A flame-retardant nylon supercritical continuous extrusion foam material and its preparation method

Abstract

This invention belongs to the field of polymer foaming technology, and particularly relates to a method for preparing a flame-retardant nylon supercritical continuous extrusion foam material, comprising the following steps: S1 Preparation of chain extender masterbatch: After premixing a polyamide carrier with an oxazoline chain extender, the mixture is melt-blended and granulated in a twin-screw extruder for preparing chain extender masterbatch, and dried until the moisture content is ≤300ppm to obtain the chain extender masterbatch. This invention avoids premature contact between the chain extender and the flame retardant, thus preventing side reactions and ensuring stable and controllable melt rheological properties.

Description

Technical Field

[0001] This invention belongs to the field of polymer foaming technology, and particularly relates to a flame-retardant nylon supercritical continuous extrusion foaming material and its preparation method. Background Technology

[0002] Nylon (polyamide) foam, with its high specific strength, chemical resistance, wear resistance, and recyclability, has become one of the core materials for achieving industrial lightweighting under the global "dual carbon" strategy. It is widely used in new energy vehicle interior parts, electronic device housings, rail transit vehicle components, and building insulation panels. With the continuous upgrading of safety standards across industries, the market has placed more stringent comprehensive performance requirements on nylon foam: it must not only meet the UL94V-0 high flame retardancy standard for a 1.6mm thickness, but also possess a high closed-cell rate of ≥90%, excellent mechanical properties, and long-term stability at 80℃.

[0003] supercritical Continuous extrusion foaming technology has become the mainstream technology for the industrial production of nylon foam materials due to its advantages such as being environmentally friendly and pollution-free, having controllable foaming ratio, and high production efficiency. However, existing supercritical extrusion foaming technology for flame-retardant nylon still faces four common industry pain points that urgently need to be addressed, severely restricting its large-scale application in high-end fields: The inherent contradiction between flame retardancy and foaming is difficult to reconcile: To meet the UL94V-0 flame retardant requirement, current technologies typically require the addition of more than 30% inorganic flame retardants. Traditional halogenated flame retardants have been gradually restricted from use by the EU REACH regulation and China RoHS standard due to environmental concerns; single phosphorus-based flame retardants have poor compatibility with nylon matrices, significantly reducing melt strength; while the mainstream phosphorus-silicon binary flame retardant system can improve flame retardant efficiency to some extent, it is not suitable for supercritical applications. Even under the strong plasticizing effect, the melt viscosity can still drop sharply by 30%-50%, causing problems such as cell merging, collapse, and increased open cell ratio.

[0004] Current technologies are generally caught in a dilemma: "Flame retardancy meets the standard, but foaming fails; foaming is qualified, but flame retardancy is insufficient." When the amount of flame retardant added meets the UL94V-0 requirement, the closed-cell rate of the material is usually less than 85%, and the mechanical property loss exceeds 40%. If the amount of flame retardant added is reduced to ensure foaming performance, it cannot pass the vertical burning test for a 1.6mm thickness. Currently, there is no mature industrial technology that can simultaneously and stably achieve both UL94V-0 flame retardancy and a closed-cell rate of ≥90% for a 1.6mm thickness.

[0005] Inorganic flame retardants have poor dispersibility and low processing stability. Existing technologies widely use aluminum phosphonate, melamine cyanurate, and cage-type silsesquioxanes, all of which are inorganic or low-molecular-weight organic-inorganic composite flame retardants. They have strong surface polarity, poor compatibility with non-polar nylon matrices, and are prone to agglomeration. Even with high-speed extrusion, it is still difficult to achieve nanoscale uniform dispersion, resulting in localized enrichment or absence of flame retardants. The performance fluctuation between batches can reach 5%-10%, and the product qualification rate is generally below 85%.

