Preparation method of melamine polyphosphate

Abstract

The invention discloses a preparation method of melamine polyphosphate, which belongs to flame retardant production, and comprises the following steps: S1, forming an ammonium dihydrogen phosphate melamine diamide mixed solution; s2, forming a melamine polyphosphate intermediate; s3, performing thermal condensation reaction in a melamine phosphate intermediate thermal condensation reaction device to obtain melamine polyphosphate; comprising a kettle body and a stirring system used for stirring, the kettle body is composed of a kettle bottom, a kettle body and a kettle cover, a reaction cavity is defined by the kettle bottom, the kettle body and the kettle cover, a heat conduction oil jacket is arranged outside the kettle body and the kettle bottom, the heat conduction oil jacket is provided with a heat conduction oil inlet and a heat conduction oil outlet, a feeding port is formed in the kettle cover, and a discharging pipe is arranged on the kettle body. And a plurality of heat transfer solid spheres which are uniformly distributed during working are arranged in the reaction cavity. According to the invention, the phenomena of wall sticking and shaft sticking are avoided, the caking phenomenon is basically avoided, and condensed discharged materials can be directly screened.

Description

TECHNICAL FIELD

[0001] The present application relates to the production of flame retardants, in particular to a method for preparing melamine polyphosphate. BACKGROUND

[0002] Polymer materials are widely used in production and life. However, most of the polymer materials are easy to burn, so there is a serious fire hazard. In such an environment, it is particularly important to modify the polymer materials for flame retardation. Melamine polyphosphate, referred to as MPP, is a phosphorus-nitrogen intumescent flame retardant, which has good thermal stability, excellent flame retardant performance, good compatibility with the base material, no halogen, low smoke and low toxicity, etc. The flame retardant decomposes endothermically above 350℃, acting as a heat sink to cool the polymer. The released phosphoric acid further reacts with the polymer to form carbon and suppresses the release of free radical gases into the oxygen phase. At the same time, the nitrogen released by the degradation of melamine makes the carbon expand to further protect the polymer. It is suitable for use in functional materials such as engineering plastics, resins, polyurethane elastomers, etc. with higher processing temperature, and in fire-resistant coatings, coating layers of propellants, coating layers of electric wires, etc. It also has special applications in glass fiber reinforced nylon-66. Therefore, the research on melamine polyphosphate is of great significance.

[0003] At present, the synthesis methods for preparing melamine polyphosphate include one-step method and two-step method.

[0004] The one-step method is to directly synthesize melamine polyphosphate by reacting melamine with polyphosphoric acid under certain conditions. The problem of this method is that the hydrolysis of polyphosphoric acid is not easy to control, and the product quality is unstable.

[0005] The two-step method is to synthesize melamine phosphate intermediate by reacting melamine and phosphoric acid first, and then to prepare melamine polyphosphate by thermal condensation. The two-step method is the common synthesis process in China. Since melamine and phosphoric acid both have three active groups, the reaction mode is relatively complex at high temperature. Due to the great difference in equipment and process control, the polymerization degree of the obtained melamine polyphosphate is greatly different, the initial thermal decomposition temperature is low, and the product performance is unstable. At the same time, the reaction is a solid phase reaction, so the mass transfer and heat transfer are difficult, the wall sticking is serious, and the production has certain difficulty. CN118812452A discloses a process for preparing melamine polyphosphate by two-step method, in the first step, ammonium phosphate and melamine diacyl are added, wherein the ammonium phosphate ensures that the phosphate ions in the solution are excessive, and at the same time, excessive ammonium ions exist, so that it is not easy to generate by-products such as double melamine phosphate and double melamine phosphate during the synthesis process; the addition of trace melamine diacyl destroys the hydrogen bond balance in the reaction system, so that the reaction system is not easy to condense and other phenomena, reduces the viscosity of the reaction system, ensures the uniformity of the reaction, and thus obtains a melamine phosphate intermediate with high purity; CN118812452A better solves the problem of the first step, but the second step of CN118812452A is high-temperature reaction (i.e. sintering) of melamine phosphate intermediate in a rotary kiln. As a sintering device, the rotary kiln is the same as the hot air drying device, the paddle dryer, the kneader, the discharging machine and the like. The material in the reactor is easy to stick, which leads to slow heat transfer and adhesion on the shaft, resulting in unstable product performance and affecting the product quality. SUMMARY

