Low-warpage glass fiber reinforced mobile phone rear cover material and preparation method thereof

Abstract

The invention relates to the technical field of polyester materials, in particular to a low-warping glass fiber reinforced mobile phone rear cover material and a preparation method thereof. The method comprises the following steps: melting and mixing PBT and PET resins with an epoxy functional polymer chain extender, sequentially adding a carboxylated trimesoyl amide nucleating agent, bifunctional grafted dopamine nanoparticles, a core-shell structure toughening agent and glass fibers in stages, extruding, cooling and pelletizing to obtain the PBT / PET composite material. According to the material, buckling deformation caused by fiber orientation and crystallization shrinkage is effectively reduced, meanwhile, appearance whitening is improved, the coating adhesive force and impact resistance reliability are improved, and the material is suitable for thin-wall products such as 5G mobile phone rear covers.

Description

Technical Field

[0001] This invention relates to the field of polyester materials technology, and in particular to a low-warpage glass fiber reinforced mobile phone back cover material and its preparation method. Background Technology

[0002] With the increasing demands on signal transmission from 5G communication technology, metal mobile phone back covers are gradually being replaced by polymer materials due to electromagnetic shielding effects. Glass fiber reinforced polyester has become the mainstream choice due to its high rigidity, heat resistance, and cost advantages, but it has inherent defects in thin-wall injection molding. The orientation gradient formed by the glass fibers in the melt flow direction leads to a significant difference in shrinkage rates between the parallel and perpendicular directions, causing warping and deformation of the product. This problem is particularly prominent in large-area thin-walled parts such as mobile phone back covers, not only affecting assembly accuracy but also potentially causing out-of-tolerance appearance gaps.

[0003] To suppress warping, traditional methods typically increase the glass fiber content to enhance rigidity, but this introduces new problems. High fiber density exacerbates melt flow resistance, reduces fiber distribution uniformity, and causes stress concentration at the interface between crystalline and amorphous regions during crystallization, resulting in surface fiber floating and increased whitening. Simultaneously, excessive glass fiber exposure on the product surface disrupts coating adhesion continuity, leading to defects such as orange peel and flaking after spraying. More seriously, weak points at the fiber-matrix interface easily become crack initiation sites, causing brittle fracture upon drop impact, threatening reliability.

[0004] Existing technologies attempt to reduce shrinkage differences by adding nucleating agents to increase the crystallization rate. However, common nucleating agents have poor compatibility with polyester and are difficult to disperse stably in the matrix. While some modified nanoparticles can improve interfacial bonding, they often separate from nucleating agents and toughening agents, resulting in insufficient synergy in the multiphase system. Furthermore, although the use of chain extenders can adjust melt strength, improper matching of their reactivity with the nucleation sequence can disrupt the crystallization process and amplify anisotropy. These factors combined make it difficult to balance warp control, appearance quality, and mechanical reliability in existing glass fiber reinforced polyester materials, thus limiting their application in high-end electronic products. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a low-warpage glass fiber reinforced mobile phone back cover material and its preparation method, so as to solve the problem that existing glass fiber reinforced polyester mobile phone back covers are warped and deformed due to the anisotropy of fiber orientation and crystallization shrinkage, while increasing the fiber content leads to appearance deterioration and decreased interface reliability. The problem is that dimensional stability and comprehensive performance need to be balanced through the coordinated control of material composition and process.

[0006] To achieve the above objectives, the present invention provides a method for preparing a low-warpage glass fiber reinforced mobile phone back cover material, comprising the following steps:

[0007] (1) Polybutylene terephthalate resin and polyethylene terephthalate resin are added to a co-rotating twin-screw extruder for melt mixing, and epoxy functional polymer chain extender is added.

[0008] (2) After the melt obtained in step (1) is completely melted, add carboxylated trimesoamide nucleating agent and continue mixing;

[0009] (3) Add bifunctional group-grafted dopamine nanoparticles during the mixing process in step (2) and continue mixing;

[0010] (4) During the mixing process in step (3), a core-shell toughening agent is added and mixing continues;

[0011] (5) Add chopped glass fiber during the mixing process in step (4) and continue mixing;

[0012] (6) The mixed melt is extruded, cooled, and pelletized to obtain the low warp glass fiber reinforced mobile phone back cover material.

[0013] Preferably, in step (1), the polybutylene terephthalate resin and the polyethylene terephthalate resin are added through the main feed port, and the epoxy functional polymer chain extender is added simultaneously with the resin through the main feed port; in step (2), the carboxylated trimesoamide nucleating agent is added through side feed port I; in step (3), the bifunctional group grafted dopamine nanoparticles are added through side feed port II; in step (4), the core-shell structure toughening agent is added through side feed port III; and in step (5), the glass fiber chopped strands are added through the glass fiber main feed port.

[0014] Preferably, the side feed port I is located in the 4th temperature zone, the side feed port II is located in the 5th temperature zone, and the side feed port III is located in the 7th temperature zone.

[0015] Preferably, the co-rotating twin-screw extruder has a length-to-diameter ratio of 40, a screw speed of 200 r / min-240 r / min, and a vacuum exhaust port with a vacuum degree of -0.08 MPa is provided between the 6th and 7th temperature zones.

[0016] Preferably, the temperatures of each zone from the main feed port to the die head of the co-rotating twin-screw extruder are 230℃-240℃ / 235℃-245℃ / 240℃-250℃ / 240℃-250℃ / 235℃-245℃ / 235℃-245℃ / 230℃-240℃ / 230℃-240℃ / 235℃-245℃.

[0017] Preferably, the polybutylene terephthalate resin and the polyethylene terephthalate resin are pre-dried before step (1) at a temperature of 120°C for 4 hours.

[0018] Preferably, by weight, the polybutylene terephthalate resin is 515-585 parts, the polyethylene terephthalate resin is 50 parts, the epoxy functional polymer chain extender is 4-10 parts, the carboxylated trimesoamide nucleating agent is 0.8-1.2 parts, the bifunctional group-grafted dopamine nanoparticles are 2-4 parts, the core-shell structure toughening agent is 60-80 parts, and the glass fiber chopped strands are 260-300 parts.

[0019] Preferably, it also contains 2 parts pentaerythritol tetrastearate, 2 parts antioxidant 1010, and 3 parts antioxidant 168.

