Medium-temperature curing high-temperature-resistant high-adhesion epoxy structural adhesive film as well as preparation method and application thereof

Abstract

The invention discloses a medium-temperature curing high-temperature-resistant high-adhesion epoxy structural adhesive film as well as a preparation method and application thereof. The preparation method comprises the following steps: reacting high-rigidity diisocyanate with polyether polyol to obtain a polyurethane prepolymer, then adding bisphenol epoxy resin to carry out grafting reaction, and then adding carboxyl-terminated nitrile rubber to react with an epoxy group to obtain the high-temperature-resistant high-adhesion epoxy resin. And finally, mixing with a curing system and coating to obtain the intermediate-temperature curing high-temperature-resistant high-adhesion epoxy structural adhesive film. The preparation process disclosed by the invention is reasonable, and the high-temperature resistance of the adhesive film is remarkably improved by introducing high-rigidity groups such as naphthalene ring, biphenyl or p-benzene while the excellent processing property of the adhesive film is ensured; and through the synergistic effect of the polyurethane flexible chain segment and the nitrile rubber, the toughness and the adhesive property of a resin system are improved, and the loss of the resin in the forming process is reduced.

Description

Technical Field

[0001] The invention belongs to the field of epoxy adhesives, and particularly relates to a medium-temperature curing, high-temperature resistant, high-bonding epoxy structural adhesive film, and a preparation method and application thereof. Background Art

[0002] Medium-temperature curing (120±5℃) epoxy structural adhesive films are widely used for bonding and repairing high-temperature resistant composite materials in sandwich structures of mechanical structures such as aerospace and aviation. Compared with high-temperature curing (170-180℃), medium-temperature curing films can effectively avoid the problems of stress deformation and debonding and cracking caused by inconsistent expansion coefficients of metal parts and composite materials in large composite sandwich structures. However, due to the curing temperature, the heat resistance of medium-temperature curing epoxy structural adhesive films is limited, and the general upper limit of the operating temperature is 120℃, which limits its mass application in the above-mentioned fields.

[0003] Traditional medium-temperature curing epoxy structural adhesive films are mostly thermoplastics such as polysulfone, polyethersulfone or nitrile rubber modified epoxy resin systems, both of which have high bonding strength. However, in order to achieve high bonding performance, the introduction of a large number of thermoplastics usually leads to a sharp increase in the viscosity of the epoxy resin, which not only makes processing difficult but also prone to phase separation. In addition, while nitrile rubber toughens epoxy, it will reduce the glass transition temperature of the system, making it difficult to meet the technical requirements of high temperature resistance of structural adhesive films.

[0004] At present, some research has been devoted to solving the above problems. For example, Chinese patent application CN117186817A uses high-reactivity, high-temperature resistant epoxy resin and high-toughness multifunctional epoxy resin and toughening agent system to prepare epoxy structural adhesive film with excellent bonding performance. However, the glass transition temperature of the film is only 139.2℃, the shear strength at 130℃ is only 11.7MPa, and the retention rate of high-temperature shear strength at 130℃ is only 37.5%. For another example, Chinese patent application CN108624002A uses "special epoxy resin-aromatic amine curing agent" as the curing system and special thermoplastic resin and rubber elastomer as toughening agents to prepare a high-temperature durable epoxy structural adhesive system. The temperature resistance grade of this adhesive system reaches 175℃, and the glass transition temperature is 190℃. However, this system uses aromatic amine curing agent and requires high-temperature curing at 175-180℃, which is difficult to meet the technical requirements of medium-temperature curing of structural adhesive film.

[0005] Therefore, there is an urgent need for an epoxy structural adhesive film that is medium-temperature curing, high-temperature resistant, and has excellent bonding properties. Summary of the invention

[0006] In order to solve at least some of the technical problems in the above-mentioned prior art, the present invention improves the high temperature resistance of the adhesive film by introducing high rigidity groups such as naphthalene rings, biphenyl or benzene, and increases toughness and improves bonding performance through the synergistic effect of polyurethane flexible segments and nitrile rubber, thereby obtaining an epoxy structural adhesive film that is cured at medium temperature, resistant to high temperatures, and has excellent bonding and process performance. Specifically, the present invention includes the following contents.

