Intrinsic flame-retardant high-temperature-resistant epoxy structural adhesive film and application thereof

Abstract

The application discloses an intrinsic flame-retardant high-temperature-resistant epoxy structural adhesive film and application thereof. The application utilizes a phosphorus-containing polyol to react with a general diisocyanate to obtain an isocyanate-terminated polyurethane prepolymer, then liquid epoxy resin is added, in the presence of a catalyst, to initiate ring-opening reaction of isocyanate and epoxy groups to generate an oxazolidone heterocycle, then cashew phenol modified linear phenolic resin is introduced to react with epoxy groups, to obtain modified epoxy resin with halogen-free flame-retardant, high-temperature-resistant and high-adhesion characteristics, finally, the modified epoxy resin is mixed with a latent curing system uniformly and coated to prepare a halogen-free flame-retardant high-adhesion epoxy structural adhesive film. The preparation process of the application is reasonable, while ensuring excellent process performance of the adhesive film, the phosphorus-nitrogen synergistic flame-retardant effect and the phenolic resin are used to improve the flame-retardant and heat-resistant performance of the adhesive film, and the synergistic effect of the strong polar urethane structure and the modified linear phenolic resin increases the adhesion performance of the resin system.

Description

[0001] Cross-references to related applications This application is a divisional application of CN202610002281.7, filed on January 4, 2026, entitled "A halogen-free flame-retardant high-adhesion epoxy structural film and its preparation method and application", which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention belongs to the field of epoxy adhesive technology, and in particular relates to an intrinsically flame-retardant and high-temperature resistant epoxy structural film and its applications. Background Technology

[0003] With increasingly stringent environmental regulations worldwide (such as the EU RoHS Directive and REACH Regulation), and the ever-increasing demands from industries such as aerospace, rail transportation, and high-end electronics for the fire safety performance of materials (such as low heat release, low smoke density, and low toxicity), the development of novel halogen-free flame-retardant structural films that can replace traditional halogen-based flame-retardant epoxy systems has become an important research direction in this field.

[0004] Currently, research on halogen-free flame-retardant epoxy structural films mainly focuses on the formulation and application of flame retardants such as phosphorus-based (e.g., ammonium polyphosphate), nitrogen-based (e.g., melamine derivatives), silicon-based (e.g., silicone resins, silsesquioxanes), and inorganic hydroxides. However, to achieve the ideal flame retardant rating (e.g., UL 94 V-0), a high amount of flame retardant is often required, which can easily lead to a significant deterioration in the mechanical properties of the epoxy resin matrix, especially bond strength, peel strength, and glass transition temperature. In addition, most inorganic or organic flame-retardant fillers have poor interfacial compatibility with the epoxy matrix, which can easily cause stress concentration and become the starting point for material failure.

[0005] Several studies have been conducted to address these issues. For example, Chinese invention patent application CN102174173A discloses a flame-retardant latent epoxy curing agent and a method for preparing a halogen-free flame-retardant single-component epoxy resin composition. Although the resin system achieves UL 94V-0 flame retardancy, due to the rigid structure of DOPO itself, its modified derivatives exhibit significant brittleness after curing when used for flame-retardant epoxy films, making it difficult to meet the technical requirements for high peel strength in flame-retardant epoxy structural films. Another example is Chinese invention patent application CN101602925A, which discloses a halogen-free epoxy resin flame-retardant adhesive and a method for preparing its film. This method uses a compound of phosphorus-containing epoxy resin, phenolic epoxy resin, and nitrile rubber. While the prepared film exhibits certain flame-retardant properties, the introduction of nitrile rubber reduces the film's heat resistance. Furthermore, the film's peel strength is only 16 N / cm, still failing to meet the technical requirements for heat resistance and high adhesion of halogen-free flame-retardant epoxy films.

[0006] Therefore, overcoming the challenge of balancing flame retardancy, heat resistance, and adhesion, and developing epoxy structural adhesive films that combine ultra-high flame retardancy, high temperature resistance, and excellent adhesion, is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address at least some of the technical problems in the prior art, this invention introduces a phosphate ester structure and an oxazolidinone nitrogen heterocyclic structure into the main chain of an epoxy resin molecule. This achieves a synergistic flame-retardant effect of phosphorus and nitrogen, complemented by the high char residue of the phenolic resin backbone. Furthermore, the synergistic effect of the strongly polar urethane structure and the flexible long alkyl chains in the modified linear phenolic resin enhances the adhesive properties, resulting in a halogen-free, flame-retardant, high-temperature resistant epoxy structural adhesive film with excellent adhesive and processability properties. Specifically, this invention includes the following:

[0008] In a first aspect, the present invention provides an intrinsically flame-retardant and high-temperature resistant epoxy structural film, which is prepared from raw materials comprising: 1-50 parts by weight of general-purpose diisocyanate, 0.5-25 parts by weight of phosphorus-containing polyol, 5-200 parts by weight of liquid epoxy resin, 0.1-10 parts by weight of cashew nut shell modified linear phenolic resin, 0.01-2 parts by weight of catalyst, and 0.5-20 parts by weight of latent curing system. The epoxy structural film has a flame retardancy rating of not less than V-0, a room temperature tensile shear strength of not less than 31 MPa, a 100°C tensile shear strength of not less than 23 MPa, and a 90° core-to-board peel strength of not less than 63 N / cm.