[0006] In view of the above defects, the present application provides a preparation method of melamine polyphosphate, which has no wall sticking and shaft sticking phenomenon in the condensation reaction, and basically no caking phenomenon occurs. The condensation discharge can be directly screened.

[0007] The present application provides a preparation method of melamine polyphosphate.

[0008] The technical scheme is as follows: a preparation method of melamine polyphosphate, comprising the following steps:

[0009] S1, taking ammonium dihydrogen phosphate and melamine diacyl, mixing uniformly and dissolving in water to form an ammonium dihydrogen phosphate and melamine diacyl mixed solution;

[0010] S2, taking melamine, adding water, stirring and heating to 80-100℃; slowly adding the mixed aqueous solution of ammonium dihydrogen phosphate and melamine amide into the melamine solution, stirring while adding; then adding phosphoric acid into the melamine solution, stirring while adding; after the addition is completed, reacting for 1-4 hours; after the reaction is completed, cooling and crystallizing, filtering, drying, and crushing to obtain melamine polyphosphate intermediate;

[0011] S3, putting the melamine polyphosphate intermediate of S2 into a melamine phosphate intermediate thermal condensation reaction device to obtain melamine polyphosphate through thermal condensation reaction;

[0012] The melamine phosphate intermediate thermal condensation reaction device comprises a kettle body and a stirring system for stirring, the kettle body is composed of a kettle bottom, a kettle body and a kettle cover, the kettle bottom, the kettle body and the kettle cover form a reaction cavity, the kettle body and the kettle bottom are provided with a heat conducting oil jacket, the heat conducting oil jacket is provided with a heat conducting oil inlet and a heat conducting oil outlet, the kettle cover is provided with a feeding port, the kettle body is provided with a discharging pipe, and a plurality of heat transfer solid spheres uniformly distributed during work are arranged in the reaction cavity.

[0013] Optionally, the discharging pipe is connected to the kettle body near the kettle bottom, and a discharging valve is installed on the discharging pipe.

[0014] Optionally, the inlet of the discharging pipe is provided with a discharging grid filter screen.

[0015] Optionally, the heat transfer solid spheres are one or both of hollow stainless steel spheres and ceramic spheres.

[0016] Optionally, the diameter of the spheres is 5-20mm.

[0017] Optionally, the stirring system comprises a driving motor, a speed reducer, a stirring shaft and a plurality of stirring blades, the speed reducer is connected to the output shaft of the driving motor, the stirring shaft is connected to the output shaft of the speed reducer, the plurality of stirring blades are installed on the stirring shaft, the driving motor and the speed reducer are installed outside the kettle body, and the stirring shaft penetrates into the reaction cavity through the kettle cover downward; the rotating speed of the stirring shaft is 10-300r / min.

[0018] Optionally, the stirring system further comprises a bottom paddle, the bottom paddle is installed on the end of the stirring shaft and is close to the kettle bottom, and the part of the bottom paddle away from the stirring shaft is in an arc shape gradually away from the kettle bottom.

[0019] Optionally, the kettle cover is provided with a nitrogen inlet.

[0020] Optionally, the kettle cover is provided with an air outlet, a gas permeable cap is installed on the air outlet, and a water ring vacuum pump is installed on the outlet pipeline of the gas permeable cap.

[0021] Optionally, in S1-S2, the molar ratio of phosphoric acid to melamine is 0.9-1.2, the weight ratio of the mixture of ammonium dihydrogen phosphate and melamine diamide to melamine is 0.04-0.2, and the weight ratio of water to melamine is 3-10.

