Preparation process of waterborne polyurethane resin

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a preparation process of waterborne polyurethane resin. According to the invention, by adopting a process of reducing the viscosity of the polyurethane resin by adopting supercritical gas and then emulsifying, the preparation of the waterborne polyurethane resin without auxiliary emulsification of an organic solvent is realized, the emulsification time is remarkably shortened, the energy consumption is reduced, and the emulsion with small particle size, high stability and no emulsifier residue is obtained; the matched synthesis device is reasonable in structural design, integrates the functions of reaction, stirring, heating, supercritical fluid generation and accurate conveying, proportional feeding, static mixing, circulating reflux and the like, can realize efficient circulation and uniform mixing of supercritical COs and a resin system, supports continuous and automatic production, is beneficial to improving the production efficiency and the product quality consistency, and is suitable for industrial production. And the method is suitable for industrial popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a preparation process of a waterborne polyurethane resin. Background Art

[0002] Waterborne polyurethane (WPU) is a new type of polyurethane resin that uses water as the dispersion medium instead of organic solvents. It is also known as water-dispersible polyurethane, water-based polyurethane, or water-based polyurethane. Since the 1980s, advancements in synthesis technology have led to continuous improvements in the performance of WPU, prompting its rapid development. Applications include coatings, adhesives, leather, textiles, paper, plastics, and rubber. Since the beginning of the 21st century, the growing global demand for environmental protection has further accelerated the development of the WPU industry.

[0003] The development of waterborne polyurethane preparation technology has gone through the process of external emulsification to internal emulsification. The external emulsification method is to evenly disperse the PU molecules in water through the action of strong shear force by adding an external emulsifier. Because the external emulsification process requires a long and strong emulsification process, and the obtained waterborne polyurethane emulsion has a large particle size and poor stability, and the emulsion also contains residual externally added emulsifiers, which affects the final polyurethane performance, the external emulsification method is not currently the mainstream method for the industrial preparation of waterborne polyurethane emulsions. The self-emulsification method refers to the process of polyurethane synthesis, in which hydrophilic groups are added to the chain segments, so that the polymer can self-disperse to form an emulsion. The emulsion formed has a smaller particle size and narrower distribution than the emulsion prepared by the external emulsification method, and the formed film has excellent performance. It is currently the most commonly used preparation method. According to the type of hydrophilic group, self-emulsifying waterborne polyurethane can be divided into anionic, cationic and non-ionic waterborne polyurethanes.

[0004] Due to the high viscosity of the polyurethane reaction system during the preparation process, in order to reduce the difficulty of emulsification and obtain a smaller emulsion particle size and good emulsion stability of waterborne polyurethane, the use of low-viscosity, low-boiling point solvents such as acetone during the resin synthesis and emulsification process is currently the main method for producing waterborne polyurethane. The obtained waterborne resin needs to be removed from the organic solvent before it can be produced as a finished product. However, waterborne polyurethane resins on the market basically contain trace amounts of organic solvents. For example, Chinese patent CN104910342B discloses a method for preparing waterborne polyurethane, which comprises the following steps: first, adding a diisocyanate and a chain extender to a polyether diol or / and a polyester diol, stirring and reacting at 70-80°C for 1-4 hours, cooling to 30-40°C, adding a neutralizing agent for neutralization, and adjusting the viscosity with acetone to obtain a prepolymer; second, adding distilled water to the prepolymer, stirring and emulsifying and dispersing, adding a sulfonic acid chain extender, stirring and reacting for 0.5-4 hours, and distilling under reduced pressure to remove the acetone to obtain the waterborne polyurethane. However, due to equipment and process limitations, waterborne polyurethanes emulsified with acetone to adjust viscosity still retain residual acetone after the solvent removal process. While the content is generally less than 0.5%, it can still affect the polyurethane's performance. Furthermore, with increasing environmental regulations, achieving zero-VOC waterborne polyurethane resins through organic solvent-free emulsification has become a major challenge in the preparation of waterborne polyurethane resins.

