Intrinsic flame-retardant nylon resin and preparation method thereof

Abstract

The invention provides intrinsic flame-retardant nylon resin and a preparation method thereof. The preparation method comprises the following steps: S1, preparing reaction monomers into a monomer aqueous solution, wherein the reaction monomers comprise a reaction type flame-retardant monomer, binary acid and diamine; wherein the reactive flame-retardant monomer comprises one or a combination of two of 2, 4, 6-tris (4-aminophenyl)-1, 3, 5-triazine and 2, 4, 6-tris [(p-carboxyphenyl) amino]-1, 3, 5-triazine, and the reactive flame-retardant monomer comprises one or a combination of two of 2, 4, 6-tris [(p-carboxyphenyl) amino]-1, 3, 5-triazine; the reactive flame-retardant monomer accounts for 1-50% of the reactive monomer in percentage by mass; s2, carrying out prepolymerization reaction on the monomer aqueous solution to obtain a nylon prepolymer; and S3, carrying out melt extrusion treatment on the nylon prepolymer to obtain the intrinsic flame-retardant nylon resin. The intrinsic flame-retardant nylon resin has good flame retardant property and mechanical property.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular, to an intrinsically flame-retardant nylon resin and a preparation method thereof. Background Art

[0002] In recent years, electronic and electrical products have been continuously developing towards integration and miniaturization. At the same time, higher requirements have been put forward for the electronic component assembly technology, making lead-free reflow soldering (SMT) an important assembly method. However, lead-free reflow soldering requires components to be exposed to high temperatures of 250-280°C for a long time, and the resin materials used must have excellent heat resistance to meet the requirements. Traditional engineering plastics (such as PA66, PBT, etc.) simply cannot meet this requirement due to their relatively low melting points, and high-temperature engineering plastics have emerged as the times require. Semi-aromatic polyamides (PPAs), also known as high-temperature nylons, are widely used in the connector field due to their high melting points, high heat distortion temperatures, high strengths, etc. Semi-aromatic nylons can be divided into two categories: long-chain and short-chain. Long-chain semi-aromatic nylons, such as PA10T, PA12T, and PA14T, are obtained by condensing long-chain diamines with terephthalic acid; short-chain semi-aromatic nylons, such as PA4T, PA5T, and PA6T, are obtained by condensing short-chain diamines with terephthalic acid. Nylon materials are easy to burn, especially after adding glass fibers, because the "wick effect" caused by adding glass fibers to the resin will further reduce the flame-retardant performance of nylon materials. In order to meet the high flame-retardant performance requirements in different scenarios, it is often necessary to carry out flame-retardant modification on nylon resins to achieve the fire prevention function of nylon.

[0003] The flame-retardant modification of nylon mainly includes blending flame-retardant modification and copolymerization flame-retardant modification. Currently, the method of blending flame-retardant modification is widely used. Traditional halogen-containing flame-retardant materials have been widely used due to their low cost and high strength, but they will produce a large amount of toxic gases when burned, causing health hazards and damaging the environment and ecological systems. Since semi-aromatic nylons have relatively high melting points, almost all halogen-free flame retardants (such as MCA, MPP, etc.) cannot be used when blended with high-temperature nylons due to thermal stability problems. Most of the halogen-free flame retardants for high-temperature nylons currently used in the industry are aluminum diethylphosphinate (ADP). However, the cost of aluminum diethylphosphinate flame retardant is relatively high, and the addition amount in the high-temperature nylon system is relatively large. It is often necessary to add about 20% to make the vertical burning performance (0.8 mm thickness) of the material reach the V-0 level. The relatively high ADP addition amount not only brings an increase in cost, but also causes a series of problems such as deterioration of the mechanical properties, fluidity, and color of the material, and corrosion of equipment and molds and precipitation of mold scale during the later product processing, which limits its application range.