[0020] Preferably, the pentaerythritol tetrastearate, antioxidant 1010, and antioxidant 168 are added from the main feed port of the extruder.

[0021] Preferably, the carboxylated trimesoamide nucleating agent is obtained by alkaline hydrolysis and acid precipitation of a trimesoamide intermediate containing an ester-terminated group.

[0022] Preferably, the ester-terminated trimesoamide intermediate is obtained by amidation reaction of trimesoyl chloride, dodecylamine and methyl 6-aminohexanoate hydrochloride; the mass ratio of trimesoyl chloride, dodecylamine and methyl 6-aminohexanoate hydrochloride is 10:14:7.

[0023] Preferably, the bifunctionalized dopamine nanoparticles are prepared by the following steps: reacting dopamine nanoparticles with epichlorohydrin under alkaline conditions to obtain epoxy-functionalized dopamine nanoparticles; reacting the epoxy-functionalized dopamine nanoparticles with succinic anhydride in anhydrous N,N-dimethylformamide to obtain bifunctionalized dopamine nanoparticles; the mass ratio of dopamine nanoparticles to epichlorohydrin is 8:20; the mass ratio of epoxy-functionalized dopamine nanoparticles to succinic anhydride is 9:8.

[0024] Preferably, the epoxy functional polymer chain extender has an epoxy equivalent of 300-320 g / eq and an average molecular weight of 7000-7500.

[0025] Preferably, the chopped glass fiber is E-glass with a diameter of 12-14 μm and a cutting length of 4-5 mm.

[0026] Preferably, the core-shell toughening agent is sourced from Dow Chemical Company, brand name EXL-2690.

[0027] Furthermore, the present invention also provides a low-warpage glass fiber reinforced mobile phone back cover material, which is obtained by the above-mentioned preparation method of the low-warpage glass fiber reinforced mobile phone back cover material.

[0028] The beneficial effects of this invention are:

[0029] This invention utilizes reactive chain extension between epoxy functional polymer chain extenders and polyester end groups to effectively increase the melt molecular weight and entanglement density, resulting in more uniform dispersion and orientation of glass fibers in the matrix. Increased melt strength suppresses excessive gradient changes in fiber flow orientation, significantly reducing warping caused by shrinkage anisotropy. Simultaneously, residual epoxy groups provide anchoring points for subsequent functional components, enhancing the continuity of multiphase interfacial bonding.

[0030] Carboxylated trimesin nucleating agents form stable and dispersed heterogeneous nucleation sites in the polyester matrix, inducing the crystallization process to start at a higher temperature and reducing the supercooling difference between the crystallization temperature and the melting temperature. The refinement and homogenization of crystal size weakens the interfacial stress between crystalline and amorphous regions, further suppressing warping and reducing surface whitening caused by grain boundary light scattering. The synergistic effect of its carboxyl functional groups and the epoxy functional polymer chain extender immobilizes the nucleating agent in the matrix, avoiding uneven shrinkage caused by localized enrichment.

[0031] Bifunctional dopamine-grafted nanoparticles utilize the dual reactivity of epoxy and carboxyl groups to construct a flexible bonding layer between the glass fiber surface and the polyester matrix. This structure alleviates interfacial stress caused by the difference in thermal expansion coefficients between the fiber and the matrix, improving coating adhesion and impact resistance. Its nanoscale effect effectively passively inhibits microcrack propagation and, in synergy with core-shell toughening agents, forms a multi-level energy dissipation mechanism, absorbing energy through plastic deformation during drop impacts and preventing brittle cracking.

[0032] Multiple components are added in stages through a side feed port in a specific order, allowing for controllable blending timing and dispersion of each functional unit in the melt. Epoxy functional polymer chain extenders are added before nucleating agents and interface modifiers, providing a foundation for subsequent reactions; nucleating agents are injected after the melt is fully plasticized to prevent premature decomposition; and glass fibers are introduced last to reduce mechanical shear damage. This process design ensures synergy between chemical reactions and physical dispersion among components, ultimately resulting in products with low warpage, high apparent quality, and reliable durability even under thin-walled conditions. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0034] Example 1:

[0035] Step 1: Preparation of dopamine nanoparticles

[0036] Weigh 10g of dopamine hydrochloride and 1g of tris(hydroxymethyl)aminomethane and add them to 189g of deionized water. Stir for 10min, adjust the pH of the solution to 8.5 with 5% sodium hydroxide aqueous solution, stir at 300r / min for 6h at room temperature, centrifuge at 10000r / min for 10min, discard the supernatant, wash 3 times with deionized water, and vacuum dry at 50℃ for 12h to obtain dopamine nanoparticles.

[0037] Step 2: Preparation of epoxy-functionalized dopamine nanoparticles

[0038] Weigh 8g of dopamine nanoparticles and add them to 80g of 2% sodium hydroxide aqueous solution. Disperse the mixture by sonication for 15min. Then, add 20g of epichlorohydrin under ice-water bath conditions, control the system temperature to not exceed 40℃, stir at 300r / min for 4h, centrifuge at 10000r / min for 10min, discard the supernatant, wash with deionized water 3 times, and then vacuum dry at 50℃ for 12h to obtain epoxy-functionalized dopamine nanoparticles.

[0039] Step 3: Preparation of dopamine nanoparticles grafted with bifunctional groups

[0040] 9g of epoxy-functionalized dopamine nanoparticles were weighed and added to 150g of anhydrous N,N-dimethylformamide. The mixture was ultrasonically dispersed for 20min. Then, 8g of succinic anhydride and 2g of triethylamine were added. The mixture was stirred at 300r / min for 6h at 60℃. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 10000r / min for 10min. The supernatant was discarded, and the mixture was washed twice with anhydrous N,N-dimethylformamide and twice with anhydrous ethanol. Then, it was dried at 60℃ for 12h to obtain 10g of bifunctional grafted dopamine nanoparticles.