[0007] A first aspect of the present invention provides a method for preparing a medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film, which comprises the following steps:

[0008] (1) reacting a high-rigidity diisocyanate with a polyether polyol at 70-100° C. for 2-4 hours in the presence of a catalyst to obtain an isocyanate-terminated polyurethane prepolymer;

[0009] (2) subjecting the isocyanate-terminated polyurethane prepolymer to a grafting reaction with a bisphenol epoxy resin at 100-130° C. for 2-5 hours to obtain an intrinsically flexible high-temperature resistant epoxy resin;

[0010] (3) reacting the intrinsically flexible high temperature resistant epoxy resin with the carboxyl-terminated nitrile rubber at 130-160° C. for 2-5 hours to obtain a high temperature resistant and highly adhesive epoxy resin;

[0011] (4) mixing the high temperature resistant high adhesion epoxy resin with a latent curing system to obtain a medium temperature curing high temperature resistant high adhesion adhesive film epoxy resin;

[0012] (5) coating the medium temperature curing high temperature resistant high adhesion adhesive film with epoxy resin to obtain a medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film.

[0013] In certain embodiments, according to the preparation method of the present invention, in step (1), the catalyst includes at least one of a tertiary amine, an organic metal compound, an alkali metal phenolate and an alkali metal alcoholate; the high-rigidity diisocyanate includes at least one of 1,5-naphthalene diisocyanate, dimethyl diphenyl diisocyanate and p-phenylene diisocyanate; and the polyether polyol includes at least one of polypropylene glycol, polyoxypropylene triol, polytetramethylene glycol, polybutadiene diol and polybutadiene-propylene copolymer glycol.

[0014] In certain embodiments, according to the preparation method of the present invention, in step (1), the molar ratio of the high rigidity diisocyanate to the polyether polyol is (8-5):4, calculated as -NCO:-OH; and the amount of the catalyst used is 0.05-1% of the weight of the terminal isocyanate polyurethane prepolymer.

[0015] In certain embodiments, according to the preparation method of the present invention, in step (2), the bisphenol epoxy resin includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, bisphenol AD ​​epoxy resin and hydrogenated bisphenol A epoxy resin.

[0016] In certain embodiments, according to the preparation method of the present invention, in step (2), the amount of the isocyanate-terminated polyurethane prepolymer is 10-40% by weight of the bisphenol-type epoxy resin.

[0017] In certain embodiments, according to the preparation method of the present invention, in step (3), the amount of the carboxyl-terminated nitrile rubber is 5-20% by weight of the intrinsically flexible high temperature resistant epoxy resin.

[0018] In certain embodiments, according to the preparation method of the present invention, in step (4), the latent curing system includes at least one of dicyandiamide, modified dicyandiamide and urea derivatives.

[0019] In certain embodiments, according to the preparation method of the present invention, in step (4), the amount of the latent curing system is 5-10% by weight of the high temperature resistant high adhesion epoxy resin.

[0020] The second aspect of the present invention provides a medium-temperature curing high-temperature resistant high-adhesion epoxy structural adhesive film, which is obtained by the preparation method of the present invention.

[0021] The third aspect of the present invention provides the use of the medium-temperature curing high-temperature resistant and high-adhesion epoxy structural adhesive film of the present invention in the bonding or repair of high-temperature resistant materials.

[0022] The present invention has the following beneficial effects:

[0023] First, compared with diphenylmethane diisocyanate and toluene diisocyanate in the prior art, the molecules of the diisocyanate used in the present invention have higher rigidity, regularity and symmetry, and by introducing high rigidity naphthalene rings, biphenyl or benzene groups in the epoxy resin structure, the resin matrix is ​​given good high temperature resistance. Secondly, the high rigidity group can fundamentally improve the phase separation degree of polyurethane, so that the polyurethane modified epoxy resin obtains more excellent bonding performance, and at the same time, after the curing of the nitrile rubber segment, the "interpenetrating network" and "sea-island" state microscopic phase separation structure are used to collaboratively achieve the high bonding performance of epoxy resin for adhesive film. In addition, the present invention improves the viscosity of the epoxy structure adhesive film and reduces the fluidity of the adhesive film by reasonably controlling the raw material ratio and the modified process route, effectively avoiding the problem of local poor glue on the upper panel and the honeycomb bonding surface caused by the low viscosity during the curing process of the adhesive film, and significantly improving the processability of the adhesive film while ensuring the bonding performance of the sandwich structure. DETAILED DESCRIPTION

