Low-warpage PA66 material and preparation method thereof

Abstract

The invention provides a low-warpage PA66 material and a preparation method thereof, and the preparation method comprises the following steps: mixing PA66 resin, modified mica, short carbon fiber, oxidized polyethlene wax and a titanate coupling agent, discharging and sieving to obtain a uniform premix; extruding and granulating through double screws; performing injection molding; and carrying out hot-bath shaping to obtain the product. According to the invention, by adopting a scale-fiber composite reinforcing system, modified mica sheets (transverse shrinkage inhibition) and short carbon fibers (longitudinal reinforcement) are compounded according to a specific proportion to form a cross lock catch structure, and bidirectional shrinkage stress is counteracted, so that the warping degree is reduced; the gradient microporous buffer layer is introduced, a 50-200 [mu] m closed pore structure is formed on the surface layer through a foaming agent ethanol solution in the injection molding stage, and internal stress is absorbed through elastic deformation of micropores, so that the residual stress is reduced, the impact strength is improved, and the brittleness problem of a traditional low-warping material is avoided.

Description

Technical Field This invention relates to the field of functional plastics, specifically to a low-warpage PA66 material and its preparation method. Background Technology Polyamide 66 (PA66), as an important engineering plastic, is widely used in the automotive, electronics, and other fields due to its excellent mechanical properties, heat resistance, and chemical stability. However, PA66 material exhibits significant warpage during molding, primarily due to its high crystallinity and anisotropic shrinkage characteristics. During injection molding, the shrinkage rate of PA66 melt in the flow direction can differ from that perpendicular to the flow direction by 1.5-2.5%, leading to severe dimensional deformation in the finished product and affecting assembly accuracy and performance. To reduce the warpage of PA66, the industry mainly adopts the following methods: (1) Fiber reinforcement technology: Usually about 30% glass fiber is added. Although it can improve rigidity, it will lead to more severe anisotropic shrinkage. The orientation of the fiber in the flow direction will increase the transverse shrinkage rate by 50-80%. Floating fibers appear on the surface of the product, affecting the appearance quality; (2) Mineral filler modification: Talc, mica and other sheet fillers can partially improve warpage, but when the amount added exceeds 15%, it will lead to a 40-50% decrease in impact strength. Uneven dispersion of fillers can easily cause stress concentration; (3) Blending modification: Blending with other polymers (such as PPO, ABS) can reduce crystallinity, but it often sacrifices the heat resistance and strength of the material. Compatibility problems lead to interface defects. In recent years, researchers have attempted to improve the warpage problem of PA66 through various approaches, but these methods generally suffer from issues such as complex processes, high costs, or performance sacrifices, making it difficult to meet the demands of industrial production. Therefore, developing a PA66 modification technology that combines low warpage, high performance, low cost, and good processability has become a key issue that urgently needs to be addressed in the field of engineering plastics. Summary of the Invention

[0001] The technical problem to be solved: This invention employs a flake-fiber composite reinforcement system, combining modified mica flakes (for transverse shrinkage suppression) with chopped carbon fibers (for longitudinal reinforcement) in a specific ratio to form a "cross-locking" structure, which counteracts bidirectional shrinkage stress and thus reduces warpage. By introducing a gradient microporous buffer layer, a 50-200μm closed-cell structure is formed on the surface during the injection molding stage using a foaming agent ethanol solution. The microporous elastic deformation absorbs internal stress, thereby reducing residual stress, improving impact strength, and avoiding the brittleness problem of traditional low-warpage materials.

