A composite toughened interface adhesive, its preparation method and interface treatment method

Abstract

This invention relates to the field of polymer composite materials technology, specifically to a composite toughening interface adhesive, its preparation method, and its interface treatment method. The adhesive comprises 40%~90% silicone resin, 1%~5% catalyst, 1%~20% whiskers, 0.1%~5% fiber filaments, and 0.1%~5% wetting and dispersing agent. This invention constructs a multi-level energy-absorbing network through a silicone resin matrix and whiskers / fiber filaments as biphase fillers, simultaneously toughening and activating the surface with the catalyst. This solves the problem of existing technologies being unable to simultaneously achieve substrate toughening and interface strengthening. After modification, the impact strength of the PI substrate is increased by 126%, and the flexural strength by 39%. The tensile strength and shear strength of the PMI foam core material are increased by 117% and 91%, respectively. No bulging or delamination occurs at the interface at 150℃. This invention is suitable for high-temperature stealth metamaterials in shipbuilding and aerospace applications.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and in particular to a composite toughening interface adhesive, its preparation method, and its interface treatment method. Background Technology

[0002] Polyimide (PI) film, commonly known as gold film, contains a stable imide heterocyclic structure in its main chain. It possesses ultra-high temperature resistance above 400℃, excellent insulation and dielectric properties, radiation resistance, abrasion resistance, and chemical corrosion resistance, making it one of the best-performing high-end flexible polymer films currently available. Its common applications cover civilian fields such as flexible circuit boards, high-temperature insulating devices, electromagnetic wires, and automotive electronic components. In the high-end military field, relying on its core advantages of low dielectric constant, low dielectric loss, and high-temperature resistance without deformation, PI metamaterial substrates have become the preferred flexible substrate for electromagnetic metamaterial absorbing layers and wave-transparent functional layers, and are widely used in ship stealth structures, aerospace wave-transparent radomes, and airborne high-temperature electromagnetic protection devices. As new-generation aircraft and ship equipment develop towards higher speeds, higher temperatures, and longer lifespans, the service temperature of electromagnetic metamaterials has exceeded 150°C, placing higher demands on PI metamaterial substrates: the substrate itself needs to possess excellent impact and bending toughness to prevent cracking under dynamic loads; and the substrate and foam core material need to achieve high-strength interfacial bonding to prevent interfacial delamination failure caused by high-temperature thermal expansion and contraction.

[0003] Currently, when virgin PI metamaterial substrates are applied to high-temperature metamaterial substrates, there are two unavoidable technical shortcomings: (1) The substrate is inherently brittle and lacks toughness at high and low temperatures: Pure PI polymer chain segments are extremely rigid. Under normal temperature, they are prone to microcracks when subjected to impact and bending loads. Under high temperature, the thermal motion of polymer chain segments intensifies, the thermal expansion coefficients of the substrate and the foam core material do not match, and stress concentration will rapidly expand the microcracks, eventually leading to substrate fracture and overall structural failure; (2) The surface interface of the film is severely passivated: The molecular arrangement on the surface of PI metamaterial substrates is dense and regular, with no polar active functional groups and extremely low surface energy. The mechanical interlocking and chemical bonding ability with organic adhesives and PMI foam core materials is extremely poor. After bonding with conventional epoxy adhesives, the interface bonding force is weak. After long-term aging at high temperature, bulging, delamination, and peeling failure are very likely to occur, which is the key bottleneck restricting the service life of PI-based metamaterials.

[0004] Publication No. CN113652675B describes a method for in-situ catalytic chemical plating of plasma-modified polyimide films. This method improves the surface roughness of the PI metamaterial substrate through argon plasma etching and introduces oxygen-containing polar groups to enhance surface energy, potentially increasing the film's adhesive peel strength by 62%. However, this process only achieves surface modification, with a modified layer thickness only at the nanometer level. At temperatures above 150°C, the polar groups rapidly degrade, completely diminishing the interface strengthening effect. Furthermore, the plasma equipment is expensive and unsuitable for large-area continuous film production. The core journal *Surface Technology*, Volume 41, 2012, titled "The Influence of Plasma Treatment Conditions on the Surface Treatment Effect of Polyimide Films," describes a method using oxygen plasma combined with chemical grafting to modify the PI metamaterial substrate. This method can improve the film's hydrophilicity and adhesive strength in the short term, but the chemical reagents corrode the PI metamaterial substrate, causing a 10%-18% decrease in the film's mechanical strength. Additionally, the process generates acid and alkaline wastewater, resulting in poor environmental performance. Publication No.: CN115873249A discloses a plasma-treated fiber-reinforced polyimide material and its preparation method. This method improves the bulk toughness of the PI metamaterial substrate through fiber blending modification, increasing the film's bending strength by 15%. However, this approach only improves the substrate's bulk toughness and cannot solve the problem of interfacial passivation, leaving the adhesive interface failure issue unresolved. Currently, in published patents and academic literature, PI metamaterial substrate modification schemes can only achieve either interface strengthening or bulk toughening, failing to address both needs simultaneously. Furthermore, existing processes generally suffer from poor high-temperature stability, substrate damage, high costs, and inability to achieve industrial-scale mass production. There is currently no integrated modification scheme suitable for high-temperature electromagnetic metamaterials that can simultaneously achieve substrate toughening and interfacial surface energy enhancement.

