Carbon-forming agent and flame retardant for environmentally friendly high-needle-flame performance flame-retardant materials, preparation method and use thereof

Abstract

The present invention provides a charring agent and a preparation method thereof, the method comprising adding a nitrogen-containing compound and an aldehyde-containing compound in a molar ratio of 1:1-3 to a reaction vessel, adjusting the pH to 8-10 for reaction; adjusting the pH to 1-2 with an inorganic acid, adding an organic acid for reaction; washing the obtained reaction product, filtering and drying it to obtain the charring agent. The present invention also provides a flame retardant comprising the charring agent, and a flame-retardant polypropylene material comprising the flame retardant and an optional flame retardant synergist. The high needle flame performance flame-retardant polypropylene material prepared using the high-efficiency flame retardant comprising the charring agent of the present invention has the advantages of being environmentally friendly, highly flame-retardant, high-strength, and easy to injection mold.

Description

Technical Field

[0001] The present invention relates to a charring agent and its preparation method, a flame retardant containing the charring agent and its use, and a flame-retardant polypropylene material containing the flame retardant. More specifically, it relates to an environmentally friendly, high-needle-flame-performance flame-retardant polypropylene material and its preparation method. The high-needle-flame-performance flame-retardant polypropylene material prepared using the high-efficiency flame retardant containing the charring agent of the present invention has advantages such as environmental friendliness, high flame retardancy, high strength, and ease of injection molding. Background Art

[0002] Flame-retardant polymer materials, such as polypropylene, are widely used in home appliances, automobile manufacturing and other fields due to their excellent flame retardant properties, low specific gravity, low cost and easy injection molding. Currently, the most commonly used flame retardant systems are bromine-antimony and phosphorus-nitrogen-bromine systems, which can reach V0 level when burned vertically and meet the conventional needle flame GBT 5169.5 test standard.

[0003] However, with the increasing demand for domestic product exports, some overseas customers, especially those in Europe, have placed higher demands on the environmental protection and flame retardancy of the products. Environmental factors have limited the application of traditional bromine-antimony and phosphorus-nitrogen-bromine flame retardant systems in flame-retardant polymer materials. Due to environmental protection and safety requirements, halogen-free intumescent flame retardants are increasingly used in polymer materials. Polymer materials containing traditional halogen-free intumescent flame retardants can achieve a vertical combustion V0 level of flame retardancy while meeting environmental protection requirements and can pass the conventional needle flame GBT 5169.5 test. However, for products with higher needle flame flame retardancy requirements, traditional halogen-free intumescent flame retardants are difficult to meet the corresponding flame retardancy requirements; although high needle flame flame retardancy can be achieved by significantly increasing the content of traditional flame retardants, the injection molding performance and mechanical properties of the material have been severely reduced, and it is no longer practical.

[0004] Therefore, there is an urgent need in this field to develop a flame retardant that can meet the requirements of high needle flame retardancy while maintaining the original injection molding properties and mechanical properties of the polymer material. Summary of the Invention

[0005] A first aspect of the present invention provides a method for preparing a carbon-forming agent, the method comprising:

[0006] (1) adding a nitrogen-containing compound and an aldehyde-containing compound into a reaction vessel at a molar ratio of 1:1-3, and adding an alkaline solution to adjust the pH to 8-10 for reaction;

[0007] (2) After adjusting the pH to 1-2 with an inorganic acid, an organic acid is added to carry out the reaction;

[0008] (3) The obtained reaction product is washed, filtered and dried to obtain a carbon-forming agent.

[0009] In a preferred embodiment of the present invention, the nitrogen-containing compound is at least one compound selected from the group consisting of melamine, ethylenediamine, ethanolamine and cyanuric chloride.

[0010] In a preferred embodiment of the present invention, the aldehyde-containing compound is at least one compound selected from the group consisting of formaldehyde, acetaldehyde, aliphatic aldehyde-containing compounds, alicyclic aldehyde-containing compounds and aromatic aldehyde compounds.

