Polyester composite and process for the production thereof

Abstract

The application belongs to the technical field of polymer compound, and discloses a polyester composite material and a production process thereof. The polyester composite material comprises a polyester matrix, a short-cut glass fiber reinforced filler and a gradient interface layer between the polyester matrix and the short-cut glass fiber reinforced filler. The gradient interface layer comprises a liquid crystal polyester layer and a dispersion layer containing a nano nucleating agent from inside to outside. The production process comprises filler gradient coating, melt blending and orientation-induced crystallization molding under the synergistic action of a shear field and an oscillation pressure field. Through the technical scheme, a high-orientation transcrystalline structure is formed in the interface region, and the mechanical properties, the heat distortion temperature and the long-term thermal and oxidative stability of the material are improved.

Description

Technical Field

[0001] This invention belongs to the field of polymer compound composition technology, and relates to a polyester composite material and its production process. Background Technology

[0002] Polyester engineering plastics, due to their excellent mechanical properties, processability, and cost advantages, have been widely used in fields requiring high comprehensive material performance, such as automotive parts, electronic and electrical housings, and industrial structural components. To meet the increasing demands for lightweighting and functionalization, the industry commonly uses inorganic fillers (such as chopped glass fiber and talc) to reinforce and modify the polyester matrix, aiming to improve its rigidity, dimensional stability, and heat distortion temperature while maintaining processing convenience. Under this technical approach, the interfacial bonding state between the filler and the matrix becomes a key factor determining the overall performance of the composite material, while the limitations of polyester's intrinsic thermal properties also constitute a bottleneck for its application under high-temperature conditions.

[0003] In existing technologies, to improve the interfacial compatibility between inorganic fillers and organic polyester matrices, silane or titanate coupling agents are typically used to pretreat the filler surface, aiming to enhance the interfacial adhesion between the two phases through chemical bridging. This method alleviates stress concentration caused by interfacial debonding to some extent and has a positive impact on the tensile strength and impact toughness of the composite material. Simultaneously, to improve the heat resistance of polyester, the industry has also explored introducing nucleating agents to promote crystallization and increase crystallinity, or introducing rigid segments through copolymerization modification to increase the glass transition temperature and heat distortion temperature. These strategies have demonstrated certain technical value in specific application scenarios, especially under medium- and low-temperature conditions and static loads, and can meet conventional engineering requirements.

[0004] While coupling agent treatment can improve interfacial wettability, the resulting interfacial layer is typically amorphous and limited in thickness, making it difficult to maintain stable stress transfer under high temperatures or dynamic loads. Furthermore, this interfacial layer lacks synergy with the polyester matrix in terms of chemical structure and crystallization behavior, failing to effectively guide the matrix to form an ordered crystal structure in the interfacial region. Correspondingly, while conventional nucleating agents can increase the overall crystallization rate, they struggle to achieve precise control of crystal orientation in the critical filler-matrix interface region. This results in the presence of predominantly random spherulites near the interface, whose melting point and modulus are significantly lower than the ideal crystal structure, leading to softening or cracking under thermo-mechanical coupling conditions. Summary of the Invention

[0005] To achieve the above-mentioned objectives, this invention provides a polyester composite material and its production process. The polyester composite material constructs a gradient coating layer composed of liquid crystal polyester and a nucleating agent on the surface of the reinforcing filler, and applies a synergistic external field effect of shear field and oscillating pressure field during the molding process to induce the polyester matrix to form a highly oriented transcrystalline structure in the interface region. This achieves chemical structure matching at the molecular scale, crystal orientation control at the mesoscale, and synergistic enhancement of mechanical and thermal properties at the macroscale.

[0006] The polyester composite material of the present invention comprises a polyester matrix, reinforcing fillers, and a gradient interface layer disposed between the reinforcing fillers and the polyester matrix; the gradient interface layer comprises a first coating layer and a second coating layer from the inside to the outside; the first coating layer is a liquid crystal polyester layer, the chemical main chain structure of which has a structural unit similarity of not less than 70% with that of the polyester matrix; the second coating layer is a nucleating agent dispersion layer, wherein nucleating agent particles with a particle size of 50 nm to 200 nm are uniformly dispersed; the reinforcing fillers are short-cut glass fibers with a length of 0.2 mm to 3.0 mm and a diameter of 10 μm to 20 μm; the polyester matrix is ​​one of polybutylene terephthalate, polyethylene terephthalate, or copolymers thereof, and its intrinsic viscosity is 0.8 dL / g to 1.2 dL / g.

