Alkylphosphonic acid complex salt, its preparation method and use

Abstract

The present invention discloses an alkylphosphonic acid complex salt, its preparation method, and its use. The alkylphosphonic acid complex salt is a complex salt comprising an alkylphosphonate, water of crystallization, and hydroxide ions, and may further comprise an alkylphosphonic acid hydrogen salt and / or a phosphite. When the complex salt is combined with aluminum diethylphosphinate as a flame retardant synergist to flame retardant PA66 and PA6, it can effectively improve the flame retardancy in the solidification phase, ensure a dense and complete carbon layer structure after combustion, and effectively reduce the tendency for mold deposits to form during the injection molding process of flame-retardant nylon, thereby expanding the application fields of flame-retardant nylon.

Description

[Technical Field]

[0001] The present invention relates to the technical field of organic synthesis, and specifically to alkylphosphonic acid complex salts and their preparation and use. [Background technology]

[0002] Aluminum phosphite is currently widely used as a flame retardant synergist due to its excellent flame retardant synergy with aluminum diethylphosphinate, as well as its low water solubility and low acidity. It exhibits excellent flame retardancy when used with glass fiber-reinforced engineering plastics, such as nylon and polyester. According to Chinese Patent CN104114485A, mixtures of aluminum hydrogen phosphite and aluminum salts are significantly more stable than pure aluminum phosphite. However, aluminum phosphite and aluminum hydrogen phosphite contain phosphorus-hydrogen bonds with strong reducing properties, resulting in poor thermal stability. Furthermore, during high-temperature decomposition, they are prone to generating phosphine gas, which is highly toxic and flammable in air, posing a significant safety risk. Furthermore, aluminum phosphite is an inorganic salt and has poor compatibility with polymer matrices. Therefore, increasing its addition as a flame retardant synergist significantly impacts the mechanical and processing properties of the matrix, significantly limiting its application.

[0003] Chinese Patent CN105646938A states that compared with aluminum phosphite, aluminum alkylphosphonate has a phosphorus-carbon bond instead of a phosphorus-hydrogen bond, which improves compatibility with resin matrix materials, and at the same time does not generate highly toxic and flammable phosphine gas during the decomposition process and has higher thermal stability.

[0004] Aluminum phosphite and alkyl aluminum phosphite act as flame retardant synergists for aluminum diethylphosphinate. Although they do not have excellent flame retardancy themselves, they can improve the flame retardancy of aluminum diethylphosphinate to some extent. The flame retardant system of aluminum alkylphosphonate and diethylaluminum phosphite can effectively reduce screw corrosion during resin processing, and the resulting flame-retardant polymer matrix has excellent whiteness.

[0005] The main cause of death during a fire is smoke. The higher the flame-retardant effect during the solidification phase, the greater the smoke reduction effect during a fire. In other words, for the same flame-retardant grade, the better the flame-retardant effect during the solidification phase, the more advantageous its application. In actual manufacturing processes, when flame-retardant PA66 and PA6 are used in combination with aluminum phosphite or aluminum alkylphosphonate and aluminum diethylphosphinate, mold deposits tend to occur during the injection molding process. Furthermore, the resulting materials have poor flame-retardant properties during the solidification phase, limiting their application. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to overcome the drawbacks of the prior art and to provide an alkylphosphonic acid complex salt which, when used in combination with aluminum diethylphosphinate as a flame retardant for flame-retardant PA66 and PA6, can reduce the generation of mold deposits during the injection molding process, and, in cooperation with aluminum diethylphosphinate, can significantly reduce the decomposition and gasification of aluminum diethylphosphinate, thereby enhancing the flame retardancy effect during the solidification phase in the flame retardancy of flame-retardant PA66 and PA6.

[0007] Another object of the present invention is to provide a method for producing the alkylphosphonic acid complex salt.

[0008] Another object of the present invention is to provide the use of said alkylphosphonic acid complex salt as a flame retardant synergist for diethylphosphinate.

[0009] To achieve the above object, the present invention is achieved by the following technical solutions.

[0010] An alkylphosphonic acid complex salt, characterized in that the structural formula is represented by formula (I): JPEG2026502066000002.jpg22128(I) (In formula (I), R is ethyl, x represents 2.25 to 2.99, y represents 0 to 0.39, z represents 0 to 0.10, a represents 0.02 to 1.0, and b represents 1.0 to 2.0, M is aluminum, n=2, and m=3.

