Preparation method and application of medium-temperature curing high Tg epoxy resin structural adhesive

Abstract

The invention belongs to the technical field of epoxy resin structural adhesives, and discloses a preparation method and application of a medium-temperature cured high-Tg epoxy resin structural adhesive. 30-60 parts of liquid multifunctional epoxy resin, 10-30 parts of toughening agent, 0.5-2 parts of tertiary amine catalyst, 10-40 parts of solid bisphenol A epoxy resin, 6-12 parts of curing agent, and 2-5 parts of accelerator are weighed according to weight parts; the liquid multifunctional epoxy resin is equally divided into 2 parts according to weight, and one part is used to prepare curing agent paste; the temperature of pure liquid bisphenol A epoxy resin is raised to 80-150 DEG C, the toughening agent and the tertiary amine catalyst are added, and a prepolymerization reaction is carried out under nitrogen protection, solid bisphenol A epoxy resin is added to the reaction for heat preservation, and curing agent paste is added after cooling, and the epoxy resin structural adhesive is stirred and discharged to obtain the epoxy resin structural adhesive, wherein the curing temperature is about 120 DEG C, so that the high-Tg structural adhesive used at high temperature can be cured at a relatively low temperature, and the high-temperature resistant mechanical properties of the high-Tg epoxy resin structural adhesive are guaranteed at the same time.

Description

Technical Field

[0001] The invention relates to an epoxy resin formula system and a preparation method thereof, and belongs to the field of resin adhesive film materials. Background Art

[0002] In recent years, organic adhesives have been used more and more widely, and bonding technology has also matured and has become one of the three major contemporary connection technologies: bonding, welding, and mechanical connection. Among them, epoxy resin contains a variety of polar groups and highly active epoxy groups, which can be combined with a variety of polar materials. At the same time, when epoxy resin is cured, basically no low-molecular volatiles are produced, and the volume shrinkage of the adhesive layer is small, about 1% to 2%, which is one of the varieties with the smallest curing shrinkage among thermosetting resins. The linear expansion coefficient of epoxy cured products is also very small, so the internal stress is small and the effect on the bonding strength is small. In addition, the creep of epoxy cured products is small, so the dimensional stability of the adhesive layer is good, and its bonding strength is very high, and its application is very wide. At present, epoxy resins are mainly divided into three categories: low-temperature (80℃ and below) curing, medium-temperature (80-120℃) curing, and high-temperature (150℃ and above) curing, corresponding to low, medium and high temperature usage scenarios respectively.

[0003] At present, aviation epoxy resin structural adhesives are increasingly required to be resistant to high temperatures, that is, high Tg epoxy resin structural adhesives are required. Many manufacturers lack high-temperature curing conditions or need to reduce energy consumption and are not suitable for using high-temperature cured high-Tg epoxy resins. That is, structural adhesives (high Tg epoxy resins) used at high temperatures need to be cured at lower temperatures. However, after high Tg epoxy resins are generally cured at lower temperatures, the tensile shear strength of high Tg epoxy resins used at higher temperatures will decrease significantly, making it difficult to meet high-temperature use requirements. Summary of the invention

[0004] In order to solve the problems in the background technology, the present invention provides a method for preparing a medium-temperature high-Tg epoxy resin structural adhesive and its application, so that the structural adhesive can be cured at a lower temperature and then used at a higher temperature and still ensure a high tensile shear strength to meet the requirements of high temperature use.

