High-voltage-resistant red phosphorus flame-retardant polyamide composition and preparation method thereof

Abstract

The invention discloses a high-voltage-resistant red phosphorus flame-retardant polyamide composition and a preparation method thereof, and belongs to the technical field of flame-retardant materials. The composition comprises the following components in percentage by mass: 30-80 wt% of aliphatic polyamide, 2-10 wt% of red phosphorus, 0.5-10 wt% of aromatic zinc carboxylate, 0.5-5 wt% of hydroxyapatite, 5.0-20 wt% of a toughening agent, 10-50 wt% of a reinforcing agent and 0-5 wt% of other auxiliaries, the sum of the contents of all the components is 100 wt%, and the raw material components are subjected to melt blending processing through a single-screw or double-screw extruder. The invention provides the high-voltage-resistant red phosphorus flame-retardant polyamide composition, the natural color and black CTI (comparative tracking index) of the composition is greater than 500V, the IPT (inclined plane tracking) of the composition is greater than 1.5 kV, the composition has high-level flame retardance and cost effect, and meanwhile, the problem of hydrogen phosphide precipitation of a material is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flame-retardant materials, and particularly relates to a high-voltage-resistant red phosphorus flame-retardant polyamide composition and a preparation method thereof. BACKGROUND

[0002] As one of the most ideal materials for lightweight and efficient structural design, polyamide composite materials have the advantages of high specific strength, corrosion resistance, fatigue resistance, good dimensional stability, and strong designability, and have been widely used in the fields of new energy electric vehicles (EV) and photovoltaic (PV) connectors. According to the power formula P=U×I, when the voltage (U) is increased, the current (I) will be inversely reduced, and the line loss (Ploss) is proportional to the square of the current (I) - Ploss=I²R. The reduction of current will cause the loss to decrease in a square level. Therefore, in order to improve the efficiency of energy conversion and transmission, both new energy vehicles and photovoltaic fields are accelerating the technology platform towards higher voltage and larger electrical load. For example, new energy vehicle battery technology has popularized 400V voltage and is evolving towards 800V voltage, and future electric vehicles are expected to achieve shorter charging time, longer endurance and more effective energy management. The 1500V system of photovoltaic power grid continues to popularize, and the 2000V system is pilot promoted in large power stations, which significantly improves the power density of inverters and reduces the system balancing cost and loss.

[0003] Under high voltage working conditions, the short circuit risk of components using high molecular materials will be higher than that under low voltage working conditions. Tracking is the main cause of insulation failure of high molecular materials under humid conditions. When the high molecular material components are attached with water, dust and other substances on the surface during use, if repeated micro-discharge occurs, a conductive path may be generated on the surface, resulting in dielectric breakdown phenomenon (tracking), and sometimes short circuit between electrodes. In addition, carbonization of high molecular materials under high temperature arc is also an important factor leading to product tracking, and further inducing creeping, breakdown and fire.

[0004] In the industry, the relative tracking index (CTI) and inclined plane tracking (IPT) are mainly used to evaluate the resistance of thermoplastics to tracking under the combined effect of electric field and electrolyte. CTI is a test method to evaluate the accelerated tracking of insulating materials under humid and contaminated conditions. It applies a voltage between two electrodes placed on the material surface and applies 50 or 100 drops of contaminating liquid (0.1% ammonium chloride aqueous solution), thereby accelerating the aging process to form carbide conductive channels (tracks) to assess the material's ability to resist the chain reaction of "leakage → arcing → carbonization → conductivity". The CTI value is defined as the highest voltage value at which no tracking (conductive channel) is formed and no burning / breakdown occurs. IPT is a test method for evaluating the corrosion resistance and tracking resistance of insulating materials under high voltage (>1kV) discharge effects in humid and contaminated conditions. It applies a high power frequency voltage to the surface of an inclined sample and continuously applies a contaminating liquid (0.1% ammonium chloride aqueous solution), and measures the time required for the tracking to extend from the starting point to a specified distance (e.g., 25mm), thus evaluating the tracking development rate and durability of the material under a specific voltage.

