Low-temperature-resistant epoxy adhesive composition and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, in particular to a low-temperature-resistant epoxy adhesive composition and a preparation method thereof. The low-temperature-resistant epoxy adhesive composition is prepared from the following raw materials in parts by mass: 100 parts of bisphenol epoxy resin, 125 to 145 parts of a modified polyamide curing agent, 10 to 20 parts of a flame retardant, 10 to 20 parts of a toughening agent and 5 to 20 parts of a reinforcing agent, the synthesis method of the modified polyamide curing agent comprises the following steps: under the protection of inert gas, heating polyacid to 120-200 DEG C, dropwise adding three-arm amine into a reaction system, and stirring to react for 2-10 hours; and finally, cooling the reaction material, then carrying out reduced pressure distillation to remove moisture in the system, and cooling to obtain the modified polyamide curing agent. The epoxy adhesive material prepared by the invention can maintain excellent mechanical strength and flexibility in a low-temperature environment, has better low-temperature resistance, and can meet the use requirements of polar equipment exposed to extremely cold and severe working conditions for a long time.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a low-temperature resistant epoxy adhesive composition and its preparation method. Background Technology

[0002] Epoxy adhesives, with their excellent bonding properties, chemical stability, and long-term durability, have become key materials in many fields such as aerospace, automotive, electronic packaging, and marine engineering. However, conventional epoxy adhesives suffer from limited molecular chain movement at low temperatures (≤-40℃), making it difficult to release internal stress and leading to increased brittleness and a significant decrease in bond strength. This technical bottleneck severely restricts their engineering applications in cold regions and extreme environments. For example, in polar equipment, high-altitude facilities, or cryogenic storage and transportation equipment, epoxy adhesives need to maintain high strength while possessing good flexibility and impact resistance, requirements that ordinary epoxy resin systems struggle to meet.

[0003] To address the low-temperature performance bottleneck of epoxy adhesives, current research focuses on toughening and modifying the epoxy resin matrix or curing agent. This is primarily achieved through chemical grafting or physical blending to introduce flexible structures such as flexible alkyl chains, ether-containing segments, and polyether polyols. These flexible units' molecular mobility at low temperatures enhances the system's flexibility. However, while improving low-temperature performance, these methods often sacrifice material strength and disrupt the original reactivity balance of the epoxy resin. Such materials struggle to simultaneously maintain mechanical strength (tensile strength > 20 MPa), adhesive properties (tensile shear strength > 10 MPa), and flexibility (elongation > 20%) at low temperatures. Furthermore, they lead to increased curing temperatures (some systems require over 100℃ for complete curing) and prolonged curing times (5-7 days or more at room temperature). This places higher demands on construction equipment, increases energy consumption and operational difficulty during large-area construction, and limits their application in environments where heating is not possible. In summary, existing research has not been able to effectively solve the technical challenges of achieving high flexibility, high mechanical strength, and bonding performance of epoxy adhesives in low-temperature environments, thus restricting the application of epoxy adhesives in low-temperature environments. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned shortcomings of the prior art by providing a low-temperature resistant epoxy adhesive composition and its preparation method.

[0005] The first objective of this invention is to provide a low-temperature resistant epoxy adhesive composition comprising the following raw materials in parts by weight: 100 parts of bisphenol type epoxy resin, 125-145 parts of modified polyamide curing agent, 10-20 parts of flame retardant, 10-20 parts of toughening agent, and 5-20 parts of reinforcing agent. The synthesis method of modified polyamide curing agent is as follows: Under inert gas protection, the polyacid is heated to 120-200°C, the three-arm amine is added dropwise to the reaction system, and the reaction is stirred for 2-10 hours; finally, the reactants are cooled, and then the water in the system is removed by vacuum distillation, and cooled to obtain the modified polyamide curing agent; Polyacids include substances with the following structural formulas: , ; Three-arm amines include substances with the following structural formulas:

[0006] R3=(CH2CH2O) n CH2CH2, n=1-3; R4=C 24 H 33 N3O3.

[0007] Furthermore, the synthesis method of polyacid is as follows: 100 parts of docosatriene, 50-100 parts of conjugated linoleic acid and 0.9-1.2 parts of activated clay catalyst are added to a reaction vessel, and the temperature is increased to 200-250℃ at a rate of 5-10℃ / min, so that the pressure inside the reaction vessel is increased to 0.1-1.0MPa, and the reaction is carried out continuously for 4-8 hours under these conditions to finally obtain polyacid.

