High-temperature-resistant adhesive suitable for adhesion of large-size and non-planar composite materials and preparation method of high-temperature-resistant adhesive

Abstract

The invention relates to a high-temperature-resistant organic adhesive and a preparation method thereof, in particular to a high-temperature-resistant adhesive suitable for adhesion of large-size and non-planar composite materials and a preparation method of the high-temperature-resistant adhesive. The problems of low bonding strength, poor bonding reliability under high and low temperature circulation and insufficient heat resistance existing in bonding of an existing polyimide adhesive and a large-size non-planar composite material are solved. The invention relates to a high-temperature-resistant adhesive applicable to adhesion of large-size and non-planar composite materials. The high-temperature-resistant adhesive is prepared from 100 parts by weight of polyimide precursor resin and 100-200 parts by weight of a solvent, the preparation method comprises the following steps: 1, preparing polyimide precursor resin; 2, weighing; and 3, preparing the adhesive. The invention relates to a high-temperature-resistant adhesive for bonding large-size and non-planar composite materials and a preparation method of the high-temperature-resistant adhesive.

Description

Technical Field

[0001] The invention relates to a high-temperature resistant organic adhesive and a preparation method thereof. Background Art

[0002] As transportation vehicles like aircraft, high-speed trains, and automobiles rapidly evolve toward heavier loads and higher speeds, lightweight design has become a core strategy for improving transportation efficiency and energy efficiency. Increasing the use of composite materials in these applications can effectively reduce their overall weight. Currently, composite materials have become one of the four major material systems, alongside metals, polymers, and inorganic non-metallic materials, and composite materials account for 20% to 50% of an aircraft's mass. With the increasing use of composite materials, joining methods between composites has gained increasing attention. Adhesive bonding, due to its advantages such as eliminating drilling-induced stress concentration, effectively preventing crack propagation, and fatigue resistance, has become a primary joining method for composite structures. However, as composite structures grow larger and feature more complex curved surfaces, traditional adhesives face challenges with toughness mismatches and low bond strength when bonding large-scale composites. Consequently, reliable joining technology between composite materials has become a bottleneck restricting structural lightweighting and reliability.

[0003] Currently, most composite materials are reinforced with carbon fiber, whose axial modulus far exceeds that of traditional adhesives. This difference in modulus leads to uneven distribution of interfacial stress when external forces are applied, especially at high temperatures (>300°C). The softening of the adhesive layer exacerbates interfacial shear slip, and the bond strength rapidly decays. Furthermore, the difference in thermal expansion coefficients between carbon fiber and adhesives, as well as the lack of a directional reinforcement mechanism in traditional adhesives, results in disordered molecular chains that are difficult to coordinate with the mechanical behavior of the fibers. Consequently, shear slip or debonding is prone to occur at the interface under high temperatures and high-low temperature cycles.

[0004] When bonding some large-scale, non-planar and other complex composite materials, when large-scale composite materials are cured at high temperatures, significant thermal stress is generated at the interface between the adhesive layer and the composite material due to differences in thermal expansion coefficients and temperature gradients, which can easily cause cracks in the adhesive layer or even interface peeling. Traditional thermosetting polyimides have high curing shrinkage rates, and the heat transfer during the curing process is uneven, resulting in local stress accumulation and decreased bonding strength. Especially under high and low temperature cyclic loads, interface defects accelerate expansion. In addition, when bonding curved composite materials (such as wing skins and tank shells), the change in curvature causes the adhesive layer to bear multi-directional stress, the molecular chain orientation of the adhesive layer is disordered, the shear resistance is insufficient, and it is easy to crack at the edges or where the curvature suddenly changes.

[0005] How to improve the bonding interface with large-sized, non-planar composite materials, increase the bonding strength after curing, and obtain the bonding effect under higher temperatures and high and low temperature cycles is a technical problem that urgently needs to be solved in the existing technology. Summary of the Invention

[0006] The present invention aims to solve the problems of low bonding strength, poor bonding reliability under high and low temperature cycles, and insufficient heat resistance in the bonding of existing polyimide adhesives to large-sized, non-planar composites, and further provide a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composites and a preparation method thereof.