[0004] The method of in-situ copolymerization flame retardant modification refers to connecting reactive flame retardants to the polyamide chain through chemical bonds to achieve molecular-level modification. There is no migration, agglomeration, and precipitation of flame retardants, and it has intrinsic flame retardant properties. Therefore, the research on adding halogen-free reactive flame retardants to the high-temperature nylon polymerization process to copolymerize halogen-free intrinsically flame-retardant high-temperature polyamides has become a hot topic. CN116004001A discloses a halogen-free flame-retardant semi-aromatic polyamide composite material, its preparation method and application. This method uses an organic phosphinic halogen-free flame retardant containing a benzene ring to blend with high-temperature nylon and reinforcing materials to obtain a halogen-free flame-retardant semi-aromatic polyamide composite material, which reduces the corrosion of the flame retardant to equipment to a certain extent and improves the mechanical properties of the material. CN110218311A discloses a phosphorus-containing flame-retardant high-temperature copolymerized nylon and its preparation method. This method copolymerizes a phosphorus-based flame retardant monomer with a specific structure having double acid functional groups and an aromatic ring structure in the semi-aromatic polyamide chain segment through in-situ polymerization, and can have excellent flame retardant properties and mechanical properties. However, no matter which reactive flame retardant is added, it will inevitably lead to a decrease in the mechanical properties of high-temperature nylon, and the process flow is long. If an enhanced flame-retardant high-temperature nylon composite material needs to be prepared, it needs to be further blended with glass fibers, etc. Secondary melt processing is likely to cause the decomposition of nylon resin, resulting in a decrease in mechanical properties, or problems such as the generation of black spots and color change. Summary of the Invention

[0005] In order to solve the above problems in the prior art, the object of the present invention is to provide an intrinsically flame-retardant nylon resin and its preparation method. This intrinsically flame-retardant nylon resin has good flame retardant properties and mechanical properties.

[0006] To achieve the above object, according to the first aspect of the present invention, there is provided a preparation method of an intrinsically flame-retardant nylon resin, which includes:

[0007] S1, preparing the reaction monomers into a monomer aqueous solution, wherein the reaction monomers include a reactive flame retardant monomer, a dicarboxylic acid, and a diamine; wherein, the reactive flame retardant monomer includes one or a combination of two of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-tris[(p-carboxyphenyl)amino]-1,3,5-triazine; the mass percentage of the reactive flame retardant monomer in the reaction monomers is 1-50%.

[0008] S2, carrying out a prepolymerization reaction on the monomer aqueous solution, and then carrying out post-treatment to obtain a nylon prepolymer;

[0009] S3, carrying out melt extrusion treatment on the nylon prepolymer in a twin-screw extruder under the conditions of 220-350°C and an oxygen volume content lower than 5% to obtain the intrinsically flame-retardant nylon resin.

[0010] By copolymerizing a reactive flame retardant monomer with a diamine and a diacid, the present invention polymerizes the flame retardant monomer onto the nylon molecular weight, effectively solving the problems of reduced thermal decomposition temperature and mechanical property attenuation of the material caused by the addition of the flame retardant, reducing problems such as corrosion and discoloration caused by the precipitation of the flame retardant during the later use of the material, and also reducing the adverse effects of the flame retardant on the dyeing of the material. The production process using the method of the present invention is more environmentally friendly, and the obtained product has excellent mechanical properties and stable quality.

[0011] The present invention obtains a nylon resin with intrinsic flame retardant properties. Compared with the flame retardant nylon composite materials prepared by the traditional blending method, the flame retardant in the nylon resin of the present invention does not precipitate, and the long-term flame retardant performance is better.

[0012] The present invention finds that existing reactive flame retardants such as 2-carboxyethyl phenylphosphinic acid (CEPPA), [(6-oxo-6H-dibenz-(c,e)(1,2)-oxaphosphorin-6-yl)-methyl]-succinic acid (DDP), p-carboxyphenyl phenylphosphinic acid (CPPPA), etc. will have great side effects on the mechanical properties of flame retardant nylon, greatly limiting their application scenarios. The specific reactive flame retardant adopted by the present invention can improve the flame retardant effect of nylon without affecting its mechanical properties, and has more application prospects.

[0013] In the present invention, through melt extrusion treatment, it can play a role in increasing viscosity and increasing the molecular weight of the nylon resin. At the same time, by controlling the oxygen content during melt extrusion, color change or carbonization to form black spots of the resin material can be avoided, so as to contaminate the subsequent materials.

[0014] Preferably, the pH of the monomer aqueous solution is adjusted by adjusting the amount of the diacid or the diamine.

[0015] Preferably, in the monomer aqueous solution, the water is deionized water.

[0016] In some preferred embodiments of the present invention, the mass percentage of the reactive flame retardant monomer in the reaction monomers is 2-20%.

[0017] Preferably, the mass concentration of the reaction monomers in the monomer aqueous solution is 50-95%. Preferably, a low-concentration monomer aqueous solution is first prepared, and then the low-concentration monomer aqueous solution is heated and concentrated until the mass concentration of the reaction monomers therein is 50-95%.

[0018] Preferably, in S2, the post-treatment includes: spray discharging and dry pulverizing the product of the prepolymerization reaction at 1.5-5 MPa.

[0019] Preferably, in step S3, the method for controlling the oxygen content may use methods such as vacuum pumping, protective atmosphere protection, and natural exhaust to continuously discharge the water vapor generated during the melt extrusion and viscosity increase process to isolate oxygen in the air. Preferably, the protective atmosphere includes one or a combination of two or more of nitrogen, argon, helium, and carbon dioxide.