[0009] In some embodiments, the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to the present invention, wherein the general-purpose diisocyanate includes at least one of diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0010] In some embodiments, the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to the present invention, wherein the phosphorus-containing polyol comprises at least one of N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl ester, N,N-di(2-hydroxyethyl)aminomethyl phosphate dimethyl ester, and organophosphate diol.

[0011] In some embodiments, the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to the present invention, wherein the catalyst comprises at least one selected from 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, n-butyllithium, and zinc carboxylate.

[0012] In some embodiments, the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to the present invention, wherein the liquid epoxy resin includes at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenol AD ​​type epoxy resin.

[0013] In some embodiments, the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to the present invention, wherein the latent curing system includes at least one of dicyandiamide, modified dicyandiamide, and urea derivatives.

[0014] A second aspect of the present invention provides a method for preparing an intrinsically flame-retardant and high-temperature resistant epoxy structural film, comprising the following steps: (1) React a general-purpose diisocyanate with a phosphorus-containing polyol at 60-80℃ for 2-4 h to obtain a polyurethane prepolymer with terminal isocyanate group, wherein the molar ratio of the general-purpose diisocyanate to the phosphorus-containing polyol is (8-5):4, based on -NCO:-OH. (2) Under the presence of a catalyst, the terminal isocyanate polyurethane prepolymer and liquid epoxy resin are reacted at 140-170℃ for 2-5 h to obtain an intrinsic flexible flame-retardant epoxy resin, wherein the mass ratio of the terminal isocyanate polyurethane prepolymer to the liquid epoxy resin is (20:80)-(35:65). (3) React the intrinsic flexible flame-retardant epoxy resin with cashew phenol modified linear phenolic resin at 100-120°C until the viscosity of the material at 100°C is 100,000-200,000 cps, to obtain intrinsic flame-retardant high-temperature resistant epoxy resin. (4) Mix the intrinsic flame-retardant and high-temperature resistant epoxy resin with a latent curing system to obtain a resin composition, and then coat it to obtain an intrinsic flame-retardant and high-temperature resistant epoxy structural film.

[0015] In some embodiments, according to the method for preparing the intrinsic flame-retardant and high-temperature resistant epoxy structural film of the present invention, the amount of the catalyst is 0.05-1% of the weight of the intrinsic flexible flame-retardant epoxy resin.

[0016] In some embodiments, according to the method for preparing the intrinsically flame-retardant and high-temperature resistant epoxy structural film of the present invention, the amount of the cashew phenol-modified linear phenolic resin is 5-15% of the weight of the intrinsically flexible flame-retardant epoxy resin. In some embodiments, according to the method for preparing the intrinsically flame-retardant and high-temperature resistant epoxy structural film of the present invention, the amount of the latent curing system is 5-15% of the weight of the intrinsically flame-retardant epoxy resin.

[0017] A third aspect of the invention provides the application of the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to the invention in the bonding or repair of flame-retardant composite materials.

[0018] This invention introduces phosphate ester structures, oxazolidinone nitrogen heterocyclic structures, and phenolic skeletons simultaneously into the epoxy resin backbone. Through the synergistic effect of phosphorus-nitrogen catalytic char formation and the rigid heterocyclic structure and highly cross-linked network, it endows the epoxy resin with highly efficient intrinsic flame-retardant properties and significantly increases the glass transition temperature of the cured product, achieving an integrated improvement in both flame retardancy and heat resistance. Secondly, the introduction of highly polar urethane and oxazolidinone structures gives the modified epoxy resin superior adhesion properties. Combined with the long alkyl chain flexible structure in the cashew phenol-modified linear phenolic resin, this further endows the epoxy film with excellent adhesion and flexibility. Furthermore, after a two-step chain extension reaction, the epoxy resin not only increases the distance between rigid cross-linking points in the cross-linked network of the cured product, significantly improving the resin's toughness, but also greatly increases the molecular weight and viscosity of the modified resin. This effectively avoids the problem of localized resin deficiency at the bonding surface between the top panel and the honeycomb structure, significantly improving the film's processability while ensuring the bonding performance of the sandwich structure. Detailed Implementation

[0019] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0020] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that the upper and lower limits of the range and each intermediate value between them are specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0021] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention.

[0022] Preparation method One aspect of the present invention provides a method for preparing a halogen-free flame-retardant high-adhesion epoxy structural film, which includes steps (1)-(4), and will be described in detail below.

[0023] Step (1) of the present invention is the step of preparing isocyanate-terminated polyurethane prepolymer, specifically: reacting a general-purpose diisocyanate with a phosphorus-containing polyol at 60-80℃ (e.g., 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80℃) for 2-4 h (e.g., 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4 h) to obtain the isocyanate-terminated polyurethane prepolymer.

