High-temperature-resistant hot melt adhesive and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant hot melt adhesive and a preparation method thereof, and relates to the technical field of hot melt adhesives. The high-temperature-resistant hot melt adhesive is prepared from the following raw materials in parts by weight: 25 to 35 parts of modified polyimide resin, 20 to 30 parts of modified benzoxazine resin, 8 to 12 parts of carboxyl-terminated nitrile rubber, 5 to 8 parts of C5 / C9 copolymerized petroleum resin, 3 to 5 parts of hydrophobic modified nano silicon dioxide, 1 to 2 parts of silicone powder, 0.5 to 1.0 part of antioxidant 1010, 0.3 to 0.8 part of zinc stearate and 0.05 to 0.1 part of tetrabutylammonium bromide. The high-temperature-resistant hot melt adhesive is scientific in raw material ratio, core resin is modified to improve heat resistance and compatibility, filler such as hydrophobic nano silicon dioxide is added to enhance performance, the preparation process is controllable, nitrogen protection is achieved in the whole process, moisture absorption is prevented through granulation and drying treatment, and a finished product is excellent in high-temperature resistance, good in comprehensive performance and good in storage stability.

Description

Technical Field

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

[0002] Hot melt adhesives are widely used in electronics, aerospace, and automotive manufacturing due to their advantages such as convenient application, high bonding efficiency, and solvent-free production. High-temperature resistant hot melt adhesives are particularly crucial bonding materials in high-end manufacturing. Currently, the industry primarily prepares high-temperature resistant hot melt adhesives using unmodified polyimide resins or benzoxazine resins as the core matrix, combined with ordinary rubber, inorganic fillers, and additives through simple blending. Some processes involve simple graft modification of the single resin or the addition of fillers such as conventional nano-silica or ordinary petroleum resins to enhance performance.

[0003] However, existing technologies for preparing high-temperature resistant hot melt adhesives still have many problems that urgently need to be solved: First, the core resin has not undergone multi-step modification or the degree of modification is insufficient. The compatibility between polyimide and benzoxazine resin is poor, and the system exhibits significant phase separation after blending, making it difficult to balance the high-temperature resistance and adhesive strength of the hot melt adhesive. Debonding and deformation problems easily occur under high-temperature environments. Second, most of the inorganic fillers used are unmodified, with strong surface hydrophilicity and weak bonding force with the resin matrix. They are prone to agglomeration and cannot effectively improve the mechanical properties and weather resistance of the material. Third, the interfacial bonding effect between the rubber toughening component and the resin matrix is ​​poor, resulting in insufficient toughness of the hot melt adhesive, which is prone to cracking under external impact. Fourth, some preparation processes lack precise temperature and time control and lack full nitrogen protection, making the raw materials prone to oxidation and degradation. This leads to poor storage stability of the finished hot melt adhesive, and its performance drops significantly after absorbing moisture. Fifth, the additives lack targeted formulation, and the antioxidant properties and processing fluidity of the system are not adequately controlled. Melt fracture easily occurs during processing, affecting the product molding quality.

[0004] The aforementioned problems make it difficult for existing high-temperature resistant hot melt adhesives to meet the high requirements of high-temperature bonding, mechanical strength, weather resistance and processability in the high-end manufacturing field. Therefore, the development of a high-temperature resistant hot melt adhesive with good compatibility, excellent high-temperature resistance, good comprehensive mechanical properties and stable processing and storage has become an urgent need in the industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-temperature resistant hot melt adhesive and its preparation method, which solves the problems of poor resin compatibility, insufficient high-temperature resistance, easy agglomeration of fillers, weak interfacial bonding, and poor toughness in existing hot melt adhesives.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high-temperature resistant hot melt adhesive comprises the following raw materials in parts by weight: 25-35 parts modified polyimide resin, 20-30 parts modified benzoxazine resin, 8-12 parts carboxyl-terminated nitrile butadiene rubber, 5-8 parts C5 / C9 copolymer petroleum resin, 3-5 parts hydrophobic modified nano silica, 1-2 parts silicone powder, 0.5-1.0 parts antioxidant 1010, 0.3-0.8 parts zinc stearate, and 0.05-0.1 parts tetrabutylammonium bromide.

