Preparation Method of Flame Retardant, Washable and Melting-Drip-Resistant Polyurethane Coating

Abstract

The present invention relates to a preparation method of a flame-retardant, washable, and melt-drop resistant polyurethane coating. Poly(tetrahydrofuran) glycol, polycaprolactone diol, isocyanate, and dibutyltin dilaurate are added to a flask. Then, a thermometer, a glass stopper, a stirring paddle, and a nitrogen tube are respectively inserted into the flask mouth. The temperature is raised to 80 - 85 °C and the reaction is carried out for 1 - 2 h. Then, a charring agent is added to the flask and the reaction is carried out for 1.5 - 2.5 h to obtain a polyurethane prepolymer. The polyurethane prepolymer is cooled to 45 - 55 °C, 2,2-dimethylolpropionic acid is added, and the reaction time is 1 - 2 h. Then, a porous carbon layer modifier and a glucose modifier are added, and the reaction is carried out at 65 - 70 °C for 1 - 2 h. Then, triethylamine is added and the reaction is carried out for 1 - 2 h. The temperature is lowered to room temperature, water is added, and the stirring reaction is carried out for 1 - 2 h. The pH of the system is adjusted to 7 - 8 to obtain a flame-retardant, washable, and melt-drop resistant polyurethane coating. The obtained polyurethane coating has good properties such as flame retardancy, washability, and melt-drop resistance.

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, washable, and melt-drop resistant waterborne polyurethane coatings. Background Art

[0002] Temporary protective coatings are similar to general protective coatings and can play a protective and decontamination role on the surface of the object to be protected. The difference is that the former has a short action time and mainly plays a protective role during processing, transportation, or temporary storage. After the processing, transportation, and storage processes are completed, the coating film layer needs to be removed from the surface of the protected object. After the coating film is removed, the original functions and properties of the original protected object should not be damaged or negatively affected. Such coatings that play a temporary protective role are also called removable coatings or washable coatings. After being applied to the object to be protected, the washable coating can form a tightly structured film layer, which can isolate the protected material from the outside world. At the same time, during the film-forming process, the surface adsorption, adhesion, and other effects can adsorb the dirt of the protected object.

[0003] The washable coating is usually removed from the surface of the protected object by soaking or rinsing with a specific solvent. It is required that the film has a certain solubility in the solvent, and the solvent includes water, acid-base solution, or a specifically formulated paint remover, etc. It is mainly used for the surface protection of glass and metal, or the dust collection and air purification of walls and floors.

[0004] As the cornerstone of electronic components, in the manufacturing process of PCB circuit boards, the drilling accuracy is one of the core indicators to measure the quality of PCBs. With the continuous introduction and high attention of government policies and regulations, removable coatings are the key to promoting the industrial transformation and upgrading of the Chinese coating industry to practice high-quality development and green sustainable development, and washable coatings are the key to affecting the drilling accuracy of PCBs. Applying the removable coating on an aluminum plate, then attaching the aluminum plate with the removable coating to the circuit board (copper substrate, copper-clad laminate), and then drilling can improve the drilling accuracy of the circuit board. As a consumable, after the drilling operation is completed, the PCB needs to be cleaned to remove the coating film. Currently, the washable coatings used in PCB board processing on the market generally have the following pain points: First, PCB drilling relies on the coating film on the aluminum plate for drilling, but traditional washable coatings have poor heat resistance and cannot withstand the heat generated during the drilling operation, causing partial or complete melting of the coating film and affecting the drilling accuracy; Second, the splashed coating during drilling is easily adhered to the epoxy resin through holes of the PCB and is difficult to handle. The residual coating is prone to cause moisture, mildew, and corrosion of the circuit board, affecting the service performance and life of the circuit board; Third, the resin adhesion between the PCB and the aluminum plate is not moderate, with poor adhesion, poor compatibility with the metal (aluminum plate), and difficulty in protection. If the adhesion is too strong, it is also difficult to be cleaned.

[0005] Jia Danfeng (Jia Danfeng. Preparation of Washable Temporary Protection Coating [D]. South China University of Technology, 2017) et al. prepared water-soluble acrylic resin through solution radical polymerization method, using acrylic acid (AA), 2-hydroxyethyl methacrylate (HEMA), and acrylamide (AM) as functional monomers, butyl acrylate and methyl methacrylate as soft and hard monomers, azobisisobutyronitrile (AIBN) as initiator, and dimethylethanolamine as neutralizer. Then, the water-soluble acrylic resin was compounded with emulsion to prepare a water-based compound resin for resin coatings. The water-based compound resin was compounded with fillers, water-soluble polymers, and other additives to prepare a washable temporary protection coating. It was found that the adhesion of the film was grade 2, and the water-washing demoulding time at 50 °C was 50 s, showing a good water-washing time. However, this technology did not consider the defect that the temporary coating film adhered to the metal material when heated during use, resulting in the film melting and being difficult to clean, nor did it study the core indicators such as the drilling accuracy of PCB.

[0006] The 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 PVA resin. At the same time, a small amount of acrylic acid-modified polyurethane PUA resin is used as the second modified resin, which can improve the bonding force with soft PVC and resist cracking caused by deformation of the material. The invention also adds a carboxylic acid-type propyl betaine amphoteric surfactant to the paint, which has the dual effects of thickening and improving water-washing residue, thus accelerating the dissolution rate of the paint film during water washing. Therefore, the paint provided by the invention has excellent flexibility, is not easy to crack, and has a good water-washing effect. However, this patent is related to the cleaning of soft PVC, which is different from the usage environment of the paints used for aluminum plates and PCB epoxy resin plates, and does not involve the standard requirements for the flame retardancy of acrylate.