[0024] To improve the flame retardancy, high-temperature resistance, and adhesion of the epoxy structural film, the molar ratio of the general-purpose diisocyanate to the phosphorus-containing polyol can be controlled within a suitable range. In this invention, the molar ratio of the general-purpose diisocyanate to the phosphorus-containing polyol, calculated as -NCO:-OH, is (8-5):4, for example, 8:4, 7.5:4, 7:4, 6.5:4, 6:4, 5.5:4, or 5:4. In a preferred embodiment, the molar ratio of the general-purpose diisocyanate to the phosphorus-containing polyol is 8:4. In another preferred embodiment, the molar ratio of the general-purpose diisocyanate to the phosphorus-containing polyol is 6.5:4. In yet another preferred embodiment, the molar ratio of the general-purpose diisocyanate to the phosphorus-containing polyol is 5:4.

[0025] To achieve the excellent flame retardancy, high temperature resistance, and adhesion of the halogen-free flame-retardant high-adhesion epoxy structural film, the phosphorus content of the phosphorus-containing polyol in this invention can be controlled within a suitable range. In this invention, the phosphorus content of the phosphorus-containing polyol is 10-15%, preferably 10.2-14.5%, even more preferably 10.4-14%, further preferably 10.6-13.5%, more preferably 10.8-13%, and even more preferably 11-13%, for example 11, 11.2, 11.4, 11.6, 11.8, 12, 12.2, 12.4, 12.6, 12.8, and 13%. The phosphorus-containing polyol is not particularly limited, as long as it has a suitable phosphorus content. Examples include, but are not limited to, diethyl N,N-di(2-hydroxyethyl)aminomethylene phosphate, dimethyl N,N-di(2-hydroxyethyl)aminomethyl phosphate, and organophosphate diols. In one preferred embodiment, the phosphorus-containing polyol is diethyl N,N-di(2-hydroxyethyl)aminomethylene phosphate with a phosphorus content of 12.1%. In another preferred embodiment, the phosphorus-containing polyol is diethyl N,N-di(2-hydroxyethyl)aminomethylene phosphate with a phosphorus content of 12.1% and dimethyl N,N-di(2-hydroxyethyl)aminomethyl phosphate with a phosphorus content of 13.6%. In yet another preferred embodiment, the phosphorus-containing polyol is an organophosphate diol with a phosphorus content of 11-13%.

[0026] Step (2) of the present invention is a step of preparing intrinsic flexible flame-retardant epoxy resin, specifically: under the presence of a catalyst, the isocyanate-terminated polyurethane prepolymer and liquid epoxy resin are reacted at 140-170℃ (e.g. 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170℃) for 2-5 h (e.g. 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5 h) to obtain intrinsic flexible flame-retardant epoxy resin, wherein the isocyanate and epoxy group undergo a ring-opening reaction to generate an oxazolidinone structure.

[0027] In step (2) of this invention, in order to generate oxazolidinone from the isocyanate-terminated polyurethane prepolymer and liquid epoxy resin, thereby improving the flame retardancy, high temperature resistance, and adhesion of the halogen-free flame-retardant high-adhesion epoxy structural film, the isocyanate-terminated polyurethane prepolymer and liquid epoxy resin need to react under suitable temperature conditions in the presence of a catalyst. The catalyst is not particularly limited, but examples include, but are not limited to, 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, n-butyllithium, and zinc carboxylate. In a preferred embodiment, the catalyst is 2-methylimidazole. In another preferred embodiment, the catalyst is n-butyllithium and zinc carboxylate. In yet another preferred embodiment, the catalyst is 2-ethyl-4-methylimidazole.

[0028] To better promote the formation of oxazolidinone from the isocyanate-terminated polyurethane prepolymer and liquid epoxy resin, thereby improving the flame retardancy, high-temperature resistance, and adhesion of the epoxy structural film of the present invention, the amount of catalyst can be controlled within a suitable range. In this invention, the amount of catalyst is 0.05-1% of the weight of the intrinsically flexible flame-retardant epoxy resin, for example, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0. 42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1%. In a preferred embodiment, the amount of catalyst is 1% of the weight of the intrinsically flexible flame-retardant epoxy resin. In another preferred embodiment, the amount of catalyst is 0.525% of the weight of the intrinsically flexible flame-retardant epoxy resin. In yet another preferred embodiment, the amount of catalyst is 0.05% of the weight of the intrinsically flexible flame-retardant epoxy resin.

[0029] To achieve excellent flame retardancy, high-temperature resistance, and adhesion of the epoxy structural film, the mass ratio of the isocyanate-terminated polyurethane prepolymer to the liquid epoxy resin can be controlled within a suitable range. In this invention, the mass ratio of the isocyanate-terminated polyurethane prepolymer to the liquid epoxy resin is (20:80)–(35:65), for example, 20:80, 21:79, 22:78, 23:77, 24:76, 25:75, 26:74, 27:73, 28:72, 29:71, 30:70, 31:69, 32:68, 33:67, 34:66, and 35:65. In a preferred embodiment, the mass ratio of the isocyanate-terminated polyurethane prepolymer to the liquid epoxy resin is 35:65. In another preferred embodiment, the mass ratio of the isocyanate-terminated polyurethane prepolymer to the liquid epoxy resin is 27.5:72.5. In yet another preferred embodiment, the mass ratio of the terminal isocyanate-based polyurethane prepolymer to the liquid epoxy resin is 20:80.