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that the upper and lower limits of the scope and each intermediate value therebetween are specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0026] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0027] Preparation method

[0028] One aspect of the present invention provides a method for preparing a medium-temperature curing high-temperature resistant high-adhesion epoxy structural adhesive film.

[0029] In a preferred embodiment, the preparation method of the present invention comprises the following steps:

[0030] (1) reacting a high rigidity diisocyanate with a polyether polyol at 70-100° C., for example, 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., or 100° C., in the presence of a catalyst, for 2-4 hours, for example, 2, 2.5, 3, 3.5, or 4 hours, to obtain an isocyanate-terminated polyurethane prepolymer;

[0031] (2) subjecting the isocyanate-terminated polyurethane prepolymer to a grafting reaction with a bisphenol epoxy resin at 100-130° C., for example, 100° C., 105° C., 110° C., 115° C., 120° C., 125° C., and 130° C., for a reaction time of 2-5 h, for example, 2, 2.5, 3, 3.5, 4, 4.5, and 5 h, to obtain an intrinsically flexible high-temperature resistant epoxy resin;

[0032] (3) reacting the intrinsic flexible high temperature resistant epoxy resin with the carboxyl-terminated nitrile rubber at 130-160° C., for example, 130° C., 135° C., 140° C., 145° C., 150° C., 155° C., and 160° C., for a reaction time of 2-5 h, for example, 2, 2.5, 3, 3.5, 4, 4.5, and 5 h, to obtain a high temperature resistant and highly adhesive epoxy resin;

[0033] (4) mixing the high temperature resistant high adhesion epoxy resin with a latent curing system to obtain a medium temperature curing high temperature resistant high adhesion adhesive film epoxy resin;

[0034] (5) coating the medium temperature curing high temperature resistant high adhesion adhesive film with epoxy resin to obtain a medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film.

[0035] In step (1) of the present invention, the catalyst comprises at least one of a tertiary amine, an organometallic compound, an alkali metal phenolate and an alkali metal alcoholate. In a preferred embodiment, the catalyst is a tertiary amine. In another preferred embodiment, the catalyst is an alkali metal phenolate and an alkali metal alcoholate. In another preferred embodiment, the catalyst is an organometallic compound.

[0036] In step (1) of the present invention, the high rigidity diisocyanate includes at least one of 1,5-naphthalene diisocyanate, dimethyl diphenyl diisocyanate and p-phenylene diisocyanate. In a preferred embodiment, the high rigidity diisocyanate is 1,5-naphthalene diisocyanate. In another preferred embodiment, the high rigidity diisocyanate is 1,5-naphthalene diisocyanate and dimethyl diphenyl diisocyanate. In another preferred embodiment, the high rigidity diisocyanate is p-phenylene diisocyanate.

[0037] In step (1) of the present invention, the polyether polyol comprises at least one of polypropylene glycol, polyoxypropylene triol, polytetrahydrofuran diol, polybutadiene glycol and polybutadiene-propylene copolymer glycol. In a preferred embodiment, the polyether polyol is polypropylene glycol. In another preferred embodiment, the polyether polyol is polybutadiene glycol and polybutadiene-propylene copolymer glycol. In another preferred embodiment, the polyether polyol is polytetrahydrofuran diol.