[0007] A high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials, which is prepared by weight from 100 parts of a polyimide precursor resin and 100 to 200 parts of a solvent A;

[0008] The polyimide precursor resin is prepared from aromatic diamine, aromatic dianhydride and solvent B; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(0.95-1.05); the mass ratio of the aromatic diamine to the solvent B is 1:(2-20);

[0009] The repeating unit of polyamic acid in the polyimide precursor resin is:

[0010]

[0011] The R2 is One or a combination of several of them.

[0012] A method for preparing a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials is carried out according to the following steps:

[0013] 1. Preparation of polyimide precursor resin:

[0014] ① Weigh aromatic diamine, aromatic dianhydride and solvent B;

[0015] The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(0.95-1.05); the mass ratio of the aromatic diamine to the solvent B is 1:(2-20);

[0016] ② Under a nitrogen atmosphere at a temperature of 40°C to 48°C and stirring conditions, the weighed solvent B and aromatic diamine are stirred and dissolved for 1 hour to 5 hours to obtain an aromatic diamine solution. Under a nitrogen atmosphere and stirring conditions, the temperature of the aromatic diamine solution is raised to 50°C to 60°C, and the weighed aromatic dianhydride is added to the aromatic diamine solution in three equal portions. Then, under a nitrogen atmosphere at a temperature of 50°C to 60°C and stirring conditions, the reaction is stirred for 3 hours to 5 hours. Finally, under a nitrogen atmosphere, the reaction temperature is lowered from 50°C to 60°C to 25°C to 30°C, and the reaction is allowed to stand for 5 hours to 10 hours under a nitrogen atmosphere at a temperature of 25°C to 30°C to obtain a reaction solution.

[0017] ③ Lowering the temperature of the reaction solution from 25°C to 30°C to 4°C to 6°C, then adding the reaction solution dropwise into ethanol and allowing it to stand, and finally filtering and drying to obtain a polyimide precursor resin;

[0018] The repeating unit of polyamic acid in the polyimide precursor resin is:

[0019]

[0020] The R2 is One or a combination of several of them;

[0021] 2. Weighing:

[0022] Weigh 100 parts of polyimide precursor resin and 100 to 200 parts of solvent A by weight;

[0023] 3. Preparation of adhesive:

[0024] The weighed polyimide precursor resin is heated and stirred at a temperature of 80°C to 120°C for 2h to 5h, then cooled to 20°C to 25°C, and the weighed solvent A is added and stirred at a temperature of 20°C to 25°C for 10min to 30min to obtain a high-temperature resistant adhesive suitable for bonding large-size, non-planar composite materials.

[0025] The beneficial effects of the present invention are:

[0026] Through innovative molecular structure design and optimized preparation processes, this paper has successfully developed a high-temperature resistant polyimide adhesive suitable for bonding large, non-planar composite materials. Its overall performance significantly outperforms traditional adhesives. Specific beneficial effects are reflected in the following aspects:

[0027] Traditional adhesives have a large difference in modulus from carbon fiber reinforced composites (CFRP) due to the disordered arrangement of molecular chains, which leads to interfacial stress concentration and shear slip problems. The present invention uses monomers with fully aromatic, coplanar non-isomerization and biphenyl structures (such as 3,3',4,4'-biphenyltetracarboxylic dianhydride and ether-bonded diamines) to synthesize polyimide precursor resins. During the high-temperature imidization process, the coplanar π-π conjugation effect significantly reduces the steric hindrance between the molecular chains, prompting them to spontaneously form a highly regular linear arrangement along the axial direction of the carbon fiber. This orientation mechanism works synergistically with the crystallization shrinkage effect of carbon fibers at high temperatures (300℃~400℃), transfers tension through interfacial shear, further strengthens the directional arrangement of the molecular chains, effectively alleviates the problem of uneven interfacial stress distribution, and inhibits the generation of microcracks. After the molecular chains are oriented along the direction of the composite fibers, the shear strength of the interface between the adhesive layer and the composite is greatly improved.

[0028] Traditional polyimide adhesives are prone to molecular chain relaxation and creep at high temperatures, resulting in rapid attenuation of bonding strength. The present invention significantly improves the high-temperature (320°C) creep resistance of the adhesive layer by introducing a fully aromatic biphenyl rigid main chain and combining it with the molecular stacking effect of the coplanar structure. The rigid skeleton of the biphenyl structure inhibits the free rotation and slip of the molecular chain at high temperatures, while the coplanar arrangement enhances the intermolecular force, stabilizing the glass transition temperature (Tg) of the adhesive layer after curing at 366°C to 375°C, which is more than 10% higher than that of traditional polyimide adhesives. In addition, during the high-temperature curing process, the difference in thermal expansion coefficient between the adhesive layer and the composite material is effectively compensated, reducing the accumulation of thermal stress.

