Tin fluorophosphate glass coated red phosphorus flame retardant and preparation method thereof

Abstract

The invention discloses a tin fluorophosphate glass coated red phosphorus flame retardant and a preparation method thereof. The product is formed by coating the surface of red phosphorus particles with a layer of tin fluorophosphate glass flame retardant. The preparation method comprises the following steps: (1) preparing low-melting-point tin fluorophosphate glass; (2) primarily mixing the crushed material obtained in the step (1) with red phosphorus, putting into a high-energy mill, and mixing and crushing under the protection of nitrogen; (3) heating the mixture powder obtained in the step (2) under a stirring condition, and forming a tin fluorophosphate glass coating layer on the surface of the red phosphorus particles; and (4) cooling the reaction in the step (3) while stirring to obtain the tin fluorophosphate red phosphorus flame retardant product. The technological process is short, operation and control are simple and convenient, and no three wastes are generated in the technological process. The red phosphorus coating layer prepared by the method has excellent chemical and thermal stability, and the prepared coating red phosphorus has better processability and flame retardance.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry and relates to an environmentally friendly preparation method of low-melting-point tin fluorophosphate glass coated with a red phosphorus flame retardant. Background Art

[0002] Red phosphorus, an allotrope of the element phosphorus and an inorganic polymer, has traditionally been used primarily in the manufacture of safety matches, fireworks, pesticides, and metal phosphides. Driven by the rapid growth in synthetic materials and the demand for halogen-free flame retardants, the use of phosphorus-based flame retardants is rapidly increasing. As a highly effective halogen-free flame retardant, red phosphorus is gradually expanding its application. However, red phosphorus presents significant safety and protection issues during production, storage, transportation, and use. It suffers from a low ignition point, is prone to spontaneous combustion, has explosive dust, and readily undergoes disproportionate reactions with airborne moisture to produce phosphorus oxyacids and release the highly toxic and flammable gas phosphine. Furthermore, when used as a flame retardant, red phosphorus improves its flame retardancy as its particle size decreases. However, these issues are exacerbated as the particle size decreases, severely impacting its processing, mechanical, and electrical properties when used with polymers. Furthermore, red phosphorus exhibits poor compatibility when mixed with polymers.

[0003] When red phosphorus is used as a flame retardant, the most effective and common way to overcome the above-mentioned problems is to microencapsulate red phosphorus. The principle is to use red phosphorus particles as the core material and form a coating layer on the outside as the wall material to wrap the red phosphorus particles, so that the red phosphorus is isolated from the outside world such as moisture and air, thereby achieving the purpose of stabilizing the red phosphorus. At the same time, it can greatly improve the mixing and processing performance between the red phosphorus flame retardant and the polymer.

[0004] In the current common red phosphorus microencapsulation process, red phosphorus is first dispersed in an aqueous phase and wet-milled. The resulting red phosphorus suspension of acceptable particle size is then treated using a sol-gel method. Depending on the wall material deposited on the surface of the red phosphorus particles, different microencapsulation methods are used, including inorganic, organic, organic-inorganic, and inorganic-organic. These methods, on the one hand, generate a large amount of wastewater containing inorganic or organic substances that requires treatment during the preparation process. On the other hand, a small number of extremely fine red phosphorus particles produced during the wet milling process can easily penetrate into the wastewater during filtration and washing, resulting in red phosphorus loss and making wastewater treatment extremely difficult.

[0005] Low melting point phosphate glass (LMP), a novel synergistic flame retardant for synthetic materials, has attracted attention due to its unique thermal behavior and chemical properties. LMP softens or melts at relatively low temperatures. When mixed with polymers and thermally processed, it forms a polymer-phosphate glass alloy. When this mixture burns, the phosphate glass forms a continuous glassy protective layer covering the material surface, significantly enhancing the stability of the carbonized layer and its oxygen and heat insulation properties. This phosphate glass exhibits a certain degree of fluidity and good processing compatibility at polymer processing temperatures. Furthermore, it contains the flame-retardant element phosphorus, which minimizes the processing properties of polymers when used for flame-retardant modification.

