A low-density composite material based on glass microbeads and epoxy resin and a method for producing the same

Abstract

The application relates to the field of composite materials, in particular to a low-density composite material based on glass microbeads and epoxy resin and a preparation method thereof; the raw materials of the composite material are as follows: epoxy resin, modified hollow glass microbeads, a composite amine curing agent, an interface promoter, a dispersing defoaming agent, a toughening agent and nano hollow silica microbeads; the modified hollow glass microbeads are hollow glass microbeads modified by a composite coupling agent, the composite coupling agent is compounded by a KH-550 silane coupling agent and a KH-560 silane coupling agent according to a mass ratio of 1:(0.3-0.8); the application can effectively solve the core technical problem of poor interface compatibility, can improve the overall compression resistance of the composite material while ensuring the low density of the material, can balance the curing speed and the mechanical toughness, and can solve the problem that a single curing agent is fast and brittle or tough and slow.

Description

Technical Field

[0001] This application relates to the field of composite materials, and more specifically, to a low-density composite material based on glass microspheres and epoxy resin and a method for preparing the same. Background Technology

[0002] Low-density composite materials have irreplaceable application value in fields such as deep-sea exploration and aerospace due to their advantages of lightweight and high strength. Among them, the composite system with epoxy resin as the matrix and hollow glass microspheres as lightweight fillers has become a research hotspot because epoxy resin has strong adhesion and good chemical stability, while hollow glass microspheres have low density and excellent compressive strength.

[0003] In existing technologies, the preparation of glass microsphere / epoxy resin composites often employs simple mixing and room-temperature curing or single-temperature curing processes, which have the following core defects: First, the surface of hollow glass microspheres is hydrophilic, resulting in poor interfacial compatibility with the hydrophobic epoxy resin matrix. This easily leads to microsphere agglomeration and interfacial delamination, causing a decline in the mechanical properties of the composite material and failing to meet the strength requirements of high-end applications. Second, the curing system often uses a single amine curing agent, which either results in slow curing speed and low efficiency, or high brittleness and poor impact resistance after curing, making it difficult to balance curing efficiency and mechanical toughness. Third, the mixing ratio of microspheres and epoxy resin is difficult to control precisely. Either insufficient microsphere addition leads to high material density, or excessive addition leads to uneven mixing and increased porosity, further affecting the material's density and stability.

[0004] Therefore, in view of the shortcomings of existing technologies, developing a low-density composite material of glass microspheres / epoxy resin / amine curing agent with good interfacial compatibility, low density, high strength, excellent toughness, stable preparation process, and scalable production has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] This application provides a low-density composite material based on glass microspheres and epoxy resin and its preparation method. This application effectively solves the core technical problem of poor interfacial compatibility by modifying hollow glass microspheres with a specific coupling agent. At the same time, by combining the bimodal gradient gradation of hollow glass microspheres and the role of nano-hollow silica microspheres as a buffer phase against breakage, the overall compressive strength of the composite material is improved while ensuring the low density of the material. In addition, based on the good compatibility of the composite material system, this application uses a composite amine curing agent to balance curing speed and mechanical toughness, solving the problem of "fast curing leads to brittleness, and toughness leads to slow curing" of a single curing agent.

[0006] In a first aspect, this application provides a low-density composite material based on glass microspheres and epoxy resin, employing the following technical solution: A low-density composite material based on glass microspheres and epoxy resin, the composite material being prepared from the following raw materials in parts by weight: 40-60 parts epoxy resin, 50-80 parts modified hollow glass microspheres, 10-25 parts composite amine curing agent, 1-5 parts interface promoter, 0.5-2 parts dispersant and defoamer, 3-8 parts toughening agent, and 0.5-2 parts nano-hollow silica microspheres; The modified hollow glass microspheres are hollow glass microspheres modified with a composite coupling agent. The hollow glass microspheres are composed of hollow glass microspheres with particle sizes of 20–40 μm and 50–80 μm in a mass ratio of 1:(0.6–1.2). The particle size of the nano-hollow silica microspheres is 10–30 nm. The composite coupling agent is composed of KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:(0.3–0.8). The composite amine curing agent is composed of aliphatic amines, aromatic amines and microcapsule-modified imidazole, with the mass ratio of aliphatic amines to aromatic amines being 1:(1.2-2.0); the amount of microcapsule-modified imidazole is 5-12 wt% of the total mass of aliphatic amines and aromatic amines.