[0007] The invention patent CN2015105882116 discloses a carburizing prevention coating that can be removed by water washing after quenching, which is prepared from the following components in 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 preparation method of the above carburizing prevention coating that can be removed by water washing after quenching. The carburizing prevention coating can be removed by water washing after carburizing heat treatment, thus solving the problem that traditional carburizing prevention coatings are difficult to peel off after carburizing heat treatment. In the carburizing prevention coating formula, inorganic high-temperature resistant materials are used as carburizing prevention agents. The carburizing prevention coating formed after brushing on the workpiece surface has good adhesion, does not peel off or flow at high temperature, and does not affect the carburizing atmosphere. This invention does not involve using polyurethane resin as the film-forming agent.

[0008] The invention patent 201910576686.1 relates to a glue-coated aluminum base cover plate for PCB drilling and its preparation method. Among them, the water-soluble composite polymer resin layer has moderate toughness and can play a guiding role during the falling process of the drill bit, thereby improving the drilling accuracy. At the same time, the hot-melt resin in the water-soluble composite polymer resin layer can lubricate the drill bit and cool the drill pin during drilling, thereby effectively improving the hole wall roughness, reducing wire entanglement, lowering the drill bit temperature, and extending the service life of the drill pin. In addition, the water-soluble composite polymer resin layer has good water solubility, is easy to process after drilling, and is not easily attached to the holes of the PCB, thus ensuring the drilling quality. The disadvantage of this resin is that it has not studied whether the glue can be cleaned when attached to the PCB holes during drilling, nor has it deeply studied the bonding of the film generated by the heat of the drill bit.

[0009] The invention patent 201310504176.6 involves the following steps: (1) performing pre-process treatment, drilling through-holes, copper deposition, surface electroplating, outer layer circuit pattern transfer, pattern electroplating, etc. on the circuit board substrate; (2) performing back drilling on the PCB board 4 and detecting whether the depth of the back drilled hole is qualified; (3) performing alkaline etching and photosensitive solder mask on the drilled back holes, and finally obtaining the finished product. The key points of its technical solution are: during back drilling, it is necessary to correspondingly modify the drill tape coefficient used in the through-hole drilling process according to the expansion and contraction data that occur during the process from through-hole drilling to back drilling on the PCB board 4, so as to keep the drill tape data consistent with the actual expansion and contraction; the drilling surface during the through-hole drilling process is the same as the drilling surface during back drilling; a layer of phenolic backing plate 6 is laid on the top of the PCB board 4; it can effectively improve the depth accuracy and position accuracy of the back drilled holes of the existing PCB board 4 to ensure the integrity of signal transmission of the PCB board 4. This invention has not studied the cleaning of the glue film, the bonding of the drill bit film, and the adhesion of debris.

[0010] In summary, the prior art does not involve the research on the water-washable coating waterborne polyurethane coating of the aluminum cover plate, nor does it comprehensively study the combustion melt droplets and heat resistance (pkHHR, THR) of the water-washable coating when coated on the aluminum cover plate, the water-washability of the film on the aluminum cover plate, the hole position accuracy, hole wall roughness, and drill bit temperature of the PCB core, as well as the melt of the hole diameter, etc. Moreover, it has not comprehensively studied the degradation of the water-washable coating. These above indicators are the key to evaluating the performance of the water-washable coating. Therefore, the research is imperative. Summary of the Invention

[0011] The present invention aims to solve the problems of polyurethane coatings that require low heat release, melt drip resistance, washability, and degradability in PCB processing. In view of the drawbacks of existing washable coatings, a prepolymerization reaction of a charring agent and multi-hydroxy single-walled carbon nanotubes is utilized, and chain extension is carried out with a porous carbon layer modifier and a glucose modifier, and high-charring agent modification is used to solve the problem of no melt dripping and low heat release of polyurethane when heated, thereby improving the flame retardancy of polyurethane; the washability of the glucose modifier and the degradability of polycaprolactone diol and glucose are utilized to improve the degradability and washability of polyurethane.

[0012] A preparation method of a flame-retardant, washable, and melt drip-resistant waterborne polyurethane coating is carried out as follows:

[0013] (1) Raw material pretreatment: Poly(tetramethylene ether) glycol and polycaprolactone diol are vacuum dried for 12 - 24 h.

[0014] (2) Prepolymerization: 16 - 20 parts of poly(tetramethylene ether) glycol, 8 - 10 parts of polycaprolactone diol, and 12 - 17 parts of isocyanate are added to a flask, 0.2 - 0.7 part of dibutyltin dilaurate is dropped in, a thermometer, a glass stopper, a stirring paddle, and a nitrogen tube are inserted at the mouth of the flask respectively, the temperature is raised to 80 - 85 °C, the rotation speed is 200 - 250 r / min, and the reaction is carried out for 1 - 2 h. Then, 4.7 - 5.2 parts of a charring agent, 0.1 - 0.2 part of multi-hydroxy single-walled carbon nanotubes, and 0.05 part of crotonic acid are added to the flask, and the reaction is carried out at 75 - 85 °C for 1.5 - 2.5 h to obtain a polyurethane prepolymer.

