Preparation Method of Flame Retardant, High Refractive Index and Melting Drop-Resistant Polyurethane Coating

Abstract

The present invention relates to a preparation method of a flame-retardant, high-refractive-index, melt-drop resistant waterborne polyurethane coating. A diol, an isocyanate and dibutyltin dilaurate are added to a 500 mL flask, and the temperature is raised to 70-85 °C, and the mixture is stirred and reacted for 1-2 h to obtain a polyurethane prepolymer; then a charring agent is added to the polyurethane prepolymer, and the reaction is continued for 1-2 h; the temperature is lowered to 60 °C, and then 2,2-dimethylolbutyric acid and amino carbon nanotubes are added and reacted for 0.5-1 h; then a high-refractive-index material is added, and the reaction is carried out at 65-70 °C for 1-2 h, the temperature is lowered to 40 °C, and then triethylamine is added and reacted for 0.5-1 h; deionized water is added, and at a rotation speed of 2000 r / min, an ammonium polyphosphate solution is added, and high-speed shear emulsification is carried out for 0.5-1 h to obtain a flame-retardant, high-refractive-index, melt-drop resistant waterborne polyurethane coating. This polyurethane coating has high flame retardancy, high refractive index and no melt-dropping property.

Description

Technical Field

[0001] The present invention relates to a preparation method of waterborne polyurethane coatings, and particularly to a preparation method of flame-retardant, high-refractive-index, and melt-drop-resistant waterborne polyurethane coatings. Background Art

[0002] Waterborne polyurethane (WPU) has been widely used in the fields of finishing agents, coatings, and adhesives due to its good mechanical properties, environmental friendliness, and easy modification characteristics, and is applied to various industries such as woodware, automobiles, airplanes, machinery, electrical appliances, instruments, plastics, leather, paper, fabrics, petrochemicals, etc. However, as an excellent polymer material, WPU has a relatively low limiting oxygen index (LOI), usually about 18%, which means it is very easy to be ignited in the air. And once ignited, the fire will spread rapidly, generating a large amount of smoke and toxic gases, posing a great threat to human health. In addition, due to its fast burning speed and accompanied by high-temperature melt dripping, it is extremely easy to cause secondary fires, causing more serious hazards. Therefore, improving the flame retardancy of WPU is an important research direction in the field of WPU.

[0003] According to the different ways of introducing flame retardants into WPU, it can be divided into additive flame retardancy and reactive flame retardancy. Compared with additive flame retardants, reactive flame retardants can overcome problems such as poor compatibility with WPU, easy migration, large dosage, and reduction of the mechanical properties of WPU, and play a better flame retardant effect. So far, a large number of studies on reactive flame-retardant WPU have been reported, including nitrogen-based, phosphorus-based, and silicon-based compounds. Among them, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is a new type of flame retardant intermediate. Due to its cyclic O=P-O bond, it has higher thermal stability and chemical stability than general non-cyclic organic phosphorus flame retardants. Therefore, it has received extensive attention. Based on the addition reaction of the P-H bond of DOPO with the C=C, C=O, and C=N double bonds of the substrate under heating conditions, researchers have designed and synthesized many DOPO derivative flame retardants.

[0004] Yaofa Luo et al. synthesized the PNB organic flame retardant using 4-formylphenylboronic acid, 4-aminobenzenethiol, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as raw materials. Then, the PNB flame retardant was introduced into the molecular chain of hydroxyl-terminated polybutadiene-acrylonitrile (HTBN) to successfully prepare the macromolecular flame retardant APFBH for the preparation of flame-retardant waterborne polyurethane. When APFBH is 7.5%, a LOI value of 29.8% and a UL-94 of V-0 grade can be achieved, greatly improving the melt dripping phenomenon. As the content of APFBH increases, the tensile strength and elongation at break of FR-WPU first increase and then decrease. The flame retardant performance of WPU is improved, but the quality of the carbon layer formed is still not ideal, and there is still room for improvement in the LOI value, and the mechanical properties of the polyurethane decrease.

[0005] The invention patent CN119320596A of Duan Baorong et al., "Preparation method of flame-retardant, washable, and melt-drop resistant polyurethane coating", aims to solve the problems of polyurethane coatings required in PCB processing that need low heat release, melt-drop resistance, washability, and degradability. Aiming at the disadvantages of existing washable coatings, the pre-polymerization reaction of a charring agent and multi-hydroxyl single-walled carbon nanotubes is used, and the chain extension of a porous carbon layer modifier and a glucose modifier, as well as the modification with a high amount of charring agent, are used to solve the problem of no melt-drop and low heat release of polyurethane when heated, and improve the flame retardancy of polyurethane; the washability of the glucose modifier, and the degradability of polycaprolactone diol and glucose are used to improve the degradability and washability of polyurethane. The oxygen index of this invention is relatively low, and the refractive resistance of polyurethane is not involved.

[0006] The invention patent CN113956777B of Duan Baorong et al. uses polypropylene glycol and polytetrahydrofuran ether diol as polyols, modified HGB-NCO as isocyanate, 2,2-dithiodiethanol chain extender and intumescent flame retardant as monomer raw materials, and synthesizes HGB-waterborne polyurethane prepolymer through pre-polymerization reaction. Then a neutralizing agent is added to neutralize the prepolymer, and finally an equal proportion of water is added for emulsification to finally obtain HGB-WPU. Among them, hollow glass microspheres are a new type of hollow material, which has the advantages of low thermal conductivity and non-combustibility. Moreover, hollow glass microspheres are mainly composed of soda lime borosilicate and are themselves non-combustible substances. Adding them to WPU (waterborne polyurethane) reduces its volume fraction and indirectly plays the role of a flame retardant. In addition, due to the light weight and heat insulation advantages of hollow glass microspheres, they can migrate from the inside of the coating to the surface of the sample during the combustion of HGB-WPU, thus isolating the fire source and playing a good role in flame retardancy, enhancing the stability of the carbon layer, and reducing the melt-drop phenomenon. Due to the large particle size of HGB, the stability of the resulting polyurethane is poor, and the storage period of the obtained polyurethane coating is short, restricting industrialization.

[0007] In recent years, intelligent optoelectronic devices such as flexible displays and micro sensors have developed rapidly, and high-performance optical materials are the basis for realizing the functions of advanced optical devices. Although traditional inorganic optical materials have advantages such as high strength, high refractive index, and low dispersion, their disadvantages of high brittleness, high weight, and high processing difficulty limit their development in advanced optical devices. Organic optical materials have become the preferred materials for advanced optical devices due to their advantages such as adjustable performance, light texture, easy processing, etc., and are applied in fields such as high-performance substrates, packaging materials for light-emitting diodes (LEDs), and microlenses for charge-coupled devices (CCDs) or complementary metal-oxide-semiconductor (CMOS) image sensors. However, compared with inorganic optical materials, the molecular structure characteristics of organic optical materials result in poor thermal stability and low refractive index. Among them, the refractive index is the most critical parameter of optical organic materials, and the disadvantage of low refractive index hinders the progress of high-precision optical devices.

[0008] At present, in addition to requiring good heat resistance and flame retardancy, the use of polyurethane in these fields also requires good refractive resistance. However, there is almost no research on the refractive index of waterborne polyurethane at present.

[0009] The invention patent CN111303478A relates to a naked-eye 3D display screen material and a preparation method thereof. The method includes the following steps: providing a polymer solution in which a matrix material is dissolved in a volatile solvent, where the matrix material is an optically transparent material and the volatile solvent is not miscible with water; in a constant temperature and humidity sealed container, casting the polymer solution on an optically transparent substrate, and promoting the nucleation and growth of water droplets on the surface of the polymer solution through the volatilization of the volatile solvent; then standing the optically transparent substrate cast with the polymer solution in a constant temperature and humidity sealed container until the volatile solvent and water droplets are completely volatilized, and forming a microscopic structure of spherical pits left by the water droplets on the surface of the matrix material, thus obtaining the naked-eye 3D display screen material. The resin materials used are mainly styrene-butadiene-styrene block copolymer, polycarbonate, polyethyleneimine or polymethyl methacrylate, and their light transmittance is lower than 95%. The flame retardancy and melt dripping resistance in terms of heat resistance performance are not emphasized, and they are not used in polyurethane.

