Liquid epoxy resin composite material repair adhesive and preparation method thereof

Abstract

The present invention relates to the technical field of epoxy resin composite material repair, and in particular to a liquid epoxy resin composite material repair adhesive and a preparation method thereof. In the preparation method, a powdered curing agent is mixed with a monofunctional epoxy resin to react, and then liquid imidazole is added and stirred to react to obtain a modified imidazole liquid curing agent; a thixotropic agent and a toughening agent are added to the epoxy resin, stirred evenly, and then cooled to room temperature to obtain a modified epoxy resin system; the modified epoxy resin system and the modified imidazole liquid curing agent are mixed evenly in proportion to obtain a liquid epoxy resin composite material repair adhesive. While ensuring a relatively high glass transition temperature of the epoxy resin, the curing temperature of the curing agent can be relatively low, and the mechanical properties of the adhesive remain unchanged when used under high temperature conditions. The heat resistance of the adhesive is better, and the repair adhesive can simultaneously meet the requirements of low-temperature curing and high-temperature use, and the processability of the adhesive can be guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resin composite material repair, in particular to a liquid epoxy resin composite material repair adhesive and a preparation method thereof. Background Art

[0002] Resin-based composites offer unique advantages such as high specific strength and stiffness, strong designability, excellent fatigue resistance, superior electromagnetic properties, good corrosion resistance, and easy integral molding. They have been widely used in the aviation field, effectively reducing aircraft structural weight and improving their technical and tactical performance. The extensive use of composite materials in aircraft also creates a series of problems. For example, defects or damage inevitably occur in composite components during production, use, and maintenance. Therefore, repairs are necessary to maintain the original performance of the composites and reduce the cost of their use and maintenance.

[0003] To ensure that the mechanical properties of the base material are not compromised, the International Aircraft Corporation Composite Repair Manual (SRM) and related technical reports clearly stipulate that the maximum curing temperature of the repair material should generally be approximately 30°C to 50°C lower than the curing temperature of the underlying composite material, or no higher than the maximum dry operating temperature of the composite structure. Repairs performed at the original curing temperature of the underlying structure carry a significant risk of delamination, deformation, and other issues. At the same time, the heat resistance rating of the base composite material must still be matched, requiring the repair adhesive to achieve high mechanical and heat resistance at a lower curing temperature. However, generally speaking, curing temperature directly affects the degree of cure and glass transition temperature of the epoxy resin. Lower curing temperatures result in lower glass transition temperatures and reduced heat resistance.

[0004] Low-temperature curing, high-heat-resistant epoxy resin adhesives are primarily made from multifunctional epoxy resins with rigid backbones or those that increase crosslink density, and curing agents. However, because the rigid backbone in the resin structure also increases steric hindrance during the reaction, it can be difficult to simultaneously meet the requirements of both low-temperature curing and high heat resistance. Currently, Cytec's FM-73 film, Henkel's EA 9696 film, and EA9390 two-component adhesives are commonly used for composite material repair. FM-73 and EA 9696 films cure at 125°C, with a long-term use temperature of 82°C after curing. EA9390 two-component adhesive can cure below 100°C and has a glass transition temperature of 140°C. However, these repair adhesives struggle to meet the requirements for high-temperature epoxy matrix composites, which typically have a glass transition temperature of 150°C.

[0005] Therefore, the inventors provide a method for preparing a liquid low-temperature curing high-heat-resistant epoxy resin composite material repair adhesive. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] The purpose of the present invention is to provide a liquid epoxy resin composite material repair adhesive and a preparation method thereof, so as to solve the technical problem that existing composite material repair adhesives are difficult to simultaneously meet the requirements of low temperature curing and high temperature use for high temperature epoxy matrix composite material repair.

[0008] (2) Technical solution

[0009] In a first aspect, the technical solution of the present invention provides a method for preparing a liquid epoxy resin composite material repair adhesive, which is characterized by comprising the steps of:

[0010] S1. The powdered curing agent is mixed with a monofunctional epoxy resin to react, and then liquid imidazole is added, stirred and mixed, and reacted to obtain a modified imidazole liquid curing agent;

[0011] S2. The thixotropic agent and toughening agent are added to the epoxy resin, stirred, and cooled to room temperature to obtain a modified epoxy resin system;

[0012] S3. The modified epoxy resin system obtained in step S2 and the modified imidazole liquid curing agent obtained in step S1 are mixed evenly in proportion to obtain a liquid epoxy resin composite material repair adhesive.

[0013] Wherein, the mixing mass ratio of the modified epoxy resin system to the modified imidazole liquid curing agent is 100:(10-35).

