Method for synthesizing waterborne polyurethane resin by adopting prepolymer dispersion method

Abstract

The invention discloses a method for synthesizing waterborne polyurethane resin by adopting a prepolymer dispersion method, and relates to the technical field of waterborne polyurethane processing, and the method comprises the following steps: (1) preparing raw materials; (2) prepolymerization; (3) refluxing; (4) neutralization reaction; (5) dispersing, emulsifying and carrying out chain extension reaction; and (6) packaging a finished product. The waterborne polyurethane resin is synthesized by introducing the modified cellulose nanofibers and the functionalized nanosilicon dioxide and combining a prepolymer dispersion method, and the finally synthesized waterborne polyurethane resin has excellent comprehensive performance, especially water resistance and mechanical performance; therefore, the prepared waterborne polyurethane resin can be better applied to the fields of new energy automobiles, intelligent manufacturing, environment-friendly building materials and the like, the use value of the product is greatly improved, and the service life of the product is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of waterborne polyurethane processing, and in particular relates to a method for synthesizing waterborne polyurethane resin by adopting a prepolymer dispersion method. Background Art

[0002] Polyurethane resin is a special polymer. Due to its good wear resistance, corrosion resistance, high strength and low weight, it is widely used in new energy, lithium batteries, photovoltaics, food packaging, automobiles, aerospace, construction, machinery manufacturing, petrochemicals, light industry, metallurgy, electronics and electrical appliances, ships and other fields.

[0003] Waterborne polyurethane resin refers to polyurethane that uses water as a dispersion medium. With the strengthening of people's environmental awareness and environmental protection laws and regulations, the research and development of environmentally friendly waterborne polyurethane has received increasing attention. Its application has been continuously expanded from leather finishing agents to coatings, adhesives and other fields, and is gradually occupying the market of solvent-based polyurethane, representing the development direction of coatings and adhesives. Among waterborne resins, waterborne polyurethane is still a representative of excellent resins and one of the hot spots in modern waterborne resin research. However, compared with traditional polyurethane resins, there is a certain gap in mechanical properties and water resistance, which limits its scope of application.

[0004] The patent with publication number CN110746571B discloses an APAO modified polyurethane water-based resin, which is composed of 25.0-60.0 parts of diisocyanate, 20.0-45.0 parts of oligomer polyol, hydroxyethyl acrylate grafted APAO, 4.0-10.0 parts, chain extender 6.0-15.0 parts, dimethylol propionic acid 2.5-5.0 parts, hydroxypropyl acrylate 0.5-1.2 parts, dibutyltin dilaurate 0.03-0.1 parts, ethanol 2.5-10.0 parts, ethylenediamine 3.0-6.0 parts, neutralizer 2.5-10.0 parts, deionized water 120.0-180.0 parts; the APAO modified polyurethane water-based resin prepared by the present invention has the characteristics of excellent adhesion, water resistance, aging resistance, salt spray resistance, good anti-sagging and the like; it can be used for water-based wood coatings, water-based industrial coatings, waterproof coatings, etc. Although the invention improves the water resistance problem of water-based polyurethane resin, there is still a situation where the mechanical properties are not significant.

[0005] Based on this, we proposed a method for synthesizing waterborne polyurethane resin using a prepolymer dispersion method, hoping to solve the shortcomings of the existing technology. Summary of the invention

[0006] The purpose of the present invention is to provide a method for synthesizing waterborne polyurethane resin by using a prepolymer dispersion method in view of the existing problems.