[0029] In response to the dynamic load (such as vibration and impact) requirements of composite materials under complex working conditions, the present invention introduces ether bond flexible units (such as 4,4'-diaminodiphenyl ether) into the rigid main chain to form a "rigid and flexible" molecular structure. The rotational freedom of the ether bond gives the adhesive layer excellent impact toughness, dissipates energy through local deformation of the molecular chain under dynamic load, increases the impact toughness of the adhesive layer, avoids interfacial cracking caused by stress concentration, and achieves toughness matching between the adhesive layer and the composite material. In addition, the hydrophobic properties of the ether bond (the contact angle is increased to above 85°) effectively block the penetration of water molecules, and the bonding strength attenuation in a hot and humid environment (85℃ / 85%RH) is less, which is significantly better than the 20% to 30% attenuation rate of traditional adhesives. The hydrophobic properties of the ether bond effectively reduce the diffusion of water molecules, ensuring the bonding performance of the adhesive layer in a hot and humid environment. The synergistic effect of the rigid main chain and the ether bond flexible unit enables the adhesive to take into account both high temperature strength and impact toughness, reducing the impact of environmental aging.

[0030] Traditional adhesives have the problem of uneven multi-directional stress distribution when bonding curved surfaces. The present invention uses a molecular chain orientation and modulus matching mechanism to ensure that the adhesive layer can maintain uniform stress transmission in areas with varying curvatures.

[0031] Through molecular structural innovation and process optimization, this invention addresses key technical challenges in bonding large, non-planar composite materials, including low bond strength, poor bonding reliability under high- and low-temperature cycling, and insufficient heat resistance. Its high-temperature performance and environmental adaptability offer broad application prospects in aircraft (such as power equipment hatches) and high-speed rail (body coverings). BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a photo of a composite bonded part after shearing at room temperature using the high-temperature resistant adhesive suitable for bonding large-sized, non-planar composites prepared in Example 1;

[0033] Figure 2 This is the thermal weight loss curve of the high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1 before and after curing in air atmosphere;

[0034] Figure 3 This is the DSC curve of the cured high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1;

[0035] Figure 4 This is the infrared spectrum of the high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1 after curing:

[0036] Figure 5 This is a photo of a large-sized, non-planar composite material bonded with a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1;

[0037] Figure 6 Dimensional test diagram of a large-sized, non-planar composite material bonded with a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1;

[0038] Figure 7 This is a flat tensile test curve of the large-sized, non-planar composite material bonded with the high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1 after being cut into strips. DETAILED DESCRIPTION

[0039] Specific embodiment 1: This embodiment is a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials, which is prepared by weight from 100 parts of polyimide precursor resin and 100 to 200 parts of solvent A;

[0040] The polyimide precursor resin is prepared from aromatic diamine, aromatic dianhydride and solvent B; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(0.95-1.05); the mass ratio of the aromatic diamine to the solvent B is 1:(2-20);

[0041] The repeating unit of polyamic acid in the polyimide precursor resin is:

[0042]

[0043] The R2 is One or a combination of several of them.

[0044] The aromatic diamine described in this specific embodiment is fully aromatic, coplanar non-isomerized and biphenyl structured, and also contains ether bonds, and can be efficiently oriented under the action of coplanar π-π conjugation, and also has a certain degree of flexibility.

[0045] In this specific embodiment, aromatic diamine and aromatic dianhydride are used to form a polyimide precursor resin.

