Modified PA6 material and preparation method thereof

Abstract

The invention belongs to the technical field of modified copolymer nylon, and particularly relates to a modified PA6 material and a preparation method thereof. The invention aims to solve the problems that the existing copolymerization modified PA6 material has strong hygroscopicity and does not have high insulativity. Caprolactam and laurolactam are mixed and copolymerized to obtain a PA6 / 12 random copolymer; blending the modified graphene oxide, boron nitride nanosheets and polyamide oligomer in advance to obtain a composite suspension; the PA6 / 12 random copolymer is subjected to surface coating and then fed into an extruder, the composite suspension liquid is added after complete melting, a flame retardant additive is added after uniform mixing, and finally the modified PA6 material is obtained through extrusion. The modified PA6 material prepared by the invention has low water absorption and good insulativity, and is not easy to leak and trace in a high-temperature working scene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of modified copolymer nylon, and particularly relates to a modified PA6 material and a preparation method thereof. BACKGROUND

[0002] Nylon material is one of the most widely used and largest yield engineering plastics, including PA6, PA66 and PA46 and various types, and has important application value in various fields due to excellent tensile strength, wear resistance, chemical resistance and relatively low cost.

[0003] Among them, PA6 (polycaprolactam) is a typical nylon material, which contains a large number of polar amide groups in the molecular chain, which is easy to absorb water during use, resulting in a slow decrease in stiffness and strength within a certain period of time. At the same time, PA6 is easy to swell after absorbing water, resulting in dimensional changes of parts, which is a fatal defect for applications requiring high precision (such as electronic connectors and precision gears). Therefore, modified PA6 materials gradually replace the basic PA6 materials and are concerned by the industry, such as copolymer modified PA6, composite modified PA6, etc., which have a certain degree of improvement in mechanical properties and functionality. In the fields of new energy vehicles, new infrastructure and advanced manufacturing, modified PA6 materials have been widely used.

[0004] Although the modification technology of PA6 is quite mature, there are still some key technical problems. Although copolymer modification can reduce the water absorption rate, it usually sacrifices heat resistance or increases cost. In fiber reinforced composite materials, even if the PA6 matrix is low in hygroscopicity, the poor interface between the fiber and the matrix may become a capillary channel for water penetration, re-introducing the problem of hygroscopicity; further, in order to improve the mechanical properties of modified PA6, the addition of various fillers also limits its composite functionality, and nano fillers or powdered additives are easy to agglomerate in the melt, forming stress concentration points, which in turn weaken the material properties. At the same time, inorganic fillers and organic PA6 matrix are naturally incompatible, and must rely on efficient compatibilizer technology to build a stable interface bond. Especially in the field of insulating components used in high-voltage battery modules and precision engineering instruments, although the existing modified PA6 materials have insulation, they also have significant tracking and leakage problems in long-term high-temperature and high-voltage operation.

[0005] In order to solve the problems of high hygroscopicity and lack of high insulation of the existing copolymer modified PA6 material, a modified PA6 material and a preparation method thereof are provided. SUMMARY

[0006] The application aims to provide a modified PA6 material and a preparation method thereof. The application mixes caprolactam and laurolactam to obtain a PA6 / 12 random copolymer; pre-blends modified graphene oxide, boron nitride nanosheet and polyamide oligomer to obtain a composite suspension; feeds the PA6 / 12 random copolymer into an extruder after surface coating, adds the composite suspension after complete melting, adds a flame retardant aid after uniform mixing, and finally extrudes to obtain the modified PA6 material.

[0007] To achieve the above-mentioned purpose, the application provides the following technical scheme. A preparation method of a modified PA6 material, comprising the following steps: Unless otherwise specified, the parts in the application refer to mass parts.

