A heat-resistant chitosan-modified polyurethane UV-curable coating and its preparation method

Abstract

The present invention relates to the technical field of UV-curable coatings, and discloses a high-temperature resistant chitosan-modified polyurethane UV-curable coating and a preparation method thereof. Using dipropylene glycol diacrylate and the like as reactive diluents, benzoin dimethyl ether and the like as photoinitiators, and using the alkenyl group of acryloyl chloride grafted chitosan as a crosslinking site, an ultraviolet curing crosslinking reaction occurs with the terminal alkenyl group of the alkenyl naphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, so that the polyurethane crosslinking system contains a rigid naphthalene ring, improving the chemical stability and dimensional stability of the polyurethane crosslinking network, which is beneficial to improving the hardness, impact resistance and tensile properties of the photocured paint film. At the same time, the polyurethane contains phosphorus amide and sulfur flame retardant elements, forming an intumescent flame retardant system with the naphthalene ring with a high carbon content and chitosan, which can increase the thermal decomposition temperature and char formation of the paint film, and enhance the high-temperature resistance and flame retardant properties of the paint film.

Description

Technical Field

[0001] The present invention relates to the technical field of UV - curable coatings, and specifically to a heat - resistant chitosan - modified polyurethane UV - curable coating and a preparation method thereof. Background Art

[0002] Polyurethane ultraviolet (UV) - curable coatings have the advantages of fast curing speed, environmental protection, easy construction, etc., and are widely used in various fields of the national economic production; traditional polyurethane UV - curable coatings use hydroxyethyl acrylate, etc. as capping agents to prepare acrylate - based polyurethanes and their UV - curable coatings, which have problems such as low mechanical strength, poor heat resistance and flame retardancy. Developing new polyurethane UV - curable coatings and improving the mechanical properties, heat resistance and other properties of the coating film are research hotspots.

[0003] Patent CN112142944B discloses that using diol polymers, diisocyanates, carboxyl - containing chain extenders, thiol capping agents, etc. as raw materials, a low - energy UV - curable polyurethane acrylate prepolymer and its UV - curable coating are prepared, which have the advantages of fast UV - curing speed, good toughness, stable storage, etc., but do not solve the problems of poor heat resistance and flame retardancy of polyurethane UV - curable coatings;

[0004] Chitosan is a natural polysaccharide derivative, non - toxic and environmentally friendly, contains rigid molecular chains, and has good antibacterial properties and high char - forming properties, and has good application prospects in the fields of antibacterial agents, flame retardants, toughening agents, etc. Patent CN114539623B discloses that using phytic acid, chitosan, etc. as reactants, a chitosan - based flame retardant is prepared, which can improve the flame retardant performance of polyurethane materials, but this polyurethane does not have a UV - curing effect; the present invention prepares a heat - resistant chitosan - modified polyurethane UV - curable coating, aiming to improve the mechanical properties, heat resistance and flame retardancy of polyurethane UV - curable coatings. Summary of the Invention

[0005] The technical problem solved by the present invention is: to provide a heat - resistant chitosan - modified polyurethane UV - curable coating and a preparation method thereof, which solve the problems of poor mechanical properties, heat resistance and flame retardancy of traditional polyurethane UV - curable coatings.

[0006] The technical solution provided by the present invention is:

[0007] A heat-resistant chitosan-modified polyurethane UV-curable coating, comprising the following components in parts by weight: 100 parts of vinylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, 1-10 parts of acryloyl chloride-grafted chitosan, 8-15 parts of reactive diluent, 2.6-5 parts of photoinitiator, 0.2-0.8 part of defoamer, 0.2-0.5 part of leveling agent; wherein the photoinitiator is any one of dimethoxybenzene, ethoxybenzene or benzophenone; the reactive diluent is any one of dipropylene glycol diacrylate, pentaerythritol triallyl ether or pentaerythritol triacrylate.

