Compound double microcapsule flame retardant and application thereof, flame-retardant impregnated film paper and preparation method thereof

Abstract

The present application belongs to the technical field of veneer impregnated film paper, and particularly relates to a compound double-microcapsule flame retardant and application thereof, a flame-retardant impregnated film paper, a preparation method and application thereof. The compound double-microcapsule flame retardant provided by the present application comprises an ammonium polyphosphate (APP) microcapsule flame retardant and a perfluorohexanone double-layer microcapsule flame retardant. The core material of the ammonium polyphosphate microcapsule flame retardant is ammonium polyphosphate, and the wall material is melamine formaldehyde resin. The core material of the perfluorohexanone double-layer microcapsule flame retardant is perfluorohexanone, the inner layer wall material is a calcium alginate and chitosan polyelectrolyte complex, and the outer layer wall material is a polymer. The present application can take into account the chemical compatibility of APP and triamine glue, and simultaneously realize stable loading of perfluorohexanone in the film paper system, successfully constructing an impregnated film paper relay type three-dimensional flame-retardant system with an active fire extinguishing and condensed phase flame-retardant synergistic mechanism, and without affecting the appearance and gluing performance of veneer, meeting the application requirements in the field of furniture and interior decoration.

Description

Technical Field

[0001] This invention belongs to the technical field of decorative impregnated paper, specifically relating to compounded dual microcapsule flame retardants and their applications, flame-retardant impregnated paper, preparation methods and their applications. Background Technology

[0002] Impregnated paper-faced engineered wood panels have become a mainstream material for custom furniture, cabinets, and interior decoration due to their realistic surface texture, wear and stain resistance, high production efficiency, and controllable cost. However, these products have a paper-based veneer impregnated with melamine-formaldehyde resin (melamine glue) and a core layer of wood shavings or fiberboard. Both the substrate and the veneer are flammable organic polymer materials. Once exposed to a fire source, they are highly susceptible to ignition and rapid spread, releasing large amounts of dense smoke and toxic gases, seriously threatening human life and property safety.

[0003] In existing technologies, flame-retardant treatments for this type of board mainly focus on two approaches: First, impregnating the entire wood substrate with flame retardant. This method not only requires a large amount of flame retardant and is costly, but water-soluble flame retardants are also prone to migration and precipitation within the board due to changes in ambient humidity, leading to whitening and frosting on the board surface, severely deteriorating the bonding strength and appearance durability of the veneer. Second, applying a transparent flame-retardant varnish to the surface after the boards are laminated. Although this method is simple to operate, the adhesion between the coating and the impregnated paper surface is limited, making it prone to aging and cracking during long-term use. Furthermore, the coating thickness is difficult to control uniformly, often resulting in surface defects such as decreased gloss and blurred texture. More importantly, the above post-treatment methods are all passive flame retardants, unable to actively intervene in the gas-phase combustion chain reaction at the moment of a fire, resulting in generally low flame-retardant efficiency.

[0004] Regarding the selection of flame retardants, ammonium polyphosphate (APP), as the core acid source of intumescent flame retardant systems, has advantages such as high phosphorus content, good thermal stability, and environmental friendliness. However, its abundant free hydroxyl groups on its surface are prone to chemical cross-linking reactions with the active functional groups such as hydroxymethyl and imino groups in the melamine prepolymer during storage and impregnation. This side reaction leads to an exponential increase in the viscosity of the resin system, and the gelation time is drastically shortened from the normal 5 minutes to less than 1.5 minutes, resulting in a surge in waste liquid in the impregnation tank, uneven penetration of the base paper, and serious damage to the stability of the continuous impregnation production process. To solve this problem, related technologies have attempted to use silane coupling agents or surfactants to physically coat and modify APP. However, the physical coating layer has poor compatibility with the melamine matrix, and the interfacial bonding is weak after hot pressing, failing to fundamentally eliminate the interference of active groups. On the other hand, perfluorohexanone, as a novel halon alternative fire extinguishing agent, has attracted much attention due to its excellent fire extinguishing efficiency, low ozone depletion potential, and zero global warming potential. Its fire extinguishing mechanism lies in the fact that after being heated and vaporized, it decomposes and releases fluorine free radicals, which efficiently capture H· and OH· free radicals in the flame, thereby cutting off the combustion chain reaction. However, perfluorohexanone is a liquid at room temperature with a boiling point of only 49°C, which is completely incompatible with the water-based melamine adhesive system. Direct addition will cause severe stratification and flocculation. Moreover, its low boiling point means that a large amount of it will volatilize and dissipate during the drying stage after impregnation, making it unable to be effectively loaded into the film paper.

[0005] In summary, existing flame retardant technologies generally face problems such as poor compatibility between flame retardants and impregnation resin processes, and the inability to stably load gas-phase active fire extinguishing components into water-based resin systems. As a result, they cannot achieve synergy between active fire extinguishing and condensed phase flame retardancy, and it is difficult to balance the flame retardant efficiency, smoke suppression performance, and impregnation process adaptability of impregnated paper-faced engineered wood panels. Summary of the Invention

[0006] The purpose of this invention is to provide a compounded dual-microcapsule flame retardant and its application, a flame-retardant impregnated paper, a preparation method and its application. The compounded dual-microcapsule flame retardant provided by this invention can take into account the chemical compatibility of APP and melamine glue, and at the same time achieve stable loading of perfluorohexanone in the impregnated paper system. It successfully constructs a relay-type three-dimensional flame retardant system for impregnated paper with a synergistic mechanism of active fire extinguishing and condensed phase flame retardancy, without affecting the appearance of the finish and the bonding performance. It successfully takes into account flame retardant efficiency, smoke suppression performance and impregnation process adaptability, and meets the application requirements of the furniture and interior decoration fields.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a compounded dual-microcapsule flame retardant, comprising ammonium polyphosphate microcapsule flame retardant and perfluorohexanone dual-layer microcapsule flame retardant; the ammonium polyphosphate microcapsule flame retardant has a core-shell structure, with ammonium polyphosphate as the core material and melamine-formaldehyde resin as the wall material; the perfluorohexanone dual-layer microcapsule flame retardant has a dual-shell core-shell structure, with perfluorohexanone as the core material, an inner wall material of calcium alginate and chitosan polyelectrolyte complex, and an outer wall material of a polymer, wherein the polymer includes one or more of melamine-formaldehyde resin, polyurea, polyurethane, and polymethyl methacrylate; the mass ratio of the ammonium polyphosphate microcapsule flame retardant to the perfluorohexanone dual-layer microcapsule flame retardant is 4~6:1.

[0008] Preferably, the preparation method of the ammonium polyphosphate microcapsule flame retardant includes the following steps: Ammonium polyphosphate suspension and melamine-formaldehyde resin prepolymer are mixed and coated to obtain the ammonium polyphosphate microcapsule flame retardant; the ammonium polyphosphate suspension contains ammonium polyphosphate, water and sodium hexametaphosphate; the raw materials for preparing the melamine-formaldehyde resin prepolymer include melamine, formaldehyde solution, water and pH adjuster, and the solid content of the melamine-formaldehyde resin prepolymer is 45-55%; the mass ratio of ammonium polyphosphate to the melamine-formaldehyde resin prepolymer is 2-4:1.

[0009] Preferably, the preparation method of the melamine-formaldehyde resin prepolymer includes the following steps: mixing melamine, formaldehyde solution, water and pH adjuster to obtain a mixed solution with a pH value of 8.5~9.5; the molar ratio of melamine to formaldehyde in the formaldehyde solution is 1:2.5~1:3.5; heating the mixed solution to carry out a prepolymerization reaction to obtain the melamine-formaldehyde resin prepolymer; the temperature of the prepolymerization reaction is 85~95℃ and the time is 60~120min; The conditions for the coating reaction include: pH value of 4.5~5.5, reaction temperature of 70~80℃, and reaction time of 1.5~3h.

[0010] Preferably, the preparation method of the perfluorohexanone bilayer microcapsule flame retardant includes the following steps: Perfluorohexanone, sodium alginate aqueous solution, and emulsifier are mixed to obtain an emulsion; the emulsion is mixed with calcium chloride aqueous solution to carry out a cross-linking reaction to obtain calcium alginate gel beads; the calcium alginate gel beads are mixed with chitosan solution to form a composite to form the inner layer of calcium alginate and chitosan polyelectrolyte complex, thus obtaining primary microcapsules. The polymer is encapsulated in the primary microcapsules to obtain the perfluorohexanone bilayer microcapsule flame retardant.

