Preparation method and application of melamine cyanuric acid coated phosphorus flame retardant

Abstract

The invention provides a preparation method of a melamine cyanuric acid coated phosphorus flame retardant and application of the flame retardant in flame-retardant waterborne polyurethane artificial leather. According to the preparation method, melamine cyanuric acid is coated on the surface of phosphorus flame retardant powder in an in-situ polymerization manner, and an ethanol-free solvent is used as a reaction medium in the reaction process, so that the preparation method has the advantages of environment friendliness, safety and high yield and conversion rate; and the phosphorus-based flame retardant coated with the melamine cyanuric acid has a synergistic effect on the flame retardant property.

Description

Technical Field

[0001] The invention belongs to the field of polymer composite materials, and particularly relates to a preparation method of a melamine cyanuric acid-coated phosphorus flame retardant and application of the melamine cyanuric acid-coated phosphorus flame retardant in flame-retardant waterborne polyurethane artificial leather. Background Art

[0002] Polyurethane (PU), also known as polyurethane, is a high molecular weight polymer made by the polycondensation of polyisocyanates and polyols, and its main chain contains multiple carbamate 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, not easily volatile, and easy to clean after use. Compared with other solvent-based polyurethanes, it has the advantages of being environmentally friendly and low-cost. According to the type of hydrophilic groups on the main chain and side chains of waterborne polyurethane, waterborne polyurethane can be divided into: non-ionic waterborne polyurethane, cationic waterborne polyurethane, and anionic waterborne polyurethane. The structure of non-ionic waterborne polyurethane contains hydrophilic hydroxymethyl or hydroxyethyl as hydrophilic groups, the structure of cationic waterborne polyurethane usually contains cationic hydrophilic groups such as ammonium ions, and the structure of anionic waterborne polyurethane usually contains anionic hydrophilic groups such as carboxylic acid and sulfonic acid. Among them, anionic water-based polyurethane has significant advantages over other types of water-based resins in terms of comprehensive performance and technical maturity. Especially in leather processing, it can replace oily polyurethane to reduce pollution and toxicity.

[0003] Artificial leather is made by foaming or laminating various formulations of PVC or PU onto a textile or non-woven base. It can be processed to achieve varying colors, gloss, strength, and patterns depending on the application scenario. It offers a wide variety of patterns, excellent waterproofing, neat edges, high utilization rates, and a price lower than genuine leather. Conventional water-based polyurethane and its substrate are both flammable (LOI < 22%). However, with rising 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 categorized by their flame retardant elements, including halogen, nitrogen, silicon, and phosphorus. Compared to other types of flame retardants, phosphorus-based flame retardants are more environmentally friendly and have higher flame retardant efficiency. Aluminum diethylphosphinate (ADP), a member of the phosphorus-based flame retardant family, not only exhibits flame retardancy in the gas phase but also exhibits a certain degree of flame retardancy in the solid phase. When thermally decomposed, it produces free radical quenchers such as PO·, which capture flammable free radicals (such as HO· and H·) generated during combustion, terminating their further reaction with oxygen and thus blocking the combustion reaction. Furthermore, the phosphates formed by its decomposition promote the dehydration of the material into char, effectively isolating it from oxygen and heat. However, due to the strong acidity of aluminum diethylphosphinate (pH ≈ 4.2), its surface acidity can convert previously stable carboxylates (such as -COO-) in anionic waterborne polyurethanes into water-insoluble carboxylic acids (-COOH), destabilizing the emulsion and causing demulsification.

[0005] Although the prior art, such as patent CN116162343A, discloses a melamine cyanurate (MCA)-coated aluminum diethylphosphinate intumescent flame-retardant thermoplastic polyurethane and its preparation method. However, in the reaction system, ethanol is used as the reaction medium, and its applicability has certain limitations. The boiling point of ethanol at normal pressure is 78°C and the flash point is 13°C, which is not suitable for salt-forming reactions at normal pressure and high temperature. The price of ethanol is usually several times that of deionized water, and the cost is relatively high. The amount of melamine cyanuric acid used for coating in the above patent is relatively low, and dipentaerythritol needs to be compounded to form an intumescent flame retardant, which has low environmental protection. In addition, the purpose of coating aluminum diethylphosphinate with melamine cyanurate in this patent is to reduce the agglomeration of aluminum diethylphosphinate, and it is an intumescent flame retardant for thermoplastic polyurethane. There is no mention of the demulsification phenomenon that may be caused when phosphorus-based flame retardants are used in water-based polyurethane. Therefore, it is impossible to predict whether the melamine cyanurate-coated aluminum diethylphosphinate prepared in the above patent can be applied to anionic waterborne polyurethane artificial leather.

