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

Abstract

The present application relates to a kind of halogen-free flame-retardant nylon composite and preparation method, the halogen-free flame-retardant composite is made of the following weight fraction (%) raw materials: nylon resin 61.5~90%, halogen-free flame retardant 0.2~1.5%, nucleating agent 5~20%, heat stabilizer 5~15%, dispersing agent 0.1~2%.Preparation method is according to weight ratio raw materials, after mixing, is added into double screw machine and is extruded by melting, granulation.The present application is obtained by reasonable formula collocation, and the halogen-free flame-retardant nylon composite of stable can reach UL 94V0 level, and physical mechanical property and processing performance are excellent.Its preparation process is simple, low in cost, especially suitable for the application in electronic and electrical industry, with wide application prospect.

Description

Technical Field

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

[0002] Nylon, also known as polyamide, is one of the five major engineering plastics. It has excellent impact resistance, heat resistance, abrasion resistance, chemical resistance and electrical properties, and is a widely used thermoplastic engineering plastic.

[0003] Melamine cyanurate (MCA) is a high-performance nitrogen-based halogen-free flame retardant, especially suitable for unreinforced nylon materials. Its flame retardant mechanism is different from other flame retardants. MCA relies on rapidly increasing the fluidity of the flame-retardant nylon material during combustion. Through the dripping phenomenon during combustion, a large amount of combustion heat is carried away, thereby achieving the flame retardant effect.

[0004] However, this flame-retardant mechanism places extremely stringent requirements on the production formulation and processes of nylon materials. It is prone to problems such as flame retardant agglomeration or the introduction of other incompatible impurities, leading to a "wick effect." This not only delays the dripping of burning material but also causes the molten, flaming droplets to ignite the underlying absorbent cotton, resulting in failure to pass the UL94 V0 test. Experience shows that even 0.01% of agglomerates or infusible materials forming a "wick" can cause burning and dripping, igniting the absorbent cotton and only achieving the UL 94 V2 level.

[0005] However, even in unreinforced MCA flame-retardant nylon applications, necessary heat stabilizers, nucleating agents, and other additives still need to be added to meet the needs of most customers, especially for thin-walled, high-volume electronic and electrical products such as connectors, coil frames, and cable ties, where the requirements for material flowability and production cycle are extremely stringent. The addition of some conventional functional additives, however, significantly affects the flame-retardant effect of the material. Currently, many manufacturers produce MCA flame-retardant nylon with extremely unstable flame-retardant performance, often measuring only a V2 level. Therefore, how to improve the flame-retardant effect of MCA flame-retardant nylon to meet the application needs of various downstream manufacturers has always been a hot research topic in the industry.

[0006] Some material manufacturers can reduce the "wick effect" and improve flame retardancy by optimizing the dispersion process and enhancing the microscopic dispersion of flame retardants and other additives in the system. Patent CN101679743A provides a method to improve the dispersibility of MCA using surfactants, thereby achieving a V0 flame retardant rating for nylon. Patent CN115368730A improves the flame retardant effect of nylon by adjusting the pH value of MCA. However, these methods do not fundamentally solve the "wick effect" problem and suffer from significant production instability. During production, the material may initially test as flame retardant at V0, but the final test may show a V2 rating.

[0007] Patent CN201910323025.8 describes a method that uses a mixture of molten sebacic acid and hexamethylenediamine to coat a compound flame retardant with an average particle size (D50) of less than 3 μm, thereby improving the compatibility and bonding strength between the compound flame retardant and nylon 66 resin. Patent CN201910775378.1 describes a method that uses an amorphous α-olefin copolymer emulsion to better link nylon and MCA flame retardant, reducing the possibility of igniting flammable substances upon dripping. These methods address the "wick effect" by improving compatibility; however, they lack economic and operational advantages. Patent CN201510588777.9 describes a method that uses a compound of inorganic and organic nucleating agents to accelerate the crystallization of MCA flame-retardant nylon, improving the material's rigidity and appearance, but it does not effectively solve the problems of the "wick effect" and flame-retardant stability.

[0008] How to achieve a stable UL94 V0 level for MCA flame-retardant nylon using a simple and effective production method has become a pressing problem in the industry. Summary of the Invention

[0009] To address the shortcomings of existing technologies and solve the problem of flame retardant stability of halogen-free flame-retardant nylon, this paper proposes a halogen-free flame-retardant nylon composite material using a blending extrusion method.

[0010] The technical solution adopted by this invention to solve its technical problem is: to provide a halogen-free flame-retardant nylon composite material, which is made from the following raw materials in parts by weight:

[0011]

[0012]

[0013] In the halogen-free flame-retardant nylon composite material of the present invention, the nylon resin is nylon 66, nylon 6, or one or more of other aliphatic polyamides, preferably nylon 66.

