Polyamide 66 resin slice and preparation method thereof

Abstract

The method comprises the following steps: adding dried adipic acid, dried hexamethylenediamine, an end-capping reagent, a catalyst, a flexibilizer, a lubricant, a light stabilizer and a heat stabilizer into a reaction kettle, and sequentially carrying out melt polycondensation at the stages of prepolymerization, pre-polymerization and final polymerization under the conditions of nitrogen protection and no additional water, so as to obtain the polyamide 66 resin slice. A final polymerization stage is matched with a decompression vacuumizing process, and finally, a finished product is obtained through bracing and pelletizing. According to the invention, by utilizing an anhydrous addition direct melt polymerization method and cooperating with a synergistic effect aid, the prepared resin has the characteristics of good melt fluidity, high thermal stability, few gel and black spots and the like, is low in end breakage rate and high in full roll rate when being applied to chinlon spinning, and is particularly suitable for the field of civil chinlon spinning.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyamide 66 resin preparation, and particularly relates to a polyamide 66 resin chip and a preparation method thereof. BACKGROUND

[0002] The existing industrialized polyamide 66 production mostly adopts a process route of salting-prepolymerization-flashing-polymerization, that is, first, adipic acid and hexamethylene diamine are respectively prepared into aqueous solutions with a certain concentration, and then the two solutions are mixed in a mixing tank to generate a polyamide 66 salt solution, and at the same time, the amount of liquid hexamethylene diamine is adjusted to control the pH value, and then the salt solution is sent into a polymerization kettle for polycondensation reaction, and water is removed by evaporation to promote the polycondensation balance to move to the direction of generating polymers.

[0003] In this kind of traditional process, in order to ensure the flowability of polyamide 66 in the reactor and pipeline, the temperature of the inner wall of the equipment and the conveying pipeline is usually maintained above 270 DEG C. Under long-term high-temperature conditions, even if the system is in an oxygen-free environment, polyamide 66 will also undergo thermal degradation and crosslinking to generate insoluble and infusible gels. At the same time, due to factors such as long residence time of the material in the equipment, uneven heating at high temperature, and liquid surface fluctuation spatter, local carbonization is easily caused, forming scarring or wrapped black spots. These gels and black spots are mixed in the resin chip, which will cause spinneret blockage in the process of polyamide 66 spinning, or cause broken yarns, mixed yarns, twisted yarns and other problems in the drawing and post-processing, seriously affecting the spinning continuity and production efficiency, and limiting the application of polyamide 66 in the high-end field of civilian polyamide fibers.

[0004] On the other hand, the process of salting with aqueous solution inevitably involves the evaporation and flashing steps of a large amount of aqueous solution, resulting in high production energy consumption, high cost, long product category switching period, and easy introduction of high gel and black spot content. Some technical solutions attempt to reduce water consumption to reduce energy consumption, but the adverse effects of the introduction of water on energy consumption and quality have not been fundamentally eliminated.

[0005] In the prior art, there are also schemes for modifying polyamide 66 by adding antioxidants, heat stabilizers and toughening agents and other additives to improve the thermal stability or mechanical properties of the resin. For example, some documents use organic acids, copper salts, phosphorus-containing compounds, hindered amines as antioxidants or stabilizers, and some schemes for improving the balance of rigidity and toughness and aging resistance by compounding modification in the extrusion granulation stage. However, these technologies mostly realize modification in the extruder after polymerization, and do not reduce the generation amount of gels and black spots from the whole process system.

[0006] Other technologies focus on optimizing equipment and processes, such as continuous polymerization processes, online titration to control monomer molar ratios, falling film or drop-sheet polycondensation, and solid-state polymerization to increase viscosity, aiming to improve molecular weight control, shorten reaction time, or avoid black spots and discoloration. However, these methods often require high-end equipment, involve complex modifications, and increase costs. Furthermore, their effectiveness in reducing gel and black spot content is limited, making it difficult to meet the stringent requirements of nylon spinning, especially for high-end civilian fibers, for high resin continuity and low defects.

[0007] In summary, existing polyamide 66 resin production processes generally suffer from problems such as high energy consumption, high cost, high gel and black spot content, and poor continuity of nylon spinning, which particularly restricts its promotion and application in the field of high-end nylon spinning for civilian use. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a polyamide 66 resin chip and its preparation method.

