High-adhesion-strength high-temperature-resistant fluorine-free adhesive and preparation method thereof

Abstract

This invention discloses a high-strength, high-temperature resistant fluorine-free adhesive and its preparation method, belonging to the field of adhesive preparation technology. It addresses the technical problem that the bonding strength and high-temperature resistance of existing fluorine-free adhesives need further improvement. This invention uses a main resin as the primary film-forming component, combined with toughening resin and functional additives to construct a high-temperature resistant fluorine-free adhesive system. The main resin provides a heat-resistant framework and a curing network foundation, the toughening resin improves stress dispersion and interfacial coordination in the adhesive layer, and the functional additives enhance filler dispersion and interfacial bonding. This results in a high-temperature resistant fluorine-free adhesive with good heat resistance stability, reliable interfacial adhesion, and strong-toughness synergy, making it suitable for bonding applications under high-temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of adhesive preparation technology, specifically to a high-strength, high-temperature resistant, fluorine-free adhesive and its preparation method. Background Technology

[0002] In the existing technology, adhesive materials suitable for high-temperature environments have been widely used in fields such as electronic device assembly, flexible circuit connection, metal component composite and insulation structure bonding. Common systems mainly include epoxy resin adhesives, phenolic resin adhesives, silicone adhesives, polyimide adhesives and benzoxazine adhesives. In order to meet the requirements of heat resistance, related materials usually improve the network stability after curing by introducing heat-resistant structures such as aromatic rings and heterocyclic rings, and adjust the heat resistance, interface adaptability and processing performance of the adhesive layer by combining inorganic fillers, coupling components or multi-component resin blends.

[0003] However, in order to ensure that the adhesive layer still has a certain structural stability at high temperatures, existing high-temperature resistant adhesive materials usually adopt a rigid resin skeleton or a curing system with a high crosslinking density. Although such structures help maintain heat resistance, they also make the adhesive layer itself less flexible. During the process of being subjected to force or heat, it is difficult to release local stress in time, which leads to stress concentration in the adhesive layer or at the bonding interface. Especially under peeling, thermal cycling or continuous high temperature conditions, the adhesive layer is prone to increased embrittlement and accelerated crack propagation, thus affecting the reliability of the bond.

[0004] In addition, existing high-temperature resistant adhesives often incorporate inorganic components such as hexagonal boron nitride, silicon dioxide, and alumina to improve the heat resistance of the adhesive layer or impart specific functions. However, there is often insufficient interfacial compatibility between inorganic components and organic resins, which can easily lead to uneven dispersion, local agglomeration, or unstable interfacial bonding. This not only affects the continuity of the adhesive layer structure but also weakens the effective transfer of load between the substrate and the interface. Under higher temperature conditions, these problems may be further amplified, leading to interfacial relaxation and the expansion of local defects, thereby restricting the improvement of the overall adhesive performance.

[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a high-strength, high-temperature resistant fluorine-free adhesive and its preparation method, which solves the technical problem that the bonding strength and high-temperature resistance of fluorine-free adhesives in the prior art need to be further improved.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A high-strength, high-temperature resistant, fluorine-free adhesive comprises the following raw materials in parts by weight: 130-170 parts N,N-dimethylacetamide, 90-110 parts main resin, 13-18 parts toughening resin, and 1.2-1.8 parts functional additives. The main resin is a resin with benzoxazine end-capped structures at both ends of its molecular chain and aromatic polyimide segments in its main chain. The toughening resin is an organic-inorganic hybrid toughening resin containing triazine structural units and a siloxane network structure. The functional additives are hexagonal boron nitride flakes with a polydopamine-modified layer on their surface.

[0009] Furthermore, the preparation method of the toughening resin is as follows: dimethyl sulfoxide, anhydrous ethanol and deionized water are added to a reaction vessel and stirred. After mixing evenly, melamine is added, and after stirring evenly again, triethylamine is added. Then, 3-glycidyl etheroxypropyltrimethoxysilane is added, and the reaction vessel is heated to 80-85°C and stirred for 5-7 hours. The toughening resin is then obtained through post-treatment.

[0010] Furthermore, in the preparation of the toughening resin, the molar ratio of melamine to 3-glycidoxypropyltrimethoxysilane is 1:2.2-2.8, and the amounts of dimethyl sulfoxide, anhydrous ethanol, deionized water, and triethylamine added are based on melamine, at 4.5-6.0 mL / g, 4.5-6.0 mL / g, 0.35-0.50 mL / g, and 0.08-0.15 mL / g, respectively. The post-treatment includes: vacuum distillation until no liquid is collected after the reaction, and vacuum drying of the obtained material in a drying oven at 65-75℃ for 6-8 hours to obtain the toughening resin.

[0011] Furthermore, the main resin is prepared by the following method:

[0012] A1. N-methylpyrrolidone, 4,4'-diaminodiphenyl ether and p-aminophenol are added to a reaction vessel and stirred. After mixing evenly, the reaction vessel is cooled to 5-10℃. Then, pyromellitic dianhydride is added in three batches with an interval of 5 minutes between additions. After the addition is complete, stirring is continued for 3-4 hours. Then, acetic anhydride and pyridine are added. The reaction vessel is heated to 95-100℃ and stirred for 4-5 hours. The hydroxyl polyimide precursor resin is obtained after post-treatment.

[0013] A2. Add the hydroxyl polyimide precursor resin and 1,4-dioxane to the reactor and stir. After mixing evenly, add aniline and stir evenly. Then add paraformaldehyde and heat the reactor to 95-100℃. Keep it at this temperature and stir for 7-9 hours. The main resin is obtained after post-treatment.

