A method for continuously preparing an aqueous polyurethane dispersion through a microreactor

Abstract

The present invention belongs to the technical field of polymers and discloses a method for continuously preparing an aqueous polyurethane dispersion through a microreactor. The method includes a prepolymerization process for generating a polyurethane prepolymer, a primary chain extension process for performing the first chain extension on the prepolymer, a polymerization process for polymerizing the chain-extended prepolymer and a diol, and a neutralization process, which are carried out in sequence. The prepolymerization process, the primary chain extension process, the prepolymer, the polymerization process, and the neutralization process are all carried out through a microchannel mixer and a microchannel reactor connected in sequence. By using a microchannel mixer and a microchannel reactor for the prepolymerization, chain extension, polymerization, and neutralization processes of the dispersion, the mass transfer and heat transfer effects can be effectively improved, the polymerization stability can be enhanced, and the obtained aqueous polyurethane has advantages such as a concentrated molecular weight distribution, a low particle size polydispersity coefficient, controllable structure, stable quality, excellent performance, and basically no scale-up effect, which is beneficial to industrial scale-up and has good industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the field of polymers, and particularly to a method for continuously preparing aqueous polyurethane dispersions through a microreactor. Background Art

[0002] Aqueous polyurethane dispersions use deionized water as the dispersion medium, which can greatly reduce the use of volatile organic solvents (VOCs). They are non-toxic, odorless, green environmental protection organic polymer materials. During use, after the water evaporates, a polyurethane film is formed, making the film-forming substance of the aqueous polyurethane dispersion have the same excellent physical and chemical properties as polyurethane materials. By adjusting the formula and chemical modification, aqueous polyurethane materials can obtain high-performance materials with different softness and hardness and different chemical resistances, and are widely used in fields such as wood coatings, textile coatings, synthetic leather, plastic coatings, metal coatings, personal care, coating agents, adhesives, sealants, aqueous inks, etc.

[0003] Currently, the most common production process for aqueous polyurethane is batch production, that is, first preparing a polyurethane prepolymer with a hydrophilic group in the main chain in a prepolymerization reactor, and then transferring the material to a dispersion reactor for neutralization and emulsification. This production process mainly has the following disadvantages: (1) The reaction time is too long (4 - 6 hours), the production efficiency is low, and the production cost is high; (2) The production process is overly dependent on manual labor, and the degree of automation is low; (3) The temperature distribution in the reactor is uneven, the product quality is unstable, and there are large differences between batches.

[0004] Continuous production can solve the bottleneck problems existing in traditional batch production. Patent CN202011253943.7 uses a twin-screw extruder as the synthesis reactor for aqueous polyurethane, which can realize the continuous preparation of aqueous polyurethane. However, the twin-screw extruder has a large equipment volume, complex operation, is difficult to precisely control the reaction conditions, and easily causes fluctuations in product quality. Patent CN 201711466121.5 uses a tubular reactor as the synthesis reactor for aqueous polyurethane, which can realize the continuous preparation of aqueous polyurethane. However, the internal components of this reactor are complex, difficult to process and install, and not conducive to industrial scale-up. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for continuously preparing aqueous polyurethane dispersions through a microreactor. This method uses a microchannel mixer and a microchannel reactor for the prepolymerization, chain extension, polymerization, and neutralization processes of the dispersion, which can effectively improve the mass transfer and heat transfer effects, improve the polymerization stability. The obtained aqueous polyurethane has advantages such as a concentrated molecular weight distribution, a low particle size polydispersity coefficient, controllable structure, stable quality, excellent performance, etc., and basically has no scale-up effect, which is conducive to industrial scale-up and has good industrial application prospects.

[0006] To achieve the above object, the present application discloses:

[0007] A method for continuously preparing an aqueous polyurethane dispersion through a microreactor, the method comprising a prepolymerization process for generating a polyurethane prepolymer, a primary chain extension process for performing a first chain extension on the prepolymer, a polymerization process for polymerizing the chain-extended prepolymer and a diol, and a neutralization process, which are carried out in sequence.

[0008] The prepolymerization process, the primary chain extension process, the prepolymer, the polymerization process, and the neutralization process are all carried out through a microchannel mixer and a microchannel reactor connected in sequence.

[0009] Preferably, all raw materials must be subjected to ultrasonic degassing treatment before use. The ultrasonic power is preferably 30-180 W, more preferably 120-180 W; the ultrasonic frequency is preferably 20-100 kHz, more preferably 20-60 kHz; the ultrasonic time is preferably 10-40 min, more preferably 10-20 min.

