High-CTI, halogen-free flame-retardant polyamide composite, preparation method therefor and use thereof

Abstract

Disclosed are a high-CTI, halogen-free flame-retardant polyamide composite, a preparation method therefor and a use thereof. The polyamide composite, in parts by weight, comprises the following components: 40-70 parts of polyamide resin, 20-40 parts of glass fiber, 8-18 parts of hypophosphite, and 1-6 parts of melamine derivative; the polyamide resin is a composite of PA66 and PA6, the mass ratio of PA66 to PA6 is (1.5-9):1, the elemental iron content of the hypophosphite is ≤70ppm, the pH of the hypophosphite is 4-5, the terminal amino content of the PA66 resin is 50-82 ppm, and the viscosity number of the PA6 resin is 2.0-2.5. The polyamide composite of the present invention successfully increases the CTI value of the material, and the flame-retardant performance meets application requirements, providing more possibilities for the development of new energy voltage platforms from 400V to 800V and higher.

Description

A high CTI halogen-free flame-retardant polyamide composite and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular to a high CTI halogen-free flame-retardant polyamide composite, a preparation method thereof, and an application thereof. Background Art

[0002] Flame-retardant polyamides are widely used in electronics, automotive, and rail transportation due to their excellent flame retardancy, mechanical properties, electrical properties, and heat resistance. Comparative tracking (CTI) is a key parameter characterizing a material's electrical performance. A higher CTI indicates a shorter creepage distance, allowing greater freedom in structural design at high voltages. Halogen-free flame-retardant polyamides typically have a CTI between 600 and 700 V.

[0003] However, as the voltage platform of new energy develops from 400V to 800V and above, the market has put forward higher requirements on the electrical properties of flame-retardant nylon. In order to better match the wide application of the material in the voltage platform of 800V and above and improve the safety performance of the material, it is currently necessary to further improve the CTI of halogen-free flame-retardant polyamide to meet the needs of industries such as electronics, automobiles and rail transportation. Summary of the Invention

[0004] In view of the defects in the prior art, the present invention provides a high CTI halogen-free flame retardant polyamide composite and a preparation method and application thereof.

[0005] The present invention provides a high CTI halogen-free flame retardant polyamide composite, comprising the following components, calculated by weight: 40-70 parts of a polyamide resin, such as 40, 43, 45, 50, 55, 60, 65, or 70 parts; 20-40 parts of a reinforcing filler, such as 20, 23, 25, 28, 30, 35, 38, or 40 parts; 8-18 parts of a hypophosphite, such as 8, 10, 12, 14, 16, or 18 parts; and 1-6 parts of a melamine derivative, such as 1, 2, 3, 4, 5, or 6 parts.

[0006] Wherein, the polyamide resin is a composite of PA66 and PA6, and the mass ratio of PA66 to PA6 is (1.5-9):1;

[0007] The iron content of the hypophosphite is ≤70ppm, preferably 30-70ppm, such as 30, 35, 38, 40, 42, 45, 50, 55, 58, 60, 65, 70ppm;

[0008] The pH of the hypophosphite is 4-5, such as 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5;

[0009] The terminal amino group content of the PA66 resin is 50-82 ppm, such as 50, 52, 55, 60, 62, 65, 68, 70, 75, 78, 80, 82 ppm, and the viscosity number of the PA6 resin is 2.0-2.5, such as 2.0, 2.1, 2.2, 2.3, 2.4, 2.5;

[0010] The test method for the terminal amino group content is as follows: take 0.5g of polymer, add 45mL of phenol and 3mL of anhydrous methanol, heat to reflux, observe that the sample is completely dissolved, cool to room temperature, and titrate the terminal amino group content with a standardized hydrochloric acid standard solution using a Metrohm 848Titrino plus fully automatic potentiometric titrator;

[0011] The viscosity number test method is as follows: the test is conducted according to ISO 307: 2007. The relative viscosity of polyamide at a concentration of 0.25 g / dL is measured in 98% concentrated sulfuric acid at 25±0.01°C using an NCY-2 automatic viscometer manufactured by Shanghai Starda Scientific Instrument Co., Ltd.

