Water-resistant waterborne polyurethane and method for preparing the same

Abstract

The application discloses a water-based polyurethane with good water resistance and a preparation method thereof, and comprises the following preparation steps: (1) vacuum dehydration of polyol, anionic hydrophilic chain extender and nonionic hydrophilic chain extender containing polyoxyethylene side chains, and then polymeric reaction of polyisocyanate to obtain a polyurethane prepolymer; (2) dispersion of the polyurethane prepolymer into water under high-speed stirring to obtain a prepolymer emulsion; and (3) dropwise addition of a mixed solution of a non-water-soluble diamine-based post-chain extender containing a hydrophobic chain segment and an organic solvent into the prepolymer emulsion, and stirring reaction to obtain the water-based polyurethane with good water resistance. The water-based polyurethane prepared by the application has the advantages of excellent stability, small particle size and good water resistance.

Description

Technical Field

[0001] This invention relates to the field of waterborne polyurethane technology, and more specifically to waterborne polyurethane nanoemulsions with good water resistance and their preparation methods. Background Technology

[0002] Waterborne polyurethane uses water as the dispersion medium, contains little or no VOCs, and is characterized by its non-toxicity, safety, reliability, environmental friendliness, and excellent overall performance. Waterborne polyurethane molecules have a block structure with alternating soft and hard segments, exhibiting excellent "tailorability." By optimizing the composition and structure of waterborne polyurethane, it can be endowed with superior mechanical properties, high adhesion, and good heat resistance. Therefore, waterborne polyurethane is widely used in waterborne coatings, digital inkjet inks, adhesives, leather finishing agents, and other fields.

[0003] In the synthesis of waterborne polyurethane, hydrophilic groups need to be introduced to disperse it in water and form a stable emulsion. The content of hydrophilic groups is the most direct and critical factor affecting the particle size of waterborne polyurethane emulsions; the higher the content of hydrophilic groups, the smaller the emulsion particle size. Generally speaking, waterborne polyurethane emulsions with small particle sizes, especially those with nanoscale dimensions, have characteristics such as storage stability, ease of film formation, and excellent film performance. Especially when waterborne polyurethane emulsions are used in waterborne digital inkjet printing inks, nanoscale waterborne polyurethane emulsions can greatly reduce the risk of inkjet printer head clogging, ensuring the continuity and stability of the printing process, which is crucial for the quality of inkjet printed products and their continuous industrial production processes. However, generally speaking, the smaller the particle size of the waterborne polyurethane emulsion, the more hydrophilic groups in its molecular structure, and the worse the water resistance of the obtained product, which may ultimately lead to the waterborne polyurethane losing its application value. Therefore, it is necessary to prepare a waterborne polyurethane with small particle size and good water resistance.

[0004] Introducing hydrophobic segments into the molecular structure of waterborne polyurethane and increasing their content is an effective method to improve the water resistance of waterborne polyurethane. Depending on the synthesis process of waterborne polyurethane, hydrophobic groups can be introduced before or after the polyurethane prepolymer is emulsified and dispersed to form an emulsion. For the former, highly hydrophobic polyurethane prepolymers can be synthesized by preferentially selecting polyols, small-molecule diols, or hydrophobic isocyanates containing hydrophobic segments. However, these highly hydrophobic polymers are difficult to form stable waterborne polyurethane emulsions with nanoparticle sizes when emulsified with water. For the latter, the polyurethane prepolymer can be emulsified in water to obtain a waterborne polyurethane prepolymer emulsion with nanoparticle sizes. Then, hydrophobic segments can be introduced through a post-chain extension reaction (generally using diamine-based chain extenders), thereby obtaining a waterborne polyurethane emulsion containing hydrophobic segments while maintaining or slightly altering the emulsion particle size. Studies have shown that water-soluble hydrophobic diamine chain extenders are an effective method for preparing aqueous polyurethane emulsions with both hydrophobicity and nanoparticle size. However, to obtain stronger hydrophobicity, insoluble diamine chain extenders can be used. However, insoluble diamine chain extenders (generally diamine compounds containing long carbon chains, polyaromatic rings, or polyalicylic rings) are difficult to disperse uniformly in emulsion systems formed from common polyurethane prepolymers. Therefore, the chain extension reaction of these insoluble diamines is not uniform, which leads to larger particle size and decreased stability in the chain-extended aqueous polyurethane emulsion. Currently, there is limited research on these insoluble diamine chain extenders. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for preparing waterborne polyurethane. The waterborne polyurethane provided by the present invention has small particle size, excellent stability, and good water resistance.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a waterborne polyurethane with good water resistance includes the following preparation steps:

[0008] (1) After vacuum dehydration of polyol, anionic hydrophilic chain extender and nonionic hydrophilic chain extender containing polyoxyethylene side chain, polyisocyanate is added to carry out polymerization reaction to obtain polyurethane prepolymer.

