A thermosensitive foamed polyimide adhesive filler resin powder and its preparation method

Abstract

A thermosensitive foaming polyimide adhesive filler resin powder and its preparation method are disclosed. By weight, the raw materials comprise 100 parts of polyimide precursor powder; 1 to 10 parts of latent thermosensitive foaming agent; 0.5 to 5 parts of nano-reinforcing filler; and 0.1 to 2 parts of interfacial coupling agent, prepared using this method. This invention successfully prepares a thermosensitive foaming adhesive filler resin powder through precise molecular weight control and latent foaming agent formulation. The product of this invention has the following advantages: First, it achieves filling (volume expansion 5-20 times) and structural bonding (shear strength > 8 MPa) in one step. Second, the powder form is easy to store and transport, and can be activated by a simple hot air gun or oven without the need for complex molds. Third, it inherits the high-temperature resistance (>300℃), flame retardancy, and low smoke density properties of polyimide, filling the gap in high-end field filling materials.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing and adhesive technology, and in particular to a thermosensitive foaming polyimide adhesive filler resin powder and its preparation method. Background Technology

[0002] In modern aerospace, microelectronics packaging, and precision instrument manufacturing, it is often necessary to fill cavities and gaps in complex structures to achieve purposes such as vibration reduction, heat insulation, electromagnetic shielding, or structural reinforcement. Traditional filling materials are mainly classified into the following categories: Pre-formed polyurethane (PU) or polyimide (PI) foam blocks: As disclosed in patents CN105153422B and CN106866964A, the preparation process typically involves first preparing large blocks of foam, then mechanically cutting and filling them according to the shape of the gaps. This method is not only cumbersome, but also difficult to fill micron-sized or extremely complex irregular cavities. After filling, the foam only contacts the bonded surface through friction, lacking chemical bonding strength and easily detaching.

[0003] Liquid foam adhesives: such as two-component polyurethane foam or silicone. Although these materials have good flowability, they have poor temperature resistance (usually below 150°C) and large curing shrinkage, which cannot meet the stringent requirements of the aerospace industry for high temperature resistance above 300°C and dimensional stability.

[0004] Existing polyimide powder foaming technologies, as described in patents CN102964834B and CN109880096A, are mostly focused on preparing bulk foam materials. Their powder formulation designs do not consider the balance between "adhesion" and "foaming ratio." Traditional PI powder often forms a closed-cell structure during foaming, lacking surface adhesion and failing to form a strong interfacial bond with the matrix.

[0005] The existing technology has the following drawbacks: First, foaming and bonding separate, requiring additional adhesive application for fixation after filling. Second, pre-formed foam is difficult to adapt to complex surfaces; liquid adhesives lack sufficient temperature resistance. Third, traditional PI foam powder preparation requires high-temperature treatment, which easily leads to the failure of heat-sensitive foaming agents. Summary of the Invention

[0006] This invention provides a heat-sensitive foaming polyimide adhesive filler resin powder and its preparation method to overcome the shortcomings of the prior art. The polyimide resin powder and its preparation process can both expand in volume to fill gaps and generate adhesive force through molecular chain activation when heated.

[0007] In order to achieve the objectives of this invention, the following technologies are proposed: On the one hand, a thermosensitive foaming polyimide adhesive filler resin powder is provided, which, by weight, comprises 100 parts of polyimide precursor powder; 1 to 10 parts of latent thermosensitive foaming agent; 0.5 to 5 parts of nano-reinforcing filler and 0.1 to 2 parts of interfacial coupling agent.

[0008] Furthermore, the polyimide precursor powder is a solid powder of polyamic acid (PAA) or polyamic ester (PE) with a number-average molecular weight (Mn) of 5000 g / mol to 50000 g / mol, and also exhibits thermosetting activity at 250°C to 350°C. By controlling the molecular weight of the polyamic acid, a suitable melt viscosity is ensured at the foaming temperature (around 200°C)—neither too low a viscosity leading to gas escape (bubbling) nor too high a viscosity hindering foaming. Simultaneously, the incompletely imidized molecular chain ends contain a large number of carboxyl and amine groups, which can form hydrogen bonds or chemical bonds with the surfaces of metals and composite materials under heating and pressure, achieving "in-situ bonding."

[0009] Furthermore, the latent thermosensitive blowing agent is a modified azodicarbonamide and benzenesulfonyl hydrazine derivative or microencapsulated thermally expanding microspheres. The initial decomposition temperature of the latent thermosensitive blowing agent is 180℃ to 220℃. The selection of a blowing agent with an initial decomposition temperature of 180℃ to 220℃ matches the imidization temperature window of polyimide (typically 200℃ to 300℃). The gases produced by the decomposition of the blowing agent (such as N2 and CO2) act as physical expansion agents, while the imidization reaction of the resin itself provides curing support.