[0015] (3) Chain extension: The polyurethane prepolymer is cooled to 45 - 55 °C, 1 - 2 parts of 2,2-dimethylolpropionic acid are added, and the reaction is carried out for 1 - 2 h. Then, 1 - 1.5 parts of a porous carbon layer modifier and 1.2 - 1.4 parts of a glucose modifier are added, and the reaction is carried out at 65 - 70 °C for 1 - 2 h. Then, 1 - 2 parts of triethylamine are added, and the reaction is carried out for 1 - 2 h.

[0016] (4) Emulsification: The temperature is lowered to room temperature, 140 - 170 parts of water are added, and the stirring reaction is carried out at a rotation speed of 1000 - 1250 r / min for 1 - 2 h, and the pH of the system is adjusted to 7 - 8 to obtain a flame-retardant, washable, and melt drip-resistant waterborne polyurethane coating.

[0017] The molecular weight of poly(tetramethylene ether) glycol is 2000 g / mol, and the molecular weight of polycaprolactone diol is 500 g / mol;

[0018] The isocyanate is any one of IPDI, HDI, and MDI;

[0019] The preparation method of the charring agent is as follows: Add 12.3 g of p-hydroxybenzaldehyde into a beaker, stir and dissolve it with 180 - 280 mL of ethanol, pour it into a 1000 mL three-necked flask, with a stirring speed of 250 r / min, heat up to 50 - 60 °C, slowly drop 6.0 - 6.5 g of ethylenediamine diluted with 20 mL of ethanol into the three-necked flask through a constant-pressure dropping funnel over 30 min, continue to react for 1 - 2.5 h, then add 21.6 - 27.3 g of DOPO and 3.5 - 6.2 g of 3,4-epoxy-1-butene, add 0.74 - 1.85 g of initiator A, react at 70 - 80 °C for 1 - 2 h, stop heating, cool to room temperature, filter by suction, wash with ethanol 3 times, and dry in vacuum at 60 °C for 18 - 24 h to obtain the charring agent.

[0020] Initiator A is any one of azobisisobutyronitrile and azobisisovaleronitrile.

[0021] The preparation method of the porous carbon layer modifier is as follows:

[0022] (1) Cut the vegetable tanned leather scraps into blocks with a length and width of 1 cm each, place them in a vacuum tube furnace, pre-carbonize at 400 °C for 3 - 4 h under a nitrogen atmosphere, mix the obtained carbonized product and KOH in a weight ratio of 1:3, then add 300% water by weight of the above mixture and stir at 40 - 50 °C for 12 - 24 h, then dry the product, and again under nitrogen protection, carbonize and keep warm at 500 - 600 °C for 1 - 2 h, and finally dry it to obtain a porous carbon layer;

[0023] (2) Mix 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 p-toluenesulfonic acid, 0.11 - 0.23 g of initiator B, stir at 50 - 60 °C for 2 - 4 h, dry the product, then add 50 mL of DMF and 2.35 - 3.28 g of erythritol, adjust the pH to 7.5, stir and react at 60 - 70 °C for 1 - 2 h, then add 2.74 - 3.15 g of phosphorus trichloride, react at 30 - 40 °C for 1 - 2 h, then add 5.98 - 6.21 g of myristic acid, react at 35 - 45 °C for 1 - 2 h, then add 6.24 - 8.62 g of neopentyl glycol, react at 50 - 60 °C for 30 - 60 min, dry the obtained product to obtain the porous carbon layer modifier.

[0024] Initiator B is a product obtained by mixing benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1.

[0025] The preparation method of the glucose modifier is as follows: Add 1 - 1.3 g of benzoyl chloride and 35 mL of benzene to 4.1 g of soluble glucose, stir and react at 30 - 40 °C for 30 - 40 min, perform rotary evaporation at 40 - 50 °C, and dry to obtain the glucose reactant; then add 20 mL of deionized water at 70 °C to the glucose modifier, stir for 40 - 60 min, add 0.04 - 0.06 g of ammonium persulfate at 50 - 60 °C to obtain soluble glucose A; simultaneously mix 5.8 g of acrylamide, 2.3 g of cetyl dimethyl allyl ammonium chloride, and 2 g of N,N - methylene bisacrylamide, dissolve them in 10 mL of deionized water, then slowly pour this solution into the soluble glucose solution A, adjust the pH of the soluble glucose solution to 7.0 with 1 mol / L aqueous NaOH solution, stir and maintain at 50 - 70 °C for 2 - 3 h, place it in an electrothermal blast drying oven and react at 90 °C for 2 - 3 h, and finally take it out and dry for 24 h to obtain the glucose modifier.

[0026] The advantages of the present invention are as follows:

[0027] (1) A flame - retardant, washable, and melt - drip - resistant polyurethane coating was prepared, aiming to obtain a water - washable and melt - drip - resistant water - borne flame - retardant polyurethane coating after being soaked in water for a short time. By using the prepolymerization reaction of a char - forming agent and multi - hydroxyl nanotubes, crotonic acid enhances the compactness of multi - hydroxyl nanotubes, and the porous carbon layer modifier and glucose modifier are used for chain extension and high - char - forming agent modification. When the polyurethane is heated, no melt - dripping occurs and the heat release is low, improving the flame retardancy of the polyurethane; by using the washability of the glucose modifier and the biodegradability of polycaprolactone diol and glucose, the biodegradability and washability of the polyurethane are improved.