[0005] Therefore, the present invention provides a preparation process for a water-based polyurethane resin without organic solvent-assisted emulsification, which uses supercritical gas to reduce the viscosity of the polyurethane resin and then emulsifies the low-viscosity polyurethane resin, in order to solve the above technical problems. Summary of the Invention

[0006] In response to the aforementioned problems in the prior art, the present invention aims to provide a process for preparing a waterborne polyurethane resin. By employing a process in which supercritical gas is used to reduce the viscosity of the polyurethane resin prior to emulsification, the present invention achieves the preparation of a waterborne polyurethane resin without the aid of organic solvent-assisted emulsification. This significantly shortens the emulsification time and reduces energy consumption, resulting in an emulsion with small particle size, high stability, and no emulsifier residue. The accompanying synthesis device is rationally designed, integrating functions such as reaction, stirring, heating, supercritical fluid generation and precise delivery, proportional feeding, static mixing, and recirculation. This enables efficient and uniform mixing of supercritical CO2 with the resin system, supporting continuous and automated production, improving production efficiency and product quality consistency, reducing environmental impact, and making it suitable for industrial application.

[0007] In order to solve the above problems, the technical solutions adopted by the present invention are as follows: A preparation process of a waterborne polyurethane resin comprises the following steps: Put the polyol and the hydrophilic chain extender into the reactor, add the catalyst, add the isocyanate dropwise under nitrogen protection, and react at 60-80°C until the NCO content reaches a preset value; then introduce carbon dioxide gas and nitrogen gas, control the pressure at 7.5-8.5 MPa, maintain the reaction temperature and pressure, and react for 0.5-4 hours under stirring; continue to maintain the pressure in the reactor, lower the reaction temperature to 40-60°C, and introduce water or an aqueous solution of a salt-forming agent to simultaneously perform shear emulsification; then reduce the temperature and pressure, and continue shear emulsification to obtain a zero-VOC waterborne polyurethane resin without organic solvent-assisted emulsification; The preparation process is applicable to the preparation of anionic, cationic and nonionic waterborne polyurethanes.

[0008] Furthermore, the amount of carbon dioxide used is 5-50 wt% of the amount of polyurethane resin in the reactor; the preferred amount is 10-30 wt%; and nitrogen is supplemented to ensure that the reactor pressure reaches the set value (7.5-8.5 MPa). Before the introduction of carbon dioxide and nitrogen, the reaction time is 1-3 hours, and after the introduction of carbon dioxide and nitrogen, the reaction time is continued for 0.5-4 hours.

[0009] Furthermore, it also includes a chain extension reaction, which includes the following steps: cooling the reaction system of the water-based polyurethane resin without organic solvent-assisted emulsification to 5-15°C, adding an aqueous solution of an amine chain extender, and continuing the shear emulsification reaction for 1-3 hours to obtain the chain-extended water-based polyurethane resin without organic solvent-assisted emulsification.

[0010] Furthermore, the amine chain extender includes one or more of ethylenediamine, butanediamine, hexamethylenediamine or isophoronediamine.

[0011] Further, the following steps are included: Put polyol and hydrophilic chain extender into a reactor, add a catalyst, add isocyanate dropwise under nitrogen protection, and react at 60-80°C until the NCO content reaches a preset value; then add diol chain extender dropwise and react for 0.5-1h; then introduce carbon dioxide gas and nitrogen, control the pressure at 7.5-8.5MPa, maintain the reaction temperature and pressure, and react for 0.5-4h under stirring; continue to maintain the pressure of the reactor, reduce the reaction temperature to 40-60°C, and introduce water or an aqueous solution of a salt-forming agent within 0.5h, and shear emulsify for 0.5-1h; then reduce the temperature and pressure, and continue shear emulsification for 0.5-2h to obtain a waterborne polyurethane resin without organic solvent-assisted emulsification.

[0012] Furthermore, the diol chain extender includes one or more of ethylene glycol, diethylene glycol, 1,4-butanediol or 1,6-hexanediol.