[0008] The preparation method of the heat-resistant chitosan-modified polyurethane UV-curable coating comprises the following steps:

[0009] S1. Dry and dehydrate the polyether diol, mix it with 2,4-toluene diisocyanate, dropwise add dibutyltin dilaurate at a temperature of 60-70 °C under a nitrogen atmosphere, react for 2-3 h, add 2,2-dimethylolpropionic acid, and continue to react for 2-3 h to obtain a polyurethane prepolymer. Finally, cool the temperature to 40-50 °C, add a vinylnaphthalenediamine phosphoryl mercaptoethylamine compound for end-capping, react for 3-5 h, cool, add triethylamine for neutralization to obtain a vinylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, add water for dispersion, and heat to volatilize acetone to obtain a polyurethane emulsion.

[0010] S2. Add acryloyl chloride-grafted chitosan, reactive diluent, photoinitiator, defoamer, and leveling agent to the polyurethane emulsion, and disperse at high speed to obtain a heat-resistant chitosan-modified polyurethane UV-curable coating.

[0011] Further, the ratio of the polyether diol, 2,4-toluene diisocyanate, dibutyltin dilaurate, 2,2-dimethylolpropionic acid, and vinylnaphthalenediamine phosphoryl mercaptoethylamine compound in S1 is 1 g: (0.4-0.5) g: (0.001-0.002) g: (0.07-0.09) g: (0.05-0.08) g.

[0012] Further, the preparation method of the vinylnaphthalenediamine phosphoryl mercaptoethylamine compound comprises the following steps:

[0013] S11. Add 2,3-diaminonaphthalene to a 1,2-dichloroethane solvent, stir to dissolve, dropwise add phosphorus oxychloride at 0-5 °C, then heat to 80-90 °C and reflux for 6-18 h, cool, rotary evaporate to remove the solvent, wash with dichloromethane, and dry to obtain Intermediate 1.

[0014] S12. Add Boc-L-cysteine and sodium hydroxide to a tetrahydrofuran solvent, heat to 60 - 70 °C, stir and reflux for 1 - 2 h, then dropwise add Intermediate 1 under a nitrogen atmosphere, react for 36 - 72 h, cool, rotary evaporate to remove the solvent, wash successively with water and acetone, and dry to obtain Intermediate 2.

[0015] S13. Add Intermediate 2, allylamine, N,N-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine to a tetrahydrofuran solvent, react at room temperature for 6 - 18 h, rotary evaporate to remove the solvent, wash with acetone, and dry. Add the product to dichloromethane, add trifluoroacetic acid, react at room temperature for 2 - 4 h, add sodium hydroxide for neutralization, rotary evaporate to remove the solvent, and wash successively with water and acetone to obtain an alkenylnaphthalenediamine phosphoryl mercaptoethylamine compound.

[0016] Further, in S11, the ratio of 2,3-diaminonaphthalene to phosphorus oxychloride is 1 g : (1.25 - 1.4) g.

[0017] Further, in S12, the ratio of Boc-L-cysteine, sodium hydroxide, and Intermediate 1 is 1 g : (0.3 - 0.45) g : (1.1 - 1.3) g.

[0018] Further, in S13, the ratio of Intermediate 2, allylamine, N,N-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 1 g : (0.15 - 0.22) g : (0.6 - 0.75) g : (0.08 - 0.1) g.

[0019] The technical effects produced by the present invention are as follows: The present invention uses 2,3-diaminonaphthalene, phosphorus oxychloride, Boc-L-cysteine, allylamine, etc. as reaction raw materials to prepare a novel alkenylnaphthalenediamine phosphoryl mercaptoethylamine compound. As a capping agent, its amino group reacts with the terminal isocyanate group of the polyurethane prepolymer to obtain an alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, realizing the capping of the polyurethane prepolymer, thereby introducing alkenyl, rigid naphthalene ring, phosphoramide, and sulfur flame retardant elements into the polyurethane molecular chain.