[0010] To sum up, although polyurethane is widely used, there are still problems such as low oxygen index, large amount of smoke released, and still some melt dripping if not properly controlled. For specific fields that require high refraction, there is also volume shrinkage of the film during the cooling process of the polyurethane film formation, and polyurethane still does not meet the usage requirements. Therefore, a polyurethane material with high refraction and auxiliary heat resistance is needed. Summary of the Invention

[0011] In view of the low oxygen index of polyurethane, large amount of smoke released, and the presence of partial melting droplets when used improperly, and the partial shrinkage of polyurethane in the process of film formation and cooling, the present invention uses polypropylene glycol and polytetrahydrofuran ether glycol as polyols, isophorone diisocyanate and hexamethylene diisocyanate as isocyanates, and synthesizes a prepolymer under the condition of dibutyltin dilaurate as a catalyst; then adds a charring agent modified by N-vinylcarbazole for chain extension. This charring agent can inhibit the formation of melting droplets during the combustion of polyurethane, and the formed poly-N-vinylcarbazole has strong rigidity and small cooling shrinkage of the polyurethane film. Then, the chain extender 2,2-dihydroxybutyric acid (DMBA) and amino carbon nanotubes are used for the second chain extension, introducing amino carbon nanotubes with a dense carbon layer and good thermal conductivity under heating conditions into the polyurethane chain segments to make up for the insufficient denseness of charring property in the first chain extension. Then, a high refractive index material and 2,5-dimethylthio-1,4-dithiane are introduced for the third chain extension. The high refractive index material is a high refractive index compound doped with nitrogen, phosphorus and sulfur containing imino groups. Sulfur is introduced into 2,5-dimethylthio-1,4-dithiane to make up for the insufficient refractive index of the high refractive index material, and at the same time avoid yellowing inside the polyurethane and improve the yellowing resistance of the polyurethane. Triethylamine is used to neutralize the prepolymer, and water is used for emulsification, and finally a flame-retardant, high refractive index, melt-droplet-resistant and water-based polyurethane coating is obtained.

[0012] A preparation method of a flame-retardant, high refractive index, melt-droplet-resistant and water-based polyurethane coating, comprising the following steps:

[0013] (1) Take 30 - 32 g of diol, 14.92 g of isocyanate and 0.2 - 0.3 g of dibutyltin dilaurate, add them to a 500 mL three-necked flask, under the protection of nitrogen, heat up to 70 - 85 °C, rotate at 300 - 500 r / min, and stir and react for 1 - 2 h to obtain a polyurethane prepolymer;

[0014] (2) Then add 4.2 - 8.4 g of a charring agent to the polyurethane prepolymer, continue to react at 70 - 80 °C for 1 - 2 h; cool down to 60 °C, then add 0.73 - 0.89 g of 2,2-dimethylolbutyric acid and 2.4 - 2.6 g of amino carbon nanotubes, react at 60 - 65 °C for 1 - 2 h; then add 1.64 - 2.46 g of a high refractive index material and 1.06 - 1.21 g of 2,5-dimethylthio-1,4-dithiane, react at 65 - 70 °C for 1 - 2 h, cool down to 40 °C, then add 2.1 g of triethylamine, and react for 0.5 - 1 h; cool down to room temperature, add 50 - 80 mL of deionized water, under the rotation speed of 2000 r / min, carry out high-speed shear emulsification for 0.5 - 1.5 h, then add 13.15 g of ammonium polyphosphate solution dissolved in 10 g of water and 0.2 - 0.3 g of an organic-inorganic negative heat material, under the rotation speed of 1000 - 2000 r / min, carry out high-speed shear emulsification for 0.5 - 1 h, and wait for the foam to disappear to obtain a flame-retardant, high refractive index, melt-droplet-resistant and water-based polyurethane coating.

[0015] The diol is any one of polypropylene glycol and polytetrahydrofuran ether diol, or a mixture of the two in any ratio.

[0016] The isocyanate is any one of isophorone diisocyanate and hexamethylene diisocyanate, or a mixture of the two in any ratio.

[0017] The number-average molecular weights of polypropylene glycol and polytetrahydrofuran ether diol are both 2000 g / mol.

[0018] Preparation method of a flame-retardant, high-refraction, melt-drop resistant waterborne polyurethane coating, and preparation method of the charring agent:

[0019] (1) Add 24.4 g of p-hydroxybenzaldehyde (PHBA) to a beaker, dissolve it with 150 - 200 mL of ethanol by stirring, transfer it to a 500 mL three-necked flask, under the protection of nitrogen, heat up to 60 - 70 °C, with a stirring speed of 300 - 500 r / min. Dilute 6 - 6.2 g of ethylenediamine with 50 mL of ethanol, and then drop it into the p-hydroxybenzaldehyde solution. The dropping time is 30 - 50 min, and continue to react for 2 - 2.5 h; cool to room temperature, wash with ethanol 2 - 3 times, and dry in vacuum at 60 - 70 °C for 12 - 24 h to obtain a pale yellow charring intermediate powder PHE.

[0020] (2) Put 26.8 g of the PHE obtained in step (1) into a beaker, add 150 - 200 mL of ethanol as a solvent, pour it into a 500 mL three-necked flask. Under the protection of nitrogen, heat up to 70 - 80 °C, add 42 - 43.2 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 0.7 - 1.2 g of N-vinylcarbazole, stir at a speed of 200 - 300 r / min, and react for 3 - 6 h; stop heating, cool to room temperature, wash with ethanol 2 - 3 times and then recrystallize with methanol 2 - 3 times to obtain a white charring agent powder PHED, and dry in vacuum at 60 - 70 °C for 24 h to obtain the charring agent.

[0021] The preparation method of amino carbon nanotubes is as follows:

[0022] 0.6 - 0.7 g of carbon nanotubes are ultrasonically dispersed for 2 - 3 h under the action of 80 - 90 mL of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1. After ultrasonic treatment, the mixed solution is diluted with 80 - 100 mL of water. The acid solution is filtered by a vacuum pump and washed with deionized water until neutral, and then dried overnight at 105 °C to obtain carboxylated carbon nanotubes. Then, 3.00 - 3.25 g of phosphorus trichloride is dissolved in DMF solution, 0.205 g of carboxylated carbon nanotubes and 4.3 g of aluminum hydroxybis(2 - ethylhexanoate) are added, and the reaction is carried out at 50 - 60 °C for 30 - 60 min. Then, it is placed in a constant temperature oil bath at 70 - 80 °C and 7.2 - 7.5 g of acrylamide is added to react for 24 - 48 h. It is washed successively with 10 mL of DMF and 30 mL of toluene, filtered and then vacuum - dried overnight at 105 °C to obtain amino - functionalized carbon nanotubes.