[0009] This invention is achieved through the following technical solution: A method for preparing polyamide 66 resin chips, characterized by comprising the following steps: S1, add the polyamide 66 polymerization raw material to the polymerization reactor; S2, the materials in the polymerization reactor are heated, melted, mixed and polycondensed to obtain polyamide 66 melt; S3, the polyamide 66 melt is stretched into strips and granulated to obtain polyamide 66 resin chips; The polyamide 66 polymerization raw materials include dried adipic acid and hexamethylenediamine. Step S2 is carried out under a nitrogen protective atmosphere and no additional water is added to the reaction system. In step S1, based on the total mass of adipic acid and hexamethylenediamine, 0.05-0.3 wt% of end-capping agent, 0.1-0.4 wt% of catalyst, 0.02-0.1 wt% of toughening agent, 0.02-0.15 wt% of lubricant, as well as light stabilizer and heat stabilizer are added to the polymerization reactor, so that the end-capping agent, catalyst, toughening agent, lubricant, 0.001-0.01 wt% of light stabilizer and 0.005-0.02 wt% of heat stabilizer participate together with adipic acid and hexamethylenediamine in the subsequent polycondensation reaction; The polycondensation reaction consists of three stages: prepolymerization, prepolymerization, and final polymerization, and the system is first depressurized and then evacuated during the final polymerization stage to obtain a polyamide 66 resin melt suitable for nylon spinning.

[0010] Preferably, based on the total mass of adipic acid and hexamethylenediamine, the amount of end-capping agent added is 0.1–0.2 wt%, the amount of catalyst added is 0.25–0.4 wt%, the amount of toughening agent added is 0.05–0.1 wt%, the amount of lubricant added is 0.02–0.1 wt%, the amount of light stabilizer added is 0.0025–0.01 wt%, and the amount of heat stabilizer added is 0.001–0.015 wt%.

[0011] Preferably, the capping agent is one or more of acetic acid, butyric acid, propionic acid, purified terephthalic acid, and adipic acid; The catalyst is one or more of the following: ammonium dihydrogen phosphate, ammonium hydrogen phosphate, zinc phosphite, potassium hypophosphite, sodium hypophosphite, and zinc hypophosphite. The toughening agent is one or both of POE-g-MAH polyolefin elastomer grafted with maleic anhydride and SEBS-g-MAH hydrogenated styrene-butadiene block copolymer grafted with maleic anhydride. The lubricant is one or more of polypropylene wax, polyethylene wax, oxidized polyethylene wax, erucamide, dendritic polyamide, butyl stearate, and glyceryl monostearate. The light stabilizer is one or more of the following: nickel complex light stabilizer, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, methacryloyloxyethyltrimethylammonium chloride-2,2,6,6-tetramethylpiperidinol copolymer, nano zinc oxide, and titanium dioxide. The heat stabilizer is one or more of copper acetate, cuprous iodide, potassium iodide, potassium chloride, and potassium phosphate.

[0012] Preferably, the end-capping agent should avoid direct contact with hexamethylenediamine. Common end-capping agents are liquid acids such as formic acid and acetic acid (glacial acetic acid), which end the polyamide molecular chain with a single carboxyl group; they are also called molecular weight regulators. Direct contact between the end-capping agent and hexamethylenediamine is avoided because both are highly reactive under normal conditions. Hexamethylenediamine will react directly with the aforementioned liquid acid end-capping agent, producing a large amount of volatile white fumes. After the materials are added, sealing, vacuuming, and nitrogen purging are required, and the escape of a large amount of reactant fumes can lead to material imbalance and affect the polymerization effect. Therefore, when adding materials, the end-capping agent should be mixed or buried with adipic acid (room temperature white powder) before adding hexamethylenediamine (room temperature solid) to avoid direct contact between the two.

[0013] The capping agent can be mixed with adipic acid and a molten mixture of adipic acid (polyamide 66 salt and oligomers) under a closed nitrogen atmosphere, as long as it does not come into contact with hexamethylenediamine alone.