[0006] Side reactions between chain extenders and flame retardants: To compensate for the decrease in melt strength caused by flame retardants, existing technologies often use epoxy chain extenders to modify the nylon matrix. However, epoxy groups can undergo irreversible side reactions with acidic groups in phosphorus-based flame retardants, generating insoluble crosslinking products. This leads to a complete loss of control over the melt rheological properties, further exacerbating production stability issues.

[0007] Insufficient stability with long-term use: In existing flame-retardant nylon foam materials, the flame retardant tends to migrate and precipitate into the cell walls and material surface under long-term use at 80°C. Typically, after 1000 hours of aging, the flame retardant rating drops from V-0 to V-2 or even fails completely, while the mechanical properties are retained at less than 80%, failing to meet the long-term service life requirements of automotive interiors, rail transportation, and other fields.

[0008] To address the aforementioned issues, the industry has made numerous attempts, such as using microencapsulated flame retardants to reduce migration, using multifunctional chain extenders to improve melt strength, and optimizing supercritical fluid injection processes to improve cell structure. However, these methods can only solve one pain point at a time and cannot achieve synergistic optimization of flame retardancy, foaming, and mechanical properties. Furthermore, they often significantly increase production costs.

[0009] Therefore, developing a flame-retardant nylon supercritical continuous extrusion foam material and its preparation method that can solve the above four major industry pain points and meet the requirements of high flame retardancy, high dispersibility, high closed-cell ratio, high strength and long-term stability has extremely important industrial value and market significance. Summary of the Invention

[0010] The purpose of this invention is to address the aforementioned technical problems by providing a flame-retardant supercritical continuous extrusion foamed nylon material.

[0011] In view of this, the present invention provides a method for preparing a flame-retardant nylon supercritical continuous extrusion foam material, comprising the following steps: S1 Preparation of chain extender masterbatch: After premixing polyamide carrier with oxazoline chain extender, the mixture is melt-blended and granulated in a twin-screw extruder for chain extender masterbatch preparation, and dried to a moisture content ≤300ppm to obtain chain extender masterbatch; S2 Preparation of flame retardant masterbatch: After high-speed dispersion of phosphorus-nitrogen-silicon ternary synergistic flame retardant with PA6 / 66 copolynylon carrier, maleic anhydride grafted polyolefin interface regulator and composite antioxidant, the mixture is melt-blended and granulated in a twin-screw extruder for flame retardant masterbatch preparation, and dried to a moisture content ≤300ppm to obtain flame retardant masterbatch. S3 Step-by-Step Feeding and Melting: Nylon 6 main material and the obtained chain extender masterbatch are added from the main feed port of the continuous extrusion foaming twin-screw extruder, and the obtained flame retardant masterbatch is added from the side feed port of the fifth barrel of the continuous extrusion foaming twin-screw extruder. The length-to-diameter ratio of the continuous extrusion foaming twin-screw extruder is 36-44, and the fifth barrel refers to the fifth barrel counting from the barrel where the main feed port is located. S4 Supercritical Fluid Injection and Foaming: Injected at two points, at the end of the chain extension reaction section and the middle of the homogenization section, in the continuous extrusion foaming twin-screw extruder. / Argon-gas composite supercritical fluid, and the injection pressure at the second injection point is higher than that at the first injection point; S5 Cooling, Shaping and Cutting: After gradient cooling and shaping and traction cutting, the extruded material is obtained as the flame-retardant nylon supercritical continuous extrusion foam material.

[0012] Furthermore, by weight, the raw material composition of the chain extender masterbatch is: 92-95 parts of polyamide carrier and 5-8 parts of oxazoline chain extender, wherein the polyamide carrier is selected from at least one of nylon 66 or PA6 / 66 copolynylon.

[0013] Furthermore, the twin-screw extruder used for preparing the chain extender masterbatch has a rotation speed of 200~300 rpm and an extrusion temperature gradient of 180℃→200℃→220℃; the oxazoline chain extender is 2,2'-bisoxazoline.

