Flame-retardant, washable and melt-drop-resistant polyurethane coating

Abstract

The preparation method comprises the following steps: adding polytetrahydrofuran ether glycol, polycaprolactone glycol, isocyanate and dibutyltin dilaurate into a flask, respectively inserting a thermometer, a glass plug, a stirring paddle and a nitrogen tube into a flask opening, heating to 80-85 DEG C, reacting for 1-2 hours, adding a charring agent into the flask, reacting for 1.5-2.5 hours, and cooling to room temperature to obtain the flame-retardant washable melt-drop-resistant polyurethane coating. A polyurethane prepolymer is obtained; cooling the polyurethane prepolymer to 45-55 DEG C, adding 2, 2-dimethylolpropionic acid, reacting for 1-2 hours, adding the porous carbon layer modifier and the glucose modifier, reacting for 1-2 hours at 65-70 DEG C, adding triethylamine, and reacting for 1-2 hours; and cooling to normal temperature, adding water, stirring and reacting for 1-2 hours, and adjusting the pH value of the system to 7-8 to obtain the flame-retardant washable melt-drop-resistant water-based polyurethane coating which has good flame-retardant, washable and melt-drop-resistant properties and the like.

Description

[0001] The present invention is a divisional case of 2024114285931. Technical Field

[0002] The invention relates to a method for preparing a waterborne polyurethane coating, in particular to a method for preparing a flame-retardant, water-washable and drip-resistant waterborne polyurethane coating. Background Art

[0003] Temporary protective coatings, like general protective coatings, offer protection and decontamination benefits on the surface of the object being protected. However, they differ in that their effectiveness is short-lived and primarily protects during processing, transportation, or temporary storage. After processing, transportation, or storage, the coating must be removed from the surface. This removal preserves the original functions and properties of the object being protected. These temporary protective coatings are also known as removable or washable coatings. Washable coatings form a tightly structured film upon application, isolating the material from the outside world. Furthermore, surface adsorption and adhesion during film formation help absorb dirt from the surface.

[0004] Washable coatings are typically removed from the surface by soaking or rinsing with a specific solvent. This requires the film to have a certain solubility in the solvent, which can include water, acidic or alkaline solutions, or specially formulated paint strippers. These are primarily used for protecting glass and metal surfaces, vacuuming walls and floors, and purifying the air.

[0005] PCBs, the cornerstone of electronic components, require drilling accuracy as a core quality indicator during their manufacturing process. With the continued introduction and increased attention of government policies and regulations, removable coatings are crucial for driving the transformation and upgrading of China's coatings industry towards high-quality development and green sustainability. Water-washable coatings are crucial for PCB drilling accuracy. Applying removable coating to aluminum sheets, then attaching the coated aluminum sheets to circuit boards (copper substrates, copper-clad laminates), and then drilling can improve drilling accuracy. However, as coating is a consumable material, the PCB needs to be cleaned after drilling to remove the coating film. Currently, washable paints used in PCB processing on the market generally have the following pain points: First, PCB drilling requires the use of aluminum plate coatings, but traditional washable paints have poor heat resistance and cannot withstand the heat released during drilling operations, causing the coating film to partially or completely melt, affecting drilling accuracy; second, paint splashed during drilling easily adheres to the epoxy resin through-holes of the PCB and is difficult to handle. Residual paint can easily cause moisture, mold, and corrosion of the circuit board, affecting the performance and life of the circuit board; third, the resin adhesion between the PCB and the aluminum plate is not moderate, resulting in poor adhesion, poor metal (aluminum plate) compatibility, and difficulty in protection. The strong adhesion also makes it difficult to clean.

[0006] Jia Danfeng et al. used a solution free radical polymerization method to synthesize acrylic acid (AA), hydroxyethyl methacrylate (HEMA),

[0007] A water-soluble acrylic resin was prepared using acrylamide (AM) as a functional monomer, butyl acrylate and methyl methacrylate as soft and hard monomers, azobisisobutyronitrile (AIBN) as an initiator, and dimethylethanolamine as a neutralizer. The water-soluble acrylic resin was then compounded with an emulsion to prepare a water-based compounded resin for resin coating. The water-based compounded resin was compounded with fillers, water-soluble polymers, and other additives to prepare a water-washable temporary protective coating. The film's adhesion was found to be level 2, and the demolding time at 50°C was 50 seconds, indicating a good wash time. However, this technology did not consider the potential for the temporary coating film to adhere to metal materials during use, resulting in the film melting and becoming difficult to clean. Core indicators such as PCB drilling accuracy were also not studied.

[0008] Invention patent CN202210702763.5 involves using polyvinyl alcohol (PVA) resin as the main resin to improve the flexibility of the paint film; using polyether-modified acrylic resin as the modified resin to improve the adhesion of the paint on soft PVC and improve the water solubility of the PVA resin. At the same time, a small amount of acrylic-modified polyurethane (PUA) resin is used as the second modified resin to improve the bonding strength with soft PVC and resist cracking caused by deformation of the material. The invention also adds a carboxylic acid-type propyl beet amphoteric surfactant to the paint, which has the dual effects of thickening and improving water-washing residue, thereby accelerating the dissolution rate of the paint film when washed with water. Therefore, the paint provided by the invention has excellent flexibility, is not easy to crack, and has a good water-washing effect. However, the patent involves cleaning of soft PVC, which is different from the use environment of the paint used for aluminum plates and PCB epoxy resin boards, and does not involve the standard requirements for flame retardancy of acrylic esters.

[0009] Invention patent CN2015105882116 discloses an anti-carburizing coating that can be washed and removed after quenching. The coating is prepared from the following components by mass percentage: 25-35% boric acid, 15-25% filler, 15-25% aluminum dihydrogen phosphate, 1-5% coloring pigment, and 30-40% water. The invention also discloses a method for preparing the anti-carburizing coating that can be washed and removed after quenching. The anti-carburizing coating can be removed by washing after carburizing heat treatment, thereby solving the problem that traditional anti-carburizing coatings are difficult to peel off after carburizing heat treatment. Inorganic high-temperature resistant materials are used as anti-carburizing agents in the anti-carburizing coating formula. The anti-carburizing coating formed after the anti-carburizing agent is applied to the surface of the workpiece has good adhesion, does not peel or flow at high temperatures, and does not affect the carburizing atmosphere. The invention does not involve a film-forming agent using a polyurethane resin as a film.