[0009] (2) The above polyurethane prepolymer is dispersed in water under high-speed shearing, and emulsified and sheared to obtain a prepolymer emulsion.

[0010] (3) Add dropwise a mixture of non-water-soluble diamine chain extender containing hydrophobic chain segments and organic solvent to the prepolymer emulsion obtained in step (2), stir and react to obtain waterborne polyurethane with good water resistance.

[0011] Preferably, the water-insoluble diamine chain extender containing hydrophobic segments in step (3) includes one or more of the following: 3,5-diethyltoluene diamine, 4,4-diaminodicyclohexylmethane, 4,4-diaminodiphenylmethane, N,N-bis(sec-pentylcyclohexane)diamine, 2,4,4-trimethylhexamethylenediamine, 2-aminobenzamidotoluene diamine, and 3,5-dimethylthiotoluene diamine. More preferably, 4,4′-diaminodicyclohexylmethane, which has a symmetrical structure and strong hydrophobicity, is used as the chain extender.

[0012] Preferably, the anionic hydrophilic chain extender in step (1) includes carboxylic acid chain extenders and sulfonate chain extenders, more preferably dimethylolpropionic acid (DMPA); the nonionic hydrophilic chain extender is a diol containing polyoxyethylene side chains, such as trimethylolpropane polyethylene glycol monomethyl ether, and commercially available products include Ymer from Perstorp. TM N120, Evonik's Tegomer D 3403, etc.; the polyols are polyether polyols and polycarbonate polyols with a molecular weight of 1000-2000.

[0013] Preferably, the polyether-type polyol is one or more of polytetrahydrofuran ether diol (PTMG) and polypropylene glycol (PPG); the polycarbonate-type polyol is one or more of aliphatic polycarbonate polyol and aromatic polycarbonate polyol; more preferably, aliphatic polycarbonate polyol, including PH200 from UBE and PHC from Kuraray, etc., and the resulting waterborne polyurethane has excellent water resistance.

[0014] Preferably, the polyisocyanate is hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), or dicyclohexylmethane diisocyanate (HDI). 12 At least one of MDI. More preferably isophorone diisocyanate (IPDI), the resulting waterborne polyurethane emulsion exhibits excellent properties such as resistance to yellowing, water resistance and heat resistance.

[0015] Preferably, the polyol, polyisocyanate, anionic hydrophilic chain extender, nonionic hydrophilic chain extender and post-chain extender mentioned in step (1) are added in amounts of 50% to 60%, 25% to 32%, 2.5% to 5%, 2.5% to 5%, and 2% to 4% of the solid mass of the obtained waterborne polyurethane, respectively.

[0016] Preferably, the vacuum dehydration conditions in step (1) are: heating to 110-120°C, controlling the vacuum degree in the reactor to 0.08 MPa-1 MPa after the raw material melts, and dehydrating for 1-2 hours.

[0017] Preferably, the polymerization reaction in step (1) is further enhanced by adding a catalyst and reacting at a temperature of 75-85°C for 2-3 hours. Then, a mixture of alcoholic small molecule chain extender and organic solvent is added dropwise, and the reaction continues for 1-2 hours. Finally, the temperature is lowered to 35-50°C, an organic solvent is added to reduce the viscosity of the prepolymer, and a neutralizing agent is added to react for 0.5±0.1 hours to obtain a polyurethane prepolymer.

[0018] Preferably, the alcohol-based small molecule chain extender is at least one of ethylene glycol, 1,4-butanediol, hexanediol, and diethylene glycol; the catalyst is at least one of dibutyltin dilaurate and stannous octoate; more preferably, 1,4-butanediol. After the small molecule chain extender with this symmetrical structure reacts with isocyanate, it can effectively increase the content of hard segments in the chain and promote crystallization, and the resulting waterborne polyurethane has good hardness and water resistance.

[0019] Preferably, the neutralizing agent is at least one of triethylamine, triethanolamine, N,N-dimethylethanolamine, and diethanolamine; and it is added in an amount of 95% to 100% neutralization.

[0020] Preferably, the amount of the alcohol-based small molecule chain extender and the catalyst added accounts for 3% to 6% and 0.05% to 0.1% of the solid mass of the obtained waterborne polyurethane, respectively.

[0021] Preferably, the molar ratio of NCO / OH in the waterborne polyurethane prepolymer in step (1) is 1.2 to 1.5; the organic solvent in steps (1) and (3) is acetone, and the low-boiling-point acetone can reduce the viscosity of the system and is easy to distill out.

[0022] Preferably, the stirring and dispersing speed in step (2) is 6000 r / min to 7000 r / min, and the emulsification shearing time is 5 min to 10 min.