[0020] In some preferred embodiments of the present invention, the diamine includes one or a combination of two or more of butanediamine, hexanediamine, nonanediamine, 2-methylpentanediamine, pentanediamine, and dodecanediamine.

[0021] In some preferred embodiments of the present invention, the dibasic acid includes one or a combination of two or more of terephthalic acid, adipic acid, isophthalic acid, and dodecanedioic acid.

[0022] In some preferred embodiments of the present invention, the molar ratio of the total amino groups to the total carboxyl groups in the reaction monomers is 0.7 - 1.1:1.

[0023] In some preferred embodiments of the present invention, the pH of the aqueous monomer solution is 6 - 11, preferably 7 - 9.

[0024] In some preferred embodiments of the present invention, the conditions for the prepolymerization reaction are: pressure 1.5 - 6 MPa, temperature 160 - 300 °C, and time 0.5 - 8 h. Preferably, the prepolymerization reaction temperature is 245 - 290 °C.

[0025] In some preferred embodiments of the present invention, in step S2, the prepolymerization reaction includes: raising the temperature to 160 - 240 °C, concentrating water for 1 - 4 h, and simultaneously increasing the pressure in the reaction vessel. After the pressure in the kettle rises to 1.8 - 2.5 MPa, start exhausting; and raise the temperature to 240 - 300 °C and continue the reaction for 1 - 4 h; then cool down to 245 - 260 °C and discharge to obtain the nylon prepolymer.

[0026] In some preferred embodiments of the present invention, in the twin-screw extruder, the ratio of the length to the diameter of the screw is 25:1 - 80:1.

[0027] In some preferred embodiments of the present invention, the rotation speed of the twin-screw extruder is 100 - 500 rpm, and the feeding speed is 5 - 35 kg / h. Preferably, the rotation speed of the twin-screw extruder is 100 - 300 rpm, and the feeding speed is 6 - 15 kg / h.

[0028] In some preferred embodiments of the present invention, the twin-screw extruder is provided with one or more exhaust ports, and the exhaust ports are connected to a vacuum pumping device or communicate with the atmosphere. Preferably, the number of the exhaust ports is 1 to 6. Preferably, the oxygen content at a position 0 cm to 8 cm above each exhaust port is ≤ 5%.

[0029] In some preferred embodiments of the present invention, the twin-screw extruder is provided with a main feeding system and a side feeding system, and the main feeding system and the side feeding system are equipped with loss-in-weight feeders to accurately measure the feeding rate.

[0030] In some preferred embodiments of the present invention, the water content of the nylon prepolymer is ≤ 10 w%.

[0031] In some preferred embodiments of the present invention, the raw materials of the intrinsically flame-retardant nylon resin further include additives, and the additives are added to the aqueous monomer solution. The additives include one or a combination of two or more of a flame retardant, a dispersant, a compatibilizer, an antioxidant, a nucleating agent, a lubricant, a filler, and an antistatic agent.

[0032] In some preferred embodiments of the present invention, the raw materials of the intrinsically flame-retardant nylon resin further include additives, and the additives and the nylon prepolymer are subjected to the melt extrusion treatment together in the twin-screw extruder. Among them, the additives include one or a combination of two or more of a flame retardant, a dispersant, a compatibilizer, an antioxidant, a nucleating agent, a lubricant, a filler, and an antistatic agent.

[0033] Without additional addition of a flame retardant, compared with the same kind of ordinary high-temperature resistant nylon resin, the mechanical properties of the intrinsically flame-retardant nylon resin of the present invention are basically not attenuated, and the flame retardant performance is good. The present invention can also additionally add a flame retardant, and these flame retardants can produce a synergistic effect with the reactive flame retardant monomers participating in the copolymerization to further improve the flame retardant performance of the nylon resin. Compared with the blended flame-retardant high-temperature resistant nylon, when the addition ratio of the flame retardant is the same, the intrinsically flame-retardant high-temperature resistant nylon resin prepared by additionally adding a flame retardant in the present invention has better mechanical properties, and the mechanical properties decline less significantly compared with the original resin. In the preparation method of the present invention, the reactive flame retardant monomers participate in the polymerization together with other monomers, and the flame retardant has better compatibility with the matrix resin and is more uniformly dispersed, which can effectively reduce problems such as die fouling and corrosion caused by the precipitation of the flame retardant during the processing.