[0006] In fact, ethanol has a certain demulsification effect on polyurethane emulsions. Even trace amounts of residual ethanol in the resulting melamine cyanurate-coated aluminum diethylphosphinate can degrade the stability of the anionic waterborne polyurethane resin. The inventors discovered that using an ethanol-free solvent, preferably deionized water, not only effectively reduces costs but also improves emulsion stability. Furthermore, cyanuric acid and melamine themselves have very low solubility in ethanol, but their solubility increases in hot water. Furthermore, since water has a boiling point approximately 20°C higher than ethanol, using water as the reaction medium allows the reaction to proceed at higher temperatures, which increases the solubility of cyanuric acid and melamine. Therefore, compared to ethanol, the same amount of water as the reaction medium can produce a higher yield and purity of the melamine cyanuric acid product. Conversely, using ethanol as the reaction medium results in a smaller amount of melamine cyanuric acid product due to the lower reaction temperature and raw material solubility. The coating effect of ethanol as a shell layer does not meet expectations, leading to increased demulsification.

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

[0008] Based on the problems mentioned in the above background technology, the present invention uses melamine cyanuric acid to coat the phosphorus-based flame retardant powder, which not only avoids the demulsification of anionic water-based polyurethane caused by excessive acidity on the surface of the 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 the phosphorus-based flame retardant in the gas phase, thereby achieving a synergistic flame retardant effect.

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

[0010] The first aspect of the present invention provides a method for preparing a melamine cyanuric acid-coated phosphorus flame retardant. The method uses phosphorus flame retardant powder as a core material and melamine cyanuric acid as a shell material to prepare flame retardant microcapsules with a core-shell structure by in-situ polymerization. The system uses an ethanol-free solvent as a reaction medium and melamine (MEL) and cyanuric acid (CA) as reaction raw materials, and has the advantages of high yield and good stability. During the preparation process, cyanuric acid can be adsorbed on the surface of the phosphorus flame retardant powder through electrostatic action, and then reacts with melamine. Finally, melamine cyanuric acid is synthesized on the surface of the phosphorus flame retardant powder to obtain flame retardant microcapsules.

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

[0012] (1) After uniformly dispersing an ethanol-free solvent, an emulsifier, cyanuric acid, and a phosphorus-based flame retardant powder under the action of a dispersing shearing machine, the powder is added to a reactor equipped with a condensing device, and the reaction system is heated to the reaction temperature, and the mixture is stirred and mixed under mechanical stirring to obtain a suspension;

[0013] (2) Dispersing melamine in a solvent free of ethanol, and then slowly and evenly adding the melamine to the suspension obtained in (1) above within 30 minutes, maintaining the reaction temperature and continuing to stir and react, to obtain a suspension of melamine cyanuric acid coated flame retardant;

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

[0015] Furthermore, the ethanol-free solvent in step (1) and step (2) may preferably be 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 is no particular limitation on the emulsifier used in step (1), and it can be an emulsifier commonly used in the art and not participating in the reaction.

[0018] Furthermore, in step (1), the ratio of the mass of the solvent not containing ethanol to the sum of the masses of cyanuric acid and melamine can be 10-20:1.

[0019] Furthermore, the reaction temperature of step (1) can be 95-100° C., the stirring speed can be 400-450 rpm, and the stirring time can be 2-3 h.

[0020] Furthermore, the reaction temperature of step (2) can be 95-100° C., the stirring speed can be 500-600 rpm, and the stirring time can be 4-5 h.

[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 cyanuric acid and melamine to the mass of the phosphorus 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 producing flame-retardant waterborne polyurethane artificial leather. This method uses the aforementioned melamine cyanuric acid-coated phosphorus flame retardant as a flame retardant, polyester fabric as a substrate, and a lamination process to produce the artificial leather. The specific preparation process is as follows:

[0023] (1) preparing three waterborne polyurethane resins, namely, a surface layer resin, a middle layer resin, and a bottom layer resin, and dispersing them by high-speed shearing to obtain a mixture. The middle layer resin and the bottom layer resin each contain 20 to 25 parts by weight of the melamine cyanuric acid-coated phosphorus flame retardant;

[0024] (2) coating 15 strips of surface resin on the surface of the release paper, and then placing the release paper in an oven to dry the surface resin;