[0011] In a preferred embodiment of the present invention, the organic acid is a C2-C10 carboxylic acid having at least one carboxylic acid group and at least one hydroxyl group. Preferably, the organic acid is at least one compound selected from the group consisting of citric acid, malic acid, lactic acid, and salicylic acid.

[0012] The second aspect of the present invention provides a carbon-forming agent prepared by the above method.

[0013] A third aspect of the present invention provides a char-forming agent comprising a cross-linked structure formed by the reaction of melamine, citral and citric acid as shown in the following formula:

[0014] The weight average molecular weight of the carbon-forming agent is 30,000-50,000.

[0015] The fourth aspect of the present invention provides the use of an organic acid in preparing the char-forming agent.

[0016] A fifth aspect of the present invention provides a flame retardant, which comprises the charring agent and ammonium polyphosphate described in the present invention, wherein the weight ratio of the charring agent to ammonium polyphosphate is (1-3): (1-10).

[0017] In a preferred embodiment of the present invention, the weight ratio of the carbon-forming agent to ammonium polyphosphate is 1:(2-4).

[0018] In a preferred embodiment of the present invention, the flame retardant further comprises ferric malate as a flame retardant synergist, and the weight ratio of the flame retardant synergist to the total amount of the charring agent and ammonium polyphosphate is (0.01-1): (15-35), preferably (0.1-0.8): (15-35), and most preferably (0.1-0.5): (20-35).

[0019] The sixth aspect of the present invention provides the use of ferric malate as a flame retardant synergist. In a preferred embodiment of the present invention, ferric malate is used as a flame retardant synergist of the flame retardant of the present invention.

[0020] The seventh aspect of the present invention provides the use of the flame retardant in combination with polyethylene, polypropylene, polystyrene, nylon, polyester, and polyurethane.

[0021] An eighth aspect of the present invention provides a flame retardant polypropylene material, comprising:

[0022]

[0023] The flame retardant is the flame retardant described in the present invention, the flame retardant catalyst is ferric malate, and other additives are antioxidants, lubricants or masterbatches.

[0024] A ninth aspect of the present invention provides a product made of flame-retardant polypropylene material.

[0025] The tenth aspect of the present invention provides a method for preparing a flame-retardant polypropylene material, which comprises mixing a polypropylene resin, a flame retardant, an optional flame retardant synergist, an optional toughening agent, an optional compatibilizer and optional other auxiliary agents and extruding and granulating the mixture.

[0026] The eleventh aspect of the present invention provides use of a combination of a charring agent obtained by the preparation method of the present invention and ferric malate in improving the flame retardant properties and mechanical properties of a flame retardant polypropylene material. DETAILED DESCRIPTION

[0027] The inventors of the present invention discovered that after melamine is methylolated, the length of the melamine molecular chain increases and the ends of the molecular chain are rich in active hydroxyl groups. Subsequently, an esterification and dehydration reaction occurs with a carboxyl-rich organic acid, causing the entire macromolecular chain to continue to expand and significantly increasing the carbon content. At the same time, under the catalytic action of a flame retardant synergist, a dehydration cross-linking reaction between the molecular chain ends creates a cross-linked network structure that runs through the main macromolecular chain. Ultimately, the char formation rate and char layer strength of the polymer are significantly improved. Simply adding a small amount of a flame retardant containing this char-forming agent to a polypropylene material can significantly improve the material's flame retardancy while maintaining the polypropylene material's original injection molding and mechanical properties. This is the basis for the present invention.

[0028] The various aspects of the present invention are described in detail below:

[0029] carbon-forming agent

[0030] In the method of the present invention, a nitrogen-containing compound such as melamine is reacted with an aldehyde-containing compound, the melamine is methylolated, and then further reacted with an organic acid to introduce the organic acid at the end of the molecular chain. Any organic acid having at least one carboxylic acid group and at least one hydroxyl group can be used in the present invention. The organic acid and the methylolated compound first undergo a dehydration crosslinking reaction to form an ester compound. Secondly, because the organic acid itself contains both hydroxyl and carboxyl active functional groups, a dehydration crosslinking reaction continues between the macromolecular chain end groups, resulting in microscopic manifestations of the polymer molecular chain ends entangled with each other to form an interpenetrating polymer network structure.