[0023] Preparation method of high - refractive - index material:

[0024] (1) Add 10.7 g of 2 - carboxyethylphenylphosphinic acid into a 250 - mL three - necked flask, add 50 - 60 mL of thionyl chloride, install a tail - gas treatment device with saturated sodium hydroxide solution, heat up to 70 - 80 °C, slowly pass nitrogen, stir and react for 2 - 3 h, cool to room temperature, and remove thionyl chloride by rotary evaporation to obtain an oily liquid, namely phosphorus - containing impurities;

[0025] (2) Under nitrogen protection, dissolve 54 - 57 g of 4 - aminothiophenol in 200 mL of 1,3 - dimethyl - 2 - imidazolidinone, add 40 - 42 g of sodium carbonate and 150 mL of toluene and stir. Heat up to 120 - 140 °C to collect the evaporated toluene. After the toluene is removed, cool to 110 - 120 °C. Then, add a mixed solution of 29 g of 2,5 - dichlorothiophene and 50 - 60 mL of DMI into the reaction flask, react for 6 - 8 h, then add 21.5 - 22 g of the phosphorus - containing impurities obtained in step (1), react at 90 - 110 °C for 1 - 2 h. Then, pour the obtained product into 1 L of ice water, let it stand until the product solidifies into a solid, filter to collect the solid, and wash it with a large amount of deionized water. Finally, a pale - yellow solid is obtained as the crude product. The crude product can be recrystallized with absolute ethanol and mixed with 1.3 g of thiadiazole to obtain a pure white needle - shaped solid, namely the high - refractive - index material.

[0026] The degree of polymerization of the ammonium polyphosphate described is less than 20.

[0027] Preparation method of organic - inorganic negative thermal material:

[0028] 1.26 g of an aqueous oxalic acid solution with a mass percentage of 10% was gradually added dropwise to 20 mL of a mixed aqueous solution containing 0.2 - 0.3 g of cadmium nitrate tetrahydrate, 0.18 - 0.22 g of zirconium oxynitrate hydrate, and 0.14 - 0.18 g of aluminum nitrate. Then, 10 - 15 mL of concentrated nitric acid was gradually added dropwise thereto. Under room temperature conditions, it was stirred at 800 - 1000 rpm for 30 - 60 min to obtain a white mixed solution. After being washed multiple times with deionized water and ethanol, it was dried at 110 - 140 °C to obtain a white product. Then, the obtained particles were crushed into particles smaller than 10 μm to obtain an organic-inorganic negative thermal material.

[0029] The advantages of the present invention are as follows:

[0030] (1) In the present invention, p-hydroxybenzaldehyde and ethylenediamine are used as raw materials for reaction. Ethanol is used as the reaction solvent to improve the reaction rate and form an intermediate PHE. Then, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is added to react with the intermediate PHE to form a flame retardant PHED with high char-forming ability and two hydroxyl functional groups (reacting with the isocyanate group of waterborne polyurethane). The raw materials used in the preparation process of this flame retardant have relatively low costs; the flame retardant PHED contains phosphorus and nitrogen elements. Phosphorus compounds can be decomposed into phosphoric acid, metaphosphoric acid, and polyphosphoric acid at high temperatures. These compounds can act as inhibitors in the combustion reaction. Phosphoric acid, metaphosphoric acid, and polyphosphoric acid can react with the material and can coat the surface of the material to form a barrier that is difficult to burn, effectively inhibiting the combustion reaction. Secondly, phosphorus compounds need to absorb heat to decompose during combustion, which will reduce the temperature of the combustion reaction, thereby slowing down the speed of the combustion reaction. The nitrogen compounds in the flame retardant decompose at high temperatures to produce nitrogen compounds such as hydrogen gas (N 2 ), ammonia gas (NH 3 ), nitrogen trioxide (NO 3 ), etc. These gases will form a stable protective layer on the surface of the material, dilute the oxygen concentration, prevent the continuous combustion and conduction of the flame and heat to the material, and play a flame retardant role. At the same time, these gases can react with the free radicals generated during combustion to form stable compounds, blocking the chain reaction, thereby slowing down the combustion process and inhibiting the spread of the flame. At the same time, a large amount of heat is absorbed during the decomposition of the nitrogen compounds in the flame retardant, thereby lowering the surface temperature of the material and slowing down the combustion rate. This endothermic effect can prevent the flame from spreading into the interior of the material and protect the polyurethane material; N-vinylcarbazole in the char former polymerizes with the double bond of DOPO, introducing nitrogen-containing polycyclic compounds into the char former, improving the heat resistance of the polyurethane and also significantly reducing the area shrinkage rate of the polyurethane film during cooling.

[0031] (2) Since traditional carbon nanotubes are thin and light, when used in waterborne polyurethane, they can cause a decrease in melt dripping, but do not significantly increase its oxygen index. Therefore, it is necessary to improve the compactness of the products during combustion so that the carbon layer can bear the combustion heat in an environment with a high oxygen content. Under the strong acid oxidation conditions of sulfuric acid and nitric acid, a large number of hydroxyl and carboxyl groups are generated on the surface of carbon nanotubes. Phosphorus trichloride reacts with some of the hydroxyl and carboxyl groups in carboxylated carbon nanotubes and bis(2-ethylhexanoic acid) hydroxyaluminum, introducing an acyl chloride bond into the system, and then reacting with acrylamide to introduce an imine group into the system. This imine group can react with some isocyanate groups during the chain extension stage of polyurethane, introducing the char-forming part into the polyurethane system. In this reaction, phosphorus trichloride enhances the acidity under heating conditions, making the carbon layer formed by carbon nanotubes more compact, while bis(2-ethylhexanoic acid) hydroxyaluminum enhances the compactness of the carbon layer of carbon nanotubes, and the alumina generated by its combustion has good thermal conductivity, improving the flame retardancy of carbon nanotubes.

[0032] (3) Using polypropylene glycol and polytetrahydrofuran ether glycol as polyols, isophorone diisocyanate and hexamethylene diisocyanate as isocyanates, a prepolymer is synthesized under the condition of dibutyltin dilaurate as a catalyst; then a charring agent is added for chain extension. This charring agent can inhibit the melt dripping during the combustion of polyurethane. Then, a chain extender 2,2-dihydroxybutyric acid (DMBA) and amino carbon nanotubes are used for the second chain extension, introducing amino carbon nanotubes with a dense carbon layer and good thermal conductivity under heating conditions into the polyurethane chain segment to make up for the insufficient compactness of the charring property during the first chain extension. Then, a high refractive index material and 2,5-dimethylthio-1,4-dithiane are introduced for the third chain extension. This high refractive index material is a high refractive index compound doped with nitrogen, phosphorus, and sulfur containing imino groups. Sulfur is introduced into 2,5-dimethylthio-1,4-dithiane to make up for the deficiency of the refractive index of the high refractive index material and avoid yellowing inside the polyurethane, improving the yellowing resistance of the polyurethane. The neutralizing agent triethylamine neutralizes the prepolymer, and finally water is added for emulsification to finally obtain a flame-retardant, high refractive index, melt-drop resistant waterborne polyurethane coating.

[0033] (4) Using a charring agent can solve the problem of melt dripping during the combustion of the polyurethane film. The oxygen index of the obtained polyurethane film is around 28%. When using a charring agent and APP for synergistic flame retardancy, the oxygen index of the obtained polyurethane film can exceed 32%, but it will cause melt dripping during the combustion of the polyurethane film. Therefore, amino carbon nanotubes are distributed in the polyurethane chain segment to enhance the distribution of the dense carbon layer, so that when the polyurethane burns, a dense carbon layer is distributed in the amorphous polyurethane, and the dripping of the combustion melt is inhibited.

[0034] (5) In the present invention, the hydroxyl group in 2-carboxyethylphenylphosphinic acid reacts with thionyl chloride to replace the carboxyl hydroxyl and phosphorus hydroxyl groups of 2-carboxyethylphenylphosphinic acid, increasing the phosphorus content in the system to improve the refractive index of the polyurethane.

