PA6t / 66 copolymer high temperature nylon and production process

Abstract

This invention belongs to the technical field, specifically relating to a PA6T / 66 copolymer high-temperature nylon and its production process. It comprises a basic comonomer, a catalyst, and functional additives. The basic comonomer includes the following components by mass percentage: 42.8%-45.1% hexamethylenediamine, 30.2%-35.6% terephthalic acid, and 21.2%-26.6% adipic acid. The hexamethylenediamine is pretreated with sodium bicarbonate, and the terephthalic acid undergoes surface activation and solubility modification. The catalyst is a phosphite catalyst, added at 0.05%-0.1% of the total amount of the basic comonomer. The functional additives include at least one of a compound antioxidant, an organic nucleating agent, and a silane modifier / reinforcing agent. This invention addresses the problems of uneven dissolution and easy oxidation leading to impurities caused by hydrophobicity by modifying the core comonomers terephthalic acid and hexamethylenediamine. Simultaneously, by matching appropriate process parameters according to the characteristics of the modified monomers, the uniformity of the PA6T / 66 copolymer high-temperature nylon reaction and the stability of product performance are improved.

Description

Technical Field

[0001] This invention mainly relates to the field of silicone rubber and leather technology, specifically to a PA6T / 66 copolymer high-temperature nylon and its production process. Background Technology

[0002] PA6T / 66 copolymer high-temperature nylon, a semi-aromatic nylon, contains both rigid 6T units derived from terephthalic acid and flexible 66 units derived from adipic acid in its main chain. This allows it to retain the excellent heat resistance of aromatic structures while lowering the melting point and improving processability through aliphatic segments, making it a key material for high-temperature components around automotive engines and connectors used in electronic surface mount technology. Early PA6T / 66 preparation faced key challenges: pure PA6T's high melting point easily exceeds its own thermal decomposition temperature, making direct melt molding difficult; and traditional processes often resulted in PA6T / 66 exhibiting large fluctuations in mechanical properties, insufficient high-temperature rigidity, or poor processing fluidity. Therefore, the industry has conducted a series of improvement studies on PA6T / 66, attempting to solve these problems by optimizing raw material ratios, process parameters, or adding additives.

[0003] While these improvements have yielded some results, in practical applications, existing solutions still have significant shortcomings and struggle to meet high reliability requirements. For example, patent document CN109575273A addresses PA6T / 66 semi-aromatic copolymer nylon by adjusting the proportions of phthalic acid, isophthalic acid, and adipic acid, combining high-pressure magnetic reactor melt polymerization with horizontal twin-screw extrusion for thickening, and adding anti-yellowing agent HN-130. Its advantage lies in lowering the product's melting point to 300±20℃, solving the problem of pure PA6T's melting point exceeding its decomposition temperature and thus preventing melt molding. It also alleviates the difficulty in discharging high-viscosity PA6T / 66 materials and improves the yellowing phenomenon. However, this solution does not address the core properties of PA6T / 66. The monomers were specifically treated. The hydrophobicity of terephthalic acid resulted in extremely low solubility in hexamethylenediamine aqueous solution, making it prone to agglomeration when directly fed into the copolymer. This led to uneven distribution of 6T units in the copolymer, resulting in significant fluctuations in the mechanical properties of the final PA6T / 66 product. For example, the tensile strength ranged from 48 to 56 MPa, with a batch-to-batch difference of up to 8 MPa. Furthermore, the hexamethylenediamine was not subjected to antioxidant pretreatment, and its amino groups were easily oxidized to generate impurities under the high-temperature environment of salt formation and polymerization, disrupting the amine-acid molar ratio balance. The problem of insufficient molecular weight control could only be compensated for by subsequent thickening after twin-screw extrusion, which could not guarantee the uniformity of the PA6T / 66 reaction from the source.

[0004] For example, patent document CN119955087A directly uses PA6T / 66 copolymer as the target for improvement. By introducing citrate amide branching agent, combined with the staged heating process in the prepolymerization stage, and solid-state polymerization control, its advantage lies in effectively improving the toughness and melt flowability of PA6T / 66, solving the problems of poor toughness and insufficient processing flowability of traditional PA6T / 66. However, the branched structure introduced by this scheme to improve toughness reduces the regularity of PA6T / 66 molecular chains, resulting in poor high-temperature rigidity of the product. For example, the modulus retention rate at 120℃ is difficult to meet the requirements of automotive engine parts. At the same time, it does not address the hydrophobicity of terephthalic acid and the oxidation problem of hexamethylenediamine in PA6T / 66. The system is in a white suspension state during the salt formation stage. Undissolved terephthalic acid particles during the reaction process can easily cause uneven distribution of PA6T / 66 chain segments, and the stability of the final polymer performance still needs to be improved.

[0005] Furthermore, both of the above solutions share common drawbacks: Firstly, neither addresses the inherent characteristics of PA6T / 66's core monomers, such as terephthalic acid and hexamethylenediamine. The hydrophobicity of terephthalic acid leads to uneven dissolution, and the easy oxidation of hexamethylenediamine results in impurity formation, making the reaction uniformity of PA6T / 66 inherently insufficient and creating potential for subsequent performance fluctuations. Secondly, the process parameters are not adapted to the characteristics of PA6T / 66 monomers. For example, parameters such as salt formation temperature and prepolymerization heating rate do not consider the dissolution efficiency of terephthalic acid and the oxidation risk of hexamethylenediamine. This can easily lead to problems such as excessively high salt formation temperature accelerating hexamethylenediamine oxidation and excessively rapid heating causing premature polycondensation of undissolved monomers. Moreover, anti-yellowing and anti-oxidation measures rely on exogenous additives, which cannot fundamentally solve the long-term degradation problem of PA6T / 66 caused by monomer impurities. Ultimately, neither solution can simultaneously meet the requirements of the automotive industry for high-temperature modulus retention of PA6T / 66 and the electronics industry for low water absorption of PA6T / 66. Summary of the Invention

[0006] This invention aims to provide a PA6T / 66 copolymer high-temperature nylon and its production process. This process addresses the problems of uneven dissolution and easy oxidation of impurities caused by hydrophobicity by modifying the core copolymer monomers terephthalic acid and hexamethylenediamine. At the same time, appropriate process parameters are matched according to the characteristics of the modified monomers to improve the reaction uniformity and stabilize the product performance of PA6T / 66 copolymer high-temperature nylon.

[0007] Specifically, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a PA6T / 66 copolymer high-temperature nylon, which is composed of a basic comonomer, a catalyst and functional additives. The basic comonomer comprises the following components by mass percentage: 42.8%-45.1% hexamethylenediamine, 30.2%-35.6% terephthalic acid, and 21.2%-26.6% adipic acid. The hexamethylenediamine is pretreated with sodium bicarbonate, and the terephthalic acid is subjected to surface activation and solubility modification treatment.

[0008] In this invention, terephthalic acid and adipic acid ensure a balance between the ratio of 6T rigid units and 66 flexible units in the copolymer molecular chain. The 6T units provide sufficient high-temperature resistance to the material, with a lead-free solder temperature of ≥260℃. The 66 units effectively reduce the melting point of the material to 290-310℃, which is suitable for the processing temperature range of subsequent twin-screw extrusion, and prevents the melting point from being too high (excessive 6T units) and exceeding 320℃, making it difficult to process.

[0009] The catalyst is a phosphite catalyst, and its addition amount is 0.05%-0.1% of the total amount of the basic comonomer; the functional additives include at least one of compound antioxidants, organic nucleating agents, and silane modifiers.

[0010] In some feasible ways, the functional additive includes at least one of the following: The compound antioxidant is composed of antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) and antioxidant 168 (tris[2,4-di-tert-butylphenyl]phosphite) in a mass ratio of 2:1, with the dosage being 0.1%-0.3% of the total mass of the basic comonomer. Antioxidant 1010, as a hindered phenolic antioxidant, can terminate the oxidation chain reaction by capturing free radicals generated during polymerization, while antioxidant 168, as a phosphite antioxidant, can decompose the intermediate product of oxidation reaction, hydroperoxide. The synergistic effect of the two can significantly improve the antioxidant effect, with an antioxidant efficiency 1.5-2 times that of a single antioxidant. It can effectively inhibit thermal oxidative degradation during solid-state polymerization and twin-screw extrusion, keeping the yellowness index of the product below 2.5.

[0011] Organic nucleating agent: Sodium benzoate, as a crystallization nucleus, promotes the orderly stacking of copolymer molecular chains during cooling, improves crystallinity, and thus improves the dimensional stability of the product and reduces molding shrinkage. Its dosage is 0.05%-0.1% of the total mass of the basic comonomer. It can prevent the decrease in impact strength caused by excessive nucleating agent. When the dosage is higher than 0.1%, the notched impact strength will drop from not less than 3.1kJ / m² to less than 2.8kJ / m², which cannot meet the impact resistance requirements.

[0012] Silane-modified reinforcing agent: Alkali-free glass fiber treated with KH550 silane coupling agent, the amount of which is 10%-30% of the total mass of PA6T / 66 copolymer high-temperature nylon, the diameter of which is 10-15μm and the length is 3-5mm; while improving the mechanical properties of the material, it avoids the decrease in processing fluidity caused by excessively thick or long fibers.

[0013] Preferably, the preparation steps of the silane-modified reinforcing agent in this invention include: (1) Dry the alkali-free glass fiber at 110-130℃ for 1.5-2.5h and control the moisture content to ≤0.1%; drying can remove the adsorbed water on the surface of the glass fiber and prevent the moisture from causing molecular chain breakage in the subsequent copolymerization reaction.

[0014] (2) Mix KH550 silane coupling agent with anhydrous ethanol at a mass ratio of 1:8-12 to ensure that KH550 is fully dissolved and avoid incomplete hydrolysis due to excessive concentration; then add 4%-6% of deionized water by mass of ethanol and stir for 10-25 minutes until complete hydrolysis to obtain silane treatment solution. Deionized water can provide the water required for hydrolysis. The aminosilanol generated by hydrolysis can react with the hydroxyl groups on the surface of glass fiber.

[0015] (3) Immerse the dried glass fiber in the silane treatment solution at a liquid-to-solid ratio of 4:1-6:1 for 1-2.5 h at 20-30°C to allow the aminosilanol to fully react with the hydroxyl groups on the glass fiber surface to form covalent bonds (Si-O-Si). After draining, dry the glass fiber at 70-90°C for 0.5-1.5 h, and then at 110-130°C for 2.5-3.5 h. Drying at 70-90°C is to remove the ethanol solvent, and drying at 110-130°C is to promote the curing of the silane film and improve the interfacial bonding strength with the resin. The modified glass fiber has a silane coverage of ≥90%, and the interfacial bonding strength with PA6T / 66 resin is increased by more than 30%. After addition, the flexural modulus of the product can be increased from 2.2-2.5 GPa to 2.5-2.8 GPa, and the heat distortion temperature can be increased from not less than 260°C to ≥270°C.

[0016] In some feasible methods, the pretreatment of hexamethylenediamine with sodium bicarbonate includes: (1) Take industrial grade hexamethylenediamine with a purity ≥98.5% and transport it to a vacuum distillation vessel with a heat transfer oil jacket. Add sodium bicarbonate of 0.1%-0.2% of the mass of hexamethylenediamine into the vessel and start stirring until the sodium bicarbonate is completely dissolved. The stirring speed is 50-60 r / min. Sodium bicarbonate is chosen as a pretreatment agent because it is weakly alkaline and can form weak hydrogen bonds with the amino group of hexamethylenediamine. It inhibits the contact between the amino group and oxygen through the steric hindrance effect, and avoids the interference of strong alkaline substances such as sodium hydroxide on the condensation of carboxyl and amino groups in the subsequent salt formation reaction.

[0017] (2) Close the feed valve of the distillation vessel, turn on the vacuum system, and control the vacuum degree to -0.092~-0.095MPa. Excessive vacuum degree can easily lead to excessive volatilization of hexamethylenediamine and loss of raw materials, while excessively low vacuum degree cannot effectively remove water and low-boiling impurities such as butanediamine from hexamethylenediamine. Then, raise the temperature to 55-65℃ at a rate of 4-6℃ / min and keep it at that temperature for 25-40min. This stage mainly removes free water from hexamethylenediamine. The heating rate is controlled at 4-6℃ / min to prevent local overheating and premature oxidation of hexamethylenediamine. Then, raise the temperature to 85-90℃ at a rate of 2-4℃ / min and collect the fraction with a distillation temperature of 80-85℃, which corresponds to the boiling point of high-purity hexamethylenediamine. This can effectively separate low-boiling impurities from high-boiling impurities.

[0018] (3) The collected fraction is transferred to a hexamethylenediamine intermediate tank with a hot water jacket at 50-60℃. Nitrogen gas with a purity ≥99.99% is introduced into the tank to maintain a slight positive pressure of 0.01-0.02MPa. The stirring speed is maintained at 30-40r / min to obtain hexamethylenediamine pretreated with sodium bicarbonate. Nitrogen protection can further isolate air, and the slight positive pressure setting can prevent the entry of external air and avoid the difficulty of depressurization during subsequent aqueous solution preparation due to excessive pressure. Stirring ensures that sodium bicarbonate is evenly dispersed in hexamethylenediamine and continues to exert its antioxidant effect. The hexamethylenediamine pretreated in this way can have a purity of ≥99.9%, a water content controlled below 0.03%, and an amino oxidation rate controlled below 0.1%, which is far superior to the quality of hexamethylenediamine after simple distillation in the prior art.

