Polyamide composite material as well as preparation method and application thereof

Abstract

The invention discloses a polyamide composite material which comprises the following components in parts by weight: 60-80 parts of polyamide resin; 20 to 40 parts of boron nitride coated carbon fiber; in the boron nitride coated carbon fiber, boron nitride forms a coating layer on the outer surface of the carbon fiber, the average thickness of the boron nitride layer ranges from 40 nm to 100 nm, and the average diameter of the carbon fiber ranges from 4 micrometers to 10 micrometers. The boron nitride coated carbon fiber is selected, so that the thermal conductivity of boron nitride can be effectively improved, and the friction coefficient can be obviously reduced.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polyamide composite material, its preparation method, and its application. Background Technology

[0002] Nylon (PA) thermoplastic engineering plastics, due to their inherently low thermal conductivity, largely limit their application in fields with high heat dissipation requirements. To improve the thermal conductivity of PA materials, the industry often uses the addition of fillers with high thermal conductivity. Carbon fiber (CF), due to its excellent axial thermal conductivity (thermal conductivity along the fiber axis can reach 100-400 W / (m·K)), is considered a potential thermally conductive reinforcement. However, because carbon fiber exhibits significant anisotropy in thermal conductivity (its radial thermal conductivity is typically only 1-5 W / (m·K)), and the PA matrix itself is a polymer with extremely low thermal conductivity (the thermal conductivity of pure PA is typically around 0.2-0.3 W / (m·K)), the overall improvement in the thermal conductivity of the composite material is severely limited by the low thermal conductivity of the PA matrix. Even at conventional high filler ratios, such as 30-50 wt% carbon fiber, the improvement in the thermal conductivity of PA / CF composites remains limited, making it difficult to meet the stringent requirements for efficient heat dissipation in many high-end applications.

[0003] In conventional melt processing such as injection molding and extrusion, carbon fibers inevitably undergo preferential orientation along the melt flow direction due to the shearing effect of the melt flow. This orientation behavior leads to a certain degree of improvement in the thermal conductivity of PA / CF composites along the fiber axis (i.e., the melt flow direction), for example, reaching 3-5 W / (m·K). However, in the direction perpendicular to the fiber axis (i.e., perpendicular to the melt flow direction, i.e., the Z-axis direction), the low radial thermal conductivity of the carbon fibers and the low thermal conductivity of the PA matrix are superimposed, resulting in a still very low thermal conductivity in this direction, typically only 0.5-1.0 W / (m·K), and even approaching the thermal conductivity level of pure PA matrix in some cases. This anisotropy of thermal conductivity caused by the molding process further exacerbates the application bottleneck of PA / CF composites in scenarios requiring three-dimensional uniform heat dissipation. Summary of the Invention

[0004] The purpose of this invention is to provide a polyamide composite material with good thermal conductivity and low coefficient of friction, as well as its preparation method and application.

[0005] This invention is achieved through the following technical solution: A polyamide composite material, by weight, comprises the following components: 60-80 parts of polyamide resin; 20-40 parts of boron nitride coated carbon fiber; In the boron nitride-coated carbon fiber, boron nitride forms a coating layer on the outer surface of the carbon fiber, the average thickness of the boron nitride layer is in the range of 40-100 nm, and the average diameter of the carbon fiber is in the range of 4-10 micrometers. The relative viscosity of the polyamide resin is 2.38-2.8.

[0006] In the polyamide composite material of the present invention, the content of polyamide resin can be any value or a range between 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 67 parts, 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, and 80 parts; the content of boron nitride-coated carbon fiber can be any value or a range between 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, and 40 parts; the average thickness of the boron nitride-coated carbon fiber can be 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, or 70 nm. The average diameter of the carbon fiber can be any value or a range between 4 micrometers, 5 micrometers, 6 micrometers, 7 micrometers, 8 micrometers, 90 micrometers, 95 micrometers, and 100 micrometers; the average diameter of the carbon fiber can be any value or a range between 4 micrometers, 5 micrometers, 6 micrometers, 7 micrometers, 8 micrometers, 9 micrometers, and 10 micrometers; the relative viscosity of the polyamide resin can be any value or a range between 2.38, 2.4, 2.45, 2.5, 2.55, 2.60, 2.65, 2.70, 2.75, and 2.80.