[0022] Optionally, in S3, the reaction is carried out at 250-270 degrees for 1-3 hours, at 270-90 degrees for 1-3 hours, and at 280-320 degrees for 1-5 hours, and the pressure is -0.05 MPa to 0.1 MPa. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0024] Figure 1 The figure is a schematic diagram of the overall structure of the melamine phosphate intermediate thermal condensation reaction device of the present application.

[0025] In the figure, 1 is a driving motor, 2 is a speed reducer, 3 is a bearing cooling circulating water outlet, 4 is a bearing cooling circulating water inlet, 5 is a feeding port, 6 is a nitrogen inlet, 7 is a gas-permeable cap, 8 is a water ring vacuum pump, 9 is a heat-conducting oil jacket, 10 is a heat-conducting oil outlet, 11 is an insulation layer, 12 is a discharge grid filter screen, 13 is a discharge valve, 14 is a base, 15 is a heat-conducting solid sphere, 16 is a heat-conducting oil inlet, 17 is a kettle body, 18 is a kettle cover, 19 is a reaction cavity, 20 is a stirring shaft, 21 is a stirring blade, and 22 is a bottom paddle. DETAILED DESCRIPTION

[0026] The present application will be further described below with reference to the drawings.

[0027] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", and "connection" should be understood broadly, for example, it can be a fixed connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are terms of reference and indicate the orientation or position of the illustrated object based on the orientation or position shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0029] The terms "first", "second", "third", "fourth" and the like used in the description and claims of the present application, and the above-mentioned drawings, if any, are used to distinguish similar objects, and do not necessarily indicate a particular order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0030] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] The technical solutions of the present application will be described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in some embodiments.

[0032] Please refer to Figure 1 , Figure 1 The overall structure of the melamine phosphate intermediate thermal condensation reaction device of the present application is shown in the figure.

[0033] The application relates to a melamine phosphate intermediate thermal condensation reaction device, which comprises a kettle body 17 and a stirring system for stirring, the kettle body 17 is composed of a kettle bottom, a kettle body and a kettle cover 18, the kettle bottom, the kettle body and the kettle cover 18 enclose a reaction cavity 19, a heat conducting oil jacket 9 is arranged outside the kettle body and the kettle bottom, the heat conducting oil jacket 9 is provided with a heat conducting oil inlet 16 and a heat conducting oil outlet 10, a feeding port 5 is arranged on the kettle cover 18, a discharging pipe is arranged on the kettle body 17, and a plurality of heat transfer solid spheres 15 are arranged in the reaction cavity 19 and are uniformly distributed during work.

[0034] Through the arrangement of the heat conducting oil jacket 9, the stirring system and the heat transfer solid spheres 15, the heat conducting oil jacket 9 provides the required temperature during the thermal condensation reaction of the melamine phosphate intermediate, the stirring system stirs and drives the materials in the reaction cavity 19 and the heat transfer solid spheres 15 to move, the heat transfer solid spheres 15 crush the bonded materials during movement, avoid incomplete reaction caused by bonding, and transfer heat among the materials, so that the local overheating phenomenon is avoided. The heat source adopted by the application is heat conducting oil, the outer wall of the kettle body is heated, so that the phenomenon of uneven heating of the materials on the outer wall is avoided, and the uniformity of the thermal polymerization reaction is ensured.

[0035] The skilled person should know that the kettle bottom is integrally formed with the kettle body, and the kettle cover 18 is detachably and sealingly connected with the kettle body, which is prior art, and the skilled person can manufacture and install according to needs.

[0036] In one or more specific embodiments of the application, in order to obtain better reaction effect, the heat transfer solid spheres 15 can be one or both of hollow stainless steel balls and ceramic balls, preferably ceramic balls, and the diameter of the spheres is 5-20 mm.