[0010] In the above method, a fluid channel is provided in the microchannel reactor; the fluid channel is formed by alternately connecting a plurality of fine channels and thick channels; the width of the thick channel is greater than that of the fine channel; a turbulence chip is provided in the middle of the thick channel; the turbulence chip has a structure that is thick at both ends and thin in the middle; the end of the turbulence chip facing the fluid input has a concave portion; the concave direction of the concave portion is opposite to the fluid flow direction. The cross sections of the fine channel and the thick channel are preferably circular, semicircular, trapezoidal, or rectangular; the material of the microchannel reactor is preferably 304 stainless steel, 316L stainless steel, Hastelloy B, Hastelloy C, titanium alloy, silicon carbide, polyether ether ketone, more preferably 316L stainless steel.

[0011] Preferably, each microchannel reactor and the microchannel mixer are connected in series through a microtube. The inner diameter of the microtube is preferably 0.5-3 mm, more preferably 0.5-2 mm, and more preferably 0.5-1 mm; the outer diameter is preferably 1.5-8 mm, more preferably 3-6 mm; the material of the microtube is preferably 304 stainless steel, 316L stainless steel, polytetrafluoroethylene, soluble polytetrafluoroethylene, perfluoroethylene propylene copolymer, more preferably 316L stainless steel and polytetrafluoroethylene.

[0012] In the above method, there is also a secondary chain extension process after the neutralization process; the secondary chain extension process uses a diamine chain extender and deionized water for chain extension reaction; the secondary chain extension process is also carried out through a microchannel mixer and a microchannel reactor connected in sequence or through a reaction kettle; the reaction conditions for the secondary chain extension process include: the reaction temperature is 0-60 °C, preferably 5-40 °C, more preferably 5-20 °C, the mass flow rates of the diamine chain extender and deionized water are 6-10 g / min, and the reaction time is 15-60 min.

[0013] During the prepolymerization process, the reaction raw materials are mixed by a microchannel mixer and then further mixed by a static mixer, and finally enter the corresponding microchannel reactor for reaction.

[0014] In the above method, the microchannel reactor is composed of one or more layers of microchannels connected in series; the microchannels of each layer are in a serpentine layout.

[0015] In the above method, the microchannel reactor is composed of 2 to 5 layers of microchannels; there is a temperature control structure for controlling the temperature of the microchannels between adjacent layers of microchannels.

[0016] In the above method, the width ratio of the thin channel to the thick channel is 1:2 to 3; the width of the widest position of the turbulator chip is 1.3 to 1.7 times the width of the thin channel; the width of the narrowest position of the turbulator chip is 0.9 to 1.1 times the width of the thin channel; the diameter of the concave part of the turbulator chip is 0.6 to 0.9 times the width of the thin channel; the radian of the concave part of the turbulator chip is 100 to 140°.

[0017] In the above method, the width of the thin channel is 0.1 - 1 mm.

[0018] In the above method, the width of the mixing channel of the microchannel mixer is 0.1 - 1 mm; the material of the microchannel mixer is preferably 304 stainless steel, 316L stainless steel, silicon carbide, polytetrafluoroethylene, polyether ether ketone, Hastelloy C, Hastelloy B, and more preferably 316L stainless steel. The static mixer includes a pipe body and a core disposed inside the pipe body; the core and the pipe body form a mixing channel; the core configuration of the static mixer is preferably SV type, SK type, SX type, SH type, SL type, etc., more preferably SK type and SV type, and more preferably SK type; the outer diameter of the core is preferably 0.5 - 3 mm, more preferably 0.5 - 1.5 mm; the material of the static mixer is preferably 304 stainless steel, 316L stainless steel, silicon carbide, etc., more preferably 316L stainless steel.

[0019] In the above method, the raw materials for the prepolymerization process are diisocyanate, oligomeric diol and catalyst; the reaction temperature for the prepolymerization process is 60 - 180 °C, preferably 80 - 160 °C; the mass flow rate of diisocyanate is 0.50 - 3.00 g / min; preferably 1.00 - 2.00 g / min, and the mass flow rate of oligomeric diol is 0.50 - 10.0 g / min, preferably 1.00 - 8.00 g / min;

[0020] The raw materials for the first chain extension process are prepolymers, hydrophilic chain extenders, and solvents. The reaction temperature for the first chain extension process is 60 - 180°C, preferably 100 - 180°C. The mass flow rates of the hydrophilic chain extender and the solvent are 0.60 - 3.00 g / min, preferably 0.90 - 2.80 g / min.

[0021] The reaction temperature for the polymerization process is 60 - 180°C, preferably 80 - 170°C. The mass flow rate of the diol is 0.02 - 0.40 g / min, preferably 0.05 - 0.35 g / min.

