A low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste and a preparation method thereof

Abstract

A low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste and its preparation method are disclosed, relating to the field of adhesive technology. The aim is to address the insufficient long-term high-temperature creep resistance of existing lightweight epoxy adhesives. The paste is prepared from the following raw materials: Raw materials are weighed, and amide-containing trifunctional benzoxazine resin, amide-containing difunctional benzoxazine resin, amide-containing monofunctional benzoxazine resin, multifunctional epoxy resin, bisphenol A type epoxy resin, and toughening agent are added to a reaction vessel. The mixture is heated and stirred to obtain a homogeneous resin premix. The mixture is then cooled, and hollow glass microspheres, a coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid are added, and the mixture is stirred to obtain an intermediate product. Finally, a curing agent is added and stirred to obtain the low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste. This invention is applicable to structural bonding applications in aerospace, rail transportation, and electronic packaging where lightweighting and long-term high-temperature reliability are critical.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste adhesive and its preparation method. Background Technology

[0002] Epoxy resin adhesives are widely used in structural bonding fields such as aerospace and rail transportation due to their excellent bonding properties, mechanical strength, and chemical resistance. However, when conventional epoxy adhesives are used for long-term service at high temperatures (>150℃), the molecular chain segment movement intensifies, making them prone to creep deformation and leading to bond failure. Meanwhile, in lightweight applications such as aerospace, lower adhesive density is better, but simply adding lightweight fillers such as hollow glass microspheres to reduce density often sacrifices mechanical properties and high-temperature creep resistance. Therefore, developing a paste-like adhesive that combines low density and excellent high-temperature creep resistance has significant industrial value.

[0003] Benzoxazine resin is a novel thermosetting resin with advantages such as low curing shrinkage, high glass transition temperature, and good high-temperature modulus retention. In recent years, it has been widely used to modify epoxy resins to improve their heat resistance. Existing technologies have numerous reports on the blending of benzoxazine with epoxy resin in adhesives, composite materials, and other fields. CN120699575A discloses an adhesive film for semiconductor packaging, whose main components include benzoxazine resin, bisphenol-type epoxy resin, and alicyclic epoxy resin. While it exhibits good resistance to damp heat, it primarily focuses on the semiconductor packaging field and does not address the long-term creep resistance of structural adhesives under constant high-temperature loads, nor does it solve the technical problem of reducing density. CN120888262A discloses an epoxy resin adhesive that introduces a silane-containing polyetheramine-type benzoxazine intermediate to improve heat resistance, but it also fails to address the material's density and high-temperature creep behavior. Furthermore, CN105694756A discloses a benzoxazine structural adhesive film with a carrier, which is significantly different from the carrier-free low-density paste adhesive of this invention. It primarily addresses the problems of short shelf life and high toxicity of combustion fumes in existing structural adhesive films. Moreover, its benzoxazine does not contain amide groups, and it does not address long-term creep resistance at high temperatures. Summary of the Invention

[0004] The present invention aims to address the problem of insufficient high-temperature long-term creep resistance of lightweight epoxy adhesives in the prior art, and provides a low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste and its preparation method.

[0005] This invention provides a low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste, which is prepared from the following raw materials in parts by weight: 5-10 parts of amide-containing trifunctional benzoxazine resin, 10-25 parts of amide-containing difunctional benzoxazine resin, 2-6 parts of amide-containing monofunctional benzoxazine resin, 30-60 parts of polyfunctional epoxy resin, 20-40 parts of bisphenol A type epoxy resin, 8-20 parts of toughening agent, 15-30 parts of hollow glass microspheres, 1-3 parts of coupling agent, 2-5 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 16-30 parts of curing agent.

[0006] Furthermore, the molecular structural formula of the amide-containing trifunctional benzoxazine resin is as follows:

[0007] .

[0008] Furthermore, the molecular structural formula of the amide-containing bifunctional benzoxazine resin is any one of the following:

[0009] , , .

[0010] Furthermore, the molecular structural formula of the amide-containing monofunctional benzoxazine resin is any one of the following:

[0011] , .

[0012] Furthermore, the multifunctional epoxy resin is one or a mixture of several of AG70, AG80, TDE-85, F44, F48, and F51.

[0013] Furthermore, the bisphenol A type epoxy resin is one or a mixture of several of E44, E51, and E54.