[0014] Wherein, in step S1, the powdered curing agent is 2-(4-aminophenyl)-5-aminobenzimidazole;

[0015] In step S1, the monofunctional epoxy resin is selected from o-cresol glycidyl ether or benzyl glycidyl ether;

[0016] In step S1, the reaction temperature of the powdered curing agent and the monofunctional epoxy resin is 70-100° C., and the reaction time is 30 min to 60 min.

[0017] Wherein, in step S1, the mixing mass ratio of the powdered curing agent to the monofunctional epoxy resin is 1:(1-3).

[0018] Wherein, in step S1, the liquid imidazole is selected from one of 1-aminoethyl-2-methylimidazole and 2-ethyl-4-methylimidazole;

[0019] In step S1, the reaction temperature after adding liquid imidazole is 80-120° C., and the reaction time is 10 min-20 min.

[0020] Wherein, in step S1, the mixing mass ratio of the liquid imidazole, the powdered curing agent and the monofunctional epoxy resin mixture is (1-3):1.

[0021] Wherein, in step S2, the epoxy resin is selected from one or more of bisphenol A epoxy resin, naphthalene epoxy resin, 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, p-aminophenol epoxy resin, 4,4'-diaminodiphenylmethane epoxy resin, and hydroquinone diglycidyl ether.

[0022] Wherein, in step S2, the thixotropic agent is talcum powder, and the addition amount of the thixotropic agent is 0.2% to 1% of the total mass of the epoxy resin.

[0023] Wherein, in step S2, the added amount of the toughening agent is 1% to 8% of the total mass of the epoxy resin.

[0024] In a second aspect, the present application also provides a liquid epoxy resin composite material repair adhesive, which is made by the above method.

[0025] (3) Beneficial effects

[0026] For high-temperature epoxy matrix composite materials, in the above-mentioned technical solution of the present application, a powdered curing agent is mixed and stirred with a monofunctional epoxy resin to react. The monofunctional epoxy resin can be grafted with the powdered curing agent. The product obtained after the reaction is a crystalline curing agent, that is, a viscous liquid resin. Liquid imidazole is then added. The crystalline curing agent can be better dissolved in the liquid imidazole curing agent, thereby improving the dispersibility of the traditional curing agent. After stirring the reaction, the curing agent can be fully and evenly dispersed, and the modified imidazole liquid curing agent has better dispersibility. The unmodified powdered curing agent cannot be dissolved in the liquid imidazole curing agent directly, and the target product cannot be obtained.

[0027] Moreover, the activity of the modified imidazole liquid curing agent is enhanced. First, the state of the modified curing agent changes from solid to liquid, the molecular freedom is greater, the reaction probability is greater, and therefore the activity is naturally higher. Secondly, since liquid imidazole is added during the modification process, it can participate in the curing of the epoxy resin together with the original powder curing agent during the curing process, so that the activity is further improved, so that the effect of low-temperature curing can be achieved. At the same time, since the powder curing agent itself has a high heat resistance of the cured product, the product after curing with the modified curing agent can still maintain a high glass transition temperature, that is, a liquid epoxy resin composite material repair adhesive is obtained.

[0028] In this way, the solution of the present application can ensure a higher glass transition temperature of the epoxy resin while allowing the curing temperature of the curing agent to be lower. The mechanical properties of the adhesive remain unchanged when used under high temperature conditions, the heat resistance of the adhesive is better, and the repair adhesive can meet both low-temperature curing and high-temperature use, while ensuring the processability of the adhesive. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are further described in detail below with reference to the examples. The detailed description of the following examples is intended to illustrate the principles of the present invention, but is not intended to limit the scope of the present invention. That is, the present invention is not limited to the described embodiments and covers any modifications, replacements, and improvements to the steps, modules, and connection modes without departing from the spirit of the present invention.

[0030] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the embodiments.

[0031] The method for preparing the liquid epoxy resin composite material repair adhesive according to the embodiment of the present invention is characterized by comprising the steps of:

[0032] S1. The powdered curing agent is mixed with a monofunctional epoxy resin to react, and then liquid imidazole is added, stirred and mixed, and reacted to obtain a modified imidazole liquid curing agent;

[0033] S2. The thixotropic agent and toughening agent are added to the epoxy resin, stirred, and cooled to room temperature to obtain a modified epoxy resin system;

[0034] S3. The modified epoxy resin system obtained in step S2 and the modified imidazole liquid curing agent obtained in step S1 are mixed evenly in proportion to obtain a liquid epoxy resin composite material repair adhesive.