[0012] The amount of the polyamide resin in the composition is not less than 46%; the mass percentage of PA66 in the composition is not less than 32%.

[0013] At high temperatures, PA66 has a better carbon-forming effect than PA6. Therefore, the appropriate introduction of low-molecular-weight PA6 resin can undergo amide exchange with PA66 during the discharge process, destroying the structural regularity of PA66, thereby reducing its carbon-forming effect and improving its CTI. PA66 resin with a high amino content can have a good binding force with halogen-free flame retardants, promoting the dispersion of halogen-free flame retardants in the composite system. The amino group of PA66 resin has a certain alkalinity, which can neutralize the acidity of halogen-free flame retardants and reduce the carbon-forming effect of halogen-free flame retardants during the discharge process, thereby improving the CTI of halogen-free flame retardant polyamide composites. Since leakage tracking damage mainly occurs on the surface, and the higher the molecular weight of PA6 (higher viscosity), the lower the PA6 content on the surface of the halogen-free flame retardant polyamide composite, and it cannot play a role in inhibiting carbon formation.

[0014] The hypophosphite of the present invention can be commercially available or synthesized by itself. The synthesis process of hypophosphite is very mature, and any process in the prior art is applicable to the present invention, such as "Synthesis and flame retardant application of new halogen-free flame retardant diethyl aluminum hypophosphite, Wang Yingzhou et al., Journal of Nanjing Normal University (Natural Science Edition), Vol. 39, No. 2", which mentions various preparation methods. The present invention found that controlling the Fe element content and pH value in hypophosphite within a suitable range can promote the gas phase arc extinguishing effect of hypophosphite, reduce its condensed phase catalytic carbonization effect, and thus improve the CTI of halogen-free flame retardant polyamide. The iron content of the hypophosphite is tested using an inductively coupled plasma spectrometer (ICP) according to GB T 27598-2011; hypophosphite can promote the degradation of polyamide into carbon, and the lower the pH value and the higher the Fe ion content, the more obvious the catalytic degradation into carbon, resulting in a lower CTI of the halogen-free flame retardant polyamide composite. The iron content and pH value of the hypophosphite can be controlled by controlling the number of washes of the hypophosphite flame retardant and the content of the acid and base reagents during the synthesis process. For example, when the iron content is lower than the desired value, the number of washes can be reduced, and when the pH is lower than the desired value, the acid reagent content can be reduced. For example, the process for synthesizing the hypophosphite flame retardant of the present invention is as follows: In a reactor, the sodium salt corresponding to the hypophosphite used is dissolved in water and stirred thoroughly to dissolve to obtain a sodium salt solution. Aluminum sulfate is dissolved in water in a beaker, and then concentrated sulfuric acid at a concentration of 98 wt% is added to the aluminum sulfate solution, stirred thoroughly to mix evenly, and transferred to a dropping funnel. The reactor is heated to a high temperature, and then the aluminum sulfate solution containing sulfuric acid is added dropwise, and then the reaction is continued while the temperature is maintained. The precipitate is filtered while hot and washed multiple times, with the number of washes controlled as needed. The material is transferred to an oven for drying. After drying, the temperature is cooled to room temperature and discharged to obtain the hypophosphite flame retardant of the present invention.

[0015] Since the raw materials for synthesizing hypophosphite, such as aluminum sulfate or aluminum hydroxide, usually contain a certain amount of iron, the final synthesized hypophosphite contains iron in ionic state, which changes the degree to which hypophosphite catalyzes the degradation of polyamide into carbon, thereby affecting the CTI value of the material.

[0016] Furthermore, the polyamide composite comprises the following components in parts by weight:

[0017] Furthermore, the hypophosphite is one or more of aluminum hypophosphite, diethyl aluminum hypophosphite, and isopropyl aluminum hypophosphite, preferably diethyl aluminum hypophosphite.

[0018] Furthermore, the reinforcing filler is glass fiber, and the glass fiber is selected from one of E glass fiber, H glass fiber, S glass fiber, D glass fiber and C glass fiber, preferably E glass fiber.