[0014] Furthermore, the toughening agent is liquid nitrile rubber, including but not limited to one of carboxyl-terminated liquid nitrile rubber, epoxy-terminated liquid nitrile rubber, or amino-terminated liquid nitrile rubber.

[0015] Furthermore, the density of the hollow glass microspheres is 0.25~0.46 g / cm³. 3 .

[0016] Further, the coupling agent is one of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, isopropyltris(dioctylpyrophosphate)titanate, and isopropyltris(isostearoyl)titanate.

[0017] Further, the curing agent is one or a mixture of several of the following: 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-bis(4-(3-aminophenoxy)phenyl)propane, and 4,4'-bis(3-aminophenoxy)diphenyl sulfone.

[0018] This invention provides a method for preparing the above-mentioned low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste, comprising the following steps:

[0019] Step 1: Weigh the following raw materials according to the following weight proportions: 5-10 parts of amide-containing trifunctional benzoxazine resin, 10-25 parts of amide-containing difunctional benzoxazine resin, 2-6 parts of amide-containing monofunctional benzoxazine resin, 30-60 parts of polyfunctional epoxy resin, 20-40 parts of bisphenol A type epoxy resin, 8-20 parts of toughening agent, 15-30 parts of hollow glass microspheres, 1-3 parts of coupling agent, 2-5 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 16-30 parts of curing agent;

[0020] Step 2: Add the amide-containing trifunctional benzoxazine resin, amide-containing difunctional benzoxazine resin, amide-containing monofunctional benzoxazine resin, multifunctional epoxy resin, bisphenol A type epoxy resin, and toughening agent to a reactor equipped with a heating and stirring device. Heat to 120℃~150℃ and stir at 500 r / min~1000 r / min for 1 h~4 h to obtain a uniform resin premix. Then cool to 80℃~110℃, add hollow glass microspheres, coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and stir at 100 r / min~500 r / min for 0.5 h~2 h to obtain an intermediate product.

[0021] Step 3: Add curing agent to intermediate product and stir at 200 r / min to 600 r / min for 0.5 h to 1 h at room temperature to obtain the low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention constructs a three-dimensional crosslinked network with multiple hydrogen bonds by compounding amide-containing trifunctional, difunctional, and monofunctional benzoxazine resins with multifunctional epoxy resins and bisphenol A type epoxy resins. Multiple hydrogen bonds are formed between amide groups, between amide groups and hydroxyl groups generated from the ring-opening of epoxy and benzoxazine, and between ether bonds and hydroxyl and amide groups. These bonds act like "molecular springs," reversibly breaking and reconstructing at high temperatures, effectively dissipating creep energy. The synergistic regulation of crosslinking density and chain segment flexibility by benzoxazine resins with different functionalities enables the network to suppress molecular chain slippage even at 177°C, thus achieving excellent anti-creep performance.

[0024] 2. In this invention, the branched side chains and numerous ether bonds in the amide-containing benzoxazine resin molecule structure synergistically work with the liquid nitrile rubber toughening agent to form flexible stress-dispersing micro-regions in the three-dimensional cross-linked network. This effectively alleviates internal stress after curing and inhibits crack propagation, thus giving the paste adhesive both high adhesive strength and good impact toughness. Tests show that the room temperature shear strength is greater than 30 MPa and the floating roller peel strength is greater than 3.5 kN / m.

[0025] 3. This invention uniquely introduces 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid as a dual-functional additive for interfacial compatibility and high-temperature resistance. The carboxyl group in its molecular structure can form chemical bonds with the surface of hollow glass microspheres and the resin matrix, significantly improving the interfacial bonding force between the lightweight filler and the matrix, and avoiding the degradation of adhesive performance due to density reduction; at the same time, its nitrogen-containing fused heterocyclic structure can further improve the thermal stability of the adhesive.

[0026] This invention achieves a comprehensive improvement in the overall performance of the paste adhesive through multi-component synergistic design. The paste adhesive possesses multiple characteristics, including low density, high bond strength, high-temperature creep resistance, and long fatigue life, meeting the stringent requirements of high-end fields such as aerospace and rail transportation for lightweight, high reliability, and long lifespan of structural adhesive materials. This paste adhesive is particularly suitable for structural bonding applications in aerospace, rail transportation, and electronic packaging, where lightweight design and long-term high-temperature reliability are critical. Detailed Implementation

[0027] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0028] Specific Embodiment 1: This embodiment of the invention provides a low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste, which is prepared from the following raw materials in parts by weight: 5-10 parts of amide-containing trifunctional benzoxazine resin, 10-25 parts of amide-containing difunctional benzoxazine resin, 2-6 parts of amide-containing monofunctional benzoxazine resin, 30-60 parts of multifunctional epoxy resin, 20-40 parts of bisphenol A type epoxy resin, 8-20 parts of toughening agent, 15-30 parts of hollow glass microspheres, 1-3 parts of coupling agent, 2-5 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 16-30 parts of curing agent.

