Preparation method of bismaleimide resin-based light synthetic core material adhesive film with low thermal expansion coefficient

Abstract

The invention relates to a preparation method of a low-thermal-expansion-coefficient bismaleimide resin-based light synthetic core material adhesive film, and belongs to the field of low-thermal-expansion-coefficient bismaleimide resin-based light synthetic core materials, and the specific scheme comprises the following steps: step 1, pre-polymerizing an allyl compound and bismaleimide resin to obtain pre-polymerized resin A; step 2, uniformly dispersing epoxy resin, a curing agent, a flexibilizer and the surface-functionalized boron nitride nanotube to obtain ground blended resin B; step 3, performing vacuum kneading on the prepolymerized resin A, the ground blended resin B and the zirconium tungstate loaded hollow silicon dioxide to obtain a sizing material for the light synthetic core material adhesive film; and 4, calendaring the rubber material to form a film, and compounding the film with a carrier to obtain the uncured bismaleimide resin-based light synthetic core material rubber film with the low thermal expansion coefficient. The problems of high thermal expansion coefficient, high density, large thermal stress and the like of a bismaleimide resin-based light synthetic core material adhesive film in the prior art are solved.

Description

Technical Field

[0001] This invention belongs to the field of lightweight synthetic core materials based on bismaleimide resin with low coefficient of thermal expansion, and specifically relates to a method for preparing a lightweight synthetic core material film based on bismaleimide resin with low coefficient of thermal expansion. Background Technology

[0002] In the aerospace industry, high reliability, lightweight design, and high efficiency are continuously pursued goals. Employing lightweight materials, optimizing structural design, and combining advanced forming processes are effective ways to achieve these goals. To significantly reduce structural weight and improve cost-effectiveness, the application of lightweight composite sandwich structures is increasing. Common core material types include honeycomb structures, lattice structures, foam structures, and synthetic core films. Among these, synthetic core films possess excellent process adaptability and ease of handling before curing, with a thickness as low as 0.5 mm and support for flexible cutting; after curing, they transform into lightweight materials with good mechanical properties and isotropic characteristics. Furthermore, this material can be co-cured with prepregs without the need for additional adhesives, showing broad application prospects. Bismaleimide resin-based carbon fiber composites are widely used in the manufacture of lightweight, high-rigidity components for high-speed aircraft due to their excellent high-temperature resistance, damp-heat resistance, and mechanical strength. Correspondingly, bismaleimide resin-based lightweight synthetic core films exhibit excellent matching in terms of heat resistance and mechanical behavior, thus becoming a key core material for manufacturing such composite sandwich structures. However, in high-speed aircraft applications, aerodynamic heating causes a rapid rise in structural temperature, resulting in significant thermal expansion of the core material. This expansion not only causes dimensional instability and internal stress concentration in components but may also induce microcracks that are difficult to detect, ultimately affecting the service life of the structure and flight safety. Therefore, developing a lightweight synthetic core film with a low coefficient of thermal expansion for co-curing bismaleimide resin-based composite materials is of significant engineering importance for improving the structural reliability of high-speed aircraft. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of high thermal expansion coefficient, high density and high thermal stress of bismaleimide resin-based lightweight synthetic core film in the prior art, and to provide a method for preparing bismaleimide resin-based lightweight synthetic core film with low thermal expansion coefficient.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion, wherein the lightweight synthetic core film based on bismaleimide resin comprises bismaleimide resin, allyl compound, commercial epoxy resin, curing agent, lightweight filler with low coefficient of thermal expansion, toughening agent and carrier, and the lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion is prepared by a prepolymerization, grinding and dispersion, vacuum kneading and hot calendering composite film forming method.

[0006] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion includes the following steps:

[0007] Step 1: Preparation of prepolymerized resin

[0008] The allyl compound was heated and stirred in a prepolymer reactor. After heating to 140-145°C, bismaleimide resin was added. The mixture was stirred until it became uniform and transparent. After stirring and reacting at 130-140°C for 30-40 minutes, it was cooled to obtain prepolymer resin A.

[0009] Step 2: Preparation of the Grinding Blend Resin

[0010] Epoxy resin, curing agent, toughening agent and surface-functionalized boron nitride nanotubes are mixed by stirring to form a coarse mixture. The coarse mixture is then ground and dispersed 3-5 times on a ceramic three-roll mill to obtain a ground blended resin B. The surface functional groups of the surface-functionalized boron nitride nanotubes are maleimide groups.

