Preparation method of waterborne polyurethane fireproof coating

Abstract

The invention relates to the technical field of coatings, and discloses a preparation method of a waterborne polyurethane fireproof coating, dihydroxymethyl imidazole DOPO, which contains dicarboxyl and dihydroxyl groups, can be used as a waterborne chain extender of polyurethane, and is subjected to a polymerization reaction with polyester polyol and diisocyanate to obtain the waterborne polyurethane fireproof coating. And the emulsion is not layered or precipitated after being placed for a long time, and has good emulsion stability. And the dimethylol imidazole DOPO contains a water-resistant aromatic ring structure, so that the water absorption rate of a polyurethane paint film is reduced, and the water resistance is improved. A nitrogen-phosphorus synergistic flame-retardant system is formed by the dihydroxymethyl imidazole DOPO and is bonded into a polyurethane molecular chain, so that a good intrinsic flame-retardant effect is achieved on a polyurethane paint film, the heat release rate peak value and the total heat release amount during polyurethane combustion are remarkably reduced, and the flame-retardant property of polyurethane is enhanced.

Description

[0001] This application is a divisional application of the application filed on July 7, 2025, with application number 2025109265792 and invention title "A preparation process for a water-based polyurethane fire retardant coating". Technical Field

[0002] This invention relates to the field of coating technology, specifically to a method for preparing a water-based polyurethane fire-retardant coating. Background Technology

[0003] Coatings are widely used in wooden furniture, machinery and equipment, etc. Among them, polyurethane coatings have the advantages of good film-forming properties and excellent mechanical strength and elasticity of the paint film. However, current polyurethane coatings usually use acetone, toluene and other solvents as solvents, which have problems such as easy solvent volatility, large pollution and harm to human health. Therefore, it is necessary to develop new environmentally friendly water-based coatings.

[0004] Traditional waterborne polyurethanes are prepared using 2,2-dihydroxymethylacrylic acid and sodium dihydroxy-3-propanesulfonate as hydrophilic chain extenders. These waterborne polyurethanes suffer from problems such as easy water absorption and poor water resistance; furthermore, current waterborne polyurethane coatings are flammable, limiting their practical application in fireproofing. DOPO is a novel phosphorophenanthrene flame retardant intermediate with excellent thermal stability, chemical stability, and flame retardancy, and is widely used in polyurethane and other coatings. This invention aims to prepare a novel dihydroxymethylimidazolium DOPO chain extender and a water-resistant waterborne polyurethane fireproof coating. Summary of the Invention

[0005] Technical problem solved: A water-based polyurethane fire-retardant coating was prepared using dihydroxymethylimidazolium DOPO as a chain extender, which solved the problems of poor water resistance and poor fire retardancy of polyurethane coatings.

[0006] Technical solution: A method for preparing a waterborne polyurethane fire-retardant coating: Polyester polyol is vacuum dried and dehydrated, then added to a reaction flask with diisocyanate, nitrogen gas is introduced, and the reaction is carried out at 60-75℃ for 2-3 hours. Then the temperature is lowered to 40-50℃, acetone, dimethylolimidazole DOPO as a chain extender, and dibutyltin dilaurate are added, stirred and dissolved, and the reaction is continued for 1-2 hours. The acetone is concentrated and removed, triethylamine and water are added for neutralization, and defoamer, leveling agent and film-forming aid are added. The mixture is stirred evenly to obtain the waterborne polyurethane fire-retardant coating.

[0007] Furthermore, the mass of diisocyanate and dihydroxymethylimidazolium DOPO is 45-52% and 2-15% of that of the polyester polyol, respectively.

[0008] Furthermore, diisocyanates include hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, and terephthalic diisocyanate.

[0009] Furthermore, dihydroxymethylimidazolium DOPO is prepared according to the following process: S1. Maleic anhydride-DOPO, dibromoneopentyl glycol, and solvent were added to a reaction flask, the mixture was stirred, the solvent was concentrated, and the product was purified by recrystallization in toluene to obtain dibromomethylcarboxylic acid DOPO intermediate. S2. Dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate were added to acetonitrile, and the mixture was stirred and reacted. The solvent was concentrated, and the product was purified by recrystallization in toluene to give dihydroxymethylimidazolium DOPO; the structural formula is as follows. .

[0010] Furthermore, the molar ratio of maleic anhydride-DOPO to dibromoneopentyl glycol is 1:2.2-2.6.