[0029] Specific Implementation Method Two: The molecular structural formula of the amide-containing trifunctional benzoxazine resin described in this implementation method is as follows:

[0030] .

[0031] Other components and parameters are the same as in Specific Implementation Method 1.

[0032] Specific Implementation Method 3: The molecular structure of the amide-containing bifunctional benzoxazine resin described in this implementation method is any one of the following:

[0033] , , Other components and parameters are the same as in specific implementation method one or two.

[0034] Specific Implementation Method Four: The molecular structure of the amide-containing monofunctional benzoxazine resin described in this implementation method is any one of the following:

[0035] , Other components and parameters are the same as in any one of the specific embodiments one to three.

[0036] Specific Embodiment Five: The multifunctional epoxy resin described in this embodiment is one or a mixture of several of AG70, AG80, TDE-85, F44, F48, and F51. Other components and parameters are the same as in Specific Embodiments One to Four.

[0037] The multifunctional epoxy resin selected in this embodiment is inexpensive and readily available.

[0038] Specific Embodiment Six: The bisphenol A type epoxy resin described in this embodiment is one or a mixture of several of E44, E51, and E54. Other components and parameters are the same as in Specific Embodiments One to Five.

[0039] Specific Embodiment Seven: The toughening agent described in this embodiment is liquid nitrile rubber, including but not limited to one of carboxyl-terminated liquid nitrile rubber, epoxy-terminated liquid nitrile rubber, or amino-terminated liquid nitrile rubber. Other components and parameters are the same as in Specific Embodiments One to Six.

[0040] Specific Implementation Method Eight: The density of the hollow glass microspheres described in this implementation method is 0.25~0.46 g / cm³. 3 Other components and parameters are the same as in any one of the specific embodiments one to seven.

[0041] Specific Embodiment Nine: The coupling agent described in this embodiment is one of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, isopropyltris(dioctylpyrophosphate)titanate, and isopropyltris(isostearoyl)titanate. Other components and parameters are the same as in Specific Embodiments One to Eight.

[0042] Specific Embodiment Ten: The curing agent described in this embodiment is one or a mixture of several of the following: 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-bis(4-(3-aminophenoxy)phenyl)propane, and 4,4'-bis(3-aminophenoxy)diphenyl sulfone. Other components and parameters are the same as in Specific Embodiments One to Nine.

[0043] The curing agent selected in this invention is an aromatic amine curing agent that combines high temperature resistance and a certain degree of flexibility.

[0044] Specific Implementation Method Eleven: This implementation method for preparing low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste includes the following steps:

[0045] Step 1: Weigh the following raw materials according to the following weight proportions: 5-10 parts of amide-containing trifunctional benzoxazine resin, 10-25 parts of amide-containing difunctional benzoxazine resin, 2-6 parts of amide-containing monofunctional benzoxazine resin, 30-60 parts of polyfunctional epoxy resin, 20-40 parts of bisphenol A type epoxy resin, 8-20 parts of toughening agent, 15-30 parts of hollow glass microspheres, 1-3 parts of coupling agent, 2-5 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 16-30 parts of curing agent;

[0046] Step 2: Add the amide-containing trifunctional benzoxazine resin, amide-containing difunctional benzoxazine resin, amide-containing monofunctional benzoxazine resin, multifunctional epoxy resin, bisphenol A type epoxy resin, and toughening agent to a reactor equipped with a heating and stirring device. Heat to 120℃~150℃ and stir at 500 r / min~1000 r / min for 1 h~4 h to obtain a uniform resin premix. Then cool to 80℃~110℃, add hollow glass microspheres, coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and stir at 100 r / min~500 r / min for 0.5 h~2 h to obtain an intermediate product.

[0047] Step 3: Add curing agent to intermediate product and stir at 200 r / min to 600 r / min for 0.5 h to 1 h at room temperature to obtain the low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste.