[0007] The present invention is achieved through the following technical solutions: A method for synthesizing waterborne polyurethane resin by prepolymer dispersion method comprises the following steps: (1) Raw material preparation: Weigh corresponding parts by mass of 30-50 parts of polyester polyol, 18-45 parts of isocyanate, 2.5-3.9 parts of dihydromethylpropionic acid, 8.9-11.9 parts of modified cellulose nanofibers, 4.5-10.5 parts of functionalized nano-silica, 17.3-19.3 parts of neutralizer, 29.1-32.3 parts of chain extender, and 90-150 parts of deionized water for later use; (2) Prepolymerization: At room temperature and pressure, polyester polyol, isocyanate and dihydromethylpropionic acid are pumped into the polyurethane resin reactor according to the process ratio, the stirring device is turned on to stir the materials, and then N-methylpyrrolidone is added to adjust the viscosity; (3) Reflux: Functionalized nano-silica was dispersed in deionized water under ultrasonic conditions, and then modified cellulose nanofibers were added to the dispersion, and stirred at a constant temperature and speed of 45°C and 120rpm for 9 hours, and then added to the prepolymer after filtration, drying and grinding, and refluxed at 70°C for 4 hours; (4) Neutralization reaction: When the isocyanate content reaches the specified value of 2.5%, cool it down to below 50°C, transfer it to a high-speed disperser, and add a neutralizer for neutralization; (5) Dispersion emulsification and chain extension reaction: Add deionized water and stir at high speed to disperse evenly, then use chain extender to extend the chain in water to generate waterborne polyurethane; (6) Finished product packaging: Cooling water is introduced into the jacket to cool the material to 40°C, the nitrogen control valve is opened to introduce nitrogen into the kettle, the bottom valve of the kettle is opened, and the material is pressed into the packaging barrel to be packaged to obtain the finished polyurethane resin.

[0008] Preferably, the polyester polyol is one or a combination of polycaprolactone diol, polytetrahydrofuran diol, and 1,4-butanediol.

[0009] Preferably, the isocyanate is one or a combination of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate.

[0010] Preferably, the neutralizing agent is one of hydrazine hydrate and triethylamine.

[0011] Preferably, the chain extender is one or a combination of ethylenediamine and dimethylolbutyric acid.

[0012] Preferably, the preparation method of the modified cellulose nanofibers is: cellulose nanofibers and anhydrous ethanol are uniformly mixed in a mass ratio of 1:20, ultrasonically dispersed at room temperature for 20 to 40 minutes, then allylmethyldimethoxysilane is added in an amount 0.4 times the mass of the cellulose nanofibers, and ultrasonic dispersion is continued for 5 to 9 minutes, tannic acid aqueous solution is added, ultrasonically vibrated for 8 to 16 minutes, refluxed at 80°C and 300rpm for 10 to 16 hours, filtered, washed with anhydrous ethanol 4 times, and vacuum dried at 60°C for 6 to 9 hours to obtain modified cellulose nanofibers.

[0013] Preferably, the mass concentration of the tannic acid aqueous solution is 13-17 wt %, and the ratio of the tannic acid aqueous solution to the cellulose nanofibers is 1 mL: 0.8-0.9 g.

[0014] Preferably, the preparation method of the functionalized nano-silica is as follows: placing the nano-silica in a normal pressure plasma device, treating it with plasma at 40-60W and 70-80°C for 60-100s under the condition of helium with a carrier gas of 20-30L / min, and then adding it to a reactor with silk fibroin, glycerol and silane coupling agent KH570 after deep cold crushing treatment, reacting at 80-90°C for 7-10h, filtering and performing low-temperature vacuum drying at 30-40°C to obtain the functionalized nano-silica.

[0015] Preferably, the temperature of the deep cold pulverization treatment is -80~-60°C, and the rotation speed of the pulverization treatment is 4000rpm.

[0016] Preferably, the mass ratio of the cryogenically treated silk fibroin to the plasma-treated nano-silica is 1:10-20, the mass ratio of the silane coupling agent KH570 to the plasma-treated nano-silica is 1:8-16, and the mass ratio of the glycerol to the cryogenically crushed silk fibroin is 1:15-23.

[0017] Nano silicon dioxide has a three-dimensional network structure and a large specific surface area, so it shows great activity. Under certain conditions, the alkoxy groups on the surface of nano silicon dioxide will be hydrolyzed into Si-O-Si bonds and form a cross-linked structure. Introducing it into the processing of waterborne polyurethane resin can improve the solvent resistance and mechanical properties of waterborne polyurethane resin. However, nano silicon dioxide is very easy to agglomerate during use, so the improvement effect on the performance of waterborne polyurethane resin is not significant. The present invention first performs plasma treatment on it, and the plasma will produce partial etching on the surface of nano silicon dioxide, and can produce active groups, which lays a good foundation for subsequent reactions. At this time, it is reacted with silk protein, glycerol, and silane coupling agent KH570 after deep cold crushing. On the one hand, the silane coupling agent is modified by -C=C- double bonds, which helps to improve the interaction between organic and inorganic interfaces. On the other hand, through the hydrogen bonding between a large number of hydroxyl groups on the surface of nano SiO2 particles and silk protein, the interaction between macromolecular chains is enhanced, and the mechanical strength of the material is increased. Thereby improving the performance of waterborne polyurethane resin. At the same time, glycerol cooperates with the reaction conditions to increase the β-folding content in the silk fibroin, thereby synergizing with each other to further enhance the mechanical, water resistance, and aging resistance properties of the waterborne polyurethane resin.