[0006] In "Low-melting phosphate glasses as flame-retardant synergists to epoxy: Barrier effects vs flame retardancy. Polymer Degradation and Stability. Volume 185, March 2021, 109495," significant improvements in flame retardancy were observed in epoxy resin (EP) composites containing low-melting-point phosphate glass (LMP). EP / 9% APP (polyphosphate) / 1% (LMP) achieved a V0 rating in the UL-94 test, and the peak heat release rate was approximately 40% lower than that of EP / 10% APP in the cone calorimeter test. The results indicate that LMP glass primarily exhibits a physical barrier effect in condensed-phase flame retardancy. By simulating different combustion temperatures, LMP glass revealed different flame retardant properties. The mechanism was further elucidated: matching the phase transition temperature range of LMP glass with the combustion temperature helps optimize flame retardancy.

[0007] In U.S. Patent No. 4,544,695A, "Low melting phosphate-sulfate glasses as intumescent flame and / or smoke retardants for polymers," a low-melting-point phosphate-sulfate glass mixture added to a polymer exhibits a good flame retardant effect. This is because the expansion of the char layer formed after combustion enhances the flame retardant properties.

[0008] In "Development of new sustainable inorganic flame retardant additive system for polyamide 6,6 with improved performance. polymer engineering and science Volume 55, Issue 8 August 2015 Pages 1741-1748", the effects of a new environmentally friendly inorganic low-melting-point phosphate glass (LMP) flame retardant on nylon 66 (PA66) were reported. When added to the polymer nylon 66, it was shown that the inorganic phosphate glass was well dispersed in the PA66 matrix, reducing the peak heat release rate and total heat release of the mixture PA66 / inorganic phosphate glass. The low-melting-point phosphate glass effectively formed a glassy char layer during combustion. It was found that the low-melting-point inorganic phosphate glass was an extremely effective flame retardant for nylon 66.

[0009] In “Development of New Sustainable Inorganic Flame Retardant Additive System for Polyamide 6,6 With Improved Performance. Polymer Engineering&ScienceVolume 55, Issue 8 pp. 1741-1748”, the rheological properties of tin fluorophosphate glass and nylon 66 composites were studied. Scanning electron microscopy showed that tin fluorophosphate glass and nylon 66 exhibited good compatibility at higher temperatures. Cone calorimetry data showed that tin fluorophosphate glass reduced the peak heat release rate and the total amount of heat released of nylon 66. Tin fluorophosphate glass-nylon 66 formed a glassy char layer during combustion.

[0010] In "Effect of Different Phosphate Glass Compositions on the Process-Induced Macromolecular Dynamics of Polyamide 66. Polymers 2020, 12(5), 1179", the mechanism of action of the tin fluorophosphate system on nylon 66 was studied. Tin fluorophosphate can catalyze the simultaneous breakage and crosslinking reaction of nylon 66 chains, forming a mixture of distinct crosslinked and depolymerized native amide end chain fragments, confirming the strong interaction between nylon 66 and the tin fluorophosphate system. From the perspective of flame retardancy, this will help form an efficient glassy carbon barrier layer on the surface of nylon 66. Summary of the Invention

[0011] The present invention aims to provide a method for preparing a red phosphorus flame retardant with a short process flow, simple and convenient operation, safety, and easy industrialization. The low-melting-point tin fluorophosphate glass-coated red phosphorus flame retardant prepared by the method has excellent stability, processability, and flame retardancy. The coating process does not involve the problem of three wastes, and is an environmentally friendly clean production process.

[0012] The present invention uses phosphate glass with a low glass transition temperature and melting point to coat red phosphorus, in particular tin fluorophosphate glass. The tin fluorophosphate glass and red phosphorus are mixed and crushed by a solid-state mechanochemical method. Under the temperature condition that is higher than the glass transition temperature of the tin fluorophosphate glass and lower than the ignition point of the red phosphorus, the tin fluorophosphate glass is attached to the surface of the red phosphorus to form a continuous and dense coating layer, thereby achieving the coating of the red phosphorus with tin fluorophosphate.

