Preparation method and application of melamine cyanurate coated phosphorus-based flame retardant

Abstract

The application provides a preparation method of melamine cyanurate coated phosphorus flame retardant and application of the flame retardant in flame-retardant water-based polyurethane artificial leather. In the preparation method, melamine cyanurate is coated on the surface of phosphorus flame retardant powder in an in-situ polymerization manner, and a solvent containing no ethanol is used as a reaction medium in the reaction process, so that the advantages of environmental protection, safety, high yield and high conversion rate are achieved, and the melamine cyanurate coated phosphorus flame retardant has a synergistic effect on the flame-retardant performance.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials, specifically relating to a method for preparing a melamine cyanuric acid-coated phosphorus-based flame retardant and the application of the melamine cyanuric acid-coated phosphorus-based flame retardant in flame-retardant waterborne polyurethane artificial leather. Background Technology

[0002] Polyurethane (PU), short for polyurethane, is a high-molecular polymer obtained by the condensation polymerization of polyisocyanates and polyols. Its main chain contains multiple urethane groups (-NHCOO-). Waterborne polyurethane (WPU) is a liquid polyurethane material prepared by dissolving or dispersing polyurethane in water. It is widely used in clothing fabrics, home decoration fabrics, and automotive interiors. Waterborne polyurethane is relatively stable, does not easily volatilize, and is easy to clean after use. Compared with other solvent-based polyurethanes, it has advantages such as environmental friendliness and low cost. Based on the types of hydrophilic groups on the main chain and branches of waterborne polyurethane, it can be divided into: nonionic waterborne polyurethane, cationic waterborne polyurethane, and anionic waterborne polyurethane. Nonionic waterborne polyurethane contains hydrophilic groups such as hydrophilic hydroxymethyl or hydroxyethyl groups in its structure. Cationic waterborne polyurethane usually contains cationic hydrophilic groups such as ammonium ions in its structure. Anionic waterborne polyurethane usually contains anionic hydrophilic groups such as carboxylic acids and sulfonic acids. Among them, anionic waterborne polyurethane has significant advantages over other types of waterborne resins in terms of overall performance and technological maturity. In particular, it can replace oil-based polyurethane in leather processing, reducing pollution and toxicity.

[0003] Artificial leather is made by foaming or coating various formulations of PVC or PU onto a woven or non-woven fabric base. It can be processed into different colors, glosses, strengths, and patterns to suit different applications, offering advantages such as a wide variety of colors and patterns, good water resistance, neat edges, high utilization rate, and a relatively lower price compared to genuine leather. While conventional water-based polyurethane and its substrates are flammable materials (LOI < 22%), with increasingly stringent fire safety standards in automotive interiors and apparel fabrics, flame-retardant treatment of artificial leather has become a rigid requirement.

[0004] Flame retardants can be classified into halogen-based, nitrogen-based, silicon-based, and phosphorus-based types based on their flame-retardant elements. Compared to other types of flame retardants, phosphorus-based flame retardants offer superior environmental friendliness and higher flame-retardant efficiency. Aluminum diethylphosphinate (ADP), a member of the phosphorus-based flame retardant family, not only exhibits flame-retardant properties in the gas phase but also in the solid phase. When thermally decomposed, it produces free radical quenchers such as PO•, which can capture flammable free radicals (HO•, H•, etc.) generated during combustion, terminating their further reaction with oxygen and thus blocking the combustion reaction. Furthermore, the phosphoric acid substances formed during its decomposition can promote the dehydration and char formation of materials, effectively isolating oxygen and heat. However, due to the strong acidity of aluminum diethylphosphinate (pH≈4.2), the acidity on its surface can cause the originally stable carboxylates (such as -COO-) in anionic waterborne polyurethane to transform into water-insoluble carboxylic acids (-COOH), leading to the destruction of emulsion stability and demulsification.

