A flame-retardant epoxy resin adhesive and its preparation method

Abstract

This invention relates to the field of epoxy resin technology and discloses a flame-retardant epoxy resin adhesive and its preparation method. The method involves adding a solvent, epoxy resin, polyphosphoramide flame retardant, and defoamer to a container, stirring and dispersing, and then adding a polyamine curing agent to obtain the flame-retardant epoxy resin adhesive. The carbon spirocyclic structure of the polyphosphoramide flame retardant serves as a carbon source, the phosphate ester as an acid source, and a large amount of nitrogen as a gas source, forming an intumescent flame retardant that significantly improves the flame-retardant properties of the epoxy resin. The polyphosphoramide flame retardant contains terminal amino groups, which can participate in the curing reaction of the epoxy resin, promoting cross-linking and curing. It also contains a large number of polar urethane groups, forming strong interactions with polymer and metal substrates, improving the peel strength between the epoxy resin and the substrate, resulting in better adhesion and better practical applications in adhesives and other fields.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin technology, specifically to a flame-retardant epoxy resin adhesive and its preparation method. Background Technology

[0002] Epoxy resin possesses high mechanical strength, heat resistance, corrosion resistance, and insulation properties, making it widely used in adhesives, coatings, and castings. However, epoxy resin is flammable and melts and drips when burning, making it difficult to meet fire retardant requirements. Furthermore, cured epoxy resin has poor toughness and is prone to cracking, which affects its corrosion resistance and durable adhesion.

[0003] Common flame retardants for epoxy resins include inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide. However, inorganic flame retardants have drawbacks, such as requiring large amounts. Organic flame retardants mainly include ammonium polyphosphate, DOPO, and intumescent flame retardants. Among them, intumescent flame retardants combine the functions of acid source, gas source, and carbon source, exhibiting excellent flame retardant properties such as char formation, anti-dripping, and smoke suppression. However, if organic intumescent flame retardants have poor compatibility with epoxy resins, it can affect their mechanical and adhesive properties. Summary of the Invention

[0004] This invention solves the problem of poor flame retardancy of epoxy resin, while improving the flexibility and adhesion of epoxy resin.

[0005] The technical solution of the present invention is: a flame-retardant epoxy resin adhesive, comprising the following components in parts by weight: 100 parts epoxy resin, 7-12 parts solvent, 15-25 parts polyphosphoramide flame retardant, 0.6-1 parts defoamer, and 7.2-11.7 parts polyamine curing agent.

[0006] Furthermore, the solvent is acetone, toluene, xylene, ethylene glycol butyl ether, or propylene glycol methyl ether.

[0007] Furthermore, polyamine curing agents include ethylenediamine, diethylenetriamine, and triethylenetetramine.

[0008] The preparation method of flame-retardant epoxy resin adhesive is as follows: (1) Add dichloromethane, toluene-2,4-diisocyanate, Boc-diethylene glycolamine (CAS No. 139115-91-6), and dibutyltin dilaurate (DBTDL) to a flask equipped with a stirrer and a reflux condenser. Heat to 35-40℃ and stir for 2-3 hours. Filter and add trifluoroacetic acid (TFA) to the filtrate. Stir at 20-25℃ for 3-4 hours. Concentrate the solution by rotary evaporation to remove dichloromethane and trifluoroacetic acid. Add the concentrate to a saturated sodium bicarbonate solution and extract with dichloromethane. After separation, collect the organic phase, add anhydrous sodium sulfate to dry and remove water. Filter and concentrate the filtrate by rotary evaporation. The concentrate is purified by silica gel column chromatography to obtain the diamino monomer. The preparation reaction formula is as follows: .

[0009] (2) In an ice-water bath, add the reaction solvent, triethylamine (TEA), diamino monomer, and pentaerythritol diphosphate diphosphonate chloride to a flask equipped with a stirrer and a reflux condenser. Heat to 40-50°C and react for 12-18 hours. After filtration, wash the precipitate successively with water, dichloromethane, and ethanol, and dry to obtain polyphosphoramide flame retardant. The preparation reaction formula is as follows: .