[0005] Red phosphorus is a highly efficient flame retardant for polyamides. Compared to brominated and organophosphorus flame retardants, red phosphorus is less expensive, has excellent electrical properties, and has minimal impact on the mechanical properties of polymers, especially impact characteristics. Based on these advantages, red phosphorus flame-retardant polyamides are widely used in new energy vehicles and photovoltaic fields. However, the disadvantages of red phosphorus are also obvious. Red phosphorus has poor processing stability and is prone to degradation and release of phosphorus compounds (such as phosphine) when exposed to moisture or over-processed. Phosphine compounds are acidic substances that corrode and carbonize the material surface, deteriorating the material's resistance to electrical tracking. More importantly, due to the synergistic effect of coordination and chemisorption, core metal materials in power transmission fields such as copper, silver, and nickel have a strong adsorption capacity for phosphorus compounds like phosphine. The continuously released phosphine forms a phosphide film on the metal surface, causing a sharp increase in resistance, significantly hindering electron transmission, and endangering power transmission safety. Finally, pure red phosphorus is dark red, and black products require the addition of a sufficient amount of carbon black to cover the natural color of red phosphorus, further weakening the electrical tracking resistance of black red phosphorus flame-retardant polyamide composites.

[0006] While the CTI value of unbleached red phosphorus flame-retardant polyamide composites can typically reach 500V to 600V, their use in high-temperature and humid environments is limited due to the tendency for phosphorus to leach out. Black red phosphorus flame-retardant polyamide composites, on the other hand, usually have a CTI value below 400V. Traditional red phosphorus flame-retardant polyamides are no longer sufficient to meet the high-voltage application demands of new energy vehicles and photovoltaic products. Therefore, improving the voltage withstand performance of red phosphorus flame-retardant polyamide compositions to ensure that the prepared products maintain stable insulation even under long-term high-temperature and humid conditions is crucial for safety in high-voltage applications.

[0007] In existing technologies, red phosphorus can be stabilized and phosphine precipitation can be improved by adding metals and their compounds. For example, patent document CN104125979B uses a copper oxide / zinc oxide mixture as a stabilizer for red phosphorus flame-retardant polyamide to prevent red phosphorus degradation; CN102093711A uses specific copper and zinc compounds as inhibitors to reduce phosphorus compound precipitation, but such metal compounds are prone to ionization and degrade the electrical properties of the polymer. CN115989272A proposes using long-chain aliphatic polyamide to improve the tracking performance on inclined surfaces at voltages above 1kV; CN112608595B uses long-chain carbon polyamide to improve the voltage resistance of red phosphorus flame-retardant polyamide compositions in humid environments and uses chromium complexes as a black dye for manufacturing black products, but none of these solutions provide a high-voltage improvement scheme for carbon black-based black red phosphorus flame-retardant polyamide products.

[0008] In summary, known molding compositions fail to provide a high-voltage-resistant red phosphorus flame-retardant polyamide composition that is stable in temperature and humidity environments. Summary of the Invention

[0009] In view of the above-mentioned shortcomings of the prior art, the main objective of the present invention is to provide a high voltage resistant red phosphorus flame retardant polyamide composition, specifically a red phosphorus flame retardant polyamide composition with a relative tracking index (CTI) greater than 500V for natural and black colors, an IPT greater than 1.5kV for inclined surfaces, and improved flame retardant properties and phosphine evolution.

[0010] Another object of the present invention is to provide a method for preparing the high voltage-resistant red phosphorus flame-retardant polyamide composition, which is simple in process and easy to industrialize.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A first aspect of the present invention provides a high-voltage resistant red phosphorus flame-retardant polyamide composition, comprising the following components in weight percentage:

[0013] (A) Aliphatic polyamide 30~80wt%;

[0014] (B) Red phosphorus 2~10wt%;

[0015] (C) Aromatic carboxylic acid zinc 0.5~10wt%;

[0016] (D) Hydroxyapatite 0.5~5wt%;

[0017] (E) Toughening agent 5.0~20wt%;

[0018] (F) Reinforcing agent 10~50wt%;

[0019] (G) Other additives 0~5wt%;

[0020] The sum of the mass percentages of components (A) to (G) is 100 wt%.

[0021] Component (A) is an aliphatic polyamide, which is a semi-crystalline polymer with a melting temperature of 150°C to 300°C. The melting temperature was characterized by differential scanning calorimetry (DSC) with a heating and cooling rate of 10°C / min.

[0022] In some embodiments, the aliphatic polyamide is selected from one or more of the following: PA-XY (X = number of carbon atoms in the diamine, Y = number of carbon atoms in the dicarboxylic acid) obtained by polycondensation of aliphatic dicarboxylic acid and aliphatic diamine having not less than four carbon atoms, and PA-Z (Z = number of carbon atoms in the lactam, i.e., number of carbon atoms in the repeating unit) obtained by ring-opening polymerization of lactam.