[0030] Step (3) of this invention is the step of preparing halogen-free flame-retardant high-adhesion epoxy resin, specifically: reacting the intrinsically flexible flame-retardant epoxy resin with cashew nut phenol modified linear phenolic resin at 100-120℃ (100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120℃) until the viscosity of the material at 100℃ is 100,000-200,000 cps, preferably 110,000-190,000 cps, even more preferably 120,000-189,000 cps, further preferably 130,000-188,000 cps, more preferably 140,000-187,000 cps, and even more preferably 150,000-186,000 cps. After stopping the reaction (e.g., 150000, 152000, 154000, 156000, 158000, 160000, 162000, 164000, 166000, 168000, 170000, 172000, 174000, 176000, 178000, 180000, 182000, 184000, 186000 cps), a halogen-free flame-retardant high-adhesion epoxy resin is obtained.

[0031] To achieve excellent flame retardancy, high-temperature resistance, and adhesion of the epoxy structural film, the amount of cashew nut shell modified linear phenolic resin can be controlled within a suitable range. In this invention, the amount of cashew nut shell modified linear phenolic resin is 5-15% of the weight of the intrinsic flexible flame-retardant epoxy resin, for example, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 13.5, 14, 14.5, or 15%. In a preferred embodiment, the amount of cashew nut shell modified linear phenolic resin is 5% of the weight of the intrinsic flexible flame-retardant epoxy resin. In another preferred embodiment, the amount of cashew nut shell modified linear phenolic resin is 10% of the weight of the intrinsic flexible flame-retardant epoxy resin. In yet another preferred embodiment, the amount of cashew nut shell modified linear phenolic resin is 15% of the weight of the intrinsic flexible flame-retardant epoxy resin.

[0032] Step (4) of this invention is the step of preparing a halogen-free flame-retardant high-adhesion epoxy structural film, specifically: mixing the halogen-free flame-retardant high-adhesion epoxy resin with a latent curing system to obtain a resin composition, and then coating it to obtain a halogen-free flame-retardant high-adhesion epoxy structural film. The coating method is not particularly limited, and conventional equipment and methods in the art can be used, such as coating with a calender. The latent curing system is not particularly limited, and examples include, but are not limited to, dicyandiamide, modified dicyandiamide, urea derivatives, etc. In this invention, the amount of the latent curing system is 5-15% of the weight of the halogen-free flame-retardant high-adhesion epoxy resin, for example, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 13.5, 14, 14.5, 15%. In a preferred embodiment, the amount of the latent curing system is 10% of the weight of the halogen-free flame-retardant high-adhesion epoxy resin. In another preferred embodiment, the amount of dicyandiamide is 7.5% of the weight of the halogen-free flame-retardant high-adhesion epoxy resin, and the amount of the latent curing system is 5% of the weight of the halogen-free flame-retardant high-adhesion epoxy resin.

[0033] In this invention, the universal diisocyanate is a diisocyanate that does not contain rigid groups, examples of which include, but are not limited to, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. In a preferred embodiment, the universal diisocyanate is diphenylmethane diisocyanate. In another preferred embodiment, the universal diisocyanate is toluene diisocyanate and isophorone diisocyanate. In yet another preferred embodiment, the universal diisocyanate is hexamethylene diisocyanate.

[0034] In this invention, the liquid epoxy resin is not particularly limited, and examples include, but are not limited to, bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol AD ​​type epoxy resin. In a preferred embodiment, the liquid epoxy resin is a bisphenol A type epoxy resin. In another preferred embodiment, the liquid epoxy resin is both a bisphenol A type epoxy resin and a bisphenol F type epoxy resin. In yet another preferred embodiment, the liquid epoxy resin is a bisphenol AD ​​type epoxy resin.

[0035] Epoxy structural film In one aspect, the present invention provides a halogen-free flame-retardant high-adhesion epoxy structural film, which is obtained by the preparation method described in the present invention.

[0036] In a preferred embodiment, the halogen-free flame-retardant high-adhesion epoxy structural film of the present invention is prepared from raw materials comprising: 1-50 parts by weight of general-purpose diisocyanate, 0.5-25 parts by weight of phosphorus-containing polyol, 5-200 parts by weight of liquid epoxy resin, 0.1-10 parts by weight of cashew nut phenol modified linear phenolic resin, 0.01-2 parts by weight of catalyst, and 0.5-20 parts by weight of latent curing system.

[0037] In a preferred embodiment, the halogen-free flame-retardant high-adhesion epoxy structural film of the present invention is prepared from raw materials comprising: 5-45 parts by weight of general-purpose diisocyanate, 2-20 parts by weight of phosphorus-containing polyol, 10-180 parts by weight of liquid epoxy resin, 0.5-8 parts by weight of cashew nut phenol modified linear phenolic resin, 0.02-1.8 parts by weight of catalyst, and 2-18 parts by weight of latent curing system.

[0038] In a preferred embodiment, the halogen-free flame-retardant high-adhesion epoxy structural film of the present invention is prepared from raw materials comprising: 10-40 parts by weight of general-purpose diisocyanate, 5-18 parts by weight of phosphorus-containing polyol, 30-160 parts by weight of liquid epoxy resin, 1-8 parts by weight of cashew nut phenol modified linear phenolic resin, 0.05-1.6 parts by weight of catalyst, and 5-16 parts by weight of latent curing system.