[0010] (3) Add solvent, epoxy resin, polyphosphoramide flame retardant and defoamer to the container, stir and disperse, add polyamine curing agent to obtain flame retardant epoxy resin adhesive.

[0011] Furthermore, in (1), the molar ratio of toluene-2,4-diisocyanate, Boc-diethylene glycolamine, and dibutyltin dilaurate is 1:(2-2.4):(0.005-0.008).

[0012] Furthermore, in (2), the reaction solvent is dichloromethane, acetonitrile, or tetrahydrofuran.

[0013] Furthermore, in (2), the molar ratio of triethylamine, diamino monomer, and pentaerythritol diphosphate diphosphoryl chloride is (2-2.1):(1.06-1.1):1.

[0014] The beneficial technical effects of this invention are as follows: adding polyphosphoramide flame retardant to epoxy resin, which contains a spirocyclic phosphoramide structure, with the carbon spirocyclic structure as a carbon source, phosphate ester as an acid source, and a large amount of nitrogen as a gas source, forms an intumescent flame retardant, which significantly improves the flame retardant performance of epoxy resin.

[0015] The polyphosphoramide flame retardant of the present invention contains terminal amino groups, which can replace part of the polyamine curing agent and participate in the curing reaction of epoxy resin, promoting the cross-linking and curing of epoxy resin. The polyphosphoramide flame retardant contains multiple flexible ether bonds, which are bonded to the epoxy resin curing system, which is beneficial to improving the toughness of epoxy resin.

[0016] The polyphosphoramide flame retardant of the present invention contains a large number of polar urethane groups, which form a strong interaction with polymer substrates such as PET polyester and metal substrates such as steel sheets. This can improve the peel strength between epoxy resin and substrate, improve the bonding performance, and have better practical applications in adhesives and other fields. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Pentaerythritol diphosphate diphosphoryl chloride was prepared according to the method described in the journal article "Synthesis and Characterization of Flame Retardant Polypentaerythritol Phosphate" (Volume 36, Issue 3).

[0019] Example 1: (1) Dichloromethane, toluene-2,4-diisocyanate, Boc-diglycolamine, and dibutyltin dilaurate in a molar ratio of 1:2:0.007 were added to a flask equipped with a stirrer and a reflux condenser. The concentration of toluene-2,4-diisocyanate in the solution was controlled to be 0.2 mol / L. The mixture was heated to 35°C and stirred for 3 h. After filtration, trifluoroacetic acid was added to the filtrate (the volume fraction of trifluoroacetic acid in the solution was controlled to be 30%). The mixture was stirred for 3 h at 25°C. The solution was concentrated by rotary evaporation. The concentrate was added to a saturated sodium bicarbonate solution and extracted with dichloromethane. After separation, the organic phase was collected. Anhydrous sodium sulfate was added to dry the solution to remove water. After filtration, the filtrate was concentrated by rotary evaporation. The concentrate was purified by silica gel column chromatography to obtain a diamino monomer.

[0020] (2) In an ice-water bath, add dichloromethane, triethylamine in a molar ratio of 2:1.08:1, diamino monomer, pentaerythritol diphosphate diphosphoryl chloride to a flask equipped with a stirrer and a reflux condenser. Control the concentration of diamino monomer in the solution to 0.4 mol / L, heat to 40°C, react for 18 h, filter, wash the precipitate with water, dichloromethane and ethanol in sequence, and dry to obtain polyphosphoramide flame retardant.

[0021] (3) Add 7 parts by weight of propylene glycol methyl ether, 100 parts by weight of epoxy resin E44, 15 parts by weight of polyphosphoramide flame retardant, and 0.7 parts by weight of defoamer BYK-053 to the container, stir and disperse, and add 11.7 parts by weight of diethylenetriamine to obtain flame retardant epoxy resin adhesive.