[0011] Preferably, the average particle size of the ammonium polyphosphate microcapsule flame retardant is 5-30 μm; and the average particle size of the perfluorohexanone bilayer microcapsule flame retardant is 10-50 μm.

[0012] This invention provides the application of the compounded dual microcapsule flame retardant described in the above technical solution in the preparation of flame-retardant impregnated paper.

[0013] This invention provides a method for preparing flame-retardant impregnated paper, comprising the following steps: The base paper is first impregnated in urea-formaldehyde resin, and then first dried to obtain a first-impregnated paper. The first-impregnated paper is subjected to a second impregnation, which includes impregnating the surface of the first-impregnated paper with flame-retardant-free melamine-formaldehyde resin and the back side with flame-retardant melamine-formaldehyde resin, followed by a second drying to obtain the flame-retardant impregnated film paper; the flame-retardant melamine-formaldehyde resin includes melamine-formaldehyde resin prepolymer and the compounded dual-microcapsule flame retardant described in the above technical solution.

[0014] Preferably, the mass percentage of the compounded dual microcapsule flame retardant to the mass of the melamine-formaldehyde resin prepolymer is 20-40%; the flame-retardant melamine-formaldehyde resin has a Forte 4 cup viscosity of 25-40 s at 25°C; the second drying temperature is 100-120°C, and the second drying ends when the volatile content is 4%-8% and the pre-curing degree is 40%-60%.

[0015] The present invention provides a flame-retardant impregnated paper prepared by the preparation method described in the above technical solution.

[0016] The present invention provides a flame-retardant impregnated paper-faced engineered wood panel, comprising a substrate and a facing layer disposed on the surface of the substrate, wherein the facing layer is made of the flame-retardant impregnated paper described in the above technical solution, and the back side of the flame-retardant impregnated paper is in contact with the substrate.

[0017] This invention provides a compounded dual-microcapsule flame retardant, comprising ammonium polyphosphate microcapsule flame retardant and perfluorohexanone dual-layer microcapsule flame retardant; the ammonium polyphosphate microcapsule flame retardant has a core-shell structure, with ammonium polyphosphate as the core material and melamine-formaldehyde resin as the wall material; the perfluorohexanone dual-layer microcapsule flame retardant has a dual-shell core-shell structure, with perfluorohexanone as the core material, an inner wall material of calcium alginate and chitosan polyelectrolyte complex, and an outer wall material of a polymer, wherein the polymer includes one or more of melamine-formaldehyde resin, polyurea, polyurethane, and polymethyl methacrylate; the mass ratio of the ammonium polyphosphate microcapsule flame retardant to the perfluorohexanone dual-layer microcapsule flame retardant is 4~6:1. Compared with the prior art, this invention has the following beneficial effects: This invention employs melamine-formaldehyde resin to in-situ encapsulate ammonium polyphosphate, forming core-shell structured ammonium polyphosphate microcapsules as condensed-phase flame-retardant microcapsules. This encapsulation layer completely physically isolates the active hydroxyl groups on the APP surface, fundamentally preventing the possibility of chemical cross-linking between them and the external melamine prepolymer. Experimental data from this invention confirms that after adding the ammonium polyphosphate microcapsule flame retardant of this invention, the gelation time of the modified resin system (i.e., flame-retardant melamine-formaldehyde resin) significantly recovers from 1 minute 30 seconds without encapsulation to 4 minutes 30 seconds to 5 minutes 30 seconds, perfectly matching the process window of pure melamine resin. Simultaneously, the viscosity of the flame-retardant melamine-formaldehyde resin remains stable during room temperature storage, significantly extending the workable period (storage period) of the impregnated film paper and substantially reducing the waste liquid rate and cleaning frequency of the impregnation production line. More importantly, the wall material of the ammonium polyphosphate microcapsule flame retardant is the same material as the matrix resin. During the hot pressing and curing process, the wall material melts and co-crosslinks with the external resin to form an integrated continuous network structure, which ensures that the flexibility of the impregnated paper and the surface bonding strength of the impregnated paper-faced artificial board meet the requirements of the national standard GB / T 17657-2022.

[0018] To address the inherent drawbacks of perfluorohexanone (PFH) such as its extremely low boiling point and incompatibility with water-based resins, this invention designs a PFH bilayer microcapsule flame retardant. The inner wall material is a composite of calcium alginate and chitosan polyelectrolyte, while the outer wall material is a polymer. This invention utilizes a bilayer structure, achieving three key benefits: First, the dense outer polymer shell imparts excellent mechanical strength to the microcapsules, ensuring a breakage rate of less than 5% under harsh processing conditions such as high-speed stirring, roller impregnation, and hot air drying, thus guaranteeing the effective loading of PFH. Second, the inner natural polymer gel material exhibits thermosensitive properties. At room temperature, it remains dense, preventing core material leakage, while under high-temperature fire conditions, it undergoes a thermal gelation transformation, providing a buffer channel for the thermal vaporization of PFH and enabling gradient-controlled release. Third, calcium alginate and chitosan themselves contain abundant nitrogen and oxygen elements, which can synergistically participate in the char formation reaction during thermal decomposition, complementing the fire-extinguishing function of PFH. Therefore, this invention successfully integrates a highly efficient and clean perfluorohexanone fire extinguishing agent into an impregnated paper system, breaking the technical limitation that traditional decorative materials cannot actively extinguish fires.

[0019] This invention employs a synergistic approach of ammonium polyphosphate microcapsule flame retardant and perfluorohexanone (PFH) bilayer microcapsule flame retardant. The condensed-phase flame retardancy of the ammonium polyphosphate microcapsules coated with melamine-formaldehyde resin and the active gas-phase fire extinguishing effect of the PFH bilayer microcapsules form a relay-style three-dimensional flame retardant network of "first gas-phase inhibition, then condensed-phase isolation." Within the initial seconds of a fire, the outer wall microcapsules of the PFH bilayer microcapsule flame retardant rupture, and PFH rapidly vaporizes, releasing fluorine free radicals. These free radicals quench the H· and OH· free radicals in the core flame area, nipping the fire in the bud and significantly reducing heat feedback. This active intervention greatly alleviates the heat load on the condensed phase, allowing the APP component to efficiently catalyze the dehydration and char formation of the substrate at low addition levels, forming a dense and expanded heat-insulating and oxygen-barrier char layer. Subsequently, this char layer acts as a physical barrier, effectively preventing the escape of internal flammable gases and the inward transfer of external heat, thereby extending the time window for PFH to continuously exert its gas-phase inhibition effect. The two work synergistically through a relay of "rapid flame retardation in the gas phase and long-lasting heat insulation in the condensed phase," resulting in a significant synergistic effect. The results of this invention's embodiments show that, with the total amount of the compounded dual-microcapsule flame retardant accounting for only 20-40% of the mass of melamine-formaldehyde resin (i.e., melamine-formaldehyde resin prepolymer), the flame retardant performance of impregnated paper-faced engineered wood panels can stably meet the requirements of GB / T 8624-2012 B1(C) or B1(B) grade standards. Simultaneously, the smoke density rating (SDR) is significantly lower than that of non-flame-retardant panels, and the smoke toxicity is significantly improved, achieving highly efficient flame retardancy while substantially reducing additive costs.

[0020] This invention provides a method for preparing flame-retardant impregnated paper. The method involves dispersing the compounded dual-microcapsule flame retardant in the melamine resin (i.e., melamine-formaldehyde resin) used for back coating during a second impregnation process. The flame-retardant component is precisely positioned on the decorative back layer through a two-stage impregnation process. This process design avoids contamination of the impregnated paper's surface pattern and color by the flame retardant, ensuring the surface quality of the impregnated paper. Simultaneously, the microencapsulated flame retardant is uniformly and stably suspended in the resin system, without sedimentation or agglomeration. After curing, the microcapsules are firmly anchored within the melamine resin cross-linking network, eliminating the risk of migration and precipitation. The impregnated paper surface is smooth and even, with uniform gloss and clear, realistic wood grain printing, fully maintaining the decorative aesthetic effect of non-flame-retardant products. Furthermore, the preparation method provided by this invention does not require large-scale modifications to existing impregnation production lines, has strong process compatibility, and is easily achievable for continuous industrial production, showing promising economic and social benefits.