[0010] Invention patent 201910576686.1 relates to a PCB drilling glue-coated aluminum cover plate and its preparation method, wherein the toughness of the water-soluble composite polymer resin layer is moderate, which can play a guiding role during the falling of the drill needle, thereby improving the drilling accuracy; at the same time, the hot melt type resin in the water-soluble composite polymer resin layer can play a role in lubricating the drill bit and cooling the drill needle during drilling, thereby effectively improving the hole wall roughness, reducing the wire winding, reducing the drill bit temperature, and prolonging the service life of the drill needle; in addition, the water-soluble composite polymer resin layer has good water solubility, is easy to handle after drilling, and is not easy to adhere to the holes of the PCB, thereby ensuring the drilling quality. The disadvantage of the resin is that it has not been studied whether the glue adhered to the PCB hole during drilling can be cleaned, and the adhesion of the film generated by the heated drill bit has not been thoroughly studied.

[0011] Invention patent 201310504176.6 relates to a process including the following steps: (1) performing pre-process treatment on the circuit board substrate, drilling through holes and copper deposition, plate surface electroplating, outer layer circuit pattern transfer, and pattern electroplating; 2) performing back drilling on the PCB 4, and detecting whether the back drilling depth is qualified; 3) performing alkaline etching and photosensitive solder mask on the drilled back drilling hole, and finally obtaining the finished product. The technical solution is as follows: during back drilling, the drill tape coefficient used in the drill through hole process is modified according to the expansion and contraction data appearing in the process from drilling through holes to back drilling holes of the PCB 4, to keep the drill tape data consistent with the actual expansion and contraction; the drill-in surface in the drill through hole process is consistent with the drill-in surface during back drilling; a layer of phenolic pad 6 is added on the top surface of the PCB 4; the depth accuracy and position accuracy of the back drilling hole of the existing PCB 4 can be effectively improved to ensure the integrity of the signal transmission of the PCB 4. The invention does not study the cleaning of the glue film, the adhesion of the drill bit film, and the adhesion of the fragments.

[0012] In summary, the existing technology does not involve the study of water-washable coatings for aluminum cover plates, and does not comprehensively study the combustion melting, heat resistance (pkHHR, THR), water-washability of the film on the aluminum cover plate, PCB core hole position accuracy, hole wall roughness, drill bit temperature, and hole diameter melting, etc. indicators, and more comprehensive study of the degradation of water-washable coatings. The above indicators are key to evaluating the performance of water-washable coatings, so research is necessary. SUMMARY

[0013] The present invention aims to solve the problem of requiring a polyurethane coating with low heat release, droplet resistance, water washability and degradability in PCB processing. In view of the drawbacks of existing water-washable coatings, the present invention utilizes a carbonizing agent and a polyhydroxy single-walled nanotube prepolymerization reaction, a porous carbon layer modifier and a glucose modifier chain extension, and a high carbonizing agent modification to solve the problem of polyurethane having no droplets and low heat release when heated, thereby improving the flame retardancy of polyurethane; the water washability of the glucose modifier and the degradability of polycaprolactone diol and glucose are utilized to improve the degradability and water washability of the polyurethane.

[0014] A method for preparing a flame-retardant, washable, and drip-resistant water-based polyurethane coating is provided, wherein the preparation is performed as follows:

[0015] (1) Raw material pretreatment: vacuum drying polytetrahydrofuran ether diol and polycaprolactone diol for 12 to 24 hours;

[0016] (2) Prepolymerization: Add 16-20 parts of polytetramethylene glycol, 8-10 parts of polycaprolactone glycol, and 12-17 parts of isocyanate into a flask, drop 0.2-0.7 parts of dibutyltin dilaurate, insert a thermometer, a glass stopper, a stirring paddle, and a nitrogen tube into the mouth of the flask, heat to 80-85°C, rotate at 200-250 r / min, and react for 1-2 hours. Add 4.7-5.2 parts of a carbonizing agent, 0.1-0.2 parts of a polyhydroxy single-walled polymer, and 0.05 parts of crotonic acid into the flask, and react at 75-85°C for 1.5-2.5 hours to obtain a polyurethane prepolymer.

[0017] (3) Chain extension: Cool the polyurethane prepolymer to 45-55°C, add 1-2 parts of 2,2-dihydroxymethylpropionic acid, and react for 1-2 hours. Then add 1-1.5 parts of porous carbon layer modifier and 1.2-1.4 parts of glucose modifier, and react at 65-70°C for 1-2 hours. Then add 1-2 parts of triethylamine and react for 1-2 hours.

[0018] (4) Emulsification: Cool to room temperature, add 140-170 parts of water, stir at a speed of 1000-1250 r / min for 1-2 hours, adjust the pH of the system to 7-8, and obtain a flame-retardant, washable, and drip-resistant water-based polyurethane coating.

[0019] The molecular weight of polytetramethylene ether glycol is 2000 g / mol, and the molecular weight of polycaprolactone glycol is 500 g / mol;

[0020] Isocyanate is any one of IPDI, HDI, and MDI;

[0021] The preparation method of the carbonization agent is as follows: 12.3 g of p-hydroxybenzaldehyde is added into a beaker, dissolved by stirring with 180-280 mL of ethanol, poured into a 1000 mL three-necked flask, the stirring speed is 250 r / min, the temperature is raised to 50-60 ℃, 20 mL of 6.0-6.5 g of ethylenediamine diluted with ethanol is slowly added into the three-necked flask through a constant pressure dropping funnel, the dropping time is 30 min, the reaction is continued for 1-2.5 h, then 21.6-27.3 g of DOPO and 3.5-6.2 g of 3,4-epoxy-1-butene are added, 0.74-1.85 g of initiator A is added, the reaction is carried out at 70-80 ℃ for 1-2 h, the heating is stopped, the temperature is cooled to room temperature, the product is filtered, washed with ethanol for 3 times, and dried at 60 ℃ under vacuum for 18-24 h to obtain the carbonization agent.

[0022] The initiator A is any one of azobisisobutyronitrile and azobisisovaleronitrile.

[0023] The preparation method of the porous carbon layer modifier is as follows:

[0024] (1) The plant tannage scrap is cut into blocks with a length and width of 1 cm, placed into a vacuum tube furnace, pre-carbonized at 400 ℃ for 3-4 h under nitrogen atmosphere, mixed with KOH at a weight ratio of 1:3, then 300% water by weight is added into the mixture, stirred at 40-50 ℃ for 12-24 h, then the product is dried, carbonized again at 500-600 ℃ for 1-2 h under nitrogen protection, and finally dried to obtain the porous carbon layer.