[0035] (6) Taking advantage of the easy departure of the chlorine atoms on 2,5-dichlorothiophene to generate a carbocation and chloride ions, while sodium carbonate provides an alkaline environment to convert the mercapto group (Ar-SH) on 4-aminothiophenol into a Lewis base (Ar-S-), and the Lewis base attacks the carbocation as a nucleophile to form a thioether bond. Moreover, the generated HCl is immediately captured by the alkaline environment and becomes a chloride salt, promoting the nucleophilic substitution reaction. Introducing atoms or groups with a high molar refraction index such as sulfur atoms can increase the refractive index of the material. Reacting the amino group of this product with the acyl chloride and phosphorus chloride of the phosphorus dopant, and mixing it with thiadiazole to form a high-refractive compound doped with nitrogen, phosphorus, and sulfur containing an imino group. Introducing the high-refractive-index material into the polyurethane chain segment, due to the ring rigidity effect of 2-carboxyethylphenylphosphinic acid, 2,5-dichlorothiophene, and 4-aminothiophenol, the refractive index of the polyurethane is increased, and the shrinkage rate of the polyurethane film during heating and cooling decreases.

[0036] (7) For the metal-organic framework material connected by a small molecule oxalic acid ligand, with the synergistic effect of cadmium, zirconium, and aluminum, due to the torsion and deformation within the inorganic layer of cadmium oxide, zirconium oxide, and aluminum oxide, negative thermal expansion is generated within the inorganic layer. Acting synergistically with the positive thermal expansion within the organic layer, the obtained material has negative thermal expansion in the two-dimensional plane, so that its expansion at high temperatures during polyurethane film formation is not too large, and it inhibits the expansion recovery of the inhibited part during normal temperature use. Specific implementation mode

[0037] The present invention will be further described below with reference to examples.

[0038] For the chemical materials not specified by the manufacturer involved in the embodiments of the present invention, similar products of Shanghai Macklin Biochemical Co., Ltd. can be used for replacement. Example 1

[0039] A preparation method of a flame-retardant, high-refractive-index, and melt-drop-resistant polyurethane coating adopts the following steps:

[0040] (1) Take 30 g of polypropylene glycol (number average molecular weight is 2000 g / mol), 14.92 g of isophorone diisocyanate, and 0.2 g of dibutyltin dilaurate and add them to a 500 mL three-necked flask. Under the protection of nitrogen, heat up to 70 °C and stir and react at a rotation speed of 300 r / min for 1 h to obtain a polyurethane prepolymer;

[0041] (2) Then, 4.2 g of a charring agent was added to the polyurethane prepolymer, and the reaction was continued at 70 °C for 1 h. The temperature was lowered to 60 °C, and then 0.73 g of 2,2-dimethylolbutyric acid and 2.4 g of amino-functionalized carbon nanotubes were added, and the reaction was carried out at 60 °C for 1 h. Then, 1.64 g of a high refractive index material and 1.06 g of 2,5-dimethylthio-1,4-dithiane were added, and the reaction was carried out at 65 °C for 1 h. The temperature was lowered to 40 °C, and then 2.1 g of triethylamine was added and the reaction was carried out for 0.5 h. The temperature was lowered to room temperature, 50 mL of deionized water was added, and high-speed shear emulsification was carried out at a rotation speed of 2000 r / min for 0.5 h. Then, 13.15 g of an ammonium polyphosphate (the degree of polymerization of ammonium polyphosphate is less than 20) solution dissolved in 10 g of water and 0.2 g of an organic-inorganic negative thermal material were added, and high-speed shear emulsification was carried out at a rotation speed of 1000 r / min for 0.5 h. After the foam disappeared, a flame-retardant, high refractive index, and melt-drop resistant polyurethane coating was obtained.

[0042] The preparation method of the charring agent described above:

[0043] (1) 24.4 g of p-hydroxybenzaldehyde (PHBA) was added to a beaker, stirred and dissolved with 150 mL of ethanol, transferred to a 500 mL three-necked flask, and under the protection of nitrogen, the temperature was raised to 60 °C, and the stirring speed was 300 r / min. 6 g of ethylenediamine was diluted with 50 mL of ethanol and then added dropwise to the p-hydroxybenzaldehyde solution. The dropping time was 30 min, and the reaction was continued for 2 h. After cooling to room temperature, suction filtration was carried out to obtain a pale yellow crude charring intermediate, which was washed twice with ethanol and vacuum dried at 60 °C for 12 h to obtain a pale yellow charring intermediate powder PHE.

[0044] (2) 26.8 g of the PHE obtained in step (1) was placed in a beaker, 150 mL of ethanol was added as a solvent, poured into a 500 mL three-necked flask, and under the protection of nitrogen, the temperature was raised to 70 °C, 42 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 0.7 g of N-vinylcarbazole were added, the rotation speed was 200 r / min, and the stirring reaction was carried out for 3 h. Heating was stopped, and after cooling to room temperature, it was washed twice with ethanol and recrystallized multiple times with methanol to obtain a white charring agent powder PHED, which was vacuum dried at 60 °C for 24 h to obtain the charring agent.

[0045] The preparation method of the amino-functionalized carbon nanotubes is as follows:

[0046] 0.6 g of carbon nanotubes was ultrasonically dispersed for 2 h under the action of 80 mL of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1. After ultrasonic treatment, the mixed solution was diluted with 80 mL of water. The acid solution was filtered by a vacuum pump and washed with deionized water until neutral, and then dried overnight at 105 °C to obtain carboxylated carbon nanotubes. 3.00 g of phosphorus trichloride was dissolved in 10 mL of DMF solution, 0.205 g of carboxylated carbon nanotubes and 4.3 g of aluminum hydroxybis(2-ethylhexanoate) were added, and the reaction was carried out at 50 °C for 30 min. Then it was placed in an oil bath at a constant temperature of 70 °C, and 7.2 g of acrylamide was added and reacted for 24 h. It was washed successively with 10 mL of DMF and 30 mL of toluene, filtered and then vacuum dried overnight at 105 °C to obtain amino carbon nanotubes.

[0047] Preparation method of high refractive index material:

[0048] (1) 10.7 g of 2-carboxyethylphenylphosphinic acid was added into a 250 mL three-necked flask, 50 mL of thionyl chloride was added, a tail gas treatment device saturated with sodium hydroxide solution was installed, a magnetic stirrer was added, the temperature was raised to 70 °C, nitrogen was slowly introduced, and the reaction was carried out for 2 h. After cooling to room temperature, thionyl chloride was removed by rotary evaporation to obtain an oily liquid, which was a phosphorus impurity;

[0049] (2) Under nitrogen protection, 54 g of 4-aminothiophenol was dissolved in 200 mL of 1,3-dimethyl-2-imidazolidinone (DMI), 40 g of sodium carbonate and 150 mL of toluene were added and stirred. The temperature was raised to 120 °C to collect the evaporated toluene. After the toluene was removed, the temperature was lowered to 110 °C. Then a mixed solution of 29 g of 2,5-dichlorothiophene and 50 mL of DMI was added to the reaction flask, and the reaction was carried out for 6 h. Then 21.5 g of the phosphorus impurity obtained in step (1) was added, and the reaction was carried out at 90 °C for 1 h. Then the obtained product was poured into 1 L of ice water, and after standing until the product solidified into a solid, the solid was collected by filtration and washed with a large amount of deionized water. Finally, a pale yellow solid was obtained as the crude product. The crude product could be recrystallized with absolute ethanol to obtain a pure white needle-like solid, which was mixed with 1.3 g of thiadiazole to obtain a high refractive index material.