[0007] The thickness of the liquid crystal polyester layer is 50 nm to 300 nm, and it is formed by coating the surface of chopped glass fibers with hydroxyl-terminated thermotropic liquid crystal polyester through solution deposition. The repeating units of the liquid crystal polyester include p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and ethylene terephthalate structural units, with a molar ratio of (40:30:30) to (60:20:20). The glass transition temperature of the liquid crystal polyester is not lower than 120 °C, and the clearing temperature is not lower than 280 °C. The nucleating agent is talc, sodium benzoate, phosphate nucleating agent or a compound thereof, wherein the phosphate nucleating agent is one of aluminum phosphite or zirconium phosphate. The mass fraction of the nucleating agent in the second coating layer is 15% to 40%. The thickness of the second coating layer is 20 nm to 100 nm.

[0008] The manufacturing process of this invention includes the following steps:

[0009] Step 1: Gradient Coating Treatment of the Reinforcing Filler. Short-cut glass fibers are placed in a fluidized bed reactor and suspended at a temperature of 80℃ to 120℃ under a nitrogen atmosphere with a fluidizing gas velocity of 0.5 m / s to 2.0 m / s. A liquid crystal polyester tetrahydrofuran solution with a concentration of 1.0 wt% to 5.0 wt% is sprayed onto the surface of the suspended fibers at a rate of 0.1 mL / min to 0.5 mL / min. After spraying, the fibers are dried at 100℃ for 30 minutes to form the first coating layer. Subsequently, an ethanol dispersion containing a nucleating agent (nucleating agent concentration of 2.0 wt% to 8.0 wt%) is sprayed onto the surface of the liquid crystal polyester-coated fibers at the same spraying rate. After spraying, the fibers are vacuum dried at 80℃ for 60 minutes to form the second coating layer, thus obtaining the gradient-coated filler.

[0010] Step 2: Melt blending of the composite material. Gradient-coated filler and polyester matrix are added to a twin-screw extruder at a mass ratio of (20:80) to (40:60); the twin-screw extruder has a screw length-to-diameter ratio of 40:1 and a screw speed of 200 rpm to 400 rpm; the set temperatures for each zone are as follows: feeding section 220℃, compression section 240℃, metering section 250℃, and die section 255℃; during melt blending, the material undergoes a shear rate of not less than 200 s in the metering section. -1 The strong shearing action causes the gradient coating layer to partially melt and initially fuse with the polyester matrix, but retains the orientation-inducing ability of the liquid crystal polyester.

[0011] Step 3: Orientation-Induced Crystallization Molding. The granules obtained in Step 2 are molded in an injection molding machine. The injection molding machine is equipped with an oscillating pressure control system, which applies sinusoidal oscillating pressure with a frequency of 1Hz to 10Hz and an amplitude of 5MPa to 20MPa during the holding pressure stage. At the same time, the mold runner is designed as a convergent-expanding structure, so that the melt generates at least [amount not specified] when passing through the fiber-rich area. The local shear rate; under the combined action of the shear field and the oscillating pressure field, the liquid crystal polyester in the gradient coating layer is highly oriented along the axial direction of the short-cut glass fiber, and its ordered structure serves as a crystal nucleus template, inducing the polyester matrix to form a transcrystalline layer with a thickness of 1μm to 5μm in its interface region; the crystal orientation degree of the transcrystalline layer is not less than 0.85, and its melting point is 8℃ to 15℃ higher than that of the spherulites in the matrix.