[0014] Further, in step A1, the molar ratio of pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and p-aminophenol is 1:0.85-0.95:0.18-0.22, and the amounts of N-methylpyrrolidone, acetic anhydride, pyridine, and deionized water added are based on pyromellitic dianhydride, and are 6.3-8.5 mL / g, 0.9-1.2 mL / g, 0.8-1.0 mL / g, and 60-80 mL / g, respectively. The post-treatment includes: subsequently pouring five times the volume of deionized water into the reaction solution to precipitate the solid, filtering and collecting the precipitated solid, washing it 2-3 times with deionized water, and then placing it in a drying oven at 110-120℃ for vacuum drying for 10-12 h to obtain hydroxyl polyimide precursor resin;

[0015] Further, in step A2, the amount of aniline and formaldehyde structural units added in the paraformaldehyde are based on the terminal phenolic hydroxyl groups in the hydroxyl polyimide precursor resin, which are 0.9-1.1 equivalents and 1.8-2.2 equivalents, respectively; the amount of 1,4-dioxane and anhydrous ethanol added are based on the hydroxyl polyimide precursor resin, which are 5-7 mL / g and 25-35 mL / g, respectively. The post-treatment includes: after the reaction is completed, the mixture is concentrated under reduced pressure to 25-40% of the original volume, and then poured into anhydrous ethanol three times the volume of the reaction solution to precipitate the solid. The filter cake is then vacuum dried in a drying oven at 75-85℃ for 10-12 h to obtain the main resin.

[0016] Furthermore, the preparation method of the functional additive is as follows: deionized water and tris(hydroxymethyl)aminomethane are added to a reaction vessel and stirred. After mixing evenly, 5wt% sodium hydroxide aqueous solution is added to adjust the pH of the system to 8.4-8.6. Then, hexagonal boron nitride is added and dispersed evenly. Dopamine hydrochloride is then added. The reaction vessel is kept at 25-30℃ and stirred for 5-7 hours. The functional additive is obtained after post-treatment.

[0017] Furthermore, in the preparation of the functional additive, the amounts of tris(hydroxymethyl)aminomethane and dopamine hydrochloride added are based on hexagonal boron nitride, at 0.10-0.15 g / g and 0.18-0.24 g / g, respectively; the amounts of deionized water and anhydrous ethanol added are based on hexagonal boron nitride, at 40-60 mL / g and 8-12 mL / g, respectively. The post-treatment includes: after the reaction is completed, filtering and collecting the filter cake, washing the filter cake sequentially with deionized water and anhydrous ethanol, and then placing it in a drying oven at 55-65℃ for vacuum drying for 10-12 h to obtain the functional additive.

[0018] The present invention also discloses a method for preparing a high-temperature resistant fluorine-free adhesive with high bonding strength, comprising the following steps: adding N,N-dimethylacetamide into a reaction vessel and stirring, then adding the main resin, stirring evenly, adding toughening resin, continuing to stir evenly, adding functional additives, dispersing and degassing to obtain a high-temperature resistant fluorine-free adhesive.

[0019] Furthermore, in the preparation process of the high-temperature resistant fluorine-free adhesive, the dispersion conditions are 2000-3000 r / min for 15-25 min; the degassing conditions are 45-50℃, vacuum degree -0.08MPa for 20-30 min.

[0020] The present invention has the following beneficial effects:

[0021] 1. The main resin prepared by this invention constitutes a continuous phase in the adhesive system, which is the basis for the formation of a dense structure in the adhesive layer and the bearing of the main load transfer. It is obtained by subsequent reaction from hydroxyl polyimide precursor resin and has both a relatively stable main chain structure and reaction characteristics suitable for curing into a network. During the curing process of the adhesive layer, it can form a continuous and complete bulk support. After the toughening resin is introduced into this continuous phase, it does not destroy its integrity, but makes the load transfer from the interface to the bulk more gradual. The functional additives dispersed in the system further maintain the structural continuity of the contact area between the adhesive layer and the substrate. As a result, the adhesive layer exhibits good synergistic load-bearing characteristics under different action states such as shear stress, interface deformation and peeling propagation. The service condition of the material under room temperature and heating conditions also has strong consistency.

[0022] 2. The toughening resin prepared in this invention is not simply configured for flexibility adjustment, but rather participates in the organization process of the internal structure of the adhesive layer together with the main resin. After curing, the main resin provides a continuous skeleton, while the toughening resin makes the connection between different regions within the skeleton more balanced, thus reducing abrupt differences in the chain segment response during heating. After the functional additives are further dispersed in the above structure, the connection between the micro-regions within the system becomes more stable, and the tendency for local areas to relax prematurely under heat is suppressed. Based on this, the adhesive layer maintains a relatively complete structural morphology and a relatively smooth mechanical response as the temperature gradually increases and approaches the thermal transition range, so that a good continuous correspondence can be maintained between the thermal process and the bonding service process.

[0023] 3. The functional additives prepared in this invention are not primarily used to add a single filler component, but rather to maintain a relatively stable dispersion state after entering the organic phase composed of the main resin and toughening resin. This allows for a clearer and more continuous phase transition within the adhesive layer. As the temperature continues to rise, the network structure formed by the main resin provides basic support for the whole, the toughening resin slows down the local incoordination caused by the accumulation of thermal stress between different regions, and the functional additives make the heat transfer process within the adhesive layer more uniform. Consequently, the material is less likely to experience premature local structural loosening, interface mismatch, or concentrated quality changes during the heating process. The structural retention state of the adhesive layer at higher temperatures can form a more natural transition between its adhesive application state and its bonding state. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a SEM image of the functional additive prepared in Example 6 of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In this application, the hexagonal boron nitride used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number B874955; the paraformaldehyde used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number P804537.

