Flame-retardant plywood board and preparation method thereof

Abstract

The invention discloses a flame-retardant plywood board and a preparation method thereof. The flame-retardant plywood board comprises plywood, adhesive layers coated on the two sides of the plywood and technical wood attached to the surfaces of the adhesive layers. The adhesive layer is prepared from the following raw materials in parts by weight: 20-30 parts of urea-formaldehyde resin adhesive and 8-15 parts of flame-retardant powder; the flame-retardant powder comprises a double-ligand metal complex flame retardant and starch in a mass ratio of (7-8): (2-3); the double-ligand metal complexing flame retardant is prepared by complexing an organic phosphoric acid ligand, thiohydracrylic acid and metal salt and then reacting with caustic alkali; the mass ratio of the organic phosphoric acid ligand to the thiohydracrylic acid to the metal salt to the caustic alkali is (15-20): (1-2): 10: (10-12); the metal salt is selected from at least one of aluminum salt, magnesium salt and calcium salt. According to the invention, the problem that the plywood board cannot give consideration to both flame retardance and mechanical property due to poor compatibility of the current complex flame retardant and urea resin and competitive complexation can be solved.

Description

Technical Field

[0001] This application relates to the field of flame-retardant plywood, and in particular to a flame-retardant plywood sheet and its preparation method. Background Technology

[0002] Plywood, as an important engineered wood product in the construction, decoration, and furniture manufacturing industries, is widely used due to its excellent mechanical properties and processability. This type of board is typically made by hot-pressing a wood veneer with a surface decorative layer such as engineered wood using urea-formaldehyde resin adhesive, achieving both structural strength and aesthetic appeal. However, the inherent flammability of wood and organic resins poses significant safety hazards to plywood. To overcome this problem, flame retardants are usually added to the urea-formaldehyde resin to improve the board's flame-retardant properties. Compounds containing phosphorus and nitrogen are widely used due to their synergistic flame-retardant mechanism in both the gas and condensed phases. To further enhance flame-retardant efficiency, existing technologies often combine phosphorus and nitrogen-containing flame retardants (such as phytic acid and ammonium polyphosphate) with metal ions (Mg... 3+ Ca 2+ Al 3+ (etc.) coordinate to form metal-organic complexes, and utilize the catalytic char formation of metal ions to improve the flame retardant effect.

[0003] However, this complex-type flame retardant still has significant drawbacks in practical applications. Specifically, the organometallic complex has low compatibility with urea-formaldehyde resin and poor dispersibility in the resin system, leading to uneven distribution of the flame-retardant components and affecting the stability of the flame-retardant effect. More critically, the high-valence metal ions (such as Al) in the complex-type flame retardant... 3+ Metals can competitively complex with the active functional groups (amino (—NH2), hydroxymethyl (—CH2OH), and imino (—NH—)) on the urea-formaldehyde resin molecular chain. This unintended metal complexation not only interferes with the normal condensation and curing process of urea-formaldehyde resin and destroys the integrity of its three-dimensional cross-linked network structure, but also significantly reduces the chemical bonding ability between the resin and wood. Ultimately, this leads to a significant decrease in the cohesive force of the plywood adhesive layer and the interfacial adhesion strength, resulting in reduced adhesive strength. While meeting flame retardant requirements, the core mechanical properties of the material are sacrificed. Summary of the Invention

[0004] To address the problem that current complexed flame retardants have poor compatibility with urea-formaldehyde resin, resulting in competitive complexation and making it impossible for plywood to simultaneously achieve flame retardant and mechanical properties, this application provides a flame-retardant plywood board and its preparation method.

[0005] In a first aspect, this application provides a flame-retardant plywood board, comprising plywood, an adhesive layer coated on both sides of the plywood, and engineered wood adhered to the surface of the adhesive layer; the adhesive layer comprises 20-30 parts of urea-formaldehyde resin and 8-15 parts of flame-retardant powder; the flame-retardant powder comprises a dual-ligand metal complex flame retardant and starch in a mass ratio of 7-8:2-3; the dual-ligand metal complex flame retardant is prepared by complexing an organophosphate ligand, mercaptopropionic acid, and a metal salt, followed by reaction with a caustic alkali; the mass ratio of the organophosphate ligand, mercaptopropionic acid, metal salt, and caustic alkali is 15-20:1-2:10:10-12; the metal salt is selected from at least one of aluminum salt, magnesium salt, and calcium salt.

[0006] In any of the above technical solutions, the organophosphate ligand is selected from any one or more of aminotrimethylenephosphonic acid, polyaminopolyether methylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, and hydroxyethylidene diphosphonic acid.

[0007] In any of the above technical solutions, the dual-ligand metal complex flame retardant is prepared by the following method: adding an organophosphate complexing agent and mercaptopropionic acid to water and mixing to obtain a dual-ligand solution; mixing the dual-ligand solution with a metal salt solution to carry out a complexing reaction to obtain a complexing solution; then adding a caustic alkali solution to the complexing solution, complexing and precipitating the complex, filtering out the complex, washing and drying to obtain the final product.