[0046] The beneficial effects of this specific embodiment are:

[0047] This specific embodiment successfully developed a high-temperature resistant polyimide adhesive suitable for bonding large-scale, non-planar composite materials through innovative molecular structure design and preparation process optimization. Its overall performance is significantly superior to traditional adhesives. Specific beneficial effects are reflected in the following aspects:

[0048] Traditional adhesives have a large difference in modulus from carbon fiber reinforced composites (CFRP) due to the disordered arrangement of molecular chains, resulting in interfacial stress concentration and shear slip problems. This specific embodiment uses monomers with fully aromatic, coplanar non-isomerization and biphenyl structures (such as 3,3',4,4'-biphenyltetracarboxylic dianhydride and ether-bonded diamines) to synthesize polyimide precursor resins. During the high-temperature imidization process, the coplanar π-π conjugation effect significantly reduces the steric hindrance between the molecular chains, prompting them to spontaneously form a highly regular linear arrangement along the axial direction of the carbon fiber. This orientation mechanism synergizes with the crystallization shrinkage effect of carbon fibers at high temperatures (300℃~400℃), transfers tension through interfacial shear, further strengthens the directional arrangement of the molecular chains, effectively alleviates the problem of uneven interfacial stress distribution, and suppresses the generation of microcracks. After the molecular chains are oriented along the direction of the composite fibers, the shear strength of the interface between the adhesive layer and the composite is greatly improved.

[0049] Traditional polyimide adhesives are prone to molecular chain relaxation and creep at high temperatures, resulting in rapid attenuation of bonding strength. This specific embodiment significantly improves the high-temperature (320°C) creep resistance of the adhesive layer by introducing a fully aromatic biphenyl rigid main chain and combining it with the molecular stacking effect of the coplanar structure. The rigid skeleton of the biphenyl structure inhibits the free rotation and slip of the molecular chain at high temperatures, while the coplanar arrangement enhances the intermolecular force, stabilizing the glass transition temperature (Tg) of the adhesive layer after curing at 366°C to 375°C, which is more than 10% higher than that of traditional polyimide adhesives. In addition, during the high-temperature curing process, the difference in thermal expansion coefficient between the adhesive layer and the composite material is effectively compensated, reducing the accumulation of thermal stress.

[0050] In response to the dynamic load (such as vibration and impact) requirements of composite materials under complex working conditions, this specific embodiment introduces ether bond flexible units (such as 4,4'-diaminodiphenyl ether) into the rigid main chain to form a "rigid and flexible" molecular structure. The rotational freedom of the ether bond gives the adhesive layer excellent impact toughness, dissipates energy through local deformation of the molecular chain under dynamic load, increases the impact toughness of the adhesive layer, avoids interfacial cracking caused by stress concentration, and achieves toughness matching between the adhesive layer and the composite material. In addition, the hydrophobic properties of the ether bond (the contact angle is increased to above 85°) effectively block the penetration of water molecules, and the bonding strength attenuation in a hot and humid environment (85℃ / 85%RH) is less, which is significantly better than the 20% to 30% attenuation rate of traditional adhesives. The hydrophobic properties of the ether bond effectively reduce the diffusion of water molecules, ensuring the bonding performance of the adhesive layer in a hot and humid environment. The synergistic effect of the rigid main chain and the ether bond flexible unit enables the adhesive to take into account both high temperature strength and impact toughness, reducing the impact of environmental aging.

[0051] Traditional adhesives have the problem of uneven multi-directional stress distribution when bonding curved surfaces. This specific embodiment uses the molecular chain orientation and modulus matching mechanism to ensure that the adhesive layer can maintain uniform stress transmission in areas with varying curvature.

[0052] This specific embodiment, through molecular structure innovation and process optimization, addresses key technical challenges in bonding large, non-planar composite materials, including low bond strength, poor bonding reliability under high- and low-temperature cycling, and insufficient heat resistance. Its high-temperature performance and environmental adaptability offer broad application prospects in aircraft (such as power equipment hatches) and high-speed rail (body coverings).

[0053] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the solvent A and solvent B are both a mixture of N,N-dimethylacetamide and water, and the mass ratio of N,N-dimethylacetamide to water is 10:(0.5-1). Other aspects are the same as specific embodiment 1.

[0054] Specific embodiment 3: This embodiment differs from either specific embodiment 1 or 2 in that the aromatic diamine is one or a combination of 4,4'-diaminodiphenyl ether, 1,3-bis(3'-aminophenoxy)benzene, and 3,3'-diaminodiphenyl ether. Other aspects are the same as specific embodiments 1 or 2.

[0055] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the aromatic dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride. Other aspects are the same as specific embodiments 1 to 3.