[0020] The present invention uses dipropylene glycol diacrylate, etc. as active diluents, benzoin dimethyl ether, etc. as photoinitiators, and the alkenyl group of acryloyl chloride grafted chitosan as a crosslinking site to undergo a UV curing crosslinking reaction with the terminal alkenyl group of the alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, making the polyurethane crosslinked system contain a rigid naphthalene ring, improving the chemical stability and dimensional stability of the polyurethane crosslinked network, and being beneficial to improving the hardness, impact resistance, and tensile properties of the photocured paint film. At the same time, the polyurethane contains phosphoramide and sulfur flame retardant elements, forming an intumescent flame retardant system with the high-carbon-content naphthalene ring and chitosan, which can increase the thermal decomposition temperature and char formation of the paint film, and enhance the high-temperature resistance and flame retardant properties of the paint film. Detailed implementation mode

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0022] The preparation method of acryloyl chloride grafted chitosan is as follows: Add 1 g of chitosan to 8 mL of methanesulfonic acid, stir and dissolve at room temperature, dropwise add acryloyl chloride at 0 °C, react for 8 h, add acetone and ether for precipitation, centrifuge and separate, wash with ether, and dry to obtain acryloyl chloride grafted chitosan.

[0023] Example 1

[0024] (1) Add 2 g of 2,3-diaminonaphthalene to 1,2-dichloroethane solvent, stir and dissolve, dropwise add 2.6 g of phosphorus oxychloride at 5 °C, then heat to 90 °C and reflux for 6 h, cool, rotary evaporate to remove the solvent, wash with dichloromethane, and dry to obtain Intermediate 1. The reaction route is as follows:

[0025]

[0026] (2) Add 3 g of Boc-L-cysteine and 0.9 g of sodium hydroxide to tetrahydrofuran solvent, heat to 65 °C, stir and reflux for 2 h, then dropwise add 3.3 g of Intermediate 1 under a nitrogen atmosphere, react for 72 h, cool, rotary evaporate to remove the solvent, wash with water and acetone in sequence, and dry to obtain Intermediate 2. The reaction route is as follows:

[0027]

[0028] (3) Add 3 g of Intermediate 2, 0.66 g of allylamine, 2.25 g of N,N-dicyclohexylcarbodiimide, and 0.3 g of 4-dimethylaminopyridine to tetrahydrofuran solvent, react at room temperature for 12 h, rotary evaporate to remove the solvent, wash with acetone, and dry. Add the product to dichloromethane, add trifluoroacetic acid (TFA), react at room temperature for 3 h, add sodium hydroxide for neutralization, rotary evaporate to remove the solvent, wash with water and acetone in sequence to obtain the alkenyl naphthalene diamine phosphoryl mercaptoethylamine compound. The reaction formula is as follows:

[0029]

[0030] (4) 30 g of polyether diol NJ-220 (average molecular weight 2000) was dried and dehydrated, mixed with 12 g of 2,4-toluene diisocyanate, 0.03 g of dibutyltin dilaurate was added dropwise at 70 °C under a nitrogen atmosphere, reacted for 3 h, 2.6 g of 2,2-dimethylolpropionic acid was added, and the reaction continued for 3 h to obtain a polyurethane prepolymer. Finally, the temperature was lowered to 50 °C, 1.5 g of alkenylnaphthalenediamine phosphoryl mercaptoethylamine compound was added for capping, reacted for 3 h, cooled, and triethylamine was added for neutralization to obtain an alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer. Water was added for dispersion, and acetone was volatilized by heating to obtain a polyurethane emulsion.

[0031] (5) 0.5 g of acryloyl chloride grafted chitosan, 4 g of active diluent dipropylene glycol diacrylate, 1.3 g of photoinitiator benzoin dimethyl ether, 0.2 g of defoamer polyoxyethylene polyoxypropylene pentaerythritol ether, and 0.25 g of leveling agent polyether polyester modified silicone were added to the polyurethane emulsion containing 50 g of alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, and dispersed at high speed to obtain a high-temperature resistant chitosan-modified polyurethane UV-curable coating.

[0032] Example 2

[0033] (1) 2 g of 2,3-diaminonaphthalene was added to 1,2-dichloroethane solvent, stirred and dissolved, 2.8 g of phosphorus oxychloride was added dropwise at 0 °C, then the temperature was raised to 90 °C and refluxed for 6 h, cooled, the solvent was removed by rotary evaporation, washed with dichloromethane, and dried to obtain Intermediate 1.

[0034] (2) 3 g of Boc-L-cysteine and 0.9 g of sodium hydroxide were added to tetrahydrofuran solvent, the temperature was raised to 70 °C, stirred and refluxed for 1 h, then 3.5 g of Intermediate 1 was added dropwise under a nitrogen atmosphere, reacted for 48 h, cooled, the solvent was removed by rotary evaporation, washed successively with water and acetone, and dried to obtain Intermediate 2.