[0013] Tin fluorophosphate glass is commonly used in lead-free packaging for electronic materials. It has a low coefficient of thermal expansion, making its stability less affected by temperature fluctuations. When coated with red phosphorus, it forms a dense and stable coating. It can evenly melt onto the surface of red phosphorus particles to form a continuous phosphate glass coating, effectively encapsulating the particles and preventing oxidation or disproportionation reactions at higher temperatures. This results in a coated red phosphorus with high chemical and thermal stability.

[0014] The tin fluorophosphate glass used in the present invention has a glass transition temperature below 150°C, and under many conditions, due to changes in its composition, its glass transition temperature can be lower than 130°C. This characteristic allows the coating process to be carried out at a temperature far below the ignition point of red phosphorus, making the process highly safe. Generally speaking, tin fluorophosphate glass with a lower glass transition temperature has a lower melting point (200°C-250°C). However, when the polymer to which the tin fluorophosphate glass is added is heat-processed (for example, the heat processing temperature of nylon 66 is approximately 280°C), the processing temperature is higher than the melting point of the tin fluorophosphate, ensuring that the tin fluorophosphate glass is in a molten state. Compared with other non-melting red phosphorus coatings, the tin fluorophosphate glass can evenly melt on the surface of the red phosphorus particles under shear and mixing conditions with the polymer to form a continuous tin fluorophosphate glass coating, thereby effectively protecting the stability of the coating on the red phosphorus particles.

[0015] When added to a polymer, the tin fluorophosphate glass-coated red phosphorus flame retardant obtained by the present invention exhibits good fluidity and compatibility with nylon 66 during extrusion, injection molding, mixing, and thermal processing. The tin fluorophosphate glass has high dispersibility in nylon 66, significantly improving the chemical stability and process safety of the tin fluorophosphate-coated red phosphorus flame retardant during thermal processing of nylon 66.

[0016] The tin fluorophosphate glass-coated red phosphorus flame retardant will form an efficient glassy carbon barrier layer on the surface of nylon 66 when burning, thereby reducing the peak heat release rate and the total amount of heat released of nylon 66, and improving the flame retardant properties of the overall tin fluorophosphate glass-coated red phosphorus / nylon 66 system.

[0017] The tin fluorophosphate glass red phosphorus flame retardant of the present invention is realized by the following technical solution: tin fluorophosphate glass with a low glass transition temperature and melting point is used, and a tin fluorophosphate glass coating layer is coated on the surface of red phosphorus with an average particle size of less than 20 microns. The weight fraction of the coating layer formed by the tin fluorophosphate glass in the product is between 10% and 25%.

[0018] The product is prepared by the following steps: Step (1): SnF2, SnO, and Ammonium Polyphosphate (NH4PO3) n The raw materials, tin pyrophosphate (Sn2P2O7), ammonium fluoride (NH4F), and stannous pyrophosphate (Sn2P2O7), are mixed and crushed in a specific ratio. The mixture is then placed in a nickel crucible and melted in a high-temperature electric furnace at 450°C. This process releases water and ammonia, ensuring the complete melting of the raw materials and forming a uniform molten glass. The crucible containing the molten glass is then removed and slowly cooled to room temperature. Finally, the cooled glass mass is processed into a fine glass powder using a pulverizer, resulting in low-melting-point tin fluorophosphate glass powder. Step (2): mixing the tin fluorophosphate glass and red phosphorus obtained in step (1) so that the weight fraction of the tin fluorophosphate glass coating layer in the product is 10%-25%, respectively, and loading them into four 4L ball mills pre-placed with stainless steel balls and replaced with nitrogen, vibrating and covering the ball mills, and loading them into a vertical planetary mill for crushing to an average particle size of less than 20 μm, with a mixing and crushing time of 0.5 hour to 1 hour. After crushing, the ball mills are removed from the ball mills and the grinding balls are separated to obtain a mixed powder of the tin fluorophosphate glass and red phosphorus; Step (3): Under nitrogen protection, the mixed powder obtained in step (2) is heated and stirred in a mixing device with a temperature control function for heat treatment, and the tin fluorophosphate glass forms a coating layer on the surface of the red phosphorus particles; wherein the heat treatment temperature is 150°C to 180°C, and the time is 0.5 hour to 1 hour; Step (4): Cooling the material after heat treatment in step (3) to room temperature to obtain a tin fluorophosphate coated red phosphorus flame retardant product.