[0031] Taking the reaction of melamine with citral followed by further reaction with citric acid as an example, the resulting polymer network structure has a cross-linked structure as shown in the following formula:

[0032]

[0033] The wavy lines indicate crosslinking sites, where the carbonyl groups formed by the hydration reaction of carboxylic acid groups and hydroxyl groups serve as crosslinking sites. In the structure shown above, the carboxylic acid group COOH can further dehydrate with the hydroxyl group OH on citral to form a carbonyl group, or it can dehydrate with the hydroxyl group OH on citric acid to form a carbonyl group, further crosslinking to form a network structure. The following shows the structure formed by further dehydration and crosslinking of a carboxylic acid group on the crosslinked structure with the hydroxyl OH on citral:

[0034]

[0035] Those skilled in the art will appreciate that the COOH groups in this structure can further undergo dehydration and cross-linking with the OH groups in the reaction system to form a polymer with an ultra-high molecular weight macromolecular structure, the weight average molecular weight of which is approximately 30,000-50,000.

[0036] The charring agent prepared by this method is a polymer with a unique macromolecular structure. This hyperbranched macromolecular structure has excellent charring ability, and the resulting char layer has ideal thickness and strength. Therefore, when used in combination with flame retardants (especially phosphorus-based flame retardants), it can exert unexpected synergistic effects, imparting excellent flame retardancy to the material while maintaining excellent mechanical properties.

[0037] In the present invention, the carbonizing agent is prepared by the following method, which comprises:

[0038] (1) adding a nitrogen-containing compound and an aldehyde-containing compound into a reaction vessel at a molar ratio of 1:1-3, and adding an alkaline solution to adjust the pH to 8-10 for reaction;

[0039] (2) After adjusting the pH to 1-2 with an inorganic acid, an organic acid is added to carry out the reaction;

[0040] (3) The obtained reaction product is washed, filtered and dried to obtain a carbon-forming agent.

[0041] In one embodiment of the present invention, the molar ratio of the nitrogen-containing compound to the aldehyde-containing compound is preferably 1:3.

[0042] In one embodiment of the present invention, the nitrogen-containing compound is at least one compound selected from the group consisting of melamine, ethylenediamine, ethanolamine, and cyanuric chloride. Melamine is preferably used as the nitrogen-containing compound due to its advantages of wide availability and high nitrogen content.

[0043] In one embodiment of the present invention, the aldehyde-containing compound is at least one compound selected from the group consisting of an aliphatic aldehyde-containing compound, an alicyclic aldehyde-containing compound, and an aromatic aldehyde compound. Specifically, preferred aldehyde-containing compounds include formaldehyde, acetaldehyde, citral, benzaldehyde, and the like. More preferably, the aldehyde-containing compound is citral.

[0044] In a specific embodiment of the present invention, the organic acid is a C2-C10 carboxylic acid having at least one carboxylic acid group and at least one hydroxyl group. Preferably, the organic acid is at least one compound selected from the group consisting of citric acid, malic acid, lactic acid, and salicylic acid. Citric acid and malic acid are polycarboxylic acid compounds with strong reactivity and are readily available and environmentally friendly. Salicylic acid has the advantages of being widely available and environmentally friendly, and its carbon-rich molecular structure also helps to increase the char yield. Therefore, the most preferred organic acids are citric acid, malic acid, and salicylic acid.

[0045] In one embodiment of the present invention, the carbon-forming agent is prepared by the following method:

[0046] 1) Add the nitrogen-containing compound and the aldehyde-containing compound into a reaction kettle according to the ratio, then add an appropriate amount of deionized water, and then add an appropriate amount of NaOH solution to adjust the pH to a weak alkaline environment of about 9;

[0047] 2) Set the reactor temperature to 70-80°C, slowly start the stirrer, and react at this constant temperature for 1 hour;

[0048] 3) Add an appropriate amount of hydrochloric acid to the reactor to adjust the pH to about 1-2, then add an appropriate amount of organic acid and continue the reaction for 1-4 hours;

[0049] 4) After the reaction is completed, the mixture is washed with deionized water and then dried in an oven at 100-110° C. to obtain a carbon-forming agent.