[0002] Technical solution: A low-warpage PA66 material, comprising the following components by weight: 100 parts PA66 resin, 8-12 parts modified mica, 2-5 parts chopped carbon fiber, 0.8-1 parts oxidized polyethylene wax, 0.2 parts titanate coupling agent, and 0.5-1 parts foaming agent ethanol solution; The modified mica is prepared as follows: Step 1: Mix 20 parts of mica flakes with 6 parts of hexadecyltrimethylammonium bromide, add 400 parts of water, stir at 80°C for 4 hours, and centrifuge to obtain exfoliated mica; Step 2: Disperse the exfoliated mica in an ethanol / water mixture (volume ratio 3:1), add 2 parts of tetraethyl orthosilicate and ammonia water with pH=9.5, and react at 60℃ for 6 hours to generate nano-SiO2 protrusions on the surface of the mica sheets, thus obtaining nano-coral-like mica. Step 3: The modified mica was obtained by treating it with γ-aminopropyltriethoxysilane and drying it under vacuum at 120°C for 2 hours. Furthermore, the length of the chopped carbon fiber is 0.2-1 mm. Furthermore, in step 1, the mica flakes have a particle size of 10-20 μm. Furthermore, the treatment with γ-aminopropyltriethoxysilane in step 3 is specifically as follows: γ-aminopropyltriethoxysilane is slowly added to an ethanol / water (95:5) solution, acetic acid is added dropwise to adjust the pH to 4.5, the mixture is magnetically stirred for 30 min, and allowed to stand for 1 h to obtain a hydrolysate. Nano-coral mica is mixed with the hydrolysate at a mass ratio of 1:10, and the mixture is reacted at 75°C and 300 rpm for 4 h. After centrifugation, the mixture is washed with ethanol. The above-mentioned method for preparing a low-warpage PA66 material includes the following steps: (1) Add PA66 resin to a high-speed mixer and mix at room temperature for 1-2 minutes. Add modified mica and short-cut carbon fibers preheated to 80°C and mix for 3-5 minutes. Add oxidized polyethylene wax and titanate coupling agent and mix for 1 minute. Sieve the discharged material through a sieve (80 mesh) to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion. Premixed material is added to the main feed port, the speed is 300-400 rpm, the foaming agent ethanol solution is injected laterally in zone 4, the vacuum is turned on to exhaust (-0.08 MPa), and the pellets are cut by water cooling. (3) Injection molding: Three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: slow speed 30mm / s; after mold opening, the product is removed; (4) Hot water bath shaping: Set the constant temperature water bath to 83-86℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Furthermore, the extruder parameters in step (2) are: screw diameter of 50mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃. Furthermore, the preparation method of the foaming agent ethanol solution in step (2) is as follows: azodicarbonamide and citric acid are mixed at a mass ratio of 20:1, anhydrous ethanol is slowly added, the solid content is controlled at 20-25%, and the mixture is stirred in a water bath at 40°C for 30 minutes until completely dissolved. Undissolved particles are removed with a 5μm filter screen and the mixture is sealed and stored away from light. Furthermore, the injection molding parameters in step (3) are set as follows: melt temperature is 265℃, injection pressure is 75-80MPa, and holding pressure is 65MPa. Beneficial effects: 1. This invention employs a flake-fiber composite reinforcement system, which combines modified mica flakes (for transverse shrinkage suppression) with chopped carbon fibers (for longitudinal reinforcement) in a specific ratio to form a "cross-locking" structure, thereby offsetting bidirectional shrinkage stress and reducing warpage. 2. This invention introduces a gradient microporous buffer layer, which forms a 50-200μm closed-cell structure on the surface during the injection molding stage using a foaming agent ethanol solution. The microporous elastic deformation absorbs internal stress, thereby reducing residual stress, improving impact strength, and avoiding the brittleness problem of traditional low warpage materials. 3. This invention treats mica sheets with KH-550 silane coupling agent to construct nanoscale SiO2 protrusions and amine active sites on their surface, thereby improving the interfacial shear strength of mica-PA66, reducing material density, and achieving lightweighting. 4. This invention uses a three-stage injection speed control and an injection curve of "slow-fast-slow" (20-50-30mm / s) to regulate the fiber orientation distribution, thereby reducing the range of dimensional fluctuations in injection molded parts. 