[0028] (2) In the present invention, the aldehyde group of p - hydroxybenzaldehyde and the amino group of ethylenediamine are used. Through the condensation of the aldehyde group and the imino group to form a Schiff base, this reaction occurs easily to generate an imine bond; then, under the action of an initiator, the char - forming agent intermediate, DOPO, and 3,4 - epoxy - 1 - butene undergo a radical reaction. Among them, the P - H of DOPO reacts with the C=N or C=C double bond through an addition reaction; ethylenediamine provides a nitrogen source, generating non - flammable gases such as nitrogen during the combustion process, causing the carbon layer to expand. p - Hydroxybenzaldehyde and DOPO provide a carbon source, forming a dense carbon layer on the surface during combustion to isolate heat and oxygen. The phosphorus element in DOPO will capture the oxygen free radicals released by combustibles, reducing the possibility of combustion to achieve the flame - retardant effect.

[0029] (3) The present invention utilizes vegetable tanned leather scraps to be carbonized in a nitrogen atmosphere to isolate oxygen, uses KOH to increase its fluffiness, and continues carbonization 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, the excess hydroxyl groups react with phosphorus trichloride, and the excess phosphorus-chlorine bonds react with myristic acid with phase change. Then, neopentyl glycol with a high degree of branching is used to react with the excess phosphorus-chlorine bonds, and hydroxyl groups are introduced into the system, so that a large amount of phase change materials are introduced onto 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 groups react with the remaining isocyanate.

[0030] (4) The present invention uses partial hydroxyl groups of soluble glucose to react with the acyl chloride of benzoyl chloride, and uses the hydroxyl groups in the remaining glucose to react with amino or imino groups. Under the condition of ammonium persulfate as an initiator, acrylamide, cetyl dimethyl allyl ammonium chloride, and N,N-methylenebisacrylamide are subjected to a free radical solution reaction to form a soluble acrylate resin. Then, in an alkaline environment, the reaction of glucose is accelerated. The obtained soluble glucose has three functions: a. increasing the melting temperature of polyurethane; b. improving the water solubility of polyurethane; c. increasing the swelling of polyurethane during heating and washing with water, so that it can be quickly peeled off from the epoxy resin PCB board, and thus achieving moderate compatibility with the PCB board.

[0031] In the present invention, the parts involved are equivalent to g, and the soluble glucose is glucose. Specific embodiments

[0032] The present invention will be further described below with reference to examples.

[0033] For the chemical materials not specified by the manufacturer involved in the examples of the present invention, similar products of Shanghai Macklin Biochemical Co., Ltd. can be used for replacement.

[0034] Example 1

[0035] A method for preparing a flame-retardant, washable, and melt-drop resistant polyurethane coating is prepared according to the following method steps:

[0036] (1) Raw material pretreatment: Poly(tetrahydrofuran) glycol (molecular weight 2000 g / mol) and polycaprolactone glycol (molecular weight 500 g / mol) are vacuum dried for 12 h.

[0037] (2) Prepolymerization: Add 16 parts of polytetrahydrofuran ether diol, 8 parts of polycaprolactone diol, and 12 parts of IPDI into a flask, drop in 0.2 parts of dibutyltin dilaurate, insert a thermometer, a glass stopper, a stirring paddle, and a nitrogen tube at the mouth of the flask respectively, heat up to 80 °C, with a rotation speed of 200 r / min, react for 1 h, add 4.7 parts of charring agent, 0.1 part of multi-hydroxyl single-walled carbon nanotubes, and 0.05 part of crotonic acid into the flask, and react at 75 °C for 1.5 h to obtain a polyurethane prepolymer;

[0038] (3) Chain extension: Cool the polyurethane prepolymer to 45 °C, add 1 part of 2,2-dimethylolpropionic acid, react for 1 h, then add 1 part of porous carbon layer modifier and 1.2 parts of glucose modifier, react at 65 °C for 1 h, then add 1 part of triethylamine and react at 65 °C for 1 h;

[0039] (4) Emulsification: Cool to room temperature, add 140 parts of water, stir and react at a rotation speed of 1000 r / min for 1 h, adjust the pH of the system to 7 - 8 to obtain a flame-retardant, washable, and melt-drop resistant polyurethane coating.

[0040] The preparation method of the charring agent is as follows: Add 12.3 g of p-hydroxybenzaldehyde into a beaker, stir and dissolve it with 180 mL of ethanol, pour it into a 1000 mL three-necked flask, with a stirring speed of 250 r / min, heat up to 50 °C, slowly drop 6.0 g of ethylenediamine diluted with 20 mL of ethanol into the three-necked flask through a constant pressure dropping funnel for 30 min, continue to react for 1 h, then add 21.6 g of DOPO and 3.5 g of 3,4-epoxy-1-butene, add 0.74 g of initiator azobisisobutyronitrile, react at 70 °C for 1 h, stop heating, cool to room temperature, filter by suction, wash with ethanol 3 times, and dry in vacuum at 60 °C for 18 h to obtain the charring agent.

[0041] The preparation method of the porous carbon layer modifier is as follows:

[0042] (1) Cut vegetable tanned leather scraps into blocks with a length and width of 1 cm each, place them in a vacuum tube furnace, pre-carbonize at 400 °C for 3 h under a nitrogen atmosphere, mix the obtained carbonized product and KOH at a weight ratio of 1:3, then add 300% of its weight of water to the above mixture, stir at 40 °C for 12 h, then dry the product, and again carbonize and keep warm at 500 °C for 1 h under nitrogen protection, and finally dry it to obtain a porous carbon layer;

[0043] (2) Add 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 B (a product of mixing benzoyl peroxide and ammonium persulfate at a weight ratio of 1.5:1) into a container. Stir at 50 °C for 2 h, dry the product, then add 50 mL of DMF and 2.35 g of erythritol, adjust the pH to 7.5, stir and react at 60 °C for 1 h, then add 2.74 g of phosphorus trichloride, react at 30 °C for 1 h, then add 5.98 g of myristic acid, react at 35 °C for 1 h, then add 6.24 g of neopentyl glycol, react at 50 °C for 30 min, dry the obtained product to obtain the modified porous carbon layer.