[0035] (3) 3 g of Intermediate 2, 0.45 g of allylamine, 2.1 g of N,N-dicyclohexylcarbodiimide, and 0.28 g of 4-dimethylaminopyridine were added to tetrahydrofuran solvent, reacted at room temperature for 18 h, the solvent was removed by rotary evaporation, washed with acetone, and dried. The product was added to dichloromethane, trifluoroacetic acid was added, reacted at room temperature for 3 h, sodium hydroxide was added for neutralization, the solvent was removed by rotary evaporation, and washed successively with water and acetone to obtain the alkenylnaphthalenediamine phosphoryl mercaptoethylamine compound.

[0036] (4) 30 g of polyether diol NJ-220 (average molecular weight 2000) was dried and dehydrated, mixed with 13 g of 2,4-toluene diisocyanate, 0.06 g of dibutyltin dilaurate was added dropwise at a temperature of 60 °C under a nitrogen atmosphere, and the reaction was carried out for 3 h. Then 2.7 g of 2,2-dimethylolpropionic acid was added, and the reaction was continued for 2 h to obtain a polyurethane prepolymer. Finally, the temperature was lowered to 50 °C, 1.8 g of alkenylnaphthalenediamine phosphorylmercaptoethylamine compound was added for end-capping, and the reaction was carried out for 5 h. After cooling, triethylamine was added for neutralization to obtain an alkenylnaphthalenediamine phosphorylmercapto-modified polyurethane prepolymer. Water was added for dispersion, and acetone was evaporated by heating to obtain a polyurethane emulsion.

[0037] (5) 2 g of acryloyl chloride-grafted chitosan, 6 g of active diluent pentaerythritol triacrylate, 2.5 g of photoinitiator benzoin ethyl ether, 0.1 g of defoamer polyoxyethylene polyoxypropylene pentaerythritol ether, and 0.25 g of leveling agent polyether polyester-modified silicone were added to the polyurethane emulsion containing 50 g of alkenylnaphthalenediamine phosphorylmercapto-modified polyurethane prepolymer, and high-speed dispersion was carried out to obtain a high-temperature-resistant chitosan-modified polyurethane UV-curable coating.

[0038] Example 3

[0039] (1) 2 g of 2,3-diaminonaphthalene was added to 1,2-dichloroethane solvent, stirred and dissolved, 2.5 g of phosphorus oxychloride was added dropwise at 0 °C, then the temperature was raised to 90 °C and refluxed for 12 h. After cooling, the solvent was removed by rotary evaporation, washed with dichloromethane, and dried to obtain Intermediate 1.

[0040] (2) 3 g of Boc-L-cysteine and 0.9 g of sodium hydroxide were added to tetrahydrofuran solvent, the temperature was raised to 70 °C, and stirred and refluxed for 1 h. Then 3.9 g of Intermediate 1 was added dropwise under a nitrogen atmosphere, and the reaction was carried out for 48 h. After cooling, the solvent was removed by rotary evaporation, washed with water and acetone in sequence, and dried to obtain Intermediate 2.

[0041] (3) 3 g of Intermediate 2, 0.45 g of allylamine, 2.25 g of N,N-dicyclohexylcarbodiimide, and 0.3 g of 4-dimethylaminopyridine were added to tetrahydrofuran solvent, and the reaction was carried out at room temperature for 12 h. The solvent was removed by rotary evaporation, washed with acetone, and dried. The product was added to dichloromethane, trifluoroacetic acid was added, and the reaction was carried out at room temperature for 3 h. Sodium hydroxide was added for neutralization, the solvent was removed by rotary evaporation, and washed with water and acetone in sequence to obtain alkenylnaphthalenediamine phosphorylmercaptoethylamine compound.