[0014] In the halogen-free flame-retardant nylon composite material of the present invention, the halogen-free flame retardant is melamine cyanurate (MCA).

[0015] In the halogen-free flame-retardant nylon composite material of this invention, the nucleating agent is a sorbitol acetal-based nucleating agent. The nucleating agent can accelerate the crystallization rate of the nylon material, making it easier to mold and demold. Although sorbitol acetal-based nucleating agents are third-generation transparent polypropylene nucleating agents, experiments have shown that they not only possess a certain nucleating effect in MCA flame-retardant nylon but also do not affect the flame retardancy of the material at all. Unlike traditional nylon nucleating agents that require the formation of crystal nuclei, this type of nucleating agent is highly compatible with nylon. During processing, it melts and disperses together with the nylon, ultimately forming a nanoscale network state, thus avoiding the "wick effect."

[0016] In the halogen-free flame-retardant nylon composite material of the present invention, the heat stabilizer is N,N'-bis(2,2,6,6-tetramethyl-4-yl)-1,3-phenylenediamide. This type of heat stabilizer, also known as a multifunctional nylon additive, contains functional groups that not only provide antioxidant, heat-stabilizing, UV-resistant, and lubricating properties, but also reduce the amount of such functional additives required. Furthermore, this additive can achieve high compatibility with nylon through cross-linking amidation, reducing the possibility of igniting flammable absorbent cotton when MCA flame-retardant nylon drips.

[0017] In the halogen-free flame-retardant nylon composite material of this invention, the dispersant is distilled water. During the mixing process, distilled water allows powders such as MCA to adhere uniformly to the surface of the nylon resin, thus better dispersing the MCA. Simultaneously, during the high-temperature melting and processing of nylon, trace amounts of water promote appropriate hydrolysis of the nylon, improving the material's fluidity. Furthermore, by using vacuum extraction, it removes low-molecular-weight substances that easily generate a wick effect, making it easier for the nylon to melt and drip during flame-retardant testing, thus reducing the risk of dripping and igniting the absorbent cotton. Finally, excess water is removed by a vacuum pump and will not remain in the material, affecting its performance.

[0018] A method for preparing a halogen-free flame-retardant nylon composite material, comprising the following steps:

[0019] ② Weigh the raw materials according to the aforementioned weight ratio;

[0020] ② Add nylon resin and dispersant additives to a high-speed mixer and mix for 3-10 minutes. Then add halogen-free flame retardant, nucleating agent and heat stabilizer, and mix for 15-30 minutes.

[0021] ③ The mixture obtained in step ② is placed in a twin-screw extruder, melt-extruded, and granulated. The screw length-to-diameter ratio is 32-48, and the process conditions are: zone 1 temperature 200-240℃, zone 2 temperature 230-270℃, zone 3 temperature 200-240℃, zone 4 temperature 220-260℃, die head temperature 240-280℃, barrel residence time 0.5-2 minutes, and melt pressure 10-20MPa.

[0022] The halogen-free flame-retardant composite nylon material of this invention solves the "wick effect" problem of MCA flame-retardant nylon, and has the characteristic of consistently achieving flame retardancy V0, while also exhibiting excellent comprehensive physical properties and processing performance. Its raw materials are all commercially available, the preparation process is simple, and the cost is relatively low. It can meet various application needs of halogen-free flame-retardant nylon in the market, and is particularly suitable for applications in the electronics and electrical industries, showing promising development prospects. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments.

[0024] For ease of description, the nylon resin used in this invention is all nylon 66, produced by Zhejiang Huafeng Company, with the trade name EP-158; the flame retardant MCA is produced by Zhejiang Xusheng Company, with the trade name MC-25; the nucleating agent is produced by Milliken Company, USA, with the trade name 3988; the heat stabilizer is produced by Clariant AG, Germany, with the trade name S-EED; and the dispersant distilled water is self-made. The nucleating agent used in Comparative Example 2 is a long-chain calcium carboxylate salt, produced by Clariant AG, Germany, with the trade name CAV102. Antioxidant 1171 is a 1:1 mixture of antioxidants 1098 and 168, produced by BASF AG, Germany. The inorganic nucleating agent used in Comparative Example 5 is a mixture of montmorillonite, ultrafine talc powder, and calcium carbonate.

[0025] Example 1.

