A flame-retardant PA66 composite material for monofilament forming, its preparation method and application

Abstract

The present invention discloses a flame-retardant PA66 composite material for monofilament forming, its preparation method and application. The flame-retardant PA66 composite material is prepared from the following components by weight: 60-80 parts of PA66 resin, 8-15 parts of composite flame retardant, 10-20 parts of toughening agent, 0.1-0.3 parts of antioxidant, 0.1-0.5 parts of lubricant, and 1-4 parts of compatibilizer; wherein, the composite flame retardant is composed of aluminum methylcyclohexylphosphinate, N,N'-ethylene bis(tetrabromophthalimide) and montmorillonite in a mass ratio of (4-7):(3-5):(1-3). The composite flame retardant adopted in the present invention shows a mechanism of synergistic flame retardancy in the gas phase and the condensed phase, and by adding additives such as compatibilizer, lubricant, toughening agent, antioxidant and other additives, the monofilament prepared by the present invention has good formability, and at the same time has good high-temperature resistance, mechanical properties and excellent flame retardant properties, and can be better applied in braided network tube products.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer flame retardant materials, and particularly relates to a flame retardant PA66 composite material for monofilament forming, a preparation method thereof, and an application thereof. Background Art

[0002] Nylon (abbreviation: PA) is a general term for thermoplastic resins containing repeating amide groups in the main molecular chain, and is one of the five major general engineering plastics in the world. PA66 in nylon resins is often referred to as nylon 66, which has excellent mechanical properties, heat resistance, electrical insulation, chemical corrosion resistance, and excellent processing properties. However, since the PA66 resin can only reach the V-2 flame retardant grade, and the molten droplets during combustion are prone to cause secondary ignition and trigger a larger fire, its application fields are greatly limited. Especially in the industrial / automotive electronic and electrical fields, these products are all directly or indirectly in contact with the power-using environment, and electric leakage, short circuit, electric arc, etc. in the circuit are all likely to cause a fire. Therefore, in practical applications, many PA66 products are required to be flame retardant modified to meet the V-0 fire protection grade requirements specified by UL.

[0003] Currently, the main method for preparing flame retardant nylon materials is to directly blend and disperse additive flame retardants such as halogen flame retardants, nitrogen-based flame retardants, phosphorus-based flame retardants, and phosphorus-nitrogen flame retardants into the nylon matrix. Halogen-based flame retardants are inexpensive, have good stability, low addition amounts, and good compatibility with synthetic resin materials. However, the exhaust gas generated during their combustion will pollute the environment and even pose a threat to human health. When nitrogen-based flame retardants are used alone, the flame retardant test results of the materials cannot reach the V0 level in the UL standard, or cannot reach a stable V0 flame retardant grade, with particularly large fluctuations. In phosphorus-based flame retardants, the synthesis process route of organic hypophosphites is complex and the cost is high, while low-cost hypophosphates have disadvantages such as insufficient flame retardant efficiency, poor compatibility with PA66, and poor processing stability. MCA (melamine cyanurate) of phosphorus-nitrogen flame retardants has very good effects on nylon and polyester without adding glass fiber, but for nylon and polyester after adding glass fiber, the flame retardant effect is lost; MPP (melamine polyphosphate) of nitrogen-phosphorus systems has insufficient thermal stability, is prone to foaming during the processing, and the phenomenon of flame retardant decomposition; the organic hypophosphites of nitrogen-phosphorus systems have excellent properties, but their extremely high price limits their wide application. And the above materials can only be applied to thick products such as injection molded products, and are prone to filament breakage during the preparation of monofilaments and fibers. The main reason is that the compatibility between the flame retardant and PA66 is poor, and it is easy to cause the degradation and foaming of PA66 when contacting with PA66. Some have decomposition products adhering to the mold, thus affecting the final monofilament extrusion molding and stretching molding, and are prone to filament breakage or unable to be processed into monofilaments with qualified appearance and mechanical properties.