[0035] For high-temperature epoxy matrix composite materials, in the above-mentioned specific embodiment of the present application, a powdered curing agent is mixed and stirred with a monofunctional epoxy resin to react. The monofunctional epoxy resin can be grafted with the powdered curing agent. The product obtained after the reaction is a crystalline curing agent, that is, a viscous liquid resin. Liquid imidazole is then added. The crystalline curing agent can be better dissolved in the liquid imidazole curing agent, thereby improving the dispersibility of the traditional curing agent. After stirring the reaction, the curing agent can be fully and evenly dispersed, and the modified imidazole liquid curing agent has better dispersibility. The unmodified powdered curing agent cannot be dissolved in the liquid imidazole curing agent directly, and the target product cannot be obtained.

[0036] Moreover, the activity of the modified imidazole liquid curing agent is enhanced. First, the state of the modified curing agent changes from solid to liquid, the molecular freedom is greater, the reaction probability is greater, and therefore the activity is naturally higher. Secondly, since liquid imidazole is added during the modification process, it can participate in the curing of the epoxy resin together with the original powder curing agent during the curing process, so that the activity is further improved, so that the effect of low-temperature curing can be achieved. At the same time, since the powder curing agent itself has a high heat resistance of the cured product, the product after curing with the modified curing agent can still maintain a high glass transition temperature, that is, a liquid epoxy resin composite material repair adhesive is obtained.

[0037] In this way, while ensuring a higher glass transition temperature of the epoxy resin, the curing temperature of the curing agent can be lower, the mechanical properties of the adhesive remain unchanged when used under high temperature conditions, the heat resistance of the adhesive is better, the repair adhesive can meet the requirements of low-temperature curing and high-temperature use at the same time, and the processability of the adhesive can be guaranteed.

[0038] In addition, in the above technical implementation, when preparing the modified epoxy resin system, a thixotropic agent and a toughening agent are added to the epoxy resin, stirred evenly, and then cooled to room temperature. By regulating the thixotropic agent, toughening agent and epoxy resin, a resin system with both rigidity and flexibility and good processability is obtained. At the same time, it has good thixotropy to ensure that the repair adhesive will not drip or flow significantly during the gluing process, causing uneven glue liquid.

[0039] Furthermore, the modified epoxy resin system and the modified imidazole liquid curing agent are mixed in a mass ratio of 100:(10-35). When the two are evenly mixed, a liquid low-temperature curing, highly heat-resistant epoxy resin composite repair adhesive is obtained. This adhesive can be cured below 100°C, with a glass transition temperature above 150°C and excellent bonding properties, with Al-Al bonding performance exceeding 20 MPa at room temperature and exceeding 15 MPa at 200°C.

[0040] As a preferred embodiment, in step S1, the powdered curing agent is 2-(4-aminophenyl)-5-aminobenzimidazole; and the monofunctional epoxy resin is selected from o-cresol glycidyl ether or benzyl glycidyl ether.

[0041] Specifically, in step S1, the powdered curing agent and the monofunctional epoxy resin are stirred and reacted at a reaction temperature of 70 to 100° C., a reaction time of 30 to 60 minutes, and a mixing reaction condition of a stirring speed of 100 rpm.

[0042] Specifically, in step S1, the mixing mass ratio of the powdered curing agent to the monofunctional epoxy resin is 1:(1-3).

[0043] Preferably, in step S1, the liquid imidazole is selected from 1-aminoethyl-2-methylimidazole or 2-ethyl-4-methylimidazole. In step S1, the reaction temperature after adding the liquid imidazole is 80-120°C, the reaction time is 10-20 minutes, and the mixing condition is a stirring speed of 60 rpm.

[0044] / min.

[0045] Furthermore, in step S1, the mixing mass ratio of the liquid imidazole, the powdered curing agent and the monofunctional epoxy resin mixture is (1-3):1.

[0046] As a preferred embodiment, in step S2, the epoxy resin is selected from one or more of bisphenol A epoxy resin, naphthalene epoxy resin, 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, p-aminophenol epoxy resin, 4,4'-diaminodiphenylmethane epoxy resin, and hydroquinone diglycidyl ether.

[0047] Specifically, in step S2, the thixotropic agent is Byk 1958 talc powder, and the addition amount of the thixotropic agent is 0.2% to 1% of the total mass of the epoxy resin. The toughening agent is a conventional toughening agent, specifically Benlong F351, and the addition amount of the toughening agent is 1% to 8% of the total mass of the epoxy resin.

[0048] Another aspect of the present invention provides a liquid epoxy resin composite material repair adhesive, which is prepared by the above method.