[0025] (2) 0.5 g of the porous carbon layer, 4.5-6.7 g of pyrrole, 2.26-3.14 g of DOPO, 0.7-1.4 g of 3,4-epoxy-1-butene, 100 mL of ethanol, 0.4-0.6 g of sodium p-toluenesulfonate, and 0.11-023 g of initiator B are stirred at 50-60 ℃ for 2-4 h, the product is dried, then 50 mL of DMF and 2.35-3.28 g of erythritol are added, the pH is adjusted to 7.5, the reaction is carried out at 60-70 ℃ for 1-2 h, then 2.74-3.15 g of phosphorus trichloride is added, the reaction is carried out at 30-40 ℃ for 1-2 h, then 5.98-6.21 g of myristic acid is added, the reaction is carried out at 35-45 ℃ for 1-2 h, then 6.24-8.62 g of neopentyl glycol is added, the reaction is carried out at 50-60 ℃ for 30-60 min, the obtained product is dried to obtain the porous carbon layer modifier.

[0026] The initiator B is a product obtained by mixing benzoyl peroxide and ammonium persulfate at a weight ratio of 1.5:1.

[0027] The preparation method of the glucose modified product is as follows: 1-1.3 g of benzoyl chloride and 35 mL of benzene are added to 4.1 g of soluble glucose, the mixture is stirred at 30-40 ° C for 30-40 min, rotary evaporated at 40-50 ° C, and dried to obtain a glucose reactant; 20 mL of 70 ° C deionized water is added to the glucose modified product, stirred for 40-60 min, and 0.04-0.06 g of ammonium persulfate is added at 50-60 ° C to obtain soluble glucose A; at the same time, 5.8 g of acrylamide, 2.3 g of hexadecyldimethylallyl ammonium chloride and 2 g of N,N-methylenebisacrylamide are mixed and added to 10 Dissolve the solution in 1 mL of deionized water, then slowly pour the solution into the soluble glucose solution A, adjust the pH of the soluble glucose solution to 7.0 with a 1 mol / L NaOH aqueous solution, stir at 50-70 °C for 2-3 h, place in an electric blast drying oven at 90 °C for reaction 2-3 h, and finally take out and dry for 24 h to obtain the glucose modification.

[0028] The advantages of the present invention are:

[0029] (1) A flame-retardant, washable, and drip-resistant water-based polyurethane coating was prepared, aiming to obtain a water-based flame-retardant polyurethane coating that can be washed with water in a short time after being immersed in water and is drip-resistant. The carbonizing agent and the prepolymerization reaction of polyhydroxy nanotubes were used, crotonic acid was used to enhance the density of the polyhydroxy nanotubes, the porous carbon layer modifier and the glucose modifier were used to extend the chain, and the high carbonizing agent was used for modification, so that the polyurethane had no dripping and low heat release when heated, thereby improving the flame retardancy of the polyurethane. The water-washability of the glucose modifier and the degradability of polycaprolactone diol and glucose were used to improve the degradability and water-washability of the polyurethane.

[0030] (2) The present invention utilizes the aldehyde group of p-hydroxybenzaldehyde and the amino group of ethylenediamine to form a Schiff base through condensation of the aldehyde group and the imino group. This reaction occurs easily to generate an imine bond. Then, under the action of an initiator, the carbonizing agent intermediate, DOPO and 3,4-epoxy-1-butene undergo a free radical reaction, wherein the pH of DOPO reacts with the C=N or C=C double bond through an addition reaction. Ethylenediamine provides a nitrogen source, and during the combustion process, it produces nitrogen and other inflammable gases, causing the carbon layer to expand. p-hydroxybenzaldehyde and DOPO provide a carbon source, and during combustion, a dense carbon layer is formed to cover the surface, isolating heat and oxygen. The phosphorus element in DOPO captures the oxygen free radicals released by the combustible material, reducing the possibility of combustion, thereby achieving a flame retardant effect.

[0031] (3) The present invention utilizes vegetable tanned leather shavings to be carbonized in a nitrogen atmosphere, isolated from oxygen, and uses KOH to increase its fluffiness. The carbonization is continued to obtain a porous carbon layer. Pyrrole, DOPO and 3,4-epoxy-1-butene are dispersed in the porous carbon layer and polymerized under the action of an initiator. The phase change material erythritol reacts with the NH bond of pyrrole, and the excess hydroxyl reacts with phosphorus trichloride. The excess phosphorus-chloride bond then reacts with myristic acid with a phase change. Then, neopentyl glycol with a high branching and the excess phosphorus-chloride bond are used to introduce hydroxyl groups into the system, so that a large amount of phase change material is introduced into the porous carbon layer. When the material is heated, it can absorb part of the heat and delay the possibility of combustion. At the same time, a large amount of carbon in the porous carbon layer reduces the possibility of combustion, and the hydroxyl group is used to react with the remaining isocyanate.

[0032] (4) The present invention utilizes part of the hydroxyl groups of soluble glucose to react with the acyl chloride of benzoyl chloride, and utilizes the hydroxyl groups in the remaining glucose to react with the amino group or the imino group. Under the condition of ammonium persulfate as an initiator, acrylamide, hexadecyldimethylallyl ammonium chloride and N,N-methylenebisacrylamide are subjected to a free radical solution reaction to form a soluble acrylic resin. Then, under an alkaline environment, the glucose reaction is accelerated. The obtained soluble glucose has three functions: a) increasing the melting temperature of polyurethane, b) improving the water solubility of polyurethane, and c) increasing the swelling of polyurethane when heated and washed with water, so that it can be quickly peeled off from the epoxy resin PCB board, thereby achieving moderate compatibility with the PCB board.

[0033] In the present invention, parts and g are equivalent, and soluble glucose is glucose. DETAILED DESCRIPTION

[0034] The present invention is further described below with reference to examples.

[0035] Chemical materials of unspecified manufacturers involved in the embodiments of the present invention can be replaced with similar products from Shanghai MacLean Biochemical Co., Ltd.

