Intrinsic flame-retardant nylon 6 resin as well as preparation method and application thereof

Abstract

The invention discloses an intrinsic flame-retardant nylon 6 resin and a preparation method and application thereof, the intrinsic flame-retardant nylon 6 resin is prepared by the following steps: respectively salifying a sulfur-containing diacid monomer, a phosphorus-containing diacid monomer and a nitrogen-containing diacid monomer with an aliphatic diamine monomer in pure water to obtain a nylon salt solution S1, a nylon salt solution S2 and a nylon salt solution S3; and adding the nylon salt liquids S1, S2 and S3, caprolactam, a catalyst and a stabilizer into a reaction kettle, replacing air in the reaction kettle with inert gas for 3-4 times after feeding, and carrying out melt polycondensation to obtain the intrinsic flame-retardant nylon 6 resin. The intrinsic flame-retardant nylon 6 disclosed by the invention is very outstanding in heat resistance, weather resistance, processability, flame retardance, mechanical strength and the like, and the preparation method disclosed by the invention has the advantages of simple process flow, capability of realizing industrial continuous production and the like; the related products are widely used in the fields of textile industry, automobile industry, electronic and electric appliances, national defense and military industry, aerospace and the like.

Description

Technical Field

[0001] This invention relates to the field of copolymer nylon 6 resin technology, specifically to an intrinsic flame-retardant nylon 6 resin, its preparation method, and its application. Background Technology

[0002] Polyamide, commonly known as nylon, is a general term for resins containing repeating amide groups in their molecular chains. It is mainly formed by the condensation polymerization of lactams, amino acids, or nylon salts (obtained by the salt-forming reaction of diacids and diamines in pure water). Nylon is a class of thermoplastic resins with excellent comprehensive properties. Among the five major general-purpose engineering plastics, it has the largest production volume, the most varieties, and the widest range of applications. After more than 70 years of development, the application of nylon has expanded from traditional spinning to film packaging, engineering plastics, and other fields, and its market share is gradually shifting towards the engineering plastics and film industries.

[0003] However, due to the large number of amide bonds in its molecular structure, nylon is highly hygroscopic and prone to absorbing water and moisture. Furthermore, it suffers from low impact strength in dry conditions or at low temperatures, opacity, poor solubility, and poor dimensional stability, limiting its applications. To expand the application range of nylon, existing nylons are typically chemically or physically modified to impart new structures, properties, and application areas. Copolymerization modification is a direct and efficient method. Copolymer nylons obtained through binary, ternary, or multi-component copolymerization can optimize mechanical strength, surface properties, heat resistance, barrier properties, flame retardancy, water absorption, or dimensional stability, thereby matching the performance requirements of nylon materials for specific applications.

[0004] Chinese Patent CN 117777435B relates to a semi-aromatic copolymer nylon, a semi-aromatic nylon composition, its preparation method, and its application. The raw material of the semi-aromatic copolymer nylon includes the following components by mass: (a1) 30-65 parts of 6T unit; (a2) 30-60 parts of 4T, 5T, or M5T unit; (a3) ​​0-15 parts of 9T, 10T, or 12T unit; (a4) 0-3 parts of cyclic polymer unit. The sum of components (a1) to (a4) constitutes 100 parts by mass of semi-aromatic copolymer nylon, which is then melt-extruded with a heat-stable, hydrolysis-resistant, and alcoholysis-resistant masterbatch to prepare a semi-aromatic nylon composition. This composition is mainly used in the automotive field. This resin has excellent temperature resistance and solvent resistance, but it does not have flame retardancy and has a low flame retardancy rating, thus limiting its application areas. Chinese patent CN109705341B discloses a PN-Si synergistic flame-retardant copolymer nylon 66 and its preparation method. The preparation method of the PN-Si synergistic flame-retardant copolymer nylon 66 includes the following steps: adding a phosphorus-containing flame retardant prepolymer, a nitrogen-containing flame retardant, and a silicon-containing flame retardant during the polymerization of nylon 66 to obtain the PN-Si synergistic flame-retardant copolymer nylon 66. Due to the synergistic effect, the flame retardant has high flame retardant efficiency and exhibits good mechanical strength. However, since the matrix resin is nylon 66, its heat resistance is lower than that of high-temperature nylon, limiting its application in environments with stringent temperature requirements. In addition, Chinese patents CN116162348B, CN118834241B, CN119931036B, and CN119708640B have also reported on the preparation of flame-retardant nylon 6 resin through various means, achieving improved flame retardant performance while sacrificing other properties to varying degrees.