[0022] The reaction temperature for the neutralization process is 50 - 120°C, preferably 60 - 100°C. The mass flow rate of the neutralizing agent used in the neutralization process is 0.06 - 0.50 g / min, preferably 0.15 - 0.45 g / min.

[0023] In the above method, in the prepolymerization process, the first chain extension process, the polymerization process, and the neutralization process, the residence times of the reaction materials in the microchannel reactor are 0.5 - 5 min, 0.5 - 5 min, 0.5 - 5 min, and 1 - 5 min, respectively.

[0024] The diisocyanate is one or more of isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and cyclohexane diisocyanate.

[0025] The oligomeric diol is one or more of polyethylene glycol, polypropylene glycol, polybutylene adipate glycol, polyethylene adipate glycol, polycaprolactone diol, polycarbonate diol, and poly(propylene carbonate) diol with a number average molecular weight of 500 - 6000.

[0026] The catalyst is one or more of stannous octoate, dibutyltin dilaurate, bismuth neodecanoate, bismuth laurate, and dibutyltin diacetate.

[0027] The hydrophilic chain extender is one or more of dimethylolpropionic acid, dimethylolbutyric acid, methyldiethanolamine, diethanolamine, triethanolamine, and triisopropanolamine.

[0028] The solvent is one or more of N,N - dimethylformamide, N,N - dimethylacetamide, N - methylpyrrolidone, butyl acetate, dipropylene glycol dimethyl ether, N,N - diethylformamide, and N - ethylpyrrolidone.

[0029] The small molecule diol is one or more of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,2 - propanediol, 1,3 - propanediol, 1,4 - butanediol, 1,3 - butanediol, 1,5 - pentanediol, neopentyl glycol, 1,6 - hexanediol, 1,8 - octanediol;

[0030] The neutralizing agent is one or more of triethylamine, dimethylethanolamine, formic acid, acetic acid;

[0031] The diamine is one or more of ethylenediamine, hydrazine hydrate, 2 - methyl - 1,5 - pentanediamine, 2 - [(2 - aminoethyl)amino]ethanesulfonic acid sodium salt, triethylenetetramine, diethylenetriamine, diaminodicyclohexylmethane, isophoronediamine, toluenediamine;

[0032] The mass ratio of the catalyst to the oligomeric diol is 1:1000 - 1:20;

[0033] The mass ratio of the hydrophilic chain extender to the solvent is 1:1 - 1:10;

[0034] The mass ratio of the diamine chain extender to deionized water is 1:40 - 1:120.

[0035] This application has at least the following beneficial effects:

[0036] The method of the present invention uses a microchannel mixer and a microchannel reactor for the prepolymerization, chain extension, polymerization, and neutralization processes of the dispersion, which can effectively improve the mass transfer and heat transfer effects, improve the polymerization stability. The obtained aqueous polyurethane has advantages such as a concentrated molecular weight distribution, a low particle size polydispersity coefficient, controllable structure, stable quality, excellent performance, and basically no scale - up effect, which is conducive to industrial scale - up and has good industrial application prospects.

[0037] In the preferred embodiment of the present invention, a turbulator chip with a specific structure is used to improve the mixing effect. Specifically, since the polyurethane reaction is a strongly exothermic reaction, the strong heat exchange ability of the microchannel reactor and the short residence time of the material can ensure the uniformity of the reaction liquid temperature during the reaction process; in the later stage of the polyurethane reaction, the viscosity of the reaction liquid will increase, and the active molecules mainly diffuse radially. The sub - micron - level channels ensure a short diffusion time, which is conducive to improving the reaction degree and controlling the molecular weight distribution of the product.

[0038] In the preferred embodiment of the present invention, side reactions can be effectively controlled by controlling the reaction time and reaction temperature, and the microchannel mixer and microchannel reactor used in the present invention can achieve precise control of the reaction time and temperature.

[0039] The present invention adopts a distributed and successive microchannel reaction. During this process, the types of various reaction raw materials can be flexibly adjusted to adapt to the production of different types of polyurethanes. Description of the Drawings

[0040] Figure 1 It is a graph of molecular weight and molecular weight distribution of Examples 1-3 and Comparative Examples 1-6 of the present invention;

[0041] Figure 2 It is a graph of particle size and particle size distribution of Examples 1-3 and Comparative Examples 1-6 of the present invention;

[0042] Figure 3 It is a graph of molecular weight and molecular weight distribution of Examples 1-11 of the present invention;

[0043] Figure 4 It is a graph of particle size and particle size distribution of Examples 1-11 of the present invention;

[0044] Figure 5 It is a flowchart of the present invention;