[0028] Experimental group 1

[0029] This embodiment provides a method for preparing a main resin, including the following steps:

[0030] Step I: Preparation of hydroxyl polyimide precursor resin

[0031] Weigh out 63.0 mL of N-methylpyrrolidone, 7.8 g of 4,4'-diaminodiphenyl ether, and 0.9 g of p-aminophenol and add them to the reaction vessel. Stir and mix thoroughly. Then, cool the reaction vessel to 5°C. Add 10.0 g of pyromellitic dianhydride in three batches at 5 min intervals. After the addition is complete, continue stirring for 3 h. Then add 9.0 mL of acetic anhydride and 8.0 mL of pyridine. Heat the reaction vessel to 95°C and stir for 4 h. Then pour it into 600.0 mL of deionized water to precipitate the solid. Filter and collect the precipitated solid, wash it twice with deionized water, and then place it in a drying oven at 110°C and vacuum dry for 10 h to obtain hydroxyl polyimide precursor resin.

[0032] Step II: Preparation of the main resin

[0033] Weigh 30.0 g of hydroxyl polyimide precursor resin and 150.0 mL of 1,4-dioxane and add them to the reaction vessel. Stir and mix thoroughly. Then add 0.9 molar equivalents of aniline from the terminal phenolic hydroxyl groups of the hydroxyl polyimide precursor resin and stir thoroughly. Then add 1.8 molar equivalents of paraformaldehyde from the terminal phenolic hydroxyl groups of the hydroxyl polyimide precursor resin, calculated as formaldehyde structural units. Then heat the reaction vessel to 95°C and keep it at that temperature for 7 hours with stirring. After the reaction is completed, concentrate the mixture under reduced pressure to 25.0% of the original volume. Then pour it into 750.0 mL of anhydrous ethanol to precipitate the solid. Dry the filter cake under vacuum in a drying oven at 75°C for 10 hours to obtain the main resin.

[0034] The reaction principle for preparing the main resin is as follows:

[0035] The anhydride group in the pyromellitic dianhydride molecule undergoes a nucleophilic ring-opening reaction with the amino groups in the 4,4'-diaminodiphenyl ether and p-aminophenol molecules to form an intermediate containing a polyamic acid structure. Subsequently, in the acetic anhydride and pyridine system, the polyamic acid structure undergoes further dehydration and cyclization, transforming into an imide ring structure, thereby obtaining a polyimide resin containing phenolic hydroxyl structural units. Then, the ortho-active sites of the phenolic hydroxyl groups in the polyimide resin undergo a condensation reaction with the formaldehyde structural units provided by aniline and paraformaldehyde to form a benzoxazine ring structure, allowing the benzoxazine structural units to be incorporated into the polyimide molecular backbone to obtain the main resin.

[0036] The mechanism of action of the main resin in high-temperature fluorine-free adhesive is as follows:

[0037] The hydroxyl polyimide precursor resin, host resin, and related structural sources involved in this step collectively determine the skeletal characteristics, interfacial state, and thermo-mechanical response of the final adhesive layer of the high-temperature resistant fluorine-free adhesive. Among them, the aromatic polyimide backbone constructed from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether provides the system with high heat-resistant skeletal strength and dimensional stability. The phenolic hydroxyl structure introduced by p-aminophenol not only retains the basis of intermolecular polar interactions but also provides an active source for subsequent functionalization grafting. The host resin formed on this basis further integrates benzoxazine structural units into the polyimide molecular skeleton, giving the material system both a high heat-resistant continuous phase and a functional structure that can be further networked. Thus, after the adhesive layer is cured, a structural system with rigid support, moderate strain coordination, and strong interfacial interaction capabilities is formed.

[0038] Therefore, this part of the structure in the final high-temperature resistant fluorine-free adhesive is beneficial in two ways: firstly, it helps to improve the glass transition temperature, thermal decomposition stability and structural retention capacity of the adhesive layer; secondly, it helps to enhance the continuity of load transfer between the interface and the substrate, suppress local relaxation, strain concentration and interface mismatch during heating and stress, so that the material exhibits a more coordinated comprehensive performance in terms of room temperature tensile shear strength, 150℃ tensile shear strength, 180° peel strength and thermal stability.

[0039] Experimental group 2

[0040] This embodiment provides a method for preparing a main resin, including the following steps:

[0041] Step I: Preparation of hydroxyl polyimide precursor resin

[0042] Weigh out 85.0 mL of N-methylpyrrolidone, 8.7 g of 4,4'-diaminodiphenyl ether, and 1.1 g of p-aminophenol and add them to a reaction vessel. Stir and mix thoroughly. Then, cool the reaction vessel to 10°C. Add 10.0 g of pyromellitic dianhydride in three batches at 5 min intervals. After the addition is complete, continue stirring for 4 h. Then add 12.0 mL of acetic anhydride and 10.0 mL of pyridine. Heat the reaction vessel to 100°C and stir for 5 h. Then pour the mixture into 800.0 mL of deionized water to precipitate the solid. Filter and collect the precipitated solid, wash it three times with deionized water, and then place it in a drying oven at 120°C and vacuum dry for 12 h to obtain hydroxyl polyimide precursor resin.