[0005] In summary, there is a wide variety of flame-retardant nylon resins reported to date. However, there are no reports in the existing technology on nylon 6 resins that achieve intrinsic flame retardancy while also possessing excellent heat resistance, weather resistance, processability, and mechanical strength through copolymerization, containing sulfur, phosphorus, and nitrogen elements in the molecular backbone, with ternary synergy. These reports also include methods for preparing and applying such nylon 6 resins. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the above-mentioned defects of the prior art and provide an intrinsically flame-retardant nylon 6 resin with a simple process flow, capable of continuous industrial production, as well as its preparation method and applications, which combines heat resistance, weather resistance, processability, flame retardancy, and mechanical strength. The technical solution adopted by this invention to solve its technical problem is as follows: An intrinsically flame-retardant nylon 6 resin contains sulfur, phosphorus, and nitrogen elements in its molecular backbone, achieving intrinsic flame retardancy through ternary synergy.

[0007] A method for preparing intrinsically flame-retardant nylon 6 resin includes the following steps: ① A sulfur-containing diacid monomer and an aliphatic diamine monomer are salted in pure water to obtain nylon salt solution S1; ② A phosphorus-containing diacid monomer and an aliphatic diamine monomer are salted in pure water to obtain nylon salt solution S2; ③ A nitrogen-containing diacid monomer and an aliphatic diamine monomer are salted in pure water to obtain nylon salt solution S3; ④ A certain proportion of nylon salt solutions S1, S2, S3, caprolactam, catalyst, and stabilizer are added to a reaction vessel. After adding the materials, the air in the reaction vessel is replaced with inert gas 3-4 times to carry out melt polycondensation. Then, inert gas is added again, and the materials are discharged to obtain intrinsically flame-retardant nylon 6 resin.

[0008] The inventive concept of the intrinsic flame-retardant nylon 6 resin of the present invention is as follows: diacid monomers containing sulfur, phosphorus and nitrogen elements are respectively salted with aliphatic diamine monomers to obtain nylon salt solutions S1, S2 and S3, which are then prepared by polymerization reaction to obtain intrinsic flame-retardant nylon 6 resin with heat resistance, weather resistance, processability, flame retardancy and mechanical strength.

[0009] The molar ratio of the sulfur-containing diacid monomer to the aliphatic diamine monomer is 0.96–1.00:1.00. The sulfur-containing diacid monomer is selected from one or more of 3,3'-thiodipropionic acid, 3,3'-dithiodipropionic acid, 2,5-thiophene dicarboxylic acid, and 3,4-thiophene dicarboxylic acid. The aliphatic diamine monomer is selected from one or more of 1,5-pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,9-dioxo-1,12-dodecanediamine, and 1,14-tetradecanediamine. The amount of water used is 30–40% of the total mass of the diacid monomer and the diamine monomer.

[0010] The molar ratio of the phosphorus-containing diacid monomer to the aliphatic diamine monomer is 0.96–1.00:1.00. The phosphorus-containing diacid monomer is selected from one or more of 2'-carboxyphenyl-2-carboxyethyl-phenyl phosphate, 3'-carboxyphenyl-2-carboxyethyl-phenyl phosphate, and 4'-carboxyphenyl-2-carboxyethyl-phenyl phosphate. The aliphatic diamine monomer is selected from one or more of 1,5-pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,9-dioxo-1,12-dodecanediamine, and 1,14-tetradecanediamine. The amount of water used is 30–40% of the total mass of the diacid monomer and the diamine monomer.

[0011] The molar ratio of the nitrogen-containing diacid monomer to the aliphatic diamine monomer is 0.96–1.00:1.00. The nitrogen-containing diacid monomer is selected from one or more of imidazole-4,5-dicarboxylic acid, pyridazine-4,5-dicarboxylic acid, and 2,2'-bipyridine-6,6'-dicarboxylic acid. The aliphatic diamine monomer is selected from one or more of 1,5-pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,9-dioxo-1,12-dodecanediamine, and 1,14-tetradecanediamine. The amount of water used is 30–40% of the total mass of the diacid monomer and the diamine monomer.

[0012] The mass ratio of the above nylon salt solution S1, S2, S3 and caprolactam is 1:1~2:0.8~2:12~20.

[0013] The amount of the catalyst used is 0.1 to 0.5% of the total mass of nylon salt solution S1, S2, S3 and caprolactam. The catalyst includes one or more of sodium hypophosphite, potassium hypophosphite or magnesium hypophosphite.

