Preparation process of waterborne polyurethane fireproof coating

Abstract

The invention relates to the technical field of coatings, and discloses a preparation process 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

Technical Field

[0001] The invention relates to the technical field of coatings, in particular to a preparation process of a waterborne polyurethane fire retardant coating. Background Art

[0002] Paints are widely used in wooden furniture, mechanical equipment, etc. Among them, polyurethane paints have the advantages of good film-forming properties, excellent mechanical strength and elasticity of the paint film; however, current polyurethane paints usually use acetone, toluene, etc. as solvents, which have problems such as easy volatility of solvents, high pollution, and harm to human health; therefore, it is necessary to develop new environmentally friendly water-based paints.

[0003] Traditional waterborne polyurethanes are prepared using hydrophilic chain extenders such as 2,2-dihydroxymethylacrylate and sodium dihydroxy-3-propanesulfonate. These waterborne polyurethanes readily absorb water and have poor water resistance. Furthermore, current waterborne polyurethane paint films are flammable, limiting their practical application in fire protection. DOPO, a novel phosphaphenanthrene flame retardant intermediate, exhibits excellent thermal and chemical stability and flame retardancy, finding widespread application in polyurethane and other coatings. This invention aims to prepare a novel dihydroxymethylimidazole (DOPO) chain extender and a water-resistant waterborne polyurethane fire-retardant coating. Summary of the Invention

[0004] Technical problem solved: A water-based polyurethane fire-retardant coating was prepared using dihydroxymethylimidazole (DOPO) as a chain extender, which solved the problems of poor water resistance and fire retardancy of polyurethane coatings.

[0005] Technical solution: A preparation process of a waterborne polyurethane fire retardant coating comprises the following steps: vacuum drying and dehydrating a polyester polyol, then adding the polyester polyol and a diisocyanate into a reaction flask, introducing nitrogen, reacting at 60-75° C. for 2-3 hours, then lowering the temperature to 40-50° C., adding acetone, dihydroxymethylimidazole (DOPO) as a chain extender, and dibutyltin dilaurate, stirring and dissolving, continuing the reaction for 1-2 hours, concentrating to remove the acetone, adding triethylamine and water for neutralization, adding a defoamer, a leveling agent, and a film-forming aid, and stirring evenly to obtain the waterborne polyurethane fire retardant coating.

[0006] Furthermore, the mass of diisocyanate and dihydroxymethylimidazole DOPO is 45-52% and 2-15% of the polyester polyol, respectively.

[0007] Furthermore, the diisocyanate includes hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, and p-phenylene diisocyanate.

[0008] Furthermore, dihydroxymethylimidazole DOPO is prepared according to the following process: S1. Add maleic anhydride-DOPO, dibromoneopentyl glycol, and solvent to a reaction flask, stir to react, concentrate the solvent, and purify the product by recrystallization in toluene to obtain a dibromomethylcarboxyl DOPO intermediate; S2, adding dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate to acetonitrile, stirring to react, concentrating the solvent, and recrystallizing the product in toluene to obtain dihydroxymethylimidazole DOPO; the structural formula is .

[0009] Furthermore, the molar ratio of maleic anhydride-DOPO to dibromoneopentyl glycol is 1:2.2-2.6.

[0010] Furthermore, the solvent includes toluene, xylene, and 1,4-dioxane.

[0011] Furthermore, the reaction in S1 is carried out at a temperature of 85-100° C. for 12-24 h.

[0012] Furthermore, the molar ratio of dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate is 1:(2-2.5):(4.5-6).

[0013] Furthermore, the reaction in S2 is carried out at a temperature of 70-80° C. for 12-18 hours.

[0014] The technical effect of the present invention is as follows: a new type of dihydroxymethylimidazole DOPO is prepared by an acid anhydride esterification reaction between maleic anhydride-DOPO and dibromoneopentyl glycol, followed by a substitution reaction with (1H-imidazol-5-yl)methanol. The dicarboxyl and dihydroxy groups contained in the new dihydroxymethylimidazole DOPO can be used as a water-based chain extender for polyurethane, and can undergo a polymerization reaction with polyester polyol and diisocyanate to obtain a water-based polyurethane fire retardant coating.