[0012] In a preferred embodiment of the present invention, the hydroxyl end-capping degree of the liquid crystal polyester is above 95%. During the melt blending process, the terminal hydroxyl groups and the terminal carboxyl groups of the polyester matrix undergo an ester exchange reaction to form a chemical bonding interface, thereby improving the interfacial bonding strength. The degree of ester exchange reaction is achieved by controlling the blending temperature and residence time, and the reaction conversion rate is controlled between 30% and 60% to avoid excessive crosslinking that would reduce the melt fluidity.

[0013] In another preferred embodiment of the present invention, the timing of the application of the oscillating pressure field is precisely synchronized with the melt cooling curve; specifically, the oscillating pressure is started when the melt temperature drops to 10°C to 20°C above the crystallization temperature Tc of the polyester matrix, and continues until the temperature drops to 15°C below Tc; Tc is the crystallization peak temperature of the polyester matrix measured by differential scanning calorimetry at a cooling rate of 10°C / min; through this timing control, it is ensured that the external field action occurs during the critical window period of crystal nucleation and early growth, maximizing the orientation induction efficiency.

[0014] Furthermore, in the gradient coating layer, the mass ratio of liquid crystal polyester to nucleating agent is (60:40) to (80:20); this ratio has been experimentally verified to achieve the best balance between interfacial chemical compatibility and crystallization induction ability; when the proportion of liquid crystal polyester is too low, the interfacial chemical matching is insufficient, resulting in a decrease in stress transfer efficiency; when the proportion of nucleating agent is too low, the transverse crystal nucleation density is insufficient, and a continuous high-orientation interfacial layer cannot be formed.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The production process of this invention solves the technical contradiction of the separation between interfacial compatibility and heat resistance improvement in the prior art through the synergistic mechanism of gradient coating and external field induction. The liquid crystal polyester in the gradient coating layer is not only highly matched with the polyester matrix in chemical structure, but also has molecular orientation ability in the molten state. During the molding process, the shear field causes the liquid crystal polyester to align along the fiber axis, while the oscillating pressure field promotes the regular stacking of polyester molecular chains on the surface of the liquid crystal template through periodic compression-relaxation, thereby realizing the directional growth of transcrystalline. The transcrystalline region has higher crystal perfection and melting point, effectively delaying the softening behavior of the interfacial region at high temperature.

[0017] 2. The polyester composite material of the present invention is suitable for manufacturing components that have stringent requirements for rigidity, dimensional stability and long-term thermo-oxidative stability, such as housings for electric drive systems of new energy vehicles, heat dissipation structural components for 5G communication base stations, high-precision industrial gears and high-temperature resistant connectors.

[0018] 3. This invention achieves precise control of the crystal structure of the interface region of polyester composite materials by constructing a gradient interface layer with matching chemical structure and combining the synergistic external field induction of shear field and oscillating pressure field. It fundamentally solves the dual bottlenecks of weak interface bonding and insufficient heat resistance in traditional technology, and provides a polyester composite material with high rigidity, high heat resistance and excellent long-term service stability and its industrially feasible production process. Detailed Implementation

[0019] This invention provides a polyester composite material and its production process. By constructing a gradient coating layer composed of liquid crystal polyester and nucleating agent on the surface of the reinforcing filler, and applying the synergistic external field effect of shear field and oscillating pressure field during the molding process, the polyester matrix is ​​induced to form a highly oriented transcrystalline structure in the interface region, thereby achieving chemical structure matching at the molecular scale, crystal orientation control at the mesoscale, and synergistic enhancement of mechanical and thermal properties at the macroscale.

[0020] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0021] Example 1: Polyester matrix: Polybutylene terephthalate, intrinsic viscosity 0.8 dL / g;

[0022] Liquid crystal polyester: the molar ratio of structural units is 40:30:30 (p-hydroxybenzoic acid: 6-hydroxy-2-naphthoic acid: polyethylene terephthalate), hydroxyl end-capping degree is 95%, glass transition temperature is 120℃, and clearing point temperature is 280℃;

[0023] Nucleating agent: Aluminum phosphite, 15% by mass in the second coating layer;

[0024] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 80:20;

[0025] Gradient coating process: fluidized bed temperature 80℃, fluidizing gas velocity 0.5m / s; liquid crystal polyester tetrahydrofuran solution concentration 1.0wt%, spray rate 0.1mL / min; nucleating agent ethanol dispersion concentration 2.0wt%, spray rate 0.1mL / min; drying conditions: drying at 100℃ for 30 minutes (first coating layer), vacuum drying at 80℃ for 60 minutes (second coating layer).