[0014] Furthermore, by weight, the raw material composition of the flame retardant masterbatch is as follows: 61-71.5 parts of PA6 / 66 copolymer nylon, 22-32 parts of phosphorus-nitrogen-silicon ternary synergistic flame retardant, 3-5 parts of maleic anhydride grafted polyolefin, and 0.6-0.9 parts of composite antioxidant; the twin-screw extruder used for preparing the flame retardant masterbatch has a rotation speed of 200-300 rpm and an extrusion temperature of 230-250℃; The phosphorus-nitrogen-silicon ternary synergistic flame retardant is composed of aluminum diethylphosphinate, microencapsulated melamine cyanurate and methylphenyl silicone powder in a mass ratio of (14-18):(5-8):(3-6).

[0015] Furthermore, the mass ratio of PA6 to PA66 in the PA6 / 66 copolynylon is 7:3, and the intrinsic viscosity is 1.8-2.0 dL / g; the composite antioxidant is a mixture of hindered phenol 1076 and phosphite 626 in a mass ratio of 2:1.

[0016] Furthermore, by weight, the total raw material composition is: 57-64 parts of nylon 6 main material, 6-9 parts of chain extender masterbatch, and 30-38 parts of flame retardant masterbatch; the nylon 6 main material is pre-dried to a moisture content of ≤300ppm.

[0017] Furthermore, the temperature gradient of the twin-screw extruder for continuous extrusion foaming is as follows: 175-185℃ for the pre-melting section, 240-255℃ for the chain extension reaction section, 220-230℃ for the flame-retardant mixing section, and 210-220℃ for the homogenization foaming section; the screw speed is 90-110 rpm.

[0018] Furthermore, the aforementioned / Argon-Gaseous Supercritical Fluid The mass ratio of the raw material to argon is 5:5; when the melt viscosity is 1500-2000 Pa·s, the pressure at the first injection point is 22-24 MPa, and the injection amount is 1.8-2.3% of the total raw material mass; when the melt viscosity is 2000-2500 Pa·s, the pressure at the second injection point is 25-27 MPa, and the injection amount is 1.5-2.0% of the total raw material mass.

[0019] Furthermore, the gradient cooling temperature range is 38-48℃, the cooling rate is 8-11℃ / s, and the cooling medium is an air-water mixture system.

[0020] A flame-retardant nylon supercritical continuous extrusion foam material is prepared by the above-mentioned method.

[0021] The beneficial effects of this invention are: This invention utilizes a "stepwise isolation modification with dual masterbatches + highly dispersed phosphorus-nitrogen-silicon ternary system +" The innovative system design of "argon gas dual-point pressurization injection" solves four major industry pain points of existing technologies: Solving the problem of poor dispersibility of inorganic flame retardants: The traditional inorganic flame retardant is replaced by aluminum diethylphosphonate (organically modified phosphorus-based), microencapsulated melamine cyanurate (polymer-coated nitrogen-based), and methyl phenyl silicone powder (high molecular weight silicon-based). All three have excellent compatibility with the nylon matrix and their dispersibility is improved by more than 50% compared with traditional inorganic flame retardants. They can achieve nanoscale uniform dispersion without additional surface treatment, which significantly reduces agglomeration.

[0022] To avoid side reactions between chain extenders and flame retardants: By using a process design that combines stepwise preparation of dual masterbatches with side feeding of flame retardant masterbatch in the fifth barrel section, the chain extension reaction is ensured to be completed before the flame retardant is added, eliminating the chance of contact between oxazoline chain extenders and phosphorus-based flame retardants. The melt rheological properties are stable and controllable, the continuous production performance fluctuation is ≤1.2%, and the product qualification rate is ≥99%.