[0005] In order to achieve the above objectives, the present invention is implemented by the following technical solutions:

[0006] The medium temperature curing epoxy resin system of the present invention is composed of the following materials by weight: 30-60 parts of liquid multifunctional epoxy resin, 10-30 parts of toughening agent, 0.5-2 parts of tertiary amine catalyst, 10-40 parts of solid bisphenol A epoxy resin, 6-12 parts of curing agent, and 2-5 parts of accelerator;

[0007] Furthermore, the liquid multifunctional epoxy resin is one or more of trifunctional epoxy resin and tetrafunctional epoxy resin, including but not limited to one or more of Huayi AG601, Huayi AG602, Huayi AG70, Huayi AFG-90MH, Huayi AFG-90H, etc.;

[0008] Further, the toughening agent is carboxyl-terminated nitrile rubber CTBN;

[0009] Further, the tertiary amine catalyst includes but is not limited to one or more of triethylamine, triethylenediamine, N,N-dimethylcyclohexylamine, etc.;

[0010] Further, the solid bisphenol A epoxy resin is one or more of E20, E14, and E12;

[0011] Further, the curing agent is dicyandiamide or modified dicyandiamide;

[0012] Furthermore, the accelerator is a latent accelerator with an active temperature above 110° C., preferably one or more of Aziken UR700, Aziken UR800, and Ajinomoto PN-50.

[0013] The present invention discloses a method for preparing a medium-temperature high-Tg epoxy resin structural adhesive and its application. The preparation method comprises the following steps:

[0014] (1) Weighing: Weigh 30-60 parts of liquid multifunctional epoxy resin, 10-30 parts of toughening agent, 0.5-2 parts of tertiary amine catalyst, 10-40 parts of solid bisphenol A epoxy resin, 6-12 parts of curing agent, and 2-5 parts of accelerator according to weight parts;

[0015] (2) preparing a resin mixture: the liquid multifunctional epoxy resin weighed in step (1) is divided into two parts by mass, the first part being a pure liquid bisphenol A epoxy resin, and the second part being mixed with a curing agent and an accelerator by a high-speed disperser and a three-roll mill to form a curing agent paste;

[0016] (3) Prepolymerization: Raise the temperature of pure liquid bisphenol A epoxy resin to 80-150°C, add toughening agent and tertiary amine catalyst, and immediately introduce nitrogen into the reactor for protection, and keep the temperature at 80-150°C for 90-150 minutes;

[0017] (4) Mixing solid and liquid resin components: adding solid bisphenol A epoxy resin to the resin after the prepolymerization reaction in step (3), and stirring thoroughly for 30-90 minutes to completely dissolve the solid resin;

[0018] (5) Blending and discharging: The temperature of the material in step (4) is lowered to 65-70° C., and the curing agent paste in step (2) is added, and stirred for 30 minutes until the mixture is uniformly mixed, and then the mixture is discharged to obtain a high Tg epoxy resin structural adhesive.

[0019] The curing conditions for the application of epoxy resin structural adhesive are: curing at 120°C for 2 hours.

[0020] The Tg (DSC method) range of the obtained epoxy resin structural adhesive is: above 180° C. (180-190° C.); the room temperature tensile shear strength range is: 30-32Mpa; the tensile shear strength (150° C.) range is: 27-29Mpa.

[0021] The beneficial effects of the present invention are:

[0022] (1) In the present invention, the multifunctional epoxy resin is used as the main body, wherein the epoxy groups are more, the metal adhesion is better, the bonding is more reliable after curing, and the cross-linking reaction with the curing agent has a higher cross-linking density, thereby improving the heat resistance of the resin; the nitrile rubber itself has a good affinity with both metal and epoxy resin, which can not only increase the bonding effect between the epoxy resin and the metal, but also increase the flexibility and plasticity of the epoxy resin, and have a toughening effect on the epoxy resin. By adding a reasonable proportion, the hardness and toughness of the epoxy resin can be improved, thereby improving the tensile strength, fracture toughness and impact resistance, which can improve the test performance of the tensile shear strength that characterizes the bonding force. The carboxyl group in the carboxyl-terminated nitrile rubber can react with the epoxy resin to first form an ester bond or an ether bond The hydroxyl group opened by the epoxy group will continue to react with the terminal carboxyl group to form an ester bond under the action of tertiary amine catalysts. Therefore, the molecular chain amount, chain length and cross-linking density of the resin can be increased, and the melting point and heat resistance of the resin can be improved.