[0015] The waterborne polyurethane fire-retardant coating prepared by the present invention exhibits good emulsion stability, exhibiting no stratification or precipitation after prolonged exposure. Furthermore, the dihydroxymethylimidazole (DOPO) contains a water-resistant aromatic ring structure, which helps reduce the water absorption of the polyurethane paint film and improve its water resistance.

[0016] The imidazole and DOPO groups contained in the dihydroxymethylimidazole DOPO of the present invention form a nitrogen-phosphorus synergistic flame retardant system and are bonded to the polyurethane molecular chain, thereby exerting a good intrinsic flame retardant effect on the polyurethane paint film, significantly reducing the peak heat release rate and total heat release during combustion of the polyurethane, and enhancing the flame retardant properties of the polyurethane. DETAILED DESCRIPTION

[0017] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the examples, which are not intended to limit the present invention.

[0018] Example 1 Maleic anhydride-DOPO, dibromoneopentyl glycol, and 1,4-dioxane solvent were added to a reaction flask at a molar ratio of 1:2.6. The reaction was stirred at 90°C for 12 hours. The solvent was concentrated and the product was purified by recrystallization from toluene to obtain a dibromomethylcarboxyl DOPO intermediate. A dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate in a molar ratio of 1:2.2:6 were added to acetonitrile, stirred at 70°C for 18 hours, and the solvent was concentrated. The product was recrystallized and purified from toluene to obtain dihydroxymethylimidazole DOPO.

[0019] 100 parts by weight of polyester polyol was vacuum dried and dehydrated, and then added to a reaction flask with 52 parts by weight of toluene diisocyanate, nitrogen was introduced, and the reaction was carried out at 60°C for 3 hours. Then the temperature was reduced to 45°C, acetone, 2 parts by weight of dihydroxymethylimidazole DOPO as a chain extender, and 0.03 parts by weight of dibutyltin dilaurate were added, stirred to dissolve, and the reaction was continued for 1 hour. The acetone was concentrated to remove the acetone, and triethylamine and water were added for neutralization. 0.1 parts of defoaming agent STA-5300, 0.4 parts of leveling agent PUR2150, and 3 parts of film-forming aid alcohol ester twelve were added, and the mixture was stirred evenly to obtain a waterborne polyurethane fire retardant coating.

[0020] Example 2 Maleic anhydride-DOPO, dibromoneopentyl glycol, and toluene solvent were added to a reaction flask at a molar ratio of 1:2.4. The mixture was stirred at 85°C for 24 hours. The solvent was concentrated and the product was purified by recrystallization from toluene to obtain a dibromomethylcarboxyl DOPO intermediate. A dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate were added to acetonitrile in a molar ratio of 1:2.5:5. The reaction was stirred at 70°C for 12 hours. The solvent was concentrated, and the product was purified by recrystallization from toluene to obtain dihydroxymethylimidazole DOPO.

[0021] 100 parts by weight of polyester polyol was vacuum dried and dehydrated, and then added to a reaction bottle with 48 parts by weight of isophorone diisocyanate, and nitrogen was introduced. The reaction was carried out at 75° C. for 2 hours, and then the temperature was reduced to 40° C., and acetone, 6 parts by weight of dihydroxymethylimidazole 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 1 hour. The acetone was concentrated to remove the acetone, and triethylamine and water were added for neutralization. 0.3 parts of defoaming agent STA-5300, 0.3 parts of leveling agent PUR2150, and 6 parts of film-forming aid alcohol ester twelve were added, and the mixture was stirred evenly to obtain a waterborne polyurethane fire retardant coating.

[0022] Example 3 Maleic anhydride-DOPO, dibromoneopentyl glycol, and xylene solvent were added to a reaction flask at a molar ratio of 1:2.6. The mixture was stirred at 100°C for 24 hours. The solvent was concentrated and the product was purified by recrystallization from toluene to obtain a dibromomethylcarboxyl DOPO intermediate. A dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate in a molar ratio of 1:2:5 were added to acetonitrile, stirred at 80°C for 12 hours, and the solvent was concentrated. The product was recrystallized and purified from toluene to obtain dihydroxymethylimidazole DOPO.