[0023] Achieving synergistic optimization of flame retardancy, foaming properties, and mechanical properties: The new phosphorus-nitrogen-silicon ternary system has a 45% higher flame retardant efficiency than the traditional system, and can stably achieve UL94V-0 rating with a thickness of only 1.6mm, while reducing the total amount of flame retardant added by 10%. Methylphenyl silicone powder has both flame retardant and melt reinforcement functions, which can compensate for the decrease in melt strength caused by flame retardants, making the material closed-cell rate ≥98.5% and tensile strength ≥38MPa, thus solving the industry problem of "contradiction between flame retardancy and foaming".

[0024] Significantly improves long-term stability: The synergistic effect of microencapsulation and high molecular weight silicon-based flame retardants effectively inhibits the migration and precipitation of flame retardants. After aging at 80℃ for 1000 hours, the migration of flame retardants is ≤0.18%, the flame retardant rating remains V-0, and the tensile strength retention rate is ≥93%, which can meet the long-term service life requirements of automobiles, rail transportation and other fields. Detailed Implementation

[0025] The technical solutions in the embodiments of this application will be clearly described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0026] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0027] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0028] It should be noted that in the description of this application, the directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" indicate the orientation or positional relationship based on the orientation or positional relationship of the equipment during normal use. They are only used for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0029] It should be noted that, in this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0030] The following embodiments and comparative examples of the present invention all adopt the following general process conditions, and parameters not specifically mentioned are performed accordingly: Twin-screw extruder for preparing chain extender masterbatch: length-to-diameter ratio L / D=40, extrusion temperature gradient 180℃→200℃→220℃, moisture content of masterbatch after drying 220ppm; Twin-screw extruder for flame retardant masterbatch preparation: length-to-diameter ratio L / D=40, extrusion temperature 230-250℃, moisture content of masterbatch after drying 220ppm; Twin-screw extruder for continuous extrusion foaming: length-to-diameter ratio L / D=40, fifth barrel section is a side feed port; Nylon 6 main material: intrinsic viscosity 1.85 dL / g (corresponding to relative viscosity 2.6), pre-dried to a moisture content of 210 ppm; The raw materials and masterbatches used in this invention are all dried using a vacuum drum dryer at a temperature of 120°C for 8-12 hours. Performance testing standards: Flame retardant performance: UL94-2016 vertical burning test, sample thickness 1.6mm; Mechanical properties: GB / T1040.2-2006 Tensile strength, GB / T1843-2008 Notched impact strength of simply supported beam; Aging performance: GB / T7141-2008 hot air aging test, conditions 80℃×1000h; Flame retardant migration: Surface precipitation amount was determined by gas chromatography-mass spectrometry (GC-MS). Cell structure: Average pore size, cell wall thickness and pore size distribution coefficient were measured by scanning electron microscopy image analysis, and closed-cell rate was measured by mercury porosimetry. Dispersion: The dispersion state of flame retardant particles was observed by transmission electron microscopy (TEM), and the size and number of agglomerates were counted. Example

[0031] This embodiment provides a method for preparing a flame-retardant nylon supercritical continuous extrusion foam material, the steps of which are as follows: Preparation of chain extender masterbatch: 93.5 parts by weight of nylon 66 and 6.5 parts by weight of 2,2'-bisoxazoline were premixed in a high-speed mixer at 1000-1200 rpm for 3-5 min, and then melt-blended and granulated in a twin-screw extruder for chain extender masterbatch preparation at 250 rpm, and dried to a moisture content of ≤300 ppm. Preparation of flame retardant masterbatch: 18 parts by weight of aluminum diethylphosphinate, 8 parts by weight of microencapsulated melamine cyanurate, 4 parts by weight of methyl phenyl silicone powder, 64.2 parts by weight of PA6 / 66 copolynylon (PA6:PA66=7:3, intrinsic viscosity 1.88dL / g), 5 parts by weight of maleic anhydride grafted polyolefin, and 0.8 parts by weight of composite antioxidant (hindered phenol 1076: phosphite 626=2:1) ​​were dispersed in a high-speed mixer at 1800-2200 rpm for 5-8 min, then melt-blended and granulated in a twin-screw extruder for flame retardant masterbatch preparation at 260 rpm, and dried to a moisture content ≤300ppm; Stepwise feeding: 63 parts by weight of nylon 6 main material and 7.5 parts by weight of chain extender masterbatch are added from the main feed port of the continuous extrusion foaming twin-screw extruder, and 29.5 parts by weight of flame retardant masterbatch are added from the side feed port of the fifth barrel. Supercritical foaming: The continuous extrusion foaming uses a twin-screw extruder with a temperature gradient of 175℃ / 180℃ / 242℃ / 225℃ / 215℃ and a screw speed of 100 rpm; injection is performed at the end of the chain extension reaction section. Argon-argon composite fluid (mass ratio 5:5), pressure 23 MPa, injection volume 2.0% of total raw material mass; the same composite fluid is injected in the middle of the homogenization section, pressure 26 MPa, injection volume 1.7% of total raw material mass; Cooling, shaping and cutting: The extrudate is cooled at a gradient of 38-48℃ (cooling rate 9℃ / s, air-water mixed medium) and then traction-cut to obtain flame-retardant nylon supercritical continuous extrusion foam material. Example