[0008] This application employs an organophosphate ligand and mercaptopropionic acid to form a dual-ligand system, which is then complexed with a metal salt and finally treated with a caustic alkali to precipitate a solid flame retardant. This flame retardant has three main advantages: First, it increases the crosslinking density. During hot pressing, the thiol groups of mercaptopropionic acid can nucleophilically substitute with the hydroxymethyl groups of urea-formaldehyde resin, forming stable thioether bonds; its carboxyl groups condense with the amino groups in the resin to form amide bonds. These newly added chemical bonds significantly increase the crosslinking density of the adhesive layer, compensating for the loss of bonding points due to competitive complexation by metal ions, thereby enhancing the cohesive force and interfacial adhesion of the adhesive layer. Second, it improves compatibility. The dual ligands, through the synergistic coordination of phosphate and thiol groups, more firmly coat metal ions, increasing their polarity and improving their affinity with the resin matrix. Third, it enhances water resistance. The high-crosslinking density adhesive layer forms a dense network, hindering water penetration; simultaneously, the hydroxyl groups in starch form hydrogen bonds with the resin, enhancing the adhesive layer's resistance to hydrolysis, allowing the board to maintain excellent bonding strength even in humid environments.

[0009] In addition, the addition of caustic alkali promotes the complete precipitation and stabilization of the complex, preventing the flame retardant components from migrating in the resin or to the outside world, ensuring the longevity of the flame retardant effect, and reducing corrosion of metal components.

[0010] In any of the above technical solutions, the caustic alkali is sodium hydroxide or potassium hydroxide.

[0011] In any of the above technical solutions, the starch is industrial starch with a branched starch content of more than 70%, preferably corn starch, to act as a char-forming agent and to play a certain toughening role in the adhesive layer.

[0012] In any of the above technical solutions, the metal salt is a water-soluble metal salt.

[0013] In any of the above technical solutions, the raw materials of the urea-formaldehyde resin adhesive, by weight, include: 60-100 parts formaldehyde, 95-105 parts urea, 1-3 parts polyvinyl alcohol, and 5-10 parts phosphate-modified amino silicone oil.

[0014] In any of the above technical solutions, the phosphate-modified amino silicone oil is prepared by Schiff base condensation of diethyl (formylmethyl) phosphate and bisamino silicone oil in a molar ratio of 1:1 to 1.05.

[0015] Although dual-ligand flame retardants improve bonding strength, the excessive cross-linking compensation of the rigid urea-formaldehyde resin with mercaptopropionic acid ligands may lead to a rapid increase in the brittleness of the adhesive layer, resulting in a decrease in screw-holding force. This manifests in the performance of the boards as being prone to cracking during drilling. This application introduces phosphate-modified amino silicone oil into the synthesis of urea-formaldehyde resin, achieving a balance between rigidity and flexibility, and synergistic flame retardancy. Firstly, the flexible characteristics of the silicon-oxygen-silicon segments (-Si-O-Si-) can be interwoven into the rigid network of the urea-formaldehyde resin, absorbing stress and inhibiting crack propagation, significantly improving the toughness of the adhesive layer and enhancing crack resistance during drilling (increased screw-holding force).

[0016] Secondly, the introduced diphosphate groups decompose at high temperatures to generate phosphoric acid, which promotes char formation and forms a "phosphorus-silicon-metal" multi-element synergistic flame retardant system with the dual-ligand flame retardant. At the same time, the diphosphate groups can directly coordinate with the metal ions in the flame retardant, reducing their competitive complexation with the active groups of the resin and improving the bonding strength of the adhesive layer.

[0017] It should be noted that the phosphate-modified amino silicone oil should be added after the initial reaction with urea, and condensed with the hydroxymethyl urea formed after the initial addition of urea to avoid silicone oil self-polymerization or insufficient reaction sites.

[0018] In any of the above technical solutions, the viscosity of the bis(amino) silicone oil is 200–3000 mm. 2 / s (25℃).

[0019] In any of the above technical solutions, the bis(3-aminopropyl)-terminated polydimethylsiloxane or aminoethylaminopropyl polydimethylsiloxane is used.

[0020] In any of the above technical solutions, the Schiff base condensation is carried out under the catalysis of p-toluenesulfonic acid, and the reaction temperature is 70-90℃.

[0021] This silicone oil must employ a dual-amino structure, ensuring that one amino group is grafted with a phosphate ester group via Schiff base condensation, while the other amino group condenses with the hydroxymethyl group of the urea-formaldehyde resin, forming a "resin-silicone oil" bridging structure. Single-amino silicone oils can only graft but cannot bridge, resulting in limited toughening effects. Furthermore, its viscosity range should be controlled between 200 and 3000 mm. 2 / s. When the viscosity is too low, the chain segments are too short, resulting in a weak toughening effect; when the viscosity is too high, the solubility in the reaction system is poor, making it difficult to disperse and react evenly in the resin, leading to local agglomeration and failure.

