~10 parts of silane coupling agent A and 0.1~1 parts of polymerization inhibitor are added, the vacuum pumping system is started, and the pressure inside the reactor is adjusted to -0.08~-0.1MPa. The reaction is maintained under this high temperature and high vacuum condition for 2~3 hours; the active groups contained in silane coupling agent A undergo condensation or addition reactions with the hydroxyl groups in the phosphorus-containing epoxy intermediate, introducing unsaturated double bonds into the resin backbone. At the same time, the trace amounts of water and low molecular weight by-products generated during the reaction are forcibly removed by the high vacuum environment, so that the reaction equilibrium shifts towards the product direction;

[0011] S30: Dilution Molding and Filtration: Cool the reaction system to 80~90℃, add 30~50 parts of the pre-prepared reactive phosphorus-silicon synergistic flame retardant diluent to the reactor, maintain the stirring speed at 300~600 rpm, mix and dissolve for 1~2 hours, during which the temperature of the material in the reactor is monitored in real time by a temperature sensor and controlled not to exceed 100℃; after the material is mixed evenly, pressure filter it through a 200-mesh stainless steel filter to remove mechanical impurities in the material, and obtain the finished environmentally friendly flame retardant vinyl resin.

[0012] According to this application, by directly using phosphoric acid to perform ring-opening modification of epoxy resin in step S10, the traditional mode of relying solely on the later addition of flame retardants for vinyl resins is changed, allowing phosphorus to enter the resin molecular chain and constructing an inherently flame-retardant structure. In step S20, silane coupling agent A is introduced, which not only introduces double bonds participating in the later curing reaction, but more importantly, utilizes the hydrolysis of alkoxy groups in the silane monomer under residual acidic conditions and trace amounts of water vapor to generate silanol groups. These silanol groups then undergo further dehydration condensation reactions to construct a three-dimensional Si-O-Si inorganic network in situ. This network interweaves with the organic segments of the vinyl resin to form a dense interpenetrating network structure. When heated, phosphorus captures free radicals in the gas phase, while the Si-O-Si network promotes the formation of a char layer and enhances its physical strength in the condensed phase, producing a phosphorus-silicon synergistic flame-retardant effect.

[0013] Furthermore, the preparation method of the reactive phosphorus-silicon synergistic flame retardant diluent used in step S30 includes the following steps:

[0014] T10: Preparation: Prepare the raw materials according to the following weight parts: 100 parts phenol, 20-50 parts paraformaldehyde, 3-10 parts silane coupling agent B, 10-30 parts phosphoric acid, 0.1-0.5 parts catalyst, 0.1-0.5 parts polymerization inhibitor hydroquinone, and 50-100 parts toluene solvent.

[0015] T20: Hydroxylation reaction: Toluene, phenol and paraformaldehyde are added to a reaction vessel equipped with a reflux condenser and heated to 80~90℃ under stirring. The electrophilic substitution reaction between the active hydrogen at the ortho and para positions of phenol and formaldehyde is utilized. The reaction is carried out for 2~3 hours to generate a mixed solution containing ortho-hydroxymethylphenol and p-hydroxymethylphenol.

[0016] T30: Esterification reaction: Heat the system to 140~150℃, add phosphoric acid and catalyst, and introduce phosphoric acid into the phenolic skeleton through the dehydration esterification reaction of the hydroxyl group in the phosphoric acid molecule with the hydroxymethyl group on the phenol ring. Keep the reaction at the temperature for 2~3 hours, and continuously remove the reaction water generated during the process through a water separator.

[0017] T40: Double bond grafting and post-treatment: The system temperature was lowered to 110~120℃, silane coupling agent B and polymerization inhibitor hydroquinone were added, and the reaction was carried out for 2~3 hours to allow silane coupling agent B to be grafted onto the phosphorus-containing phenolic intermediate through its active group, thus constructing a phosphorus-silicon synergistic structure; finally, vacuum distillation was carried out under the conditions of pressure -0.08~-0.1MPa and temperature 120~130℃ to remove residual toluene solvent and water, and a pale yellow transparent liquid was obtained.

[0018] The reactive phosphorus-silicon synergistic flame-retardant diluent of this application provides abundant char-forming precursors through its phenolic skeleton, inherent flame-retardant properties through its phosphate ester groups, and excellent compatibility and reactivity with the host resin due to the siloxane structure and unsaturated double bonds introduced by the silane coupling agent B. During the diluent preparation process, by controlling the reaction temperature of step T20 at 80-90°C, excessive polycondensation of formaldehyde and phenol is limited, thereby controlling the molecular weight of the product within a low range. This results in a liquid state at room temperature and excellent viscosity-reducing ability, thus replacing styrene.

[0019] Further, in step S10, the epoxy resin is one or more of bisphenol A type epoxy resins E51, E44, E20, and E12; preferably, E51 and E44 are mixed at a mass ratio of 1:0.5~1.5. E51 epoxy resin has a higher epoxy value, which can provide more reaction sites to combine with phosphoric acid and increase the phosphorus content; E44 epoxy resin has a longer molecular chain, which can increase the flexibility of the cured product. By compounding the two, the crosslinking density and toughness balance of the resin are adjusted.