[0014] The amount of the stabilizer used is 0.2-0.5% of the total mass of nylon salt solution S1, S2, S3, and caprolactam. The stabilizer includes Changhe Chemical CHPHOS. ® 4500, CHPHOS ® 8502, or CHPHOS ® One or more of 8503.

[0015] The specific process of the above-mentioned melt polycondensation is as follows: First, a heating and pressure holding reaction is carried out, followed by slow gas release and a second heating and pressure holding reaction. After releasing the gas to atmospheric pressure and removing water from the system, a vacuum is gradually applied for a decompression reaction. The first heating and pressure holding reaction refers to heating to 210–220°C and maintaining the pressure inside the reactor at 2.2–2.5 MPa for 1.5–2.0 hours. The slow gas release and second heating and pressure holding reaction refers to continuing to heat to 245–255°C, slowly releasing gas during the heating process to maintain the pressure inside the reactor at 0.8–1.0 MPa for 1.5–2.0 hours. The gradual vacuuming for decompression... The reaction is as follows: first, the pressure is evacuated to -0.01 to -0.03 MPa, and then maintained for 15 to 25 minutes; then, the pressure is evacuated to -0.03 to -0.05 MPa, and then maintained for 15 to 25 minutes; finally, the pressure is evacuated to -0.05 to -0.07 MPa, and then maintained for 20 to 30 minutes. Before the melt polycondensation, the air in the reactor is replaced with inert gas 3 to 4 times and then filled with inert gas to 0.1 to 0.2 MPa. After the melt polycondensation, inert gas is filled to 0.2 to 0.3 MPa. The inert gas includes one or more of carbon dioxide, nitrogen, argon, or helium.

[0016] An application of intrinsically flame-retardant nylon 6 resin, which is used in the textile industry, automotive industry, electronics and electrical appliances, defense and military industry and aerospace fields.

[0017] Compared with the closest existing technology, the technical solution provided by the present invention has the following beneficial effects: (1) The intrinsic flame-retardant nylon 6 resin of the present invention has a relative viscosity of up to 2.60 and a mechanical strength that is very close to that of ordinary nylon 6 resin, exhibiting good mechanical strength macroscopically; the melting point is slightly reduced and the melt index is increased, exhibiting excellent processing performance; the initial decomposition temperature is as high as 386.0℃, which is higher than that of nylon 6 resin, exhibiting good heat resistance and weather resistance; the limiting oxygen index is as high as 31.8%, and the combustion rating reaches V-0. The sulfur, phosphorus, nitrogen and other elements introduced into its molecular structure synergistically retard the flame and form a protective carbonized layer at high temperature. This carbonized layer can isolate oxygen and heat, thereby preventing the spread of flame and significantly improving the flame-retardant performance.

[0018] (2) The intrinsic flame-retardant nylon 6 resin of the present invention has diversified products. The copolymerization ratio of nylon salt solution S1, S2, S3 and caprolactam can be flexibly adjusted to customize the production of copolymer nylon 6 resin with different temperature resistance, flame retardancy and mechanical strength grades to match the performance requirements of specific application sites. (3) The production process involved in the method of the present invention is simple and can realize continuous industrial production; the products involved are widely used in textile industry, automobile industry, electronics and electrical appliances, national defense and military industry and aerospace and other fields. Detailed Implementation

[0019] The present invention will be further described below with reference to the embodiments; the inert gas used in the embodiments and comparative examples of the present invention is a high-purity gas with a purity of ≥99.999%; the raw materials or chemical reagents used in the embodiments and comparative examples of the present invention can be obtained through conventional commercial channels unless otherwise specified.