[0026] Melt blending: gradient coated filler to polyester matrix mass ratio 20:80; twin-screw extruder screw length-to-diameter ratio 40:1, screw speed 200 rpm; temperature zones: feeding section 220℃, compression section 240℃, metering section 250℃, die section 255℃; metering section shear rate...

[0027] Molding process: During the holding pressure stage of the injection molding machine, the oscillation pressure frequency is 1Hz and the amplitude is 5MPa; the mold runner is a convergent-expanding type, and the local shear rate of the melt is 500s. -1 Mold temperature 80℃, cooling rate 20℃ / min; interfacial transverse crystal layer thickness 1μm, crystal orientation degree 0.85.

[0028] Example 2: Polyester matrix: polyethylene terephthalate, intrinsic viscosity 1.0 dL / g;

[0029] Liquid crystal polyester: structural unit molar ratio is 50:25:25, hydroxyl end-capping degree is 96%, glass transition temperature is 125℃, and clearing temperature is 285℃;

[0030] Nucleating agent: Zirconium phosphate, 25% by mass in the second coating layer;

[0031] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 70:30;

[0032] Gradient coating process: fluidized bed temperature 90℃, fluidizing gas velocity 1.0m / s; liquid crystal polyester tetrahydrofuran solution concentration 2.0wt%, spray rate 0.2mL / min; nucleating agent ethanol dispersion concentration 4.0wt%, spray rate 0.2mL / min; drying conditions same as in Example 1;

[0033] Melt blending: gradient coated filler to polyester matrix mass ratio 30:70; twin-screw extruder screw speed 300 rpm; metering section shear rate The remaining parameters are the same as in Example 1;

[0034] Molding process: oscillation pressure frequency 5Hz, amplitude 10MPa; local shear rate of melt The mold temperature is 100℃, and the cooling rate is 30℃ / min; the thickness of the transverse crystal layer at the interface is 3μm, and the crystal orientation degree is 0.88.

[0035] Example 3: Polyester matrix: Polybutylene terephthalate-polyethylene terephthalate copolymer, intrinsic viscosity 1.2 dL / g;

[0036] Liquid crystal polyester: structural unit molar ratio is 60:20:20, hydroxyl end-capping degree is 97%, glass transition temperature is 130℃, and clearing temperature is 290℃;

[0037] Nucleating agent: Talc, 40% by mass in the second coating layer;

[0038] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 60:40;

[0039] Gradient coating process: fluidized bed temperature 120℃, fluidizing gas velocity 2.0m / s; liquid crystal polyester tetrahydrofuran solution concentration 5.0wt%, spray rate 0.5mL / min; nucleating agent ethanol dispersion concentration 8.0wt%, spray rate 0.5mL / min; drying conditions same as in Example 1;

[0040] Melt blending: gradient coated filler to polyester matrix mass ratio 40:60; twin-screw extruder screw speed 400 rpm; metering section shear rate The remaining parameters are the same as in Example 1;

[0041] Molding process: oscillation pressure frequency 10Hz, amplitude 20MPa; local shear rate of melt The mold temperature is 120℃, and the cooling rate is 50℃ / min; the thickness of the transverse crystal layer at the interface is 5μm, and the crystal orientation degree is 0.90.