[0007] Furthermore, the modified polyimide resin is prepared using the following specific steps: A1. Add thermoplastic polyimide to N,N-dimethylformamide, heat to 80-90℃ and stir to dissolve. Add 4,4'-diaminodiphenyl ether and react at 110℃ for 6 hours to fully aminate the resin end groups. Then heat to 150℃ and add isoquinoline to catalyze imidization and ring closure for 4 hours. Through the reaction of excess aromatic diamine with the anhydride-terminated PI end groups, the anhydride groups are converted to amino groups, achieving end-amino sealing and providing active reaction sites for subsequent allyl grafting. At the same time, the complete imide ring structure of PI is restored, ensuring that the heat resistance of the resin is not reduced. After the reaction, pour into deionized water to precipitate, filter and wash, and vacuum dry at 100-110℃ for 12 hours to obtain end-amino-terminated thermoplastic polyimide. A2. Add amino-terminated thermoplastic polyimide to N,N-dimethylformamide, heat to 80-90℃ and stir until completely dissolved to form a homogeneous solution. Add allyl bromide and anhydrous potassium carbonate, heat to 100-110℃ and react at a constant temperature for 6-8 hours. Control the amount of allyl bromide to ensure that the amino-terminated polyimide is monosubstituted, introduce allyl side chains at the ends of the PI molecular chain, and retain the active secondary amino group and allyl double bond. The secondary amino group is used for subsequent reactions, and the allyl double bond serves as the crosslinking site during the final curing of the hot melt adhesive. After the reaction, pour the product into deionized water to precipitate, filter, wash with deionized water 3-4 times, and vacuum dry at 100-110℃ for 12-16 hours to obtain the first modified thermoplastic polyimide. A3. The first-modified thermoplastic polyimide was added to N-methylpyrrolidone, heated to 70-80℃ and stirred until completely dissolved. Epichlorohydrin and triethylamine were added, and the mixture was heated to 90-95℃ and reacted at a constant temperature for 4-6 hours. The active hydrogen of the secondary amine reacted with epichlorohydrin in a ring-opening addition reaction. Under these conditions, the allyl double bond remained stable and did not participate in the reaction, generating a β-hydroxy-γ-chloropropyl side chain (chlorohydrin structure), which effectively controlled the molecular chain length and introduced hydroxyl reaction sites. After the reaction, the product was poured into anhydrous ethanol to precipitate, filtered, washed 2-3 times with anhydrous ethanol, and dried under vacuum at 80-90℃ for 8-10 hours to obtain the second-modified thermoplastic polyimide. A4. Add the second modified thermoplastic polyimide to toluene, heat to 85-90℃ and stir until completely dissolved. Add silane coupling agent KH560 and dibutyltin dilaurate, heat to 100-110℃ and reflux for 5-7 hours. Under the catalysis of dibutyltin dilaurate, the epoxy group of KH560 undergoes an etherification reaction with the hydroxyl group of the chlorohydrin structure, grafting the siloxane segment onto the PI molecular chain. In this step, the allyl double bond remains stable. The final modified PI resin contains both siloxane groups to improve filler compatibility and allyl double bonds to provide thermosetting crosslinking ability. After the reaction is completed, remove toluene by vacuum distillation to obtain a viscous resin. Vacuum dry at 120-130℃ for 10-12 hours to remove residual solvent. After cooling to room temperature, pulverize and pass through a 40-mesh sieve to obtain the modified polyimide resin.

[0008] Furthermore, the ratio of thermoplastic polyimide, N,N-dimethylformamide, 4,4'-diaminodiphenyl ether, and isoquinoline in A1 is 100g:500ml:15-20g:5ml.

[0009] Furthermore, the ratio of the amino-terminated thermoplastic polyimide, N,N-dimethylformamide, allyl bromide, and anhydrous potassium carbonate in A2 is 100g: 500-600ml: 3-4g: 2-2.5g.

[0010] Furthermore, the ratio of the first modified thermoplastic polyimide, N-methylpyrrolidone, epichlorohydrin, and triethylamine in A3 is 100g: 400-500ml: 8-10g: 1-1.2g.

[0011] Furthermore, the ratio of the second modified thermoplastic polyimide, toluene, silane coupling agent KH560, and dibutyltin dilaurate in A4 is 100g: 350-450ml: 8-10g: 0.5-0.8g.

[0012] Furthermore, the modified benzoxazine resin is prepared using the following specific steps: B1. Add benzoxazine resin to a mixer, heat to 90-100℃, and mix until the resin is completely melted under nitrogen protection. Slowly add maleic anhydride and benzoyl peroxide to the molten benzoxazine resin and continue mixing for 3-4 hours. Through a free radical substitution reaction initiated by benzoyl peroxide, the anhydride group of maleic anhydride is grafted to the benzyl hydrogen site of the benzoxazine molecular chain, introducing a polar anhydride group as a specific reaction site, improving the compatibility of benzoxazine with rubber and polyimide resin, and reducing the brittleness of the resin. After the reaction is completed, take out the molten product, cool it to room temperature, pulverize it, and pass it through a 40-mesh sieve to obtain the first modified benzoxazine resin. B2. The first modified benzoxazine resin is added to a mixer and heated to 120-150℃ to melt. A terminal amino polyether with a molecular weight of 2000 is added, and the mixture is stirred for 2-3 hours. The amino groups of the terminal amino polyether undergo a specific amidation reaction with the maleic anhydride groups grafted onto the benzoxazine molecular chain to generate stable amide bonds. The flexible polyether segments are covalently grafted onto the benzoxazine molecular chain, which effectively solves the problem of high brittleness of pure benzoxazine resin after curing. At the same time, the introduction of polyether segments improves hot melt processability and retains the high heat resistance of benzoxazine. After cooling and pulverizing, the resin is passed through a 40-mesh sieve to obtain the modified benzoxazine resin.