[0007] By adopting the above technical solutions, this application uses a composite coupling agent of KH-550 and KH-560 to modify hollow glass microspheres, so that amine and epoxy groups are grafted onto the surface of the microspheres simultaneously. These groups can form stable chemical bonds with the epoxy resin matrix and amine curing agent, respectively, thereby improving the compatibility between the glass microspheres and the resin matrix. In addition, this application uses KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:(0.3-0.8) to modify the glass microspheres. Combined with hollow glass microspheres with particle sizes of 20-40 μm and 50-80 μm in a mass ratio of 1:(0.6-1.2), the silane coupling agent can form an ideal monolayer coverage on the surface of the glass microspheres. This avoids the formation of a weak boundary layer due to improper modification, which would lead to a decrease in strength. It also avoids abnormal viscosity and consistency, which would affect the compatibility of the composite material system. Meanwhile, this application introduces nano-hollow silica microspheres as a breakage-resistant buffer phase, forming a multi-point support structure during stirring, pouring, and curing, thereby reducing the breakage rate of large-diameter hollow glass microspheres and further improving the compressive strength of the composite material under the same density conditions. In addition, this application also introduces a composite amine curing agent, which, after compounding, can balance curing speed and mechanical toughness, solving the problem of "fast curing leads to brittleness, and toughness leads to slow curing" of single curing agents. Furthermore, microcapsule-modified imidazole, as a latent curing component, forms a latent curing layer with aliphatic amines and aromatic amines. The fast-curing synergistic system allows the system to have a working period of ≥8 hours at room temperature, which can meet the long construction window requirements of large components, on-site pouring, and deep-sea buoyancy materials. At the same time, it can achieve low-temperature rapid curing at 60–80℃ with a curing shrinkage rate of ≤0.3%, reducing internal stress, reducing defects such as cracking and deformation of products, and significantly improving molding stability and dimensional accuracy.

[0008] Furthermore, the composite material of this application exhibits excellent comprehensive performance due to the combined effect of various components, and can be widely used in high-end fields such as deep-sea buoyancy equipment, lightweight aerospace components, and underwater acoustic devices, with broad market prospects; the preparation process is simple and can be mass-produced, resulting in significant economic and social benefits.

[0009] Furthermore, the preparation method of the modified hollow glass microspheres includes the following steps: Hollow glass microspheres are placed in an oven and dried at 110-120℃ for 3-4 hours to remove surface moisture and impurities, and then cooled to room temperature for later use. KH-550 silane coupling agent and KH-560 silane coupling agent are mixed, and a mixed solvent of ethanol and water in a mass ratio of (5-9):(8-12) is added. The pH value is adjusted to 4.2-4.8, and the mixture is stirred evenly to obtain a composite coupling agent solution, wherein the mass fraction of the composite coupling agent in the solution is 3-5%. The dried hollow glass microspheres were added to the composite coupling agent solution, with a mass ratio of microspheres to coupling agent solution of 100:(6-8). The mixture was stirred at a low speed of 200-250 rpm for 40-60 minutes at 25-30℃ to ensure that the coupling agent fully coated the surface of the microspheres. The mixed system was filtered to obtain glass microspheres coated with coupling agent. These microspheres were then placed in an oven and dried at 85-95℃ for 2-3 hours to obtain modified hollow glass microspheres.

[0010] By adopting the above technical solutions, this application enables the microspheres to simultaneously and uniformly graft appropriate amounts of amine and epoxy groups onto their surface through a modification step, thereby forming a dual chemical bond with the matrix and curing agent, completely solving the problem of poor interfacial compatibility. Furthermore, in this solution, the pH value is typically adjusted using acidic solutions (mainly hydrochloric acid or sulfuric acid) or alkaline solutions (mainly sodium hydroxide and ammonia).

[0011] Furthermore, the fatty amine is diethylenetriamine (DETA) or 593 curing agent, and the aromatic amine is 4,4′-diaminodiphenyl sulfone (DDS) or m-phenylenediamine (m-XDA).

[0012] Furthermore, the interface promoter is a compound of 2-methylimidazole and triethanolamine in a mass ratio of 1:(0.5-1.0).

[0013] By adopting the above technical solutions, the interface promoter of this application can promote the reaction between the coupling agent and the epoxy resin and curing agent, and further enhance the interfacial bonding force.

[0014] Furthermore, the toughening agent is a compound of carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) and nano-SiO2 in a mass ratio of 3:(0.5-1.5).

[0015] By adopting the above technical solutions, the toughening agent of this application can improve the impact resistance and toughness of composite materials without affecting the low-density properties of the materials.

[0016] Furthermore, the epoxy resin is a compound made by combining one of bisphenol A type epoxy resin E-44 or bisphenol A type epoxy resin E-51 with tetrafunctional epoxy resin AG-80 at a mass ratio of 1:(0.4-0.8).

[0017] By adopting the above technical solutions, the compounded epoxy resin takes into account both matrix strength and molding fluidity, avoiding the problems of single epoxy resins either having insufficient strength or too high viscosity to be easily mixed.

[0018] Furthermore, the dispersing defoamer is a compound of BYK-163 and organosilicon defoamer in a mass ratio of (1.2-2.5):(0.6-1.2).

[0019] By adopting the above technical solutions, the compounded dispersant and defoamer can effectively prevent the agglomeration of hollow glass microspheres, and at the same time completely eliminate the bubbles generated during the preparation process, thereby improving the density of the material.

[0020] Furthermore, the raw materials of the composite material also include 2-6 parts of a composite halogen-free flame retardant, which is a compound of ammonium polyphosphate (APP) and melamine cyanurate (MCA) in a mass ratio of 1:(0.5-1).

