High glowing filament halogen-free flame-retardant polyamide and preparation method thereof

Abstract

The invention relates to the technical field of engineering plastics, and particularly discloses high glowing filament halogen-free flame-retardant polyamide and a preparation method thereof.The high glowing filament halogen-free flame-retardant polyamide is prepared from, by mass, 40%-60% of polyamide resin, 20%-40% of a reinforcing agent, 10%-20% of a halogen-free flame retardant, 1%-2% of a flame-retardant synergist and 2%-3% of auxiliaries; the main component of the flame-retardant synergist is silicon dioxide. Silicon dioxide with ultralow heat conductivity coefficient, extremely low density and high porosity is introduced into a polyamide flame-retardant composite system, the material is endowed with good adhesion and maintains high mechanical performance due to the unique three-dimensional porous network structure of silicon dioxide, the heat insulation efficiency can be greatly improved, and the flame-retardant effect is effectively achieved; the flame retardant grade of UL94 / 1.6 mm V0 is reached, and the high GWIT performance of the material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering plastics, and in particular to a high-glow-wire halogen-free flame-retardant polyamide and a preparation method thereof. Background Art

[0002] Polyamide 66 (PA66), a key engineering plastic, is widely used in the electronics, automotive, and other industries due to its excellent melt flow, heat resistance, and mechanical properties. However, the material's molecular chain is rich in aliphatic methylene units, making it inherently flammable. During combustion, it easily produces molten droplets that can ignite surrounding combustibles, posing a risk of secondary ignition. Furthermore, the presence of glass fiber reinforcement can cause a significant "wick effect." When used in electrical equipment or vehicles, sparks generated by circuit failures can trigger fires, posing a serious threat to normal production and life. This situation has prompted the industry to impose higher safety and technical requirements on the flame retardancy and glow-wire properties (especially the glow-wire ignition temperature (GWIT)) of high-end materials, making the exploration of flame-retardant modification of polyamide materials particularly important.

[0003] Although traditional halogenated flame retardants are the most widely used type of flame retardant in polyamides, these additives have significant technical limitations: poor high-temperature resistance and the release of toxic gases during combustion, failing to meet environmental and health requirements. With the increasing refinement of environmental regulations and public safety awareness, halogen-free flame retardant systems have become a research and development focus. Organic phosphinates (such as aluminum diethylphosphinate), as typical phosphorus-based flame retardants, rely primarily on the release of inert free radicals through thermal decomposition, effectively interrupting the combustion chain reaction and inhibiting flame spread. However, these systems suffer from poor water resistance and are sensitive to moisture, prone to component migration and precipitation in humid environments, resulting in a loss of flame retardancy. Existing technologies often combine these with aluminum phosphite flame retardants to improve heat resistance and prevent precipitation. However, both flame retardant components in these flame retardant systems primarily function through vapor-phase flame retardancy, resulting in insufficient char formation efficiency in the condensed phase, making it difficult to form a complete and dense carbon layer. Ultimately, the GWIT performance of these materials fails to meet the requirements of high-end electronic devices. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a high glow-wire halogen-free flame-retardant polyamide and a preparation method thereof. By optimizing the flame retardant compounding ratio and introducing a flame retardant synergist, the carbonization efficiency and thermal insulation efficiency are significantly improved, thereby obtaining a high GWIT value silk halogen-free flame-retardant polyamide.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a high glow-wire halogen-free flame-retardant polyamide, which is prepared from the following components in percentage by mass: 40% to 60% polyamide resin, 20% to 40% reinforcing agent, 10% to 20% halogen-free flame retardant, 1% to 2% flame retardant synergist, and 2% to 3% auxiliary agent; the main component of the flame retardant synergist is silicon dioxide.

[0006] As a further improvement to the above-mentioned embodiment of the present invention, the flame retardant synergist is one of nanosilica, hydrophobic fumed nanosilica, hydrophobic precipitated nanosilica, and silica aerogel. Hydrophobic fumed nanosilica is prepared using a vapor phase method, while hydrophobic precipitated nanosilica is prepared using a precipitation method. Preferably, the flame retardant synergist is silica aerogel. Silica aerogel can effectively promote the carbonization of the substrate, thereby providing excellent flame retardancy. Adding silica aerogel as a flame retardant synergist to a halogen-free flame-retardant PA66 system not only eliminates harmful substances such as halogens, ensuring safety, but also improves the material's flame retardancy and enhances the product's GWIT. Furthermore, silica aerogel has a large number of internal pores and possesses a certain degree of adhesiveness, which can simultaneously enhance the material's mechanical properties. Most preferably, the silica aerogel has a pore size of 5-40 nm and a particle size of 0.1-4 mm.