[0019] Furthermore, the melamine derivative is melamine polyphosphate, which can degrade to produce non-combustible gases such as ammonia and water, and can synergize with hypophosphite to catalyze polyamide into carbon.

[0020] The present invention also provides a method for preparing the polyamide composite, comprising the following steps:

[0021] The components are weighed in parts by weight, and the components are put into a mixer for mixing until uniform to obtain a premix, and then the obtained premix is ​​put into a screw extruder for melt mixing, and extruded into pellets to obtain the high CTI halogen-free flame retardant polyamide composite.

[0022] Furthermore, the screw speed of the screw extruder is 250 rpm-350 rpm, the aspect ratio is 40:1-48:1, and the barrel temperature is 200° C.-280° C.

[0023] The present invention also provides applications of the polyamide composite in the electrical and electronic and new energy industries, specifically applications in high-voltage connectors, new energy battery end plates and brackets, and the like.

[0024] In summary, compared with the prior art, the present invention achieves the following technical effects:

[0025] (1) The polyamide composite of the present invention successfully improves the CTI value of halogen-free flame retardant polyamide.

[0026] (2) The flame retardant properties of the polyamide composite of the present invention meet the application requirements, and the vertical combustion performance reaches V-0 grade. DETAILED DESCRIPTION

[0027] In order to help those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts should fall within the scope of protection of the present invention.

[0028] Example

[0029] The present invention is further described below with reference to specific examples and comparative examples. The following specific examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the following examples, and are particularly not limited to the types of the various component raw materials used in the following specific examples.

[0030] 1. The sources of raw materials for the embodiments and comparative examples are as follows:

[0031] PA66#1: brand PA66 EP-158, amino group content 50ppm, Huafeng Group;

[0032] PA66#2: brand PA66 EP-158N, amino group content 82ppm, Huafeng Group;

[0033] PA66#3: PA66 EPR27, amino group content 40ppm, Shenma Group;

[0034] PA66#4: brand PA66 EP1106, amino group content 68ppm, Huafeng Group;

[0035] PA6#1: brand PA6 HY-2800A, viscosity number 2.8, Haiyang Chemical Fiber;

[0036] PA6#2: brand PA6 HY-2500A, viscosity number 2.4, Haiyang Chemical Fiber;

[0037] PA6#3: brand PA6 M2400, viscosity number 2.5, Xinhui Meida;

[0038] PA6#4: brand PA6 M2000, viscosity number 2.0, Xinhui Meida;

[0039] Glass fiber #1: E glass fiber, grade ECS10-3.0-568H, China Jushi Co., Ltd.

[0040] Glass fiber #2: S glass fiber, brand S-1HM435TM-10-3.0, Taishan Glass Fiber Co., Ltd.

[0041] Hypophosphite #1: diethylaluminum hypophosphite, brand OP1230, iron content 172 ppm, pH 4.1, Klein Co., Ltd.

[0042] Hypophosphite #2: diethylaluminum hypophosphite, homemade, 50 ppm iron, pH 4.2;

[0043] Hypophosphite #3: diethylaluminum hypophosphite, homemade, 70 ppm iron, pH 4.1;

[0044] Hypophosphite #4: Isopropyl aluminum hypophosphite, homemade, 62 ppm iron, pH 4.1;

[0045] Hypophosphite #5: diethylaluminum hypophosphite, homemade, 70 ppm iron, pH 5.0;

[0046] Hypophosphite #6: diethylaluminum hypophosphite, homemade, 90 ppm iron, pH 3.7;

[0047] Hypophosphite #7: diethylaluminum hypophosphite, homemade, 68 ppm iron, pH 3.6;

[0048] Melamine polyphosphate: brand BUDIT 3141, Budenheim Iberica, Germany;