[0050] The alkaline aqueous solution and inorganic acid used to adjust the pH in the method of the present invention are not particularly limited. Various available alkaline compounds and inorganic acids may be used, as long as they do not limit the purpose of the present invention. For example, the alkaline aqueous solution may be an aqueous NaOH solution, an aqueous KOH solution, or the like, and the inorganic acid may be hydrochloric acid, sulfuric acid, or the like.

[0051] flame retardants

[0052] Intumescent flame retardants are a known type of flame retardant for polypropylene. These flame retardants can be obtained by mixing the high-efficiency char-forming agent described in this invention with ammonium polyphosphate according to a suitable ratio. Surprisingly, the present invention has discovered that flame retardants containing the char-forming agent of this invention can improve the flame retardancy of materials such as polypropylene while maintaining the mechanical properties of the material and reducing the risk of flame retardant precipitation.

[0053] The intumescent flame retardant of the present invention comprises the charring agent and ammonium polyphosphate described in the present invention, wherein the weight ratio of the charring agent and ammonium polyphosphate is (1-3): (1-10), preferably 1: (2-4), and more preferably 1:3.

[0054] Flame retardant synergist

[0055] The present invention also found that a high-efficiency flame retardant can be prepared by mixing ferric malate as a flame retardant synergist with the above-mentioned intumescent flame retardant. The weight ratio of the flame retardant synergist to the intumescent flame retardant is (0.01-1): (15-35), preferably (0.1-0.8): (15-35), and most preferably (0.1-0.5): (20-35). A high-efficiency flame retardant containing a very small amount of ferric malate can achieve the target flame retardant effect with a smaller addition amount, which is beneficial for maintaining the mechanical properties of the material and reducing the risk of flame retardant precipitation. This is because ferric malate, as a flame retardant synergist, can catalyze the dehydration and cross-linking reaction between the PP macromolecular chain and the intumescent flame retardant during the combustion reaction, achieving rapid and large-scale generation of a strong and thick carbon layer, making it difficult for heat during the combustion reaction to penetrate the condensed phase formed by the carbon layer, preventing oxygen from entering the combustion area, thereby achieving a good flame retardant effect.

[0056] The flame retardant synergist can be a commercially available iron malate product or prepared by reacting malic acid with Fe(OH)3.

[0057] In a preferred embodiment of the present invention, the flame retardant synergist is prepared by the following method:

[0058] 1) Dissolve malic acid in water;

[0059] 2) Dissolve Fe(OH)3 in water, and then slowly add the malic acid solution dropwise to the Fe(OH)3 solution at a molar ratio of Fe(OH)3:malic acid = 1:1-2;

[0060] 3) After evaporation, cooling and crystallization are carried out to obtain iron malate product.

[0061] The molecular structural formula of the flame retardant catalyst is as follows:

[0062]

[0063] When malic acid reacts with metal ions, it can be used as a chelate to form a structurally stable complex with the metal ions; the present invention uses malic acid and Fe 3+ Reaction, using malic acid and transition metal Fe 3+The structural stability of the ionic reaction products and the flame-retardant synergistic mechanism of transition metal oxoates effectively improve the efficiency of flame retardants. Ferric malate, as a flame-retardant synergist, catalyzes the dehydration and crosslinking reactions between the PP macromolecular chains and the intumescent flame retardant during the combustion reaction, rapidly and extensively generating a strong, thick char layer. Heat from the combustion reaction is unable to penetrate the condensed phase formed by the char layer, preventing oxygen from entering the combustion zone, thereby achieving excellent flame retardancy.

[0064] The intumescent flame retardant of the present invention or the high-efficiency flame retardant further comprising a flame retardant synergist can be used in conjunction with polyethylene, polypropylene, polystyrene, nylon, polyester, and polyurethane to improve the flame retardancy and mechanical properties of these polymers.