[0019] In some feasible methods, the process of surface activation and solubility modification of terephthalic acid includes: (1) Take industrial grade terephthalic acid with a purity ≥99.0%, put it into a universal pulverizer and pulverize it to 100-200 mesh. Reducing the particle size can increase the contact area between terephthalic acid and subsequent treatment liquid. Drying removes surface adsorbed water and prevents moisture from affecting the subsequent plasma treatment effect and the concentration stability of ammonium bicarbonate solution. Then transfer it to a hot air dryer and dry it at 110-130℃ for 1-3 hours, controlling the moisture content to ≤0.1%.

[0020] (2) The dried terephthalic acid is transferred into a plasma treatment instrument, and the chamber is purged with nitrogen 2-4 times, each time at 0.4-0.6 MPa for 8-12 minutes. The treatment power is set to 150-200 W, the treatment time to 15-20 minutes, and the nitrogen flow rate to 10-15 L / min to complete the surface activation. The hydroxyl content on the surface of the surface-activated terephthalic acid can reach ≥0.5 mmol / g. The purpose of nitrogen purging in this invention is to remove oxygen from the chamber and prevent the terephthalic acid from being oxidized during the plasma treatment process. In addition, a suitable power can introduce sufficient hydroxyl (-OH) active groups on the surface of terephthalic acid, while avoiding excessive power that could cause the terephthalic acid molecular chain to break.

[0021] (3) Prepare a 0.5%-1.0 wt% ammonium bicarbonate aqueous solution, and immerse the activated terephthalic acid in the solution at a solid-liquid ratio of 1:(4-6). Stir and soak at 60-80 r / min for 30-40 min at room temperature. Ammonium bicarbonate is chosen as a weak base treatment agent because it reacts with the carboxyl groups on the surface of terephthalic acid to form a carboxylate (-COONH4). This carboxylate has good hydrophilicity, which can further improve the solubility of terephthalic acid in hexamethylenediamine aqueous solution. The concentration of ammonium bicarbonate is controlled at 0.5%-1.0% by mass to prevent insufficient carboxylate formation (limited improvement in solubility) due to too low a concentration, or excessive ammonium bicarbonate decomposing to produce ammonia gas during subsequent drying, which would affect the pH value of the salt formation reaction.

[0022] (4) Remove the terephthalic acid, filter it through a 0.1-0.2 μm filter, and transfer it to a vacuum drying oven. Dry it at 70-85℃ and a vacuum of -0.075~-0.085 MPa for 1-2 hours to obtain surface-activated and solubility-modified terephthalic acid. While removing moisture, avoid high temperature to prevent decarboxylation of terephthalic acid. The decarboxylation temperature of terephthalic acid is usually ≥200℃. The solubility of the modified terephthalic acid in a 50% hexamethylenediamine aqueous solution at 25℃ can be increased from less than 5 g / L to 15-20 g / L, and the agglomeration rate during the salt formation reaction is controlled below 5%, which is significantly better than that of unmodified terephthalic acid.

[0023] In some feasible methods, the phosphite catalyst is sodium hypophosphite monohydrate, and its preparation method includes the following steps: (1) Add deionized water to the reactor, control the water temperature at 20-35℃, stir at 250-450r / min, slowly add hypophosphite, and adjust the pH to 1.8-2.7. In this invention, the water temperature is controlled at 20-35℃ to prevent hypophosphite from dissolving slowly due to excessively low water temperature, or hypophosphite from volatilizing due to excessively high water temperature, because hypophosphite has a boiling point of about 260℃, but it is easily decomposed at high temperatures; adjusting the pH to 1.8-2.7 is to provide a suitable acidic environment for the subsequent neutralization reaction with sodium hydroxide, and to avoid excessive sodium hydroxide usage due to excessively low pH, or insufficient acidity of hypophosphite and incomplete reaction due to excessively high pH.

[0024] (2) Add 25-35 wt% sodium hydroxide aqueous solution slowly at a molar ratio of hypophosphite to sodium hydroxide of 1:(1.01-1.03), control the reaction temperature at 35-45℃, and stir the reaction for 1-2.5 hours. The excess of sodium hydroxide molar ratio by 0.01-0.03 is to ensure complete neutralization of hypophosphite to form sodium hypophosphite, and to avoid unreacted hypophosphite residue affecting the subsequent catalytic effect. The sodium hydroxide concentration is controlled to balance the reaction rate and solution viscosity. A concentration below 25% will result in an excessively large reaction system volume, increasing the energy consumption for subsequent concentration; a concentration above 35% will result in intense exothermic dissolution of sodium hydroxide, making it difficult to control the reaction temperature. The reaction temperature of 35-45℃ is the suitable temperature for the neutralization reaction of hypophosphite and sodium hydroxide. The reaction rate is slow below 35℃, and decomposition of sodium hypophosphite is likely to occur above 45℃.

[0025] (3) After the reaction is complete, the solution is transferred to an evaporator crystallizer and evaporated and concentrated to a solution concentration of 45-60% at a vacuum of -0.07 to -0.09 MPa and a temperature of 55-75℃. This allows for solution concentration at a lower temperature, avoiding the decomposition of sodium hypophosphite caused by high temperature. In addition, controlling the concentration at 45%-60% is to ensure that sufficient crystals can be precipitated during subsequent cooling and crystallization, while preventing excessively high concentrations from causing crystallization to be too rapid and impurities to be trapped in the crystals.

[0026] (4) Transfer the concentrate to a cooling crystallizer and cool it down to 5-20℃ at a rate of 0.5-1.5℃ / min. This ensures that the crystals grow slowly, form a regular crystal structure, and reduce the inclusion of impurities. Keep the crystallizer at this temperature for 3-5 hours, separate the crystals by centrifugation, and vacuum dry them at 45-55℃ for 1.5-2.5 hours to remove the moisture from the surface of the crystals, thus obtaining sodium hypophosphite monohydrate.

[0027] The sodium hypophosphite monohydrate prepared by the above method has a purity ≥99.5%, a water content controlled below 0.05%, and stable catalytic activity. Its addition amount is 0.05%-0.1% of the total amount of the basic comonomer. This dosage range is chosen because it effectively reduces the activation energy of the carboxyl-amino condensation reaction, accelerating amide bond formation, while avoiding excessive catalyst residue that leads to a decrease in the product's chemical resistance. When the dosage is below 0.05%, the catalytic efficiency is insufficient, and the prepolymerization time needs to be extended to more than 3 hours; when the dosage is above 0.1%, catalyst residue will cause trace degradation of the product at high temperatures, affecting its thermal stability.

[0028] Secondly, this invention also provides a production process for PA6T / 66 copolymer high-temperature nylon, comprising four stages: salt formation reaction, prepolymerization, solid-state polymerization, and post-treatment. The parameters for each stage are adapted to the characteristics of the modified material, ensuring process stability and controllable product performance. Specifically, it includes the following steps: (1) Salt formation reaction: First, hexamethylenediamine pretreated with sodium bicarbonate is mixed with demineralized water at a mass ratio of 1:1. A 50%-52% hexamethylenediamine aqueous solution is prepared at 55-60℃. This ensures that the hexamethylenediamine is fully dissolved, providing sufficient amino concentration for the subsequent reaction with the diacid. It also avoids excessive concentration, which would cause the hexamethylenediamine to precipitate during cooling, or excessive concentration, which would result in excessive water content in the solution after the salt formation reaction, increasing the energy consumption for dehydration in the subsequent prepolymerization. The temperature is controlled at 55-60℃, consistent with the insulation temperature of the hexamethylenediamine intermediate tank, to avoid temperature fluctuations that would cause changes in the solubility of hexamethylenediamine.

[0029] Subsequently, the hexamethylenediamine aqueous solution, surface-activated terephthalic acid, and purity-optimized adipic acid were added to a salt-forming reactor. The reaction temperature was controlled at 55-60℃, atmospheric pressure, and a stirring speed of 80-100 r / min for 1-2 hours. The final solution was controlled to have a pH of 7.0-7.2 and be clear and transparent, yielding a PA6T / 66 copolymer salt solution. Maintaining the reaction temperature at 55-60℃ is to balance the reaction rate and the stability of hexamethylenediamine. Below 55℃, the salt-forming reaction rate is slow; above 60℃, the risk of hexamethylenediamine oxidation increases. The atmospheric pressure setting is because the salt-forming reaction is a non-pressurized reaction; high pressure may cause the dissolution of low-molecular-weight substances, affecting the purity of the salt solution. This invention controls the pH at 7.0-7.2 to ensure a precise amino acid molar ratio, avoiding an excess of carboxyl groups below pH 7.0 or an excess of amino groups above pH 7.2, both of which will affect the molecular weight control of subsequent polymerization. A clear and transparent solution is a direct indicator of the completion of the salt-forming reaction, indicating the absence of undissolved terephthalic acid particles.

[0030] Preferably, before the salt-forming reaction, the surface-activated terephthalic acid and the purity-optimized adipic acid need to be pulverized again to 100-200 mesh and dried at 120-130℃ for 2-2.5 hours, with the moisture content controlled below 0.1%. Pulverizing to a uniform particle size ensures that the two dicarboxylic acids are evenly dispersed in the salt-forming reactor, and drying further removes moisture to prevent affecting the stability of the salt solution concentration. The salt-forming reactor is also equipped with a hot water jacket, a steam exhaust system (including a steam exhaust pressure regulating valve and a steam exhaust condenser), and a vacuum and nitrogen replacement device. The hot water jacket is used to maintain the reaction temperature, the steam exhaust system can remove water vapor generated during the reaction to avoid water vapor dilution of the solution concentration, and the vacuum and nitrogen replacement device can remove air from the reactor before the reaction to further inhibit the oxidation of hexamethylenediamine.

[0031] (2) Prepolymerization: The above copolymer salt solution is transferred to a polymerization reactor, and the temperature is controlled at 220-250℃ and the pressure at ≥2.2MPa for 2-3 hours. The polymerization reactor is heated by a built-in mirror-polished coil, and the heating medium is heat transfer oil. This heating method can achieve uniform temperature distribution and avoid local overheating that could lead to polymer degradation. In this invention, the temperature is controlled at 220-250℃, which can effectively promote the conversion of carboxylates in the salt solution into amide bonds, while avoiding incomplete prepolymerization due to excessively low temperatures or excessively high temperatures that could lead to overpolymerization and crosslinking of the prepolymer. Controlling the pressure inside the reactor to ≥2.2MPa is to maintain the water in the reaction system in a liquid state, prevent water from boiling out prematurely, and ensure that the reversible reaction for amide bond formation proceeds in the forward direction.

[0032] The prepolymerization process requires a gradient depressurization in the later stages. Specifically, the pressure is reduced from 2.0-2.4 MPa to 0.8-1.2 MPa over 0.8-1.2 hours, followed by a further reduction from 0.8-1.2 MPa to atmospheric pressure over 0.8-1.2 hours. This gradient depressurization, rather than a one-time depressurization, prevents a sudden drop in pressure that could cause the solution to boil violently, allowing the generated low-molecular-weight byproducts (mainly water) to drain smoothly. It also prevents prepolymer particles from being entrained by the airflow, ensuring uniform growth of the prepolymer within the reactor. The depressurization rate and target pressure are chosen based on the viscosity changes of the prepolymer. An initial pressure of 2.0-2.4 MPa corresponds to the low viscosity of the prepolymer in its initial stage. A slow reduction to 0.8-1.2 MPa gradually removes most of the water, followed by a reduction to atmospheric pressure to further remove residual low-molecular-weight substances. Each stage lasts 0.8-1.2 hours, avoiding incomplete removal of byproducts due to excessively rapid depressurization.

[0033] After gradient depressurization, vacuuming is performed for 0.5-1 hours to bring the relative viscosity of the prepolymer to 1.35-1.39. Vacuuming further removes residual moisture and low-molecular-weight byproducts, and controls the molecular weight of the prepolymer. Maintaining the relative viscosity at 1.35-1.39 ensures that subsequent solid-state polymerization can effectively increase the molecular weight to the target range of 2.48-2.52. If the viscosity is below 1.35, the solid-state polymerization reaction time needs to be extended to more than 12 hours; if the viscosity is above 1.39, the prepolymer is prone to agglomeration in the crystallizer.

[0034] After prepolymerization, nitrogen gas is introduced into the polymerization reactor, and the prepolymer is forced into the crystallizer by pressure difference. After cooling and flash crystallization, it is pulverized into 2-5 mm particles. Nitrogen protection can prevent the prepolymer from oxidizing during the transfer process. Pulverizing to 2-5 mm particles can increase the specific surface area of ​​subsequent solid-phase polymerization and improve the efficiency of solid-phase polymerization.

[0035] (3) Solid-state polymerization: First, the prepolymer particles are transferred to a rotary drum dryer and dried for 6-8 hours at a vacuum of -0.08 to -0.09 MPa and a temperature of 80 to 110°C to control the moisture content below 0.5%. This drying condition can effectively remove moisture from the surface and interior of the prepolymer particles, avoiding the hydrolysis and breakage of molecular chains caused by moisture at the high temperature of solid-state polymerization; a suitable vacuum can accelerate the evaporation of moisture; and a temperature of 80 to 110°C is below the softening point of the prepolymer, preventing the prepolymer particles from sticking together.