[0037] In one or more specific embodiments of the application, the stirring system comprises a driving motor 1, a speed reducer 2, a stirring shaft 20 and a plurality of stirring blades 21, the speed reducer 2 is connected with the output shaft of the driving motor 1, the stirring shaft 20 is connected with the output shaft of the speed reducer 2, the plurality of stirring blades 21 are installed on the stirring shaft 20, the driving motor 1 and the speed reducer 2 are installed outside the kettle body 17, and the stirring shaft 20 penetrates the kettle cover 18 downwards into the reaction cavity 19; the rotating speed of the stirring shaft 20 is 10-300 r / min.

[0038] In one or more specific embodiments of the application, the stirring system further comprises a bottom paddle 22, the bottom paddle 22 is installed on the end of the stirring shaft 20 and is close to the kettle bottom, and the section of the bottom paddle 22 far away from the stirring shaft 20 is an arc shape gradually far away from the kettle bottom. The bottom paddle 22 is arranged to continuously provide kinetic energy for the solid spheres 15 deposited on the kettle bottom, so that the solid spheres 15 can fully grind the agglomerates.

[0039] In one or more embodiments of the present application, the discharge pipe is connected to the kettle body near the kettle bottom, and a discharge valve 13 is installed on the discharge pipe. The discharge pipe is provided on one side of the side edge to facilitate the heat conduction oil of the bottom jacket portion, and the other side to mount the bottom paddle 22.

[0040] In one or more embodiments of the present application, in order to prevent the particle size of the discharge from being too large, the inlet of the discharge pipe is provided with a discharge grid filter screen 12.

[0041] In one or more embodiments of the present application, in order to ensure safe production, the top bearing of the stirring shaft 20 adopts a water-cooled jacket bearing seat, which is provided with a bearing cooling circulating water outlet 3 and a bearing cooling circulating water inlet 4. Through the water-cooled jacket bearing seat, the heat generated by the stirring work of the stirring shaft 20 is taken away in time, and the normal production is maintained.

[0042] In one or more embodiments of the present application, in order to improve the reaction effect, a nitrogen inlet 6 is provided on the kettle cover 18 for introducing protective gas during the reaction process to protect the reaction.

[0043] In one or more embodiments of the present application, in order to maintain the temperature of the reaction cavity 19, a heat preservation layer 11 is provided outside the heat conducting oil jacket 9.

[0044] In one or more embodiments of the present application, in order to effectively control the reaction temperature, a temperature control unit (not shown in the figure) is also provided. The temperature control unit is a prior art and can be directly purchased from the market. Those skilled in the art can also install it according to the needs without creating labor. The temperature control unit is used to monitor the temperature of the material in the reaction cavity 19, and the heat conducting oil in the heat conducting oil jacket 12 is controlled according to the temperature. When the temperature exceeds the threshold, the heat supply is reduced or increased.

[0045] In one or more embodiments of the present application, an air outlet is provided on the kettle cover 18, the air outlet is installed with a gas permeable cap 7, the outlet pipeline of the gas permeable cap 7 is installed with a water ring vacuum pump 8, a sintered plate filter element is arranged in the gas permeable cap 7, the filter element adopts 0.7Mpa inert gas pulse backflushing, the backflushing period is 30S, the aeration time is 1S, the sintered plate needs to be cleaned and replaced regularly, and the reaction conditions are not affected.

[0046] In the present application, under the control of the driving motor 1, the reaction material is fed through the feed inlet, heated by the heat source to generate a polymerization reaction, dispersed and re-polymerized under the action of the heat-conducting solid sphere 15, and the polymerization reaction is fast, uniform and complete. The water produced in the reaction is removed by the water ring vacuum pump 8 or carried out by nitrogen, so as to ensure the smooth progress of the polymerization reaction and reduce the material adhesion. After the reaction is completed, the prepared melamine polyphosphate product is discharged through the discharge pipe.

[0047] The melamine phosphate intermediate thermal condensation reaction device of the present application is installed on the base 14.