[0022] In any of the above technical solutions, the method for preparing the urea-formaldehyde resin adhesive is as follows: Formaldehyde and polyvinyl alcohol are added to water and mixed to prepare a reaction solution. The temperature is raised to 30-40°C, the pH is adjusted to 8.0-9.0, 60%-70% of the total urea is added, and the mixture is stirred to dissolve. The temperature is then raised to 80-85°C and the reaction is maintained for 30-40 minutes. The pH is adjusted to 3.5-4.5, 20%-30% of the total urea and phosphate-modified amino silicone oil are added, and the reaction is maintained at 80-85°C for 30-60 minutes. The remaining urea is added, the temperature is lowered to below 60°C, and the pH is adjusted to 7.0-8.0. The product is then discharged when the temperature is lowered to below 40°C.

[0023] In any of the above technical solutions, the plywood is obtained by alternatingly stacking veneers and resin layers; the veneers are prepared by being impregnated and dried in sequence with a ligand solution, a metal ion solution and an alkaline solution, wherein the ligand solution contains 45-55 wt% organophosphate ligands and 8-15 wt% mercaptopropionic acid.

[0024] The veneer undergoes a stepwise impregnation process involving ligand molecules and metal ions, enabling the regulation of the complexation morphology of the flame retardant within the pores of the wood material. Through segmented control of hot-pressing temperature and pressure, the chemical bonding reaction between the adhesive and the flame retardant, as well as the esterification reaction between the wood material and the flame retardant, are achieved. This enhances the integration of the wood-flame retardant-adhesive profile, thereby improving the cross-linking reinforcement effect and contributing to increased bonding strength and flame retardant performance.

[0025] In any of the above technical solutions, the metal ion is Mg. 2+ Ca 2+ Al 3+ Any one or more of them.

[0026] In any of the above technical solutions, the mass concentration of the metal ion solution is 15-25 wt%.

[0027] In any of the above technical solutions, the alkaline solution is a sodium hydroxide solution with a mass concentration of 5-15 wt%.

[0028] In any of the above technical solutions, the veneer is eucalyptus veneer.

[0029] In any of the above technical solutions, the raw material of the resin layer is E0 grade urea-formaldehyde resin adhesive.

[0030] Secondly, this application provides a method for preparing flame-retardant plywood, comprising: According to the composition ratio of any of the flame-retardant plywood boards, flame retardant starch is mixed to obtain flame retardant powder, and then the flame retardant powder is mixed with urea-formaldehyde resin glue and stirred until homogeneous to obtain flame retardant adhesive. Flame-retardant adhesive is applied to the surface of the finished plywood, then engineered wood is attached, and the plywood is hot-pressed in a press at a temperature of 115-135℃ and a pressure of 0.6-1MPa for 2-5 minutes to obtain flame-retardant plywood.

[0031] In summary, this application has the following beneficial effects: This application resolves the contradiction between flame retardancy and mechanical properties of plywood through the synergistic effect of a dual-ligand metal complex flame retardant and a phosphate-modified amino silicone oil. The dual-ligand structure improves flame retardancy efficiency while compensating for bonding losses caused by competitive metal ion complexation through crosslinking of thiol / carboxyl groups with the resin, significantly enhancing bond strength and water resistance. The introduction of the phosphate-modified amino silicone oil imparts flexibility to the adhesive layer, offsetting the brittleness caused by excessive crosslinking of the dual-ligands. Furthermore, through the synergistic effect of phosphorus-silicon flame retardant elements and the metal coordination protection mechanism, flame retardancy and structural stability are further optimized, achieving a balanced improvement in both the efficient flame retardancy and mechanical properties of the plywood. Detailed Implementation Preparation Example

[0032] Preparation Example 1-1, a dual-ligand metal complex flame retardant, was prepared according to the following procedure: 180g of polyamino-polyether methylenephosphonic acid and 15g of mercaptopropionic acid were added to 500mL of deionized water and stirred at 40℃ to prepare a dual-ligand solution. Separately, 100g of magnesium chloride was dissolved in 400mL of water to prepare a metal salt solution. Under nitrogen protection, the metal salt solution was added dropwise to the dual-ligand solution at a rate of 2mL / min, and the mixture was stirred at room temperature for 2 hours to complex. Then, 1100g of 10% sodium hydroxide solution was added dropwise to promote complexation and precipitation of a white precipitate. After stirring for another hour, the mixture was filtered. The filter cake was washed three times with deionized water, dried under vacuum at 60℃ for 12 hours, and ground through a 200-mesh sieve to obtain the dual-ligand metal complex flame retardant.

[0033] Preparation Examples 1-2, dual-ligand metal complex flame retardants, were prepared according to the following procedures: 150g of hydroxyethylidene diphosphonic acid and 10g of mercaptopropionic acid were dissolved in 400mL of deionized water and stirred at 35℃. Separately, 100g of aluminum chloride was dissolved in 300mL of water and added dropwise to the ligand solution at a rate of 1.5mL / min. Complexation was carried out at room temperature for 3 hours under nitrogen protection. 1000g of 10% potassium hydroxide solution was slowly added, resulting in a colloidal precipitate. After aging for 1.5 hours, the precipitate was filtered, washed four times with water, dried at 55℃ for 24 hours, and ground through a 200-mesh sieve to obtain the dual-ligand metal complex flame retardant.

