Low-temperature curing epoxy structural adhesive film and preparation method thereof

Abstract

The application discloses a low-temperature curing epoxy structural adhesive film and a preparation method thereof, and relates to the technical field of composite material preparation. The structural adhesive film is prepared by hot-melt compounding of liquid bisphenol A type epoxy resin, solid bisphenol A type epoxy resin, multifunctional epoxy resin, toughening agent, curing agent and accelerator and a carrier. The structural adhesive film comprises the following components: liquid bisphenol A type epoxy resin, solid bisphenol A type epoxy resin, multifunctional epoxy resin, toughening agent, curing agent and accelerator. The toughening agent comprises the following components: thermoplastic resin, core-shell rubber and silicone modified toughening agent. The curing agent is imidazole adduct. The accelerator is polysilazane. The application has the advantages of long room-temperature applicable period, good process coating property, completed curing under the condition of 85 DEG C, and excellent tensile shear performance and 90 DEG C peeling performance.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation technology, and in particular to a low-temperature curing epoxy structural film and its preparation method. Background Technology

[0002] In the aerospace field, adhesive bonding is the primary method for connecting composite materials, such as plates to plates and plates to cores, or for structural components. Structural adhesive bonding effectively avoids stress defects in mechanical connections and also improves fatigue resistance and weight reduction. Currently, medium- and high-temperature epoxy structural adhesive films are mainly used in this field. These films require heating the composite materials or metal parts to 120°C or higher for curing. However, some components, due to uneven thickness of the bonded structural parts and inconsistent thermal deformation and expansion coefficients, may experience stress during high-temperature curing, leading to potential stress hazards during service and even adhesive failure.

[0003] Low-temperature curing epoxy structural films have become a research and development focus in the industry, with curing and accelerating systems such as DMP-30 or thiol being representative examples. However, these low-temperature curing and accelerating systems suffer from poor latency, short room temperature pot life, and poor resistance to damp heat, which pose significant drawbacks for their application in the aerospace field. Summary of the Invention

[0004] The purpose of this invention is to provide a low-temperature curing epoxy structural film and its preparation method. This invention uses liquid bisphenol A epoxy resin, modified or unmodified solid bisphenol A epoxy resin, multifunctional epoxy resin, and toughening agent to ensure that the epoxy structural film has good adhesion. The curing system is composed of imidazole adduct curing agent and polysilazane as accelerator, and is cured at 85°C. It does not lose its adhesion after being stored at room temperature for 2 months and has a good latency period.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A low-temperature curing epoxy structural adhesive film is prepared by hot-melt composite of liquid bisphenol A type epoxy resin, solid bisphenol A type epoxy resin, multifunctional epoxy resin, toughening agent, curing agent, accelerator and carrier.

[0007] By weight, it includes the following components:

[0008] 15-25 parts liquid bisphenol A epoxy resin, 10-20 parts solid bisphenol A epoxy resin, 5-15 parts multifunctional epoxy resin, 30-60 parts toughening agent, 5-20 parts curing agent, 1-5 parts accelerator.

[0009] The toughening agent, by weight, comprises the following components:

[0010] 5-15 parts thermoplastic resin, 15-30 parts core-shell rubber, 5-15 parts organosilicon-modified toughening agent;

[0011] The curing agent is an imidazole adduct;

[0012] The accelerator is polysilazane.

[0013] This invention uses liquid bisphenol A epoxy resin, solid bisphenol A epoxy resin, and multifunctional epoxy resin as raw materials, and thermoplastic resin, core-shell rubber, and organosilicon-modified toughening agent as composite toughening agents to ensure good adhesion of the epoxy structural film. Imidazole adducts are used as the main curing agent to ensure the tensile and shear properties of the system. However, because imidazole cured products are brittle and lack the toughness required for film peel performance, polysilazane is used as a system promoter. Polysilazane is a polymer containing Si-NH, which can combine with epoxy groups in the system to generate a flexible structure containing O-Si in the three-dimensional cross-linked structure, providing toughness to the system and improving peel performance. In addition, polysilazane can react with epoxy groups to generate -OH, giving the system good adhesion to the substrate and further improving the adhesive strength of the system. This invention utilizes imidazole adducts and polysilazane as the curing system, enabling epoxy structural adhesive films to cure at 85°C and maintain tackiness for two months at room temperature, demonstrating a good latency period. It overcomes the technical problems of existing technologies using DMP-30 or thiol-based curing and accelerator systems, which suffer from poor latency, short room temperature pot life, and poor resistance to damp heat. In the field of composite materials, it offers significant advantages for bonding materials such as sheets to sheets and sheets to cores.