[0038] In order to improve the high temperature resistance of the medium temperature curing high temperature resistant high bonding epoxy structural adhesive film, the molar ratio of high rigidity diisocyanate to polyether polyol should not be too high or too low, and the amount of catalyst should be controlled within an appropriate range. In the present invention, the molar ratio of the diisocyanate to the polyether polyol is (8-5):4, such as 8:4, 7.5:4, 7:4, 6.5:4, 6:4, 5.5:4, 5:4, based on -NCO:-OH. The amount of the catalyst is 0.05-1% of the weight of the terminal isocyanate polyurethane prepolymer, such as 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%. In a preferred embodiment, the molar ratio of the diisocyanate to the polyether polyol is 8:4, and the amount of the catalyst is 1% of the weight of the terminal isocyanate polyurethane prepolymer. In another preferred embodiment, the molar ratio of the diisocyanate to the polyether polyol is 6.5:4, and the amount of the catalyst is 0.525% by weight of the isocyanate-terminated polyurethane prepolymer. In another preferred embodiment, the molar ratio of the diisocyanate to the polyether polyol is 5:4, and the amount of the catalyst is 0.05% by weight of the isocyanate-terminated polyurethane prepolymer.

[0039] In step (2) of the present invention, the bisphenol epoxy resin includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, bisphenol AD ​​epoxy resin and hydrogenated bisphenol A epoxy resin. In a preferred embodiment, the bisphenol epoxy resin is bisphenol A epoxy resin. In another preferred embodiment, the bisphenol epoxy resin is bisphenol S epoxy resin and bisphenol AD ​​epoxy resin. In another preferred embodiment, the bisphenol epoxy resin is bisphenol AD ​​epoxy resin.

[0040] In order to modify the epoxy resin and improve the high temperature resistance of the medium temperature curing high temperature resistant high bonding epoxy structural adhesive film, the amount of the terminal isocyanate polyurethane prepolymer should not be too high or too low. In the present invention, the amount of the terminal isocyanate polyurethane prepolymer is 10-40% of the weight of the bisphenol epoxy resin, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%. In a preferred embodiment, the amount of the terminal isocyanate polyurethane prepolymer is 10% of the weight of the bisphenol epoxy resin. In another preferred embodiment, the amount of the terminal isocyanate polyurethane prepolymer is 25% of the weight of the bisphenol epoxy resin. In another preferred embodiment, the amount of the terminal isocyanate polyurethane prepolymer is 40% of the weight of the bisphenol epoxy resin.

[0041] In order to improve the high bonding performance of the medium temperature curing high temperature resistant high bonding epoxy structural adhesive film, the amount of the terminal carboxyl nitrile rubber should not be too high or too low. In step (3) of the present invention, the amount of the terminal carboxyl nitrile rubber is 5-20% of the weight of the intrinsic flexible high temperature resistant epoxy resin, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%. In a preferred embodiment, the amount of the terminal carboxyl nitrile rubber is 5% of the weight of the intrinsic flexible high temperature resistant epoxy resin. In another preferred embodiment, the amount of the terminal carboxyl nitrile rubber is 12.5% ​​of the weight of the intrinsic flexible high temperature resistant epoxy resin. In another preferred embodiment, the amount of the terminal carboxyl nitrile rubber is 20% of the weight of the intrinsic flexible high temperature resistant epoxy resin.

[0042] In step (4) of the present invention, the latent curing system comprises at least one of dicyandiamide, modified dicyandiamide and urea derivatives. In a preferred embodiment, the latent curing system is a modified dicyandiamide curing system. In another preferred embodiment, the latent curing system is a combined curing system of modified dicyandiamide and urea derivatives. In another preferred embodiment, the latent curing system is a urea derivative curing system.

[0043] In a preferred embodiment, the latent curing system is used in an amount of 5-10% by weight of the high temperature resistant high adhesion epoxy resin, such as 5%, 6%, 7%, 8%, 9%, 10%.

[0044] The preparation method of the invention significantly improves the high temperature resistance of the adhesive film by introducing high rigidity naphthalene ring, biphenyl or p-phenyl groups, and increases the toughness and bonding performance of the resin system through the synergistic effect of polyurethane flexible segments and nitrile rubber.

[0045] Epoxy structural film

[0046] The present invention further provides a medium-temperature curing high-temperature resistant high-adhesion epoxy structural adhesive film, which is obtained by the preparation method of the present invention.

[0047] In the present invention, the medium-temperature curing high-temperature resistant and high-adhesion epoxy structural adhesive film is prepared from the following raw materials: 0.01-10 parts by weight of a catalyst, 1-20 parts by weight of a high-rigidity diisocyanate, 1-20 parts by weight of a polyether polyol, 50-120 parts by weight of a bisphenol-type epoxy resin, 5-30 parts by weight of a terminal carboxyl nitrile rubber and 5-20 parts by weight of a latent curing system.