[0011] Furthermore, solvents include toluene, xylene, and 1,4-dioxane.

[0012] Furthermore, the reaction in S1 is carried out at a temperature of 85-100℃ for 12-24 hours.

[0013] Furthermore, the molar ratio of dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate is 1:(2-2.5):(4.5-6).

[0014] Furthermore, the reaction in S2 is carried out at a temperature of 70-80°C for 12-18 hours.

[0015] The technical effect of this invention is as follows: By using maleic anhydride-DOPO and dibromoneopentyl glycol for an anhydride esterification reaction, and then for a substitution reaction with (1H-imidazol-5-yl)methanol, a novel dihydroxymethylimidazolium DOPO is prepared. The dicarboxyl and dihydroxy groups contained therein can be used as waterborne chain extenders for polyurethanes, and can be polymerized with polyester polyols and diisocyanates to obtain waterborne polyurethane fire-retardant coatings.

[0016] The waterborne polyurethane fire-retardant coating prepared by this invention exhibits excellent emulsion stability, with no emulsion stratification or sedimentation even after prolonged standing. Furthermore, the dihydroxymethylimidazolium (DOPO) contains a water-resistant aromatic ring structure, which helps reduce the water absorption rate of the polyurethane film and improves its water resistance.

[0017] The imidazole and DOPO groups contained in the dihydroxymethylimidazolium DOPO of this invention form a nitrogen-phosphorus synergistic flame retardant system and are bonded to the polyurethane molecular chain, which has a very good intrinsic flame retardant effect on the polyurethane coating film, significantly reduces the peak heat release rate and total heat release during polyurethane combustion, and enhances the flame retardant performance of polyurethane. Detailed Implementation

[0018] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0019] Example 1 Maleic anhydride-DOPO, dibromoneopentyl glycol, and 1,4-dioxane solvent in a molar ratio of 1:2.6 were added to a reaction flask, and the mixture was stirred at 90°C for 12 h. The solvent was concentrated, and the product was purified by recrystallization in toluene to obtain dibromomethylcarboxylic acid DOPO intermediate. Dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate in a molar ratio of 1:2.2:6 were added to acetonitrile, and the mixture was stirred at 70°C for 18 h. The solvent was concentrated, and the product was purified by recrystallization in toluene to obtain dihydroxymethylimidazolium DOPO.

[0020] 100 parts by weight of polyester polyol were vacuum dried and dehydrated, and then added to a reaction flask with 52 parts by weight of toluene diisocyanate. Nitrogen gas was introduced, and the reaction was carried out at 60°C for 3 hours. Then the temperature was lowered to 45°C, and acetone, 2 parts by weight of dimethylolimidazolium DOPO as a chain extender, and 0.03 parts by weight of dibutyltin dilaurate were added. The mixture was stirred and dissolved, and the reaction was continued for 1 hour. The acetone was removed by concentration, and triethylamine and water were added for neutralization. 0.1 parts of defoamer STA-5300, 0.4 parts of leveling agent PUR2150, and 3 parts of film-forming aid alcohol ester dodecyl were added. The mixture was stirred evenly to obtain a waterborne polyurethane fireproof coating.

[0021] Example 2 Maleic anhydride-DOPO, dibromoneopentyl glycol, and toluene solvent in a molar ratio of 1:2.4 were added to a reaction flask and stirred at 85°C for 24 h. The solvent was concentrated and the product was purified by recrystallization in toluene to obtain dibromomethylcarboxylic acid DOPO intermediate. Dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate in a molar ratio of 1:2.5:5 were added to acetonitrile. The mixture was stirred at 70°C for 12 h. The solvent was concentrated, and the product was purified by recrystallization in toluene to obtain dihydroxymethylimidazolium DOPO.

[0022] 100 parts by weight of polyester polyol were vacuum dried and dehydrated, and then added to a reaction flask with 48 parts by weight of isophorone diisocyanate. Nitrogen gas was introduced, and the reaction was carried out at 75°C for 2 hours. Then the temperature was lowered to 40°C, and acetone, 6 parts by weight of dimethylolimidazole DOPO as a chain extender, and 0.02 parts by weight of dibutyltin dilaurate were added. The mixture was stirred to dissolve and the reaction was continued for 1 hour. The acetone was removed by concentration, and triethylamine and water were added for neutralization. 0.3 parts of defoamer STA-5300, 0.3 parts of leveling agent PUR2150, and 6 parts of film-forming aid alcohol ester dodecyl were added and stirred evenly to obtain a waterborne polyurethane fireproof coating.