[0023] (2) According to the literature on prepolymerization of epoxy resin and liquid carboxyl-terminated nitrile rubber (CTBN) (Liu Junning, Lv Yong, FRP / Composites, Issue 4, 2011), the first two reactions are extremely slow without a catalyst, and the third reaction is unlikely to occur. Therefore, the present invention uses a tertiary amine catalyst for prepolymerization to ensure that the reaction can proceed fully, thereby ensuring the prepolymerization effect and improving the temperature resistance of the resin mixture. The above prepolymerization reaction needs to be carried out under nitrogen protection, otherwise the loss of epoxy groups will occur, resulting in poor performance after curing.

[0024] (3) In the present invention, the addition of solid bisphenol A epoxy can adjust the viscosity and viscous state of the mixture. If both liquid resin and liquid carboxyl-terminated nitrile rubber are used, the mixture will be sticky and have a low viscosity, which is not conducive to later production and use. The addition of solid resin can increase the viscosity and deteriorate the fluidity, which is convenient for the subsequent production of adhesive film or coating use, and can also reduce the viscosity, which is conducive to the laying operation of the adhesive film. The solid bisphenol A epoxy needs to be added after the prepolymerization reaction. This is because there are epoxy groups in the solid bisphenol A epoxy resin. If it is added in advance, it will also participate in the prepolymerization reaction of the nitrile rubber. The curing agent of the present invention is not as heat-resistant as the multifunctional epoxy after being cured with the bisphenol A epoxy resin at a temperature of 120°C, which affects the bonding effect of the nitrile rubber at high temperature.

[0025] (3) The dicyandiamide in the curing agent of the present invention is a latent high-temperature curing agent, which normally requires a curing temperature of more than 150°C. The present invention adds an accelerator to reduce the curing temperature to about 120°C. There are many studies on accelerators in this field, and the present invention studies and selects the active temperature of the accelerator. The activation temperature cannot be too low, which will affect the shelf life of the mixture. A latent accelerator with an activity of more than 110°C is selected. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 150gsm adhesive film made from epoxy resin premix;

[0027] Figure 2 It is a single lap tensile shear test specimen for aluminum alloy. DETAILED DESCRIPTION

[0028] Example 1

[0029] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0030] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0031] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0032] Tertiary amine catalyst: triethylamine: 0.5 parts

[0033] Solid bisphenol A epoxy resin: E20: 10 parts

[0034] Curing agent: dicyandiamide: 6 parts

[0035] Accelerator: Azken UR700: 2 parts

[0036] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is a pure liquid multifunctional epoxy resin, and the second part of the liquid multifunctional epoxy resin is mixed with a curing agent and an accelerator by a high-speed disperser and a three-roll mill to form a curing agent paste; the pure liquid multifunctional epoxy resin component is added into a reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and a tertiary amine catalyst are added in sequence, nitrogen is introduced, and the prepolymerization reaction is fully kept at 80°C for 90 minutes, solid bisphenol A epoxy resin is added, and the heat is kept for 30 minutes, the kettle temperature is lowered to 65-70°C, the curing agent paste is added, and it is stirred for 30 minutes, and the material is discharged to obtain a resin premix.

[0037] The main performance tests of the resin system are as follows:

[0038] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 42000cps Gel time (120℃) ASTMD2471 13min

[0039] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0040] Performance of the sample after curing

[0041] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 31Mpa Tensile shear strength (150℃) GB / T7124 28Mpa Resin Tg (DSC method) GB / T19466.2 185℃

[0042] Example 2

[0043] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0044] Liquid multifunctional epoxy resin: Huayi AFG-90H: 60 parts