[0013] Furthermore, the polyol includes one or more of polytetramethylene glycol ether, polypropylene glycol ether, polyadipate polyester, polycaprolactone, and polycarbonate; The isocyanate includes one or more of diphenylmethane diisocyanate MDI, toluene diisocyanate TDI, hexamethylene diisocyanate HDI, isophorone diisocyanate IPDI, and 4,4-diisocyanate dicyclohexylmethane HMDI; The catalyst is an organic tin catalyst; preferably stannous octoate or dibutyltin dilaurate.

[0014] Furthermore, the hydrophilic chain extender of the anionic waterborne polyurethane includes one or more of dimethylol propionic acid, dimethylol butyric acid, 1,2-propylene glycol-3-sulfonate sodium, 1,4-butanediol-2-sulfonate sodium, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonate sodium, and 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt; The anionic waterborne polyurethane salt-forming agent includes one or more of triethylamine, NaOH, KOH, Cs2CO3, and K2CO3.

[0015] Furthermore, the cationic waterborne polyurethane hydrophilic chain extender includes one or more of diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-propyldiethanolamine, N-benzyldiethanolamine, tert-butyldiethanolamine, dimethylethanolamine, bis(2-hydroxyethyl)benzylaniline and bis(2-hydroxypropyl)aniline; The salt-forming agent of the cationic waterborne polyurethane includes one or more of formic acid, glycolic acid, acetic anhydride and glacial acetic acid.

[0016] Furthermore, the polyol of the non-ionic waterborne polyurethane is one or more of polyethylene glycol, trimethylolpropane polyethylene glycol monomethyl ether, or a copolyether containing an ethylene oxide segment.

[0017] Preferably, the present invention provides a synthesis device for preparing waterborne polyurethane resin, comprising: Reactor, stirring device, feeding port, heating device, pressure gauge, thermometer, emulsifying device, discharge port, first control valve, delivery pump, first three-way valve, proportional feeder, static mixer, feed port, gas cylinder, second control valve, supercritical CO2 generator, check valve, water storage tank, third control valve, booster delivery pump, water inlet, air outlet, second three-way valve, exhaust port, nitrogen cylinder, emulsion collection device; The reactor is provided with a stirring device; a feeding port is provided on the top of the reactor; a pressure gauge and a thermometer are also provided on the top of the reactor; a heating device is provided on the side wall of the reactor; and an emulsifying device is provided at the bottom of the reactor; The reaction kettle is connected in sequence with the discharge port, the first control valve, the conveying pump, the first three-way valve, the proportional feeder, the static mixer and the feed port to form a closed loop; one side of the first three-way valve is used for connecting an emulsion collecting device; The supercritical CO2 generating device is communicated with the proportional feeder through the check valve, and is communicated with the gas cylinder through the second control valve; The water inlet of the reaction kettle is connected with the water storage tank through the booster conveying pump and the third control valve; The gas outlet of the reaction kettle is communicated with the exhaust port and the nitrogen cylinder respectively through the second three-way valve.

[0018] Preferably, the preparation process comprises the following steps: Step (1) synthesis of resin or prepolymer: a metered polyol and a hydrophilic chain extender are put into the reaction kettle through the feed port, an appropriate amount of organotin catalyst is added, the second three-way valve is opened to introduce nitrogen, and isocyanate is gradually added dropwise under nitrogen protection, and the reaction is carried out at 60-80℃ for 1-3.5h until the NCO content reaches the preset value. If necessary, continue to add a dihydric alcohol chain extender dropwise at this temperature for 0.5-1h.

[0019] Step (2) supercritical CO2 viscosity reduction: when the viscosity of the reaction system rises, a certain amount of carbon dioxide gas is first introduced, and nitrogen is introduced at the same time to ensure that the pressure of the reaction kettle reaches 7.5-8.5MPa. The specific operation is to open the first control valve and start the conveying pump, and when the material starts to circulate, the supercritical CO2 generating device is opened to mix the supercritical CO2 with the reaction material through the static mixer. After inputting the metered CO2, the gas cylinder is replaced with a nitrogen steel cylinder, and nitrogen is supplemented to ensure that the pressure of the reaction system reaches 7.5-8.5MPa. Continue to circulate and stir for 1.5-4h at the reaction temperature and this pressure.