[0042] (4) 30 g of polyether diol NJ-220 (average molecular weight 2000) was dried and dehydrated, mixed with 13 g of 2,4-toluene diisocyanate, 0.06 g of dibutyltin dilaurate was added dropwise at 70 °C under a nitrogen atmosphere, and the reaction was carried out for 3 h. Then, 2.7 g of 2,2-dimethylolpropionic acid was added, and the reaction was continued for 2 h to obtain a polyurethane prepolymer. Finally, the temperature was lowered to 40 °C, 2.1 g of alkenylnaphthalenediamine phosphorylmercaptoethylamine compound was added for end-capping, and the reaction was carried out for 5 h. After cooling, triethylamine was added for neutralization to obtain an alkenylnaphthalenediamine phosphorylmercapto-modified polyurethane prepolymer. Water was added for dispersion, and acetone was volatilized by heating to obtain a polyurethane emulsion.

[0043] (5) 3.5 g of acryloyl chloride-grafted chitosan, 6 g of reactive diluent pentaerythritol triallyl ether, 2.1 g of photoinitiator benzophenone, 0.1 g of defoamer polyoxyethylene polyoxypropylene pentaerythritol ether, and 0.25 g of leveling agent polyether polyester-modified silicone were added to the polyurethane emulsion containing 50 g of alkenylnaphthalenediamine phosphorylmercapto-modified polyurethane prepolymer, and high-speed dispersion was carried out to obtain a high-temperature-resistant chitosan-modified polyurethane UV-curable coating.

[0044] Example 4

[0045] (1) 2 g of 2,3-diaminonaphthalene was added to 1,2-dichloroethane solvent, stirred and dissolved, 2.5 g of phosphorus oxychloride was added dropwise at 0 °C, then the temperature was raised to 85 °C and refluxed for 12 h. After cooling, the solvent was removed by rotary evaporation, washed with dichloromethane, and dried to obtain Intermediate 1.

[0046] (2) 3 g of Boc-L-cysteine and 1.35 g of sodium hydroxide were added to tetrahydrofuran solvent, the temperature was raised to 65 °C, and stirred and refluxed for 2 h. Then, 3.3 g of Intermediate 1 was added dropwise under a nitrogen atmosphere, and the reaction was carried out for 72 h. After cooling, the solvent was removed by rotary evaporation, washed with water and acetone in turn, and dried to obtain Intermediate 2.

[0047] (3) 3 g of Intermediate 2, 0.66 g of allylamine, 1.8 g of N,N-dicyclohexylcarbodiimide, and 0.28 g of 4-dimethylaminopyridine were added to tetrahydrofuran solvent, and the reaction was carried out at room temperature for 18 h. The solvent was removed by rotary evaporation, washed with acetone, and dried. The product was added to dichloromethane, trifluoroacetic acid was added, and the reaction was carried out at room temperature for 4 h. Sodium hydroxide was added for neutralization, the solvent was removed by rotary evaporation, and washed with water and acetone in turn to obtain the alkenylnaphthalenediamine phosphorylmercaptoethylamine compound.

[0048] (4) 30 g of polyether diol NJ-220 (average molecular weight 2000) was dried and dehydrated, mixed with 15 g of 2,4-toluene diisocyanate, 0.03 g of dibutyltin dilaurate was added dropwise at a temperature of 60 °C in a nitrogen atmosphere, reacted for 3 h, 2.7 g of 2,2-dimethylolpropionic acid was added, and the reaction continued for 3 h to obtain a polyurethane prepolymer. Finally, the temperature was lowered to 45 °C, 2.4 g of alkenylnaphthalenediamine phosphoryl mercaptoethylamine compound was added for capping, reacted for 4 h, cooled, and triethylamine was added for neutralization to obtain an alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer. Water was added for dispersion, and acetone was evaporated by heating to obtain a polyurethane emulsion.

[0049] (5) 5 g of acryloyl chloride grafted chitosan, 7.5 g of active diluent pentaerythritol triacrylate, 1.8 g of photoinitiator benzophenone, 0.4 g of defoamer polyoxyethylene polyoxypropylene pentaerythritol ether, and 0.1 g of leveling agent polyether polyester modified silicone were added to the polyurethane emulsion containing 50 g of alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, and dispersed at high speed to obtain a high-temperature resistant chitosan-modified polyurethane UV curable coating.