[0020] Example 1 (1) Weigh 174.6g (0.98mol) of 3,3'-thiodipropionic acid (178.2g / mol) containing sulfur atoms and 102.2g (1.00mol) of 1,5-pentanediamine to form a salt in 83.1g (30%) pure water to obtain nylon salt solution S1; (2) Weigh 327.6 g (0.98 mol) of phosphorus-containing diacid monomer 4'-carboxyphenyl-2-carboxyethyl-phenyl phosphate (334.3 g / mol) and 102.2 g (1.00 mol) of 1,5-pentanediamine and salt them in 128.9 g (30%) pure water to obtain nylon salt solution S2; (3) Weigh 153.0g (0.98mol) of nitrogen-containing diacid monomer imidazole-4,5-dicarboxylic acid (156.1g / mol) and 102.2g (1.00mol) of 1,5-pentanediamine and form a salt in 76.6g (30%) pure water to obtain nylon salt solution S3; (4) Add 359.9g of nylon salt solution S1, 558.7g of nylon salt solution S2, 331.8g of nylon salt solution S3, 5400.0g of caprolactam, 10.8g of sodium hypophosphite, and 16.2g of Changhe Chemical CHPHOS ® 4500 was added to the reactor. After feeding, the air inside the reactor was replaced with inert gas 3-4 times, and high-purity nitrogen was introduced to 0.15 MPa before melt polycondensation: the temperature was first raised to 212℃ and the pressure inside the reactor was maintained at 2.2 MPa for a first heating and pressure holding reaction for 2.0 h. The temperature was then raised to 248℃, and the gas was slowly released during the heating process to maintain the pressure inside the reactor at 1.0 MPa. After a second heating and pressure holding reaction for 1.5 h, the gas was released to reduce the pressure inside the reactor to atmospheric pressure. After draining the water from the system, a vacuum pump was used to gradually evacuate the system for a depressurization reaction: the vacuum was first evacuated to -0.02 MPa and held for 20 min, then evacuated to -0.04 MPa and held for 20 min, and finally evacuated to -0.06 MPa and held for 25 min. High-purity nitrogen was then introduced to 0.3 MPa, and the material was discharged to obtain intrinsic flame-retardant nylon 6 resin.

[0021] Example 2 (1) Weigh 206.1g (0.98mol) of 3,3'-dithiodipropionic acid (210.3g / mol) containing sulfur atoms and 102.2g (1.00mol) of 1,5-pentanediamine to form a salt in 92.5g (30%) pure water to obtain nylon salt solution S1; (2) Weigh 327.6 g (0.98 mol) of phosphorus-containing diacid monomer 4'-carboxyphenyl-2-carboxyethyl-phenyl phosphate (334.3 g / mol) and 102.2 g (1.00 mol) of 1,5-pentanediamine and salt them in 128.9 g (30%) pure water to obtain nylon salt solution S2; (3) Weigh 153.0g (0.98mol) of nitrogen-containing diacid monomer imidazole-4,5-dicarboxylic acid (156.1g / mol) and 102.2g (1.00mol) of 1,5-pentanediamine and form a salt in 76.6g (30%) pure water to obtain nylon salt solution S3; (4) Add 400.8g of nylon salt solution S1, 558.7g of nylon salt solution S2, 331.8g of nylon salt solution S3, 5400.0g of caprolactam, 10.8g of sodium hypophosphite, and 16.2g of Changhe Chemical CHPHOS ®4500 was added to the reactor. After feeding, the air inside the reactor was replaced with inert gas 3-4 times, and high-purity nitrogen was introduced to 0.15 MPa before melt polycondensation: the temperature was first raised to 212℃ and the pressure inside the reactor was maintained at 2.2 MPa for a first heating and pressure holding reaction for 2.0 h. The temperature was then raised to 245℃, and the gas was slowly released during the heating process to maintain the pressure inside the reactor at 1.0 MPa. A second heating and pressure holding reaction was carried out for 1.5 h. After releasing the gas, the pressure inside the reactor was reduced to atmospheric pressure. After draining the water from the system, a vacuum pump was used to gradually evacuate the system for a depressurization reaction: the vacuum was first evacuated to -0.02 MPa and held for 20 min, then evacuated to -0.04 MPa and held for 20 min, and finally evacuated to -0.06 MPa and held for 25 min. High-purity nitrogen was then introduced to 0.3 MPa, and the material was discharged to obtain intrinsic flame-retardant nylon 6 resin.