[0020] Step (3) emulsification of waterborne polyurethane: maintain the pressure of the reaction kettle above 7.4MPa, reduce the temperature of the reaction material to 40-60℃, open the booster conveying pump and input the aqueous solution containing a salt-forming agent (if necessary) within 0.5h, open the emulsification pump in the reaction kettle for high-speed shearing emulsification for 0.5-1h, and continue to open the conveying pump until the preparation is completed.

[0021] Step (4) CO2 removal: after the input of the aqueous solution is completed, the second three-way valve is opened to release pressure, and high-speed shearing emulsification is continued for 0.5-2h, while the reaction system is cooled to 25℃.

[0022] Step (5) amine chain extension of waterborne polyurethane: if it is necessary to continue to chain extend the waterborne polyurethane, the reaction system needs to be cooled to 5-15℃, the aqueous solution of amine chain extender is conveyed through the booster conveying pump, and the circulation and shearing emulsification reaction is continued for 1-3h.

[0023] After completing the above preparation process, the first three-way valve is switched to obtain an organic solvent-free emulsified (chain-extended) waterborne polyurethane resin.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation process of the waterborne polyurethane resin provided by the present invention reduces the viscosity of the polyurethane resin by supercritical gas before emulsification, thereby realizing the preparation of the waterborne polyurethane resin without organic solvent-assisted emulsification, significantly shortening the emulsification time, reducing energy consumption, and obtaining a waterborne polyurethane emulsion with small particle size, narrow particle size distribution, high stability, and no emulsifier residue, thereby improving the performance of the final product.

[0025] (2) The synthesis device of the present invention has a reasonable structural design and integrates multifunctional modules such as a reactor, stirring, heating, supercritical CO2 generation and precise delivery, proportional feeding, static mixing and circulation reflux. It can achieve efficient circulation and uniform mixing of supercritical CO2 and polyurethane prepolymer, significantly reduce the viscosity of the resin system, and facilitate the subsequent emulsification process. Moreover, through this device, emulsification can be achieved in a short time under mild conditions without the need for additional organic solvents or high-concentration emulsifiers, avoiding the problem of emulsifier residue, and obtaining a water-based polyurethane emulsion with a narrow particle size distribution and good stability. The device also supports continuous and automated operation, facilitating precise control of process parameters and large-scale production, thereby improving production efficiency, reducing energy consumption, and ensuring product quality consistency and environmental performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a synthesis device for preparing waterborne polyurethane resin provided by the present invention; In the figure: reactor 1, stirring device 2, feeding port 3, heating device 4, pressure gauge 5, thermometer 6, emulsifying device 7, discharge port 8, first control valve 9, delivery pump 10, first three-way valve 11, proportional feeder 12, static mixer 13, feed port 14, gas cylinder 15, second control valve 16, supercritical CO2 generating device 17, check valve 18, water storage tank 19, third control valve 20, booster delivery pump 21, water inlet 22, air outlet 23, second three-way valve 24, exhaust port 25, nitrogen cylinder 26, emulsion collecting device 27.

[0027] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, the synthesis device for preparing waterborne polyurethane resin provided by the present invention includes a reactor 1, wherein the reactor 1 is provided with a stirring device 2 for stirring the reaction materials; a feeding port 3 is provided on the top of the reactor 1 for adding raw materials into the reactor 1, and the feeding port 3 can be connected to an external storage tank or pipeline. The reactor 1 is also provided with a pressure gauge 5 and a thermometer 6 for monitoring the temperature and pressure in the reactor. A heating device 4 is provided on the side wall of the reactor 1 for heating the materials in the reactor to ensure the temperature conditions required for the reaction. An emulsifying device 7 is provided at the bottom of the reactor 1 for improving the emulsification efficiency. The reactor 1 is also provided with a discharge port 8, and a first control valve 9 is provided on the discharge port 8 for controlling the discharge of the reaction liquid.