[0007] Preferably, in the boron nitride-coated carbon fiber, the average thickness of the boron nitride layer ranges from 60 to 80 micrometers.

[0008] The average thickness of the boron nitride layer was measured by scanning electron microscopy.

[0009] The boron nitride content of the boron-coated carbon fiber ranges from 1% to 3 wt%. It can be any value from 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, to 3.0 wt%, or a range between these values. The testing method is as follows: TGA testing at 750℃ in air for 1 hour. The principle is that at 750℃ in air, the carbon fiber will undergo a combustion reaction to produce carbon dioxide, and the remaining mass is the weight of the boron nitride.

[0010] The polyamide resin is selected from at least one of semi-aromatic polyamide resin and aliphatic polyamide resin, and the aliphatic polyamide resin may also be a polylactam resin; the semi-aromatic polyamide resin is selected from at least one of PA4T, PA6T, PA9T, PA10T, PA6I, PAMXD6, PA6I, PA66 / 6, PA6 / 66, PA6T / 6I, PA6T / 66; the aliphatic polyamide resin is selected from at least one of PA46, PA66, PA6, PA11, PA12, PA610, PA612, PA1010, PA1012, PA1212. PA66 and PA6 are preferred.

[0011] Preferably, the polyamide resin has a relative viscosity of 2.5-2.7.

[0012] The test method for the relative viscosity of polyamide resin is as follows: refer to ISO 307:2019.

[0013] The boron nitride mentioned can be hexagonal boron nitride, with a diameter ranging from 10 to 300 nm and a layer thickness ranging from 1 to 100 nm. Boron nitride has a multilayer stacked structure, with a single layer thickness between 1 and 15 nm. During the process of coating carbon fiber with boron nitride, the boron nitride layers will decompose.

[0014] Boron nitride-coated carbon fiber can be a commercially available product or it can be obtained by making it in-house. In-house preparation methods include: Step A: Immerse the carbon fiber in a nitric acid solution with a mass fraction of 25-35%, stir at 40-60℃ for 2-4 hours, remove and rinse repeatedly with deionized water until neutral, and then dry at 80-100℃ for 12-24 hours to obtain carbon fiber with surface oxidation treatment. Step B: Prepare a 0.1-0.3 mol / L tris(hydroxymethyl)aminomethane buffer solution. Adjust the pH to 8.5-8.8 with dilute hydrochloric acid, then add dopamine hydrochloride to a concentration of 1.5-2.5 g / L. Disperse the solution evenly by sonication. Place the carbon fiber and boron nitride separately in the above buffer solution, stir and react. After filtration, obtain activated carbon fiber and activated boron nitride. The mass ratio of carbon fiber to dopamine hydrochloride is (8-12):1, and the mass ratio of boron nitride to dopamine hydrochloride is (1-3):1.

[0015] Step C: Disperse the activated boron nitride in tris(hydroxymethyl)aminomethane buffer (pH 8.5-8.8), add a dispersant (which can be polyvinylpyrrolidone, concentration 0.1-1.0 g / L), stir evenly, add the activated carbon fiber, stir to react, control the coating thickness by controlling the ratio of boron nitride to carbon fiber, filter and dry to obtain boron nitride coated carbon fiber.

[0016] An additive of 0.5-1.5% may be added as needed; the additive is selected from at least one of antioxidants and lubricants.

[0017] The antioxidants are hindered phenolic antioxidants, phosphite antioxidants, and thioester antioxidants. The hindered phenolic antioxidant is selected from one or more of the following: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], (2,4,6-trioxo-1,3,5-triazine-1,3,5(2H,4H,6H)-triyl)trivinyltris[3-(3,5-di-tert-butyl-4-hydroxyphenyl)acrylate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, and 1,3,5-(3,5-di-tert-butyl-4-hydroxybenzyl)-triazine-2,4,6-(1H,3H,5H)-trione. The phosphite antioxidant is tris(2,4-di-tert-butylphenyl) phosphite and / or pentaerythritol di(2,4-di-tert-butylphenyl) phosphite. The thioester antioxidant is bis(octadecyl) thiodipropionate and / or dilauryl thiodipropionate.