[0025] (3) Coating 20 strips of middle layer resin on the surface of the surface layer resin, and then placing the release paper in an oven to dry the middle layer resin;

[0026] (4) Coating 30 strips of base resin on the surface of the middle layer resin, then laminating polyester fabric on the undried base resin, and then placing the release paper in an oven to dry;

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

[0028] Furthermore, the top layer resin in step (1) is formulated as a water-based polyurethane resin with color powder added, and the viscosity is adjusted to 3000-4000 mPa·s using a thickener. The middle layer resin is formulated as a water-based polyurethane resin with 20-25 parts by weight of a melamine cyanuric acid-coated phosphorus flame retardant added, and the viscosity is adjusted to 5000-7000 mPa·s using a thickener. The bottom layer resin is formulated as a water-based polyurethane resin with 20-25 parts by weight of a melamine cyanuric acid-coated phosphorus flame retardant added, 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 is no particular limitation on the thickener, and it can be any thickener commonly used in the art.

[0031] Generally, the greater the number of coating stripes, i.e., the thickness, the higher the viscosity required to ensure uniform application of the flame retardant. A more dilute solution is difficult to apply to a high number of coating stripes. Therefore, controlling the viscosity of the surface layer resin, middle layer resin, and bottom layer resin of the present invention within the above-mentioned ranges enables uniform coating.

[0032] Furthermore, there is no specific limitation on the aqueous resin used in the surface layer, middle layer, and bottom layer in step (1), and they may be polyether-based aqueous resins, polyester-based aqueous resins, or polyether-polyester mixed aqueous resins. Specifically, the aqueous resins used in the surface layer and middle layer in step (1) may be the yellowing-resistant polyether-based anionic aqueous resin M-26 produced by the applicant, and the aqueous resin used in the bottom layer may be the high-solid-content polyether-based anionic aqueous resin XB-41 produced by the applicant.

[0033] Furthermore, in step (2) and step (3), the drying temperature of the surface layer resin and the middle layer resin is 90-100° C., and the drying time is 15-20 min.

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

[0035] The present invention is beneficial in that:

[0036] (1) The present invention adopts a one-bath method to coat melamine cyanuric acid on the surface of the phosphorus-based flame retardant powder in an in-situ polymerization manner. During the reaction process, a solvent free of ethanol is used as the reaction medium to avoid demulsification of the polyurethane caused by the reaction medium such as ethanol in the prior art, thereby improving the stability of the emulsion. Compared with uncoated aluminum diethylphosphinate and the coated phosphorus-based flame retardant prepared by the ethanol system, the melamine cyanuric acid-coated phosphorus-based flame retardant prepared by the ethanol-free solvent has better stability in anionic waterborne polyurethane. Specifically, as demonstrated in the examples of the present invention, uncoated aluminum diethylphosphinate and the coated phosphorus-based flame retardant prepared by the ethanol system quickly demulsify after being fully dispersed in the anionic waterborne polyurethane, while the coated phosphorus-based flame retardant prepared by the water system can be stable in the resin for more than one week without sedimentation, and can meet the requirements of continuous production batching, storage and use.

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

[0038] (3) Melamine cyanuric acid and phosphorus-based flame retardants have a synergistic flame retardant effect when used in combination. Melamine cyanuric acid-coated phosphorus-based flame retardants also have a synergistic flame retardant effect. In the gas phase, melamine cyanuric acid can release inert gases such as NH3 during pyrolysis, and phosphorus-based flame retardants can produce free radicals such as PO• during pyrolysis, and the two have a complementary effect. The melamine cyanuric acid-coated phosphorus-based flame retardant of the present invention is suitable for gas phase flame retardancy and also has a certain flame retardant effect in the solid phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 These are infrared spectra of aluminum diethylphosphinate (ADP) and melamine cyanuric acid-coated aluminum diethylphosphinate (ADP@MCA) of Example 3.

[0040] Figure 2 These are microscopic morphologies of aluminum diethylphosphinate and melamine cyanuric acid-coated aluminum diethylphosphinate of Example 3, wherein (a) is aluminum diethylphosphinate, and (b) is melamine cyanuric acid-coated aluminum diethylphosphinate of Example 3.

[0041] Figure 3 The thermogravimetric curves and differential thermogravimetric curves of aluminum diethylphosphinate (ADP), melamine cyanuric acid-coated aluminum diethylphosphinate in different reaction media (water system, ethanol system), cyanuric acid (CA) and melamine (MEL) are shown, where (a) is the thermogravimetric curve and (b) is the differential thermogravimetric curve. DETAILED DESCRIPTION

[0042] The present invention can be realized by the following examples: The materials used in the examples and comparative examples of the present invention can all be purchased from the market.