[0045] Liquid toughening agent: carboxyl-terminated nitrile rubber: 30 parts

[0046] Tertiary amine catalyst: N, N-dimethylcyclohexylamine: 2 parts

[0047] Solid bisphenol A epoxy resin: E12: 40 parts

[0048] Curing agent: dicyandiamide: 12 parts

[0049] Accelerator: Ajinomoto PN-50: 5 parts

[0050] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is a pure liquid multifunctional epoxy resin, and the second part is mixed with a curing agent and an accelerator by a high-speed disperser and a three-roll mill to form a curing agent paste; the pure liquid multifunctional epoxy resin component is added into a reaction kettle, the temperature is raised to 150°C, carboxyl-terminated nitrile rubber and a tertiary amine catalyst are added in sequence, nitrogen is introduced, and the prepolymerization reaction is fully kept at 150°C for 150 minutes, solid bisphenol A epoxy resin is added, and the heat is kept for 90 minutes, the kettle temperature is lowered to 65-70°C, the curing agent paste is added, and it is stirred for 30 minutes, and the material is discharged to obtain a resin premix.

[0051] The main performance tests of the resin system are as follows:

[0052] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 43500cps Gel time (120℃) ASTMD2471 12min

[0053] The resin premix was made into a 150 gsm resin adhesive film, which was then used to make a single lap test specimen using an aluminum alloy plate 2A12 (conforming to the requirements of GJB2053A standard), and then oven-cured at 120° C. for 2 hours.

[0054] Performance of the sample after curing

[0055]

[0056]

[0057] Example 3

[0058] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0059] Liquid multifunctional epoxy resin: Huayi AG602: 22.5 parts, Huayi AG70: 22.5 parts

[0060] Liquid toughening agent: carboxyl-terminated nitrile rubber: 20 parts

[0061] Tertiary amine catalyst: triethylamine: 0.75 parts, triethylenediamine: 0.75 parts

[0062] Solid bisphenol A epoxy resin: E12: 12.5 parts, E14: 12.5 parts

[0063] Curing agent: dicyandiamide: 9 parts

[0064] Accelerator: Azcon UR700: 1.75 parts, Azcon UR800: 1.75 parts

[0065] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is a pure liquid multifunctional epoxy resin, and the second part is mixed with a curing agent and an accelerator by a high-speed disperser and a three-roll mill to form a curing agent paste; the pure liquid multifunctional epoxy resin component is added into a reaction kettle, the temperature is raised to 115°C, and the carboxyl-terminated nitrile rubber and a catalyst are added in sequence, nitrogen is introduced, and the mixture is fully kept warm at 115°C for prepolymerization reaction for 120 minutes, solid bisphenol A epoxy resin is added, and the mixture is kept warm for 60 minutes, the kettle temperature is lowered to 65-70°C, and the curing agent paste is added, stirred for 30 minutes, and discharged to obtain a resin premix.

[0066] The main performance tests of the resin system are as follows:

[0067] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 45300cps Gel time (120℃) ASTMD2471 12min

[0068] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0069] Performance of the sample after curing

[0070] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 32Mpa Tensile shear strength (150℃) GB / T7124 29Mpa Resin Tg (DSC method) GB / T19466.2 181℃

[0071] Example 4

[0072] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0073] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0074] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0075] Tertiary amine catalyst: triethylamine: 0.5 parts

[0076] Solid bisphenol A epoxy resin: E20: 10 parts

[0077] Curing agent: dicyandiamide: 6 parts

[0078] Accelerator: Azken UR700: 2 parts

[0079] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is a pure liquid multifunctional epoxy resin, and the second part is mixed with a curing agent and an accelerator by a high-speed disperser and a three-roll mill to form a curing agent paste; the pure liquid multifunctional epoxy resin component is added into a reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and a catalyst are added in sequence, nitrogen is introduced, and the prepolymerization reaction is fully kept at 80°C for 150 minutes (the prepolymerization time is extended), solid bisphenol A epoxy resin is added, and the temperature is kept for 30 minutes, the kettle temperature is lowered to 65-70°C, the curing agent paste is added, and it is stirred for 30 minutes, and the material is discharged to obtain a resin premix.