[0048] The paste-like adhesive prepared in this invention, after curing at 120℃ / 3h + 180℃ / 2h, has a density of less than 0.9 g / cm³, a room temperature shear strength greater than 30 MPa, and a floating roller peel strength greater than 3.5 kN / m. Under a constant load of 5.5 MPa at 177℃ for 1000 h, the shear creep deformation is ≤0.20 mm. Under stress ratio R=0.1, frequency 10 Hz, and maximum stress of 10 MPa, the fatigue test passed 1.0 × 10⁻⁶. 6 No damage occurred.

[0049] The embodiments of the present invention will be described in detail below. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation schemes and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0050] Example 1:

[0051] The preparation method of the low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste in this embodiment is specifically carried out according to the following steps:

[0052] Step 1: Weigh out the following components by weight: 8 parts of amide-containing trifunctional benzoxazine resin, 18 parts of amide-containing difunctional benzoxazine resin, 4 parts of amide-containing monofunctional benzoxazine resin, 45 parts of polyfunctional epoxy resin, 30 parts of bisphenol A type epoxy resin, 12 parts of toughening agent, 20 parts of hollow glass microspheres, 2 parts of coupling agent, 3 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 22 parts of curing agent.

[0053] The molecular structure of the amide-containing trifunctional benzoxazine resin is as follows:

[0054] .

[0055] The molecular structure of the amide-containing bifunctional benzoxazine resin is as follows:

[0056] .

[0057] The molecular structure of the amide-containing monofunctional benzoxazine resin is as follows:

[0058] .

[0059] The multifunctional epoxy resin is AG80, the bisphenol A type epoxy resin is E51, the toughening agent is carboxyl-terminated liquid nitrile rubber, and the density of the hollow glass microspheres is 0.30 g / cm³. 3 The coupling agent is γ-aminopropyltrimethoxysilane, and the curing agent is 4,4'-diaminodiphenyl ether.

[0060] Step 2: Weigh the amide-containing trifunctional benzoxazine resin, amide-containing difunctional benzoxazine resin, amide-containing monofunctional benzoxazine resin, polyfunctional epoxy resin, bisphenol A type epoxy resin, and toughening agent into a reactor equipped with a heating and stirring device. Heat to 130℃ and stir at 800 r / min for 2 h to obtain a homogeneous resin premix. Then, cool the reactor to 100℃, add hollow glass microspheres, a coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and stir at 300 r / min for 1 h to obtain an intermediate product.

[0061] Step 3: Add curing agent to the intermediate product obtained in step 2, and stir and mix at 400 r / min for 0.5 h at room temperature to obtain a uniform low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste.

[0062] Example 2:

[0063] The preparation method of the low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste in this embodiment is specifically carried out according to the following steps:

[0064] Step 1: Weigh out the following components by weight: 8 parts of amide-containing trifunctional benzoxazine resin, 22 parts of amide-containing difunctional benzoxazine resin, 5 parts of amide-containing monofunctional benzoxazine resin, 38 parts of polyfunctional epoxy resin, 35 parts of bisphenol A type epoxy resin, 15 parts of toughening agent, 24 parts of hollow glass microspheres, 2.5 parts of coupling agent, 2 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 25 parts of curing agent.

[0065] The molecular structure of the amide-containing trifunctional benzoxazine resin is as follows:

[0066] .

[0067] The molecular structure of the amide-containing bifunctional benzoxazine resin is as follows:

[0068] .

[0069] The molecular structure of the amide-containing monofunctional benzoxazine resin is as follows:

[0070] .

[0071] The multifunctional epoxy resin is a mixture of AG70 and F44 in a 1:1 mass ratio; the bisphenol A type epoxy resin is a mixture of E44 and E51 in a 2:5 mass ratio; the toughening agent is amino-terminated liquid nitrile rubber; and the density of the hollow glass microspheres is 0.33 g / cm³. 3 The coupling agent is isopropyltris(isostearoyl)titanate, and the curing agent is 2,2'-bis(4-(3-aminophenoxy)phenyl)propane.

[0072] Step 2: Weigh the amide-containing trifunctional benzoxazine resin, amide-containing difunctional benzoxazine resin, amide-containing monofunctional benzoxazine resin, polyfunctional epoxy resin, bisphenol A type epoxy resin, and toughening agent into a reactor equipped with a heating and stirring device. Heat to 140℃ and stir at 600 r / min for 3 h to obtain a homogeneous resin premix. Then, cool the reactor to 90℃, add hollow glass microspheres, a coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and stir at 500 r / min for 1.5 h to obtain an intermediate product.