[0056] Specific embodiment 5: This embodiment is a method for preparing a high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials, which is carried out according to the following steps:

[0057] 1. Preparation of polyimide precursor resin:

[0058] ① Weigh aromatic diamine, aromatic dianhydride and solvent B;

[0059] The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(0.95-1.05); the mass ratio of the aromatic diamine to the solvent B is 1:(2-20);

[0060] ② Under a nitrogen atmosphere at a temperature of 40°C to 48°C and stirring conditions, the weighed solvent B and aromatic diamine are stirred and dissolved for 1 hour to 5 hours to obtain an aromatic diamine solution. Under a nitrogen atmosphere and stirring conditions, the temperature of the aromatic diamine solution is raised to 50°C to 60°C, and the weighed aromatic dianhydride is added to the aromatic diamine solution in three equal portions. Then, under a nitrogen atmosphere at a temperature of 50°C to 60°C and stirring conditions, the reaction is stirred for 3 hours to 5 hours. Finally, under a nitrogen atmosphere, the reaction temperature is lowered from 50°C to 60°C to 25°C to 30°C, and the reaction is allowed to stand for 5 hours to 10 hours under a nitrogen atmosphere at a temperature of 25°C to 30°C to obtain a reaction solution.

[0061] ③ Lowering the temperature of the reaction solution from 25°C to 30°C to 4°C to 6°C, then adding the reaction solution dropwise into ethanol and allowing it to stand, and finally filtering and drying to obtain a polyimide precursor resin;

[0062] The repeating unit of polyamic acid in the polyimide precursor resin is:

[0063]

[0064] The R2 is One or a combination of several of them;

[0065] 2. Weighing:

[0066] Weigh 100 parts of polyimide precursor resin and 100 to 200 parts of solvent A by weight;

[0067] 3. Preparation of adhesive:

[0068] The weighed polyimide precursor resin is heated and stirred at a temperature of 80°C to 120°C for 2h to 5h, then cooled to 20°C to 25°C, and the weighed solvent A is added and stirred at a temperature of 20°C to 25°C for 10min to 30min to obtain a high-temperature resistant adhesive suitable for bonding large-size, non-planar composite materials.

[0069] Specific embodiment 6: This embodiment differs from specific embodiment 5 in that the stirring speed in step 1② is 100 rpm to 200 rpm. Other aspects are the same as specific embodiment 5.

[0070] Specific embodiment 7: This embodiment differs from either specific embodiment 5 or 6 in that in step 1 ③, the reaction solution is added dropwise to ethanol at a dropping speed of 0.5 mL / s to 1 mL / s. The rest is the same as specific embodiment 5 or 6.

[0071] Specific embodiment eight: This embodiment differs from specific embodiments five to seven in that: in step one (3), the step is left to stand for 8 to 12 hours. The rest is the same as specific embodiments five to seven.

[0072] Specific embodiment 9: This embodiment differs from specific embodiments 5 to 8 in that the drying in step 1 (3) is carried out at a temperature of 40° C. to 80° C. for 24 to 48 hours. Other aspects are the same as specific embodiments 5 to 8.

[0073] Specific embodiment 10: This embodiment differs from any one of specific embodiments 5 to 9 in that the stirring speed in step 3 is 100 rpm to 200 rpm. Other aspects are the same as specific embodiments 5 to 9.

[0074] The following examples are used to verify the beneficial effects of the present invention:

[0075] Example 1:

[0076] A high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials, which is prepared from 100 parts by weight of a polyimide precursor resin and 100 parts by weight of a solvent A;

[0077] The polyimide precursor resin is prepared from aromatic diamine, aromatic dianhydride and solvent B; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:0.95; the mass ratio of the aromatic diamine to the solvent B is 1:10;

[0078] The repeating unit of polyamic acid in the polyimide precursor resin is:

[0079]

[0080] The R2 is

[0081] The solvent A and solvent B are both a mixture of N,N-dimethylacetamide and water, and the mass ratio of the N,N-dimethylacetamide to water is 10:0.5.

[0082] The aromatic diamine is 4,4'-diaminodiphenyl ether.