[0080] The main performance tests of the resin system are as follows:

[0081] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 45100cps Gel time (120℃) ASTMD2471 12min

[0082] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0083] Performance of the sample after curing

[0084] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 32Mpa Tensile shear strength (150℃) GB / T7124 30Mpa Resin Tg (DSC method) GB / T19466.2 182℃

[0085] Example 5

[0086] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0087] Liquid multifunctional epoxy resin: Huayi AFG-90H: 60 parts

[0088] Liquid toughening agent: carboxyl-terminated nitrile rubber: 30 parts

[0089] Tertiary amine catalyst: N, N-dimethylcyclohexylamine: 2 parts

[0090] Solid bisphenol A epoxy resin: E12: 40 parts

[0091] Curing agent: dicyandiamide: 12 parts

[0092] Accelerator: PN-50: 5 parts

[0093] The liquid multifunctional epoxy resin is divided into two parts by mass, the first part is pure liquid multifunctional epoxy resin, and the second part is mixed with curing agent and accelerator by high-speed disperser and three-roll mill to form curing agent paste; the pure liquid multifunctional epoxy resin component is added into the reaction kettle, the temperature is raised to 150°C, carboxyl-terminated nitrile rubber and catalyst are added in sequence, nitrogen is introduced and prepolymerization reaction is fully kept at 150°C for 90 minutes (prepolymerization time is shortened), solid bisphenol A epoxy resin is added, and the temperature is kept for 90 minutes, the kettle temperature is lowered to 65-70°C, curing agent paste is added, stirred for 30 minutes, and discharged.

[0094] The main performance tests of the resin system are as follows:

[0095] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 43000cps Gel time (120℃) ASTMD2471 12min

[0096] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0097] Performance of the sample after curing

[0098] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 31Mpa Tensile shear strength (150℃) GB / T7124 27Mpa Resin Tg (DSC method) GB / T19466.2 184℃

[0099] Comparative Example 1

[0100] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0101] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0102] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0103] Tertiary amine catalyst: triethylamine: 0.5 parts

[0104] Solid bisphenol A epoxy resin: E20: 10 parts

[0105] Curing agent: dicyandiamide: 6 parts

[0106] Accelerator: UR700: 2 parts

[0107] The liquid multifunctional epoxy resin is divided into two parts by mass, the first part is pure liquid multifunctional epoxy resin, and the second part is mixed with curing agent and accelerator by high-speed disperser and three-roll mill to form curing agent paste; the pure liquid multifunctional epoxy resin component is added into the reaction kettle, the temperature is raised to 80°C, nitrogen is introduced, solid bisphenol A epoxy resin is added, and the temperature is kept warm for 30 minutes, and terminal carboxyl nitrile rubber and catalyst are added in sequence, and prepolymerization reaction is carried out at 80°C for 90 minutes under nitrogen protection, and the kettle temperature is lowered to 65-70°C, and curing agent paste is added, stirred for 30 minutes, and discharged.

[0108] The main performance tests of the resin system are as follows:

[0109] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 44000cps Gel time (120℃) ASTMD2471 11min

[0110] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0111] Performance of the sample after curing

[0112] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 27Mpa Tensile shear strength (150℃) GB / T7124 16Mpa Resin Tg (DSC method) GB / T19466.2 155℃

[0113] Comparative Example 2

[0114] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0115] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0116] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0117] Tertiary amine catalyst: triethylamine: 0.5 parts

[0118] Solid bisphenol A epoxy resin: E20: 10 parts

[0119] Curing agent: dicyandiamide: 6 parts

[0120] Accelerator: UR700: 2 parts

[0121] The liquid multifunctional epoxy resin is divided into two parts by mass, the first part is pure liquid multifunctional epoxy resin, and the second part is mixed with curing agent and accelerator by high-speed disperser and three-roll mill to form curing agent paste; the pure liquid multifunctional epoxy resin component is added into the reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and catalyst are added in sequence, the prepolymerization reaction is fully kept warm at 80°C for 90 minutes (without nitrogen), solid bisphenol A epoxy resin is added, the temperature is kept warm for 30 minutes, the kettle temperature is lowered to 65-70°C, the curing agent paste is added, stirred for 30 minutes, and the material is discharged.