[0004] Therefore, how to provide a flame-retardant PA66 composite material for monofilament forming with excellent flame-retardant effect, low cost and good mechanical properties is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0005] The present invention aims at the deficiencies of the existing technology and provides a flame-retardant PA66 composite material for monofilament forming, its preparation method and application. The flame-retardant PA66 composite material prepared by the method of the present invention has excellent properties, and solves the problems of poor flame-retardant effect, high cost and inability to prepare monofilaments of the existing flame-retardant PA66 materials.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A flame-retardant PA66 composite material for monofilament forming is prepared from the following components by weight: 60-80 parts of PA66 resin, 8-15 parts of composite flame retardant, 10-20 parts of toughening agent, 0.1-0.3 part of antioxidant, 0.1-0.5 part of lubricant, 1-4 parts of compatibilizer;

[0008] Wherein, the composite flame retardant is composed of aluminum methylcyclohexylphosphinate (AMHP), N,N'-ethylene bis(tetrabromophthalimide) (EPT) and montmorillonite in a mass ratio of (4-7):(3-5):(1-3).

[0009] Preferably, the average particle size of the aluminum methylcyclohexylphosphinate is 3-6 μm, the average particle size of the N,N'-ethylene bis(tetrabromophthalimide) is 3-6 μm, and the average particle size of the montmorillonite is 1-6 μm.

[0010] Preferably, the mass ratio of aluminum methylcyclohexylphosphinate, N,N'-ethylene bis(tetrabromophthalimide) and montmorillonite in the composite flame retardant is 3:2:1.

[0011] Preferably, the toughening agent is one or more of HDPE, maleic anhydride grafted POE, maleic anhydride grafted PE.

[0012] Preferably, the antioxidant is a compound mixture of one or several of AT-1010, AT-168, AT-10, AT-626, AT-3114.

[0013] Preferably, the lubricant is one or a mixture of two or more of fatty acid, zinc stearate, calcium stearate, aluminum stearate, fatty acid amines or ethylene-acrylic acid copolymer.

[0014] Preferably, the compatibilizer is polyethylene or polypropylene grafted with maleic anhydride.

[0015] The present invention also discloses a method for preparing flame-retardant PA66 monofilaments, which comprises the following steps:

[0016] S1: Weigh each raw material according to the above-mentioned parts by weight;

[0017] S2: Dry the PA66 resin, compound flame retardant, toughening agent, antioxidant, lubricant and compatibilizer, and then put them into a high-speed mixer for stirring to obtain a mixture;

[0018] S3: Put the obtained mixture into a twin-screw extruder, spin it under a molten state, cool it, stretch it, and shape it to obtain flame-retardant PA66 monofilaments.

[0019] Further, the parameters of the seven-zone temperature of the screw extruder are respectively set to 260°C - 270°C, 270°C - 280°C, 275°C - 285°C, 280°C - 285°C, 280°C - 285°C, 275°C - 285°C, and 280°C - 290°C, and the rotation speed is 70 - 85 rpm;

[0020] The conditions for stretching: temperature 180 - 195°C, rotation speed 40 - 60 rpm, and draw ratio 4 - 6;

[0021] The conditions for shaping: temperature 240 - 250°C, rotation speed 40 - 60 rpm;

[0022] The conditions for cooling: temperature 60 - 75°C, rotation speed 20 - 25 rpm.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. The composite flame retardant adopted in the present invention shows a mechanism of synergistic flame retardancy in the gas phase and condensed phase. In the gas phase, AMHP and EPT are cracked to obtain phosphinic acid free radicals, Br·, and small-molecule substances of the remaining benzene ring of EPT. The phosphinic acid free radicals and Br· capture combustible small-molecule free radicals and reduce combustion. The flame-retardant small-molecule substances of the remaining benzene ring of EPT can react with -NH 2Combined with free radicals such as these, it plays a role in quenching free radicals and diluting flammable gases. Before the degradation of PA66 in the condensed phase, it does not undergo a cross-linking and curing reaction with the compound flame retardant. Instead, metal ions combine with the cracked carbon chains through M-O bonding to form a cross-linked carbon layer, and montmorillonite plays an enhancing and promoting role in the formation of the cross-linked carbon layer, increasing the char residue amount. EPT / montmorillonite will lower the decomposition temperature of PA66, but AMHP increases the decomposition temperature of PA66, so that the final decomposition temperature of PA66 will not decrease and cause foaming. AMHP has relatively little influence on the crystallization and melting behavior of PA66. Due to the hydrogen bond interaction between the imide bond of EPT and the amide bond of PA66, the γ crystal form of PA66 gradually decreases and even disappears, and Tc and the crystallinity are improved, enhancing the tensile strength and thermal properties of the material. The addition of the flame retardant of the present invention also significantly reduces the moisture absorption rate and water absorption rate of flame-retardant PA66.