5. This invention utilizes a hot water bath post-treatment process to allow the product to relax without constraint in an 85°C hot water bath, thereby eliminating processing freeze stress, reducing secondary shrinkage rate, and improving long-term dimensional stability. Detailed Implementation Example 1 The preparation method of modified mica is as follows: Step 1: Mix 20g of mica flakes with a particle size of 10-20μm with 6g of cetyltrimethylammonium bromide, add 400g of water, stir at 80℃ for 4h, and centrifuge to obtain exfoliated mica; Step 2: Disperse the exfoliated mica in 40g of ethanol / water mixture (volume ratio 3:1), add 2g of tetraethyl orthosilicate and ammonia water with pH=9.5, react at 60℃ for 6h, and generate nano-SiO2 protrusions on the surface of the mica sheets to obtain nano-coral-like mica. Step 3: Slowly add 0.4g of γ-aminopropyltriethoxysilane to 10g of ethanol / water (95:5) solution, adjust the pH to 4.5 by adding acetic acid dropwise, stir magnetically for 30min, let stand for 1h to obtain hydrolysate, mix nano-coral mica with hydrolysate at a mass ratio of 1:10, react at 75℃ and 300rpm for 4h, centrifuge, wash with ethanol, and vacuum dry at 120℃ for 2h to obtain modified mica. The specific surface area of ​​the modified mica was determined to be 37-50 m². 2 / g, with a thermal expansion coefficient of 6.2×10 -6 / ℃. Example 2 The preparation method of the foaming agent ethanol solution is as follows: mix azodicarbonamide and citric acid at a mass ratio of 20:1, slowly add anhydrous ethanol, control the solid content at 23%, stir in a water bath at 40℃ for 30 minutes until completely dissolved, remove undissolved particles with a 5μm filter, and store in a sealed container away from light. Example 3 A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 8 parts of modified mica preheated to 80°C and 4 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Example 4 A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of modified mica preheated to 80°C and 4 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Example 5 A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 12 parts of modified mica preheated to 80°C and 4 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Example 6 A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of modified mica preheated to 80°C and 2 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Example 7 A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of modified mica preheated to 80°C and 5 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Example 8 A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of modified mica preheated to 80°C and 4 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.5 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Example 9 A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of modified mica preheated to 80°C and 4 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 1 part of foaming agent ethanol solution is injected laterally in zone 4, vacuum exhaust is turned on (-0.08 MPa), and water cooling is used for pelleting; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Comparative Example 1 The difference between this embodiment and Embodiment 4 is that short-cut carbon fibers are not added. Specifically: A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of modified mica preheated to 80°C and mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent and mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Comparative Example 2 The difference between this embodiment and Embodiment 4 is that unmodified mica is used. Specifically: A method for preparing a low-warpage PA66 material includes the following steps: (1) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of mica preheated to 80°C and 4 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (2) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (3) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, and three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; second stage filling 60%: high speed 50mm / s; third stage filling 100%: deceleration 30mm / s; after mold opening, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Comparative Example 3 The difference between this embodiment and Embodiment 4 is that a consistent injection rate is used. Specifically: A method for preparing a low-warpage PA66 material includes the following steps: (4) Add 100 parts of PA66 resin to a high-speed mixer and mix at room temperature for 2 minutes. Add 10 parts of modified mica preheated to 80°C and 4 parts of short-cut carbon fibers with a length of 0.2-1 mm. Mix for 4 minutes. Add 1 part of oxidized polyethylene wax and 0.2 parts of titanate coupling agent. Mix for 1 minute. Discharge the material through an 80-mesh sieve to obtain a uniform premix. (5) Granulation is carried out by twin-screw extrusion with a screw diameter of 50 mm, L / D = 40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃; premixed material is added to the main feed port, the speed is 300 rpm, 0.8 parts of foaming agent ethanol solution are injected laterally in zone 4, vacuum exhaust (-0.08 MPa) is turned on, and water cooling pelleting is performed; (6) Injection molding: The injection parameters are set as follows: melt temperature is 265℃, injection pressure is 80MPa, holding pressure is 65MPa, injection speed is 30mm / s; after the mold is opened, the product is taken out. (4) Hot water bath shaping: Set the constant temperature water bath to 85℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product. Warpage was measured according to ISO 527 (200×200mm plate); Tensile strength was determined according to GB / T 1040.2-2006; The flexural modulus was determined according to GB / T 9341-2008; Impact strength was determined according to GB / T 1843-2008; Density was determined according to GB / T 1843-2008; The heat distortion temperature was determined according to GB / T 1634.2-2004; The surface roughness Ra was measured according to GB / T 3505-2009, and the results are shown in Table 1: Table 1