[0005] While existing technologies, such as patent CN116162343A, disclose a method for preparing melamine cyanurate (MCA)-coated diethylphosphinate aluminum intumescent flame-retardant thermoplastic polyurethane, the use of ethanol as the reaction medium in the reaction system has certain limitations. Ethanol has a boiling point of 78°C and a flash point of 13°C at normal pressure, making it unsuitable for high-temperature salt formation reactions at normal pressure. Furthermore, ethanol is typically several times more expensive than deionized water, resulting in higher costs. The amount of melamine cyanurate used in the aforementioned patent is relatively low, and it requires the formulation of pentaerythritol to form an intumescent flame retardant, leading to low environmental friendliness. In addition, this patent uses melamine cyanurate to coat diethylphosphinate aluminum to reduce its agglomeration, and it is intended for use as an intumescent flame retardant in thermoplastic polyurethanes, without mentioning the potential demulsification that may occur when phosphorus-based flame retardants are used in water-based polyurethanes. Therefore, it is impossible to predict whether the melamine cyanurate-coated aluminum diethylphosphinate prepared by the above patent can be used in anionic waterborne polyurethane artificial leather.

[0006] In fact, ethanol has a certain demulsifying effect on polyurethane emulsions, and trace amounts of residual ethanol in the melamine cyanurate-coated aluminum diethylphosphinate can degrade the stability of anionic waterborne polyurethane resins. The inventors discovered that using an ethanol-free solvent, preferably deionized water, can effectively reduce costs and improve emulsion stability. Furthermore, melamine and cyanuric acid have very low solubility in ethanol, but their solubility increases in hot water. Since water has a boiling point approximately 20°C higher than ethanol, using water as the reaction medium allows for reactions at higher temperatures, which in turn increases the solubility of melamine and cyanuric acid. Therefore, compared to ethanol, the same amount of water as the reaction medium yields a higher yield and purity of melamine cyanuric acid product. Conversely, if ethanol is used as the reaction medium, due to the low reaction temperature and low raw material solubility, the amount of melamine cyanuric acid product obtained is small, and its coating effect as a shell cannot meet expectations, leading to easier demulsification.

[0007] Therefore, the present invention provides a low-cost, safe, environmentally friendly, and efficient method that improves the compatibility of phosphorus-based flame retardant powder in anionic waterborne polyurethane flame retardant coating systems for polyester fabrics, prevents demulsification, and increases the reaction yield and conversion rate, while simultaneously improving the flame retardancy of anionic waterborne polyurethane artificial leather. Summary of the Invention

[0008] Based on the problems mentioned in the background art, the present invention uses melamine cyanuric acid to coat phosphorus-based flame retardant powder, which not only avoids the demulsification of anionic waterborne polyurethane caused by excessive acidity on the surface of phosphorus-based flame retardant powder, but also the inert gases such as NH3 generated during the decomposition of melamine cyanuric acid can effectively enhance the flame retardancy of phosphorus-based flame retardants in the gas phase, thereby achieving a synergistic flame retardant effect.

[0009] In addition, the present invention uses an ethanol-free solvent to prepare melamine cyanuric acid-coated phosphorus flame retardants. Compared with the prior art which uses ethanol as the reaction medium, the reaction yield and conversion rate are higher, the product purity is also higher, and ethanol avoids demulsification of the polyurethane solution.

[0010] The first aspect of this invention provides a method for preparing a melamine cyanuric acid-coated phosphorus-based flame retardant. This method uses phosphorus-based flame retardant powder as the core material and melamine cyanuric acid as the shell material, preparing core-shell structured flame retardant microcapsules through in-situ polymerization. This system uses an ethanol-free solvent as the reaction medium and melamine (MEL) and cyanuric acid (CA) as reactants, offering advantages such as high yield and good stability. During the preparation process, cyanuric acid is adsorbed onto the surface of the phosphorus-based flame retardant powder via electrostatic interaction, then reacts with melamine, finally synthesizing melamine cyanuric acid on the surface of the phosphorus-based flame retardant powder, thereby obtaining the flame retardant microcapsules.

[0011] The preparation method according to the first aspect of the present invention specifically includes the following steps:

[0012] (1) After the ethanol-free solvent, emulsifier, cyanuric acid and phosphorus flame retardant powder are evenly dispersed under the action of a dispersing shear machine, they are added to a reaction vessel equipped with a condenser. Then the reaction system is heated to the reaction temperature and thoroughly stirred and mixed under mechanical stirring to obtain a suspension.

[0013] (2) Disperse melamine in a solvent that does not contain ethanol, and then slowly and evenly add it to the suspension obtained in (1) above within 30 min. Keep the reaction temperature and continue stirring and reacting to obtain a suspension of melamine cyanuric acid coated flame retardant.