[0014] Preferably, the heating and melting method and sequence of step S2 includes any one of the following: (1) Mix adipic acid with hexamethylenediamine, end-capping agent, catalyst, toughening agent, lubricant, light stabilizer and heat stabilizer and heat together to melt; (2) First, heat and melt hexamethylenediamine, then add end-capping agent, catalyst, toughening agent, lubricant, light stabilizer and heat stabilizer, mix and heat to melt, and mix with heated and melted adipic acid; (3) Adipic acid and hexamethylenediamine are heated and melted separately and then mixed. Then, end-capping agent, catalyst, toughening agent, lubricant, light stabilizer and heat stabilizer are added, mixed and heated and melted. Preferably, in step S1, the polymerization reactor is kept dry, and nitrogen is introduced before heating to ensure that the oxygen content inside the reactor is not higher than 0.02%, and the pressure inside the reactor is pressurized to 0.1 MPa; after the feeding is completed, the system pressure is controlled at 0.05 to 0.2 MPa, and the temperature is controlled in a stepwise manner.

[0015] Preferably, the prepolymerization temperature in the prepolymerization stage is 220–250°C, the prepolymerization pressure is 1.2–1.8 MPa, and the prepolymerization time is 1–3 h.

[0016] Preferably, the prepolymerization and final polymerization stages are two-stage polymerization, specifically: in the prepolymerization stage, the material is heated to 250-265°C and the pressure inside the reactor is maintained at 1.2-1.8 MPa by venting water vapor; in the final polymerization stage, the material is further heated to 265-285°C, and the pressure is reduced to atmospheric pressure or slightly positive pressure within 0.5-2 hours, followed by vacuuming for 5-30 minutes, with a vacuum degree of 60-90 kPa absolute pressure.

[0017] Preferably, the endpoint of the polymerization reaction is determined by online measurement of shear viscosity during the final polymerization stage, and the shear viscosity is controlled within the range of 200 to 800 Pa·s.

[0018] The polyamide 66 resin chips of the present invention have a gel content of 0.1wt‰ to 1wt‰, a black spot count of no more than 5 per kg, a moisture content of no more than 0.07%, and a number-average molecular weight of 10,000 to 30,000 for polyamide 66. Furthermore, when the polyamide 66 resin chips are used for nylon civilian spinning, the breakage rate during the spinning process is no higher than 1 time / h, the evenness rate (CV) is no higher than 0.5%, the full roll rate is no less than 98%, and the waste yarn rate is no higher than 0.8%.

[0019] The beneficial effects of this invention are as follows: This invention utilizes a direct melt polymerization method without added water, and synthesizes a polyamide 66 resin with good spinning continuity by adding catalysts, end-capping agents, toughening agents, lubricants, and light / heat stabilizers with synergistic effects. It has the characteristics of good melt flowability, good thermal stability, high impact strength, low gel and black spot content, and low spinning breakage rate, evenness rate, waste rate, and high full roll rate, making it particularly suitable for the civilian nylon spinning field. Detailed Implementation

[0020] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0023] raw material: All raw materials used in the experiment were readily available to those skilled in the art through conventional means. Specifically, polypropylene wax, polyethylene wax, oxidized polyethylene wax, and calcium stearate were sourced from Qingdao Sainuo New Materials Co., Ltd., and dendritic polyamide was sourced from Weihai Chenyuan Molecular New Materials Co., Ltd. The remaining reagents were sourced from Anhui Zesheng Technology Co., Ltd., Shanghai Maclean Biochemical Technology Co., Ltd., and Wenzhou Banglu Chemical Co., Ltd.

[0024] equipment: All equipment used in the experiment was standard experimental and testing equipment. Among them, the polymerization reactor was manufactured by Yantai Langchuan Equipment Manufacturing Co., Ltd., the universal testing machine and impact testing machine for mechanical testing were manufactured by Zwick (Germany), the differential scanning calorimeter for thermal analysis was manufactured by PE Platinum Elman, the thermogravimetric analyzer was manufactured by TA Instruments (USA), and the spinning performance testing equipment and technology were imported from Rhodia Group (France) by a domestic chemical textile company.

[0025] Example 1 (Equimolar ratio of adipic acid and hexamethylenediamine) (1) Add 1671.19g of adipic acid, 1328.86g of hexamethylenediamine, 6.0g of acetic acid, 6.0g of sodium hypophosphite, 0.05g of copper acetate, 3.0g of POE-g-MAH (polyolefin elastomer grafted with maleic anhydride), 0.1g of potassium chloride, 0.4g of polyethylene wax, and 0.3g of bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0026] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 220℃, the pressure reaches 1.4MPa. Maintain the pressure and temperature for 1.5h.