[0019] In step (2), the average particle size of the material is controlled to be less than 20 microns. If the particle size is too large, the resulting microencapsulated red phosphorus product will have a large particle size, which will deteriorate the uniformity of dispersion with the polymer when used as a flame retardant. If the particle size is too small, the energy consumption of the pulverization process will increase, the surface activity of the red phosphorus will increase, and the process will be more dangerous. In addition, the corresponding coating amount must be large, which will reduce the red phosphorus content and thus affect the flame retardant properties of the final product.

[0020] In the present invention, the high-energy pulverizing equipment can be a stirred mill, a planetary mill, a ball mill, a vibration mill, etc., and the temperature-controlled mixing equipment can be a ribbon mixer, an internal mixer, a kneader, etc.

[0021] Furthermore, the heating and removing of volatile components in the mixture in step (1) is carried out in a high-temperature oven; the heat treatment of the mixture powder in step (3) and the cooling of the mixture powder in step (4) are carried out by indirect heating or cooling with thermal oil, and are carried out in the same equipment.

[0022] The selection of chemical composition of low-melting-point tin fluorophosphate glass is particularly important, which determines many physical and chemical properties of low-melting-point tin fluorophosphate glass and the performance of microencapsulated red phosphorus products coated with it. In the present invention, the phosphorus pentoxide content in the low-melting-point tin phosphate glass is more preferably between 26% and 32%. If the phosphorus pentoxide content is lower than 25%, its glass transition temperature and melting point increase, and it is difficult to form a uniform and dense coating layer on the surface of red phosphorus in step (3); if the phosphorus pentoxide content is higher than 32%, its glass transition temperature and melting point are lower, and in step (2), the mixture has a certain viscosity, making it difficult to crush. In step (3), the agglomeration of the various parts of the material during heating also affects the coating uniformity. In addition, since the low-melting-point tin fluorophosphate glass with a high phosphorus pentoxide content has a certain hygroscopicity, it is difficult to use it as a coating. The stability of the microencapsulated red phosphorus in the coating layer is greatly reduced; the fluorine content in the low-melting-point tin phosphate glass is more preferably between 7% and 12%. If the fluorine content is lower than 7%, its glass transition temperature and melting point increase, making it difficult to form a uniform and dense coating layer on the surface of the red phosphorus in step (3). If the fluorine content is higher than 12%, its glass transition temperature and melting point are lower. In step (2), the mixture has a certain viscosity, making it difficult to crush. In step (3), the heating of the various parts of the material agglomerates, affecting the coating uniformity. In addition, the addition of a large proportion of fluorine source to the raw materials causes a large amount of fluorine volatilization during the glass melting process, resulting in losses and also affecting the environment. Since a small amount of fluorine still volatilizes when heated, the microencapsulated red phosphorus using it as a coating layer has occupational health and environmental problems during polymer thermal processing (extrusion, injection molding, etc.).

[0023] The mass fraction of low-melting-point tin fluorophosphate glass in the encapsulated red phosphorus product is 10%-25%. When it is less than 10%, it is difficult to form a uniform and dense coating layer on the surface of the red phosphorus in step (3) with less coating material; when it is higher than 25%, a large amount of coating material in step (3) easily causes the mixture to agglomerate and affects the uniformity of the coating. Generally speaking, when the glass transition temperature of the low-melting-point tin fluorophosphate glass is low, its mass fraction in the microencapsulated red phosphorus is at a lower limit. If the glass transition temperature of the low-melting-point tin fluorophosphate glass is high, its mass fraction in the microencapsulated red phosphorus flame retardant is at a higher limit. There is no special restriction on the tin content. Tin, as a cation that balances fluorine and phosphorus pentoxide, makes the pH value of the tin fluorophosphate glass greater than 6, which can make the tin fluorophosphate coating non-acidic. If the coating is acidic, the stability of the coated red phosphorus flame retardant with the tin fluorophosphate glass coating is poor. DETAILED DESCRIPTION

[0024] The protection content of the present invention is described in detail through the following specific implementation methods. The specific embodiment described in detail is only an example within the scope defined in the claims and is only used for a specific example and does not represent the full scope of protection required by the claims.