[0034] Preferably, the additives and the nylon prepolymer are melt-extruded together, which avoids the thermal decomposition and the decline of mechanical properties caused by the secondary melt processing during the modification of the high-temperature nylon resin, and can effectively reduce the problems of black spots or color change caused by the high-temperature oxidation of nylon.

[0035] Preferably, the flame retardant includes one or a combination of two or more of aluminum alkyl hypophosphite, dialkyl aluminum hypophosphite, red phosphorus, boehmite, aluminum hydroxide, magnesium hydroxide, and antimony trioxide. Preferably, the mass percentage of the flame retardant in the intrinsically flame-retardant nylon resin is 0-40%.

[0036] Preferably, the dispersant includes one or a combination of two or more of polyethylene wax, polypropylene wax, erucamide, oleic acid amide, calcium stearate, lithium stearate, silicone oil, silicone, lignite wax, stearamide, and ethylene bis-stearamide. Preferably, the mass percentage of the dispersant in the intrinsically flame-retardant nylon resin is 0-10%.

[0037] Preferably, the compatibilizer includes one or a combination of two of maleic anhydride and polyacrylate. Preferably, the mass percentage of the compatibilizer in the intrinsically flame-retardant nylon resin is 0-6%.

[0038] Preferably, the antioxidant includes one or a combination of two or more of antioxidant 168, antioxidant 619F, antioxidant 1076, antioxidant 1098, antioxidant 1010, antioxidant B215, and antioxidant H10. Preferably, the addition amount of the antioxidant accounts for 0-1% of the mass of the intrinsically flame-retardant nylon resin.

[0039] In some preferred embodiments of the present invention, the additive is added through the side feeding system of a twin-screw extruder.

[0040] According to another aspect of the present invention, there is also provided an intrinsically flame-retardant nylon resin prepared by the above preparation method.

[0041] In some preferred embodiments of the present invention, the intrinsically flame-retardant nylon resin is granular and is cylindrical or approximately cylindrical.

[0042] The preparation method of the present invention can save the steps of flame-retardant blending modification, not only can avoid problems such as black spots, color change, and mechanical property degradation caused by resin thermal degradation during secondary melting and blending extrusion in the flame-retardant modification of high-temperature nylon, but also saves energy consumption and a large amount of labor and material costs. Specific Embodiments

[0043] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0044] In the following examples and comparative examples, unless otherwise specified, the ratios and percentages are calculated by mass.

[0045] Example 1:

[0046] This embodiment provides a method for preparing an intrinsically flame-retardant nylon resin, including:

[0047] Vacuumize a 20-liter polymerization kettle and protect it with nitrogen. Add 7 kg of pure water into it, then add 1.543 kg of hexamethylenediamine, start stirring, add 0.34 kg of reactive flame-retardant monomer 2,4,6-tris(4-aminophenyl)-1,3,5-triazine. After stirring and dissolving, add 1.26 kg of terephthalic acid and 1.19 kg of adipic acid, and then add 2 g of antioxidant sodium hypophosphite. Heat to 70 °C to dissolve and obtain a monomer aqueous solution, and adjust the pH value of the monomer aqueous solution to 8.50 with a small amount of hexamethylenediamine or adipic acid.

[0048] Place the 20-liter polymerization kettle containing the monomer aqueous solution in an oil bath and evaporate and concentrate the water at 180 °C; after the concentration of the monomer aqueous solution system increases to 75%, continue to raise the temperature of the oil bath to 290 °C. When the pressure in the kettle rises to 2.0 MPa, start exhausting. When the temperature in the kettle reaches 245 °C, discharge it to a crushing kettle to obtain a nylon prepolymer and crush it.

[0049] Transfer the nylon prepolymer to a twin-screw extruder with a diameter of 26 mm (the length-diameter ratio is 68:1. Unless otherwise specified below, the length-diameter ratio of the twin-screw extruder used is the same as this). The temperature of the first zone is 240 °C, the second zone is 295 °C, the third zone is 295 °C, the fourth zone is 300 °C, the fifth zone is 300 °C, the sixth zone is 305 °C, the seventh zone is 305 °C, the eighth zone is 310 °C, the ninth zone is 310 °C, the tenth zone is 310 °C, the eleventh zone is 315 °C, and the head temperature is 315 °C. It is equipped with 2 exhaust ports and 2 vacuum ports. The exhaust ports are protected with nitrogen. The main motor speed of the extruder is 200 rpm, the feeding speed is 10 kg / h, and the melt is cooled underwater and pelletized after being dried by a blower to obtain an intrinsically flame-retardant nylon resin.

