Halogen-free flame-retardant nylon composite material and preparation method thereof

Abstract

The invention discloses a halogen-free flame-retardant nylon composite material and a preparation method thereof. The composite material comprises 61.5-90% of nylon resin, 0.2-1.5% of a phosphorus-nitrogen-silicon flame retardant, 5-20% of a silicate and beta-nucleating agent compound, 5-15% of a dynamically vulcanized elastomer, 0.1-2% of a light stabilizer and 1-3% of a nanoscale inorganic filler. The phosphorus-nitrogen-silicon flame retardant is composed of ammonium polyphosphate, melamine silicate and nano silicon dioxide, and melamine cyanurate is synthesized in situ in the twin-screw extrusion process. The preparation method comprises the steps of precise temperature control extrusion, three-zone in-situ reaction, nanofiller vacuum dehydration and NIRS real-time drying monitoring. The material has high flame retardance, excellent electrical property and mechanical strength, is suitable for electric vehicle battery shells, rail transit high-voltage connectors and aerospace interior trim parts, and meets the requirements of high safety and high reliability.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a halogen-free flame-retardant nylon composite material and its preparation method. Background Technology

[0002] Nylon resin is widely used in electronics, electrical appliances, and transportation equipment due to its excellent mechanical strength, heat resistance, and processing performance. With increasingly stringent environmental regulations, halogen-free flame retardancy has become an inevitable direction for nylon modification. However, existing technologies face three major challenges: 1. Conflict between flame retardancy and electrical performance: Traditional halogen-free flame retardants (such as ammonium polyphosphate) require high addition levels (>15%) to achieve UL94 V-0 rating, but excessive filling causes a sharp drop in CTI value, which cannot meet the requirements of high-voltage components; 2. Deterioration of mechanical properties: Poor compatibility between flame retardant and matrix leads to stress concentration points and a decrease in impact strength; 3. Bottlenecks in process control: Flame retardants are prone to decomposition at high temperatures, and the moisture absorption of nanofillers leads to the extrusion of air bubbles, resulting in a low yield rate.

[0003] Therefore, there is an urgent need to develop a halogen-free flame-retardant nylon composite material that combines high flame retardancy, high electrical properties, strong toughness, and stable processing. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] Therefore, to solve the above-mentioned technical problems, the present invention provides the following technical solution: a halogen-free flame-retardant nylon composite material, comprising the following components by mass percentage: Nylon resin: 61.5~90%; Phosphorus-nitrogen-silicon flame retardant: 0.2~1.5%; Silicate-β-nucleating agent complex: 5~20%; Dynamically vulcanized elastomer: 5~15%; Light stabilizer: 0.1~2%; Nanoscale inorganic fillers: 1~3%; The phosphorus-nitrogen-silicon flame retardant includes ammonium polyphosphate, melamine silicate, nano-silica, and melamine cyanurate (MCA) generated in situ by the reaction of melamine silicate with cyanuric acid. The dynamically vulcanized elastomer is a blend of EPDM and MAH grafted material, with a grafting degree ≥5%; In the silicate-β-nucleating agent complex, the silicate is a layered silicate, and the β-nucleating agent is a compound that can induce nylon to form a β-crystal form.

[0006] In a preferred embodiment of the halogen-free flame-retardant nylon composite material of the present invention, the layered silicate is montmorillonite, and the β-nucleating agent is a rare earth compound or an amide nucleating agent.

[0007] As a preferred embodiment of the halogen-free flame-retardant nylon composite material of the present invention, the nano-scale inorganic filler is nano-montmorillonite or nano-silica with a particle size ≤100nm.

[0008] As a preferred embodiment of the halogen-free flame-retardant nylon composite material of the present invention, the initial mass ratio of ammonium polyphosphate, melamine silicate and nano silica is 1:1:0.5~3:1:2, and the molar ratio of melamine silicate to cyanuric acid is 1:0.8~1:1.2.