[0025] The raw materials used in the present invention are as follows: Tin fluoride: produced by Suzhou Yongda Fine Chemical Co., Ltd. SnF2≥99% Ammonium polyphosphate: produced by Hubei Lianxing Chemical Co., Ltd. P205≥72% Stannous pyrophosphate: Jiangxi Ganzhou Baita Metal Materials Co., Ltd. Sn2P207≥98% Ammonium fluoride: Shandong Yinglang Chemical. NH4F≥99% Stannous oxide: Wuxi Fanchuan Tin Industry Co., Ltd. SnO ≥ 99% Industrial red phosphorus: produced by Yunnan Jianglin Group Co., Ltd., with an average particle size of less than 100 microns PA66: DuPont, brand 101F Fiberglass: Jushi Group Co., Ltd. ECS14-4.5-588 Equipment used for flame retardant evaluation of flame retardants Extruder: TSH-35B from Nanjing Tengdahe Machinery Equipment Co., Ltd. Injection molding machine: SA860 / 26G from Haitian Plastic Machinery Group Co., Ltd. UL94 horizontal and vertical combustion test machine: Guangzhou Automation Equipment Co., Ltd. GC-UL-A Flame retardant performance evaluation: The flame retardant was mixed with nylon 66 and glass fiber in a certain proportion. The pellets were drawn into strips in an extruder, cooled, crushed, and dried to obtain flame-retardant nylon 66 granules. Experimental specimens were made using an injection molding machine. 1.6 mm thick specimens were selected for UL-94 rating using the vertical method specified in the "Standard for the Determination of Combustion Properties of Plastics - Horizontal and Vertical Methods" (GB / T 2408-2008).

[0026] Determination of tin fluorophosphate glass indicators Determination of glass transition temperature of tin fluorophosphate glass: Differential scanning calorimetry according to GB / T3600.2-2018 Determination of fluorine and phosphorus content in tin fluorophosphate glass: A certain amount of tin fluorophosphate glass was weighed and dissolved in dilute hydrochloric acid. The solution was kept warm and dissolved. The tin fluorophosphate glass was dissolved. The phosphorus pentoxide content of the dissolved sample was determined according to the general method for determination of phosphorus pentoxide content in inorganic chemical products GB / T23843-2009, and the fluorine content was determined according to the general method for determination of fluorine content in inorganic chemical products using ion selective electrode method, GB / T21057-2007.

[0027] Determination of coating content: Weigh 10 grams of coated red phosphorus and add it to 200 grams of dilute hydrochloric acid (10%). Place it in a 70°C water bath and keep warm for 2 hours until the coating dissolves. After filtering, wash it twice with dilute hydrochloric acid, then wash the filter cake several times with distilled water. Vacuum dry the filter cake and weigh the filter cake to obtain the weight of the red phosphorus. Calculate the coating content.

[0028] PH value determination: Accurately weigh 10.0 g of the final product into a 200 ml beaker, add 90 ml of distilled water, stir continuously for 10 minutes, and then measure the pH using a PHSJ-4A laboratory pH meter produced by Shanghai Yidian Scientific Instrument Co., Ltd.

[0029] Particle size analysis: Zhuhai OMEC LS-909 laser particle size analyzer was used for particle size determination.

