A high-cti halogen-free flame-retardant polyamide composite and a preparation method and application thereof

Abstract

The application discloses a kind of high CTI halogen-free flame-retardant polyamide composite and its preparation method and application.The polyamide composite includes the following components by weight parts: polyamide resin 40-70 parts, glass fiber 20-40 parts, hypophosphite 8-18 parts, melamine derivative 1-6 parts, the polyamide resin is the composite of PA66 and PA6, the mass ratio of PA66 and PA6 is (1.5-9):1, the iron element content of the hypophosphite is ≤70ppm, the pH of the hypophosphite is 4-5, the end amino content of the PA66 resin is 50-82ppm, the viscosity number of the PA6 resin is 2.0-2.5, the polyamide composite of the application successfully improves the CTI value of material and the flame-retardant performance meets application requirement, provides more possibility for the development of new energy voltage platform from 400V to 800V and above.

Description

TECHNICAL FIELD

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

[0002] Flame-retardant polyamides are widely used in the fields of electronic appliances, automobiles and rail transportation due to their excellent flame-retardant properties, mechanical properties, electrical properties and heat resistance. Compared with the tracking index (CTI), the CTI is an important parameter for characterizing the electrical properties of a material. The higher the CTI of a material, the shorter the creepage distance, and the higher the degree of freedom in structural design of the material under high voltage. The CTI of halogen-free flame-retardant polyamides is generally between 600-700V.

[0003] However, as the voltage platform of new energy develops from 400V to 800V and above, the market has higher requirements for the electrical properties of flame-retardant nylon. In order to better match the wide application of materials under a voltage platform of 800V and above, and improve the safety performance of the materials, it is necessary to further improve the CTI of halogen-free flame-retardant polyamides to meet the needs of the electronic appliance, automobile and rail transportation industries. SUMMARY

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

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

[0006] 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 PA66 resin has an end amino group content of 50-82 ppm, such as 50, 52, 55, 60, 62, 65, 68, 70, 75, 78, 80, 82 ppm, and a viscosity number of 2.0-2.5, such as 2.0, 2.1, 2.2, 2.3, 2.4, 2.5;

[0010] The test method for the end amino group content is as follows: 0.5 g of the polymer is added to 45 mL of phenol and 3 mL of anhydrous methanol, heated to reflux, and after the sample is completely dissolved, cooled to room temperature, and titrated with a calibrated hydrochloric acid standard solution to determine the end amino group content, and titrated with a Metrohm 848Titrino plus automatic potentiometric titrator;

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

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

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

[0014] The hypophosphite salt of the present application can be commercially available or synthesized by itself. The synthesis process of hypophosphite salt is very mature, and any process in the prior art is suitable for the present application. Various preparation methods are mentioned in "Synthesis and flame-retardant application of new halogen-free flame retardant aluminum diethyl hypophosphite", Wang Yingzhou et al., Nanjing Normal University Journal (Natural Science Edition), Vol. 39, No. 2". It is found that controlling the content of Fe element and pH value of the hypophosphite salt in a suitable range can promote the gas-phase arc-extinguishing effect of the hypophosphite salt and reduce its condensed-phase catalytic carbonization, thereby improving the CTI of the halogen-free flame-retardant polyamide. The content of Fe element in the hypophosphite salt is tested by inductively coupled plasma spectrometer (ICP) according to GB T 27598-2011; the hypophosphite salt can promote the degradation of polyamide into carbon, and the lower the pH value and the higher the content of Fe ion, the more obvious the catalytic degradation into carbon, resulting in a lower CTI of the halogen-free flame-retardant polyamide composite. The content of Fe element and the pH value of the hypophosphite salt can be controlled by controlling the number of washing times of the hypophosphite flame retardant and the content of acid and alkali reagents in the synthesis process, for example, when the content of Fe element is lower than the required value, the number of washing times is reduced, and when the pH value is lower than the required value, the content of acid reagent is reduced. Exemplarily, the process for synthesizing the hypophosphite flame retardant of the present application is as follows: a sodium salt corresponding to the used hypophosphite salt is dissolved in water in a reaction kettle, and stirred to dissolve to obtain a sodium salt solution. Aluminum sulfate is dissolved in water in a beaker, and a certain concentration of 98wt% concentrated sulfuric acid is added to the aluminum sulfate solution, stirred to mix uniformly, and transferred to a dropping funnel. The reaction kettle is heated, the temperature is raised, the aluminum sulfate solution containing sulfuric acid is added dropwise, and then the reaction is continued while keeping the temperature. Hot filtration is performed, and the precipitate is washed multiple times. The number of washing times is controlled according to the requirement. The material is transferred to an oven for drying, the temperature is lowered to room temperature after drying is completed, and the material is discharged, thereby obtaining the hypophosphite salt flame retardant of the present application.