[0021] Secondly, this application provides a method for preparing a low-density composite material based on glass microspheres and epoxy resin, using the following technical solution: A method for preparing a low-density composite material based on glass microspheres and epoxy resin includes the following steps: Preparation of epoxy resin premix Preheat the epoxy resin at 45-50℃ for 15-20 minutes. Add toughening agent, interface accelerator, and dispersant / defoamer to the preheated epoxy resin in sequence. Stir at 250-300 rpm for 8-10 minutes. After stirring evenly, place the mixture in a vacuum degassing chamber and degas for 25-30 minutes under a vacuum of -0.090~-0.095 MPa to remove air bubbles from the system, obtaining an epoxy resin premix for later use.

[0022] Mixing of composite systems: A composite amine curing agent is added to the epoxy resin premix to ensure thorough mixing. Modified hollow glass microspheres and nano-hollow silica microspheres are added to the mixture to obtain a uniform composite material mixture. The composite material mixture is then placed in a vacuum degassing chamber at a vacuum level of -0.090 to -0.095 MPa to degas and completely remove any air mixed in during the mixing process. Molding and curing: Preheat the mold to 50-60℃, evenly apply release agent to the inner wall of the mold, and slowly pour the composite material mixture into the mold, filling it to 95-98% of the mold volume; place the mold containing the composite material mixture into a vacuum molding machine, apply a pressure of 0.8-1.5MPa, and maintain a vacuum of -0.090~-0.095MPa, holding the pressure for 15-20 minutes to allow the mixture to fully fill the mold and remove residual air bubbles; The process employs a "step-by-step temperature curing" technique, with the following parameters: first, curing at 75-85℃ for 2-2.5 hours; then, curing at 115-125℃ for 2-2.5 hours; and finally, curing at 140-150℃ for 3-4 hours. After curing, the heating device is turned off, and the mold is allowed to cool to room temperature with the furnace before demolding to obtain the composite material blank. Post-processing: The composite material blank is placed in an oven and post-cured at 120-130℃ for 2-3 hours to obtain a low-density composite material product.

[0023] By adopting the above technical solutions, this application uses a "stepped temperature curing" process, which can avoid internal stress concentration caused by excessive curing speed, reduce crack generation, and ensure complete curing, thereby improving the mechanical properties of the material. The post-curing operation can eliminate internal residual stress and further improve the strength and stability of the material.

[0024] Furthermore, in the mixing step of the composite system, the modified hollow glass microspheres are added to the above mixture in 3-4 portions. After each addition, the mixture is stirred at a speed of 150-180 rpm for 5-8 minutes. After all the materials are added, the mixture is stirred for another 10-15 minutes to obtain a uniform composite material mixture.

[0025] By adopting the above technical solutions and using distributed feeding and low-speed stirring, the glass microspheres can be mixed evenly while avoiding breakage and aggregation.

[0026] In summary, this application has the following beneficial effects: 1. Interface Modification Innovation: Hollow glass microspheres are modified using a composite coupling agent of KH-550 and KH-560, which simultaneously grafts amine and epoxy groups onto the surface of the microspheres. These groups can form stable chemical bonds with the epoxy resin matrix and amine curing agent, respectively. This completely solves the technical problems of poor interfacial compatibility, microsphere agglomeration, and interfacial delamination after modification with traditional single coupling agents, and significantly improves the interfacial bonding strength and mechanical properties of the composite material. At the same time, the composite interface promoter is added to further enhance the interfacial reaction and achieve a "seamless connection" of the interface.

[0027] 2. Raw material system innovation: ① The epoxy resin uses a blend of bisphenol A and tetrafunctional epoxy, balancing molding flowability and matrix strength, and addressing the performance limitations of single epoxy resins; ② The curing agent uses a blend of aliphatic amines and aromatic amines, overcoming the limitation of single curing agents being "brittle when curing quickly and tough when curing slowly," balancing curing efficiency and mechanical toughness; ③ The toughening agent uses a blend of carboxyl-terminated butadiene-acrylonitrile rubber and nano-SiO2, significantly improving the impact resistance of the material without increasing its density, and addressing the brittleness of epoxy composites; ④ The dispersing and defoaming agents are used in combination to simultaneously achieve uniform dispersion of microspheres and complete elimination of bubbles, improving the material's density.

[0028] 3. Process Innovation: ① The "step-by-step feeding and low-speed stirring" mixing method effectively avoids the breakage of hollow glass microspheres, ensuring that the microspheres are evenly dispersed in the matrix, and precisely controlling the amount of microspheres added to achieve the best balance between density and strength; ② The design of a composite process of "vacuum degassing + vacuum molding + stepped temperature rise curing" completely eliminates air bubbles and residual stress inside the material, reduces crack defects, ensures complete curing of the material, and further improves the compressive strength, toughness and dimensional stability of the material; ③ The entire process parameters are precise and controllable, the operation is simple, no complex equipment is required, and large-scale production can be achieved, reducing production costs.

[0029] 4. Excellent comprehensive performance: The composite material prepared by this invention has a density as low as 0.40-0.70 g / cm³, which is far lower than that of existing similar materials. At the same time, it has a compressive strength ≥40MPa, a water absorption rate <0.15%, an impact strength ≥5.0kJ / m², and a thermal conductivity as low as 0.08-0.25W / (m·K). It achieves the synergistic advantages of "low density, high strength, high toughness, low water absorption, and low thermal conductivity", which can adapt to harsh service environments such as deep sea and aerospace, and has a wider range of applications and stronger practicality. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the embodiments.