[0018] The surface of cellulose nanofibers contains a large number of hydroxyl groups. The surface of cellulose nanofibers is modified with allylmethyldimethoxysilane and tannic acid aqueous solution to obtain modified cellulose nanofibers. The methoxy groups on allylmethyldimethoxysilane react with the hydroxyl groups on the surface of cellulose nanofibers, and allylmethyldimethoxysilane is grafted on the surface of cellulose nanofibers to improve the compatibility of cellulose nanofibers with subsequent nano-silica and other raw material components, improve dispersion, prevent agglomeration, and improve water resistance. Tannic acid (TA) contains a large number of catechol and pyrogallol structures, which are cross-linked with nanocellulose through hydrogen bonds and ionic bonds, reduce viscosity, promote emulsification, and help form a product with stable performance.

[0019] On this basis, the hydroxyl functional groups on the surface of modified cellulose nanofibers are grafted onto functionalized nano-silica to give the water-based polyurethane resin strong water resistance and strong mechanical properties, and can further prevent the agglomeration of nanomaterials, thereby further enhancing the improvement of the performance of water-based polyurethane resin by functionalized nano-silica.

[0020] Compared with the prior art, the present invention has the following advantages: 1. The present invention introduces modified cellulose nanofibers and functionalized nano-silica and synthesizes an aqueous polyurethane resin by combining a prepolymer dispersion method, and prepares a two-component aqueous polyurethane coating with the prepared aqueous polyurethane resin. The coating film has excellent performance in multiple indicators such as hardness, adhesion, impact resistance, and water resistance, and is significantly better than the comparative group and the control group. The pencil hardness and adhesion of Examples 1 to 9 are not much different, the maximum impact resistance is 70 cm in Example 5, the maximum water resistance is 19 d in Example 5, the maximum number of ethanol wiping resistance is 165 times in Example 5, and Example 5 has the best comprehensive performance.

[0021] 2. The liquid protective films made of waterborne polyurethane resin prepared by the methods of Examples 1 to 9 of the present invention have excellent performance in 25 mm peeling force and tear strength. Example 5 with the best comprehensive performance has a certain degree of peelability, indicating that the cohesive force of the film-forming resin is large enough to ensure that the film is not easy to break or remain on the substrate during the peeling process. It can ensure the adhesion of the coating to the substrate and can be easily peeled off when it is needed. It also has good tear strength and has good practical application performance.

[0022] 3. The present invention can effectively improve the comprehensive properties of waterborne polyurethane resin, especially water resistance and mechanical properties, by introducing the prepared modified cellulose nanofibers and functionalized nano-silica, so that the prepared waterborne polyurethane resin can be better applied in the fields of new energy vehicles, intelligent manufacturing, environmentally friendly building materials, etc., greatly improving the use value of the product and helping to extend the service life of the product. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Unless otherwise specified, the raw materials used in the present invention are all conventional products purchased from the market.

[0025] Isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, industrial grade: purchased from Wanhua Chemical; Dihydromethylpropionic acid, dihydroxymethylbutyric acid, analytical grade: purchased from Aladdin; Nano-silicon dioxide: purchased from Taicang Hongxing Chemical Company; Cellulose nanofibers: diameter 20~50nm, length 1~10µm, purchased in Hangzhou Tannic acid, analytical grade: Shanghai Dibai Chemical Technology Co., Ltd. Preparation Example 1 The preparation method of modified cellulose nanofibers is as follows: cellulose nanofibers and anhydrous ethanol are uniformly mixed in a mass ratio of 1:20, ultrasonically dispersed at room temperature for 20 minutes, then allylmethyldimethoxysilane is added in an amount 0.4 times the mass of the cellulose nanofibers, ultrasonic dispersion is continued for 5 minutes, tannic acid aqueous solution with a mass concentration of 13wt% is added, and the ratio of tannic acid aqueous solution to cellulose nanofibers is 1mL:0.8g. After ultrasonic vibration for 8 minutes, reflux reaction is carried out at 80°C and 300rpm for 10 hours, filtered, washed with anhydrous ethanol 4 times, and vacuum dried at 60°C for 6 hours to obtain modified cellulose nanofibers I.