[0005] Therefore, there is an urgent need to propose a composite toughening interface adhesive, preparation method, and interface treatment method to solve the problem that existing polyimide metamaterial substrate modification technologies cannot simultaneously address the issues of insufficient substrate toughness and interface passivation. Summary of the Invention

[0006] In view of this, the present invention aims to propose a composite toughened interface adhesive, a preparation method and an interface treatment method to solve the problem that existing polyimide metamaterial substrate modification technologies cannot simultaneously solve the problems of insufficient substrate toughness and interface passivation.

[0007] This invention utilizes crosslinking of silicone resin to form a high-temperature resistant flexible matrix, providing basic toughness and high-temperature stability. Whiskers achieve crack sealing and hindrance at the microscale, while fibers bear load transfer and stress dispersion at the macroscale. These two elements synergistically construct a multi-level energy-absorbing network structure, achieving bidirectional toughening of the PI substrate. This significantly improves the substrate's impact and bending resistance, with no significant attenuation of mechanical properties under high-temperature conditions of 150-250℃. Simultaneously, this invention uses an acid-base composite catalyst to etch and activate the surface molecules of the PI metamaterial substrate during the coating and curing process, introducing polar active functional groups and increasing surface micro-roughness. This simultaneously increases the film surface energy, eliminates the interface passivation effect, and enhances the chemical bonding and mechanical interlocking between the PI substrate and the PMI foam core material, achieving interface adhesion strengthening. Ultimately, this invention solves the two major technical defects of PI metamaterial substrates—intrinsic brittleness and interface passivation—with a single process. It resists crack propagation caused by dynamic loads and thermal stress, and eliminates the service risks of interface delamination, bulging, and peeling under high-temperature conditions.

[0008] The technical solution of this invention is implemented as follows:

[0009] The first objective of this invention is to disclose a composite toughened interface adhesive comprising the following components by weight percentage:

[0010] Organosilicon resin 40%~90%;

[0011] Catalyst 1%~5%;

[0012] Whiskers 1%~20%;

[0013] Fiber filaments 0.1%~5%;

[0014] Wetting and dispersing agent: 0.1%~5%.

[0015] Optionally, the silicone resin is one or more of polymethyl silicone resin, polyethyl silicone resin, polyaryl silicone resin, and polyalkylaryl silicone resin.

[0016] Optionally, the catalyst is an acid catalyst or a base catalyst;

[0017] The acid catalyst is one or more of sulfuric acid, formic acid, and acetic acid;

[0018] The alkaline catalyst is one or more of diethylenetriamine, triethylenetetramine, sodium hydroxide, and sodium carbonate.

[0019] Optionally, the whiskers are one or more of the following: alumina whiskers, silicon carbide whiskers, calcium carbonate whiskers, boron carbide whiskers, calcium sulfate whiskers, aluminum sulfate whiskers, silicon oxide whiskers, and beryllium oxide whiskers.

[0020] Optionally, the fiber filament is one or more of carbon fiber, basalt fiber, aramid fiber, polyphenylene sulfide fiber, glass fiber, polyester fiber, and polyamide fiber.

[0021] Optionally, the whisker has a diameter of 0.03~10μm; the fiber has a diameter of 0.1~50μm and a length of 0.1~5cm.

[0022] The second objective of this invention is to disclose a method for preparing a composite toughened interface adhesive, which includes the following steps:

[0023] The silicone resin, wetting and dispersing agent, whiskers and fiber filaments are mixed and premixed and dispersed at the first stirring speed until the solid filler is uniformly dispersed in the resin matrix.

[0024] Adjust the stirring speed to the second stirring speed, add the catalyst, and continue stirring until the catalyst is completely mixed to obtain the composite toughened interface adhesive.

[0025] Optionally, the first stirring speed is 1000~2000 r / min, and the premixing and dispersion time is 30~90 min; the second stirring speed is 500~1000 r / min, and the stirring time after adding the catalyst is 5~10 min.

[0026] The third objective of this invention is to disclose an interface treatment method for a composite toughened interface adhesive, using any of the composite toughened interface adhesives described above, comprising the following steps:

[0027] The surface of the polyimide metamaterial substrate is cleaned.

[0028] The composite toughened interface adhesive is coated onto the surface of the polyimide metamaterial substrate to form an adhesive layer.

[0029] A release layer is applied to the surface of the coated film, and the adhesive is cured by applying pressure and heating.

[0030] After cooling, the release layer is removed to obtain the interface-strengthened polyimide metamaterial substrate.

[0031] Optionally, the thickness of the adhesive layer is 20~50μm; the pressure applied is 0.2~4MPa; the heating temperature is 150~250℃; and the curing holding and pressure holding time is 30~200min.