[0027] (3) The temperature is raised to 250°C, and the pressure inside the reactor is maintained at 1.4 MPa by venting the water vapor inside the reactor.

[0028] (4) Continue heating to 265℃, and after releasing the pressure to normal pressure, evacuate to absolute pressure of 75KPa.

[0029] (5) The material is pulled out, granulated, and dried to obtain polyamide 66 resin chips.

[0030] Example 2 (molar ratio of adipic acid to hexamethylenediamine is 1:1.001) (1) Add 1671.19g adipic acid, 1330.14g hexamethylenediamine, 6.0g acetic acid, 6.0g sodium hypophosphite, 0.05g copper acetate, 3.0g POE-g-MAH (polyolefin elastomer grafted with maleic anhydride), 0.1g potassium chloride, 0.4g polyethylene wax, and 0.3g sebacic acid bis(2,2,6,6-tetramethyl-4-piperidinyl) ester to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0031] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 240℃, the pressure reaches 1.6MPa. Maintain the pressure and temperature for 1.5h.

[0032] (3) The temperature is raised to 265℃, and the pressure inside the reactor is maintained at 1.6MPa by venting the water vapor inside the reactor.

[0033] (4) Continue heating to 285℃, and after releasing the pressure to normal pressure, evacuate to absolute pressure of 75KPa.

[0034] (5) The material is pulled out, granulated, and dried to obtain polyamide 66 resin chips.

[0035] Example 3 (molar ratio of adipic acid to hexamethylenediamine is 1.001:1) (1) Add 1672.86g of adipic acid, 1328.86g of hexamethylenediamine, 6.0g of acetic acid, 6.0g of sodium hypophosphite, 0.05g of copper acetate, 3.0g of POE-g-MAH (polyolefin elastomer grafted with maleic anhydride), 0.1g of potassium chloride, 0.4g of polyethylene wax, and 0.3g of bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0036] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 250℃, the pressure reaches 1.8MPa. Maintain the pressure and temperature for 1.5h.

[0037] (3) Heat to 265℃, and release pressure appropriately during the process to maintain pressure of 1.8MPa.

[0038] (4) Continue heating to 285℃, release the pressure to normal pressure, and then evacuate to absolute pressure of 75KPa.

[0039] (5) The material is pulled out, granulated, and dried to obtain polyamide 66 resin chips.

[0040] Comparative Example 1 (conventional aqueous solution polymerization, equimolar ratio of adipic acid to hexamethylenediamine) (1) Add 1671.19g of adipic acid, 1328.86g of hexamethylenediamine, 6.0g of acetic acid, 6.0g of sodium hypophosphite, and 1000g of deionized water to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0041] (2) Continue to heat up and gradually increase the pressure. During the process of the temperature rising from room temperature to 230℃, the pressure is controlled by the exhaust valve. When the temperature reaches 230℃, the pressure is maintained at 1.4MPa for 1.5h.

[0042] (3) Heat to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0043] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to absolute pressure of 75KPa.

[0044] (5) The material is pulled out, granulated, and dried to obtain polyamide 66 resin chips.

[0045] Comparative Example 2 (equimolar ratio of adipic acid and hexamethylenediamine, without the addition of additives) (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 6.0g of acetic acid, and 6.0g of sodium hypophosphite to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0046] (2) Continue to heat up and gradually increase the pressure. During the process of the temperature rising from room temperature to 230℃, the pressure is controlled by the exhaust valve. When the temperature reaches 230℃, the pressure is maintained at 1.4MPa for 1.5h.

[0047] (3) Heat to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0048] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to absolute pressure of 75KPa.

[0049] (5) The material is pulled out, granulated, and dried to obtain polyamide 66 resin chips.

[0050] Performance Evaluation The products obtained in the examples and comparative examples were subjected to gelation, black spot content, and mechanical property tests. The specific test methods are as follows: 1. Gel content test (1) Take a certain mass of polyamide 66 resin slices of M0 to be tested and dissolve them in 98% anhydrous formic acid for 24 hours.

[0051] (2) Select a microporous filter membrane of appropriate specifications with a minimum pore size of 0.22 μm. Soak it in formic acid solution until the mass is constant. The mass of the filter membrane is recorded as M1.

[0052] (3) Install a sand core filter and a circulating water vacuum pump. During the filtration process, it is necessary to prevent contamination by foreign matter, and when the filtrate level is low, add a certain amount of formic acid and repeat several times.