[0026] Preparation Example 2 The preparation method of modified cellulose nanofibers is as follows: cellulose nanofibers and anhydrous ethanol are uniformly mixed in a mass ratio of 1:20, ultrasonically dispersed at room temperature for 30 minutes, then allylmethyldimethoxysilane is added in an amount 0.4 times the mass of the cellulose nanofibers, and ultrasonic dispersion is continued for 7 minutes, and a tannic acid aqueous solution with a mass concentration of 15wt% is added, and the ratio of the tannic acid aqueous solution to the cellulose nanofibers is 1mL:0.85g. After ultrasonic vibration for 12 minutes, reflux reaction is carried out at 80°C and 300rpm for 13 hours, filtered, washed with anhydrous ethanol 4 times, and vacuum dried at 60°C for 7.5 hours to obtain modified cellulose nanofibers II.

[0027] Preparation Example 3 The preparation method of modified cellulose nanofibers is as follows: cellulose nanofibers and anhydrous ethanol are uniformly mixed in a mass ratio of 1:20, ultrasonically dispersed at room temperature for 40 minutes, then allylmethyldimethoxysilane is added in an amount of 0.4 times the mass of the cellulose nanofibers, and ultrasonic dispersion is continued for 9 minutes, and a tannic acid aqueous solution with a mass concentration of 17wt% is added, and the ratio of the tannic acid aqueous solution to the cellulose nanofibers is 1mL:0.9g. After ultrasonic oscillation for 16 minutes, reflux reaction is carried out at 80°C and 300rpm for 16 hours, filtered, washed with anhydrous ethanol 4 times, and vacuum dried at 60°C for 9 hours to obtain modified cellulose nanofibers III.

[0028] Preparation Example 4 The preparation method of the functionalized nano-silica is as follows: placing the nano-silica in a normal pressure plasma device, performing a plasma treatment at 40W and 70°C for 60s under the condition of a helium carrier gas of 20L / min, then adding the silk fibroin, glycerol and silane coupling agent KH570 which have been subjected to a deep-cold crushing treatment at -80°C and 4000rpm into a reaction kettle, reacting at 80°C for 7h and then filtering, and performing a low-temperature vacuum drying treatment at 30°C to obtain the functionalized nano-silica; the mass ratio of the deep-cold-treated silk fibroin to the plasma-treated nano-silica is 1:10, the mass ratio of the silane coupling agent KH570 to the plasma-treated nano-silica is 1:8, and the mass ratio of the glycerol to the deep-cold-cold-crushed silk fibroin is 1:15.

[0029] Preparation Example 5 The preparation method of the functionalized nano-silica is as follows: placing the nano-silica in a normal pressure plasma device, performing a plasma treatment at 50W and 75°C for 80s under the condition of a helium carrier gas of 25L / min, then adding the silk fibroin, glycerol and silane coupling agent KH570 that have been cryogenically crushed at -70°C and 4000rpm into a reaction kettle, reacting at 85°C for 8.5h and then filtering, and performing a low-temperature vacuum drying treatment at 35°C to obtain the functionalized nano-silica; the mass ratio of the silk fibroin that has been cryogenically treated to the nano-silica that has been plasma treated is 1:15, the mass ratio of the silane coupling agent KH570 to the nano-silica that has been plasma treated is 1:12, and the mass ratio of the glycerol to the silk fibroin that has been cryogenically crushed is 1:19.