[0050] Example 2:

[0051] This embodiment provides a method for preparing an intrinsically flame-retardant nylon resin, including:

[0052] Vacuumize a 20-liter polymerization kettle and protect it with nitrogen. Add 7 kg of pure water into it, then add 1.83 kg of hexamethylenediamine, start stirring, add 0.43 kg of reactive flame-retardant monomer 2,4,6-tris[(p-carboxyphenyl)amino]-1,3,5-triazine. After stirring and dissolving, add 1.15 kg of terephthalic acid and 1.09 kg of adipic acid, and then add 2 g of antioxidant sodium hypophosphite. Heat to 70 °C to dissolve and obtain a monomer aqueous solution, and adjust the pH value of the monomer aqueous solution to 8.50 with a small amount of hexamethylenediamine or adipic acid.

[0053] A 20-liter polymerization kettle containing an aqueous monomer solution was placed in an oil bath and evaporated to concentrate the water at 180 °C; after the concentration of the aqueous monomer solution system was increased to 75%, the oil bath was further heated to 290 °C. When the pressure in the kettle rose to 2.0 MPa, exhaust gas was started. When the temperature in the kettle reached 245 °C, the material was discharged into a crushing kettle to obtain a nylon prepolymer and crushed.

[0054] The nylon prepolymer was transferred to a twin-screw extruder with a diameter of 26 mm. The temperature of zone 1 was 240 °C, the temperature of zone 2 was 295 °C, the temperature of zone 3 was 295 °C, the temperature of zone 4 was 300 °C, the temperature of zone 5 was 300 °C, the temperature of zone 6 was 305 °C, the temperature of zone 7 was 305 °C, the temperature of zone 8 was 310 °C, the temperature of zone 9 was 310 °C, the temperature of zone 10 was 310 °C, the temperature of zone 11 was 315 °C, and the temperature of the die head was 315 °C. It was equipped with 2 exhaust ports and 2 vacuum ports. The exhaust ports were protected by nitrogen. The main motor speed of the extruder was 200 rpm, the feeding speed was 10 kg / h, and the melt was cooled underwater and pelletized after being dried by a blower to obtain the intrinsically flame-retardant nylon resin.

[0055] Example 3:

[0056] This example provides a method for preparing an intrinsically flame-retardant nylon resin, including:

[0057] The 20-liter polymerization kettle was evacuated and protected with nitrogen. 7 kg of pure water was added thereto, then 0.95 kg of hexamethylenediamine and 0.95 kg of 2-methylpentamethylenediamine were added. Stirring was started, 0.41 g of the reactive flame retardant monomer 2,4,6-tris(4-aminophenyl)-1,3,5-triazine was added, 3.0 kg of terephthalic acid was added, and 1.5 g of the antioxidant sodium hypophosphite was added. It was heated to 80 °C to dissolve to prepare an aqueous monomer solution, and the pH value of the aqueous monomer solution was adjusted to 7.88 with a small amount of 2-methylpentamethylenediamine or terephthalic acid.

[0058] A 20-liter polymerization kettle containing an aqueous monomer solution was placed in an oil bath and evaporated to concentrate the water at 200 °C; after the concentration of the aqueous monomer solution system was increased to 75%, the oil bath was further heated to 290 °C. When the pressure in the kettle rose to 2.3 MPa, exhaust gas was started. When the temperature in the kettle reached 260 °C, the material was discharged into a crushing kettle to obtain a nylon prepolymer and crushed.

[0059] Transfer the nylon prepolymer into a twin-screw extruder with a diameter of 26 mm. The temperature of zone 1 is 250 °C, zone 2 is 300 °C, zone 3 is 300 °C, zone 4 is 300 °C, zone 5 is 300 °C, zone 6 is 305 °C, zone 7 is 305 °C, zone 8 is 310 °C, zone 9 is 310 °C, zone 10 is 310 °C, zone 11 is 315 °C, and the head temperature is 315 °C. It is equipped with 2 exhaust ports and 2 vacuum ports. The exhaust ports are protected by nitrogen. The main rotation speed of the extruder is 300 rpm, and the feeding speed is 8 kg / h. The melt is cooled underwater and pelletized after being dried by a blower to obtain the intrinsically flame-retardant nylon resin.

[0060] Example 4:

[0061] This example provides a preparation method of an intrinsically flame-retardant nylon resin, including:

[0062] Vacuumize a 20-liter polymerization kettle and protect it with nitrogen. Add 7 kg of pure water into it, then add 1.05 kg of hexamethylenediamine and 1.05 kg of 2-methylpentanediamine. Start stirring, add 0.41 g of the reactive flame retardant monomer 2,4,6-tris[(p-carboxyphenyl)amino]-1,3,5-triazine, add 2.79 kg of terephthalic acid, and then add 1.5 g of the antioxidant sodium hypophosphite. Heat to 80 °C to dissolve and prepare the monomer aqueous solution, and adjust the pH value of the monomer aqueous solution to 7.88 with a small amount of 2-methylpentanediamine or terephthalic acid.