[0043] Example 1

[0044] (1) In a 3 L beaker, add 1 L of deionized water, 3 g of emulsifier, 50 g of cyanuric acid, and 300 g of aluminum diethylphosphinate. Mix them uniformly using a dispersing shear at 1000 rpm to obtain a suspension.

[0045] (2) Pour the above suspension into a 3 L flask and place it in an oil bath at 95 °C with a condenser reflux device. Maintain the speed at 400 rpm and stir to disperse and dissolve for 3 h.

[0046] (3) Disperse 50 g of melamine in 100 g of deionized water and slowly drip it into the flask prepared in step (2) using a dropper over 30 min. Continue the reaction at 95°C for 5 h with a stirring speed of 550 rpm to ensure that the melamine cyanuric acid is evenly coated on the surface of the aluminum diethylphosphinate.

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

[0048] (5) Prepare water-based polyurethane resins for the surface layer, middle layer, and bottom layer, respectively. The surface layer resin is 100g of water-based polyurethane with 5g of color powder and 0.5g of silicone wear-resistant additive added. The middle and bottom layer resins are 100g of water-based polyurethane resin with 20g of melamine cyanuric acid-coated aluminum diethylphosphinate added. After obtaining the mixture by high-speed shear dispersion, the viscosity of the water-based polyurethane resins for the surface layer, middle layer, and bottom layer is adjusted to 3000mPa·s, 6000mPa·s, and 8000mPa·s, respectively. Among them, the water-based polyurethane used in the surface layer and middle layer resins is the yellowing-resistant polyether anionic water-based resin M-26 produced by the applicant, and the water-based polyurethane used in the bottom layer is the high-solid content polyether anionic water-based resin XB-41 produced by the applicant.

[0049] (6) Fifteen strips of surface resin were coated on the surface of the release paper, followed by baking at 95°C for 15 minutes. Twenty strips of middle resin were coated on the dried surface resin, followed by baking at 95°C for 15 minutes. Thirty strips of bottom resin were coated on the dried middle resin, and then a polyester fabric was laminated on the undried resin and baked at 130°C for 20 minutes. Finally, the coated fabric was removed to obtain a flame-retardant anionic water-based polyurethane artificial leather.

[0050] Example 2

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

[0052] Example 3

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

[0054] Example 4

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

[0056] Example 5

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

[0058] Example 6

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

[0060] Example 7

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

[0062] Comparative Example 1

[0063] (1) Prepare waterborne polyurethane resins for the surface layer, middle layer, and bottom layer, respectively. The surface layer resin is 100 g of waterborne polyurethane with 5 g of color powder and 0.5 g of silicone wear-resistant additive added. The middle and bottom layer resins are each 100 g of waterborne polyurethane resin. After obtaining the mixture by high-speed shear dispersion, the viscosity of the surface layer, middle layer, and bottom layer resins is adjusted to 3000 mPa·s, 6000 mPa·s, and 8000 mPa·s, respectively. The waterborne polyurethane used in the surface layer, middle layer, and bottom layer is the same as that in Example 1.

[0064] (2) Fifteen strips of surface resin were applied to the surface of the release paper, followed by baking at 95°C for 15 minutes. Twenty strips of middle resin were applied to the dried surface resin, followed by baking at 95°C for 15 minutes. Thirty strips of base resin were applied to the dried middle resin, followed by laminating polyester fabric to the undried resin and baking at 130°C for 20 minutes. Finally, the coated fabric was removed to obtain anionic waterborne polyurethane artificial leather.

[0065] Comparative Example 2

[0066] The flame retardant anionic waterborne polyurethane artificial leather was prepared in the same process as in Comparative Example 1, except that 20 g of aluminum diethylphosphinate was added to 100 g of waterborne polyurethane resin in the middle and bottom layer resins.

[0067] Comparative Example 3

[0068] Flame-retardant anionic waterborne polyurethane artificial leather was prepared by 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 example

[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 the present 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 The absorption peak corresponding to CH is 1152 cm -1 and 1069cm -1 The absorption peaks at 3232cm correspond to P=O and PO groups respectively. In the infrared spectrum of melamine cyanuric acid coated aluminum diethylphosphinate, not only the above absorption peaks of aluminum diethylphosphinate can be observed, but also some new absorption peaks appear. -1 The absorption peak corresponding to the hydrogen bond formed by melamine and cyanuric acid is 1780 cm -1 The absorption peak at 1662 cm corresponds to the C=O group of cyanuric acid; -1 The absorption peak at 1533 cm corresponds to the NH2 group of melamine; -1 The absorption peak at corresponds to the C=N group of the triazine ring. The above results prove the presence of aluminum diethylphosphinate and melamine cyanuric acid.