[0009] As a preferred embodiment of the halogen-free flame-retardant nylon composite material of the present invention, the material has a limiting oxygen index (LOI) ≥ 35%, a glow wire ignition temperature (GWFI) ≥ 775°C, and a comparative tracking index (CTI) ≥ 600V.

[0010] A method for preparing a halogen-free flame-retardant nylon composite material, applicable to any of the above-mentioned halogen-free flame-retardant nylon composite materials, characterized by comprising the following steps: Step A: Weigh out the following components by weight: nylon resin, ammonium polyphosphate, melamine silicate, nano silica, cyanuric acid, silicate and β-nucleating agent complex, dynamic vulcanized elastomer, light stabilizer, and nano-scale inorganic filler. Step B: Add the mixture to the twin-screw extruder and control the temperature distribution of the twin-screw extruder as follows: conveying zone 210~230℃, melting zone 230~250℃, reaction zone 240~260℃, venting zone 240~260℃, homogenization zone 230~250℃, cooling zone 220~240℃, and main extruder speed 240~400 rpm; Step C: In the reaction zone of step B, melamine silicate and cyanuric acid react at 240~260℃ for 2~5 minutes to synthesize MCA in situ; Step D: Melt extrusion followed by cooling and granulation; Step E: Dry the granulated product at 80~100℃, and terminate the process when the moisture content is ≤0.02% by real-time monitoring using near-infrared spectroscopy, thereby obtaining halogen-free flame-retardant nylon composite material.

[0011] In a preferred embodiment of the preparation method of the halogen-free flame-retardant nylon composite material of the present invention, the nanoscale inorganic filler in step A is added after being vacuum dehydrated to a moisture content of ≤0.02%.

[0012] As a preferred embodiment of the preparation method of the halogen-free flame-retardant nylon composite material of the present invention, the vacuum dehydration conditions in step A are: vacuum degree ≤ -0.09MPa, temperature 80~100℃, and time 10~30 minutes.

[0013] In a preferred embodiment of the preparation method of the halogen-free flame-retardant nylon composite material of the present invention, the length-to-diameter ratio of the twin-screw extruder in step B is 48:1, the dynamically vulcanized elastomer is added through the side feed port of the conveying zone, and the dehydrated nano-scale inorganic filler is added through the side feed port of the homogenization zone.

[0014] In a preferred embodiment of the preparation method of the halogen-free flame-retardant nylon composite material of the present invention, in step C, the catalyst triethylamine is added to the reaction, and the amount of triethylamine is 0.5~2% of the total mass of ammonium polyphosphate, melamine silicate and nano silica.

[0015] The beneficial effects of this invention are: 1. This invention constructs a phosphorus-nitrogen-silicon cross-linked network through a "three-in-one" flame retardant system (MCA+APP+nano SiO2), forming a dense silicon-carbon layer on the combustion surface, which improves oxygen barrier efficiency and requires less flame retardant, avoiding the decrease in CTI caused by high filler content. The silicate / β-nucleating agent composite simultaneously achieves β-crystal-induced toughening and layered smoke suppression, while maintaining a high impact strength retention rate.

[0016] 2. The MCA of this invention nucleates in situ in nylon melt, resulting in high dispersion uniformity; vacuum dehydration removes the hydroxyl groups of the nanofiller, exhibiting excellent CTI value performance, which can perfectly adapt to high-voltage application scenarios; three-zone temperature control combined with NIRS moisture content monitoring greatly improves the yield rate.