[0049] In the above specific embodiments of the present application, an imidazole liquid high-heat-resistant epoxy curing agent is obtained by preparing a modified imidazole curing agent, which solves the problem that imidazole solid powder curing agents are difficult to disperse evenly, and greatly improves the processability of the adhesive; by designing the epoxy resin formula, regulating the ratio of thixotropic agent, toughening agent and various epoxy resins, a resin system with both rigidity and flexibility and good processability is obtained, and at the same time has good thixotropy to ensure that the repair adhesive will not drip or flow significantly during the gluing process, causing uneven glue liquid; by preparing the modified imidazole curing agent and formula regulation, the preparation of liquid low-temperature curing high-heat-resistant epoxy resin composite material repair adhesive is finally realized, which can be cured below 100°C. At the same time, the glass transition temperature of the cured product is above 150°C, and the bonding performance is excellent, with Al-Al bonding performance >20MPa at room temperature and Al-Al bonding performance >15MPa at 200°C.

[0050] In the above specific implementation of the present invention:

[0051] 1. The amine group (such as primary amine) on the powder curing agent is grafted with the monofunctional epoxy through a ring-opening reaction. The product obtained after the reaction is a crystalline curing agent that can be better dissolved in the liquid imidazole curing agent. The unmodified powder curing agent cannot be dissolved in the liquid imidazole curing agent directly, and the target product cannot be obtained.

[0052] 2. First, the state of the modified curing agent changes from solid to liquid, the molecular freedom is greater, the reaction probability is greater, and therefore the activity is naturally higher. Secondly, since liquid imidazole is added during the modification process, it can participate in the curing of the epoxy resin together with the original powder curing agent during the curing process, which further improves the activity and thus achieves the effect of low-temperature curing. At the same time, since the powder curing agent itself has a high heat resistance, the product cured with the modified curing agent can still maintain a high glass transition temperature.

[0053] The following describes it in detail through specific embodiments.

[0054] Example 1

[0055] Mix 10 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 15 g of benzyl glycidyl ether, add a condensing device and start stirring the reaction at a stirring speed of 100 rpm, a reaction temperature of 75°C, and a reaction time of 40 min. After stirring the reaction, a viscous liquid resin is obtained. Then, 10 g of 1-aminoethyl-2-methylimidazole is added, the stirring speed is 60 rpm, the reaction temperature is 120°C, and the reaction time is 20 min. After stirring evenly, a modified imidazole liquid curing agent is obtained.

[0056] Weigh 60 g of AG80 epoxy resin, 20 g of EBA65 epoxy resin, and 20 g of hydroquinone diglycidyl ether, add 0.5 parts of thixotropic agent 1958 talc powder and 3 parts of toughening agent F351 to 100 parts of the mixed epoxy resin, stir at 50°C for 20 minutes, stir evenly, and cool to room temperature for use.

[0057] Take 100 g of the mixed epoxy resin obtained in the above step and 20 g of the modified imidazole liquid curing agent, mix them evenly, and obtain a liquid low-temperature curing high-heat-resistant epoxy resin composite material repair adhesive.

[0058] Example 2

[0059] Mix 10 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 20 g of o-cresol glycidyl ether, add a condensing device and start stirring the reaction at a stirring speed of 100 rpm, a reaction temperature of 75°C, and a reaction time of 40 min. After stirring the reaction, a viscous liquid resin is obtained. Then, 10 g of 2-ethyl-4-methylimidazole is added, the stirring speed is 60 rpm, the reaction temperature is 110°C, and the reaction time is 20 min. After stirring evenly, a modified imidazole liquid curing agent is obtained.

[0060] Weigh 50g of AG80 epoxy resin and 50g of EBA65 epoxy resin, add 1 part of thixotropic agent 1958 and 2 parts of toughening agent F351 to 100 parts of the mixed epoxy resin, stir at 50°C for 20 minutes, stir evenly, and cool to room temperature for use.

[0061] Take 100 g of the mixed epoxy resin obtained in the above step and 25 g of the modified imidazole liquid curing agent, mix them evenly, and obtain a liquid low-temperature curing high-heat-resistant epoxy resin composite material repair adhesive.

[0062] Example 3

[0063] Mix 10 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 25 g of benzyl glycidyl ether, add a condensing device and start stirring the reaction at a stirring speed of 100 rpm, a reaction temperature of 80°C, and a reaction time of 30 min. After stirring the reaction, a viscous liquid resin is obtained. Then, 20 g of 1-aminoethyl-2-methylimidazole is added, the stirring speed is 60 rpm, the reaction temperature is 120°C, and the reaction time is 20 min. After stirring evenly, a modified imidazole liquid curing agent is obtained.