[0008] Copolymerization: under nitrogen protection, mix caprolactam and laurolactam at a molar ratio of 85:15, use oxalic acid as an initiator, heat to 260-280℃, and react for 12 hours under an operating pressure of 1.5 MPa. Extrude the polymer melt into a strip, remove unreacted monomers and oligomers by hot water extraction after cooling, and dry to obtain a PA6 / 12 random copolymer.

[0009] Mix 100 parts of the PA6 / 12 random copolymer with 2 parts of modified hydrotalcite at a rotation speed of 1500 rpm for 5-10 min to perform surface coating treatment.

[0010] The preparation method of the modified hydrotalcite is as follows: disperse 100 parts of aluminum-magnesium hydrotalcite powder in ethanol, add a sodium stearate solution dropwise, stir at 70℃ for 4 hours, wash the obtained solid product with hot water and ethanol, and dry to obtain the modified hydrotalcite. The molar ratio of magnesium to aluminum in the aluminum-magnesium hydrotalcite powder is 3:1, and the addition amount of the sodium stearate is 3 parts.

[0011] Surface amination is performed on the graphene oxide to obtain modified graphene oxide.

[0012] Preferably, the surface amination process is as follows: disperse 1 part of graphene oxide in deionized water, ultrasonically treat for 20 min, add 50 parts of ethylenediamine, react in a water bath at 80℃ for 8 hours under nitrogen protection, centrifugally wash the obtained solid product multiple times, and dry to obtain the modified graphene oxide. The sheet thickness of the graphene oxide used is less than 5 nm.

[0013] Ultrasonically disperse 0.2 parts of modified graphene oxide in 20 parts of polyamide oligomer, and then add 10-15 parts of boron nitride nanosheet to obtain a composite suspension.

[0014] Preferably, the specific process of ultrasonic dispersion is as follows: the polyamide oligomer is heated to 180-200℃, then the NMP dispersion of modified graphene oxide is added, the boron nitride nanosheet is added after ultrasonic homogenization, and the composite suspension is obtained after the organic solvent is removed by vacuum treatment under an operating pressure of 0.1 atm. The polyamide oligomer is a hydroxyl-terminated PA6 oligomer with a number average molecular weight of 1000-3000 g / mol; the average flake diameter of the boron nitride nanosheet is 10-20 μm, and the flake thickness is less than 200 nm.

[0015] The flame retardant aid is obtained by pre-mixing 10 parts of melamine phosphate and 4 parts of zinc borate.

[0016] 100 parts of PA6 / 12 random copolymer are fed into an extruder, and 25-35 parts of the composite suspension is added after melting at 260℃. The operating temperature of the extruder is increased to 280℃, and 15 parts of the flame retardant aid is added. After mixing, the modified PA6 material product is obtained after water bath cooling and drying.

[0017] According to the operating sequence of the extruder barrel, the feeding sequence of the present application is as follows: the first barrel is the main feeding port, the operating temperature is 260℃, and the PA6 / 12 random copolymer treated by surface coating is added; the second barrel to the fourth barrel are the melt plasticizing regions; the composite suspension is added through a metering pump in the fifth barrel region; the sixth barrel is a conventional stretch shear treatment part; the seventh barrel is a side feeding port, the flame retardant aid is added and mixed, and the operating temperature is increased to 280℃; the eighth barrel is a conventional stretch shear treatment part; the ninth barrel is an exhaust zone, and the operating pressure is 0.1 atm; the tenth barrel to the twelfth barrel are homogenization pressure regions, and finally the melt is extruded by weak shear force.

[0018] Compared with the prior art, the present application has the following beneficial effects: During the ring-opening polymerization stage, a certain proportion of long-chain lactam monomers is introduced, and long alkyl chains are randomly embedded in the PA6 molecular main chain, which reduces the concentration of polar amide groups at the molecular level and forms a PA6 / 12 random copolymer with low amide density. In-situ copolymerization in the process ensures uniform combination of the two monomers and avoids the phase separation problem that may occur in physical blending. The long-chain methylene segment is a natural hydrophobic group, which reduces the equilibrium water absorption and saturated water absorption of the PA6 matrix from the source. Functionally, most of the excellent mechanical properties and cost advantages of PA6 are retained, and the reserved amide groups and end groups provide active sites for subsequent reactive combination with other aids.