[0007] As a further improvement to the above-mentioned solution of the present invention, the reinforcing agent is at least one of glass fiber, talc, kaolin, wollastonite, calcium carbonate, and montmorillonite. Preferably, the reinforcing agent is glass fiber, and most preferably, the glass fiber is chopped glass fiber with a monofilament diameter of 9-11 μm. By adding the reinforcing agent, the mechanical properties of the PA66 resin matrix can be effectively improved, with tensile strength reaching 2-3 times that of the original material, significantly improving impact strength, and the unit reinforcement cost is lower than that of most nanofillers.

[0008] As a further improvement to the above-mentioned solution of the present invention, the halogen-free flame retardant is at least one of aluminum diethylphosphinate and aluminum phosphite. Preferably, the halogen-free flame retardant is a combination of aluminum diethylphosphinate and aluminum phosphite. By adopting the above-mentioned technical solution, the combustion chain reaction can be blocked through gas phase flame retardancy, thereby improving flame retardancy. At the same time, the problem of component migration and precipitation in humid environments can be alleviated, and the degradation of flame retardant properties can be delayed.

[0009] As a further improvement to the above-mentioned solution of the present invention, the polyamide resin is polyamide 66, with a relative viscosity of 2.7 dL / g. This moderate relative viscosity ensures good melt flow and a wider processing temperature range, reducing process sensitivity, facilitating the injection molding of complex components, and minimizing defects such as flash and material shortages during the molding process, while maintaining the inherent properties of PA66.

[0010] As a further improvement of the above solution of the present invention, the auxiliary agent can be any one or a mixture of antioxidants, lubricants, masterbatches, release agents, anti-dripping agents or antistatic agents; preferably, the auxiliary agent includes lubricants, antioxidants and masterbatches.

[0011] As a further improvement of the above solution of the present invention, the lubricant is at least one of modified ethylene bis fatty acid amide, pentaerythritol stearate and ethylene-acrylic acid copolymer wax powder, and the mass percentage of the lubricant in the high glow-wire halogen-free flame-retardant polyamide is 0.05%~0.7%.

[0012] As a further improvement to the above-mentioned solution of the present invention, the antioxidant is at least one of antioxidant 1098 and antioxidant 168, and the mass percentage of the antioxidant in the high glow-wire halogen-free flame-retardant polyamide is 0.05% to 0.2%. Preferably, the antioxidant is a mixture of antioxidant 1098 and antioxidant 168, with the mass ratio of the two being (1-3):1. Antioxidant 1098 has excellent material compatibility and low volatility, is resistant to thermal oxidation and extraction, and exhibits color stability before and after aging. The auxiliary antioxidant 168 is a phosphite antioxidant with a higher temperature resistance rating, high steric hindrance, resistance to hydrolysis and yellowing, and excellent high-temperature stability and low volatility at high temperatures. When the two antioxidants are used in combination, they produce a significant synergistic stabilizing effect in the PA66 matrix.

[0013] And / or, the masterbatch is a black masterbatch, and the mass percentage of the lubricant in the high glow-wire halogen-free flame-retardant polyamide is 0.5% to 2%.

[0014] The present invention also provides a method for preparing the high glow-wire halogen-free flame-retardant polyamide as described above, comprising the following steps: premixing a polyamide resin, a halogen-free flame retardant, a flame retardant synergist, and an additive in proportion, feeding the premix into a twin-screw extruder from a main feed port, adding a reinforcing agent in proportion from a side feed port, melting, extruding, and granulating to obtain the high glow-wire halogen-free flame-retardant polyamide.

[0015] As a further improvement of the above-mentioned solution of the present invention, the stirring speed of the premix is ​​500 r / min and the time is 3-5 min; and / or the temperature of each zone of the twin-screw extruder is: 240-255°C in zone 1, 245-255°C in zone 2, 265-280°C in zones 3 to 7, 240-260°C in zones 8 to 9, 230-250°C in zones 10 to 11, and 265-280°C in the die head; the main engine speed of the twin-screw extruder is 300-400 r / min.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention introduces silica with ultra-low thermal conductivity, extremely low density and high porosity into a polyamide flame-retardant composite system. Not only does the unique three-dimensional porous network structure of silica give the material good adhesion and maintain high mechanical properties, but it also enables the material to gel and solidify during combustion, ultimately forming a carbonized layer, making it difficult for heat to penetrate the condensed phase, effectively preventing the diffusion of oxygen into the combustion area, thereby preventing the continuous decomposition of combustibles, significantly improving thermal insulation efficiency, and effectively achieving a flame retardant effect, achieving a UL94 / 1.6 mm V0 flame retardant rating, and improving the material's high GWIT performance. No flames are generated during the test process.