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

[0016] Further, the polyamide composite comprises the following components by weight:

[0017]

[0018] Further, the hypophosphite salt is one or more of aluminum hypophosphite, diethyl hypophosphite, and isopropyl hypophosphite, and is preferably diethyl hypophosphite.

[0019] Further, 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, and is preferably E glass fiber.

[0020] Further, the melamine derivative is melamine polyphosphate. Melamine polyphosphate can generate non-combustible gases such as ammonia and water on one hand, and can synergize with hypophosphite to catalyze the carbonization of polyamide on the other hand.

[0021] The application further provides a preparation method of the polyamide composite, comprising the following steps:

[0022] The components are weighed by weight parts, 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 extrusion granulation to obtain the high-CTI halogen-free flame-retardant polyamide composite.

[0023] Further, the screw speed of the screw extruder is 250 rpm-350 rpm, the length-diameter ratio is 40:1-48:1, and the barrel temperature is 200℃-280℃.

[0024] The application further provides an application of the polyamide composite in the electronic and electrical and new energy industries, specifically in high-voltage connectors, new energy battery end plates and supports and the like.

[0025] In summary, compared with the prior art, the application achieves the following technical effects:

[0026] (1) The polyamide composite of the application successfully improves the CTI value of the halogen-free flame-retardant polyamide.

[0027] (2) The flame-retardant property of the polyamide composite of the application meets the application requirements, and the vertical burning property reaches the V-0 level. DETAILED DESCRIPTION

[0028] In order for those skilled in the art to better understand the application, the technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor should fall within the scope of protection of the application.

[0029] EMBODIMENTS

[0030] The application will be further described below in combination with specific embodiments and comparative examples. The following specific embodiments are preferred embodiments of the application, but the embodiments of the application are not limited to the following examples, especially not limited to the types of raw materials used in the following specific examples.

[0031] I. Sources of raw materials for the examples and comparative examples are as follows:

[0032] PA66#1: Grade PA66 EP-158, terminal amino content 50ppm, Huafeng Group;

[0033] PA66#2: Grade PA66 EP-158N, terminal amino content 82ppm, Huafeng Group;

[0034] PA66#3: Grade PA66 EPR27, terminal amino content 40ppm, Shenma Group;

[0035] PA66#4: Grade PA66 EP1106, terminal amino content 68ppm, Huafeng Group;

[0036] PA6#1: Grade PA6 HY-2800A, viscosity number 2.8, Haiyang Chemical Fiber;

[0037] PA6#2: Grade PA6 HY-2500A, viscosity number 2.4, Haiyang Chemical Fiber;

[0038] PA6#3: Grade PA6 M2400, viscosity 2.5, Xinhui Meida;

[0039] PA6#4: Grade PA6 M2000, viscosity 2.0, Xinhui Meida;

[0040] Glass fiber #1: E glass fiber, grade ECS10-3.0-568H, China Jushi Co., Ltd.;

[0041] Glass fiber #2: S glass fiber, grade S-1HM435TM-10-3.0, Taishan Glass Fiber Co., Ltd.;

[0042] Hypophosphite #1: Diethylaluminum hypophosphite, grade OP1230, iron content 172ppm, pH 4.1, Klein Ltd.