[0019] The boron nitride nanosheets are blended with polyamide oligomers and injected into a twin-screw extruder after the random copolymer is completely melted. The dispersibility of the pre-dispersed boron nitride nanosheets in the thermoplastic nylon matrix is improved, and the low hygroscopicity of the PA6 / 12 random copolymer matrix ensures the phonon transmission efficiency of the boron nitride and the polymer interface, ensuring good thermal conductivity of the final modified PA6 material. At the same time, the introduction of boron nitride improves the insulation of the modified PA6 material, and the well-dispersed boron nitride nanosheets will gradually orient during the subsequent stretching and shearing process, forming a partially parallel lamellar structure, which improves the high-voltage resistance of the modified PA6 material.

[0020] A small amount of zinc borate and melamine phosphate is introduced as a flame retardant aid in the later stage of extrusion, and the modified graphene oxide is blended with boron nitride nanosheets and polyamide oligomers in advance. Graphene oxide itself is an electrical insulator, and its surface amino groups can chemically bond with a large number of polar groups in the PA6 / 12 random copolymer matrix. The two-dimensional sheet structure and excellent mechanical and thermal properties of graphene oxide, combined with uniformly dispersed boron nitride nanosheets, further enhance the thermal conductivity of the modified PA6 material, compensating for the negative impact of the reduced thermal conductivity caused by the introduction of flame retardant aids. At the same time, melamine phosphate and zinc borate, as inorganic powders, have weak interfacial bonding with the PA6 / 12 random copolymer, which can cause a decrease in material strength and toughness, but the modified graphene oxide can partially coat the surface of these particles, partially restoring the mechanical strength of the material.

[0021] Before the PA6 / 12 random copolymer is fed into the twin-screw extruder, a small amount of modified hydrotalcite is coated on its surface by a surface coating method. Modified hydrotalcite, as a thermal stabilizer, also has the typical functions of an acid substance capturing agent and an anion exchanger. Melamine phosphate flame retardant may decompose or hydrolyze slightly when heated for a long time, producing conductive phosphoric acid, and uniformly dispersed modified hydrotalcite will actively capture and neutralize these acidic substances, fixing them in its own layered structure through a chemical reaction, becoming harmless stable salt. This fundamentally prevents the destruction of electrical properties by acidic ions, ensuring the long-term safety of the flame retardant system under high voltage. Moreover, the modified hydrotalcite will partially insert between the boron nitride nanosheets and the modified graphene oxide nanosheets during the melting and shearing process, effectively inhibiting the agglomeration of graphene oxide, and the modified hydrotalcite can neutralize the residual acidic functional groups on the surface of graphene oxide, improving its interfacial compatibility with the matrix, ensuring the final good insulation and heat resistance of the modified PA6 material. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flow chart of the preparation method of the modified PA6 material in the present application. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Reference Figure 1 The process flow diagram shown illustrates that this invention provides a method for preparing modified PA6 material, the technical solution of which is as follows:

[0025] Example 1: Under nitrogen protection, caprolactam and dodecanolactam were mixed at a molar ratio of 85:15, with oxalic acid as the initiator, and the mixture was heated to 260°C and reacted at an operating pressure of 1.5 MPa for 12 hours. The polymer melt was extruded into strips, cooled, and then extracted with hot water to remove unreacted monomers and oligomers. After drying, PA6 / 12 random copolymer was obtained. The number average molecular weight of the PA6 / 12 random copolymer obtained by this method was 30,000-35,000 g / mol.

[0026] 100 parts of PA6 / 12 random copolymer and 2 parts of modified hydrotalcite were mixed at 1500 rpm for 5 min for surface coating treatment.