[0030] Determination of phosphine generation: Accurately weigh 10.00 g of sample and suspend it in a 500 mL three-necked flask containing 100 mL of distilled water. A condenser reflux device is installed at the flask outlet, maintaining the vapor phase outlet temperature below 30°C. The flask is heated in a 120°C silicone oil bath for 2 hours. Driven by nitrogen, the generated phosphine reacts with HgCl to form insoluble P(HgCl)₃. P(HgCl)₃ is oxidized by iodine, and the excess iodine is titrated with sodium thiosulfate. The amount of phosphine released per gram of red phosphorus per hour is calculated, expressed in μg / g.h.

[0031] Step (1) Preparation of low melting point tin fluorophosphate glass: Weigh tin fluoride, ammonium polyphosphate, tin oxide, and tin pyrophosphate as shown in Table 1. Mix the ammonium fluoride evenly according to the formula ratio and crush to obtain a mixture. Place the mixture in a nickel crucible and place it in a high-temperature electric furnace. Heat it to approximately 250°C at a heating rate of 5°C / min. Hold the temperature for 15 minutes and vent the system gas. Subsequently, heat it to approximately 450°C at a heating rate of 10°C / min and hold the temperature for 1 hour to obtain a clear glass liquid. After cooling, crush the mixture and pass it through a 200-mesh sieve to obtain a low-melting-point tin fluorophosphate glass powder.

[0032] Table 1 lists four embodiments of the present invention, in which the proportions of the fluorophosphate glass components are expressed by weight.

[0033] Table 1: Raw material ratios of tin fluorophosphate glass and determination of tin fluorophosphate indicators

[0034] Examples 1-1 to 1-8

[0035] Step (2): Mixing and crushing The tin fluorophosphate glass and red phosphorus obtained in step (1) are mixed in the product according to the ratio shown in Table 2 to form a coating layer of the tin fluorophosphate glass. The mixture is then loaded into four 4L ball mills that have been pre-filled with stainless steel balls and replaced with nitrogen. After compaction, the ball mills are covered and placed in a vertical planetary mill for pulverization. After varying the crushing time, the average particle size is controlled to be less than 20 μm. After pulverization, the ball mills are removed and the grinding balls are separated to obtain a pulverized mixture.

[0036] Table 2 Grinding conditions in step (2), heat treatment in step (3), finished product particle size, and finished product flame retardant number

[0037] Step (3): Heat treatment coating The mixture obtained in step (2) is placed in a temperature-controlled mixing device, heated to the desired temperature, and heat-treated for a certain period of time under nitrogen protection and stirring conditions to form a coating layer on the surface of the red phosphorus particles with low melting point tin fluorophosphate glass powder.

[0038] Step (4): Cooling of finished product The material after heat treatment in step (3) is cooled to room temperature to obtain a low melting point tin fluorophosphate coated red phosphorus flame retardant product. The test results of the relevant products are listed in Table 3. Table 3 Product-related test results

[0039] From the above product test results, it can be seen that the coated red phosphorus product obtained by adopting the scheme of the present invention has a low amount of phosphine generation and a pH value close to neutral. Therefore, the obtained coated red phosphorus product has good stability.

[0040] Step (2) was carried out in a vertical planetary mill equipped with four 4 L stainless steel ball mill jars, using stainless steel balls as the grinding media.

[0041] Steps (3) and (4) are carried out in the same 5L kneader with a jacket, in which heat-conducting oil is used to heat or cool the material, and a temperature detection and display device is provided; The low glass transition temperature of the low-melting tin fluorophosphate glass allows the coating process to be carried out at lower temperatures, preventing oxidation or disproportionation of red phosphorus at high temperatures, significantly improving the chemical and thermal stability and process safety of the coated red phosphorus. Furthermore, the low glass transition temperature of the tin fluorophosphate glass during coating facilitates the formation of a uniform, thin coating structure around the red phosphorus. This low-melting-point coating effectively improves the uniformity of the red phosphorus dispersion in the nylon matrix and reduces agglomeration, thereby achieving excellent flame retardancy at a low addition rate while maintaining optimal mechanical and processing properties. Compared to other non-melting red phosphorus coatings, the tin fluorophosphate coating exhibits higher mechanical stability under the continuous shear mixing of the screw, significantly reducing cracking or flaking, ensuring a stable and uniform distribution of the red phosphorus coating and maintaining the long-term flame retardancy of the nylon. The tin fluorophosphate glass and red phosphorus flame retardant work synergistically, forming a protective tin fluorophosphate glass-phosphate-carbon layer on the nylon surface during combustion, enhancing the flame retardancy of the nylon.