[0022] Example 3 (1) Weigh 206.1g (0.98mol) of 3,3'-dithiodipropionic acid (210.3g / mol) containing sulfur atoms and 102.2g (1.00mol) of 1,5-pentanediamine to form a salt in 92.5g (30%) pure water to obtain nylon salt solution S1; (2) Weigh 327.6 g (0.98 mol) of phosphorus-containing diacid monomer 4'-carboxyphenyl-2-carboxyethyl-phenyl phosphate (334.3 g / mol) and 102.2 g (1.00 mol) of 1,5-pentanediamine and salt them in 128.9 g (30%) pure water to obtain nylon salt solution S2; (3) Weigh 153.0g (0.98mol) of nitrogen-containing diacid monomer imidazole-4,5-dicarboxylic acid (156.1g / mol) and 102.2g (1.00mol) of 1,5-pentanediamine and form a salt in 76.6g (30%) pure water to obtain nylon salt solution S3; (4) Add 400.8g of nylon salt solution S1, 558.7g of nylon salt solution S2, 331.8g of nylon salt solution S3, 4810.0g of caprolactam, 9.6g of sodium hypophosphite, and 15.1g of Changhe Chemical CHPHOS ®4500 was added to the reactor. After feeding, the air inside the reactor was replaced with inert gas 3-4 times, and high-purity nitrogen was introduced to 0.15 MPa before melt polycondensation: the temperature was first raised to 212℃ and the pressure inside the reactor was maintained at 2.2 MPa for a first heating and pressure holding reaction for 2.0 h. The temperature was then raised to 245℃, and the gas was slowly released during the heating process to maintain the pressure inside the reactor at 1.0 MPa. A second heating and pressure holding reaction was carried out for 1.5 h. After releasing the gas, the pressure inside the reactor was reduced to atmospheric pressure. After draining the water from the system, a vacuum pump was used to gradually evacuate the system for a depressurization reaction: the vacuum was first evacuated to -0.02 MPa and held for 20 min, then evacuated to -0.04 MPa and held for 20 min, and finally evacuated to -0.06 MPa and held for 25 min. High-purity nitrogen was then introduced to 0.3 MPa, and the material was discharged to obtain intrinsic flame-retardant nylon 6 resin.

[0023] Example 4 (1) Weigh 206.1g (0.98mol) of 3,3'-dithiodipropionic acid (210.3g / mol) containing sulfur atoms and 102.2g (1.00mol) of 1,5-pentanediamine to form a salt in 92.5g (30%) pure water to obtain nylon salt solution S1; (2) Weigh 327.6 g (0.98 mol) of phosphorus-containing diacid monomer 4'-carboxyphenyl-2-carboxyethyl-phenyl phosphate (334.3 g / mol) and 102.2 g (1.00 mol) of 1,5-pentanediamine and salt them in 128.9 g (30%) pure water to obtain nylon salt solution S2; (3) Weigh 153.0g (0.98mol) of nitrogen-containing diacid monomer imidazole-4,5-dicarboxylic acid (156.1g / mol) and 102.2g (1.00mol) of 1,5-pentanediamine and form a salt in 76.6g (30%) pure water to obtain nylon salt solution S3; (4) Add 400.8g of nylon salt solution S1, 558.7g of nylon salt solution S2, 331.8g of nylon salt solution S3, 6012.0g of caprolactam, 12.0g of sodium hypophosphite, and 17.5g of Changhe Chemical CHPHOS ®8502 was added to the reactor. After feeding, the air inside the reactor was replaced with inert gas 3-4 times, and high-purity nitrogen was introduced to 0.15 MPa before melt polycondensation: the temperature was first raised to 212℃ and the pressure inside the reactor was maintained at 2.2 MPa for a first heating and pressure holding reaction for 2.0 h. The temperature was then raised to 252℃, and the gas was slowly released during the heating process to maintain the pressure inside the reactor at 1.0 MPa. A second heating and pressure holding reaction was carried out for 1.5 h. After releasing the gas, the pressure inside the reactor was reduced to atmospheric pressure. After draining the water from the system, a vacuum pump was used to gradually evacuate the system for a depressurization reaction: the vacuum was first evacuated to -0.02 MPa and held for 20 min, then evacuated to -0.04 MPa and held for 20 min, and finally evacuated to -0.06 MPa and held for 25 min. High-purity nitrogen was then introduced to 0.3 MPa, and the material was discharged to obtain intrinsic flame-retardant nylon 6 resin.