[0041] Step 4: Synthesis of the ester-terminated trimesin intermediate

[0042] 10g of trimesoyl chloride was weighed and added to 200g of anhydrous dichloromethane. The mixture was stirred in an ice-water bath for 10 min to obtain a dichloromethane solution containing trimesoyl chloride. Separately, 14g of dodecylamine and 7g of methyl 6-aminohexanoate hydrochloride were weighed and dissolved in 150g of anhydrous dichloromethane. Then, 15g of triethylamine was added and the mixture was stirred in an ice-water bath for 30 min to obtain a dichloromethane solution containing amine. Subsequently, the dichloromethane solution containing amine was added dropwise to the dichloromethane solution containing trimesoyl chloride over a period of 1 h using a dropping funnel in an ice-water bath. After the addition was completed, the ice-water bath was removed, and the mixture was allowed to rise naturally to room temperature. The reaction was continued to be stirred for 12 h. After the reaction was completed, the mixture was washed three times with deionized water, the organic phase was separated, and the organic phase was evaporated under reduced pressure and dissolved in ethanol. The mixture was filtered while hot to remove a small amount of insoluble matter. After cooling and crystallization, the mixture was filtered and dried under vacuum at 50°C for 12 h to obtain a trimesoyl chloride intermediate containing an ester-terminated group.

[0043] Step 5: Preparation of carboxylated trimesoamide nucleating agent

[0044] 16g of the ester-terminated trimesin intermediate was weighed and added to an ethanol / water mixed solvent consisting of 95g ethanol and 95g deionized water. The mixture was heated to 80℃ and stirred for 20min. Then, 100g of 10% sodium hydroxide solution was added, and the system was kept at 80℃ and stirred for 2h for hydrolysis. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the solution was adjusted to 2.1 by adding 10% hydrochloric acid solution dropwise. The solid precipitated, and the solid was filtered, washed three times with deionized water, then washed twice with ethanol, and finally dried under vacuum at 60℃ for 12h to obtain the carboxylated trimesin nucleating agent.

[0045] Step 6: Pre-drying and weighing of resin and additives

[0046] Weigh out 584g of polybutylene terephthalate resin granules (BASF, brand B4520), 50g of polyethylene terephthalate resin granules CZ302 (Jiangsu Xingye Plastics Co., Ltd., brand CZ302), 2g of pentaerythritol tetrastearate, 2g of antioxidant 1010 and 3g of antioxidant 168. Mix the above resins and solid additives evenly and place them in a hot air drying oven to dry at 120°C for 4 hours.

[0047] Step 7: Preparation of glass fiber reinforced polyester granules

[0048] In a co-rotating twin-screw extruder (L / D ratio 40), the temperatures of the zones from the main feed port to the die head are set sequentially as follows: 230℃ / 235℃ / 240℃ / 240℃ / 235℃ / 235℃ / 230℃ / 230℃ / 235℃. The screw speed is set to 200 r / min, and a vacuum exhaust port (vacuum degree -0.08 MPa) is set between the 6th and 7th temperature zones. After the extruder is started and the temperature stabilized, 584 g of dried polybutylene terephthalate resin, 50 g of polyethylene terephthalate resin, 2 g of pentaerythritol tetrastearate, 2 g of antioxidant 1010, and 3 g of antioxidant 168 are added at once through the main feed port. At the same time, 4 g of epoxy functional polymer chain extender (BASF, brand name ADR4468, epoxy equivalent approximately 310 g / eq, average molecular weight approximately 725) is added. 0), after the melt has completely melted and its viscosity has stabilized at the end of the third temperature zone of the extruder, a side feed port I is set in the fourth temperature zone, and 0.8g of carboxylated trimesoamide nucleating agent is added to the melt through the side feeder; then, a side feed port II is set in the fifth temperature zone, and 2g of bifunctional group-grafted dopamine nanoparticles are added through the second side feeder; a side feed port III is set in the seventh temperature zone of the extruder, and 60g of core-shell structure toughening agent (Dow Chemical Company, brand name EXL-2690) is added through the side feeder; then, a glass fiber main feed port is set in the eighth temperature zone, and 260g of glass fiber chopped strands (Jushi Group, brand name 534A, E glass, filament diameter approximately 13μm, cut length 4.5mm) are continuously added from this port. After mixing, the melt is extruded through the die head, water-cooled, stretched, and pelletized to obtain low-warpage glass fiber reinforced mobile phone back cover material;

[0049] Step 8: Injection molding of the phone back cover

[0050] The low-warpage glass fiber reinforced mobile phone back cover material was dried at 80℃ for 3 hours, and then injection molded using a horizontal injection molding machine and a mobile phone back cover mold with a wall thickness of 1.0mm. The barrel temperature was set to 245℃ / 250℃ / 255℃ / 255℃ from the feeding section to the nozzle, and the mold temperature was controlled at 90℃. After demolding, it was kept at 110℃ for 20 minutes, and then naturally cooled to room temperature to obtain the mobile phone back cover product.

[0051] Example 2:

[0052] Step 1: Preparation of dopamine nanoparticles

[0053] Weigh 10g of dopamine hydrochloride and 1g of tris(hydroxymethyl)aminomethane and add them to 189g of deionized water. Stir for 10min, adjust the pH of the solution to 8.5 with 5% sodium hydroxide aqueous solution, stir at 300r / min for 6h at room temperature, centrifuge at 10000r / min for 10min, discard the supernatant, wash 3 times with deionized water, and vacuum dry at 50℃ for 12h to obtain dopamine nanoparticles.

[0054] Step 2: Preparation of epoxy-functionalized dopamine nanoparticles

[0055] Weigh 8g of dopamine nanoparticles and add them to 80g of 2% sodium hydroxide aqueous solution. Disperse the mixture by sonication for 15min. Then, add 20g of epichlorohydrin under ice-water bath conditions, control the system temperature to not exceed 40℃, stir at 300r / min for 4h, centrifuge at 10000r / min for 10min, discard the supernatant, wash with deionized water 3 times, and then vacuum dry at 50℃ for 12h to obtain epoxy-functionalized dopamine nanoparticles.

[0056] Step 3: Preparation of dopamine nanoparticles grafted with bifunctional groups

[0057] 9g of epoxy-functionalized dopamine nanoparticles were weighed and added to 150g of anhydrous N,N-dimethylformamide. The mixture was ultrasonically dispersed for 20min. Then, 8g of succinic anhydride and 2g of triethylamine were added. The mixture was stirred at 300r / min for 6h at 60℃. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 10000r / min for 10min. The supernatant was discarded, and the mixture was washed twice with anhydrous N,N-dimethylformamide and twice with anhydrous ethanol. Then, it was dried at 60℃ for 12h to obtain 10g of bifunctional grafted dopamine nanoparticles.