[0011] Step 3: Set the heating temperature of the vacuum kneader to 60~70℃ for preheating. Add the ground and blended resin B to the preheated vacuum kneader and knead for 5~15 minutes. Then add the prepolymerized resin A and continue kneading for 10~15 minutes. Add the zirconium tungstate-loaded hollow silica and knead for 15~25 minutes. During the kneading process, vacuum the air to obtain a lightweight synthetic core material adhesive film. The temperature of the adhesive is controlled at 80~100℃ and the vacuum degree is controlled at -0.095MPa~-0.090MPa.

[0012] Step 4: The adhesive is calendered into a film on a two-roll calender and then compounded with a carrier to obtain an uncured, low-thermal-expansion-coefficient bismaleimide resin-based lightweight synthetic core film.

[0013] The preparation method of the zirconium tungstate-supported hollow silica is as follows: hollow silica microspheres are dispersed in an ethanol aqueous solution with a volume fraction of 90-95% and ultrasonically dispersed for 30-60 min. γ-aminopropyltriethoxysilane is added at 3-5% of the total mass of the hollow silica microspheres, and the mixture is magnetically stirred at 40-50°C for 6-8 h. Zirconium tungstate powder is added at 30-50% of the total mass of the hollow silica microspheres, and the mixture is magnetically stirred at room temperature for 6-12 h. The solvent is removed by filtration to obtain zirconium tungstate-supported hollow silica. The product is washed 2-3 times with deionized water, and the product is freeze-dried to obtain zirconium tungstate-supported hollow silica filler. The mass-to-volume ratio of hollow silica microspheres to the ethanol aqueous solution is 1 g: 200-300 ml.

[0014] The preparation method of the surface-functionalized boron nitride nanotubes is as follows: Deionized water and anhydrous ethanol are mixed evenly at a volume ratio of 1:1~3 to obtain a mixed solution. Boron nitride nanotubes are added to the mixed solution at a rate of 1~1.5 g / 100 ml. The mixture is magnetically stirred evenly at room temperature, and then treated with ultrasound for 3~5 h. γ-aminopropyltriethoxysilane (3~5% of the total mass of boron nitride nanotubes) is added, and the mixture is magnetically stirred at 40~50 °C for 6~8 h. The solvent is removed by filtration, and after washing, the obtained solid is freeze-dried to obtain amino-functionalized boron nitride nanotubes. The amino-functionalized boron nitride nanotubes are added to chloroform solvent and ultrasonically dispersed for 30~60 min. Then, diphenylmethane bismaleimide (10~15% of the mass of the amino-functionalized boron nitride nanotubes) is added, and the mixture is magnetically stirred at 60~80 °C for 6~8 h. The solvent is removed by filtration, and the obtained solid is vacuum-dried to obtain maleimide-functionalized boron nitride nanotubes.

[0015] The bismaleimide resin includes commercially available diphenylmethane bismaleimide, ether-containing bismaleimide, and aliphatic bismaleimide, in a ratio of 100:20~70:10~20.

[0016] Furthermore, the structural formula of the bismaleimide containing the ether bond is shown in Formula I.

[0017] (Formula I)

[0018] Furthermore, the structural formula of aliphatic bismaleimide is shown in Formula II.

[0019] (Formula II)

[0020] The allyl compound includes diallyl bisphenol A and bisphenol A allyl ether, with a mass ratio of 100:10~30, and a molar ratio of maleimide group to allyl group of 1:0.8~0.9.

[0021] The commercially available epoxy resin comprises bisphenol F glycidyl ether, AFG-90, and AG-80, with a mass ratio of 100:10~30:10~30. The mass ratio of bismaleimide resin to epoxy resin is 100:30~70. The curing agent comprises 4,4'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl ether, with a mass ratio of 100:20~50. The molar ratio of -NH groups to epoxy groups in the curing agent is 1:1.

[0022] The low thermal expansion lightweight filler comprises zirconium tungstate-supported hollow silica and surface-functionalized boron nitride nanotubes, with a mass ratio of zirconium tungstate-supported hollow silica to surface-functionalized boron nitride nanotubes of 100:10~20, and a mass ratio of bismaleimide resin to low thermal expansion lightweight filler of 100:100~300; the size of the zirconium tungstate-supported hollow silica is 6~12μm, and the mass ratio of zirconium tungstate to hollow silica is 100:200~300; the diameter of the surface-functionalized boron nitride nanotubes is 60~100nm, and the length is 10~20μm.

[0023] The toughening agent comprises one or any combination of PAI micropowder, PEI micropowder, and thermoplastic polyimide micropowder (micropowder A) and core-shell structured methyl methacrylate-butadiene-styrene copolymer micropowder (micropowder B). The core structure of the core-shell structured methyl methacrylate-butadiene-styrene copolymer is butadiene-styrene copolymer, and the shell structure is polymethyl methacrylate. The toughening agent micropowder size is 10-30 μm, and the mass ratio of bismaleimide resin to toughening agent is 100:10-30. The mass ratio of one or any combination of PAI micropowder, PEI micropowder, and thermoplastic polyimide micropowder to the core-shell structured methyl methacrylate-butadiene-styrene copolymer micropowder is 100:20-30.