[0050] Preparation method of organic-inorganic negative thermal material:

[0051] 1.26 g of an aqueous oxalic acid solution with a mass percentage of 10% was gradually added dropwise to a mixed aqueous solution of 0.2 g of cadmium nitrate tetrahydrate, 0.18 g of zirconium oxynitrate hydrate and 0.14 g of aluminum nitrate, and 10 mL of concentrated nitric acid was gradually added dropwise thereto. Under room temperature conditions, it was stirred at 800 rpm for 30 min to obtain a white mixed solution. After being washed repeatedly with deionized water and ethanol, it was dried at 110 °C to obtain a white product. The obtained particles were crushed into particles smaller than 10 μm to obtain an organic-inorganic negative thermal material. Example Two

[0052] Preparation method of flame-retardant, high-refractive-index and melt-drop resistant polyurethane coating, comprising the following steps:

[0053] (1) Take 32 g of polytetrahydrofuran ether diol (number average molecular weight is 2000 g / mol), 14.92 g of hexamethylene diisocyanate and 0.3 g of dibutyltin dilaurate, add them into a 500 mL three-necked flask, under the protection of nitrogen, heat up to 85 °C, stir and react at a rotation speed of 500 r / min for 2 h to obtain a polyurethane prepolymer;

[0054] (2) Then add 8.4 g of charring agent to the polyurethane prepolymer, continue to react at 80 °C for 2 h; cool down to 60 °C, then add 0.89 g of 2,2-dimethylolbutyric acid and 2.6 g of amino carbon nanotubes, react at 65 °C for 2 h; then add 2.46 g of high-refractive-index material and 1.21 g of 2,5-dimethylthio-1,4-dithiane, react at 70 °C for 2 h, cool down to 40 °C, then add 2.1 g of triethylamine, react for 1 h; cool down to room temperature, add 80 mL of deionized water, perform high-speed shear emulsification at a rotation speed of 2000 r / min for 1.5 h, then add 13.15 g of ammonium polyphosphate (the polymerization degree of ammonium polyphosphate is less than 20) solution dissolved in 10 g of water and 0.2 - 0.3 g of organic-inorganic negative thermal material, perform high-speed shear emulsification at a rotation speed of 2000 r / min for 1 h, wait for the foam to disappear, and obtain the flame-retardant, high-refractive-index and melt-drop resistant polyurethane coating.

[0055] Preparation method of flame-retardant, high-refractive-index and melt-drop resistant polyurethane coating, the preparation method of the charring agent described:

[0056] (1) Add 24.4 g of p-hydroxybenzaldehyde PHBA into a beaker, stir and dissolve it with 200 mL of ethanol, transfer it into a 500 mL three-necked flask, under the protection of nitrogen, heat up to 70 °C, the stirring speed is 500 r / min, dilute 6.2 g of ethylenediamine with 50 mL of ethanol, and drop it into the p-hydroxybenzaldehyde solution, the dropping time is 50 min, continue to react for 2.5 h; cool down to room temperature, perform suction filtration to obtain a light yellow crude charring intermediate, wash it 3 times with ethanol, and vacuum dry it at 70 °C for 24 h to obtain light yellow charring intermediate powder PHE;

[0057] (2) Take 26.8 g of PHE described in step (1) in a beaker, add 1200 mL of ethanol as a solvent, pour it into a 500 mL three-necked flask, under the protection of nitrogen, heat up to 80 °C, add 43.2 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO and 1.2 g of N-vinylcarbazole, with a rotation speed of 300 r / min, stir and react for 6 h; stop heating, cool to room temperature, filter by suction to obtain a white crude charring agent, wash it 3 times with ethanol and recrystallize it multiple times with methanol to obtain a white charring agent powder PHED, dry it in vacuum at 70 °C for 24 h to obtain the charring agent.

[0058] The preparation method of amino-functionalized carbon nanotubes is as follows:

[0059] Take 0.7 g of carbon nanotubes, under the action of 90 mL of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1, perform ultrasonic dispersion treatment for 3 h. After ultrasonic treatment, dilute the mixed solution with 100 mL of water, filter it by suction with a vacuum pump, and wash it with deionized water until neutral, then dry it at 105 °C overnight to obtain carboxylated carbon nanotubes; dissolve 3.25 g of phosphorus trichloride in 10 mL of DMF solution, add 0.205 g of carboxylated carbon nanotubes and 4.3 g of bis(2-ethylhexanoic acid) hydroxyaluminum, react at 60 °C for 60 min, then place it in an 80 °C constant temperature oil bath and add 7.5 g of acrylamide, react for 48 h, wash it successively with 10 mL of DMF and 30 mL of toluene, filter it, and dry it in vacuum at 105 °C overnight to obtain amino-functionalized carbon nanotubes.

[0060] The preparation method of the high refractive index material:

[0061] (1) Add 10.7 g of 2-carboxyethylphenylphosphinic acid into a 250 mL three-necked flask, add 60 mL of thionyl chloride, install a tail gas treatment device with saturated sodium hydroxide solution, heat up to 80 °C, slowly pass nitrogen, stir and react for 3 h, cool to room temperature, and remove thionyl chloride by rotary evaporation to obtain an oily liquid, obtaining a phosphorus-containing impurity;

[0062] (2) Under the protection of nitrogen, dissolve 57 g of 4-aminothiophenol in 200 mL of 1,3-dimethyl-2-imidazolidinone, add 42 g of sodium carbonate and 150 mL of toluene and stir, heat up to 140 °C to collect the evaporated toluene, and cool to 120 °C after the toluene is removed; then add a mixed solution of 29 g of 2,5-dichlorothiophene and 60 mL of DMI into the reaction flask, react for 8 h, then add 22 g of the phosphorus-containing impurity obtained in step (1), react at 110 °C for 2 h, pour the obtained product into 1 L of ice water, let it stand until the product solidifies into a solid, filter by suction to collect the solid, and wash it with a large amount of deionized water. Finally, a pale yellow solid is obtained as the crude product. The crude product can be recrystallized with absolute ethanol to obtain a pure white needle-like solid, and mix it with 1.3 g of thiadiazole to obtain the high refractive index material.

[0063] Preparation method of organic-inorganic negative thermal material:

[0064] 1.26 g of 10% oxalic acid aqueous solution by mass was gradually added dropwise to 20 mL of a mixed aqueous solution of 0.3 g of cadmium nitrate tetrahydrate, 0.22 g of zirconium oxynitrate hydrate, and 0.18 g of aluminum nitrate, and 15 mL of concentrated nitric acid was gradually added dropwise thereto. Under room temperature conditions, it was stirred at 1000 rpm for 60 min to obtain a white mixed solution, which was washed repeatedly with deionized water and ethanol and dried at 140 °C to obtain a white product. The obtained particles were crushed into less than 10 μm to obtain the organic-inorganic negative thermal material. Example 3

[0065] Preparation method of flame-retardant, high-refractive-index, melt-drop-resistant waterborne polyurethane coating, which adopts the following steps:

[0066] (1) 15.5 g of polypropylene glycol, 15.5 g of polytetrahydrofuran ether glycol (the number-average molecular weights of polypropylene glycol and polytetrahydrofuran ether glycol are both 2000 g / mol), 7.46 g of isophorone diisocyanate, 7.46 g of hexamethylene diisocyanate, and 0.25 g of dibutyltin dilaurate were added to a 500 mL three-necked flask. Under nitrogen protection, the temperature was raised to 80 °C and stirred at 400 r / min for 1.5 h to obtain a polyurethane prepolymer;

[0067] (2) Then 6.3 g of a charring agent was added to the polyurethane prepolymer, and the reaction continued at 75 °C for 1.5 h; the temperature was lowered to 60 °C, and then 0.81 g of 2,2-dimethylolbutyric acid and 2.5 g of amino carbon nanotubes were added, and the reaction was carried out at 60 °C for 1.5 h; then 2.05 g of a high-refractive-index material and 1.14 g of 2,5-dimethylthio-1,4-dithiane were added, and the reaction was carried out at 65 °C for 1.5 h. The temperature was lowered to 40 °C, and then 2.1 g of triethylamine was added and the reaction was carried out for 0.75 h; the temperature was lowered to room temperature, 62 mL of deionized water was added, and high-speed shear emulsification was carried out at 2000 r / min for 1 h. Then 13.15 g of a solution of ammonium polyphosphate (the degree of polymerization of ammonium polyphosphate is less than 20) dissolved in 10 g of water and 0.25 g of the organic-inorganic negative thermal material were added, and high-speed shear emulsification was carried out at 1500 r / min for 0.75 h. After the foam disappeared, a flame-retardant, high-refractive-index, melt-drop-resistant waterborne polyurethane coating was obtained.