[0023] In some embodiments, the aliphatic dicarboxylic acid is selected from the group consisting of: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, octadecanoic acid, and eicosanoic acid.

[0024] In some embodiments, the aliphatic diamine having at least four carbon atoms is selected from the group consisting of: butanediamine, pentapentanediamine, ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, tridecanediamine, tetradecanediamine, pentadecanediamine, hexadecanediamine, heptadecadecanediamine, octadecanediamine, nonadecadecanediamine, eicosanediamine, 2-methyl-1,8-octanediamine, 2,2,4-trimethylhexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine.

[0025] In some embodiments, the lactam is selected from the group consisting of α-pyrrolidone (butyrolactam), ε-caprolactam, heptanolactam, undecanolactam, and dodecanolactam.

[0026] In some embodiments, the aliphatic polyamide and monomer are selected from the following table:

[0027]

[0028] In some embodiments, the aliphatic polyamide is PA66 and / or PA6.

[0029] In some embodiments, the structure of the PA-XY type polyamide is shown in Formula I:

[0030] (I)

[0031] In formula (I), A1 represents a proton (H+) or an acetyl group (CH3-CO-); B1 represents a hydroxyl group (-OH).

[0032] The structure of the PA-Z type polyamide is shown in Formula II:

[0033] (II)

[0034] In formula (II), A1 represents a proton (H+) or an acetyl group (CH3-CO-); B1 represents a hydroxyl group (-OH).

[0035] The acetyl group (CH3-CO-) is formed by the chemical reaction of acetic acid (CH3-COOH) and the terminal amino group (-NH2) of the polyamide molecular chain. When A1 represents the acetyl group (CH3-CO-), it means that the terminal amino group of this part is replaced by the terminal carboxyl group for capping.

[0036] In some embodiments, the molecular chains of the PA-XY type polyamide and PA-Z type polyamide contain 10~60 mEq / kg terminal amino groups, preferably 10~45 mEq / kg terminal amino groups, more preferably 10~30 mEq / kg terminal amino groups, and the terminal amino group content is controlled by chemically reacting acetic acid with the terminal amino groups of the molecular chain.

[0037] In polyamides, the electronegativity and conjugation effect of the oxygen atom in the terminal carboxyl group inhibit reactivity, while the lone pair electrons of the nitrogen atom in the terminal amine group can freely participate in the reaction. This results in the nitrogen atom adjacent to the terminal amine group being much more reactive than the terminal carboxyl group. The reactive terminal amine group degrades the flame retardant properties of polyamide materials, necessitating the addition of a higher proportion of flame retardant to achieve flame suppression. However, an excessively high proportion of flame retardant is detrimental to the composition's tracking resistance. During the polyamide polymerization stage, adding acidic substances allows the terminal amine groups to react and be eliminated during polymerization, thereby reducing the content of terminal amine groups in the polymer and improving the composition's flame retardancy and tracking resistance.

[0038] Component (B) is red phosphorus, a powder with a D50 particle size of 1~20μm. It can be added directly or pre-stabilized by coating before use. Alternatively, red phosphorus can be prepared as a masterbatch before use. When red phosphorus is prepared as a masterbatch, the concentration of red phosphorus is 30~60wt%. Based on the flammability and explosiveness of red phosphorus powder, pre-coated red phosphorus masterbatch is preferred.

[0039] Component (C) is zinc aromatic carboxylate, which is a compound of an aromatic dicarboxylic acid and zinc ions.

[0040] In some embodiments, the aromatic dicarboxylic acid is selected from the group consisting of: terephthalic acid, isophthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, isophthalic acid, and terephthalic acid, preferably terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and more preferably terephthalic acid, as detailed below:

[0041]

[0042] In some embodiments, the zinc source of the aromatic zinc carboxylate is selected from one or more of zinc carbonate, basic zinc carbonate, and zinc nitrate, preferably zinc nitrate.