[0042] Example 4: Polyester matrix: Polybutylene terephthalate, intrinsic viscosity 0.9 dL / g;

[0043] Liquid crystal polyester: structural unit molar ratio is 45:28:27, hydroxyl end-capping degree is 95%, glass transition temperature is 122℃, and clearing temperature is 282℃;

[0044] Nucleating agent: Sodium benzoate, 20% by mass in the second coating layer;

[0045] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 75:25;

[0046] Gradient coating process: fluidized bed temperature 100℃, fluidizing gas velocity 1.2m / s; liquid crystal polyester tetrahydrofuran solution concentration 3.0wt%, spray rate 0.3mL / min; nucleating agent ethanol dispersion concentration 3.0wt%, spray rate 0.3mL / min; drying conditions same as in Example 1;

[0047] Melt blending: gradient coated filler to polyester matrix mass ratio 25:75; twin-screw extruder screw speed 250 rpm; metering section shear rate The remaining parameters are the same as in Example 1;

[0048] Molding process: oscillation pressure frequency 3Hz, amplitude 8MPa; local shear rate of melt The mold temperature is 90℃, and the cooling rate is 25℃ / min; the thickness of the transverse crystal layer at the interface is 2μm, and the crystal orientation degree is 0.86.

[0049] Example 5: Polyester matrix: polyethylene terephthalate, intrinsic viscosity 1.1 dL / g;

[0050] Liquid crystal polyester: structural unit molar ratio is 55:22:23, hydroxyl end-capping degree is 96%, glass transition temperature is 128℃, and clearing temperature is 288℃;

[0051] Nucleating agent: aluminum phosphite-zirconium phosphate complex (mass ratio 1:1), nucleating agent mass fraction in the second coating layer is 30%;

[0052] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 65:35;

[0053] Gradient coating process: fluidized bed temperature 110℃, fluidizing gas velocity 1.5m / s; liquid crystal polyester tetrahydrofuran solution concentration 4.0wt%, spray rate 0.4mL / min; nucleating agent ethanol dispersion concentration 6.0wt%, spray rate 0.4mL / min; drying conditions same as in Example 1;

[0054] Melt blending: gradient coated filler to polyester matrix mass ratio 35:65; twin-screw extruder screw speed 350 rpm; metering section shear rate 280 s. -1 The remaining parameters are the same as in Example 1;

[0055] Molding process: oscillation pressure frequency 8Hz, amplitude 15MPa; local shear rate of melt The mold temperature is 110℃, and the cooling rate is 40℃ / min; the thickness of the transverse crystal layer at the interface is 4μm, and the crystal orientation degree is 0.89.

[0056] Example 6: Polyester matrix: Polybutylene terephthalate-polyethylene terephthalate copolymer, intrinsic viscosity 0.8 dL / g;

[0057] Liquid crystal polyester: structural unit molar ratio is 48:26:26, hydroxyl end-capping degree is 97%, glass transition temperature is 124℃, and clearing point temperature is 284℃;

[0058] Nucleating agent: Talc-sodium benzoate complex (mass ratio 2:1), nucleating agent mass fraction in the second coating layer is 35%;

[0059] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 62:38;

[0060] Gradient coating process: fluidized bed temperature 95℃, fluidizing gas velocity 1.8m / s; liquid crystal polyester tetrahydrofuran solution concentration 2.5wt%, spray rate 0.25mL / min; nucleating agent ethanol dispersion concentration 5.0wt%, spray rate 0.25mL / min; drying conditions same as in Example 1;

[0061] Melt blending: gradient coated filler to polyester matrix mass ratio 32:68; twin-screw extruder screw speed 320 rpm; metering section shear rate The remaining parameters are the same as in Example 1;

[0062] Molding process: oscillation pressure frequency 6Hz, amplitude 12MPa; local shear rate of melt The mold temperature is 105℃, and the cooling rate is 35℃ / min; the thickness of the transverse crystal layer at the interface is 3.5μm, and the crystal orientation degree is 0.87.

[0063] Example 7: Polyester matrix: Polybutylene terephthalate, intrinsic viscosity 1.2 dL / g;

[0064] Liquid crystal polyester: structural unit molar ratio is 52:24:24, hydroxyl end-capping degree is 98%, glass transition temperature is 126℃, and clearing temperature is 286℃;

[0065] Nucleating agent: Zirconium phosphate, with a mass fraction of 28% in the second coating layer;

[0066] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 72:28;

[0067] Gradient coating process: fluidized bed temperature 105℃, fluidizing gas velocity 1.6m / s; liquid crystal polyester tetrahydrofuran solution concentration 3.5wt%, spray rate 0.35mL / min; nucleating agent ethanol dispersion concentration 7.0wt%, spray rate 0.35mL / min; drying conditions same as in Example 1;