[0024] The carrier is a glass fiber nonwoven fabric or an aramid fiber nonwoven fabric, with a unit area mass of 6~15g / m². 2 .

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention first designs and prepares low thermal expansion lightweight zirconium tungstate-supported hollow silica microspheres and maleimide-functionalized boron nitride nanotubes. By controlling the structure and ratio of bismaleimide resin, the structure and ratio of allyl compound, the structure and composition of zirconium tungstate-supported hollow silica microspheres and maleimide-functionalized boron nitride nanotubes, the structure and ratio of epoxy resin and curing agent, and the structure and ratio of toughening agent, a low thermal expansion coefficient bismaleimide resin-based lightweight synthetic core film is obtained. This invention introduces low-thermal-expansion lightweight zirconium tungstate-supported hollow silica microspheres into the resin system for designing lightweight synthetic core films. The thermal expansion characteristics of zirconium tungstate reduce the coefficient of thermal expansion of the synthetic core material, while the lightweight zirconium tungstate-supported hollow silica microspheres reduce the density of the synthetic core film. In the filler system, maleimide-functionalized boron nitride nanotubes are introduced. Firstly, the high thermal conductivity of boron nitride nanotubes improves the thermal conductivity of the lightweight core material, preventing deformation caused by heat concentration. Secondly, their low thermal expansion characteristics further reduce the coefficient of thermal expansion of the lightweight core material. Introducing ether-bonded bismaleimides into the bismaleimide resin system improves the intrinsic toughness of the resin matrix, facilitating thermal stress dissipation. Introducing aliphatic bismaleimides reduces the melt viscosity of the resin matrix, which is beneficial for the addition and dispersion of lightweight fillers. The synergistic in-situ toughening effect of the micronized toughening agent further enhances the toughness and crack propagation resistance of the synthetic core film. The combination of the above design concepts endows the bismaleimide resin-based lightweight synthetic core film of this invention with lightweight properties and a low coefficient of thermal expansion. Furthermore, based on the aforementioned synergistic effect, the prepared bismaleimide resin-based lightweight synthetic core film possesses excellent adhesion, heat resistance, and mechanical properties. The unit area mass of this lightweight synthetic core film is reduced by more than 20% compared to existing materials. The coefficient of thermal expansion of the cured lightweight synthetic core material before the glass transition temperature is ≤20 ppm / ℃, the room temperature compressive strength of the cured lightweight synthetic core material is ≥100 MPa, and the room temperature compressive modulus of the cured lightweight synthetic core material is ≥1500 MPa. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of zirconium tungstate-supported hollow silica microspheres;

[0028] Figure 2 This is the TMA curve of the cured bismaleimide resin-based lightweight synthetic core film in Example 1. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion, wherein the lightweight synthetic core film based on bismaleimide resin comprises bismaleimide resin, allyl compound, commercial epoxy resin, curing agent, lightweight filler with low coefficient of thermal expansion, toughening agent and carrier, and the lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion is prepared by a prepolymerization, grinding and dispersion, vacuum kneading and hot calendering composite film forming method.

[0032] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion includes the following steps:

[0033] Step 1: Preparation of prepolymerized resin

[0034] The allyl compound was heated and stirred in a prepolymer reactor. After heating to 140°C, bismaleimide resin was added and the mixture was stirred until a uniform and transparent state was formed. After stirring and reacting at 130°C for 30 minutes, the mixture was cooled to obtain prepolymer resin A.

[0035] Step 2: Preparation of the Grinding Blend Resin

[0036] Epoxy resin, curing agent, toughening agent and surface-functionalized boron nitride nanotubes are mixed by stirring to form a coarse mixture. The coarse mixture is then ground and dispersed three times on a ceramic three-roll mill to obtain a ground blended resin B. The surface functional groups of the surface-functionalized boron nitride nanotubes are maleimide groups.

[0037] Step 3: Set the heating temperature of the vacuum kneader to 60℃ for preheating. Add the ground and blended resin B to the preheated vacuum kneader and knead for 5 minutes. Then add the prepolymerized resin A and continue kneading for 10 minutes. Add the zirconium tungstate-loaded hollow silica and knead for 15 minutes. During the kneading process, vacuum the air to obtain a lightweight synthetic core material adhesive film. The temperature of the adhesive is controlled at 80℃ and the vacuum degree is controlled at -0.095MPa.