[0083] The aromatic dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0084] A method for preparing a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials is carried out according to the following steps:

[0085] 1. Preparation of polyimide precursor resin:

[0086] ① Weigh aromatic diamine, aromatic dianhydride and solvent B;

[0087] ② Under the conditions of a nitrogen atmosphere, a temperature of 40°C and a stirring speed of 150 rpm, the weighed solvent B and aromatic diamine were stirred and dissolved for 5 hours to obtain an aromatic diamine solution. Under the conditions of a nitrogen atmosphere and a stirring speed of 150 rpm, the temperature of the aromatic diamine solution was raised to 50°C, and the weighed aromatic dianhydride was added to the aromatic diamine solution in three equal portions. Then, under the conditions of a nitrogen atmosphere, a temperature of 50°C and a stirring speed of 150 rpm, the reaction was stirred for 3 hours. Finally, under the conditions of a nitrogen atmosphere, the reaction temperature was lowered from 50°C to 25°C, and the reaction was allowed to stand for 10 hours under the conditions of a nitrogen atmosphere and a temperature of 25°C to obtain a reaction solution.

[0088] ③ The reaction liquid temperature was lowered from 25°C to 4°C, and then the reaction liquid was added dropwise to ethanol at a dropping rate of 1 mL / s and allowed to stand for 8 hours. Finally, the mixture was filtered and dried to obtain a polyimide precursor resin.

[0089] 2. Weighing:

[0090] Weigh 100 parts of polyimide precursor resin and 100 parts of solvent A by weight;

[0091] 3. Preparation of adhesive:

[0092] The weighed polyimide precursor resin was heated and stirred at a temperature of 80°C and a stirring speed of 150 rpm for 5 hours, then cooled to 20°C. The weighed solvent A was added and stirred at a temperature of 20°C and a stirring speed of 150 rpm for 30 minutes to obtain a high-temperature resistant adhesive suitable for bonding large-size, non-planar composites.

[0093] The drying described in step 1 (3) is specifically carried out at a temperature of 80° C. for 48 hours.

[0094] Example 2: This example differs from Example 1 in that the aromatic diamine is a mixture of 1,3-bis(3'-aminophenoxy)benzene and 3,3'-diaminodiphenyl ether in a molar ratio of 7:3. Other aspects are the same as Example 1.

[0095] Example 3: This example differs from Example 1 in that the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:0.98, and the mass ratio of the N,N-dimethylacetamide to water is 10:1. Other conditions are the same as in Example 1.

[0096] Example 4: This example differs from Example 1 in that the aromatic diamine is 3,3'-diaminodiphenyl ether and the mass ratio of N,N-dimethylacetamide to water is 10:0.6. Other components are the same as Example 1.

[0097] Example 5: This example differs from Example 1 in that the aromatic diamine is 4,4'-diaminodiphenyl ether and the mass ratio of N,N-dimethylacetamide to water is 10:0.7. Other components are the same as Example 1.

[0098] Example 6: This example differs from Example 1 in that the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:1.05, and the mass ratio of the N,N-dimethylacetamide to water is 10:0.9. Other conditions are the same as in Example 1.

[0099] Example 7: This example is different from Example 1 in that it is prepared from 100 parts by weight of polyimide precursor resin and 200 parts by weight of solvent A. Other steps are the same as those in Example 1.

[0100] Comparative Experiment 1: This comparative experiment differs from Example 1 in that the aromatic diamine is p-phenylenediamine. Other aspects are the same as Example 1.

[0101] Comparative Experiment 2: This comparative experiment differs from Example 1 in that the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:1.2. Other conditions are the same as in Example 1.

[0102] Comparative Experiment 3: This comparative experiment differs from Example 1 in that, in step 1 (2), the aromatic diamine solution was heated to 80°C under a nitrogen atmosphere and the aromatic dianhydride was added to the aromatic diamine solution in three equal portions. The mixture was then stirred for 3 hours under a nitrogen atmosphere at 80°C and a stirring speed of 150 rpm. All other conditions were the same as in Example 1.

[0103] Comparative Experiment 4: This comparative experiment differs from Example 1 in that the mass ratio of the aromatic diamine to solvent B is 1:30. Others are the same as Example 1.