[0018] The lubricant may be at least one of fluorosilicone polymer lubricants, stearate lubricants, fatty acid lubricants, and stearate ester lubricants; the stearate lubricant is selected from at least one of calcium stearate, magnesium stearate, and zinc stearate; the fatty acid lubricant is selected from at least one of fatty acids, fatty acid derivatives, and fatty acid esters; and the stearate ester lubricant is selected from pentaerythritol stearate.

[0019] The preparation method of the polyamide composite material of the present invention includes the following steps: polyamide resin and boron nitride-coated carbon fibers are mixed evenly according to a specified ratio, and then extruded and granulated using a twin-screw extruder to obtain the polyamide composite material. The temperature range of the screw barrel is 250-280℃, and the rotation speed range is 200-500 rpm.

[0020] The polyamide composite material of the present invention is used to prepare automotive functional parts, aerospace parts, especially transmission and sliding parts.

[0021] The present invention has the following beneficial effects: First, this invention, by coating carbon fibers with boron nitride, can construct a continuous and uniform boron nitride coating layer on the surface of the carbon fibers. This coating layer can effectively bridge the radial heat transfer paths of adjacent carbon fibers, significantly improving the radial thermal conductivity of the carbon fibers, and in particular breaking through the thermal resistance bottleneck caused by the low radial (Z-axis) thermal conductivity of traditional carbon fibers.

[0022] Secondly, the present invention uses a polyamide resin with a specific relative viscosity to improve the dispersion of boron nitride-coated carbon fibers, thereby improving thermal conductivity.

[0023] Third, the present invention also has the advantage of a low coefficient of friction, which can reduce friction loss, extend service life, and also reduce noise and vibration. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0025] The raw materials for this invention are sourced as follows: PA66-A: Relative viscosity 2.4, PA66U3600NC01SS, purchased from Invista; PA66-B: Relative viscosity is 2.7, PA66EP-158, purchased from Zhejiang Huafeng; PA66-C: Relative viscosity 2.75, PA66 U4800 NC01 SS, purchased from Invista; PA66-D: Relative viscosity 2.2, PA66EP-122, purchased from Zhejiang Huafeng; PA66-E: Relative viscosity 3.15, PA66 T31, purchased from Zhejiang Huafeng; PA6-A: Relative viscosity is 2.45, PA6 M2400, purchased from Xinhui Meida; PA6-B: Relative viscosity is 2.5, PA6 HYF2500A, purchased from Haiyang, Jiangsu; PA6-C: Relative viscosity is 2.68, PA6 BE3270, purchased from Jiangsu Hongsheng; PA6-D: Relative viscosity 2.75, HYG-2700E, purchased from Haiyang Technology; PA612: Relative viscosity is 2.38, PA612 A120, purchased from Shanghai Yinggu; PA MXD6: Relative viscosity 2.5, PA MXD6, purchased from Shanghai Yinggu; PA6I / 6T: Relative viscosity 2.6, TZ326, purchased from Shandong Xianglong; Boron nitride: Hexagonal boron nitride, with an average diameter of 150nm and a layer thickness of 10-20nm, grade PN02, purchased from Zibo Jingyi Ceramics Technology Co., Ltd.; Carbon fiber: SYT45S, with an average diameter of 7μm, purchased from Zhongfu Shenying; Modified carbon fiber-1: Boron nitride coating thickness is 40nm, self-made; Modified carbon fiber-2: Boron nitride coating thickness is 60nm, self-made; Modified carbon fiber-3: Boron nitride coating thickness of 80nm, self-made; Modified carbon fiber-4: Boron nitride coating thickness of 100nm, self-made; Modified carbon fiber-5: Boron nitride coating thickness of 20nm, self-made; Modified carbon fiber-6: Boron nitride coating thickness of 120nm, self-made; The self-made method is as follows: Step A, immerse carbon fiber in a 31% nitric acid solution and stir at 50°C for 2.5 hours. After removal, rinse repeatedly with deionized water until neutral, and then dry at 90°C for 15 hours to obtain carbon fiber with surface oxidation treatment; Step B, prepare a 0.15 mol / L tris(hydroxymethyl)aminomethane buffer solution, adjust the pH to 8.5 with dilute hydrochloric acid, add dopamine hydrochloride to a concentration of 2.0 g / L, and ultrasonically disperse evenly for later use. Place carbon fiber and boron nitride separately in the above buffer solution, stir to react, and filter to obtain activated carbon fiber and activated boron nitride; wherein, the mass ratio of carbon fiber to dopamine hydrochloride is 10:1, and the mass ratio of boron nitride to dopamine hydrochloride is 2:1. Step C: Disperse the activated boron nitride in tris(hydroxymethyl)aminomethane buffer (pH 8.5-8.8), add the dispersant polyvinylpyrrolidone (concentration 0.4 g / L), stir evenly, add the activated carbon fiber, stir to react, control the coating thickness by controlling the ratio of boron nitride to carbon fiber, filter and dry to obtain boron nitride coated carbon fiber.