[0011] The alkylphosphonic acid complex salt according to the present invention is a complex salt comprising an alkylphosphonate, water of crystallization, and hydroxide ions, and may further comprise an alkylphosphonic acid hydrogen salt and / or a phosphite. When the alkylphosphonic acid complex salt is combined with aluminum diethylphosphinate and used as a flame retardant in flame-retardant PA66 and PA6, the decomposition and gasification of aluminum diethylphosphinate can be significantly reduced, effectively improving the flame retardancy of the flame-retardant PA66 and PA6 during the solidification phase, and simultaneously reducing the generation of mold deposits during the injection molding process.

[0012] Preferably, x represents 2.45 to 2.90, y represents 0.05 to 0.09, z represents 0.01 to 0.10, and a represents 0.1 to 1.0.

[0013] Preferably, the particle size D50 of the alkylphosphonic acid complex salt is 1 to 100 μm.

[0014] The method for producing the alkylphosphonic acid complex salt includes the steps of reacting alkylphosphonic acid with aluminum hydroxide in water, followed by precipitation, filtration, washing, and drying at 105 to 120°C in that order to obtain the alkylphosphonic acid complex salt, and the reaction temperature is 60 to 150°C. When the reaction temperature is 60 to 130°C, a hydrogen alkylphosphonate is produced.

[0015] Preferably, the method for producing the alkylphosphonic acid complex salt further comprises the steps of mixing the alkylphosphonic acid with phosphorous acid, reacting the resulting mixture with aluminum hydroxide in water, and then sequentially carrying out precipitation, filtration, washing, and drying at 105 to 120°C to obtain the alkylphosphonic acid complex salt, wherein the reaction temperature is 60 to 150°C. The phosphite can be produced by mixing the alkylphosphonic acid with phosphorous acid, and then reacting the resulting mixture with aluminum hydroxide in water. Specifically, the alkylphosphonic acid can be produced by any one of the following methods.

[0016] First method: The alkylphosphonic acid diester is hydrolyzed under basic conditions to produce an alkylphosphonate, which is further oxidized to give an alkylphosphonic acid. Second method: Phosphorous acid is reacted with ethylene in an aqueous solution in the presence of an initiator to give an alkylphosphonic acid.

[0017] Specifically, the first method involves mixing diethyl ethylphosphonate with an aqueous sodium hydroxide solution, heating the mixture to 85-95°C, maintaining the temperature for 4-6 hours, and then cooling to obtain an ethyl phosphonate, and then adding an aqueous sulfuric acid solution to obtain ethyl phosphonic acid.

[0018] In the second method, solid phosphorous acid, water, and sodium persulfate are placed in an autoclave, and the autoclave is purged with nitrogen gas. Ethylene is supplied to maintain a constant pressure of 1.4-1.8 MPa using a pressure reducer. The autoclave is heated to 80-90°C and the temperature is maintained for 5-7 hours. During this 5-7 hour period, aqueous sodium persulfate solution is continuously added. The autoclave is then maintained at 85-95°C for 0.5-1.5 hours, and the autoclave is cooled and vented to obtain ethylphosphonic acid.

[0019] Preferably, the initiator is an organic persulfide.

[0020] The present invention protects the use of said alkylphosphonic acid complex salt as a flame retardant synergist for aluminum diethylphosphinate.

[0021] A composition comprising 1 to 7 parts by weight of the alkylphosphonic acid complex salt and 10 to 15 parts by weight of aluminum diethylphosphinate.

[0022] The present invention also covers the use of said composition as a flame retardant in flame retarding PA66, PA6.