[0014] (3) After the reaction is complete, the product is filtered, washed, dried and ground to obtain a white powder of melamine cyanuric acid-coated phosphorus flame retardant.

[0015] Furthermore, the ethanol-free solvent in steps (1) and (2) is preferably an ethanol-free aqueous solvent, more preferably deionized water.

[0016] Furthermore, the phosphorus-based flame retardant powder in step (1) may include aluminum diethylphosphinate. In this case, the melamine cyanuric acid-coated phosphorus-based flame retardant is specifically melamine cyanuric acid-coated aluminum diethylphosphinate (ADP@MCA).

[0017] Furthermore, there are no particular restrictions on the emulsifier used in step (1), which can be any emulsifier commonly used in the art that does not participate in the reaction.

[0018] Furthermore, in step (1), the ratio of the mass of the solvent without ethanol to the sum of the masses of cyanuric acid and melamine can be 10~20:1.

[0019] Furthermore, the reaction temperature in step (1) can be 95~100℃, the stirring speed can be 400~450rpm, and the stirring time can be 2~3h.

[0020] Furthermore, the reaction temperature in step (2) can be 95~100℃, the stirring speed can be 500~600rpm, and the stirring time can be 4~5h.

[0021] Furthermore, the mass ratio of cyanuric acid to melamine can be 1 to 1.05:1, preferably 1:1. In addition, the mass ratio of the sum of the masses of cyanuric acid and melamine to the mass of the phosphorus-based flame retardant powder can be 0.33 to 3:1, preferably 0.33 to 1:1.

[0022] A second aspect of the present invention provides a method for manufacturing flame-retardant waterborne polyurethane artificial leather. This method uses the aforementioned melamine cyanuric acid-coated phosphorus-based flame retardant as the flame retardant, employs polyester fabric as the substrate, and manufactures the artificial leather through a lamination process. The specific preparation process is as follows:

[0023] (1) Three waterborne polyurethane resin formulations, namely top layer resin, middle layer resin and bottom layer resin, were prepared separately and dispersed by high-speed shear to obtain a mixture. The middle layer resin and the bottom layer resin each contained 20-25 parts by weight of the melamine cyanuric acid-coated phosphorus-based flame retardant.

[0024] (2) Coat the surface of the release paper with 15 strips of surface resin, and then put the release paper into an oven to dry the surface resin;

[0025] (3) Coat the surface of the top layer resin with 20 strips of middle layer resin, and then put the release paper into the oven to dry the middle layer resin;

[0026] (4) Coat the surface of the intermediate resin with 30 strips of bottom resin, then attach polyester fabric to the wet bottom resin, and then put the release paper into the oven to dry.

[0027] (5) After the resin is completely dried, remove the fabric to obtain flame-retardant waterborne polyurethane artificial leather with a melamine cyanuric acid-coated phosphorus flame retardant coating.

[0028] Further, in step (1), the formulation of the top layer resin is waterborne polyurethane resin with added color powder, and the viscosity is adjusted to 3000~4000 mPa·s using a thickener. The formulation of the middle layer resin is waterborne polyurethane resin with added 20~25 parts by weight of melamine cyanuric acid-coated phosphorus flame retardant, and the viscosity is adjusted to 5000~7000 mPa·s using a thickener. The formulation of the bottom layer resin is waterborne polyurethane resin with added 20~25 parts by weight of melamine cyanuric acid-coated phosphorus flame retardant, and the viscosity is adjusted to 8000~10000 mPa·s using a thickener.

[0029] Furthermore, since the flame retardant of the present invention exists in the middle layer resin and the bottom layer resin, and the coating thickness of the bottom layer resin is greater than that of the middle layer resin, the content of the flame retardant in the bottom layer resin should be greater than or equal to the content of the flame retardant in the middle layer resin.

[0030] There are no particular limitations on the thickener; it can be any thickener commonly used in the art.

[0031] Generally, the greater the number of coating layers, i.e., the greater the thickness, the higher the required viscosity. This ensures that the flame retardant is applied evenly, as dilute solutions are difficult to use for coatings with a high number of layers. Therefore, by controlling the viscosities of the topcoat resin, middlecoat resin, and bottomcoat resin of this invention within the aforementioned ranges, uniform coating can be achieved.