[0050] Comparative Example 1

[0051] 30 g of polyether diol NJ-220 (average molecular weight 2000) was dried and dehydrated, mixed with 12 g of 2,4-toluene diisocyanate, 0.03 g of dibutyltin dilaurate was added dropwise at a temperature of 70 °C in a nitrogen atmosphere, reacted for 3 h, 2.6 g of 2,2-dimethylolpropionic acid was added, and the reaction continued for 3 h to obtain a polyurethane prepolymer. Finally, the temperature was lowered to 50 °C, 1.1 g of hydroxyethyl acrylate was added for capping, reacted for 3 h, cooled, and triethylamine was added for neutralization to obtain a hydroxyethyl acrylate-modified polyurethane prepolymer. Water was added for dispersion, and acetone was evaporated by heating to obtain a polyurethane emulsion.

[0052] 0.5 g of acryloyl chloride grafted chitosan, 4 g of active diluent dipropylene glycol diacrylate, 1.3 g of photoinitiator benzoin dimethyl ether, 0.2 g of defoamer polyoxyethylene polyoxypropylene pentaerythritol ether, and 0.25 g of leveling agent polyether polyester modified silicone were added to the polyurethane emulsion containing 50 g of hydroxyethyl acrylate-modified polyurethane prepolymer, and dispersed at high speed to obtain a chitosan-modified UV curable coating.

[0053] Comparative Example 2

[0054] (4) 30 g of polyether diol NJ-220 (average molecular weight 2000) was dried and dehydrated, mixed with 12 g of 2,4-toluene diisocyanate, 0.03 g of dibutyltin dilaurate was added dropwise at 70 °C under a nitrogen atmosphere, reacted for 3 h, 2.6 g of 2,2-dimethylolpropionic acid was added, and the reaction continued for 3 h to obtain a polyurethane prepolymer. Finally, the temperature was lowered to 50 °C, 1.5 g of alkenylnaphthalenediamine phosphoryl mercaptoethylamine compound was added for capping, reacted for 3 h, cooled, and triethylamine was added for neutralization to obtain an alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer. Water was added for dispersion, and acetone was evaporated by heating to obtain a polyurethane emulsion.

[0055] (5) 4 g of reactive diluent dipropylene glycol diacrylate, 1.3 g of photoinitiator benzoin dimethyl ether, 0.2 g of defoamer polyoxyethylene polyoxypropylene pentaerythritol ether, and 0.25 g of leveling agent polyether polyester modified silicone were added to the polyurethane emulsion containing 50 g of alkenylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, and dispersed at high speed to obtain a high-temperature resistant modified UV-curable coating.

[0056] The UV-curable coating was cured by irradiation in a UV light curing machine.

[0057] The photocuring time was tested according to the method of GB / T 1728-2020.

[0058] The hardness of the cured paint film was tested according to the method of GB / T 6739-2006. The impact resistance was tested according to the method of GB / T 1732-2020

[0059] The tensile properties of the cured paint film were tested according to the method of GB / T 1040.1-2006. The tensile rate was 50 mm / min.

[0060] The heat resistance of the cured paint film was tested using a thermogravimetric analyzer under a nitrogen atmosphere, and the test temperature was 20 - 700 °C.

[0061] The flame retardant properties of the cured paint film were tested for the limiting oxygen index according to the method of GB / T 2406.1-2008.

[0062]

[0063] In Comparative Example 1, traditional hydroxyethyl acrylate was used as the capping agent, and the prepared polyurethane did not contain a rigid naphthalene ring structure. The hardness, impact resistance, tensile strength, and elongation at break of the photocured paint film were much lower than those of Examples 1-4.

[0064]

[0065] In Comparative Example 1, the polyurethane cured paint film does not contain naphthalene rings, phosphoramide, and sulfur flame retardant elements with high char-forming properties, cannot promote the dehydration and carbonization of chitosan, and cannot form an intumescent flame retardant system with chitosan. The thermal decomposition temperature and limiting oxygen index of the obtained photocurable coating are much lower than those in Examples 1-4, and the high temperature resistance and flame retardancy are poor.

[0066] In Comparative Example 2, acryloyl chloride was not added to graft chitosan, and its mass retention rate and limiting oxygen index are lower than those in Examples 1-4.