[0032] Compared with existing technologies, the composite toughened interface adhesive, preparation method, and interface treatment method of the present invention have the following advantages:

[0033] 1. This invention constructs a multi-level energy-absorbing network structure by combining an organosilicon resin matrix with whiskers and fiber filaments as biphase reinforcing fillers. With the surface activation effect of an acid-base compound catalyst, it solves the technical problem that existing polyimide metamaterial substrate modification technologies cannot simultaneously achieve substrate toughening and interfacial bonding strengthening. After modification, the impact strength of the PI metamaterial substrate is increased by 126%, the flexural strength is increased by 39%, and the tensile strength is increased by 117% and the shear strength is increased by 91% after bonding with PMI foam core material. After long-term high-temperature insulation at 150℃, there is no bulging or delamination at the interface, achieving a dual leap in substrate mechanical toughness and interfacial bonding reliability.

[0034] 2. This invention introduces an acid-base compound catalyst into the composite toughening interface adhesive, which simultaneously activates the surface molecules of the PI metamaterial substrate during the curing process of the silicone resin, introduces polar active groups, and increases surface roughness. This solves the problems of poor high-temperature stability of modified layers and rapid decay of interface strengthening effect under high-temperature conditions caused by existing surface treatment technologies such as plasma modification and chemical grafting. As a result, the modified PI metamaterial substrate still maintains excellent interfacial adhesion performance under high-temperature conditions of 150-250℃.

[0035] 3. This invention uses whiskers and fibers as biphase reinforcing fillers in an organosilicon resin matrix. It utilizes the crack deflection, pull-out effect and bridging effect of whiskers to achieve microscale crack hindrance, and utilizes the load transfer and stress dispersion of fibers to achieve macroscale crack confinement. This solves the problems of high intrinsic brittleness, insufficient high and low temperature toughness, and easy generation of microcracks and propagation fracture under impact and bending loads in pure PI metamaterial substrates.

[0036] 4. The present invention has a simple process, no substrate damage, excellent high-temperature stability, no need for large equipment, can be produced continuously, effectively improves the overall mechanical stability and interface reliability of PI-based stealth metamaterial sandwich structure, extends the service life of equipment, and meets the engineering application requirements of next-generation ship and aviation high-temperature stealth electromagnetic materials.

[0037] 5. This invention solves the problem of uneven toughening effect caused by the difficulty in uniformly dispersing solid fillers (whiskers, fibers) in the organosilicon resin matrix and easy precipitation and stratification during the preparation of adhesives by adopting a two-step process of "high-speed premixing and dispersion followed by low-speed catalytic mixing". This ensures the uniform construction of multi-level energy absorption network in the coating and the stability of toughening effect. Detailed Implementation

[0038] To make the technical means and the objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below.

[0039] In this invention, 'interface passivation' specifically refers to a particular interfacial failure state in which the polyimide metamaterial substrate, due to its dense surface molecular arrangement, lack of polar active groups, and extremely low surface energy, cannot establish effective chemical bonding and physical anchoring with organic adhesives. Its technical characteristics include a large contact angle, poor wettability, and low peel strength, which is fundamentally different from metal passivation in the electrochemical field or interfacial passivation in the semiconductor field.

[0040] The composite toughened interface adhesive provided by this invention comprises silicone resin, a catalyst, whiskers, fibers, and a wetting and dispersing agent. The silicone resin, as the matrix material of the adhesive, comprises 40% to 90% by mass, preferably 60% to 85%, and more preferably 75% to 80%. After curing, the silicone resin forms a highly cross-linked network macromolecular structure, endowing the adhesive with excellent flexibility, high-temperature resistance, and aging resistance.

[0041] In one specific embodiment, the silicone resin is one or more selected from polymethyl silicone resin, polyethyl silicone resin, polyaryl silicone resin, and polyalkylaryl silicone resin. Preferably, the silicone resin is polymethylphenyl silicone resin, which combines the flexibility of methyl silicone resin and the heat resistance of phenyl silicone resin, making it more suitable for toughening modification requirements under high-temperature service conditions.

[0042] Based on the silicone resin matrix, this invention also introduces a catalyst into the adhesive to achieve the dual functions of curing reaction regulation and interface activation. The mass percentage of the catalyst is 1% to 5%, preferably 2% to 4%, and more preferably 3%. The catalyst used in this invention has a dual function: on the one hand, it catalyzes the cross-linking and curing reaction of the silicone resin; on the other hand, it activates the surface molecules of the polyimide metamaterial substrate during the curing process, introduces polar active groups, and increases the surface micro-roughness, thereby improving the surface energy of the substrate.

[0043] In one specific embodiment, the catalyst is an acid catalyst or a base catalyst. The acid catalyst is one or more of sulfuric acid, formic acid, and acetic acid; the base catalyst is one or more of diethylenetriamine, triethylenetetramine, sodium hydroxide, and sodium carbonate. Preferably, the catalyst is a base catalyst, more preferably diethylenetriamine or triethylenetetramine. The reason for preferring amine-based base catalysts is that, while promoting the curing of silicone resin, they can achieve chemical activation of surface molecules under mild conditions through nucleophilic reactions between the amine groups and the imide rings in the polyimide molecular chain, without damaging the mechanical properties of the substrate.