[0032] Furthermore, there are no specific restrictions on the water-based resins used in the top, middle, and bottom layers in step (1). They can be polyether-type water-based resins, polyester-type water-based resins, or a mixture of polyether and polyester water-based resins. Specifically, the water-based resins used in the top and middle layers in step (1) can be the applicant's self-produced yellowing-resistant polyether-type anionic water-based resin M-26, and the water-based resins used in the bottom layer can be the applicant's self-produced high-solids-content polyether-type anionic water-based resin XB-41.

[0033] Furthermore, in steps (2) and (3), the drying temperature of the surface resin and the intermediate resin is 90~100℃, and the drying time is 15~20min.

[0034] Furthermore, in step (4), the drying temperature of the bottom resin is 130~135℃ and the drying time is 15~20min.

[0035] The advantages of this invention are:

[0036] (1) This invention employs a one-bath method to coat the surface of melamine cyanuric acid onto the surface of phosphorus-based flame retardant powder via in-situ polymerization. During the reaction, an ethanol-free solvent is used as the reaction medium, avoiding the demulsification caused by ethanol-based reaction media in existing technologies and improving emulsion stability. Compared to uncoated aluminum diethylphosphonate and coated phosphorus-based flame retardants prepared using an ethanol system, the melamine cyanuric acid-coated phosphorus-based flame retardant prepared using an ethanol-free solvent exhibits superior stability in anionic waterborne polyurethane. Specifically, as demonstrated in the embodiments of this invention, uncoated aluminum diethylphosphonate and coated phosphorus-based flame retardants prepared using an ethanol system rapidly demulsify after complete dispersion in anionic waterborne polyurethane, while the coated phosphorus-based flame retardant prepared using an aqueous system remains stable in the resin for over a week without sedimentation, meeting the requirements for continuous production, batching, storage, and use.

[0037] (2) In the preparation method of the melamine cyanuric acid-coated phosphorus-based flame retardant of the present invention, an ethanol-free solvent is used in the reaction process. Preferably, deionized water is used as the reaction medium. Compared with ethanol, the reaction can be carried out under high temperature and high pressure, the solubility of the reactants is improved, and higher yield and conversion rate can be achieved. In addition, in the preparation method of the melamine cyanuric acid-coated phosphorus-based flame retardant of the present invention, cyanuric acid does not need to be completely dissolved before use, reducing the consumption of raw materials.

[0038] (3) Melamine cyanuric acid and phosphorus-based flame retardants have a synergistic flame-retardant effect when used in combination. The phosphorus-based flame retardant coated with melamine cyanuric acid also has a synergistic flame-retardant effect. In the gas phase, melamine cyanuric acid releases inert gases such as NH3 during pyrolysis, while the phosphorus-based flame retardant generates free radicals such as PO• during pyrolysis; the two have a complementary effect. The melamine cyanuric acid-coated phosphorus-based flame retardant of this invention is suitable for gas-phase flame retardancy and also has a certain flame-retardant effect in the solid phase. Attached Figure Description

[0039] Figure 1 Infrared spectra of aluminum diethylphosphonate (ADP) and aluminum diethylphosphonate (ADP@MCA) coated with melamine cyanuric acid as described in Example 3.

[0040] Figure 2 The images show the microstructures of aluminum diethylphosphonate and aluminum diethylphosphonate coated with melamine cyanuric acid as described in Example 3. In Example 3, (a) shows aluminum diethylphosphonate and (b) shows aluminum diethylphosphonate coated with melamine cyanuric acid as described in Example 3.

[0041] Figure 3 Thermogravimetric (TGA) curves and differential TGA curves are shown for aluminum diethylphosphonate (ADP), aluminum diethylphosphonate coated with melamine cyanuric acid (water system, ethanol system) under different reaction media, cyanuric acid (CA) and melamine (MEL), where (a) is the TGA curve and (b) is the differential TGA curve. Detailed Implementation

[0042] The present invention can be implemented through the following embodiments. The materials used in the embodiments and comparative examples of the present invention are all commercially available.