[0026] Premix 93.2% nylon 66 resin and 0.1% distilled water (by weight) in a mixing tank for 5 minutes. Then add 5% flame retardant MC-25, 0.8% nucleating agent 3988, and 0.9% heat stabilizer S-EED, and stir for 16 minutes. The mixed material is then melt-blended, extruded, and granulated in a twin-screw extruder. The twin-screw extruder has a screw diameter of 35mm, a screw length-to-diameter ratio of 3:2, and extrusion temperatures of 210℃ (zone 1), 240℃ (zone 2), 230℃ (zone 3), 250℃ (zone 4), and a die head temperature of 255℃. The residence time is 1-2 minutes, and the pressure is 15MPa.

[0027] Example 2.

[0028] 90.6% nylon 66 resin and 0.2% distilled water by weight were premixed in a mixing tank for 8 minutes. Then, 8% flame retardant MC-25, 0.5% nucleating agent 3988, and 0.7% heat stabilizer S-EED were added, and the mixture was stirred for 22 minutes. The premixed material was then melt-blended, extruded, and granulated in a twin-screw extruder. The twin-screw extruder had a screw diameter of 52 mm, a screw length-to-diameter ratio of 3:6, and extrusion temperatures of 215℃ (zone 1), 265℃ (zone 2), 250℃ (zone 3), 260℃ (zone 4), and a die head temperature of 270℃. The residence time was 1-2 minutes, and the pressure was 13 MPa.

[0029] Example 3.

[0030] Premix 89.1% nylon 66 resin and 0.2% distilled water in a mixing tank for 7 minutes. Then add 10% flame retardant MC-25, 0.3% nucleating agent 3988, and 0.4% heat stabilizer S-EED, and stir for 25 minutes. Afterward, melt-mix the premixed material in a twin-screw extruder, extrude, and granulate. The twin-screw extruder has a screw diameter of 65mm, a screw length-to-diameter ratio of 40, and extrusion temperatures of 220℃ in zone 1, 265℃ in zone 2, 250℃ in zone 3, 240℃ in zone 4, and a die head temperature of 265℃. The residence time is 1-2 minutes, and the pressure is 15MPa.

[0031] Example 4.

[0032] Premix 86.8% nylon 66 resin and 0.3% distilled water in a mixing tank for 5 minutes. Then add 12% flame retardant MC-25, 0.4% nucleating agent 3988, and 0.5% heat stabilizer S-EED, and stir for 27 minutes. Afterward, melt-mix the premixed material in a twin-screw extruder, extrude, and granulate. The twin-screw extruder has a screw diameter of 60 mm, a screw length-to-diameter ratio of 4:4, and extrusion temperatures of 225℃ (zone 1), 255℃ (zone 2), 240℃ (zone 3), 235℃ (zone 4), and a die head temperature of 260℃. The residence time is 1-2 minutes, and the pressure is 19 MPa.

[0033] Example 5.

[0034] Premix 84.3% nylon 66 resin and 0.4% distilled water in a mixing tank for 9 minutes. Then add 15% flame retardant MC-25, 0.6% nucleating agent 3988, and 0.6% heat stabilizer S-EED, and stir for 21 minutes. The mixed material is then melt-blended, extruded, and granulated in a twin-screw extruder. The twin-screw extruder has a screw diameter of 60 mm, a screw length-to-diameter ratio of 40, and extrusion temperatures of 220℃ (zone 1), 250℃ (zone 2), 235℃ (zone 3), 230℃ (zone 4), and a die head temperature of 255℃. The residence time is 1-2 minutes, and the pressure is 14 MPa.

[0035] Example 6.

[0036] Premix 81.1% nylon 66 resin and 0.5% distilled water in a mixing tank for 7 minutes. Then add 18% flame retardant MC-25, 0.2% nucleating agent 3988, and 0.2% heat stabilizer S-EED, and stir for 19 minutes. The mixed material is then melt-blended, extruded, and granulated in a twin-screw extruder. The twin-screw extruder has a screw diameter of 75mm, a screw length-to-diameter ratio of 3:6, and extrusion temperatures of 215℃ (zone 1), 245℃ (zone 2), 230℃ (zone 3), 230℃ (zone 4), and a die head temperature of 250℃. The residence time is 1-2 minutes, and the pressure is 15MPa.

[0037] Comparative Example 1.

[0038] Mix 90% nylon 66 resin and 10% flame retardant MC-25 by weight for 25 minutes. Then, melt-mix the mixture in a twin-screw extruder, extrude, and granulate. The twin-screw extruder has a screw diameter of 65mm, a screw length-to-diameter ratio of 40, and extrusion temperatures of 220℃ in zone 1, 260℃ in zone 2, 250℃ in zone 3, 240℃ in zone 4, and a die head temperature of 260℃. The residence time is 1-2 minutes, and the pressure is 16MPa.