[0064] Weigh 80 g of AG80 epoxy resin, 10 g of EBA65 epoxy resin, 5 g of hydroquinone diglycidyl ether, and 5 g of E51 epoxy resin, add 1 part of thixotropic agent 1958 and 5 parts of toughening agent F351 to 100 parts of the mixed epoxy resin, stir at 50°C for 20 minutes, stir evenly, and cool to room temperature for use.

[0065] Take 100 g of the mixed epoxy resin obtained in the above step and 15 g of the modified imidazole liquid curing agent, mix them evenly, and obtain a liquid low-temperature curing high-heat-resistant epoxy resin composite material repair adhesive.

[0066] The repair adhesive prepared by the preparation method of the liquid low-temperature curing high-heat-resistant epoxy resin composite material repair adhesive of the present application can be cured below 100°C and has good bonding performance and heat resistance.

[0067] The liquid low-temperature curing, high-heat-resistant epoxy resin composite repair adhesive obtained in the above example was subjected to single lap shear tests on Al plates and T700 grade composite test plates. The curing conditions were 100°C for 2 hours. The sample preparation standard was based on GB / T 7124-2008. The test results are shown in Table 1 below.

[0068]

[0069] As shown in Table 1 above, in the first test item, at a room temperature of 23°C, the bonding properties of the adhesives obtained in Example 1, Example 2, and Example 3 were 24.0 MPa, 21.2 MPa, and 23.1 MPa, respectively; in the second test item, at a high temperature of 200°C, the bonding properties of the adhesives obtained in Example 1, Example 2, and Example 3 were 15.3 MPa, 14.6 MPa, and 13.6 MPa, respectively; in the third test item, at a room temperature of 23°C, the bonding properties of the adhesives obtained in Example 1, Example 2, and Example 3 were 24.0 MPa, 21.2 MPa, and 23.1 MPa, respectively. The above three test items all reflect that the adhesives prepared in the embodiments of the present application have good bonding properties at room temperature (23°C) or high temperature (200°C) after curing at low temperature.

[0070] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art without departing from the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of the claims of the present application.

Claims

1. A method for preparing a liquid epoxy resin composite material repair adhesive, characterized in that: Including steps: S1. A powdered curing agent and a monofunctional epoxy resin are mixed and reacted, and then liquid imidazole is added, stirred, mixed, and reacted to obtain a modified imidazole liquid curing agent; the powdered curing agent is 2-(4-aminophenyl)-5-aminobenzimidazole; the monofunctional epoxy resin is selected from o-cresol glycidyl ether or benzyl glycidyl ether; and the liquid imidazole is selected from 1-aminoethyl-2-methylimidazole or 2-ethyl-4-methylimidazole; S2. The thixotropic agent and toughening agent are added to the epoxy resin, stirred, and cooled to room temperature to obtain a modified epoxy resin system; S3. The modified epoxy resin system obtained in step S2 and the modified imidazole liquid curing agent obtained in step S1 are mixed evenly in proportion to obtain a liquid epoxy resin composite material repair adhesive.

2. The preparation method according to claim 1, wherein The mixed mass ratio of the modified epoxy resin system to the modified imidazole liquid curing agent is 100:(10-35).

3. The preparation method according to claim 1, wherein In step S1, the reaction temperature of the powdered curing agent and the monofunctional epoxy resin is 70-100° C., and the reaction time is 30 min-60 min.

4. The preparation method according to claim 3, wherein In step S1, the mixing mass ratio of the powdered curing agent to the monofunctional epoxy resin is 1:(1-3).

5. The preparation method according to claim 1 or 4, wherein In step S1, the reaction temperature after adding liquid imidazole is 80-120° C., and the reaction time is 10 min-20 min.

6. The preparation method according to claim 1, wherein In step S1, the mixing mass ratio of the liquid imidazole, the powdered curing agent and the monofunctional epoxy resin mixture is (1-3):

1.

7. The preparation method according to claim 1, wherein In step S2, the epoxy resin is selected from one or more of bisphenol A epoxy resin, naphthalene epoxy resin, 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, p-aminophenol epoxy resin, 4,4'-diaminodiphenylmethane epoxy resin, and hydroquinone diglycidyl ether.

8. The preparation method according to claim 1 or 7, wherein In step S2, the thixotropic agent is talcum powder, and the added amount of the thixotropic agent is 0.2% to 1% of the total mass of the epoxy resin.

9. The preparation method according to claim 1, wherein In step S2, the amount of the toughening agent added is 1% to 8% of the total mass of the epoxy resin.

10. A liquid epoxy resin composite material repair adhesive made by the method according to any one of claims 1 to 9.

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