[0043] Example 1

[0044] (1) Add 1L of deionized water, 3g of emulsifier, 50g of cyanuric acid and 300g of aluminum diethylphosphonate to a 3L beaker, and mix them evenly at a speed of 1000rpm using a dispersing shear machine to obtain a suspension.

[0045] (2) Pour the above suspension into a 3L flask and place it in an oil bath at 95°C. At the same time, reflux condenser is set up and the stirring speed is kept at 400 rpm. Stir, disperse and dissolve for 3 hours.

[0046] (3) Disperse 50g of melamine into 100g of deionized water, and slowly drop it into the flask from step (2) over 30 minutes. Continue the reaction at 95°C for 5 hours with a stirring speed of 550 rpm, so that melamine cyanuric acid can be uniformly coated on the surface of aluminum diethylphosphinate.

[0047] (4) After the reaction was completed, the system was cooled to room temperature, and the product was filtered, washed, dried and gently ground to obtain melamine cyanuric acid coated aluminum diethylphosphinate with a yield of 93%.

[0048] (5) Prepare top, middle, and bottom layer waterborne polyurethane resins separately. The top layer resin consists of 100g of waterborne polyurethane with 5g of color powder and 0.5g of silicone wear-resistant additive. The middle and bottom layer resins consist of 100g of waterborne polyurethane resin with 20g of melamine cyanuric acid-coated aluminum diethylphosphinate. After obtaining the mixture through high-speed shear dispersion, adjust the viscosity of the top, middle, and bottom layer waterborne polyurethane resins to 3000mPa·s, 6000mPa·s, and 8000mPa·s, respectively. The waterborne polyurethane used in the top and middle layer resins is the applicant's self-produced yellowing-resistant polyether anionic waterborne resin M-26, and the waterborne polyurethane used in the bottom layer is the applicant's self-produced high-solids-content polyether anionic waterborne resin XB-41.

[0049] (6) Coat the surface of the release paper with 15 strips of topcoat resin, and then bake at 95°C for 15 min. Coat the dried topcoat resin with 20 strips of middlecoat resin, and then bake at 95°C for 15 min. Coat the dried middlecoat resin with 30 strips of bottomcoat resin, then laminate polyester fabric onto the undried resin and bake at 130°C for 20 min. Finally, remove the coated fabric to obtain flame-retardant anionic waterborne polyurethane artificial leather.

[0050] Example 2

[0051] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as in Example 1, except that the amount of aluminum diethylphosphonate in step (1) was 200g and the yield of aluminum diethylphosphonate coated with melamine cyanuric acid was 91%.

[0052] Example 3

[0053] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as in Example 1, except that the amount of aluminum diethylphosphonate in step (1) was 100g and the yield of aluminum diethylphosphonate coated with melamine cyanuric acid was 89%.

[0054] Example 4

[0055] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as in Example 1, except that the amount of aluminum diethylphosphonate in step (1) was 50 g, and the yield of aluminum diethylphosphonate coated with melamine cyanuric acid was 88%.

[0056] Example 5

[0057] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as in Example 1, except that the amount of aluminum diethylphosphonate in step (1) was 33.3 g, and the yield of aluminum diethylphosphonate coated with melamine cyanuric acid was 89%.

[0058] Example 6

[0059] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as in Example 1, except that the amount of aluminum diethylphosphinate in step (1) was 200g, the volume of deionized water in step (1) was 2L, and the yield of melamine cyanuric acid coated aluminum diethylphosphinate was 89%.

[0060] Example 7

[0061] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as in Example 1, except that the amount of aluminum diethylphosphinate in step (1) was 100g, the oil bath temperature in step (2) was 100°C, the stirring and dissolution time was 2h, and the reaction time in step (3) was 4h. The yield of aluminum diethylphosphinate coated with melamine cyanuric acid was 88%.

[0062] Comparative Example 1

[0063] (1) Prepare top, middle, and bottom layers of waterborne polyurethane resin separately. The top layer resin consists of 100g of waterborne polyurethane with 5g of color powder and 0.5g of silicone wear-resistant additive. The middle and bottom layers each consist of 100g of waterborne polyurethane resin. After obtaining the mixture through high-speed shear dispersion, adjust the viscosity of the top, middle, and bottom layers to 3000mPa·s, 6000mPa·s, and 8000mPa·s, respectively. The waterborne polyurethane used in the top, middle, and bottom layers is the same as in Example 1.