[0048] In the present invention, the glass transition temperature, room temperature shear strength, peel strength and high temperature shear strength of the epoxy structural adhesive film can be measured by methods and devices known in the art, and there is no particular limitation on this.

[0049] In a preferred embodiment, the medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film of the present invention has a glass transition temperature of 153.1-155.7°C.

[0050] In a preferred embodiment, the medium-temperature curing high-temperature resistant high-adhesion epoxy structural adhesive film of the present invention has a room temperature tensile shear strength of not less than 35 MPa.

[0051] In a preferred embodiment, the medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film of the present invention has a 90° board-core peel strength of not less than 75 N / cm.

[0052] In a preferred embodiment, the medium-temperature curing high-temperature resistant high-adhesion epoxy structural adhesive film of the present invention has a 130° C. tensile shear strength of not less than 25 MPa.

[0053] In a preferred embodiment, the medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film of the present invention has a 150° C. tensile shear strength of not less than 15 MPa.

[0054] application

[0055] In one aspect of the present invention, there is provided an application of the medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film according to the present invention in bonding or repairing high temperature resistant composite materials. The high temperature resistant composite materials include but are not limited to high temperature resistant composite materials for mechanical structures. The mechanical structures include but are not limited to aviation mechanical structures, automobile mechanical structures, marine mechanical structures, wind power equipment mechanical structures, etc.

[0056] Example 1

[0057] This embodiment shows the preparation method and performance test of the medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film.

[0058] 1. Preparation method

[0059] In the presence of a tertiary amine catalyst, 1,5-naphthalene diisocyanate and polypropylene glycol are reacted at a molar ratio of -NCO:-OH=8:4 at 70°C for 4 hours to obtain a terminal isocyanate polyurethane prepolymer, wherein the amount of the catalyst is 1 part by weight relative to 100 parts by weight of the terminal isocyanate polyurethane prepolymer; the terminal isocyanate polyurethane prepolymer obtained in the above step is further grafted with bisphenol A epoxy resin at 100°C for 5 hours to prepare an intrinsic flexible high temperature resistant epoxy resin, wherein relative to 100 parts by weight of the bisphenol A epoxy resin, The amount of the terminal isocyanate polyurethane prepolymer is 10 parts by weight; the intrinsic flexible high-temperature resistant epoxy resin obtained in the above step and the terminal carboxyl nitrile rubber are continuously reacted at 130°C for 5 hours to prepare a high-temperature resistant and high-bonding epoxy resin, wherein the amount of the terminal carboxyl nitrile rubber is 20 parts by weight relative to 100 parts by weight of the intrinsic flexible high-temperature resistant epoxy resin; 10 parts by weight of the modified dicyandiamide curing system are added to 100 parts by weight of the high-temperature resistant and high-bonding epoxy resin obtained in the above step, mixed evenly, and coated with a calender to prepare a medium-temperature cured high-temperature resistant and high-bonding epoxy structural adhesive film.

[0060] 2. Performance Testing

[0061] The film was cured at 120°C for 2 h, and the glass transition temperature, room temperature shear strength, 90° peel strength, shear strength at 130°C, and shear strength at 150°C of the structural adhesive film were tested. The results are shown in Table 1.

[0062] Example 2

[0063] This embodiment shows the preparation method and performance test of the medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film.