[0072] 2. Microscopic Surface Morphology of Aluminum Diethylphosphinate and Melamine Cyanuric Acid Coated Aluminum Diethylphosphinate

[0073] The microscopic surface morphology of aluminum diethylphosphinate and melamine cyanuric acid coated aluminum diethylphosphinate of Example 3 of the present invention was characterized and tested using a Regulus 8230 high-resolution cold field emission scanning electron microscope. Figure 2 As shown in (a), the surface of the uncoated aluminum diethylphosphinate is relatively smooth. Figure 2 As shown in (b), many rod-shaped melamine cyanuric acid particles appeared on the surface of aluminum diethylphosphinate after melamine cyanuric acid coating, and the overall shape was irregular. The above results indicate that melamine cyanuric acid was successfully coated on the surface of aluminum diethylphosphinate.

[0074] 3. Thermogravimetric Analysis

[0075] The thermal stability of aluminum diethylphosphinate, melamine cyanuric acid-coated aluminum diethylphosphinate (water system) of Example 3, melamine cyanuric acid-coated aluminum diethylphosphinate (ethanol system) of Comparative Example 3, cyanuric acid and melamine were characterized and tested under nitrogen environment using a TG 209F3 thermogravimetric analyzer. Figure 3 It can be seen that the thermal decomposition of aluminum diethylphosphinate, cyanuric acid, and melamine occurs in a single stage, and the thermal decomposition temperatures of melamine and cyanuric acid are significantly lower than those of aluminum diethylphosphinate and melamine cyanuric acid-coated aluminum diethylphosphinate. The decomposition temperatures of melamine are in the range of 235–350°C, cyanuric acid is in the range of 265–400°C, and aluminum diethylphosphinate is in the range of 370–490°C. In contrast, the thermal decomposition of melamine cyanuric acid-coated aluminum diethylphosphinate occurs in two stages. The first stage, occurring in the temperature range of 300–385°C, is primarily responsible for the thermal decomposition of the melamine cyanuric acid shell material. The second stage, occurring in the temperature range of 385–475°C, primarily involves the thermal decomposition of the aluminum diethylphosphinate core material.

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

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

[0078] [Table 1]

[0079]

[0080] As shown in Table 1, the T 1% (Temperature at 1% weight loss) are 247°C and 273°C, respectively, which are lower than 404°C for aluminum diethylphosphinate and 314°C and 308°C for aluminum diethylphosphinate coated with melamine cyanuric acid. 5% and T 50% The same pattern can also be found. This result shows that melamine cyanuric acid was successfully synthesized in the system. The residual carbon rates of melamine and cyanuric acid were only 0.1% and 0.7% respectively, and the residual carbon rate of diethylphosphinate aluminum was 9.6%. Since melamine cyanuric acid mainly exerts its flame retardant effect in the gas phase, its flame retardant effect in the solid phase is weaker than that of diethylphosphinate aluminum. Therefore, the residual carbon rate of melamine cyanuric acid-coated diethylphosphinate aluminum is lower than that of diethylphosphinate aluminum, which are 4.7% and 7.8% respectively. This result also shows that melamine cyanuric acid-coated diethylphosphinate aluminum also has a certain flame retardant effect in the solid phase.

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

[0082] The emulsion stability, combustion level, limiting oxygen index, wear resistance and folding resistance of each anionic waterborne polyurethane artificial leather 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 diethylphosphinate (Comparative Example 2) and aluminum diethylphosphinate coated with melamine cyanuric acid in ethanol (Comparative Example 3) rapidly demulsified after high-speed shear dispersion in anionic waterborne polyurethane. The resulting emulsions were unstable and unsuitable for coating to produce artificial leather. In contrast, aluminum diethylphosphinate coated with melamine cyanuric acid in water exhibited significantly improved emulsion stability. Furthermore, increasing the coating ratio of melamine cyanuric acid to aluminum diethylphosphinate significantly increased the emulsion's stability, reaching stability for up to a week or more.