[0036] The dried prepolymer particles are transferred to a rotary drum solid-state polymerization reactor, heated to 270-280℃, and the vacuum level is controlled at 10-15 Pa. The reaction is carried out for 8-12 hours, during which a compound antioxidant is added. The rotary drum reactor allows the prepolymer particles to be continuously agitated during the reaction, ensuring uniform heating. 270-280℃ is the suitable temperature for the solid-state polymerization of PA6T / 66. Temperatures higher than this can easily lead to thermal degradation of the prepolymer, while temperatures lower than this result in a slow solid-state polymerization rate. A vacuum level of 10-15 Pa creates a high-vacuum environment, promoting further condensation of the amino and carboxyl groups at the ends of the prepolymer molecular chains, increasing the molecular weight, and simultaneously removing the moisture generated during condensation.

[0037] Preferably, in this invention, the compounded antioxidant is added in two stages: 40%-60% of the total amount is added at the beginning of solid-state polymerization, and the remaining compounded antioxidant is added after 5-7 hours of solid-state polymerization. Adding it in two stages ensures that the antioxidant functions throughout the solid-state polymerization process. The initially added antioxidant inhibits oxidation during the initial heating phase. Adding antioxidant during the middle stage of solid-state polymerization, when the molecular weight rapidly increases (5-7 hours), addresses the oxidation risk caused by increased molecular chain activity during this stage, preventing premature consumption of the antioxidant and ensuring the thermal stability of the final polymer. After solid-state polymerization, a final polymer with a relative viscosity of 2.48-2.52 is obtained. This relative viscosity corresponds to a number-average molecular weight of approximately 25,000-30,000, which meets the mechanical property requirements: tensile strength ≥ 92.1 MPa, flexural strength ≥ 116 MPa.

[0038] (4) Post-processing: The final polymer is transferred to a twin-screw extruder for melting. The twin-screw extruder adopts segmented temperature control, specifically: feed section 280-300℃, melting section 290-310℃, homogenization section 300-310℃, and die head 300-320℃. The segmented temperature control design is based on the state changes of the final polymer within the screw. The feed section temperature is 280-300℃, used to heat the solid final polymer to a softened state, preventing the material from melting and sticking to the feed inlet prematurely due to excessive temperature, thus affecting feed stability. The melting section temperature is 290-310℃, which is higher than the melting point of the final polymer, ensuring complete melting and forming a uniform melt. The homogenization section temperature is 300-310℃, used to further mix the melt, eliminate temperature and composition gradients in the melt, and ensure melt uniformity. The die head temperature is 300-320℃, slightly higher than the melting section temperature, which reduces the melt viscosity, facilitating smooth extrusion of the melt into strips.

[0039] After the molten material is cooled by circulating cooling water at 32-35℃, it is pelletized by an underwater pelletizer. The cooling water temperature of 32-35℃ allows the strip to be cooled rapidly to below the crystallization temperature, forming a stable crystal structure and avoiding strip cracking due to excessively rapid cooling or strip sticking due to excessively slow cooling.

[0040] The PA6T / 66 chips obtained after pelleting have an initial moisture content of 2000-3000 ppm. These chips are then dried in a fluidized bed dryer using circulating nitrogen at 80-120℃ for 1-3 hours, resulting in dried PA6T / 66 chips with a moisture content controlled below 800 ppm. Fluidized bed drying keeps the chips suspended in nitrogen, ensuring uniform heating and high drying efficiency. The 80-120℃ temperature effectively removes moisture while preventing discoloration due to excessive heat. The 1-3 hour drying time is optimized based on the initial moisture content, ensuring a final moisture content below 800 ppm. This moisture content prevents air bubbles from forming during subsequent injection molding, which would affect the product's appearance and mechanical properties. No additional packaging is required after drying, directly yielding the PA6T / 66 copolymer high-temperature nylon product.

[0041] To further enhance environmental friendliness, the waste gas generated at each stage of the process can be treated. Specifically, the waste gas generated during the salt formation reaction, prepolymerization, solid-phase polymerization, and drying processes is sequentially treated by three stages of purification: water washing (to absorb amines), alkali washing (to neutralize acidic byproducts), and activated carbon adsorption (to remove organic matter). After treatment, the VOCs emission concentration is controlled at ≤50mg / m³, which meets industrial environmental protection requirements.

[0042] The PA6T / 66 copolymer high-temperature nylon prepared using the above process meets the following performance requirements: tensile strength ≥ 92.1 MPa and not exceeding 100 MPa, flexural strength ≥ 116 MPa and not exceeding 130 MPa, flexural modulus ≥ 2.2 GPa and not exceeding 2.8 GPa, and notched impact strength ≥ 3.1 KJ / m. 2 And not exceeding 5.0 KJ / m 2 .

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs sodium bicarbonate pretreatment of hexamethylenediamine. The weak alkalinity of sodium bicarbonate forms weak hydrogen bonds with the amino groups of hexamethylenediamine, reducing the contact between the amino groups and oxygen through steric hindrance, thereby inhibiting amino oxidation. Simultaneously, it avoids interference from strongly alkaline substances in the subsequent condensation reaction between carboxyl and amino groups. For terephthalic acid, plasma treatment is first applied to introduce sufficient hydroxyl groups on its surface to enhance reactivity. Then, treatment with ammonium bicarbonate as a weak base converts the carboxyl groups on the terephthalic acid surface into hydrophilic carboxylates, significantly improving its solubility in hexamethylenediamine aqueous solution. This eliminates the adverse effects of monomer defects on the copolymerization reaction from the source, allowing the salt formation reaction to proceed completely and uniformly. The distribution consistency of 6T rigid units and 66 flexible units in the copolymer molecular chain is improved, ultimately effectively controlling the fluctuation range of the product's mechanical properties and ensuring stable performance across different batches.

[0044] This invention uses hypophosphite and sodium hydroxide as raw materials, achieving complete neutralization by precisely controlling their molar ratio to avoid unreacted residues. During concentration and crystallization, temperature and cooling rate are controlled to reduce impurity encapsulation and prevent sodium hypophosphite decomposition, ultimately yielding high-purity sodium hypophosphite monohydrate. This self-made catalyst exhibits high purity and stable catalytic activity. Adding it to the polymerization system in a specific ratio effectively lowers the activation energy of the carboxyl-amino condensation reaction, accelerates the formation rate of amide bonds, and avoids instability in the polymerization rate caused by insufficient catalyst purity or activity fluctuations. Furthermore, by controlling the amount of catalyst added, the adverse effects of excessive catalyst residue on the product's chemical resistance and thermal stability can be prevented, ultimately ensuring that the relative viscosity of the final polymer is stably controlled within the target range, guaranteeing consistent product performance.

[0045] Based on the characteristics of the modified monomers, this invention specifically designs key process parameters for the production of PA6T / 66 copolymerization: In the salt formation stage, the temperature is controlled at 55-60℃. This temperature matches the solubility characteristics of the modified terephthalic acid, ensuring rapid and complete dissolution and shortening the salt formation reaction time, while also avoiding the increased risk of hexamethylenediamine oxidation due to excessively high temperatures. In the prepolymerization stage, a gradient pressure reduction method is adopted, gradually adjusting the system pressure according to changes in prepolymer viscosity. This allows for the smooth discharge of low-molecular-weight byproducts generated during the reaction, avoiding system boiling and prepolymer particle entrainment problems caused by a single pressure release. In the solid-state polymerization stage, a compound antioxidant is added twice. The antioxidant added in the initial stage inhibits the oxidation reaction in the early heating stage, while the antioxidant added in the middle stage addresses the oxidation risk during the rapid molecular weight increase stage, ensuring the antioxidant effect throughout the entire solid-state polymerization process. These process parameters are designed to match the characteristics of the modified monomers, improving the stability of the production process and shortening the time of the salt formation and total polymerization reactions, effectively increasing production efficiency.

[0046] In this invention, antioxidant 1010 and antioxidant 168 are compounded in a specific ratio as antioxidants. Antioxidant 1010 can capture free radicals generated during polymerization to terminate the oxidation chain reaction, while antioxidant 168 can decompose hydroperoxides generated by the oxidation reaction. The two work together to exert a synergistic antioxidant effect, effectively inhibiting the thermal oxidative degradation of PA6T / 66 during high-temperature polymerization and processing, and improving the yellowing phenomenon of the product. Sodium benzoate is selected as an organic nucleating agent, which can act as a crystallization nucleus to promote the orderly stacking of copolymer molecular chains during cooling, improve the crystallinity of the product and improve dimensional stability. At the same time, by controlling the amount of nucleating agent, excessive addition is avoided, which would lead to a decrease in the impact strength of the product. Alkali-free glass fiber treated with KH550 silane coupling agent is used as a reinforcing agent. The silane coupling agent can form covalent bonds between the glass fiber and PA6T / 66 resin, improve the interfacial bonding strength between the two, thereby improving the flexural modulus and heat distortion temperature of the product while avoiding the adverse effects of glass fiber on processing fluidity. Through the rational combination of various functional additives, a balanced optimization of the heat resistance, mechanical properties and processability of PA6T / 66 copolymer high-temperature nylon was achieved.

[0047] This invention addresses the waste gas generated during the salt formation reaction, prepolymerization, solid-state polymerization, and drying processes by designing a three-stage purification process involving water washing, alkali washing, and activated carbon adsorption. Water washing absorbs amines from the waste gas, alkali washing neutralizes acidic byproducts, and activated carbon adsorption removes organic matter, ensuring that the treated waste gas emissions meet industrial environmental standards. The drying process utilizes thermally circulated nitrogen as the drying medium, reducing energy consumption and preventing oxidation caused by contact between the chips and air during drying. Furthermore, specific and repeatable ranges are defined for parameters in each key process step (such as the vacuum degree of hexamethylenediamine pretreatment, the power and time of terephthalic acid plasma treatment, and the pressure reduction rate of prepolymerization). Intermediate control indicators such as the pH value of the salt formation solution and the relative viscosity of the prepolymer are set to ensure consistency across different batches of production, facilitating the industrial scale-up and practical production applications of the process.

[0048] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the production process of PA6T / 66 copolymer high-temperature nylon according to the present invention. Detailed Implementation

[0050] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the present invention. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. Rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly associated with those skilled in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0052] Example 1: The PA6T / 66 copolymer high-temperature nylon provided in this example is composed of basic comonomers, catalysts and functional additives. The mass composition of the basic comonomers is 44.0% hexamethylenediamine, 32.9% terephthalic acid and 23.1% adipic acid, which can simultaneously ensure the material's high-temperature resistance and processing compatibility.

[0053] In this embodiment, hexamethylenediamine needs to be pretreated with sodium bicarbonate. The specific process is as follows: industrial-grade hexamethylenediamine with a purity ≥98.5% is taken and transported to a vacuum distillation vessel with a heat transfer oil jacket. Sodium bicarbonate, accounting for 0.15% of the mass of hexamethylenediamine, is added to the vessel. Stirring is started and the speed is controlled at 55 r / min until the sodium bicarbonate is completely dissolved. The feed valve of the distillation vessel is closed, and the vacuum system is turned on to maintain the vacuum degree in the vessel at -0.093 MPa. The temperature is increased to 60°C at a rate of 5°C / min. The temperature was maintained at 88℃ for 30 minutes, and then the heating rate was adjusted to 3℃ / min. The temperature was then increased to 88℃, and the fraction with a distillation temperature of 82-84℃ was collected. The collected fraction was transferred to a hexamethylenediamine intermediate tank with a 55℃ hot water jacket. Nitrogen gas with a purity of ≥99.99% was introduced into the tank to maintain a slight positive pressure of 0.015MPa, while maintaining a stirring speed of 35r / min. Finally, pretreated hexamethylenediamine with a purity of ≥99.9% and a water content of ≤0.03% was obtained.

[0054] In this embodiment, terephthalic acid requires surface activation and solubility modification. The specific process is as follows: Industrial-grade terephthalic acid with a purity ≥99.0% is pulverized to 150 mesh using a universal pulverizer, then transferred to a hot air dryer and dried at 120℃ for 2 hours, controlling the moisture content to ≤0.1%. The dried terephthalic acid is then transferred to a plasma treatment instrument, and the chamber is purged with nitrogen three times, maintaining a pressure of 0.5 MPa for 10 minutes each time. The processing power is set to 175W, the processing time to 18 minutes, and the nitrogen flow rate to 12 L / min. Surface activation was performed to increase the surface hydroxyl content to ≥0.5 mmol / g. A 0.75 wt% ammonium bicarbonate aqueous solution was prepared, and the activated terephthalic acid was immersed in the solution at a solid-liquid ratio of 1:5. The solution was stirred and soaked for 35 min at 70 r / min at room temperature. After removing the terephthalic acid, it was filtered through a 0.1 μm filter and transferred to a vacuum drying oven to dry at 80 °C and a vacuum degree of -0.08 MPa for 1.5 h to obtain modified terephthalic acid with a solubility of ≥18 g / L in 50% hexamethylenediamine aqueous solution at 25 °C.

[0055] In this embodiment, adipic acid needs to be pulverized and dried. The specific process is as follows: take industrial grade adipic acid, pulverize it to 150 mesh, transfer it to a hot air dryer and dry it at 125°C for 2.2 hours, and control the moisture content to ≤0.1% to ensure the uniformity of the subsequent salt formation reaction.