[0021] In summary, the compounded dual-microcapsule flame retardant provided by this invention, when applied to flame-retardant impregnated paper, achieves a relay-style three-dimensional flame retardancy through first gas phase inhibition and then condensed phase isolation, with an oxygen index of 34%~38%, without affecting the appearance of the finish or the bonding performance. It can effectively balance flame retardancy efficiency, smoke suppression performance, and impregnation process adaptability, meeting the application requirements of the furniture and interior decoration fields. Attached Figure Description

[0022] Figure 1 Characterization photograph of the perfluorohexanone bilayer microcapsules prepared in Example 1 of this invention. Detailed Implementation

[0023] This invention provides a compounded dual-microcapsule flame retardant, comprising ammonium polyphosphate microcapsule flame retardant and perfluorohexanone bilayer microcapsule flame retardant. The ammonium polyphosphate microcapsule flame retardant has a core-shell structure, with ammonium polyphosphate as the core material and melamine-formaldehyde resin as the wall material. The perfluorohexanone bilayer microcapsule flame retardant has a dual-shell core-shell structure, with perfluorohexanone as the core material, an inner wall material of calcium alginate and chitosan polyelectrolyte composite, and an outer wall material of a polymer, wherein the polymer includes one or more of melamine-formaldehyde resin, polyurea, polyurethane, and polymethyl methacrylate. The mass ratio of the ammonium polyphosphate microcapsule flame retardant to the perfluorohexanone bilayer microcapsule flame retardant is 4-6:1. In this invention, the calcium alginate and chitosan polyelectrolyte composite is formed by combining calcium alginate and chitosan. The polymer is formed through in-situ polymerization or interfacial polymerization.

[0024] In this invention, unless otherwise specified, all raw materials / components used in preparation are commercially available products well-known to those skilled in the art. Unless otherwise specified, all percentages in this invention refer to mass percentages. Unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent; for example, formaldehyde solution is a 37% (w / w) aqueous solution of formaldehyde. Room temperature in this invention generally refers to a temperature between 15°C and 30°C, and is generally defined as 25°C.

[0025] The compounded dual-microcapsule flame retardant provided by this invention includes ammonium polyphosphate microcapsule flame retardant. In this invention, the ammonium polyphosphate microcapsule flame retardant has a core-shell structure, with ammonium polyphosphate as the core material and melamine-formaldehyde resin as the wall material. The average particle size of the ammonium polyphosphate microcapsule flame retardant is preferably 5-30 μm. In this invention, the ammonium polyphosphate microcapsule flame retardant is preferably made from melamine-formaldehyde resin prepolymer as raw material, and a coating layer wall material is formed on the surface of ammonium polyphosphate through in-situ polymerization. This invention solves the compatibility problem between ammonium polyphosphate and melamine-formaldehyde resin prepolymer by coating ammonium polyphosphate with melamine-formaldehyde resin to form condensed-phase flame-retardant microcapsules; it completely isolates the surface active groups of ammonium polyphosphate, preventing it from undergoing cross-linking reactions with the external melamine-formaldehyde resin prepolymer. The melamine-formaldehyde resin wall material and the external melamine-formaldehyde resin are homologous materials and can be co-cured during hot pressing to form an integrated cross-linked network. Compared with uncoated ammonium polyphosphate, the viscosity change and gelation time of the coated resin are closer to those of pure melamine-formaldehyde resin (curing time is extended from 1 min 30 s (using uncoated ammonium polyphosphate resin) to 4 min 30 s to 5 min 30 s), the impregnation process window is restored, the flexibility and shelf life of the impregnated paper are significantly improved, and the surface bonding strength meets the standard requirements.

[0026] In this invention, the preparation method of the ammonium polyphosphate microcapsule flame retardant includes the following steps: Ammonium polyphosphate suspension and melamine-formaldehyde resin prepolymer are mixed and coated to obtain the ammonium polyphosphate microcapsule flame retardant. In this invention, the ammonium polyphosphate suspension comprises ammonium polyphosphate, water, and sodium hexametaphosphate. The degree of polymerization n of the ammonium polyphosphate is preferably >1500, and in the examples it can be 1500~2000. The water can be deionized water. The preferred method for preparing the ammonium polyphosphate suspension includes: adding the ammonium polyphosphate to water, then adding the sodium hexametaphosphate, and performing shear dispersion to obtain the ammonium polyphosphate suspension. The mass ratio of the ammonium polyphosphate to the sodium hexametaphosphate is 200:1~1.5. This invention does not have special requirements for the amount of water. The preferred rotation speed of the shear dispersion is 3000~4000 rpm, and the preferred time is 30~50 min. In this invention, the raw materials for preparing the melamine-formaldehyde resin prepolymer preferably include melamine, formaldehyde solution, water, and pH adjuster. The mass fraction of the formaldehyde solution is 37%. The water can be deionized water. The pH adjuster preferably includes triethanolamine and / or sodium hydroxide. In this invention, the solid content of the melamine-formaldehyde resin prepolymer is 45-55%, and in the examples it can be 52% or 53%. The mass ratio of the ammonium polyphosphate to the melamine-formaldehyde resin prepolymer is preferably 2-4:1, and in the examples it can be 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0027] In this invention, the preparation method of the melamine-formaldehyde resin prepolymer preferably includes the following steps: mixing melamine, formaldehyde solution, water, and a pH adjuster to obtain a mixed solution with a pH value of 8.5-9.5 (preferably 9-9.5); the molar ratio of melamine to formaldehyde in the formaldehyde solution is preferably 1:2.5-1:3.5; heating the mixed solution to carry out a prepolymerization reaction to obtain the melamine-formaldehyde resin prepolymer. In this invention, the temperature of the prepolymerization reaction is preferably 85-95°C, and the time is preferably 60-120 min, which can be 90 min in the examples. The prepolymerization reaction is carried out under stirring conditions.

[0028] In this invention, the preferred method for mixing the ammonium polyphosphate suspension and the melamine-formaldehyde resin prepolymer is to dropwise add the melamine-formaldehyde resin prepolymer to the ammonium polyphosphate suspension, then stir and mix for 15-20 minutes to allow the melamine-formaldehyde resin prepolymer to be uniformly adsorbed onto the ammonium polyphosphate, resulting in a mixed solution. Then, this invention preferably uses a pH adjuster to adjust the pH of the mixed solution to 4.5-5.5 for the coating reaction. The pH adjuster can be acetic acid. The preferred conditions for the coating reaction include: a pH of 4.5-5.5, a reaction temperature of 70-80°C (75°C in the examples), and a reaction time of 1.5-3 hours. After the coating reaction, this invention preferably cools the obtained reaction solution to room temperature and sequentially filters, washes with water, and dries to obtain the ammonium polyphosphate microcapsule flame retardant. The water washing uses deionized water three times. The drying is preferably vacuum drying, with a preferred temperature of 75-80°C and a preferred time of 5-6 hours. In this invention, the encapsulation rate of the ammonium polyphosphate microcapsule flame retardant is preferably 15-30%.

[0029] The compounded dual-microcapsule flame retardant provided by this invention includes a perfluorohexanone dual-layer microcapsule flame retardant. In this invention, the perfluorohexanone dual-layer microcapsule flame retardant has a dual-shell core-shell structure, with perfluorohexanone as the core material, an inner wall material of calcium alginate and chitosan polyelectrolyte complex, and an outer wall material of a polymer, wherein the polymer includes one or more of melamine-formaldehyde resin, polyurea, polyurethane, and polymethyl methacrylate. In this invention, the average particle size of the perfluorohexanone dual-layer microcapsule flame retardant is preferably 10-50 μm. In this invention, the perfluorohexanone dual-layer microcapsule flame retardant is preferably first passed through Ca... 2+Cross-linking and polyelectrolyte composites form the inner layer of a calcium alginate and chitosan polyelectrolyte complex, i.e., the inner wall material. Then, through in-situ polymerization or interfacial polymerization, the outer layer of the microcapsule is formed, i.e., the outer wall material. This invention preferably uses a double-layer structure of calcium alginate / chitosan inner layer and melamine-formaldehyde resin or polyurea outer layer to encapsulate perfluorohexanone, forming active fire-extinguishing microcapsules. This achieves gradient-controlled release of perfluorohexanone, overcoming the defects of perfluorohexanone's low boiling point (49°C) and poor compatibility with water-based resins (severe delamination), making it suitable for impregnated paper systems. The outer layer provides processing mechanical strength, ensuring a microcapsule breakage rate of less than 5% during stirring, impregnation, and drying; the inner layer provides a temperature-sensitive buffer, enabling gradient-controlled release of perfluorohexanone. In the early stages of a fire, after the outer layer ruptures, perfluorohexanone undergoes controlled vaporization, releasing fluorine free radicals that actively capture H· and OH· free radicals in the gas-phase combustion chain reaction, rapidly inhibiting flame development and gaining a critical time window for char formation.