[0030] The discharge port 8 of the reactor 1 is connected to a delivery pump 10 via a first control valve 9. The outlet of the delivery pump 10 is connected to a proportional feeder 12 via a first three-way valve 11. The proportional feeder 12 is used to accurately measure and deliver materials. The outlet of the proportional feeder 12 is connected to a static mixer 13, which is used to thoroughly mix the reaction liquid with the supercritical CO2 fluid. The reactor 1 is also provided with a feed port 14, which is connected to the outlet of the static mixer 13 and is used to reflux the mixture into the reactor 1. That is, the reactor 1 forms a loop connection through the discharge port 8, the first control valve 9, the delivery pump 10, the first three-way valve 11, the proportional feeder 12, the static mixer 13, and the feed port 14.

[0031] The apparatus further includes a supercritical CO2 generator 17 for generating supercritical CO2 fluid. The supercritical CO2 generator 17 is connected to a second control valve 16 and a gas cylinder 15 via a pipeline. The supercritical CO2 fluid is delivered to the inlet of the proportional feeder 12 through a check valve 18, where it merges with the reaction liquid flow and enters the static mixer 13, achieving efficient cyclic mixing of the supercritical CO2 and the reaction liquid.

[0032] In addition, the reactor 1 is provided with a water inlet 22, which is connected to the water storage tank 19 through a pipeline. The water storage tank 19 is connected to the booster delivery pump 21 through the third control valve 20 to achieve quantitative delivery of the water phase.

[0033] An air outlet 23 is provided on the upper portion of the reactor 1, and the air outlet 23 is connected to an exhaust port 25 and a nitrogen bottle 26 through a second three-way valve 24, so that gas replacement or exhaust operation can be performed to ensure the safety and stability of the reaction atmosphere.

[0034] The final synthesized emulsion resin is discharged from the discharge port 8 through the delivery pump 10 and the first three-way valve 11 and then collected in the emulsion collection device 27.

[0035] Example 1 80 kg of polytetramethylene ether glycol (PTMEG1000) with a molecular weight of 1000 g / mol and 80 kg of polytetramethylene ether glycol (PTMEG 2000) with a molecular weight of 2000 g / mol were added to reactor 1 through feed port 3, and 0.1 kg of dibutyltin dilaurate was added. Under nitrogen protection, a mixture of 40 kg of isophorone diisocyanate (IPDI) and 80 kg of 4,4-diisocyanatodicyclohexylmethane (HMDI) was added dropwise to reactor 1. The temperature was raised to 75°C and stirred for reaction for 2 h. The temperature was raised to 80°C and 64 kg of polyethylene glycol with a molecular weight of 1000 g / mol was added and reacted for 1 h. 40 kg of trimethylolpropane polyethylene glycol monomethyl ether (mPEG) with a molecular weight of 420 g / mol and 2 kg of 1,4-butanediol (BDO) were added. While adding trimethylolpropane polyethylene glycol monomethyl ether and 1,4-butanediol, supercritical CO2 generator 17 was activated. The supercritical CO2 was mixed with the reaction materials through static mixer 13 and circulated through transfer pump 10. 42 kg of carbon dioxide was used, and nitrogen was introduced to pressurize reactor 1 to 7.8 MPa. At this pressure, the reaction temperature was maintained at 80°C and the reaction was allowed to proceed for 1.5 hours.

[0036] Lower the temperature of reactor 1 to 45°C, observe the pressure of reactor 1, and if necessary, add nitrogen to maintain the pressure of reactor 1 above 7.4 MPa.

[0037] At this temperature, 560 kg of deionized water was fed into the reactor 1 via the booster pump 21. Simultaneously, the emulsifier 7 was turned on, and the material was kept circulating under high-speed shear emulsification for 0.5 h. After the deionized water was fed, the second three-way valve 24 was switched to release pressure to maintain the reactor 1 at normal pressure.

[0038] The temperature of the raw materials in Reactor 1 was lowered to 15°C. At this temperature, 8 kg of an aqueous solution containing 30% ethylenediamine (EDA) was continuously fed into Reactor 1. High-speed shear emulsification was continued for 1.5 hours in a circulating state. After completion of the high-speed shear emulsification, a nonionic waterborne polyurethane resin with a solids content of 40% was obtained.