[0039] In a preferred embodiment, the halogen-free flame-retardant high-adhesion epoxy structural film of the present invention is prepared from raw materials comprising: 10-35 parts by weight of general-purpose diisocyanate, 6-16 parts by weight of phosphorus-containing polyol, 35-150 parts by weight of liquid epoxy resin, 2-8 parts by weight of cashew nut phenol modified linear phenolic resin, 0.06-1.5 parts by weight of catalyst, and 6-15 parts by weight of latent curing system.

[0040] The performance testing of the halogen-free flame-retardant high-adhesion epoxy structural film of the present invention can be performed using methods and apparatus known in the art, and is not particularly limited thereto. In a preferred embodiment, the halogen-free flame-retardant high-adhesion epoxy structural film of the present invention has a flame retardancy rating of not less than V-0, a room temperature tensile shear strength of not less than 31 MPa, a 100°C tensile shear strength of not less than 23 MPa, and a 90° core-to-board peel strength of not less than 63 N / cm.

[0041] application One aspect of the present invention provides the application of the halogen-free flame-retardant high-adhesion epoxy structural film according to the present invention in the bonding or repair of flame-retardant composite materials. Examples of the flame-retardant composite materials include, but are not limited to, aerospace components (e.g., but not limited to main load-bearing structural components, engine components, radomes, control surfaces, fairings, protective materials, etc.), rail transit components (e.g., but not limited to front grilles, interior and exterior trim panels, floors, seat frames, etc.), high-end electronic components (e.g., but not limited to transformers, insulators, electronic circuit boards, etc.), and building materials (structural components, wall panels, floors, etc.).

[0042] Example 1 This embodiment illustrates the preparation method and performance testing of a halogen-free flame-retardant high-adhesion epoxy structural film.

[0043] 1. Preparation method (1) Diphenylmethane diisocyanate and N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl phosphate (phosphorus content 12.1%) were reacted at 60℃ for 4 h at a molar ratio of -NCO:-OH=8:4 to obtain isocyanate-terminated polyurethane prepolymer. (2) In the presence of a 2-methylimidazole catalyst, the isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol A type epoxy resin at 140°C for 5 h to prepare an intrinsic flexible flame-retardant epoxy resin. The amount of 2-methylimidazole is 1 part by weight, the amount of isocyanate-terminated polyurethane prepolymer is 35 parts by weight, and the amount of bisphenol A type epoxy resin is 65 parts by weight, relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin. (3) The intrinsic flexible flame-retardant epoxy resin obtained in the above steps is reacted with cashew phenol-modified linear phenolic resin at 100°C for 3 h. At this time, the viscosity of the material at 100°C is 152432 cps, and halogen-free flame-retardant high-adhesion epoxy resin can be obtained. Among them, the amount of cashew phenol-modified linear phenolic resin is 5 parts by weight relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin.

[0044] (4) Add dicyandiamide to the halogen-free flame-retardant high-adhesion epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a halogen-free flame-retardant high-adhesion epoxy structural film. The amount of dicyandiamide used is 10 parts by weight relative to 100 parts by weight of the halogen-free flame-retardant high-adhesion epoxy resin.

[0045] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0046] Example 2 This embodiment illustrates the preparation method and performance testing of a halogen-free flame-retardant high-adhesion epoxy structural film.

[0047] 1. Preparation method (1) Toluene diisocyanate and isophorone diisocyanate were reacted with N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl phosphate (phosphorus content 12.1%) and N,N-di(2-hydroxyethyl)aminomethyl phosphate dimethyl phosphate (phosphorus content 13.6%) at a molar ratio of -NCO:-OH = 6.5:4 at 70 °C for 3 h to obtain isocyanate-terminated polyurethane prepolymer; (2) In the presence of n-butyllithium and zinc carboxylate catalysts, the isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol A type epoxy resin and bisphenol F type epoxy resin at 155°C for 3.5 h to prepare intrinsic flexible flame-retardant epoxy resin. The amount of n-butyllithium and zinc carboxylate is 0.525 parts by weight, the amount of isocyanate-terminated polyurethane prepolymer is 27.5 parts by weight, and the amount of bisphenol A type epoxy resin and bisphenol F type epoxy resin is 72.5 parts by weight, relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin. (3) The intrinsic flexible flame-retardant epoxy resin obtained in the above steps is reacted with cashew phenol-modified linear phenolic resin at 110°C for 2 hours. At this time, the viscosity of the material at 100°C is 183827 cps, thus obtaining halogen-free flame-retardant high-adhesion epoxy resin. The amount of cashew phenol-modified linear phenolic resin used is 10 parts by weight relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin.

[0048] (4) Add dicyandiamide and urea derivatives to the halogen-free flame-retardant high-adhesion epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a halogen-free flame-retardant high-adhesion epoxy structural film. The amount of dicyandiamide and urea derivatives is 7.5 parts by weight relative to 100 parts by weight of the halogen-free flame-retardant high-adhesion epoxy resin.