[0017] 3. The material obtained by this invention has high tensile strength and excellent notched impact strength, and in low-temperature environments, the material retains a very high toughness rate, exhibiting excellent high strength characteristics and good environmental adaptability. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a flowchart illustrating the preparation method of the present invention. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

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

[0021] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0022] Example 1 Reference Figure 1 This is the first embodiment of the present invention, which provides a method for preparing a halogen-free flame-retardant nylon composite material, comprising the following steps: Weigh the following materials according to the specified ratio: PA6 resin 75%, phosphorus-nitrogen-silicon flame retardant (APP:melamine silicate:nano SiO2=1:1:1) 1.0%, montmorillonite / rare earth β-nucleating agent complex 12%, EPDM-g-MAH (grafting degree 8%) 10%, light stabilizer 0.5%, dehydrated nano-montmorillonite (moisture content 0.018%) 1.5%; Cyanuric acid was added to the mixture at a molar ratio of melamine silicate of 1:1. Twin-screw extrusion: conveying zone 220℃, melting zone 240℃, reaction zone 250℃ (in-situ reaction for 4 min), exhaust zone 250℃, homogenization zone 240℃, cooling zone 230℃, rotation speed 350 rpm, length-to-diameter ratio 48:1; Side feeding: EPDM-g-MAH enters the conveying zone, and nano-montmorillonite enters the homogenization zone; After granulation, the product was dried at 100℃ for 10 hours (NIRS monitoring, termination when moisture content ≤0.02%) to obtain composite material P1.

[0023] Comparative Example 1 The difference between this comparative example and Example 1 is that the flame retardant in this comparative example is replaced with premixed MCA (equal amount to replace melamine silicate + cyanuric acid), step C reaction is cancelled, the temperature of the reaction zone is reduced to 230°C, and the rest is the same as in Example 1, to obtain comparative material D1.

[0024] Example 2 This is the second embodiment of the present invention, which differs from the first embodiment in that: the ratio of phosphorus-nitrogen-silicon flame retardant is adjusted to APP:melamine silicate:nano SiO2=2:1:1.5; the β-nucleating agent is replaced with an amide (N,N'-dicyclohexylterephthalamide); the vacuum dehydration conditions are set to -0.095 MPa / 95℃ / 20 min, and the rest is the same as in Example 1, to obtain composite material P2.

[0025] Comparative Example 2 The difference between this comparative example and Example 1 is that the ratio of phosphorus-nitrogen-silicon flame retardant in this comparative example is changed to APP:melamine silicate:nano SiO2=1:0.3:3, while the rest is the same as in Example 1, and comparative material D2 is obtained.

[0026] Example 3 This is the third embodiment of the present invention. The difference between this embodiment and the first embodiment is that: in step C, triethylamine catalyst (1.2% of the total mass of flame retardant) is added, the moisture content of the nanofiller after dehydration is ≤0.015%, and the drying process is controlled in real time by NIRS (0.02% is achieved by drying at 85℃ for 9 hours). The rest is the same as in embodiment 1, and composite material P3 is obtained.

[0027] Comparative Example 3 differs from Example 1 in that the nano-montmorillonite was not dehydrated (initial moisture content 0.8%), step D vacuum treatment was omitted, and the rest was the same as in Example 1, resulting in comparative material D3.

[0028] Example 4 This is the fourth embodiment of the present invention, which differs from the first embodiment in that: this embodiment provides a process for industrial continuous production verification of the present solution, and the specific steps are as follows: 1. Continuous production: Continuous production is carried out using a Φ52 mm twin-screw extruder (L / D ratio L / D=48:1).

[0029] 2. Raw material ratio and feeding rate: PA6 resin: 45 kg / h; Phosphorus-nitrogen-silicon flame retardant (APP:melamine silicate:nano SiO2=1:1:1): 0.6 kg / h; Cyanuric acid (used for in-situ synthesis of MCA): 0.3 kg / h; Silicate-β-nucleating agent complex: 7.2 kg / h; Dynamically vulcanized elastomer (EPDM-g-MAH, grafting degree 8%): 6 kg / h; Light stabilizer: 0.3 kg / h; Dehydrated nano-SiO2 (moisture content ≤0.015%): 0.9 kg / h.