[0104] (1) The adhesives prepared in Examples 1 to 7 and Comparative Experiments 1 to 4 were placed on two polyimide carbon fiber reinforced composites (manufacturer Solvay, model K3B / AS4, width 2.5 cm, length 10 cm) were bonded together, and the curing process was as follows: first, heating at 80°C and 0.1 MPa for 5 h, then heating at 120°C and 0.1 MPa for 3 h, after vacuuming, heating at 300°C and 1.5 MPa for 8 h, and finally heating at 380°C and 1.5 MPa for 2 h to obtain a composite bonded part, which was then subjected to various performance tests. The test conditions refer to the following standards (methods):

[0105] 1. Shear Strength: The tensile shear strength of the adhesive was measured in accordance with GB / T7124-2008; the shear impact strength of the adhesive was measured in accordance with GB / T 6328-1999; and the tensile shear strength at 320°C was measured in accordance with GJB444-1988. The room temperature shear strength after high and low temperature cycling was determined by the following steps: 100 to 300 cycles were performed from 25°C to 320°C at a heating and cooling rate of 5°C / min, with a holding time of 10 minutes at both 25°C and 320°C, followed by testing the room temperature shear strength. The room temperature shear strength after damp heat aging was determined by the following steps: 85°C / 85% RH was used to age the test specimens at 85°C and 85% humidity for 168 hours, 500 hours, and 1000 hours, respectively, followed by testing the room temperature shear strength.

[0106] 2. The bonding effect of composite materials is visually inspected to observe the damaged or detached surface. Composite material damage is considered composite material failure, no residual adhesive is considered interface debonding, and residual adhesive is considered adhesive layer damage; bonding failure is considered detachment.

[0107] (2) Adhesive test, curing process is: place the adhesive in a vacuum oven, reduce the pressure to 0.1MPa, heat at 80℃ for 5h, 150℃ for 3h, 200℃ for 1h, 300℃ for 1h, and 380℃ for 1h:

[0108] 1. Adhesive Tg determination: DSC is used to measure the Tg of the adhesive after curing.

[0109] 2. Contact angle measurement: Use a contact angle meter to measure the water contact angle of the adhesive coating surface.

[0110] 3. Thermal gravimetric test: In air atmosphere, conduct thermal gravimetric curve test on the adhesive before and after curing.

[0111] 4. Infrared test: Perform infrared test on the cured adhesive.

[0112] (3) Bonding of large-size, non-planar composite materials:

[0113] The adhesives prepared in Examples 1 to 7 and Comparative Experiments 1 to 4 were placed on the large-sized non-planar polyimide carbon fiber reinforced composite T-beam to be bonded (manufacturer Solvay, model K3B / AS4, 40 cm long, 7 cm wide, 5.3 cm high, angle 90°) was bonded to a polyimide reinforced composite (8 cm wide, 12.5 cm long). The polyimide reinforced composite was homemade (glass cloth was immersed in a polyimide precursor solution, fished out and dried to obtain a prepreg. The two layers of prepreg were placed in an autoclave for curing to obtain a polyimide reinforced composite. The polyimide precursor solution was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride BP DA and p-phenylenediamine (PDA) were prepared using the following curing process: first, heating at 80°C and 0.1 MPa for 5 h, then heating at 120°C and 0.1 MPa for 3 h, and after vacuuming, heating at 300°C and 1.5 MPa for 8 h, and finally heating at 380°C and 1.5 MPa for 2 h to obtain a large-sized, non-planar composite adhesive part;

[0114] Large-sized non-planar composite materials were cut into 2.5cm×10cm strips and subjected to various performance tests.

[0115] 1. Shear strength: The tensile shear strength of the adhesive is measured according to GB / T7124-2008; the shear impact strength of the adhesive is measured according to GB / T 6328-1999.

[0116] Table 1

[0117]

[0118]

[0119] Table 2

[0120]

[0121]

[0122] Figure 1 This is a photo of a composite bonded part after room temperature shearing using the high-temperature resistant adhesive suitable for bonding large-sized, non-planar composites prepared in Example 1. As can be seen from the figure, the composite panel in Example 1 failed after the single lap shear test.

[0123] Figure 2 The thermal weight loss curve of the high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1 before and after curing in air atmosphere. As can be seen from the figure, the temperature T at which the adhesive decomposes 5% is d5％ 583℃, with excellent temperature resistance.

[0124] Figure 3 This is the DSC curve of the high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1 after curing. As can be seen from the figure, the Tg of the polyimide adhesive in Example 1 after curing is 372°C.

[0125] Figure 4 The infrared spectrum of the high temperature resistant adhesive suitable for bonding large-sized and non-planar composite materials prepared in Example 1 after curing: As can be seen from the figure, from 1780cm -1 and 1720cm -1 The presence of a symmetrical carbonyl absorption peak proves that the imidization is complete.