[0045] Figure 6 It is a three-dimensional view of the static mixer of the present invention;

[0046] Figure 7 It is an exploded view of the microchannel reactor of the present invention;

[0047] Figure 8 It is a schematic diagram of the fluid channel of the microchannel reactor of the present invention;

[0048] Figure 9 It is a partial enlarged view of the fluid channel of the microchannel reactor of the present invention;

[0049] Figure 10 Infrared spectrum diagram of the aqueous polyurethane film of Example 1;

[0050] Figure 11 Stress-strain curve diagram of the aqueous polyurethane film of Example 1;

[0051] Figure 12 Thermogravimetric curve diagram of the aqueous polyurethane film of Example 1;

[0052] Figure 13 DSC curve diagram of the aqueous polyurethane film of Example 1.

[0053] Detailed Description of the Specific Embodiments

[0054] Next, the embodiments of the present invention will be used to clearly and completely describe the present invention. In the description of the present invention, it should be noted that for those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0055] Example 1

[0056] Before elaborating on the specific production method of the present invention, the system of the present invention will be clarified. Refer to Figure 3 , the system includes a micro - mixer 1, a static mixer, MR1, a micro - mixer 2, MR2, a micro - mixer 3, MR3, a micro - mixer 4, MR4, and a high - speed disperser connected in sequence;

[0057] MR1, MR2, MR3, and MR4 are all micro - chip reactors; refer to Figures 4 to 7 , each micro - chip reactor has 3 layers of micro - channels; the micro - channel reactor is composed of 3 layers of micro - channels connected in series; there is a temperature - control structure 17 for controlling the temperature of the micro - channels between adjacent two layers of micro - channels. Each layer of micro - channels is serpentine; the fluid channels forming the micro - channels are formed by alternating connection of a number of fine channels 11 and thick channels 12, and the width of the thick channels is greater than that of the fine channels; a turbulence - generating chip 13 is provided in the middle of the thick channels; the turbulence - generating chip has a structure that is thick at both ends and thin in the middle; the end of the turbulence - generating chip facing the fluid input has a concave part 14; the concave direction of the concave part is opposite to the fluid flow direction. The cross - sections of the fine channels and the thick channels are circular; the width ratio of the fine channels to the thick channels is 1:2.5; the width of the widest position of the turbulence - generating chip is 1.5 times the width of the fine channels, the width of the narrowest position of the turbulence - generating chip is 1 times the width of the fine channels, the diameter of the concave part of the turbulence - generating chip is 0.8 times the width of the fine channels, and the radian of the concave part of the turbulence - generating chip is 120°; the width of the fine channels is 0.8 mm. The static mixer includes a pipe body 15 and a core 16 provided in the pipe body; the core and the pipe body form a mixing channel; the width of the mixing channel is 0.8 mm, the core is of SK type, and the outer diameter of the core is 1 mm;

[0058] Raw material preparation: Isophorone diisocyanate is raw material A, a mixture of stannous octoate and polypropylene glycol (Mn = 2000) is raw material B, where the mass ratio of stannous octoate to polypropylene glycol (Mn = 2000) is 1:200, a mixture of dimethylolpropionic acid and N,N-dimethylformamide is raw material C, where the mass ratio of dimethylolpropionic acid to N,N-dimethylformamide is 1:3, 1,4-butanediol is raw material D, triethylamine is raw material E, a mixture of ethylenediamine and deionized water is raw material F, where the mass ratio of ethylenediamine to deionized water is 1:100. Raw materials A - E are stored in raw material tanks A - E respectively. After being treated with ultrasound at 150 W and 60 kHz for 20 min, the temperature is raised to 40 °C for standby. Raw material F is stored in raw material tank F. After being treated with ultrasound at 150 W and 60 kHz for 10 min, the temperature is lowered to 15 °C for standby;

[0059] Preparation method: First, raw material A and raw material B enter the micro-mixer 1 and the static mixer in sequence through the feed pumps respectively to obtain the mixed solution Ⅰ. The flow rates of feed pump A and feed pump B are 1.44 g / min and 2.67 g / min respectively. The mixed solution 1 enters the MR1 set at 140 °C for reaction, and the residence time is 1 min to obtain the prepolymer Ⅰ;

[0060] Then, raw material C enters the micro-mixer 2 through the feed pump to be mixed with the prepolymer Ⅰ to obtain the mixed solution Ⅱ. The flow rate of feed pump C is 1.27 g / min. The mixed solution Ⅱ enters the MR2 set at 150 °C for reaction, and the residence time is 2 min to obtain the prepolymer Ⅱ;