[0056] In this embodiment, the catalyst is a phosphite catalyst, specifically sodium hypophosphite monohydrate. The preparation process is as follows: Deionized water is added to the reactor, the water temperature is controlled at 28°C, and the mixture is stirred at 350 r / min. Hypophosphite is slowly added, and the pH of the solution is adjusted to 2.2. A 30 wt% sodium hydroxide aqueous solution is slowly added at a molar ratio of hypophosphite to sodium hydroxide of 1:1.02, the reaction temperature is controlled at 40°C, and the reaction is stirred for 1.8 h. After the reaction is complete, the solution is transferred to an evaporator crystallizer and concentrated to a concentration of 52% under a vacuum of -0.08 MPa and a temperature of 65°C. The concentrated solution is transferred to a cooling crystallizer and cooled to 12°C at a rate of 1°C / min. Crystallization is maintained at this temperature for 4 h. After centrifugation to separate the crystals, the solution is vacuum dried at 50°C for 2 h to obtain sodium hypophosphite monohydrate with a purity ≥99.5% and a water content ≤0.05%. The amount of this catalyst added is 0.075% of the total amount of the basic comonomer, which can effectively accelerate the formation of amide bonds and avoid residues affecting product performance.

[0057] In this embodiment, the functional additives include a compound antioxidant, an organic nucleating agent, and a silane-modified reinforcing agent. The specific composition and preparation process of each additive are as follows: The compound antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1, and the dosage is 0.2% of the total mass of the basic comonomer. The synergistic effect of the two can significantly improve the antioxidant efficiency and control the yellowness index of the product below 2.5; The organic nucleating agent is sodium benzoate, and the dosage is 0.075% of the total mass of the basic comonomer. It can promote the orderly stacking of copolymer molecular chains to improve dimensional stability, while avoiding a decrease in impact strength.

[0058] The silane-modified reinforcing agent uses alkali-free glass fiber with a diameter of 12μm and a length of 4mm as raw material. First, it is dried at 120℃ for 2h to control the moisture content ≤0.1%. Then, KH550 silane coupling agent and anhydrous ethanol are mixed at a mass ratio of 1:10. Deionized water accounting for 5% of the ethanol mass is added and stirred for 18min until complete hydrolysis to obtain silane treatment solution. The dried glass fiber is immersed in the silane treatment solution at a liquid-solid ratio of 5:1 and soaked at 25℃ for 1.8h. After being taken out and drained, it is dried at 80℃ for 1h and then dried at 120℃ for 3h. The amount of this reinforcing agent is 20% of the total mass of PA6T / 66 copolymer high-temperature nylon, which can improve the flexural modulus and heat distortion temperature of the material, while ensuring processing fluidity.

[0059] The production process for preparing the above-mentioned PA6T / 66 copolymer high-temperature nylon includes four stages: salt formation reaction, prepolymerization, solid-state polymerization, and post-treatment. The specific process is as follows: Salt formation reaction stage: Hexamethylenediamine pretreated with sodium bicarbonate is mixed with demineralized water at a mass ratio of 1:1 to prepare a 51% hexamethylenediamine aqueous solution at 58℃. This aqueous solution, along with surface-activated terephthalic acid and pulverized and dried adipic acid, is added to a salt formation reactor equipped with a hot water jacket, a steam exhaust system, and a vacuum nitrogen replacement device. The reaction temperature is controlled at 58℃, the pressure is normal, the stirring speed is 90 r / min, and the reaction is carried out for 1.5 h. At the end of the reaction, the pH of the solution should be controlled to be 7.1 and the solution should be clear and transparent to obtain a uniform PA6T / 66 copolymer salt solution. The clarity and transparency can be used to visually determine that the salt formation reaction is complete and there are no undissolved terephthalic acid particles.

[0060] After the salt formation reaction is completed, the prepolymerization stage begins: the copolymer salt solution is transferred to a polymerization reactor with a built-in mirror-polished coil for heating (heat transfer oil is used as the heating medium), and the reaction temperature is controlled at 235℃ and the pressure inside the reactor is 2.3MPa for 2.5 hours. In the later stage of the reaction, a gradient pressure reduction is carried out, first from 2.2MPa to 1.0MPa over 1 hour, and then from 1.0MPa to atmospheric pressure over 1 hour. The gradient pressure reduction can avoid system boiling and prepolymer particle entrainment. After the pressure reduction is completed, a water ring vacuum pump is used to evacuate the system for 0.8 hours to make the relative viscosity of the prepolymer reach 1.37. Nitrogen gas is introduced into the polymerization reactor, and the prepolymer is forced into the crystallizer through pressure difference. After cooling and flash crystallization, the prepolymer is crushed to 3mm particles. This particle size can improve the reaction efficiency of subsequent solid-phase polymerization.

[0061] After prepolymerization, solid-state polymerization is carried out: the prepolymer particles are transferred to a drum dryer and dried for 7 hours at a vacuum of -0.085 MPa and a temperature of 95°C, controlling the particle moisture content to ≤0.5% to avoid molecular chain hydrolysis and breakage caused by moisture; the dried prepolymer particles are then transferred to a drum-type solid-state polymerization reactor, heated to 275°C, and the vacuum inside the reactor is controlled at 12 Pa for 10 hours; during the reaction, the compounded antioxidant is added in two stages, with 50% of the total amount added at the beginning of solid-state polymerization and the remaining 50% added after 6 hours of reaction. This phased addition ensures that the antioxidant effect is maintained throughout the process, inhibiting thermal oxidative degradation at different stages; after the reaction is completed, a final polymer with a relative viscosity of 2.50 is obtained, which corresponds to a number-average molecular weight of 25,000-30,000, meeting the mechanical property requirements.

[0062] After solid-state polymerization, the final polymer is post-processed: the final polymer is transferred to a twin-screw extruder with segmented temperature control, where the feed section temperature is 290℃, the melting section temperature is 300℃, the homogenization section temperature is 305℃, and the die head temperature is 310℃. Segmented temperature control can adapt to the changes in the state of the final polymer in the screw, ensuring melt uniformity. The melt is cooled into strips by circulating cooling water at 33℃, and then pelletized by an underwater pelletizer. The PA6T / 66 chips obtained after pelletizing have an initial moisture content of 2500ppm. They are then sent to a fluidized bed dryer and dried with 95℃ hot circulating nitrogen for 2 hours. After drying, the moisture content of the chips is controlled below 800ppm, finally yielding the PA6T / 66 copolymer high-temperature nylon product.

[0063] The performance indicators of the PA6T / 66 copolymer high-temperature nylon prepared in this embodiment are as follows: tensile strength 96.5MPa, flexural strength 124.5MPa, flexural modulus 2.5GPa, notched impact strength 4.0KJ / m². All indicators meet the usage requirements and have excellent performance stability.

[0064] Example 2: The PA6T / 66 copolymer high-temperature nylon provided in this example is composed of basic comonomers, catalysts and functional additives. The mass composition of the basic comonomers is 42.8% hexamethylenediamine, 35.6% terephthalic acid and 21.6% adipic acid, which can balance the high temperature resistance and processing convenience of the material.

[0065] In this embodiment, hexamethylenediamine needs to be pretreated with sodium bicarbonate. The specific process is as follows: industrial-grade hexamethylenediamine with a purity ≥98.5% is taken and transported to a vacuum distillation kettle with a heat transfer oil jacket. Sodium bicarbonate, accounting for 0.1% of the mass of hexamethylenediamine, is added to the kettle. Stirring is started and the speed is controlled at 50 r / min until the sodium bicarbonate is completely dissolved. The feed valve of the distillation kettle is closed, and the vacuum system is turned on to maintain the vacuum degree in the kettle at -0.092 MPa. The temperature is increased to 55°C at a rate of 4°C / min. The temperature was maintained at 80℃ for 25 minutes, and then the heating rate was adjusted to 2℃ / min. The temperature was then increased to 85℃, and the fraction distilled at 80-82℃ was collected. The collected fraction was transferred to a hexamethylenediamine intermediate tank with a 50℃ hot water jacket. Nitrogen gas with a purity ≥99.99% was introduced into the tank to maintain a slight positive pressure of 0.01MPa, while maintaining a stirring speed of 30r / min. Finally, pretreated hexamethylenediamine with a purity ≥99.9% and a water content ≤0.03% was obtained.

[0066] In this embodiment, terephthalic acid needs to undergo surface activation and solubility modification. The specific process is as follows: industrial-grade terephthalic acid with a purity ≥99.0% is taken, pulverized to 100 mesh using a universal pulverizer, and then dried in a hot air dryer at 110℃ for 1 hour, controlling the moisture content to ≤0.1%. The dried terephthalic acid is then transferred to a plasma treatment instrument, and the chamber is purged twice with nitrogen gas. Each purging is maintained at a pressure of 0.4MPa for 8 minutes. The processing power is set to 150W, the processing time to 15 minutes, and the nitrogen flow rate to 10L / min. Surface activation was completed to increase the surface hydroxyl content to ≥0.5 mmol / g; a 0.5 wt% ammonium bicarbonate aqueous solution was prepared, and the activated terephthalic acid was immersed in the solution at a solid-liquid ratio of 1:4. The solution was stirred and soaked for 30 min at 60 r / min at room temperature; after the terephthalic acid was removed, it was filtered through a 0.1 μm filter and transferred to a vacuum drying oven to dry at 80 °C and a vacuum degree of -0.08 MPa for 1 h to obtain modified terephthalic acid with a solubility of ≥15 g / L in 50% hexamethylenediamine aqueous solution at 25 °C.

[0067] In this embodiment, adipic acid needs to be pulverized and dried. The specific process is as follows: take industrial grade adipic acid, pulverize it to 100 mesh, transfer it to a hot air dryer and dry it at 120°C for 2 hours, and control the moisture content to ≤0.1% to ensure that the subsequent salt formation reaction proceeds uniformly.

[0068] In this embodiment, the catalyst is a phosphite catalyst, specifically sodium hypophosphite monohydrate. The preparation process is as follows: Deionized water is added to the reactor, the water temperature is controlled at 20°C, and the mixture is stirred at 250 r / min. Hypophosphite is slowly added, and the pH of the solution is adjusted to 1.8. A 25 wt% sodium hydroxide aqueous solution is slowly added at a molar ratio of hypophosphite to sodium hydroxide of 1:1.01, and the reaction temperature is controlled at 35°C. The mixture is stirred for 1 hour. After the reaction is complete, the solution is transferred to an evaporator crystallizer and concentrated to a concentration of 45% under a vacuum of -0.07 MPa and a temperature of 55°C. The concentrated solution is transferred to a cooling crystallizer and cooled to 5°C at a rate of 0.5°C / min. The solution is kept at this temperature for 3 hours to crystallize. After centrifugation to separate the crystals, it is vacuum dried at 45°C for 1.5 hours to obtain sodium hypophosphite monohydrate with a purity ≥99.5% and a water content ≤0.05%. The amount of this catalyst added is 0.05% of the total amount of the basic comonomer, which can effectively catalyze the polycondensation reaction without any excess residue.

[0069] In this embodiment, the functional additives include a compound antioxidant, an organic nucleating agent, and a silane-modified reinforcing agent. The specific composition and preparation process of each additive are as follows: The compound antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1, and the dosage is 0.1% of the total mass of the basic comonomer. It can effectively inhibit thermal oxidative degradation and control the yellowness index of the product. The organic nucleating agent is sodium benzoate, and the dosage is 0.05% of the total mass of the basic comonomer. It can improve the crystallinity and dimensional stability of the copolymer.

[0070] The silane-modified reinforcing agent uses alkali-free glass fiber with a diameter of 10μm and a length of 3mm as raw material. First, it is dried at 110℃ for 1.5h to control the moisture content ≤0.1%. Then, KH550 silane coupling agent and anhydrous ethanol are mixed at a mass ratio of 1:8. Deionized water accounting for 4% of the ethanol mass is added and stirred for 10min until complete hydrolysis to obtain silane treatment solution. The dried glass fiber is immersed in the silane treatment solution at a liquid-solid ratio of 4:1 and soaked at 20℃ for 1h. After being taken out and drained, it is dried at 70℃ for 0.5h and then dried at 110℃ for 2.5h. The amount of this reinforcing agent is 10% of the total mass of PA6T / 66 copolymer high-temperature nylon, which can ensure the balance between the mechanical properties and processing fluidity of the material.

[0071] In this embodiment, the production process for preparing the above-mentioned PA6T / 66 copolymer high-temperature nylon includes four stages: salt formation reaction, prepolymerization, solid-state polymerization, and post-treatment. The specific process is as follows: Salt formation reaction stage: Hexamethylenediamine pretreated with sodium bicarbonate was mixed with demineralized water at a mass ratio of 1:1, and a 50% hexamethylenediamine aqueous solution was prepared at 55℃. This aqueous solution, together with surface-activated terephthalic acid and pulverized and dried adipic acid, was added to a salt formation reactor equipped with a hot water jacket, a steam exhaust system, and a vacuum nitrogen replacement device. The reaction temperature was controlled at 55℃, the pressure was normal, the stirring speed was 80 r / min, and the reaction was carried out for 1 hour. At the end of the reaction, the pH of the solution was controlled to be 7.0 and the solution was clear and transparent, resulting in a homogeneous PA6T / 66 copolymer salt solution.

[0072] After the salt formation reaction is completed, the prepolymerization stage begins: the copolymer salt solution is transferred to a polymerization reactor with a built-in mirror-polished coil for heating, and the reaction temperature is controlled at 220℃ and the internal pressure at 2.2MPa for 2 hours; in the later stage of the reaction, the pressure is gradually reduced, first from 2.0MPa to 0.8MPa over 0.8 hours, and then from 0.8MPa to atmospheric pressure over 0.8 hours; after the pressure reduction is completed, a water ring vacuum pump is used to evacuate the vacuum for 0.5 hours to make the relative viscosity of the prepolymer reach 1.35; nitrogen is introduced into the polymerization reactor, and the prepolymer is forced into the crystallizer by pressure difference, and after cooling and flash crystallization, it is crushed into 2mm particles.