[0030] 3. Process control: Temperature and reaction conditions: The reaction zone was set at 255°C and the reaction time was 3.5 minutes for in-situ synthesis of MCA. Catalyst: Triethylamine is injected online at a rate of 0.05 kg / h (accounting for 1.2% of the total mass of the flame retardant).

[0031] Side feeding: Feeding to the conveyor zone: EPDM-g-MAH; Feed to the homogenization zone: dehydrated nano-SiO2.

[0032] Drying process: The drying kiln is set to 100℃ / 10 hours and uses near-infrared spectroscopy (NIRS) closed-loop control to monitor the moisture content in real time. Drying is terminated when the moisture content is ≤0.02%.

[0033] The composite material P4 was prepared by the above steps.

[0034] Table 1 shows the comparative data of flame retardant and electrical properties of halogen-free flame retardant nylon composite materials prepared in Examples 1-4 and Comparative Examples 1-4.

[0035] Table 1:

[0036] Table 2 shows the comparative data of mechanical and microscopic properties of halogen-free flame-retardant nylon composite materials prepared in Examples 1 and 3 and Comparative Examples 1 and 3.

[0037] Table 2:

[0038] The dispersion levels are: A = uniform with no agglomeration, and D = severe agglomeration.

[0039] From the performance comparison data of the above embodiments and comparative examples, it can be seen that: 1. Comparative Example 1 (P1) and Comparative Example 1 (D1): D1 uses premixed MCA instead of in-situ synthesis, resulting in a 15.3% decrease in LOI value (36.5%→31.2%) and a 100V reduction in CTI (625V→525V). SEM shows severe agglomeration of the flame retardant (rating C). This demonstrates that the in-situ reaction promotes the directional bonding of melamine silicate and cyanuric acid in the molten state, forming nanoscale dispersed MCA, achieving a highly efficient synergistic effect in the phosphorus-nitrogen-silicon flame retardant system, and avoiding the interfacial defects of premixed flame retardants.

[0040] 2. Comparative Example 2 (P2) and Comparative Example 2 (D2): D2 adjusted the flame retardant ratio to APP:melamine silicate:nano SiO2 = 1:0.3:3 (exceeding the range provided by this solution), and its LOI plummeted to 29.5% (below the industry safety threshold of 32%), and GWFI decreased by 80°C; verifying that 1:1:0.5~3:1:2 is the "golden window" for the synergistic effect of phosphorus-nitrogen-silicon three-phase, excessive nano SiO2 disrupts the continuity of the flame retardant network, while excessively low melamine silicate content inhibits the in-situ formation of MCA.

[0041] 3. Comparative Example 3 (P3) and Comparative Example 3 (D3): D3 did not dehydrate the nanofiller (water content 0.8%), and the CTI dropped to 550V (below the 600V threshold of high voltage devices), and the impact strength decreased by 40%. This shows that water content ≤0.02% is the core to ensure the dielectric performance of nanofillers. Trace amounts of water molecules ionize under high voltage, causing leakage channels and inducing hydrolysis and embrittlement of the matrix.

[0042] 4. Example 4 (P4) under continuous production conditions: Through precise temperature control of the reaction zone (255℃±2℃) and closed-loop monitoring of moisture content by NIRS, the performance of P4 is highly consistent with that of laboratory batch P1; it is confirmed that the in-situ synthesis reaction and the stringent dehydration process are compatible with the production line, providing mass production guarantee for high-end scenarios such as power battery casings.

[0043] In summary, this invention achieves a breakthrough in balancing high performance with LOI≥35%, GWFI≥775℃, and CTI≥600V through in-situ synthesis of MCA, precise component ratio, and strict process control. This solves the industry problem of halogen-free flame-retardant nylon's inability to simultaneously achieve "high flame retardancy, high electrical properties, and strong toughness".