[0061] Then, raw material D enters the micro-mixer Ⅲ through the feed pump to be mixed with the prepolymer Ⅱ to obtain the mixed solution Ⅲ. The flow rate of feed pump D is 0.07 g / min. The mixed solution Ⅲ enters the MR3 set at 140 °C for reaction, and the residence time is 2 min to obtain the prepolymer Ⅲ;

[0062] Then, raw material E enters the micro-mixer Ⅳ through the feed pump to be mixed with the prepolymer Ⅲ to obtain the mixed solution Ⅳ. The flow rate of feed pump E is 0.20 g / min. The mixed solution Ⅳ enters the MR4 set at 60 °C for reaction, and the residence time is 2 min to obtain the prepolymer Ⅳ;

[0063] Finally, raw material F enters the high-speed disperser through the feed pump to be emulsified and dispersed with the prepolymer Ⅳ. The flow rate of feed pump F is 8.89 g / min, the emulsification temperature is 10 °C, and the emulsification time is 30 min to obtain the aqueous polyurethane dispersion.

[0064] Example 2

[0065] Raw material preparation: Refer to Example 1 for raw material preparation. The difference is that: raw material A is dicyclohexylmethane diisocyanate;

[0066] Preparation method: Refer to Experimental Example 1 for preparation, with the differences being that the flow rate of Feed Pump A is 1.49 g / min, the temperature of MR1 is 150 °C; the temperature of MR2 is 160 °C; the flow rate of Feed Pump D is 0.02 g / min, the temperature of MR3 is 150 °C; the flow rate of Feed Pump F is 8.08 g / min.

[0067] Example 3

[0068] Raw material preparation: Refer to Example 1 for raw material preparation, with the difference being that Raw Material A is hexamethylene diisocyanate;

[0069] Preparation method: Refer to Experimental Example 1 for preparation, with the differences being that the flow rate of Feed Pump A is 1.36 g / min; the flow rate of Feed Pump D is 0.15 g / min; the flow rate of Feed Pump F is 8.51 g / min.

[0070] Example 4

[0071] Raw material preparation: Refer to Example 1 for raw material preparation;

[0072] Preparation method: Refer to Experimental Example 1 for preparation, with the differences being that the flow rate of Feed Pump A is 1.00 g / min; the flow rate of Feed Pump B is 1.85 g / min; the flow rate of Feed Pump C is 0.90 g / min; the flow rate of Feed Pump D is 0.05 g / min; the flow rate of Feed Pump E is 0.14 g / min; the flow rate of Feed Pump F is 6.17 g / min.

[0073] Example 5

[0074] Raw material preparation: Refer to Example 2 for raw material preparation;

[0075] Preparation method: Refer to Experimental Example 2 for preparation, with the differences being that the flow rate of Feed Pump A is 1.00 g / min; the flow rate of Feed Pump B is 1.79 g / min; the flow rate of Feed Pump C is 0.85 g / min; the flow rate of Feed Pump D is 0.01 g / min; the flow rate of Feed Pump E is 0.13 g / min; the flow rate of Feed Pump F is 5.42 g / min.

[0076] Example 6

[0077] Raw material preparation: Refer to Example 3 for raw material preparation;

[0078] Preparation method: The preparation was carried out with reference to Experimental Example 3, except that: the flow rate of feed pump A was 1.00 g / min; the flow rate of feed pump B was 1.96 g / min; the flow rate of feed pump C was 0.93 g / min; the flow rate of feed pump D was 0.11 g / min; the flow rate of feed pump E was 0.15 g / min; the flow rate of feed pump F was 6.26 g / min.

[0079] Example 7

[0080] Raw material preparation: The raw materials were prepared with reference to Example 1;

[0081] Preparation method: The preparation was carried out with reference to Experimental Example 1, except that: the flow rate of feed pump A was 3.00 g / min; the flow rate of feed pump B was 5.56 g / min; the flow rate of feed pump C was 2.65 g / min; the flow rate of feed pump D was 0.15 g / min; the flow rate of feed pump E was 0.42 g / min; the flow rate of feed pump F was 18.52 g / min.

[0082] Example 8

[0083] Raw material preparation: The raw materials were prepared with reference to Example 2;

[0084] Preparation method: The preparation was carried out with reference to Experimental Example 2, except that: the flow rate of feed pump A was 3.00 g / min; the flow rate of feed pump B was 5.38 g / min; the flow rate of feed pump C was 2.56 g / min; the flow rate of feed pump D was 0.04 g / min; the flow rate of feed pump E was 0.40 g / min; the flow rate of feed pump F was 16.27 g / min.