[0043] In some embodiments, the aromatic zinc carboxylate is synthesized using a hydrothermal method, the method comprising:

[0044] (1) Using distilled water as a medium, aromatic dicarboxylic acid and zinc source were mixed at concentrations of 0.17 mol / L and 0.3 mol / L respectively to obtain an initial suspension. Then, a sodium hydroxide solution with a concentration of 0.5 mol / L was used as a precipitant to adjust the pH of the initial suspension to neutral (pH 7). The suspension was placed in a heat-collecting magnetic stirrer and stirred in a constant temperature water bath at 80℃ for 2 hours by adjusting the stirrer. Then, the pH of the suspension was adjusted to 8~9 by sodium hydroxide precipitant and stirred for another hour.

[0045] (2) Transfer the solution obtained in step (1) into a pressure-resistant reaction vessel. After nitrogen purging, heat the reaction vessel to 200°C at a rate of 2°C / min and maintain the temperature for 100 hours to carry out the reaction.

[0046] (3) Remove the water vapor from the reaction tank, then cool the reaction tank to room temperature to obtain colorless flaky crystals. Filter the crystals, wash and dry them with distilled water to obtain the final product.

[0047] Component (D) is hydroxyapatite, which has a unique hexagonal crystal structure. Phosphate groups are bonded by covalent bonds, while calcium ions are bonded to phosphate groups by ionic bonds. The hydroxyl groups (-OH) exist as independent anions. This structure endows hydroxyapatite with excellent ion exchange and adsorption capabilities. The calcium ions (CaO) in the crystal lattice... 2+ It can undergo ion exchange with metals, and the hydroxyl functional groups (-OH) on its surface can also adsorb free acid radical ions.

[0048] The chemical formula of the hydroxyapatite is Ca. 10 (PO4)6(OH)2, the structure is shown in formula (Ⅲ):

[0049] (III)

[0050] The hydroxyapatite has a purity greater than 99.0% and a pH value (10% suspension) of 6-8. It is prepared by chemical precipitation, sol-gel method or hydrothermal synthesis method, with hydrothermal synthesis method being preferred.

[0051] Component (E) is a toughening agent, which is a graft of rubber or thermoplastic elastomer and maleic anhydride.

[0052] In some embodiments, the rubber is selected from the group consisting of: ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile rubber (NBR), chlorohydrin rubber (ECO), and acrylate rubber (ACM).

[0053] In some embodiments, the thermoplastic elastomer is selected from the group consisting of styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-propylene-styrene (SEPS), and styrene-ethylene-butene-styrene block copolymer (SEBS).

[0054] In some embodiments, the thermoplastic elastomer is selected from EPDM and / or SEBS, with EPDM being particularly preferred.

[0055] Component (F) is a reinforcing agent selected from one or more of glass fibers, glass microspheres and mineral fillers (such as talc, mica, kaolin, calcium carbonate, calcium silicate, magnesium carbonate), preferably glass fibers.

[0056] Component (G) is other additives selected from one or more of colorants, release agents, heat stabilizers, flow improvers and crystallization promoters.

[0057] A second aspect of the present invention provides a method for preparing the high-voltage resistant red phosphorus flame-retardant polyamide composition, comprising melt-blending the raw material components using a single-screw or twin-screw extruder.

[0058] The high-voltage resistant red phosphorus flame-retardant polyamide composition is a melt-prepared blend, which is processed by a single-screw or twin-screw extruder; the length-to-diameter ratio (L / D) of the extruder is 32~52, preferably 40~44; the processing temperature is set to 150~300℃, and the screw speed is set to 200~500rpm.

[0059] Pre-drying: The aliphatic polyamide and red phosphorus masterbatch are dried in an air-conditioned oven at 80°C until the moisture content is less than 0.05%.

[0060] Feeding sequence: After the extruder is heated and melted, the reinforcing agent is added through a side feed port. Other material components are premixed and then metered and added through the main feed port of the extruder.

[0061] Venting: Venting is performed at normal pressure through openings in 1-2 barrels in front of the feed port on the extruder side, and venting is performed at pressurized openings in the second-to-last barrel of the die head, with a pressure range of 30-70 cm-Hg.

[0062] The melt from the twin-screw extruder is extruded through a die, cooled in a water tank, and then cut into pellets by a pelletizer. The collected pellets are dried to a moisture content of less than 0.1% before being packaged.