[0017] The preparation process of the present invention is simple and easy, and large-scale industrial production can be achieved using conventional equipment. The obtained PA66 material has outstanding flame retardant properties, glow-wire properties and mechanical properties, and can be widely used in the fields of electronics, electrical engineering, automobiles, etc. DETAILED DESCRIPTION

[0018] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0020] The specific information of the raw materials used in the following examples and comparative examples is as follows: Polyamide resin: PA66, HY1800, Jiangsu Huayang Nylon Co., Ltd. Reinforcement: glass fiber, ECS10-4.5-568H, China Jushi Co., Ltd. Halogen-free flame retardant: LFR-5009, Liside; Flame retardant synergist 1: silica aerogel, commercially available; Flame retardant synergist 2: nanosilica, AEROSIL® 200, DEGUSSA; Flame retardant synergist 3: hydrophobic fumed nanosilica, SJ-R400, Sanjia Chemical; Flame retardant synergist 4: hydrophobic precipitated nanosilica, SR-570, Celico New Materials; Antioxidant 1: IRGANOX 1098, BASF; Antioxidant 2: IRGANOX 168, BASF; Lubricant: A-C540A, Honeywell; Black masterbatch, commercially available.

[0021] The above raw materials are only for illustrating the sources and components of the reagents used in the experiments of the present invention so as to fully disclose the information, and do not mean that the present invention cannot be achieved by using other similar reagents or reagents provided by other suppliers.

[0022] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0023] Preparation methods for the Examples and Comparative Examples: According to the proportions in Table 1, polyamide resin, halogen-free flame retardant, flame retardant synergist, antioxidant, lubricant, and masterbatch were premixed in a high-speed mixer at a stirring rate of 500 r / min for 3-5 minutes to ensure uniform dispersion of the components and obtain a uniform premix. The premix was then fed into a twin-screw extruder through the main feed port, and a reinforcing agent was simultaneously added through the side feed port. The mixture was melted, extruded, cooled, and shaped, and then pelletized to obtain a high-glow-wire halogen-free flame-retardant polyamide. The temperatures in each zone of the twin-screw extruder were: 240-255°C for zone 1, 245-255°C for zone 2, 265-280°C for zones 3-7, 240-260°C for zones 8-9, 230-250°C for zones 10-11, and 265-280°C for the die head. The main speed of the twin-screw extruder was 300-400 r / min.

[0024] Table 1 Distribution ratio of each group in Examples 1-6 and Comparative Examples 1-4 (by weight)

[0025] The high glow-wire halogen-free flame-retardant polyamides prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests. The results are shown in Table 2. The relevant performance test methods are as follows: (1) Tensile strength: tested in accordance with GB / T 1040-2018 standard; tensile speed is 10 mm / min; (2) Flame retardant grade: tested according to UL94 test standard, the test piece thickness is 1.6mm.

[0026] (3) Glow-wire test (GWIT): Tested in accordance with GB / T 5169.13-2013 / IEC 60695-2-13:2010.

[0027] Table 2 Performance test results

[0028] According to the results in Table 2, we can see that: Examples 1-4, by adding a certain amount of silica aerogel, nanosilica, hydrophobic fumed nanosilica, and hydrophobic precipitated nanosilica to the polyamide material, each improved the flame retardancy and glow-wire performance of the polyamide material. This is likely due to the Si atoms in the synergist participating in carbonization, forming a Si-C structure and a dense and relatively stable barrier carbon layer, which enhances the flame retardancy. The addition of silica aerogel in Example 1 had the most significant effect, and the addition of silica aerogel in Example 1 had no negative impact on the mechanical properties of the material. In contrast, nanosilica, hydrophobic fumed nanosilica, and hydrophobic precipitated nanosilica had limited improvements in the glow-wire performance of the material and did have some impact on the mechanical properties.

[0029] A comparison of Examples 1, 5, and 6 shows that, under conditions of different reinforcing agent contents, while maintaining year-on-year increases or decreases in the polyamide material, halogen-free flame retardant, and silica aerogel, the flame retardant grade (1.6 mm) and GWIT (1 mm) can still maintain V0 and 700°C, and the improvement effect of silica aerogel is not affected by the reinforcing agent and polyamide resin contents.