[0031] Example A low-density composite material based on glass microspheres and epoxy resin, the composite material being prepared from the following raw materials in parts by weight: 40-60 parts epoxy resin, 50-80 parts modified hollow glass microspheres, 10-25 parts composite amine curing agent, 1-5 parts interface promoter, 0.5-2 parts dispersant and defoamer, 3-8 parts toughening agent, and 0.5-2 parts nano-hollow silica microspheres; The epoxy resin is a compound made by combining one of bisphenol A type epoxy resin E-44 or bisphenol A type epoxy resin E-51 with tetrafunctional epoxy resin AG-80 at a mass ratio of 1:(0.4-0.8).

[0032] The composite amine curing agent is composed of aliphatic amines, aromatic amines, and microencapsulated modified imidazoles, with a mass ratio of aliphatic amines to aromatic amines of 1:(1.2-2.0). The amount of microencapsulated modified imidazoles is 5-12 wt% of the total mass of the aliphatic amines and aromatic amines. The aliphatic amine is diethylenetriamine (DETA) or 593 curing agent, and the aromatic amine is 4,4′-diaminodiphenyl sulfone (DDS) or m-phenylenediamine (m-XDA).

[0033] The interface accelerator is a compound of 2-methylimidazole and triethanolamine at a mass ratio of 1:(0.5-1.0); the toughening agent is a compound of carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) and nano-SiO2 at a mass ratio of 3:(0.5-1.5); the dispersing defoamer is a compound of BYK-163 and silicone defoamer at a mass ratio of (1.2-2.5):(0.6-1.2). The modified hollow glass microspheres are hollow glass microspheres modified with a composite coupling agent. The hollow glass microspheres are composed of hollow glass microspheres with particle sizes of 20–40 μm and 50–80 μm in a mass ratio of 1:(0.6–1.2). The particle size of the nano-hollow silica microspheres is 10–30 nm. The composite coupling agent is a mixture of KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:(0.3–0.8). Specifically, the preparation method of the modified hollow glass microspheres includes the following steps: Hollow glass microspheres were placed in an oven and dried at 110-120℃ for 3-4 hours to remove surface moisture and impurities, and then cooled to room temperature for later use. KH-550 silane coupling agent and KH-560 silane coupling agent were mixed, and a mixed solvent of ethanol and water in a mass ratio of (5-9):(8-12) was added to adjust the pH value to 4.2-4.8. The mixture was stirred evenly to obtain a composite coupling agent solution, wherein the mass fraction of the composite coupling agent in the solution was 3-5%. The dried hollow glass microspheres were added to the composite coupling agent solution, with a mass ratio of microspheres to coupling agent solution of 100:(6-8). The mixture was stirred at a low speed of 200-250 rpm for 40-60 minutes at 25-30℃ to ensure that the coupling agent fully coated the surface of the microspheres. The mixture was filtered to obtain glass microspheres coated with coupling agent, which were then placed in an oven and dried at 85-95℃ for 2-3 hours to obtain modified hollow glass microspheres.

[0034] The raw materials for the composite material also include 2-6 parts of a composite halogen-free flame retardant, which is a compound of ammonium polyphosphate (APP) and melamine cyanurate (MCA) in a mass ratio of 1:(0.5-1).

[0035] This application also provides a method for preparing a low-density composite material based on glass microspheres and epoxy resin, including the following steps: Preparation of epoxy resin premix Preheat the epoxy resin at 45-50℃ for 15-20 minutes. Add toughening agent, interface accelerator, and dispersant / defoamer to the preheated epoxy resin in sequence. Stir at 250-300 rpm for 8-10 minutes. After stirring evenly, place the mixture in a vacuum degassing chamber and degas for 25-30 minutes under a vacuum of -0.090~-0.095 MPa to remove air bubbles from the system, obtaining an epoxy resin premix for later use.

[0036] Mixing of composite systems: A composite amine curing agent is added to the epoxy resin premix to ensure thorough mixing. Modified hollow glass microspheres and nano-hollow silica microspheres are added to the mixture to obtain a uniform composite material mixture. The composite material mixture is then placed in a vacuum degassing chamber at a vacuum level of -0.090 to -0.095 MPa to degas and completely remove any air mixed in during the mixing process. Molding and curing: Preheat the mold to 50-60℃, evenly apply release agent to the inner wall of the mold, and slowly pour the composite material mixture into the mold, filling it to 95-98% of the mold volume; place the mold containing the composite material mixture into a vacuum molding machine, apply a pressure of 0.8-1.5MPa, and maintain a vacuum of -0.090~-0.095MPa, holding the pressure for 15-20 minutes to allow the mixture to fully fill the mold and remove residual air bubbles; The process employs a "step-by-step temperature curing" technique, with the following parameters: first, curing at 75-85℃ for 2-2.5 hours; then, curing at 115-125℃ for 2-2.5 hours; and finally, curing at 140-150℃ for 3-4 hours. After curing, the heating device is turned off, and the mold is allowed to cool to room temperature with the furnace before demolding to obtain the composite material blank. Post-processing: The composite material blank is placed in an oven and post-cured at 120-130℃ for 2-3 hours to obtain a low-density composite material product.