[0032] The only difference between this embodiment and Embodiment 1 is that: Flame retardant masterbatch formulation: 16 parts aluminum diethylphosphinate, 7 parts microencapsulated melamine cyanurate, 5 parts methyl phenyl silicone powder, 66.2 parts PA6 / 66 copolynylon, 5 parts maleic anhydride grafted polyolefin, and 0.8 parts composite antioxidant. Total raw material ratio: 60 parts nylon 6 main material, 9 parts chain extender masterbatch, and 31 parts flame retardant masterbatch; Extrusion temperature gradient: 175℃ / 180℃ / 250℃ / 230℃ / 220℃; Screw speed: 110 rpm; Fluid injection parameters: first point 24MPa / 2.3%, second point 27MPa / 2.0%. Example

[0033] The only difference between this embodiment and Embodiment 1 is that: Flame retardant masterbatch formulation: 14 parts aluminum diethylphosphinate, 5 parts microencapsulated melamine cyanurate, 3 parts methyl phenyl silicone powder, 70.2 parts PA6 / 66 copolynylon, 7 parts maleic anhydride grafted polyolefin, and 0.8 parts composite antioxidant. Total raw material ratio: 65 parts nylon 6 main material, 6 parts chain extender masterbatch, and 29 parts flame retardant masterbatch; Extrusion temperature gradient: 185℃ / 190℃ / 235℃ / 220℃ / 210℃; Screw speed: 90 rpm; Fluid injection parameters: 22MPa / 1.8% at the first point, and 25MPa / 1.5% at the second point. Example

[0034] The only difference between this embodiment and Embodiment 1 is that: Flame retardant masterbatch formulation: 17 parts aluminum diethylphosphinate, 6 parts microencapsulated melamine cyanurate, 4 parts methyl phenyl silicone powder, 67.2 parts PA6 / 66 copolynylon, 5 parts maleic anhydride grafted polyolefin, and 0.8 parts composite antioxidant. Total raw material ratio: 62 parts nylon 6 main material, 8 parts chain extender masterbatch, and 30 parts flame retardant masterbatch; Extrusion temperature gradient: 180℃ / 185℃ / 245℃ / 228℃ / 212℃; Screw speed: 105 rpm; Fluid injection parameters: first point 23.5MPa / 2.1%, second point 26.5MPa / 1.8%. Example

[0035] The only difference between this embodiment and Embodiment 1 is that: Flame retardant masterbatch formulation: 15 parts aluminum diethylphosphinic acid, 6 parts microencapsulated melamine cyanurate, 6 parts methyl phenyl silicone powder, 67.1 parts PA6 / 66 copolynylon, 5 parts maleic anhydride grafted polyolefin, and 0.8 parts composite antioxidant. Total raw material ratio: 64 parts nylon 6 main material, 7 parts chain extender masterbatch, and 29 parts flame retardant masterbatch; Extrusion temperature gradient: 182℃ / 188℃ / 240℃ / 223℃ / 218℃; Screw speed: 95 rpm; Fluid injection parameters: 22.5 MPa / 1.9% at the first point, and 25.5 MPa / 1.6% at the second point. Example