[0067] The above examples are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing examples, or perform equivalent replacements on some of the technical features; and these modifications or replacements will not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A preparation method of a chitosan-modified polyurethane UV-curable coating with high temperature resistance, characterized in that, The heat-resistant chitosan-modified polyurethane UV-curable coating comprises the following components in parts by weight: 100 parts of vinylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, 1-10 parts of acryloyl chloride-grafted chitosan, 8-15 parts of reactive diluent, 2.6-5 parts of photoinitiator, 0.2-0.8 part of defoamer, and 0.2-0.5 part of leveling agent; The preparation method comprises the following steps: S1. Dry and dehydrate polyether diol, mix it with 2,4-toluene diisocyanate, dropwise add dibutyltin dilaurate at a temperature of 60-70 °C under a nitrogen atmosphere, react for 2-3 h, add 2,2-dimethylolpropionic acid, and continue to react for 2-3 h to obtain a polyurethane prepolymer. Finally, cool the temperature to 40-50 °C, add a vinylnaphthalenediamine phosphoryl mercaptoethylamine compound for end-capping, react for 3-5 h, cool, add triethylamine for neutralization to obtain a vinylnaphthalenediamine phosphoryl mercapto-modified polyurethane prepolymer, add water for dispersion, and heat to volatilize acetone to obtain a polyurethane emulsion; S2. Add acryloyl chloride-grafted chitosan, reactive diluent, photoinitiator, defoamer, and leveling agent to the polyurethane emulsion, and disperse at high speed to obtain a heat-resistant chitosan-modified polyurethane UV-curable coating; The preparation method of the vinylnaphthalenediamine phosphoryl mercaptoethylamine compound comprises the following steps: S11. Add 2,3-diaminonaphthalene to a 1,2-dichloroethane solvent, stir to dissolve, dropwise add phosphorus oxychloride at 0-5 °C, then heat to 80-90 °C and reflux for 6-18 h, cool, rotary evaporate, wash, and dry to obtain Intermediate 1; S12. Add Boc-L-cysteine and sodium hydroxide to a tetrahydrofuran solvent, heat to 60-70 °C, stir and reflux for 1-2 h, then dropwise add Intermediate 1 under a nitrogen atmosphere, and reflux and react for 36-72 h, cool, rotary evaporate, wash, and dry to obtain Intermediate 2; S13. Add Intermediate 2, allylamine, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine to a tetrahydrofuran solvent, react at room temperature for 6-18 h, rotary evaporate to remove the solvent, wash with acetone, and dry. Add the product to dichloromethane, add trifluoroacetic acid, react at room temperature for 2-4 h, add sodium hydroxide for neutralization, and rotary evaporate and wash to obtain the vinylnaphthalenediamine phosphoryl mercaptoethylamine compound; In the S11, the ratio of 2,3-diaminonaphthalene to phosphorus oxychloride is 1 g:(1.25-1.4) g; In the S12, the ratio of Boc-L-cysteine, sodium hydroxide, and Intermediate 1 is 1 g:(0.3-0.45) g:(1.1-1.3) g; In the S13, the ratio of Intermediate 2, allylamine, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 1 g:(0.15-0.22) g:(0.6-0.75) g:(0.08-0.1) g.

2. The preparation method of the high-temperature resistant chitosan-modified polyurethane UV-curing coating according to claim 1, characterized in that, The reactive diluent is any one of dipropylene glycol diacrylate, pentaerythritol triallyl ether, or pentaerythritol triacrylate.

3. The preparation method of the heat-resistant chitosan-modified polyurethane UV-curable coating according to claim 1, characterized in that, The photoinitiator is any one of dimethoxybenzil, benzoin ethyl ether, or benzophenone.

4. The preparation method of the heat-resistant chitosan-modified polyurethane UV-curable coating according to claim 1, characterized in that, In S1, the ratio of polyether diol, 2,4-toluene diisocyanate, dibutyltin dilaurate, 2,2-dimethylolpropionic acid, and alkenyl naphthalene diamine phosphoryl mercaptoethylamine compound is 1 g: (0.4 - 0.5) g: (0.001 - 0.002) g: (0.07 - 0.09) g: (0.05 - 0.08) g.

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