[0008] Furthermore, the synthesis method of the three-arm amine is as follows: 100g of hexamethylene diisocyanate trimer and 40-80g of oligoether diamine are mixed, heated to 60-100℃, and stirred for 4-10h to finally obtain the three-arm amine.

[0009] Furthermore, the molar ratio of oligoether diamine to dimer acid is (2.0-3.0):1.

[0010] Furthermore, the molar ratio of oligoether diamine to dimer acid is 2.5:1.

[0011] Furthermore, the bisphenol type epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin and allyl epoxy resin.

[0012] Furthermore, the flame retardant is selected from at least one of aluminum hydroxide, zinc borate, triphenyl phosphate, tricresyl phosphate, and guanidine polyphosphate.

[0013] Furthermore, the toughening agent is selected from at least one of the following nano-core-shell toughening agents: MX125 styrene-butadiene rubber core nano-core-shell toughening agent, MX154 butadiene rubber core nano-core-shell toughening agent, and MX960 organosilicon core nano-core-shell toughening agent.

[0014] Furthermore, the reinforcing agent is selected from at least one of kaolin, fumed silica, and carbon fiber.

[0015] The second objective of this invention is to provide a method for preparing the low-temperature resistant epoxy adhesive composition as described above, comprising the following steps: adding 100 parts of bisphenol type epoxy resin and 10-20 parts of toughening agent sequentially to a vacuum mixing tank and stirring thoroughly, degassing under vacuum, stirring evenly and then discharging the mixture, followed by grinding and dispersing using a three-roll mill to obtain component A; adding 125-145 parts of modified polyamide curing agent, 5-20 parts of reinforcing agent and 10-20 parts of flame retardant to a vacuum mixing tank and dispersing thoroughly and evenly, degassing under vacuum, stirring evenly and then discharging the mixture to obtain component B; mixing component A and component B evenly and then curing.

[0016] This invention utilizes polyacids and tri-arm amine molecules to precisely design modified polyamide curing agents. Based on the controllable reaction between the abundant carboxyl groups in polyacids and tri-arm amines, it achieves precise control over the types, distribution, and reactivity of functional groups in the adhesive system, constructing a flexible crosslinking network adapted to low-temperature environments and a high crosslinking density. This enables the adhesive to possess excellent tensile and shear strengths, effectively resisting the damage to the bonding structure caused by low-temperature environments.

[0017] The modified polyamide curing agent provided by this invention features polyacid molecules with long carbon chains and three-arm amine molecules with long polyether segments. When these molecules participate in the construction of the polymer network, the long-chain structures act as "flexible bridges," interweaving within the network system and reducing the local regularity of the polymer network. At low temperatures, the molecular chains are more prone to twisting and oscillation, effectively promoting the dynamic movement of the molecular chains and significantly improving the overall flexibility of the material. This makes epoxy adhesive materials less prone to embrittlement and cracking due to excessive rigidity at low temperatures, better meeting the requirements for material flexibility under low-temperature conditions.

[0018] The polyacid provided by this invention contains a multi-arm long carbon chain structure, and the three-arm flexible amine contains polyether flexible segments. The multi-arm long carbon chain gives the adhesive molecular chain more flexible movement space, while the polyether flexible segments further enhance the flexibility of the molecular chain. The two work synergistically to significantly improve the flexibility of the adhesive, enabling the adhesive to maintain good deformation ability even at low temperatures. At the same time, the multifunctional structure can precisely control the crosslinking density of the polymer, ensuring its mechanical strength at low temperatures.

[0019] This invention innovatively provides a variety of low molecular weight polyacids and three-arm flexible amines. These raw materials combine the advantages of multifunctionality and long-chain structure. Multifunctionality increases intermolecular reaction sites, while the long-chain structure ensures molecular chain flexibility and interaction. Based on this, their components can be flexibly compounded over a wide range, and by adjusting the ratio of different polyacids and three-arm flexible amines, curing requirements at room temperature and low temperature environments can be met.

[0020] Experimental results show that the epoxy adhesive material prepared by this invention exhibits excellent performance due to the advantages of its molecular structure design, with a mechanical strength >20 MPa and an elongation >20%. Therefore, it can still maintain excellent mechanical strength and flexibility in low-temperature environments and has good low-temperature resistance, which can meet the requirements of polar equipment that is exposed to extreme cold and harsh working conditions for a long time. Attached Figure Description

[0021] Figure 1 The infrared spectrum of the modified polyamide curing agent prepared in Example 3 is shown. Detailed Implementation

[0022] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0023] The following are some of the raw materials used in this embodiment and comparative example: The main reactions for the synthesis of polyacids are shown below:

[0024] The main reactions for the synthesis of three-armed amines are shown below:

[0025] Wherein, R3=(CH2CH2O) n CH2CH2, n=1-3. R4(NCO)3 is specifically a hexamethylene diisocyanate trimer.