[0036] Example 1

[0037] The preparation method of the flame-retardant, washable, and drip-resistant water-based polyurethane coating is prepared according to the following steps:

[0038] (1) Raw material pretreatment: vacuum drying of polytetramethylene glycol (molecular weight 2000 g / mol) and polycaprolactone glycol (molecular weight 500 g / mol) for 12 h;

[0039] (2) Prepolymerization: 16 parts of polytetramethylene glycol, 8 parts of polycaprolactone glycol, and 12 parts of IPDI were added to a flask, and 0.2 parts of dibutyltin dilaurate were added dropwise. A thermometer, a glass stopper, a stirring paddle, and a nitrogen tube were inserted into the mouth of the flask. The temperature was raised to 80°C, the rotation speed was 200 r / min, and the reaction was carried out for 1 hour. 4.7 parts of a carbonizing agent, 0.1 parts of polyhydroxy single-walled carbon nanotubes, and 0.05 parts of crotonic acid were added to the flask, and the reaction was carried out at 75°C for 1.5 hours to obtain a polyurethane prepolymer.

[0040] (3) Chain extension: Cool the polyurethane prepolymer to 45°C, add 1 part of 2,2-dimethylolpropionic acid, and react for 1 hour. Then add 1 part of porous carbon layer modifier and 1.2 parts of glucose modifier, and react at 65°C for 1 hour. Then add 1 part of triethylamine and react at 65°C for 1 hour.

[0041] (4) Emulsification: Cool to room temperature, add 140 parts of water, stir and react at a speed of 1000 r / min for 1 hour, adjust the pH of the system to 7~8, and obtain a flame-retardant, water-washable, and drip-resistant water-based polyurethane coating.

[0042] The preparation method of the carbonizing agent is as follows: 12.3 g of p-hydroxybenzaldehyde is added to a beaker, stirred and dissolved with 180 mL of ethanol, poured into a 1000 mL three-necked flask, stirred at a speed of 250 r / min, heated to 50°C, and 6.0 g of ethylenediamine diluted with 20 mL of ethanol is slowly added dropwise to the three-necked flask through a constant pressure dropping funnel for 30 minutes, and the reaction is continued for 1 hour. Then, 1.6 g of DOPO2 and 3.5 g of 3,4-epoxy-1-butene are added, and 0.74 g of initiator azobisisobutyronitrile is added. The reaction is carried out at 70°C for 1 hour, the heating is stopped, the mixture is cooled to room temperature, filtered, washed with ethanol 3 times, and vacuum dried at 60°C for 18 hours to obtain the carbonizing agent.

[0043] The preparation method of the porous carbon layer modified material is as follows:

[0044] (1) Cut the vegetable tanned leather scraps into blocks with a length and width of 1 cm, place them in a vacuum tube furnace, and heat them at 400 °C for 3 h for pre-carbonization under a nitrogen atmosphere. Mix the obtained carbonized product with KOH in a weight ratio of 1:3, then add 300% water by weight to the above mixture and stir it at 40 °C for 12 h. Then, dry the product and carbonize it again at 500 °C for 1 h under nitrogen protection. Finally, dry it to obtain a porous carbon layer.

[0045] (2) 0.5 g of porous carbon layer, 4.5 g of pyrrole, 2.26 g of DOPO, 0.7 g of 3,4-epoxy-1-butene, 100 mL of ethanol, 0.4 g of sodium p-toluenesulfonate, and 0.11 g of initiator (a mixture of benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1) were stirred at 50 °C for 2 h, and the product was dried. 50 mL of DMF and 2.35 g of erythritol were added, and the pH was adjusted to 7.5. The mixture was stirred and reacted at 60 °C for 1 h. 2.74 g of phosphorus trichloride was added and reacted at 30 °C for 1 h. 5.98 g of myristic acid was added and reacted at 35 °C for 1 h. 6.24 g of neopentyl glycol was added and reacted at 50 °C for 30 min. The resulting product was dried to obtain a porous carbon layer modified product.

[0046] The preparation method of the glucose modified product is as follows: 1 g of benzoyl chloride and 35 mL of benzene are added to 4.1 g of soluble glucose, the mixture is stirred at 30°C for 30 min, rotary evaporated at 40°C, and dried to obtain a glucose reactant; 20 mL of 70°C deionized water is then added to the glucose reactant, stirred for 40 min, and 0.04 g of ammonium persulfate is added at 50°C to obtain soluble glucose A; at the same time, 5.8 g of acrylamide, 2.3 g of hexadecyldimethylallylammonium chloride, and 2 g of N,N-methylenebisacrylamide are mixed and dissolved in 10 mL of deionized water, and then the solution is slowly poured into the soluble glucose solution A, the pH of the soluble glucose solution is adjusted to 7.0 with a 1 mol / L NaOH aqueous solution, stirred at 50°C for 2 h, placed in an electric blast drying oven at 90°C for reaction for 2 h, and finally taken out and dried for 24 h to obtain the glucose modified product.

[0047] Example 2

[0048] A method for preparing a flame-retardant, washable, and drip-resistant water-based polyurethane coating is provided, wherein the preparation is performed as follows:

[0049] (1) Raw material pretreatment: vacuum drying of polytetramethylene glycol (molecular weight 2000 g / mol) and polycaprolactone glycol (molecular weight 500 g / mol) for 24 h;

[0050] (2) Prepolymerization: 20 parts of polytetramethylene glycol, 10 parts of polycaprolactone glycol and 17 parts of HDI were added to a flask, 0.7 parts of dibutyltin dilaurate were added dropwise, a thermometer, a glass stopper, a stirring paddle and a nitrogen tube were inserted into the mouth of the flask, the temperature was raised to 85°C, the speed was 250 r / min, and the reaction was carried out for 2 hours. 5.2 parts of a carbonizing agent, 0.2 parts of polyhydroxy single-walled carbon nanotubes and 0.05 parts of crotonic acid were added to the flask, and the reaction was carried out at 85°C for 2.5 hours to obtain a polyurethane prepolymer;

[0051] (3) Chain extension: The polyurethane prepolymer was cooled to 55 °C, 2 parts of 2,2-dimethylolpropionic acid were added, and the reaction was continued for 2 h. Then 1.5 parts of porous carbon layer modifier and 1.4 parts of glucose modifier were added, and the reaction was continued at 70 °C for 2 h. Then 2 parts of triethylamine were added, and the reaction was continued at 70 °C for 2 h.

[0052] (4) Emulsification: Cool to room temperature, add 170 parts of water, stir and react at a speed of 1250 r / min for 2 hours, adjust the pH of the system to 7~8, and obtain a flame-retardant, water-washable, and drip-resistant water-based polyurethane coating.