[0048] Example 1

[0049] A method for preparing melamine polyphosphate, comprising the following steps:

[0050] S1, take 88 grams of ammonium dihydrogen phosphate and melamine diamide (ammonium dihydrogen phosphate: melamine diamide weight ratio is 99:1), mix uniformly and then dissolve in 500 grams of water to obtain an ammonium dihydrogen phosphate-melamine diamide mixed solution.

[0051] S2, take 1260 grams of melamine, add 5000 grams of water, stir and heat to 90°C; slowly drop the ammonium dihydrogen phosphate-melamine diamide mixed solution into the melamine solution, stir while dropping, and control the dropping speed at 3-6 minutes; then drop 1150 grams of phosphoric acid (commercially available, 85wt% industrial phosphoric acid) into the melamine solution, stir while dropping, and control the dropping speed at 3 seconds / drop; after the dropping is completed, react at 90°C for 2 hours. After the reaction is completed, cool and crystallize, filter, wash 3 times with atomized water, then dry at 130 degrees for 4 hours, crush to obtain melamine polyphosphate intermediate.

[0052] S3, put the melamine polyphosphate intermediate of S2 into the melamine phosphate intermediate thermal condensation reaction device of the present application, start rotating (rotation speed 20 r / min), heat to 260°C, react for 2 hours, heat to 280°C, react for 2 hours, heat to 300°C, react for 4 hours, after the reaction is completed, turn off the heat conducting oil, naturally cool for 0.5-2h, reduce the temperature in the reaction cavity to the discharge temperature of 230-250 degrees, then discharge the material through the discharge pipe to the storage bin outside the system for further cooling, to obtain melamine polyphosphate.

[0053] In S3, continuously pass inert protective gas (nitrogen, flow rate 4 L / min), the pressure is -0.05 MPa to 0.1 MPa, the heat transfer solid spheres 15 are ceramic spheres, the sphere diameter is 10-15 mm, and the mass of the ceramic spheres is 7550 g. In this step, the generated water is carried out by nitrogen or a water ring vacuum pump.

[0054] In the condensation reaction process of S3 of the present application, there is basically no wall sticking and shaft sticking phenomenon, and there is basically no caking phenomenon. The discharge of S3 is a small particle size powder, which can be directly screened.

[0055] The melamine polyphosphate prepared in S3 is directly screened, and then analyzed for nitrogen (N) content, phosphorus (P) content, whiteness, and 1% thermal weight loss / °C. The results are shown in Table 1 below.

[0056] Comparative Example 1

[0057] The present comparative example is compared with Example 1, the difference being that S3 is: the melamine polyphosphate intermediate of S2 is put into a rotary furnace, rotation is started (rotation speed 20 r / min), the temperature is raised to 260°C, reaction is carried out for 2 hours, the temperature is raised to 280°C, reaction is carried out for 2 hours, the temperature is raised to 300°C, reaction is carried out for 4 hours, after the reaction is completed, the temperature is naturally lowered for 0.5-2 h, the temperature in the rotary furnace is lowered to the discharge temperature of 230-250°C, and then the product is discharged.

[0058] The reaction process of S3 is carried out under inert protective gas (nitrogen, flow rate 4 L / min), and the pressure is -0.05 MPa to 0.1 MPa.

[0059] During the condensation reaction process of the present comparative example S3, there is a relatively serious wall sticking and shaft phenomenon, and the caking phenomenon is serious, and the discharge of S3 needs to be crushed before screening.

[0060] After the melamine polyphosphate prepared from S3 is crushed and screened, the nitrogen (N) content, phosphorus (P) content, whiteness and 1% thermal weight loss / °C are analyzed, and the results are shown in Table 1.