[0049] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0050] Example 3 This embodiment illustrates the preparation method and performance testing of a halogen-free flame-retardant high-adhesion epoxy structural film.

[0051] 1. Preparation method (1) Hexamethylene diisocyanate and organophosphate diol (brand name: Exolit OP 560, phosphorus content 11-13%) were reacted at 80℃ for 2 h with a molar ratio of -NCO:-OH=5:4 to obtain isocyanate-terminated polyurethane prepolymer. (2) In the presence of a 2-ethyl-4-methylimidazole catalyst, the isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol AD ​​type epoxy resin at 170°C for 2 h to prepare an intrinsic flexible flame-retardant epoxy resin. The amount of 2-ethyl-4-methylimidazole is 0.05 parts by weight, the amount of isocyanate-terminated polyurethane prepolymer is 20 parts by weight, and the amount of bisphenol AD ​​type epoxy resin is 80 parts by weight, relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin. (3) The intrinsic flexible flame-retardant epoxy resin obtained in the above steps is reacted with cashew nut phenol modified linear phenolic resin at 120°C for 1 h. At this time, the viscosity of the material at 100°C is 162939 cps, and halogen-free flame-retardant high-adhesion epoxy resin can be obtained. Among them, the amount of cashew nut phenol modified linear phenolic resin is 15 parts by weight relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin.

[0052] (4) Add modified dicyandiamide to the halogen-free flame-retardant high-adhesion epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a halogen-free flame-retardant high-adhesion epoxy structural film. The amount of modified dicyandiamide used is 5 parts by weight relative to 100 parts by weight of the halogen-free flame-retardant high-adhesion epoxy resin.

[0053] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0054] Comparative Example 1 This comparative example illustrates the preparation method and performance testing of epoxy structural adhesive films.

[0055] 1. Preparation method (1) Diphenylmethane diisocyanate and N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl phosphate (phosphorus content 12.1%) were reacted at 60℃ for 4 h at a molar ratio of -NCO:-OH=8:4 to obtain isocyanate-terminated polyurethane prepolymer. (2) In the presence of a 2-methylimidazole catalyst, the isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol A type epoxy resin at 130°C for 5 h to prepare an intrinsic flexible flame-retardant epoxy resin. The amount of 2-methylimidazole is 1 part by weight, the amount of isocyanate-terminated polyurethane prepolymer is 35 parts by weight, and the amount of bisphenol A type epoxy resin is 65 parts by weight, relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin. (3) Add dicyandiamide to the intrinsically flexible flame-retardant epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a modified epoxy structural adhesive film. The amount of dicyandiamide used is 10 parts by weight relative to 100 parts by weight of the modified epoxy resin.

[0056] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0057] Comparative Example 2 This comparative example illustrates the preparation method and performance testing of epoxy structural adhesive films.

[0058] 1. Preparation method (1) Diphenylmethane diisocyanate and N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl phosphate (phosphorus content 12.1%) were reacted at 60℃ for 4 h at a molar ratio of -NCO:-OH=8:4 to obtain isocyanate-terminated polyurethane prepolymer. (2) The isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol A type epoxy resin at 100°C for 5 h to prepare intrinsic flexible flame retardant epoxy resin. The amount of isocyanate-terminated polyurethane prepolymer is 35 parts by weight and the amount of bisphenol A type epoxy resin is 65 parts by weight relative to 100 parts by weight of intrinsic flexible flame retardant epoxy resin. (3) The intrinsic flexible flame-retardant epoxy resin obtained in the above steps is reacted with cashew phenol-modified linear phenolic resin at 100°C for 3 h. At this time, the viscosity of the material at 100°C is 104384 cps, and halogen-free flame-retardant epoxy resin can be obtained. Among them, the amount of cashew phenol-modified linear phenolic resin is 5 parts by weight relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin.

[0059] (4) Add dicyandiamide to the halogen-free flame-retardant epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a halogen-free flame-retardant epoxy structural film. The amount of dicyandiamide used is 10 parts by weight relative to 100 parts by weight of the halogen-free flame-retardant high-adhesion epoxy resin.

[0060] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0061] Comparative Example 3 This comparative example illustrates the preparation method and performance testing of epoxy structural adhesive films.

[0062] 1. Preparation method (1) Diphenylmethane diisocyanate and polytetramethylene ether glycol were reacted at 60°C for 4 h at a molar ratio of -NCO:-OH=8:4 to obtain isocyanate-terminated polyurethane prepolymer; (2) In the presence of a 2-methylimidazole catalyst, the isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol A type epoxy resin at 130°C for 5 h to prepare an intrinsic flexible epoxy resin. The amount of 2-methylimidazole is 1 part by weight, the amount of isocyanate-terminated polyurethane prepolymer is 35 parts by weight, and the amount of bisphenol A type epoxy resin is 65 parts by weight, relative to 100 parts by weight of intrinsic flexible epoxy resin. (3) The intrinsic flexible epoxy resin obtained in the above steps and the cashew phenol-modified linear phenolic resin are reacted at 100°C for 3 h. At this time, the viscosity of the material at 100°C is 138282 cps, and halogen-free flame-retardant high-adhesion epoxy resin can be obtained. Among them, the amount of cashew phenol-modified linear phenolic resin is 5 parts by weight relative to 100 parts by weight of intrinsic flexible epoxy resin.