[0026] The main reactions in the synthesis of polyamide curing agents are shown below:

[0027] In this context, R5 represents the three-arm amine segment, and R6 represents a polyacid or H.

[0028] Example 1 Synthesis method of raw materials for modified polyamide curing agents: The first step is the synthesis of polyacids: 100g of dodecanetriene, 60g of conjugated linoleic acid and 1.0g of activated clay catalyst are added to the reactor, and the temperature is increased to 200℃ at a rate of 5℃ / min, so that the pressure inside the reactor is increased to 0.5MPa. The reaction is carried out continuously for 6 hours under these conditions to finally obtain polyacids.

[0029] The second step is the synthesis of the three-armed amine: 100g of hexamethylene diisocyanate trimer and 80g of oligoether diamine are mixed, heated to 100℃, and stirred for 6 hours to finally obtain the three-armed amine.

[0030] Example 2 Under inert gas protection, 100g of the polyacid prepared in Example 1 was heated to 120-200°C, and 60.1g of the tri-arm amine prepared in Example 1 was added dropwise to the reaction system. The mixture was stirred and reacted for 2-10 hours. Finally, the reactants were cooled, and the water in the system was removed by vacuum distillation. After cooling, the modified polyamide curing agent was obtained. The molar ratio of the tri-arm amine to the polyacid was 2.5:1.

[0031] The modified polyamide was tested and found to have an ammonia value of 125 mg / KOH / g and a viscosity of 35600 cP.

[0032] Figure 1 The infrared spectrum of the modified polyamide curing agent prepared in this embodiment is shown. The infrared spectrum indicates that the 2800-3000 cm⁻¹... -1 The peak vibration indicates the presence of methyl and methylene groups. (1050 cm⁻¹) -1 The peak vibration indicates the presence of CO bonds, demonstrating the successful introduction of the ether-containing segment. (1600-1800 cm⁻¹) -1 The peak vibration indicates the formation of amide bonds.

[0033] Example 3 Under inert gas protection, 100g of the polyacid prepared in Example 1 was heated to 120-200°C, and 60.1g of the tri-arm amine prepared in Example 1 was added dropwise to the reaction system. The mixture was stirred and reacted for 2-10 hours. Finally, the reactants were cooled, and the water in the system was removed by vacuum distillation. After cooling, the modified polyamide curing agent was obtained. The molar ratio of the tri-arm amine to the polyacid was 3.0:1.

[0034] The modified polyamide was tested and found to have an ammonia value of 175 mg / KOH / g and a viscosity of 2640 cP.

[0035] Example 4 Under inert gas protection, 100g of the polyacid prepared in Example 1 was heated to 120-200°C, and 60.1g of the tri-arm amine prepared in Example 1 was added dropwise to the reaction system. The mixture was stirred and reacted for 2-10 hours. Finally, the reactants were cooled, and the water in the system was removed by vacuum distillation. After cooling, the modified polyamide curing agent was obtained. The molar ratio of the tri-arm amine to the polyacid was 3.5:1.

[0036] The modified polyamide was tested and found to have an ammonia value of 246 mg / KOH / g and a viscosity of 738 cP.

[0037] Table 1 Examples 2-4 and Test Results

[0038] Table 2. Gel chromatography test results for polyacids, tri-arm amines, and Examples 2-4

[0039] Gel chromatography results showed that the polyacid's molecular weight was between that of the dimer and trimer, and its molecular weight distribution was narrow, indicating that the system formed a complex mainly composed of dimers and trimers. The molecular weight of the three-arm amine was similar to that of the trimer, and its molecular weight distribution was also narrow, indicating that the system formed a complex mainly composed of trimers. Examples 2-4 showed that adjusting the ammonia value had a significant impact on the molecular weight of the polyamide curing agent. Among them, Example 3 had a moderate molecular weight, ensuring molecular linkage and appropriate viscosity, which was beneficial for processing and performance improvement. Therefore, Example 3 was selected as the preferred curing agent.

[0040] Example 5 100g of bisphenol-type epoxy resin and 10g of toughening agent were sequentially added to a vacuum mixing vessel and stirred thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged. The mixture was then dispersed by grinding with a three-roll mill to obtain component A. In the second step, 125g of the modified polyamide curing agent, 10g of the reinforcing agent, and 10g of the flame retardant prepared in Example 3 were added to a vacuum mixing vessel and dispersed thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged to obtain component B. Finally, components A and B were mixed thoroughly and cured to obtain the epoxy adhesive.