[0058] Step 4: Synthesis of the ester-terminated trimesin intermediate

[0059] 10g of trimesoyl chloride was weighed and added to 200g of anhydrous dichloromethane. The mixture was stirred in an ice-water bath for 10 min to obtain a dichloromethane solution containing trimesoyl chloride. Separately, 14g of dodecylamine and 7g of methyl 6-aminohexanoate hydrochloride were weighed and dissolved in 150g of anhydrous dichloromethane. Then, 15g of triethylamine was added and the mixture was stirred in an ice-water bath for 30 min to obtain a dichloromethane solution containing amine. Subsequently, the dichloromethane solution containing amine was added dropwise to the dichloromethane solution containing trimesoyl chloride over a period of 1 h using a dropping funnel in an ice-water bath. After the addition was completed, the ice-water bath was removed, and the mixture was allowed to rise naturally to room temperature. The reaction was continued to be stirred for 12 h. After the reaction was completed, the mixture was washed three times with deionized water, the organic phase was separated, and the organic phase was evaporated under reduced pressure and dissolved in ethanol. The mixture was filtered while hot to remove a small amount of insoluble matter. After cooling and crystallization, the mixture was filtered and dried under vacuum at 50°C for 12 h to obtain a trimesoyl chloride intermediate containing an ester-terminated group.

[0060] Step 5: Preparation of carboxylated trimesoamide nucleating agent

[0061] 16g of the ester-terminated trimesin intermediate was weighed and added to an ethanol / water mixed solvent consisting of 95g ethanol and 95g deionized water. The mixture was heated to 80℃ and stirred for 20min. Then, 100g of 10% sodium hydroxide solution was added, and the system was kept at 80℃ and stirred for 2h for hydrolysis. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the solution was adjusted to 2.1 by adding 10% hydrochloric acid solution dropwise. The solid precipitated, and the solid was filtered, washed three times with deionized water, then washed twice with ethanol, and finally dried under vacuum at 60℃ for 12h to obtain the carboxylated trimesin nucleating agent.

[0062] Step 6: Pre-drying and weighing of resin and additives

[0063] Weigh out 550g of polybutylene terephthalate resin granules (BASF, brand B4520), 50g of polyethylene terephthalate resin granules CZ302 (Jiangsu Xingye Plastics Co., Ltd., brand CZ302), 2g of pentaerythritol tetrastearate, 2g of antioxidant 1010 and 3g of antioxidant 168. Mix the above resins and solid additives evenly and place them in a hot air drying oven to dry at 120°C for 4 hours.

[0064] Step 7: Preparation of glass fiber reinforced polyester granules

[0065] In a co-rotating twin-screw extruder (L / D ratio 40), the temperatures of the zones from the main feed port to the die head are set sequentially as follows: 235℃ / 240℃ / 245℃ / 245℃ / 240℃ / 240℃ / 235℃ / 235℃ / 240℃. The screw speed is set to 220 r / min, and a vacuum exhaust port (vacuum degree -0.08 MPa) is set between the 6th and 7th temperature zones. After the extruder is started and the temperature stabilized, 550g of dried polybutylene terephthalate resin, 50g of polyethylene terephthalate resin, 2g of pentaerythritol tetrastearate, 2g of antioxidant 1010, and 3g of antioxidant 168 are added at once through the main feed port. Simultaneously, 7g of epoxy functional polymer chain extender (BASF, brand ADR4468, epoxy equivalent approximately 310g / eq, average molecular weight approximately 72) is added. 50) After the melt has completely melted and the viscosity has stabilized at the end of the third temperature zone of the extruder, a side feed port I is set in the fourth temperature zone, and 1g of carboxylated trimesoamide nucleating agent is added to the melt through the side feeder; then, a side feed port II is set in the fifth temperature zone, and 3g of bifunctional group-grafted dopamine nanoparticles are added through the second side feeder; a side feed port III is set in the seventh temperature zone of the extruder, and 70g of core-shell structure toughening agent (Dow Chemical Company, brand name EXL-2690) is added through the side feeder; then, a glass fiber main feed port is set in the eighth temperature zone, and 280g of glass fiber chopped strands (Jushi Group, brand name 534A, E glass, filament diameter about 13μm, cut length 4.5mm) are continuously added from this port. After mixing, the melt is extruded through the die head, water-cooled, stretched, and pelletized to obtain low-warpage glass fiber reinforced mobile phone back cover material;

[0066] Step 8: Injection molding of the phone back cover

[0067] The low-warpage glass fiber reinforced mobile phone back cover material was dried at 80℃ for 3 hours, and then injection molded using a horizontal injection molding machine and a mobile phone back cover mold with a wall thickness of 1.0mm. The barrel temperature was set to 245℃ / 250℃ / 255℃ / 255℃ from the feeding section to the nozzle, and the mold temperature was controlled at 90℃. After demolding, it was kept at 110℃ for 20 minutes, and then naturally cooled to room temperature to obtain the mobile phone back cover product.

[0068] Example 3:

[0069] Step 1: Preparation of dopamine nanoparticles

[0070] Weigh 10g of dopamine hydrochloride and 1g of tris(hydroxymethyl)aminomethane and add them to 189g of deionized water. Stir for 10min, adjust the pH of the solution to 8.5 with 5% sodium hydroxide aqueous solution, stir at 300r / min for 6h at room temperature, centrifuge at 10000r / min for 10min, discard the supernatant, wash 3 times with deionized water, and vacuum dry at 50℃ for 12h to obtain dopamine nanoparticles.

[0071] Step 2: Preparation of epoxy-functionalized dopamine nanoparticles

[0072] Weigh 8g of dopamine nanoparticles and add them to 80g of 2% sodium hydroxide aqueous solution. Disperse the mixture by sonication for 15min. Then, add 20g of epichlorohydrin under ice-water bath conditions, control the system temperature to not exceed 40℃, stir at 300r / min for 4h, centrifuge at 10000r / min for 10min, discard the supernatant, wash with deionized water 3 times, and then vacuum dry at 50℃ for 12h to obtain epoxy-functionalized dopamine nanoparticles.

[0073] Step 3: Preparation of dopamine nanoparticles grafted with bifunctional groups

[0074] 9g of epoxy-functionalized dopamine nanoparticles were weighed and added to 150g of anhydrous N,N-dimethylformamide. The mixture was ultrasonically dispersed for 20min. Then, 8g of succinic anhydride and 2g of triethylamine were added. The mixture was stirred at 300r / min for 6h at 60℃. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 10000r / min for 10min. The supernatant was discarded, and the mixture was washed twice with anhydrous N,N-dimethylformamide and twice with anhydrous ethanol. Then, it was dried at 60℃ for 12h to obtain 10g of bifunctional grafted dopamine nanoparticles.