[0073] Step 3: Add curing agent to the intermediate product obtained in step 2, and stir and mix at 300 r / min for 1 h at room temperature to obtain a uniform low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste.

[0074] Example 3:

[0075] The preparation method of the low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste in this embodiment is specifically carried out according to the following steps:

[0076] Step 1: Weigh out the following components by weight: 6 parts of amide-containing trifunctional benzoxazine resin, 12 parts of amide-containing difunctional benzoxazine resin, 6 parts of amide-containing monofunctional benzoxazine resin, 55 parts of polyfunctional epoxy resin, 20 parts of bisphenol A type epoxy resin, 10 parts of toughening agent, 27 parts of hollow glass microspheres, 1.5 parts of coupling agent, 3 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 19 parts of curing agent.

[0077] The molecular structure of the amide-containing trifunctional benzoxazine resin is as follows:

[0078] .

[0079] The molecular structure of the amide-containing bifunctional benzoxazine resin is as follows:

[0080] .

[0081] The molecular structure of the amide-containing monofunctional benzoxazine resin is as follows:

[0082] .

[0083] The multifunctional epoxy resin is a mixture of AG70, TDE85, and F48 in a mass ratio of 1:3:1; the bisphenol A type epoxy resin is E54; the toughening agent is terminal epoxy-terminated liquid nitrile rubber; and the density of the hollow glass microspheres is 0.38 g / cm³. 3 The coupling agent is isopropyltris(dioctylpyrophosphoryloxy)titanate, and the curing agent is a mixture of 3,3'-diaminobenzophenone and 4,4'-bis(3-aminophenoxy)diphenyl sulfone in a mass ratio of 1:1.

[0084] Step 2: Weigh the amide-containing trifunctional benzoxazine resin, amide-containing difunctional benzoxazine resin, amide-containing monofunctional benzoxazine resin, polyfunctional epoxy resin, bisphenol A type epoxy resin, and toughening agent into a reactor equipped with a heating and stirring device. Heat to 120°C and stir at 1000 r / min for 1.5 h to obtain a homogeneous resin premix. Then, cool the reactor to 80°C, add hollow glass microspheres, a coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and stir at 200 r / min for 0.5 h to obtain an intermediate product.

[0085] Step 3: Add curing agent to the intermediate product obtained in step 2, and stir and mix at 550 r / min for 1 h at room temperature to obtain a uniform low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste.

[0086] Example 4:

[0087] The preparation method of the low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste in this embodiment is specifically carried out according to the following steps:

[0088] Step 1: Weigh out the following components by weight: 10 parts of amide-containing trifunctional benzoxazine resin, 15 parts of amide-containing difunctional benzoxazine resin, 2 parts of amide-containing monofunctional benzoxazine resin, 40 parts of polyfunctional epoxy resin, 25 parts of bisphenol A type epoxy resin, 18 parts of toughening agent, 15 parts of hollow glass microspheres, 3 parts of coupling agent, 2.5 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 28 parts of curing agent.

[0089] The molecular structure of the amide-containing trifunctional benzoxazine resin is as follows:

[0090] .

[0091] The molecular structure of the amide-containing bifunctional benzoxazine resin is as follows:

[0092] .

[0093] The molecular structure of the amide-containing monofunctional benzoxazine resin is as follows:

[0094] .

[0095] The multifunctional epoxy resin is a mixture of AG70 and AG80 in a mass ratio of 1:3; the bisphenol A type epoxy resin is a mixture of E44 and E54 in a mass ratio of 1:2; the toughening agent is carboxyl-terminated liquid nitrile rubber; and the density of the hollow glass microspheres is 0.25 g / cm³. 3 The coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane, and the curing agent is 3,4'-diaminodiphenyl ether.

[0096] Step 2: Weigh the amide-containing trifunctional benzoxazine resin, amide-containing difunctional benzoxazine resin, amide-containing monofunctional benzoxazine resin, polyfunctional epoxy resin, bisphenol A type epoxy resin, and toughening agent into a reactor equipped with a heating and stirring device. Heat to 130℃ and stir at 550 r / min for 4 hours to obtain a homogeneous resin premix. Then, cool the reactor to 110℃, add hollow glass microspheres, a coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and stir at 120 r / min for 2 hours to obtain an intermediate product.