[0030] The amount of silica aerogel added in Comparative Example 1 is too small, and the effect of improving the flame retardancy and glow-wire properties of the material is not obvious.

[0031] Comparative Examples 2 and 3 show that as the amount of silica aerogel added increases, the mechanical properties of the material show a significant deterioration trend. This is likely due to the small density and particle size of the nano-silica particles, which hinder uniform dispersion. This leads to severe stratification during mixing, resulting in unstable flame retardancy and other properties. A reasonable silica aerogel addition of 1.5% can increase the GWIT value to 700°C, resulting in a material with a high GWIT.

[0032] Comparative Example 4 does not add silica aerogel. Although an appropriate amount of phosphorus-containing flame retardant is added, the 1.6mm flame retardancy of the material can only reach V0, and the GWIT / 1mm value can only reach 600°C. It cannot be used in fields with high requirements for electrical performance.

[0033] The present application introduces silica aerogel, which has a high effect on improving the flame retardancy and glow-wire properties of the material without having a negative impact on the mechanical properties of the material.

[0034] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0035] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A high glow-wire halogen-free flame-retardant polyamide, characterized in that: The invention is prepared from the following components in percentage by mass: 40% to 60% polyamide resin, 20% to 40% reinforcing agent, 10% to 20% halogen-free flame retardant, 1% to 2% flame retardant synergist, and 2% to 3% auxiliary agent; the main component of the flame retardant synergist is silicon dioxide.

2. The high glow-wire halogen-free flame-retardant polyamide according to claim 1, characterized in that: The flame retardant synergist is one of nano-silica, hydrophobic gas-phase nano-silica, hydrophobic precipitated nano-silica, and silica aerogel.

3. The high glow-wire halogen-free flame-retardant polyamide according to claim 1, characterized in that: The reinforcing agent is at least one of glass fiber, talc, kaolin, wollastonite, calcium carbonate, and montmorillonite, and the glass fiber is chopped glass fiber with a single fiber diameter of 9-11 μm.

4. The high glow-wire halogen-free flame-retardant polyamide according to claim 1, characterized in that: The halogen-free flame retardant is at least one of aluminum diethylphosphinate and aluminum phosphite.

5. The high glow-wire halogen-free flame-retardant polyamide according to claim 1, characterized in that: The polyamide resin is polyamide 66, and the relative viscosity is 2.7 dL / g.

6. The high glow-wire halogen-free flame-retardant polyamide according to claim 1, characterized in that: The auxiliary agents include lubricants, antioxidants and masterbatches.

7. The high glow-wire halogen-free flame-retardant polyamide according to claim 6, characterized in that: The lubricant is at least one of modified ethylene bis fatty acid amide, pentaerythritol stearate and ethylene-acrylic acid copolymer wax powder; in the high glow-wire halogen-free flame-retardant polyamide, the mass percentage of the lubricant is 0.05% to 0.7%.

8. The high glow-wire halogen-free flame-retardant polyamide according to claim 6, characterized in that: The antioxidant is at least one of antioxidant 1098 and antioxidant 168; in the high glow-wire halogen-free flame-retardant polyamide, the mass percentage of the antioxidant is 0.05% to 0.2%; and / or, the masterbatch is a black masterbatch, and in the high glow-wire halogen-free flame-retardant polyamide, the mass percentage of the lubricant is 0.5% to 2%.

9. A method for preparing the high glow-wire halogen-free flame-retardant polyamide according to any one of claims 1 to 8, characterized in that: It includes the following steps: After premixing polyamide resin, halogen-free flame retardant, flame retardant synergist and additives in proportion, the premix is ​​fed into a twin-screw extruder from a main feed port, and a reinforcing agent is added in proportion from a side feed port. After melting, extrusion and granulation, a high glow-wire halogen-free flame retardant polyamide is obtained.

10. The method for preparing high glow-wire halogen-free flame-retardant polyamide according to claim 9, characterized in that: The stirring speed of the premix is ​​500 r / min and the time is 3-5 min; and / or, the temperature of each zone of the twin-screw extruder is: 240-255°C in zone 1, 245-255°C in zone 2, 265-280°C in zones 3 to 7, 240-260°C in zones 8 to 9, 230-250°C in zones 10 to 11, and 265-280°C in the die head; the main engine speed of the twin-screw extruder is 300-400 r / min.

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