[0023] Example 3 Maleic anhydride-DOPO, dibromoneopentyl glycol, and xylene solvent in a molar ratio of 1:2.6 were added to a reaction flask and stirred at 100°C for 24 h. The solvent was concentrated and the product was purified by recrystallization in toluene to obtain dibromomethylcarboxylic acid DOPO intermediate. Dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate in a molar ratio of 1:2:5 were added to acetonitrile, and the mixture was stirred at 80°C for 12 h. The solvent was concentrated, and the product was purified by recrystallization in toluene to obtain dihydroxymethylimidazolium DOPO.

[0024] 100 parts by weight of polyester polyol were vacuum dried and dehydrated, and then added to a reaction flask with 45 parts by weight of hexamethylene diisocyanate. Nitrogen gas was introduced, and the reaction was carried out at 75°C for 3 hours. Then the temperature was lowered to 40°C, and acetone, 10 parts by weight of dimethylolimidazolium DOPO as a chain extender, and 0.02 parts by weight of dibutyltin dilaurate were added. The mixture was stirred and dissolved, and the reaction was continued for 2 hours. The acetone was removed by concentration, and triethylamine and water were added for neutralization. 0.6 parts of defoamer STA-5300, 0.1 parts of leveling agent PUR2150, and 6 parts of film-forming aid alcohol ester dodecyl were added. The mixture was stirred evenly to obtain a waterborne polyurethane fireproof coating.

[0025] Example 4 Maleic anhydride-DOPO, dibromoneopentyl glycol, and toluene solvent in a molar ratio of 1:2.2 were added to a reaction flask and stirred at 100°C for 24 h. The solvent was concentrated and the product was purified by recrystallization in toluene to obtain dibromomethylcarboxylic acid DOPO intermediate. Dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate in a molar ratio of 1:2.2:4.5 were added to acetonitrile, and the mixture was stirred at 80°C for 15 h. The solvent was concentrated, and the product was purified by recrystallization in toluene to obtain dihydroxymethylimidazolium DOPO.

[0026] 100 parts by weight of polyester polyol were vacuum dried and dehydrated, and then added to a reaction flask with 50 parts by weight of terephthalic diisocyanate. Nitrogen gas was introduced, and the reaction was carried out at 70°C for 3 hours. Then the temperature was lowered to 50°C, and acetone, 15 parts by weight of dimethylolimidazolium DOPO as a chain extender, and 0.03 parts by weight of dibutyltin dilaurate were added. The mixture was stirred and dissolved, and the reaction was continued for 2 hours. The acetone was removed by concentration, and triethylamine and water were added for neutralization. 0.6 parts of defoamer STA-5300, 0.1 parts of leveling agent PUR2150, and 4 parts of film-forming aid alcohol ester dodecyl were added. The mixture was stirred evenly to obtain a waterborne polyurethane fireproof coating.

[0027] Comparative Example 1 100 parts by weight of polyester polyol were vacuum dried and dehydrated, and then added to a reaction flask with 52 parts by weight of toluene diisocyanate. Nitrogen gas was introduced, and the reaction was carried out at 60°C for 3 hours. Then the temperature was lowered to 45°C, and acetone, 2 parts by weight of 1,4-butanediol chain extender, and 0.03 parts by weight of dibutyltin dilaurate were added. The mixture was stirred and dissolved, and the reaction was continued for 1 hour. Then 2,2-dimethylolpropionic acid was added, and the reaction was carried out for 40 minutes. The acetone was removed by concentration, and triethylamine and water were added for neutralization. 0.1 parts of defoamer STA-5300, 0.4 parts of leveling agent PUR2150, and 3 parts of film-forming aid alcohol ester dodecyl were added and stirred evenly to obtain a waterborne polyurethane coating.

[0028] Stability test of waterborne polyurethane coatings: The polyurethane coatings were left to stand at 25℃ for 7-30 days, and the stability of the emulsion was observed.

[0029] Table 1 Stability of Waterborne Polyurethane Emulsions

[0030] Examples 1-4, using DOPO containing dicarboxylic acid dimethylol hydroxyimidazole as a chain extender, yielded waterborne polyurethanes that exhibited excellent dispersibility and emulsion stability in aqueous media. However, after 30 days of storage, the waterborne polyurethanes of Examples 3-4 showed a small amount of flocculent precipitate in the emulsion, which may be due to excessive addition of DOPO, affecting the emulsion stability of the waterborne polyurethanes.