[0068] Preparation method of flame-retardant, high-refractive-index, melt-drop-resistant waterborne polyurethane coating, the preparation method of the charring agent described:

[0069] (1) Add 24.4 g of p-hydroxybenzaldehyde (PHBA) to a beaker, stir and dissolve it with 175 mL of ethanol, transfer it to a 500 mL three-necked flask, under the protection of nitrogen, heat up to 65 °C, with a stirring speed of 400 r / min. Dilute 6.1 g of ethylenediamine with 50 mL of ethanol, then drop it into the p-hydroxybenzaldehyde solution. The dropping time is 40 min, and continue to react for 2 h. Cool to room temperature, filter by suction to obtain a light yellow crude carbonization intermediate, wash it twice with ethanol, and dry it in vacuum at 65 °C for 18 h to obtain a light yellow carbonization intermediate powder PHE;

[0070] (2) Take 26.8 g of the PHE obtained in step (1) in a beaker, add 175 mL of ethanol as a solvent, pour it into a 500 mL three-necked flask. Under the protection of nitrogen, heat up to 75 °C, then add 42.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 0.95 g of N-vinylcarbazole. The stirring speed is 250 r / min, and react for 4.5 h. Stop heating, cool to room temperature, filter by suction to obtain a white crude charring agent. After washing it twice with ethanol and recrystallizing it several times with methanol, a white charring agent powder PHED is obtained. Dry it in vacuum at 65 °C for 24 h to obtain the charring agent.

[0071] The preparation method of amino-functionalized carbon nanotubes is as follows:

[0072] Under the action of 85 mL of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1, ultrasonically disperse 0.65 g of carbon nanotubes for 2.5 h. After ultrasonic treatment, dilute the mixed solution with 90 mL of water, filter it by a vacuum pump, and wash it with deionized water until neutral. Dry it overnight at 105 °C to obtain carboxylated carbon nanotubes. Then dissolve 3.12 g of phosphorus trichloride in 10 mL of DMF solution, add 0.205 g of carboxylated carbon nanotubes and 4.3 g of aluminum bis(2-ethylhexanoate), react at 55 °C for 45 min, then place it in an oil bath at 75 °C and add 7.35 g of acrylamide to react for 36 h. Wash it successively with 10 mL of DMF and 30 mL of toluene, filter it, and dry it in vacuum at 105 °C overnight to obtain amino-functionalized carbon nanotubes.

[0073] The preparation method of the high refractive index material:

[0074] (1) Add 10.7 g of 2-carboxyethylphenylphosphinic acid to a 250 mL three-necked flask, add 55 mL of thionyl chloride, install a tail gas treatment device with saturated sodium hydroxide solution, heat up to 75 °C, slowly pass nitrogen, stir and react for 2.5 h, cool to room temperature, and rotary evaporate to remove thionyl chloride to obtain an oily liquid, obtaining a phosphorus-containing impurity;

[0075] (2) Under nitrogen protection, dissolve 55.5 g of 4-aminothiophenol in 200 mL of 1,3-dimethyl-2-imidazolidinone, add 41 g of sodium carbonate and 150 mL of toluene, stir, heat up to 130 °C to collect the evaporated toluene, and cool down to 115 °C after the toluene is removed; then add a mixed solution of 29 g of 2,5-dichlorothiophene and 55 mL of DMI to the reaction flask, react for 7 h, add 21.7 g of the phosphorus dopant in step (1), react at 100 °C for 1.5 h, pour the obtained product into 1 L of ice water, let it stand until the product solidifies into a solid, filter to collect the solid, and wash it with a large amount of deionized water. Finally, a pale yellow solid is obtained as the crude product, and the crude product can be recrystallized with absolute ethanol to obtain a pure white needle-like solid, which is mixed with 1.3 g of thiadiazole to obtain a high refractive index material.

[0076] Preparation method of organic-inorganic negative thermal material:

[0077] Gradually drop 1.26 g of an aqueous oxalic acid solution with a mass percentage of 10% into a mixed aqueous solution of 0.25 g of cadmium nitrate tetrahydrate, 0.2 g of zirconium oxynitrate hydrate, and 0.16 g of aluminum nitrate in 20 mL, and gradually add 12.5 mL of concentrated nitric acid dropwise thereto. Under room temperature conditions, stir at a rotation speed of 900 rpm for 45 min to obtain a white mixed solution. Wash it repeatedly with deionized water and ethanol, and dry it at 120 °C to obtain a white product. Crush the obtained particles into particles smaller than 10 μm to obtain an organic-inorganic negative thermal material.

[0078] Pour the prepared polyurethane coating into a polytetrafluoroethylene mold, control the thickness to 3 mm, and perform tests such as melt drop test and cone calorimetry.

[0079] Melt drop test

[0080] (1) Sample preparation: Put the prepared polyurethane film into a constant temperature and humidity chamber set at 23 °C ± 0.5 °C and humidity 50% ± 5% for 48 h, then take it out and cut it into specimens of 110 cm × 10 cm × 3 mm. Prepare 2 sets of specimens, with 5 specimens in each group.

[0081] (2) Parameter setting: Clamp about 5 mm from the upper end to make the specimen vertical downward. Place a rosin wood board at the lower end of the sample, and pad about 0.3 g of absorbent cotton on the board. Place it evenly on the board. Adjust the gas flow rate to 105 ± 5 mL / min to make the height of the flame reach 20 ± 1 mm, and set the combustion time to 10 s.

[0082] (3) Flame application and recording: After setting the parameters, start flame application for ignition. After 10 s of ignition, press the afterflame time start button. When the specimen finishes burning and only has sparks left, press the afterflame combustion end button to enter the afterglow time. When it completely extinguishes, press the afterglow time end button to record the afterflame time and afterglow time of combustion.

[0083] (4)Observation of molten droplets: During the combustion process, pay attention to observing whether molten droplets are generated during combustion, and whether secondary combustion will be caused when the generated molten droplets drip onto the cotton ball below, and record the observation results.

[0084] Using ASTM E1354 - 1990 (2004 standard), analyzed and measured by the cone calorimeter 2000 of FTT Company in the UK. The test specimen is 10 cm × 10 cm with a thickness of 3 mm, and the heat radiation power is 12 kW / m 2 , measure the maximum heat release rate pkHHR in kW / m 2 , total heat release THR in MJ / m², the smoke production rate pSPR reaches the peak value in m 2 / s and the maximum total smoke release (TSR) in m 2 / m 2 .

[0085] The yellowing resistance is determined by observing the color change under ultraviolet light during simulated sunlight irradiation for 48 hours, and the yellowing resistance is determined using a bulb - type yellowing resistance instrument of model HZ - 3017 for testing.

[0086] The transmittance of the polymer film is tested using a UV - 7504 type ultraviolet - visible spectrophotometer.

[0087] The refractive index of the emulsion is tested using an Abbe refractometer.

[0088] The shrinkage rate of the film is the ratio of the area of the polyurethane emulsion film formed at 80 °C to the area after cooling to room temperature. The percentage of the difference between the area at room temperature and the area of the film formed at 80 °C divided by the area of the film formed at 80 °C is the shrinkage rate.