[0023] 100 parts by weight of polyester polyol was vacuum dried and dehydrated, and then added to a reaction bottle with 45 parts by weight of hexamethylene diisocyanate, and nitrogen was introduced. The reaction was carried out at 75°C for 3 hours, and then the temperature was reduced to 40°C. Acetone, 10 parts by weight of dihydroxymethylimidazole DOPO as a chain extender, and 0.02 parts by weight of dibutyltin dilaurate were added, stirred to dissolve, and the reaction was continued for 2 hours. The acetone was concentrated to remove the acetone, and triethylamine and water were added for neutralization. 0.6 parts of defoaming agent STA-5300, 0.1 parts of leveling agent PUR2150, and 6 parts of film-forming aid alcohol ester twelve were added, and the mixture was stirred evenly to obtain a waterborne polyurethane fire retardant coating.

[0024] Example 4 Maleic anhydride-DOPO, dibromoneopentyl glycol, and toluene solvent were added to a reaction flask at a molar ratio of 1:2.2. The mixture was stirred at 100°C for 24 hours. The solvent was concentrated and the product was purified by recrystallization from toluene to obtain a dibromomethylcarboxyl DOPO intermediate. A dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate in a molar ratio of 1:2.2:4.5 were added to acetonitrile, stirred at 80°C for 15 hours, and the solvent was concentrated. The product was recrystallized and purified from toluene to obtain dihydroxymethylimidazole DOPO.

[0025] 100 parts by weight of polyester polyol was vacuum dried and dehydrated, and then added to a reaction bottle with 50 parts by weight of p-phenylene diisocyanate, nitrogen was introduced, and the reaction was carried out at 70°C for 3 hours. Then the temperature was lowered to 50°C, acetone, 15 parts by weight of dihydroxymethylimidazole DOPO as a chain extender, and 0.03 parts by weight of dibutyltin dilaurate were added, stirred to dissolve, and the reaction was continued for 2 hours. The acetone was concentrated to remove the acetone, and triethylamine and water were added for neutralization. 0.6 parts of defoaming agent STA-5300, 0.1 parts of leveling agent PUR2150, and 4 parts of film-forming aid alcohol ester twelve were added, and the mixture was stirred evenly to obtain a waterborne polyurethane fire retardant coating.

[0026] Comparative Example 1 100 parts by weight of polyester polyol was vacuum dried and dehydrated, and then added to a reaction bottle with 52 parts by weight of toluene diisocyanate, and nitrogen was introduced. The reaction was carried out at 60°C for 3 hours, and then the temperature was reduced to 45°C. Acetone, 2 parts by weight of 1,4-butanediol chain extender, and 0.03 parts by weight of dibutyltin dilaurate were added, stirred to dissolve, and the reaction was continued for 1 hour. 2,2-dihydroxymethylpropionic acid was added and reacted for 40 minutes. The acetone was concentrated to remove the acetone, and triethylamine and water were added for neutralization. 0.1 parts of defoaming agent STA-5300, 0.4 parts of leveling agent PUR2150, and 3 parts of film-forming aid alcohol ester twelve were added and stirred evenly to obtain a waterborne polyurethane coating.

[0027] Stability test of waterborne polyurethane coating: let the polyurethane coating stand at 25°C for 7-30 days and observe the emulsion stability.

[0028] Table 1 Stability of waterborne polyurethane emulsion

[0029] The waterborne polyurethanes obtained in Examples 1-4 using dicarboxylic dimethylol imidazole (DOPO) as a chain extender exhibited excellent dispersibility and emulsion stability in aqueous media. However, after 30 days of storage, the waterborne polyurethanes in Examples 3-4 exhibited a small amount of flocculent precipitate in the emulsion. This may be due to excessive addition of dicarboxylic dimethylol imidazole (DOPO), which affected the emulsion stability of the waterborne polyurethane.

[0030] The polyurethane coating was poured into a mold and dried and cured at 60° C. for 6 h to obtain a polyurethane paint film.