[0039] Example 2 100 kg of 2000 g / mol polybutylene adipate (PBA2000) and 4.2 kg of dimethylolpropionic acid (DMPA) were added to reactor 1 through feed port 3. 0.1 kg of stannous octoate was added, and nitrogen was introduced. The temperature was raised to 65°C, and 12.23 kg of toluene diisocyanate (TDI) was added dropwise to reactor 1. The reaction was stirred for 1.5 hours. 0.25 kg of 1,4-butanediol was added to reactor 1, and 24 kg of carbon dioxide was introduced into reactor 1 by supercritical CO2 generator 17. The reaction was continued at 65°C for 2 hours with material circulation. The pressure in reactor 1 was monitored and nitrogen was introduced as needed to ensure a pressure of 7.8-8.2 MPa.

[0040] Dissolve 1.35 kg of triethylamine (TEA) in 176 kg of deionized water. Lower the temperature of reactor 1 to 30°C, then add the deionized water containing the triethylamine. Operate high-speed shear emulsification device 7 with material circulation. Circulate the material and perform shear emulsification for 0.5 h. Then, release the pressure by opening the second three-way valve 24 of reactor 1. Continue high-speed shear emulsification for 1 h to obtain an anionic waterborne polyurethane resin with a solids content of 40%.

[0041] Example 3 160 kg of 2000 g / mol polytetramethylene glycol (PTMEG) and 8.9 kg of dimethylol propionic acid (DMPA) were placed in reactor 1. 0.12 kg of stannous octoate was added, and nitrogen was introduced. The temperature was raised to 75°C, and 45.6 kg of isophorone diisocyanate (IPDI) was added dropwise to reactor 1. The reaction was stirred for 2.5 hours. At this reaction temperature, 30 kg of carbon dioxide was introduced into reactor 1, along with nitrogen to ensure a pressure of 7.8 MPa. The reaction was continued with stirring for 0.5 hours with material circulation.

[0042] Maintaining material circulation, dissolve 2.4 kg of triethylamine in 289 kg of deionized water. Lower the temperature of reactor 1 to 42°C, add the deionized water containing the triethylamine, and simultaneously activate high-speed shear emulsification device 7. Shear emulsification is performed for 0.5 h. Then, the second three-way valve 24 of reactor 1 is opened to release pressure, and the temperature of reactor 1 is lowered to 25°C. High-speed shear emulsification is continued for 1.5 h.

[0043] The temperature of the material in reactor 1 was further lowered to 8°C, and 4 kg of a deionized water solution containing 30% ethylenediamine (EDA) was added. High-speed shear emulsification was continued for 2 hours with material circulation. This yielded an anionic waterborne polyurethane resin with a solids content of 42%.

[0044] Example 4 Place 160 kg of 2000 g / mol polypropylene glycol ether (PPG) and 3.67 kg of sodium N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonate (BES-Na) into reactor 1. Add 0.1 kg of dibutyltin dilaurate. Under nitrogen protection, raise the temperature to 80°C. Add 37 kg of isophorone diisocyanate (IPDI) dropwise to reactor 1, stirring for 2.5 hours. At this reaction temperature, start pump 10 and, while circulating the material, introduce 30 kg of carbon dioxide into reactor 1. Simultaneously, purify the nitrogen atmosphere to ensure a pressure of 7.8 MPa. Continue stirring for 0.5 hours.

[0045] Keep the material circulating, lower the temperature of reactor 1 to 55°C, add 310kg of deionized water, and start the high-speed shear emulsification device 7 for 0.5h. Then open the second three-way valve 24 to release the pressure to ensure that the pressure of reactor 1 is at normal pressure.

[0046] The temperature of the material in reactor 1 was lowered to 5°C, and 4 kg of a deionized water solution containing 30% ethylenediamine (EDA) was added. High-speed shear emulsification was continued for 2.5 hours with material circulation. This yielded an anionic waterborne polyurethane resin with a solids content of 40%.