[0022] Example 2: (1) Dichloromethane, toluene-2,4-diisocyanate, Boc-diglycolamine, and dibutyltin dilaurate in a molar ratio of 1:2.4:0.005 were added to a flask equipped with a stirrer and a reflux condenser. The concentration of toluene-2,4-diisocyanate in the solution was controlled to be 0.2 mol / L. The mixture was heated to 40°C and stirred for 2 hours. After filtration, trifluoroacetic acid was added to the filtrate (the volume fraction of trifluoroacetic acid in the solution was controlled to be 30%). The mixture was stirred for 3 hours at 25°C. The solution was concentrated by rotary evaporation. The concentrate was added to a saturated sodium bicarbonate solution and extracted with dichloromethane. After separation, the organic phase was collected. Anhydrous sodium sulfate was added to dry the solution to remove water. After filtration, the filtrate was concentrated by rotary evaporation. The concentrate was purified by silica gel column chromatography to obtain a diamino monomer.

[0023] (2) In an ice-water bath, add acetonitrile, triethylamine in a molar ratio of 2.1:1.1:1, diamino monomer, and pentaerythritol diphosphate diphosphoryl chloride to a flask equipped with a stirrer and a reflux condenser. Control the concentration of diamino monomer in the solution to 0.4 mol / L, heat to 50°C, react for 12 h, filter, wash the precipitate with water, dichloromethane, and ethanol in sequence, and dry to obtain polyphosphoramide flame retardant.

[0024] (3) Add 12 parts by weight of propylene glycol methyl ether, 100 parts by weight of epoxy resin E44, 20 parts by weight of polyphosphoramide flame retardant, and 0.6 parts by weight of defoamer BYK-053 to the container, stir and disperse, and add 9.6 parts by weight of diethylenetriamine to obtain flame retardant epoxy resin adhesive.

[0025] Example 3: (1) Dichloromethane, toluene-2,4-diisocyanate, Boc-diglycolamine, and dibutyltin dilaurate in a molar ratio of 1:2:0.008 were added to a flask equipped with a stirrer and a reflux condenser. The concentration of toluene-2,4-diisocyanate in the solution was controlled to be 0.15 mol / L. The mixture was heated to 40°C and stirred for 2 hours. After filtration, trifluoroacetic acid was added to the filtrate (the volume fraction of trifluoroacetic acid in the solution was controlled to be 35%). The mixture was stirred for 3 hours at 25°C. The solution was concentrated by rotary evaporation. The concentrate was added to a saturated sodium bicarbonate solution and extracted with dichloromethane. After separation, the organic phase was collected. Anhydrous sodium sulfate was added to dry the solution to remove water. After filtration, the filtrate was concentrated by rotary evaporation. The concentrate was purified by silica gel column chromatography to obtain a diamino monomer.

[0026] (2) In an ice-water bath, add dichloromethane, triethylamine in a molar ratio of 2:1.06:1, diamino monomer, and pentaerythritol diphosphate diphosphoryl chloride to a flask equipped with a stirrer and a reflux condenser. Control the concentration of diamino monomer in the solution to 0.4 mol / L, heat to 40°C, react for 18 h, filter, wash the precipitate with water, dichloromethane, and ethanol in sequence, and dry to obtain polyphosphoramide flame retardant.

[0027] (3) Add 10 parts by weight of xylene, 100 parts by weight of epoxy resin E44, 25 parts by weight of polyphosphoramide flame retardant, and 1 part by weight of defoamer BYK-053 to the container, stir and disperse, and add 7.2 parts by weight of diethylenetriamine to obtain flame retardant epoxy resin adhesive.

[0028] Comparative Example 1 differs from Example 1 in that no polyphosphoramide flame retardant is added.

[0029] (1) Add 7 parts by weight of propylene glycol methyl ether, 100 parts by weight of epoxy resin E44, and 0.7 parts by weight of defoamer BYK-053 to a container, stir and disperse, and add 11.7 parts by weight of diethylenetriamine to obtain epoxy resin.