[0023] A reinforced flame-retardant nylon comprising 45 to 65 parts by weight of PA66, 0 to 10 parts by weight of PA6, 20 to 30 parts by weight of glass fiber, 1 to 7 parts by weight of the alkylphosphonic acid complex salt, and 10 to 15 parts by weight of aluminum diethylphosphinate.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The alkylphosphonic acid complex salt according to the present invention is a complex salt comprising an alkylphosphonate, water of crystallization, and hydroxide ions, and may further comprise an alkylphosphonic acid hydrogen salt and / or a phosphite. When the alkylphosphonic acid complex salt is combined with aluminum diethylphosphinate as a flame retardant synergist to form a flame retardant, it can effectively reduce the decomposition and gasification of aluminum diethylphosphinate, improve the flame retardant effect in the polymer solidification phase, and ensure a dense and complete carbon layer structure after combustion. At the same time, when used in flame-retardant PA66 and flame-retardant PA, it can effectively reduce the generation of mold deposits during the injection molding process. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Comparative Example 6 after combustion. [Figure 2] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Comparative Example 7 after combustion. [Figure 3] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Comparative Example 8 after combustion. [Figure 4] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Comparative Example 9 after combustion. [Figure 5] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Comparative Example 10 after combustion. [Figure 6] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Comparative Example 11 after combustion. [Figure 7] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 8 after combustion. [Figure 8] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 9 after combustion. [Figure 9] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 10 after combustion. [Figure 10]1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 11 after combustion. [Figure 11] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 12 after combustion. [Figure 12] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 13 after combustion. [Figure 13] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 14 after combustion. [Figure 14] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 15 after combustion. [Figure 15] 1 is an electron microscope image of the surface carbon layer of the flame-retardant test piece produced in Example 16 after combustion. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be described in more detail below with reference to specific examples. These examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention. Unless otherwise specified, all test methods used in the following examples are conventional methods. Materials and reagents used are commercially available unless otherwise specified.

[0028] Example 1 The alkylphosphonic acid complex salt was produced by the following method including the following steps S1 and S2. Step S1: Solid phosphorous acid, water, and sodium persulfate were placed in an autoclave, followed by nitrogen gas substitution, and ethylene was supplied to maintain a constant pressure of 1.6 MPa using a pressure reducer. The autoclave was heated to 85°C and the temperature was maintained for 6 hours. During this 6-hour period, aqueous sodium persulfate solution was continuously added, and the temperature was then maintained at 90°C for another 1 hour. After cooling and venting, an aqueous ethylphosphonic acid solution was obtained. The aqueous sodium persulfate solution was prepared from 5 g of sodium persulfate and 20 g of water. Step S2: The aqueous solution of ethylphosphonic acid and aluminum hydroxide were mixed, placed in an autoclave, and reacted at T1°C for 2 hours. The mixture was then cooled and filtered, and the cake was washed three times with three times the amount of water and dried at T2°C until it reached a constant weight, yielding an alkylphosphonic acid complex salt.

[0029] Examples 2 to 5 The production methods of Examples 2 to 5 were the same as the production method of Example 1, except that in step S2, phosphorous acid was added to an aqueous solution of ethylphosphonic acid, and then mixed with aluminum hydroxide, and the mixture was placed in an autoclave and reacted at T1°C for 2 hours, followed by cooling and filtration in that order. The cake was washed three times with three times the amount of water, and then dried at T2°C until it reached a constant weight, thereby obtaining an alkylphosphonic acid complex salt.

[0030] Example 6 The production method according to Example 6 was the same as that of Example 1, except that the reaction temperature and the heat drying temperature in step S2 were different.

[0031] Example 7 The alkylphosphonic acid complex salt was produced by the following method including the following steps S1 and S2. Step S1: 166 g of diethyl ethylphosphonate was mixed with 800 g of a 15 wt % aqueous solution of sodium hydroxide, heated to 90°C, maintained at that temperature for 5 hours, and cooled to obtain an ethyl phosphonate salt. 735 g of a 20 wt % aqueous solution of sulfuric acid was added to obtain an aqueous solution of ethyl phosphonic acid. Step S2: The aqueous solution of ethylphosphonic acid and 61 g of aluminum hydroxide were mixed, placed in an autoclave, and reacted at 130°C for 2 hours. The mixture was then cooled and filtered, and the cake was washed three times with three times the amount of water and dried at 105°C until it reached a constant weight, yielding an alkylphosphonic acid complex salt.

[0032] The amounts of raw materials used and process parameters for Examples 1 to 6 are shown in Table 1.

[0033] Table 1: Amounts of raw materials used and process parameters for Examples 1 to 6 JPEG2026502066000003.jpg43170

[0034] Comparative Examples 1 to 3 The alkylphosphonic acid complex salt was produced by the following method including the following steps. Step S1: Solid phosphorous acid, water, and sodium persulfate were placed in an autoclave, followed by nitrogen gas substitution, and ethylene was supplied to maintain a constant pressure of 1.6 MPa using a pressure reducer. The autoclave was heated to 85°C and the temperature was maintained for 6 hours. During this 6-hour period, aqueous sodium persulfate solution was continuously added, and the temperature was then maintained at 90°C for another 1 hour. After cooling and venting, an aqueous ethylphosphonic acid solution was obtained. The aqueous sodium persulfate solution was prepared from 5 g of sodium persulfate and 20 g of water. Step S2: The aqueous solution of ethylphosphonic acid was neutralized with a 20% aqueous solution of sodium hydroxide to a pH of 7 to obtain an aqueous solution of sodium ethylphosphonate. Step S3: The aqueous solution of sodium ethylphosphonate was placed in an autoclave and heated to T3. The aqueous solution of aluminum sulfate was continuously added using a metering pump for 120 minutes to allow the reaction to proceed. The reaction mixture was then cooled and filtered, and the cake was washed three times with three times the amount of water. The cake was then dried at T4 until it reached a constant weight, yielding an alkylphosphonic acid complex salt.