[0065] Flame retardant polypropylene material

[0066] The flame retardant polypropylene material can be prepared by mixing polypropylene resin, flame retardant, flame retardant synergist, optional toughening agent, optional compatibilizer and optional other auxiliary agents and extruding and granulating.

[0067] The polypropylene material comprises:

[0068]

[0069] In one embodiment of the present invention, the raw material components are mixed uniformly by a high-speed mixer according to the above formula, and then blended and granulated using a twin-screw extruder. The extruder temperature is set to 180-210°C to obtain an environmentally friendly flame-retardant polypropylene material with high needle flame performance.

[0070] In a preferred embodiment, the polypropylene resin is a mixture of K7726H:K8003=1:1, which has good fluidity and toughness.

[0071] In a preferred embodiment, the flame retardant comprises the char-forming agent of the present invention and ammonium polyphosphate, wherein the weight ratio of the char-forming agent to ammonium polyphosphate is (1-3):(1-10), preferably 1:(2-4), and more preferably 1:3. Preferably, the polypropylene material further comprises ferric malate as a flame retardant synergist.

[0072] In a preferred embodiment, the toughening agent is ethylene propylene diene monomer rubber, ethylene-propylene copolymer elastomer, ethylene-octene copolymer elastomer, etc., preferably ethylene-octene copolymer elastomer.

[0073] In a preferred embodiment, the compatibilizer is polypropylene grafted with maleic anhydride, polyolefin elastomer grafted with maleic anhydride, silane coupling agent, titanate coupling agent, etc., preferably polyolefin elastomer grafted with maleic anhydride.

[0074] In a preferred embodiment, the other additives are antioxidants, lubricants or masterbatches.

[0075] There is no specific limitation on the toughening agent, compatibilizer and other additives used in the present invention. Various available processing aids can be used as long as they do not limit the purpose of the present invention.

[0076] Products

[0077] The present invention also provides a product made from the flame-retardant polypropylene material of the present invention. The product is a housing for a converter socket, a jack socket, etc. The product has high flame retardancy and good mechanical properties.

[0078] The beneficial effects of the present invention are:

[0079] This invention utilizes a melamine-based, high-carbon polymer with a unique hyperbranched interpenetrating network structure as a charring agent, and iron malate as a flame retardant synergist. This high-efficiency flame retardant, prepared by mixing with ammonium polyphosphate, exhibits excellent flame retardancy. The resulting flame-retardant polypropylene material, produced through blending and modification, combines environmental friendliness with high needle flame resistance, excellent mechanical properties, and the absence of precipitation.

[0080] In the present invention, the terms "comprising," "including," or "using" indicate that various components can be used together in the mixture or composition of the present invention. Therefore, the terms "consisting essentially of" and "consisting of" are encompassed by the terms "comprising," "including," or "using." It should be understood that the degrees of "high," "low," and so on, as used herein, are well known in the art. For example, with respect to "high flame retardancy," those skilled in the art can determine whether a material's flame retardancy is high or low based on existing materials.

[0081] Unless otherwise specified, all raw materials used in the present invention can be obtained commercially or prepared according to conventional methods in the art. Unless otherwise defined or indicated, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. Other aspects of the present invention will be apparent to those skilled in the art from the disclosure herein.

[0082] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention and are not intended to limit the scope of the invention. The experimental methods for the following examples, for which specific conditions are not specified, are generally measured according to national standards. If there is no corresponding national standard, the methods are carried out according to general international standards, conventional conditions, or according to the conditions recommended by the manufacturer. Unless otherwise stated, all parts are by weight, all percentages are by weight, and the polymer molecular weight is the weight-average molecular weight.