[0013] Furthermore, the ratio of benzoxazine resin, maleic anhydride, and benzoyl peroxide in B1 is 100g:7-10g:0.3-0.5g.

[0014] Furthermore, the ratio of the first modified benzoxazine resin and the amino-terminated polyether in B2 is 100g:15-20g.

[0015] Furthermore, the specific preparation steps for the hydrophobically modified nano-silica are as follows: Vapor-phase nano-silica was mixed with silane coupling agent KH550 and anhydrous ethanol, ultrasonically dispersed at 300W for 40 min, heated to 70℃ and stirred for 2 h, dried under reduced pressure, and passed through a 200-mesh sieve to obtain hydrophobically modified nano-silica. Hydrophobic silane groups were grafted onto the nanoparticle surface by reacting the aminopropyl groups of silane coupling agent KH550 with the hydroxyl groups on the nano-silica surface, significantly reducing surface hydrophilicity and preventing nanoparticle aggregation in the resin matrix. Simultaneously, the aminopropyl groups formed chemical bonds with the epoxy and carboxyl groups of the modified resin, enhancing interfacial bonding.

[0016] Furthermore, the ratio of fumed nano-silica, silane coupling agent KH550, and anhydrous ethanol used in the hydrophobic modified nano-silica is 50g:5g:50ml.

[0017] A method for preparing a high-temperature resistant hot melt adhesive, characterized by comprising the following steps: S1. Add 8-12 parts of carboxyl-terminated nitrile butadiene rubber, 5-8 parts of C5 / C9 copolymer petroleum resin, 3-5 parts of hydrophobic modified nano silica, 1-2 parts of silicone powder, 0.5-1.0 parts of antioxidant 1010, 0.3-0.8 parts of zinc stearate, and 0.05-0.1 parts of tetrabutylammonium bromide to a high-speed mixer. Set the mixing temperature to 50-60℃, the mixing speed to 400-500 r / min, and mix for 30 min under nitrogen protection to obtain a premixed filler system. S2. Add 25-35 parts of modified polyimide resin and 20-30 parts of modified benzoxazine resin to the main feed bin of the twin-screw extruder, and add the premixed filler to the auxiliary feed bin. The extruder is protected by nitrogen throughout the process. Set the temperature of the feeding zone to 170-180℃, the melting zone to 180-190℃, the reaction zone to 210-220℃, the die head to 210℃, and the screw speed to 200-250 r / min. Control the residence time of the material in the reaction zone to 2-3 minutes. The raw material is extruded to obtain molten hot melt adhesive strips. S3. Immediately feed the extruded molten hot melt adhesive strip into a water-cooled granulator. The cooling water temperature is kept constant at 25-30℃. The strip is rapidly cooled and solidified, and granulated to obtain cylindrical hot melt adhesive granules. Place the hot melt adhesive granules in a forced-air drying oven and dry at 80℃ for 2 hours to completely remove surface moisture and prevent moisture absorption during storage, thus obtaining the finished high-temperature resistant hot melt adhesive.

[0018] This invention provides a high-temperature resistant hot melt adhesive and its preparation method, which has the following beneficial effects: 1. The high-temperature resistant hot melt adhesive prepared by this invention possesses excellent high-temperature resistance and structural stability. Through multi-step modification of polyimide and benzoxazine resin, the compatibility of the two core resins is significantly improved, solving the phase separation problem of traditional systems. This allows the hot melt adhesive to maintain good bonding strength and morphology even at high temperatures, without debonding or deformation. Simultaneously, the modified resin molecular structure is more stable, and with the synergistic effect of antioxidant 1010, the thermo-oxidative stability of the material is effectively improved, further enhancing its high-temperature resistance and making it suitable for high-temperature applications in high-end manufacturing fields.

[0019] 2. The overall mechanical properties of the hot melt adhesive of this invention are significantly improved. The toughening effect of the carboxyl-terminated nitrile rubber and the modified resin matrix achieve good interfacial bonding. In addition, the hydrophobically modified nano-silica is evenly dispersed in the resin system and has strong bonding force, avoiding the mechanical property degradation caused by the agglomeration of ordinary fillers. It not only makes up for the brittleness of the resin base material, but also improves the tensile strength, impact resistance and bonding toughness of the hot melt adhesive, making the hot melt adhesive less prone to cracking when subjected to external force, and ensuring the structural integrity of the bonded part.