[0047] Example 5 100 kg of polyethylene adipate (PEA2000) with a molecular weight of 2000 g / mol and 3.8 kg of N-methyldiethanolamine (MDEA) were placed in reactor 1. 0.1 kg of stannous octoate was added, and the mixture was purged with nitrogen. The temperature was raised to 65°C, and 6.1 kg of toluene diisocyanate (TDI) and 5.9 kg of hexamethylene diisocyanate (HDI) were added dropwise to reactor 1. The mixture was stirred and reacted for 1.5 hours. 0.25 kg of 1,4-butanediol was added to reactor 1. Simultaneously, pump 10 was started, and 22 kg of carbon dioxide was introduced into reactor 1 using supercritical CO2 generator 17. Material circulation was maintained, and the reaction was continued at 65°C for 2 hours. The pressure in reactor 1 was monitored and nitrogen was added as needed to ensure a pressure of 7.8-8.0 MPa.

[0048] Dissolve 0.81 kg of glacial acetic acid (TEA) in 176 kg of deionized water. Lower the temperature of reactor 1 to 30°C, then add the deionized water containing the glacial acetic acid. Simultaneously, start the high-speed shear emulsification device 7, maintain material circulation, and perform shear emulsification for 0.5 hours. Then, open the second three-way valve 24 of reactor 1 to release the pressure, and continue high-speed shear emulsification for 1 hour to obtain a cationic waterborne polyurethane resin with a solids content of 40%.

[0049] Comparative Example 1 96 kg of 2000 g / mol polytetramethylene glycol (PTMEG) and 5.34 kg of dimethylol propionic acid (DMPA) were placed in a reactor. 0.07 kg of stannous octoate was added. Under nitrogen protection, the temperature was raised to 75°C. 23.36 kg of isophorone diisocyanate (IPDI) was added dropwise to the reactor, and the reaction was stirred for 2.5 hours. The temperature was then lowered to 35°C, and 18 kg of acetone was added, followed by a further stirring reaction for 0.5 hour.

[0050] Dissolve 1.4 kg of triethylamine in 174 kg of deionized water. Add this deionized water containing triethylamine to the reactor and simultaneously activate the high-speed shear emulsification device for 0.5 hours. Continue lowering the reactor temperature to 8°C, adding 2.4 kg of a deionized water solution containing 30% ethylenediamine (EDA), and continue high-speed shear emulsification for 2 hours. Maintain the reactor temperature at 15°C and vacuum-dry the acetone for 2 hours to obtain an anionic waterborne polyurethane resin with a solids content of 42%. The residual acetone content in the waterborne resin is 45 g / L.

[0051] Test: A laser particle size analyzer was used to test the particle size of the PU water-based resin. A high-speed centrifuge was used to test the emulsion stability at 10,000 rpm for 30 minutes, and the state of the emulsion in the centrifuge tube was observed. The residual acetone in the PU water-based resin was tested by gas chromatography.

[0052] Test results: Table 1

[0053] From the above results, it can be seen that the water-based polyurethane resin preparation process provided by the present invention utilizes supercritical gas to efficiently reduce the viscosity of the polyurethane prepolymer before emulsification, thereby realizing the preparation of a water-based polyurethane emulsion that does not rely on organic solvents to assist in viscosity reduction. This not only greatly shortens the emulsification time and reduces energy consumption, but also can produce a high-quality emulsion with a small particle size, narrow particle size distribution, high stability and no emulsifier residue, significantly improving the overall performance and application value of the final product.

[0054] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A process for preparing a waterborne polyurethane resin, characterized in that: The following steps are involved: Putting a polyol and a hydrophilic chain extender into a reactor, adding a catalyst, and dropwise adding isocyanate under nitrogen protection, reacting at 60-80°C until the NCO content reaches a preset value; then introducing carbon dioxide gas and nitrogen, controlling the pressure at 7.5-8.5 MPa, maintaining the reaction temperature and pressure, and reacting for 0.5-4 hours under stirring; continuing to maintain the pressure in the reactor, lowering the reaction temperature to 40-60°C, and introducing water or an aqueous solution of a salt-forming agent while simultaneously performing shear emulsification; then lowering the temperature and pressure, and continuing the shear emulsification to obtain a waterborne polyurethane resin without organic solvent-assisted emulsification; The preparation process is applicable to the preparation of anionic, cationic and nonionic waterborne polyurethanes.