[0083] Raw material source and preparation:

[0084] (1) Polypropylene (PP) resin:

[0085] K7726H, purchased from Yanshan Petrochemical; K8003, purchased from Shanghai Secco Petrochemical;

[0086] (2) Traditional intumescent flame retardants:

[0087] Phosphorus-nitrogen flame retardant, model IFR-3, purchased from Qingdao Fangda Chemical Co., Ltd. According to the product manual, it is a compound of melamine and ammonium polyphosphate, and does not have a molecular network branching and cross-linking process;

[0088] (3) The intumescent flame retardant of the present invention is prepared by the following method:

[0089] Intumescent flame retardant 1: 12.6g of melamine and 45.6g of citral were added to a reactor in a molar ratio of 1:3. 20g of deionized water was then added, followed by a 10% by weight NaOH solution to adjust the pH to a weakly alkaline environment of approximately 9. The reactor temperature was set to 80°C, and the stirrer was slowly turned on, and the reaction was carried out at this constant temperature for 1 hour. 10% by weight hydrochloric acid was added to the reactor to adjust the pH to 2, followed by the addition of 57.6g of citric acid, and the reaction was continued for 1-4 hours. After the reaction, the mixture was washed with deionized water and then dried in an oven at 100°C to obtain a high-efficiency char-forming agent. The obtained high-efficiency char-forming agent was mixed with ammonium polyphosphate in a weight ratio of 1:3 to obtain intumescent flame retardant 1.

[0090] Intumescent flame retardant 2: According to the preparation method of intumescent flame retardant 1, the melamine was replaced by 6.0g of ethylenediamine, and the other raw materials and reaction conditions remained unchanged to obtain intumescent flame retardant 2.

[0091] Intumescent flame retardant 3: Intumescent flame retardant 3 was obtained by following the preparation method of intumescent flame retardant 1, except that citric acid was replaced with 41.4 g of salicylic acid. Other raw materials and reaction conditions remained unchanged.

[0092] Intumescent flame retardant 4: Intumescent flame retardant 4 was obtained by following the preparation method of intumescent flame retardant 1, except that citric acid was replaced with 40.2 g of malic acid. Other raw materials and reaction conditions remained unchanged.

[0093] Intumescent flame retardant 5: Intumescent flame retardant 5 was obtained by following the preparation method of intumescent flame retardant 1, except that citral was replaced with 31.8 g of benzaldehyde, and other raw materials and reaction conditions remained unchanged.

[0094] Comparative Intumescent Flame Retardant 6: The preparation method of Intumescent Flame Retardant 1 was followed, but only the reaction process of melamine and citral was retained, and no acid was added for the reaction, to obtain Intumescent Flame Retardant 6.

[0095] (3) The flame retardant synergist is prepared by the following method:

[0096] Dissolve 13.4 g of malic acid in 50 ml of hot water at 100°C; weigh 21.2 g of Fe(OH)3 and dissolve it in water, then slowly add the malic acid solution dropwise to the Fe(OH)3 solution; evaporate and cool to crystallize to obtain iron malate product.

[0097] (4) Toughening agent:

[0098] Model 8150, purchased from Dow Chemical;

[0099] (5) Compatibilizer

[0100] Model FB521A, purchased from Jiayirong Polymer Co., Ltd.;

[0101] (6) Other additives

[0102] Other additives used in the examples include antioxidants 1010 and 168, purchased from BASF; lubricant RDMB-508D, purchased from Changzhou Rongdian Chemical Co., Ltd.; and masterbatch PE carrier black masterbatch, purchased from Shanghai Toyo Ink Co., Ltd.

[0103] According to the formula shown in the table below, the raw material components were mixed evenly by a low-speed mixer, and then blended and granulated using a twin-screw extruder. The temperature from the feeding section to the die head of the extruder was set according to a gradient of 180-200°C, with the feeding section temperature being 180°C and the die head temperature being 200°C, to obtain an environmentally friendly flame-retardant polypropylene material with high needle flame performance. The raw material formula composition is shown in Table 1 below:

[0104] Table 1 Flame retardant polypropylene material composition

[0105]

[0106]

[0107] Product performance test:

[0108] (1) Melt flow rate GB / T 3682.1:

[0109] The melt flow rate test was conducted at a temperature of 230°C and a load of 2.16 kg to characterize the injection molding performance of the material.

[0110] (2) Needle flame GBT 5169.5:

[0111] The sample thickness is 1.5 mm. The flame is applied for 30 seconds according to the needle flame method described in GBT 5169.5. This is used to characterize the flame retardant properties of the material.