[0035] Comparative Example 4 The production method of Comparative Example 4 was the same as those of Comparative Examples 1 to 3, except that in step S2, phosphorous acid was added to an aqueous solution of ethylphosphonic acid, and the solution was further neutralized with a 20% aqueous solution of sodium hydroxide to a pH of 7, thereby obtaining an aqueous solution of sodium ethylphosphonate / sodium phosphite.

[0036] The amounts of raw materials used and process parameters for Comparative Examples 1 to 4 are shown in Table 2.

[0037] Table 2 Raw materials and process parameters for Comparative Examples 1 to 4 JPEG2026502066000004.jpg33169

[0038] Comparative Example 5 The sample prepared in Example 4 was dried by heating at 150° C. until it reached a constant weight.

[0039] The particle diameter D50 of the alkylphosphonic acid complex salts produced in Examples 1 to 7 was 1 to 100 μm. The measurement method was to wet an appropriate amount of sample with a small amount of ethanol, add it to water, and gently stir it with a glass rod, and then measure it using a Malvern laser diffraction particle size distribution analyzer. The measurement results are shown in Table 3.

[0040] Table 3: Measurement results of D50 for each example JPEG2026502066000005.jpg15163

[0041] Regarding the alkylphosphonic acid complex salts produced in the above Examples 1 to 7 and Comparative Examples 1 to 5, 1 H-NMR spectroscopy was performed.

[0042] The method for measuring the water of crystallization is as follows: the produced alkylphosphonic acid composite salt is heated and dried, then quickly removed and placed in a desiccator, cooled to room temperature, and weighed to give m1; the alkylphosphonic acid composite salt is then heated and dried at 150°C until a constant weight is reached, then removed and quickly placed in a desiccator, cooled to room temperature, and weighed to give m0; the water of crystallization content is calculated as "crystallization water content = (m1 - m0) × M / (18 × m0)," where M is the molecular weight of the alkylphosphonic acid composite salt in a state free of water of crystallization.

[0043] The method for calculating hydroxide ions is as follows: After measuring the content of each component in the alkylphosphonic acid complex salt, the amount is calculated according to the formula a=m×n-2x-y-2z, specifically: (1) 1 x, y, and z were measured by H-NMR spectroscopy, (2) measuring the mass content of phosphorus in the alkylphosphonic acid complex salt according to GB11893-1989; (3) Determine the mass content of aluminum in alkylphosphonic acid complex salt according to GB5009.182-2017; (4) The molar ratio of phosphorus to aluminum was calculated using steps (2) and (3), and the mass content of hydroxide ions was calculated by the subtraction method using the results of step (1) and the measurement results of water of crystallization, to obtain the value of a (a = m × n - 2x - y - 2z).

[0044] The measurement results are shown in Table 4.

[0045] Table 4 Measurement results for Examples 1 to 7 and Comparative Examples 1 to 5 JPEG2026502066000006.jpg63155

[0046] As is clear from Table 4, all of the alkyl phosphonic acid complex salts produced by the present invention are complex salts containing alkyl phosphonate, water of crystallization, and hydroxide ions. The incorporation of alkyl phosphonic acid hydrogen salt can be controlled by changing the reaction temperature T1. When T1 is 60 to 130°C, the produced alkyl phosphonic acid complex salt contains alkyl phosphonic acid hydrogen salt, and when T1 is 130 to 150°C, the produced alkyl phosphonic acid complex salt does not contain alkyl phosphonic acid hydrogen salt. Furthermore, the presence or absence of phosphorous acid can be controlled to determine whether or not the alkyl phosphonic acid complex salt contains phosphite. In Comparative Examples 1 to 4, the alkyl phosphonic acid complex salts produced by first hydrolyzing an aqueous ethyl phosphonic acid solution under basic conditions and then subjecting it to a metathesis reaction with an aluminum salt did not contain hydroxide ions. In Comparative Example 5, the alkyl phosphonic acid complex salt produced in Example 4 was heated and dried at 150°C until it reached a constant weight, after which it no longer contained water of crystallization.