[0097] Step 3: Add curing agent to the intermediate product obtained in step 2, and stir and mix at 250 r / min for 0.5 h at room temperature to obtain a uniform low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste.

[0098] Comparative Example 1:

[0099] The difference between this comparative example and Example 1 is that: in step one, neither amide-containing trifunctional benzoxazine resin nor amide-containing monofunctional benzoxazine resin is added, and the amount of amide-containing difunctional benzoxazine resin is adjusted to 30 parts. Other components, amounts, steps and parameters are the same as in Example 1.

[0100] Comparative Example 2:

[0101] The difference between this comparative example and Example 1 is that: in step one, no amide-containing trifunctional benzoxazine resin is added, the amide-containing monofunctional benzoxazine resin is still 4 parts, and the amount of amide-containing difunctional benzoxazine resin is adjusted to 26 parts. Other components, amounts, steps and parameters are the same as in Example 1.

[0102] Comparative Example 3:

[0103] The difference between this comparative example and Example 1 is that: in step one, the amide-containing trifunctional benzoxazine resin, the amide-containing difunctional benzoxazine resin, and the amide-containing monofunctional benzoxazine resin were not used; all were replaced with commercially available common difunctional benzoxazine resins, the molecular structure of which is: The other components, dosages, steps, and parameters are the same as in Example 1.

[0104] Comparative Example 4:

[0105] The difference between this comparative example and Example 1 is that 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid is not added in step one, while the other components, amounts, steps and parameters are the same as in Example 1.

[0106] Comparative Example 5:

[0107] The difference between this comparative example and Example 1 is that: in step one, the multifunctional epoxy resin AG80 is not added, and the amount of bisphenol A type epoxy resin E51 is adjusted to 75 parts (keeping the total number of epoxy resin parts unchanged at 75 parts). Other components, amounts, steps and parameters are the same as in Example 1.

[0108] Comparative Example 6:

[0109] The difference between this comparative example and Example 1 is that no carboxyl-terminated liquid nitrile rubber is added in step one, while the other components, dosages, steps, and parameters are the same as in Example 1.

[0110] The epoxy resin adhesives prepared in Examples 1 to 4 and the adhesives prepared in Comparative Examples 1 to 6 were cured at 120℃ / 3h + 180℃ / 2h and their performance was tested. The results are shown in Table 1.

[0111] The testing standards adopted are as follows:

[0112] (1) Density: Tested according to Method A immersion method in GB / T 1033.1-2008 standard.

[0113] (2) Room temperature shear strength: The bonded material is 2A12 aluminum alloy. Before bonding, the surface is subjected to phosphoric acid anodizing treatment. After curing, the test is carried out according to GB / T 7124-2008 standard.

[0114] (3) Peel strength of floating roll: Tested according to GB / T 7122-2025 standard.

[0115] (4) Shear creep: The test was conducted according to GB / T 7750-1987 standard. The test temperature was 177℃. The deformation of the adhesive layer after 1000h under a constant load of 5.5MPa was recorded, i.e., creep deformation at 177℃ / 5.5MPa / 1000h.

[0116] (5) Fatigue test: The test shall be conducted in accordance with GB / T 27595-2011 standard. Among them, the stress ratio R=0.1, the frequency is 10 Hz, and the maximum stress is 10 MPa.

[0117] Table 1 Performance Summary Table

[0118]

[0119] (1) The test results from Examples 1 to 4 show that the low-density, high-temperature creep-resistant benzoxazine hybrid epoxy paste prepared in this invention, after curing at 120℃ / 3h + 180℃ / 2h, has a density of less than 0.9 g / cm³, a room temperature shear strength greater than 30 MPa, and a floating roller peel strength greater than 3.5 kN / m; under a constant load of 5.5 MPa at 177℃ for 1000 h, the shear creep deformation is ≤0.20 mm; under a sinusoidal load with a stress ratio R=0.1 and a frequency of 10 Hz, the maximum load is 10 MPa, and the fatigue test passes 1.0×10 6 No damage occurred. It possesses multiple characteristics including low density, high adhesive strength, high-temperature creep resistance, and long fatigue life. This invention achieves precise control of the cross-linked network structure through the accurate compounding of three benzoxazine compounds with different functionalities, simultaneously achieving low density (≤0.9 g / cm³). 3 It exhibits high-temperature creep resistance (≤0.20 mm) at 177℃.