[0020] Further, the silane coupling agent A in step S20 is one of vinyltriethoxysilane (A151), vinyltrimethoxysilane (A171), γ-methacryloyloxypropyltrimethoxysilane (A174), and γ-methacryloyloxypropyltrimethoxysilane (KH-570); preferably A174 or KH-570. These silane coupling agents have a methacryloyloxy group at the end of their molecules, and their double bond activity is highly compatible with the curing system of vinyl resins, enabling them to participate in free radical copolymerization reactions.

[0021] Further, the polymerization inhibitor is one or more of hydroquinone, p-benzoquinone, and 2,6-di-tert-butyl-p-cresol; preferably, hydroquinone and 2,6-di-tert-butyl-p-cresol are used in a 1:1 mass ratio. The combined polymerization inhibitors, through different polymerization inhibition mechanisms, suppress the self-polymerization of double bonds during the heating synthesis stage, preventing the resin from gelling during production.

[0022] Further, the silane coupling agent B in step T10 is one of A151, A171, A174, and KH-570; preferably A151 or KH-570. By introducing silicon into the diluent molecule, it forms a Si-O-Si network with the silicon in the main resin during the curing process, thereby enhancing the uniformity of the distribution of the inorganic phase in the organic phase.

[0023] Furthermore, the catalyst in step T30 is one of concentrated sulfuric acid, Lewis acid, or dimethylbenzylamine; preferably, it is a boron trifluoride diethyl ether complex among Lewis acids. The boron trifluoride diethyl ether complex exhibits high catalytic efficiency in the esterification reaction and is easily removed or passivated in the later stages of the reaction, reducing its impact on the long-term stability of the resin.

[0024] Furthermore, the vacuum dehydration conditions in steps S20 and T40 are both controlled within -0.08 to -0.1 MPa. Within this pressure range, the boiling point of water is significantly reduced, which can efficiently remove the water generated in the reaction without damaging the resin molecular chain, preventing residual water from causing uncontrolled hydrolysis and condensation of the silane coupling agent during storage.

[0025] Secondly, this application provides an environmentally friendly flame-retardant vinyl resin, prepared according to the method described in any embodiment of the first aspect.

[0026] Because this environmentally friendly flame-retardant vinyl resin is prepared using the specific method described above, its molecular structure contains a large number of phosphate ester bonds and siloxane bonds. During the curing process, the resin matrix and the reactive diluent undergo free radical cross-linking through unsaturated double bonds to form the first organic network layer; simultaneously, the Si-O-Si structure formed by the hydrolysis and condensation of alkoxy groups in the silane coupling agent forms the second inorganic network layer. The two networks interpenetrate at the molecular level, resulting in the final cured product exhibiting extremely high heat distortion temperature and excellent mechanical strength.

[0027] This invention solves the problems of excessive VOCs caused by the reliance on styrene diluents in traditional vinyl ester resins, and the degradation of mechanical properties caused by additive flame retardants, through a combination of technical means. The specific technical features and their mechanisms of action are as follows:

[0028] Construction of a phosphorus-silicon intrinsically flame-retardant system: This invention does not rely on the physical addition of flame-retardant powders, but rather chemically bonds phosphorus to the resin backbone and diluent molecules in the form of phosphate esters through the ring-opening reaction of phosphate on epoxy groups (S10) and the esterification reaction of phosphate on hydroxymethyl groups (T30). During material combustion, phosphorus decomposes to produce phosphate derivatives, which capture active free radicals in the gas phase, interrupting the chain combustion reaction. Simultaneously, the silane coupling agent, through a hydrolysis-condensation reaction, forms an in-situ Si-O-Si network, which transforms into a dense silica ceramic layer at high combustion temperatures, covering the material surface. This synergistic effect of phosphorus (gas phase) and silicon (condensed phase) allows the resin to achieve an extremely high limiting oxygen index even with low flame-retardant element content.

[0029] Complete Replacement of Styrene by Reactive Diluents: The reactive phosphorus-silicon synergistic flame-retardant diluents (T10 to T40) prepared in this invention adopt a phenolic skeleton design with a molecular weight distribution between 300 and 800. This low molecular weight structure endows the product with a low viscosity (500 to 1500 mPa·s) at room temperature, effectively reducing the viscosity of the modified epoxy resin system. Because unsaturated double bonds are grafted onto the ends of the diluent molecular chains, it completely enters the cross-linking network of the resin during curing, without generating any small-molecule volatiles, thereby controlling the VOC content below 5 g / L and solving the irritating odor and environmental hazards of styrene.

[0030] The reinforcing effect of the organic-inorganic interpenetrating network: By simultaneously introducing a silane coupling agent into the main resin and diluent, this invention introduces silicon-oxygen bonds into the curing system. The bond energy of the silicon-oxygen bond (approximately 450 kJ / mol) is much higher than that of the carbon-carbon bond (approximately 347 kJ / mol), and the Si-O-Si network exhibits excellent chemical stability. The presence of this inorganic network significantly improves the retention rate of the resin's mechanical properties under harsh environments such as humidity and high temperature. Experimental data show that the heat distortion temperature of the resin prepared by this invention is increased by 12 to 20 °C compared to traditional vinyl ester resins, and the retention rate of mechanical properties under humid environments is over 90%.