[0075] Step 4: Synthesis of the ester-terminated trimesin intermediate

[0076] 10g of trimesoyl chloride was weighed and added to 200g of anhydrous dichloromethane. The mixture was stirred in an ice-water bath for 10 min to obtain a dichloromethane solution containing trimesoyl chloride. Separately, 14g of dodecylamine and 7g of methyl 6-aminohexanoate hydrochloride were weighed and dissolved in 150g of anhydrous dichloromethane. Then, 15g of triethylamine was added and the mixture was stirred in an ice-water bath for 30 min to obtain a dichloromethane solution containing amine. Subsequently, the dichloromethane solution containing amine was added dropwise to the dichloromethane solution containing trimesoyl chloride over a period of 1 h using a dropping funnel in an ice-water bath. After the addition was completed, the ice-water bath was removed, and the mixture was allowed to rise naturally to room temperature. The reaction was continued to be stirred for 12 h. After the reaction was completed, the mixture was washed three times with deionized water, the organic phase was separated, and the organic phase was evaporated under reduced pressure and dissolved in ethanol. The mixture was filtered while hot to remove a small amount of insoluble matter. After cooling and crystallization, the mixture was filtered and dried under vacuum at 50°C for 12 h to obtain a trimesoyl chloride intermediate containing an ester-terminated group.

[0077] Step 5: Preparation of carboxylated trimesoamide nucleating agent

[0078] 16g of the ester-terminated trimesin intermediate was weighed and added to an ethanol / water mixed solvent consisting of 95g ethanol and 95g deionized water. The mixture was heated to 80℃ and stirred for 20min. Then, 100g of 10% sodium hydroxide solution was added, and the system was kept at 80℃ and stirred for 2h for hydrolysis. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the solution was adjusted to 2.1 by adding 10% hydrochloric acid solution dropwise. The solid precipitated, and the solid was filtered, washed three times with deionized water, then washed twice with ethanol, and finally dried under vacuum at 60℃ for 12h to obtain the carboxylated trimesin nucleating agent.

[0079] Step 6: Pre-drying and weighing of resin and additives

[0080] Weigh out 515g of polybutylene terephthalate resin granules (BASF, brand B4520), 50g of polyethylene terephthalate resin granules CZ302 (Jiangsu Xingye Plastics Co., Ltd., brand CZ302), 2g of pentaerythritol tetrastearate, 2g of antioxidant 1010 and 3g of antioxidant 168. Mix the above resins and solid additives evenly and place them in a hot air drying oven to dry at 120°C for 4 hours.

[0081] Step 7: Preparation of glass fiber reinforced polyester granules

[0082] In a co-rotating twin-screw extruder (L / D ratio 40), the temperatures of the zones from the main feed port to the die head are set sequentially as follows: 240℃ / 245℃ / 250℃ / 250℃ / 245℃ / 245℃ / 240℃ / 240℃ / 245℃. The screw speed is set to 240 r / min. A vacuum exhaust port (vacuum degree -0.08 MPa) is set between the 6th and 7th temperature zones. After the extruder is started and the temperature stabilizes, 515g of dried polybutylene terephthalate resin, 50g of polyethylene terephthalate resin, 2g of pentaerythritol tetrastearate, 2g of antioxidant 1010, and 3g of antioxidant 168 are added at once through the main feed port. At the same time, 10g of epoxy functional polymer chain extender (BASF, brand name ADR4468, epoxy equivalent approximately 310g / eq, average molecular weight approximately 72) is added. 50) After the melt has completely melted and the viscosity has stabilized at the end of the third temperature zone of the extruder, a side feed port I is set in the fourth temperature zone, and 1.2g of carboxylated trimesoamide nucleating agent is added to the melt through the side feeder; then, a side feed port II is set in the fifth temperature zone, and 4g of bifunctional group-grafted dopamine nanoparticles are added through the second side feeder; a side feed port III is set in the seventh temperature zone of the extruder, and 80g of core-shell structure toughening agent (Dow Chemical Company, brand name EXL-2690) is added through the side feeder; then, a glass fiber main feed port is set in the eighth temperature zone, and 300g of glass fiber chopped strands (Jushi Group, brand name 534A, E glass, filament diameter about 13μm, cut length 4.5mm) are continuously added from this port. After mixing, the melt is extruded through the die head, water-cooled, stretched, and pelletized to obtain low-warpage glass fiber reinforced mobile phone back cover material;

[0083] Step 8: Injection molding of the phone back cover

[0084] The low-warpage glass fiber reinforced mobile phone back cover material was dried at 80℃ for 3 hours, and then injection molded using a horizontal injection molding machine and a mobile phone back cover mold with a wall thickness of 1.0mm. The barrel temperature was set to 245℃ / 250℃ / 255℃ / 255℃ from the feeding section to the nozzle, and the mold temperature was controlled at 90℃. After demolding, it was kept at 110℃ for 20 minutes, and then naturally cooled to room temperature to obtain the mobile phone back cover product.

[0085] Comparative Example 1:

[0086] The difference between Comparative Example 1 and Example 2 is that 7g of epoxy functional polymer chain extender (brand name ADR4468) was not added in step 7 of Example 2, while the other conditions were the same as in Example 2.

[0087] Comparative Example 2:

[0088] The difference between Comparative Example 2 and Example 2 is that the preparation of the carboxylated trimellitic amide nucleating agent obtained in step 5 of Example 2 is not carried out. Instead, the ester-terminated trimellitic amide intermediate obtained in step 4 of Example 2 is used. In step 7 of Example 2, 1g of the ester-terminated trimellitic amide intermediate is added through side feed port I to replace 1g of the carboxylated trimellitic amide nucleating agent. The other conditions are the same as in Example 2.

[0089] Comparative Example 3:

[0090] The difference between Comparative Example 3 and Example 2 is that step 3 of Example 2, which involves the preparation of bifunctional group-grafted dopamine nanoparticles, is not performed. Instead, the epoxy-functionalized dopamine nanoparticles obtained in step 2 of Example 2 are used. In step 7 of Example 2, 3g of epoxy-functionalized dopamine nanoparticles are added through side feed port II to replace 3g of bifunctional group-grafted dopamine nanoparticles. All other conditions are the same as in Example 2.