[0026] Antioxidant: A compound of antioxidant 1098 and antioxidant 608 in a mass ratio of 1:2, commercially available; Lubricant: Pentaerythritol stearate, commercially available; Preparation method of polyamide composite materials in Examples 1-4 and Comparative Examples: Polyamide resin and boron nitride-coated carbon fibers were mixed evenly according to the specified ratio, and then extruded and granulated using a twin-screw extruder to obtain the polyamide composite material. The barrel temperature range was 250-280℃, and the rotation speed range was 350 rpm.

[0027] Comparative Example 5: Preparation method of polyamide composite material: Polyamide resin, boron nitride, and carbon fiber were mixed evenly according to the formula, and then extruded and granulated using a twin-screw extruder to obtain the polyamide composite material. The barrel temperature range was 250-280℃, and the rotation speed range was 350 rpm.

[0028] Test methods: (1) Thermal conductivity: The PA / carbon fiber composite materials prepared in each embodiment and comparative example were injection molded into square plates of 100mm*100mm*2mm. The thermal conductivity of the solid material in the X and Z directions was determined by the flash method according to GB / T22588-2008.

[0029] (2) Coefficient of friction: The injection molded square plate is 45mm*45mm*3mm. The test is carried out according to JIS-K7218:2013. The grinding material is S45C carbon steel, the load is 20N, the rotation speed is 640rpm, and the time is 2h.

[0030] Table 1: Component content and test results of polyamide composites in Examples 1-8 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 PA66-A 60 70 80 70 70 70 PA66-B 70 PA66-C 70 Modified carbon fiber-1 40 30 20 30 30 Modified carbon fiber-2 30 Modified carbon fiber-3 30 Modified carbon fiber-4 30 antioxidants 0.3 0.3 lubricant 0.2 Thermal conductivity in the X direction (W / (m·K)) 8.74 5.27 4.38 5.43 5.35 5.89 6.03 5.77 Thermal conductivity in the Z direction (W / (m·K)) 2.47 2.03 1.61 2.19 2.04 2.38 2.53 2.16 coefficient of friction 0.15 0.19 0.24 0.2 0.22 0.21 0.22 0.22 As can be seen from Examples 2 / 4 / 5, the polyamide resin of Example 4 with the preferred relative viscosity has a better thermal conductivity, especially the thermal conductivity in the Z direction is significantly improved.

[0031] As can be seen from Examples 2 / 6 / 7 / 8, modified carbon fibers with a boron nitride coating thickness of 60-80 nm have better thermal conductivity, especially when the boron nitride coating thickness is 80 nm, the thermal conductivity in the Z direction is significantly higher.