[0030] Preparation Example 6 The preparation method of the functionalized nano-silica is as follows: placing the nano-silica in a normal pressure plasma device, and subjecting the nano-silica to plasma treatment at 60W and 80°C for 100s under the condition of a carrier gas of 30L / min of helium, then adding the nano-silica to a reactor with silk fibroin, glycerol and silane coupling agent KH570 subjected to deep-cold crushing at -60°C and 4000rpm, reacting at 90°C for 10h, and then filtering, and subjecting the functionalized nano-silica to low-temperature vacuum drying at 40°C; the mass ratio of the deep-cold-treated silk fibroin to the plasma-treated nano-silica is 1:20, the mass ratio of the silane coupling agent KH570 to the plasma-treated nano-silica is 1:16, and the mass ratio of the glycerol to the deep-cold-crushed silk fibroin is 1:23. Example 1

[0031] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 8.9 parts of modified cellulose nanofiber I in Preparation Example 1, 4.5 parts of functionalized nano-silica in Preparation Example 4, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0032] The preparation method comprises the following steps: (1) Raw material preparation: Weigh the raw materials according to the corresponding mass parts for later use; (2) Prepolymerization: At room temperature and pressure, polyester polyol, isocyanate and dihydromethylpropionic acid are pumped into the polyurethane resin reactor according to the process ratio, the stirring device is turned on to stir the materials, and then N-methylpyrrolidone is added to adjust the viscosity; (3) Reflux: Functionalized nano-silica was dispersed in deionized water under ultrasonic conditions, and then modified cellulose nanofibers were added to the dispersion, and stirred at a constant temperature and speed of 45°C and 120rpm for 9 hours, and then added to the prepolymer after filtration, drying and grinding, and refluxed at 70°C for 4 hours; (4) Neutralization reaction: When the isocyanate content reaches the specified value of 2.5%, cool it down to below 50°C, transfer it to a high-speed disperser, and add a neutralizer for neutralization; (5) Dispersion emulsification and chain extension reaction: Add deionized water and stir at high speed to disperse evenly, then use chain extender to extend the chain in water to generate waterborne polyurethane; (6) Finished product packaging: Cooling water is introduced into the jacket to cool the material to 40°C, the nitrogen control valve is opened to introduce nitrogen into the kettle, the bottom valve of the kettle is opened, and the material is pressed into the packaging barrel to be packaged to obtain the finished polyurethane resin. Example 2

[0033] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 8.9 parts of modified cellulose nanofiber I in Preparation Example 1, 4.5 parts of functionalized nano-silica in Preparation Example 5, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0034] The preparation method is the same as Example 1. Example 3

[0035] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 8.9 parts of modified cellulose nanofiber I in Preparation Example 1, 4.5 parts of functionalized nano-silica in Preparation Example 6, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0036] The preparation method is the same as Example 1. Example 4

[0037] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 10.4 parts of modified cellulose nanofiber II in Preparation Example 2, 7.5 parts of functionalized nano-silica in Preparation Example 4, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0038] The preparation method is the same as Example 1. Example 5

[0039] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 10.4 parts of modified cellulose nanofiber II in Preparation Example 2, 7.5 parts of functionalized nano-silica in Preparation Example 5, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0040] The preparation method is the same as Example 1. Example 6

[0041] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 10.4 parts of modified cellulose nanofiber II in Preparation Example 2, 7.5 parts of functionalized nano-silica in Preparation Example 6, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0042] The preparation method is the same as Example 1. Example 7

[0043] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 11.9 parts of modified cellulose nanofiber III in Preparation Example 2, 10.5 parts of functionalized nano-silica in Preparation Example 4, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0044] The preparation method is the same as Example 1. Example 8

[0045] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 11.9 parts of modified cellulose nanofiber III in Preparation Example 2, 10.5 parts of functionalized nano-silica in Preparation Example 5, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0046] The preparation method is the same as Example 1. Example 9

[0047] A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 11.9 parts of modified cellulose nanofiber III in Preparation Example 2, 10.5 parts of functionalized nano-silica in Preparation Example 6, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0048] The preparation method is the same as Example 1.