[0053] The preparation method of the carbonizing agent is as follows: 12.3 g of p-hydroxybenzaldehyde is added to a beaker, stirred and dissolved with 280 mL of ethanol, poured into a 1000 mL three-necked flask, stirred at a speed of 250 r / min, heated to 60°C, and 6.5 g of ethylenediamine diluted with 20 mL of ethanol is slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The addition time is 30 minutes, and the reaction is continued for 2.5 hours. Then, 27.3 g of DOPO and 6.2 g of 3,4-epoxy-1-butene are added, and 1.85 g of azobisisovaleronitrile as an initiator is added. The reaction is carried out at 80°C for 2 hours, the heating is stopped, the mixture is cooled to room temperature, filtered, washed with ethanol three times, and vacuum dried at 60°C for 24 hours to obtain the carbonizing agent.

[0054] The preparation method of the porous carbon layer modified material is as follows:

[0055] (1) Cut the vegetable tanned leather scraps into blocks with a length and width of 1 cm, place them in a vacuum tube furnace, and heat them at 400 °C for 4 h for pre-carbonization under a nitrogen atmosphere. Mix the obtained carbonized product with KOH at a weight ratio of 1:3, then add 300% water by weight to the above mixture and stir at 50 °C for 24 h. Then, dry the product and carbonize it again at 600 °C for 2 h under nitrogen protection. Finally, dry it to obtain a porous carbon layer.

[0056] (2) 0.5 g of porous carbon layer, 6.7 g of pyrrole, 3.14 g of DOPO, 1.4 g of 3,4-epoxy-1-butene, 100 mL of ethanol, 0.6 g of sodium p-toluenesulfonate, and 0.23 g of initiator (a mixture of benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1) were stirred at 60 ° C for 4 h, and the product was dried. Then, 50 mL of DMF and 3.28 g of erythritol were added, and the pH was adjusted to 7.5. The mixture was stirred and reacted at 70 ° C for 2 h. Then, 3.15 g of phosphorus trichloride was added and the mixture was reacted at 40 ° C for 2 h. Then, 6.21 g of myristic acid was added and the mixture was reacted at 45 ° C for 2 h. Then, 8.62 g of neopentyl glycol was added and the mixture was reacted at 60 ° C for 60 min. The resulting product was dried to obtain a porous carbon layer modified product.

[0057] The preparation method of the glucose modified product is as follows: 1.3 g of benzoyl chloride and 35 mL of benzene are added to 4.1 g of soluble glucose, the mixture is stirred at 40°C for 40 minutes, the mixture is rotary evaporated at 50°C, and the glucose reactant is dried; 20 mL of 70°C deionized water is then added to the glucose reactant, the mixture is stirred for 60 minutes, and 0.06 g of ammonium persulfate is added at 60°C to obtain soluble glucose A; at the same time, 5.8 g of acrylamide, 2.3 g of hexadecyldimethylallylammonium chloride, and 2 g of N,N-methylenebisacrylamide are mixed and dissolved in 10 mL of deionized water. The solution is then slowly poured into the soluble glucose solution A, the pH of the soluble glucose solution is adjusted to 7.0 with a 1 mol / L NaOH aqueous solution, the mixture is stirred at 70°C for 3 hours, the mixture is placed in an electric forced air drying oven at 90°C for 3 hours, and finally, the mixture is removed and dried for 24 hours to obtain the glucose modified product.

[0058] Example 3

[0059] A method for preparing a flame-retardant, washable, and drip-resistant water-based polyurethane coating is provided, which is prepared by the following method:

[0060] (1) Raw material pretreatment: vacuum drying of polytetramethylene glycol (molecular weight 2000 g / mol) and polycaprolactone glycol (molecular weight 500 g / mol) for 18 h;

[0061] (2) Prepolymerization: 18 parts of polytetramethylene glycol, 9 parts of polycaprolactone glycol and 14.5 parts of MDI were added to a flask, 0.45 parts of dibutyltin dilaurate were added dropwise, a thermometer, a glass stopper, a stirring paddle and a nitrogen tube were inserted into the mouth of the flask respectively, the temperature was raised to 85°C, the speed was 225r / min, and the reaction was carried out for 1.5h. 4.95 parts of a carbonizing agent, 0.15 parts of polyhydroxy single-walled carbon nanotubes and 0.05 parts of crotonic acid were added to the flask, and the reaction was carried out at 80°C for 2h to obtain a polyurethane prepolymer;

[0062] (3) Chain extension: The polyurethane prepolymer was cooled to 50 °C, 1.5 parts of 2,2-dimethylol propionic acid was added, and the reaction was continued for 1.5 h. Then 1.25 parts of porous carbon layer modifier and 1.3 parts of glucose modifier were added, and the reaction was continued at 65 °C for 1.5 h. Then 1.5 parts of triethylamine was added, and the reaction was continued at 65 °C for 1.5 h.

[0063] (4) Emulsification: Cool to room temperature, add 155 parts of water, stir and react at a speed of 1100 r / min for 1.5 hours, adjust the pH of the system to 7~8, and obtain a flame-retardant, water-washable, and drip-resistant water-based polyurethane coating.

[0064] The preparation method of the carbonization agent is as follows: 12.3 g of p-hydroxybenzaldehyde is added into a beaker, stirred and dissolved with 230 mL of ethanol, poured into a 1000 mL three-necked flask, the stirring speed is 250 r / min, the temperature is raised to 55°C, 20 mL of 6.25 g of ethylenediamine diluted with ethanol is slowly added into the three-necked flask through a constant pressure dropping funnel, the dropping time is 30 min, the reaction is continued for 1.75 h, then 24.4 g of DOPO and 4.85 g of 3,4-epoxy-1-butene are added, 1.3 g of azobisisobutyronitrile is added, the reaction is carried out at 75°C for 1.5 h, the heating is stopped, the temperature is cooled to room temperature, filtration is performed, ethanol washing is performed for 3 times, and vacuum drying is performed at 60°C for 21 h to obtain the carbonization agent.