[0010] Furthermore, the nano-reinforcing filler is one or more of nano-silica, nano-alumina, and carbon nanotubes that have been surface-modified with a silane coupling agent; The particle size of the nano-reinforced filler ranges from 10 nm to 100 nm; The introduction of nano-reinforced fillers not only improves the mechanical strength of the foam cell walls after foaming, but also significantly enhances the shear strength by bridging the resin and the substrate through coupling agents.

[0011] Furthermore, the interface coupling agent is one of the following: epoxy silane coupling agent, amino / diaminoalkoxy silane, methacryloxy silane, and multifunctional long-chain silane. Specifically, the interface coupling agent may be selected from amino / diaminoalkoxy silane (γ-aminopropyltriethoxy silane or diamino silane); epoxy silane coupling agent (3-glycidoxypropyltrimethoxy silane); methacryloxy silane (such as KH-570); and multifunctional long-chain silane (such as Shin-Etsu X-12-981S / 984S).

[0012] Another approach provides a method for preparing a thermosensitive foamed polyimide adhesive filler resin powder, including the following steps: Step 01, precursor solution synthesis: under an inert atmosphere, aromatic diamine is dissolved in a strongly polar aprotic solvent, and aromatic tetracarboxylic dianhydride is added in batches, with the solid content controlled at 15% to 30%. The reaction is carried out at 0°C to 25°C for 4 to 10 hours to obtain a polyamic acid solution. Step 02, chemical imidization / esterification modification: acetic anhydride and catalyst are added to the polyamic acid solution obtained in step 01 to carry out partial chemical imidization or alcohol reagents are added to carry out esterification reaction; Step 03, composite blending: the latent heat-sensitive foaming agent, nano-reinforced filler and interfacial coupling agent are pre-dispersed in a small amount of solvent to form a slurry, which is then added to the solution obtained in step 02 and ultrasonically dispersed for 30 to 60 minutes to form a composite solution. Step 04, precipitation and separation: The composite solution from step 03 is dropped into a non-benign precipitant and stirred to precipitate a solid precipitate or granulated by spray drying. Step 05, post-processing: The obtained wet solid is vacuum dried to remove residual solvent until the water content is less than 0.5%; Step 06, crushing and grading: The dried solid block is mechanically crushed at low temperature and passed through a 200-400 mesh sieve to obtain heat-sensitive foamed polyimide adhesive filler resin powder.

[0013] Furthermore, the non-benign precipitant is one or a mixture of deionized water, ethanol, methanol, or acetone.

[0014] The advantages of the above technical solution are: This invention successfully prepared a heat-sensitive foaming adhesive filler resin powder through precise molecular weight control and the compounding of a latent foaming agent. The product of this invention has the following advantages: First, it achieves filling (volume expansion 5-20 times) and structural bonding (shear strength >8 MPa) in one step. Second, the powder form is easy to store and transport, and can be activated by a simple hot air gun or oven without the need for complex molds. Third, it inherits the high-temperature resistance (>300℃), flame retardancy, and low smoke density properties of polyimide, filling the gap in high-end field filling materials. Attached Figure Description

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0016] Figure 1 The results of the thermosensitive foamed polyimide adhesive filler resin powder prepared in Example 1 are shown in the figure.

[0017] Figure 2 The image shows the result of the thermosensitive foaming polyimide adhesive filler resin powder prepared in Example 1 being foamed at 180°C.

[0018] Figure 3 The image shows the result of the thermosensitive foaming polyimide adhesive filler resin powder prepared in Example 1 being foamed at 250°C.

[0019] Figure 4 The results of foaming the thermosensitive foamed polyimide adhesive filler resin powder prepared in Example 1 in aluminum honeycomb are shown. Figure 1 .

[0020] Figure 5 The results of foaming the thermosensitive foamed polyimide adhesive filler resin powder prepared in Example 1 in aluminum honeycomb are shown. Figure 2 .

[0021] Figure 6 The image shows the result of the thermosensitive foaming polyimide adhesive filler resin powder prepared in Example 1 being foamed in a high-temperature material. Detailed Implementation

[0022] Example 1: Standard adhesive filler powder (BTDA-ODA) Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0023] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0024] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0025] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0026] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0027] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve. Figure 1 As shown.

[0028] Test results: Powder bulk density 0.45 g / cm³ 3 Heat on a hot plate at 200°C for 5 minutes (e.g., Figure 2 and Figure 3 As shown in the figure, the volume expanded 12 times, and the foaming ratio was controllable. After foaming and curing, the shear strength with the aluminum alloy specimen reached 8.5 MPa. Foaming tests were conducted for different adhesive media, and the foaming results are as follows. Figures 4 to 6 As shown.