[0126] Figure 5 This is a photo of a large-sized, non-planar composite material bonded with a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1; Figure 6 This is a dimensional test diagram of a large-sized, non-planar composite material bonded with a high-temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials prepared in Example 1. As can be seen from the figure, the adhesive can bond large-sized, non-planar composite materials.

[0127] Figure 7 This is a horizontal tensile test curve of a large, non-planar composite material bonded with the high-temperature-resistant adhesive suitable for bonding large, non-planar composite materials, prepared in Example 1, after being cut into strips. As can be seen from the figure, the high-temperature-resistant adhesive suitable for bonding large, non-planar composite materials exhibits a maximum tensile shear strength of 15.8 MPa, demonstrating very high bonding strength.

Claims

1. A high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials, characterized in that It is prepared from 100 parts of polyimide precursor resin and 100 to 200 parts of solvent A by weight; The polyimide precursor resin is prepared from aromatic diamine, aromatic dianhydride and solvent B; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(0.95-1.05); the mass ratio of the aromatic diamine to the solvent B is 1:(2-20); The repeating unit of polyamic acid in the polyimide precursor resin is: The R2 is One or a combination of several of them.

2. The high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 1, characterized in that The solvent A and the solvent B are both mixed solutions of N,N-dimethylacetamide and water, and the mass ratio of the N,N-dimethylacetamide to water is 10:(0.5-1).

3. The high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 1, characterized in that The aromatic diamine is one of 4,4'-diaminodiphenyl ether, 1,3-bis(3'-aminophenoxy)benzene and 3,3'-diaminodiphenyl ether or a combination of several thereof.

4. The high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 1, characterized in that The aromatic dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride.

5. The method for preparing a high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 1, characterized in that It is carried out in the following steps:

1. Preparation of polyimide precursor resin: ① Weigh aromatic diamine, aromatic dianhydride and solvent B; The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(0.95-1.05); the mass ratio of the aromatic diamine to the solvent B is 1:(2-20); ② Under a nitrogen atmosphere at a temperature of 40°C to 48°C and stirring conditions, the weighed solvent B and aromatic diamine are stirred and dissolved for 1 hour to 5 hours to obtain an aromatic diamine solution. Under a nitrogen atmosphere and stirring conditions, the temperature of the aromatic diamine solution is raised to 50°C to 60°C, and the weighed aromatic dianhydride is added to the aromatic diamine solution in three equal portions. Then, under a nitrogen atmosphere at a temperature of 50°C to 60°C and stirring conditions, the reaction is stirred for 3 hours to 5 hours. Finally, under a nitrogen atmosphere, the reaction temperature is lowered from 50°C to 60°C to 25°C to 30°C, and the reaction is allowed to stand for 5 hours to 10 hours under a nitrogen atmosphere at a temperature of 25°C to 30°C to obtain a reaction solution. ③ Lowering the temperature of the reaction solution from 25°C to 30°C to 4°C to 6°C, then adding the reaction solution dropwise into ethanol and allowing it to stand, and finally filtering and drying to obtain a polyimide precursor resin; The repeating unit of polyamic acid in the polyimide precursor resin is: The R2 is One or a combination of several of them; 2. Weighing: Weigh 100 parts of polyimide precursor resin and 100 to 200 parts of solvent A by weight; 3. Preparation of adhesive: The weighed polyimide precursor resin is heated and stirred at a temperature of 80°C to 120°C for 2h to 5h, then cooled to 20°C to 25°C, and the weighed solvent A is added and stirred at a temperature of 20°C to 25°C for 10min to 30min to obtain a high-temperature resistant adhesive suitable for bonding large-size, non-planar composite materials.

6. The method for preparing a high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 5, characterized in that The stirring speed described in step 1② is 100rpm~200rpm.

7. The method for preparing a high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 5, characterized in that In step 1 (3), the reaction solution is added dropwise to ethanol at a dropping speed of 0.5 mL / s to 1 mL / s.

8. The method for preparing a high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 5, characterized in that In step 1③, let it stand for 8h to 12h.

9. The method for preparing a high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 5, characterized in that The drying described in step 1 (3) is specifically carried out at a temperature of 40°C to 80°C for 24h to 48h.

10. The method for preparing a high temperature resistant adhesive suitable for bonding large-sized, non-planar composite materials according to claim 5, characterized in that The stirring speed in step 3 is 100 rpm to 200 rpm.

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