[0063] Red phosphorus readily degrades in warm and humid environments, continuously releasing phosphine. Phosphine contaminates and corrodes core metal materials in power transmission, such as copper, silver, and nickel, leading to a sharp increase in resistance and jeopardizing power transmission safety. It is known that adding metals and their compounds can stabilize red phosphorus and improve phosphine release, and using long-chain aliphatic polyamides can alleviate electrochemical corrosion caused by polymer moisture absorption. However, metal compounds are prone to ionization and degrade the electrical properties of the polymer, and the reduced oxygen index of long-chain aliphatic polyamides degrades their flame-retardant properties. Furthermore, existing technologies have failed to address the poor arc resistance of red phosphorus flame-retardant black products containing carbon black. This invention proposes a high-voltage resistant red phosphorus flame-retardant polyamide composition, whose beneficial effects are reflected in the following aspects:

[0064] I. Using general-purpose aliphatic polyamide (PA66) as the main base material, the terminal amino groups of PA66 are capped with acetic acid during the polymerization stage to reduce activity, thereby improving the flame retardancy and electrical tracking resistance of the composition. Capping the terminal amino groups with carboxylic acid is a low-cost, simple process that does not affect mechanical properties and can effectively improve the problem of electrical tracking.

[0065] 2. Hydroxyapatite is used as an electrochemical staining modifier and phosphide precipitation absorber. Its special hexagonal crystal structure has excellent ion exchange and adsorption capabilities. Calcium ions in the crystal lattice can exchange ions with divalent heavy metals, and the hydroxyl functional groups on the surface can adsorb free phosphorus compounds and other acid radicals.

[0066] Third, aromatic zinc carboxylate possesses both synergistic flame-retardant and polymer-stabilizing properties. Zinc compounds have thermal stabilizing effects on polyamides and red phosphorus, and can improve phosphorus precipitation. The inventors of this invention have discovered through research that aromatic zinc carboxylate exhibits excellent flame-retardant effects. For example, zinc terephthalate degrades at approximately 400°C in an oxygen atmosphere, with the main products being carbon dioxide, carboxylic acid, and zinc oxide. Zinc oxide is a commonly used synergist in polyamide flame-retardant systems; carbon dioxide dilutes oxygen; and carboxylic acid catalyzes carbonization of the polymer surface to isolate oxygen. All of these products have flame-suppressing effects. More importantly, aromatic zinc carboxylate exhibits high stability under temperature, humidity, and discharge conditions, does not release carboxylic acid or metal ions, and has no negative impact on electrical tracking performance.

[0067] Fourth, the high voltage-resistant red phosphorus flame-retardant polyamide composition in this invention is a black red phosphorus flame-retardant polyamide composition with added carbon black, which also has excellent tracking resistance improvement effect. Detailed Implementation

[0068] To more fully understand and demonstrate the technical solutions, objectives, and advantages of the present invention, the technical effects produced by the present invention will be further described in detail and completely below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. It should be noted that other embodiments obtained by those skilled in the art without departing from the concept of the present invention are all within the protection scope of the present invention.

[0069] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0070] The following commercially available materials were used in the examples and comparative examples:

[0071] PA66-1: Polyamide 66 purchased from Yangnong Company, with a relative viscosity of 2.7 and an amino-terminated content of approximately 25 mEq / kg.

[0072] PA66-2: Polyamide 66 purchased from Yangnong Company, with a relative viscosity of 2.7 and an amino-terminated content of approximately 55 mEq / kg.

[0073] PA66-3: Polyamide 66 purchased from Yangnong Company, with a relative viscosity of 2.7 and an amino-terminated content of approximately 85 mEq / kg.

[0074] PA6: Polyamide 6, trade name LX275, purchased from Luxi Chemical Company.

[0075] PA610: Purchased from Huafeng Company, polyamide 610, trade name LC1624.

[0076] PA612: Purchased from Huafeng Company as polyamide 612, trade name LC1825.

[0077] PA46: Polyamide 46 purchased from Enhuali Company.

[0078] PA56: Purchased from Cathay Corporation, polyamide 56, trade name E-2260.

[0079] PA1010: Polyamide 1010 purchased from Guangyin Company.

[0080] PA11: Purchased from Arkema, polyamide 11, trade name RILSANBMNO.

[0081] PA12: Purchased from Wanhua Company as polyamide 12, trade name Wanamid L2000.

[0082] MIX-PA: refers to a mixture obtained by mixing PA6:PA610:PA612:PA46:PA56:PA1010:PA11:PA12 in a ratio of 1:1:1:1:1:1:1:1:1.

[0083] Red phosphorus masterbatch: Purchase concentrated masterbatch with 50wt% red phosphorus content and PA6 carrier from Xinde Company, trade name FR9950KF.