[0030] In this invention, the preparation method of the perfluorohexanone bilayer microcapsule flame retardant includes the following steps: Perfluorohexanone, sodium alginate aqueous solution, and emulsifier are mixed to obtain an emulsion; the emulsion is mixed with calcium chloride aqueous solution to carry out a cross-linking reaction to obtain calcium alginate gel beads; the calcium alginate gel beads are mixed with chitosan solution to form a composite to form the inner layer of calcium alginate and chitosan polyelectrolyte complex, thus obtaining primary microcapsules. The polymer is encapsulated in the primary microcapsules to obtain the perfluorohexanone bilayer microcapsule flame retardant. In this invention, the polymer encapsulation method preferably includes in-situ polymerization or interfacial polymerization.

[0031] This invention involves mixing perfluorohexanone, an aqueous solution of sodium alginate, and an emulsifier to obtain an emulsion; mixing the emulsion with an aqueous solution of calcium chloride to undergo a cross-linking reaction to obtain calcium alginate gel beads; and mixing the calcium alginate gel beads with a chitosan solution to form an inner layer of a calcium alginate and chitosan polyelectrolyte complex, thus obtaining primary microcapsules. In this invention, the mass fraction of the aqueous solution of sodium alginate is preferably 1-2%. The emulsifier is preferably sodium dodecylbenzenesulfonate. The volume ratio of the perfluorohexanone to the aqueous solution of sodium alginate is preferably 2-3:10. The volume ratio of the perfluorohexanone to the mass ratio of the emulsifier is preferably 30 mL: 0.2-0.3 g. The preferred method for preparing the emulsion includes: premixing the aqueous solution of perfluorohexanone and sodium alginate, then adding the emulsifier and performing shear emulsification. The preferred rotation speed for shear emulsification is 1500-2000 rpm, and the preferred time is 5-10 min. Preferably, the emulsion is added dropwise to the aqueous solution of calcium chloride. The mass fraction of the calcium chloride aqueous solution is preferably 1-1.5%. The volume ratio of the sodium alginate aqueous solution to the calcium chloride aqueous solution is preferably 1:1.5-2. The crosslinking reaction is carried out under stirring conditions at room temperature for a time of 15-20 minutes. The chitosan solution is an acetic acid aqueous solution of chitosan. The mass fraction of chitosan in the chitosan solution is 1-1.5%. The pH value of the chitosan solution is preferably 4.5-5. The volume ratio of the sodium alginate aqueous solution to the chitosan solution is preferably 1:1.5-2. The composite is carried out under stirring conditions for a time of 45-50 minutes. In this invention, during the composite process, chitosan is deposited on the surface of calcium alginate through electrostatic interaction to form a polyelectrolyte composite inner layer. After the composite is completed, the obtained composite reaction solution is preferably filtered and washed sequentially to obtain the primary microcapsules.

[0032] After obtaining the primary microcapsules, the present invention encapsulates the primary microcapsules with a polymer to obtain the perfluorohexanone bilayer microcapsule flame retardant. In the present invention, the polymer preferably comprises melamine-formaldehyde resin, polyurea, polyurethane, or polymethyl methacrylate. The raw material for preparing the melamine-formaldehyde resin includes melamine-formaldehyde resin prepolymer. The raw material for preparing the polyurea includes toluene diisocyanate. The raw material for preparing the polyurethane includes polyisocyanate. The raw material for preparing the polymethyl methacrylate includes methyl methacrylate monomer.

[0033] The mass ratio of the primary microcapsules to the raw materials for preparing the polymer (melamine-formaldehyde resin prepolymer, toluene diisocyanate, polyisocyanate or methyl methacrylate monomer) is preferably 3~6:1, more preferably 3~5:1, and in the examples it can be 4:1.

[0034] In this invention, when the polymer is melamine-formaldehyde resin, the coating polymer preferably includes the following steps: dispersing the primary microcapsules in water, adding an emulsifier to obtain a primary microcapsule dispersion; mixing the primary microcapsule dispersion with a melamine-formaldehyde resin prepolymer (preparation method as described above), then adjusting the pH to 4.5-5.5, and heating to carry out an in-situ polymerization reaction. The mass ratio of the primary microcapsules to the melamine-formaldehyde resin prepolymer is preferably 3-6:1, more preferably 3-5:1, and in the examples, it can be 4:1. The emulsifier can be sodium dodecyl sulfate. The mass ratio of the initial microcapsules to the emulsifier is preferably 40:0.5. The mixing is preferably carried out under stirring conditions, and the mixing time is preferably 20-30 min. In this invention, the melamine-formaldehyde resin prepolymer is uniformly adsorbed onto the primary microcapsules through mixing. The temperature of the in-situ polymerization reaction is preferably 60-75°C, and in the examples, it can be 70°C, and the time is preferably 1.5-2.5 h. After the in-situ polymerization reaction is completed, the resulting reaction solution is cooled to room temperature and then filtered, washed, and dried sequentially to obtain the perfluorohexanone bilayer microcapsule flame retardant. The drying is preferably vacuum drying, with a preferred temperature of 50-55°C and a preferred time of 8-10 hours.

[0035] In this invention, when the polymer is polyurea, the primary microcapsules are dispersed in an oil phase containing polyisocyanate, and then interfacially polymerized in an aqueous phase containing a polyamine for 3-5 hours. The polyamine can be ethylenediamine.

[0036] In a specific embodiment of the present invention, the encapsulated polymer preferably includes the following steps: dispersing the primary microcapsules in water, adding an emulsifier to obtain a primary microcapsule dispersion; adding a toluene diisocyanate (TDI) solution dropwise to the primary microcapsule dispersion and performing shear emulsification to obtain an O / W emulsion; adding an ethylenediamine solution dropwise to the O / W emulsion and performing an interfacial polymerization reaction. The emulsifier is preferably sodium dodecyl sulfate. The mass ratio of the initial microcapsules to the emulsifier is preferably 40:0.5. The mass ratio of the primary microcapsules to the toluene diisocyanate is preferably 3~6:1, more preferably 3~5:1, and in this embodiment, 4:1. The rotation speed of the shear emulsification is pre-selected as 1500~2000 rpm, and the time is preferably 10~15 min. The toluene diisocyanate solution is preferably a toluene solution of toluene diisocyanate. The mass ratio of ethylenediamine to water in the ethylenediamine solution is preferably 1:5. The mass ratio of the initial microcapsules to ethylenediamine is preferably 2:1. The preferred temperature for the interfacial polymerization reaction is 45-50°C, and the preferred time is 3-5 hours. After cooling the resulting reaction solution to room temperature, it is sequentially filtered, washed, and dried to obtain the perfluorohexanone bilayer microcapsule flame retardant. The drying is preferably vacuum drying, and the preferred temperature for vacuum drying is 50-55°C, and the preferred time is 8-10 hours.

[0037] In this invention, when the polymer is polymethyl methacrylate (PMMA), the coating polymer preferably comprises the following steps: dispersing the primary microcapsules in an oil phase containing methyl methacrylate monomer, an oil-soluble initiator, and a crosslinking agent; adding an emulsifier and then emulsifying and dispersing in an aqueous phase; heating to 60-75°C; and polymerizing in situ under nitrogen protection for 2.5-4 hours. In this invention, the oil-soluble initiator preferably includes azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO). The crosslinking agent is preferably divinylbenzene.

[0038] In a specific embodiment of the present invention, the encapsulated polymer preferably includes the following steps: dispersing the primary microcapsules in water, adding an emulsifier to obtain a primary microcapsule dispersion; adding an oil phase solution dropwise to the primary microcapsule dispersion and performing shear emulsification to obtain an O / W emulsion; and then performing an interfacial polymerization reaction. The emulsifier is preferably Tween-80. The mass ratio of the initial microcapsules to the emulsifier is preferably 40:1. The oil phase solution includes toluene diisocyanate (TDI), polyethylene glycol (PEG-400), and an organic solvent. The organic solvent can be toluene. The mass ratio of the primary microcapsules to the toluene diisocyanate is preferably 3~6:1, more preferably 3~5:1, and in the examples, it can be 4:1. The mass ratio of the primary microcapsules to the polyethylene glycol (PEG-400) is preferably 15~25:1, more preferably 20:1. The rotation speed of the shear emulsification is pre-selected as 1500~2000 rpm, and the time is preferably 10~20 min. The interfacial polymerization reaction is carried out under nitrogen protection. The preferred temperature for the interfacial polymerization reaction is 60-75°C, and the preferred time is 2.5-4 hours. The resulting reaction solution is cooled to room temperature and then sequentially filtered, washed, and dried to obtain the perfluorohexanone bilayer microcapsule flame retardant. The drying is preferably vacuum drying, and the preferred temperature for vacuum drying is 50-55°C, and the preferred time is 8-10 hours.