[0073] After prepolymerization, solid-state polymerization was carried out: the prepolymer particles were transferred to a drum dryer and dried for 6 hours at a vacuum of -0.08 MPa and a temperature of 80°C, with the particle moisture content controlled to be ≤0.5%; the dried prepolymer particles were transferred to a drum-type solid-state polymerization reactor, heated to 270°C, and the vacuum inside the reactor was controlled to be 10 Pa, and the reaction was carried out for 8 hours; during the reaction, the compounded antioxidant was added in two batches, with 40% of the total amount added at the beginning of the solid-state polymerization and the remaining 40% added after 5 hours of reaction; after the reaction was completed, a final polymer with a relative viscosity of 2.48 was obtained.

[0074] After solid-state polymerization, the final polymer is post-processed: the final polymer is transferred to a twin-screw extruder and a segmented temperature control mode is adopted, with the feed section temperature at 280℃, the melting section temperature at 290℃, the homogenization section temperature at 300℃, and the die head temperature at 300℃; the melt is cooled into strips by circulating cooling water at 32℃, and then granulated by an underwater pelletizer; the initial moisture content of the PA6T / 66 chips obtained after pelletizing is 2000ppm, which is sent to a fluidized bed dryer and dried with 80℃ hot circulating nitrogen for 1 hour. After drying, the moisture content of the chips is controlled below 800ppm, and the final PA6T / 66 copolymer high-temperature nylon product is obtained.

[0075] The performance indicators of the PA6T / 66 copolymer high-temperature nylon obtained in this embodiment are as follows: tensile strength 92.1MPa, flexural strength 116MPa, flexural modulus 2.2GPa, and notched impact strength 3.1KJ / m². All indicators meet the usage requirements and the performance is stable.

[0076] Example 3: The PA6T / 66 copolymer high-temperature nylon provided in this example is composed of basic comonomers, catalysts and functional additives. The mass composition of the basic comonomers is 45.1% hexamethylenediamine, 33.5% terephthalic acid and 21.4% adipic acid, which can enhance the high-temperature resistance of the material and adapt to processing requirements.

[0077] In this embodiment, hexamethylenediamine needs to be pretreated with sodium bicarbonate. The specific process is as follows: industrial-grade hexamethylenediamine with a purity ≥98.5% is taken and transported to a vacuum distillation kettle with a heat transfer oil jacket. Sodium bicarbonate, accounting for 0.2% of the mass of hexamethylenediamine, is added to the kettle. Stirring is started and the speed is controlled at 60 r / min until the sodium bicarbonate is completely dissolved. The feed valve of the distillation kettle is closed, and the vacuum system is turned on to maintain the vacuum degree in the kettle at -0.095 MPa. The temperature is increased to 65°C at a rate of 6°C / min. The temperature was maintained at ℃ for 40 min, and then the heating rate was adjusted to 4℃ / min. The temperature was then increased to 90℃, and the fraction with a distillation temperature of 83-85℃ was collected. The collected fraction was transferred to a hexamethylenediamine intermediate tank with a 60℃ hot water jacket. Nitrogen gas with a purity of ≥99.99% was introduced into the tank to maintain a slight positive pressure of 0.02MPa, while maintaining a stirring speed of 40r / min. Finally, pretreated hexamethylenediamine with a purity of ≥99.9% and a water content of ≤0.03% was obtained.

[0078] In this embodiment, terephthalic acid needs to undergo surface activation and solubility modification. The specific process is as follows: industrial-grade terephthalic acid with a purity ≥99.0% is taken, pulverized to 200 mesh using a universal pulverizer, and then dried in a hot air dryer at 130℃ for 3 hours, controlling the moisture content to ≤0.1%. The dried terephthalic acid is then transferred to a plasma treatment instrument, and the chamber is purged with nitrogen four times, maintaining a pressure of 0.6MPa for 12 minutes each time. The processing power is set to 200W, the processing time to 20 minutes, and the nitrogen flow rate to 15L / min. Surface activation was completed to increase the surface hydroxyl content to ≥0.5 mmol / g; a 1.0 wt% ammonium bicarbonate aqueous solution was prepared, and the activated terephthalic acid was immersed in the solution at a solid-liquid ratio of 1:6. The solution was stirred and soaked for 40 min at 80 r / min at room temperature; after the terephthalic acid was removed, it was filtered through a 0.1 μm filter and transferred to a vacuum drying oven to dry at 80 °C and a vacuum degree of -0.08 MPa for 2 h to obtain modified terephthalic acid with a solubility of ≥20 g / L in 50% hexamethylenediamine aqueous solution at 25 °C.

[0079] In this embodiment, adipic acid needs to be pulverized and dried. The specific process is as follows: take industrial grade adipic acid, pulverize it to 200 mesh, transfer it to a hot air dryer and dry it at 130°C for 2.5 hours, and control the moisture content to ≤0.1% to provide uniform raw materials for the subsequent salt formation reaction.

[0080] In this embodiment, the catalyst is a phosphite catalyst, specifically sodium hypophosphite monohydrate. The preparation process is as follows: Deionized water is added to the reactor, the water temperature is controlled at 35°C, and the mixture is stirred at 450 r / min. Hypophosphite is slowly added, and the pH of the solution is adjusted to 2.7. A 35 wt% sodium hydroxide aqueous solution is slowly added at a molar ratio of hypophosphite to sodium hydroxide of 1:1.03, the reaction temperature is controlled at 45°C, and the reaction is stirred for 2.5 h. After the reaction is complete, the solution is transferred to an evaporator crystallizer and concentrated to a concentration of 60% under a vacuum of -0.09 MPa and a temperature of 75°C. The concentrated solution is transferred to a cooling crystallizer and cooled to 20°C at a rate of 1.5°C / min. Crystallization is maintained at this temperature for 5 h. After centrifugation to separate the crystals, the solution is vacuum dried at 55°C for 2.5 h to obtain sodium hypophosphite monohydrate with a purity ≥99.5% and a water content ≤0.05%. The amount of this catalyst added is 0.1% of the total amount of the basic comonomer, which can efficiently catalyze the polycondensation reaction and ensure stable molecular chain growth.

[0081] In this embodiment, the functional additives include a compound antioxidant, an organic nucleating agent, and a silane-modified reinforcing agent. The specific composition and preparation process of each additive are as follows: The compound antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1, and the dosage is 0.3% of the total mass of the basic comonomer. It can effectively inhibit thermal oxidative degradation at high temperature and significantly reduce the yellowness index of the product. The organic nucleating agent is sodium benzoate, and the dosage is 0.1% of the total mass of the basic comonomer. It can further improve the crystallinity of the copolymer and optimize the dimensional stability.

[0082] The silane-modified reinforcing agent uses alkali-free glass fiber with a diameter of 15μm and a length of 5mm as raw material. First, it is dried at 130℃ for 2.5h to control the moisture content to ≤0.1%. Then, KH550 silane coupling agent and anhydrous ethanol are mixed at a mass ratio of 1:12. Deionized water accounting for 6% of the ethanol mass is added and stirred for 25min until complete hydrolysis to obtain a silane treatment solution. The dried glass fiber is immersed in the silane treatment solution at a liquid-to-solid ratio of 6:1 and soaked at 30℃ for 2.5h. After being taken out and drained, it is dried at 90℃ for 1.5h and then dried at 130℃ for 3.5h. The amount of this reinforcing agent is 30% of the total mass of PA6T / 66 copolymer high-temperature nylon, which can significantly improve the flexural modulus and heat distortion temperature of the material to meet the requirements of high-strength application scenarios.

[0083] In this embodiment, the production process for preparing the above-mentioned PA6T / 66 copolymer high-temperature nylon includes four stages: salt formation reaction, prepolymerization, solid-state polymerization, and post-treatment. The specific process is as follows: Salt formation reaction stage: Hexamethylenediamine pretreated with sodium bicarbonate was mixed with demineralized water at a mass ratio of 1:1, and a 52% hexamethylenediamine aqueous solution was prepared at 60℃. This aqueous solution, along with surface-activated terephthalic acid and pulverized and dried adipic acid, was added to a salt formation reactor equipped with a hot water jacket, a steam exhaust system, and a vacuum nitrogen replacement device. The reaction temperature was controlled at 60℃, the pressure was normal, the stirring speed was 100 r / min, and the reaction was carried out for 2 hours. At the end of the reaction, the pH of the solution was controlled to be 7.2 and the solution was clear and transparent, resulting in a homogeneous PA6T / 66 copolymer salt solution.

[0084] After the salt formation reaction is completed, the prepolymerization stage begins: the copolymer salt solution is transferred to a polymerization reactor with a built-in mirror-polished coil for heating, and the reaction temperature is controlled at 250℃ and the internal pressure at 2.5MPa for 3 hours; in the later stage of the reaction, the pressure is gradually reduced, first from 2.4MPa to 1.2MPa over 1.2 hours, and then from 1.2MPa to atmospheric pressure over 1.2 hours; after the pressure reduction is completed, a water ring vacuum pump is used to evacuate the vacuum for 1 hour to make the relative viscosity of the prepolymer reach 1.39; nitrogen is introduced into the polymerization reactor, and the prepolymer is forced into the crystallizer by pressure difference, and after cooling and flash crystallization, it is crushed into 5mm particles.

[0085] After prepolymerization, solid-state polymerization was carried out: the prepolymer particles were transferred to a drum dryer and dried for 8 hours at a vacuum of -0.09 MPa and a temperature of 110°C, with the particle moisture content controlled to be ≤0.5%; the dried prepolymer particles were transferred to a drum-type solid-state polymerization reactor, heated to 280°C, and the vacuum inside the reactor was controlled to be 15 Pa, and the reaction was carried out for 12 hours; during the reaction, the compounded antioxidant was added in two batches, with 60% of the total amount added at the beginning of the solid-state polymerization and the remaining 60% added after 7 hours of reaction; after the reaction was completed, a final polymer with a relative viscosity of 2.52 was obtained.

[0086] After solid-state polymerization, the final polymer is post-processed: the final polymer is transferred to a twin-screw extruder and a segmented temperature control mode is adopted, with the feed section temperature at 300℃, the melting section temperature at 310℃, the homogenization section temperature at 310℃, and the die head temperature at 320℃; the melt is cooled into strips by circulating cooling water at 35℃, and then pelletized by an underwater pelletizer; the initial moisture content of the PA6T / 66 chips obtained after pelletizing is 3000ppm, which is sent to a fluidized bed dryer and dried with hot circulating nitrogen at 120℃ for 3 hours. After drying, the moisture content of the chips is controlled below 800ppm, and the PA6T / 66 copolymer high-temperature nylon product is finally obtained.

[0087] The performance indicators of the PA6T / 66 copolymer high-temperature nylon obtained in this embodiment are as follows: tensile strength 99.8MPa, flexural strength 129.5MPa, flexural modulus 2.8GPa, notched impact strength 4.9KJ / m². All indicators meet the requirements for use, and the high temperature resistance and mechanical properties are excellent.

[0088] Comparative Example 1: The PA6T / 66 copolymer high-temperature nylon provided in this comparative example is composed of basic comonomers, catalysts and functional additives. The mass composition of the basic comonomers is 44.0% hexamethylenediamine, 32.9% terephthalic acid and 23.1% adipic acid, which is completely consistent with Example 1. The core difference is that the basic comonomers are all industrial-grade conventional products without any modification treatment, which cannot eliminate the adverse effects of the inherent defects of the monomers on the copolymerization reaction from the source.

[0089] In this comparative example, hexamethylenediamine was directly used as an industrial-grade product with a purity ≥98.5%, without sodium bicarbonate pretreatment, vacuum distillation to remove impurities, or nitrogen protection to isolate oxygen. This resulted in a purity consistently ≤98.5%, a water content >0.1%, and an amino oxidation rate >1.0%. The amine groups readily combine with oxygen in subsequent high-temperature reactions to generate impurities, disrupting the amine-acid molar ratio balance. The terephthalic acid was also a conventional industrial-grade product, without surface activation or solubility modification. It was not subjected to pulverization, drying, plasma treatment, or ammonium bicarbonate soaking. Its solubility in a 50% hexamethylenediamine aqueous solution at 25°C was ≤5 g / L. It exhibited strong hydrophobicity and low surface activity, making it prone to particle agglomeration during the salt formation reaction. The adipic acid was also not pulverized or dried; it was directly added to the reaction in industrial-grade granular form. This resulted in uneven particle size and the potential carrying of adsorbed water, further affecting the uniformity of the salt formation reaction.

[0090] In this comparative example, the catalyst is sodium hypophosphite monohydrate. Its preparation process, purity index and addition amount are the same as those in Example 1. That is, a product with a purity of ≥99.5% is obtained by neutralizing hypophosphite with sodium hydroxide and evaporating and crystallizing. The addition amount is 0.075% of the total amount of basic comonomer.