[0041] The product underwent performance testing at 25°C. The tensile strength was 20.5 MPa, the shear strength was 12.5 MPa, and the elongation at break was 60%.

[0042] Example 6 100g of bisphenol-type epoxy resin and 10g of toughening agent were sequentially added to a vacuum mixing vessel and stirred thoroughly. After vacuum degassing and uniform mixing, the mixture was discharged and then dispersed through a three-roll mill to obtain component A. In the second step, 135g of the modified polyamide curing agent, 10g of the reinforcing agent, and 10g of the flame retardant prepared in Example 3 were added to a vacuum mixing vessel and dispersed thoroughly. After vacuum degassing and uniform mixing, the mixture was discharged to obtain component B. Finally, components A and B were mixed thoroughly and cured to obtain the epoxy adhesive.

[0043] The product underwent performance testing at 25°C. The tensile strength was 31.4 MPa, the shear strength was 17.4 MPa, and the elongation at break was 39%.

[0044] Example 7 100g of bisphenol-type epoxy resin and 10g of toughening agent were sequentially added to a vacuum mixing vessel and stirred thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged. The mixture was then dispersed by grinding with a three-roll mill to obtain component A. In the second step, 145g of the modified polyamide curing agent, 10g of the reinforcing agent, and 10g of the flame retardant prepared in Example 3 were added to a vacuum mixing vessel and dispersed thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged to obtain component B. Finally, components A and B were mixed thoroughly and cured to obtain the epoxy adhesive.

[0045] The product underwent performance testing at 25°C. The tensile strength was 34.1 MPa, the shear strength was 15.1 MPa, and the elongation at break was 20%.

[0046] Example 8 100g of bisphenol-type epoxy resin and 15g of toughening agent were sequentially added to a vacuum mixing tank and stirred thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged. The mixture was then dispersed by grinding with a three-roll mill to obtain component A. In the second step, 135g of the modified polyamide curing agent, 10g of the reinforcing agent, and 15g of the flame retardant prepared in Example 3 were added to a vacuum mixing tank and dispersed thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged to obtain component B. Finally, components A and B were mixed thoroughly and cured to obtain the epoxy adhesive.

[0047] The product underwent performance testing at 25°C. The tensile strength was 27.5 MPa, the shear strength was 13.2 MPa, and the elongation at break was 25%.

[0048] Comparative Example 1 100g of bisphenol-type epoxy resin and 15g of toughening agent were sequentially added to a vacuum mixing vessel and stirred thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged. The mixture was then dispersed by grinding with a three-roll mill to obtain component A. In the second step, 135g of the modified polyamide curing agent, 15g of the reinforcing agent, and 15g of the flame retardant prepared in Example 3 were added to a vacuum mixing vessel and dispersed thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged to obtain component B. Finally, components A and B were mixed thoroughly and cured to obtain the epoxy adhesive.

[0049] The product underwent performance testing at 25°C. The tensile strength was 29.2 MPa, the shear strength was 11.4 MPa, and the elongation at break was 12%.

[0050] Comparative Example 2 First, 100g of bisphenol-type epoxy resin and 10g of toughening agent were sequentially added to a vacuum mixing tank and stirred thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged. The mixture was then dispersed by grinding using a three-roll mill to obtain component A. Second, 135g of polyamide 650 curing agent, 10g of reinforcing agent, and 10g of flame retardant were added to the vacuum mixing tank and dispersed thoroughly. The mixture was then degassed under vacuum, stirred until homogeneous, and discharged to obtain component B. Finally, components A and B were mixed thoroughly and cured to obtain the epoxy adhesive.

[0051] The product underwent performance testing at 25°C. The tensile strength was 31.5 MPa, the shear strength was 15.3 MPa, and the elongation at break was 4.9%.

[0052] Comparative Example 3 First, 100g of bisphenol-type epoxy resin and 10g of toughening agent were sequentially added to a vacuum mixing tank and stirred thoroughly. After vacuum degassing and uniform mixing, the mixture was discharged and then dispersed through a three-roll mill to obtain component A. Second, 135g of polyamide 651 curing agent, 10g of reinforcing agent, and 10g of flame retardant were added to the vacuum mixing tank and dispersed thoroughly. After vacuum degassing and uniform mixing, the mixture was discharged to obtain component B. Finally, components A and B were mixed thoroughly and cured to obtain the epoxy adhesive.