[0031] Improved interfacial compatibility: The introduction of silane coupling agents also plays a role in interfacial bridging. When this resin is used in glass fiber or carbon fiber reinforced composites, the silanol groups in the resin can undergo condensation reactions with the hydroxyl groups on the fiber surface to form covalent bonds, thereby significantly enhancing the interfacial adhesion between the resin and the fiber. This interfacial reinforcement is directly reflected in the impact strength of the cured product, maintaining its impact strength above 15 kJ / m².

[0032] The specific implementation steps and technical details are further explained below:

[0033] In the phosphoric acid flame-retardant modification stage of the epoxy matrix (S10), controlling the dropping rate of phosphoric acid is a key technical measure. The reaction between phosphoric acid and epoxy groups is a strongly exothermic reaction. By slowly adding 2 to 5 parts per minute, combined with stirring at 200 to 500 rpm, the heat of reaction can be dissipated in time, preventing local overheating that could lead to resin color darkening or side reactions. The holding time is controlled at 2 to 3 hours, and the degree of reaction is judged by testing the change in epoxy value. When the epoxy value drops to the predetermined range, it indicates that the phosphorus element has been successfully bonded.

[0034] In the double bond grafting and vacuum dehydration stage (S20), the silane coupling agent A is introduced after phosphoric acid modification. At this time, the system contains a large number of secondary hydroxyl groups (generated from epoxy ring opening), which exhibit high reactivity with the active groups of the silane coupling agent at 140 to 150 °C. Simultaneously, the high vacuum of -0.08 to -0.1 MPa is used not only to remove the water generated in the reaction but also to promote the uniform diffusion and micro-penetration of silane monomers in the resin matrix through a reduced pressure environment, laying the foundation for the subsequent in-situ construction of a uniform Si-O-Si network.

[0035] In the preparation of the reactive diluent, toluene was used as an azeotropic solvent in the hydroxylation reaction of step T20. The presence of toluene not only adjusts the viscosity of the reaction system, but more importantly, in the esterification stage of T30, toluene forms an azeotrope with the water produced in the reaction. Water is continuously removed from the system through reflux separation, thereby disrupting the chemical equilibrium of the esterification reaction and increasing the conversion rate of phosphoric acid. In the vacuum dedistillation process of step T40, staged heating to 120-130℃ ensured that the residual amount of toluene solvent was less than 0.1%, guaranteeing the purity and environmental friendliness of the diluent.

[0036] The resulting environmentally friendly flame-retardant vinyl ester resin maintains a room temperature viscosity of 2000 to 5000 mPa·s, making it suitable for various composite molding processes such as hand lay-up, pultrusion, and filament winding. It exhibits excellent mechanical properties, with tensile strength exceeding 65 MPa and flexural strength exceeding 110 MPa. Regarding flame retardancy, due to the phosphorus-silicon synergistic effect, its limiting oxygen index (LOI) can reach 28% to 34.8%, achieving a UL94 V-0 rating in vertical burning tests, and producing extremely low smoke during combustion, fully meeting the stringent requirements of high-end applications such as electronic packaging.

[0037] This technical approach, which uses phosphorus-silicon synergistic design at the molecular level and reactive diluents to replace volatile monomers, not only solves the flame retardancy and environmental protection problems of vinyl resins, but also achieves a comprehensive improvement in the overall performance of the resin by constructing an inorganic network in situ. It has significant technological advancement and industrial application value.

[0038] In practice, the performance can be fine-tuned by adjusting the component ratios of the epoxy resin for different application scenarios. For example, in applications requiring higher chemical resistance, the proportion of E51 can be increased and the amount of phosphoric acid can be appropriately increased to enhance crosslinking density and phosphorus content; in applications requiring higher toughness, the proportion of E44 can be increased, and a silane coupling agent with long-chain alkyl modification can be selected. This highly adjustable formulation system, combined with a rigorous preparation process, makes the environmentally friendly flame-retardant vinyl resin prepared by this invention highly competitive in the field of high-performance composite materials.

[0039] Furthermore, the preparation method described in this invention has relatively conventional equipment requirements, mainly relying on a reaction vessel equipped with heating, stirring, vacuum, and water separation functions, making it easy to achieve large-scale industrial production. The byproducts of the preparation process are mainly water and recyclable toluene solvent, which is environmentally friendly and in line with the development direction of green chemistry. By precisely controlling the reaction parameters at each stage, such as temperature, pressure, time, and component ratios, it is possible to stably produce environmentally friendly flame-retardant vinyl resins with uniform quality and excellent performance.

[0040] In summary, the environmentally friendly flame-retardant vinyl resin and its preparation method provided in this application fundamentally overcome the shortcomings of traditional vinyl resins in terms of flame retardancy, environmental protection, heat resistance, and mechanical properties through flame-retardant design, reactive diluent substitution technology, and the construction of an organic-inorganic hybrid network.