[0063] Place the 20-liter polymerization kettle containing the monomer aqueous solution in an oil bath and evaporate and concentrate the water at 200 °C; after the concentration of the monomer aqueous solution system rises to 75%, continue to raise the temperature of the oil bath to 290 °C. When the pressure in the kettle rises to 2.3 MPa, start exhausting. When the temperature in the kettle reaches 260 °C, discharge the material into a crushing kettle to obtain the nylon prepolymer and crush it.

[0064] Transfer the nylon prepolymer into a twin-screw extruder with a diameter of 26 mm. The temperature of zone 1 is 250 °C, zone 2 is 300 °C, zone 3 is 300 °C, zone 4 is 300 °C, zone 5 is 300 °C, zone 6 is 305 °C, zone 7 is 305 °C, zone 8 is 310 °C, zone 9 is 310 °C, zone 10 is 310 °C, zone 11 is 315 °C, and the head temperature is 315 °C. It is equipped with 2 exhaust ports and 2 vacuum ports. The exhaust ports are protected by nitrogen. The main rotation speed of the extruder is 300 rpm, and the feeding speed is 8 kg / h. The melt is cooled underwater and pelletized after being dried by a blower to obtain the intrinsically flame-retardant nylon resin.

[0065] Example 5:

[0066] This example provides a preparation method of an intrinsically flame-retardant nylon resin, including:

[0067] Vacuum the inside of a 20-liter polymerization kettle and protect it with nitrogen. Add 7 kg of pure water into it, then add 0.95 kg of hexamethylenediamine and 0.95 kg of 2-methylpentanediamine. Start stirring, add 0.41 g of the reactive flame retardant monomer 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, add 3.0 kg of terephthalic acid, and then add 1.5 g of the antioxidant sodium hypophosphite. Heat to 80 °C to dissolve and obtain an aqueous monomer solution, and adjust the pH value of the aqueous monomer solution to 7.88 with a small amount of 2-methylpentanediamine or terephthalic acid.

[0068] Place the 20-liter polymerization kettle containing the aqueous monomer solution in an oil bath and evaporate and concentrate the water at 180 °C; after the concentration of the aqueous monomer solution system rises to 75%, continue to raise the temperature of the oil bath to 290 °C. When the pressure in the kettle rises to 2.3 MPa, start exhausting. When the temperature in the kettle reaches 260 °C, discharge to a crushing kettle to obtain a nylon prepolymer and crush it.

[0069] Melt extrusion treatment. Transfer the nylon prepolymer through the main feed port and the additives through the side feed port to a twin-screw extruder with a diameter of 26 mm. The temperature of zone 1 is 250 °C, the temperature of zone 2 is 300 °C, the temperature of zone 3 is 300 °C, the temperature of zone 4 is 300 °C, the temperature of zone 5 is 300 °C, the temperature of zone 6 is 305 °C, the temperature of zone 7 is 305 °C, the temperature of zone 8 is 310 °C, the temperature of zone 9 is 310 °C, the temperature of zone 10 is 310 °C, the temperature of zone 11 is 315 °C, and the temperature of the die head is 315 °C. It is equipped with 2 exhaust ports and 2 vacuum ports, and the exhaust ports are protected with nitrogen. The specific addition ratios are as follows:

[0070] Nylon prepolymer, the addition ratio is 91.4%;

[0071] Flame retardant: aluminum diethylphosphinate, the addition ratio is 8%;

[0072] Antioxidant: 1098, the addition ratio is 0.3%;

[0073] Lubricant: silicone powder, the addition ratio is 0.3%;

[0074] The main motor speed of the extruder is 200 rpm, the feeding speed is 10 kg / h, the melt is cooled underwater, dried by a blower and then pelletized to obtain the intrinsically flame-retardant nylon resin.

[0075] Comparative Example 1:

[0076] This comparative example provides a method for preparing a nylon resin, including:

[0077] Vacuum the 20 - liter polymerization kettle and protect it with nitrogen. Add 7 kg of pure water into it, then add 1.83 kg of hexamethylenediamine. Start stirring, add 1.26 kg of terephthalic acid and 1.19 kg of adipic acid, and then add 2 g of antioxidant sodium hypophosphite. Heat to 70 °C to dissolve and obtain the monomer aqueous solution. Adjust the pH value of the monomer aqueous solution to 8.50 with a small amount of hexamethylenediamine or adipic acid.