[0044] In addition to the catalyst, to further enhance the mechanical toughness and crack propagation resistance of the adhesive layer, this invention also adds whiskers as micro-reinforcing agents to the adhesive. The whiskers comprise 1% to 20% by mass, preferably 5% to 18%, and more preferably 8% to 15%. Whiskers possess a high specific surface area and fibrous morphology, exhibiting high energy absorption, high strength, high rigidity, and wear resistance. After the adhesive cures, the whiskers prevent the further propagation of microcracks through crack deflection, crystal fragmentation, whisker pull-out effect, and crack bridging, significantly improving the impact strength and crack propagation resistance of the adhesive layer.

[0045] In one specific embodiment, the whiskers are one or more selected from alumina whiskers, silicon carbide whiskers, calcium carbonate whiskers, boron carbide whiskers, calcium sulfate whiskers, aluminum sulfate whiskers, silicon oxide whiskers, and beryllium oxide whiskers. Preferably, the whiskers are a composite combination of silicon carbide whiskers and calcium carbonate whiskers. Specifically, the diameter of the whiskers is 0.03~10μm; the diameter of the fiber filaments is 0.1~50μm, and the length of a single fiber is 0.1~5cm. The diameter of the silicon carbide whiskers is preferably 0.03~3μm, and the diameter of the calcium carbonate whiskers is preferably 0.1~10μm. Selecting whiskers within the above diameter range ensures uniform dispersion in the resin matrix and provides sufficient specific surface area to achieve efficient crack inhibition. By using a composite of silicon carbide whiskers and calcium carbonate whiskers, the differences in diameter and hardness between the two can be utilized to achieve multiple inhibition of cracks of different sizes, further improving the toughening effect.

[0046] To achieve a cross-scale synergistic reinforcement effect with the whiskers, this invention also incorporates fiber filaments as a macroscopic reinforcement to withstand higher load stresses. The mass percentage of the fiber filaments is 0.1% to 5%, preferably 1% to 4%, and more preferably 2%. The fiber filaments possess high rigidity and can withstand significant load stresses. The matrix resin transfers the external load to the fibers through shear stress at the fiber interface, reducing the stress concentration factor and restraining the occurrence and propagation of cracks.

[0047] In one specific embodiment, the fiber filament is one or more selected from carbon fiber, basalt fiber, aramid fiber, polyphenylene sulfide fiber, glass fiber, polyester fiber, and polyamide fiber. Preferably, the fiber filament is glass fiber. The diameter of the fiber filament is preferably 0.1~50μm, and the length of a single fiber is preferably 0.1~5cm. Selecting fibers within the above-mentioned diameter range and single-fiber length ensures both uniform mixing of the composite toughening interface adhesive and effectively maintains high rigidity within the material system, sufficient to withstand large load stresses.

[0048] To ensure uniform and stable dispersion of solid fillers such as whiskers and fibers in the silicone resin matrix after their addition, this invention also introduces a wetting and dispersing agent as a key additive. The mass percentage of the wetting and dispersing agent is 0.1% to 5%, preferably 0.5% to 3%, and more preferably 1% to 2%. The function of the wetting and dispersing agent is to reduce the interfacial tension between the solid fillers (whiskers, fibers) and the resin matrix, ensuring uniform dispersion of the fillers in the system and preventing precipitation and stratification.

[0049] In one specific embodiment, the wetting and dispersing agent is a solvent-based or water-soluble wetting and dispersing agent. The solvent-based wetting and dispersing agent is one of Anli-Terra-20 or PD-85; the water-soluble wetting and dispersing agent is one of inorganic, organic, or polymeric dispersants. The inorganic water-soluble wetting and dispersing agent is one of phosphates and silicates; the organic water-soluble wetting and dispersing agent is a nonionic surfactant; the polymeric dispersant is one of sodium polyacrylate, sodium naphthalenesulfonate, and formaldehyde condensate. Preferably, the wetting and dispersing agent is a solvent-based wetting and dispersing agent, more preferably Anli-Terra-20, which has excellent compatibility with the silicone resin system.

[0050] Through the synergistic effect of the above components, the silicone resin, as a flexible matrix, provides basic toughness and high-temperature resistance; the catalyst simultaneously activates the interface during the curing process; the whiskers inhibit crack propagation at the microscale; the fibers bear the load transfer at the macroscale; and the wetting and dispersing agent ensures the uniform dispersion of each solid filler in the system. The synergistic effect of these five components gives the adhesive layer both excellent mechanical toughness and interface strengthening function, while solving the dual technical problems of insufficient toughness and interface passivation in PI metamaterial substrates.

[0051] This invention also provides a method for preparing a composite toughened interface adhesive, comprising a premixing and dispersion step and a catalytic mixing step. The preparation method is further described in detail below with reference to specific embodiments.

[0052] S1: Premixing and dispersion step.

[0053] Organosilicon resin, wetting and dispersing agent, whiskers, and fibers are added to a stirred tank and premixed and dispersed at the first stirring speed until the solid filler is uniformly dispersed in the resin matrix.