[0049] Preparation of diethylaluminum hypophosphite: In a 2L reactor, dissolve 144g of sodium diethyl hypophosphite in 381.7g of water and stir thoroughly to obtain a sodium diethyl hypophosphite solution. In a 500mL beaker, dissolve 57g of aluminum sulfate in 133g of water. Add 4.0-4.1g of 98wt% concentrated sulfuric acid to the aluminum sulfate solution, stir thoroughly, and transfer to a dropping funnel. Heat the reactor to 90°C and begin adding the sulfuric acid-containing aluminum sulfate solution dropwise. Add the solution within 2 hours and continue the reaction at this temperature for 1 hour. Filter while hot and wash the precipitate multiple times, adjusting the number of washes as needed. Transfer the mixture to an oven, heat to 120°C, and dry for 60 minutes until the moisture content of the solids is 0.1wt%. Then, heat the mixture to 180°C at a rate of 2°C / min and hold for 60 minutes. Then, heat the mixture to 320°C at a rate of 1°C / min and hold for 30 minutes. Cool the mixture to room temperature and discharge. The Fe ion content and pH value of diethylaluminum hypophosphite can be controlled by controlling the number of washings and the sulfuric acid content;

[0050] The preparation method of isopropyl aluminum hypophosphite refers to the preparation process of diethyl aluminum hypophosphite, and 172g of isopropyl sodium hypophosphite is used instead of 144g of diethyl sodium hypophosphite.

[0051] The preparation method of the polyamide composite of the embodiment and comparative example of the present invention comprises the following steps:

[0052] The components are weighed in parts by weight, and the components are put into a mixer and mixed until uniform to obtain a premix. The premix is ​​then put into a twin-screw extruder for melt mixing, and extrusion granulation is performed to obtain the high CTI halogen-free flame retardant polyamide composite, wherein the screw speed of the twin-screw extruder is 250-350 rpm, the aspect ratio is 40:1-48:1, and the barrel temperature is 200° C.-280° C.

[0053] 2. Various performance test methods

[0054] (1) Flame retardancy test: Flame retardancy test was conducted on the specimens according to the relevant standards of UL94-2016, with a sample thickness of 0.8mm. Flame retardancy is of great significance to electrical safety. The UL94 flame retardancy grade must reach V-0 to meet application requirements.

[0055] (2) Comparative tracking index (CTI) test: The test is conducted according to IEC 60112-2020, the sample size is 100*100*3mm, and the instrument test range is 0-1000V.

[0056] Table 1 Example technical solutions and effects (units are parts by weight)

[0057] Table 1 Example technical solutions and effects (units are parts by weight)

[0058] Table 2 Comparative Examples Technical Scheme and Effects (Units are parts by weight)

[0059] Comparative Examples 1-12 all had a single variable similar to Example 4, except that no melamine polyphosphate was added in Comparative Example 1, and an excess of melamine polyphosphate was added in Comparative Example 2. As shown in Example 4, Comparative Examples 1, and 2, when the melamine content was low, the carbon layer formed at high temperatures had a loose structure, low flame retardancy, and failed to generate inert gas to quench the arc during discharge, resulting in a low CTI for the halogen-free flame-retardant polyamide composite. When the melamine content was high, the high temperatures generated by the arc discharge promoted carbonization of the halogen-free flame-retardant polyamide composite, similarly resulting in a low CTI.

[0060] In Comparative Example 3, PA66 with too low a terminal amino group content was added, in Comparative Example 4, PA6 with too high a viscosity number was added, and in Comparative Example 5, PA66 with too little terminal amino group content and too high a viscosity number was added. In Comparative Example 6, the mass ratio of PA66 to PA6 was greater than 9:1, and in Comparative Example 7, the mass ratio of PA66 to PA6 was less than 1.5:1. It can be seen from Example 4 and Comparative Examples 3-7 that the terminal amino group content of PA66 resin, the mass ratio of PA66 to PA6, and the viscosity number of PA6 all have an important influence on the CTI of the halogen-free flame retardant polyamide composite. Since PA66 has a better carbon-forming effect than PA6, low-molecular-weight PA6 resin is appropriately introduced into PA66. During the discharge process, it can undergo amide exchange with PA66, destroying the structural regularity of PA66 and thus reducing its carbon-forming effect. PA66 can have a good binding force with the halogen-free flame retardant through its high amino content, promoting the dispersion of the halogen-free flame retardant in the composite system. However, if the PA6 molecular weight is higher (the viscosity is higher), the PA6 content on the surface of the halogen-free flame retardant polyamide composite is low (the mass ratio of PA66 to PA6 is greater than 9:1), and the carbon-forming effect cannot be inhibited. When the PA6 content is too high (the mass ratio of PA66 to PA6 is less than 1.5:1), the halogen-free flame retardant polyamide will be damaged by corrosion, resulting in a lower CTI. In addition, a high PA6 content will also reduce the flame retardant properties of the halogen-free flame retardant polyamide.