[0112] (3) Vertical combustion UL94 (V0 level):

[0113] The sample thickness is 1.5mm and is tested according to the vertical burning UL94 (V0 grade) method; it is used to characterize the flame retardant properties of the material.

[0114] (4) Needle flame IEC 62368:

[0115] The sample thickness is 1.5mm. According to the IEC 62368 needle flame test standard, flame is applied for 10 seconds. If the flame does not burn for more than 30 seconds, the flame is immediately repeated at the same location for 1 minute. If the flame still does not burn for more than 30 seconds, the flame is immediately repeated at the same location for 2 minutes. This is used to characterize the flame retardant properties of the material.

[0116] (5) Izod notch impact strength

[0117] The notch depth is 2 mm and the notched cantilever beam impact strength is tested at room temperature (23°C) according to the method described in GB / T 1843. This test characterizes the material's ability to resist deformation or fracture when subjected to external forces.

[0118] (6) Injection molding performance test

[0119] Set the temperature of the injection molding machine from the feeding section to the nozzle to 180-210℃, the feeding section temperature to 180℃, the nozzle temperature to 210℃, and observe whether there is flame retardant precipitation on the mold surface after continuous injection for 30 minutes. The precipitation area is less than 1cm 2 It is acceptable, the precipitation area exceeds 1cm 2 It is considered invalid.

[0120] The flame retardant polypropylene material particles prepared were subjected to performance tests according to the above standards. The test results are shown in Table 2 below:

[0121] Table 2 Performance test results

[0122]

[0123] As can be seen from Comparative Example 1, the flame retardancy of polypropylene resin itself is very poor, with a limited oxygen index of only about 18, making it a flammable material. As shown in Comparative Example 2, adding a small amount of intumescent flame retardant to polypropylene resin can enable the polypropylene material to pass the needle flame GBT 5169.5 test. As the amount of flame retardant added increases, the flame retardancy of the polypropylene material increases. Using a higher amount of traditional intumescent flame retardant can make the flame retardancy of the polypropylene material reach the UL94 V0 level smoothly, but it is difficult to break through the higher flame retardancy level of the needle flame IEC 62368 standard. As can be seen from Comparative Examples 3 and 4, further increasing the flame retardant content will lead to a serious decrease in the melt flow rate and notched impact strength performance of the material. At the same time, if the flame retardant addition is too high, there is a risk of flame retardant precipitation, causing the material to adhere to the mold and be unsuitable for further processing.

[0124] As can be seen from Comparative Example 6, the traditional intumescent flame retardant itself has a poor flame retardant effect. Although the addition of iron malate flame retardant synergist can slightly improve its flame retardant properties, the effect is not significant. Comparative Example 7 is a flame retardant obtained by reacting melamine with citral to carry out melamine hydroxymethylation, but without adding an organic acid. From the performance results of Comparative Example 7, it can be seen that since no organic acid was introduced to further carry out a cross-linking reaction, the material failed to pass the needle flame IEC 62368 test. This is because the molecular weight of the charring agent is low and no interpenetrating network structure is formed between the macromolecular chains.

[0125] As can be seen from Examples 1-4, at the same content, the use of the intumescent flame retardant 1 of the present invention can enable the polypropylene material to smoothly pass the UL94 V0 and needle flame IEC 62368 tests, providing a better flame retardant effect compared to traditional intumescent flame retardants. The molecular weight and carbon content of the charring agent prepared by the present invention are greatly improved. The interpenetrating network structure of the charring agent and the catalytic cross-linking reaction of the flame retardant synergist enable the intumescent flame retardant comprising the charring agent of the present invention to quickly and in large quantities produce a high-strength dense carbon layer during the combustion reaction, so a smaller addition amount can achieve the target flame retardant effect, which is beneficial to maintaining the injection molding and mechanical properties of the material. Comparing Example 4 with Example 5, it can be seen that increasing the addition amount of the flame retardant synergist does not significantly improve the various properties of the material, and the melt flow rate decreases slightly, indicating that its addition amount has reached saturation, once again demonstrating that a smaller amount of flame retardant synergist can play a flame retardant synergistic role.