[0027] The modified hydrotalcite is prepared as follows: 100 parts of aluminum-magnesium hydrotalcite powder are dispersed in ethanol, sodium stearate solution is added dropwise, and the mixture is stirred at 70°C for 4 hours. The resulting solid product is washed with hot water and ethanol and then dried to obtain the modified hydrotalcite. The amount of sodium stearate added is 3 parts.

[0028] One part of graphene oxide was dispersed in deionized water and ultrasonically treated for 20 min. Then, 50 parts of ethylenediamine were added, and the mixture was reacted in a water bath at 80°C for 8 hours under nitrogen protection. The solid product was obtained by centrifugation and washing multiple times and then dried to obtain modified graphene oxide.

[0029] Twenty parts of polyamide oligomer were heated to 180°C, and then 0.2 parts of NMP dispersion of modified graphene oxide were added. After ultrasonic homogenization, 10 parts of boron nitride nanosheets were added. After mixing evenly, the mixture was vacuum treated at an operating pressure of 0.1 atm to remove organic solvents, thus obtaining a composite suspension.

[0030] A flame retardant additive is obtained by pre-mixing 10 parts of melamine phosphate and 4 parts of zinc borate.

[0031] 100 parts of PA6 / 12 random copolymer was fed into the extruder, after melting at 260℃, 25 parts of the composite suspension was added. The operating temperature of the later stage of the extruder was increased to 280℃, and 15 parts of the flame retardant aid was added. After mixing, the product of the modified PA6 material was obtained after extrusion, water bath cooling and drying.

[0032] Example 2-16 was different from Example 1 in the operating parameters, and the selection range of other process steps and raw materials was the same.

[0033] The specific operating parameter changes are summarized in Table 1.

[0034] Table 1 Operating parameter changes of Examples 1-16 Co-polymerization temperature (℃) Surface coating treatment time (min) Boron nitride nanosheet addition amount (parts) Ultrasonic dispersion heating temperature (℃) Composite suspension addition amount (parts) Example 1 260 5 10 180 25 Example 2 280 10 15 200 35 Example 3 271 8 12 191 30 Example 4 265 6 14 184 27 Example 5 278 9 11 198 34 Example 6 262 7 10 182 26 Example 7 275 5 15 195 35 Example 8 268 10 13 188 31 Example 9 273 8 11 193 29 Example 10 261 6 14 181 33 Example 11 279 9 12 199 28 Example 12 266 7 13 186 32 Example 13 276 5 10 196 25 Example 14 264 10 15 183 35 Example 15 270 8 11 190 29 Example 16 269 7 14 189 31 Comparative Example 1 Different from Example 1, the lauryl lactam was replaced by equimolar amount of caprolactam, and other process parameters were the same.

[0035] Comparative Example 2 Different from Example 1, the molar ratio of lauryl lactam was changed from 15% to 5%, and other process parameters were the same.

[0036] Comparative Example 3 Different from Example 5, no boron nitride nanosheet was added, and other process parameters were the same.

[0037] Comparative Example 4 Different from Example 5, the boron nitride nanosheet was not pre-blended with the polyamide oligomer, but was added separately into the extruder in steps, and other process parameters were the same.

[0038] Comparative Example 5 Different from Example 5, the composite suspension was added together with the flame retardant aid in the seventh barrel, and other process parameters were the same.

[0039] Comparative Example 6 Different from Example 9, the modified graphene oxide was replaced by equal mass fraction of unammoniated graphene oxide, and other process parameters were the same.

[0040] Comparative Example 7 Different from Example 9, the amount of the flame retardant aid was increased to 30 parts, and other process parameters were the same.

[0041] Comparative Example 8 Different from Example 9, no polyamide oligomer was added, and the modified graphene oxide and boron nitride nanosheet were directly added and blended in solid state, and other process parameters were the same.