[0078] Place the 20 - liter polymerization kettle containing the monomer aqueous solution in an oil bath and evaporate and concentrate the water at a set temperature of 180 °C. After the concentration of the monomer aqueous solution system rises to 75%, continue to raise the temperature of the oil bath to 290 °C. When the pressure in the kettle rises to 2.0 MPa, start exhausting. When the temperature in the kettle reaches 245 °C, discharge the material to the crushing kettle to obtain and crush the nylon prepolymer.

[0079] Transfer the nylon prepolymer to a twin - screw extruder with a diameter of 26 mm. The temperature of zone 1 is 240 °C, zone 2 is 295 °C, zone 3 is 295 °C, zone 4 is 300 °C, zone 5 is 300 °C, zone 6 is 305 °C, zone 7 is 305 °C, zone 8 is 310 °C, zone 9 is 310 °C, zone 10 is 310 °C, zone 11 is 315 °C, and the head temperature is 315 °C. It is equipped with 2 exhaust ports and 2 vacuum ports. The exhaust ports are protected by nitrogen. The main motor speed of the extruder is 200 rpm, and the feeding speed is 10 kg / h. During the feeding process, add 8 wt% of melamine polyphosphate (MPP) as a flame retardant. The melt is cooled underwater, dried by a blower and then pelletized to obtain nylon resin.

[0080] Comparative Example 2:

[0081] This comparative example provides a method for preparing nylon resin. The specific preparation method is the same as that in Example 1, except that the pH value of the monomer aqueous solution is adjusted to 5.81.

[0082] Comparative Example 3:

[0083] This comparative example provides a method for preparing nylon resin, including:

[0084] First, synthesize the nylon prepolymer. The synthesis method of the nylon prepolymer is the same as that in Comparative Example 1.

[0085] Melting extrusion treatment. Transfer the nylon prepolymer through the main feeding port and the additives through the side feeding port to a twin - screw extruder with a diameter of 26 mm. The temperature of zone 1 is 250 °C, zone 2 is 300 °C, zone 3 is 300 °C, zone 4 is 300 °C, zone 5 is 300 °C, zone 6 is 305 °C, zone 7 is 305 °C, zone 8 is 310 °C, zone 9 is 310 °C, zone 10 is 310 °C, zone 11 is 315 °C, and the head temperature is 315 °C. It is equipped with 2 exhaust ports and 2 vacuum ports. The exhaust ports are protected by nitrogen. The specific mass addition ratios are as follows:

[0086] Nylon prepolymer: addition ratio is 81.4%;

[0087] Flame retardant: aluminum diethylphosphinate, addition ratio is 18%;

[0088] Antioxidant: 1098, addition ratio is 0.3%;

[0089] Lubricant: silicone powder, addition ratio is 0.3%;

[0090] The main machine speed of the extruder is 300 rpm, the feeding speed is 8 kg / h, the melt is cooled underwater, dried by a blower and then pelletized to obtain nylon resin.

[0091] Comparative Example 4:

[0092] This comparative example provides a preparation method of an intrinsically flame-retardant nylon resin. The specific preparation method is the same as that of Example 1, except that: the reactive flame-retardant monomer is replaced with 0.47 kg of [(6-oxo-6H-dibenz-(c,e)(1,2)-oxaphosphorin-6-yl)-methyl]-succinic acid (DDP).

[0093] Comparative Example 5:

[0094] This comparative example is the same as Comparative Example 3, except that the material addition amount during melt extrusion is:

[0095] Nylon prepolymer: addition ratio is 91.4%;

[0096] Flame retardant: aluminum diethylphosphinate, addition ratio is 8%;

[0097] Antioxidant: 1098, addition ratio is 0.3%;

[0098] Lubricant: silicone powder, addition ratio is 0.3%;

[0099] The main machine speed of the extruder is 300 rpm, the feeding speed is 8 kg / h, the melt is cooled underwater, dried by a blower and then pelletized to obtain nylon resin.

[0100] The nylon resins prepared in the above examples and comparative examples were vacuum dried at 100 °C for 8 hours and then subjected to various property tests. The results are shown in Table 1.

[0101] The test methods include:

[0102] 1. The test method for the exudation of flame retardant is carried out with reference to the standard of China Petroleum and Chemical Industry Federation T / CPCIF 0194-2022 "Exudation Test of Powder Flame Retardant in Thermoplastic Plastics": Add 0.2wt% of carbon black to the resin, and make test specimens through extrusion process and injection molding process. The accelerated exudation method is adopted. The test specimens are placed in a constant temperature and humidity chamber, with the temperature set at (85±2)°C and the humidity set at (85±2)%RH. Record the appearance of the test specimens every day, observe whether there is exudation of flame retardant on the surface of the test specimens, and continuously record for 7 days.