[0037] 10. A method for preparing a low-density composite material based on glass microspheres and epoxy resin according to claim 9, characterized in that, in the mixing step of the composite system, the modified hollow glass microspheres are added to the above mixture in 3-4 portions, and after each addition, the mixture is stirred at a speed of 150-180 rpm for 5-8 minutes; after all the additions are completed, the mixture is stirred for another 10-15 minutes to obtain a uniform composite material mixture.

[0038] In this embodiment, the silicone defoamer is Efka® SI 2040, a product of BASF. The nano-hollow silica microspheres were purchased from Hangzhou Jikang New Materials Co., Ltd., model SS-S200J. The microcapsule-modified imidazole was purchased from Shanghai Soke Purification Materials Co., Ltd., model SC10208E.

[0039] The following explanation is provided through specific examples.

[0040] Example 1 A low-density composite material based on glass microspheres and epoxy resin / amine curing agent is prepared from the following raw materials in parts by weight: 30 parts of bisphenol A type epoxy resin (E-51), 20 parts of tetrafunctional epoxy resin (AG-80), 65 parts of modified hollow glass microspheres, 18 parts of composite amine curing agent, 2 parts of interface accelerator (1.2 parts of 2-methylimidazole and 0.8 parts of triethanolamine), 1 part of dispersant and defoamer (0.67 parts of BYK-163 and 0.33 parts of organosilicon defoamer), 5 parts of toughening agent (4 parts of CTBN and 1 part of nano SiO2), and 1.2 parts of nano hollow silica microspheres; The composite amine curing agent is composed of DETA, DDS and microcapsule-modified imidazole, with a mass ratio of DETA to DDS of 1:1.57; the amount of microcapsule-modified imidazole is 8 wt% of the total mass of aliphatic amine and aromatic amine.

[0041] The modified hollow glass microspheres are hollow glass microspheres modified with a composite coupling agent. The hollow glass microspheres are composed of hollow glass microspheres with a particle size of 20–40 μm and 50–80 μm in a mass ratio of 1:0.8, and the true density of each is 0.30 g / cm³. The composite coupling agent is composed of KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:0.5.

[0042] The preparation method of the above composite material includes the following steps: Step 1: Preparation of modified hollow glass microspheres 1.1 Place the hollow glass microspheres in an oven and dry them at 115℃ for 3.5 hours, then cool them to room temperature; 1.2 Preparation of composite coupling agent solution: KH-550 and KH-560 are mixed at a ratio of 1:0.5, and a mixed solvent of ethanol:water = 9:10 is added. The pH is adjusted to 4.5, and the mixture is stirred evenly. The mass fraction of the coupling agent is 4%. 1.3 The microspheres and coupling agent solution were mixed at a ratio of 100:7, stirred at 28°C and 220 rpm for 50 min, filtered, and dried at 90°C for 2.5 h to obtain modified hollow glass microspheres. Step 2: Preparation of epoxy resin premix 2.1 Mix E-51 and AG-80, and preheat at 48℃ for 18 minutes; 2.2 Add toughening agent, interface promoter, and dispersant / defoamer, stir at 280 rpm for 9 min, and degas under vacuum at -0.092 MPa for 28 min to obtain a premixed solution; Step 3: Mixing of the composite system 3.1 Add the composite amine curing agent and stir at 28°C and 200 rpm for 7 minutes; 3.2 Modified hollow glass microspheres and nano hollow silica microspheres were added in three batches, with stirring for 7 minutes each time at a speed of 160 rpm. After all the microspheres were added, stirring was continued for 12 minutes. 3.3 -0.092MPa vacuum degassing for 18 min; Step 4: Molding and Curing 4.1 Preheat the mold to 55℃, apply release agent, and pour in the mixture; 4.2 Apply a pressure of 1.2 MPa to the vacuum molding machine and maintain a vacuum of -0.092 MPa for 18 minutes; 4.3 Step curing: 80℃ / 2h→120℃ / 2h→145℃ / 3.5h, cool to room temperature in the oven, and demold; Step 5: Post-processing After curing at 125℃ for 2.5 hours, the product is machined to the required dimensions to obtain the final product.

[0043] Example 2 A low-density composite material based on glass microspheres and epoxy resin / amine curing agent is prepared from the following raw materials in parts by weight: 25 parts of bisphenol A type epoxy resin (E-44), 15 parts of tetrafunctional epoxy resin (AG-80), 55 parts of modified hollow glass microspheres, 12 parts of composite amine curing agent, 1.5 parts of interface accelerator (1 part of 2-methylimidazole, 0.5 parts of triethanolamine), 0.8 parts of dispersant and defoamer (0.53 parts of BYK-163, 0.27 parts of organosilicon defoamer), 4 parts of toughening agent (3.2 parts of CTBN, 0.8 parts of nano-SiO2); 0.5 parts of nano-hollow silica microspheres; The composite amine curing agent is composed of 593 curing agent, m-XDA and microcapsule modified imidazole. The mass ratio of 593 curing agent to m-XDA is 1:1.2. The amount of microcapsule modified imidazole is 5 wt% of the total mass of aliphatic amine and aromatic amine.