[0061] In Comparative Example 8, too little hypophosphite was added, and in Comparative Example 9, an excessive amount of hypophosphite was added. It can be seen from Example 4 and Comparative Examples 8-9 that the hypophosphite content has an important influence on the CTI of the halogen-free flame retardant polyamide. Hypophosphite can promote the degradation of polyamide into carbon. When the hypophosphite content is higher, the catalytic degradation into carbon is more obvious, resulting in a lower CTI of the halogen-free flame retardant polyamide composite; however, hypophosphite can generate PO free radicals, quenching arcs and flames. Therefore, when the hypophosphite content is low, the CTI and flame retardant properties of the halogen-free flame retardant polyamide will also be poor.

[0062] The iron content of the hypophosphite in Comparative Example 10 is too high, which affects its ability to promote the degradation of polyamide into carbon, resulting in a lower CTI value. The pH value of the hypophosphite in Comparative Example 12 is not in the range of 4-5, resulting in a smaller CTI value of the composite. The iron content of the hypophosphite in Comparative Example 11 is too high and the pH value is not in the range of 4-5, which seriously affects the CTI value of the halogen-free flame retardant polyamide composite.

[0063] The vertical combustion performance and CTI test data in Tables 1 and 2 demonstrate that the polyamide composites prepared in Examples 1-25 achieve high CTI values ​​(above 750V) while maintaining a flame retardancy rating (V-0) that meets application requirements. These composites offer significant advantages over the comparative examples and can effectively meet the high standards of both customers and the market.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A polyamide composite, characterized in that: By weight, it includes the following components: Wherein, the polyamide resin is a composite of PA66 and PA6, and the mass ratio of PA66 to PA6 is (1.5-9):1; The iron content of the hypophosphite is ≤70ppm; The pH of the hypophosphite is 4-5; The terminal amino group content of the PA66 resin is 50-82ppm, and the viscosity number of the PA6 resin is 2.0-2.5; The test method for the terminal amino group content is as follows: take 0.5g of polymer, add 45mL of phenol and 3mL of anhydrous methanol, heat to reflux, observe that the sample is completely dissolved, cool to room temperature, titrate the terminal amino group content with a calibrated hydrochloric acid standard solution, and titrate with a potentiometric titrator; The viscosity number test method is: measuring the relative viscosity of polyamide with a concentration of 0.25 g / dL in 98% concentrated sulfuric acid at 25±0.01° C. using an automatic viscometer.

2. The polyamide composite according to claim 1, characterized in that By weight; Includes the following components:

3. The polyamide composite according to claim 1 or 2, characterized in that: The hypophosphite is one or more of aluminum hypophosphite, diethyl aluminum hypophosphite, and isopropyl aluminum hypophosphite.

4. The polyamide composite according to claim 1, characterized in that The reinforcing filler is glass fiber.

5. The polyamide composite according to claim 4, characterized in that The glass fiber is selected from any one of E glass fiber, H glass fiber, S glass fiber, D glass fiber and C glass fiber.

6. The polyamide composite according to claim 1, characterized in that The melamine derivative is melamine polyphosphate.

7. The method for preparing the polyamide composite according to any one of claims 1 to 6, characterized in that: The steps include: The components are weighed in parts by weight, and the components are put into a mixer for mixing until uniform to obtain a premix, and then the obtained premix is ​​put into a screw extruder for melt mixing, and extruded into granules to obtain the high CTI halogen-free flame retardant polyamide composite.

8. The preparation method according to claim 7, characterized in that: The screw extruder has a screw speed of 250 rpm-350 rpm, an aspect ratio of 40:1-48:1, and a barrel temperature of 200° C.-280° C.

9. Use of the polyamide composite according to any one of claims 1 to 6 in the electronic and electrical and new energy industries.

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