[0122] The main performance tests of the resin system are as follows:

[0123] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 44400cps Gel time (120℃) ASTMD2471 9min

[0124] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0125] Performance of the sample after curing

[0126] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 22Mpa Tensile shear strength (150℃) GB / T7124 18Mpa Resin Tg (DSC method) GB / T19466.2 169℃

[0127] Comparative Example 3

[0128] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0129] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0130] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0131] Tertiary amine catalyst: 0 parts (no catalyst added)

[0132] Solid bisphenol A epoxy resin: E20: 10 parts

[0133] Curing agent: dicyandiamide: 6 parts

[0134] Accelerator: UR700: 2 parts

[0135] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is pure liquid multifunctional epoxy resin, and the second part is mixed with curing agent and accelerator by high-speed disperser and three-roll mill to form curing agent paste; the pure liquid multifunctional epoxy resin component is added into the reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and catalyst are added in sequence, nitrogen is introduced and prepolymerization reaction is fully kept at 80°C for 90 minutes, solid bisphenol A epoxy resin is added, and the temperature is kept for 30 minutes, the kettle temperature is lowered to 65-70°C, curing agent paste is added, stirred for 30 minutes, and discharged.

[0136] The main performance tests of the resin system are as follows:

[0137] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 38000cps Gel time (120℃) ASTMD2471 11min

[0138] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0139] Performance of the sample after curing

[0140] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 31Mpa Tensile shear strength (150℃) GB / T7124 15Mpa Resin Tg (DSC method) GB / T19466.2 149℃

[0141] Comparative Example 4

[0142] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0143] Liquid bisphenol A epoxy resin: E51: 30 parts

[0144] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0145] Tertiary amine catalyst: triethylamine: 0.5 parts

[0146] Solid bisphenol A epoxy resin: E20: 10 parts

[0147] Curing agent: dicyandiamide: 6 parts

[0148] Accelerator: UR700: 2 parts

[0149] Liquid bisphenol A epoxy resin is divided into two parts by mass, the first part is pure liquid bisphenol A epoxy resin, and the second part is mixed with curing agent and accelerator by high-speed disperser and three-roll mill to form curing agent paste; the pure liquid bisphenol A epoxy resin component is added into the reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and catalyst are added in sequence, nitrogen is introduced and prepolymerization reaction is fully kept at 80°C for 90 minutes, solid bisphenol A epoxy resin is added, and the temperature is kept for 30 minutes, the kettle temperature is lowered to 65-70°C, curing agent paste is added, stirred for 30 minutes, and discharged.

[0150] The main performance tests of the resin system are as follows:

[0151] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 38000cps Gel time (120℃) ASTMD2471 13min

[0152] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0153] Performance of the sample after curing

[0154]

[0155]

[0156] Comparative Example 5

[0157] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0158] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0159] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0160] Tertiary amine catalyst: triethylamine: 0.5 parts

[0161] Solid bisphenol A epoxy resin: E20: 10 parts

[0162] Curing agent: dicyandiamide: 6 parts

[0163] Accelerator: UR500: 2 parts (replaced with 80℃ active substituted urea accelerator)

[0164] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is pure liquid multifunctional epoxy resin, and the second part is mixed with curing agent and accelerator by high-speed disperser and three-roll mill to form curing agent paste; the pure liquid multifunctional epoxy resin component is added into the reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and catalyst are added in sequence, nitrogen is introduced and prepolymerization reaction is fully kept at 80°C for 90 minutes, solid bisphenol A epoxy resin is added, and the temperature is kept for 30 minutes, the kettle temperature is lowered to 65-70°C, curing agent paste is added, stirred for 30 minutes, and discharged.