[0065] The preparation method of the porous carbon layer modifier is as follows:

[0066] (1) The plant tannage scrap is cut into blocks with a length and width of 1 cm, placed into a vacuum tube furnace, heated at 400°C for 3.5 h for pre-carbonization under a nitrogen atmosphere, the obtained carbonized product and KOH are mixed in a weight ratio of 1:3, then 300% water by weight is added into the mixture, and stirring is performed at 45°C for 18 h, then the product is dried, carbonized again at 550°C for 1.5 h under the protection of nitrogen, and finally dried to obtain the porous carbon layer;

[0067] (2) 0.5 g of the porous carbon layer, 5.6 g of pyrrole, 2.7 g of DOPO, 1.05 g of 3,4-epoxy-1-butene, 100 mL of ethanol, 0.5 g of sodium p-toluenesulfonate, and 0.17 g of an initiator (a product of mixing benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1) are stirred at 55°C for 3 h, the product is dried, then 50 mL of DMF and 2.9 g of erythritol are added, the pH is adjusted to 7.5, stirring is performed at 65°C for 1.5 h, then 2.94 g of phosphorus trichloride is added, the reaction is performed at 35°C for 1.5 h, then 6.2 g of myristic acid is added, the reaction is performed at 40°C for 1.5 h, then 7.43 g of neopentyl glycol is added, the reaction is performed at 55°C for 45 min, the obtained product is dried to obtain the porous carbon layer modifier.

[0068] The preparation method of the glucose modified product is as follows: 1.15 g of benzoyl chloride and 35 mL of benzene are added to 4.1 g of soluble glucose, the mixture is stirred at 35°C for 35 minutes, rotary evaporated at 45°C, and dried to obtain a glucose reactant; 20 mL of 70°C deionized water is then added to the glucose reactant, stirred for 45 minutes, and 0.05 g of ammonium persulfate is added at 55°C to obtain soluble glucose A; at the same time, 5.8 g of acrylamide, 2.3 g of hexadecyldimethylallylammonium chloride, and 2 g of N,N-methylenebisacrylamide are mixed and dissolved in 10 mL of deionized water, and then the solution is slowly poured into the soluble glucose solution A. The pH of the soluble glucose solution is adjusted to 7.0 with a 1 mol / L NaOH aqueous solution, stirred at 60°C for 2.5 hours, placed in an electric blast drying oven at 90°C for reaction for 2.5 hours, and finally taken out and dried for 24 hours to obtain the glucose modified product.

[0069] The prepared polyurethane coating was poured into a polytetrafluoroethylene mold with a thickness controlled at 3 mm, and tests such as droplet test and cone calorimetry were performed.

[0070] Droplet test

[0071] (1) Sample preparation: Place the prepared polyurethane film in a constant temperature and humidity chamber set at 23℃±0.5℃ and 50%±5% humidity for 48 hours. Then take it out and cut it into 110cm×10cm×3mm samples. Prepare two sets of samples, with 5 samples in each set.

[0072] (2) Parameters: Clamp the sample about 5 mm from the top, so that it is facing vertically downward. Place a rosin board under the sample, and pad about 0.3 g of absorbent cotton on the board, evenly placed on the board. Adjust the gas flow rate to 105 ± 5 mL / min so that the flame height reaches 20 ± 1 mm. Set the combustion time to 10 s.

[0073] (3) Flame recording: After setting the parameters, start the flame ignition. After the 10s ignition is over, press the afterflame time start button. When the sample combustion is finished and only sparks are left, press the afterflame combustion end button and enter the afterburning time. When the sample is completely extinguished, press the afterburning time end button and record the burning afterflame time and afterburning time.

[0074] (4) Melt droplet observation: During the combustion process, pay attention to whether the combustion produces melt droplets, and whether the melt droplets falling on the absorbent cotton below will cause secondary combustion, and record the observation results.

[0075] The ASTM E1354-1990 (2004 standard) was used, and the cone calorimeter 2000 of the British FTT company was used for analysis and measurement. The sample was 10cm×10cm, 3mm thick, and the thermal radiation power was 12kW / m 2 , determine the maximum heat release rate pkHHR kW / m2 , THR total heat release MJ / m².

[0076] Take 28 parts of the polyurethane coating of Examples 1 to 3, 0.3 parts of carboxymethyl fiber, 3.5 parts of polyvinyl pyrrolidone PVP-K30, 2 parts of polyvinyl alcohol, 5 parts of polyethylene glycol, and 1.5 parts of polyoxyethylene polypropylene ether, and add them to 30 parts of distilled water in sequence, stir evenly, add 2.0 parts of polypropylene glycol (PPG-400), 0.5 parts of leveling agent, and 0.7 parts of silane coupling agent, stir evenly, filter and let stand to defoam, and then spray.

[0077] The composite coatings of Examples 1 to 3 were sprayed onto epoxy resin circuit boards, dried at 70°C for 30 min, and then washed with a 50°C warm water solution (temperature controlled at 50°C, KMnO4 50g / L, potassium manganate 10g / L, amplitude controlled at 20mm / s, sodium hydroxide 1mol / L, and the remainder water);

[0078] Water washing test method: Determination of the film removal time of the reference compound liquid coating [1] Xie Dan, Jia Danfeng. About water-washable temporary protective coatings [J]. Aging and Application of Synthetic Materials, 2017, 46(5): 43~50.

[0079] The PCB hole position accuracy is measured by sampling and slicing under a metallographic microscope, and the hole wall roughness is measured using a secondary element device; the hole position accuracy, hole wall roughness, and aperture melt are sprayed with an application solution (coating thickness 0.04mm) on aluminum foil (0.1mm), and the lower PCB board is drilled.

[0080] The drill bit temperature was measured using a hot red temperature detector;

[0081] The pore size melt was observed visually and the results were compared to obtain data of few, less and more (if less than 30 out of 100 drilled holes had melt, it was defined as few, 31 to 70 were less, and 71 to 100 were more);

[0082] Degradability testing: After curing, the polyurethane film was cut into pieces measuring 50 mm in length, 50 mm in width, and 3 mm in thickness, and weighed (m1). The treated polyurethane film samples were buried in moist soil rich in microorganisms and maintained at a constant temperature of 25°C. After 30 days, the polyurethane film samples were removed and washed with deionized water to remove surface impurities. The washed samples were dried in a forced air drying oven at 40°C to a constant weight, and their weight was weighed and recorded (m2). The degradation rate was calculated as (m1 - m2) divided by m1, and then multiplied by 100%.