[0030] Comparative Example 2 differs from Example 1 in that ethylenediamine is used instead of the diamino monomer.

[0031] (1) In an ice-water bath, dichloromethane, triethylamine, ethylenediamine, and pentaerythritol diphosphate diphosphoryl chloride in a molar ratio of 2:1.08:1 were added to a flask equipped with a stirrer and a reflux condenser. The concentration of the diamino monomer in the solution was controlled to be 0.4 mol / L. The mixture was heated to 40°C and reacted for 18 h. After filtration, the precipitate was washed with water, dichloromethane, and ethanol in sequence and dried to obtain polyphosphoramide flame retardant.

[0032] (2) Add 7 parts by weight of propylene glycol methyl ether, 100 parts by weight of epoxy resin E44, 15 parts by weight of polyphosphoramide flame retardant, and 0.7 parts by weight of defoamer BYK-053 to the container, stir and disperse, and add 11.7 parts by weight of diethylenetriamine to obtain flame retardant epoxy resin adhesive.

[0033] Comparative Example 3 differs from Example 1 in that Boc-ethanolamine (CAS No. 26690-80-2) is used instead of the diamino monomer.

[0034] (1) Dichloromethane, toluene-2,4-diisocyanate, N-(tert-butyloxycarbonyl)ethanolamine, and dibutyltin dilaurate were added to a flask equipped with a stirrer and a reflux condenser. The concentration of toluene-2,4-diisocyanate in the solution was controlled at 0.2 mol / L. The mixture was heated to 35°C and stirred for 3 h. After filtration, trifluoroacetic acid was added to the filtrate (the volume fraction of trifluoroacetic acid in the solution was controlled at 30%). The mixture was stirred at 25°C for 3 h. The solution was concentrated by rotary evaporation. The concentrate was added to a saturated sodium bicarbonate solution and extracted with dichloromethane. After separation and separation, the organic phase was collected. Anhydrous sodium sulfate was added to dry the solution to remove water. After filtration, the filtrate was concentrated by rotary evaporation. The concentrate was purified by silica gel column chromatography to obtain a diamino monomer with the following structural formula: .

[0035] (2) In an ice-water bath, add dichloromethane, triethylamine in a molar ratio of 2:1.08:1, diamino monomer, pentaerythritol diphosphate diphosphoryl chloride to a flask equipped with a stirrer and a reflux condenser. Control the concentration of diamino monomer in the solution to 0.4 mol / L, heat to 40°C, react for 18 h, filter, wash the precipitate with water, dichloromethane and ethanol in sequence, and dry to obtain polyphosphoramide flame retardant.

[0036] (3) Add 7 parts by weight of propylene glycol methyl ether, 100 parts by weight of epoxy resin E44, 15 parts by weight of polyphosphoramide flame retardant, and 0.7 parts by weight of defoamer BYK-053 to the container, stir and disperse, and add 11.7 parts by weight of diethylenetriamine to obtain flame retardant epoxy resin adhesive.

[0037] Epoxy resin was poured into a mold and cured sequentially at room temperature for 4 hours, 70°C for 2 hours, and 110°C for 1 hour to prepare cast specimens. The impact toughness of simply supported beams was tested according to GB / T 2567-2021. Flame retardancy was tested according to GB / T 2406.1-2008 and UL94 methods. Peel strength and adhesion were tested according to GB / T 2790-1995, with test specimens consisting of PET polyester sheets and steel sheets.