[0014] Furthermore, the liquid bisphenol A type epoxy resin includes one or more of epoxy resin E-51, epoxy resin E-54, epoxy resin CYD-128, or epoxy resin CYD-127.

[0015] Furthermore, the solid bisphenol A type epoxy resin includes one or more of epoxy resin E-20, epoxy resin NPES-901, polyurethane modified NPEX-152, or polyurethane modified NPEX-153.

[0016] Furthermore, the multifunctional epoxy resin includes one or more of TDE-85, TDE-86, AFG-90, or AG-80.

[0017] Furthermore, the thermoplastic resin includes one or more of polysulfone (PSF), polyetherketone (PEK), polyetheretherketone (PEEK), or polyimide;

[0018] Core-shell rubbers include one or more of polybutadiene, polystyrene, polystyrene-butadiene rubber, or polysilicon nano-rubber;

[0019] Organosilicon-modified toughening agents include one or both of ES-3868 or ES-3866.

[0020] Furthermore, the imidazole adduct is selected from one or more of PN-40, PN-30, or PN31J. The imidazole adduct is an Ajinomoto imidazole adduct.

[0021] Furthermore, the carrier is selected from either glass fiber or polyester fiber.

[0022] Furthermore, the areal density of the carrier is 25-35 g / m².

[0023] Furthermore, the areal density of the epoxy structural adhesive film is 276-324 g / m³. 2 .

[0024] The preparation method of epoxy structural adhesive film includes the following:

[0025] 1) Add liquid bisphenol A type epoxy resin, multifunctional epoxy resin and thermoplastic resin powder into a mixing device, disperse at 120℃ for 2-3 hours, and mix thoroughly.

[0026] 2) Add solid bisphenol A type epoxy resin, core-shell rubber and organosilicon modified toughening agent, mix and disperse at 120℃ for 1-2 hours, and mix thoroughly;

[0027] 3) After cooling to 65℃, add the curing agent and stir for 10-20 minutes;

[0028] 4) Maintain the reaction temperature, add the accelerator, and stir for 5-10 minutes until the mixture is homogeneous to obtain the resin composition;

[0029] 5) The above resin composition is used to complete the film preparation by hot melt method to obtain a resin pure film with two sides; the two resin pure films are combined with the carrier to obtain an epoxy structural film.

[0030] The preparation method of epoxy structural adhesive film includes the following:

[0031] 1) Add liquid bisphenol A type epoxy resin, multifunctional epoxy resin and thermoplastic resin powder to the mixing equipment, and disperse at 120℃ for 2-3 hours while stirring, so that the thermoplastic resin powder is fully mixed in the resin system.

[0032] 2) After completing step 1), add solid bisphenol A type epoxy resin, core-shell rubber and organosilicon modified toughening agent, and mix and disperse at 120°C for 1-2 hours while stirring to ensure thorough mixing;

[0033] 3) After completing step 2) above, wait for the temperature to drop to 65℃, then add the curing agent and stir for 10-20 minutes;

[0034] 4) After step 3) above is completed, maintain the reaction temperature, add the accelerator, and stir for 5-10 minutes to mix evenly to obtain the resin composition;

[0035] 5) The above-mentioned resin composition in 4) is used to complete the film formation by hot melt method to obtain a pure resin film with a unit area weight of 135±12g / ㎡, with two sides, and is then laminated with the carrier to obtain a structural adhesive film with a unit area weight of 300±24g / ㎡.

[0036] The process flow for hot-melt structural adhesive films is as follows:

[0037] (1) Preparation of pure resin film: The process temperature of the melt plate and the coating roller is 65℃. After stabilizing at the set temperature for 30 minutes, the pure resin film preparation operation is carried out to obtain an epoxy pure resin film of 135±12g / ㎡, with two sides.

[0038] (2) Film assembly: The temperatures of the three zones of the dip roller are 50℃, 65℃ and 60℃ respectively. After stabilizing at the set temperature for 30 minutes, the upper and lower layers are pure resin films and the middle layer is a fiber carrier. The three zones of hot rollers are pressed together in a continuous operation to obtain an epoxy structural film with a surface density of 300±24g / ㎡.