[0020] 3. The hot melt adhesive of this invention possesses excellent processing performance and molding stability. The preparation process employs a premixed filler system combined with a twin-screw extruder for segmented temperature-controlled extrusion, with nitrogen protection throughout to prevent raw material oxidation and degradation. Furthermore, the synergistic effect of silicone powder and zinc stearate optimizes the melt flowability of the system, solving the problems of melt fracture and poor molding effects that often occur in traditional hot melt adhesive processing. Simultaneously, the residence time of materials in the reaction zone is precisely controlled, allowing each component to react fully without excessive cross-linking. The extruded adhesive strips, after water cooling and granulation, have a regular morphology, resulting in smoother melt coating during subsequent use.

[0021] 4. The hot melt adhesive of this invention possesses excellent storage stability and environmental adaptability. The hydrophobic modified nano-silica significantly reduces the material's moisture absorption. Combined with granulation followed by drying at 80°C for 2 hours, surface moisture is thoroughly removed, solving the problem of performance degradation caused by moisture absorption during the storage of traditional hot melt adhesives. Simultaneously, the catalytic effect of tetrabutylammonium bromide promotes more complete cross-linking of the system, resulting in tighter bonding between components. Under normal storage conditions, component separation and performance degradation do not occur, and the material exhibits better weather resistance, maintaining stable adhesive performance under different temperature and humidity environments, thus extending the product's shelf life and service life. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0023] Example 1: Preparation of high-temperature resistant hot melt adhesive. The specific preparation steps are as follows: S1. Add 8 parts of carboxyl-terminated nitrile rubber, 5 parts of C5 / C9 copolymer petroleum resin, 3 parts of hydrophobic modified nano silica, 1 part of silicone powder, 0.5 parts of antioxidant 1010, 0.3 parts of zinc stearate, and 0.05 parts of tetrabutylammonium bromide to a high-speed mixer. Set the mixing temperature to 50℃, the mixing speed to 400 r / min, and mix for 30 min under nitrogen protection to obtain a premixed filler system. S2. Add 25 parts of modified polyimide resin and 20 parts of modified benzoxazine resin to the main feed bin of the twin-screw extruder, and add the premixed filler to the auxiliary feed bin. The extruder is protected by nitrogen throughout the process. Set the feed zone temperature to 170°C, the melting zone temperature to 180°C, the reaction zone temperature to 210°C, the die head temperature to 210°C, and the screw speed to 200 r / min. Control the residence time of the material in the reaction zone to 2 min. The raw material is extruded to obtain molten hot melt adhesive strips. S3. Immediately feed the extruded molten hot melt adhesive strip into a water-cooled granulator. The cooling water temperature is kept constant at 25℃. The strip is rapidly cooled and solidified, and granulated to obtain cylindrical hot melt adhesive granules. Place the hot melt adhesive granules into a forced-air drying oven and dry at 80℃ for 2 hours to completely remove surface moisture and prevent moisture absorption during storage, thus obtaining the finished high-temperature resistant hot melt adhesive.

[0024] Example 2: Preparation of high-temperature resistant hot melt adhesive. The specific preparation steps are as follows: S1. Add 12 parts of carboxyl-terminated nitrile rubber, 8 parts of C5 / C9 copolymer petroleum resin, 5 parts of hydrophobic modified nano silica, 2 parts of silicone powder, 1.0 part of antioxidant 1010, 0.8 parts of zinc stearate, and 0.1 parts of tetrabutylammonium bromide to a high-speed mixer. Set the mixing temperature to 60℃, the mixing speed to 500 r / min, and mix for 30 min under nitrogen protection to obtain a premixed filler system. S2. Add 35 parts of modified polyimide resin and 30 parts of modified benzoxazine resin to the main feed bin of the twin-screw extruder, and add the premixed filler to the auxiliary feed bin. The extruder is protected by nitrogen throughout the process. Set the feed zone temperature to 180°C, the melting zone temperature to 190°C, the reaction zone temperature to 220°C, the die head temperature to 210°C, and the screw speed to 250 r / min. Control the residence time of the material in the reaction zone to 3 min. The raw material is extruded to obtain molten hot melt adhesive strips. S3. Immediately feed the extruded molten hot melt adhesive strip into a water-cooled granulator. The cooling water temperature is kept constant at 30℃. The strip is rapidly cooled and solidified, and granulated to obtain cylindrical hot melt adhesive granules. Place the hot melt adhesive granules into a forced-air drying oven and dry at 80℃ for 2 hours to completely remove surface moisture and prevent moisture absorption during storage, thus obtaining the finished high-temperature resistant hot melt adhesive.