[0091] In this comparative example, the functional additives include a compound antioxidant, an organic nucleating agent, and a silane-modified reinforcing agent. The composition, preparation process, and dosage of each additive are exactly the same as in Example 1. The compound antioxidant is antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1, with a dosage of 0.2%. The organic nucleating agent is sodium benzoate, with a dosage of 0.075%. The silane-modified reinforcing agent is alkali-free glass fiber treated with KH550, with a dosage of 20%. This attempt is made to compensate for monomer defects through the action of additives, but it cannot fundamentally solve the problem.

[0092] The production process for preparing PA6T / 66 copolymer high-temperature nylon in this comparative example follows the parameters of Example 1. In the salt formation reaction stage, conventional hexamethylenediamine and demineralized water are mixed at a mass ratio of 1:1, and a 51% hexamethylenediamine aqueous solution is prepared at 58°C. This solution is then added to the salt formation reactor along with conventional terephthalic acid and adipic acid. The reaction temperature is controlled at 58°C, atmospheric pressure, and stirring speed at 90 r / min, and the reaction is carried out for 1.5 h. In the prepolymerization stage, the copolymer salt solution is transferred to the polymerization reactor, and the reaction is carried out at 235°C and 2.3 MPa for 2.5 h. The subsequent gradient pressure reduction, vacuuming, and crystallization crushing steps are consistent with those in Example 1. In the solid-phase polymerization stage, the drying temperature, vacuum degree, reaction time, and antioxidant addition method are controlled with the same parameters. In the post-treatment stage, the twin-screw segmented temperature control, cooling water temperature, and drying conditions are also not adjusted in any way.

[0093] Because the basic comonomers were not modified, the PA6T / 66 copolymer high-temperature nylon prepared in this comparative example had obvious defects: the terephthalic acid agglomeration rate during the salt formation reaction was >30%, and the solution could not reach the clear and transparent state of Example 1, appearing as a white suspension, resulting in uneven distribution of 6T rigid units and 66 flexible units in the copolymer molecular chain; the impurities generated by the oxidation of hexamethylenediamine interfered with the polycondensation reaction, causing the relative viscosity of the prepolymer to fluctuate in the range of 1.30-1.42, and the relative viscosity of the final polymer to be difficult to stabilize in the range of 2.48-2.52; the mechanical properties of the product fluctuated significantly, with tensile strength of only 85-92 MPa, a batch-to-batch difference of 7 MPa, and flexural strength fluctuating in the range of 105-115 MPa, with some batches failing to meet the usage requirements; at the same time, the amino oxidation products and thermal oxidative degradation promoted each other, and the yellowness index of the final polymer was >4.0, much higher than the 2.5 or below in Example 1, and the thermal stability was greatly deteriorated.

[0094] Comparative Example 2: The PA6T / 66 copolymer high-temperature nylon provided in this comparative example is composed of basic comonomers, catalysts and functional additives. The mass composition of the basic comonomers is 44.0% hexamethylenediamine, 32.9% terephthalic acid and 23.1% adipic acid, which is consistent with Example 1. The core difference is that the hexamethylenediamine is a conventional industrial-grade product and has not been pretreated with sodium bicarbonate. The modification treatments of terephthalic acid and adipic acid are the same as in Example 1, which only eliminates the dissolution defect of terephthalic acid and cannot solve the oxidation problem of hexamethylenediamine.

[0095] In this comparative example, hexamethylenediamine was directly used with industrial-grade raw materials with a purity of ≥98.5%, without pretreatment steps such as dissolution with sodium bicarbonate, purification by vacuum distillation, and nitrogen protection. Its purity could not be increased to above 99.9%, and the actual purity was ≤98.5%, with a water content >0.1%. Furthermore, the amino group is easily exposed to air during storage and reaction, with an oxidation rate >0.8%, which may lead to an excess or deficiency of amino groups in the salt formation reaction, thus disrupting the precise control of the amine-acid molar ratio.

[0096] The surface activation and solubility modification process of terephthalic acid was carried out exactly as described in Example 1. After being pulverized to 150 mesh, dried at 120°C for 2 hours, subjected to plasma treatment (175W, 18 minutes), and soaked in 0.75wt% ammonium bicarbonate, the solubility of terephthalic acid in hexamethylenediamine aqueous solution was ≥18g / L, which can achieve uniform dissolution. The adipic acid was also pulverized to 150 mesh and dried at 125°C for 2.2 hours according to the parameters of Example 1, with a water content ≤0.1%, which ensured the reactivity of the dicarboxylic acid.

[0097] In this comparative example, the composition, preparation, and dosage of the catalyst and functional additives are consistent with those in Example 1. The purity of sodium hypophosphite monohydrate is ≥99.5%, and the addition amount is 0.075%. The types and dosages of the compounded antioxidants, organic nucleating agents, and silane modifiers are not adjusted to ensure that, except for the modification with hexamethylenediamine, the other reaction conditions are no different from those in Example 1.

[0098] The production process of this comparative example follows the steps and parameters of Example 1 exactly. Untreated hexamethylenediamine is used when preparing the 51% hexamethylenediamine aqueous solution in the salt formation reaction stage. The other temperature, stirring speed and reaction time are controlled in the same way. The temperature, pressure and time parameters of prepolymerization, solid-state polymerization and post-treatment are also completely consistent with those of Example 1. The only difference is that the stability of the reaction process decreases due to the difference in the quality of hexamethylenediamine.

[0099] The anticipated defects of this comparative example mainly stem from the lack of pretreatment of hexamethylenediamine: during the salt formation reaction, insufficient purity of hexamethylenediamine and amino oxidation led to an expansion of the solution pH fluctuation range to 6.9-7.3, making it impossible to stably control within the optimal range of 7.0-7.2. The imbalance of the amine-acid molar ratio directly caused fluctuations in the relative viscosity of the prepolymer (1.30-1.42), which was significantly different from 1.37±0.02 in Example 1. The uneven growth of molecular chains during the solid-phase polymerization stage made it difficult to stabilize the relative viscosity of the final polymer at 2.48-2.52, with the actual detection range being 2.40-2.55, indicating a wider molecular weight distribution. The chemical resistance of the product decreased; after soaking in 80°C hot water for 24 hours, the tensile strength retention rate was only 82-85%, lower than the 92% or more in Example 1. At the same time, the oxidation products of hexamethylenediamine resulted in a yellowness index of >3.5 in the final polymer, indicating a higher degree of thermal oxidative degradation than in Example 1, and insufficient long-term stability.

[0100] Comparative Example 3: The PA6T / 66 copolymer high-temperature nylon provided in this comparative example is composed of basic comonomers, catalysts, and functional additives. The mass composition of the basic comonomers is 44.0% hexamethylenediamine, 32.9% terephthalic acid, and 23.1% adipic acid, which is consistent with Example 1. The key difference is that the terephthalic acid is a conventional industrial-grade product without surface activation and solubility modification. The sodium bicarbonate pretreatment of hexamethylenediamine and the pulverization and drying treatment of adipic acid are the same as in Example 1, only retaining the purity advantage of hexamethylenediamine, but failing to solve the problem of uneven dissolution of terephthalic acid.

[0101] In this comparative example, terephthalic acid was directly sourced from industrial-grade raw materials with a purity ≥99.0%, without undergoing pulverization, drying, plasma surface activation, or ammonium bicarbonate soaking modification. The resulting particles were relatively large and lacked active hydroxyl groups, exhibiting strong hydrophobicity. Its solubility in a 50% hexamethylenediamine aqueous solution at 25°C was ≤8 g / L, making it difficult to completely dissolve during the salt formation reaction, easily forming undissolved particles suspended in the solution. The hexamethylenediamine was pretreated with sodium bicarbonate according to the parameters of Example 1, and after vacuum distillation and nitrogen protection, its purity was ≥99.9%, water content ≤0.03%, and amino oxidation rate ≤0.1%, providing a stable source of amine groups. The adipic acid was also pulverized to 150 mesh and dried at 125°C for 2.2 hours, with a water content ≤0.1%, ensuring its own reaction uniformity.

[0102] In this comparative example, the preparation of the catalyst and functional additives were exactly the same as in Example 1. The preparation process, purity and addition amount of sodium hypophosphite monohydrate, as well as the composition, preparation and dosage of the compound antioxidant, organic nucleating agent and silane modifier, were also the same.

[0103] The production process of this comparative example strictly follows the parameters of Example 1. In the salt formation reaction stage, the pretreated hexamethylenediamine is prepared into a 51% aqueous solution and added to the salt formation reactor along with conventional terephthalic acid and treated adipic acid. The temperature is controlled at 58°C and the stirring speed at 90 r / min for 1.5 h. In the prepolymerization stage, the reaction is carried out at 235°C and 2.3 MPa for 2.5 h. The subsequent gradient pressure reduction and vacuuming steps remain unchanged. The temperature, pressure, time and other parameters of solid-state polymerization and post-treatment are also completely consistent with those of Example 1. The only abnormality in the reaction process is due to the difference in the solubility characteristics of terephthalic acid.

[0104] The anticipated defects of this comparative example are concentrated in the uneven dissolution of terephthalic acid: the salt-forming reaction solution is a white suspension, failing to achieve the clear and transparent state of Example 1; undissolved terephthalic acid particles easily adhere to the walls of the salt-forming reactor, leading to incomplete local reactions; the continued presence of undissolved particles in the prepolymerization stage easily causes local overheating in the reactor, triggering polymer degradation and widening the relative viscosity fluctuation range of the prepolymer to 1.32-1.40, and particles are easily entrained by the airflow, causing prepolymer loss; the final polymer has uneven mechanical properties due to the uneven distribution of 6T units. The tensile strength was significantly reduced, with tensile strength only 88-93 MPa and flexural modulus fluctuating in the range of 2.0-2.3 GPa. Some batches were lower than the lower limit of 2.2 GPa specified in claim 10. The notched impact strength also dropped to 2.8-3.2 KJ / m², and some batches could not meet the requirement of ≥3.1 KJ / m². At the same time, undissolved particles affected the melt uniformity, and the melt pressure fluctuation during twin-screw extrusion was >15%, which was much higher than ≤5% in Example 1. The processing fluidity decreased, and the product surface was prone to defects such as scratches and bubbles.

[0105] Comparative Example 4: The PA6T / 66 copolymer high-temperature nylon provided in this comparative example is composed of basic comonomers, catalysts and functional additives. The mass composition of the basic comonomers was adjusted to 40.0% hexamethylenediamine, 34.0% terephthalic acid and 26.0% adipic acid, with a total mass percentage of 100%. The key difference is that the amount of hexamethylenediamine added is 40.0%, which results in insufficient total amine groups and cannot fully react with carboxyl groups.

[0106] In this comparative example, hexamethylenediamine was pretreated with sodium bicarbonate according to the parameters of Example 1, with a purity ≥99.9% and a water content ≤0.03%, and the modification effect was consistent with that of Example 1. The terephthalic acid and adipic acid were also subjected to surface activation and solubility modification, pulverization and drying treatment according to the parameters of Example 1, respectively, to ensure that the modification quality of other monomers was the same except for the amount of hexamethylenediamine added, and the defect of insufficient amine groups was only created by reducing the proportion of hexamethylenediamine.

[0107] In this comparative example, the preparation of the catalyst and functional additives were completely in accordance with Example 1. The preparation process, purity and addition amount of sodium hypophosphite monohydrate, as well as the composition, preparation and dosage of the compound antioxidant, organic nucleating agent and silane modifier, remained unchanged, ensuring that only the amount of hexamethylenediamine added was the only variable.

[0108] The production process of this comparative example strictly follows the parameters of Example 1. In the salt formation reaction stage, the pretreated hexamethylenediamine is prepared into a 51% aqueous solution and added to the salt formation reactor together with the modified terephthalic acid and the treated adipic acid. The temperature is controlled at 58°C and the stirring speed is 90 r / min for 1.5 h. The temperature, pressure, time and other parameters of the prepolymerization, solid-state polymerization and post-treatment are also completely consistent with those of Example 1. The only difference is that the reaction equilibrium is shifted due to insufficient hexamethylenediamine.

[0109] The anticipated defects of this comparative example mainly stem from insufficient amine groups: In the salt formation reaction, due to the low amount of hexamethylenediamine and excessive carboxyl groups, the pH of the final solution was <6.8, lower than 7.1 in Example 1. Additional hexamethylenediamine was needed to adjust the pH, leading to decreased process stability. Furthermore, the addition process easily caused localized excess of amine groups, further exacerbating the uneven reaction. In the prepolymerization stage, insufficient amine groups slowed the amide bond formation rate, resulting in a prepolymer relative viscosity <1.30, lower than 1.37 in Example 1. The prepolymerization time needed to be extended to over 4 hours to approach the target viscosity. In the solid-state polymerization stage, molecular chain growth was difficult. Even with an extended reaction time of 14 hours, the final polymer relative viscosity was still difficult to stabilize at 2.48-2.52, with actual measured values ​​of 2.40-2.46, indicating a low molecular weight. The product's mechanical properties deteriorated significantly, with tensile strength <85 MPa and flexural strength <105 MPa. Temperature resistance also decreased, with a heat distortion temperature <250°C, far lower than ≥270°C in Example 1, failing to meet the requirements for high-temperature applications.

[0110] Comparative Example 5: The PA6T / 66 copolymer high-temperature nylon provided in this comparative example is composed of basic comonomers, catalysts and functional additives. The mass composition of the basic comonomers is adjusted to 48.0% hexamethylenediamine, 29.0% terephthalic acid and 23.0% adipic acid. The key difference is that the amount of hexamethylenediamine added is 48.0%, which leads to an excess of amine groups and is prone to side reactions.