[0039] In this invention, when the polymer is polyurethane, the coating polymer preferably comprises the following steps: dispersing the primary microcapsules in an oil phase containing polyisocyanate and polyol, then emulsifying and dispersing them in an aqueous phase containing an emulsifier, and performing interfacial polymerization at 50-70°C for 2.5-4 hours. In this invention, the polyisocyanate preferably includes toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), or diphenylmethane diisocyanate (MDI). The polyol preferably includes polyethylene glycol (PEG), 1,4-butanediol, or triethanolamine.

[0040] In a specific embodiment of the present invention, the encapsulating polymer preferably includes the following steps: dispersing the primary microcapsules in water, adding a stabilizer to obtain a primary microcapsule dispersion; adding an oil phase solution dropwise to the primary microcapsule dispersion and performing shear emulsification to obtain an O / W emulsion; and then performing an interfacial polymerization reaction. The stabilizer is preferably polyvinyl alcohol (PVA-1788). The mass ratio of the initial microcapsules to the stabilizer is preferably 40:1. The oil phase solution includes methyl methacrylate (MMA) monomer, azobisisobutyronitrile (AIBN), and divinylbenzene (DVB). The organic solvent can be toluene. The mass ratio of the primary microcapsules to the methyl methacrylate (MMA) monomer is preferably 3-6:1, more preferably 3-5:1, and in the examples, it can be 4:1. The mass ratio of the primary microcapsules to the azobisisobutyronitrile (AIBN) is preferably 100:1. The mass ratio of the primary microcapsules to the divinylbenzene (DVB) is preferably 100:2. The rotational speed for shear emulsification is pre-selected as 1500-2000 rpm, and the preferred time is 10-20 min. The interfacial polymerization reaction is carried out under nitrogen protection. The preferred temperature for the interfacial polymerization reaction is 50-70℃, and the preferred time is 2.5-4 h. The resulting reaction solution is cooled to room temperature and then sequentially filtered, washed, and dried to obtain the perfluorohexanone bilayer microcapsule flame retardant. The drying is preferably vacuum drying, and the preferred temperature for vacuum drying is 50-55℃, and the preferred time is 8-10 h.

[0041] In this invention, the mass ratio of the ammonium polyphosphate microcapsule flame retardant to the perfluorohexanone bilayer microcapsule flame retardant is 4-6:1, and in the examples it can be 4:1, 4.5:1, 5:1, 5.5:1 or 6:1. This invention forms a relay-style three-dimensional flame retardant network of "first gas phase inhibition, then condensed phase isolation" by combining the condensed-phase flame retardancy of the melamine-formaldehyde resin-coated ammonium polyphosphate microcapsules with the gas-phase active fire extinguishing effect of the perfluorohexanone bilayer microcapsules. Perfluorohexanone releases fluorine free radicals in the early stages of a fire, inhibiting the gas-phase combustion chain reaction, thus buying time for condensed-phase char formation, allowing ammonium polyphosphate to catalyze the formation of a dense, expanded char layer even at a low addition amount; the char layer formed by the ammonium polyphosphate also isolates heat feedback, prolonging the action time of perfluorohexanone.

[0042] This invention provides the application of the compounded dual microcapsule flame retardant described in the above technical solution in the preparation of flame-retardant impregnated paper.

[0043] This invention provides a method for preparing flame-retardant impregnated paper, comprising the following steps: The base paper is first impregnated in urea-formaldehyde resin, and then first dried to obtain a first-impregnated paper. The first-impregnated paper is subjected to a second impregnation, which includes impregnating the surface of the first-impregnated paper with flame-retardant-free melamine-formaldehyde resin and the back side with flame-retardant melamine-formaldehyde resin, followed by a second drying to obtain the flame-retardant impregnated film paper; the flame-retardant melamine-formaldehyde resin includes melamine-formaldehyde resin and the compounded dual-microcapsule flame retardant described in the above technical solution.

[0044] This invention involves impregnating base paper in urea-formaldehyde resin for the first time, followed by a first drying process to obtain a pre-impregnated paper. In this invention, there are no special requirements regarding the type of base paper; any base paper material well-known to those skilled in the art capable of preparing impregnated film paper can be used. The preferred basis weight of the base paper is 80-85 g / m². 2 In this invention, the urea-formaldehyde resin is a urea-formaldehyde resin containing a curing agent, preferably ammonium chloride, and the mass of the curing agent accounts for 5‰ of the mass of the urea-formaldehyde resin. This invention does not have special requirements for the preparation method of the urea-formaldehyde resin; any preparation method well-known to those skilled in the art can be used. The preferred temperature for the first drying is 110~120℃. The preferred drying time is 3~5 minutes. In this invention, after the first drying, an impregnated paper is obtained, the surface of which has an impregnated resin layer, which is urea-formaldehyde resin. The mass of the impregnated resin layer formed after the first drying is 0.6~0.8 times the mass of the original paper.

[0045] After obtaining the first-impregnated paper, the present invention performs a second impregnation on the first-impregnated paper. The second impregnation includes impregnating the surface of the first-impregnated paper with flame-retardant-free melamine-formaldehyde resin and the back with flame-retardant melamine-formaldehyde resin, followed by a second drying to obtain the flame-retardant impregnated film paper. In the present invention, the flame-retardant-free melamine-formaldehyde resin is a melamine-formaldehyde resin prepolymer containing a curing agent (its preparation method is as described above). In the present invention, the flame-retardant-free melamine-formaldehyde resin comprises a melamine-formaldehyde resin prepolymer and a curing agent. The preferred preparation method of the flame-retardant-free melamine-formaldehyde resin includes: mixing the melamine-formaldehyde resin prepolymer and the curing agent to obtain the flame-retardant-free melamine-formaldehyde resin. The mass of the curing agent accounts for 2‰ of the mass of the melamine-formaldehyde resin prepolymer. The curing agent is preferably ammonium chloride.

[0046] In this invention, the flame-retardant melamine-formaldehyde resin comprises a melamine-formaldehyde resin prepolymer and the compounded dual-microcapsule flame retardant described in the above-mentioned technical solution. Preferably, the flame-retardant melamine-formaldehyde resin further comprises a curing agent, which is preferably ammonium chloride. In this invention, the mass percentage of the compounded dual-microcapsule flame retardant to the melamine-formaldehyde resin prepolymer is preferably 20-40%, and in the embodiments, it can be 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, or 40%. The mass percentage of the curing agent is 2‰ of the mass of the melamine-formaldehyde resin prepolymer.

[0047] In this invention, the preferred method for preparing the flame-retardant melamine-formaldehyde resin includes: dispersing the compounded dual-microcapsule flame retardant in a melamine-formaldehyde resin prepolymer by stirring, and then adding a curing agent to obtain the flame-retardant melamine-formaldehyde resin. The stirring and dispersion temperature is ≤40℃. The stirring and dispersion speed is preferably 200~300 rpm, and the stirring and dispersion time is preferably 15~20 min. The Forecast-4 cup viscosity of the flame-retardant melamine-formaldehyde resin at 25℃ is preferably 25~40 s. The second drying temperature is preferably 100~120℃, and the second drying is preferably stopped when the volatile matter content is 4%~8% and the pre-curing degree is 40%~60%. In this invention, after the second drying, a second-dip top-coating resin layer and a second-dip back-coating resin layer are formed on the surface of the first-dip resin layer. The second-dip top-coating resin layer is a flame-retardant-free melamine-formaldehyde resin, and the second-dip back-coating resin layer is a flame-retardant melamine-formaldehyde resin. The flame-retardant melamine-formaldehyde resin comprises a melamine-formaldehyde resin matrix and a compounded dual-microcapsule flame retardant dispersed in the melamine-formaldehyde resin matrix. The mass of the second-dip resin layer (i.e., the second-dip top-coating resin layer and the second-dip back-coating resin layer) formed after the second drying is preferably 1 to 1.5 times the mass of the base paper.

[0048] This invention provides a flame-retardant impregnated paper prepared by the preparation method described in the above-described technical solution. The flame-retardant impregnated paper provided by this invention is a flame-retardant impregnated paper based on the synergistic combination of active fire-extinguishing microcapsules and condensed-phase flame-retardant microcapsules. The flame-retardant impregnated paper sequentially comprises a first impregnated resin layer, and a second impregnated top-coating resin layer and a second impregnated back-coating resin layer located on the surface of the first impregnated resin layer. The second impregnated top-coating resin layer is a flame-retardant-free melamine-formaldehyde resin, and the second impregnated back-coating resin layer is a flame-retardant melamine-formaldehyde resin. The second impregnated back-coating resin layer contains the composite dual-microcapsule flame retardant described in the above-described technical solution.