[0025] Example 3: Preparation of high-temperature resistant hot melt adhesive. The specific preparation steps are as follows: S1. Add 10 parts of carboxyl-terminated nitrile rubber, 6 parts of C5 / C9 copolymer petroleum resin, 4 parts of hydrophobic modified nano silica, 1 part of silicone powder, 0.7 parts of antioxidant 1010, 0.5 parts of zinc stearate, and 0.07 parts of tetrabutylammonium bromide to a high-speed mixer. Set the mixing temperature to 55℃, the mixing speed to 450 r / min, and mix for 30 min under nitrogen protection to obtain a premixed filler system. S2. Add 30 parts of modified polyimide resin and 25 parts of modified benzoxazine resin to the main feed bin of the twin-screw extruder, and add the premixed filler to the auxiliary feed bin. The extruder is protected by nitrogen throughout the process. Set the feed zone temperature to 175°C, the melting zone temperature to 185°C, the reaction zone temperature to 215°C, the die head temperature to 210°C, and the screw speed to 225 r / min. Control the residence time of the material in the reaction zone to 2 min. The raw material is extruded to obtain molten hot melt adhesive strips. S3. Immediately feed the extruded molten hot melt adhesive strip into a water-cooled granulator. The cooling water temperature is kept constant at 27℃. The strip is rapidly cooled and solidified, and granulated to obtain cylindrical hot melt adhesive granules. Place the hot melt adhesive granules into a forced-air drying oven and dry at 80℃ for 2 hours to completely remove surface moisture and prevent moisture absorption during storage, thus obtaining the finished high-temperature resistant hot melt adhesive.

[0026] Example 4: Preparation of modified polyimide resin. The specific preparation steps are as follows: A1. Add 100g of thermoplastic polyimide to 500ml of N,N-dimethylformamide, heat to 80℃ and stir to dissolve. Add 15g of 4,4'-diaminodiphenyl ether and react at 110℃ for 6h to fully aminate the resin end groups. Then heat to 150℃ and add 5ml of isoquinoline to catalyze imidization and ring closure for 4h. After the reaction is complete, pour into deionized water to precipitate, filter and wash, and vacuum dry at 100℃ for 12h to obtain amino-terminated thermoplastic polyimide. A2. Add 100g of amino-terminated thermoplastic polyimide to 500ml of N,N-dimethylformamide, heat to 80℃ and stir until completely dissolved to form a homogeneous solution. Add 3g of allyl bromide and 2g of anhydrous potassium carbonate, heat to 100℃ and react at a constant temperature for 6h. After the reaction is complete, pour the product into deionized water to precipitate, filter and wash 3 times with deionized water, and dry under vacuum at 100℃ for 12h to obtain the first modified thermoplastic polyimide. A3. Add 100g of the first-modified thermoplastic polyimide to 400ml of N-methylpyrrolidone, heat to 70℃ and stir until completely dissolved, add 8g of epichlorohydrin and 1g of triethylamine, heat to 90℃ and react at a constant temperature for 4h; after the reaction is complete, pour the product into anhydrous ethanol to precipitate, filter and wash twice with anhydrous ethanol, and dry under vacuum at 80℃ for 8h to obtain the second-modified thermoplastic polyimide; A4. Add 100g of the second modified thermoplastic polyimide to 350ml of toluene, heat to 85℃ and stir until completely dissolved, add 8g of silane coupling agent KH560 and 0.5g of dibutyltin dilaurate, heat to 100℃ and reflux for 5h; after the reaction is completed, remove the toluene by vacuum distillation to obtain a viscous resin, dry it under vacuum at 120℃ for 10h to remove residual solvent, cool to room temperature and then pulverize it through a 40-mesh sieve to obtain the modified polyimide resin.

[0027] Example 5: Preparation of modified polyimide resin. The specific preparation steps are as follows: A1. Add 100g of thermoplastic polyimide to 500ml of N,N-dimethylformamide, heat to 90℃ and stir to dissolve. Add 20g of 4,4'-diaminodiphenyl ether and react at 110℃ for 6h to fully aminate the resin end groups. Then heat to 150℃ and add 5ml of isoquinoline to catalyze imidization and ring closure for 4h. After the reaction is complete, pour into deionized water to precipitate, filter and wash, and vacuum dry at 110℃ for 12h to obtain amino-terminated thermoplastic polyimide. A2. Add 100g of amino-terminated thermoplastic polyimide to 600ml of N,N-dimethylformamide, heat to 90℃ and stir until completely dissolved to form a homogeneous solution. Add 4g of allyl bromide and 2.5g of anhydrous potassium carbonate, heat to 110℃ and react at a constant temperature for 8h. After the reaction is complete, pour the product into deionized water to precipitate, filter and wash 4 times with deionized water, and vacuum dry at 110℃ for 16h to obtain the first modified thermoplastic polyimide. A3. Add 100g of the first-modified thermoplastic polyimide to 500ml of N-methylpyrrolidone, heat to 80℃ and stir until completely dissolved, add 10g of epichlorohydrin and 1.2g of triethylamine, heat to 95℃ and react at a constant temperature for 6h; after the reaction is complete, pour the product into anhydrous ethanol to precipitate, filter and wash 3 times with anhydrous ethanol, and dry under vacuum at 90℃ for 10h to obtain the second-modified thermoplastic polyimide; A4. Add 100g of the second modified thermoplastic polyimide to 450ml of toluene, heat to 90℃ and stir until completely dissolved, add 10g of silane coupling agent KH560 and 0.8g of dibutyltin dilaurate, heat to 110℃ and reflux for 7h; after the reaction is completed, remove the toluene by vacuum distillation to obtain a viscous resin, dry under vacuum at 130℃ for 12h to remove residual solvent, cool to room temperature and then pulverize through a 40-mesh sieve to obtain the modified polyimide resin.