[0043] Step II: Preparation of the main resin

[0044] Weigh 30.0 g of hydroxyl polyimide precursor resin and 210.0 mL of 1,4-dioxane and add them to the reaction vessel. Stir and mix thoroughly. Then add aniline with a molar amount of 1.0 equivalent of the terminal phenolic hydroxyl group in the hydroxyl polyimide precursor resin and stir thoroughly. Then add paraformaldehyde with a molar amount of 2.0 equivalent of the terminal phenolic hydroxyl group in the hydroxyl polyimide precursor resin (based on formaldehyde structural units). Heat the reaction vessel to 100℃ and keep it at that temperature for 9 hours. After the reaction is completed, concentrate the mixture under reduced pressure to 40.0% of the original volume. Then pour the mixture into 1050.0 mL of anhydrous ethanol to precipitate the solid. Dry the filter cake under vacuum in an oven at 85℃ for 12 hours to obtain the main resin.

[0045] Experimental group 3

[0046] This embodiment provides a method for preparing a main resin, including the following steps:

[0047] Step I: Preparation of hydroxyl polyimide precursor resin

[0048] Weigh out 74.0 mL of N-methylpyrrolidone, 8.3 g of 4,4'-diaminodiphenyl ether, and 1.0 g of p-aminophenol and add them to a reaction vessel. Stir and mix thoroughly. Then, cool the reaction vessel to 7.5 °C. Add 10.0 g of pyromellitic dianhydride in three batches at 5 min intervals. After the addition is complete, continue stirring for 3.5 h. Then add 10.5 mL of acetic anhydride and 9.0 mL of pyridine. Heat the reaction vessel to 97.5 °C and stir for 4.5 h. Then pour the mixture into 700.0 mL of deionized water to precipitate the solid. Filter and collect the precipitated solid, wash it three times with deionized water, and then place it in a drying oven at 115 °C and vacuum dry for 11 h to obtain hydroxyl polyimide precursor resin.

[0049] Step II: Preparation of the main resin

[0050] Weigh 30.0 g of hydroxyl polyimide precursor resin and 180.0 mL of 1,4-dioxane and add them to the reaction vessel. Stir and mix thoroughly. Then add aniline with a molar amount of 1.0 equivalent of the terminal phenolic hydroxyl group in the hydroxyl polyimide precursor resin and stir thoroughly. Then add paraformaldehyde with a molar amount of 2.0 equivalent of the terminal phenolic hydroxyl group in the hydroxyl polyimide precursor resin (based on formaldehyde structural units). Heat the reaction vessel to 97.5 °C and keep it at that temperature for 8 hours with stirring. After the reaction is completed, concentrate the solution under reduced pressure to 32.5% of the original volume. Then pour the solution into 900.0 mL of anhydrous ethanol to precipitate the solid. Dry the filter cake under vacuum in an oven at 80 °C for 11 hours to obtain the main resin.

[0051] Experimental group 4

[0052] This embodiment provides a method for preparing a high-temperature resistant, fluorine-free adhesive with high bonding strength, including the following steps:

[0053] Step 1: Preparation of toughening resin

[0054] Weigh out 45.0 mL of dimethyl sulfoxide, 45.0 mL of anhydrous ethanol, and 3.5 mL of deionized water and add them to the reaction vessel. Stir and mix thoroughly. Then add 10.0 g of melamine and continue stirring until homogeneous. Add 0.8 mL of triethylamine and then 41.2 g of 3-glycidyl etheroxypropyltrimethoxysilane. Heat the reaction vessel to 80°C and keep it at that temperature for 5 hours. After the reaction is complete, distill under reduced pressure until no liquid is collected. Place the obtained material in a drying oven at 65°C and vacuum dry for 6 hours to obtain the toughened resin.

[0055] The reaction principle for preparing toughened resin is as follows:

[0056] The amino group in the melamine molecule undergoes ring-opening addition with the epoxy group in the 3-glycidoxypropyltrimethoxysilane molecule to form an organic linking unit containing a β-hydroxyamine structure. At the same time, the methoxysilyl group in the 3-glycidoxypropyltrimethoxysilane molecule undergoes hydrolysis in an aqueous system to generate silanols. The silanols further condense to form a Si-O-Si structure. Thus, an organic-inorganic hybrid toughening resin containing a triazine structure, a β-hydroxyamine linking structure, and a siloxane structure is formed in the system.

[0057] The mechanism of action of toughening resin in high-temperature fluorine-free adhesives is as follows:

[0058] The toughening resin obtained in this step is mainly composed of a triazine structure introduced by melamine, a β-hydroxyamine linkage structure formed by epoxy ring opening, and a Si-O-Si siloxane structure formed by hydrolysis and condensation. Among them, the triazine structure helps to improve the heat resistance of the system, the β-hydroxyamine structure helps to enhance intermolecular interactions and provide a certain degree of flexible transition, and the siloxane structure endows the system with good stability and interfacial coordination ability. In the final high-temperature resistant fluorine-free adhesive, this toughening resin mainly plays the role of regulating the continuous phase of the main resin and the micro-region structure of the interface, which can reduce stress concentration and crack propagation, improve the synergistic deformation ability of the adhesive layer during the process of heat and stress, thereby improving the peel performance and strength retention at high temperatures, and enabling the material to achieve a better balance of strength and toughness while maintaining a high glass transition temperature and thermal stability.

[0059] Step 2: Preparation of functional additives

[0060] Weigh out: Add 200.0 mL of deionized water and 0.5 g of tris(hydroxymethyl)aminomethane to a reaction vessel and stir. After mixing evenly, add 5 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 8.4. Then add 5.0 g of hexagonal boron nitride and disperse evenly. Add 0.9 g of dopamine hydrochloride. Keep the reaction vessel at 25℃ and stir for 5 h. After the reaction is completed, filter and collect the filter cake. Wash the filter cake with deionized water and 40.0 mL of anhydrous ethanol in sequence, and then place it in a drying oven at 55℃ and vacuum dry for 10 h to obtain the functional additive.