[0038] Step 4: The adhesive is calendered into a film on a two-roll calender and then compounded with a carrier to obtain an uncured, low-thermal-expansion-coefficient bismaleimide resin-based lightweight synthetic core film.

[0039] The method for preparing zirconium tungstate-supported hollow silica is as follows: hollow silica microspheres are dispersed in an ethanol aqueous solution with a volume fraction of 90% and ultrasonically dispersed for 30 min. γ-aminopropyltriethoxysilane is added at 3% of the total mass of the hollow silica microspheres, and the mixture is magnetically stirred at 40°C for 6 h. Zirconium tungstate powder is added at 30% of the total mass of the hollow silica microspheres, and the mixture is magnetically stirred at room temperature for 6 h. The solvent is removed by filtration to obtain zirconium tungstate-supported hollow silica. The product is washed twice with deionized water, and the product is freeze-dried to obtain zirconium tungstate-supported hollow silica filler. The mass-volume ratio of hollow silica microspheres to ethanol aqueous solution is 1 g: 200 ml.

[0040] The preparation method of the surface-functionalized boron nitride nanotubes is as follows: Deionized water and anhydrous ethanol are mixed evenly at a volume ratio of 1:1 to obtain a mixed solution. Boron nitride nanotubes are added to the mixed solution at a rate of 1 g / 100 ml. The mixture is magnetically stirred evenly at room temperature and then treated with ultrasound for 3 h. 3% of the total mass of boron nitride nanotubes in γ-aminopropyltriethoxysilane is added. The mixture is magnetically stirred at 40 °C for 6 h. The solvent is removed by filtration. After washing, the obtained solid is freeze-dried to obtain amino-functionalized boron nitride nanotubes. The amino-functionalized boron nitride nanotubes are added to chloroform solvent and ultrasonically dispersed for 30 min. Then, 10% of the mass of amino-functionalized boron nitride nanotubes in diphenylmethane bismaleimide is added. The mixture is magnetically stirred at 60 °C for 6 h. The solvent is removed by filtration. The obtained solid is vacuum-dried to obtain maleimide-functionalized boron nitride nanotubes.

[0041] The bismaleimide resin comprises commercially available diphenylmethane bismaleimide, ether-bonded bismaleimide, and aliphatic bismaleimide, in a mass ratio of 100:20:10.

[0042] Furthermore, the structural formula of the bismaleimide containing the ether bond is shown in Formula I.

[0043] (Formula I).

[0044] Furthermore, the structural formula of aliphatic bismaleimide is shown in Formula II.

[0045] (Formula II).

[0046] The allyl compound includes diallyl bisphenol A and bisphenol A allyl ether in a mass ratio of 100:10, and the molar ratio of maleimide group to allyl group is 1:0.8.

[0047] The commercially available epoxy resin comprises bisphenol F glycidyl ether, AFG-90, and AG-80 in a mass ratio of 100:10:10, and the mass ratio of bismaleimide resin to epoxy resin is 100:30. The curing agent comprises 4,4'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl ether in a mass ratio of 100:20, and the molar ratio of -NH groups to epoxy groups in the curing agent is 1:1.

[0048] The low thermal expansion lightweight filler comprises zirconium tungstate-supported hollow silica and surface-functionalized boron nitride nanotubes, with a mass ratio of zirconium tungstate-supported hollow silica to surface-functionalized boron nitride nanotubes of 100:10, and a mass ratio of bismaleimide resin to the low thermal expansion lightweight filler of 100:100; the zirconium tungstate-supported hollow silica has a size of 6 μm, and the mass ratio of zirconium tungstate to hollow silica is 100:200; the surface-functionalized boron nitride nanotubes have a diameter of 60 nm and a length of 10 μm.

[0049] The toughening agent comprises PAI micropowder, PEI micropowder, and thermoplastic polyimide micropowder (in a mass ratio of 100:30:25) and core-shell methyl methacrylate-butadiene-styrene copolymer micropowder. The micropowder size is 10 μm, and the mass ratio of bismaleimide resin to the toughening agent is 100:10. The total mass ratio of the PAI micropowder, PEI micropowder, and thermoplastic polyimide micropowder to the core-shell methyl methacrylate-butadiene-styrene copolymer micropowder is 100:20.

[0050] The carrier is a glass fiber nonwoven fabric with a unit area mass of 6 g / m². 2 .

[0051] Based on the above synergistic effect, the prepared bismaleimide resin-based lightweight synthetic core film has excellent adhesion, heat resistance and mechanical properties. The unit area mass of the lightweight synthetic core film is reduced by 18% compared with the existing materials. The coefficient of thermal expansion of the cured lightweight synthetic core material before the glass transition temperature is 17.9 ppm / ℃, the room temperature compressive strength of the cured lightweight synthetic core material is 105 MPa, and the room temperature compressive modulus of the cured lightweight synthetic core material is 1550 MPa.