[0064] (2) Apply 15 strips of topcoat resin to the surface of the release paper, and then bake at 95°C for 15 min. Apply 20 strips of middlecoat resin to the dried topcoat resin, and then bake at 95°C for 15 min. Apply 30 strips of bottomcoat resin to the dried middlecoat resin, then laminate polyester fabric onto the undried resin and bake at 130°C for 20 min. Finally, remove the coated fabric to obtain anionic waterborne polyurethane artificial leather.

[0065] Comparative Example 2

[0066] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as Comparative Example 1, except that 20g of aluminum diethylphosphonate was added to 100g of waterborne polyurethane resin for both the middle and bottom layers.

[0067] Comparative Example 3

[0068] Flame-retardant anionic waterborne polyurethane artificial leather was prepared using the same process as in Example 3, except that anhydrous ethanol was used instead of deionized water as the reaction medium, the oil bath temperature in step (2) and the reaction temperature in step (3) were 85°C, and the yield of melamine cyanuric acid coated aluminum diethylphosphinate was 78%.

[0069] Test case

[0070] 1. Infrared spectral analysis of aluminum diethylphosphinate and melamine cyanuric acid-coated aluminum diethylphosphinate

[0071] The functional groups of aluminum diethylphosphinate and the melamine cyanuric acid-coated aluminum diethylphosphinate of Example 3 of this invention were characterized using a NICOLET 5700 Fourier transform infrared spectrometer. Figure 1 As shown, in the infrared spectrum of aluminum diethylphosphinate, 1403 cm⁻¹ -1 The corresponding absorption peak for CH is at 1152 cm⁻¹. -1 and 1069cm -1 The absorption peaks at these locations correspond to P=O and PO groups, respectively. In the infrared spectrum of melamine cyanuric acid-coated aluminum diethylphosphinic acid, not only are the aforementioned absorption peaks of aluminum diethylphosphinic acid observed, but some new absorption peaks also appear. (3232 cm⁻¹) -1 The absorption peak at 1780 cm⁻¹ corresponds to the hydrogen bond formed by the combination of melamine and cyanuric acid. -1 The absorption peak at 1662 cm⁻¹ corresponds to the C=O group of cyanuric acid. -1 The absorption peak corresponds to the NH2 group of melamine; 1533 cm⁻¹ -1 The absorption peak at that location corresponds to the C=N group of the triazine ring. These results confirm the presence of aluminum diethylphosphonate and melamine cyanuric acid.

[0072] 2. Microscopic surface morphology of aluminum diethylphosphinic acid and melamine cyanuric acid coated aluminum diethylphosphinic acid

[0073] The microstructure of aluminum diethylphosphonate and the melamine cyanuric acid-coated aluminum diethylphosphonate of Example 3 of this invention were characterized using a Regulus 8230 high-resolution cold field emission scanning electron microscope. Figure 2 As shown in (a), the surface of the uncoated aluminum diethylphosphonate is smoother. Figure 2 As shown in (b), numerous rod-shaped melamine cyanuric acid molecules appeared on the surface of aluminum diethylphosphinic acid after coating with melamine cyanuric acid, exhibiting an irregular overall shape. These results demonstrate that melamine cyanuric acid was successfully coated onto the surface of aluminum diethylphosphinic acid.

[0074] 3. Thermogravimetric analysis

[0075] The thermal stability of aluminum diethylphosphonate, melamine-cyanuric acid-coated aluminum diethylphosphonate (water system) from Example 3, melamine-cyanuric acid-coated aluminum diethylphosphonate (ethanol system) from Comparative Example 3, cyanuric acid, and melamine under nitrogen atmosphere was characterized using a TG 209F3 thermogravimetric analyzer. Figure 3 It can be seen that the thermal decomposition of aluminum diethylphosphonate, cyanuric acid, and melamine all occur in only one stage, and the thermal decomposition temperatures of melamine and cyanuric acid are significantly lower than those of aluminum diethylphosphonate and melamine-cyanuric acid-coated aluminum diethylphosphonate. The decomposition temperature of melamine is in the range of 235–350℃, that of cyanuric acid is in the range of 265–400℃, and that of aluminum diethylphosphonate is in the range of 370–490℃. In contrast, the thermal decomposition of melamine-cyanuric acid-coated aluminum diethylphosphonate occurs in two stages. The first stage occurs in the temperature range of 300–385℃, mainly involving the thermal decomposition of the shell material, melamine-cyanuric acid. The second stage occurs in the temperature range of 385–475℃, mainly involving the thermal decomposition of the core material, aluminum diethylphosphonate.