[0039] The beneficial effects of this invention are:

[0040] This invention uses imidazole adducts and polysilazane as the curing system, resolving the contradiction between room temperature latency and low-temperature curing inherent in traditional low-temperature curing systems. This ensures the long room temperature pot life of the prepared epoxy structural adhesive film, along with excellent process lay-up properties. It can be cured at 85°C and guarantees superior tensile shear properties and 90° peel strength. This invention overcomes the conflicting application defects of room temperature tack life and low-temperature curing in this type of structural adhesive. It is of great significance to the development of low-temperature epoxy structural adhesive film products and has broad market prospects. Detailed Implementation

[0041] The technical solution of the present invention is described clearly and completely below. Obviously, the embodiments described herein are only a part of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0042] Example 1

[0043] A low-temperature curing structural adhesive film, using imidazole adduct PN-40 and polysilazane as the curing system, comprises the following components:

[0044] Liquid bisphenol A epoxy resin CYD-128, 250g;

[0045] Polyurethane-modified solid epoxy resin NPEX-153, 180g;

[0046] Multifunctional epoxy resin AG-80, 80g;

[0047] Polysulfone (PSF), 80g; polybutadiene, 170g; silicone-modified toughening agent ES-3868(EX), 90g;

[0048] Imidazole adduct PN-40, 125g;

[0049] Polysilazane, 25g.

[0050] 250g of liquid bisphenol A epoxy resin CYD-128, 80g of multifunctional epoxy resin AG-80, and 80g of polysulfone PSF were stirred at 120℃ for 2.5h to ensure thorough mixing. While maintaining the reaction temperature, 180g of polyurethane-modified solid epoxy resin NPEX-153, 170g of polybutadiene, and 90g of silicone-modified toughening agent ES-3868(EX) were added sequentially, and stirred for 1h. After the temperature dropped to 65℃, 125g of imidazole adduct PN-40 was added, and the mixture was stirred for 15min. Then, 25g of polysilazane was added, and the mixture was stirred for 10min to ensure uniform mixing, yielding the film resin composition. The above resin composition was then used to prepare a film using a hot-melt method, as shown in the following process:

[0051] (1) Preparation of pure resin film: The process temperature of the melt plate and the coating roller is 65℃. After stabilizing at the set temperature for 30 minutes, the pure resin film preparation operation is carried out to obtain an epoxy pure resin film of 135±12g / ㎡, with two sides.

[0052] (2) Film assembly: The temperatures of the three zones of the dip roller are 50℃, 65℃ and 60℃ respectively. After stabilizing at the set temperature for 30 minutes, the upper and lower layers are pure resin films and the middle layer is a polyester fiber mesh carrier. The three zones of hot rollers are pressed together in a continuous operation to obtain an epoxy structural film with a surface density of 300±24g / ㎡.

[0053] Example 2

[0054] A low-temperature curing structural adhesive film, using imidazole adduct PN-31J and polysilazane as the curing system, comprises the following components:

[0055] Liquid bisphenol A epoxy resin E-54, 200g;

[0056] Solid epoxy resin NPES-901, 150g;

[0057] Multifunctional epoxy resin AG-80, 100g;

[0058] Polysulfone (PSF), 60g; polybutadiene, 200g; silicone-modified toughening agent ES-3866(EX), 125g;

[0059] Imidazole adduct PN-31J, 150g;

[0060] Polysilazane, 15g.

[0061] 200g of liquid bisphenol A epoxy resin E-54, 100g of multifunctional epoxy resin AG-80, and 60g of polysulfone PSF were stirred at 120℃ for 2.5h to ensure thorough mixing. While maintaining the reaction temperature, 150g of solid epoxy resin NPES-901, 200g of polybutadiene, and 125g of silicone-modified toughening agent ES-3866(EX) were added sequentially, and stirred for 1h. After the temperature dropped to 65℃, 150g of imidazole adduct PN-31J was added, and the mixture was stirred for 15min. Then, 15g of polysilazane was added, and the mixture was stirred for 10min to ensure uniform mixing, yielding the film resin composition. The above resin composition was then used to prepare the film using a hot-melt method, as shown in the following process:

[0062] (1) Preparation of pure resin film: The process temperature of the melt plate and the coating roller is 65℃. After stabilizing at the set temperature for 30 minutes, the pure resin film preparation operation is carried out to obtain an epoxy pure resin film of 135±12g / ㎡, with two sides.