[0025] 2. The average particle size of the compound flame retardant used in the present invention is small. When the addition amount of the compound flame retardant is small, the LOI increases with the decrease of the particle size, and the flame retardant performance is improved. Moreover, the size of the particle size also affects the thermal decomposition stability of the material. The smaller the particle size, the larger the specific surface area, the stronger the covering effect on the matrix material, and more protective layers can be formed during the decomposition process to prevent the further decomposition and foaming of the material, affecting the monofilament forming. A small particle size can also improve the compatibility between the flame retardant and the matrix material and the dispersibility of the flame retardant in the matrix material.

[0026] 3. The present invention also further enables the monofilament prepared by the present invention to have good formability, no foaming, good high-temperature resistance, mechanical properties and excellent flame retardant properties through the combined action of adding additives such as compatibilizers, lubricants, toughening agents, antioxidants, etc., and can be better applied in products such as braided network tubes, such as automotive circuits, aircraft circuits, ship circuits, wire and cable circuits, and household circuits. Specific Embodiments

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Examples 1-3 and Comparative Examples 1-3

[0029] Formulations of Examples 1-3 and Comparative Examples 1-3

[0030]

[0031] Sources of antioxidants used in Examples 1-3 and Comparative Examples 1-6: AT-1010, industrial pure, Shanghai Darui Fine Chemical Co., Ltd.; AT-168, industrial pure, Ciba-Geigy Corporation.

[0032] The AMHP, EPT, and montmorillonite used in Examples 1-3 and Comparative Examples 1-6 were the same, and their average particle sizes were 4.4 μm, 5.1 μm, and 4.7 μm, respectively.

[0033] Comparative Example 7

[0034] The average particle sizes of AMHP, EPT, and montmorillonite were changed to 10.2 μm, 9.3 μm, and 8.6 μm, respectively, and the rest was the same as in Example 1.

[0035] Example 4

[0036] A method for preparing flame-retardant PA66 monofilaments includes the following steps:

[0037] S1: Weigh each raw material according to the parts by weight listed in Examples 1-3 and Comparative Examples 1-7.

[0038] S2: After drying the PA66 resin, compound flame retardant, toughening agent, antioxidant, lubricant, and compatibilizer, put them into a high-speed mixer for stirring to obtain a mixed material.

[0039] S3: Put the obtained mixed material into a twin-screw extruder, draw filaments in a molten state, cool, stretch, and shape to obtain flame-retardant PA66 monofilaments.

[0040] The parameters of the seven zones of the screw extruder are set to 265 °C, 275 °C, 280 °C, 283 °C, 283 °C, 280 °C, and 285 °C, and the rotation speed is 75 rpm.

[0041] Stretching conditions: temperature 185 °C, rotation speed 50 rpm, draw ratio 5, monofilament diameter 0.25 mm.

[0042] Shaping conditions: temperature 245 °C, rotation speed 50 rpm.

[0043] Cooling conditions: temperature 65 °C, rotation speed 20 rpm.

[0044] Test Example

[0045] The mechanical properties of the flame-retardant PA66 monofilaments (0.25 mm) prepared by the method of Example 4 for Examples 1-3 and Comparative Examples 1-4 were tested, and the flame retardancy was detected by braiding a network tube. The results are shown in Table 1.