[0054] In one specific embodiment, the first stirring speed is 1000~2000 r / min, and the premixing and dispersion time is 30~90 min. Preferably, the first stirring speed is 1200~1800 r / min, more preferably 1500 r / min; the premixing and dispersion time is preferably 45~75 min, more preferably 60 min. The criteria for judging the completion of premixing and dispersion are: uniform flow of the system, no filler sedimentation, and no stratification.

[0055] This setup uses high-speed stirring for premixing and dispersion, which effectively breaks up filler agglomerates, allowing them to achieve a monodisperse state in the resin matrix and ensuring the uniformity of the multi-stage energy-absorbing network after subsequent curing.

[0056] S2: Catalytic mixing step.

[0057] After premixing and dispersion, adjust the stirring speed to the second stirring speed, add the catalyst, and continue stirring until the catalyst is completely mixed to obtain the composite toughened interface adhesive.

[0058] In one specific embodiment, the second stirring speed is 500-1000 r / min, and the stirring time after adding the catalyst is 5-10 min. Preferably, the second stirring speed is 600-800 r / min, more preferably 500 r / min; the stirring time after adding the catalyst is preferably 5-8 min, more preferably 5 min.

[0059] This setting reduces the stirring speed during the catalytic mixing stage, avoiding localized overheating and excessively rapid reactions that could affect the adhesive's pot life and storage stability. Furthermore, low-speed stirring ensures uniform catalyst dispersion while preventing excessive shearing from adversely affecting the resin system.

[0060] In one specific embodiment, both premixing and catalytic mixing are performed at room temperature, without the need for preheating. After catalytic mixing is complete, the adhesive is sealed and stored for later use.

[0061] This invention also provides a method for interface strengthening treatment of polyimide metamaterial substrates using the above-mentioned composite toughening interface adhesive, including a substrate pretreatment step, an adhesive coating step, a molding and curing step, and a post-treatment step. The treatment method is further described in detail below with reference to specific embodiments.

[0062] ST1: Substrate pretreatment step.

[0063] The surface of the polyimide metamaterial substrate is cleaned to remove dust and oil.

[0064] In one specific embodiment, the cleaning process involves wiping the surface of the polyimide metamaterial substrate with anhydrous ethanol and then air-drying it at room temperature. In another optional embodiment, the cleaning process can also involve wiping with isopropanol or acetone followed by air-drying at room temperature, as long as it effectively removes surface contaminants without damaging the substrate itself.

[0065] ST2: Adhesive coating step.

[0066] A composite toughening interface adhesive is coated onto the surface of a polyimide metamaterial substrate to form an adhesive layer.

[0067] In one specific embodiment, the adhesive is uniformly coated onto one side of the polyimide metamaterial substrate using a scraper coating process, with the adhesive layer thickness controlled to be 20-50 μm, preferably 25-40 μm, and more preferably 30 μm. In another optional embodiment, the coating can also be performed using an immersion process or a roller coating process.

[0068] Controlling the adhesive layer thickness within the above range is of great significance: when the adhesive layer is too thin (less than 20 μm), the toughening filler (whiskers, fibers) is difficult to spread fully in the coating, the multi-level energy absorption network is incomplete, and the toughening effect is limited; when the adhesive layer is too thick (greater than 50 μm), on the one hand, it increases the material cost, and on the other hand, it may affect the flexibility of the film and the overall thickness control of the subsequent sandwich structure.

[0069] ST3: Compression molding and curing step.

[0070] A release layer is applied to the surface of the coated film, and the adhesive is cured by applying pressure and heating.

[0071] In one specific embodiment, a release film is laminated onto the upper and lower surfaces of the coated film for protection, and then the film is placed in a hot press. The process parameters are controlled as follows: pressure 0.2~4MPa, temperature 150~250℃, and holding time 30~200min. Preferably, the pressure is 1~3MPa, more preferably 2MPa; the temperature is 180~220℃, more preferably 200℃; and the holding time is 60~150min, more preferably 120min.

[0072] In this step, the silicone resin in the adhesive undergoes a cross-linking and curing reaction under heating conditions, forming a highly cross-linked network macromolecular structure that firmly anchors whiskers and fibers within the cross-linked system. Simultaneously, the catalyst activates the surface molecules of the polyimide metamaterial substrate at high temperatures, introducing polar active groups and increasing surface micro-roughness. These two processes are completed concurrently in the same hot-pressing process, achieving integrated toughening and interfacial strengthening.

[0073] This setting controls the curing temperature within the range of 150~250℃, avoiding the excessively slow cross-linking and curing reaction rate of the silicone resin below 150℃, which would result in insufficient activation of the PI surface by the catalyst. Simultaneously, it prevents potential thermal damage to the PI substrate at temperatures above 250℃, which would also increase energy consumption and narrow the process window. Maintaining the temperature within the 150~250℃ range ensures complete curing and sufficient interface activation while preventing substrate damage.

[0074] ST4: Post-processing steps.

[0075] After cooling, the release layer is removed to obtain the interface-strengthened polyimide metamaterial substrate.

[0076] In one specific implementation, after curing, the coating is cooled to room temperature in the oven, and then the release film is peeled off. Oven cooling avoids stress concentration within the coating caused by rapid cooling, ensuring the long-term stability of the coating-substrate interface.