[0042] Flame retardant test examples 2-1 to 2-16

[0043] Flame retardant test and evaluation of nylon 66 Test sample preparation A certain amount of nylon 66, glass fiber and the finished flame retardant prepared in the embodiment were weighed respectively, placed in a mold bag and manually shaken to mix evenly, stretched, cooled and granulated in an extruder, dried in an oven and then injection molded in an injection molding machine. A 1.6 mm sample was selected as a test piece.

[0044] Flame retardant performance test Place the test piece in a UL94 horizontal and vertical combustion tester and test three times using the vertical method. Take the average value as the measured value. Perform the UL-94 rating according to the "Standard for the Determination of Burning Properties of Plastics - Horizontal and Vertical Methods" (GB / T2408-2008).

[0045] Table 4 Material ratio and flame retardant rating results of flame retardant nylon test pieces

[0046] From the above flame retardancy test, it can be seen that the flame retardant obtained by the scheme of the present invention has good flame retardancy when added to nylon 66, and better flame retardancy is obtained at a lower addition amount.

[0047] In summary, the tin fluorophosphate red phosphorus flame retardant prepared by the present invention has excellent chemical and thermal stability. When added to nylon 66, it has good dispersibility during thermal processing and can obtain better flame retardant properties at a lower addition amount.

Claims

1. Fluorophosphate tin glass coated with red phosphorus flame retardant, characterized by: A tin fluorophosphate glass coating layer with a low glass transition temperature is coated on the surface of red phosphorus with an average particle size of less than 20 microns.

2. The tin fluorophosphate glass coated red phosphorus flame retardant according to claim 1 is characterized in that: The glass transition temperature of the tin fluorophosphate glass is less than 130°C; the mass fraction of the tin fluorophosphate glass coating layer in the product is 10%-25%.

3. The tin fluorophosphate glass coated red phosphorus flame retardant according to claim 1, characterized in that: The mass fraction of phosphorus pentoxide in tin fluorophosphate glass is 26% to 32%, and the mass fraction of fluorine is 7% to 12%.

4. The method for preparing tin fluorophosphate glass coated with red phosphorus flame retardant according to claim 1, 2 or 3, characterized in that: The following steps are involved: (1) After crushing and mixing the tin source, phosphorus source and fluorine source in a certain proportion, heating to 250°C and keeping the temperature for 15 minutes, then heating to 450°C, melting and keeping the temperature for 1 hour, removing the volatile matter, cooling and crushing to obtain tin fluorophosphate glass powder with a low glass transition temperature for use; (2) After mixing the low glass transition temperature tin fluorophosphate glass powder with red phosphorus, the mixture is placed in a high-energy mill under nitrogen protection for mixing and crushing; the average particle size of the mixture is less than 20 microns, and the mass fraction of the low glass transition temperature tin fluorophosphate glass powder in the mixture is 10% to 25%; (3) placing the mixture powder obtained in step (2) in a temperature-controlled mixing device and heating it to 150-180° C. under nitrogen protection; heat treating it for 30-60 minutes under stirring conditions to form a coating layer of low glass transition temperature tin fluorophosphate glass on the surface of red phosphorus; (4) Cooling the mixture heat-treated in step (3) to room temperature under stirring to obtain a microencapsulated red phosphorus product coated with tin fluorophosphate having a low glass transition temperature.

5. The method for preparing tin fluorophosphate glass coated with red phosphorus flame retardant according to claim 4, characterized in that: The heating and removing of volatile components in the mixed material in step (1) is carried out in a high-temperature oven; the heat treatment of the mixed powder in step (3) and the cooling of the mixed powder in step (4) are carried out by indirect heating or cooling with heat-conducting oil, and are carried out in the same equipment.

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