[0165] The main performance tests of the resin system are as follows:

[0166] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 42000cps Gel time (120℃) ASTMD2471 13min

[0167] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0168] Performance of the sample after curing

[0169] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 25Mpa Tensile shear strength (150℃) GB / T7124 20Mpa Resin Tg (DSC method) GB / T19466.2 185℃

[0170] Comparative Example 6

[0171] The medium temperature curing epoxy resin system of the present invention is composed of the following raw materials by weight:

[0172] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0173] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0174] Tertiary amine catalyst: triethylamine: 0.5 parts

[0175] Solid bisphenol A epoxy resin: E20: 10 parts

[0176] Curing agent: dicyandiamide: 6 parts

[0177] Accelerator: 0 parts

[0178] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is a pure liquid multifunctional epoxy resin, and the second part is mixed with a curing agent by a high-speed disperser and a three-roll mill to form a curing agent paste; the pure liquid multifunctional epoxy resin component is added into a reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and a catalyst are added in sequence, nitrogen is introduced, and the prepolymerization reaction is fully kept at 80°C for 90 minutes, solid bisphenol A epoxy resin is added, and the temperature is kept for 30 minutes, the kettle temperature is lowered to 65-70°C, the curing agent paste is added, stirred for 30 minutes, and the material is discharged.

[0179] The main performance tests of the resin system are as follows:

[0180] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 42800cps Gel time (120℃) ASTMD2471 >300min(no gel) Gel time (180℃) ASTMD2471 20min

[0181] The resin mixture system is not suitable for curing at 120°C, so the resin premix was made into a 150gsm resin adhesive film and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the GJB2053A standard requirements) and oven-cured at 180°C for 2 hours.

[0182] Performance of the sample after curing

[0183] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 24Mpa Tensile shear strength (150℃) GB / T7124 23Mpa Resin Tg (DSC method) GB / T19466.2 188℃

[0184] Comparative Example 7

[0185] Liquid multifunctional epoxy resin: Huayi AG601: 30 parts

[0186] Liquid toughening agent: carboxyl-terminated nitrile rubber: 10 parts

[0187] Tertiary amine catalyst: triethylamine: 0.5 parts

[0188] Solid bisphenol A epoxy resin: E20: 10 parts

[0189] Curing agent: dicyandiamide: 6 parts

[0190] Accelerator: UR-D: 2 parts

[0191] The liquid multifunctional epoxy resin is divided into two parts by weight, the first part is a pure liquid multifunctional epoxy resin, and the second part is mixed with a curing agent and an accelerator by a high-speed disperser and a three-roll mill to form a curing agent paste; the pure liquid multifunctional epoxy resin component is added into a reaction kettle, the temperature is raised to 80°C, carboxyl-terminated nitrile rubber and a catalyst are added in sequence, nitrogen is introduced, and the prepolymerization reaction is fully kept at 80°C for 90 minutes, solid bisphenol A epoxy resin is added, and the temperature is kept for 30 minutes, the kettle temperature is lowered to 65-70°C, the curing agent paste is added, and it is stirred for 30 minutes, and the material is discharged to obtain a resin premix.

[0192] The main performance tests of the resin system are as follows:

[0193] Test items Test conditions / reference method Test Results Viscosity (70℃) ASTMD4287 43400cps Gel time (120℃) ASTMD2471 12min

[0194] The resin premix was made into a 150gsm resin adhesive film, and then a single lap test specimen was made using an aluminum alloy plate 2A12 (in accordance with the requirements of GJB2053A standard), and then oven-cured at 120°C for 2 hours:

[0195] Performance after curing

[0196] Test items Test conditions / reference method Test Results Tensile shear strength (25℃) GB / T7124 30Mpa Tensile shear strength (150℃) GB / T7124 15Mpa Resin Tg (DSC method) GB / T19466.2 161℃