[0036] The only difference between this embodiment and Embodiment 1 is that: Flame retardant masterbatch formulation: 15 parts aluminum diethylphosphinate, 5 parts microencapsulated melamine cyanurate, 3 parts methyl phenyl silicone powder, 70.9 parts PA6 / 66 copolynylon, 5.2 parts maleic anhydride grafted polyolefin, and 0.9 parts composite antioxidant; Total raw material ratio: 64 parts nylon 6 main material, 6 parts chain extender masterbatch, and 30 parts flame retardant masterbatch.

[0037] Comparative Example 1 (Traditional Inorganic Flame Retardant System) The only difference between this comparative example and Example 1 is that 22 parts by weight of aluminum phosphonate, 10 parts by weight of melamine cyanurate, and 4 parts by weight of cage-type silsesquioxane are used in the flame retardant masterbatch to replace the new ternary flame retardant system.

[0038] Comparative Example 2 (Traditional phosphorus-nitrogen binary flame retardant system) The only difference between this comparative example and Example 1 is that the flame retardant masterbatch does not contain methyl phenyl silicone powder, and the flame retardant is adjusted to 22 parts by weight of aluminum diethylphosphinate + 8 parts by weight of microencapsulated melamine cyanurate.

[0039] Comparative Example 3 (Traditional Epoxy Chain Extender) The only difference between this comparative example and Example 1 is that 2,2'-bisoxazolin is replaced in equal amounts with epoxy chain extender ADR4370 in the chain extender masterbatch.

[0040] Comparative Example 4 (Phosphorus-Silicon Binary Flame Retardant System) The only difference between this comparative example and Example 1 is that the flame retardant masterbatch does not contain microencapsulated melamine cyanurate, and the flame retardant is adjusted to 22 parts by weight of aluminum diethylphosphinate + 8 parts by weight of methylphenyl silicone powder.

[0041] Comparative Example 5 ( (composite fluid) The only difference between this comparative example and Example 1 is that the supercritical fluid is... (mass ratio 6:4).

[0042] The materials obtained in Examples 1-6 and Comparative Examples 1-5 were subjected to performance tests according to the aforementioned standards, and the results are shown in the table below: Flame retardant rating (1.6mm) V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-1 V-1 V-1 V-0 Average afterburn time t1 / t2 (s) 1.3 / 1.6 1.1 / 1.4 1.5 / 1.8 1.2 / 1.5 1.2 / 1.4 1.7 / 2.0 2.5 / 2.9 6.0 / 7.1 7.8 / 9.1 6.2 / 7.3 2.2 / 2.6 Average pore size (μm) 19 20 18 19 19 20 32 25 42 28 35 Closed-pore ratio (%) 98.5 98.1 98.7 98.3 98.5 98.2 90.2 93.8 81.5 94.2 90.8 Tensile strength (MPa) 39.2 38.5 39.9 38.9 39.4 38.7 32.5 35.5 28.7 34.8 33.6 Impact strength (kJ / m²) 7.1 6.9 7.3 7.0 7.2 7.0 5.3 5.7 4.0 5.8 5.5 Flame retardancy rating after aging at 80℃ for 1000 hours V-0 V-0 V-0 V-0 V-0 V-0 V-1 V-2 V-2 V-2 V-1 Tensile retention rate (%) after aging at 80℃ for 1000 hours 93 91 94 92 93 92 80 82 76 81 82 Flame retardant migration rate (%) after aging at 80℃ for 1000 hours 0.16 0.18 0.15 0.17 0.16 0.17 0.52 0.41 0.65 0.45 0.39 Maximum agglomerate size of flame retardant (μm) ≤0.8 ≤0.9 ≤0.7 ≤0.8 ≤0.8 ≤0.9 ≤5.2 ≤1.5 ≤3.8 ≤1.8 ≤2.5 Continuous production performance fluctuation (%) 1.1 1.3 1.0 1.2 1.1 1.2 5.8 3.0 6.7 3.2 3.8 Product pass rate (%) 99.0 98.7 99.2 98.8 99.0 98.9 78.5 87.2 70.2 84.7 83.5 The data in the table above shows that: The materials prepared in Examples 1-6 of this invention exhibit significantly superior overall performance compared to existing technologies, simultaneously meeting the requirements of UL94V-0 flame retardancy, average pore size of 18-20 μm, closed-cell rate ≥98.1%, and tensile strength ≥38.5 MPa. This demonstrates synergistic optimization of flame retardancy, foaming properties, and mechanical properties. Example 6 verifies that even when the total amount of flame retardant added is reduced to 23 parts (in the masterbatch), the UL94V-0 flame retardancy requirement for a 1.6 mm thickness can still be achieved, with no significant decrease in foaming performance and mechanical properties.