[0042] Comparative Example 9 Different from example 13, the modified hydrotalcite and the modified graphene oxide were dispersed in the polyamide oligomer at the same time, instead of being coated on the surface, and other process parameters were the same.

[0043] Comparative example 10 Different from example 13, no modified hydrotalcite was added, and other process parameters were the same.

[0044] Experimental example 1 The water absorption rate and dimensional stability before and after moisture absorption, and the dielectric properties of the modified PA6 material products prepared in examples 1-4 and comparative examples 1-2 were tested, and the related results are shown in Table 2.

[0045] The test method for water absorption rate and dimensional stability was as follows: according to ISO 62 standard, the sample was immersed in distilled water at 23°C. The sample size was 60mmx1mmx2mm, and the mass change rate (%) before and after water absorption was recorded as the water absorption rate, and the length change rate (%) was recorded to represent the dimensional stability of the sample before and after moisture absorption.

[0046] The test method for dielectric constant was as follows: according to the related test method of ASTM D150 standard, the dielectric constant of the sample before and after moisture absorption was tested and recorded, and the test frequency was 1MHz.

[0047] Table 2 Water absorption rate and performance before and after moisture absorption of the modified PA6 material prepared in examples 1-4 and comparative examples 1-2 Water absorption rate (%) Long axis length change rate (%) Dielectric constant before moisture absorption Dielectric constant after moisture absorption Example 1 2.7 0.6 4.5 7.2 Example 2 3.1 1.0 5.1 7.4 Example 3 3.2 0.8 4.8 7.1 Example 4 2.8 0.7 5.0 7.2 Comparative Example 1 5.7 1.2 4.6 13.6 Comparative Example 2 4.8 1.0 4.8 11.9 As shown in the data in Table 2, the modified PA6 material prepared in examples 1-4 was significantly better than comparative example 1 and comparative example 2 in terms of water absorption rate and dimensional stability after moisture absorption. At the same time, the dielectric constant of examples 1-4 remained good stability after moisture absorption, while the dielectric properties of comparative example 1 and comparative example 2 decreased significantly after moisture absorption. This shows that the copolymer matrix prepared by the complete technical solution of the present application has obvious advantages in reducing the moisture absorption of the material and maintaining the dimensional and electrical property stability in a humid heat environment.

[0048] Comparative example 1 used equimolar amount of caprolactam instead of lauryl lactam, i.e. the matrix was pure PA6 polymer, and the water absorption rate and the change amount of dielectric constant after moisture absorption were the highest, and the dimensional stability was also poor. This shows that the molecular main chain composed of polar amide groups is the fundamental reason for the high moisture absorption of the material. The addition of comparative example 2 reduces the proportion of lauryl lactam, resulting in lower water absorption rate and dielectric property stability than the examples. This also proves the necessity of introducing sufficient long-chain lactam monomers to inhibit the water absorption rate of the matrix.

[0049] In summary, the application introduces a specific proportion of long-chain dodecanolactam monomers in the open-loop polymerization stage, and embeds the hydrophobic long-alkyl-chain structure into the PA6 molecular backbone through in-situ random copolymerization. This design reduces the concentration of polar amide groups at the molecular level, and weakens the ability of the matrix material to combine with water molecules from the source, thereby significantly reducing the equilibrium water absorption and saturated water absorption of the material. The process ensures uniform combination of the two monomers, avoids the phase separation problem that may occur in physical blending, and cooperatively realizes the substantial improvement in the dimensional stability and electrical performance stability in a humid heat environment while retaining most of the excellent mechanical properties of PA6.

[0050] Experimental Example 2 The thermal conductivity and electrical breakdown strength of the modified PA6 material products prepared in Test Examples 5-8 and Comparative Examples 3-5 were tested, and the related results are summarized in Table 3.