[0028] Example 6: Preparation of modified benzoxazine resin. The specific preparation steps are as follows: B1. Add 100g of benzoxazine resin to a mixer, heat to 90℃, and mix until the resin is completely melted under nitrogen protection. Slowly add 7g of maleic anhydride and 0.3g of benzoyl peroxide to the molten benzoxazine resin, and continue mixing for 3 hours. After the reaction is complete, take out the molten product, cool it to room temperature, pulverize it, and pass it through a 40-mesh sieve to obtain the first modified benzoxazine resin. B2. Add 100g of the first-modified benzoxazine resin to a mixer, heat to 120℃ to melt, add 15g of amino-terminated polyether with a molecular weight of 2000, mix for 2 hours, cool and pulverize through a 40-mesh sieve to obtain the modified benzoxazine resin.

[0029] Example 7: Preparation of modified benzoxazine resin. The specific preparation steps are as follows: B1. Add 100g of benzoxazine resin to a mixer, heat to 100℃, and mix until the resin is completely melted under nitrogen protection. Slowly add 10g of maleic anhydride and 0.5g of benzoyl peroxide to the molten benzoxazine resin, and continue mixing for 4 hours. After the reaction is complete, take out the molten product, cool it to room temperature, pulverize it, and pass it through a 40-mesh sieve to obtain the first modified benzoxazine resin. B2. Add 100g of the first-modified benzoxazine resin to a mixer, heat to 150℃ to melt, add 20g of amino-terminated polyether with a molecular weight of 2000, mix for 3 hours, cool and pulverize through a 40-mesh sieve to obtain the modified benzoxazine resin.

[0030] Example 8: Preparation of hydrophobically modified nano-silica. The specific preparation steps are as follows: Take 50g of fumed silica nanoparticles, add 5g of silane coupling agent KH550 and 50ml of anhydrous ethanol, ultrasonically disperse at 300W for 40min, heat to 70℃ and stir for 2h, dry under reduced pressure and pass through a 200-mesh sieve to obtain hydrophobic modified silica nanoparticles.

[0031] Comparative Example 1: A high-temperature resistant hot melt adhesive was prepared. The specific preparation steps are as follows: The remaining steps remain unchanged, except that the modified polyimide resin prepared in Example 4 used in Example 3 is replaced with unmodified polyimide resin to prepare a high-temperature resistant hot melt adhesive.

[0032] Comparative Example 2: A high-temperature resistant hot melt adhesive was prepared. The specific preparation steps are as follows: The remaining steps remain unchanged, except that the modified benzoxazine resin prepared in Example 7 used in Example 3 is replaced with unmodified benzoxazine resin to prepare a high-temperature resistant hot melt adhesive.

[0033] Comparative Example 3: A high-temperature resistant hot melt adhesive was prepared. The specific preparation steps are as follows: The remaining steps remain unchanged, except that the modified polyimide resin prepared in Example 4 used in Example 3 is replaced with unmodified polyimide resin, and the modified benzoxazine resin prepared in Example 7 is replaced with unmodified benzoxazine resin, to prepare a high-temperature resistant hot melt adhesive.