[0084] HAP: Hydroxyapatite purchased from Budenheim Company, trade name BUDITT31.

[0085] GF: Glass fiber purchased from Shandong Fiberglass Company, trade name 995-10P, with a single filament diameter of 10μm.

[0086] GB: Glass microspheres purchased from 3M, trade name IM16K.

[0087] TD: Magnesium silicate purchased from Imfabi, trade name HTPultra5L.

[0088] Clay: Purchased from Carmin Company's washed ultrafine kaolin.

[0089] MIX-FILLER: refers to a mixture obtained by mixing GF:GB:TD:Clay in a ratio of 1:1:1:1 by Jinlun Company.

[0090] ZnO: Purchased from Zochem, zinc oxide, trade name ZOCO100.

[0091] EPDM: Purchased from Nengzhiguang Company, maleic anhydride-grafted EPDM, trade name N428.

[0092] CBK: Purchased from Cabot Corporation as 50% concentration carbon black masterbatch, trade name UN2014.

[0093] Preparation of component (C) zinc aromatic carboxylate for use in the examples and comparative examples:

[0094] Step 1: Using distilled water as a medium, terephthalic acid and zinc nitrate are mixed at concentrations of 0.17 mol / L and 0.3 mol / L respectively to obtain an initial suspension. Then, a 0.5 mol / L sodium hydroxide solution is used as a precipitant to adjust the pH of the initial suspension to neutral (pH 7). The suspension is placed in a heated magnetic stirrer and stirred in a constant temperature water bath at 80℃ for 2 hours by adjusting the stirrer. Then, the pH of the suspension is adjusted to 8-9 with sodium hydroxide precipitant and stirring is continued for 1 hour.

[0095] Step 2: Transfer the solution obtained in Step 1 into a pressure-resistant reaction vessel. After nitrogen purging, heat the reaction vessel to 200°C at a rate of 2°C / min and maintain the temperature for 100 hours to carry out the reaction.

[0096] Step 3: Remove the water vapor from the reaction tank, then cool the reaction tank to room temperature to obtain colorless flaky crystals. Filter the crystals, wash and dry them with distilled water to obtain zinc terephthalate (Zn-PTA).

[0097] Following the methods described in steps one through three above, the following zinc compounds were prepared: zinc isophthalate, zinc 1,4-naphthalenedicarboxylate, zinc 1,5-naphthalenedicarboxylate, zinc 2,6-naphthalenedicarboxylate, zinc 2,7-naphthalenedicarboxylate, zinc isophthalic acid, and zinc terephthalic acid.

[0098] MIX-Zn refers to a mixture obtained by mixing zinc isophthalate, zinc 1,4-naphthodicarboxylate, zinc 1,5-naphthodicarboxylate, zinc 2,6-naphthodicarboxylate, zinc 2,7-naphthodicarboxylate, zinc isophthalic acid, and zinc terephthalic acid in a ratio of 1:1:1:1:1:1:1, obtained by Jinlun Company. The zinc content of the mixture is approximately 29.0%.

[0099] Preparation method

[0100] As shown in Table 1, weigh each component and then add it to a twin-screw extruder for melt processing.

[0101] Extruder screw nominal diameter: 35mm;

[0102] Extruder screw length-to-diameter ratio: 40;

[0103] Processing temperature range: 150~300℃;

[0104] Main unit speed range: 300 rpm;

[0105] Pre-drying: The aliphatic polyamide and red phosphorus masterbatch are dried in a ventilated oven at 80°C until the moisture content is less than 0.05%. Water directly participates in the degradation reaction of red phosphorus, especially under high-temperature and high-shear processing conditions, which further accelerates the reaction process. Therefore, pre-drying of the polyamide and red phosphorus before processing is essential and crucial.

[0106] Feeding sequence: A side feed port is set at the heating and melting section of the extruder. The reinforcing agent is metered at the side feed port, and other material components are metered and added from the main feed port of the extruder after premixing.

[0107] Venting: Venting is performed at normal pressure through openings in 1-2 barrels in front of the feed port on the extruder side, and venting is performed at pressurized openings in the second-to-last barrel of the die head, with a pressure range of 30-70 cm-Hg.

[0108] The melt from the twin-screw extruder is extruded through a die, cooled in a water tank, and then cut into pellets by a pelletizer. The collected pellets are dried to a moisture content of less than 0.1% before being packaged.