[0034] Preparation Examples 1-3, dual-ligand metal complex flame retardants, were prepared according to the following procedures: 200g of ethylenediaminetetramethylenephosphonic acid and 20g of mercaptopropionic acid were added to 600mL of deionized water and dissolved by stirring at 50℃. Separately, 100g of calcium chloride was dissolved in 500mL of water and added dropwise at a rate of 3mL / min, complexing at room temperature for 1 hour under nitrogen protection. Then, 1200g of 10% sodium hydroxide solution was added, resulting in a dense precipitate. Stirring continued for 0.5 hours, and the precipitate was filtered, washed twice with water, dried at 65℃ for 8 hours, and ground through a 200-mesh sieve to obtain the dual-ligand metal complex flame retardant.

[0035] Preparation Examples 1-4, dual-ligand metal complex flame retardants, differ from Preparation Example 1-1 in that an equal amount of ammonium polyphosphate is used to replace mercaptopropionic acid.

[0036] Preparation Examples 1-5, monoligand metal complex flame retardants, differ from Preparation Example 1-1 in that an equal amount of polyaminopolyether methylenephosphonic acid is used instead of mercaptopropionic acid.

[0037] Preparation Examples 1-6, monoligand metal complex flame retardants, differ from Preparation Example 1-1 in that an equal amount of mercaptopropionic acid is used to replace polyaminopolyether methylenephosphonic acid.

[0038] Preparation Example 2-1, urea-formaldehyde resin adhesive, was prepared according to the following method: Step 1: Mix 1 mol of (formylmethyl) phosphate diethyl ester with 1 mol of bis(amino) silicone oil (KF-867S, viscosity 1300 mm). 2 Add 3g of p-toluenesulfonic acid to the reaction vessel, stir and react at 80°C for 4 hours under nitrogen protection to obtain phosphate-modified amino silicone oil.

[0039] Step 2: Add 800g formaldehyde, 20g polyvinyl alcohol (PVA-1788), and 200g water to the reactor and heat to 35℃. Adjust the pH to 8.5 with 10% NaOH solution, add 650g industrial-grade urea (65% of the total urea), heat to 83℃ and maintain the temperature for 35 minutes. Add 70g of the above-mentioned phosphate ester modified amino silicone oil and react at 83℃ for 30 minutes. Adjust the pH to 4.0 with 20% formic acid, add 250g urea (25%), and react at 83℃ for 25 minutes. Add the remaining 100g urea (10%), cool to 55℃, and adjust the pH to 7.5 with NaOH. Cool to 35℃ and discharge to obtain the final product.

[0040] Preparation Example 2-2, urea-formaldehyde resin adhesive, was prepared according to the following method: Step 1: Mix 1 mol of (formylmethyl) phosphate diethyl ester with 1 mol of bis(amino) silicone oil (AFS-81100, viscosity 200 mm). 2 Add 2g of p-toluenesulfonic acid to the reaction vessel, stir and react at 80°C for 3 hours under nitrogen protection to obtain phosphate-modified amino silicone oil.

[0041] Step 2: Add 650g formaldehyde, 10g polyvinyl alcohol (PVA-2088), and 150g water to the reactor and heat to 35℃. Adjust the pH to 8.5 with 10% NaOH solution, add 630g industrial-grade urea (66.3% of the total urea), heat to 80℃ and maintain the temperature for 40 minutes. Add 50g of the above-mentioned phosphate ester modified amino silicone oil and react at 83℃ for 30 minutes. Adjust the pH to 3.8 with 20% formic acid, add 240g urea (25.3%), and react at 75℃ for 60 minutes. Add the remaining 80g urea (8.4%), cool to 55℃, and adjust the pH to 7.0 with NaOH. Cool to 35℃ and discharge to obtain the final product.

[0042] Preparation Example 2-3, urea-formaldehyde resin adhesive, was prepared according to the following method: Step 1: Mix 1 mol of (formylmethyl) phosphate diethyl ester with 1 mol of bis(amino) silicone oil (AFS-81500, viscosity 3000 mm). 2 Add 4g of p-toluenesulfonic acid to the reaction vessel, stir and react at 90°C for 5 hours under nitrogen protection to obtain phosphate-modified amino silicone oil.

[0043] Step 2: Add 1000g formaldehyde, 30g polyvinyl alcohol (PVA-1788), and 300g water to the reactor and heat to 35℃. Adjust the pH to 8.0 with 10% NaOH solution, add 735g industrial-grade urea (70% of the total urea), heat to 85℃ and maintain the temperature for 30 minutes. Add 100g of the above-mentioned phosphate ester modified amino silicone oil and react at 83℃ for 30 minutes. Adjust the pH to 4.1 with 20% formic acid, add 210g urea (20%), and react at 80℃ for 60 minutes. Add the remaining 105g urea (10%), cool to 60℃, and adjust the pH to 7.0 with NaOH. Cool to 35℃ and discharge to obtain the final product.