[0047] application In Comparative Examples 6 to 11 and Examples 8 to 16, commercially available aluminum phosphite and the alkylphosphonic acid complex salts produced in Comparative Examples 1 to 5 and Examples 1 to 7 above were used as flame retardant synergists, respectively, and blended with aluminum diethylphosphinate, glass fiber, PA66, and PA6, and extruded. The amounts of each component used in Comparative Examples 6 to 11 and Examples 8 to 16 are shown in Table 5. Aluminum diethylphosphinate, glass fiber, PA66, and PA6 were all commercially available products, and the raw materials used in the parallel tests were all the same commercially available raw materials.

[0048] Table 5: Amount of each component used (parts by weight) in Comparative Examples 6 to 11 and Examples 8 to 16 JPEG2026502066000007.jpg93169

[0049] Performance analysis The mold deposit phenomenon was observed during the manufacturing process of the materials produced in Comparative Examples 6 to 11 and Examples 8 to 16. After the flame retardancy measurements were completed, the burned samples were surface treated and the structure of the surface carbon layer after the sample combustion was observed using a scanning electron microscope. Regarding the mold deposit phenomenon, "none" means that the material generates no mold deposits during the manufacturing process, "very little" means that the material generates almost no mold deposits during the manufacturing process, "slightly little" means that the material generates a small amount of mold deposits during the manufacturing process, and "large" means that the material generates a large amount of mold deposits during the manufacturing process. (1) Vertical Burning: Measurements were conducted in accordance with the UL94-2006 standard. Five test specimens were prepared for each group, and the self-extinguishing time after the first ignition, the self-extinguishing time after the second ignition, the presence or absence of molten material dripping during the burning process, and the presence or absence of ignition of cotton were recorded. "V-0" means that after two 10-second burning tests on the test specimen, the fire was extinguished within 30 seconds and no molten material dripping occurred. "V-1" means that after two 10-second burning tests on the test specimen, the fire was extinguished within 60 seconds and no molten material dripping occurred. (2) 85°C, 85% RH, 168-hour precipitation measurement: The test piece was left at a temperature of 85°C and a humidity of 85% for 168 hours, then removed and its surface was observed with a scanning electron microscope for the presence or absence of precipitation. (3) Microstructure of the carbon layer: A 0.8 mm flame-retardant test piece was taken, and the process of igniting it for 10 seconds and then extinguishing it was repeated five times. The burned part of the test piece was then gold-plated. After gold plating, the surface carbon layer structure of the burned test piece was observed using a scanning electron microscope.

[0050] The measurement results are shown in Table 6 and FIGS.

[0051] Table 6. Measurement results for Comparative Examples 6 to 11 and Examples 8 to 16 JPEG2026502066000008.jpg38170

[0052] As can be seen from Table 6, when the alkylphosphonic acid complex salt according to the present invention is combined with aluminum diethylphosphinate to form a flame retardant and used to make PA6 and PA66 flame retardant, no mold deposits are generated during the injection molding process, and the resulting material has good flame retardancy.

[0053] As is clear from Comparative Example 6, when aluminum phosphite alone is combined with aluminum diethylphosphinate to form a flame retardant, mold deposits occur during the injection molding process when used to flame retard PA6 and PA66, and the flame retardancy of the resulting material only reaches Class V-1. As is clear from Comparative Example 7, when the alkylphosphonic acid complex salt prepared in Comparative Example 1, which contains only aluminum alkylphosphonate, is combined with aluminum diethylphosphinate to form a flame retardant, mold deposits occur during the injection molding process when used to flame retard PA6 and PA66, and the flame retardancy of the resulting material only reaches Class V-1. As is clear from Comparative Example 8, when the alkylphosphonic acid complex salt prepared in Comparative Example 2, which contains only aluminum alkylphosphonate and aluminum hydrogen alkylphosphonate, is combined with aluminum diethylphosphinate to form a flame retardant, mold deposits still occur during the injection molding process when used to flame retard PA6 and PA66. As is clear from Comparative Example 9, when the alkylphosphonic acid complex salt produced in Comparative Example 3, which contains only aluminum alkylphosphonate and water of crystallization, is combined with aluminum diethylphosphinate to form a flame retardant, mold deposits occur during the injection molding process when used to flame retard PA6 and PA66. Furthermore, when the alkylphosphonic acid complex salt of the present invention is used in combination with aluminum diethylphosphinate to form a flame retardant, the resulting material has equivalent mechanical properties to those produced when commercially available aluminum phosphite is combined with aluminum diethylphosphinate to form a flame retardant, and the formation of mold deposits during the injection molding process can be effectively reduced when used to flame retard PA6 and PA66.