[0064] 1. Preparation method

[0065] In the presence of a combined catalyst of an alkali metal phenolate and an alkali metal alcoholate, 1,5-naphthalene diisocyanate and dimethylbiphenyl diisocyanate are combined with polybutadiene diol and polybutadiene-propylene copolymer diol at a molar ratio of -NCO:-OH=6.5:4 and reacted at 85°C for 3 hours to obtain a terminal isocyanate-based polyurethane prepolymer, wherein the amount of the catalyst is 0.525 parts by weight relative to 100 parts by weight of the terminal isocyanate-based polyurethane prepolymer; the terminal isocyanate-based polyurethane prepolymer obtained in the above step is combined with a bisphenol S epoxy resin and a bisphenol AD ​​epoxy resin for further grafting reaction at 115°C for 3.5 hours to prepare an intrinsically flexible high-temperature resistant epoxy resin, wherein the relative For 100 parts by weight of a combination of bisphenol S epoxy resin and bisphenol AD ​​epoxy resin, the amount of the terminal isocyanate polyurethane prepolymer is 25 parts by weight; the intrinsic flexible high temperature resistant epoxy resin obtained in the above step is continuously reacted with the terminal carboxyl nitrile rubber at 145°C for 3.5 hours to prepare a high temperature resistant and high adhesion epoxy resin, wherein the amount of the terminal carboxyl nitrile rubber is 12.5 parts by weight relative to 100 parts by weight of the intrinsic flexible high temperature resistant epoxy resin; 7.5 parts by weight of a combined curing system of modified dicyandiamide and urea derivatives are added to 100 parts by weight of the high temperature resistant and high adhesion epoxy resin obtained in the above step, mixed evenly, and coated with a calender to prepare a medium temperature curing high temperature resistant and high adhesion epoxy structural adhesive film.

[0066] 2. Performance Testing

[0067] The film was cured at 120°C for 2 h, and the glass transition temperature, room temperature shear strength, 90° peel strength, shear strength at 130°C, and shear strength at 150°C of the structural adhesive film were tested. The results are shown in Table 1.

[0068] Example 3

[0069] This embodiment shows the preparation method and performance test of the medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film.

[0070] 1. Preparation method

[0071] In the presence of an organic metal compound catalyst, p-phenylene diisocyanate and polytetrahydrofuran diol are reacted at a molar ratio of -NCO:-OH=5:4 at 100°C for 2 hours to obtain a terminal isocyanate polyurethane prepolymer, wherein the amount of the catalyst is 0.05 parts by weight relative to 100 parts by weight of the terminal isocyanate polyurethane prepolymer; the terminal isocyanate polyurethane prepolymer obtained in the above step is further grafted with a bisphenol AD ​​type epoxy resin at 130°C for 2 hours to prepare an intrinsic flexible high temperature resistant epoxy resin, wherein the amount of the catalyst is 0.05 parts by weight relative to 100 parts by weight of the bisphenol AD ​​type epoxy resin. type epoxy resin, the amount of terminal isocyanate polyurethane prepolymer is 40 parts by weight; the intrinsic flexible high temperature resistant epoxy resin obtained in the above step and the terminal carboxyl nitrile rubber are continued to react at 160°C for 2 hours to prepare a high temperature resistant and high adhesion epoxy resin, wherein, relative to 100 parts by weight of the intrinsic flexible high temperature resistant epoxy resin, the amount of the terminal carboxyl nitrile rubber is 5 parts by weight; 5 parts by weight of urea derivative curing system are added to 100 parts by weight of the high temperature resistant and high adhesion epoxy resin obtained in the above step, mixed evenly, and coated with a calender to prepare a medium temperature curing high temperature resistant and high adhesion epoxy structural adhesive film.

[0072] 2. Performance Testing

[0073] The film was cured at 120°C for 2 h, and the glass transition temperature, room temperature shear strength, 90° peel strength, shear strength at 130°C, and shear strength at 150°C of the structural adhesive film were tested. The results are shown in Table 1.

[0074] Comparative Example 1

[0075] This comparative example shows the preparation method and performance test of the medium-temperature curing epoxy structural adhesive film.