[0024] Example 5 (1) Weigh 206.1g (0.98mol) of 3,3'-dithiodipropionic acid (210.3g / mol) containing sulfur atoms and 102.2g (1.00mol) of 1,5-pentanediamine to form a salt in 92.5g (30%) pure water to obtain nylon salt solution S1; (2) Weigh 327.6 g (0.98 mol) of phosphorus-containing diacid monomer 4'-carboxyphenyl-2-carboxyethyl-phenyl phosphate (334.3 g / mol) and 102.2 g (1.00 mol) of 1,5-pentanediamine and salt them in 128.9 g (30%) pure water to obtain nylon salt solution S2; (3) Weigh 153.0g (0.98mol) of nitrogen-containing diacid monomer imidazole-4,5-dicarboxylic acid (156.1g / mol) and 102.2g (1.00mol) of 1,5-pentanediamine and form a salt in 76.6g (30%) pure water to obtain nylon salt solution S3; (4) Add 400.8g of nylon salt solution S1, 558.7g of nylon salt solution S2, 331.8g of nylon salt solution S3, 7214.4g of caprolactam, 14.0g of sodium hypophosphite, and 20.0g of Changhe Chemical CHPHOS ®8503 was added to the reactor. After feeding, the air inside the reactor was replaced with inert gas 3-4 times, and high-purity nitrogen was introduced to 0.15 MPa before melt polycondensation: the temperature was first raised to 212℃ and the pressure inside the reactor was maintained at 2.2 MPa for a first heating and pressure holding reaction for 2.0 h. The temperature was then raised to 254℃, and the gas was slowly released during the heating process to maintain the pressure inside the reactor at 1.0 MPa. After a second heating and pressure holding reaction for 1.5 h, the gas was released to reduce the pressure inside the reactor to atmospheric pressure. After draining the water from the system, a vacuum pump was used to gradually evacuate the system for a depressurization reaction: the vacuum was first evacuated to -0.02 MPa and held for 20 min, then evacuated to -0.04 MPa and held for 20 min, and finally evacuated to -0.06 MPa and held for 25 min. High-purity nitrogen was then introduced to 0.3 MPa, and the material was discharged to obtain intrinsic flame-retardant nylon 6 resin.

[0025] Example 6 (1) Weigh 206.1g (0.98mol) of 3,3'-dithiodipropionic acid (210.3g / mol) containing sulfur atoms and 172.3g (1.00mol) of 1,10-decanediamine to form a salt in 113.5g (30%) pure water to obtain nylon salt solution S1; (2) Weigh 327.6 g (0.98 mol) of phosphorus-containing diacid monomer 3'-carboxyphenyl-2-carboxyethyl-phenyl phosphate (334.3 g / mol) and 172.3 g (1.00 mol) of 1,10-decanediamine and salt them in 150.0 g (30%) pure water to obtain nylon salt solution S2; (3) Weigh 164.7g (0.98mol) of nitrogen-containing diacid monomer pyridazine-4,5-dicarboxylic acid (168.1g / mol) and 172.3g (1.00mol) of 1,10-decanediamine and salt them in 101.1g (30%) pure water to obtain nylon salt solution S3; (4) Add 491.9g of nylon salt solution S1, 649.9g of nylon salt solution S2, 438.1g of nylon salt solution S3, 7214.4g of caprolactam, 14.0g of sodium hypophosphite, and 20.0g of Changhe Chemical CHPHOS ®8503 was added to the reactor. After feeding, the air inside the reactor was replaced with inert gas 3-4 times, and high-purity nitrogen was introduced to 0.15 MPa before melt polycondensation: the temperature was first raised to 211℃ and the pressure inside the reactor was maintained at 2.2 MPa for a first heating and pressure holding reaction for 2.0 h. The temperature was then raised to 250℃, and the gas was slowly released during the heating process to maintain the pressure inside the reactor at 1.0 MPa. After a second heating and pressure holding reaction for 1.5 h, the gas was released to reduce the pressure inside the reactor to atmospheric pressure. After draining the water from the system, a vacuum pump was used to gradually evacuate the system for a depressurization reaction: the vacuum was first evacuated to -0.02 MPa and held for 20 min, then evacuated to -0.04 MPa and held for 20 min, and finally evacuated to -0.06 MPa and held for 25 min. High-purity nitrogen was then introduced to 0.3 MPa, and the material was discharged to obtain intrinsic flame-retardant nylon 6 resin.

[0026] Comparative Example 1 7000.0g caprolactam, 12.0g sodium hypophosphite, and 18.0g Changhe Chemical CHPHOS ® 8503 was added to the reactor. After feeding, the air inside the reactor was replaced with inert gas 3-4 times, and high-purity nitrogen was introduced to 0.15 MPa before melt polycondensation: the temperature was first raised to 211℃ and the pressure inside the reactor was maintained at 2.2 MPa for a first heating and pressure holding reaction for 2.0 h. The temperature was then raised to 250℃, and the gas was slowly released during the heating process to maintain the pressure inside the reactor at 1.0 MPa. A second heating and pressure holding reaction was carried out for 1.5 h. After releasing the gas, the pressure inside the reactor was reduced to atmospheric pressure. After draining the water from the system, a vacuum pump was used to gradually evacuate the system for a depressurization reaction: the vacuum was first evacuated to -0.02 MPa and held for 20 min, then evacuated to -0.04 MPa and held for 20 min, and finally evacuated to -0.06 MPa and held for 25 min. High-purity nitrogen was then introduced to 0.3 MPa, and the material was discharged to obtain ordinary nylon 6 resin.