[0063] (4) Add dicyandiamide to the modified epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a modified epoxy structural adhesive film. The amount of dicyandiamide used is 10 parts by weight relative to 100 parts by weight of the modified epoxy resin.

[0064] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0065] Comparative Example 4 This comparative example illustrates the preparation method and performance testing of epoxy structural adhesive films.

[0066] 1. Preparation method (1) Diphenylmethane diisocyanate and N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl phosphate (phosphorus content 12.1%) were reacted at 60℃ for 4 h at a molar ratio of -NCO:-OH=8:4 to obtain isocyanate-terminated polyurethane prepolymer. (2) In the presence of a 2-methylimidazole catalyst, the isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol A type epoxy resin at 130°C for 5 h to prepare an intrinsic flexible flame-retardant epoxy resin. The amount of 2-methylimidazole is 1 part by weight, the amount of isocyanate-terminated polyurethane prepolymer is 35 parts by weight, and the amount of bisphenol A type epoxy resin is 65 parts by weight, relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin. (3) The intrinsic flexible flame-retardant epoxy resin obtained in the above steps is reacted with linear phenolic resin at 100°C for 3 h. At this time, the viscosity of the material at 100°C is 149523 cps, and the modified epoxy resin can be obtained. Among them, the amount of linear phenolic resin is 5 parts by weight relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin.

[0067] (4) Add dicyandiamide to the modified epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a modified epoxy structural adhesive film. The amount of dicyandiamide used is 10 parts by weight relative to 100 parts by weight of the modified epoxy resin.

[0068] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0069] Comparative Example 5 This comparative example illustrates the preparation method and performance testing of epoxy structural adhesive films.

[0070] 1. Preparation method (1) Diphenylmethane diisocyanate and N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl phosphate (phosphorus content 12.1%) were reacted at 60℃ for 4 h at a molar ratio of -NCO:-OH=8:4 to obtain isocyanate-terminated polyurethane prepolymer. (2) In the presence of a 2-methylimidazole catalyst, the isocyanate-terminated polyurethane prepolymer obtained in the above steps is further grafted with bisphenol A type epoxy resin at 130°C for 5 h to prepare an intrinsic flexible flame-retardant epoxy resin. The amount of 2-methylimidazole is 1 part by weight, the amount of isocyanate-terminated polyurethane prepolymer is 35 parts by weight, and the amount of bisphenol A type epoxy resin is 65 parts by weight, relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin. (3) The intrinsic flexible flame-retardant epoxy resin obtained in the above steps is reacted with carboxyl-terminated nitrile rubber at 100°C for 3 h. At this time, the viscosity of the material at 100°C is 110300 cps, and the modified epoxy resin can be obtained. Among them, the amount of carboxyl-terminated nitrile rubber is 5 parts by weight relative to 100 parts by weight of intrinsic flexible flame-retardant epoxy resin.

[0071] (4) Add dicyandiamide to the modified epoxy resin obtained in the above steps, mix evenly, and coat with a calender to obtain a modified epoxy structural adhesive film. The amount of dicyandiamide used is 10 parts by weight relative to 100 parts by weight of the modified epoxy resin.

[0072] 2. Performance Testing The epoxy structural adhesive film was prepared according to the corresponding test standards, and the flame retardancy rating, room temperature tensile shear strength, 100℃ high temperature tensile shear strength and 90° core-plate peel strength of the structural adhesive film were tested respectively. The results are shown in Table 1.

[0073] Table 1. Properties of structural adhesive films in different embodiments and comparative examples Compared with the comparative example, the halogen-free flame-retardant high-adhesion epoxy structural film prepared in the example can reach the flame retardant rating of UL94V-0, the room temperature tensile shear strength is greater than 30 MPa, the high temperature tensile shear strength at 100℃ is greater than 20 MPa, the performance retention rate at 100℃ is greater than 70%, and the peel strength is greater than 60 N / cm. It has excellent flame retardant properties, temperature resistance properties and adhesion properties. In Comparative Example 1, the epoxy structural film prepared by modifying only phosphorus-containing polyols and general diisocyanates only has a flame retardancy rating of UL 94 V-1 and a peel strength of only 36 N / cm. It is difficult to meet the technical requirements of flame retardancy and high adhesion of epoxy structural films. This shows that phosphorus-containing polyols and cashew phenol-modified linear phenolic resins can synergistically improve the flame retardancy and adhesion performance of epoxy structural films. In Comparative Example 2, the isocyanate-terminated polyurethane prepolymer and bisphenol A type epoxy resin underwent a grafting reaction at a low temperature of 100℃ for 5 h. At this temperature, the isocyanate and epoxy groups cannot undergo ring-opening reaction to generate oxazolidinone heterocycles. Instead, they can only react with the hydroxyl groups in the bisphenol A type epoxy resin to produce urethane structures. Although the tensile shear strength and peel strength are excellent, the flame retardancy rating is only UL 94 V-1. This is because the modified epoxy resin main chain lacks the oxazolidinone nitrogen heterocyclic structure, failing to achieve the phosphorus-nitrogen synergistic flame retardant effect, thus reducing the flame retardancy rating. In Comparative Example 3, the modified epoxy structural film prepared by replacing the phosphorus-containing polyol with polytetramethylene ether glycol also exhibits excellent adhesion, but the flame retardancy rating is only UL 94 V-1, failing to meet the technical requirements for high flame retardancy rating of flame-retardant epoxy structural films. In Comparative Example 4, the modified epoxy structural film prepared by replacing cashew nut phenol-modified linear phenolic resin with linear phenolic resin exhibits excellent flame retardancy, but the peel strength is only 32 N / cm, failing to meet the technical requirements for high adhesion performance of flame-retardant epoxy structural films. In Comparative Example 5, the modified epoxy structural film prepared by replacing cashew nut phenol-modified linear phenolic resin with carboxyl-terminated nitrile rubber exhibits excellent room temperature adhesion, but the tensile shear strength at 100℃ is only 9 N / cm. With an MPa of less than 30% performance retention at 100℃ and a flame retardant rating of only UL 94 V-1, it is difficult to meet the performance requirements of high heat resistance and high flame retardant rating of epoxy structural films.