[0061] Table 1

[0062] Sample Example 1 Comparative Example 1 Nitrogen content / % 41.5 40.13 Phosphorus content / % 14.42 14.57 Whiteness / % 96.1 94.3 1 % thermal weight loss / °C 358.3 347.8

[0063] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing melamine polyphosphate, characterized in that, Includes the following steps: S1, take ammonium dihydrogen phosphate and melamine diamide, mix them evenly and dissolve them in water to form a mixed solution of ammonium dihydrogen phosphate and melamine diamide; S2, take melamine, add it to water, stir and heat to 80-100℃; slowly add the mixed aqueous solution of ammonium dihydrogen phosphate and melamine diamide into the melamine solution while stirring; then add phosphoric acid dropwise into the melamine solution while stirring; after the addition is complete, react for 1-4 hours; after the reaction is complete, cool and crystallize, filter, dry, and pulverize to obtain melamine polyphosphate intermediate; S3, the melamine polyphosphate intermediate of S2 is placed in the melamine phosphate intermediate thermal condensation reaction device for thermal condensation reaction to obtain melamine polyphosphate. The melamine phosphate intermediate thermal condensation reaction device includes a vessel body (17) and a stirring system for stirring. The vessel body (17) consists of a vessel bottom, a vessel body and a vessel lid (18). The vessel bottom, vessel body and vessel lid (18) form a reaction chamber (19). A heat transfer oil jacket (9) is provided outside the vessel body and the vessel bottom. The heat transfer oil jacket (9) is provided with a heat transfer oil inlet (16) and a heat transfer oil outlet (10). A feed inlet (5) is provided on the vessel lid (18). A discharge pipe is provided on the vessel body (17). The reaction chamber (19) contains a number of heat transfer solid spheres (15) that are evenly distributed during operation.

2. The method for preparing melamine polyphosphate according to claim 1, characterized in that, The discharge pipe is connected to the bottom of the vessel body, and a discharge valve (13) is installed on the discharge pipe.

3. The method for preparing melamine polyphosphate according to claim 1, characterized in that, Its features are, The discharge pipe is equipped with a discharge grid filter screen (12) at the inlet.

4. The method for preparing melamine polyphosphate according to claim 1, characterized in that, The heat transfer solid sphere (15) is one or both of hollow stainless steel spheres and ceramic spheres.

5. The method for preparing melamine polyphosphate according to claim 4, characterized in that, The diameter of the sphere is 5 to 20 mm.

6. The method for preparing melamine polyphosphate according to claim 1, characterized in that, The stirring system includes a drive motor (1), a reducer (2), a stirring shaft (20), and several stirring blades (21). The reducer (2) is connected to the output shaft of the drive motor (1), and the stirring shaft (20) is connected to the output shaft of the reducer (2). Several stirring blades (21) are installed on the stirring shaft (20). The drive motor (1) and the reducer (2) are installed outside the vessel body (17). The stirring shaft (20) passes downward through the vessel cover (18) and enters the reaction chamber (19). The stirring shaft (20) rotates at a speed of 10 to 300 r / min.

7. The method for preparing melamine polyphosphate according to claim 6, characterized in that, The stirring system also includes a bottom blade (22), which is installed at the end of the stirring shaft (20) near the bottom of the vessel. The section of the bottom blade (22) away from the stirring shaft (20) is an arc shape that gradually moves away from the bottom of the vessel.

8. The preparation method of melamine polyphosphate according to claim 1, characterized in that, The vessel lid (18) is provided with a nitrogen inlet (6) or / and The vessel lid (18) is provided with an air extraction port, which is equipped with a vent cap (7), and a water ring vacuum pump (8) is installed on the outlet pipe of the vent cap (7).

9. The method for preparing melamine polyphosphate according to any one of claims 1-8, characterized in that, In S1 to S2, melamine is used as the reference, wherein the molar ratio of phosphate to melamine is 0.9 to 1.2, the weight ratio of the mixture of ammonium dihydrogen phosphate and melamine diamide to melamine is 0.04 to 0.2, and the weight ratio of water to melamine is 3 to 10.

10. The method for preparing melamine polyphosphate according to claim 9, characterized in that, In S3, the reaction time is 1-3 hours at 250-270 degrees Celsius, 1-3 hours at 270-90 degrees Celsius, and 1-5 hours at 280-320 degrees Celsius, with a pressure of -0.05MPa to 0.1MPa.

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