[0041] Further, in step S20, the amount of polymerization inhibitor added is 0.1 to 1 part, preferably 0.3 to 0.6 parts. Within this range, the polymerization inhibitor can effectively capture the small amount of free radicals generated by thermal initiation during the high-temperature reaction, preventing premature polymerization of unsaturated double bonds, thereby ensuring the stability of the resin during the synthesis stage and subsequent storage stage.

[0042] Furthermore, in step S30, the stirring temperature during dilution molding is strictly controlled at 80~90℃, and the final material temperature does not exceed 100℃. This technique is to prevent the double bonds in the reactive phosphorus-silicon synergistic flame retardant diluent from undergoing thermal polymerization with the double bonds in the main resin without an initiator. By operating within this temperature range, rapid miscibility between the diluent and the main resin can be ensured, reducing the system viscosity, while also ensuring that the chemical activity of the resin is not lost.

[0043] Furthermore, in step T30, the amount of boron trifluoride diethyl ether catalyst added is 0.1~0.5 parts. This catalyst, as a Lewis acid, can significantly reduce the activation energy of the esterification reaction, allowing the reaction between phosphoric acid and hydroxymethyl to proceed smoothly at 140~150℃. Simultaneously, the complexing properties of boron trifluoride diethyl ether allow it to be partially removed through a vacuum degassing process after the reaction, reducing its impact on the final resin's dielectric properties.

[0044] Furthermore, in step T10, the ratio of paraformaldehyde to phenol is 20-50 parts to 100 parts. By controlling the aldehyde-phenol ratio, the functionality of the generated hydroxymethylphenol can be adjusted. A lower aldehyde-phenol ratio helps to generate a diluent precursor with predominantly bifunctional groups, thereby ensuring the viscosity-reducing effect while preventing the diluent itself from becoming too cross-linked, which could lead to resin brittleness.

[0045] Furthermore, in step S20, the amount of silane coupling agent A added is 5 to 10 parts. This amount is optimized to ensure the formation of a sufficiently dense Si-O-Si inorganic network to improve flame retardancy and heat resistance, while avoiding excessive resin costs or the generation of excessive alcohol byproducts due to excessive silane.

[0046] The resin prepared using the method of this invention exhibits a VOC content that, as detected by gas chromatography, remains consistently below 5 g / L, far exceeding the national and industry standards for low-VOC materials. In flame retardant performance testing, a vertical burning experiment was conducted using the UL94 standard. The sample extinguished within 3 seconds of being removed from the flame source, with no molten droplets produced, demonstrating excellent charring and crusting capabilities. In thermal analysis (TGA) experiments, the resin showed a char residue rate exceeding 35% at 600℃, fully demonstrating the strong charring effect of the Si-O-Si network and phosphorus elements in the condensed phase.

[0047] Furthermore, the hydrolysis resistance of the resin of this invention has been significantly enhanced. After immersion in hot water at 80°C for 1000 hours, its flexural strength retention rate still reaches over 92%. This is mainly attributed to the shielding and protective effect of the Si-O-Si inorganic network constructed by the silane coupling agent on the organic chain segments, and the better hydrolytic stability of the CO-Si covalent bond compared to the traditional ester bond. This characteristic enables the resin to have an extremely long service life in high-humidity and high-temperature environments such as marine engineering, cooling towers, and chemical corrosion protection.

[0048] In industrial applications, this resin demonstrates excellent process versatility. Because it is styrene-free, the operating environment in open molding processes (such as hand lay-up and spray molding) is odorless, significantly improving working conditions and reducing environmental protection costs for factories. In closed molding processes (such as RTM and vacuum infusion), its stable viscosity and good wettability ensure that the defect rate of large and complex components is minimized.

[0049] Finally, the environmentally friendly flame-retardant vinyl resin and its preparation method described in this invention not only represent a technological breakthrough but also offer significant economic advantages. Although components such as phosphoric acid and silane coupling agents are introduced, the invention eliminates expensive halogen flame retardants and complex post-treatment flame retardant processes, and completely replaces styrene, reducing potential risks caused by environmental non-compliance. Therefore, its overall cost is highly competitive in the market. Detailed Implementation

[0050] As described in the background section above, traditional vinyl ester resins typically use styrene as a diluent, which has strong volatility and a pungent odor. Furthermore, to impart flame-retardant properties to the resin, large amounts of halogenated flame retardants or inorganic fillers such as aluminum hydroxide are often added. This not only leads to a decrease in the resin's mechanical properties but may also produce toxic fumes during combustion.

[0051] Based on this, this application provides an environmentally friendly flame-retardant vinyl resin and its preparation method, which aims to introduce phosphorus and silicon elements into the resin backbone and diluent molecules through molecular structure design to construct an organic-inorganic interpenetrating network structure, thereby achieving styrene-free and inherently flame-retardant properties.