[0086] The horizontal combustion performance of the samples was characterized using a TTech-GB8410-2 automotive interior combustion tester in accordance with GB 8410-2006, "Combustion Characteristics of Automotive Interior Materials." The samples were clamped horizontally on a U-shaped bracket and ignited in a combustion chamber. After 15 seconds, a flame was ignited at one end. The flame retardancy rating was determined based on whether or when the flame extinguished, as well as the burning rate. The results showed that the introduction of a melamine cyanuric acid-coated aluminum diethylphosphinate flame retardant significantly improved the flame retardancy of the leather. However, with increasing flame retardant coverage, the flame retardancy decreased, but remained superior to that of leather samples without the addition of flame retardant (Comparative Example 1). Specifically, the flame retardancy of the samples reached A-0 grade when the melamine cyanuric acid to aluminum diethylphosphinate coverage ratios were 1:3, 1:2, and 1:1.

[0087] In addition, the samples' limiting oxygen index (LOI) was tested using an HC-2C oxygen index meter according to GB / T 5454-1997. By igniting the upper end of a sample held perpendicular to a sample holder within a combustion chamber and observing its combustion characteristics at varying oxygen concentrations, the minimum oxygen concentration required to sustain combustion was determined. The results showed that the LOI of the flame-retardant treated leather significantly improved compared to the untreated leather.

[0088] The wear resistance of the coated leather was tested using a DK-5612 Taber abrasion tester according to QB / T 2726-2005, "Determination of wear resistance of leather by physical and mechanical tests." The specimen was placed on a horizontal platform and rotated. Two grinding wheels were applied to the specimen with a specific pressure, their axes parallel to the horizontal plane, one facing outward and the other inward. All changes in the specimen were recorded over a specified period of time. Furthermore, the folding resistance of the coated leather was tested using an HT-8643 leather flexural tester according to QB / T 2714-2005, "Determination of folding resistance of leather by physical and mechanical tests." The upper test surface of the specimen was folded inward and clamped in a movable fixture, while the lower test surface was folded outward and clamped in a fixed fixture. The movement of the upper fixture caused the specimen to move, allowing inspection for defects during movement. The results showed that the treated leather exhibited good durability. In addition, the durability of the leather to which the flame retardant of the present invention is added is not significantly reduced compared to the leather to which the flame retardant of the present invention is not added.

[0089] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention. Although embodiments of the present invention have been shown and described, it is 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 present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a melamine cyanuric acid-coated phosphorus flame retardant, characterized in that: The following steps are involved: Step 1: adding an ethanol-free solvent, an emulsifier, cyanuric acid, and a phosphorus-based flame retardant powder into a reactor, then heating the reaction system to a reaction temperature, and thoroughly stirring and mixing to obtain a suspension; Step 2: dispersing melamine in a solvent free of ethanol, and then slowly and evenly adding the melamine to the suspension obtained in step 1, while maintaining the reaction temperature and continuing stirring and reacting; Step 3: After the reaction is completed, the product is filtered, washed, dried, and ground to obtain a white powder melamine cyanuric acid-coated phosphorus flame retardant.

2. The preparation method according to claim 1, characterized in that The phosphorus-based flame retardant is aluminum diethylphosphinate.

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

1.

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

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

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

1.

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

1.

8. The preparation method according to claim 1, characterized in that The non-ethanol-containing solvent is a non-ethanol-containing aqueous solvent.

9. The preparation method according to claim 8, characterized in that The ethanol-free aqueous solvent is deionized water.

10. A method for producing flame-retardant waterborne polyurethane artificial leather, characterized in that: The following steps are involved: Step 1, preparing three waterborne polyurethane resins of formulations, namely, a surface layer resin, a middle layer resin, and a bottom layer resin, respectively, and obtaining a mixture by high-speed shear dispersion, wherein the middle layer resin and the bottom layer resin contain a certain amount of the melamine cyanuric acid-coated phosphorus flame retardant according to claim 1; Step 2, coating the surface layer resin on the surface of the release paper, and then placing the release paper in an oven to dry the surface layer resin; Step 3, coating the middle layer resin on the surface of the dried surface layer resin, and then placing the release paper in an oven to dry the middle layer resin; Step 4: coating the bottom layer resin on the surface of the dried middle layer resin, then laminating the polyester fabric on the undried bottom layer resin, and then placing the release paper in an oven for drying; Step 5: After the resin is completely dried, the fabric is removed to obtain a flame-retardant water-based polyurethane artificial leather having a melamine cyanuric acid-coated phosphorus flame retardant coating.

11. The manufacturing method according to claim 10, characterized in that: The viscosity of the surface 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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