[0051] The thermal conductivity test method refers to the relevant test method of ASTM E1461 standard, and the thermal conductivity (W / (m·K)) in the thickness direction of the test sample is tested and recorded. The size of the test sample is 12.7mm in diameter and 2mm in thickness.

[0052] The electrical breakdown strength test method refers to the test method of ASTM D149 standard, and the breakdown test is carried out at a power frequency of 60Hz, and the maximum breakdown voltage (kV / mm) of the test sample is recorded. The size of the test sample is 100mm×100mm×2mm.

[0053] Table 3 Thermal conductivity and electrical breakdown strength of modified PA6 material products prepared in Test Examples 5-8 and Comparative Examples 3-5 Thermal conductivity (W / (m·K)) Maximum breakdown voltage (kV / mm) Example 5 1.7 45.0 Example 6 1.8 44.5 Example 7 1.7 44.5 Example 8 1.9 45.0 Comparative Example 3 0.6 25.5 Comparative Example 4 0.9 28.5 Comparative Example 5 1.3 39.5 As shown in the data in Table 3, the modified PA6 materials prepared in Examples 5-8 are significantly superior to Comparative Example 3, Comparative Example 4 and Comparative Example 5 in terms of thermal conductivity and maximum breakdown voltage, indicating that the technical solution has obvious advantages in improving the thermal conductivity and high-voltage insulation of the material.

[0054] Comparative Example 3 does not add boron nitride nanosheets, and its thermal conductivity and voltage resistance performance are the worst among all samples, proving that boron nitride is the core functional additive for achieving high thermal conductivity and high insulation performance. Comparative Example 4 separately adds boron nitride nanosheets and the base resin into the extruder, without pre-dispersion treatment, and the thermal conductivity and electrical breakdown strength of the final product are much lower than those of the examples, which shows that preparing the filler into a suspension is a key step to improve its dispersion in the matrix. Comparative Example 5 adds the composite suspension together with the flame retardant in the later stage of extrusion, and the material performance is also inferior to the examples, which proves the importance of adding the thermal conductive filler as early as possible after the complete melting of the polymer to form a uniform dispersion structure.

[0055] In summary, the boron nitride nanosheet is blended with the polyamide oligomer to prepare a composite suspension, and the composite suspension is injected into a twin-screw extruder after the base resin is completely melted. This pre-dispersion treatment significantly improves the dispersibility of the boron nitride nanosheet in the thermoplastic nylon matrix. The uniformly dispersed boron nitride not only constructs an efficient phonon transmission network to ensure good thermal conductivity of the material, but also forms a partially parallel lamellar structure during the subsequent tensile shear process, thereby synchronously improving the insulation and high-voltage resistance of the modified PA6 material, and achieving synergistic enhancement of the thermal conductivity and insulation performance.

[0056] Experimental Example 3 The thermal conductivity, tensile properties and flame retardant properties of the modified PA6 material products prepared in Test Examples 9-12 and Comparative Examples 6-8 were tested. The relevant results are summarized in Table 4.

[0057] The test method for thermal conductivity refers to Experimental Example 2.

[0058] The test method for tensile properties refers to the relevant test method of ISO 527 standard. The tensile strength (MPa) of the sample was recorded, and the dumbbell-shaped sample had a total length of 170 mm, a gauge length of 80 mm, a gauge width of 10 mm, and a thickness of 4 mm.

[0059] The test method for flame retardant properties refers to the UL 94 standard. The flame retardant property grade of the sample was recorded after testing, and the sample size was 125 mm x 13 mm x 1.6 mm.