[0052] In a first aspect, this application provides a method for preparing an environmentally friendly flame-retardant vinyl resin, comprising the following steps:

[0053] S10: Epoxy-based phosphoric acid flame retardant modification: Add 100 parts of epoxy resin to the reactor, turn on the heating device to raise the temperature to 110~120℃, and after the epoxy resin is completely melted, turn on the stirring device. Under the condition of stirring speed of 200~500 rpm, add 10~50 parts of phosphoric acid dropwise through the dropping device, controlling the dropping rate to 2~5 parts per minute. After the dropping is completed, keep the reaction at 110~120℃ for 2~3 hours. During this process, the hydroxyl groups of phosphoric acid molecules undergo an addition reaction with the epoxy groups on the epoxy resin molecular chain, and the phosphorus element is covalently bonded to the epoxy backbone.

[0054] S20: Double Bond Grafting and Vacuum Dehydration: The above reaction system is heated to 140-150℃, and 5-10 parts of silane coupling agent A and 0.1-1 parts of polymerization inhibitor are added. The vacuum pumping system is started, and the pressure inside the reactor is adjusted to -0.08 to -0.1 MPa. The reaction is maintained at this temperature for 2-3 hours. Silane coupling agent A reacts with the modified epoxy intermediate, introducing unsaturated double bonds. Simultaneously, the high vacuum environment removes trace amounts of moisture and low-molecular-weight substances generated during the reaction.

[0055] S30: Dilution Molding and Filtration: Cool the reaction system to 80-90℃, add 30-50 parts of the pre-prepared reactive phosphorus-silicon synergistic flame retardant diluent to the reactor, maintain a stirring speed of 300-600 rpm, and mix and dissolve for 1-2 hours, controlling the material temperature not to exceed 100℃ during this period. After uniform mixing, pressure filter through a 200-mesh stainless steel filter to obtain the finished environmentally friendly flame retardant vinyl resin.

[0056] In some embodiments, the preparation method of the reactive phosphorus-silicon synergistic flame retardant diluent used in step S30 includes the following steps:

[0057] T10: Preparation: Prepare raw materials according to the following weight parts: 100 parts phenol, 20-50 parts paraformaldehyde, 3-10 parts silane coupling agent B, 10-30 parts phosphoric acid, 0.1-0.5 parts catalyst, 0.1-0.5 parts polymerization inhibitor hydroquinone, and 50-100 parts toluene solvent.

[0058] T20: Hydroxylation reaction: Toluene, phenol and paraformaldehyde are added to a reactor equipped with a reflux condenser, and the temperature is raised to 80~90℃ under stirring. The reaction is carried out for 2~3 hours to generate a mixed solution containing hydroxymethylphenol.

[0059] T30: Esterification reaction: Heat the system to 140~150℃, add phosphoric acid and catalyst, keep the reaction at this temperature for 2~3 hours, and remove the generated reaction water through a water separator during the process.

[0060] T40: Double bond grafting and post-treatment: The system temperature was lowered to 110~120℃, silane coupling agent B and polymerization inhibitor hydroquinone were added, and the reaction was carried out for 2~3 hours. Finally, vacuum distillation was carried out under the conditions of -0.08~-0.1MPa pressure and 120~130℃ to remove residual toluene solvent and water, and a pale yellow transparent liquid was obtained.

[0061] In some embodiments, in step S10, the epoxy resin is one or more of bisphenol A type epoxy resins E51, E44, E20, and E12; preferably, E51 and E44 are mixed at a mass ratio of 1:0.5 to 1.5.

[0062] In some embodiments, the silane coupling agent A in step S20 is one of vinyltriethoxysilane (A151), vinyltrimethoxysilane (A171), γ-methacryloyloxypropyltrimethoxysilane (A174), and γ-methacryloyloxypropyltrimethoxysilane (KH-570); preferably A174 or KH-570.

[0063] In some embodiments, the polymerization inhibitor is one or more of hydroquinone, p-benzoquinone, and 2,6-di-tert-butyl-p-cresol; preferably, hydroquinone and 2,6-di-tert-butyl-p-cresol are used in a 1:1 mass ratio.

[0064] In some embodiments, the silane coupling agent B in step T10 is one of A151, A171, A174, and KH-570; preferably A151 or KH-570.

[0065] In some embodiments, the catalyst in step T30 is one of concentrated sulfuric acid, Lewis acid, and dimethylbenzylamine; preferably, it is a boron trifluoride diethyl ether complex of Lewis acid.

[0066] Secondly, this application provides an environmentally friendly flame-retardant vinyl resin, prepared according to the method described in any embodiment of the first aspect.

[0067] The technical solution of this application will be described in detail below through specific embodiments.

[0068] Example 1

[0069] Preparation of reactive phosphorus-silicon synergistic flame retardant diluent:

[0070] T10: Take 100 parts by weight of phenol, 35 parts of paraformaldehyde, 6 parts of silane coupling agent KH-570, 20 parts of phosphoric acid, 0.3 parts of boron trifluoride ether complex, 0.3 parts of hydroquinone, and 75 parts of toluene.

[0071] T20: Toluene, phenol and paraformaldehyde are added to the reactor, and the temperature is raised to 85°C under stirring. The reaction is carried out for 2.5 hours.

[0072] T30: Heat to 145℃, add phosphoric acid and boron trifluoride diethyl ether complex, keep the reaction at this temperature for 2.5h, and remove the water through a water separator.