[0038] Table 1

[0039] Compared to Comparative Example 1, the epoxy resins in each embodiment exhibit higher impact toughness, greater peel strength, and a higher limiting oxygen index, achieving UL94 ratings from V-1 to V-0. They demonstrate excellent toughness, adhesion, and flame retardancy, primarily due to the addition of polyphosphoramide flame retardant. This polyphosphoramide flame retardant contains a spirocyclic phosphoramide structure, with the carbon spirocyclic structure acting as a carbon source, phosphate ester as an acid source, and a large amount of nitrogen as a gas source, forming an intumescent flame retardant that significantly improves the flame retardant properties of the epoxy resin. Furthermore, the polyphosphoramide flame retardant contains terminal amino groups, which can replace some polyamine curing agents, participating in the curing reaction of the epoxy resin and promoting cross-linking and curing. The polyphosphoramide flame retardant also contains multiple flexible ether bonds, which bond into the epoxy resin curing system, contributing to improved toughness. The polyphosphoramide flame retardant contains a large number of polar urethane groups, forming strong interactions with polymer substrates such as PET polyester and metal substrates such as steel sheets, thus improving the peel strength between the epoxy resin and the substrate and enhancing adhesion.

[0040] Comparative Example 1 did not add polyphosphoramide flame retardant, and the amount of added diethylenetriamine was relatively small, which is not conducive to the curing and cross-linking reaction of epoxy resin and will affect the impact toughness and peel strength of the cured epoxy resin.

[0041] The polyphosphoramide flame retardant in Comparative Example 2 does not contain ether bonds and urethane groups, and the epoxy resin has lower impact toughness and peel strength.

[0042] The polyphosphoramide flame retardant in Comparative Example 3 does not contain ether bonds, and the epoxy resin has lower impact toughness.

Claims

1. A flame-retardant epoxy resin adhesive, characterized in that, The flame-retardant epoxy resin adhesive comprises the following components in parts by weight: 100 parts epoxy resin, 7-12 parts solvent, 15-25 parts polyphosphoramide flame retardant, 0.6-1 part defoamer, and 7.2-11.7 parts polyamine curing agent; The polyphosphoramide flame retardant is prepared by the following method: In an ice-water bath, a reaction solvent, triethylamine, diamino monomer, and pentaerythritol diphosphate diphosphoryl chloride are added to a flask to carry out the reaction. After filtration, the precipitate is washed and dried to obtain the polyphosphoramide flame retardant. The structural formula of the diamino monomer is: .

2. The flame-retardant epoxy resin adhesive according to claim 1, characterized in that, The solvent is acetone, toluene, xylene, ethylene glycol butyl ether, or propylene glycol methyl ether.

3. The flame-retardant epoxy resin adhesive according to claim 1, characterized in that, The reaction solvent is dichloromethane, acetonitrile, or tetrahydrofuran.

4. The flame-retardant epoxy resin adhesive according to claim 1, characterized in that, The polyamine curing agent includes ethylenediamine, diethylenetriamine, and triethylenetetramine.

5. The flame-retardant epoxy resin adhesive according to claim 1, characterized in that, The molar ratio of triethylamine, diamino monomer, and pentaerythritol diphosphate diphosphoryl chloride is (2-2.1):(1.06-1.1):

1.

6. The flame-retardant epoxy resin adhesive according to claim 1, characterized in that, The reaction was carried out at 40-50°C for 12-18 hours.

7. The flame-retardant epoxy resin adhesive according to claim 1, characterized in that, The diamino monomer is prepared by the following method: dichloromethane, toluene-2,4-diisocyanate, Boc-diglycolamine, and dibutyltin dilaurate are added to a flask, heated to 35-40°C, stirred for 2-3 hours, filtered, trifluoroacetic acid is added to the filtrate, and stirred for 3-4 hours at 20-25°C. The solution is concentrated by rotary evaporation, extracted, and purified by silica gel column chromatography to obtain the diamino monomer.

8. The flame-retardant epoxy resin adhesive according to claim 7, characterized in that, The molar ratio of toluene-2,4-diisocyanate, Boc-diethylene glycolamine, and dibutyltin dilaurate is 1:(2-2.4):(0.005-0.008).

9. A method for preparing a flame-retardant epoxy resin adhesive as described in any one of claims 1-8, characterized in that, The preparation method is as follows: add solvent, epoxy resin, polyphosphoramide flame retardant, and defoamer to a container, stir and disperse, add polyamine curing agent, and obtain flame retardant epoxy resin adhesive.

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