[0044] Preparation Examples 2-4, urea-formaldehyde resin adhesive, differ from Preparation Example 1-1 in that step 1 is omitted, and step 2 uses an equal amount of bis(amino) silicone oil (KF-867S, viscosity 1300 mm). 2 / s) Replace phosphate-modified amino silicone oil.

[0045] Preparation Examples 2-5, urea-formaldehyde resin adhesive, differ from Preparation Example 1-1 in that step 1 is omitted, and in step 2, an equal amount of melamine is used to replace the phosphate-modified amino silicone oil. Example

[0046] Example 1: A fire-retardant plywood board is prepared according to the following steps: Step 1-1: Place eucalyptus veneer (0.26-0.28 mm thick) in a pressure impregnation tank filled with a polyaminopolyether methylene phosphonic acid solution (50 wt%). Vacuum the tank to -0.09 MPa and maintain this pressure for 0.5 hours. Then increase the pressure to 1.2 MPa and maintain this pressure for 1.5 hours. After impregnation, remove the wood and drain until no water drips.

[0047] Steps 1-2: Immerse the eucalyptus veneer in a mercaptopropionic acid solution (10wt%), pressurize to 1.2MPa, and maintain the pressure for 1.5 hours. Remove the wood and drain it until there is no dripping water.

[0048] Steps 1-3: Then immerse the eucalyptus veneer in a magnesium chloride solution (20wt%), pressurize it to 1.2MPa, and maintain the pressure for 1.5 hours. Remove the wood and drain it until there is no dripping water.

[0049] Steps 1-4: Finally, immerse the eucalyptus veneer in a NaOH solution (10wt%), pressurize it to 1.2MPa, and maintain the pressure for 1.5 hours. Rinse the wood with tap water 3-5 times. Remove the wood, drain it until there is no dripping water, and dry it at 50℃ to obtain flame-retardant modified eucalyptus veneer.

[0050] Steps 1-5: Apply E0 grade urea-formaldehyde resin adhesive evenly to the flame-retardant modified eucalyptus veneer, with an application rate of 220g / m² on both sides. 2After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board. After cold pressing (pressure 0.8MPa, time 90min) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), plywood is obtained.

[0051] Step 2-1: The dual-ligand metal complex flame retardant from Preparation Example 1-1 was uniformly mixed with corn starch in a 7:3 ratio and ball-milled in a planetary ball mill at 1500 r / min for 20 min to obtain flame retardant powder. 120 g of flame retardant powder was mixed with 240 g of urea-formaldehyde resin adhesive obtained from Preparation Example 2-1, and then stirred using a high-speed mixer at 800 r / min for 10 minutes to ensure uniform mixing of the flame retardant powder and urea-formaldehyde adhesive, thus obtaining a flame retardant adhesive.

[0052] Step 2-2: Apply flame retardant adhesive at 200g / m³ 2 The appropriate amount of adhesive is applied to the surface of the finished plywood (products of steps 1-5), and then 0.5mm thick engineered wood (maple) is applied. After that, it is hot-pressed in a press at 125℃ and 0.8MPa for 4 minutes to obtain the flame-retardant plywood target material.

[0053] Example 2: A flame-retardant plywood board is prepared according to the following steps: Step 1-1: Place eucalyptus veneer (0.26-0.28 mm thick) in a pressure impregnation tank filled with hydroxyethylidene diphosphonic acid solution (50 wt%), evacuate to -0.09 MPa and maintain constant pressure for 0.5 h, then increase the pressure to 1.2 MPa and maintain constant pressure for 1.5 h. After impregnation, remove the wood and drain until no water drips.

[0054] Steps 1-2: Immerse the eucalyptus veneer in a mercaptopropionic acid solution (10wt%), pressurize to 1.2MPa, and maintain the pressure for 1.5 hours. Remove the wood and drain it until there is no dripping water.

[0055] Steps 1-3: Then immerse the eucalyptus veneer in an aluminum chloride solution (20wt%), pressurize it to 1.2MPa, and maintain the pressure for 1.5 hours. Remove the wood and drain it until there is no dripping water.

[0056] Steps 1-4: Finally, immerse the eucalyptus veneer in a NaOH solution (10wt%), pressurize it to 1.2MPa, and maintain the pressure for 1.5 hours. Rinse the wood with tap water 3-5 times. Remove the wood, drain it until there is no dripping water, and dry it at 50℃ to obtain flame-retardant modified eucalyptus veneer.

[0057] Steps 1-5: Apply E0 grade urea-formaldehyde resin adhesive evenly to the flame-retardant modified eucalyptus veneer, with an application rate of 220g / m² on both sides. 2After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board. After cold pressing (pressure 0.8MPa, time 90min) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), plywood is obtained.

[0058] Step 2-1: The dual-ligand metal complex flame retardant from Preparation Example 1-2 was uniformly mixed with corn starch at a ratio of 8:2 and ball-milled in a planetary ball mill at 1500 r / min for 20 min to obtain flame retardant powder. 80 g of flame retardant powder was mixed with 200 g of urea-formaldehyde resin adhesive obtained from Preparation Example 2-2, and then stirred using a high-speed mixer at 800 r / min for 10 minutes to ensure uniform mixing of the flame retardant powder and urea-formaldehyde adhesive, thus obtaining a flame retardant adhesive.