[0073] T40: Cool to 115℃, add KH-570 and hydroquinone, and react for 2.5 h. Vacuum distill at -0.09 MPa and 125℃ to remove solvent and water, obtaining the diluent.

[0074] Preparation of environmentally friendly flame-retardant vinyl resin:

[0075] S10: Add 100 parts of epoxy resin (E51 to E44 mass ratio 1:1) to the reactor, heat to 115℃, add 30 parts of phosphoric acid dropwise at a stirring speed of 350 rpm at a dropping rate of 3.5 parts per minute, and keep the reaction at 115℃ for 2.5 hours.

[0076] S20: Heat to 145℃, add 7.5 parts of silane coupling agent KH-570 and 0.5 parts of polymerization inhibitor (hydroquinone and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:1), adjust the pressure to -0.09MPa, and keep the reaction at this temperature for 2.5h.

[0077] S30: Cool to 85℃, add 40 parts of the diluent prepared above, stir and mix for 1.5h, control the material temperature not to exceed 100℃, and filter through a 200-mesh filter under pressure to obtain the finished resin.

[0078] Example 2

[0079] Preparation of reactive phosphorus-silicon synergistic flame retardant diluent:

[0080] T10: Take 100 parts of phenol, 20 parts of paraformaldehyde, 3 parts of silane coupling agent A151, 10 parts of phosphoric acid, 0.1 parts of boron trifluoride ether complex, 0.1 parts of hydroquinone, and 50 parts of toluene.

[0081] T20: Heat to 80℃ and react for 2 hours.

[0082] T30: Heat to 140℃, add phosphoric acid and catalyst, and maintain the temperature for 2 hours.

[0083] T40: Cool to 110℃, add A151 and hydroquinone, and react for 2 hours. Vacuum distillation is then carried out at a pressure of -0.08 MPa and a temperature of 120℃.

[0084] Preparation of environmentally friendly flame-retardant vinyl resin:

[0085] S10: Add 100 parts of epoxy resin E51, heat to 110℃, stir at 200 rpm, add 10 parts of phosphoric acid at a rate of 2 parts per minute, and keep the reaction at this temperature for 2 hours.

[0086] S20: Heat to 140℃, add 5 parts of silane coupling agent A151 and 0.1 parts of polymerization inhibitor, pressure -0.08MPa, and keep the reaction at this temperature for 2 hours.

[0087] S30: Cool to 80℃, add 30 parts of the above diluent, stir for 1 hour, and filter to obtain the finished resin.

[0088] Example 3

[0089] Preparation of reactive phosphorus-silicon synergistic flame retardant diluent:

[0090] T10: Take 100 parts of phenol, 50 parts of paraformaldehyde, 10 parts of silane coupling agent KH-570, 30 parts of phosphoric acid, 0.5 parts of boron trifluoride ether complex, 0.5 parts of hydroquinone, and 100 parts of toluene.

[0091] T20: Heat to 90℃ and react for 3 hours.

[0092] T30: Heat to 150℃, add phosphoric acid and catalyst, and keep the temperature for 3 hours.

[0093] T40: Cool to 120℃, add KH-570 and hydroquinone, and react for 3 hours. Vacuum distillation is then carried out at a pressure of -0.1 MPa and a temperature of 130℃.

[0094] Preparation of environmentally friendly flame-retardant vinyl resin:

[0095] S10: Add 100 parts of epoxy resin E44, heat to 120℃, stir at 500 rpm, add 50 parts of phosphoric acid at a rate of 5 parts per minute, and keep the reaction at this temperature for 3 hours.

[0096] S20: Heat to 150℃, add 10 parts of silane coupling agent KH-570 and 1 part of polymerization inhibitor, pressure -0.1MPa, and keep the reaction at this temperature for 3 hours.

[0097] S30: Cool to 90℃, add 50 parts of the above diluent, stir for 2 hours, and filter to obtain the finished resin.

[0098] Example 4

[0099] In this embodiment, the preparation of the reactive phosphorus-silicon synergistic flame retardant diluent is the same as in Example 1.

[0100] Preparation of environmentally friendly flame-retardant vinyl resin:

[0101] S10: Add 100 parts of epoxy resin (E51 to E44 mass ratio 1:1.5) to the reactor, heat to 115℃, add 40 parts of phosphoric acid dropwise at a rate of 4 parts per minute while stirring at 400 rpm, and keep the reaction at 115℃ for 2.5 hours.

[0102] S20: Heat to 145℃, add 8.5 parts of silane coupling agent A174 and 0.6 parts of polymerization inhibitor, adjust the pressure to -0.09MPa, and keep the reaction at this temperature for 2.5h.

[0103] S30: Cool to 85℃, add 45 parts of the diluent prepared above, stir and mix for 1.5h, filter, and obtain the finished resin.

[0104] Comparative Example 1

[0105] Comparative Example 1 provides a conventional vinyl resin.

[0106] Preparation method: Add 100 parts of epoxy resin E51 and 45 parts of methacrylic acid to a reaction vessel, and react at 110 to 120°C until the acid value is below 10 mg KOH / g. After cooling, add 50 parts of styrene diluent and mix thoroughly.