[0027] Performance testing To evaluate the relative viscosity, mechanical properties, heat resistance, and flame retardant properties of the intrinsic flame-retardant nylon 6 resin of Examples 1-6 and the ordinary nylon 6 resin of Comparative Example 1, tests were conducted under the following conditions: Relative viscosity test conditions: The sample to be tested was placed in a vacuum drying oven at 120℃ for 4 hours and a concentrated sulfuric acid solution with a concentration of 0.010 g / ml was prepared. The solution was tested using an automatic viscometer in accordance with the standard GB / T 38138-2019. Tensile, bending, and impact strength test conditions: Place the specimen to be tested in a constant temperature and humidity chamber for 24 hours, and then use a testing machine to conduct tests in sequence according to standards GB / T 1040.2-2006, GB / T 9341-2008, and GB / T 1043.1-2008; Melting point test conditions: Weigh 5-10 mg of the sample to be tested, heat the sample to 300℃ for 3 min under high-purity nitrogen protection, quench it with liquid nitrogen, then heat the quenched sample to 300℃, cool it to room temperature, and then heat it to 300℃ again. The heating rate is 10℃ / min, referring to standard GB / T 19466.3-2004. Initial decomposition temperature test conditions: Weigh 3-8 mg of the sample to be tested, and under the protection of high-purity nitrogen, heat the sample to 700℃. The temperature corresponding to a 5% weight loss is the initial decomposition temperature, referring to standard GB / T 33047.1-2016. Melt flow index test method: The sample to be tested was dried at 120℃ for 4 hours and tested using an MTS ZRZ1452 melt flow index tester. The test standard was ASTM D1238. Limiting oxygen index test method: The size of the test sample is 80mm×10mm×4mm. The test is conducted according to GB / T 2406.2-2009 standard. The gas flow rate is 40mm / s, the initial oxygen concentration is 25%, and the top surface ignition method is used. Flame retardant performance test method: The test specimen is 125mm×13mm×1.6mm in size, and is tested according to ANSI / UL94-2013 standard using the vertical burning method; The results are shown in Table 1.

[0028] Table 1. Performance data of intrinsic flame-retardant nylon 6 resin of the present invention in Examples 1-6 and Comparative Example 1. As shown in Table 1, the intrinsic flame-retardant nylon 6 resins of the present invention in Examples 1-6 have a relative viscosity as high as 2.60, and their mechanical strength is very close to that of ordinary nylon 6 resin, exhibiting good mechanical strength macroscopically; the melting point is slightly lower, and the melt index is increased, exhibiting excellent processing performance; the initial decomposition temperature is as high as 386.0℃, which is higher than that of nylon 6 resin, exhibiting good heat resistance and weather resistance; the limiting oxygen index is as high as 31.8%, and the flammability rating reaches V-0, exhibiting excellent flame-retardant performance.

[0029] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending approval.

Claims

1. An inherently flame retardant nylon 6 resin characterized in that: The intrinsic flame-retardant nylon 6 resin is realized by containing sulfur, phosphorus and nitrogen elements in the molecular main chain, and ternary synergistic effect.

2. A process for the preparation of the inherently flame retardant nylon 6 resin according to claim 1, characterized in that, The method comprises the following steps: (1) a sulfur-containing diacid monomer and an aliphatic diamine monomer are salted in pure water to obtain a nylon salt solution S1; (2) a phosphorus-containing diacid monomer and an aliphatic diamine monomer are salted in pure water to obtain a nylon salt solution S2; (3) a nitrogen-containing diacid monomer and an aliphatic diamine monomer are salted in pure water to obtain a nylon salt solution S3; (4) a certain proportion of the nylon salt solutions S1, S2, S3, caprolactam, a catalyst and a stabilizer are put into a reaction kettle, the air in the reaction kettle is replaced with inert gas for 3-4 times after feeding, melt polycondensation is carried out, inert gas is filled again, and the intrinsic flame-retardant nylon 6 resin is obtained.

3. The method for preparing an intrinsically flame-retardant nylon 6 resin according to claim 2, characterized in that: In step (1), the molar ratio of the sulfur-containing diacid monomer to the aliphatic diamine monomer is 0.96-1.00:1.00, the sulfur-containing diacid monomer is selected from one or more of 3,3'-thiodipropionic acid, 3,3'-dithiodipropionic acid, 2,5-thiophene dicarboxylic acid and 3,4-thiophene dicarboxylic acid, the aliphatic diamine monomer is selected from one or more of 1,5-pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,9-dioxo-1,12-dodecanediamine and 1,14-tetradecanediamine, and the amount of water is 30-40% of the total mass of the diacid monomer and the diamine monomer.