[0044] The modified hollow glass microspheres are hollow glass microspheres modified with a composite coupling agent. The hollow glass microspheres are composed of hollow glass microspheres with a particle size of 20–40 μm and 50–80 μm in a mass ratio of 1:0.6, and the true density of each is 0.25 g / cm³. The composite coupling agent is composed of KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:0.3.

[0045] The preparation method is basically the same as in Example 1, except for the following parameters: In step 1, the mass ratio of microbeads to coupling agent solution is 100:6, the stirring time is 40 min, and the drying temperature is 85℃. In step 3, the composite amine curing agent is stirred at 180 rpm, and the microbeads are added in 4 batches at 150 rpm. In step 4, the step curing parameters are 80℃ / 2h→120℃ / 2h→140℃ / 3h.

[0046] Example 3 A low-density composite material based on glass microspheres and epoxy resin / amine curing agent is prepared from the following raw materials in parts by weight: 28 parts of bisphenol A type epoxy resin (E-51), 22 parts of tetrafunctional epoxy resin (AG-80), 75 parts of modified hollow glass microspheres, 22 parts of composite amine curing agent, 3 parts of interface accelerator (1.8 parts of 2-methylimidazole and 1.2 parts of triethanolamine), 1.5 parts of dispersant and defoamer (1 part of BYK-163 and 0.5 parts of silicone defoamer), 7 parts of toughening agent (5.6 parts of CTBN and 1.4 parts of nano-SiO2); 2 parts of nano-hollow silica microspheres; The composite amine curing agent is composed of DETA, DDS and microcapsule-modified imidazole, with a mass ratio of DETA to DDS of 1:2.0; the amount of microcapsule-modified imidazole is 12 wt% of the total mass of the fatty amine and aromatic amine.

[0047] The modified hollow glass microspheres are hollow glass microspheres modified with a composite coupling agent. The hollow glass microspheres are composed of hollow glass microspheres with a particle size of 20–40 μm and 50–80 μm in a mass ratio of 1:1.2, and the true density of each is 0.45 g / cm³. The composite coupling agent is composed of KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:0.8.

[0048] The preparation method is basically the same as in Example 1, except for the following parameters: In step 1, the mass ratio of microbeads to coupling agent solution is 100:8, the stirring time is 60 min, and the drying temperature is 95℃; In step 4, the step curing parameters are 80℃ / 2h→120℃ / 2h→150℃ / 4h, and the pressure is 1.5MPa.

[0049] Example 4 The difference between Example 4 and Example 1 is that the raw materials for the composite material also include 2 parts of a composite halogen-free flame retardant, which is a compound of ammonium polyphosphate (APP) and melamine cyanurate (MCA) at a mass ratio of 1:0.5. The composite halogen-free flame retardant, along with modified hollow glass microspheres and nano-hollow silica microspheres, are added to the mixture in portions.

[0050] Example 5 The difference between Example 5 and Example 1 is that the raw materials for the composite material also include 4 parts of a composite halogen-free flame retardant, which is a compound of ammonium polyphosphate (APP) and melamine cyanurate (MCA) at a mass ratio of 1:0.8. The composite halogen-free flame retardant, along with modified hollow glass microspheres and nano-hollow silica microspheres, are added to the mixture in portions.

[0051] Example 6 The difference between Example 6 and Example 1 is that the raw materials for the composite material also include 6 parts of a composite halogen-free flame retardant, which is composed of ammonium polyphosphate (APP) and melamine cyanurate (MCA) in a mass ratio of 1:1. The composite halogen-free flame retardant is added to the mixture in several batches along with the modified hollow glass microspheres and nano-hollow silica microspheres.

[0052] Comparative Example The difference between Comparative Example 1 and Example 1 is that: glass microspheres modified with a single KH-550 coupling agent (i.e., KH-560 is replaced with an equal amount of KH-550 coupling agent), a single E-51 epoxy resin (i.e., AG-80 resin is replaced with an equal amount of E-51 epoxy resin), a single DDS curing agent (i.e., DDS curing agent is replaced with an equal amount of DETA curing agent), no interface accelerator, conventional mixing, and single temperature rise curing (120℃ / 6h).

[0053] The difference between Comparative Example 2 and Example 1 is that the glass microspheres were not modified, the other raw materials were the same as those in Example 1, and the preparation process was the same as that in Example 1.

[0054] The difference between Comparative Example 3 and Example 1 is that a single DETA curing agent is used, that is, the DDS curing agent is replaced with an equal amount of DETA curing agent, the remaining raw materials are the same as those in Example 1, and the preparation process is the same as that in Example 1.

[0055] The difference between Comparative Example 4 and Example 1 is that the KH-550 coupling agent was replaced with an equal amount of KH-560 coupling agent, and the rest were the same.

[0056] The difference between Comparative Example 5 and Example 1 is that the mass ratio of KH-550 coupling agent to KH-560 coupling agent is 1:1.2, and the rest are the same.

[0057] The difference between Comparative Example 6 and Example 1 is that hollow glass microspheres with a particle size of 20–40 μm were replaced with an equal amount of hollow glass microspheres with a particle size of 50–80 μm, otherwise the same.