[0049] This invention provides a flame-retardant impregnated paper-faced engineered wood panel, comprising a substrate and a facing layer disposed on the surface of the substrate. The facing layer is made of the flame-retardant impregnated paper described in the above-mentioned technical solution, and the back side of the flame-retardant impregnated paper is in contact with the substrate. Specifically, the surface of the flame-retardant impregnated paper-faced engineered wood panel is made of flame-retardant-free melamine-formaldehyde resin, and the facing layer in contact with the substrate contains the compounded dual-microencapsulated flame retardant described in the above-mentioned technical solution.

[0050] This invention provides a method for preparing the flame-retardant impregnated paper-faced artificial board, preferably comprising the following steps: pressing the flame-retardant impregnated paper onto the surface of a substrate, wherein the back side of the impregnated paper is in contact with the substrate; the pressing operation parameters preferably include: hot pressing unit pressure preferably 2.0~2.2MPa; temperature preferably 190~200℃; time preferably 20~40s.

[0051] To further illustrate the present invention, the technical solutions provided by the present invention are described in detail below with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention. In the following embodiments and comparative examples, unless otherwise specified, all materials used are commercially available products.

[0052] Example 1 S1. Preparation of melamine-formaldehyde resin prepolymer Add 150g of melamine, 200g of formaldehyde solution (mass fraction 37%) and 30g of deionized water to a three-necked flask, adjust the pH to 9.0~9.5 with triethanolamine and sodium hydroxide, stir and react at 95℃ for 90min to obtain a melamine-formaldehyde resin prepolymer with a solid content of 52%.

[0053] S2, Preparation of Ammonium Polyphosphate Microencapsulated Flame Retardant (MFAPP) 200g of ammonium polyphosphate (APP degree of polymerization 1500~2000) was added to 800g of deionized water, along with 1.5g of sodium hexametaphosphate. The mixture was sheared and dispersed at 3000rpm for 30min to obtain an ammonium polyphosphate suspension. 100g of the melamine-formaldehyde resin prepolymer (solid content 52%) prepared in step S1 was added dropwise to the ammonium polyphosphate suspension (mass ratio of ammonium polyphosphate to melamine-formaldehyde resin prepolymer was 2:1). The mixture was stirred for 15min to ensure uniform adsorption of the melamine-formaldehyde resin prepolymer. The pH was adjusted to 5.5 with acetic acid, and the temperature was raised to 75℃ for 3h. After cooling to room temperature, the mixture was filtered, washed three times with deionized water, and vacuum dried at 80℃ for 5h to obtain the ammonium polyphosphate microcapsule flame retardant. The coating rate was determined to be 50% (titration method), the average particle size was 15μm, and the effective component of ammonium polyphosphate was 79% (i.e., the mass percentage of APP in the ammonium polyphosphate microcapsule flame retardant, of which the solid content of 100g of melamine-formaldehyde resin prepolymer prepared in step S1 was 52%).

[0054] Preparation of S3, perfluorohexanone bilayer microcapsule flame retardant S3a. Inner Layer Preparation: Mix 30 mL of perfluorohexanone with 100 mL of 1 wt% sodium alginate aqueous solution, add 0.3 g of sodium dodecylbenzenesulfonate, and shear emulsify at 1500 rpm for 10 min to form a homogeneous emulsion. Add the emulsion dropwise to 150 mL of 1 wt% CaCl2 aqueous solution and stir for 20 min to form calcium alginate gel beads. Transfer the calcium alginate gel beads to 200 mL of 1 wt% chitosan acetate solution (pH 4.5) and stir for 45 min. Chitosan is deposited on the surface of the calcium alginate gel beads through electrostatic attraction, forming a polyelectrolyte composite inner layer. Filter and wash to obtain primary microcapsules.

[0055] S3b, Outer Layer Preparation (Melamine-Formaldehyde Resin Outer Layer Type): 40g of the primary microcapsules prepared in step S3a were dispersed in 400mL of deionized water, and 0.5g of sodium dodecyl sulfate was added as an emulsifier. The mixture was stirred until homogeneous. 10g of melamine-formaldehyde resin prepolymer (solid content 52%) prepared in step S1 (25% by weight of the primary microcapsules) was added, with a mass ratio of primary microcapsules to melamine-formaldehyde resin prepolymer of 4:1. The mixture was stirred for 20min to ensure uniform adsorption of the melamine-formaldehyde resin prepolymer. The pH was adjusted to 5.0, and the temperature was raised to 70℃. The reaction was allowed to proceed for 2h. After cooling, filtration, washing, and vacuum drying at 50℃ for 8h, perfluorohexanone bilayer microcapsule flame retardant (e.g., ...) was obtained. Figure 1 (As shown). The average particle size of the perfluorohexanone bilayer microcapsule flame retardant prepared in this embodiment is 25 μm.

[0056] S4. Preparation of compounded dual-microcapsule flame retardant Weigh out 25 parts by weight of the ammonium polyphosphate microcapsule flame retardant prepared in step S2 and 5 parts by weight of the perfluorohexanone bilayer microcapsule flame retardant prepared in step S3 (the mass ratio of MFAPP to perfluorohexanone bilayer microcapsule flame retardant is 5:1) to obtain the compounded bilayer microcapsule flame retardant.

[0057] S5, Formulation of flame-retardant melamine-formaldehyde resin Take 1000g of the melamine-formaldehyde resin prepolymer prepared in step S1 and add 300g of the compounded dual-microcapsule flame retardant prepared in step S4 (the total amount of the compounded dual-microcapsule flame retardant added accounts for 30% of the mass of the melamine-formaldehyde resin prepolymer). Stir at low speed (300rpm) for 15min, strictly controlling the dispersion temperature not to exceed 35℃, to ensure that the two microcapsule flame retardants are uniformly dispersed. Add 2g of ammonium chloride curing agent to obtain flame-retardant melamine-formaldehyde resin.

[0058] Preparation of flame-retardant-free melamine-formaldehyde resin: Take 1000g of the melamine-formaldehyde resin prepolymer prepared in step S1, add 2g of curing agent ammonium chloride to obtain flame-retardant-free melamine-formaldehyde resin.

[0059] S6. Impregnation and Drying A two-stage impregnation process is employed.

[0060] The synthesis process of urea-formaldehyde resin is as follows: 260g of 37% formaldehyde solution is added to a reactor, and stirring is started at 300r / min. The pH is adjusted to 7.5-8.5 with 30% sodium hydroxide solution. 70g of urea is added, and the temperature is raised to 90℃ at 1-2℃ / min. The reaction is maintained at this temperature for 45min to complete hydroxymethylation. Then, the pH is slowly adjusted to 5.0-5.5 with formic acid. The reaction is maintained at this temperature and the viscosity is monitored. When the viscosity of the Forte 4 cup (25℃) reaches 14-18s, sodium hydroxide is immediately used to neutralize to pH 7.0-7.5 to terminate the condensation. The remaining 30g of urea is added, and the reaction is carried out at 75℃ for 30min. Finally, the temperature is lowered to below 40℃, and the solid content is adjusted to 48%-52% and the pH to 7.0-7.5. The material is filtered to obtain urea-formaldehyde resin. Ammonium chloride, a curing agent, is added to the urea-formaldehyde resin. The mass of ammonium chloride accounts for 5‰ of the mass of the urea-formaldehyde resin to obtain urea-formaldehyde resin containing curing agent.

[0061] Quantitative 80g / m 2 The base paper is immersed in urea-formaldehyde resin containing a curing agent, and then dried at 120°C for 3 minutes to obtain the first-impregnated paper. The amount of urea-formaldehyde resin impregnated in the first-impregnated paper is 0.8 times the mass of the base paper (that is, the first-impregnated dried paper is 0.8 times heavier than the base paper). Second impregnation: The surface of the paper after the first impregnation is impregnated with flame-retardant-free melamine-formaldehyde resin, and the back is impregnated with the flame-retardant melamine-formaldehyde resin prepared in step S5. The second impregnation drying temperature is 120℃, and the paper is dried until the volatile content is 8% and the pre-curing degree is 60%, thus obtaining flame-retardant impregnated paper. In the second impregnation process of flame-retardant impregnated paper, the amount of resin impregnated is 1.5 times the weight of the original paper (i.e., the dried paper after the second impregnation is 1.5 times heavier than the original paper).