[0077] Example 1

[0078] The composite toughening interface adhesive provided in this embodiment is prepared from the following raw materials in the following mass percentages: 75% polymethylphenyl silicone resin, 3% silicon carbide whiskers (0.5 μm in diameter), 15% calcium carbonate whiskers (2 μm in diameter), 2% glass fiber (10 μm in diameter and 5 mm in length), 3% diethylenetriamine, and 2% wetting and dispersing agent (Anli-Terra-20).

[0079] The preparation process is as follows: Weighed polymethylphenyl silicone resin, silicon carbide whiskers, calcium carbonate whiskers, glass fiber, and wetting and dispersing agent are added to a stirring tank and premixed and dispersed at 1000 r / min for 60 min; then the stirring speed is reduced to 500 r / min, diethylenetriamine is added and stirring is continued for 5 min for catalytic mixing, so that the catalyst is completely mixed, and the composite toughened interface adhesive is obtained.

[0080] The composite toughening interface adhesive was prepared to strengthen the interface of the PI metamaterial substrate. The steps are as follows: (1) Wipe the surface of the PI metamaterial substrate with anhydrous ethanol to remove dust and oil stains and then air dry at room temperature; (2) Use a scraper coating process to uniformly coat the above adhesive on one side of the PI metamaterial substrate, and control the thickness of the adhesive layer to be 20-50μm; (3) Apply release film to the upper and lower surfaces of the coated film for protection, put it into a hot press, and control the pressure to be 2MPa, the temperature to be 200℃, and the heat and pressure holding time to be 120min; (4) After curing, cool to room temperature with the furnace and peel off the release film.

[0081] The core material containing PI metamaterial substrate is made of 4 layers of PMI foam + 3 layers of PI metamaterial substrate + 6 layers of epoxy film through a molding process. The molding process parameters are: pressure 0.2MPa, temperature 120℃, and heat preservation and pressure holding time 120min.

[0082] The impact strength of the sample was tested according to GB / T9341, and the result was 17.2 kJ / m². The bending strength of the sample was tested according to GB / T9341, and the result was 101.5 MPa. The tensile strength of the core material containing PI metamaterial substrate was tested according to GB / T1452, and the result was 2.6 MPa. The shear strength of the core material containing PI metamaterial substrate was tested according to GB / T1455, and the result was 2.1 MPa. After being kept at 150℃ for 6 hours, the core material interface had a good appearance, with no bulging or delamination.

[0083] Example 2

[0084] The composite toughening interface adhesive provided in this embodiment is prepared from the following raw materials in the indicated mass percentages: 80% polymethylphenyl silicone resin, 2% silicon carbide whiskers (0.5 μm in diameter), 11% calcium carbonate whiskers (2 μm in diameter), 2% glass fiber (10 μm in diameter and 5 mm in length), 3% diethylenetriamine, and 2% wetting and dispersing agent (Anli-Terra-20).

[0085] The preparation process is as follows: Weighed polymethylphenyl silicone resin, silicon carbide whiskers, calcium carbonate whiskers, glass fiber, and wetting and dispersing agent are added to a stirring tank and premixed and dispersed at 1000 r / min for 60 min; then the stirring speed is reduced to 500 r / min, diethylenetriamine is added and stirring is continued for 5 min for catalytic mixing, so that the catalyst is completely mixed, and the composite toughened interface adhesive is obtained.

[0086] The prepared composite toughening interface adhesive was used to perform interface strengthening treatment on the PI metamaterial substrate, and the treatment steps were the same as in Example 1.

[0087] The specimen was prepared according to GB / T9341 and the impact strength was tested. The test result was 15.5 kJ / m². The specimen was prepared according to GB / T9341 and the bending strength was tested. The test result was 99.3 MPa.

[0088] Example 3

[0089] The composite toughening interface adhesive provided in this embodiment is prepared from the following raw materials in the following mass percentages: 80% polymethylphenyl silicone resin, 5% silicon carbide whiskers (0.5 μm in diameter), 8% calcium carbonate whiskers (2 μm in diameter), 2% glass fiber (10 μm in diameter and 5 mm in length), 3% diethylenetriamine, and 2% wetting and dispersing agent (Anli-Terra-20).

[0090] The preparation process is as follows: Weighed polymethylphenyl silicone resin, silicon carbide whiskers, calcium carbonate whiskers, glass fiber, and wetting and dispersing agent are added to a stirring tank and premixed and dispersed at 1000 r / min for 60 min; then the stirring speed is reduced to 500 r / min, diethylenetriamine is added and stirring is continued for 5 min for catalytic mixing, so that the catalyst is completely mixed, and the composite toughened interface adhesive is obtained.

[0091] The prepared composite toughening interface adhesive was used to perform interface strengthening treatment on the PI metamaterial substrate, and the treatment steps were the same as in Example 1.

[0092] The specimen was prepared according to GB / T9341 and the impact strength was tested. The test result was 16.3 kJ / m². The specimen was prepared according to GB / T9341 and the bending strength was tested. The test result was 101.1 MPa.

[0093] Comparative Example 1

[0094] The raw material composition and preparation method of this comparative example are basically the same as those of Example 1, except that no fiber filaments are added to the raw material.