[0083] Table 1 Film-forming properties of flame-retardant, water-washable, and drip-resistant polyurethane coatings

[0084] Example 1 Example 2 Example 3 Comparative Example Burning droplet phenomenon No melting and no dripping No melting and no dripping No melting and no dripping No melting and no dripping pkH 40.58 40.62 39.89 49.32 THR 119.16 118.42 117.68 151.25 Water washability (50℃,s) 38 35 32 208 Hole position accuracy (mil) 1.4 1.5 1.7 2.7 Hole wall roughness (μm) 6 7 5 22 Drill bit temperature (℃) 72 79 82 114 Pore ​​Melt few few few many Degradation rate 32.4 31.2 31.5 10.3

[0085] From Table 1, the flame retardant (combustion melt dripping phenomenon), pkHHR, THR (Example three of 2023111285422) of the polyurethane film are all significantly improved; the application has advantages over the comparative document in water washability, hole site accuracy, hole wall roughness, drill bit temperature and hole diameter melt; the adhesion of the application is moderate, the degradation rate is excellent, the PCB hole diameter melt is small, and it is easy to clean; the film around the aluminum cover plate is almost not bonded after the drill bit is heated, while the comparative document has the problem of film bonding around the aluminum cover plate after the drill bit is heated, and the PCB hole diameter melt is large and difficult to clean.

[0086] Table 2 Flame-retardant, water-washable, melt-drip-resistant water-based polyurethane coating properties

[0087] index Example 3 No added material pkH 66.23 No carbon added THR 141.45 No carbon added Burning droplet phenomenon A small amount of molten droplets No carbon added Hole position accuracy (mil) 4.5 No carbon added Hole wall roughness (μm) 28 No carbon added Drill bit temperature (℃) 92 No carbon added Pore ​​Melt many No carbon added pkH 51.13 Added carbon agent, without DOPO THR 131.86 Added carbon agent, without DOPO Burning droplet phenomenon A small amount of molten droplets Added carbon agent, without DOPO Hole position accuracy (mil) 3.6 Added carbon agent, without DOPO Hole wall roughness (μm) 24 Added carbon agent, without DOPO Drill bit temperature (℃) 89 Added carbon agent, without DOPO Pore ​​Melt less Added carbon agent, without DOPO pkH 50.89 Added carbonizing agent, without 3,4-epoxy-1-butene THR 135.62 Added carbonizing agent, without 3,4-epoxy-1-butene Burning droplet phenomenon A small amount of molten droplets Added carbonizing agent, without 3,4-epoxy-1-butene Hole position accuracy (mil) 3.8 Added carbonizing agent, without 3,4-epoxy-1-butene Hole wall roughness (μm) 22 Added carbonizing agent, without 3,4-epoxy-1-butene Drill bit temperature (℃) 84 Added carbonizing agent, without 3,4-epoxy-1-butene Pore ​​Melt less Added carbonizing agent, without 3,4-epoxy-1-butene pkH 45.21 Without polyhydroxy carbon nanotubes THR 125.62 Without polyhydroxy carbon nanotubes pkH 44.64 No crotonic acid added THR 128.79 No crotonic acid added

[0088] From Table 2, it can be seen that the charring agent not only affects the flame retardancy (pkHHR, THR and melt dripping) of the polyurethane film, but also affects the drilling accuracy and hole diameter roughness (polyurethane sprayed on the aluminum cover plate, PCB drilling accuracy and hole diameter roughness and hole diameter melt) and drill bit temperature. From Table 2, it can be seen that the indicators without adding charring agent are not as good as those with the above-mentioned substances. The addition of multi-hydroxyl carbon nanotubes and crotonic acid forms a dense carbon layer on the polyurethane combustion surface, reducing pkHHR and THR.

[0089] Table 3 Effect of porous carbon layer modifier on flame-retardant, water-washable, melt-drip-resistant water-based polyurethane coating application properties

[0090] index Example 3 No added material pkH 88.12 Without porous carbon layer modification THR 143.62 Without porous carbon layer modification Burning droplet phenomenon There are a lot of molten droplets Without porous carbon layer modification Hole position accuracy (mil) 3.5 Without porous carbon layer modification Hole wall roughness (μm) 25 Without porous carbon layer modification Drill bit temperature (℃) 99 Without porous carbon layer modification Pore ​​Melt many Without porous carbon layer modification pkH 75.13 Add porous carbon layer modifier, but not add erythritol THR 132.12 Add porous carbon layer modifier, but not add erythritol Burning droplet phenomenon A small amount of molten droplets Add porous carbon layer modifier, but not add erythritol Drill bit temperature (℃) 85 Add porous carbon layer modifier, but not add erythritol Pore ​​Melt less Add porous carbon layer modifier, but not add erythritol pkH 72.13 Add porous carbon layer modifier, but not add myristic acid THR 131.89 Add porous carbon layer modifier, but not add myristic acid Burning droplet phenomenon A small amount of molten droplets Add porous carbon layer modifier, but not add myristic acid Drill bit temperature (℃) 87 Add porous carbon layer modifier, but not add myristic acid Pore ​​Melt less Add porous carbon layer modifier, but not add myristic acid Hole position accuracy (mil) 2.7 Add porous carbon layer modifier, but not add myristic acid Hole wall roughness (μm) 18 Add porous carbon layer modifier, but not add myristic acid Drill bit temperature (℃) 93 Add porous carbon layer modifier, but not add phosphorus trichloride Pore ​​Melt less Add porous carbon layer modifier, but not add phosphorus trichloride Drill bit temperature (℃) 91 No neopentyl glycol added Hole wall roughness (μm) 12 No neopentyl glycol added

[0091] From Table 3, it can be seen that the porous carbon layer modifier, phosphorus trichloride, myristic acid and erythritol all improve the flame retardancy, hole site accuracy and hole wall roughness of the polyurethane resin. Neopentyl glycol affects the drill bit temperature and hole wall roughness of the drilling.

[0092] Table 4 Effect of glucose modifier on flame-retardant, water-washable, melt-drip-resistant water-based polyurethane coating and application properties

[0093] index Example 3 No added material Burning droplet phenomenon A small amount of molten droplets No glucose modification Drill bit temperature (℃) 87 No glucose modification Pore ​​Melt less No glucose modification Hole position accuracy (mil) 2.4 No glucose modification Hole wall roughness (μm) 16 No glucose modification Water washability (50℃,s) 92 No glucose modification Degradation rate (%) 11.2 No glucose modification Burning droplet phenomenon A small amount of molten droplets Added glucose modifier, without benzoyl chloride Drill bit temperature (℃) 83 Added glucose modifier, without benzoyl chloride Pore ​​Melt few Added glucose modifier, without benzoyl chloride Hole position accuracy (mil) 2.1 Added glucose modifier, without benzoyl chloride Hole wall roughness (μm) 12 Added glucose modifier, without benzoyl chloride Water washability (50℃,s) 54 Added glucose modifier, without benzoyl chloride Water washability (50℃,s) 55 With glucose modifier, without N,N-methylenebisacrylamide Water washability (50℃,s) 64 Add glucose modification, without adding hexadecyldimethylallyl ammonium chloride

[0094] From Table 4, it can be seen that the hole site accuracy, hole wall roughness and water washability indicators decrease without adding the above-mentioned substances. It shows that glucose modifier, benzoyl chloride, N,N-methylene bisacrylamide and cetyl dimethyl alkyl ammonium chloride play a core role.