[0062] This embodiment provides a flame-retardant impregnated paper-faced engineered wood panel. The specific preparation method includes: pressing the impregnated paper onto the engineered wood panel substrate, wherein the back of the impregnated paper is in contact with the engineered wood panel substrate; wherein the pressing operation parameters are: hot pressing unit pressure 2.0 MPa; temperature 200℃; time 30s.

[0063] Example 2 Compared with Example 1, in Example 2, the outer layer of the perfluorohexanone bilayer microcapsule flame retardant was replaced with polyurea instead of melamine-formaldehyde resin, while the remaining components and preparation methods were the same as in Example 1.

[0064] When the outer layer of the perfluorohexanone bilayer microcapsule flame retardant is polyurea, it is prepared by dispersing the primary microcapsules in an oil phase containing polyisocyanate, followed by interfacial polymerization in an aqueous phase containing polyamine for 4 hours. The specific steps are as follows: S3b, Outer Layer Preparation (Polyurea Outer Layer Type): The primary microcapsules were dispersed in 400 mL of deionized water, and 0.5 g of sodium dodecyl sulfate was added as an emulsifier. The mixture was stirred until evenly dispersed. 10 g of toluene diisocyanate (TDI), accounting for 25% of the mass of the primary microcapsules, was dissolved in toluene to form an oil phase, which was then added dropwise to the above aqueous phase. The mixture was sheared and emulsified at 2000 rpm for 15 min to form an O / W emulsion. A mixed solution of ethylenediamine (20 g): deionized water (100 g) = 1:5 (mass ratio) was slowly added dropwise to the emulsion. The mixture was stirred at room temperature for 10 min, then heated to 50 °C and subjected to interfacial polymerization for 4 h. After the reaction was completed, the mixture was cooled, filtered, washed three times with deionized water, and vacuum dried at 50 °C for 8 h to obtain polyurea outer layer perfluorohexanone bilayer microcapsules.

[0065] Example 3 Compared with Example 1, in Example 3, the outer layer of the perfluorohexanone bilayer microcapsule flame retardant was replaced with polyurethane instead of melamine-formaldehyde resin, while the remaining components and preparation methods were the same as in Example 1.

[0066] When the outer layer of the perfluorohexanone bilayer microcapsule flame retardant is polyurethane, it is prepared by dispersing primary microcapsules in an oil phase containing toluene diisocyanate and polyethylene glycol, then emulsifying and dispersing them in an aqueous phase containing an emulsifier, and finally performing interfacial polymerization at 60°C for 3.5 hours. The specific steps are as follows: S3b, Outer Layer Preparation (Polyurethane Outer Layer Type): 40g of primary microcapsules were dispersed in 400mL of deionized water, and 1.0g of Tween-80 was added as an emulsifier. The mixture was stirred until evenly dispersed. 10g of toluene diisocyanate (TDI) (25% by weight of the primary microcapsules) and polyethylene glycol (PEG-400) (5% by weight of the primary microcapsules) were dissolved in toluene to form an oil phase. This oil phase was added dropwise to the aqueous phase, and the mixture was sheared and emulsified at 2000rpm for 20min to form an O / W emulsion. The emulsion was transferred to a three-necked flask, heated to 60℃, and subjected to nitrogen protection for interfacial polymerization for 3.5h. After the reaction, the mixture was cooled, filtered, washed three times with deionized water, and vacuum dried at 50℃ for 8h to obtain polyurethane outer layer perfluorohexanone bilayer microcapsules.

[0067] Example 4 Compared with Example 1, in Example 4, the outer layer of the perfluorohexanone bilayer microcapsule flame retardant was replaced with polymethyl methacrylate (PMMA) instead of melamine-formaldehyde resin, while the remaining components and preparation methods were the same as in Example 1.

[0068] When the outer layer of the perfluorohexanone bilayer microcapsule flame retardant is PMMA, it is prepared by dispersing primary microcapsules in an oil phase containing methyl methacrylate monomer, azobisisobutyronitrile, and divinylbenzene, adding an emulsifier, emulsifying and dispersing in an aqueous phase, heating to 70°C, and polymerizing in situ for 3 hours under nitrogen protection. The specific steps are as follows: S3b, Outer Layer Preparation (PMMA Outer Layer Type): 40g of the primary microcapsules prepared in step S3a were dispersed in 500mL of deionized water, and 1.0g of polyvinyl alcohol (PVA-1788) was added as a stabilizer. The mixture was stirred until homogeneous. 10g of methyl methacrylate (MMA) monomer (25% by weight of the primary microcapsules), 1% of azobisisobutyronitrile (AIBN) and 2% of divinylbenzene (DVB) were mixed to form an oil phase, which was then added dropwise to the aqueous phase. The mixture was sheared and emulsified at 2500rpm for 20min to form a homogeneous emulsion. The emulsion was transferred to a three-necked flask, and nitrogen was introduced to purge oxygen. The temperature was raised to 70℃, and in-situ polymerization was carried out for 3h under nitrogen protection. After the reaction, the mixture was cooled, filtered, washed three times with deionized water, and vacuum dried at 50℃ for 8h to obtain PMMA outer layer perfluorohexanone bilayer microcapsules.

[0069] Comparative Example 1 Compared with Example 1, in Comparative Example 1, the ammonium polyphosphate was not microencapsulated; the unencapsulated ammonium polyphosphate was directly added to the melamine-formaldehyde resin. The specific steps are as follows: Weigh out 25 parts by weight of ammonium polyphosphate and 5 parts by weight of the perfluorohexanone bilayer microcapsule flame retardant prepared in step S3 (the mass ratio of ammonium polyphosphate to perfluorohexanone bilayer microcapsule flame retardant is 5:1) to obtain a compound flame retardant. Replace the compound bilayer microcapsule flame retardant in Example 1 with the compound flame retardant, and the remaining steps are the same as in Example 1.

[0070] Comparative Example 2 Compared with Example 1, Comparative Example 2 only added MFAPP and did not add perfluorohexanone bilayer microcapsules. 1000g of melamine-formaldehyde resin prepolymer prepared in step S1 was taken and MFAPP prepared in step S2 of Example 1 was added. The amount of MFAPP added was the same as the total amount of the compounded bilayer microcapsule flame retardant added in Example 1 (the amount of MFAPP added accounted for 30% of the mass of melamine-formaldehyde resin prepolymer). The other components and preparation methods were the same as in Example 1.

[0071] Comparative Example 3 Compared with Example 1, Comparative Example 3 only added perfluorohexanone bilayer microcapsule flame retardant and did not add MFAPP. 1000g of the melamine-formaldehyde resin prepolymer prepared in step S1 was taken and the perfluorohexanone bilayer microcapsule flame retardant prepared in step S3 of Example 1 was added. The amount of perfluorohexanone bilayer microcapsule flame retardant added was the same as the total amount of compounded bilayer microcapsule flame retardant added in Example 1 (the amount of perfluorohexanone bilayer microcapsule flame retardant added accounted for 30% of the mass of the melamine-formaldehyde resin prepolymer). The remaining components and preparation methods were the same as in Example 1.

[0072] Comparative Example 4 Compared with Example 1, in Comparative Example 4, the perfluorohexanone bilayer microcapsules were replaced with single-layer perfluorohexanone microcapsules (only the calcium alginate / chitosan inner layer, without the melamine-formaldehyde resin outer layer, i.e. the primary microcapsules prepared in step S3a of Example 1), and the remaining components and preparation methods were the same as in Example 1.

[0073] Comparative Example 5 Compared with Example 1, Comparative Example 5 used ordinary impregnated paper (without any flame retardant added), while the remaining components and preparation methods were the same as in Example 1. The specific steps were as follows: Take 1000g of melamine-formaldehyde resin and add 2g of curing agent ammonium chloride to obtain flame-retardant-free melamine-formaldehyde resin.

[0074] First soaking: 80g / m 2 The base paper was immersed in the urea-formaldehyde resin containing curing agent prepared in Example 1, and then dried at 120°C for 3 minutes to obtain the first-impregnated paper. The amount of urea-formaldehyde resin impregnated in the first-impregnated paper was 0.8 times the mass of the base paper. Second impregnation: The surface of the paper after the first impregnation is impregnated with flame-retardant-free melamine-formaldehyde resin, and the back is impregnated with flame-retardant-free melamine-formaldehyde resin. The second impregnation drying temperature is 120℃, and the paper is dried until the volatile content is 8% and the pre-curing degree is 60%, resulting in ordinary impregnated film paper. The amount of melamine-formaldehyde resin impregnated in the ordinary impregnated film paper is 0.7 times the weight of the original paper.