2. The process for preparing the waterborne polyurethane resin according to claim 1, wherein: The amount of the carbon dioxide used is 5-50 wt% of the amount of the polyurethane resin in the reactor.

3. The process for preparing the waterborne polyurethane resin according to claim 1, wherein: The method also includes a chain extension reaction, which includes the following steps: cooling the system of the water-based polyurethane resin without organic solvent-assisted emulsification to 5-15° C., supplying an aqueous solution of an amine chain extender, and continuing the shear emulsification reaction for 1-3 hours to obtain the chain-extended water-based polyurethane resin without organic solvent-assisted emulsification.

4. The process for preparing the waterborne polyurethane resin according to claim 3, wherein: The amine chain extender includes one or more of ethylenediamine, butanediamine, hexamethylenediamine or isophoronediamine.

5. The process for preparing the waterborne polyurethane resin according to claim 1, wherein: The following steps are involved: Put polyol and hydrophilic chain extender into a reactor, add a catalyst, add isocyanate dropwise under nitrogen protection, and react at 60-80°C until the NCO content reaches a preset value; then add diol chain extender dropwise and react for 0.5-1h; then introduce carbon dioxide gas and nitrogen, control the pressure at 7.5-8.5MPa, maintain the reaction temperature and pressure, and react for 0.5-4h under stirring; continue to maintain the pressure of the reactor, reduce the reaction temperature to 40-60°C, and introduce water or an aqueous solution of a salt-forming agent within 0.5h, and shear emulsify for 0.5-1h; then reduce the temperature and pressure, and continue shear emulsification for 0.5-2h to obtain a waterborne polyurethane resin without organic solvent-assisted emulsification.

6. The process for preparing the waterborne polyurethane resin according to claim 5, wherein: The diol chain extender includes one or more of ethylene glycol, diethylene glycol, 1,4-butanediol or 1,6-hexanediol.

7. The process for preparing the waterborne polyurethane resin according to claim 1, wherein: The polyol includes one or more of polytetramethylene ether, polypropylene glycol ether, polyadipic acid polyester, polycaprolactone, and polycarbonate; The isocyanate includes one or more of diphenylmethane diisocyanate MDI, toluene diisocyanate TDI, hexamethylene diisocyanate HDI, isophorone diisocyanate IPDI, and 4,4-diisocyanate dicyclohexylmethane HMDI; The catalyst is an organotin catalyst.

8. The process for preparing the waterborne polyurethane resin according to claim 1, wherein: The anionic waterborne polyurethane hydrophilic chain extender includes one or more of dimethylol propionic acid, dimethylol butyric acid, 1,2-propylene glycol-3-sulfonate sodium, 1,4-butanediol-2-sulfonate sodium, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonate sodium, and 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt; The anionic waterborne polyurethane salt-forming agent includes one or more of triethylamine, NaOH, KOH, Cs2CO3, and K2CO3.

9. The process for preparing the waterborne polyurethane resin according to claim 1, wherein: The hydrophilic chain extender of the cationic waterborne polyurethane includes one or more of diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-propyldiethanolamine, N-benzyldiethanolamine, tert-butyldiethanolamine, dimethylethanolamine, bis(2-hydroxyethyl)benzylaniline and bis(2-hydroxypropyl)aniline; The salt-forming agent of the cationic waterborne polyurethane includes one or more of formic acid, glycolic acid, acetic anhydride and glacial acetic acid.

10. The process for preparing the waterborne polyurethane resin according to claim 1, wherein: The polyol of the non-ionic waterborne polyurethane is one or more of polyethylene glycol, trimethylolpropane polyethylene glycol monomethyl ether, or a copolyether containing an ethylene oxide segment.

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