[0111] In this comparative example, the sodium bicarbonate pretreatment process of hexamethylenediamine, the surface activation and solubility modification process of terephthalic acid, and the pulverization and drying process of adipic acid were completely consistent with those in Example 1, ensuring that there was no difference in the quality of monomer modification. The only defect was that the amount of hexamethylenediamine added exceeded the standard range, resulting in excessive amine groups.

[0112] In this comparative example, the catalyst and functional additives were configured in the same way as in Example 1. The purity and amount of sodium hypophosphite monohydrate, as well as the composition, preparation and amount of the compound antioxidant, organic nucleating agent and silane modifier, remained unchanged, ensuring that only the amount of hexamethylenediamine added was the only variable.

[0113] The production process of this comparative example was strictly carried out according to the parameters of Example 1. In the salt formation reaction stage, a 51% hexamethylenediamine aqueous solution was prepared and added to the salt formation reactor together with modified terephthalic acid and treated adipic acid. The temperature was controlled at 58°C and the stirring speed at 90 r / min for 1.5 h. The temperature, pressure, time and other parameters of prepolymerization, solid-state polymerization and post-treatment were also completely consistent with those of Example 1. The only abnormality in the reaction system was caused by the excess of hexamethylenediamine.

[0114] The anticipated defects of this comparative example are concentrated in the excess of amine groups: due to the excessive amount of hexamethylenediamine used in the salt formation reaction, there is an excess of amine groups, resulting in a pH value > 7.5 at the final reaction point, higher than 7.1 in Example 1. The excess hexamethylenediamine is easily volatilized during the prepolymerization stage, causing pressure fluctuations in the reactor and affecting the stability of the prepolymerization. The excess amine groups remaining in the final polymer are easily reacted with oxygen, resulting in a yellowness index > 4.5, much higher than 2.5 or less in Example 1, indicating severe thermal oxidative degradation. At the same time, the residual amine groups increase the hygroscopicity of the material, with a water absorption rate > 1.2%, higher than ≤ 0.8% in Example 1, and the mechanical properties further decline after moisture absorption. The chemical resistance is also significantly deteriorated, with a mass loss rate > 3.0% after soaking in 5% hydrochloric acid solution for 24 hours, much higher than ≤ 1.5% in Example 1. Although the tensile strength and flexural strength of some batches can meet the requirements, the batch stability is poor, and the defects in hygroscopicity and chemical resistance lead to insufficient reliability of the product in long-term use.

[0115] Comparative Example 6: The PA6T / 66 copolymer high-temperature nylon provided in this comparative example is composed of basic comonomers, catalysts, and functional additives. The mass composition of the basic comonomers is 44.0% hexamethylenediamine, 32.9% terephthalic acid, and 23.1% adipic acid, consistent with Example 1. However, it has three core defects: First, the basic comonomers are all industrial-grade conventional products without any modification treatment; second, the functional additives are missing or singular, without the addition of silane modifiers and reinforcing agents, and only a single antioxidant 1010 is used; third, the catalyst is a commercially available conventional product, and high-purity sodium hypophosphite monohydrate is not prepared in-house. The combination of these factors leads to a comprehensive deterioration in product performance.

[0116] In this comparative example, hexamethylenediamine, terephthalic acid, and adipic acid were all industrial-grade conventional products, without sodium bicarbonate pretreatment, surface activation and solubility modification, or pulverization and drying. The purity of hexamethylenediamine was ≤98.5%, and the amino oxidation rate was >1.0%. The solubility of terephthalic acid was ≤5 g / L, and the particle size of adipic acid was uneven. The catalyst was commercially available sodium hypophosphite with a purity ≤98.0%, containing a small amount of impurities. The amount added was still 0.075% of the total amount of the basic comonomer, and the catalytic activity was unstable. The functional additives only included antioxidants, specifically antioxidant 1010, at a dosage of 0.2%, without any synergistic effect. No silane modifiers or organic nucleating agents were added, so the mechanical properties and crystallinity of the material could not be improved.

[0117] The production process of this comparative example uses a conventional process, which differs significantly from the optimized process of Example 1: the salt formation reaction temperature is increased to 65°C, there is no vacuum nitrogen replacement device, air cannot be isolated, the stirring speed is reduced to 60 r / min, the reaction time is 2 h, and the solution pH fluctuates between 6.9 and 7.3; in the prepolymerization stage, no gradient pressure reduction is performed, and the pressure is directly reduced from 2.3 MPa to atmospheric pressure in one go, which easily leads to the system boiling violently; in the solid-phase polymerization stage, the antioxidant is added all at once without being added in stages, and the drum drying temperature is increased to 100°C; in the post-treatment stage, the twin-screw extruder does not use segmented temperature control, and the temperature is maintained at 300°C throughout the process, the cooling water temperature is reduced to 30°C, and the drying temperature remains at 95°C but the time remains unchanged, with many process parameters deviating from the optimized range.

[0118] The most serious defects in this comparative example are: due to unmodified monomers and improper process parameters, the terephthalic acid agglomeration rate in the salt formation reaction is >40%, the solution is severely turbid, and the amine-acid molar ratio is severely imbalanced; a one-time pressure reduction in the prepolymerization stage causes the system to boil violently, prepolymer particles are entrained by the airflow, the loss rate is >5%, and the relative viscosity of the prepolymer fluctuates >0.15; due to the one-time addition of antioxidants in the solid-state polymerization stage, the antioxidant effect weakens in the later stage, the final polymer suffers severe thermal oxidative degradation, and the yellowness index is >5.0; the lack of functional additives leads to a comprehensive decline in the mechanical properties of the material. The tensile strength is 82-90 MPa, the flexural strength is 100-112 MPa, the flexural modulus is 1.9-2.2 GPa, and the notched impact strength is 2.5-3.0 KJ / m², all of which are lower than the lower limit of claim 10. At the same time, the processing performance is extremely poor. The melt pressure fluctuation during twin-screw extrusion is >20%, and a large number of bubbles and silver streaks appear on the surface of the product. Moreover, due to the lack of organic nucleating agent, the crystallinity is <35%, which is far lower than ≥45% in Example 1. The dimensional stability is poor, and the molding shrinkage rate is >2.0%, which completely fails to meet the actual application requirements.

[0119] The relevant properties of the PA6T / 66 copolymer high-temperature nylon obtained in Examples 1-3 and Comparative Examples 1-6 of this invention are shown in Tables 1 and 2 below: Table 1 compares the performance parameters of PA6T / 66 copolymer high-temperature nylon in the examples and comparative examples. Table (1)

[0120] Table 2 compares the performance parameters of PA6T / 66 copolymer high-temperature nylon in the examples and comparative examples. Table (II)

[0121] The testing methods and standards for the relevant performance parameters in Tables 1 and 2 above are as follows: 1. Tensile Strength: The test was conducted according to the national standard GB / T1040.2-2006 "Determination of Tensile Properties of Plastics - Part 2: Test Conditions for Molded and Extruded Plastics". A type 1A standard specimen with a thickness of 4 mm was used. The test was conducted at a temperature of 23℃±2℃ and a relative humidity of 50%±5% at a tensile rate of 50 mm / min. The maximum tensile force at fracture was recorded. The tensile strength (unit: MPa) was calculated based on the cross-sectional area of ​​the specimen. At least five parallel specimens were prepared for each test group, and the arithmetic mean was taken as the final result.

[0122] 2. Bending strength and flexural modulus: The tests were conducted according to the national standard GB / T9341-2008 "Determination of Flexural Properties of Plastics". A standard specimen of 80mm × 10mm × 4mm was used. Under an environment of 23℃ ± 2℃, with a span of 40mm, pressure was applied to the middle of the specimen at a bending rate of 2mm / min. The pressure value at the yield point (or fracture point, if no yielding occurs) was recorded, and the bending strength was calculated using the formula. Simultaneously, the slope of the linear segment of the stress-strain curve during bending was recorded, and the flexural modulus (unit: GPa) was calculated. At least five parallel specimens were prepared for each test group, and the arithmetic mean was taken.

[0123] 3. Notched Impact Strength: Tested according to national standard GB / T1043.1-2008. A type A notched standard specimen (notch depth 2mm, notch bottom radius 0.25mm) was used, with specimen dimensions of 80mm×10mm×4mm. A simply supported beam impact testing machine with an impact energy of 2.75J was used at an environment of 23℃±2℃. The impact energy consumed when the specimen fractured was recorded. The notched impact strength (unit: KJ / m²) was calculated based on the cross-sectional area at the notch. At least 10 parallel specimens were prepared for each test group, and the arithmetic mean was taken after removing outliers.

[0124] 4. Yellowness Index: The test was conducted in accordance with the national standard GB / T2409-2014 "Determination of Yellowness Index and Whiteness of Plastics". The transmission method was used. A transparent sample with a thickness of 2 mm was prepared. Using a spectrophotometer with D65 as the standard illuminant and 10° as the observation angle, the transmittance of the sample was measured at wavelengths of 440 nm, 550 nm, and 600 nm. The yellowness index (YI) was calculated according to the standard formula. At least three parallel samples were prepared for each test group, and the arithmetic mean was taken. The smaller the value, the lower the degree of yellowing of the sample.

[0125] 5. Heat distortion temperature: The test was conducted in accordance with the national standard GB / T1634.2-2004 "Determination of load deformation temperature of plastics - Part 2: Plastics and hard rubber". A standard specimen measuring 127mm × 12.7mm × 6.4mm was used. A static bending load of 1.82MPa was applied, and the specimen was immersed in methyl silicone oil. The temperature was increased uniformly at a rate of 120℃ / h. The temperature at which the deflection at the midpoint of the specimen reached 0.25mm was taken as the heat distortion temperature (unit: ℃). At least three parallel specimens were prepared for each test group, and the arithmetic mean was taken.

[0126] 6. Water absorption rate: The test was conducted in accordance with the national standard GB / T1034-2008 "Determination of Water Absorption of Plastics". A standard sample of 50mm×50mm×4mm was used. The sample was first dried in an oven at 105℃±2℃ to constant weight (the difference between two weighings ≤0.1mg), and the dried mass m0 was recorded. Then, the sample was completely immersed in distilled water at 23℃±1℃ for 24 hours. After soaking, the sample was removed, the surface moisture was blotted with filter paper, and the wet mass m1 was immediately weighed. The water absorption rate (%) was calculated as (m1-m0) / m0×100%. At least 3 parallel samples were prepared for each test group, and the arithmetic mean was taken.

[0127] Mass loss rate after 24 hours of immersion in 7.5% hydrochloric acid: The test was performed according to the logic adaptation of the chemical resistance test in the national standard GB / T11793-2008. A standard sample of 50mm×50mm×4mm was used. After drying to constant weight, the mass m2 was recorded. The sample was completely immersed in a 5% (mass fraction) hydrochloric acid solution at room temperature (23℃±2℃), sealed and soaked for 24 hours. After soaking, the sample was removed, the residual acid on the surface was washed off with distilled water, and then dried to constant weight, and the mass m3 was recorded. The formula for calculating the mass loss rate (%) is: (m2-m3) / m2×100%. At least 3 parallel samples were prepared for each test group, and the arithmetic mean was taken. The smaller the value, the better the acid resistance.

[0128] 8. Tensile strength retention rate after immersion in 80℃ hot water for 24 hours: Refer to GB / T1040.2-2006 Tensile Strength Test Method, combined with the logic of damp heat resistance test. First, determine the initial tensile strength σ0 of 3 parallel samples according to the tensile strength test method; then take another sample of the same specification, completely immerse it in distilled water at 80℃±1℃, seal and soak for 24 hours, remove it, dry the surface moisture, place it in an environment of 23℃±2℃ for 1 hour, and then determine its tensile strength σ1; the formula for calculating the tensile strength retention rate (%) is: σ1 / σ0×100%. At least 5 parallel samples should be prepared for each test group, and the arithmetic mean should be taken. The higher the value, the better the damp heat resistance stability.

[0129] Tensile strength batch fluctuation value: Using a custom statistical method: Five batches of PA6T / 66 copolymer high temperature nylon products were produced continuously. The tensile strength of five parallel samples of each batch was measured according to the tensile strength test method. The arithmetic mean of each batch was taken as the tensile strength value of that batch. The difference between the maximum and minimum tensile strength values ​​of the five batches was calculated, which is the tensile strength batch fluctuation value. The smaller the value, the better the production stability.

[0130] Examples 1-3 of this invention, through modification of the basic comonomers of PA6T / 66 copolymerized high-temperature nylon, preparation of highly active catalysts, and optimization of production processes and monomer characteristics, achieved comprehensive compliance with product performance standards and stable controllability. Specifically, hexamethylenediamine was pretreated with sodium bicarbonate combined with vacuum distillation and nitrogen protection, effectively increasing its purity to over 99.9% and inhibiting amino oxidation. Terephthalic acid was modified through plasma surface activation and ammonium bicarbonate aqueous solution, significantly improving its solubility in hexamethylenediamine aqueous solution. The synergistic effect of these two methods ensured uniform distribution of 6T rigid units and 66 flexible units in the copolymerization reaction, resulting in a stable tensile strength of 92.1-99.8 MPa, batch-to-batch fluctuations in tensile strength below 2.0 MPa, and a yellowing index controlled below 2.5, with no obvious oxidative yellowing.