4. The method for preparing an intrinsically flame-retardant nylon 6 resin according to claim 2, characterized in that: In step (2), the molar ratio of the phosphorus-containing diacid monomer to the aliphatic diamine monomer is 0.96-1.00:1.00, the phosphorus-containing diacid monomer is selected from one or more of 2'-carboxyphenyl-2-carboxyethyl-phenyl phosphate, 3'-carboxyphenyl-2-carboxyethyl-phenyl phosphate and 4'-carboxyphenyl-2-carboxyethyl-phenyl phosphate, the aliphatic diamine monomer is selected from one or more of 1,5-pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,9-dioxo-1,12-dodecanediamine and 1,14-tetradecanediamine, and the amount of water is 30-40% of the total mass of the diacid monomer and the diamine monomer.

5. The method for preparing an intrinsically flame-retardant nylon 6 resin according to claim 2, characterized in that: In step (3), the molar ratio of the nitrogen-containing diacid monomer to the aliphatic diamine monomer is 0.96-1.00:1.00, the nitrogen-containing diacid monomer is selected from one or more of imidazole-4,5-dicarboxylic acid, pyridazine-4,5-dicarboxylic acid and 2,2'-bipyridine-6,6'-dicarboxylic acid, the aliphatic diamine monomer is selected from one or more of 1,5-pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,9-dioxo-1,12-dodecanediamine and 1,14-tetradecanediamine, and the amount of water is 30-40% of the total mass of the diacid monomer and the diamine monomer.

6. The process for the preparation of an inherently flame retardant nylon 6 resin according to claim 2, characterized in that: In step (4), the mass ratio of the nylon salt solutions S1, S2 and S3 to caprolactam is 1:1-2:0.8-2:12-20.

7. The method for preparing an intrinsically flame-retardant nylon 6 resin according to claim 2, characterized in that: The amount of the catalyst used in step (4) is 0.1-0.5% of the total mass of the nylon salt solution S1, S2, S3 and caprolactam, and the catalyst includes one or more of sodium hypophosphite, potassium hypophosphite or magnesium hypophosphite.

8. The process for the preparation of an inherently flame retardant nylon 6 resin according to claim 2, characterized in that: In step (4), the amount of the stabilizer is 0.2-0.5% of the total mass of the nylon salt solution S1, S2, S3, and caprolactam, and the stabilizer includes Changhe Chemical CHPHOS ® 4500、CHPHOS ® 8502、or CHPHOS ® 8503.

9. The method of preparing an inherently flame retardant nylon 6 resin according to claim 2, wherein: In step (4), the specific process of melt polycondensation is as follows: first, one-time temperature rising and pressure maintaining reaction is carried out, then slow air release and two-time temperature rising and pressure maintaining reaction is carried out, air release to normal pressure, and then water in the system is discharged, and gradually vacuum pumping is carried out for pressure reduction reaction; the one-time temperature rising and pressure maintaining reaction is that the temperature is raised to 210-220℃, and the pressure in the kettle is maintained at 2.2-2.5 MPa, and the reaction is carried out for 1.5-2.0 h; the slow air release and two-time temperature rising and pressure maintaining reaction is that the temperature is continuously raised to 245-255℃, and slow air release is carried out during the temperature rising process to maintain the pressure in the kettle at 0.8-1.0 MPa, and the reaction is carried out for 1.5-2.0 h; the gradually vacuum pumping for pressure reduction reaction is that first vacuum pumping is carried out to-0.01--0.03 MPa, then pressure maintaining reaction is carried out for 15-25 min, then vacuum pumping is carried out to-0.03--0.05 MPa, then pressure maintaining reaction is carried out for 15-25 min, and finally vacuum pumping is carried out to-0.05--0.07 MPa, and then pressure maintaining reaction is carried out for 20-30 min; before the melt polycondensation, the inert gas is used to replace the air in the reaction kettle for 3-4 times, and the inert gas is filled to 0.1-0.2 MPa; after the melt polycondensation, the inert gas is filled to 0.2-0.3 MPa; and the inert gas includes one or more of carbon dioxide, nitrogen, argon or helium.

10. Use of the intrinsically flame retardant nylon 6 resin according to claim 1, characterized in that: The intrinsic flame-retardant nylon 6 resin of claim 1 is used in the fields of textile industry, automobile industry, electronic and electrical appliances, national defense and military industry, and aerospace, etc.

Images