[0054] As can be seen from Figures 7 to 15, when the alkylphosphonic acid complex salt according to the present invention was used in combination with aluminum diethylphosphinate to form a flame retardant for PA66 and PA6, the surface carbon layer structure of the flame-retardant test specimens after combustion became dense, effectively preventing flammable gases and free radicals from leaking out of the carbon layer, i.e., excellent flame-retardant performance in the solidification phase. As can be seen from Figures 1 to 6, when the alkylphosphonic acid complex salt not containing hydroxide ions and / or crystal water was used in combination with aluminum diethylphosphinate to form a flame-retardant for PA66 and PA6, the surface carbon layer of the flame-retardant test specimens after combustion was clearly missing and not dense, i.e., poor flame-retardant performance in the solidification phase. Furthermore, when the alkylphosphonic acid complex salts prepared in Comparative Examples 4 and 5 were used in combination with aluminum diethylphosphinate to form flame retardants for PA6 and PA66, mold deposits during the injection molding process were effectively reduced, but poor flame-retardant performance in the solidification phase limited its application.

[0055] Obviously, the above-described embodiments of the present invention are merely examples for clearly explaining the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art can make various other modifications and variations based on the above description. It is not necessary or possible to comprehensively list all embodiments here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. An alkylphosphonic acid complex salt, characterized in that the structural formula is represented by formula (I): (I) (In formula (I), R is ethyl, x represents 2.25 to 2.99, y represents 0 to 0.39, z represents 0 to 0.10, a represents 0.02 to 1.0, and b represents 1.0 to 2.0, M is aluminum, n=2, and m=3.

2. The alkylphosphonic acid complex salt according to claim 1, wherein x represents 2.45 to 2.90, y represents 0.05 to 0.09, z represents 0.01 to 0.10, and a represents 0.1 to 1.

0.

3. The alkylphosphonic acid complex salt according to claim 1, wherein the particle size D50 of the alkylphosphonic acid complex salt is 1 to 100 μm.

4. 2. The method for producing an alkylphosphonic acid complex salt according to claim 1, comprising the steps of reacting an alkylphosphonic acid with aluminum hydroxide in water, followed by precipitation, filtration, washing, and drying at 105 to 120°C in that order to obtain an alkylphosphonic acid complex salt, wherein the reaction temperature is 60 to 150°C.

5. The method for producing an alkylphosphonic acid complex salt according to claim 4, further comprising the steps of mixing an alkylphosphonic acid with phosphorous acid, reacting the resulting mixture with aluminum hydroxide and water, and then sequentially carrying out precipitation, filtration, washing, and drying at 105 to 120°C to obtain an alkylphosphonic acid complex salt, wherein the reaction temperature is 60 to 150°C.

6. a first method in which an alkylphosphonic acid diester is hydrolyzed under basic conditions to produce an alkylphosphonate, which is then oxidized to produce an alkylphosphonic acid; and A second method is to react phosphorous acid with ethylene in an aqueous solution in the presence of an initiator to obtain an alkylphosphonic acid; 5. The method for producing an alkylphosphonic acid complex salt according to claim 4, wherein the alkylphosphonic acid is produced by any one of the methods above.

7. Use of the alkylphosphonic acid complex salt according to any one of claims 1 to 3 as a flame retardant synergist for aluminum diethylphosphinate.

8. A composition comprising 1 to 7 parts by weight of the alkylphosphonic acid complex salt according to any one of claims 1 to 3 and 10 to 15 parts by weight of aluminum diethylphosphinate.

9. Use of the composition according to claim 8 as a flame retardant in making PA66 and PA6 flame retardant.

10. A reinforced flame-retardant nylon comprising 45 to 65 parts by weight of PA66, 0 to 10 parts by weight of PA6, 20 to 30 parts by weight of glass fiber, 1 to 7 parts by weight of the alkylphosphonic acid complex salt according to any one of claims 1 to 3, and 10 to 15 parts by weight of aluminum diethylphosphinate.

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