[0076] from Figure 3 It can also be confirmed that the amount of melamine cyanuric acid used as a shell material in the ethanol system is less than that in the water system. Therefore, it can be confirmed that, with the same amount of reaction medium, using water as the reaction medium yields more melamine cyanuric acid product compared to ethanol, thus improving reaction efficiency, conversion rate, and yield.

[0077] Some thermogravimetric data are listed in Table 1 below.

[0078] [Table 1]

[0079]

[0080] Table 1 shows that the T values ​​of melamine and cyanuric acid are... 1% The temperatures at which 1% weight loss occurs are 247°C and 273°C, respectively, lower than the 404°C of aluminum diethylphosphonate and the 314°C and 308°C of melamine cyanuric acid-coated aluminum diethylphosphonate. Similarly, T 5% and T 50% The same pattern was observed. This result indicates that melamine cyanuric acid was successfully synthesized in the system. The char residue rates of melamine and cyanuric acid were only 0.1% and 0.7%, respectively, while the char residue rate of aluminum diethylphosphinate was 9.6%. Since melamine cyanuric acid primarily exerts its flame-retardant effect in the gas phase, its flame-retardant effect in the solid phase is weaker than that of aluminum diethylphosphinate. Therefore, the char residue rate of aluminum diethylphosphinate coated with melamine cyanuric acid is lower than that of aluminum diethylphosphinate alone, at 4.7% and 7.8%, respectively. This result also indicates that aluminum diethylphosphinate coated with melamine cyanuric acid also has a certain flame-retardant effect in the solid phase.

[0081] 4. Performance Measurement of Artificial Leather in Comparative and Example Cases

[0082] The emulsion stability, flammability, limiting oxygen index, abrasion resistance, and folding resistance of the various anionic waterborne polyurethane artificial leathers prepared in the Examples and Comparative Examples were measured. The results are shown in Table 2 below.

[0083] [Table 2]

[0084]

[0085] As shown in Table 2 above, uncoated aluminum diethylphosphonate (Comparative Example 2) and aluminum diethylphosphonate coated with melamine cyanuric acid using ethanol as the reaction medium (Comparative Example 3) rapidly demulsified after high-speed shear dispersion in anionic aqueous polyurethane, resulting in unstable emulsions that could not be used to prepare artificial leather through coating. In contrast, the stability of aluminum diethylphosphonate coated with melamine cyanuric acid in an aqueous system was significantly improved in the emulsion. Furthermore, the emulsion stabilization time varied with the increase in the coating ratio of melamine cyanuric acid to aluminum diethylphosphonate, reaching a maximum of one week or more.

[0086] The horizontal flammability of the samples was characterized using a TTech-GB8410-2 automotive interior materials flammability tester, according to GB 8410-2006 "Flammability Characteristics of Automotive Interior Materials". The samples were horizontally clamped on a U-shaped support, and one end was ignited with a flame in a combustion chamber for 15 seconds. The flame retardancy rating was determined based on whether the flame extinguished, when it extinguished, and the burning rate. The results showed that the introduction of melamine cyanuric acid-coated aluminum diethylphosphinate flame retardant significantly improved the flame retardancy of the leather. However, with increasing flame retardant coating ratio, the flame retardancy showed a decreasing trend, but it was still superior to the leather sample without added flame retardant (Comparative Example 1). Specifically, when the melamine cyanuric acid to aluminum diethylphosphinate coating ratio was 1:3, 1:2, and 1:1, the flame retardancy of the samples all reached the A-0 rating.

[0087] In addition, the limiting oxygen index (LOI) of the samples was tested using an HC-2C oxygen index meter according to GB / T 5454-1997. The minimum oxygen concentration required to sustain combustion was determined by igniting the upper end of the sample held perpendicular to the sample holder inside the combustion chamber and observing its combustion characteristics under different oxygen concentrations. The results showed that the LIO of the flame-retardant treated leather was improved compared to the untreated leather.