[0052] Example 2:

[0053] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion, wherein the lightweight synthetic core film based on bismaleimide resin comprises bismaleimide resin, allyl compound, commercial epoxy resin, curing agent, lightweight filler with low coefficient of thermal expansion, toughening agent and carrier, and the lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion is prepared by a prepolymerization, grinding and dispersion, vacuum kneading and hot calendering composite film forming method.

[0054] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion includes the following steps:

[0055] Step 1: Preparation of prepolymerized resin

[0056] The allyl compound was heated and stirred in a prepolymer reactor until it reached 145°C. Then, bismaleimide resin was added and the mixture was stirred until it became uniform and transparent. After stirring and reacting at 140°C for 40 minutes, the mixture was cooled to obtain prepolymer resin A.

[0057] Step 2: Preparation of the Grinding Blend Resin

[0058] Epoxy resin, curing agent, toughening agent and surface-functionalized boron nitride nanotubes are mixed by stirring to form a coarse mixture. The coarse mixture is then ground and dispersed five times on a ceramic three-roll mill to obtain a ground blended resin B. The surface functional groups of the surface-functionalized boron nitride nanotubes are maleimide groups.

[0059] Step 3: Set the heating temperature of the vacuum kneader to 70℃ for preheating. Add the ground and blended resin B to the preheated vacuum kneader and knead for 15 minutes. Then add the prepolymerized resin A and continue kneading for 15 minutes. Add the zirconium tungstate-loaded hollow silica and knead for 25 minutes. During the kneading process, vacuum the air to obtain a lightweight synthetic core material adhesive film. The temperature of the adhesive is controlled at 100℃ and the vacuum degree is controlled at -0.090MPa.

[0060] Step 4: The adhesive is calendered into a film on a two-roll calender and then compounded with a carrier to obtain an uncured, low-thermal-expansion-coefficient bismaleimide resin-based lightweight synthetic core film.

[0061] The method for preparing zirconium tungstate-supported hollow silica is as follows: hollow silica microspheres are dispersed in a 95% (v / v) ethanol aqueous solution and ultrasonically dispersed for 60 min. 5% (v / v) of γ-aminopropyltriethoxysilane is added to the hollow silica microspheres, and the mixture is magnetically stirred at 50°C for 8 h. 50% (v / v) of zirconium tungstate powder is added to the hollow silica microspheres, and the mixture is magnetically stirred at room temperature for 12 h. The solvent is removed by filtration to obtain zirconium tungstate-supported hollow silica. The product is washed three times with deionized water, and the product is freeze-dried to obtain zirconium tungstate-supported hollow silica filler. The mass-to-volume ratio of hollow silica microspheres to the ethanol aqueous solution is 1 g: 300 ml.

[0062] The preparation method of the surface-functionalized boron nitride nanotubes is as follows: Deionized water and anhydrous ethanol are mixed evenly at a volume ratio of 1:3 to obtain a mixed solution. Boron nitride nanotubes are added to the mixed solution at a rate of 1.5 g / 100 ml. The mixture is magnetically stirred evenly at room temperature and then treated with ultrasound for 5 h. 5% of the total mass of boron nitride nanotubes γ-aminopropyltriethoxysilane is added, and the mixture is magnetically stirred at 50 °C for 8 h. The solvent is removed by filtration, and after washing, the obtained solid is freeze-dried to obtain amino-functionalized boron nitride nanotubes. The amino-functionalized boron nitride nanotubes are added to chloroform solvent and ultrasonically dispersed for 60 min. Then, 15% of the mass of amino-functionalized boron nitride nanotubes diphenylmethane bismaleimide is added, and the mixture is magnetically stirred at 80 °C for 8 h. The solvent is removed by filtration, and the obtained solid is vacuum-dried to obtain maleimide-functionalized boron nitride nanotubes.

[0063] The bismaleimide resin comprises commercially available diphenylmethane bismaleimide, ether-bonded bismaleimide, and aliphatic bismaleimide, in a mass ratio of 100:70:20.

[0064] Furthermore, the structural formula of the bismaleimide containing the ether bond is shown in Formula I.

[0065] (Formula I)

[0066] Furthermore, the structural formula of aliphatic bismaleimide is shown in Formula II.

[0067] (Formula II)

[0068] The allyl compound includes diallyl bisphenol A and bisphenol A allyl ether in a mass ratio of 100:30, and the molar ratio of maleimide group to allyl group is 1:0.9.