[0046] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-4

[0047]

[0048]

[0049] As can be seen from the data in Table 1, the monofilaments prepared in Examples 1-3 of the present invention have good formability, do not foam, have a smooth surface, excellent mechanical properties, and also have excellent flame retardant properties. When drawing in Comparative Examples 1-2 with the change of the composite flame retardant components, foaming occurs, the die head adheres, the molten material, and carbonizes for a long time and cannot form monofilaments. The properties of the products prepared with different ratios of the composite flame retardant in Comparative Examples 3-4 decline and cannot meet the requirements of strength and flame retardancy. In Comparative Examples 5-6, without adding a compatibilizer or lubricant, the surface of the monofilaments is rough, the smoothness is poor, and the mechanical properties decline slightly. In Comparative Example 7, after changing the average particle size of the flame retardant components, the coverage of the matrix material is incomplete, and the uncoated part degrades and foams, resulting in uneven thickness of the monofilaments. After increasing the particle size, the compatibility and dispersibility of the flame retardant and the matrix material become poor, thereby leading to a decrease in mechanical properties and flame retardancy.

[0050] The flame retardant PA66 monofilaments prepared by the present invention have excellent flame retardant properties, and the addition amount of the flame retardant is small, effectively avoiding the problems of performance decline and cost increase caused by the flame retardant modification of nylon materials. In addition, the flame retardant PA66 monofilaments prepared by the present invention can be used in fields such as wire and cable, automobile manufacturing, and 3D printing.

[0051] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0052] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flame-retardant PA66 composite material for monofilament forming, characterized in that, it is prepared from the following components by weight: 60-80 parts of PA66 resin, 8-15 parts of composite flame retardant, 10-20 parts of toughening agent, 0.1-0.3 parts of antioxidant, 0.1-0.5 parts of lubricant, and 1-4 parts of compatibilizer; wherein, the composite flame retardant is composed of aluminum methylcyclohexylphosphinate, N,N'-ethylenebis(tetrabromophthalimide) and montmorillonite in a mass ratio of (4-7):(3-5):(1-3); the average particle size of the aluminum methylcyclohexylphosphinate is 3-6 μm, the average particle size of the N,N'-ethylenebis(tetrabromophthalimide) is 3-6 μm, and the average particle size of the montmorillonite is 1-6 μm; the toughening agent is one of HDPE, maleic anhydride grafted POE, and maleic anhydride grafted PE; the antioxidant is AT-1010 or AT-168; the lubricant is aluminum stearate or zinc stearate; the compatibilizer is polyethylene or polypropylene grafted maleic anhydride.

2. A flame-retardant PA66 composite material for monofilament forming according to claim 1, characterized in that, the mass ratio of aluminum methylcyclohexylphosphinate, N,N'-ethylenebis(tetrabromophthalimide) and montmorillonite in the composite flame retardant is 3:2:

1.

3. A preparation method of flame-retardant PA66 monofilament, characterized in that, it includes the following steps: S1: Weigh each raw material according to the weight parts described in claim 1; S2: Dry the PA66 resin, compound flame retardant, toughening agent, antioxidant, lubricant and compatibilizer and then put them into a high-speed mixer for stirring to obtain a mixed material; S3: Put the obtained mixed material into a twin-screw extruder, spin it under molten state, cool, stretch and shape to obtain the flame-retardant PA66 monofilament.

4. A preparation method of flame-retardant PA66 monofilament according to claim 3, characterized in that, the parameters of the seven-section temperature of the screw extruder are respectively set to 260°C - 270°C, 270°C - 280°C, 275°C - 285°C, 280°C - 285°C, 280°C - 285°C, 275°C - 285°C and 280°C - 290°C, and the rotation speed is 70-85 rpm; the conditions for stretching: temperature 180 - 195°C, rotation speed 40 - 60 rpm, and the stretching ratio is 4-6; the conditions for shaping: temperature 240 - 250°C, rotation speed 40 - 60 rpm; the conditions for cooling: temperature 60 - 75°C, rotation speed 20 - 25 rpm.

5. Application of the flame-retardant PA66 monofilament obtained by the preparation method of flame-retardant PA66 monofilament according to claim 4 in braided network tube products.

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