[0109] Quantitative testing of phosphorus compound precipitation

[0110] The sample size was 80mm×10mm×4mm. The testing instruments were HACHLCK349 test kit, HACIT200 thermostat and HACHDR2800 spectrophotometer.

[0111] Place the test piece, a 50mm long silver / nickel 20 alloy, and 1mL of water into a test tube and seal it. Place the test tube in an oven at 70℃ for 28 days. Remove the silver / nickel 20 alloy and dissolve the resulting phosphides in 10mL of 0.01M HCl at 100℃. Then dilute the obtained solution with deionized water at a ratio of 1 / 50. Take 2mL of the diluted solution obtained in the above step and place it into the reagent bottle of the test kit. Seal and shake to mix thoroughly with the reagents in the bottle. Then place the reagent bottle in a thermostat and heat at 100℃ for 1 hour. Remove and cool to room temperature before placing it in a spectrophotometer for phosphorus compound content analysis.

[0112] The melt flow rate was tested according to the method specified in ISO 1133-1, at a test temperature of 275℃ and a load of 5kg.

[0113] Vertical burning performance was tested according to the method specified in UL94, with a test specimen size of 125mm × 13.0mm × 1.6mm.

[0114] The relative tracking index (CTI) was measured according to the method specified in IEC 60112, with a test piece size of 60mm × 60mm × 3mm.

[0115] The inclined plane tracking (IPT) value was measured according to the ASTM D2303 standard TTT (Time-to-Track) method. The test specimen size was 120mm × 50mm × 6mm, the test voltage was 1.5kV, the tracking extended to the specified distance of 25mm, and the test time was 60min.

[0116] If the recorded TTT>60min means that the trace extension of the sample is less than 25mm under 1.5kV, the judgment result is Pass.

[0117] If the recorded TTT < 60min (record the actual time value), it means that at 1.5kV, the sample duration is less than 60min, and / or the sample trace extension is greater than 25mm, and the result is NG.

[0118] Examples and Comparative Examples

[0119] Tables 1 and 2 list the performance test results of the compositions in each embodiment.

[0120] Table 1

[0121]

[0122] Table 2

[0123]

[0124] Comparative Examples 1, 2, and 3 verified the effect of different terminal amino content levels of PA66 on the flame retardant properties, phosphorus precipitation, and electrical tracking resistance of the polyamide composition. It was found that the higher the terminal amino content of PA66, the more deteriorated the flame retardant properties and melt flow properties of the composition, and the higher the amount of phosphine precipitation. This is because the nitrogen atoms adjacent to the terminal amino are more reactive. Increasing the terminal amino content will lead to an increase in the polarity of the polymer molecular chain end, affecting the flame retardant stability and melt flow. The reduced melt flow will cause the red phosphorus to be subjected to greater shear heat during processing, resulting in accelerated red phosphorus degradation.

[0125] Comparative Examples 4 and 5 respectively verified that both long-chain polyamide PA612 and metal oxide ZnO can improve phosphine evolution, but PA612 degrades flame retardant properties and ZnO degrades electrical tracking resistance.

[0126] Comparative Example 1 and Examples 1-3 verified that different contents of hydroxyapatite (HAP) improved the phosphating precipitation and electrical tracking resistance, and that hydroxyapatite (HAP) did not affect the flame retardant properties of the red phosphorus flame retardant polyamide composition.

[0127] Comparative Examples 6-8 verified that carbon black significantly degrades the electrical tracking resistance of the composition. The toughening agent EPDM improves both CTI and IPT, but a higher proportion of EPDM worsens phosphorus precipitation, which is related to the fact that EPDM degrades the processing properties of polyamide. The long-chain polyamide PA612 has little effect on improving the CTI value of the black (carbon black) composition, but it can improve its IPT (extending the TTT value of the sample at 1.5 kV).

[0128] Examples 4-6 verify that increasing the proportion of zinc terephthalate and hydroxyapatite can improve the flame retardant properties and electrical tracking resistance of black (carbon black) red phosphorus, and that increasing the proportion of zinc terephthalate can reduce the amount of red phosphorus added, further suppressing the tendency of phosphine precipitation.

[0129] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-voltage resistant red phosphorus flame-retardant polyamide composition, characterized in that, It includes the following components, expressed as a percentage by mass: (A) Aliphatic polyamide 30~80wt%; (B) Red phosphorus 2~10wt%; (C) Aromatic carboxylic acid zinc 0.5~10wt%; (D) Hydroxyapatite 0.5~5wt%; (E) Toughening agent 5.0~20wt%; (F) Reinforcing agent 10~50wt%; (G) Other additives 0~5wt%; The sum of the mass percentages of components (A) to (G) is 100 wt%.

2. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 1, characterized in that, The aliphatic polyamide is a semi-crystalline polymer with a melting temperature of 150~300℃. It is selected from one or more of PA-XY obtained by polycondensation reaction of aliphatic dicarboxylic acid and aliphatic diamine having not less than four carbon atoms, and PA-Z obtained by ring-opening polymerization of lactam, wherein X is the number of carbon atoms of the diamine, Y is the number of carbon atoms of the dicarboxylic acid, and Z is the number of carbon atoms of the lactam. The aliphatic dicarboxylic acid is selected from the group consisting of: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, heptaic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, octadecanoic acid, and eicosanoic acid. The aliphatic diamine having not less than four carbon atoms is selected from the group consisting of: butanediamine, pentapentanediamine, ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecylethylenediamine, dodecamethylenediamine, tridecanediamine, tetradecanediamine, pentadecanediamine, hexadecanediamine, heptadecanediamine, octadecanediamine, nonadecanediamine, eicosanediamine, 2-methyl-1,8-octanediamine, 2,2,4-trimethylhexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine; The lactam is selected from the group consisting of butyrolactam, ε-caprolactam, heptanolactam, undecanolactam and dodecanolactam.

3. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 2, characterized in that, Both the PA-XY type polyamide and the PA-Z type polyamide have 10~60 mEq / kg terminal amino groups at the end of their molecular chains; The structure of the PA-XY type polyamide is shown in Formula I: （I） In formula (I), A1 represents H+ or CH3-CO-, and B1 represents -OH; The structure of the PA-Z type polyamide is shown in Formula II: (II) In formula (II), A1 represents H+ or CH3-CO-, and B1 represents -OH.

4. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to any one of claims 1 to 3, characterized in that, The aliphatic polyamide is selected from one or more of PA6, PA11, PA12, PA46, PA56, PA66, PA610, PA612 and PA1010.

5. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 1, characterized in that, The red phosphorus is a powder with a D50 particle size of 1~20μm, which can be used directly, or after being coated, or after being prepared into a masterbatch.

6. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 5, characterized in that, When the red phosphorus is prepared as a masterbatch, the red phosphorus concentration is 30~60wt%.

7. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 1, characterized in that, The aromatic zinc carboxylic acid is a compound of an aromatic dicarboxylic acid and a zinc ion; wherein: The aromatic dicarboxylic acid is selected from the group consisting of: terephthalic acid, isophthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, isophthalic acid, and terephthalic acid. The zinc source for the zinc ions is selected from one or more of zinc carbonate, basic zinc carbonate, and zinc nitrate.

8. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 1, characterized in that, The chemical formula of the hydroxyapatite is Ca. 10 (PO4)6(OH)2, the structure is shown in formula (Ⅲ): （Ⅲ） The hydroxyapatite is prepared by chemical precipitation, sol-gel method or hydrothermal synthesis, with a purity greater than 99.0%, and simultaneously meets the requirement that the pH value of a 10% hydroxyapatite suspension is 6-8.

9. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 1, characterized in that, The toughening agent is a graft of rubber or thermoplastic elastomer and maleic anhydride; wherein: The rubber is selected from the group consisting of the following substances: ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, chlorohydrin rubber, and acrylate rubber. The thermoplastic elastomer is selected from the group consisting of: styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, styrene-ethylene-propylene-styrene, and styrene-ethylene-butene-styrene block copolymers.

10. The high-voltage resistant red phosphorus flame-retardant polyamide composition according to claim 1, characterized in that, The reinforcing agent is selected from one or more of glass fiber, glass microspheres, talc, mica, kaolin, calcium carbonate, calcium silicate, and magnesium carbonate; And / or the other additives are selected from one or more of colorants, release agents, heat stabilizers, flow improvers and crystallization promoters.

11. A method for preparing the high-voltage resistant red phosphorus flame-retardant polyamide composition according to any one of claims 1 to 10, characterized in that, include: The raw material components are produced by melt blending using a single-screw or twin-screw extruder, wherein the length-to-diameter ratio (L / D) of the single-screw or twin-screw extruder is 32-52; the processing temperature is 150-300 ℃; and the screw speed is 200-500 rpm.

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