[0039] Comparative Example 2.

[0040] Mix 89.3% nylon 66 resin, 10% flame retardant MC-25, 0.3% nucleating agent CAV102, and 0.4% antioxidant 1171 by weight, and stir for 25 minutes. Then, melt-blend the mixture in a twin-screw extruder, extrude, and granulate. The twin-screw extruder has a screw diameter of 65 mm, a screw length-to-diameter ratio of 40, and extrusion temperatures of 220℃ (zone 1), 265℃ (zone 2), 250℃ (zone 3), 240℃ (zone 4), and a die head temperature of 265℃. The residence time is 1-2 minutes, and the pressure is 15 MPa.

[0041] Comparative Example 3.

[0042] Mix 89.3% nylon 66 resin, 10% flame retardant MC-25, 0.3% nucleating agent 3988, and 0.4% heat stabilizer S-EED by weight, and stir for 25 minutes. Then, melt-blend, extrude, and granulate the mixture in a twin-screw extruder. The twin-screw extruder has a screw diameter of 65mm, a screw length-to-diameter ratio of 40, and extrusion temperatures of 225℃ (zone 1), 260℃ (zone 2), 250℃ (zone 3), 240℃ (zone 4), and a die head temperature of 260℃. The residence time is 1-2 minutes, and the pressure is 16MPa.

[0043] Comparative Example 4.

[0044] Premix 89.3% nylon 66 resin and 0.2% distilled water in a mixing tank for 5 minutes, then add 10% flame retardant MC-25 and 0.3% nucleating agent 3988 and stir for 25 minutes. Afterward, the mixed material is melt-blended, extruded, and granulated in a twin-screw extruder. The twin-screw extruder has a screw diameter of 65mm, a screw length-to-diameter ratio of 40, and extrusion temperatures of 220℃ (zone 1), 265℃ (zone 2), 250℃ (zone 3), 240℃ (zone 4), and a die head temperature of 265℃. The residence time is 1-2 minutes, and the pressure is 15MPa.

[0045] Comparative Example 5.

[0046] Premix 89.3% nylon 66 resin and 0.2% distilled water in a mixing tank for 5 minutes, then add 10% flame retardant MC-25 and 0.4% inorganic nucleating agent and stir for 25 minutes. Afterward, the mixed material is melt-blended, extruded, and granulated in a twin-screw extruder. The twin-screw extruder has a screw diameter of 65mm, a screw length-to-diameter ratio of 40, and extrusion temperatures of 220℃ in zone 1, 265℃ in zone 2, 250℃ in zone 3, 240℃ in zone 4, and a die head temperature of 265℃. The residence time is 1-2 minutes, and the pressure is 17MPa.

[0047] The halogen-free flame-retardant nylon composite materials prepared in the first six examples and five comparative examples were tested, and their performance evaluation methods and implementation standards were as follows:

[0048] The granulated material was dried in an 80℃ forced-air oven for 3-6 hours. The dried material was then injection molded on an injection molding machine, with the mold temperature controlled at 80℃. Tensile strength testing was performed according to ASTM D638, with a specimen size of 180×12.7×3.2mm and a tensile speed of 50mm / min. Flexural performance testing was performed according to ASTM D790, with a specimen size of 128×13×3.2mm, a bending speed of 3mm / min, and a span of 64mm. Cantilever beam impact strength testing was performed according to ASTM D256, with a specimen size of 63.5×12.7×4.2mm and a notch size one-fifth of the specimen thickness. Melt flow index testing was performed according to ASTM D1238, with test conditions of 275℃ and a 5kg weight.

[0049] Molding cycle refers to the total time required for an injection molding machine to complete one mold of a product. The shorter the molding cycle, the higher the efficiency, which is mainly related to the material's flowability and demolding properties. In this study, the baked finished product will be directly injection molded into 32 10×5mm connector molds, and the molding cycle length will be used to judge the material's processing performance.

[0050] Flame retardancy testing was conducted according to the UL94 method, with sample dimensions of 128×13×1.6mm. To verify the stability of the material's flame retardancy performance, four sets of tests were performed for each example and comparative example, with five samples per set, for a total of 20 tests. The sum of the burning times of each of the 20 tests and the probability of dripping burning cotton in each of the 20 tests were statistically analyzed as a reference for flame retardancy stability.

[0051] The comprehensive mechanical properties of the examples and comparative examples were evaluated by testing tensile strength, flexural strength, impact strength, melt flow index, and flame retardancy. The results are shown in Tables 1 and 2.