[0034] Performance testing Test conditions: Softening point test: The ring and ball method is adopted. After the sample is prepared according to GB / T 4507-2014 standard, it is tested by the ring and ball softening point tester. Hot melt stability test: Take a 100mL container and fill it with 2 / 3 of the volume of hot melt adhesive sample. Place it in a 210℃ oven and keep it at a constant temperature for 4 hours. Take a sample every 1 hour to test the viscosity, calculate the viscosity change rate, and record the appearance. Peel strength test: After melting the sample in a 200℃ oven, it was pressed into a 1mm thick specimen, cut to a size of 100mm×25mm, and bonded between a 0.1mm thick aluminum foil and a 150mm×25mm PP substrate (melt bonding at 200℃, rolling back and forth 3 times with a 2kg roller). The sample was subjected to a temperature and humidity cycle of (40℃, 95%RH) 24h → (23℃, 50%RH) 1h → (85℃, 24h) → (23℃, 50%RH) 1h → (-30℃, 4h) → (23℃, 50%RH) 1h 3 times. After standing for 24h, the peel strength at room temperature was tested. The high temperature peel strength test conditions were 180℃ for 30min and then immediately tested. Shear strength test: According to ISO 4587-2 standard, the sample was melted in an oven at 200℃ and pressed into a 1mm thick specimen. The specimen was cut to a size of 12.5mm×25mm and bonded between a 100mm×25mm×0.1mm aluminum foil and a PP substrate of the same size (melt bonding at 200℃, rolling back and forth 3 times with a 2kg roller). After being placed under standard conditions for 3 days, the room temperature shear strength was tested. Static load test (creep): The sample was melted in an oven at 200℃ and pressed into a 1mm thick specimen. A 25mm×25mm specimen was cut and bonded between a 25mm×25mm×1mm aluminum sheet and a 100mm×100mm×1mm PP board. A 400mm×0.05mm nylon thread was placed horizontally in the center of the aluminum sheet. After melting and bonding at 200℃ and cooling, a 500g weight was suspended on the thread and placed in an oven at 180℃ for 24 hours. The initial displacement and the displacement after 24 hours were recorded, and the creep rate was calculated.

[0035] ; The performance test results of each embodiment of this high-temperature resistant hot melt adhesive are significantly better than those of the comparative examples. Example 3 has the best overall performance, with a softening point of 210℃, a hot melt stability viscosity change rate of only 6.8%, a room temperature peel strength of 4.8 N / mm, a 180℃ high temperature peel strength of 3.2 N / mm, a room temperature shear strength of 32.5 MPa, and a creep rate of only 1.8% under 24 hours of static load at 180℃. In contrast, the comparative examples, due to the use of unmodified resin, show a significant decrease in high-temperature resistance, hot melt stability, adhesive strength, and creep resistance. In particular, Comparative Example 3, which simultaneously replaced two unmodified resins, has the worst performance indicators, with a softening point of only 185℃, a viscosity change rate of 35.2%, a 180℃ peel strength of only 0.9 N / mm, and a creep rate as high as 18.5%. This fully demonstrates that the modification treatment of polyimide and benzoxazine resin, as well as the scientific ratio of each component, can significantly improve the high-temperature resistance, adhesive performance, structural stability, and processing and use performance of the hot melt adhesive.

[0036] The above description is merely an example and illustration 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 invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A high-temperature resistant hot melt adhesive, characterized in that: It contains the following raw materials in parts by weight: 25-35 parts modified polyimide resin, 20-30 parts modified benzoxazine resin, 8-12 parts carboxyl-terminated nitrile butadiene rubber, 5-8 parts C5 / C9 copolymer petroleum resin, 3-5 parts hydrophobically modified nano silica, 1-2 parts silicone powder, 0.5-1.0 parts antioxidant 1010, 0.3-0.8 parts zinc stearate, and 0.05-0.1 parts tetrabutylammonium bromide.

2. The high-temperature resistant hot melt adhesive according to claim 1, characterized in that: The modified polyimide resin is prepared using the following specific steps: A1. Add thermoplastic polyimide to N,N-dimethylformamide, heat to 80-90℃ and stir to dissolve, add 4,4'-diaminodiphenyl ether, react at 110℃ for 6h to fully aminate the resin end groups, then heat to 150℃ and add isoquinoline to catalyze imidization and ring closure for 4h. After the reaction is complete, pour into deionized water to precipitate, filter and wash, and vacuum dry at 100-110℃ for 12h to obtain amino-terminated thermoplastic polyimide; A2. Add amino-terminated thermoplastic polyimide to N,N-dimethylformamide, heat to 80-90℃ and stir until completely dissolved to form a homogeneous solution. Add allyl bromide and anhydrous potassium carbonate, heat to 100-110℃ and react at a constant temperature for 6-8 hours. After the reaction is complete, pour the product into deionized water to precipitate, filter and wash with deionized water 3-4 times, and vacuum dry at 100-110℃ for 12-16 hours to obtain the first modified thermoplastic polyimide. A3. Add the first-modified thermoplastic polyimide to N-methylpyrrolidone, heat to 70-80℃ and stir until completely dissolved, add epichlorohydrin and triethylamine, heat to 90-95℃ and react at a constant temperature for 4-6 hours; after the reaction is complete, pour the product into anhydrous ethanol to precipitate, filter and wash with anhydrous ethanol 2-3 times, and vacuum dry at 80-90℃ for 8-10 hours to obtain the second-modified thermoplastic polyimide; A4. Add the second modified thermoplastic polyimide to toluene, heat to 85-90℃ and stir until completely dissolved, add silane coupling agent KH560 and dibutyltin dilaurate, heat to 100-110℃ and reflux for 5-7 hours; after the reaction is completed, remove toluene by vacuum distillation to obtain a viscous resin, dry under vacuum at 120-130℃ for 10-12 hours to remove residual solvent, cool to room temperature and then pulverize through a 40-mesh sieve to obtain the modified polyimide resin.