[0103] 2. Tensile test method: Test according to the standard ISO 527.

[0104] 3. Flexural strength test method: Test according to the standard ISO 178.

[0105] 4. Flame retardancy test method: Determine according to GB / T 2408-2021.

[0106] 5. Limiting oxygen index (LOI) test: Determine with reference to the standard GB / T 2406.2-2009.

[0107] Table 1

[0108]

[0109] It can be seen from the comparison of the experimental results of the examples and comparative examples shown in Table 1 that: By adopting the technical solution of the present invention, a variety of intrinsically flame-retardant and high-temperature-resistant nylon products with different flame retardancy and mechanical properties can be prepared. Compared with the materials obtained by directly blending nylon resin and flame retardant, the flame retardancy of the intrinsically flame-retardant nylon resin products prepared by the present invention has been greatly improved, and the tensile strength decreases little after copolymerization modification, and the flame retardant hardly exudes; at the same time, compared with the flame-retardant nylon obtained by other reactive flame-retardant monomers, the mechanical properties of the flame-retardant nylon material obtained by the present invention are higher.

Claims

1. A method for preparing an intrinsic flame retardant nylon resin, wherein: include: S1, preparing a reactive monomer into a monomer aqueous solution, wherein the reactive monomer comprises a reactive flame retardant monomer, a dibasic acid, and a diamine; wherein the reactive flame retardant monomer comprises one or a combination of two of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-tris[(p-carboxyphenyl)amino]-1,3,5-triazine; and the mass percentage of the reactive flame retardant monomer in the reactive monomer is 1 to 50%; S2, subjecting the monomer aqueous solution to a prepolymerization reaction, and then post-treating the reaction to obtain a nylon prepolymer; S3, melt-extruding the nylon prepolymer in a twin-screw extruder at 220-350° C. and with an oxygen volume content of less than 5% to obtain the intrinsic flame-retardant nylon resin.

2. The method for preparing an intrinsic flame-retardant nylon resin according to claim 1, wherein: The diamine includes one or a combination of two or more of butanediamine, hexamethylenediamine, nonanediamine, 2-methylpentanediamine, pentanediamine, and dodecanediamine; and / or, The dibasic acid includes one or a combination of two or more of terephthalic acid, adipic acid, isophthalic acid, and dodecanedioic acid.

3. The method for preparing the intrinsic flame retardant nylon resin according to claim 1, wherein: The molar ratio of the total amino groups to the total carboxyl groups in the reactive monomers is 0.7-1.1:1; and / or, The pH of the monomer aqueous solution is 6 to 11; and / or, The conditions of the prepolymerization reaction are: pressure of 1.5-6 MPa, temperature of 160-300° C., and time of 0.5-8 h.

4. The method for preparing the intrinsic flame retardant nylon resin according to claim 1, wherein: In the twin-screw extruder, the aspect ratio of the screw is 25:1 to 80:1; The rotation speed of the twin-screw extruder is 100-500 rpm, and the feeding speed is 5-35 kg / h.

5. The method for preparing the intrinsic flame retardant nylon resin according to claim 1 or 4, wherein: The twin-screw extruder is provided with one or more exhaust ports, and the exhaust ports are connected to a vacuum pump or communicated with the atmosphere.

6. The method for preparing an intrinsic flame-retardant nylon resin according to claim 1, wherein: The mass percentage of the reactive flame retardant monomer in the reactive monomer is 2-20%.

7. The method for preparing an intrinsic flame-retardant nylon resin according to claim 1, wherein: The water content of the nylon prepolymer is ≤10w%.

8. The method for preparing an intrinsic flame-retardant nylon resin according to claim 1, wherein: The raw materials of the intrinsic flame retardant nylon resin also include additives, which are added to the monomer aqueous solution. The additives include one or a combination of two or more of flame retardants, dispersants, compatibilizers, antioxidants, nucleating agents, lubricants, fillers, and antistatic agents.

9. The method for preparing an intrinsic flame-retardant nylon resin according to claim 1, wherein: The raw materials of the intrinsic flame-retardant nylon resin also include additives, and the additives are melt-extruded together with the nylon prepolymer in the twin-screw extruder, wherein the additives include one or a combination of two or more of flame retardants, dispersants, compatibilizers, antioxidants, nucleating agents, lubricants, fillers, and antistatic agents.

10. An intrinsic flame retardant nylon resin, wherein: The intrinsic flame retardant nylon resin is prepared according to the method for preparing the intrinsic flame retardant nylon resin according to any one of claims 1 to 9.

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