[0197] There is little difference between Examples 1-5, the glass transition temperatures Tg are all above 180°C, and the tensile shear strength decreases slightly at 150°C. In Comparative Example 1, after the prepolymerization reaction was replaced by adding solid bisphenol A epoxy resin, Tg was significantly reduced, and the tensile shear strength at high temperature was also significantly reduced; in Comparative Example 2, after the prepolymerization reaction was not carried out under a nitrogen environment, Tg was reduced, and the tensile shear strength at both room temperature and high temperature was significantly reduced; in Comparative Example 3, after no tertiary amine catalyst was added, Tg and tensile shear strength at high temperature were significantly reduced; in Comparative Example 4, after the liquid multifunctional epoxy was replaced with liquid bisphenol A epoxy resin, Tg was reduced more, and the tensile shear strength at both room temperature and high temperature was greatly reduced; in Comparative Example 5, after replacing with a promoter with lower temperature activity, the tensile shear strength at room temperature and high temperature was reduced; Comparative Example 6 was no longer suitable for curing at a medium temperature of 120°C after removing the promoter, and after high-temperature curing at 180°C, the tensile shear strength at room temperature and high temperature was not as good as the result of medium-temperature curing in the embodiment; in Comparative Example 7, after replacing another substituted urea promoter with 110°C activity, Tg was reduced, and the tensile shear strength at room temperature was equivalent to that in the embodiment, but the strength at high temperature was significantly reduced.

[0198] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a medium temperature curing high Tg epoxy resin structural adhesive, characterized in that: The specific steps are: (1) Weigh the following raw materials by weight: 30-60 parts of liquid multifunctional epoxy resin, 10-30 parts of toughening agent, 0.5-2 parts of tertiary amine catalyst, 10-40 parts of solid bisphenol A epoxy resin, 6-12 parts of curing agent, and 2-5 parts of accelerator; the curing agent is dicyandiamide or modified dicyandiamide; the liquid multifunctional epoxy resin is one or more of trifunctional epoxy resin and tetrafunctional epoxy resin; the toughening agent is carboxyl-terminated nitrile rubber; the accelerator is one or more of Azcon UR700, Azcon UR800, and Ajinomoto PN-50; (2) preparing a resin mixture: the liquid multifunctional epoxy resin weighed in step (1) is divided into two parts by mass, the first part being a pure liquid multifunctional epoxy resin, and the second part being mixed with a curing agent and an accelerator by a high-speed disperser and a grinder to form a curing agent paste; (3) Prepolymerization: Raise the temperature of pure liquid multifunctional epoxy resin to 80-150°C, add toughening agent and tertiary amine catalyst, and continuously introduce nitrogen into the reactor for protection. Prepolymerization reaction is carried out at 80-150°C for 90-150 minutes. (4) Mixing solid and liquid resin components: adding solid bisphenol A epoxy resin to the resin after the prepolymerization reaction in step (3), and stirring the mixture to fully dissolve the solid bisphenol A epoxy resin; (5) Blending and discharging: The temperature of the material in step (4) is lowered to 65-70° C., and the curing agent paste in step (2) is added, and the mixture is stirred and mixed evenly to obtain the epoxy resin structural adhesive.

2. The method for preparing the medium temperature curing high Tg epoxy resin structural adhesive according to claim 1, characterized in that: The tertiary amine catalyst is one or more of triethylamine, triethylenediamine and N,N-dimethylcyclohexylamine.

3. The method for preparing the medium temperature curing high Tg epoxy resin structural adhesive according to claim 1, characterized in that: The solid bisphenol A epoxy resin is one or more of E20, E14 and E12.

4. The high Tg epoxy resin structural adhesive prepared by the method according to any one of claims 1 to 3, characterized in that: The curing conditions of high Tg epoxy resin structural adhesive are 120°C for 2 hours.

5. Application of the high Tg epoxy resin structural adhesive prepared by the method according to any one of claims 1 to 3, characterized in that: The applications include bonding of aerospace mechanical structures.

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