[0091] Comparative Example 4:

[0092] The difference between Comparative Example 4 and Example 2 is that step 3 of Example 2, which involves the preparation of bifunctional group-grafted dopamine nanoparticles, is not performed. Instead, the dopamine nanoparticles obtained in step 1 of Example 2 are used. In step 7 of Example 2, 3g of dopamine nanoparticles are added through side feed port II to replace 3g of bifunctional group-grafted dopamine nanoparticles. The other conditions are the same as in Example 2.

[0093] Comparative Example 5:

[0094] The difference between Comparative Example 5 and Example 2 is that in step 7 of Example 2, the addition position of 3g of bifunctional group-grafted dopamine nanoparticles was changed from feed port II on the 5th temperature zone side of the extruder to feed port III on the 7th temperature zone side of the extruder, and 70g of core-shell toughening agent were added simultaneously. This changed the addition sequence of bifunctional group-grafted dopamine nanoparticles from after the nucleating agent and before the toughening agent to simultaneous with the toughening agent and before the glass fiber short filaments. The other conditions were the same as in Example 2.

[0095] Comparative Example 6:

[0096] The difference between Comparative Example 6 and Example 2 is that in step 7 of Example 2, the amount of epoxy functional polymer chain extender (brand name ADR4468) added was adjusted from 7g to 14g, while the other conditions were the same as in Example 2.

[0097] Performance testing:

[0098] Sample preparation and conditioning: The special material granules of the examples and comparative examples were dried at 80℃ for 3 hours according to step 8 of Example 2, and then injection molded into mobile phone back cover products with a wall thickness of 1.0 mm using a horizontal injection molding machine. At the same time, standard strip specimens for mechanical and thermal testing were obtained by injection molding using the same injection molding machine and the same barrel temperature curve (245℃ / 250℃ / 255℃ / 255℃ from the feeding section to the nozzle) and the same mold temperature (90℃). The tensile, bending, impact, load deformation temperature and water absorption specimens were all obtained by injection molding from the same batch of granules. After demolding, all specimens were kept at 110℃ for 20 minutes and then naturally cooled to room temperature. They were then conditioned for 48 hours at a temperature of 23℃ and a relative humidity of 50% according to GB / T 2918-2018 "Standard Environment for Conditioning and Testing of Plastic Specimens" to ensure the comparability and repeatability of the test results.

[0099] Differential scanning calorimetry characterization: 5.0 mg of the special material particles from each example and comparative example were weighed and placed in an aluminum crucible and sealed. Under nitrogen protection, the flow rate was 50 mL / min. The test was performed according to the first heating-cooling-second heating procedure, that is, the temperature was increased from 30℃ to 260℃ at 10℃ / min and held for 3 min to eliminate thermal history, then cooled to 30℃ at 10℃ / min and held for 3 min, and then heated to 260℃ again at 10℃ / min. The crystallization peak temperature Tc of the cooling curve and the melting peak temperature Tm of the second heating curve were recorded, and the supercooling ΔT = Tm - Tc was calculated. The results are shown in Table 1.

[0100] Mobile phone back cover warpage (flatness deviation) test: Following the evaluation principles of GB / T 11337-2004 "Flatness Error Detection" and GB / T 1958-2017 "Product Geometric Technical Specification (GPS) Geometric Tolerance Detection and Verification", the warpage of mobile phone back covers was quantified. Each mobile phone back cover was placed on a three-point support fixture (the support points were located at three non-collinear positions on the same assembly datum plane) with its inner surface as the test surface. It was then allowed to stand at 23℃ for 2 hours to eliminate thermal disturbance during clamping. A coordinate measuring machine was used to collect coordinates of at least 25 measuring points in the effective plane area using a 5mm×5mm grid. The minimum containment area method was used to fit two parallel containment planes and obtain the flatness error value F. The mobile phone back cover warpage W = F (unit: mm) was defined. Five samples were tested for each product, and the average value was taken. The results are shown in Table 1.

[0101] Tensile properties: The tensile properties of the samples were tested according to GB / T 1040.1-2025 "Determination of tensile properties of plastics - Part 1: General rules" and GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molding and extruded plastics". Type 1A dumbbell specimens (gauge length 50 mm, thickness 4 mm) were used, and the test speed was 50 mm / min until the specimen broke. The tensile strength and elongation at break were recorded. Five tests were conducted for each sample and the average value was taken. The results are shown in Table 1.

[0102] Bending performance: The bending performance of the samples was tested according to GB / T 9341-2008 "Determination of bending performance of plastics". Rectangular specimens (80mm×10mm×4mm) were used. The three-point bending span was set to 64mm. The fillet radius of the loading head and support was 5mm. The test speed was 2.0mm / min. The bending strength and bending modulus were recorded. Five tests were conducted on each sample and the average value was taken. The results are shown in Table 1.

[0103] Notched impact strength of cantilever beams: The notched impact performance of the samples was tested according to GB / T 1843-2008 "Determination of impact strength of plastic cantilever beams". 80mm×10mm×4.0mm specimens were used, with a type A notch (notch depth 2.0mm, notch bottom radius 0.25mm) machined in the middle of the specimen. The test temperature was 23℃, the pendulum energy was 5J, and the notched impact strength of the cantilever beams was recorded. Ten tests were conducted on each sample, and the average value was taken. The results are shown in Table 1.

[0104] Load deformation temperature: The heat deformation resistance of the samples was tested according to GB / T 1634.2-2019 "Determination of load deformation temperature of plastics - Part 2: Plastics and hard rubber". 80mm×10mm×4.0mm specimens were used. The loading method was three-point loading of the edge bending. The stress of the outer fiber was set to 1.80MPa. The heating rate was 120℃ / h. The temperature when the deflection reached 0.34mm was recorded as the load deformation temperature. Three tests were conducted for each sample and the average value was taken. The results are shown in Table 1.

[0105] Whiteness test: The apparent whitening tendency of the samples was tested according to GB / T 2913-1982 "Test Method for Whiteness of Plastics". Flat samples (60mm×60mm×1.0mm) were injection molded in the same batch as the mobile phone back cover. A whiteness meter was used to test 5 different positions of each flat sample under D65 light source and 10° field of view, and the average value was taken as the whiteness value of the flat sample. Then, 5 flat samples were tested for each sample and the average value was taken. The results are shown in Table 1.