[0029] Example 2: High heat resistance type (BPDA-ODA) Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 44.4 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% in excess of the amount of 3,3',4,4'-biphenyltetracarboxylic dianhydride to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0030] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0031] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0032] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0033] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0034] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0035] Test results: The glass transition temperature (Tg) increased from 280℃ to 320℃, and the shear strength was 9.2 MPa.

[0036] Example 3 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0037] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0038] Step 3: Mix and disperse 10g of modified azodicarbonamide foaming agent, 0.5g of foam stabilizer (nonionic fluorocarbon surfactant), 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0039] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0040] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0041] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0042] Test results: The foaming ratio reached 20 times, and the density was as low as 0.06 g / cm³. 3 .

[0043] Example 4 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0044] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0045] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 3g of dicyandiamide (DICY) as a latent curing agent, 2g of nano-SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0046] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0047] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0048] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0049] Test results: The foaming and curing time was shortened to 3 minutes.

[0050] Example 5 Step 1: Under nitrogen protection, 29.2 g of a mixture of 4,4'-diaminodiphenyl ether and 25.03 g of polyetheramine D-400 (in a 7:3 molar ratio) was dissolved in 390 g of N-methylpyrrolidone and cooled to 5°C in an ice-water bath. 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride was added in batches, and the reaction was carried out at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added was approximately 7% excess over the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride to ensure that the resulting polyimide resin was amino-terminated, thereby improving the adhesion effect.)

[0051] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0052] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0053] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0054] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0055] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0056] Test results: The material has a certain degree of resilience after foaming and curing, with a compression resilience rate of 85%.

[0057] Example 6 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0058] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0059] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 5g of surface-treated nano aluminum nitride (AlN), and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0060] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0061] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0062] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0063] Test results: The thermal conductivity of the foam increased to 0.45 W / (m·K).

[0064] Example 7 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0065] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0066] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0067] Step 4: The mixed solution is directly fed into a spray dryer (inlet air 200℃, outlet air 80℃) to obtain microsphere powder with good sphericity.

[0068] Test results: The powder has excellent flowability.

[0069] Example 8 Step 1: Under nitrogen protection, 29.2 g of 4,4'-diaminodiphenyl ether was dissolved in 300 g of N-methylpyrrolidone, and the solution was cooled to 5°C in an ice-water bath. 43.8 g of 4,4'-(hexafluoroisopropene)phthalic anhydride was added in batches, and the mixture was reacted at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added was approximately 7% in excess of the amount of 4,4'-(hexafluoroisopropene)phthalic anhydride to ensure that the resulting polyimide resin was amino-terminated, thereby improving the adhesion effect.)

[0070] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0071] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0072] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0073] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0074] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0075] Test results: The dielectric constant of the foam (1 GHz) is as low as 1.7.

[0076] Example 9 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0077] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0078] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano-SiO2, 2g of organomontmorillonite (OMMT), and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0079] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0080] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0081] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0082] Test results: Limiting oxygen index (LOI) reached 42%, achieving UL94 V-0 flame retardancy rating.

[0083] Example 10 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0084] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0085] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0086] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0087] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0088] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0089] Step 7: After encapsulating the powder, leave it at room temperature for 6 months, and then conduct a foaming adhesion test.

[0090] Results: The performance retention rate was over 95%, demonstrating the excellent stability of the latent system.

[0091] Example 11 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0092] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0093] Step 3: Mix and disperse 2g of nano-SiO2 and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0094] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0095] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0096] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0097] Test results: After heating, it only melts and bonds without volume expansion, and cannot fill gaps larger than 50μm.

[0098] Example 12 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0099] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0100] Step 3: Mix and disperse 5g of azodicarbonamide foaming agent with a decomposition temperature of 160℃, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0101] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0102] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0103] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0104] Test results: The foaming agent decomposed before the solvent was completely removed and the precursor was softened, causing gas to escape, resulting in the final product collapsing, having uneven density, and lacking adhesive strength.

[0105] Example 13 The foam material described therein was prepared according to the invention patent application number CN2015106441939, wherein the reaction time was shortened to 1 hour and Mn < 3,000.

[0106] Test results: When foaming, the melt viscosity is too low, the gas cannot be encapsulated, forming large voids or bubbles, and the structure collapses.

[0107] Example 14 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0108] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0109] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent and 2g of nano-SiO2 in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0110] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0111] Step 5: Filter and dry under vacuum at 60°C for 24 hours.

[0112] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0113] Test results: The shear strength was only 3.2 MPa, and the interface failure was obvious, proving the key role of the coupling agent in the "adhesion-filling" synergy.