[0044] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A halogen-free flame-retardant nylon composite material, characterized in that: Includes the following components by mass percentage: Nylon resin: 61.5~90%; Phosphorus-nitrogen-silicon flame retardant: 0.2~1.5%; Silicate-β-nucleating agent complex: 5~20%; Dynamically vulcanized elastomer: 5~15%; Light stabilizer: 0.1~2%; Nanoscale inorganic fillers: 1~3%; The phosphorus-nitrogen-silicon flame retardant includes ammonium polyphosphate, melamine silicate, nano-silica, and melamine cyanurate generated in situ by the reaction of melamine silicate with cyanuric acid. The dynamically vulcanized elastomer is a blend of EPDM and MAH grafts; In the silicate-β-nucleating agent complex, the silicate is a layered silicate, and the β-nucleating agent is a compound that can induce nylon to form a β-crystal form.

2. The halogen-free flame-retardant nylon composite material as described in claim 1, characterized in that: The layered silicate is montmorillonite, and the β-nucleating agent is a rare earth compound or an amide-based nucleating agent.

3. The halogen-free flame-retardant nylon composite material as described in claim 2, characterized in that: The nanoscale inorganic filler is nano-montmorillonite or nano-silica with a particle size ≤100nm.

4. The halogen-free flame-retardant nylon composite material as described in claim 3, characterized in that: The initial mass ratio of ammonium polyphosphate, melamine silicate, and nano silica is 1:1:0.5 to 3:1:2, and the molar ratio of melamine silicate to cyanuric acid is 1:0.8 to 1:1.

2.

5. The halogen-free flame-retardant nylon composite material as described in claim 4, characterized in that: The material has a limiting oxygen index of ≥35%, a glow wire ignition temperature of ≥775℃, and a comparative tracking index of ≥600V.

6. A method for preparing a halogen-free flame-retardant nylon composite material, the method being applicable to the halogen-free flame-retardant nylon composite material according to any one of claims 1 to 5, characterized in that: Includes the following steps: Step A: Weigh out the following components by weight: nylon resin, ammonium polyphosphate, melamine silicate, nano silica, cyanuric acid, silicate and β-nucleating agent complex, dynamic vulcanized elastomer, light stabilizer, and nano-scale inorganic filler. Step B: Add the mixture to the twin-screw extruder and control the temperature distribution of the twin-screw extruder as follows: conveying zone 210~230℃, melting zone 230~250℃, reaction zone 240~260℃, venting zone 240~260℃, homogenization zone 230~250℃, cooling zone 220~240℃, and main extruder speed 240~400 rpm; Step C: In the reaction zone of step B, melamine silicate and cyanuric acid react at 240~260℃ for 2~5 minutes to synthesize MCA in situ; Step D: Melt extrusion followed by cooling and granulation; Step E: Dry the granulated product at 80~100℃, and terminate the process when the moisture content is ≤0.02% by real-time monitoring using near-infrared spectroscopy, thereby obtaining halogen-free flame-retardant nylon composite material.

7. The method for preparing a halogen-free flame-retardant nylon composite material as described in claim 6, characterized in that: The nanoscale inorganic filler in step A is added after being vacuum dehydrated to a moisture content of ≤0.02%.

8. The method for preparing a halogen-free flame-retardant nylon composite material as described in claim 7, characterized in that: The vacuum dehydration conditions in step A are: vacuum degree ≤ -0.09MPa, temperature 80~100℃, and time 10~30 minutes.

9. The method for preparing a halogen-free flame-retardant nylon composite material as described in claim 8, characterized in that: In step B, the length-to-diameter ratio of the twin-screw extruder is 48:

1. The dynamically vulcanized elastomer is added through the feed port on the side of the conveying zone, and the dehydrated nano-sized inorganic filler is added through the feed port on the side of the homogenization zone.

10. The method for preparing a halogen-free flame-retardant nylon composite material as described in claim 9, characterized in that: In step C, triethylamine is added as a catalyst, and its amount is 0.5-2% of the total mass of ammonium polyphosphate, melamine silicate, and nano silica.

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