3. The high-temperature resistant hot melt adhesive according to claim 2, characterized in that: The ratio of thermoplastic polyimide, N,N-dimethylformamide, 4,4'-diaminodiphenyl ether, and isoquinoline in A1 is 100g:500ml:15-20g:5ml; The ratio of amino-terminated thermoplastic polyimide, N,N-dimethylformamide, allyl bromide, and anhydrous potassium carbonate in the A2 structure is 100g: 500-600ml: 3-4g: 2-2.5g. The ratio of the first modified thermoplastic polyimide, N-methylpyrrolidone, epichlorohydrin, and triethylamine in A3 is 100g: 400-500ml: 8-10g: 1-1.2g; The ratio of the second modified thermoplastic polyimide, toluene, silane coupling agent KH560, and dibutyltin dilaurate in A4 is 100g: 350-450ml: 8-10g: 0.5-0.8g.

4. The high-temperature resistant hot melt adhesive according to claim 1, characterized in that: The modified benzoxazine resin is prepared using the following specific steps: B1. Add benzoxazine resin to a mixer, heat to 90-100℃, and mix until the resin is completely melted under nitrogen protection. Slowly add maleic anhydride and benzoyl peroxide to the molten benzoxazine resin and continue mixing for 3-4 hours. After the reaction is complete, take out the molten product, cool it to room temperature, pulverize it, and pass it through a 40-mesh sieve to obtain the first modified benzoxazine resin. B2. Add the first modified benzoxazine resin to a mixer, heat it to 120-150℃ to melt it, add an amino-terminated polyether with a molecular weight of 2000, mix for 2-3 hours, cool and pulverize it through a 40-mesh sieve to obtain the modified benzoxazine resin.

5. The high-temperature resistant hot melt adhesive according to claim 4, characterized in that: The ratio of benzoxazine resin, maleic anhydride, and benzoyl peroxide in B1 is 100g:7-10g:0.3-0.5g; The ratio of the first modified benzoxazine resin and the amino-terminated polyether in B2 is 100g:15-20g.

6. The high-temperature resistant hot melt adhesive according to claim 1, characterized in that: The specific preparation steps for the hydrophobically modified nano-silica are as follows: Vapor-phase nano-silica was taken, and silane coupling agent KH550 and anhydrous ethanol were added. The mixture was ultrasonically dispersed at 300W for 40 minutes, heated to 70℃ and stirred for 2 hours. After drying under reduced pressure, it was passed through a 200-mesh sieve to obtain hydrophobically modified nano-silica.

7. The high-temperature resistant hot melt adhesive according to claim 6, characterized in that: The ratio of fumed nano-silica, silane coupling agent KH550, and anhydrous ethanol used in the hydrophobic modified nano-silica is 50g:5g:50ml.

8. A method for preparing a high-temperature resistant hot melt adhesive, characterized in that: Specifically, it includes the following steps: S1. Add 8-12 parts of carboxyl-terminated nitrile butadiene rubber, 5-8 parts of C5 / C9 copolymer petroleum resin, 3-5 parts of hydrophobic modified nano silica, 1-2 parts of silicone powder, 0.5-1.0 parts of antioxidant 1010, 0.3-0.8 parts of zinc stearate, and 0.05-0.1 parts of tetrabutylammonium bromide to a high-speed mixer. Set the mixing temperature to 50-60℃, the mixing speed to 400-500 r / min, and mix for 30 min under nitrogen protection to obtain a premixed filler system. S2. Add 25-35 parts of modified polyimide resin and 20-30 parts of modified benzoxazine resin to the main feed bin of the twin-screw extruder, and add the premixed filler to the auxiliary feed bin. The extruder is protected by nitrogen throughout the process. Set the temperature of the feeding zone to 170-180℃, the melting zone to 180-190℃, the reaction zone to 210-220℃, the die head to 210℃, and the screw speed to 200-250 r / min. Control the residence time of the material in the reaction zone to 2-3 minutes. The raw material is extruded to obtain molten hot melt adhesive strips. S3. Immediately feed the extruded molten hot melt adhesive strip into a water-cooled granulator. The cooling water temperature is kept constant at 25-30℃. The strip is rapidly cooled and solidified, and granulated to obtain cylindrical hot melt adhesive granules. Place the hot melt adhesive granules in a forced-air drying oven and dry at 80℃ for 2 hours to completely remove surface moisture and prevent moisture absorption during storage, thus obtaining the finished high-temperature resistant hot melt adhesive.