[0053] (4) After filtration, rinse with a certain amount of deionized water and anhydrous ethanol, remove the filter membrane and dry it to constant weight. Its mass is recorded as M2.

[0054] The gel content G in polyamide 66 is calculated using the following formula: G = (M2-M1) / M0 × 100%.

[0055] 2. Black spot content test Weigh 500g of sample and place it in a white porcelain dish. Under light, use tweezers to remove particles with black or yellow spots that are visible to the naked eye and count the number of particles, in units of particles per kilogram (particles / kg).

[0056] 2. Mechanical property testing Tests were conducted according to the standards GB / T1042-92 for tensile strength, GB / T9341-88 for bending, and GB / T1843-1996 for impact.

[0057] 3. Thermodynamic property testing The thermodynamic properties of polyamide 66 resin were analyzed and tested using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

[0058] 4. The breakage rate is the number of wire breaks that occur in a single spindle or the entire production line per unit time (e.g., per hour).

[0059] 5. The yarn unevenness index is the coefficient of variation of the linear density of the yarn detected by the capacitive yarn evenness tester, which reflects the thickness fluctuation of the yarn along its length.

[0060] 6. The full roll rate is the percentage of spindles that are successfully wound to the specified full roll size (excluding spindles that are not fully wound due to breakage).

[0061] 7. The waste filament rate index is the percentage of waste filaments (broken filaments, poorly wound filaments, transition filaments, etc.) generated during the production process to the total output.

[0062] The results are shown in Tables 1 and 2.

[0063] Table 1 shows the test results of the mechanical properties of polyamide 66 resin in the examples and comparative examples. Table 2 shows the test results of the spinning performance of polyamide 66 resin in the examples and comparative examples. As shown in Table 1, the thermodynamic properties of the polyamide 66 resins prepared in Examples 1-3 and Comparative Examples 1-2 differ significantly. Regarding mechanical properties, the polyamide 66 resins prepared in Examples 1-3 exhibit superior performance in all aspects compared to Comparative Examples 1-2, particularly showing a significant improvement in tensile strength, impact strength, and flexural strength.

[0064] As shown in Table 2, the content of gel and black spots in the polyamide 66 resin prepared in Examples 1-3 was significantly lower than that in Comparative Examples 1-2, proving that the invention has a significant effect on reducing the content of gel and black spots in polyamide 66 resin. Further comparison shows that the addition of toughening agent, lubricant and light / heat stabilizer has a significant synergistic effect, achieving the effect that the addition of a single component cannot achieve, thereby further reducing the content of gel and black spots, making this type of polyamide 66 resin suitable for civilian nylon spinning.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing polyamide 66 resin chips, characterized in that: Includes the following steps: S1, add the polyamide 66 polymerization raw material to the polymerization reactor; S2, the materials in the polymerization reactor are heated, melted, mixed and polycondensed to obtain polyamide 66 melt; S3, the polyamide 66 melt is stretched into strips and granulated to obtain polyamide 66 resin chips; The polyamide 66 polymerization raw materials include dried adipic acid and hexamethylenediamine. Step S2 is carried out under a nitrogen protective atmosphere and no additional water is added to the reaction system. In step S1, based on the total mass of adipic acid and hexamethylenediamine, 0.05-0.3 wt% of end-capping agent, 0.1-0.4 wt% of catalyst, 0.02-0.1 wt% of toughening agent, 0.02-0.15 wt% of lubricant, as well as light stabilizer and heat stabilizer are added to the polymerization reactor, so that the end-capping agent, catalyst, toughening agent, lubricant, 0.001-0.01 wt% of light stabilizer and 0.005-0.02 wt% of heat stabilizer participate together with adipic acid and hexamethylenediamine in the subsequent polycondensation reaction; The polycondensation reaction consists of three stages: prepolymerization, prepolymerization, and final polymerization, and the system is first depressurized and then evacuated during the final polymerization stage to obtain a polyamide 66 resin melt suitable for nylon spinning.

2. The method for preparing polyamide 66 resin chips according to claim 1, characterized in that: Based on the total mass of adipic acid and hexamethylenediamine, the amount of end-capping agent added is 0.1–0.2 wt%, the amount of catalyst added is 0.25–0.4 wt%, the amount of toughening agent added is 0.05–0.1 wt%, the amount of lubricant added is 0.02–0.1 wt%, the amount of light stabilizer added is 0.0025–0.01 wt%, and the amount of heat stabilizer added is 0.001–0.015 wt%.