[0088] The abrasion resistance of coated leather was characterized using a DK-5612 Taber abrasion tester according to QB / T 2726-2005 "Determination of Abrasion Resistance in Physical and Mechanical Tests of Leather". The sample was placed on a horizontal platform and rotated. Two grinding wheels were applied with specific pressure and rotated on the sample, with their axes parallel to the horizontal plane, one facing outwards and the other inwards. All changes in the sample were recorded over a certain time. Additionally, the flexural strength of coated leather was characterized using an HT-8643 leather flexural strength tester according to QB / T 2714-2005 "Determination of Folding Fastness in Physical and Mechanical Tests of Leather". The upper test surface of the sample was folded inwards and clamped in a movable fixture, while the lower test surface was folded outwards and clamped in a fixed fixture. The movement of the upper fixture caused the sample to move, allowing for the examination of defects generated during the movement. The results showed that the treated leather exhibited good durability. Furthermore, the durability of leather with the flame retardant of the present invention added is not significantly reduced compared to leather without the flame retardant of the present invention added.

[0089] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or basic characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the scope of the invention. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a melamine cyanuric acid-coated phosphorus-based flame retardant for anionic waterborne polyurethane, characterized in that, Includes the following steps: Step 1: Add the ethanol-free solvent, emulsifier, cyanuric acid and phosphorus-based flame retardant powder to the reaction vessel, then heat the reaction system to the reaction temperature, stir and mix thoroughly to obtain a suspension; Step 2: Disperse melamine in an ethanol-free solvent, and then slowly and evenly add it to the suspension obtained in Step 1. Maintain the reaction temperature and continue stirring and reacting to coat the surface of the phosphorus-based flame retardant powder with melamine cyanuric acid by in-situ polymerization. Step 3: After the reaction is complete, the product is filtered, washed, dried, and ground to obtain a white powder of melamine cyanuric acid-coated phosphorus-based flame retardant. The phosphorus-based flame retardant is aluminum diethylphosphonate, and the ethanol-free solvent is deionized water.

2. The preparation method according to claim 1, characterized in that, The ratio of the mass of the ethanol-free solvent in step 1 to the sum of the masses of the cyanuric acid and the melamine is 10~20:

1.

3. The preparation method according to claim 1, characterized in that, In step 1, the reaction temperature is 95~100℃, the stirring speed is 400~450rpm, and the stirring time is 2~3h.

4. The preparation method according to claim 1, characterized in that, In step 2, the reaction temperature is 95~100℃, the stirring speed is 500~600rpm, and the stirring time is 4~5h.

5. The preparation method according to claim 1, characterized in that, The mass ratio of cyanuric acid to melamine is 1~1.05:

1.

6. The preparation method according to claim 1, characterized in that, The ratio of the sum of the masses of cyanuric acid and melamine to the mass of the phosphorus-based flame retardant powder is 0.33 to 3:

1.

7. A method for manufacturing flame-retardant waterborne polyurethane artificial leather, characterized in that, Includes the following steps: Step 1: Prepare waterborne polyurethane resins with three formulations: top layer resin, middle layer resin, and bottom layer resin, and disperse them by high-speed shearing to obtain a mixture. The middle layer resin and the bottom layer resin contain a certain amount of melamine cyanuric acid-coated phosphorus flame retardant according to claim 1. Step 2: Coat the surface layer resin onto the surface of the release paper, and then place the release paper in an oven to dry the surface layer resin; Step 3: Coat the surface of the dried top layer resin with the middle layer resin, and then place the release paper in an oven to dry the middle layer resin; Step 4: Coat the surface of the dried intermediate resin with the bottom resin, then attach the polyester fabric to the wet bottom resin, and then put the release paper into an oven to dry. Step 5: After the resin is completely dried, remove the fabric to obtain flame-retardant waterborne polyurethane artificial leather with a melamine cyanuric acid-coated phosphorus-based flame retardant coating.

8. The manufacturing method according to claim 7, characterized in that, The viscosity of the top layer resin is 3000~4000 mPa·s, the viscosity of the middle layer resin is 5000~7000 mPa·s, and the viscosity of the bottom layer resin is 8000~10000 mPa·s.

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