[0059] Step 2-2: Apply flame retardant adhesive at 200g / m³ 2 The appropriate amount of adhesive is applied to the surface of the finished plywood (products of steps 1-5), and then 0.5mm thick engineered wood (maple) is applied. After that, it is hot-pressed in a press at 125℃ and 0.8MPa for 4 minutes to obtain the flame-retardant plywood target material.

[0060] Example 3: A fire-retardant plywood board was prepared according to the following steps: Step 1-1: Place eucalyptus veneer (0.26-0.28 mm thick) in a pressure impregnation tank filled with ethylenediaminetetramethylenephosphonic acid solution (50 wt%), evacuate to -0.09 MPa and maintain constant pressure for 0.5 h, then increase the pressure to 1.2 MPa and maintain constant pressure for 1.5 h. After impregnation, remove the wood and drain until no water drips.

[0061] Steps 1-2: Immerse the eucalyptus veneer in a mercaptopropionic acid solution (10wt%), pressurize to 1.2MPa, and maintain the pressure for 1.5 hours. Remove the wood and drain it until there is no dripping water.

[0062] Steps 1-3: Then immerse the eucalyptus veneer in a calcium chloride solution (20wt%), pressurize it to 1.2MPa, and maintain the pressure for 1.5 hours. Remove the wood and drain it until there is no dripping water.

[0063] Steps 1-4: Finally, immerse the eucalyptus veneer in a NaOH solution (10wt%), pressurize it to 1.2MPa, and maintain the pressure for 1.5 hours. Rinse the wood with tap water 3-5 times. Remove the wood, drain it until there is no dripping water, and dry it at 50℃ to obtain flame-retardant modified eucalyptus veneer.

[0064] Steps 1-5: Apply E0 grade urea-formaldehyde resin adhesive evenly to the flame-retardant modified eucalyptus veneer, with an application rate of 220g / m² on both sides. 2After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board. After cold pressing (pressure 0.8MPa, time 90min) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), plywood is obtained.

[0065] Step 2-1: The dual-ligand metal complex flame retardant from Preparation Example 1-3 was uniformly mixed with corn starch in a 7:3 ratio and ball-milled in a planetary ball mill at 1500 r / min for 20 min to obtain flame retardant powder. 150 g of flame retardant powder was mixed with 300 g of urea-formaldehyde resin adhesive obtained from Preparation Example 2-3, and then stirred at 800 r / min for 10 minutes using a high-speed mixer to ensure uniform mixing of the flame retardant powder and urea-formaldehyde adhesive, thus obtaining a flame retardant adhesive.

[0066] Step 2-2: Apply flame retardant adhesive at 200g / m³ 2 The appropriate amount of adhesive is applied to the surface of the finished plywood (products of steps 1-5), and then 0.5mm thick engineered wood (maple) is applied. After that, it is hot-pressed in a press at 125℃ and 0.8MPa for 4 minutes to obtain the flame-retardant plywood target material.

[0067] Example 4, a flame-retardant plywood board, differs from Example 1 in that, in step 2-1, the urea-formaldehyde resin adhesive obtained in Preparation Example 2-4 is replaced with an equal mass of the urea-formaldehyde resin adhesive obtained in Preparation Example 2-1.

[0068] Example 5, a flame-retardant plywood board, differs from Example 1 in that, in step 2-1, the urea-formaldehyde resin adhesive obtained in Preparation Example 2-5 is replaced with an equal mass of the urea-formaldehyde resin adhesive obtained in Preparation Example 2-1.

[0069] Example 6, a flame-retardant plywood board, differs from Example 1 in that, in step 2-1, an equal mass of commercially available E0 grade urea-formaldehyde resin adhesive is used to replace the urea-formaldehyde resin adhesive obtained in Preparation Example 2-1.

[0070] Example 7: A flame-retardant plywood board is prepared according to the following steps: Step 1: Apply E0 grade urea-formaldehyde resin adhesive evenly to the eucalyptus veneer (thickness 0.26-0.28mm), with an application rate of 220g / m² on both sides. 2 After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board. After cold pressing (pressure 0.8MPa, time 90min) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), plywood is obtained.

[0071] Step 2-1: The dual-ligand metal complex flame retardant from Preparation Example 1-1 was uniformly mixed with corn starch in a 7:3 ratio and ball-milled in a planetary ball mill at 1500 r / min for 20 min to obtain flame retardant powder. 120 g of flame retardant powder was mixed with 240 g of urea-formaldehyde resin adhesive obtained from Preparation Example 2-1, and then stirred using a high-speed mixer at 800 r / min for 10 minutes to ensure uniform mixing of the flame retardant powder and urea-formaldehyde adhesive, thus obtaining a flame retardant adhesive.