[0031] Water resistance test of polyurethane paint films: Weigh a certain mass of polyurethane paint film and immerse it in water for 12 hours. Remove the film, wipe off the surface moisture, and weigh it. Calculate the water absorption rate W, W = (m - m0) / m0. m is the mass after water absorption, and m0 is the mass before water absorption. The lower the water absorption rate, the better the water resistance.

[0032] Table 2 Polyurethane water absorption test

[0033] In Examples 1-4, dihydroxymethylimidazole (DOPO) containing a dicarboxyl group was used as a hydrophilic chain extender, and the water-based polyurethanes prepared had a low water absorption rate of only 1.96-8.49%. This is because dihydroxymethylimidazole (DOPO) contains a water-resistant aromatic ring structure, which helps to reduce the water absorption rate of the polyurethane paint film and improve the water resistance.

[0034] Flame retardancy test of polyurethane paint film: Cone calorimeter was used for testing, and the thermal radiation condition was 35kW / m 2 The paint film size is 4cm×4cm×0.1cm. The smaller the peak heat release rate and total heat release, the better the flame retardancy.

[0035] Table 3 Polyurethane flame retardancy test

[0036] Compared with Comparative Example 1, Examples 1-4 use dihydroxymethylimidazole DOPO containing imidazole and DOPO structures as a chain extender to obtain a polyurethane coating, and imidazole and DOPO form a nitrogen-phosphorus synergistic flame retardant system that is bonded to the polyurethane molecular chain, which has a good intrinsic flame retardant effect, significantly reduces the peak heat release rate and total heat release during combustion of the polyurethane, and enhances the flame retardant properties of the polyurethane.

[0037] In order to make it easier for ordinary technicians in this field to understand the improvements of the present invention over the prior art, some descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Those skilled in the art should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A preparation process of a waterborne polyurethane fire retardant coating, characterized in that: The waterborne polyurethane fire retardant coating is prepared according to the following process: vacuum drying and dehydrating polyester polyol, then adding it and diisocyanate into a reaction bottle, introducing nitrogen, reacting at 60-75° C. for 2-3 hours, then lowering the temperature to 40-50° C., adding acetone, dihydroxymethylimidazole DOPO as a chain extender, and dibutyltin dilaurate, stirring to dissolve, continuing the reaction for 1-2 hours, concentrating to remove acetone, adding triethylamine and water for neutralization, adding a defoamer, a leveling agent, and a film-forming aid, and stirring evenly to obtain the waterborne polyurethane fire retardant coating.

2. The preparation process of the waterborne polyurethane fire retardant coating according to claim 1, characterized in that: The mass of the diisocyanate and dihydroxymethylimidazole DOPO is 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 diisocyanate includes hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, and p-phenylene diisocyanate.

4. The preparation process of the waterborne polyurethane fire retardant coating according to claim 1, characterized in that: The dihydroxymethylimidazole DOPO is prepared according to the following process: S1. Add maleic anhydride-DOPO, dibromoneopentyl glycol, and solvent to a reaction flask, stir to react, concentrate the solvent, and purify the product by recrystallization in toluene to obtain a dibromomethylcarboxyl DOPO intermediate; S2, adding dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate to acetonitrile, stirring to react, concentrating the solvent, and recrystallizing the product in toluene to obtain dihydroxymethylimidazole DOPO; the structural formula is .

5. The preparation process of the waterborne polyurethane fire retardant coating according to claim 4, characterized in that: The molar ratio of maleic anhydride-DOPO to dibromoneopentyl glycol is 1:2.2-2.

6.

6. The preparation process of the waterborne polyurethane fire retardant coating according to claim 4, characterized in that: The solvent includes toluene, xylene, and 1,4-dioxane.

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

8. The preparation process of the waterborne polyurethane fire retardant coating according to claim 4, characterized in that: The molar ratio of the dibromomethylcarboxyl DOPO intermediate, (1H-imidazol-5-yl)methanol, and potassium carbonate is 1:(2-2.5):(4.5-6).

9. The preparation process of the waterborne polyurethane fire retardant coating according to claim 4, 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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