[0120] (2) Combining the technical solutions of Comparative Example 1, Comparative Example 2, and Example 1, it can be seen from the data in Table 1 that Comparative Example 1 only used amide-containing difunctional benzoxazine resin, while amide-containing trifunctional and monofunctional benzoxazine resins were omitted. Comparative Example 2 only used amide-containing monofunctional benzoxazine resin and amide-containing difunctional benzoxazine resin. The prepared paste adhesive had relatively low room temperature shear strength and floating roll peel strength. Under a constant load of 5.5 MPa at 177°C for 1000 h, the shear creep deformation exceeded 0.25 mm. At the same time, the fatigue test failed to pass the 1.0 × 10⁻⁶ test. 6 This indicates that benzoxazine resins containing amide groups—trifunctional, difunctional, and monofunctional—are all indispensable; otherwise, it is impossible to construct a three-dimensional cross-linked network with multiple hydrogen bonds through compounding with various epoxy resins. Furthermore, the synergistic effect of benzoxazine resins with different functionalities in regulating cross-linking density and chain segment flexibility cannot be utilized, resulting in relatively poor creep resistance.

[0121] (3) Combining the technical solutions of Comparative Example 3 and Example 1, it can be seen from the data in Table 1 that in Comparative Example 3, commercially available ordinary difunctional benzoxazine was used to replace the amide-containing trifunctional, difunctional, and monofunctional benzoxazine resins of the present invention, and its molecular structure does not contain amide groups and branched side chains. The results show that the creep deformation of Comparative Example 3 is as high as 0.57 mm, at which point the adhesive layer has cracked and the bonded part has failed. The fatigue test result is only 5.2 × 10⁻⁶ mm. 4 The room temperature shear strength (20.8 MPa) and floating roll peel strength (1.7 kN / m) were significantly lower than those in Example 1. This indicates that the amide groups and the multiple hydrogen bond network they form are the core mechanism of the creep resistance of this invention. The multiple hydrogen bonds formed between amide groups and between amide groups and the hydroxyl groups generated by ring opening of epoxy and benzoxazine act like "molecular springs," reversibly breaking and reconstructing at high temperatures, effectively dissipating creep energy. Ordinary benzoxazine lacks this structural feature and cannot form a multiple hydrogen bond reinforcement network with other components of this invention, demonstrating the uniqueness and irreplaceability of the amide-containing benzoxazine resin structural design of this invention.

[0122] (4) Combining the technical solutions of Comparative Example 4 and Example 1, it can be seen from the data in Table 1 that Comparative Example 4 did not add 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid. The results show that the room temperature shear strength and floating roll peel strength are 26.5 MPa and 2.8 kN / m, respectively, which are significantly lower than those of Example 1; the creep deformation at 177℃ reaches 0.48 mm, at which point the adhesive layer has cracked and the bonded part has failed. The fatigue test result is only 2.1 × 10 5This indicates that the 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, uniquely introduced in this invention, serves as a dual-functional additive for interfacial compatibility and high-temperature resistance. The carboxyl groups in its molecular structure can form chemical bonds with the surface of hollow glass microspheres and the resin matrix, significantly improving the interfacial bonding force between the lightweight filler and the matrix, thus preventing the degradation of adhesive performance due to reduced density. Simultaneously, its nitrogen-containing fused heterocyclic structure further enhances the thermal stability of the adhesive. Without this additive, weakened interfacial bonding leads to increased creep and decreased fatigue life. This additive is a key component for achieving a synergistic effect of low density, high creep resistance, and high fatigue life.

[0123] (5) Combining the technical solutions of Comparative Example 5 and Example 1, it can be seen from the data in Table 1 that the multifunctional epoxy resin AG80 was omitted in Comparative Example 5, and only bisphenol A type epoxy resin was used. The results show that the creep deformation increased to 0.52 mm, at which point the adhesive layer had already cracked, and the bonded part failed. The fatigue test result decreased to 7.5 × 10⁻⁶ mm. 4 This fully demonstrates that the high crosslinking density and rigid network skeleton provided by multifunctional epoxy resin are essential for the paste adhesive of this invention to withstand long-term high-temperature loads of 177°C. Although bisphenol A type epoxy resin has good processability, its crosslinking density is limited and cannot effectively suppress molecular chain slippage at high temperatures. This invention, through the compounding of multifunctional epoxy and bisphenol A type epoxy, balances processability and high-temperature creep resistance.