[0072] Step 2-2: Apply flame-retardant adhesive at a rate of 200 g / m2 to the surface of the finished plywood (product of Step 1-5), then attach 0.5 mm thick engineered wood (maple), and then hot press it in a press at 125°C and 0.8 MPa for 4 minutes to obtain the flame-retardant plywood target material. Comparative Example

[0073] Comparative Example 1, a flame-retardant plywood board, differs from Example 7 in that, in step 2-1, the dual-ligand metal complex flame retardant of Preparation Example 1-1 is replaced by an equal mass of the dual-ligand metal complex flame retardant of Preparation Example 1-4.

[0074] Comparative Example 2, a flame-retardant plywood board, differs from Example 7 in that, in step 2-1, the monoligand metal complex flame retardant of Preparation Example 1-5 is replaced with the diligand metal complex flame retardant of Preparation Example 1-1 by an equal mass of the monoligand metal complex flame retardant of Preparation Example 1-5.

[0075] Comparative Example 3, a flame-retardant plywood board, differs from Example 7 in that, in step 2-1, the monoligand metal complex flame retardant of Preparation Examples 1-6 is replaced with the diligand metal complex flame retardant of Preparation Example 1-1 by means of an equal mass of the monoligand metal complex flame retardant of Preparation Examples 1-6.

[0076] Comparative Example 4, a flame-retardant plywood board, differs from Example 7 in that, in step 2-1, an equal mass of ammonium polyphosphate replaces the dual-ligand metal complex flame retardant of Preparation Example 1-1. Performance testing

[0077] Experiment 1: Limiting Oxygen Index (LOI) Test The test was conducted according to GB / T 2406.2-2009, "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test". Samples measuring 125mm × 13mm × 3mm were cut from the finished sheets of each example and comparative example, with five parallel samples per group. The samples were vertically fixed in the combustion chamber of a JF-3 type oxygen indexer. Starting with an oxygen concentration of 30%, a nitrogen-oxygen mixture (flow rate 10L / min) was introduced, and the top of the sample was ignited. The minimum oxygen concentration required for a combustion length of 50mm was recorded (accurate to 0.1%). The test was repeated until a stable LOI value was obtained, and the average value was taken.

[0078] Experiment 2: Adhesion Strength Test The test shall be conducted in accordance with the provisions of "4.15 Determination of Surface Bonding Strength - Method 2" in GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels".

[0079] Experiment 3: Screw holding force test The test shall be conducted in accordance with the provisions of "4.21 Determination of Screw Holding Force" in GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels".

[0080] Table 1. Performance Test Results

[0081] Analysis of experimental results: Compared to Comparative Examples 1 to 4 and Examples 1 to 3, the LOI (Lack of Integrity) is significantly higher, all exceeding 37%, demonstrating the flame-retardant advantage of the synergistic effect of the dual-ligand flame retardant (phosphorus-nitrogen-metal) and silicone oil phosphorus-silicon compared to single-ligand flame retardants or conventional phosphorus-nitrogen flame retardants. The bond strength is significantly improved in the range of 1.25-1.34 MPa, possibly because the cross-linking of mercaptopropionic acid with the resin via thioether / amide bonds compensates for the loss of resin cross-linking performance caused by metal complexation. The screw-holding force is significantly improved in the range of 890-970 N / mm, possibly because the silicone oil bridging structure formed by the introduction of the flexible silicone oil chain (-Si-O-) effectively enhances the toughness of the adhesive layer and inhibits brittle cracking.

[0082] In Example 4 (using unmodified bisamino silicone oil), the LOI decreased to 35.7%, possibly due to the lack of phosphate ester groups, resulting in the loss of the "phosphorus-silicon synergistic" flame retardant effect. The adhesive strength (1.65 MPa) and screw-holding force (850 N / mm) decreased, possibly because while the unmodified bisamino silicone oil could achieve some toughening for cooking, it could not protect the resin crosslinking groups through the coordination of metal ions with phosphate ester groups. This led to some active groups being competitively complexed by metal ions in the flame retardant, resulting in a decrease in the cohesive strength of the adhesive layer.

[0083] In Example 5 (melamine replacing bis(amino) silicone oil), the screw holding force dropped sharply to 730 N / mm. This may be because melamine increases the crosslinking density but lacks flexible chain segments to absorb stress, leading to increased brittleness of the adhesive layer and subsequent drilling cracking. The LOI decreased to 34.4%, which may be due to the lack of synergistic flame-retardant effect of phosphorus and char-forming enhancement effect of silicon in the resin.

[0084] In Example 7 (no veneer pretreatment group), the LOI decreased to 32.3%, possibly because the flame-retardant barrier of the veneer layer was not formed by the impregnation process, and the flame retardant was relied upon only for the adhesive layer. The bond strength (1.22 MPa) decreased, possibly because the veneer surface lacked mercaptopropionic acid, which weakened the chemical bond between the veneer and the adhesive layer.