[0049] Comparative Example 1 A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 0 parts of modified cellulose nanofiber II in Preparation Example 2, 7.5 parts of functionalized nano-silica in Preparation Example 5, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0050] The preparation method comprises the following steps: (1) Raw material preparation: Weigh the raw materials according to the corresponding mass parts for later use; (2) Prepolymerization: At room temperature and pressure, polyester polyol, isocyanate and dihydromethylpropionic acid are pumped into the polyurethane resin reactor according to the process ratio, the stirring device is turned on to stir the materials, and then N-methylpyrrolidone is added to adjust the viscosity; (3) Reflux: Functionalized nano-silica was added to the prepolymer and refluxed at 70°C for 4 h; (4) Neutralization reaction: When the isocyanate content reaches the specified value of 2.5%, cool it down to below 50°C, transfer it to a high-speed disperser, and add a neutralizer for neutralization; (5) Dispersion emulsification and chain extension reaction: Add deionized water and stir at high speed to disperse evenly, then use chain extender to extend the chain in water to generate waterborne polyurethane; (6) Finished product packaging: Cooling water is introduced into the jacket to cool the material to 40°C, the nitrogen control valve is opened to introduce nitrogen into the kettle, the bottom valve of the kettle is opened, and the material is pressed into the packaging barrel to be packaged to obtain the finished polyurethane resin.

[0051] Comparative Example 2 A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 10.4 parts of modified cellulose nanofiber II in Preparation Example 2, 0 parts of functionalized nanosilica in Preparation Example 5, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid, and 120 parts of deionized water.

[0052] The preparation method comprises the following steps: (1) Raw material preparation: Weigh the raw materials according to the corresponding mass parts for later use; (2) Prepolymerization: At room temperature and pressure, polyester polyol, isocyanate and dihydromethylpropionic acid are pumped into the polyurethane resin reactor according to the process ratio, the stirring device is turned on to stir the materials, and then N-methylpyrrolidone is added to adjust the viscosity; (3) Reflux: The modified cellulose nanofibers were added to the prepolymer and refluxed at 70°C for 4 h; (4) Neutralization reaction: When the isocyanate content reaches the specified value of 2.5%, cool it down to below 50°C, transfer it to a high-speed disperser, and add a neutralizer for neutralization; (5) Dispersion emulsification and chain extension reaction: Add deionized water and stir at high speed to disperse evenly, then use chain extender to extend the chain in water to generate waterborne polyurethane; (6) Finished product packaging: Cooling water is introduced into the jacket to cool the material to 40°C, the nitrogen control valve is opened to introduce nitrogen into the kettle, the bottom valve of the kettle is opened, and the material is pressed into the packaging barrel to be packaged to obtain the finished polyurethane resin.

[0053] Comparative Example 3 A waterborne polyurethane resin synthesized by a prepolymer dispersion method comprises 10 parts of polycaprolactone diol, 30 parts of polytetramethylene glycol, 14 parts of isophorone diisocyanate, 17 parts of 4,4'-dicyclohexylmethane diisocyanate, 3.2 parts of dihydromethylpropionic acid, 18.3 parts of hydrazine hydrate, 15 parts of ethylenediamine, 15.6 parts of dihydroxymethylbutyric acid and 120 parts of deionized water.

[0054] The preparation method comprises the following steps: (1) Raw material preparation: Weigh the raw materials according to the corresponding mass parts for later use; (2) Prepolymerization: At room temperature and pressure, polyester polyol, isocyanate and dihydromethylpropionic acid are pumped into the polyurethane resin reactor according to the process ratio, the stirring device is turned on to stir the materials, and then N-methylpyrrolidone is added to adjust the viscosity; (3) Reflux: Reflux reaction at 70°C for 4 h; (4) Neutralization reaction: When the isocyanate content reaches the specified value of 2.5%, cool it down to below 50°C, transfer it to a high-speed disperser, and add a neutralizer for neutralization; (5) Dispersion emulsification and chain extension reaction: Add deionized water and stir at high speed to disperse evenly, then use chain extender to extend the chain in water to generate waterborne polyurethane; (6) Finished product packaging: Cooling water is introduced into the jacket to cool the material to 40°C, the nitrogen control valve is opened to introduce nitrogen into the kettle, the bottom valve of the kettle is opened, and the material is pressed into the packaging barrel to be packaged to obtain the finished polyurethane resin.

[0055] Control group Publication No. CN 110746571 B discloses an APAO-modified polyurethane water-based resin and a preparation method thereof, and sample 1 in a specific implementation manner.