[0124] (6) Combining the technical solutions of Comparative Example 6 and Example 1, it can be seen from the data in Table 1 that Comparative Example 6 did not add a carboxyl-terminated liquid nitrile rubber toughening agent, and the other components were the same as in Example 1. The results show that the room temperature shear strength of Comparative Example 6 dropped sharply to 19.4 MPa, and the floating roll peel strength was only 1.5 kN / m, which was much lower than that of Example 1; the creep deformation at 177℃ reached 0.50 mm and the rubber layer cracked, and the fatigue test result was only 6.1 × 10⁻⁶. 4 This indicates that the lack of a liquid nitrile rubber toughening agent in this invention prevents it from producing a synergistic toughening effect with the branched side chains and numerous ether bonds in the amide-containing benzoxazine resin molecular structure. Consequently, the flexible stress dispersion micro-regions formed in the three-dimensional cross-linked network are limited, failing to effectively alleviate curing internal stress and inhibit crack propagation. This results in poor impact resistance, significantly deteriorated shear strength and peel strength, and a sharp decline in high-temperature creep resistance and fatigue resistance.

Claims

1. A low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste, characterized in that, The paste-like adhesive is prepared from the following raw materials in parts by weight: 5-10 parts of amide-containing trifunctional benzoxazine resin, 10-25 parts of amide-containing difunctional benzoxazine resin, 2-6 parts of amide-containing monofunctional benzoxazine resin, 30-60 parts of polyfunctional epoxy resin, 20-40 parts of bisphenol A type epoxy resin, 8-20 parts of toughening agent, 15-30 parts of hollow glass microspheres, 1-3 parts of coupling agent, 2-5 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 16-30 parts of curing agent.

2. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 1, characterized in that, The molecular structural formula of the amide-containing trifunctional benzoxazine resin is: 。 3. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 2, characterized in that, The molecular structure of the amide-containing bifunctional benzoxazine resin is any one of the following: 、 、 。 4. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 3, characterized in that, The molecular structure of the amide-containing monofunctional benzoxazine resin is any one of the following: 、 。 5. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 4, characterized in that, The multifunctional epoxy resin is one or a mixture of several of AG70, AG80, TDE-85, F44, F48, and F51.

6. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 5, characterized in that, The bisphenol A type epoxy resin is one or a mixture of several of E44, E51, and E54.

7. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 6, characterized in that, The toughening agent is liquid nitrile rubber.

8. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 7, characterized in that, The density of the hollow glass microspheres is 0.25~0.46 g / cm³. 3 .

9. The low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to claim 8, characterized in that, The coupling agent is γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, isopropyltris(dioctylpyrophosphate)titanate or isopropyltris(isostearoyl)titanate.

10. The method for preparing the low-density, high-temperature, creep-resistant benzoxazine hybrid epoxy paste according to any one of claims 1 to 9, characterized in that, The method includes the following steps: Step 1: Weigh the following raw materials according to the following weight proportions: 5-10 parts of amide-containing trifunctional benzoxazine resin, 10-25 parts of amide-containing difunctional benzoxazine resin, 2-6 parts of amide-containing monofunctional benzoxazine resin, 30-60 parts of polyfunctional epoxy resin, 20-40 parts of bisphenol A type epoxy resin, 8-20 parts of toughening agent, 15-30 parts of hollow glass microspheres, 1-3 parts of coupling agent, 2-5 parts of 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and 16-30 parts of curing agent; Step 2: Add the amide-containing trifunctional benzoxazine resin, the amide-containing difunctional benzoxazine resin, the amide-containing monofunctional benzoxazine resin, the polyfunctional epoxy resin, the bisphenol A type epoxy resin, and the toughening agent to a reactor equipped with a heating and stirring device. Heat the mixture to 120℃~150℃ and stir to obtain a uniform resin premix. Then cool the mixture to 80℃~110℃, add hollow glass microspheres, a coupling agent, and 2-methyl-pyrazolo[1,5-A]pyrimidine-6-carboxylic acid, and stir to obtain an intermediate product. Step 3: Add curing agent to intermediate product and stir to mix at room temperature to obtain low-density high-temperature creep-resistant benzoxazine hybrid epoxy paste.

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