[0060] Table 4 Thermal conductivity, tensile properties and flame retardant properties of the modified PA6 material prepared in Test Examples 9-12 and Comparative Examples 6-8 Thermal conductivity (W / (m·K)) Tensile strength (MPa) Flame retardant performance grade Example 9 1.8 118.7 V-0 Example 10 1.9 121.9 V-0 Example 11 1.9 120.5 V-0 Example 12 1.8 119.4 V-0 Comparative Example 6 1.5 82.5 V-0 Comparative Example 7 1.2 62.8 V-0 Comparative Example 8 0.7 51.6 V-0 As shown in the data in Table 4, the modified PA6 material prepared in Examples 9-12 still maintains a very high thermal conductivity and tensile strength while achieving a V-0 flame retardant grade. In contrast, Comparative Examples 6, 7 and 8 also achieve the same flame retardant grade, but their tensile strength and thermal conductivity both decrease significantly. This indicates that the present technical solution can effectively compensate for the loss of mechanical and thermal properties caused by the introduction of flame retardant additives, achieving a good balance between flame retardancy, thermal conductivity and mechanical properties.

[0061] Comparative Example 6 uses graphene oxide without surface amination, which has much lower tensile strength than the examples, indicating that the amination modification of the surface of graphene oxide is essential to enhance the mechanical properties of the material. Comparative Example 7 increases the amount of flame retardant additive, resulting in a significant deterioration of the tensile strength and thermal conductivity of the material, which proves that excessive amounts of inorganic powder filler can severely damage the comprehensive performance of the material due to weak interfacial bonding. Comparative Example 8 does not use polyamide oligomer to pre-disperse the filler, but directly blends in solid state, resulting in the most severe loss of mechanical and thermal properties, highlighting the key role of the pre-dispersion process in ensuring the functionality of the filler and maintaining the mechanical properties of the matrix.

[0062] In summary, the present application synergistically utilizes the functions of various components. Melamine phosphate and zinc borate as inorganic powder flame retardants have weak interfacial bonding with the polymer matrix, which can lead to a decrease in material strength and toughness. The present solution introduces surface-aminated modified graphene oxide, the surface of which can chemically bond with the polar groups in the PA6 / 12 random copolymer matrix. At the same time, its two-dimensional sheet structure will partially coat the surface of the flame retardant particles, improving the interfacial stress transfer and thus partially restoring the mechanical strength of the material. In addition, the modified graphene oxide and the uniformly dispersed boron nitride nanosheet work together to further enhance the thermal conductivity of the modified PA6 material, effectively compensating for the negative impact of the decrease in thermal conductivity caused by the introduction of the flame retardant additive.

[0063] Experimental Example 4 The comparative tracking index (CTI) and volume resistivity of the modified PA6 materials prepared in Examples 13-16 and Comparative Examples 9-10 were tested, and the results are summarized in Table 5.

[0064] The test method for the comparative tracking index (CTI) refers to IEC 60112, and the CTI values of the sample before and after 500 hours of hot air aging at 150°C are tested, respectively. The sample size is 60mm x 60mm x 3mm.

[0065] The test method for volume resistivity refers to the test method of ASTM D257, and the volume resistivity of the sample before and after hot air aging is tested, respectively. The sample size is 100mm in diameter and 3mm in thickness.

[0066] Table 5 CTI values and volume resistivity of the modified PA6 materials prepared in Examples 13-16 and Comparative Examples 9-10 CTI value before aging (V) CTI value after aging (V) Pre-aging bulk resistivity (10 14 Ω-cm) Volume resistivity after aging (10 14 Ω·cm)]]> Example 13 645, PLC0 625, PLC0 22.4 8.9 Example 14 645, PLC0 630, PLC0 21.7 8.4 Example 15 650, PLC0 625, PLC0 21.9 8.5 Example 16 645, PLC0 620, PLC0 22.1 8.2 Comparative Example 9 630, PLC0 550, PLC1 20.9 4.2 Comparative Example 10 635, PLC0 450, PLC2 22.1 1.8 As shown in the data of Table 5, the modified PA6 materials prepared in Examples 13-16 maintained very high levels of both comparative tracking index and volume resistivity before and after long-term hot air aging, and the CTI value after aging still maintained the highest performance level of PLC0. In contrast, the materials of Comparative Example 9 and Comparative Example 10 showed significant degradation in electrical properties after aging, and the CTI level decreased significantly. This indicates that the present technical solution has a significant advantage in ensuring the stability of the electrical properties of the material during long-term service in a high-temperature environment.