[0056] 1. Material coating performance index test The above-mentioned Examples 1 to 5 and Comparative Examples 1 to 3 were prepared into waterborne polyurethane resin samples according to the corresponding preparation methods, and the sample 1 of the control group was mixed with a waterborne isocyanate curing agent, and a two-component waterborne polyurethane coating was prepared with a substance molar ratio of n(NCO):n(OH)=1.4:1. The corresponding coating samples were recorded as Examples 1 to 5, Comparative Examples 1 to 3 and the control group. The prepared coating was applied to the polished substrate surface by spraying, and then allowed to stand at 25°C for 24 hours. After the coating was completely dried, the performance test could be carried out.

[0057] The test methods and results are shown in Table 1 below: Table 1 Pencil hardness Adhesion / Grade Impact resistance / cm Water resistance (25℃ deionized water) / d Ethanol wiping resistance / times standard GB / T 6739—2022 GB / T 9286—2021 GB / T 1732—2020 GB / T 1733—1993 GB / T 23989—2009 Example 1 2H 1 53 14 149 Example 2 2H 1 65 16 159 Example 3 3H 1 68 17 161 Example 4 3H 1 62 18 162 Example 5 3H 1 70 19 165 Example 6 3H 1 62 16 154 Example 7 3H 1 64 17 158 Example 8 3H 1 66 15 161 Example 9 2H 1 58 13 152 Comparative Example 1 H 3 33 10 141 Comparative Example 2 2H 2 45 12 146 Comparative Example 3 H 5 25 7 127 Control group H 4 40 8 132 As can be seen from Table 1 above, the two-component waterborne polyurethane coatings made of the waterborne polyurethane resins prepared by the methods of Examples 1 to 9 of the present invention have excellent performance in multiple indicators such as hardness, adhesion, impact resistance, and water resistance of the coating films, and are significantly better than the comparative group and the control group. The pencil hardness and adhesion of Examples 1 to 9 are not much different, the maximum impact resistance is 70 cm in Example 5, the maximum water resistance is 19 d in Example 5, the maximum number of ethanol wiping resistance is 165 times in Example 5, and Example 5 has the best comprehensive performance.

[0058] 2. Performance test of resin body protection film The above Examples 1-5 and Comparative Examples 1-3 were prepared into waterborne polyurethane resin samples according to the corresponding preparation methods, and Sample 1 of the control group was respectively prepared into liquid protective films together with a defoamer, a thickener, a preservative, a wetting dispersant, and a wax emulsion.

[0059] Note that the raw material composition ratios and methods for preparing the protective films in the above different embodiments are the same.

[0060] 2.1 Peelability Take an appropriate amount of the liquid protective film and spray it on the 170mm×120mm car paint surface. Leave it at room temperature for 24 hours. The protective film can be peeled off smoothly by hand or with a high-pressure water gun specially used for car washing.

[0061] 2.2 Breaking strength and elongation at break The breaking strength (≥18MPa) and elongation at break (≥450%) of liquid protective film directly affect the peelability and peeling integrity of the film layer. They are the most important indicators of liquid protective film performance and are measured according to GB / T528-1998.

[0062] The performance test results are shown in Table 2 below.

[0063] Table 2 25mm peeling force / N Breaking strength / MPa Example 1 1.7 17.2 Example 2 1.5 18.6 Example 3 1.3 19.2 Example 4 1.2 18.9 Example 5 1.0 20.3 Example 6 0.8 20.1 Example 7 0.9 19.3 Example 8 1.0 19.1 Example 9 1.3 18.6 Comparative Example 1 2.6 18.0 Comparative Example 2 2.0 18.3 Comparative Example 3 5.0 17.2 Control group 4.3 14.6 As can be seen from Table 2, the liquid protective films made of waterborne polyurethane resin prepared by the methods of Examples 1 to 9 of the present invention have excellent performance in 25 mm peeling force and tear strength. Example 5 with the best comprehensive performance has a certain degree of peelability, indicating that the cohesive force of the film-forming resin is large enough to ensure that the film is not easy to break or remain on the substrate during the peeling process, which can ensure the adhesion of the coating film to the substrate and can be easily peeled off when peeling is required, and has good tear strength and has good practical application performance.