[0107] Comparative Example 2

[0108] Comparative Example 2 provides an additive flame-retardant vinyl resin.

[0109] Preparation method: 20 parts of ammonium polyphosphate (APP) and 10 parts of aluminum hydroxide powder were added to the resin obtained in Comparative Example 1 and dispersed evenly by high-speed mixer.

[0110] Comparative Example 3

[0111] Comparative Example 3 provides a vinyl resin containing phosphorus only in the main chain.

[0112] Preparation method: The modified resin in steps S10 and S20 was prepared according to the method of Example 1, but in step S30, the self-made reactive phosphorus-silicon synergistic flame retardant diluent was not used, but 40 parts of styrene was used for dilution.

[0113] Comparative Example 4

[0114] Comparative Example 4 provides a resin that uses only a homemade diluent but whose main chain is not modified.

[0115] Preparation method: Vinyl resins were prepared using conventional methods (such as the product of the reaction between epoxy and methacrylic acid in Comparative Example 1), but the reactive phosphorus-silicon synergistic flame retardant diluent prepared in Example 1 was used instead of styrene during the dilution stage.

[0116] The resins prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to performance tests. The test items included: viscosity (25°C), tensile strength, flexural strength, heat distortion temperature (HDT), limiting oxygen index (LOI), vertical flammability rating (UL94), and VOC content. The test results are shown in the table below:

[0117]

[0118] Based on the data analysis in the table above, the environmentally friendly flame-retardant vinyl resins prepared in Examples 1 to 4 all exhibit significant characteristics in various properties.

[0119] Regarding flame retardant performance, the limiting oxygen index (LOI) of Examples 1 to 4 were all between 31.5% and 36.8%, and their vertical flammability ratings all reached V-0. In contrast, the conventional resin (Comparative Example 1) had an LOI of only 19.5% and no flame retardant rating; although the additive flame retardant resin (Comparative Example 2) had a higher LOI, it still did not reach V-0. This indicates that by bonding phosphorus to the main chain through step S10 and introducing phosphorus into the diluent through step T30, combined with the Si-O-Si network constructed in situ using a silane coupling agent, a phosphorus-silicon synergistic flame retardant effect was achieved.

[0120] Regarding mechanical properties and heat resistance, the tensile strength of Examples 1 to 4 ranged from 68 to 75 MPa, the flexural strength from 115 to 130 MPa, and the heat distortion temperature from 132 to 145 °C. However, the additive flame-retardant resin (Comparative Example 2) exhibited a significant decrease in tensile and flexural strength due to the addition of inorganic powder. Data from Comparative Examples 3 and 4 indicate that, with only main-chain modification or with only the use of a self-made diluent, both the heat resistance and mechanical strength were lower than those of the synergistic system described in this application.

[0121] Regarding environmental performance, the VOC content of Examples 1 to 4 is extremely low, all below 5 g / L, while the VOC content of Comparative Examples 1 to 3, which are diluted with styrene, all exceed 300 g / L. This demonstrates that the self-made reactive phosphorus-silicon synergistic flame retardant diluent in this application can completely replace styrene and eliminate the emission of volatile organic compounds.

[0122] Further analysis of the process details of Examples 1 to 4:

[0123] In step S10, the dropping rate of phosphoric acid is controlled at 2 to 5 parts per minute. Experiments showed that if the dropping rate is too fast (e.g., greater than 10 parts / min), the heat accumulation of the reaction causes the local temperature of the material to rise instantaneously to above 160°C, the product color changes from pale yellow to dark brown, and the viscosity increases abnormally. Through the slow dropping and medium-speed stirring described in this application, the reaction is stable, and the ring-opening conversion rate of the epoxy groups remains above 95%.

[0124] In step S20, maintaining a high vacuum (-0.08 to -0.1 MPa) is crucial for the stability of the final product. Within this pressure range, the moisture generated during the reaction is removed. If the vacuum is insufficient (e.g., -0.04 MPa), residual moisture will cause slow hydrolysis and condensation of the silane coupling agent during storage, resulting in a viscosity increase of over 50% within 3 months. However, using the method of this application, the viscosity change rate of the resin is less than 10% after 6 months of storage at room temperature.

[0125] In step T20 of the preparation of the reactive diluent, the temperature is controlled between 80 and 90°C. If the temperature exceeds 100°C, phenol and formaldehyde will undergo excessive condensation polymerization, forming a phenolic resin with a large molecular weight, causing the diluent to become a semi-solid or high-viscosity liquid at room temperature and lose its diluting ability. Through the temperature control of this application, the molecular weight distribution of the diluent is between 300 and 800, and the room temperature viscosity is controlled between 500 and 1500 mPa·s.

[0126] In the T30 esterification reaction, the use of toluene as an azeotropic solvent ensured the complete removal of reaction water. Observation using a water separator indicated that the esterification reaction had reached equilibrium when the water content ceased to increase. The subsequent T40 vacuum desolventizing process reduced the residual toluene to below 0.1%, ensuring the environmental friendliness of the diluent.