[0052] Table 1 Examples

[0053]

[0054]

[0055] Table 2 Comparative Examples

[0056]

[0057] As seen in the examples, the halogen-free flame-retardant nylon materials of the present invention consistently achieve UL94 V0. However, when the MCA content exceeds 15%, the total combustion time increases, and the flame-retardant effect decreases. This may be because too much MCA powder makes it difficult for the flame retardant to disperse, causing agglomeration, which lowers the material's melt flow index and delays the melt dripping time. Examples 2, 3, and 4 show the shortest total combustion time and the most stable flame-retardant effect.

[0058] Example 3, compared with Comparative Example 1 which did not contain any additives, showed better melt flow index, injection molding cycle, and flame retardant effect than Comparative Example 1. This indicates that the additives added in this invention not only improve the processing performance of the material but also have a good synergistic flame retardant effect with the flame retardant MCA. This point was fully confirmed in Comparative Examples 3 and 4.

[0059] Comparative Example 2 uses commercially available antioxidants and nucleating agents. From the flame retardant results, it exhibits a significant "wick effect," resulting in a long burning time and 70% of the sample tests dripping burning cotton, making it difficult to consistently achieve the V0 rating.

[0060] In Comparative Example 5, the added inorganic nucleating agent affects the polymer's microstructure, creating a wick effect and intensifying combustion. It also increases the viscosity of the plastic, reducing the heat carried away by the plastic's flow and molten droplets. Its extremely poor compatibility with the plastic leads to uneven plasticization throughout the formulation, reducing the flame-retardant effect. Plastics containing silica powder form stable silicon bromide on their surface during combustion, interfering with the plastic's gas-phase flame retardancy. Plastics containing calcium carbonate have an antagonistic effect on flame retardancy, requiring a higher dosage of flame retardant. Therefore, in the selection of nucleating agents, inorganic nucleating agents have a negative impact on the formulation.

[0061] In summary, the halogen-free flame-retardant nylon composite material prepared in the embodiments of this invention perfectly solves the "wick effect" problem of MCA flame-retardant nylon, and has the characteristic of stably achieving flame retardancy V0, enabling long-term stable mass production. Its raw materials are all commercially available, the preparation process is simple, and the cost is relatively low, meeting various application needs of halogen-free flame-retardant nylon in the market. It is particularly suitable for applications in the electronics and electrical industries and has excellent development prospects.

[0062] The above provides a detailed description of a halogen-free flame-retardant nylon composite material provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A halogen-free flame-retardant nylon composite material, characterized in that, Made from the following parts by weight of raw materials: Nylon resin 77.5~95% Halogen-free flame retardant 5-12% Nucleating agent 0.1~1% Heat stabilizer 0.1~1% Dispersant 0.1~0.5%; The halogen-free flame retardant is melamine cyanurate (MCA). The nucleating agent is a sorbitol acetal nucleating agent with a commercial brand number of 3988. The heat stabilizer is S-EED; The dispersant is distilled water; The preparation method of the halogen-free flame-retardant nylon composite material includes the following steps: ① Weigh the raw materials according to the aforementioned weight ratio; ② Add nylon resin and dispersant to a high-speed mixer and mix for 3-10 minutes. Then add halogen-free flame retardant, nucleating agent and heat stabilizer, and mix for 15-30 minutes. ③ The mixture obtained in step ② is placed in a twin-screw extruder, melt-extruded, and granulated. The screw length-to-diameter ratio is 32~48, and the process conditions are: zone 1 temperature 200~240℃, zone 2 temperature 230~270℃, zone 3 temperature 200~240℃, zone 4 temperature 220~260℃, die head temperature 240~280℃, barrel residence time 0.5~2 minutes, and melt pressure 10~20 MPa.

2. The halogen-free flame-retardant nylon composite material according to claim 1, characterized in that, The nylon resin is one or a mixture of several of nylon 66, nylon 6, or other aliphatic polyamides.

3. A method for preparing the halogen-free flame-retardant nylon composite material according to claim 1 or 2, characterized in that, Includes the following steps: ① Weigh the raw materials according to the aforementioned weight ratio; ② Add nylon resin and dispersant to a high-speed mixer and mix for 3-10 minutes. Then add halogen-free flame retardant, nucleating agent and heat stabilizer, and mix for 15-30 minutes. ③ The mixture obtained in step ② is placed in a twin-screw extruder, melt-extruded, and granulated. The screw length-to-diameter ratio is 32~48, and the process conditions are: zone 1 temperature 200~240℃, zone 2 temperature 230~270℃, zone 3 temperature 200~240℃, zone 4 temperature 220~260℃, die head temperature 240~280℃, barrel residence time 0.5~2 minutes, and melt pressure 10~20 MPa.

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