Claims

1. A low-warpage PA66 material, characterized in that, By weight, it includes the following components: 100 parts PA66 resin, 8-12 parts modified mica, 2-5 parts chopped carbon fiber, 0.8-1 parts oxidized polyethylene wax, 0.2 parts titanate coupling agent, and 0.5-1 parts foaming agent ethanol solution; The modified mica is prepared as follows: Step 1: Mix 20 parts of mica flakes with 6 parts of hexadecyltrimethylammonium bromide, add 400 parts of water, stir at 80°C for 4 hours, and centrifuge to obtain exfoliated mica; Step 2: Disperse the exfoliated mica in an ethanol / water mixture, add 2 parts of tetraethyl orthosilicate and ammonia water with pH=9.5, and react at 60℃ for 6 hours to generate nano-SiO2 protrusions on the surface of the mica sheets, thus obtaining nano-coral-like mica. Step 3: The modified mica was obtained by treating it with γ-aminopropyltriethoxysilane and drying it under vacuum at 120°C for 2 hours.

2. The low-warpage PA66 material according to claim 1, characterized in that, The length of the chopped carbon fiber is 0.2-1 mm.

3. The low-warpage PA66 material according to claim 1, characterized in that, In step 1, the mica flakes have a particle size of 10-20 μm.

4. The low-warpage PA66 material according to claim 1, characterized in that, The treatment with γ-aminopropyltriethoxysilane in step 3 is as follows: γ-aminopropyltriethoxysilane is slowly added to an ethanol / water solution, acetic acid is added dropwise to adjust the pH to 4.5, the mixture is magnetically stirred for 30 min, and allowed to stand for 1 h to obtain a hydrolysate. Nano-coral mica is mixed with the hydrolysate at a mass ratio of 1:10, and the mixture is reacted at 75°C and 300 rpm for 4 h. The mixture is then centrifuged and washed with ethanol.

5. A method for preparing a low-warpage PA66 material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Add PA66 resin to a high-speed mixer and mix at room temperature for 1-2 minutes. Add modified mica and short-cut carbon fibers preheated to 80°C and mix for 3-5 minutes. Add oxidized polyethylene wax and titanate coupling agent and mix for 1 minute. Discharge and sieve to obtain a uniform premix. (2) Granulation is carried out by twin screw extrusion. Premixed material is added to the main feed port, the speed is 300-400 rpm, foaming agent ethanol solution is injected laterally in zone 4, vacuum exhaust is turned on, and water cooling is used for pelleting. (3) Injection molding: Three-stage injection speed is adopted: first stage filling 30%: low speed 20mm / s; Second stage filling 60%: high speed 50mm / s; Third stage filling 100%: deceleration 30mm / s; Remove the product after mold opening; (4) Hot water bath shaping: Set the constant temperature water bath to 83-86℃, immerse the product completely and treat for 30 minutes; Natural aging: Place it flat in an environment of 23℃ and 50%RH and let it stand for 24 hours to obtain the product.

6. The method for preparing a low-warpage PA66 material according to claim 5, characterized in that, The extruder parameters in step (2) are: screw diameter 50mm, L / D=40, temperature zones: zone 1 temperature 240℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 265℃, and die head temperature 250℃.

7. The method for preparing a low-warpage PA66 material according to claim 5, characterized in that, The preparation method of the foaming agent ethanol solution in step (2) is as follows: Azodicarbonamide and citric acid are mixed at a mass ratio of 20:1, anhydrous ethanol is slowly added, the solid content is controlled at 20-25%, and the mixture is stirred in a water bath at 40°C for 30 minutes until completely dissolved. Undissolved particles are removed with a 5μm filter screen and stored in a sealed container away from light.

8. The method for preparing a low-warpage PA66 material according to claim 5, characterized in that, In step (3), the injection molding parameters are set as follows: melt temperature is 265℃, injection pressure is 75-80MPa, and holding pressure is 65MPa.

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