[0063] (2) Film assembly: The temperatures of the three zones of the dip roller are 50℃, 65℃ and 60℃ respectively. After stabilizing at the set temperature for 30 minutes, the upper and lower layers are pure resin films and the middle layer is a glass fiber carrier. The three zones of hot rollers are pressed together in a continuous operation to obtain an epoxy structural film with a surface density of 300±24g / ㎡.

[0064] Comparative Example 1

[0065] The curing system consists of imidazole adduct PN-31J and secondary thiol (pentaerythritol tetrakis(3-mercaptobutyric acid) ester):

[0066] 200g of liquid bisphenol A epoxy resin E-54, 100g of multifunctional epoxy resin AG-80, and 60g of polysulfone PSF were stirred at 120°C for 3.0h to ensure thorough mixing. While maintaining the reaction temperature, 150g of solid epoxy resin NPES-901, 200g of core-shell rubber (polybutadiene), and 125g of silicone-modified toughening agent ES-3866(EX) were added sequentially, and stirred for 1h. After the temperature dropped to 65°C, 100g of imidazole adduct PN-31J was added, and the mixture was stirred for 15min. Then, 65g of secondary thiol (pentaerythritol tetrakis(3-mercaptobutyric acid) ester) was added, and the mixture was stirred for 10min to ensure uniform mixing, yielding a film resin composition. The above resin composition was used to prepare a film using the hot-melt method of Example 1, yielding a two-sided unit area weight of 135±12g / m². 2 A pure resin film was prepared and then composited with a polyester fiber mesh carrier to obtain a low-temperature curing structural adhesive film with a unit area weight of 300±24g / ㎡.

[0067] Comparative Example 2

[0068] The curing system consists of dicyandiamide curing agent DICY, urea accelerator UR300, and DMP-30.

[0069] 250g of CYD-128, 80g of AG-80, and 80g of polysulfone PSF were stirred at 120℃ for 3.0h to ensure thorough mixing. While maintaining the reaction temperature, 180g of NPEX-153, 170g of core-shell rubber (PBd), and 90g of silicone-modified toughening agent ES-3866(EX) were added sequentially, stirring for 1h. After the temperature dropped to 65℃, 70g of dicyandiamide curing agent (DICY) was added. After stirring for 10min, 50g of urea accelerator (UR300) was added. After stirring for 5min, 30g of DMP-30 was added, and the mixture was stirred for 10min to ensure uniform mixing, yielding a film resin composition. The above resin composition was then used to form a film using a hot-melt method, yielding a two-sided unit area weight of 135±12g / m². 2 A pure resin film was prepared and then composited with a polyester fiber mesh carrier to obtain a low-temperature curing structural adhesive film with a unit area weight of 300±24g / ㎡.

[0070] Performance testing:

[0071] Domestic 2A12-T4 aluminum material was used. The surface treatment of the aluminum material was carried out in accordance with HBZ197 "Specification for Phosphoric Anodic Anodizing Process of Structural Adhesive Aluminum Alloy". Metal single lap tensile shear strength test specimens and 90° plate-to-plate peel test specimens (metal to metal) were completed. The metal was cured in an autoclave at a curing temperature of 85℃ / 4h and a positive pressure of 0.2MPa.

[0072] The room temperature tensile shear test was completed according to GB 7124-2008, the high temperature tensile shear test was completed according to GJB 444-1988, the room temperature 90° peel strength test was completed according to GJB 446-1988, and the high temperature 90° peel strength test was completed according to GJB 447-88. The dry and wet glass transition temperatures of the structural adhesive film after curing were tested using the DSC method. The tack grade was evaluated using HB 7736.8. The wet treatment method was boiling in water for 72 hours. The data are shown in Table 1.

[0073] Table 1 Performance data of low-temperature curing structural adhesive films

[0074]

[0075]

[0076] As can be seen from the test data of Examples 1-2 and Comparative Example 1 in Table 1, Comparative Example 1, which uses imidazole adduct PN-31J and secondary thiol (tetra(3-mercaptobutyric acid) pentaerythritol ester) as the curing system, has significantly lower tensile shear strength, 90°C peel performance, heat resistance, and room temperature tack retention after curing than Examples 1 and 2. This indicates that the epoxy structural film prepared by the present invention using imidazole adduct and polysilazane as the curing system has significantly better performance than that of Comparative Example 1.