[0106] Coating adhesion: The adhesion of the sprayed samples of mobile phone back covers was evaluated according to GB / T 9286-2021 "Cross-cut test for paints and varnishes". Each sample of mobile phone back cover products was wiped clean with anhydrous ethanol and dried in an oven at 60℃ for 10 min before spraying. After spraying, the dry film thickness was controlled at 30μm and cured at 80℃ for 30 min. After being placed at room temperature for 24 h, a 6×6 grid was cut on a flat area with a 1mm spacing cross-cutting knife and cut through to the substrate. Pressure-sensitive tape with a width of 25mm and a peel strength of 7.0N / 25mm was applied and peeled off at a uniform speed in a 60° direction within 1 second. The cross-cut adhesion level was determined according to the standard. The results are shown in Table 1.

[0107] Drop test: The impact reliability of mobile phone back covers was compared according to GB / T 2423.7-2018 "Environmental testing - Part 2: Test methods - Test Ec: Impact caused by rough handling (mainly for equipment-type samples)". Each mobile phone back cover was fixed with a rigid simulated body block with a mass of 180g to form an equipment-type sample. The sample was subjected to free drop impact from a height of 1.0m at 23℃. The drop medium was a 10mm thick hardwood board covered with a 3mm hard rubber pad and placed on a steel plate base. The sample was dropped once on each of the 6 faces, 4 edges, and 4 corners (a total of 14 drops). After the drops, cracks and chipping were visually inspected and counted using a 10x magnified microscope. The results are shown in Table 1.

[0108] Table 1 Performance Test Results

[0109] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Crystallization peak temperature / ℃ 201.2 203.8 203 200.1 202.4 201.8 200.9 199.6 201.0 Melting peak temperature / °C 224.7 225.0 225.3 224.8 224.9 225.1 224.6 224.9 225.2 Supercooling / ℃ 23.5 21.2 22.3 24.7 22.5 23.3 23.7 25.3 24.2 Warpage / mm 0.26 0.18 0.23 0.52 0.34 0.31 0.46 0.39 0.21 Tensile strength / MPa 142.5 147.8 150.6 141.0 146.2 143.8 138.9 144.7 152.0 Elongation at break / % 3.1 3.3 2.7 3.6 3.0 3.1 2.5 3.5 2.4 Bending strength / MPa 228.4 232.7 239.8 226 231.2 229.1 222.8 230.0 242.5 Flexural modulus / MPa 9700 9900 10450 9600 10050 9800 9550 9750 10600 <![CDATA[Impact strength / (kJ / m 2 )]]> 10.4 12.1 11.2 11.8 10.9 10.6 9.3 12.8 9.8 Load deformation temperature / ℃ 199.4 200.8 202.1 198.9 201.0 200.1 199.0 199.7 203.0 Whiteness / % 7.2 5.9 7.8 8.6 9.1 8.0 10.5 7.6 6.8 Cross-grain adhesion / grade 1 0 1 2 3 2 4 2 0 Number of cracks after rough operation impact / 1 0 2 4 5 3 6 1 3

[0110] Data Analysis:

[0111] As can be seen from the data in Examples 1-3 of Table 1, the glass fiber reinforced polyester material prepared by this invention maintains good consistency in crystallization behavior, dimensional stability, and mechanical properties. The crystallization peak temperature is at a relatively high level with low supercooling, indicating that the carboxylated trimesoamide nucleating agent, with the participation of the residual epoxy groups in the epoxy functional polymer chain extender, can form relatively uniform nucleation sites in the polybutylene terephthalate / polyethylene terephthalate matrix. Simultaneously, the bifunctional grafted dopamine nanoparticles interact at multiple points with the polyester end groups and the nucleating agent, synchronously regulating the wetting of the crystal nucleation and glass fiber chopped strand interface. This results in lower warpage, less apparent whitening tendency, and better coating adhesion in the injection-molded thin-walled mobile phone back cover. Furthermore, the core-shell toughening agent provides an effective energy dissipation path without significantly sacrificing rigidity and heat resistance, enabling the product to have high crack resistance reliability under drop impact conditions, demonstrating the synergistic effect of interface regulation and toughness design.

[0112] As can be seen from the data in Example 2 and Comparative Example 1 in Table 1, after removing the epoxy functional polymer chain extender, the warpage of the phone back cover increased, the coating adhesion deteriorated, and whitening worsened, while the toughness index showed a certain recovery. This is because the absence of the chain extender resulted in insufficient molecular weight and melt strength in the polyester melt, leading to an increased orientation gradient of the chopped glass fibers and amplified shrinkage anisotropy, causing warpage. Simultaneously, the reduction in residual epoxy groups made it difficult to anchor the carboxylated trimesoamide nucleating agent and the dopamine nanoparticles grafted with bifunctional groups, increasing interfacial micro-defects and causing a decrease in adhesion and appearance stability.

[0113] As can be seen from the data in Example 2 and Comparative Example 2 in Table 1, when the nucleating agent was replaced by a carboxylated trimellitic amide nucleating agent with an ester-terminated trimellitic amide intermediate, crystal nucleation still showed a relatively rapid trend, but warpage and whitening tendency increased, and coating adhesion also decreased. The main reason is that the ester-terminated group weakens the reaction fixation effect with the residual epoxy group, making the nucleating agent more likely to migrate and become locally enriched, resulting in a spatial gradient between crystallization and shrinkage, and increasing the internal stress of thin-walled products. This result indicates that, in addition to nucleation efficiency, the fixability of nucleation sites is also crucial for dimensional stability.

[0114] As can be seen from the data in Table 1 for Example 2 and Comparative Example 3, when only epoxy-functionalized dopamine nanoparticles are used without carboxyl group functionality, the warpage, adhesion, and crack resistance reliability are all difficult to achieve the comprehensive level of Example 2. This is because although epoxy-functionalized dopamine nanoparticles can react with polyester end groups and improve wetting, without the participation of carboxyl groups, it is difficult to form multi-point synergistic connections with the carboxylated trimesoamide nucleating agent. Interface regulation tends to favor a single reaction pathway, making it difficult to simultaneously achieve both crystallization uniformity and coating interface stability.