[0085] Example 9

[0086] Raw material preparation: The raw materials were prepared with reference to Example 3;

[0087] Preparation method: The preparation was carried out with reference to Experimental Example 3, except that: the flow rate of feed pump A was 3.00 g / min; the flow rate of feed pump B was 5.89 g / min; the flow rate of feed pump C was 2.80 g / min; the flow rate of feed pump D was 0.33 g / min; the flow rate of feed pump E was 0.44 g / min; the flow rate of feed pump F was 18.77 g / min.

[0088] Example 10

[0089] Raw material preparation: The raw materials were prepared with reference to Example 1;

[0090] Preparation method: The preparation was carried out with reference to Experimental Example 1, except that the width of the fine channels inside the microchannel reactor was 0.5 mm.

[0091] Example 11

[0092] Raw material preparation: Refer to Example 1 for raw material preparation;

[0093] Preparation method: Refer to Experimental Example 1 for preparation, except that the width of the fine channels inside the microchannel reactor is 1.2 mm.

[0094] Comparative Example 1

[0095] In this Comparative Example 1, an aqueous polyurethane dispersion was prepared using a tubular reactor, and the implementation was as follows:

[0096] Raw material preparation: Refer to Example 1 for raw material preparation;

[0097] Preparation method: First, raw material A and raw material B were respectively fed into mixer 1 through feed pumps successively to obtain mixture I. The flow rates of feed pump A and feed pump B were 1.44 g / min and 2.67 g / min respectively. After mixture 1 was preheated to 60 °C, it entered the first tubular reactor (VR1) set at 85 °C for reaction, with a residence time of 30 min, to obtain prepolymer I;

[0098] Then, raw material C was mixed with prepolymer I in mixer 2 through a feed pump to obtain mixture II. The flow rate of feed pump C was 1.27 g / min. Mixture II entered VR2 set at 75 °C for reaction, with a residence time of 60 min, to obtain prepolymer II;

[0099] Then, raw material D was mixed with prepolymer II in micromixer III through a feed pump to obtain mixture III. The flow rate of feed pump D was 0.07 g / min. Mixture III entered VR3 set at 75 °C for reaction, with a residence time of 30 min, to obtain prepolymer III;

[0100] Then, raw material E was mixed with prepolymer III in micromixer IV through a feed pump to obtain mixture IV. The flow rate of feed pump E was 0.20 g / min. Mixture IV entered VR4 set at 40 °C for reaction, with a residence time of 10 min, to obtain prepolymer IV;

[0101] Finally, raw material F was emulsified and dispersed with prepolymer IV in a high-speed disperser through a feed pump. The flow rate of feed pump F was 8.89 g / min, the emulsification temperature was 10 °C, and the emulsification time was 30 min to obtain an aqueous polyurethane dispersion.

[0102] Comparative Example 2

[0103] In this Comparative Example 2, an aqueous polyurethane dispersion was prepared by the batch method, and the implementation was as follows:

[0104] First, 40.00 g of polypropylene glycol (Mn = 2000) and 21.67 g of isophorone diisocyanate were added to an intermittent reactor and reacted at 75 °C for 1 h. Then, 4.00 g of dimethylolpropionic acid and 0.06 g of stannous octoate were added, and the temperature was raised to 85 °C and reacted for 1.5 h. Then, 1.00 g of 1,4-butanediol was added and the reaction continued for 1 h. During this period, an appropriate amount of N,N-dimethylformamide was added to reduce the reaction viscosity. Then, the temperature was lowered to 50 °C, and 3.02 g of triethylamine was added and reacted for 0.5 h to obtain a polyurethane prepolymer. Then, the polyurethane prepolymer was slowly poured into a jacketed dispersion tank containing 132 g of deionized water and 1.32 g of ethylenediamine and dispersed at high speed at 15 °C for 30 min to obtain an aqueous polyurethane dispersion.

[0105] Comparative Example 3

[0106] In this Comparative Example 3, an aqueous polyurethane dispersion was prepared using a tubular reactor, and the implementation was as follows:

[0107] Raw material preparation: Refer to Comparative Example 1 for raw material preparation, with the difference that: Raw material A is dicyclohexylmethane diisocyanate;

[0108] Preparation method: Refer to Comparative Example 1 for preparation, with the difference that: The flow rate of feed pump A is 1.49 g / min; the flow rate of feed pump D is 0.02 g / min; the flow rate of feed pump F is 8.08 g / min.

[0109] Comparative Example 4

[0110] In this Comparative Example 4, an aqueous polyurethane dispersion was prepared by the batch method, and the implementation was as follows:

[0111] Refer to Comparative Example 2 for the experiment, with the difference that: The diisocyanate is dicyclohexylmethane diisocyanate, and the addition amount is 22.36 g; the addition amount of 1,4-butanediol is 0.31 g; the amounts of deionized water and ethylenediamine used are 115 g and 1.15 g, respectively.