[0043] Hypophosphite #2: Diethylaluminum hypophosphite, self-made, iron content 50ppm, pH 4.2;

[0044] Hypophosphite #3: Diethylaluminum hypophosphite, self-made, iron content 70ppm, pH 4.1;

[0045] Hypophosphite #4: Isopropyl aluminum hypophosphite, self-made, iron content 62 ppm, pH 4.1;

[0046] Hypophosphite #5: Diethylaluminum hypophosphite, self-made, iron content 70ppm, pH 5.0;

[0047] Hypophosphite #6: Diethylaluminum hypophosphite, self-made, iron content 90ppm, pH 3.7;

[0048] Phosphite 7: Diethyl aluminum phosphite, self-made, iron element content 68 ppm, pH 3.6;

[0049] Melamine polyphosphate: brand BUDIT 3141, Germany Budenheim Iberica;

[0050] Preparation method of diethyl aluminum phosphite: 144 g of sodium diethyl phosphite is dissolved in 381.7 g of water in a 2 L reaction kettle, and the solution is obtained by fully stirring and dissolving. In a 500 mL beaker, 57 g of aluminum sulfate is dissolved in 133 g of water, and 4.0-4.1 g of concentrated sulfuric acid with a concentration of 98 wt% is added to the aluminum sulfate solution, fully stirred and mixed uniformly, and transferred to a dropping funnel. Heat the reaction kettle to 90℃, start dropping the aluminum sulfate solution containing sulfuric acid, complete dropping within 2 hours, and continue to react for 1 hour. Filter while hot, and wash the precipitate multiple times, and control the number of washing times as needed. Transfer the material to an oven, heat to 120℃, dry for 60 min, and then heat to 180℃ at a rate of 2℃ / min, keep for 60 min, and then heat to 320℃ at a rate of 1℃ / min, keep for 30 min, cool to room temperature, and discharge. The Fe ion content and pH value of diethyl aluminum phosphite are controlled by controlling the number of washing times and the content of sulfuric acid;

[0051] Preparation method of aluminum isopropyl phosphite, referring to the preparation process of diethyl aluminum phosphite, using 172 g of isopropyl sodium phosphite instead of 144 g of diethyl sodium phosphite.

[0052] The preparation method of the polyamide composite of the embodiment and the comparative example of the present application comprises the following steps:

[0053] The components are weighed by weight parts, 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 twin-screw extruder for melt mixing and extrusion granulation to obtain the high-CTI halogen-free flame-retardant polyamide composite. The screw rotation speed of the twin-screw extruder is 250-350 rpm, the length-diameter ratio is 40:1-48:1, and the barrel temperature is 200℃-280℃.

[0054] II. Performance test methods

[0055] (1) Flame retardant performance test: according to the relevant standards of UL94-2016, the sample is tested for flame retardant performance, and the sample thickness is 0.8 mm. Flame retardant performance is of great significance to electrical safety, and the UL94 flame retardant grade needs to reach V-0 to meet the application requirements.

[0056] (2) Compared with tracking index (CTI) test: according to IEC 60112-2020, the sample size is 100*100*3mm, and the instrument test range is 0-1000V.

[0057] Table 1 Example technical solutions and effects (unit: weight parts)

[0058]

[0059] Table 1 Example technical solutions and effects (unit: weight parts)

[0060]

[0061] Table 2 Comparative example technical solutions and effects (unit: weight parts)

[0062]

[0063] Comparative examples 1-12 are all single variables of example 4, comparative example 1 does not add melamine polyphosphate, and comparative example 2 adds excessive melamine polyphosphate. From example 4, comparative example 1 and comparative example 2, when the content of melamine is low, the carbon layer structure formed at high temperature is loose, the flame retardant efficiency is low, and in the discharge process, it cannot produce inert gas to extinguish the arc, resulting in low CTI of halogen-free flame-retardant polyamide composite; when the content of melamine is high, under the high temperature generated by arc discharge, the halogen-free flame-retardant polyamide composite is promoted to carbonize, which also leads to low CTI.