[0095] The composite toughened interface adhesive provided in this comparative example is prepared from the following raw materials in weight percentages: 75% polymethylphenyl silicone resin, 3% silicon carbide whiskers (0.5 μm in diameter), 15% calcium carbonate whiskers (2 μm in diameter), 3% diethylenetriamine, and 2% wetting and dispersing agent (Anli-Terra-20).

[0096] The preparation process is as follows: Weighed polymethylphenyl silicone resin, silicon carbide whiskers, calcium carbonate whiskers and wetting and dispersing agent are added to a stirring tank and stirred at 1000 r / min for 60 min for premixing and dispersion; then the stirring speed is reduced to 500 r / min, diethylenetriamine is added and stirred for 5 min for catalytic mixing to obtain composite toughened interface adhesive.

[0097] The prepared composite toughening interface adhesive was used to perform interface strengthening treatment on the PI metamaterial substrate, and the treatment steps were the same as in Example 1.

[0098] The specimen was prepared according to GB / T9341 and the impact strength was tested. The test result was 11.9 kJ / m². The specimen was prepared according to GB / T9341 and the bending strength was tested. The test result was 90.5 MPa.

[0099] Comparative Example 2

[0100] The raw material composition and preparation method of this comparative example are basically the same as those of Example 2, except that no fiber filaments and whiskers are added to the raw materials.

[0101] The composite toughened interface adhesive provided in this comparative example is prepared from the following raw materials in weight percentages: 80% polymethylphenyl silicone resin, 3% diethylenetriamine, and 2% wetting and dispersing agent (Anli-Terra-20).

[0102] The preparation process is as follows: Weighed polymethylphenyl silicone resin and wetting and dispersing agent are added to a stirring tank and stirred at 1000 r / min for 60 min for premixing and dispersion; then the stirring speed is reduced to 500 r / min, diethylenetriamine is added and stirred for 5 min for catalytic mixing to obtain composite toughened interface adhesive.

[0103] The prepared composite toughening interface adhesive was used to perform interface strengthening treatment on the PI metamaterial substrate, and the treatment steps were the same as in Example 1.

[0104] The specimen was prepared according to GB / T9341 and the impact strength was tested. The test result was 7.6 kJ / m². The specimen was prepared according to GB / T9341 and the bending strength was tested. The test result was 75.1 MPa.

[0105] Comparative Example 3

[0106] This comparative example did not treat the PI metamaterial substrate with a composite toughening interface adhesive; instead, an epoxy film was used to directly bond the PMI foam and the PI metamaterial substrate.

[0107] The core material containing PI metamaterial substrate is made of 4 layers of PMI foam + 3 layers of PI metamaterial substrate + 6 layers of epoxy film through a molding process. The molding process parameters are: pressure 0.2MPa, temperature 120℃, and heat preservation and pressure holding time 120min.

[0108] PI metamaterial substrate samples were prepared according to GB / T9341 and the impact strength was tested, with a result of 7.28 kJ / m². PI metamaterial substrate samples were also prepared according to GB / T9341 and the flexural strength was tested, with a result of 72.8 MPa. Samples were prepared according to GB / T1452 and the tensile strength of the core material containing PI metamaterial substrate was tested, with a result of 1.2 MPa. Samples were prepared according to GB / T1455 and the shear strength of the core material containing PI metamaterial substrate was tested, with a result of 1.1 MPa. After being kept at 150℃ for 6 hours, bulging and delamination occurred at the core material interface.

[0109] The formulations of the composite toughening interface adhesives of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0110] Table 1. Formulation composition of composite toughened interface adhesives in Examples 1-3 and Comparative Examples 1-3

[0111]

[0112] The performance test results of the PI metamaterial substrates and the core materials containing PI metamaterial substrates in Examples 1-3 and Comparative Examples 1-3 are shown in Table 2.

[0113] Table 2 Performance test results of Examples 1-3 and Comparative Examples 1-3

[0114]

[0115] As shown in Tables 1 and 2, comparing Example 1 and Comparative Example 1, it can be seen that after adding glass fiber to the same formula, the impact strength increased from 11.9 kJ / m² to 17.2 kJ / m² (an increase of about 45%), and the flexural strength increased from 90.5 MPa to 101.5 MPa (an increase of about 12%). This indicates that the addition of fiber can effectively bear the load transfer, constrain crack propagation, and form a cross-scale synergistic toughening effect with whiskers.

[0116] As can be seen from the comparison between Example 2 and Comparative Example 2, after adding both whiskers and fibers, the impact strength increased from 7.6 kJ / m² to 15.5 kJ / m² (an increase of 104%), and the flexural strength increased from 75.1 MPa to 99.3 MPa (an increase of 32%). These values ​​are far higher than the expected results of simply adding whiskers or no filler at all, which fully demonstrates the significant synergistic reinforcement effect between the "whiskers + fibers" biphase reinforced fillers.