[0112] Comparative Example 5

[0113] In this Comparative Example 5, an aqueous polyurethane dispersion was prepared using a tubular reactor, and the implementation was as follows:

[0114] Raw material preparation: Refer to Comparative Example 1 for raw material preparation, with the difference that: Raw material A is hexamethylene diisocyanate;

[0115] Preparation method: Refer to Comparative Example 1 for preparation, with the difference that: The flow rate of feed pump A is 1.36 g / min; the flow rate of feed pump D is 0.15 g / min; the flow rate of feed pump F is 8.51 g / min.

[0116] Comparative Example 6

[0117] In this Comparative Example 6, an aqueous polyurethane dispersion was prepared by an intermittent method as follows:

[0118] The experiment was carried out with reference to Comparative Example 2, except that: the diisocyanate was hexamethylene diisocyanate with an addition amount of 20.34 g; the addition amount of 1,4-butanediol was 2.32 g; the amounts of deionized water and ethylenediamine were 164 g and 1.64 g respectively.

[0119] Result detection

[0120] The dispersions of the above examples and comparative examples were sent for inspection to detect the molecular weight, molecular weight distribution, particle size, and polydispersity coefficient;

[0121] The test results are as shown in Figure 1 , Figure 2 , Figure 3 and Figure 4 ;

[0122] It can be seen from Figure 1 and Figure 2 that compared with the reaction method in a tubular reactor and the reaction method in an intermittent autoclave, the method of the present invention has a narrower molecular weight distribution, a smaller dispersion coefficient, and a relatively smaller particle size.

[0123] It can be seen from Figure 3 and Figure 4 that in Examples 1, 4, 7 (or Examples 2, 5, 8 or Examples 3, 6, 9) of the present invention, by changing the mass flow rate of the raw materials to obtain different flow rates, the higher the flow rate, the more uniform the mixing of the reaction materials, and a narrower molecular weight distribution and a smaller dispersion coefficient can be obtained. However, the flow rate cannot be too high, as too high a flow rate will lead to too large a pressure drop inside the reactor. At the same time, too high a flow rate will greatly shorten the residence time, and too short a residence time will cause the reaction to be incomplete; in Examples 1, 10, 11 of the present invention, by changing the size of the fine channels inside the microchannel reactor, it can be seen that when the size of the fine channels decreases, the radial diffusion of the materials in the fine channels is more uniform, the reaction will be more complete, which is beneficial to increasing the molecular weight and reducing the particle size. However, the size of the fine channels cannot be too small, as too small a size will lead to too large a pressure drop inside the reactor, and in severe cases, it will even cause the channels to be blocked, making the reaction unable to proceed continuously.

[0124] Figure 10 , Figure 11 , Figure 12 , Figure 13 are respectively the infrared spectrum diagram, stress-strain curve diagram, thermogravimetric curve diagram, and differential scanning calorimetry curve diagram of Example 1 and Comparative Example 1.

[0125] It can be seen from the characteristic functional groups in the Figure 10 infrared spectrum diagram that the experimental methods of Example 1 and Comparative Example 1 successfully synthesized aqueous polyurethane; it can be seen from Figure 11It can be seen from the stress-strain curve that the aqueous polyurethane of Example 1 has a higher tensile strength than that of Comparative Example 1; through Figure 12 It can be seen from the thermogravimetric curve that the aqueous polyurethane of Example 1 has better heat resistance than that of Comparative Example 1; through Figure 13 It can be seen from the differential scanning calorimetry curve that Example 1 and Comparative Example 1 have similar glass transition temperatures (Tg).

[0126] This shows that the pre-polymerization, chain extension, polymerization and neutralization processes are all carried out using a microchannel mixer and a microchannel reactor, which can effectively improve the mass transfer and heat transfer effects, improve the polymerization stability, and the obtained aqueous polyurethane has the advantages of concentrated molecular weight distribution, low particle size polydispersity coefficient, controllable structure, stable quality, excellent performance, etc., and there is basically no scale-up effect, which is beneficial to industrial scale-up and has good industrial application prospects.