[0061] The reaction principle for preparing functional additives is as follows:

[0062] Under weakly alkaline conditions, tris(hydroxymethyl)aminomethane and sodium hydroxide work together to regulate and maintain the alkaline environment of the system, causing dopamine hydrochloride to be converted into free dopamine. The catechol structure in dopamine is oxidized and further cyclized, coupled and polymerized to form polydopamine. After hexagonal boron nitride is dispersed in the system, polydopamine is gradually deposited and coated on its surface, thus obtaining a hexagonal boron nitride functional additive with a polydopamine-modified layer on the surface.

[0063] The mechanism of action of functional additives in high-temperature resistant fluorine-free adhesives is as follows:

[0064] The functional additive obtained in this step mainly consists of hexagonal boron nitride and a polydopamine modification layer introduced on its surface. Hexagonal boron nitride itself has high heat resistance and structural stability, which can provide a stable inorganic functional phase for the system. The polydopamine modification layer helps to enhance its compatibility and interfacial bonding ability with the organic resin system. In the final high-temperature resistant fluorine-free adhesive, this functional additive can improve the dispersion state of the filler in the adhesive layer, enhance the continuity of the interfacial area, and reduce local defects and stress concentration. This helps to improve the high-temperature strength retention, peel performance, and thermal stability of the adhesive layer, so that the material as a whole exhibits better heat resistance and mechanical synergy.

[0065] Step 3: Preparation of high-temperature resistant fluorine-free adhesive

[0066] Weigh out 130 parts by weight of N,N-dimethylacetamide and add it to the reaction vessel and stir. Then add 90 parts of the main resin prepared in Example 1 and stir evenly. Add 13 parts of toughening resin and continue stirring evenly. Then add 1.2 parts of functional additives and disperse at 2000 r / min for 15 min. Then degas at 45℃ and vacuum degree -0.08MPa for 20 min to obtain high temperature resistant fluorine-free adhesive.

[0067] Experimental group 5

[0068] This embodiment provides a method for preparing a high-temperature resistant, fluorine-free adhesive with high bonding strength, including the following steps:

[0069] Step 1: Preparation of toughening resin

[0070] Weigh out 60.0 mL of dimethyl sulfoxide, 60.0 mL of anhydrous ethanol, and 5.0 mL of deionized water and add them to the reaction vessel. Stir and mix thoroughly. Then add 10.0 g of melamine and continue stirring until homogeneous. Add 1.5 mL of triethylamine and then 52.5 g of 3-glycidyl etheroxypropyltrimethoxysilane. Heat the reaction vessel to 85°C and keep it at that temperature for 7 hours. After the reaction is complete, distill under reduced pressure until no liquid is collected. Place the obtained material in a drying oven at 75°C and vacuum dry for 8 hours to obtain the toughened resin.

[0071] Step 2: Preparation of functional additives

[0072] Weigh out: Add 300.0 mL of deionized water and 0.8 g of tris(hydroxymethyl)aminomethane to a reaction vessel and stir. After mixing evenly, add 5 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 8.6. Then add 5.0 g of hexagonal boron nitride and disperse evenly. Then add 1.2 g of dopamine hydrochloride. Keep the reaction vessel at 30℃ and stir for 7 h. After the reaction is completed, filter and collect the filter cake. Wash the filter cake with deionized water and 60.0 mL of anhydrous ethanol in sequence, and then place it in a drying oven at 65℃ and vacuum dry for 12 h to obtain the functional additive.

[0073] Step 3: Preparation of high-temperature resistant fluorine-free adhesive

[0074] Weigh out 170 parts by weight of N,N-dimethylacetamide and add it to the reactor and stir. Then add 110 parts of the main resin prepared in Example 2 and stir evenly. Add 18 parts of toughening resin and stir evenly again. Then add 1.8 parts of functional additives and disperse at 3000 r / min for 25 min. Then degas at 50℃ and vacuum degree -0.08MPa for 30 min to obtain high temperature resistant fluorine-free adhesive.

[0075] Experimental group 6

[0076] This embodiment provides a method for preparing a high-temperature resistant, fluorine-free adhesive with high bonding strength, including the following steps:

[0077] Step 1: Preparation of toughening resin

[0078] Weigh out 52.5 mL of dimethyl sulfoxide, 52.5 mL of anhydrous ethanol, and 4.3 mL of deionized water and add them to the reaction vessel. Stir and mix thoroughly. Then add 10.0 g of melamine and continue stirring until homogeneous. Add 1.2 mL of triethylamine and then 46.8 g of 3-glycidyl etheroxypropyltrimethoxysilane. Heat the reaction vessel to 82.5 °C and keep it at that temperature with stirring for 6 hours. After the reaction is complete, distill under reduced pressure until no liquid is collected. Place the obtained material in a drying oven at 70 °C and vacuum dry for 7 hours to obtain the toughened resin.

[0079] Step 2: Preparation of functional additives

[0080] Weigh out: Add 250.0 mL of deionized water and 0.6 g of tris(hydroxymethyl)aminomethane to a reaction vessel and stir. After mixing evenly, add 5 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 8.5. Then add 5.0 g of hexagonal boron nitride and disperse evenly. Then add 1.1 g of dopamine hydrochloride. Keep the reaction vessel at 27.5 ℃ and stir for 6 h. After the reaction is completed, filter and collect the filter cake. Wash the filter cake with deionized water and 50.0 mL of anhydrous ethanol in sequence, and then place it in a drying oven at 60 ℃ and vacuum dry for 11 h to obtain the functional additive.