3. The method for preparing polyamide 66 resin chips according to claim 1 or 2, characterized in that: The capping agent is one or more of acetic acid, butyric acid, propionic acid, purified terephthalic acid, and adipic acid; The catalyst is one or more of the following: ammonium dihydrogen phosphate, ammonium hydrogen phosphate, zinc phosphite, potassium hypophosphite, sodium hypophosphite, and zinc hypophosphite. The toughening agent is one or both of POE-g-MAH polyolefin elastomer grafted with maleic anhydride and SEBS-g-MAH hydrogenated styrene-butadiene block copolymer grafted with maleic anhydride. The lubricant is one or more of polypropylene wax, polyethylene wax, oxidized polyethylene wax, erucamide, dendritic polyamide, butyl stearate, and glyceryl monostearate. The light stabilizer is one or more of the following: nickel complex light stabilizer, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, methacryloyloxyethyltrimethylammonium chloride-2,2,6,6-tetramethylpiperidinol copolymer, nano zinc oxide, and titanium dioxide. The heat stabilizer is one or more of copper acetate, cuprous iodide, potassium iodide, potassium chloride, and potassium phosphate.

4. The method for preparing polyamide 66 resin chips according to claim 1, characterized in that: The capping agent should avoid direct contact with hexamethylenediamine.

5. The method for preparing polyamide 66 resin chips according to claim 4, characterized in that: The heating and melting method and sequence of step S2 include any of the following: (1) Mix adipic acid with hexamethylenediamine, end-capping agent, catalyst, toughening agent, lubricant, light stabilizer and heat stabilizer and heat together to melt; (2) First, heat and melt hexamethylenediamine, then add end-capping agent, catalyst, toughening agent, lubricant, light stabilizer and heat stabilizer, mix and melt, and mix with heated and melted adipic acid; (3) Adipic acid and hexamethylenediamine are heated and melted separately and then mixed. Then, end-capping agent, catalyst, toughening agent, lubricant, light stabilizer and heat stabilizer are added, mixed and heated and melted. According to the method for preparing polyamide 66 resin chips as described in claim 1, the following features are provided: in step S1, the polymerization reactor is kept dry, and before heating, nitrogen gas is introduced to ensure that the oxygen content in the reactor is not higher than 0.02%, and the pressure inside the reactor is pressurized to 0.1 MPa; after the feeding is completed, the system pressure is controlled at 0.05 to 0.2 MPa.

6. The method for preparing polyamide 66 resin chips according to claim 6, characterized in that: The prepolymerization stage has a prepolymerization temperature of 220–250°C, a prepolymerization pressure of 1.2–1.8 MPa, and a prepolymerization time of 1–3 h.

7. The method for preparing polyamide 66 resin chips according to claim 7, characterized in that: The prepolymerization and final polymerization stages constitute a two-stage polymerization process. Specifically, in the prepolymerization stage, the material is heated to 250–265°C and the pressure inside the reactor is maintained at 1.2–1.8 MPa by venting water vapor. In the final polymerization stage, the material is further heated to 265–285°C, and the pressure is reduced to atmospheric pressure within 0.5–2 hours. Subsequently, a vacuum is drawn for 5–30 minutes, with a vacuum degree of 60–90 kPa absolute pressure.

8. The method for preparing polyamide 66 resin chips according to claim 8, characterized in that: The endpoint of the polymerization reaction was determined by online measurement of shear viscosity during the final polymerization stage, and the shear viscosity was controlled within the range of 200–800 Pa·s.

9. A polyamide 66 resin chip suitable for nylon spinning, prepared by the method according to any one of claims 1 to 9, characterized in that: The polyamide 66 resin chips have a gel content of 0.1wt‰ to 1wt‰, a black spot count of no more than 5 per kg, a moisture content of no more than 0.07%, and a number-average molecular weight of 10,000 to 30,000 for polyamide 66. Furthermore, when polyamide 66 resin chips are used in nylon civilian spinning, the breakage rate during the spinning process is no higher than 1 time per hour, the evenness rate (CV) is no higher than 0.5%, the full roll rate is no lower than 98%, and the waste yarn rate is no higher than 0.8%.

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