[0069] The commercially available epoxy resin comprises bisphenol F glycidyl ether, AFG-90, and AG-80 in a mass ratio of 100:30:30, and the mass ratio of bismaleimide resin to epoxy resin is 100:70. The curing agent comprises 4,4'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl ether in a mass ratio of 100:50, and the molar ratio of -NH groups to epoxy groups in the curing agent is 1:1.

[0070] The low thermal expansion lightweight filler comprises zirconium tungstate-supported hollow silica and surface-functionalized boron nitride nanotubes, with a mass ratio of zirconium tungstate-supported hollow silica to surface-functionalized boron nitride nanotubes of 100:20, and a mass ratio of bismaleimide resin to low thermal expansion lightweight filler of 100:300; the zirconium tungstate-supported hollow silica has a size of 12 μm, and the mass ratio of zirconium tungstate to hollow silica is 100:300; the surface-functionalized boron nitride nanotubes have a diameter of 100 nm and a length of 20 μm.

[0071] The toughening agent comprises PAI micropowder and PEI micropowder (in a mass ratio of 100:50) and core-shell structured methyl methacrylate-butadiene-styrene copolymer micropowder. The micropowder size is 30 μm, and the mass ratio of bismaleimide resin to toughening agent is 100:30. The total mass ratio of PAI and PEI micropowder to the mass ratio of the core-shell structured methyl methacrylate-butadiene-styrene copolymer micropowder is 100:30.

[0072] The carrier is an aramid fiber nonwoven fabric with a unit area mass of 15 g / m². 2 .

[0073] Based on the above synergistic effect, the prepared bismaleimide resin-based lightweight synthetic core film has excellent adhesion, heat resistance and mechanical properties. The unit area mass of the lightweight synthetic core film is reduced by 19% compared with the existing materials. The coefficient of thermal expansion of the cured lightweight synthetic core material before the glass transition temperature is 18.5 ppm / ℃, the room temperature compressive strength of the cured lightweight synthetic core material is 110 MPa, and the room temperature compressive modulus of the cured lightweight synthetic core material is 1570 MPa.

[0074] Example 3:

[0075] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion, wherein the lightweight synthetic core film based on bismaleimide resin comprises bismaleimide resin, allyl compound, commercial epoxy resin, curing agent, lightweight filler with low coefficient of thermal expansion, toughening agent and carrier, and the lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion is prepared by a prepolymerization, grinding and dispersion, vacuum kneading and hot calendering composite film forming method.

[0076] A method for preparing a lightweight synthetic core film based on bismaleimide resin with a low coefficient of thermal expansion includes the following steps:

[0077] Step 1: Preparation of prepolymerized resin

[0078] The allyl compound was heated and stirred in a prepolymer reactor until it reached 143°C. Then, bismaleimide resin was added and the mixture was stirred until it became uniform and transparent. After stirring and reacting at 135°C for 35 minutes, the mixture was cooled to obtain prepolymer resin A.

[0079] Step 2: Preparation of the Grinding Blend Resin

[0080] Epoxy resin, curing agent, toughening agent and surface-functionalized boron nitride nanotubes are mixed by stirring to form a coarse mixture. The coarse mixture is then ground and dispersed four times on a ceramic three-roll mill to obtain a ground blended resin B. The surface functional groups of the surface-functionalized boron nitride nanotubes are maleimide groups.

[0081] Step 3: Set the heating temperature of the vacuum kneader to 65℃ for preheating. Add the ground and blended resin B to the preheated vacuum kneader and knead for 10 minutes. Then add the prepolymerized resin A and continue kneading for 13 minutes. Add the zirconium tungstate-loaded hollow silica and knead for 20 minutes. During the kneading process, vacuum the air to obtain a lightweight synthetic core material film. The temperature of the material is controlled at 90℃ and the vacuum degree is controlled at -0.097MPa.

[0082] Step 4: The adhesive is calendered into a film on a two-roll calender and then compounded with a carrier to obtain an uncured, low-thermal-expansion-coefficient bismaleimide resin-based lightweight synthetic core film.

[0083] The preparation method of the zirconium tungstate-supported hollow silica is as follows: hollow silica microspheres are dispersed in an ethanol aqueous solution with a volume fraction of 93% and ultrasonically dispersed for 45 min. γ-aminopropyltriethoxysilane is added at 4% of the total mass of the hollow silica microspheres, and the mixture is magnetically stirred at 45°C for 7 h. Zirconium tungstate powder is added at 40% of the total mass of the hollow silica microspheres, and the mixture is magnetically stirred at room temperature for 9 h. The solvent is removed by filtration to obtain zirconium tungstate-supported hollow silica. The product is washed three times with deionized water, and the product is freeze-dried to obtain zirconium tungstate-supported hollow silica filler. The mass-volume ratio of hollow silica microspheres to ethanol aqueous solution is 1 g: 250 ml.