[0089] Table 1 Film - forming properties of flame - retardant, high - refractive - index, and molten - droplet - resistant water - borne polyurethane coatings

[0090] Example 1 Example 2 Example 3 Comparative Example Combustion droplet phenomenon Non-melting and non-dripping Non-melting and non-dripping Non-melting and non-dripping Non-melting and non-dripping pkHHR 38.45 38.87 39.01 41.26 THR 115.13 116.98 116.56 128.21 pSPR smoke generation rate 0.193 0.196 0.186 0.205 TSR 835.2 823.8 828.6 998.3 Yellowing resistance (grade) 4.0 4.0 4.0 4.0 Oxygen index (%) 33.6 33.2 33.4 28.6 Refractive index 1.83 1.88 1.81 1.31 Light transmittance (%) 95.6 95.9 95.4 84.3 Film shrinkage rate (%) 2.4 1.7 2.1 4.7

[0091] Example 1 Example 2 Example 3 Comparative Example Combustion droplet phenomenon Non-melting and non-dripping Non-melting and non-dripping Non-melting and non-dripping Non-melting and non-dripping pkHHR 38.45 38.87 39.01 41.26 THR 115.13 116.98 116.56 128.21 pSPR smoke generation rate 0.193 0.196 0.186 0.205 TSR 835.2 823.8 828.6 998.3 Yellowing resistance (grade) 4.0 4.0 4.0 4.0 Oxygen index (%) 33.6 33.2 33.4 28.6 Refractive index 1.83 1.88 1.81 1.31 Light transmittance (%) 95.6 95.9 95.4 84.3 Film shrinkage rate (%) 2.4 1.7 2.1 4.7

[0092] As can be seen from Table 1, the flame retardancy (combustion melt dripping phenomenon), pkHHR, and THR of the polyurethane film of the present invention are all significantly improved compared to Comparative Example CN118813133B (Example 1); due to the component effect of the dense carbon layer in the polyurethane chain segment of the present invention, the obtained polyurethane does not produce melt droplets and drippings during combustion, and its pkHHR and THR are both lower than those of the comparative example. The pSPR smoke generation rate during combustion reaches the peak and the highest total smoke release are both reduced relative to the comparative example. Due to the synergistic effect of the hydroxyl group in 2-carboxyethylphenylphosphinic acid, thionyl chloride, 2,5-dichlorothiophene, etc., the yellowing resistance, refractive index, and light transmittance of the obtained polyurethane film are greatly improved. Moreover, due to the synergistic effect of amino-functionalized nanotubes, APP, and charring agent, the oxygen index of the obtained polyurethane film exceeds 32%, overcoming the deficiency that it is difficult for a single type of flame retardant component to reach 32% (non-combustible substance).

[0093] Taking Example 2 of the present invention as an example, a comparative test was carried out.

[0094] Table 2 Film-forming properties of flame-retardant, high-refractive-index, and melt-drop-resistant waterborne polyurethane coatings

[0095] Example 2 Composition Combustion droplet phenomenon A large number of droplets Without amino-functionalized carbon nanotubes pkHHR 53.67 Without amino-functionalized carbon nanotubes THR 153.26 Without amino-functionalized carbon nanotubes pSPR smoke generation rate 0.387 Without amino-functionalized carbon nanotubes TSR 1035.86 Without amino-functionalized carbon nanotubes Oxygen index (%) 32.2 Without amino-functionalized carbon nanotubes Combustion droplet phenomenon With droplets but no dripping With amino-functionalized carbon nanotubes, without bis(2-ethylhexanoic acid) aluminum hydroxy pkHHR 43.35 With amino-functionalized carbon nanotubes, without bis(2-ethylhexanoic acid) aluminum hydroxy THR 143.61 With amino-functionalized carbon nanotubes, without bis(2-ethylhexanoic acid) aluminum hydroxy pSPR smoke generation rate 0.276 With amino-functionalized carbon nanotubes, without bis(2-ethylhexanoic acid) aluminum hydroxy TSR 931.57 With amino-functionalized carbon nanotubes, without bis(2-ethylhexanoic acid) aluminum hydroxy Oxygen index (%) 32.8 With amino-functionalized carbon nanotubes, without bis(2-ethylhexanoic acid) aluminum hydroxy Combustion droplet phenomenon Non-melting and non-dripping With amino-functionalized carbon nanotubes, without acrylamide pkHHR 41.16 With amino-functionalized carbon nanotubes, without acrylamide THR 123.24 With amino-functionalized carbon nanotubes, without acrylamide pSPR smoke generation rate 0.213 With amino-functionalized carbon nanotubes, without acrylamide TSR 846.21 With amino-functionalized carbon nanotubes, without acrylamide Oxygen index (%) 33.0 With amino-functionalized carbon nanotubes, without acrylamide Oxygen index (%) 28.3 Without charring agent Combustion droplet phenomenon With droplets and dripping Without charring agent Oxygen index (%) 28.6 Without APP (ammonium polyphosphate) Combustion droplet phenomenon Without droplets and without melting Without APP

[0096] As can be seen from Table 2, aluminum hydroxybis(2-ethylhexanoate), acrylamide, and amino-functionalized carbon nanotubes can all improve the flame retardancy of polyurethane. Among them, APP increases the oxygen index of polyurethane, but combustion melt droplets are generated. The ideal polyurethane flame retardancy is to increase the oxygen index without melt droplets and drippings. A more ideal flame retardant method is to carry out flame retardancy by taking away part of the heat through combustion melt droplets; the addition of the inorganic flame retardant APP makes the obtained polyurethane burn, and part of the heat is taken away through melt droplets and drippings to achieve the flame retardant effect, which is a more ideal flame retardant method. Synergistic with amino-functionalized carbon nanotubes, charring agent, and APP, while improving the flame retardancy, no melt droplets are generated, which is the ideal flame retardant method.

[0097] Table 3 Film-forming properties of flame-retardant, high-refractive-index, and melt-drop-resistant waterborne polyurethane coatings

[0098] Example 2 Composition Yellowing resistance (grade) 3.0 Without high refractive index material Refractive index 1.35 Without high refractive index material Light transmittance (%) 85.6 Without high refractive index material Yellowing resistance (grade) 3.5 With high refractive index material, without 2-carboxyethylphenylphosphinic acid Refractive index 1.62 With high refractive index material, without 2-carboxyethylphenylphosphinic acid Light transmittance (%) 90.4 With high refractive index material, without 2-carboxyethylphenylphosphinic acid Yellowing resistance (grade) 3.5 With high refractive index material, without 2,5-dichlorothiophene Refractive index 1.58 With high refractive index material, without 2,5-dichlorothiophene Light transmittance (%) 91.3 With high refractive index material, without 2,5-dichlorothiophene Yellowing resistance (grade) 3.5 With high refractive index material, without thiadiazole Refractive index 1.62 With high refractive index material, without thiadiazole Light transmittance (%) 90.5 With high refractive index material, without thiadiazole Yellowing resistance (grade) 3.5 Without 2,5-dimethylthio-1,4-dithiane Refractive index 1.75 Without 2,5-dimethylthio-1,4-dithiane Light transmittance (%) 93.3 Without 2,5-dimethylthio-1,4-dithiane Film shrinkage rate (%) 4.1 Without N-vinylcarbazole Refractive index 1.86 Without N-vinylcarbazole Film shrinkage rate (%) 3.2 Without organic-inorganic negative thermal material

[0099] As can be seen from Table 3, 4-aminothiophenol, as the core component of the high-refractive-index material, if not applied, the main material of the high-refractive-index material does not exist, and the yellowing resistance, refractive index, and light transmittance of the obtained polyurethane will decrease; it can be found from Table 3 that the high-refractive-index material, 2-carboxyethylphenylphosphinic acid, 2,5-dichlorothiophene, and 2,5-dimethylthio-1,4-dithiane can all increase the refractive index of polyurethane; N-vinylcarbazole has a nitrogen-containing condensed ring structure, and the polyurethane treated with it shows less shrinkage after curing and good heat resistance; in addition, due to the high-temperature negative expansion and room-temperature recovery of the organic-inorganic negative thermal material, the shrinkage rate of the modified polyurethane film decreases.