[0068] Melt blending: gradient coated filler to polyester matrix mass ratio 28:72; twin-screw extruder screw speed 280 rpm; metering section shear rate The remaining parameters are the same as in Example 1;

[0069] Molding process: oscillation pressure frequency 4Hz, amplitude 10MPa; local shear rate of melt The mold temperature is 95℃, and the cooling rate is 30℃ / min; the thickness of the transverse crystal layer at the interface is 2.5μm, and the crystal orientation degree is 0.88.

[0070] Example 8: Polyester matrix: polyethylene terephthalate, intrinsic viscosity 1.0 dL / g;

[0071] Liquid crystal polyester: structural unit molar ratio is 58:21:21, hydroxyl end-capping degree is 99%, glass transition temperature is 129℃, and clearing temperature is 290℃;

[0072] Nucleating agent: Aluminum phosphite, with a mass fraction of 18% in the second coating layer;

[0073] Gradient interface layer: liquid crystal polyester to nucleating agent mass ratio 78:22;

[0074] Gradient coating process: fluidized bed temperature 85℃, fluidizing gas velocity 0.8m / s; liquid crystal polyester tetrahydrofuran solution concentration 1.5wt%, spray rate 0.15mL / min; nucleating agent ethanol dispersion concentration 2.5wt%, spray rate 0.15mL / min; drying conditions same as in Example 1;

[0075] Melt blending: gradient coated filler to polyester matrix mass ratio 22:78; twin-screw extruder screw speed 220 rpm; metering section shear rate The remaining parameters are the same as in Example 1;

[0076] Molding process: oscillation pressure frequency 2Hz, amplitude 7MPa; local shear rate of melt The mold temperature is 85℃, and the cooling rate is 22℃ / min; the thickness of the transverse crystal layer at the interface is 1.5μm, and the crystal orientation degree is 0.86.

[0077] Comparative Example 1: Polyester matrix: Polybutylene terephthalate, intrinsic viscosity 0.8 dL / g (consistent with Example 1);

[0078] Reinforcing filler: Short-cut glass fiber (same as in Example 1), surface treated with silane coupling agent (KH550), without gradient interface layer;

[0079] Nucleating agent: Talc, which is directly mixed with the polyester matrix at an addition amount of 2% of the polyester matrix mass;

[0080] Melt blending: chopped glass fiber to polyester matrix mass ratio 20:80 (consistent with Example 1); twin-screw extruder parameters consistent with Example 1;

[0081] Molding process: No oscillation pressure on the injection molding machine, standard straight mold runner, and a local melt shear rate of 300 s. -1 The remaining molding parameters are the same as in Example 1.

[0082] Comparative Example 2: Polyester matrix, liquid crystal polyester parameters, reinforcing fillers: consistent with Example 1;

[0083] Interface treatment: Short-cut glass fibers are only coated with a liquid crystal polyester layer (first coating layer), without a nucleating agent dispersion layer (second coating layer); the coating process is the same as that of the first coating layer in Example 1;

[0084] Melt blending and molding process: Same as in Example 1.

[0085] Comparative Example 3: Polyester matrix, gradient interface layer parameters, reinforcing filler, gradient coating process, melt blending process: consistent with Example 1;

[0086] Molding process: No oscillation pressure on the injection molding machine, standard straight mold runner, and a local melt shear rate of 300 s. -1 The remaining molding parameters are the same as in Example 1.

[0087] Test method:

[0088] All samples were prepared into standard test strips according to the corresponding process, and the test methods were based on national standards or industry-standard methods to ensure data accuracy and comparability.

[0089] Heat distortion temperature (1.82MPa load): According to GB / T1634.2-2004, a heat distortion temperature measuring instrument was used, with a heating rate of 120℃ / h, and the temperature at which the sample began to produce the specified deformation was recorded.

[0090] Tensile strength: According to GB / T1040.2-2006, a universal testing machine was used, the specimen type was 1A, the tensile rate was 50 mm / min, and the tensile strength at the time of specimen fracture was recorded.