[0115] As can be seen from the data in Example 2 and Comparative Example 4 in Table 1, when using unmodified dopamine nanoparticles, the strength, adhesion, and drop crack resistance are significantly deteriorated, and whitening is aggravated. This is because unmodified dopamine nanoparticles tend to agglomerate in the polyester melt, forming microscopic defects and causing stress concentration. Simultaneously, the lack of reactive groups makes it difficult to form a stable bond with residual epoxy groups and polyester end groups, resulting in insufficient load transfer and interfacial wetting. Micropores and microcracks are more likely to form and propagate during impact, leading to a simultaneous decline in appearance and reliability.

[0116] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, when the addition of bifunctional grafted dopamine nanoparticles was changed from being added in the same stage as the carboxylated trimesoamide nucleating agent to being added in the same stage as the core-shell toughening agent, the toughness-related indicators improved and the number of drop cracks decreased, but the warpage and coating adhesion deteriorated. This is because the later addition causes more dopamine nanoparticles to distribute in the toughening agent phase, enhancing crack passivation and energy dissipation; at the same time, the synergistic fixation between the dopamine nanoparticles and the nucleating agent is insufficient, reducing crystallization uniformity and amplifying the shrinkage gradient of thin-walled parts, leading to an imbalance in warpage and whitening control.

[0117] As can be seen from the data in Example 2 and Comparative Example 6 in Table 1, when the amount of epoxy functional polymer chain extender is significantly increased, the strength and heat resistance indicators are improved and the coating adhesion remains good, but the elongation at break, notched impact strength, and drop crack resistance decline. The main reason is that excessive chain extender leads to excessive branching of polyester molecular chains, forming local high viscoelasticity and high stress zones; at the same time, the residual epoxy groups react excessively with nucleating agents and dopamine nanoparticles, which may cause microgelation and uneven dispersion, weakening the effective role of toughening agents, thus resulting in decreased toughness.

[0118] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a low-warpage glass fiber reinforced mobile phone back cover material, characterized in that, Includes the following steps: (1) Polybutylene terephthalate resin and polyethylene terephthalate resin are added to a co-rotating twin-screw extruder for melt mixing, and epoxy functional polymer chain extender is added. (2) After the melt obtained in step (1) is completely melted, add carboxylated trimesoamide nucleating agent and continue mixing; (3) Add bifunctional group-grafted dopamine nanoparticles during the mixing process in step (2) and continue mixing; (4) During the mixing process in step (3), a core-shell toughening agent is added and mixing continues; (5) Add chopped glass fiber during the mixing process in step (4) and continue mixing; (6) The mixed melt is extruded, cooled, and pelletized to obtain the low warp glass fiber reinforced mobile phone back cover material; In step (1), the polybutylene terephthalate resin and the polyethylene terephthalate resin are added through the main feed port, and the epoxy functional polymer chain extender is added simultaneously with the resin through the main feed port; in step (2), the carboxylated trimesoamide nucleating agent is added through side feed port I; in step (3), the bifunctional group grafted dopamine nanoparticles are added through side feed port II; in step (4), the core-shell structure toughening agent is added through side feed port III; in step (5), the glass fiber chopped filaments are added through the glass fiber main feed port; side feed port I is located in the 4th temperature zone, side feed port II is located in the 5th temperature zone, and side feed port III is located in the 7th temperature zone; By weight, the polybutylene terephthalate resin comprises 515-585 parts, the polyethylene terephthalate resin comprises 50 parts, the epoxy functional polymer chain extender comprises 4-10 parts, the carboxylated trimesoamide nucleating agent comprises 0.8-1.2 parts, the bifunctional group-grafted dopamine nanoparticles comprises 2-4 parts, the core-shell structure toughening agent comprises 60-80 parts, and the glass fiber chopped strands comprises 260-300 parts.

2. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, The co-rotating twin-screw extruder has a length-to-diameter ratio of 40, a screw speed of 200 r / min-240 r / min, and a vacuum exhaust port with a vacuum degree of -0.08 MPa is provided between the 6th and 7th temperature zones.

3. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, The temperatures of the co-rotating twin-screw extruder from the main feed port to the die head are as follows: 230℃-240℃ / 235℃-245℃ / 240℃-250℃ / 240℃-250℃ / 235℃-245℃ / 235℃-245℃ / 230℃-240℃ / 230℃-240℃ / 235℃-245℃.

4. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, Before step (1), the polybutylene terephthalate resin and the polyethylene terephthalate resin are pre-dried at a temperature of 120°C for 4 hours.

5. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, In step (1), add 2 parts of pentaerythritol tetrastearate, 2 parts of antioxidant 1010, and 3 parts of antioxidant 168; the pentaerythritol tetrastearate, antioxidant 1010, and antioxidant 168 are added from the main feed port of the extruder.

6. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, The carboxylated trimesin nucleating agent is obtained by alkaline hydrolysis and acid precipitation of a trimesin intermediate containing ester-terminated groups.

7. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, The ester-terminated trimesoamide intermediate is obtained by amidation reaction of trimesoyl chloride, dodecylamine and methyl 6-aminohexanoate hydrochloride; the mass ratio of trimesoyl chloride, dodecylamine and methyl 6-aminohexanoate hydrochloride is 10:14:

7.

8. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, The bifunctionalized dopamine nanoparticles were prepared by the following steps: reacting dopamine nanoparticles with epichlorohydrin under alkaline conditions to obtain epoxy-functionalized dopamine nanoparticles; reacting the epoxy-functionalized dopamine nanoparticles with succinic anhydride in anhydrous N,N-dimethylformamide to obtain bifunctionalized dopamine nanoparticles; the mass ratio of dopamine nanoparticles to epichlorohydrin was 8:20; the mass ratio of epoxy-functionalized dopamine nanoparticles to succinic anhydride was 9:

8.

9. The method for preparing the low-warpage glass fiber reinforced mobile phone back cover material according to claim 1, characterized in that, The epoxy functional polymer chain extender has an epoxy equivalent of 300-320 g / eq and an average molecular weight of 7000-7500; the glass fiber chopped strands are E-glass with a diameter of 12-14 μm and a cutting length of 4-5 mm; the core-shell toughening agent is from Dow Chemical Company and has the brand name EXL-2690.

10. A low-warp glass fiber reinforced mobile phone back cover material, characterized in that, The material is obtained by the preparation method of the low warp glass fiber reinforced mobile phone back cover material according to any one of claims 1-9.