[0114] Example 15 Step 1: Under nitrogen protection, dissolve 29.2 g of 4,4'-diaminodiphenyl ether in 300 g of N-methylpyrrolidone and cool to 5°C in an ice-water bath. Add 43.8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride in batches and react at room temperature for 6 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of approximately 15,000 mPa·s. (The amount of 4,4'-diaminodiphenyl ether added is approximately 7% more than the amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride added to ensure that the obtained polyimide resin is amino-terminated, thereby improving the adhesion effect).

[0115] Step 2: Add 20g of acetic anhydride and 2g of pyridine to perform partial chemical imidization (approximately 30% imidization) to improve the storage stability of the powder.

[0116] Step 3: Mix and disperse 5g of modified azodicarbonamide foaming agent, 2g of nano SiO2, and 0.5g of 3-glycidyl etheroxypropyltrimethoxysilane (KH-560) in 50g of ethanol, sonicate for 30 minutes, and then add the above solution.

[0117] Step 4: Slowly add the mixed solution dropwise into 5L of deionized water, stir vigorously, and a white flocculent precipitate will form.

[0118] Step 5: Filter and dry under vacuum at 120°C for 24 hours.

[0119] Step 6: Cryogenic pulverization with liquid nitrogen, followed by sieving through a 300-mesh sieve.

[0120] Test results: The foaming agent partially decomposed during the drying stage, resulting in a final foaming ratio of less than 5 times, and the powder clumped.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A heat-sensitive foaming polyimide adhesive filler resin powder, characterized in that, By weight, it includes 100 parts of polyimide precursor powder and 1 to 10 parts of latent heat-sensitive foaming agent. It is prepared by using 0.5 to 5 parts of nano-reinforced filler and 0.1 to 2 parts of interfacial coupling agent.

2. The thermosensitive foamed polyimide adhesive filler resin powder according to claim 1, characterized in that, The polyimide precursor powder is a solid powder of polyamic acid (PAA) or polyamic acid ester (PE) with a number-average molecular weight (Mn) of 5000 g / mol to 50000 g / mol, and also has thermosetting activity at 250°C to 350°C.

3. The thermosensitive foamed polyimide adhesive filler resin powder according to claim 1, characterized in that, The latent thermosensitive foaming agent is a modified azodicarbonamide and benzenesulfonyl hydrazine derivative or a microcapsule-encapsulated thermal expansion microsphere. The initial decomposition temperature of the latent thermosensitive foaming agent is 180℃ to 220℃.

4. The thermosensitive foamed polyimide adhesive filler resin powder according to claim 1, characterized in that, The nano-reinforced filler is one or more of nano-silica, nano-alumina, and carbon nanotubes that have been surface-modified with silane coupling agent. The particle size of the nano-reinforced filler ranges from 10 nm to 100 nm.

5. The thermosensitive foamed polyimide adhesive filler resin powder according to claim 1, characterized in that, The interface coupling agent is one of the following: epoxy silane coupling agent, amino / diaminoalkoxy silane, methacryloxy silane, or polyfunctional long-chain silane.

6. A method for preparing the thermosensitive foamed polyimide adhesive filler resin powder as described in any one of claims 1 to 3, characterized in that, Including the following steps: Step 01, precursor solution synthesis: under an inert atmosphere, aromatic diamine is dissolved in a strongly polar aprotic solvent, and aromatic tetracarboxylic dianhydride is added in batches, with the solid content controlled at 15% to 30%. The reaction is carried out at 0°C to 25°C for 4 to 10 hours to obtain a polyamic acid solution. Step 02, chemical imidization / esterification modification: acetic anhydride and catalyst are added to the polyamic acid solution obtained in step 01 to carry out partial chemical imidization or alcohol reagents are added to carry out esterification reaction. Step 03, composite blending: the latent heat-sensitive foaming agent, nano-reinforced filler and interfacial coupling agent are pre-dispersed in a small amount of solvent to form a slurry, which is then added to the solution obtained in step 02 and ultrasonically dispersed for 30 to 60 minutes to form a composite solution. Step 04, precipitation and separation: The composite solution from step 03 is dropped into a non-benign precipitant and stirred to precipitate a solid precipitate or granulated by spray drying. Step 05, post-processing: The obtained wet solid is vacuum dried to remove residual solvent until the water content is less than 0.5%; Step 06, crushing and grading: The dried solid block is mechanically crushed in a low-temperature environment and passed through a 200-400 mesh sieve to obtain heat-sensitive foamed polyimide adhesive filler resin powder.

7. The method for bonding and filling thermosensitive foamed polyimide resin powder according to claim 6, characterized in that, Non-benign precipitants are one or a mixture of deionized water, ethanol, methanol, or acetone.

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