[0091] Notched impact strength: According to GB / T1043.1-2008, a simply supported beam impact testing machine was used, the specimen type was 1U type, the notch depth was 2mm, the impact absorbed energy was recorded and the impact strength was calculated.

[0092] Linear thermal expansion coefficient (23℃ to 150℃): According to GB / T1036-2008, the linear thermal expansion coefficient of the sample along the flow direction was determined using a thermal dilatometer at a heating rate of 5℃ / min.

[0093] Tensile strength retention rate after long-term heat aging at 150℃: According to GB / T7141-2008, the sample was placed in an oven at 150℃ for 1000 hours, and after being taken out and cooled to room temperature, the tensile strength was measured and the retention rate was calculated (tensile strength after aging / tensile strength before aging × 100%).

[0094] Dimensional change rate after damp heat aging at 150℃ and 85% relative humidity: According to GB / T2423.4-2008, the sample was placed in a damp heat chamber at 150℃ and 85% relative humidity for 1000 hours. After taking it out, the length dimension was measured, and the change rate was calculated as ((dimensional after aging - dimensional before aging) / dimensional before aging × 100%).

[0095] Storage modulus at 150℃ (1Hz frequency): The storage modulus of the sample was recorded using a dynamic thermomechanical analyzer, according to GB / T29911-2013, at a test frequency of 1Hz and a temperature of 150℃.

[0096] Performance test data comparison table:

[0097]

[0098] All embodiments exhibit higher heat distortion temperature, tensile strength, notched impact strength, and storage modulus than Comparative Example 1 (traditional silane coupling agent scheme), and their linear thermal expansion coefficient and performance degradation after aging are significantly lower than those of Comparative Example 1. For example, the heat distortion temperature of Example 1 is 30°C higher than that of Comparative Example 1, and the tensile strength retention rate after 150°C heat aging is 20 percentage points higher, indicating that the patented technology of gradient interface layer + shear-oscillation pressure synergistic molding fundamentally solves the problems of weak interface bonding and insufficient heat resistance in traditional schemes.

[0099] The key comparative example of the synergistic effect of the two components of the gradient interface layer, comparing Example 1 and Comparative Example 2 (liquid crystal polyester coating only), shows that when the nucleating agent dispersion layer is missing, the material's heat distortion temperature decreases by 15°C and tensile strength decreases by 15 MPa. This indicates that the nucleating agent can effectively induce the formation of transverse crystals at the interface and improve the crystallization perfection of the interface region. Meanwhile, the liquid crystal polyester layer achieves interfacial chemical bonding through chemical structure matching (similarity to the polyester matrix structural unit ≥70%). The two work together to ensure strong interfacial bonding and high heat resistance.

[0100] The shear-oscillation pressure synergistic external field is indispensable. Comparative Example 1 and Comparative Example 3 (without synergistic external field) show that without the external field, the heat distortion temperature decreases by 10°C and the storage modulus decreases by 300MPa. This is because the external field can promote the orientation of the liquid crystal polyester along the fiber axis, providing an ordered template for transcrystalline growth. At the same time, the oscillation pressure promotes the regular stacking of polyester molecular chains, improving the transcrystalline orientation degree (0.85 in Example 1 and only 0.72 in Comparative Example 3), thereby strengthening the interfacial mechanical and thermal properties.

[0101] Parameter optimization can further improve performance. Example 3 has the best performance (heat distortion temperature 240°C, tensile strength 200MPa) because it uses a high proportion of liquid crystal polyester (structural unit molar ratio 60:20:20), a high nucleating agent content (40%), and a high shear rate. The strong oscillation pressure (10Hz, 20MPa) indicates that within the patented parameter range, improving the matching degree of the liquid crystal polyester structure, the nucleating agent concentration, and the external field strength can further optimize the interfacial transverse crystal structure and maximize the material performance.