[0044] The preparation method of the glucose modified product is as follows: Add 1 g of benzoyl chloride and 35 mL of benzene to 4.1 g of soluble glucose, stir and react at 30 °C for 30 min, perform rotary evaporation at 40 °C, and dry to obtain the glucose reactant; then add 20 mL of deionized water at 70 °C to the glucose reactant, stir for 40 min, and add 0.04 g of ammonium persulfate at 50 °C to obtain soluble glucose A; at the same time, mix 5.8 g of acrylamide, 2.3 g of cetyl dimethyl allyl ammonium chloride, and 2 g of N,N-methylenebisacrylamide, dissolve them in 10 mL of deionized water, and then slowly pour this solution into the soluble glucose solution A. Adjust the pH of the soluble glucose solution to 7.0 with 1 mol / L NaOH aqueous solution, stir and maintain at 50 °C for 2 h, place it in an electrothermal blast drying oven and react at 90 °C for 2 h, and finally take it out and dry for 24 h to obtain the glucose modified product.

[0045] Example Two

[0046] The preparation method of the flame-retardant, washable, and melt-drip resistant polyurethane coating is as follows:

[0047] (1) Raw material pretreatment: Vacuum dry polytetrahydrofuran glycol (molecular weight of 2000 g / mol) and polycaprolactone glycol (molecular weight of 500 g / mol) for 24 h;

[0048] (2) Prepolymerization: Add 20 parts of polytetrahydrofuran glycol, 10 parts of polycaprolactone glycol, and 17 parts of HDI into a flask, drop in 0.7 part of dibutyltin dilaurate, insert a thermometer, a glass stopper, a stirring paddle, and a nitrogen tube at the flask mouth respectively, raise the temperature to 85 °C, with a rotation speed of 250 r / min, react for 2 h, add 5.2 parts of charring agent, 0.2 part of multi-hydroxy single-walled carbon nanotubes, and 0.05 part of crotonic acid into the flask, and react at 85 °C for 2.5 h to obtain the polyurethane prepolymer;

[0049] (3) Chain extension: The temperature of the polyurethane prepolymer was lowered to 55 °C, 2 parts of 2,2-dimethylolpropionic acid were added, and the reaction was carried out for 2 h. Then 1.5 parts of the porous carbon layer modifier and 1.4 parts of the glucose modifier were added, and the reaction was carried out at 70 °C for 2 h. Then 2 parts of triethylamine were added, and the reaction was carried out at 70 °C for 2 h;

[0050] (4) Emulsification: The temperature was lowered to room temperature, 170 parts of water were added, and the reaction was stirred at a rotation speed of 1250 r / min for 2 h. The pH of the system was adjusted to 7-8 to obtain a flame-retardant, washable, and melt-drop-resistant polyurethane coating.

[0051] The preparation method of the charring agent is as follows: 12.3 g of p-hydroxybenzaldehyde was added to a beaker, dissolved by stirring with 280 mL of ethanol, poured into a 1000 mL three-necked flask, the stirring speed was 250 r / min, and the temperature was raised to 60 °C. 6.5 g of ethylenediamine diluted with 20 mL of ethanol was slowly added dropwise to the three-necked flask through a constant pressure dropping funnel, and the dropping time was 30 min. The reaction was continued for 2.5 h. Then 27.3 g of DOPO and 6.2 g of 3,4-epoxy-1-butene were added, 1.85 g of the initiator azodiisovaleronitrile was added, and the reaction was carried out at 80 °C for 2 h. The heating was stopped, cooled to room temperature, filtered by suction, washed 3 times with ethanol, and dried in vacuo at 60 °C for 24 h to obtain the charring agent.

[0052] The preparation method of the porous carbon layer modifier is as follows:

[0053] (1) Cut the vegetable tanned leather scraps into blocks with a length and width of 1 cm, place them in a vacuum tube furnace, pre-carbonize them at 400 °C for 4 h under a nitrogen atmosphere, mix the obtained carbonized product and KOH in a weight ratio of 1:3, then add 300% of its weight of water to the above mixture, and stir at 50 °C for 24 h. Then the product was dried, and again carbonized and kept warm at 600 °C for 2 h under nitrogen protection, and finally dried to obtain a porous carbon layer;

[0054] (2) Mix 0.5 g of the 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 B (a product obtained by mixing benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1), stir at 60 °C for 4 h, dry the product, then add 50 mL of DMF and 3.28 g of erythritol, adjust the pH to 7.5, stir and react at 70 °C for 2 h, then add 3.15 g of phosphorus trichloride, react at 40 °C for 2 h, then add 6.21 g of myristic acid, react at 45 °C for 2 h, then add 8.62 g of neopentyl glycol, react at 60 °C for 60 min, and dry the obtained product to obtain the porous carbon layer modifier.