[0053] The product underwent performance testing at 25°C. The tensile strength was 33.1 MPa, the shear strength was 16.1 MPa, and the elongation at break was 3.3%.

[0054] Table 2 Test results of products from Examples 5-9 and Comparative Examples 1-2

[0055] The comparison between the examples and comparative examples shows that the low-temperature resistant epoxy adhesive composition prepared by the present invention utilizes polyacid and tri-arm amine molecules to precisely design the modified polyamide curing agent, thereby improving the flexibility and crosslinking density of the network. While ensuring its tensile strength and tensile shear strength, it effectively enhances the elongation at break of the material, that is, enhances its low-temperature resistance, and has obvious technical advantages. For any points not covered above, existing technologies shall apply.

[0056] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A low temperature resistant epoxy adhesive composition, characterized by, The raw materials include the following mass fractions: 100 parts of bisphenol type epoxy resin, 125-145 parts of modified polyamide curing agent, 10-20 parts of flame retardant, 10-20 parts of toughening agent, and 5-20 parts of reinforcing agent. The synthesis method of the modified polyamide curing agent is as follows: under the protection of inert gas, the polybasic acid is heated to 120-200°C, the tri-arm amine is added dropwise into the reaction system, and the reaction is stirred for 2-10 h; finally, the reaction material is cooled, and then water in the system is removed by distillation under reduced pressure, and the modified polyamide curing agent is obtained after cooling. The polybasic acid includes a substance with the following structural formula: 、 ； The tri-arm amine includes a substance with the following structural formula: R3= (CH2CH20) n CH2CH2, n = 1-3; R4= C 24 H 33 N3O3.

2. The low temperature resistant epoxy adhesive composition according to claim 1, wherein The synthesis method of the polybasic acid is as follows: 100 parts of docosatriene, 50-100 parts of conjugated linoleic acid, and 0.9-1.2 parts of activated clay catalyst are added into a reaction kettle, the temperature is increased to 200-250°C at a rate of 5-10°C / min, the pressure in the reaction kettle is increased to 0.1-1.0 MPa, and the continuous reaction is carried out under the above conditions for 4-8 h, and finally the polybasic acid is obtained.

3. The low temperature resistant epoxy adhesive composition according to claim 1, wherein The synthesis method of the tri-arm amine is as follows: 100 parts of hexamethylene diisocyanate trimer and 40-80 parts of oligomeric ether diamine are mixed, heated to 60-100°C, and stirred for 4-10 h, and finally the tri-arm amine is obtained.

4. A low temperature resistant epoxy adhesive composition as claimed in claim 3, wherein, The molar ratio of the oligomeric ether diamine to the dimeric acid is (2.0-3.0):

1.

5. A low temperature resistant epoxy adhesive composition as claimed in claim 4, wherein, The molar ratio of the oligomeric ether diamine to the dimeric acid is 2.5:

1.

6. A low temperature resistant epoxy adhesive composition as claimed in claim 1, wherein, The bisphenol type epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, and allyl epoxy resin.

7. A low temperature resistant epoxy adhesive composition as claimed in claim 1, wherein, The flame retardant is selected from at least one of aluminum hydroxide, zinc borate, triphenyl phosphate, tricresyl phosphate, and polyguanidine phosphate.

8. The low temperature resistant epoxy adhesive composition according to claim 1, wherein The toughening agent is selected from at least one of nano core-shell toughening agent: MX125 butadiene rubber core nano core-shell toughening agent, MX154 butadiene rubber core nano core-shell toughening agent, and MX960 silicone core nano core-shell toughening agent.

9. The low temperature resistant epoxy adhesive composition according to claim 1, wherein The reinforcing agent is selected from at least one of kaolin, fumed white carbon black, and carbon fiber.

10. A process for preparing a low temperature resistant epoxy adhesive composition as claimed in any one of claims 1 to 9, characterized in that, The method includes the following steps: 100 parts of bisphenol type epoxy resin, 10-20 parts of toughening agent, and 10-20 parts of flame retardant are sequentially added into a vacuum stirring kettle, and fully stirred, vacuum degassed, and discharged after uniform stirring; then, the A component is obtained after being ground and dispersed by a three-roll mill; 125-145 parts of modified polyamide curing agent, 5-20 parts of reinforcing agent, and 10-20 parts of flame retardant are added into a vacuum stirring kettle, and fully dispersed and uniform, vacuum degassed, and discharged after uniform stirring; the B component is obtained; and the A component and the B component are mixed uniformly, and then cured.

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