[0076] 1. Preparation method

[0077] In the presence of a tertiary amine catalyst, diphenylmethane diisocyanate and polypropylene glycol are reacted at a molar ratio of -NCO:-OH=8:4 at 70°C for 4 hours to obtain a terminal isocyanate polyurethane prepolymer, wherein the amount of the catalyst is 1 part by weight relative to 100 parts by weight of the terminal isocyanate polyurethane prepolymer; the terminal isocyanate polyurethane prepolymer obtained in the above step is further grafted with bisphenol A type epoxy resin at 100°C for 5 hours to prepare an intrinsic flexible epoxy resin, wherein the amount of the catalyst is 1 part by weight relative to 100 parts by weight of the bisphenol A type epoxy resin. The amount of phenol A type epoxy resin and terminal isocyanate polyurethane prepolymer is 10 parts by weight; the intrinsic flexible epoxy resin obtained in the above step and the terminal carboxyl nitrile rubber are continuously reacted at 130° C. for 5 hours to prepare a modified epoxy resin, wherein the amount of the terminal carboxyl nitrile rubber is 20 parts by weight relative to 100 parts by weight of the intrinsic flexible epoxy resin; 10 parts by weight of modified dicyandiamide curing system are added to 100 parts by weight of the modified epoxy resin obtained in the above step, mixed evenly, and coated with a calender to prepare a medium-temperature curing epoxy structural adhesive film.

[0078] 2. Performance Testing

[0079] The film was cured at 120°C for 2 h, and the glass transition temperature, room temperature shear strength, 90° peel strength, shear strength at 130°C, and shear strength at 150°C of the structural adhesive film were tested. The results are shown in Table 1.

[0080] Comparative Example 2

[0081] This comparative example shows the preparation method and performance test of the medium-temperature curing epoxy structural adhesive film.

[0082] 1. Preparation method

[0083] In the presence of a tertiary amine catalyst, 1,5-naphthalene diisocyanate and polypropylene glycol are reacted at a molar ratio of -NCO:-OH=8:4 at 70°C for 4 hours to obtain a terminal isocyanate polyurethane prepolymer, wherein the amount of the catalyst is 1 part by weight relative to 100 parts by weight of the terminal isocyanate polyurethane prepolymer; the terminal isocyanate polyurethane prepolymer obtained in the above step is further grafted with bisphenol A type epoxy resin at 100°C for 5 hours to prepare an intrinsic flexible high temperature resistant epoxy resin, wherein the amount of the terminal isocyanate polyurethane prepolymer is 10 parts by weight relative to 100 parts by weight of the bisphenol A type epoxy resin; 10 parts by weight of a modified dicyandiamide curing system is added to 100 parts by weight of the intrinsic flexible high temperature resistant epoxy resin obtained in the above step, the mixture is evenly mixed, and a calender is used to apply film to prepare a medium temperature curing epoxy structural adhesive film.

[0084] 2. Performance Testing

[0085] The film was cured at 120°C for 2 h, and the glass transition temperature, room temperature shear strength, 90° peel strength, shear strength at 130°C, and shear strength at 150°C of the structural adhesive film were tested. The results are shown in Table 1.

[0086] Comparative Example 3

[0087] This comparative example shows the preparation method and performance test of the medium-temperature curing epoxy structural adhesive film.

[0088] 1. Preparation method

[0089] Bisphenol A epoxy resin and terminal carboxyl nitrile rubber are reacted at 130° C. for 5 hours to prepare a modified epoxy resin, wherein the amount of the terminal carboxyl nitrile rubber is 20 parts by weight relative to 100 parts by weight of the bisphenol A epoxy resin; 10 parts by weight of a modified dicyandiamide curing system is added to 100 parts by weight of the modified epoxy resin obtained in the above step and mixed evenly, and a calender is used to apply film to prepare a medium-temperature curing epoxy structural adhesive film.

[0090] 2. Performance Testing

[0091] The film was cured at 120°C for 2 h, and the glass transition temperature, room temperature shear strength, 90° peel strength, shear strength at 130°C, and shear strength at 150°C of the structural adhesive film were tested. The results are shown in Table 1.

[0092] Table 1 Various properties of structural adhesive films of different embodiments and comparative examples

[0093]

[0094]