[0055] The preparation method of the glucose modifier is as follows: Add 1.3 g of benzoyl chloride and 35 mL of benzene to 4.1 g of soluble glucose, stir and react at 40 °C for 40 min, perform rotary evaporation at 50 °C, and dry to obtain the glucose reactant; then add 20 mL of deionized water at 70 °C to the glucose reactant, stir for 60 min, and add 0.06 g of ammonium persulfate at 60 °C to obtain soluble glucose A; at the same time, mix 5.8 g of acrylamide, 2.3 g of cetyl dimethyl allyl ammonium chloride, and 2 g of N,N'-methylenebisacrylamide, dissolve them in 10 mL of deionized water, and then slowly pour this solution into the soluble glucose solution A. Adjust the pH of the soluble glucose solution to 7.0 with 1 mol / L NaOH aqueous solution, stir and maintain at 70 °C for 3 h, place it in an electrothermal blast drying oven and react at 90 °C for 3 h, and finally take it out and dry for 24 h to obtain the glucose modifier.

[0056] Example 3

[0057] The preparation method of the flame-retardant, washable, and melt-drop resistant polyurethane coating is carried out by the following method:

[0058] (1) Raw material pretreatment: Vacuum dry poly(tetrahydrofuran) glycol (molecular weight 2000 g / mol) and polycaprolactone diol (molecular weight 500 g / mol) for 18 h;

[0059] (2) Prepolymerization: Add 18 parts of poly(tetrahydrofuran) glycol, 9 parts of polycaprolactone diol, and 14.5 parts of MDI to a flask, drop in 0.45 parts of dibutyltin dilaurate, insert a thermometer, glass stopper, stirring paddle, and nitrogen tube at the flask mouth respectively, heat up to 85 °C, rotate at 225 r / min, react for 1.5 h, add 4.95 parts of charring agent, 0.15 parts of multi-hydroxy single-walled carbon nanotubes, and 0.05 parts of crotonic acid to the flask, and react at 80 °C for 2 h to obtain the polyurethane prepolymer;

[0060] (3) Chain extension: Cool the polyurethane prepolymer to 50 °C, add 1.5 parts of 2,2-dimethylolpropionic acid, react for 1.5 h, then add 1.25 parts of porous carbon layer modifier and 1.3 parts of glucose modifier, react at 65 °C for 1.5 h, and then add 1.5 parts of triethylamine and react at 65 °C for 1.5 h;

[0061] (4) Emulsification: Cool to room temperature, add 155 parts of water, stir and react at 1100 r / min for 1.5 h, adjust the pH of the system to 7 - 8 to obtain the flame-retardant, washable, and melt-drop resistant polyurethane coating.

[0062] The preparation method of the charring agent is as follows: Add 12.3 g of p-hydroxybenzaldehyde into a beaker, stir and dissolve it with 230 mL of ethanol, pour it into a 1000 mL three-necked flask, with a stirring speed of 250 r / min, heat up to 55 °C, slowly add 6.25 g of ethylenediamine diluted with 20 mL of ethanol dropwise to the three-necked flask through a constant-pressure dropping funnel over 30 min, continue the reaction for 1.75 h, then add 24.4 g of DOPO and 4.85 g of 3,4-epoxy-1-butene, add 1.3 g of azobisisobutyronitrile, react at 75 °C for 1.5 h, stop heating, cool to room temperature, filter by suction, wash with ethanol 3 times, and dry in vacuum at 60 °C for 21 h to obtain the charring agent.

[0063] The preparation method of the porous carbon layer modifier is as follows:

[0064] (1) Cut the vegetable tanned leather scraps into blocks with a length and width of 1 cm each, place them in a vacuum tube furnace, pre-carbonize them at 400 °C for 3.5 h under a nitrogen atmosphere, mix the obtained carbonized product and KOH in a weight ratio of 1:3, then add 300% of the weight of water to the above mixture, stir at 45 °C for 18 h, then dry the product, and carbonize and keep warm at 550 °C for 1.5 h again under nitrogen protection, and finally dry it to obtain a porous carbon layer;

[0065] (2) Mix 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 p-toluenesulfonic acid, 0.17 g of initiator B (a product obtained by mixing benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1), stir at 55 °C for 3 h, dry the product, then add 50 mL of DMF and 2.9 g of erythritol, adjust the pH to 7.5, stir and react at 65 °C for 1.5 h, then add 2.94 g of phosphorus trichloride, react at 35 °C for 1.5 h, then add 6.2 g of myristic acid, react at 40 °C for 1.5 h, then add 7.43 g of neopentyl glycol, react at 55 °C for 45 min, dry the obtained product to obtain the porous carbon layer modifier.

[0066] The preparation method of the glucose modifier is as follows: Add 1.15 g of benzoyl chloride and 35 mL of benzene to 4.1 g of soluble glucose, stir and react at 35 °C for 35 min, perform rotary evaporation at 45 °C, and dry to obtain the glucose reactant; then add 20 mL of deionized water at 70 °C to the glucose reactant, stir for 45 min, and add 0.05 g of ammonium persulfate at 55 °C to obtain soluble glucose A; at the same time, mix 5.8 g of acrylamide, 2.3 g of cetyl dimethyl allyl ammonium chloride, and 2 g of N,N'-methylenebisacrylamide, dissolve them in 10 mL of deionized water, and then slowly pour this solution into the soluble glucose solution A. Adjust the pH of the soluble glucose solution to 7.0 with 1 mol / L aqueous NaOH solution, stir and maintain at 60 °C for 2.5 h, place it in an electrothermal blast drying oven and react at 90 °C for 2.5 h, and finally take it out and dry for 24 h to obtain the glucose modifier.

[0067] Pour the prepared polyurethane coating into a polytetrafluoroethylene mold, control the thickness to 3 mm, and conduct tests such as melt drop test and cone calorimetry.

[0068] Melt drop test

[0069] (1) Sample preparation: Place the prepared polyurethane film in a thermostatic and humidistatic 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.