[0067] Comparative Example 10 did not add modified hydrotalcite, and its electrical properties deteriorated the most after heat aging, which directly proves that modified hydrotalcite is a key additive for maintaining the long-term thermal stability and electrical insulation of the material. Comparative Example 9 blended modified hydrotalcite with other additives instead of surface coating the base resin, and its performance after aging was better than that of Comparative Example 10, but still far inferior to that of the examples. This result contradicts the importance of the surface coating pretreatment process for ensuring the uniform dispersion of modified hydrotalcite and its efficient function.

[0068] In summary, the present application uses a surface coating method to pre-coat modified hydrotalcite on PA6 / 12 random copolymer particles. As a thermal stabilizer and acidic substance capturing agent, the core function of modified hydrotalcite is to neutralize the conductive phosphoric acid-type acidic substances that may be produced by the decomposition or hydrolysis of flame retardant melamine phosphate during long-term heating. Uniformly dispersed modified hydrotalcite will actively capture these acidic substances and fix them in its own layered structure, becoming harmless stable salt. This fundamentally prevents the destruction of electrical properties by acidic ions, ensuring the long-term safety of the flame retardant system under high pressure. At the same time, modified hydrotalcite can also inhibit the agglomeration of graphene oxide and improve its interfacial compatibility with the matrix, synergistically ensuring the final good insulation and heat resistance of the modified PA6 material.

[0069] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a modified PA6 material, characterized in that: The preparation method is as follows: Caprolactam and dodecanolactam were mixed and copolymerized to obtain a PA6 / 12 random copolymer. The PA6 / 12 random copolymer was surface-coated with modified hydrotalcite; The modified hydrotalcite is obtained by treating aluminum magnesium hydrotalcite powder with sodium stearate. The PA6 / 12 random copolymer is fed into an extruder, melted, and then a composite suspension is added. The temperature is increased and a flame retardant is added in the later stage of extrusion. The modified PA6 material is obtained after extrusion. The composite suspension comprises: polyamide oligomers, boron nitride nanosheets, and modified graphene oxide.

2. The method for preparing a modified PA6 material according to claim 1, characterized in that: In the copolymerization reaction, the reaction temperature is 260-280℃.

3. The method for preparing a modified PA6 material according to claim 1, characterized in that: The surface coating process is as follows: the PA6 / 12 random copolymer and the modified hydrotalcite are mixed under stirring for 5-10 minutes.

4. The method for preparing a modified PA6 material according to claim 1, characterized in that: The modified graphene oxide is prepared by dispersing graphene oxide in deionized water, adding ethylenediamine, reacting in a water bath, and washing and drying the resulting solid product to obtain the modified graphene oxide.

5. The method for preparing a modified PA6 material according to claim 1, characterized in that: The composite suspension is prepared by heating the polyamide oligomer, adding the modified graphene oxide dispersion, homogenizing by ultrasonication, adding the boron nitride nanosheets, mixing evenly, and then vacuum treating to obtain the composite suspension.

6. The method for preparing a modified PA6 material according to claim 1, characterized in that: The flame retardant additives include melamine phosphate and zinc borate; the polyamide oligomer is a hydroxyl-terminated PA6 oligomer.

7. The method for preparing a modified PA6 material according to claim 1, characterized in that: The mass ratio of the PA6 / 12 random copolymer to the composite suspension is 100:25-35.

8. A modified PA6 material, comprising: The material comprises a random copolymer of PA6 / 12, boron nitride nanosheets, modified graphene oxide, polyamide oligomers, and flame retardant additives, characterized in that the modified PA6 material is prepared by the preparation method described in any one of claims 1-7.

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