[0043] Transmission electron microscopy observations showed that the flame retardant particles in the materials prepared in Examples 1-6 of this invention were uniformly dispersed, with the maximum agglomerate size ≤0.9μm, which is much smaller than the 5.2μm of Comparative Example 1, demonstrating the excellent effect of the highly dispersed phosphorus-nitrogen-silicon ternary flame retardant system of this invention.

[0044] Comparative Example 1 uses a traditional inorganic flame retardant system. The flame retardant agglomerates severely, resulting in large pores, low closed-cell rate, and decreased mechanical properties. Moreover, the flame retardant migrates significantly after long-term aging. Comparative Example 2 uses a traditional phosphorus-nitrogen binary flame retardant system, which lacks the melt reinforcement effect of silicon-based components, resulting in insufficient melt strength, decreased closed-cell rate, and insufficient flame retardant efficiency. Comparative Example 3 uses a traditional epoxy chain extender, which results in insufficient melt strength and severe cell collapse due to side reactions with the flame retardant. Comparative Example 4 uses a phosphorus-silicon binary flame retardant system, which lacks nitrogen synergy, resulting in insufficient flame retardant efficiency and a decrease in flame retardant rating after long-term aging. Comparative Example 5 used a CO2 / N2 composite fluid. Due to the interaction between nitrogen and phosphorus-based flame retardant, the nucleation was uneven and the pore size was too large.

[0045] The flame-retardant nylon supercritical continuous extrusion foam material prepared by this invention has the advantages of lightweight, high flame retardancy, high strength, excellent processing stability and long-term use stability. It can be widely used in fields with strict requirements for material performance, including but not limited to automotive interior parts (door panels, dashboards, seat frames), electronic device housings (laptop housings, router housings), rail transit components (carriage interior panels, insulation parts), building insulation materials, etc.

[0046] The embodiments of this application have been described above in conjunction with the examples. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a flame-retardant nylon supercritical continuous extrusion foam material, comprising the following steps: S1 Preparation of chain extender masterbatch: After premixing polyamide carrier with oxazoline chain extender, the mixture is melt-blended and granulated in a twin-screw extruder for chain extender masterbatch preparation, and dried to a moisture content ≤300ppm to obtain chain extender masterbatch; S2 Preparation of flame retardant masterbatch: First, the phosphorus-nitrogen-silicon ternary synergistic flame retardant is dispersed at high speed with PA6 / 66 copolymer nylon carrier, maleic anhydride grafted polyolefin interface regulator and composite antioxidant. Then, it is melt-blended and granulated in a twin-screw extruder for flame retardant masterbatch preparation and dried to a moisture content ≤300ppm to obtain flame retardant masterbatch. S3 Step-by-Step Feeding and Melting: Nylon 6 main material and the obtained chain extender masterbatch are added from the main feed port of the continuous extrusion foaming twin-screw extruder, and the obtained flame retardant masterbatch is added from the side feed port of the fifth barrel of the continuous extrusion foaming twin-screw extruder. The length-to-diameter ratio of the continuous extrusion foaming twin-screw extruder is 36-44, and the fifth barrel refers to the fifth barrel counting from the barrel where the main feed port is located. S4 Supercritical Fluid Injection and Foaming: Injected at two points, at the end of the chain extension reaction section and the middle of the homogenization section, in the continuous extrusion foaming twin-screw extruder. / Argon-gas composite supercritical fluid, and the injection pressure at the second injection point is higher than that at the first injection point; S5 Cooling, Shaping and Cutting: After gradient cooling and shaping and traction cutting, the extruded material is obtained as the flame-retardant nylon supercritical continuous extrusion foam material.