[0058] The difference between Comparative Example 7 and Example 1 is that hollow glass microspheres with a particle size of 20–40 μm and 50–80 μm were used in a mass ratio of 1:1.5, and the rest were the same.

[0059] The difference between Comparative Example 8 and Example 1 is that no nano-hollow silica microspheres were added, otherwise they are the same.

[0060] The difference between Comparative Example 9 and Example 1 is that the particle size of the nano-hollow silica microspheres is 90-150 nm.

[0061] Performance testing The composite materials obtained in the examples and comparative examples were subjected to performance testing. The test items and test methods are as follows: Density was tested using the immersion method according to GB / T 1033.1—2008; Bending strength was tested using the three-point bending method according to GB / T 9341—2008; Impact strength was tested using a simply supported beam according to GB / T 1043.1—2008; Water absorption rate was tested according to GB / T 1034—2008 using the room temperature immersion method; Flame retardant performance was tested according to UL 94 using the vertical flame method; The test results are shown in Table 1.

[0062] Table 1. Results of Composite Material Performance Testing Firstly, the performance comparison between the examples and Comparative Example 1 shows that the composite material of this application not only has a low density but also excellent mechanical properties. This indicates that after modification with a specific coupling agent for hollow glass microspheres, this application can not only effectively solve the core technical problem of poor interfacial compatibility, but also combine the bimodal gradient gradation of hollow glass microspheres and the role of nano-hollow silica microspheres as an anti-breakage buffer phase, thereby improving the overall compressive strength of the composite material while ensuring its low density.

[0063] Furthermore, analysis of the performance of Examples 4-6 revealed that, in the system of this application, the addition of a composite halogen-free flame retardant can effectively improve the flame retardant performance of the composite material without significantly affecting mechanical properties or other properties.

[0064] Furthermore, analysis of the performance of Comparative Example 2 shows that modification of hollow glass microspheres is crucial for improving the performance of the composite material of this application. Further analysis of the performance of Comparative Examples 4 and 5 reveals that the weight and application of the silane coupling agent are critical during the modification of the hollow glass microspheres. This is because while modifying glass microspheres with silane coupling agents to improve their compatibility is a common technique in the field, this application not only requires uniform low-density dispersion of glass microspheres in the resin system, but also employs glass microspheres of different particle sizes, a bimodal gradient distribution, and nano-hollow silica microspheres as a buffer phase to prevent breakage. This means that during the modification of hollow glass microspheres in this application, the degree of surface modification for both particle sizes of glass microspheres needs to be considered to avoid the formation of a weak boundary layer due to improper modification, which could lead to a decrease in strength, and also to avoid abnormal viscosity and consistency that could negatively impact the compatibility of the composite material system. Therefore, this application uses KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:(0.3-0.8) to modify glass microspheres. This modification system can fully act on hollow glass microspheres with a mass ratio of 1:(0.6-1.2) and particle sizes of 20-40 μm and 50-80 μm, allowing the silane coupling agent to form an ideal monolayer coating on the surface of the glass microspheres, thus fully utilizing the function of the glass microspheres. Moreover, analysis of the performance of Comparative Examples 6 and 7 shows that the excellent performance of the modified microspheres in this application is inseparable from the bimodal gradient gradation of the hollow glass microspheres with particle sizes of 20-40 μm and 50-80 μm. In addition, analysis of the performance of Comparative Examples 8 and 9 shows that the introduction of nano-hollow silica microspheres with a specified particle size as an anti-breakage buffer phase in this application can further improve the compressive strength of the composite material.

[0065] Furthermore, analysis of the performance of Comparative Example 2 revealed that the composite amine curing agent introduced in this application, after compounding, can balance curing speed and mechanical toughness, solving the problem of "fast curing leading to brittleness, and toughness leading to slow curing" of single curing agents; and the microencapsulated modified imidazole, as a latent curing component, forms a latent curing layer with aliphatic amines and aromatic amines. Fast and solid collaborative system.

[0066] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-density composite material based on glass microspheres and epoxy resin, characterized in that, The composite material is prepared from the following raw materials in parts by weight: 40-60 parts epoxy resin, 50-80 parts modified hollow glass microspheres, 10-25 parts composite amine curing agent, 1-5 parts interface promoter, 0.5-2 parts dispersant and defoamer, 3-8 parts toughening agent, and 0.5-2 parts nano hollow silica microspheres. The modified hollow glass microspheres are hollow glass microspheres modified with a composite coupling agent. The hollow glass microspheres are composed of hollow glass microspheres with particle sizes of 20–40 μm and 50–80 μm in a mass ratio of 1:(0.6–1.2). The particle size of the nano-hollow silica microspheres is 10–30 nm. The composite coupling agent is composed of KH-550 silane coupling agent and KH-560 silane coupling agent in a mass ratio of 1:(0.3–0.8). The composite amine curing agent is composed of aliphatic amines, aromatic amines and microcapsule-modified imidazole, wherein the mass ratio of aliphatic amines to aromatic amines is 1:(1.2-2.0); and the amount of microcapsule-modified imidazole is 5-12 wt% of the total mass of aliphatic amines and aromatic amines.