[0064] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for synthesizing an aqueous polyurethane resin by a prepolymer dispersion method, characterized in that: The steps include: (1) Raw material preparation: Weigh corresponding parts by mass of 30-50 parts of polyester polyol, 18-45 parts of isocyanate, 2.5-3.9 parts of dihydromethylpropionic acid, 8.9-11.9 parts of modified cellulose nanofibers, 4.5-10.5 parts of functionalized nano-silica, 17.3-19.3 parts of neutralizer, 29.1-32.3 parts of chain extender, and 90-150 parts of deionized water for later use; (2) Prepolymerization: At room temperature and pressure, polyester polyol, isocyanate and dihydromethylpropionic acid are pumped into the polyurethane resin reactor according to the process ratio, the stirring device is turned on to stir the materials, and then N-methylpyrrolidone is added to adjust the viscosity; (3) Reflux: Functionalized nano-silica was dispersed in deionized water under ultrasonic conditions, and then modified cellulose nanofibers were added to the dispersion, and stirred at a constant temperature and speed of 45°C and 120rpm for 9 hours, and then added to the prepolymer after filtration, drying and grinding, and refluxed at 70°C for 4 hours; (4) Neutralization reaction: When the isocyanate content reaches the specified value of 2.5%, cool it down to below 50°C, transfer it to a high-speed disperser, and add a neutralizer for neutralization; (5) Dispersion emulsification and chain extension reaction: Add deionized water and stir at high speed to disperse evenly, then use chain extender to extend the chain in water to generate waterborne polyurethane; (6) Finished product packaging: Cooling water is introduced into the jacket to cool the material to 40°C, the nitrogen control valve is opened to introduce nitrogen into the kettle, the bottom valve of the kettle is opened, and the material is pressed into the packaging barrel to be packaged to obtain the finished polyurethane resin.

2. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 1, characterized in that: The polyester polyol is one or a combination of polycaprolactone diol, polytetrahydrofuran diol, and 1,4-butanediol.

3. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 1, characterized in that: The isocyanate is one or a combination of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate.

4. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 1, characterized in that: The neutralizing agent is one of hydrazine hydrate and triethylamine.

5. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 1, characterized in that: The chain extender is one or a combination of ethylenediamine and dimethylolbutyric acid.

6. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 1, characterized in that: The preparation method of the modified cellulose nanofiber is as follows: cellulose nanofiber and anhydrous ethanol are uniformly mixed in a mass ratio of 1:20, ultrasonically dispersed at room temperature for 20-40 minutes, then allylmethyldimethoxysilane is added in an amount of 0.4 times the mass of the cellulose nanofiber, ultrasonically dispersed for 5-9 minutes, tannic acid aqueous solution is added, ultrasonically vibrated for 8-16 minutes, refluxed at 80° C. and 300 rpm for 10-16 hours, filtered, washed with anhydrous ethanol for 4 times, and vacuum dried at 60° C. for 6-9 hours to obtain the modified cellulose nanofiber.

7. A method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 6, characterized in that: The mass concentration of the tannic acid aqueous solution is 13-17 wt %, and the ratio of the tannic acid aqueous solution to the cellulose nanofibers is 1 mL: 0.8-0.9 g.

8. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 1, characterized in that: The preparation method of the functionalized nano-silica comprises the following steps: placing the nano-silica in a normal pressure plasma device, subjecting the nano-silica to plasma treatment at 40-60W and 70-80°C for 60-100s under the condition of a helium carrier gas of 20-30L / min, then adding the nano-silica and the silk fibroin, glycerol and silane coupling agent KH570 subjected to deep cold pulverization treatment into a reaction kettle, reacting at 80-90°C for 7-10h, filtering and performing low-temperature vacuum drying at 30-40°C to obtain the functionalized nano-silica.

9. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 8, characterized in that: The temperature of the deep cold pulverization treatment is -80~-60°C, and the rotation speed of the pulverization treatment is 4000rpm.

10. The method for synthesizing waterborne polyurethane resin by prepolymer dispersion method according to claim 8, characterized in that: The mass ratio of the deep-cryogenic silk fibroin to the plasma-treated nano-silica is 1:10-20, the mass ratio of the silane coupling agent KH570 to the plasma-treated nano-silica is 1:8-16, and the mass ratio of the glycerol to the deep-cryogenic pulverization silk fibroin is 1:15-23.