[0127] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A method for continuously preparing an aqueous polyurethane dispersion through a microreactor, characterized in that The method includes a prepolymerization process for generating a polyurethane prepolymer, a first chain extension process for chain-extending the prepolymer, a polymerization process for polymerizing the chain-extended prepolymer and a diol, and a neutralization process, which are carried out in sequence. The prepolymerization process, the first chain extension process, the polymerization process, and the neutralization process are all carried out through a microchannel mixer and a microchannel reactor connected in sequence. A fluid channel is provided in the microchannel reactor; the fluid channel is formed by alternately connecting a number of thin channels and thick channels; the width of the thick channel is greater than that of the thin channel; a turbulence chip is provided in the middle of the thick channel; the turbulence chip has a structure that is thick at both ends and thin in the middle; the end of the turbulence chip facing the fluid input has a concave portion; the concave direction of the concave portion is opposite to the fluid flow direction. There is also a second chain extension process after the neutralization process; the second chain extension process uses a diamine chain extender and deionized water for the chain extension reaction; the second chain extension process is also carried out through a microchannel mixer and a microchannel reactor connected in sequence or through a reaction kettle or through a disperser. In the prepolymerization process, the reaction raw materials are mixed through a microchannel mixer and then through a static mixer, and finally enter the corresponding microchannel reactor for reaction. The width ratio of the thin channel to the thick channel is 1:2 - 3; the width of the widest position of the turbulence chip is 1.3 - 1.7 times the width of the thin channel; the width of the narrowest position of the turbulence chip is 0.9 - 1.1 times the width of the thin channel; the diameter of the concave portion of the turbulence chip is 0.6 - 0.9 times the width of the thin channel; the radian of the concave portion of the turbulence chip is 100 - 140°. The width of the thin channel is 0.1 - 1 mm. The raw materials for the prepolymerization process are diisocyanate, oligomeric diol and a catalyst; the mass flow rate of diisocyanate is 0.50 - 3.00 g / min; the mass flow rate of oligomeric diol is 0.50 - 10.0 g / min. The raw materials for the first chain extension process are the prepolymer, a hydrophilic chain extender and a solvent, and the mass flow rate of the hydrophilic chain extender and the solvent is 0.60 - 3.00 g / min. The mass flow rate of the diol is 0.02 - 0.40 g / min; the mass flow rate of the neutralizing agent used in the neutralization process is 0.06 - 0.50 g / min.

2. The method according to claim 1, wherein The microchannel reactor is composed of one or more layers of microchannels connected in series; the microchannels of each layer are in a serpentine layout.

3. The method according to claim 1, wherein The microchannel reactor is composed of 2 - 5 layers of microchannels; there is a temperature control structure for controlling the temperature of the microchannels between adjacent layers of microchannels.

4. The method according to claim 1, characterized in that The microchannel mixer includes a tube body and a core provided in the tube body; the core and the tube body form a mixing channel; the width of the mixing channel is 0.1 - 1 mm.

5. The method according to claim 1, characterized in that, The reaction temperature of the prepolymerization process is 60 - 180 °C; the reaction temperature of the first chain extension process is 60 - 180 °C; the reaction temperature of the polymerization process is 60 - 180 °C; the reaction temperature of the neutralization process is 50 - 120 °C.

6. The method according to claim 1, wherein In the pre-polymerization process, the primary chain extension process, the polymerization process, and the neutralization process, the residence times of the reaction materials in the microchannel reactor are 0.5 - 5 min, 0.5 - 5 min, 0.5 - 5 min, and 1 - 5 min, respectively; The diisocyanate is one or more of isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and cyclohexane diisocyanate; The oligomeric diol is one or more of polyethylene glycol, polypropylene glycol, polybutylene adipate glycol, polyethylene adipate glycol, polycaprolactone glycol, polycarbonate glycol, and polypropylene carbonate glycol with a number average molecular weight of 500 - 6000; The catalyst is one or more of stannous octoate, dibutyltin dilaurate, bismuth neodecanoate, bismuth laurate, and dibutyltin diacetate; The hydrophilic chain extender is one or more of dimethylolpropionic acid, dimethylolbutyric acid, methyldiethanolamine, diethanolamine, triethanolamine, and triisopropanolamine; The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, butyl acetate, dipropylene glycol dimethyl ether, N,N-diethylformamide, and N-ethylpyrrolidone; The diol is one or more of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol; The neutralizing agent is one or more of triethylamine, dimethylethanolamine, formic acid, and acetic acid; The diamine is one or more of ethylenediamine, hydrazine hydrate, 2-methyl-1,5-pentanediamine, 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt, triethylenetetramine, diethylenetriamine, diaminodicyclohexylmethane, isophoronediamine, and toluenediamine; the mass ratio of the catalyst to the oligomeric diol is 1:1000 - 1:20; The mass ratio of the hydrophilic chain extender to the solvent is 1:1 - 1:10; The mass ratio of the diamine chain extender to deionized water is 1:40 - 1:120.

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