[0095] The degradation rate without adding poly-caprolactone diol is 12.4%, which also shows that poly-caprolactone diol plays a degradation role.

Claims

1. Flame retardant, washable, drip-resistant water-based polyurethane coating, characterized by: The main raw materials used are: carbon forming agent, porous carbon layer modifier, glucose modifier, polyhydroxy single-wall carbon nanotube and crotonic acid.

2. The flame-retardant, washable, and drip-resistant water-based polyurethane coating according to claim 1, wherein the carbonizing agent is prepared by the following method: adding 12.3 g of p-hydroxybenzaldehyde to a beaker, stirring and dissolving it with 180-280 mL of ethanol, pouring it into a 1000 mL three-necked flask, stirring at a speed of 250 r / min, heating to 50-60° C., slowly adding 6.0-6.5 g of ethylenediamine diluted with 20 mL of ethanol to the three-necked flask through a constant pressure dropping funnel, the addition time is 30 min, and the reaction is continued for 1-2.5 h, then adding 21.6-27.3 g of DOPO and 3.5-6.2 g of 3,4-epoxy-1-butene, adding 0.74-1.85 g of initiator A, reacting at 70-80° C. for 1-2 h, stopping heating, cooling to room temperature, filtering, washing with ethanol three times, and vacuum drying at 60° C. for 18-24 h to obtain a carbonizing agent.

3. The flame-retardant, washable, drip-resistant water-based polyurethane coating according to claim 1, wherein the porous carbon layer modified product is prepared by: (1) Cut the vegetable tanned leather scraps into blocks with a length and width of 1 cm, place them in a vacuum tube furnace, and heat them at 400℃ for 3~4 hours under nitrogen atmosphere for pre-carbonization. Mix the obtained carbonized product with KOH in a weight ratio of 1:3, then add 300% water by weight to the above mixture, and stir at 40~50℃ for 12~24 hours. Then, dry the product, and carbonize it again at 500~600℃ for 1~2 hours under nitrogen protection, and finally dry it to obtain a porous carbon layer. (2) 0.5 g of porous carbon layer, 4.5-6.7 g of pyrrole, 2.26-3.14 g of DOPO, 0.7-1.4 g of 3,4-epoxy-1-butene, 100 mL of ethanol, 0.4-0.6 g of sodium p-toluenesulfonate, and 0.11-0.23 g of initiator B were stirred at 50-60 °C for 2-4 h. The product was dried, and then 50 mL of DMF and 2.35-3.28 g of erythritol were added to adjust the mixture. The pH value is set to 7.5, and the mixture is stirred and reacted at 60-70°C for 1-2 hours. Then, 2.74-3.15 g of phosphorus trichloride is added, and the mixture is reacted at 30-40°C for 1-2 hours. Then, 5.98-6.21 g of myristic acid is added, and the mixture is reacted at 35-45°C for 1-2 hours. Then, 6.24-8.62 g of neopentyl glycol is added, and the mixture is reacted at 50-60°C for 30-60 minutes. The obtained product is dried to obtain a porous carbon layer modified product.

4. The flame-retardant, washable, and drip-resistant water-based polyurethane coating according to claim 1, wherein the glucose modified product is prepared by adding 1 to 1.3 g of benzoyl chloride and 35 mL of benzene to 4.1 g of soluble glucose, stirring and reacting at 30 to 40 ° C for 30 to 40 minutes, rotary evaporating at 40 to 50 ° C, and drying to obtain a glucose reactant; then adding 20 mL of 70°C deionized water, stirred for 40-60 min, and 0.04-0.06 g of ammonium persulfate was added at 50-60°C to obtain soluble glucose A. At the same time, 5.8 g of acrylamide, 2.3 g of hexadecyldimethylallyl ammonium chloride, and 2 g of N,N-methylenebisacrylamide were mixed and added to 10 mL of deionized water to dissolve. Subsequently, this solution was slowly poured into the soluble glucose solution A, and the pH of the solution was adjusted to 7.0 with 1 mol / L NaOH. The solution was stirred at 50-70°C for 2-3 h, placed in an electric blast drying oven at 90°C for reaction for 2-3 h, and finally taken out and dried for 24 h to obtain the glucose modification.

5. The flame-retardant, washable, drip-resistant water-based polyurethane coating according to claims 2 to 4, wherein the preparation method is: (1) Raw material pretreatment: vacuum drying polytetrahydrofuran ether diol and polycaprolactone diol for 12 to 24 hours; (2) Prepolymerization: Add 16-20 parts of polytetramethylene glycol, 8-10 parts of polycaprolactone glycol, and 12-17 parts of isocyanate into a flask, drop 0.2-0.7 parts of dibutyltin dilaurate, insert a thermometer, a glass stopper, a stirring paddle, and a nitrogen tube into the mouth of the flask, heat to 80-85°C, rotate at 200-250 r / min, and react for 1-2 hours. Add 4.7-5.2 parts of a carbonizing agent, 0.1-0.2 parts of polyhydroxy single-walled carbon nanotubes, and 0.05 parts of crotonic acid into the flask, and react at 75-85°C for 1.5-2.5 hours to obtain a polyurethane prepolymer. (3) Chain extension: Cool the polyurethane prepolymer to 45-55°C, add 1-2 parts of 2,2-dihydroxymethylpropionic acid, and react for 1-2 hours. Then add 1-1.5 parts of porous carbon layer modifier and 1.2-1.4 parts of glucose modifier, and react at 65-70°C for 1-2 hours. Then add 1-2 parts of triethylamine and react for 1-2 hours. (4) Emulsification: Cool to room temperature, add 140-170 parts of water, stir at a speed of 1000-1250 r / min for 1-2 hours, adjust the pH of the system to 7-8, and obtain a flame-retardant, washable, and drip-resistant water-based polyurethane coating; The molecular weight of the polytetramethylene ether diol is 2000 g / mol, and the molecular weight of the polycaprolactone diol is 500 g / mol; the isocyanate is any one of IPDI, HDI, and MDI; the initiator A is any one of azobisisobutyronitrile and azobisisovaleronitrile; and the initiator B is a product of a mixture of benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1.