[0117] Comparing Example 1 and Comparative Example 3, it can be seen that after bonding the PI metamaterial substrate treated by the present invention with the PMI foam core material, the tensile strength increased from 1.2 MPa to 2.6 MPa (an increase of 117%), and the shear strength increased from 1.1 MPa to 2.1 MPa (an increase of 91%). Furthermore, after being kept at 150°C for 6 hours, no bulging or delamination occurred at the interface. In contrast, Comparative Example 3 showed obvious bulging and delamination failure under the same conditions. This indicates that the catalyst's activation effect on the PI surface molecules during the curing process effectively solved the interface passivation problem, and the interface strengthening effect has good long-term stability at high temperatures.

[0118] In summary, the present invention has the following beneficial effects:

[0119] (1) Significantly improves the mechanical toughness of PI metamaterial substrate at room temperature and high temperature: Compared with the unmodified virgin PI metamaterial substrate (Comparative Example 3), the PI metamaterial substrate modified by this invention has an impact strength increased by 126% and a bending strength increased by 39%, which effectively solves the problem of easy cracking and poor bending resistance of pure PI metamaterial substrate at high and low temperatures, and is suitable for high temperature dynamic load service conditions.

[0120] (2) Significantly improves the surface energy and interfacial bonding strength of PI metamaterial substrate: The catalyst activation effect significantly reduces the contact angle of the PI metamaterial substrate surface and significantly improves the surface energy. After bonding with PMI foam core material, the tensile strength and shear strength are increased by 117% and 91% respectively compared with conventional epoxy adhesive bonding. After long-term high temperature insulation at 150℃, there is no bulging or delamination at the interface, which completely solves the problem of low bonding strength caused by interface passivation.

[0121] (3) Simple process, no substrate damage, and excellent high-temperature stability: This invention does not require large-scale plasma equipment or chemical waste discharge. The process is simple and highly adaptable, and can be compatible with various industrial production methods such as roll coating, impregnation, and molding. Unlike existing plasma modification and chemical grafting technologies that sacrifice substrate for improved interface performance, all toughening and activation effects of this invention occur within the coating and at the coating-substrate interface, without causing any damage to the PI substrate itself.

[0122] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite toughened interface adhesive, characterized in that, Includes the following components by weight percentage: Organosilicon resin 40%~90%; Catalyst 1%~5%; Whiskers 1%~20%; Fiber filaments 0.1%~5%; Wetting and dispersing agent: 0.1%~5%.

2. The composite toughened interface adhesive according to claim 1, characterized in that, The silicone resin is one or more of polymethyl silicone resin, polyethyl silicone resin, polyaryl silicone resin, and polyalkylaryl silicone resin.

3. The composite toughened interface adhesive according to claim 1, characterized in that, The catalyst is an acid catalyst or a base catalyst; The acid catalyst is one or more of sulfuric acid, formic acid, and acetic acid; The alkaline catalyst is one or more of diethylenetriamine, triethylenetetramine, sodium hydroxide, and sodium carbonate.

4. The composite toughened interface adhesive according to claim 1, characterized in that, The whiskers are one or more of the following: alumina whiskers, silicon carbide whiskers, calcium carbonate whiskers, boron carbide whiskers, calcium sulfate whiskers, aluminum sulfate whiskers, silicon oxide whiskers, and beryllium oxide whiskers.

5. The composite toughened interface adhesive according to claim 1, characterized in that, The fiber filament is one or more of the following: carbon fiber, basalt fiber, aramid fiber, polyphenylene sulfide fiber, glass fiber, polyester fiber, and polyamide fiber.

6. The composite toughened interface adhesive according to claim 1, characterized in that, The whiskers have a diameter of 0.03~10μm; the fibers have a diameter of 0.1~50μm and a length of 0.1~5cm.

7. A method for preparing a composite toughened interface adhesive, characterized in that, The preparation of the composite toughened interface adhesive as described in any one of claims 1 to 6 comprises the following steps: The silicone resin, wetting and dispersing agent, whiskers and fiber filaments are mixed and premixed and dispersed at the first stirring speed until the solid filler is uniformly dispersed in the resin matrix. Adjust the stirring speed to the second stirring speed, add the catalyst, and continue stirring until the catalyst is completely mixed to obtain the composite toughened interface adhesive.

8. The method for preparing the composite toughened interface adhesive according to claim 7, characterized in that, The first stirring speed is 1000~2000 r / min, and the premixing and dispersion time is 30~90 min; the second stirring speed is 500~1000 r / min, and the stirring time after adding the catalyst is 5~10 min.

9. A method for interface treatment of a composite toughened interface adhesive, characterized in that, The composite toughened interface adhesive according to any one of claims 1 to 6 comprises the following steps: The surface of the polyimide metamaterial substrate is cleaned. The composite toughened interface adhesive is coated onto the surface of the polyimide metamaterial substrate to form an adhesive layer. A release layer is applied to the surface of the coated film, and the adhesive is cured by applying pressure and heating. After cooling, the release layer is removed to obtain the interface-strengthened polyimide metamaterial substrate.

10. The interface treatment method for the composite toughened interface adhesive according to claim 9, characterized in that, The thickness of the adhesive layer is 20~50μm; the pressure applied is 0.2~4MPa; the heating temperature is 150~250℃; and the curing holding and pressure holding time is 30~200min.

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