[0127] The environmentally friendly flame-retardant vinyl resin prepared in this application contains phosphate ester bonds, siloxane bonds, and unsaturated double bonds in its molecular structure. During the curing process, the double bonds of the main resin and the double bonds of the diluent undergo free radical cross-linking to form an organic network; simultaneously, the alkoxy groups remaining in the silane coupling agent further condense under the action of a curing accelerator or trace amounts of moisture, forming a Si-O-Si inorganic network. The interpenetrating structure of these two components endows the material with excellent comprehensive properties.

[0128] Furthermore, the proportions of the components in the preparation method described in this application have a certain degree of adjustability. For example, in Example 3, by increasing the ratio of paraformaldehyde and phosphoric acid, the phosphorus content and crosslinking density of the resin were further improved, resulting in an LOI of 36.8% and a heat distortion temperature of 145°C, making it suitable for aerospace or rail transportation fields where flame retardancy and heat resistance are extremely important. In Example 2, by reducing the degree of modification, a resin with lower viscosity (2100 mPa·s) was obtained, which is more suitable for vacuum induction processes.

[0129] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an environmentally friendly flame-retardant vinyl resin, characterized in that, Includes the following steps: S10: Epoxy-based phosphorus flame retardant modification: Add 100 parts of epoxy resin to the reactor, heat to 110~120℃, and after the epoxy resin is completely melted, start stirring. Under the condition of stirring speed of 200~500 rpm, add 10~50 parts of phosphoric acid dropwise through a dropping device, controlling the dropping rate to 2~5 parts per minute. After the dropping is completed, keep the reaction at 110~120℃ for 2~3 hours to form a phosphorus-containing epoxy intermediate. S20: Double bond grafting and vacuum dehydration: The reaction system is heated to 140~150℃, 5~10 parts of silane coupling agent A and 0.1~1 parts of polymerization inhibitor are added, the vacuum pumping system is started, the pressure in the reactor is adjusted to -0.08~-0.1MPa, and the reaction is kept at the pressure for 2~3 hours to obtain phosphorus-containing unsaturated resin backbone; S30: Dilution Molding and Filtration: Cool the reaction system to 80~90℃, add 30~50 parts of reactive phosphorus-silicon synergistic flame retardant diluent to the reactor, maintain the stirring speed at 300~600 rpm, mix and dissolve for 1~2 hours, control the temperature of the material in the reactor to not exceed 100℃, after mixing evenly, filter under pressure through a 200-mesh stainless steel filter screen to obtain the finished environmentally friendly flame retardant vinyl resin.

2. The method of claim 1, wherein, In step S10, the epoxy resin includes one or more of bisphenol A type epoxy resins E51, E44, E20, and E12.

3. The method of claim 2, wherein, The epoxy resin is a mixture of bisphenol A type epoxy resins E51 and E44 in a mass ratio of 1:0.5~1.

5.

4. The method of claim 1, wherein, In step S20, the silane coupling agent A includes one of vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxysilane.

5. The method of claim 1, wherein, The polymerization inhibitor includes one or more of hydroquinone, p-benzoquinone, and 2,6-di-tert-butyl-p-cresol.

6. The method of claim 5, wherein, The polymerization inhibitor is a mixture of hydroquinone and 2,6-di-tert-butyl-p-cresol in a mass ratio of 1:

1.

7. The method of claim 1, wherein, In step S30, the preparation method of the reactive phosphorus-silicon synergistic flame retardant diluent includes the following steps: T10: Raw material preparation: Prepare the following raw materials: 100 parts phenol, 20-50 parts paraformaldehyde, 3-10 parts silane coupling agent B, 10-30 parts phosphoric acid, 0.1-0.5 parts catalyst, 0.1-0.5 parts polymerization inhibitor hydroquinone, and 50-100 parts toluene solvent. T20: Hydroxylation reaction: Toluene, phenol and paraformaldehyde are added to a reaction vessel equipped with a reflux condenser, and the temperature is raised to 80~90℃ under stirring. The reaction is carried out for 2~3 hours to generate a mixed solution containing hydroxymethylphenol. T30: Esterification reaction: Heat the system to 140~150℃, add phosphoric acid and catalyst, keep the reaction at the temperature for 2~3h, and remove the reaction water generated during the process through a water separator; T40: Double bond grafting and post-treatment: The system temperature was lowered to 110~120℃, silane coupling agent B and polymerization inhibitor hydroquinone were added, and the reaction was carried out for 2~3 hours; vacuum distillation was carried out under the conditions of pressure of -0.08~-0.1MPa and temperature of 120~130℃ to remove residual toluene solvent and water, and the reactive phosphorus-silicon synergistic flame retardant diluent was obtained.

8. The method according to claim 7, characterized in that, In step T10, the silane coupling agent B includes one of vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxysilane.

9. The method according to claim 7, characterized in that, In step T30, the catalyst includes one of concentrated sulfuric acid, boron trifluoride diethyl ether complex, and dimethyl benzylamine.

10. An environmentally friendly flame-retardant vinyl resin, characterized in that, It is prepared by the method according to any one of claims 1 to 9.

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