2. The preparation method according to claim 1, characterized in that, The raw material composition of the chain extender masterbatch by weight is: 92-95 parts of polyamide carrier and 5-8 parts of oxazoline chain extender, wherein the polyamide carrier is selected from at least one of nylon 66 or PA6 / 66 copolynylon.

3. The preparation method according to claim 2, characterized in that, The twin-screw extruder used for preparing the chain extender masterbatch has a rotation speed of 200~300 rpm and an extrusion temperature gradient of 180℃→200℃→220℃; the oxazoline chain extender is 2,2'-bisoxazoline.

4. The preparation method according to claim 1, characterized in that, The raw material composition of the flame retardant masterbatch, by weight, is as follows: 61-71.5 parts of PA6 / 66 copolymer nylon, 22-32 parts of phosphorus-nitrogen-silicon ternary synergistic flame retardant, 3-5 parts of maleic anhydride grafted polyolefin, and 0.6-0.9 parts of composite antioxidant; the twin-screw extruder used for preparing the flame retardant masterbatch has a rotation speed of 200-300 rpm and an extrusion temperature of 230-250℃; The phosphorus-nitrogen-silicon ternary synergistic flame retardant is composed of aluminum diethylphosphinate, microencapsulated melamine cyanurate and methylphenyl silicone powder in a mass ratio of (14-18):(5-8):(3-6).

5. The preparation method according to claim 4, characterized in that, The PA6 / 66 copolynylon has a PA6 to PA66 mass ratio of 7:3 and an intrinsic viscosity of 1.8-2.0 dL / g; the composite antioxidant is a mixture of hindered phenol 1076 and phosphite 626 in a mass ratio of 2:

1.

6. The preparation method according to claim 1, characterized in that, By weight, the total raw material composition is: 57-64 parts of nylon 6 main material, 6-9 parts of chain extender masterbatch, and 30-38 parts of flame retardant masterbatch; the nylon 6 main material is pre-dried to a moisture content of ≤300ppm.

7. The preparation method according to claim 1, characterized in that, The temperature gradient of the twin-screw extruder for continuous extrusion foaming is as follows: pre-melting section 175-185℃, chain extension reaction section 240-255℃, flame retardant mixing section 220-230℃, homogenization foaming section 210-220℃; the screw speed is 90-110 rpm.

8. The preparation method according to claim 1, characterized in that, In the CO2 / argon composite supercritical fluid The mass ratio of the raw material to argon is 5:5; when the melt viscosity is 1500-2000 Pa·s, the pressure at the first injection point is 22-24 MPa, and the injection amount is 1.8-2.3% of the total raw material mass; when the melt viscosity is 2000-2500 Pa·s, the pressure at the second injection point is 25-27 MPa, and the injection amount is 1.5-2.0% of the total raw material mass.

9. The preparation method according to claim 1, characterized in that, The gradient cooling temperature range is 38-48℃, the cooling rate is 8-11℃ / s, and the cooling medium is an air-water mixture.

10. A flame-retardant nylon supercritical continuous extrusion foam material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.