[0070] (2) Parameter setting: Clamp about 5 mm from the upper end to make the specimen perpendicular downward. Place a rosin wood board under the lower end of the sample, and pad about 0.3 g of absorbent cotton on the board and 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. Set the ignition time to 10 s.

[0071] (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.

[0072] (4) Melt drop observation: During the combustion process, pay attention to observing whether combustion produces melt drops, and whether the melt drops falling on the absorbent cotton below will cause secondary combustion, and record the observation results.

[0073] Adopt ASTM E1354 - 1990 (2004 standard), use the cone calorimeter 2000 of FTT Company in the UK for analysis and determination. The specimen is 10 cm × 10 cm with a thickness of 3 mm, and the heat radiation power is 12 kW / m 2 , and measure the maximum heat release rate pkHHR in kW / m 2、THR total heat release MJ / m 2 .

[0074] 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, 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.

[0075] The composite coatings of Examples 1 to 3 were sprayed on the epoxy resin circuit board respectively, dried at 70° C. for 30 min, and then washed with a 50° C. warm water solution (temperature controlled at 50° C., KMnO4 50 g / L, potassium manganate 10 g / L, amplitude controlled at 20 mm / s, sodium hydroxide 1 mol / L, and the rest was water);

[0076] Water washing test method: Determination of the film removal time of the reference mixed 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.

[0077] The PCB hole position accuracy is measured by sampling and slicing under a metallographic microscope, and the hole wall roughness is measured by a secondary element device; the hole position accuracy, hole wall roughness, and hole diameter melt are sprayed with an application solution (coating thickness 0.04mm) on an aluminum foil (0.1mm), and then drilled on the lower PCB board.

[0078] The drill bit temperature is measured using a hot red temperature detector;

[0079] The pore size melt is observed by naked eyes, and the results are compared and divided into small, less and more data (if less than 30 holes have melt out of 100 holes, it is defined as small, 31 to 70 holes are less, and 71 to 100 holes are more);

[0080] Degradability test: Cut the matured polyurethane film into pieces with a length of 50 mm, a width of 50 mm and a thickness of 3 mm, and weigh them (m1). The treated polyurethane film samples are buried in moist soil rich in microorganisms and kept at a constant temperature of 25°C. After 30 days, the polyurethane film samples are taken out and washed with deionized water to remove surface impurities. The washed samples are placed in a blast drying oven at 40°C and dried to constant weight, and their weight is weighed and recorded (m2). The degradation rate is (m1-m2) divided by m1 and then multiplied by 100%.

[0081] Table 1 Film-forming properties of flame-retardant, water-washable and drip-resistant water-based polyurethane coatings

[0082]

[0083]

[0084] Compared with the comparative example (Example 3 of 2023111285422), the flame retardancy (combustion melt dripping phenomenon), pkHHR, and THR of the polyurethane film in Table 1 have been significantly improved; the present invention is superior to the comparative document in terms of water washability, hole position accuracy, hole wall roughness, drill bit temperature, and aperture melt. The adhesion of the present invention is moderate, the degradation rate is excellent, the aperture melt of the PCB board is less, and it is easy to clean. After the drill bit is heated, the film around the aluminum cover plate hardly adheres, while in the comparative document, the film around the aluminum cover plate adheres after the drill bit is heated, the aperture melt of the PCB board is more, and it is difficult to clean.

[0085] Table 2 Properties of Flame Retardant, Washable, and Melting Drop-Resistant Polyurethane Coatings

[0086]

[0087]

[0088] As can be seen from Table 2, the charring agent not only affects the flame retardancy (pkHHR, THR, and melting drop situation) of the polyurethane film, but also affects the drilling accuracy and aperture roughness (the drilling accuracy, aperture roughness, and aperture melt of the PCB when polyurethane is sprayed on the aluminum cover plate) and the drill bit temperature. As can be seen from Table 2, the indicators without the addition of the charring agent are all inferior to those with the addition of the above substances. The addition of multi-hydroxy carbon nanotubes and crotonic acid forms a dense carbon layer on the combustion surface of the polyurethane, reducing pkHHR and THR.

[0089] Table 3 Influence of Porous Carbon Layer Modifiers on the Application Properties of Flame Retardant, Washable, and Melting Drop-Resistant Polyurethane Coatings

[0090]

[0091]

[0092] As can be seen from Table 3, the porous carbon layer modifiers, phosphorus trichloride, myristic acid, and erythritol can all improve the flame retardancy, hole position accuracy, and hole wall roughness of the polyurethane resin. Neopentyl glycol affects the drill bit temperature and hole wall roughness of the drilling.

[0093] Table 4 Influence of Glucose Modifiers on the Properties of Flame Retardant, Washable, and Melting Drop-Resistant Polyurethane Coatings and Their Application

[0094]

[0095] As can be seen from Table 4, the hole position accuracy, hole wall roughness, and water washability indicators without the addition of the above substances decline. It shows that the glucose modifiers, benzoyl chloride, N,N-methylenebisacrylamide, and cetyl dimethyl allyl ammonium chloride play a core role.

[0096] The degradation rate of the sample without polycaprolactone diol was 12.4%, which also indicated that polycaprolactone diol played a role in degradation.