[0077] As can be seen from the test data of Examples 1-2 and Comparative Example 2 in Table 1, the epoxy structural adhesive film of the present invention exhibits superior tensile shear strength, 90℃ peel performance, heat resistance, and room temperature tack retention compared to Comparative Example 2 after curing. In Comparative Example 2, the epoxy structural adhesive film prepared using dicyandiamide curing agent DICY, urea accelerator UR300, and DMP-30 as the curing system was tested. The tack retention of the epoxy structural adhesive film in Comparative Example 2 was significantly lower than that of the present invention. This demonstrates that the epoxy structural adhesive film prepared by the present invention using imidazole adduct and polysilazane as the curing system significantly outperforms that of comparative example 2.

[0078] As can be seen from the test data in Table 1, the low-temperature curing epoxy structural adhesive film of this invention exhibits good mechanical properties after curing at 85℃, both at room temperature and 90℃, excellent resistance to damp heat, and a tack grade of 1 after two months at room temperature, still demonstrating good processability. This indicates that the low-temperature curing structural adhesive film of this invention possesses the characteristics of low-temperature curing and a long room temperature pot life. The formulation and preparation method of this invention not only endow the resulting epoxy structural adhesive film with toughness but also effectively improve the technical problem of short room temperature tack pot life. In the field of composite materials, it has significant application advantages for bonding materials such as sheet-to-sheet and sheet-to-core.

Claims

1. A low-temperature curing epoxy structural adhesive film, characterized in that, The epoxy structural film is prepared by hot-melt composite of liquid bisphenol A epoxy resin, solid bisphenol A epoxy resin, multifunctional epoxy resin, toughening agent, curing agent, accelerator and carrier. By weight, it includes the following components: 15-25 parts liquid bisphenol A epoxy resin, 10-20 parts solid bisphenol A epoxy resin, 5-15 parts multifunctional epoxy resin, 30-60 parts toughening agent, 5-20 parts curing agent, 1-5 parts accelerator. The toughening agent, by weight, comprises the following components: 5-15 parts thermoplastic resin, 15-30 parts core-shell rubber, 5-15 parts organosilicon-modified toughening agent; The curing agent is an imidazole adduct; The accelerator is polysilazane.

2. The epoxy structural adhesive film according to claim 1, characterized in that, The liquid bisphenol A type epoxy resin includes one or more of epoxy resin E-51, epoxy resin E-54, epoxy resin CYD-128 or epoxy resin CYD-127.

3. The epoxy structural adhesive film according to claim 1, characterized in that, Solid bisphenol A type epoxy resins include one or more of epoxy resin E-20, epoxy resin NPES-901, polyurethane modified NPEX-152, or polyurethane modified NPEX-153.

4. The epoxy structural adhesive film according to claim 1, characterized in that, Multifunctional epoxy resins include one or more of TDE-85, TDE-86, AFG-90 or AG-80.

5. The epoxy structural adhesive film according to claim 1, characterized in that, Thermoplastic resins include one or more of polysulfone (PSF), polyetherketone (PEK), polyetheretherketone (PEEK), or polyimide. Core-shell rubbers include one or more of polybutadiene, polystyrene, polystyrene-butadiene rubber, or polysilicon nano-rubber; Organosilicon-modified toughening agents include one or both of ES-3868 or ES-3866.

6. The epoxy structural adhesive film according to claim 1, characterized in that, The imidazole adduct is selected from one or more of PN-40, PN-30 or PN-31J.

7. The epoxy structural adhesive film according to claim 1, characterized in that, The carrier is selected from either glass fiber or polyester fiber.

8. The epoxy structural adhesive film according to claim 1, characterized in that, The areal density of the carrier is 25-35 g / m².

9. The epoxy structural adhesive film according to claim 1, characterized in that, The areal density of the epoxy structural adhesive film is 276-324 g / m³. 2 .

10. The method for preparing the epoxy structural adhesive film according to any one of claims 1-9, characterized in that, Includes the following: 1) Add liquid bisphenol A type epoxy resin, multifunctional epoxy resin and thermoplastic resin powder into a mixing device, disperse at 120℃ for 2-3 hours, and mix thoroughly. 2) Add solid bisphenol A type epoxy resin, core-shell rubber and organosilicon modified toughening agent, mix and disperse at 120℃ for 1-2 hours, and mix thoroughly; 3) After cooling to 65℃, add the curing agent and stir for 10-20 minutes; 4) Maintain the reaction temperature, add the accelerator, and stir for 5-10 minutes until the mixture is homogeneous to obtain the resin composition; 5) The above resin composition is used to complete the film preparation by hot melt method to obtain a resin pure film with two sides; the two resin pure films are combined with the carrier to obtain an epoxy structural adhesive film.

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