[0131] A high-purity sodium hypophosphite monohydrate catalyst, prepared by precisely controlling the reaction ratio and crystallization parameters of hypophosphite and sodium hydroxide, exhibits stable catalytic efficiency, ensuring precise control of the final polymer's relative viscosity between 2.48 and 2.52. This results in a flexural modulus of 2.2-2.8 GPa and a notched impact strength of 3.1-4.9 KJ / m², along with excellent chemical resistance. After immersion in 5% hydrochloric acid for 24 hours, the mass loss rate is no more than 1.5%, and after immersion in 80℃ hot water for 24 hours, the tensile strength retention rate is no less than 92%. Furthermore, production processes adapted to the characteristics of the modified monomers, such as salt formation reaction temperature control, prepolymerization gradient pressure reduction, phased addition of antioxidants during solid-phase polymerization, and segmented temperature control using a twin-screw extruder, further ensure that the product's heat distortion temperature remains stable above 270℃ and its water absorption rate does not exceed 0.8%. This meets the stringent requirements for high-temperature resistance, mechanical properties, and stability in applications such as high-temperature components around automotive engines and connectors used in electronic surface mount technology.

[0132] All seven comparative examples of this invention exhibit significant performance defects or stability issues, failing to meet practical application requirements. Comparative Example 1 lacked any modification treatment of the basic comonomer, resulting in low solubility and easy agglomeration of terephthalic acid during the salt formation reaction, insufficient purity of hexamethylenediamine, and easy oxidation. The final product's tensile strength was only 85-92 MPa, with batch fluctuations reaching 7.0 MPa, and a yellowness index exceeding 4.0, significantly deteriorating mechanical property stability and appearance quality. Comparative Example 2 lacked only the sodium bicarbonate pretreatment step for hexamethylenediamine, increasing the content of oxidized impurities in hexamethylenediamine and reducing the product's resistance to damp heat; the tensile strength retention rate after immersion in 80°C hot water for 24 hours was only 82-85%. Comparative Example 3 lacked only surface activation and solubility modification treatment of terephthalic acid; incomplete dissolution of terephthalic acid led to uneven copolymerization, resulting in some batches of products having flexural modulus and notched impact strength below the specified range, failing to consistently meet usage requirements. In Comparative Example 4, the amount of hexamethylenediamine added was below the specified range of 42.8%-45.1%, resulting in insufficient total amine groups and incomplete polycondensation reaction. The product's tensile strength was below 85 MPa and flexural strength was below 105 MPa, completely failing to meet performance requirements. In Comparative Example 5, the amount of hexamethylenediamine added exceeded the upper limit of 45.1%. Excessive amino residue caused the product's water absorption rate to exceed 1.2%, significantly deteriorating acid resistance. The mass loss rate after immersion in 5% hydrochloric acid for 24 hours exceeded 3.0%. Comparative Example 6 suffered from multiple defects, including unmodified basic comonomers, lack of silane modifiers and organic nucleating agents, use of a single antioxidant, and conventional production processes. The product's tensile strength was only 82-90 MPa, flexural modulus 1.9-2.2 GPa, and heat distortion temperature 245-255℃. Moreover, the batch-to-batch fluctuation of tensile strength reached 8.0 MPa. The mechanical properties, thermal stability, and production stability all failed to meet the standards, making it unsuitable for high-temperature scenarios and high-reliability applications.

[0133] Any numerical values ​​cited herein include all values ​​ranging from a lower limit to an upper limit, increasing by one unit, with at least two units between any lower and any higher value. For example, if the quantity of a component or the value of a process variable (e.g., temperature, pressure, time, etc.) is described as being from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, the purpose is to illustrate that values ​​such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also explicitly listed in this specification. For values ​​less than 1, a unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1, etc. These are merely examples intended for explicit expression, and it can be assumed that all possible combinations of values ​​listed between the minimum and maximum values ​​are similarly explicitly stated in this specification.

[0134] Unless otherwise stated, all ranges include the endpoints and all numbers between them. The terms "approximately" or "about" used with ranges apply to both endpoints of the range. Thus, "approximately 20 to 30" is intended to cover "approximately 20 to approximately 30," including at least the specified endpoints.

[0135] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this teaching should not be determined by reference to the above description, but rather by reference to the appended claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the inventors have not considered that subject matter as part of the disclosed inventive subject matter.

[0136] The present invention has been described by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvement made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, shall be within the protection scope of the present invention.

Claims

1. A PA6T / 66 copolymer high-temperature nylon, characterized in that, The product comprises a basic comonomer, a catalyst, and functional additives. The basic comonomer includes the following components by mass percentage: 42.8%-45.1% hexamethylenediamine, 30.2%-35.6% terephthalic acid, and 21.2%-26.6% adipic acid. The hexamethylenediamine is pretreated with sodium bicarbonate, and the terephthalic acid is surface activated and solubility modified. The catalyst is a phosphite catalyst, and its addition amount is 0.05%-0.1% of the total amount of the basic comonomer. The functional additives include at least one of a compound antioxidant, an organic nucleating agent, and a silane modifier / reinforcing agent. The process of surface activation and solubility modification of terephthalic acid includes: Take terephthalic acid, put it into a universal pulverizer and grind it to 100-200 mesh, then transfer it to a hot air dryer and dry it at 110-130℃ for 1-3 hours, controlling the moisture content to ≤0.1%; The dried terephthalic acid was transferred into a plasma treatment instrument, and the chamber was purged with nitrogen 2-4 times. Each time, the pressure was maintained at 0.4-0.6 MPa for 8-12 minutes. The treatment power was set to 150-200W, the treatment time to 15-20 minutes, and the nitrogen flow rate to 10-15 L / min to complete the surface activation. Prepare a 0.5%-1.0wt% ammonium bicarbonate aqueous solution, immerse the activated terephthalic acid in the solution at a solid-liquid ratio of 1:(4-6), and stir and soak at 60-80r / min for 30-40min at room temperature; The terephthalic acid was removed, filtered through a filter screen, and then transferred to a vacuum drying oven. It was dried at 70-85℃ and a vacuum degree of -0.075~-0.085MPa for 1~2 hours to obtain terephthalic acid that has been surface activated and solubility modified.

2. The PA6T / 66 copolymer high-temperature nylon according to claim 1, characterized in that, The functional additives include at least one of the following: compound antioxidant: composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1, with an amount of 0.1%-0.3% of the total mass of the basic comonomer; organic nucleating agent: sodium benzoate, with an amount of 0.05%-0.1% of the total mass of the basic comonomer; silane modified reinforcing agent: alkali-free glass fiber treated with KH550 silane coupling agent, with an amount of 10%-30% of the total mass of PA6T / 66 copolymer high-temperature nylon, wherein the glass fiber has a diameter of 10-15 μm and a length of 3-5 mm.

3. The PA6T / 66 copolymer high-temperature nylon according to claim 1, characterized in that, The process of pretreating hexamethylenediamine with sodium bicarbonate includes: (1) Take hexamethylenediamine and transfer it to a vacuum distillation vessel with a heat transfer oil jacket. Add sodium bicarbonate at a mass of 0.1%-0.2% of hexamethylenediamine into the vessel and start stirring until the sodium bicarbonate is completely dissolved. The stirring speed is 50-60 r / min. (2) Close the feed valve of the distillation vessel, turn on the vacuum system, control the vacuum degree to -0.092~-0.095MPa, raise the temperature to 55-65℃ at a rate of 4-6℃ / min and hold for 25-40min, then raise the temperature to 85-90℃ at a rate of 2-4℃ / min, and collect the fraction with a distillation temperature of 80-85℃. (3) Transfer the collected fraction into a hexamethylenediamine intermediate tank with a hot water jacket at 50-60℃, introduce nitrogen gas with a purity of ≥99.99% into the tank, maintain a slight positive pressure of 0.01-0.02MPa in the tank, and keep the stirring speed at 30-40r / min to obtain hexamethylenediamine pretreated with sodium bicarbonate.

4. The PA6T / 66 copolymer high-temperature nylon according to claim 1, characterized in that, The phosphite catalyst is sodium hypophosphite monohydrate, and its preparation method includes the following steps: (1) Add deionized water to the reactor, control the water temperature at 20-35℃, stir at 250-450r / min, slowly add hypophosphoric acid, and adjust the pH to 1.8-2.7; (2) Add 25-35 wt% sodium hydroxide aqueous solution slowly at a molar ratio of hypophosphoric acid to sodium hydroxide of 1:1.01-1.03, control the reaction temperature at 35-45℃, and stir the reaction for 1-2.5 h. (3) After the reaction is complete, the solution is transferred to an evaporator crystallizer and evaporated and concentrated to a solution concentration of 45-60% at a vacuum of -0.07 to -0.09 MPa and a temperature of 55-75℃. (4) Transfer the concentrate to a cooling crystallizer and cool it to 5-20℃ at a rate of 0.5-1.5℃ / min. Keep it at the temperature for 3-5 hours to crystallize. Separate the crystals by centrifugation and vacuum dry them at 45-55℃ for 1.5-2.5 hours to obtain sodium hypophosphite monohydrate.

5. The PA6T / 66 copolymer high-temperature nylon according to claim 1, characterized in that, The preparation steps of the silane-modified reinforcing agent include: (1) Dry the alkali-free glass fiber at 110-130℃ for 1.5-2.5h, and control the moisture content to ≤0.1%; (2) Mix KH550 silane coupling agent with anhydrous ethanol at a mass ratio of 1:8-12, add 4%-6% of deionized water by mass of ethanol, stir for 10-25 minutes until complete hydrolysis, and obtain silane treatment solution. (3) Immerse the dried glass fiber in the silane treatment solution with a liquid-solid ratio of 4:1-6:1 and soak it at 20-30℃ for 1-2.5h. After draining, dry it at 70-90℃ for 0.5-1.5h and then at 110-130℃ for 2.5-3.5h.

6. The production process of PA6T / 66 copolymer high-temperature nylon as described in claims 1 to 5, characterized in that, Includes the following steps: (1) Salt formation reaction: Hexamethylenediamine pretreated with sodium bicarbonate is mixed with deionized water at a mass ratio of 1:1, and a 50%-52% aqueous solution of hexamethylenediamine is prepared at 55-60℃; the aqueous solution of hexamethylenediamine is added to the salt formation reactor along with surface-activated terephthalic acid and adipic acid, and the reaction temperature is controlled at 55-60℃, atmospheric pressure, and stirring speed at 80-100 r / min. The reaction is carried out for 1-2 h, and the pH of the final solution is controlled at 7.0-7.2 and is clear and transparent to obtain PA6T / 66 copolymer salt solution; (2) Prepolymerization: The copolymer salt solution is transferred into the polymerization reactor, and the temperature is controlled at 220-250℃ and the pressure is ≥2.2MPa. The reaction is carried out for 2-3 hours. In the later stage, the pressure is first reduced in a gradient, and then the vacuum is evacuated by a water ring vacuum pump for 0.5-1 hours to make the relative viscosity of the prepolymer 1.35-1.

39. After nitrogen filling, the prepolymer is pressed into the crystallizer by pressure difference. After cooling and flash crystallization, it is crushed into 2-5mm particles. (3) Solid-state polymerization: The prepolymer particles are transferred to a dryer and dried at a vacuum of -0.08 to -0.09 MPa and a temperature of 80 to 110°C for 6 to 8 hours to make the moisture content ≤ 0.5%; then transferred to a reactor and heated to 270 to 280°C, with the vacuum controlled at 10 to 15 Pa, and reacted for 8 to 12 hours. During this period, a compound antioxidant is added to obtain a final polymer with a relative viscosity of 2.48 to 2.

52. (4) Post-processing: The final polymer is transferred to a twin-screw extruder for melting, and after the strip is cooled by circulating cooling water at 32-35℃, it is granulated by an underwater pelletizer. After drying the granules, PA6T / 66 copolymer high-temperature nylon product is obtained.

7. The production process according to claim 6, characterized in that, The gradient pressure reduction process described in step (2) is as follows: from 2.0-2.4 MPa to 0.8-1.2 MPa, taking 0.8-1.2 h; then from 0.8-1.2 MPa to atmospheric pressure, taking 0.8-1.2 h. And / or, the compound antioxidant described in step (3) is added in two parts: 40%-60% of the total amount is added at the beginning of solid-phase polymerization, and the remaining compound antioxidant is added when the solid-phase polymerization reaction has been carried out for 5-7 hours; And / or, the twin-screw extruder in step (4) adopts segmented temperature control, specifically: feeding section 280-300℃, melting section 290-310℃, homogenization section 300-310℃, and die head 300-320℃; And / or, the initial moisture content of the PA6T / 66 slices obtained after pelleting in step (4) is 2000-3000ppm. After the slices enter the fluidized bed dryer, they are dried with hot circulating nitrogen at a temperature of 80-120℃ for 1-3 hours. After drying, PA6T / 66 dry slices are obtained, and the moisture content of the dry slices is ≤800ppm.

8. The production process according to claim 6, characterized in that, Before the salt formation reaction, the surface-activated terephthalic acid and adipic acid are pulverized to 100-200 mesh and dried at 120-130℃ for 2-2.5 hours, with the moisture content controlled to ≤0.1%.

9. The production process according to any one of claims 6-8, characterized in that, The performance indicators of the PA6T / 66 copolymer high-temperature nylon meet the following requirements: tensile strength ≥92.1MPa and not exceeding 100MPa, flexural strength ≥116MPa and not exceeding 130MPa, flexural modulus ≥2.2GPa and not exceeding 2.8GPa, and notched impact strength ≥3.1KJ / m² and not exceeding 5.0KJ / m².

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