[0085] The adhesive strength of Comparative Example 1 (ammonium polyphosphate replacing mercaptopropionic acid) (0.80 MPa) was significantly lower than that of Example 7 (1.22 MPa). This may be because the replacement of mercaptopropionic acid with ammonium polyphosphate resulted in the absence of thioether / amide crosslinking, which could not compensate for the competitive complexation damage to the resin functional groups by metal ions. The screw-holding force decreased slightly, which may be because excessive crosslinking caused brittleness in the adhesive layer, leading to a decrease in screw-holding force. However, excessively low crosslinking density can also cause a decrease in the mechanical strength of the adhesive layer, which is not conducive to improving the adhesive strength.

[0086] The adhesive strength (0.65-0.74 MPa) of Comparative Examples 2-3 (using monoligand flame retardants) was severely degraded. This may be because Comparative Example 2 (using only organophosphoric acid) resulted in a high degree of metal ion exposure, leading to increased complexation with active groups in the resin and a lack of compensation mechanisms. Comparative Example 3 (using only mercaptopropionic acid) exhibited excessive cross-linking with the resin, causing a significant increase in brittleness and resulting in a decrease in adhesive strength and screw-holding force.

[0087] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A flame-retardant plywood board, characterized in that, The product comprises plywood, an adhesive layer coated on both sides of the plywood, and engineered wood adhered to the surface of the adhesive layer; the adhesive layer comprises 20-30 parts of urea-formaldehyde resin and 8-15 parts of flame retardant powder; the flame retardant powder comprises a dual-ligand metal complex flame retardant and starch in a mass ratio of 7-8:2-3; the dual-ligand metal complex flame retardant is prepared by complexing an organophosphate ligand, mercaptopropionic acid, and a metal salt, followed by reaction with a caustic alkali; the mass ratio of the organophosphate ligand, mercaptopropionic acid, metal salt, and caustic alkali is 15-20:1-2:10:10-12; the metal salt is selected from at least one of aluminum salt, magnesium salt, and calcium salt.

2. The flame-retardant plywood board according to claim 1, characterized in that, The organophosphate ligands are selected from any one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, and hydroxyethylidene diphosphonic acid.

3. The flame-retardant plywood board according to claim 1, characterized in that, The dual-ligand metal complex flame retardant is prepared as follows: an organophosphate complexing agent and mercaptopropionic acid are added to water and mixed to obtain a dual-ligand solution; the dual-ligand solution is mixed with a metal salt solution to carry out a complexation reaction to obtain a complex solution; then a caustic alkali solution is added to the complex solution, the complex is complexed and precipitated, the complex is filtered out, washed and dried to obtain the final product.

4. The flame-retardant plywood board according to claim 1, characterized in that, By weight, the raw materials of the urea-formaldehyde resin adhesive include: 60-100 parts formaldehyde, 95-105 parts urea, 1-3 parts polyvinyl alcohol, and 5-10 parts phosphate-modified amino silicone oil.

5. The flame-retardant plywood board according to claim 4, characterized in that, The phosphate-modified amino silicone oil is prepared by Schiff base condensation of diethyl (formylmethyl) phosphate and bis(amino) silicone oil in a molar ratio of 1:1 to 1.

05.

6. The flame-retardant plywood board according to claim 5, characterized in that, The viscosity of the diamino silicone oil is 200–3000 mm. 2 / s.

7. The flame-retardant plywood board according to claim 5, characterized in that, The Schiff base condensation was carried out under the catalysis of p-toluenesulfonic acid at a reaction temperature of 70–90 °C.

8. The flame-retardant plywood board according to claim 4, characterized in that, The method for preparing the urea-formaldehyde resin adhesive is as follows: Formaldehyde and polyvinyl alcohol are added to water and mixed to prepare a reaction solution. The temperature is raised to 30-40°C, the pH is adjusted to 8.0-9.0, 60%-70% of the total urea is added, and the mixture is stirred to dissolve. The temperature is then raised to 80-85°C and the reaction is maintained for 30-40 minutes. The pH is adjusted to 3.5-4.5, 20%-30% of the total urea and phosphate-modified amino silicone oil are added, and the reaction is maintained at 80-85°C for 30-60 minutes. The remaining urea is added, the temperature is lowered to below 60°C, and the pH is adjusted to 7.0-8.

0. The product is then discharged when the temperature is lowered to below 40°C.

9. The flame-retardant plywood board according to claim 1, characterized in that, The plywood is obtained by alternating layers of veneer and resin; the veneer is prepared by being impregnated and dried in sequence with a ligand solution, a metal ion solution and an alkaline solution, wherein the ligand solution contains 45-55 wt% organophosphate ligands and 8-15 wt% mercaptopropionic acid.

10. A method for preparing a flame-retardant plywood board, characterized in that, include: According to the composition ratio of the flame-retardant plywood board according to any one of claims 1 to 9, flame retardant starch is mixed to obtain flame retardant powder, and then the flame retardant powder is mixed with urea-formaldehyde resin glue and stirred until homogeneous to obtain flame retardant adhesive. Flame-retardant adhesive is applied to the surface of the finished plywood, then engineered wood is attached, and the plywood is hot-pressed in a press at a temperature of 115-135℃ and a pressure of 0.6-1MPa for 2-5 minutes to obtain flame-retardant plywood.

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