[0081] Step 3: Preparation of high-temperature resistant fluorine-free adhesive

[0082] Weigh out 150 parts by weight of N,N-dimethylacetamide and add it to the reactor and stir. Then add 100 parts of the main resin prepared in Example 3 and stir evenly. Add 16 parts of toughening resin and stir evenly again. Then add 1.5 parts of functional additives and disperse at 2500 r / min for 20 min. Then degas at 47.5℃ and vacuum degree -0.08MPa for 25 min to obtain high temperature resistant fluorine-free adhesive.

[0083] Control group 1

[0084] The difference between this comparative example and experimental group 6 is that step II was omitted in the preparation process of the main resin used in step three.

[0085] Control group 2

[0086] The difference between this comparative example and test group 6 is that the toughening resin was omitted in step three.

[0087] Control group 3

[0088] The difference between this comparative example and experimental group 6 is that the use of an equal amount of hexagonal boron nitride as a substitute for the functional additive was omitted in step three.

[0089] Performance testing:

[0090] The tensile shear strength at room temperature and 150℃ was determined according to GB / T 7124-2008 "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)", with specific test parameters as follows:

[0091] 304 stainless steel sheet was selected as the substrate to be bonded. The size of a single sheet was 100mm×25mm×1.6mm, the overlap length was 12.5mm, the overlap width was 25mm, and glass microspheres with a diameter of 0.20mm were used to control the thickness of the adhesive layer, so that the thickness of the adhesive layer was fixed at 0.20mm.

[0092] Before bonding, the bonding surface of the steel sheet was sanded 30 times in one direction along the length of the sample using 600-grit sandpaper. Then, the steel sheet was ultrasonically cleaned in anhydrous ethanol and acetone for 5 minutes each. After removal, it was dried in an 80℃ forced-air drying oven for 20 minutes. The high-temperature resistant fluorine-free adhesive prepared by test group 4-6 and control group 1-3 was evenly coated on the overlapping area. Glass microspheres with a diameter of 0.20 mm were added to complete the overlapping and bonding. The plates were pressed under a pressure of 0.20 MPa for 10 minutes. Then, the plates were cured in sections according to the following procedure: 80℃ for 30 minutes, 120℃ for 30 minutes, 160℃ for 60 minutes, 180℃ for 60 minutes, and 200℃ for 120 minutes. After curing, the plates were cooled in an environment of 23℃ for 60 minutes and then placed at 23℃ and 50% relative humidity for 24 hours.

[0093] In the room temperature tensile shear strength test, an electronic universal testing machine was used with the fixtures coaxially installed. Loading was performed using a load control method, and the load increase rate was set to 2812.5 N / min. The test result is expressed as room temperature tensile shear strength, in MPa.

[0094] When determining the tensile shear strength at 150℃, an electronic universal testing machine with a high-temperature environmental chamber was used. The clamps were coaxially installed. After clamping the sample, the temperature was raised to 150℃ and held for 10 minutes. Then, the load was applied according to the load control mode, and the load increase rate was set to 2812.5 N / min. The test result is expressed as the tensile shear strength at 150℃, and the unit is MPa.

[0095] The 180° peel strength was determined according to GB / T 2790-1995 "Test Method for 180° Peel Strength of Adhesives - Flexible Materials vs. Rigid Materials":

[0096] A 50 μm thick polyimide film was selected as the flexible adhesive substrate, and a 304 stainless steel sheet was selected as the rigid adhesive substrate. The stainless steel sheet was 200 mm × 25 mm × 1.5 mm in size. The adhesive width of the sample was 25 mm, the adhesive length was 150 mm, and the length of the unbonded lead-out section was 100 mm. Glass microspheres with a diameter of 0.10 mm were used to control the adhesive layer thickness, so that the adhesive layer thickness was fixed at 0.10 mm. Before bonding, the 304 stainless steel sheet was sanded 30 times in one direction along the length of the sample with 600 grit sandpaper. Then, it was ultrasonically cleaned in anhydrous ethanol and acetone for 5 min each. After that, it was placed in an 80℃ forced-air drying oven for 20 min to dry. The polyimide film was wiped once with anhydrous ethanol and then air-dried for 10 minutes. The high-temperature resistant fluorine-free adhesive prepared by test groups 4-6 and control groups 1-3 was uniformly coated on the bonding area of ​​the stainless steel sheet. Glass microspheres with a diameter of 0.10 mm were added and then bonded to the polyimide film. The film was pressed under a pressure of 0.15 mPa for 5 minutes. Then, the film was cured in stages according to the following procedure: 80℃ for 30 minutes, 120℃ for 30 minutes, 160℃ for 60 minutes, 180℃ for 60 minutes, and 200℃ for 120 minutes. After curing, the sample was placed in an environment of 23℃ for 60 minutes and then placed at 23℃ and 50% relative humidity for 24 hours.

[0097] The test was conducted using an electronic universal testing machine and a 180° peel fixture. The polyimide film was folded back 180° in the opposite direction and then clamped. The peeling speed was set to 100 mm / min. The test result is expressed as the 180° peel strength, in N / 25 mm.

[0098] See Table 1 for specific data;

[0099] Table 1 - Test data of adhesive performance of each sample

[0100]

[0101] The test samples used for glass transition temperature and 5% thermogravimetric temperature were all cured adhesive films.