[0031] The polyurethane coating is poured into a mold and dried and cured at 60°C for 6 hours to obtain a polyurethane film.

[0032] Water resistance test of polyurethane coating film: Weigh a certain mass of polyurethane coating film, immerse it in water for 12 hours, remove the film and wipe off the surface moisture, weigh it, and calculate the water absorption rate W, W=(m-m0) / m0. m is the mass after water absorption, and m0 is the mass before absorption; the lower the water absorption rate, the better the water resistance.

[0033] Table 2. Polyurethane water absorption rate test

[0034] In Examples 1-4, dihydroxymethylimidazolium DOPO containing dicarboxyl groups was used as a hydrophilic chain extender. The water-based polyurethanes prepared had low water absorption rates, ranging from only 1.96% to 8.49%. This is because dihydroxymethylimidazolium DOPO contains a water-resistant aromatic ring structure, which helps to reduce the water absorption rate of the polyurethane film and improve its water resistance.

[0035] Flame retardancy test of polyurethane coating: The test was conducted using a cone calorimeter under a heat irradiation condition of 35 kW / m². 2 The paint film dimensions are 4cm × 4cm × 0.1cm. The smaller the peak heat release rate and the total heat release, the better the flame retardancy.

[0036] Table 3. Flame retardancy test of polyurethane

[0037] Compared with Comparative Example 1, in Examples 1-4, dihydroxymethylimidazolium DOPO containing imidazole and DOPO structures was used as a chain extender to obtain polyurethane coatings. The imidazole and DOPO formed a nitrogen-phosphorus synergistic flame retardant system and were bonded to the polyurethane molecular chain, which achieved a good intrinsic flame retardant effect. It significantly reduced the peak heat release rate and total heat release during polyurethane combustion and enhanced the flame retardant performance of polyurethane.

[0038] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some descriptions of this invention have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for preparing a water-based polyurethane fire-retardant coating, characterized in that, The waterborne polyurethane fire-retardant coating is prepared according to the following process: Polyester polyol is vacuum dried and dehydrated, then added to a reaction flask with diisocyanate, nitrogen gas is introduced, and the reaction is carried out at 60-75℃ for 2-3 hours. Then the temperature is lowered to 40-50℃, acetone, dimethylolimidazole DOPO as chain extender, and dibutyltin dilaurate are added, stirred and dissolved, and the reaction is continued for 1-2 hours. The acetone is concentrated and removed, triethylamine and water are added for neutralization, and defoamer, leveling agent and film-forming aid are added. The mixture is stirred evenly to obtain the waterborne polyurethane fire-retardant coating. The dihydroxymethylimidazolium DOPO is prepared according to the following process: S1. Maleic anhydride-DOPO, dibromoneopentyl glycol, and solvent were added to a reaction flask, the mixture was stirred, the solvent was concentrated, and the product was purified by recrystallization in toluene to obtain dibromomethylcarboxylic acid DOPO intermediate. S2. Dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate were added to acetonitrile, and the mixture was stirred and reacted. The solvent was concentrated, and the product was purified by recrystallization in toluene to give dihydroxymethylimidazolium DOPO; the structural formula is as follows. ; The diisocyanates include hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, and terephthalic diisocyanate; The solvents include toluene, xylene, and 1,4-dioxane.

2. The preparation process of the waterborne polyurethane fire-retardant coating according to claim 1, characterized in that, The mass of the diisocyanate and dihydroxymethylimidazolium DOPO are 45-52% and 2-15% of the polyester polyol, respectively.

3. The preparation process of the waterborne polyurethane fire-retardant coating according to claim 1, characterized in that, The molar ratio of maleic anhydride-DOPO and dibromoneopentyl glycol is 1:2.2-2.

6.

4. The preparation process of the waterborne polyurethane fire-retardant coating according to claim 1, characterized in that, The reaction in S1 is carried out at a temperature of 85-100℃ for 12-24 hours.

5. The preparation process of the waterborne polyurethane fire-retardant coating according to claim 1, characterized in that, The molar ratio of the dibromomethylcarboxylic acid DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate is 1:(2-2.5):(4.5-6).

6. The preparation process of the waterborne polyurethane fire-retardant coating according to claim 1, characterized in that, The reaction in S2 is carried out at a temperature of 70-80°C for 12-18 hours.

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