[0075] The curing time, viscosity, oxygen index (GB / T5454) of the flame-retardant melamine-formaldehyde resin prepared in Examples 1-4 and Comparative Examples 1-5, and the flame retardancy rating (GB 8624-2012) of the impregnated paper were tested.

[0076] Table 1. Performance test results of impregnated paper, double-impregnated resin, and impregnated paper-faced engineered wood panels in Examples 1-4 and Comparative Examples 1-5.

[0077] As shown in Table 1, the flame-retardant impregnated paper panels prepared in Examples 1-4 of this invention have significantly better oxygen index and flame-retardant rating than the comparative examples. Among them, Example 1 (MF outer layer) has the highest oxygen index, reaching 38%, which is significantly better than Examples 2-4. At the same time, the impregnated paper panels can achieve a flame-retardant rating of B1 (B), indicating that melamine-formaldehyde resin has advantages as a microcapsule wall material.

[0078] Compared with Example 1, Comparative Example 1 did not microencapsulate ammonium polyphosphate, resulting in a drastic reduction in gelation time to 90s, an increase in resin viscosity to 68s, and a severe deterioration in impregnation process performance, with an oxygen index of only 30%. This demonstrates that microencapsulation of ammonium polyphosphate is crucial for solving compatibility issues.

[0079] Compared with Example 1, Comparative Example 2 only added MFAPP microcapsules, with an oxygen index of 26%. Although the compatibility problem was solved, the flame retardant efficiency was insufficient, indicating that single condensed phase flame retardancy is difficult to achieve high-efficiency flame retardant B1 (B) level and requires the cooperation of active fire extinguishing mechanism.

[0080] Compared with Example 1, Comparative Example 3 only added perfluorohexanone bilayer microcapsules, with an oxygen index of 28%, lacked condensed phase char support, resulting in insufficient flame retardancy.

[0081] Compared with Example 1, Comparative Example 4 used a single-layer perfluorohexanone microcapsule (without outer protection) with an oxygen index of 31%, which accelerated the curing of melamine-formaldehyde resin, demonstrating the key role of the outer wall material in ensuring the mechanical strength of the processing.

[0082] Compared with Example 1, Comparative Example 5 is a common impregnated paper with an oxygen index of only 22%, indicating that Examples 1-4 of the present invention significantly improve the flame retardant performance.

[0083] As can be seen from the above embodiments, the present invention provides an impregnated film paper based on the synergistic combination of active fire extinguishing microcapsules and condensed phase flame retardant microcapsules. This invention addresses the problems of poor compatibility between ammonium polyphosphate and melamine-formaldehyde resin prepolymer, and poor compatibility between perfluorohexanone and water-based resin. The present invention uses melamine-formaldehyde resin as the wall material to in-situ encapsulate ammonium polyphosphate to obtain condensed phase flame retardant microcapsules. A perfluorohexanone double-layer active fire extinguishing microcapsule is prepared by using calcium alginate / chitosan polyelectrolyte composite as the inner layer and melamine-formaldehyde resin / polyurea / polyurethane / polymethyl methacrylate as the outer layer. The two are compounded at a mass ratio of 4:1 to 6:1 and added to a second-impregnated melamine-formaldehyde resin, with the total addition amount accounting for 20% to 40% of the resin (melamine-formaldehyde resin prepolymer) mass. A flame-retardant impregnated film paper is obtained through a two-stage impregnation process. This invention solves the compatibility problem and achieves a relay-style three-dimensional flame retardancy of "first gas phase inhibition, then condensed phase isolation", with an oxygen index of 34%~38%. The decorative artificial board can reach the flame retardancy level of B1 (C) or B1 (B) without affecting the appearance of the surface and the bonding performance.

[0084] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A compound dual-microcapsule flame retardant, characterized in that, The flame retardant comprises ammonium polyphosphate microcapsule flame retardant and perfluorohexanone bilayer microcapsule flame retardant; the ammonium polyphosphate microcapsule flame retardant has a core-shell structure, with ammonium polyphosphate as the core material and melamine-formaldehyde resin as the wall material; the perfluorohexanone bilayer microcapsule flame retardant has a double-shell core-shell structure, with perfluorohexanone as the core material, calcium alginate and chitosan polyelectrolyte composite as the inner wall material, and a polymer as the outer wall material, wherein the polymer includes one or more of melamine-formaldehyde resin, polyurea, polyurethane, and polymethyl methacrylate; the mass ratio of the ammonium polyphosphate microcapsule flame retardant to the perfluorohexanone bilayer microcapsule flame retardant is 4~6:

1.

2. The compounded dual-microencapsulated flame retardant according to claim 1, characterized in that, The preparation method of the ammonium polyphosphate microcapsule flame retardant includes the following steps: Ammonium polyphosphate suspension and melamine-formaldehyde resin prepolymer are mixed and coated to obtain the ammonium polyphosphate microcapsule flame retardant; the ammonium polyphosphate suspension contains ammonium polyphosphate, water and sodium hexametaphosphate; the raw materials for preparing the melamine-formaldehyde resin prepolymer include melamine, formaldehyde solution, water and pH adjuster, and the solid content of the melamine-formaldehyde resin prepolymer is 45-55%; the mass ratio of ammonium polyphosphate to the melamine-formaldehyde resin prepolymer is 2-4:

1.

3. The compounded dual-microencapsulated flame retardant according to claim 2, characterized in that, The preparation method of the melamine-formaldehyde resin prepolymer includes the following steps: mixing melamine, formaldehyde solution, water and pH adjuster to obtain a mixed solution with a pH value of 8.5~9.5; the molar ratio of melamine to formaldehyde in the formaldehyde solution is 1:2.5~1:3.5; heating the mixed solution to carry out a prepolymerization reaction to obtain the melamine-formaldehyde resin prepolymer; the temperature of the prepolymerization reaction is 85~95℃ and the time is 60~120min; The conditions for the coating reaction include: pH value of 4.5~5.5, reaction temperature of 70~80℃, and reaction time of 1.5~3h.

4. The compounded dual-microencapsulated flame retardant according to claim 1, characterized in that, The preparation method of the perfluorohexanone bilayer microcapsule flame retardant includes the following steps: Perfluorohexanone, sodium alginate aqueous solution, and emulsifier are mixed to obtain an emulsion; the emulsion is mixed with calcium chloride aqueous solution to carry out a cross-linking reaction to obtain calcium alginate gel beads; the calcium alginate gel beads are mixed with chitosan solution to form a composite to form the inner layer of calcium alginate and chitosan polyelectrolyte complex, thus obtaining primary microcapsules. The polymer is encapsulated in the primary microcapsules to obtain the perfluorohexanone bilayer microcapsule flame retardant.

5. The compounded dual-microencapsulated flame retardant according to any one of claims 1 to 4, characterized in that, The average particle size of the ammonium polyphosphate microcapsule flame retardant is 5~30μm; the average particle size of the perfluorohexanone bilayer microcapsule flame retardant is 10~50μm.

6. The application of the compounded dual microcapsule flame retardant according to any one of claims 1 to 5 in the preparation of flame-retardant impregnated paper.

7. A method for preparing a flame-retardant impregnated paper, characterized in that, Includes the following steps: The base paper is first impregnated in urea-formaldehyde resin, and then first dried to obtain a first-impregnated paper. The first-impregnated paper is subjected to a second impregnation, which includes impregnating the surface of the first-impregnated paper with flame-retardant-free melamine-formaldehyde resin and the back side with flame-retardant melamine-formaldehyde resin, followed by a second drying to obtain the flame-retardant impregnated film paper; the flame-retardant melamine-formaldehyde resin includes melamine-formaldehyde resin prepolymer and the compounded dual-microcapsule flame retardant as described in any one of claims 1 to 5.

8. The preparation method according to claim 7, characterized in that, The mass percentage of the compounded dual microcapsule flame retardant to the mass of the melamine-formaldehyde resin prepolymer is 20-40%; the flame-retardant melamine-formaldehyde resin has a Forte 4 cup viscosity of 25-40 s at 25°C; the second drying temperature is 100-120°C, and the second drying ends when the volatile content is 4%-8% and the pre-curing degree is 40%-60%.

9. The flame-retardant impregnated paper prepared by the preparation method according to claim 7 or 8.

10. A flame-retardant impregnated paper-faced engineered wood panel, characterized in that, It includes a substrate and a finishing layer disposed on the surface of the substrate, the finishing layer being made of the flame-retardant impregnated paper as described in claim 9, the back side of the flame-retardant impregnated paper being in contact with the substrate.

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