Claims

1. A method for preparing a flame retardant, high refractive, and drip resistant water-based polyurethane coating, characterized in that: Prepare according to the following steps: (1) Add 30-32 g of diol, 14.92 g of isocyanate and 0.2-0.3 g of dibutyltin dilaurate into a 500 mL three-necked flask. Under nitrogen protection, heat to 70-85 °C, rotate at 300-500 r / min, and stir for 1-2 h to obtain a polyurethane prepolymer. (2) Add 4.2-8.4 g of carbonizing agent to the polyurethane prepolymer, and continue to react at 70-80 °C for 1-2 h; cool to 60 °C, add 0.73-0.89 g of 2,2-dihydroxymethylbutyric acid and 2.4-2.6 g of amino carbon nanotubes, and react at 60-65 °C for 1-2 h; add 1.64-2.46 g of high refractive material and 1.06-1.21 g of 2,5-dimethylmercapto-1,4-dithiane, and react at 65-70 °C for 1-2 h; cool to 40 °C, add 2.1 g of triethylamine, and react for 0.5-1 h; cool to room temperature, add 50-80 mL of deionized water, and heat at 2000 °C. r / min, high-speed shear emulsification for 0.5-1.5h, then add 13.15g of ammonium polyphosphate solution dissolved in 10g of water and 0.2-0.3g of organic and inorganic negative heat materials, and high-speed shear emulsification for 0.5-1h at a speed of 1000-2000 r / min, and wait for the foam to disappear to obtain a flame-retardant, refraction-resistant, and drip-resistant water-based polyurethane coating; The amino carbon nanotube preparation method is as follows: 0.6-0.7 g of carbon nanotubes were subjected to ultrasonic dispersion treatment for 2-3 h in the presence of 80-90 mL of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1. After ultrasonication, the mixed solution was diluted with 80-100 mL of water, the acid solution was filtered with a vacuum pump, washed with deionized water until neutral, and dried at 105°C overnight to obtain carboxylated carbon nanotubes. 3.00-3.25 g of phosphorus trichloride was dissolved in DMF solution, 0.205 g of carboxylated carbon nanotubes and 4.3 g of bis(2-ethylhexanoic acid) hydroxyaluminum were added, and the mixture was reacted at 50-60°C for 30-60 min, then placed in a constant temperature oil bath at 70-80°C, 7.2-7.5 g of acrylamide was added and reacted for 24-48 h, and the mixture was washed with 10 mL of DMF and 30 mL of toluene in sequence, filtered, and dried at 105°C in vacuum overnight to obtain amino carbon nanotubes.

2. The method for preparing the flame-retardant, high-refractive, and drip-resistant water-based polyurethane coating according to claim 1, characterized in that: The diol is any one of polypropylene glycol and polytetramethylene glycol or a mixture of the two in any ratio.

3. The method for preparing the flame-retardant, high-refractive, and drip-resistant water-based polyurethane coating according to claim 1, characterized in that: The isocyanate is any one of isophorone diisocyanate and hexamethylene diisocyanate or a mixture of the two in any ratio.

4. The method for preparing the flame-retardant, high-refractive, and drip-resistant water-based polyurethane coating according to claim 2, characterized in that: The number average molecular weights of the polypropylene glycol and polytetramethylene glycol are both 2000 g / mol.

5. The method for preparing the flame-retardant, high-refractive, and drip-resistant water-based polyurethane coating according to claim 1, characterized in that: The preparation method of the carbon-forming agent: (1) Add 24.4 g of p-hydroxybenzaldehyde PHBA into a beaker, stir and dissolve it with 150-200 mL of ethanol, transfer it into a 500 mL three-necked flask, and heat it to 60-70 °C under nitrogen protection. The stirring speed is 300-500 r / min. Dilute 6-6.2 g of ethylenediamine with 50 mL of ethanol and add it dropwise to the p-hydroxybenzaldehyde solution for 30-50 min. Continue the reaction for 2-2.5 h. Cool it to room temperature, wash it with ethanol 2-3 times, and vacuum dry it at 60-70 °C for 12-24 h to obtain a light yellow carbon-forming intermediate powder PHE. (2) Put 26.8 g of PHE described in step (1) in a beaker, add 150-200 mL of ethanol as a solvent, pour into a 500 mL three-necked flask, and heat to 70-80° C. under nitrogen protection. Add 2-43.2 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO4 and 0.7-1.2 g of N-vinylcarbazole. Stir at a speed of 200-300 r / min and react for 3-6 h. Stop heating, cool to room temperature, and filter to obtain a white crude carbon-forming agent. Wash with ethanol 2-3 times, recrystallize with methanol several times, and dry in a vacuum at 60-70° C. for 24 h to obtain the carbon-forming agent.

6. The method for preparing the flame-retardant, high-refractive, and drip-resistant water-based polyurethane coating according to claim 1, characterized in that: The preparation method of the high refractive material: (1) Add 10.7 g of 2-carboxyethylphenylphosphorous acid into a 250 mL three-necked flask, add 50-60 mL of thionyl chloride, install a tail gas saturated sodium hydroxide solution treatment device, heat to 70-80 ° C, slowly pass nitrogen, stir and react for 2-3 hours, cool to room temperature, and remove thionyl chloride by rotary evaporation to obtain an oily liquid to obtain phosphorus impurities; (2) Under nitrogen protection, dissolve 54-57 g of 4-aminothiophenol in 200 mL of 1,3-dimethyl-2-imidazolidinone, add 40-42 g of sodium carbonate and 150 mL of toluene, stir, raise the temperature to 120-140°C, collect the evaporated toluene, and cool to 110-120°C after the toluene is removed; then add a mixed solution of 29 g of 2,5-dichlorothiophene and 50-60 mL of 1,3-dimethyl-2-imidazolidinone to the reaction mixture. The mixture was placed in a bottle and reacted for 6 to 8 hours. Then 21.5 to 22 g of the phosphorus dopant of step (1) was added and reacted at 90 to 110°C for 1 to 2 hours. The obtained product was poured into 1 L of ice water and allowed to stand until the product solidified into a solid. The solid was collected by filtration and washed with a large amount of deionized water to finally obtain a pale yellow solid as a crude product. The crude product was recrystallized with anhydrous ethanol to obtain a pure white needle-shaped solid, which was then mixed with 1.3 g of thiadiazole to obtain a high refractive material.

7. The method for preparing the flame-retardant, high-refractive, and drip-resistant water-based polyurethane coating according to claim 1, characterized in that: The degree of polymerization of the ammonium polyphosphate is less than 20.

8. The method for preparing the flame-retardant, high-refractive, and drip-resistant water-based polyurethane coating according to claim 1, characterized in that: Preparation method of organic and inorganic negative heat materials: 1.26 g of 10% by mass oxalic acid aqueous solution was added dropwise into 20 mL of a mixed aqueous solution of 0.2-0.3 g of cadmium nitrate tetrahydrate, 0.18-0.22 g of zirconium oxynitrate hydrate, and 0.14-0.18 g of aluminum nitrate, and 10-15 mL of concentrated nitric acid was added dropwise thereto. The mixture was stirred at room temperature at a speed of 800-1000 rpm for 30-60 min to obtain a white mixed solution. The mixture was washed with deionized water and ethanol several times, and dried at 110-140° C. to obtain a white product. The obtained particles were crushed into particles less than 10 μm to obtain an organic-inorganic negative heat material.