[0084] The preparation method of the surface-functionalized boron nitride nanotubes is as follows: Deionized water and anhydrous ethanol are mixed evenly at a volume ratio of 1:2 to obtain a mixed solution. Boron nitride nanotubes are added to the mixed solution at a rate of 1.25 g / 100 ml. The mixture is magnetically stirred evenly at room temperature and then treated with ultrasound for 4 h. 4% of the total mass of boron nitride nanotubes in γ-aminopropyltriethoxysilane is added. The mixture is magnetically stirred at 45 °C for 7 h. The solvent is removed by filtration. After washing, the obtained solid is freeze-dried to obtain amino-functionalized boron nitride nanotubes. The amino-functionalized boron nitride nanotubes are added to chloroform solvent and ultrasonically dispersed for 45 min. Then, 12.5% ​​of the mass of amino-functionalized boron nitride nanotubes in diphenylmethane bismaleimide is added. The mixture is magnetically stirred at 70 °C for 6 h. The solvent is removed by filtration. The obtained solid is vacuum-dried to obtain maleimide-functionalized boron nitride nanotubes.

[0085] The bismaleimide resin comprises commercially available diphenylmethane bismaleimide, ether-bonded bismaleimide, and aliphatic bismaleimide, in a mass ratio of 100:45:15.

[0086] Furthermore, the structural formula of the bismaleimide containing the ether bond is shown in Formula I.

[0087] (Formula I)

[0088] Furthermore, the structural formula of aliphatic bismaleimide is shown in Formula II.

[0089] (Formula II)

[0090] The allyl compound includes diallyl bisphenol A and bisphenol A allyl ether in a mass ratio of 100:20, and the molar ratio of maleimide group to allyl group is 1:0.85.

[0091] The commercially available epoxy resin comprises bisphenol F glycidyl ether, AFG-90, and AG-80 in a mass ratio of 100:20:20, and the mass ratio of bismaleimide resin to epoxy resin is 100:50. The curing agent comprises 4,4'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl ether in a mass ratio of 100:35, and the molar ratio of -NH groups to epoxy groups in the curing agent is 1:1.

[0092] The low thermal expansion lightweight filler comprises zirconium tungstate-supported hollow silica and surface-functionalized boron nitride nanotubes, with a mass ratio of zirconium tungstate-supported hollow silica to surface-functionalized boron nitride nanotubes of 100:15, and a mass ratio of bismaleimide resin to the low thermal expansion lightweight filler of 100:200; the zirconium tungstate-supported hollow silica has a size of 9 μm, and the mass ratio of zirconium tungstate to hollow silica is 100:250; the surface-functionalized boron nitride nanotubes have a diameter of 80 nm and a length of 15 μm.

[0093] The toughening agent comprises PAI micropowder and core-shell structured methyl methacrylate-butadiene-styrene copolymer micropowder, with a micropowder size of 20 μm. The mass ratio of bismaleimide resin to toughening agent is 100:20. The mass ratio of PAI micropowder to core-shell structured methyl methacrylate-butadiene-styrene copolymer micropowder is 100:25.

[0094] The carrier is a glass fiber nonwoven fabric with a unit area mass of 11 g / m². 2 .

[0095] Based on the above synergistic effect, the prepared bismaleimide resin-based lightweight synthetic core film has excellent adhesion, heat resistance and mechanical properties. The unit area mass of the lightweight synthetic core film is reduced by 17.5% compared with the existing materials. The coefficient of thermal expansion of the cured lightweight synthetic core material before the glass transition temperature is 19.2 ppm / ℃. The room temperature compressive strength of the cured lightweight synthetic core material is 108 MPa and the room temperature compressive modulus is 1540 MPa.

[0096] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a low-thermal expansion coefficient bismaleimide resin-based lightweight synthetic core adhesive film, characterized in that: Step 1: pre-polymerizing an allyl compound and a bismaleimide resin to obtain a pre-polymerized resin A; Step 2: uniformly dispersing an epoxy resin, a curing agent, a toughening agent, and surface-functionalized boron nitride nanotubes to obtain a ground blended resin B; the surface functional groups of the surface-functionalized boron nitride nanotubes are maleimide groups; Step 3: vacuum kneading the pre-polymerized resin A, the ground blended resin B, and zirconium tungstate-loaded hollow silica to obtain a lightweight synthetic core adhesive film compound; Step 4: calendering the compound into a film and compounding it with a carrier to obtain an uncured low-thermal expansion coefficient bismaleimide resin-based lightweight synthetic core adhesive film. In Step 1, the bismaleimide resin includes commercial diphenylmethane bismaleimide, ether bond-containing bismaleimide, and aliphatic bismaleimide, with a mass ratio of 100:20-70:10-20. The ether bond-containing bismaleimide has a structural formula as shown in Formula I: The aliphatic bismaleimide has a structural formula as shown in Formula II: In Step 1, the allyl compound includes diallyl bisphenol A and bisphenol A allyl ether, with a mass ratio of 100:10-30, and a molar ratio of maleimide groups to allyl groups of 1:0.8-0.