[0032] Table 2: Component content and test results of polyamide composites in Examples 9-15 Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 PA6-A 70 PA6-B 70 PA6-C 70 PA6-D 70 PA612 70 PA MXD6 70 PA6I / 6T 70 Modified carbon fiber-1 30 30 30 30 30 30 30 antioxidants 0.3 0.3 0.3 0.3 0.3 0.3 0.3 lubricant 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Thermal conductivity in the X direction (W / (m·K)) 5.1 5.85 5.77 5.52 5.34 4.77 4.52 Thermal conductivity in the Z direction (W / (m·K)) 1.90 2.05 1.99 1.78 2.00 1.87 1.82 coefficient of friction 0.22 0.2 0.21 0.22 0.21 0.2 0.22 As can be seen from Examples 9-12, the examples of PA6 with preferred relative viscosity have better thermal conductivity.

[0033] Table 3: Component content and test results of comparative polyamide composite materials Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 PA66-A 70 70 70 PA66-D 70 PA66-E 70 Modified carbon fiber-1 30 30 Modified carbon fiber-5 30 Modified carbon fiber-6 30 carbon fiber 29.4 Boron nitride 0.6 Thermal conductivity in the X direction (W / (m·K)) 3.55 3.36 3.05 3.83 3.78 Thermal conductivity in the Z direction (W / (m·K)) 1.14 0.87 0.93 0.87 1.03 coefficient of friction 0.27 0.33 0.26 0.31 0.28 As shown in Comparative Example 1, when the relative viscosity of polyamide is too low, the polyamide melt has a weak ability to disperse fillers, which causes the fillers to easily agglomerate into clumps due to van der Waals forces or electrostatic forces during the flow process, thus hindering heat conduction.

[0034] As shown in Comparative Example 2, when the relative viscosity of polyamide is too high, it is easy to damage the boron nitride layer in the modified carbon fiber during melt extrusion, resulting in a decrease in thermal conductivity and an increase in the coefficient of friction.

[0035] As can be seen from Comparative Example 3, when the boron nitride layer is too thin, the thermal conductivity is low and the friction coefficient is high.

[0036] As shown in Comparative Example 4, when the boron nitride layer is too thick, it is difficult to bond tightly with the carbon fiber surface, and microscopic voids are easily formed at the interface. The boron nitride layer itself is relatively brittle, and with increased thickness, cracks are easily generated during subsequent processing due to the mismatch in the thermal expansion coefficients of boron nitride and carbon fiber. The air within the cracks further blocks the heat conduction path. The interfacial thermal resistance will increase significantly, resulting in a decrease in thermal conductivity.

[0037] As shown in Comparative Example 5, directly using boron nitride and carbon fiber blends and extrusions cannot effectively construct a thermally conductive network, resulting in low thermal conductivity and poor friction coefficient.

Claims

1. A polyamide composite, characterized in that, By weight parts, comprising the following components: Polyamide resin 60-80 parts; Boron nitride coated carbon fiber 20-40 parts; In the boron nitride coated carbon fiber, boron nitride forms a coating layer on the outer surface of carbon fiber, the average thickness of boron nitride layer is 40-100 nm, and the average diameter of carbon fiber is 4-10 microns; The relative viscosity of the polyamide resin is 2.38-2.

8.

2. The polyamide composite according to claim 1, characterized in that, In the boron nitride coated carbon fiber, the average thickness of the boron nitride layer is 60-80 nm.

3. The polyamide composite of claim 1, wherein, The boron nitride accounts for 1-3wt% of the total weight percentage based on the weight percentage of boron nitride coated carbon fiber.

4. The polyamide composite of claim 1, wherein, The polyamide resin is selected from at least one of semi-aromatic polyamide resin, aliphatic polyamide resin.

5. The polyamide composite of claim 1, wherein, The relative viscosity of the polyamide resin is 2.5-2.

7.

6. The polyamide composite of claim 1, wherein, By weight parts, further comprising 0.5-1.5 of auxiliary agent; the auxiliary agent is selected from at least one of antioxidant, lubricant.

7. Process for the production of a polyamide composite material according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: according to the proportion, mixing polyamide resin and boron nitride coated carbon fiber uniformly, extruding and granulating through double screw extruder to obtain polyamide composite material.

8. Use of a polyamide composite according to any one of claims 1 to 6, characterized in that For preparing functional parts for vehicles, aerospace parts. For preparing functional parts for vehicles, aerospace parts.