[0064] Comparative Example 3: PA66 with too low content of terminal amino group, Comparative Example 4: PA6 with too high viscosity, Comparative Example 5: PA66 with too low content of terminal amino group and PA6 with too high viscosity, Comparative Example 6: PA66 and PA6 with mass ratio more than 9:1, Comparative Example 7: PA66 and PA6 with mass ratio less than 1.5:1, From Example 4 and Comparative Examples 3-7, it can be seen that the content of terminal amino group of PA66 resin, the mass ratio of PA66 and PA6 and the viscosity of PA6 all have important influence on CTI of halogen-free flame-retardant polyamide composite. Since PA66 has better carbonization than PA6, proper introduction of low molecular weight PA6 resin into PA66 can cause amide exchange with PA66 during discharge process, thus destroying the structural regularity of PA66 and reducing its carbonization. PA66 can have good binding force with halogen-free flame retardant through high content of amino group, thus promoting dispersion of halogen-free flame retardant in the composite system. However, if the molecular weight of PA6 is too high (viscosity is high), the content of PA6 on the surface of halogen-free flame-retardant polyamide composite is low (mass ratio of PA66 and PA6 is more than 9:1), which cannot play a role in inhibiting carbonization. When the content of PA6 is too high (mass ratio of PA66 and PA6 is less than 1.5:1), it can cause erosion and damage of halogen-free flame-retardant polyamide, thus resulting in low CTI. In addition, high content of PA6 can also reduce the flame retardant property of halogen-free flame-retardant polyamide.

[0065] Comparative Example 8: too low content of hypophosphite, Comparative Example 9: too high content of hypophosphite, From Example 4 and Comparative Examples 8-9, it can be seen that the content of hypophosphite has important influence on CTI of halogen-free flame-retardant polyamide. Hypophosphite can promote degradation and carbonization of polyamide. When the content of hypophosphite is high, the catalytic degradation and carbonization is more obvious, thus resulting in low CTI of halogen-free flame-retardant polyamide composite. However, hypophosphite can also generate PO free radicals, which can quench electric arc and flame. Therefore, when the content of hypophosphite is low, it can also result in poor CTI and flame retardant property of halogen-free flame-retardant polyamide.

[0066] Comparative Example 10: too high content of iron element in hypophosphite, which can affect the promotion of degradation and carbonization of polyamide, thus resulting in low CTI, Comparative Example 12: pH value of hypophosphite is not in the range of 4-5, thus resulting in low CTI of the composite, Comparative Example 11: too high content of iron element in hypophosphite and pH value of hypophosphite is not in the range of 4-5, which can seriously affect CTI of halogen-free flame-retardant polyamide composite.

[0067] Based on the test data of vertical burning property and CTI value in Table 1 and Table 2, it can be seen that the polyamide composite prepared by Examples 1-25 can achieve high CTI value (more than 750 V) and keep flame retardant grade (V-0 grade) to meet the application requirements. Compared with Comparative Examples, it has obvious advantages and can effectively meet the high standard requirements of customers and market.

[0068] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A polyamide compound, characterized by, By weight parts, comprising the following components: The polyamide resin is a complex of PA66 and PA6, 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 end 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 of the end amino group content is as follows: 0.5g of polymer is taken, 45mL of phenol and 3mL of anhydrous methanol are added, and heated to reflux, after the sample is completely dissolved, cooled to room temperature, the end amino group content is titrated with a calibrated hydrochloric acid standard solution, and the titration is carried out with a potentiometric titrator; The viscosity number test method is as follows: the relative viscosity of 0.25g / dL of polyamide is measured in 98% concentrated sulfuric acid at 25±0.01℃, and an automatic viscometer is used for measurement; The melamine derivative is melamine polyphosphate; The hypophosphite is one or several of diethyl aluminum hypophosphite and isopropyl aluminum hypophosphite.

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

3. The polyamide compound according to claim 2, 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.

4. Process for the production of a polyamide compound according to any one of claims 1 to 3, characterized in that, Comprising the following steps: Each component is weighed by weight parts, the components are put into a mixer for mixing until uniform to obtain a premix, then the obtained premix is put into a screw extruder for melt mixing, and extruded and granulated to obtain the polyamide composite.

5. The preparation method according to claim 4, characterized in that, The screw speed of the screw extruder is 250rpm-350rpm, the length-diameter ratio is 40:1-48:1, and the barrel temperature is 200℃-280℃.

6. The polyamide composite according to any one of claims 1-3 is applied in the electronic, electrical and new energy industries.

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