2. The low-density composite material based on glass microspheres and epoxy resin according to claim 1, characterized in that, The method for preparing the modified hollow glass microspheres includes the following steps: Hollow glass microspheres are placed in an oven and dried at 110-120℃ for 3-4 hours to remove surface moisture and impurities, and then cooled to room temperature for later use. KH-550 silane coupling agent and KH-560 silane coupling agent are mixed, and a mixed solvent of ethanol and water in a mass ratio of (5-9):(8-12) is added. The pH value is adjusted to 4.2-4.8, and the mixture is stirred evenly to obtain a composite coupling agent solution, wherein the mass fraction of the composite coupling agent in the solution is 3-5%. The dried hollow glass microspheres were added to the composite coupling agent solution, with a mass ratio of microspheres to coupling agent solution of 100:(6-8). The mixture was stirred at a low speed of 200-250 rpm for 40-60 minutes at 25-30℃ to ensure that the coupling agent fully coated the surface of the microspheres. The mixed system was filtered to obtain glass microspheres coated with coupling agent. These microspheres were then placed in an oven and dried at 85-95℃ for 2-3 hours to obtain modified hollow glass microspheres.

3. The low-density composite material based on glass microspheres and epoxy resin according to claim 1, characterized in that, The fatty amine is diethylenetriamine (DETA) or 593 curing agent, and the aromatic amine is 4,4′-diaminodiphenyl sulfone (DDS) or m-phenylenediamine (m-XDA).

4. The low-density composite material based on glass microspheres and epoxy resin according to claim 1, characterized in that, The interface promoter is a compound of 2-methylimidazole and triethanolamine in a mass ratio of 1:(0.5-1.0).

5. The low-density composite material based on glass microspheres and epoxy resin according to claim 1, characterized in that, The toughening agent is a compound of carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) and nano-SiO2 in a mass ratio of 3:(0.5-1.5).

6. The low-density composite material based on glass microspheres and epoxy resin according to claim 1, characterized in that, The epoxy resin is a compound made by combining one of bisphenol A type epoxy resin E-44 or bisphenol A type epoxy resin E-51 with tetrafunctional epoxy resin AG-80 at a mass ratio of 1:(0.4-0.8).

7. The low-density composite material based on glass microspheres and epoxy resin according to claim 1, characterized in that, The dispersing defoamer is a compound of BYK-163 and organosilicon defoamer in a mass ratio of (1.2-2.5):(0.6-1.2).

8. The low-density composite material based on glass microspheres and epoxy resin according to claim 1, characterized in that, The raw materials of the composite material also include 2-6 parts of a composite halogen-free flame retardant, which is a compound of ammonium polyphosphate (APP) and melamine cyanurate (MCA) in a mass ratio of 1:(0.5-1).

9. A method for preparing a low-density composite material based on glass microspheres and epoxy resin as described in any one of claims 1-8, characterized in that, Includes the following steps: Preparation of epoxy resin premix Preheat the epoxy resin at 45-50℃ for 15-20 minutes. Add toughening agent, interface accelerator, and dispersant / defoamer to the preheated epoxy resin in sequence. Stir at 250-300 rpm for 8-10 minutes. After stirring evenly, place the mixture in a vacuum degassing chamber and degas for 25-30 minutes under a vacuum of -0.090~-0.095 MPa to remove air bubbles from the system, obtaining an epoxy resin premix for later use. Mixing of composite systems: A composite amine curing agent is added to the epoxy resin premix to ensure thorough mixing. Modified hollow glass microspheres and nano-hollow silica microspheres are added to the mixture to obtain a uniform composite material mixture. The composite material mixture is then placed in a vacuum degassing chamber at a vacuum level of -0.090 to -0.095 MPa to degas and completely remove any air mixed in during the mixing process. Molding and curing: Preheat the mold to 50-60℃, evenly apply release agent to the inner wall of the mold, and slowly pour the composite material mixture into the mold, filling it to 95-98% of the mold volume; place the mold containing the composite material mixture into a vacuum molding machine, apply a pressure of 0.8-1.5MPa, and maintain a vacuum of -0.090~-0.095MPa, holding the pressure for 15-20 minutes to allow the mixture to fully fill the mold and remove residual air bubbles; The process employs a "step-by-step temperature curing" technique, with the following parameters: first, curing at 75-85℃ for 2-2.5 hours; then, curing at 115-125℃ for 2-2.5 hours; and finally, curing at 140-150℃ for 3-4 hours. After curing, the heating device is turned off, and the mold is allowed to cool to room temperature with the furnace before demolding to obtain the composite material blank. Post-processing: The composite material blank is placed in an oven and post-cured at 120-130℃ for 2-3 hours to obtain a low-density composite material product.

10. The method for preparing a low-density composite material based on glass microspheres and epoxy resin according to claim 9, characterized in that, In the mixing step of the composite system, the modified hollow glass microspheres are added to the above mixture in 3-4 portions. After each addition, the mixture is stirred at a speed of 150-180 rpm for 5-8 minutes. After all the materials are added, the mixture is stirred for another 10-15 minutes to obtain a uniform composite material mixture.

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