[0102] The adhesive film was prepared as follows: The high-temperature resistant fluorine-free adhesives prepared in test groups 4-6 and control groups 1-3 were uniformly coated on the surface of the glass plate after demolding treatment. The wet film thickness was fixed at 0.40 mm. Then, the film was cured according to the following procedure: 80℃ for 30 min, 120℃ for 30 min, 160℃ for 60 min, 180℃ for 60 min, and 200℃ for 120 min. After curing, the film was allowed to cool naturally to 23℃. The cured adhesive film was then peeled off from the surface of the glass plate and cut into test samples.

[0103] The glass transition temperature was determined according to GB / T 19466.2-2004 "Differential Scanning Calorimetry (DSC) for Plastics - Part 2: Determination of Glass Transition Temperature". 5.0 mg of the cured film sample was weighed, placed in an aluminum crucible, and sealed. An empty aluminum crucible was used as a reference. The test was conducted using a differential scanning calorimeter under a nitrogen atmosphere with a nitrogen flow rate of 50 mL / min. The test procedure was as follows: the first temperature increase was from 30℃ to 300℃ at a rate of 10℃ / min; then the temperature was decreased from 300℃ to 30℃ at a rate of 10℃ / min; finally, the temperature was increased from 30℃ to 300℃ at a rate of 10℃ / min. The test result was expressed as the glass transition temperature in °C.

[0104] The 5% thermogravimetric temperature was determined according to GB / T 33047.1-2016 "Thermogravimetric Analysis (TG) of Plastic Polymers - Part 1: General Rules". 8.0 mg of the cured film sample was weighed and placed in an alumina crucible. The test was conducted using a thermogravimetric analyzer under a nitrogen atmosphere with a nitrogen flow rate of 50 mL / min. The test program was set to heat from 30℃ to 800℃ at a heating rate of 10℃ / min. The test result is expressed as the 5% thermogravimetric temperature in °C.

[0105] See Table 2 for specific data;

[0106] Table 2 - Thermal Performance Test Data for Each Sample

[0107]

[0108] Data Analysis:

[0109] Comparative analysis of the data in Tables 1-2 reveals that the high-temperature resistant fluorine-free adhesive prepared in this invention exhibits a room temperature tensile shear strength of 26.8 MPa, a 150°C tensile shear strength of 13.8 MPa, and a 180° peel strength of 45.1 N·25 mm. -1 The glass transition temperature is 247℃, and the 5% thermogravimetric temperature is 432℃. All these data are better than the control group, indicating that:

[0110] In Comparative Example 1, the hydroxyl polyimide precursor resin was used directly in the adhesive formulation without undergoing the subsequent reaction in Step II. This resulted in the system losing the further structural integration process corresponding to the main resin, causing the continuous phase of the adhesive layer to remain at the precursor chemical structure level. Consequently, there were insufficient structural units to participate in network bonding during the adhesive layer curing process, making it difficult to form a more complete and continuous support system within the body. The stress transmission path between the interface region and the body region also became less smooth. Under external load, local strain was more likely to accumulate at locations with relatively insufficient structural bonding, further inducing non-uniform deformation within the adhesive layer. Under heating conditions, the above discontinuities were more likely to transform into local loosening and interface mismatch, making it difficult for the adhesive layer to maintain a consistent response rhythm during load-bearing, deformation, and peeling expansion, ultimately resulting in an overall weakening of the composite application state.

[0111] In Comparative Example 2, omitting step one results in the loss of a key structural source for softening and transitioning the main resin continuous phase and coordinating the phases within the system. Consequently, the adhesive layer relies primarily on a single continuous phase for structural organization during its formation. Consequently, under the combined conditions of curing shrinkage, external force loading, and thermal effects, it is difficult for different micro-regions to establish a relatively smooth deformation transfer relationship. Local response differences are easily retained and gradually evolve into stress concentration points. As the stress process continues, these concentrated areas are more likely to become the starting points for crack initiation and propagation. Under elevated temperatures, the local incoordination caused by thermal stress is further amplified, weakening the cooperative deformation capacity between the interface area and the interior of the adhesive layer. As a result, the material struggles to form a coherent correspondence between different service states, such as room temperature loading, high temperature holding, and peeling propagation, leading to a decline in overall service performance.

[0112] In Comparative Example 3, the hexagonal boron nitride without the treatment in step two was used to replace the functional additive. This essentially caused the filler surface to lose the structural basis for establishing a stable transition interface with the organic phase, thereby changing the state of the filler in the system composed of the main resin and the toughening resin. Due to the weakening of interphase interaction, the filler is more likely to form local aggregation or micro-regions with insufficient interfacial connection after entering the adhesive layer. This weakens the continuity of the internal structure of the system, and it is also difficult to maintain a uniform heat and stress transfer path in the adhesive layer. As the temperature rises, the above-mentioned micro-regions are more likely to preferentially experience local relaxation, interfacial disturbance or structural instability, and further drive the surrounding area to produce discontinuous response. This change, which gradually expands from local imbalance to the whole, makes it difficult to maintain the synchronization between the structural maintenance state of the adhesive layer during the heating process and the actual bonding service state, thus leading to a decrease in the composite performance of the sample.

[0113] In conclusion, the material configuration in this application's technical solution is not based on the conventional replacement of a single component. Instead, it integrates the continuous phase construction of the main resin, the phase coordination of the toughening resin, and the interfacial transition stabilization of the functional additives into the formation and service response of the same adhesive layer. When any of the aforementioned structural elements is removed, the continuity of the adhesive layer, the micro-region connection state, and the response under thermo-mechanical coupling will all undergo varying degrees of reorganization. Moreover, this change is not limited to a single performance index but will further be transmitted to the interfacial load transfer, the maintenance of the bulk structure, and the local stability during the heating process. Therefore, the solution presents not a linear result of the simple superposition of the components, but rather a clear correspondence between the material composition, structural evolution, and the usage process. The relevant performance change trends also naturally emerge during the unfolding of the above correspondence.