Claims

1. Preparation method of flame-retardant, washable and melt-drop resistant polyurethane coating, characterized in that: (1) Raw material pretreatment: Vacuum dry polytetrahydrofuran ether glycol and polycaprolactone glycol for 12 - 24 h; (2) Prepolymerization: Add 16 - 20 parts of polytetrahydrofuran ether glycol, 8 - 10 parts of polycaprolactone glycol, and 12 - 17 parts of isocyanate into a flask, drop in 0.2 - 0.7 parts of dibutyltin dilaurate, insert a thermometer, a glass stopper, a stirring paddle, and a nitrogen tube at the mouth of the flask respectively, heat up to 80 - 85 °C, with a rotation speed of 200 - 250 r / min, react for 1 - 2 h, then add 4.7 - 5.2 parts of charring agent, 0.1 - 0.2 parts of multi-hydroxyl single-walled carbon nanotubes, and 0.05 parts of crotonic acid into the flask, react at 75 - 85 °C for 1.5 - 2.5 h to obtain a polyurethane prepolymer; (3) Chain extension: Cool the polyurethane prepolymer to 45 - 55 °C, add 1 - 2 parts of 2,2-dimethylolpropionic acid, react for 1 - 2 h, then add 1 - 1.5 parts of porous carbon layer modifier and 1.2 - 1.4 parts of glucose modifier, react at 65 - 70 °C for 1 - 2 h, and then add 1 - 2 parts of triethylamine, react for 1 - 2 h; (4) Emulsification: Cool to room temperature, add 140 - 170 parts of water, stir and react at a rotation speed of 1000 - 1250 r / min for 1 - 2 h, adjust the pH of the system to 7 - 8 to obtain a flame-retardant, washable and melt-drop resistant polyurethane coating; The preparation method of the charring agent is as follows: Add 12.3 g of p-hydroxybenzaldehyde into a beaker, stir and dissolve it with 180 - 280 mL of ethanol, pour it into a 1000 mL three-necked flask, with a stirring speed of 250 r / min, heat up to 50 - 60 °C, slowly drip 6.0 - 6.5 g of ethylenediamine diluted with 20 mL of ethanol into the three-necked flask through a constant pressure dropping funnel, with a dropping time of 30 min, continue to react for 1 - 2.5 h, then add 21.6 - 27.3 g of DOPO and 3.5 - 6.2 g of 3,4-epoxy-1-butene, add 0.74 - 1.85 g of initiator A, react at 70 - 80 °C for 1 - 2 h, stop heating, cool to room temperature, filter by suction, wash with ethanol 3 times, and dry in vacuum at 60 °C for 18 - 24 h to obtain the charring agent; The preparation method of the porous carbon layer modifier is as follows: (1) Cut vegetable tanned leather scraps into blocks with a length and width of 1 cm each, place them in a vacuum tube furnace, pre-carbonize them at 400 °C for 3 - 4 h under a nitrogen atmosphere, mix the obtained carbonized product and KOH in a weight ratio of 1:3, then add 300% of its weight of water to the mixture and stir at 40 - 50 °C for 12 - 24 h, then dry the product, and again under nitrogen protection, carbonize and keep warm at 500 - 600 °C for 1 - 2 h, and finally dry it to obtain a porous carbon layer; (2)Add 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, stir at 50 - 60 °C for 2 - 4 h, dry the product, then add 50 mL of DMF and 2.35 - 3.28 g of erythritol, adjust the pH to 7.5, stir and react at 60 - 70 °C for 1 - 2 h, then add 2.74 - 3.15 g of phosphorus trichloride, react at 30 - 40 °C for 1 - 2 h, then add 5.98 - 6.21 g of myristic acid, react at 35 - 45 °C for 1 - 2 h, then add 6.24 - 8.62 g of neopentyl glycol, react at 50 - 60 °C for 30 - 60 min, dry the obtained product to obtain the modified porous carbon layer; The preparation method of the glucose modifier is as follows: Add 1 - 1.3 g of benzoyl chloride and 35 mL of benzene to 4.1 g of soluble glucose, stir and react at 30 - 40 °C for 30 - 40 min, perform rotary evaporation at 40 - 50 °C, and dry to obtain the glucose reactant; then add 20 mL of deionized water at 70 °C to the glucose reactant, stir for 40 - 60 min, add 0.04 - 0.06 g of ammonium persulfate at 50 - 60 °C to obtain soluble glucose A; at the same time, mix 5.8 g of acrylamide, 2.3 g of cetyl dimethyl allyl ammonium chloride, and 2 g of N,N-methylenebisacrylamide, dissolve them in 10 mL of deionized water, then slowly pour this solution into the soluble glucose solution A, adjust the pH of the solution to 7.0 with 1 mol / L of NaOH, stir and maintain at 50 - 70 °C for 2 - 3 h, place it in an electrothermal blast drying oven and react at 90 °C for 2 - 3 h, and finally take it out and dry for 24 h to obtain the glucose modifier.

2. The preparation method of the flame-retardant, washable, melt-drop resistant polyurethane coating according to claim 1, characterized in that: The molecular weight of the poly(tetrahydrofuran) ether diol is 2000 g / mol, and the molecular weight of the polycaprolactone diol is 500 g / mol.

3. The preparation method of the flame-retardant, washable, melt-drop resistant polyurethane coating according to claim 1, characterized in that: The isocyanate is any one of IPDI, HDI, and MDI.

4. The preparation method of the flame-retardant, washable, melt-drip resistant polyurethane coating according to claim 1, characterized in that: The initiator A is any one of azobisisobutyronitrile and azobisisopentanenitrile.

5. The preparation method of the flame-retardant, washable, melt-drop resistant polyurethane coating according to claim 1, characterized in that: The initiator B is a product obtained by mixing benzoyl peroxide and ammonium persulfate in a weight ratio of 1.5:1.

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