[0074] This invention solves the technical problem that flame-retardant epoxy structural films are difficult to achieve simultaneously in terms of high flame retardancy, heat resistance, and high adhesion, and broadens the application of flame-retardant epoxy structural films in the bonding or repair of flame-retardant composite materials.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An intrinsically flame-retardant and high-temperature resistant epoxy structural film, characterized in that, It is prepared from the following raw materials: 1-50 parts by weight of general-purpose diisocyanate, 0.5-25 parts by weight of phosphorus-containing polyol, 5-200 parts by weight of liquid epoxy resin, and 0.1-10 parts by weight of cashew nut shell modified linear phenolic resin. 0.01-2 parts by weight of catalyst, 0.5-20 parts by weight of latent curing system, wherein the epoxy structural film has a flame retardancy rating of not less than V-0, a room temperature tensile shear strength of not less than 31 MPa, a 100°C tensile shear strength of not less than 23 MPa, and a 90° core-plate peel strength of not less than 63 N / cm.

2. The intrinsically flame-retardant and high-temperature resistant epoxy structural film according to claim 1, characterized in that, The general-purpose diisocyanate includes at least one of diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

3. The intrinsically flame-retardant and high-temperature resistant epoxy structural film according to claim 1, characterized in that, The phosphorus-containing polyol includes at least one of N,N-di(2-hydroxyethyl)aminomethylene phosphate diethyl ester, N,N-di(2-hydroxyethyl)aminomethyl phosphate dimethyl ester, and organophosphate diols.

4. The intrinsically flame-retardant and high-temperature resistant epoxy structural film according to claim 1, characterized in that, The catalyst includes at least one of 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, n-butyllithium, and zinc carboxylate.

5. The intrinsically flame-retardant and high-temperature resistant epoxy structural film according to claim 1, characterized in that, The liquid epoxy resin includes at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol AD ​​type epoxy resin.

6. The intrinsically flame-retardant and high-temperature resistant epoxy structural film according to claim 1, characterized in that, The latent curing system includes at least one of dicyandiamide, modified dicyandiamide, and urea derivatives.

7. The method for preparing an intrinsically flame-retardant and high-temperature resistant epoxy structural film according to any one of claims 1-6, characterized in that, Includes the following steps: (1) React a general-purpose diisocyanate with a phosphorus-containing polyol at 60-80℃ for 2-4 h to obtain a polyurethane prepolymer with terminal isocyanate group, wherein the molar ratio of the general-purpose diisocyanate to the phosphorus-containing polyol is (8-5):4, based on -NCO:-OH. (2) Under the presence of a catalyst, the terminal isocyanate polyurethane prepolymer and liquid epoxy resin are reacted at 140-170℃ for 2-5 h to obtain an intrinsic flexible flame-retardant epoxy resin, wherein the mass ratio of the terminal isocyanate polyurethane prepolymer to the liquid epoxy resin is (20:80)-(35:65). (3) React the intrinsic flexible flame-retardant epoxy resin with cashew phenol modified linear phenolic resin at 100-120°C until the viscosity of the material at 100°C is 100,000-200,000 cps, to obtain intrinsic flame-retardant high-temperature resistant epoxy resin. (4) Mix the intrinsic flame-retardant and high-temperature resistant epoxy resin with a latent curing system to obtain a resin composition, and then coat it to obtain an intrinsic flame-retardant and high-temperature resistant epoxy structural film.

8. The method for preparing the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to claim 7, characterized in that, The amount of cashew phenol modified linear phenolic resin is 5-15% of the weight of the intrinsic flexible flame-retardant epoxy resin.

9. The method for preparing the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to claim 7, characterized in that, The amount of the latent curing system is 5-15% of the weight of the intrinsic flame-retardant and high-temperature resistant epoxy resin.

10. The application of the intrinsically flame-retardant and high-temperature resistant epoxy structural film according to any one of claims 1-6 in the bonding or repair of flame-retardant composite materials.

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