[0095] Compared with the comparative examples, the glass transition temperature of the medium-temperature cured high-temperature resistant high-bonding epoxy structural adhesive film prepared in the embodiment is greater than 150°C, and the film has excellent room temperature tensile shear strength and 90° board-core peeling strength performance, and the 130°C and 150°C tensile shear strength retention rates reach 70% and 42% respectively, with excellent high temperature resistance. In comparative example 1, the medium-temperature cured structural adhesive film prepared by conventional diphenylmethane diisocyanate and carboxyl-terminated nitrile rubber modified epoxy resin has a glass transition temperature of only 128.2°C, and a tensile shear strength retention rate of only 29% at a high temperature of 130°C, which is difficult to meet the technical requirements of high temperature resistance of epoxy structural adhesive film; in comparative example 2, the medium-temperature cured structural adhesive film prepared by 1,5-naphthalene diisocyanate modified epoxy resin has a high glass transition temperature, but the room temperature tensile shear strength is only 28.7MPa, and the 90° board-core peeling strength is less than 40N / cm, which is difficult to achieve the technical requirements of high bonding performance of the structural adhesive film. In comparative example 3, the medium temperature curing structural adhesive film prepared by using carboxyl-terminated nitrile rubber modified epoxy resin has good room temperature bonding performance, but the glass transition temperature is only 125.2°C, and the shear strength retention rate at a high temperature of 130°C is only 26%, which is also difficult to meet the technical requirements of high temperature resistance of epoxy structural adhesive film. The present invention ultimately solves the technical problem that medium temperature curing epoxy structural adhesive film is difficult to take into account both high temperature resistance and high bonding, and broadens the application of medium temperature curing epoxy structural adhesive film in the field of high temperature resistance.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some of the technical features therein 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 temperature resistant high adhesion epoxy structural adhesive film, characterized in that: The following steps are involved: (1) reacting a high-rigidity diisocyanate with a polyether polyol at 70-100° C. for 2-4 hours in the presence of a catalyst to obtain an isocyanate-terminated polyurethane prepolymer; (2) subjecting the isocyanate-terminated polyurethane prepolymer to a grafting reaction with a bisphenol epoxy resin at 100-130° C. for 2-5 hours to obtain an intrinsically flexible high-temperature resistant epoxy resin; (3) reacting the intrinsically flexible high temperature resistant epoxy resin with the carboxyl-terminated nitrile rubber at 130-160° C. for 2-5 hours to obtain a high temperature resistant and highly adhesive epoxy resin; (4) mixing the high temperature resistant high adhesion epoxy resin with a latent curing system to obtain a medium temperature curing high temperature resistant high adhesion adhesive film epoxy resin; (5) coating the medium temperature curing high temperature resistant high adhesion adhesive film with epoxy resin to obtain a medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film.

2. The preparation method according to claim 1, characterized in that: In step (1), the catalyst includes at least one of a tertiary amine, an organic metal compound, an alkali metal phenolate and an alkali metal alcoholate; the high-rigidity diisocyanate includes at least one of 1,5-naphthalene diisocyanate, dimethyl diphenyl diisocyanate and p-phenylene diisocyanate; and the polyether polyol includes at least one of polypropylene glycol, polyoxypropylene triol, polytetramethylene glycol, polybutadiene diol and polybutadiene-propylene copolymer glycol.

3. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of the high rigidity diisocyanate to the polyether polyol is (8-5):4, calculated on the basis of -NCO:-OH, and the amount of the catalyst used is 0.05-1% of the weight of the terminal isocyanate polyurethane prepolymer.

4. The preparation method according to claim 1, characterized in that: In step (2), the bisphenol epoxy resin includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, bisphenol AD ​​epoxy resin and hydrogenated bisphenol A epoxy resin.

5. The preparation method according to claim 1, characterized in that: In step (2), the amount of the isocyanate-terminated polyurethane prepolymer used is 10-40% by weight of the bisphenol epoxy resin.

6. The preparation method according to claim 1, characterized in that: In step (3), the amount of the carboxyl-terminated nitrile rubber is 5-20% of the weight of the intrinsically flexible high temperature resistant epoxy resin.

7. The preparation method according to claim 1, characterized in that: In step (4), the latent curing system includes at least one of dicyandiamide, modified dicyandiamide and urea derivatives.

8. The preparation method according to claim 1, characterized in that: In step (4), the amount of the latent curing system is 5-10% by weight of the high temperature resistant and high adhesion epoxy resin.

9. A medium temperature curing high temperature resistant high adhesion epoxy structural adhesive film, characterized in that: Obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the medium-temperature curing high-temperature resistant and high-bonding epoxy structural adhesive film according to claim 9 in bonding or repairing high-temperature resistant composite materials.

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