[0114] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0115] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0116] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high bonding strength high temperature resistant fluorine-free adhesive, characterized in that, It comprises the following raw materials in parts by weight: 130-170 parts N,N-dimethylacetamide, 90-110 parts main resin, 13-18 parts toughening resin and 1.2-1.8 parts functional additives; The main resin is a resin with benzoxazine end caps on both ends of the molecular chain and aromatic polyimide segments in the main chain. The toughening resin is an organic-inorganic hybrid toughening resin containing triazine structural units and a siloxane network structure. The functional additive is a hexagonal boron nitride flake additive with a polydopamine-modified layer on its surface.

2. A high bonding strength, high temperature resistant, fluorine-free adhesive according to claim 1, characterized in that, The toughening resin is prepared by adding dimethyl sulfoxide, anhydrous ethanol and deionized water into a reaction vessel and stirring. After mixing evenly, melamine is added, and after stirring evenly again, triethylamine is added. Then, 3-glycidyl etheroxypropyltrimethoxysilane is added, and the reaction vessel is heated to 80-85°C and kept at that temperature for 5-7 hours. The toughening resin is then obtained after post-treatment.

3. A high bonding strength, high temperature resistant, fluorine-free adhesive according to claim 2, characterized in that, In the preparation of the toughening resin, the molar ratio of melamine to 3-glycidoxypropyltrimethoxysilane is 1:2.2-2.8, and the amounts of dimethyl sulfoxide, anhydrous ethanol, deionized water and triethylamine added are based on melamine and are 4.5-6.0 mL / g, 4.5-6.0 mL / g, 0.35-0.50 mL / g and 0.08-0.15 mL / g, respectively.

4. The high bonding strength, high temperature resistant, fluorine-free adhesive according to claim 1, characterized in that, The main resin is prepared by the following method: A1. N-methylpyrrolidone, 4,4'-diaminodiphenyl ether and p-aminophenol are added to a reaction vessel and stirred. After mixing evenly, the reaction vessel is cooled to 5-10℃. Then, pyromellitic dianhydride is added in three batches with an interval of 5 minutes between additions. After the addition is complete, stirring is continued for 3-4 hours. Then, acetic anhydride and pyridine are added. The reaction vessel is heated to 95-100℃ and stirred for 4-5 hours. The hydroxyl polyimide precursor resin is obtained after post-treatment. A2. Add the hydroxyl polyimide precursor resin and 1,4-dioxane to the reactor and stir. After mixing evenly, add aniline and stir evenly. Then add paraformaldehyde and heat the reactor to 95-100℃. Keep it at this temperature and stir for 7-9 hours. The main resin is obtained after post-treatment.

5. The high bonding strength, high temperature resistant, fluorine-free adhesive according to claim 4, characterized in that, In step A1, the molar ratio of pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and p-aminophenol is 1:0.85-0.95:0.18-0.22, and the amounts of N-methylpyrrolidone, acetic anhydride, pyridine, and deionized water added are based on pyromellitic dianhydride and are 6.3-8.5 mL / g, 0.9-1.2 mL / g, 0.8-1.0 mL / g, and 60-80 mL / g, respectively.

6. A high bonding strength, high temperature resistant, fluorine-free adhesive according to claim 4, characterized in that, In step A2, the amounts of aniline and formaldehyde structural units added are based on the terminal phenolic hydroxyl groups in the hydroxyl polyimide precursor resin, which are 0.9-1.1 equivalents and 1.8-2.2 equivalents, respectively; the amounts of 1,4-dioxane and anhydrous ethanol added are based on the hydroxyl polyimide precursor resin, which are 5-7 mL / g and 25-35 mL / g, respectively.

7. The high bonding strength, high temperature resistant, fluorine-free adhesive according to claim 1, characterized in that, The preparation method of the functional additive is as follows: deionized water and tris(hydroxymethyl)aminomethane are added to a reaction vessel and stirred. After mixing evenly, 5wt% sodium hydroxide aqueous solution is added to adjust the pH of the system to 8.4-8.

6. Then, hexagonal boron nitride is added and dispersed evenly. Dopamine hydrochloride is then added. The reaction vessel is kept at 25-30℃ and stirred for 5-7 hours. The functional additive is obtained after post-treatment.

8. The high-strength, high-temperature resistant, fluorine-free adhesive according to claim 7, characterized in that, In the preparation of the functional additives, the amounts of tris(hydroxymethyl)aminomethane and dopamine hydrochloride added are based on hexagonal boron nitride, at 0.10-0.15 g / g and 0.18-0.24 g / g, respectively; the amounts of deionized water and anhydrous ethanol added are based on hexagonal boron nitride, at 40-60 mL / g and 8-12 mL / g, respectively.

9. A method for preparing a high-adhesion, high-temperature fluorine-free adhesive as described in any one of claims 1-8, characterized in that, Includes the following steps: N,N-dimethylacetamide was added to the reactor and stirred, followed by the main resin. After stirring evenly, toughening resin was added, and after stirring evenly again, functional additives were added. After dispersion and degassing, high-temperature resistant fluorine-free adhesive was obtained.

10. The high-strength, high-temperature resistant, fluorine-free adhesive according to claim 9, characterized in that, In the preparation of high-temperature resistant fluorine-free adhesive, the dispersion conditions are 2000-3000 r / min for 15-25 min; the degassing conditions are 45-50℃, vacuum degree -0.08MPa for 20-30 min.

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