9. In Step 2, the epoxy resin includes bisphenol F glycidyl ether, AFG-90, and AG-80, with a mass ratio of 100:10-30:10-30, and a mass ratio of bismaleimide resin to epoxy resin of 100:30-70; the curing agent includes 4,4'-diamino diphenyl sulfone and 4,4'-diamino diphenyl ether, with a mass ratio of 100:20-50, and a molar ratio of -NH groups to epoxy groups in the curing agent of 1:1; the toughening agent includes micro powder A and micro powder B, the micro powder A is one or a combination of PAI micro powder, PEI micro powder, and thermoplastic polyimide micro powder, the micro powder B is a core-shell structured methyl methacrylate-butadiene-styrene copolymer micro powder, and a mass ratio of the micro powder A to the micro powder B is 100:20-30; the toughening agent micro powder has a size of 10-30 μm, and a mass ratio of bismaleimide resin to toughening agent is 100:10-30. The zirconium tungstate-loaded hollow silica and the surface-functionalized boron nitride nanotubes belong to low-thermal expansion lightweight fillers, a mass ratio of the zirconium tungstate-loaded hollow silica to the surface-functionalized boron nitride nanotubes is 100:10-20, and a mass ratio of bismaleimide resin to low-thermal expansion lightweight filler is 100:100-300. The zirconium tungstate-loaded hollow silica has a size of 6-12 μm, and a mass ratio of zirconium tungstate to hollow silica is 100:200-300; the surface-functionalized boron nitride nanotubes have a diameter of 60-100 nm and a length of 10-20 μm. The method for preparing the zirconium tungstate-loaded hollow silica is as follows: ​ ​ ​ ​ 2. The method of claim 1, wherein: ​ 3. The method of claim 2, wherein: ​ (Formula I) ​ (Formula II).

4. The production method according to claim 1 or 2, characterized by: ​ 5. The method of claim 1, wherein: ​ 6. The method of claim 1, wherein: ​ 7. The method of claim 1 or 6, wherein: ​ 8. The method of claim 1, wherein: The carrier is glass fiber non-woven fabric or aramid fiber non-woven fabric, and the mass per unit area is 6-15 g / m 2 .

9. The method of claim 1, wherein: ​ The hollow silica microspheres are dispersed into an ethanol aqueous solution with a volume fraction of 90-95%, and ultrasonic dispersion is performed to make the hollow silica microspheres uniformly dispersed. Then, 3-5% of the total mass of the hollow silica microspheres of γ-aminopropyl triethoxysilane is added, and magnetic stirring is performed at 40-50°C for 6-8h. Then, 30-50% of the total mass of the hollow silica microspheres of zirconium tungstate micro powder is added, and magnetic stirring is performed at room temperature for 6-12h. The solvent is removed by suction filtration, and the product is washed. The product is freeze-dried to obtain the zirconium tungstate-loaded hollow silica filler. The mass-to-volume ratio of the hollow silica microspheres to the ethanol aqueous solution is 1g:200-300ml.

10. The method of claim 1, wherein: The preparation method of the surface-functionalized boron nitride nanotubes is as follows: Deionized water and anhydrous ethanol are mixed uniformly in a volume ratio of 1:1-3 to obtain a mixed solution. Boron nitride nanotubes are added to the mixed solution in an amount of 1-1.5g / 100ml, and magnetic stirring is performed at room temperature until the boron nitride nanotubes are uniformly dispersed. Then, ultrasonic treatment is performed for 3-5h. Then, 3-5% of the total mass of the boron nitride nanotubes of γ-aminopropyl triethoxysilane is added, and magnetic stirring is performed at 40-50°C for 6-8h. The solvent is removed by suction filtration, and the obtained solid is vacuum-dried to obtain amino-functionalized boron nitride nanotubes. The amino-functionalized boron nitride nanotubes are added to a chloroform solvent, and ultrasonic dispersion is performed. Then, 10-15% of the mass of the amino-functionalized boron nitride nanotubes of diphenylmethane bismaleimide is added, and magnetic stirring is performed at 60-80°C for 6-8h. The solvent is removed by suction filtration, and the obtained solid is vacuum-dried to obtain maleimide group-functionalized boron nitride nanotubes.

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