[0126] As can be seen from Example 6, although the flame retardant prepared using ethylenediamine failed the needle flame IEC 62368 test and was inferior to melamine, it still provided improved flame retardancy compared to traditional flame retardants. Examples 7 and 8, respectively, used salicylic acid and malic acid for further crosslinking, both achieving the target flame retardancy while maintaining good mechanical properties. Example 9 used benzaldehyde to methylolate melamine, demonstrating that other aldehyde compounds can also achieve similar flame retardancy.

[0127] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the substantive technical content of the present invention. The substantive technical content of the present invention is broadly defined in the scope of the claims of the application. Any technical entity or method completed by others, if it is exactly the same as that defined in the scope of the claims of the application or is an equivalent variation, will be deemed to be included in the scope of the claims.

[0128] All documents mentioned in this application are incorporated herein by reference, just as if each document were incorporated herein by reference individually. It should also be understood that after reading the above disclosure, those skilled in the art may make various changes or modifications to the present invention, and that such equivalents also fall within the scope of the claims appended hereto.

Claims

1. A method for preparing a carbon-forming agent, the method comprising: (1) adding a nitrogen-containing compound and an aldehyde-containing compound into a reaction vessel at a molar ratio of 1:3, and adjusting the pH to 8-10 for reaction, wherein the nitrogen-containing compound is at least one compound selected from the group consisting of melamine and ethylenediamine; (2) after adjusting the pH to 1-2 with an inorganic acid, adding an organic acid to carry out the reaction, wherein the organic acid is at least one compound selected from the group consisting of citric acid, malic acid, lactic acid and salicylic acid; (3) The obtained reaction product is washed, filtered, and dried to obtain a carbon-forming agent.

2. The method according to claim 1, wherein The aldehyde-containing compound is at least one compound selected from the group consisting of an aliphatic aldehyde-containing compound, an alicyclic aldehyde-containing compound, and an aromatic aldehyde compound.

3. A carbon-forming agent prepared by the method according to any one of claims 1 to 2.

4. A char-forming agent comprising a cross-linked structure formed by the reaction of melamine, citral and citric acid as shown in the following formula: ， The weight average molecular weight of the carbon-forming agent is 30,000-50,000.

5. Use of an organic acid in the preparation of the char-forming agent as claimed in claim 3, wherein the organic acid is at least one compound selected from the group consisting of citric acid, malic acid, lactic acid and salicylic acid.

6. A flame retardant, comprising the char-forming agent according to claim 3 or 4 and ammonium polyphosphate, wherein the weight ratio of the char-forming agent to the ammonium polyphosphate is (1-3): (1-10). 7 . The flame retardant according to claim 6 , further comprising ferric malate as a flame retardant synergist, wherein the weight ratio of the flame retardant synergist to the total amount of the char former and ammonium polyphosphate is (0.01-1):(15-35).

8. The use of the flame retardant according to claim 6 or 7, characterized in that The flame retardant is used in combination with polyethylene, polypropylene, polystyrene, nylon, polyester or polyurethane.

9. A flame retardant polypropylene material, comprising: 10-100 parts of polypropylene resin; 10-50 parts of flame retardant; Flame retardant synergist 0-1 part; Toughener 0-10 parts; Compatibilizer 0-5 parts; Other additives 0-5 parts; The flame retardant is the flame retardant according to claim 6, the flame retardant synergist is ferric malate, and other additives are antioxidants, lubricants or masterbatches.

10. A product prepared using the flame-retardant polypropylene material according to claim 9.

11. A method for preparing a flame-retardant polypropylene material, the method comprising mixing a polypropylene resin, the flame retardant according to claim 6, an optional flame retardant synergist, an optional toughening agent, an optional compatibilizer and optional other additives and extruding and granulating the mixture.

12. Use of the combination of the char-forming agent according to claim 3 or 4 and ferric malate in improving the flame retardant properties and mechanical properties of flame retardant polypropylene materials.

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