[0102] In summary, this patent achieves simultaneous improvement in the interfacial bonding and heat resistance of polyester composite materials through the synergistic technology of gradient interface layer construction and external field-induced crystallization. It is applicable to high-end fields such as the housing of electric drive system for new energy vehicles and structural components of 5G communication base stations, and has significant technical advantages and application value.

[0103] The above are merely preferred embodiments of the present invention and are 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 within the protection scope of the present invention.

Claims

1. A polyester composite material, characterized in that, It includes a polyester matrix, reinforcing fillers, and a gradient interface layer disposed between the reinforcing fillers and the polyester matrix; The gradient interface layer comprises a first covering layer and a second covering layer from the inside out; The first coating layer is a liquid crystal polyester layer, whose chemical main chain structure has a structural unit similarity of more than 70% with the polyester matrix. The hydroxyl end-capping degree of the liquid crystal polyester is more than 95%. It undergoes transesterification reaction with the terminal carboxyl groups of the polyester matrix during melt blending to form a chemical bonding interface. The conversion rate of the transesterification reaction is 30% to 60%. The second coating layer is a nucleating agent dispersion layer, wherein nucleating agent particles are uniformly dispersed therein; The reinforcing filler is chopped glass fiber; The preparation of the polyester composite material includes the following steps: Step 1: Short-cut glass fibers are placed in a fluidized bed reactor and suspended at 80°C to 120°C under a nitrogen atmosphere with a fluidizing gas velocity of 0.5 m / s to 2.0 m / s. A liquid crystal polyester tetrahydrofuran solution with a concentration of 1.0 wt% to 5.0 wt% is sprayed onto the fiber surface at a rate of 0.1 mL / min to 0.5 mL / min. After drying, a first coating layer is formed. Subsequently, an ethanol dispersion containing a nucleating agent is sprayed at the same spray rate, and after vacuum drying, a second coating layer is formed, resulting in a gradient-coated filler. Step 2: Add the gradient-coated filler and polyester matrix to a twin-screw extruder at a mass ratio of (20:80) to (40:60). The screw length-to-diameter ratio is 40:1, and the screw speed is 200 rpm to 400 rpm. The temperatures in each zone are as follows: feeding section 220℃, compression section 240℃, metering section 250℃, and die section 255℃. The material experiences a shear rate higher than 200 s in the metering section. -1 Shearing action; Step 3: The obtained granules are molded in an injection molding machine. During the holding pressure stage, the injection molding machine applies sinusoidal oscillating pressure with a frequency of 1Hz to 10Hz and an amplitude of 5MPa to 20MPa. At the same time, the mold runner has a convergent-expansion structure, so that the melt generates a flow rate of more than 500 seconds in the fiber-rich region. -1 The local shear rate induces the formation of a transverse crystal layer with a thickness of 1 μm to 5 μm and a crystal orientation degree higher than 0.85 in the interface region.

2. The polyester composite material according to claim 1, characterized in that, The polyester matrix is ​​one of polybutylene terephthalate, polyethylene terephthalate, or copolymers thereof, and its intrinsic viscosity is from 0.8 dL / g to 1.2 dL / g.

3. The polyester composite material according to claim 1, characterized in that, The liquid crystal polyester layer is formed by coating the surface of the chopped glass fiber with hydroxyl-terminated thermotropic liquid crystal polyester through solution deposition.

4. The polyester composite material according to claim 1, characterized in that, The liquid crystal polyester comprises p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and ethylene terephthalate structural units, with a molar ratio of (40:30:30) to (60:20:20).

5. The polyester composite material according to claim 1, characterized in that, The nucleating agent is talc, sodium benzoate, phosphate nucleating agent or a complex thereof, and the mass fraction of the nucleating agent in the second coating layer is 15% to 40%.

6. The polyester composite material according to claim 1, characterized in that, The glass transition temperature of the liquid crystal polyester is higher than 120°C, and the clearing temperature is higher than 280°C.

7. The polyester composite material according to claim 1, characterized in that, The mass ratio of liquid crystal polyester to nucleating agent in the gradient interface layer is (60:40) to (80:20).

8. The polyester composite material according to claim 5, characterized in that, The phosphate nucleating agent is either aluminum phosphite or zirconium phosphate.

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