[0023] Preferably, the stirring reaction in step (3) is carried out at a speed of 4000 r / min to 5000 r / min for 20 ± 10 min, then the stirring speed is reduced to 2000 ± 1000 r / min and the stirring reaction is continued for 30 ± 10 min. Finally, the organic solvent in the emulsion system is removed and allowed to stand for 24 ± 12 h.

[0024] The waterborne polyurethane prepared by the above method has a solid content of 30% to 35%.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) The waterborne polyurethane nanoemulsion prepared by the present invention has good stability and water resistance. It uses water as the dispersion medium, does not contain organic solvents, is green and environmentally friendly, and has a simple process and easy reaction control.

[0027] (2) This invention uses polyether diol and polycarbonate diol as polyols. Polycarbonate diol has good water resistance and high mechanical strength, while polyether diol has good flexibility. The combination of the two can achieve a balance between softness and hardness.

[0028] (3) This invention uses both anionic and nonionic hydrophilic monomers as internal emulsifiers, resulting in a waterborne polyurethane emulsion with nanoparticle size and good stability. In particular, the use of nonionic hydrophilic monomers containing polyoxyethylene side chains results in longer polyoxyethylene hydrophilic segments distributed on the side chains of the polyurethane molecules. This not only endows the waterborne polyurethane emulsion with resistance to Ca2+, but also... 2+ Na + The excellent stability of plasma also greatly improves the emulsifying ability of waterborne polyurethane systems, enhancing their ability to emulsify non-water-soluble hydrophobic substances.

[0029] (4) This invention uses a non-water-soluble diamine containing hydrophobic chain segments as a post-chain extender to extend the chain of polyurethane prepolymer emulsions. Utilizing the emulsifying ability of the waterborne polyurethane prepolymer emulsion system prepared by using anionic and nonionic hydrophilic monomers as composite internal emulsifiers, the non-water-soluble diamine post-chain extender can penetrate the interior of the polyurethane prepolymer latex particles and react with NCO groups. Without significantly altering the emulsion particle size and stability (or with minimal change), hydrophobic groups are introduced into the main chain structure of the polyurethane molecule, thereby improving the water resistance of the waterborne polyurethane. Attached Figure Description

[0030] Figure 1 These are photographs showing the appearance of the aqueous polyurethane emulsions prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention.

[0031] Figure 2 The graphs show the changes in particle size before and after chain extension of the aqueous polyurethane emulsions prepared in Examples 1-4 and Comparisons 1-2 of this invention. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0033] Example 1

[0034] In a four-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 40.0 g of PH200 (2000 molecular weight), 40.0 g of polypropylene glycol (PPG) (2000 molecular weight), 5.0 g of dimethylolpropionic acid, and 6.0 g of Ymer. TMN120 was heated to 110℃. After the raw materials melted, the vacuum degree inside the reactor was controlled at 0.08 MPa, and dehydration was carried out for 1 hour. The reaction temperature was adjusted to 75℃, and 44.0 g of isophorone diisocyanate and 0.1 g of dibutyltin dilaurate were added according to the formula. The reaction was continued for 2 hours. After the reaction was completed, a mixture of 8.0 g of 1,4-butanediol and 25.0 g of acetone was added dropwise, and the reaction was continued at 75℃ for 2 hours. Finally, the temperature was lowered to 35℃, acetone was added to reduce the viscosity of the prepolymer, and then 3.5 g of triethylamine was added to neutralize the reaction for 30 minutes to obtain the NCO-terminated polyurethane prepolymer. After transferring the synthesized polyurethane prepolymer to a dispersion tank, 330.0 g of deionized water was poured in while increasing the stirring speed to 6000 r / min. Emulsification and shearing were performed for 5 min to disperse and emulsify the prepolymer via phase inversion. Then, a mixture of 5.0 g of 4,4-diaminodicyclohexylmethane and 10.0 g of acetone was added dropwise to initiate a post-chain extension reaction. The reaction was carried out at a stirring speed of 4000 r / min for 20 min, followed by reducing the stirring speed to 2000 r / min and reacting for another 30 min. The product was then discharged, and a small amount of acetone was removed under vacuum. After standing and aging for 24 h, the product was filtered through a 200-mesh filter. A waterborne polyurethane with a solid content of 30.1% was obtained.

[0035] Example 2

[0036] In a four-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 42.0 g of PH200 (2000 molecular weight), 40.0 g of polypropylene glycol (PPG) (2000 molecular weight), 4.7 g of dimethylolpropionic acid, and 5.7 g of Ymer. TM N120 was heated to 114℃. After the raw materials melted, the vacuum degree inside the reactor was controlled at 0.1 MPa, and dehydration was carried out for 1.5 hours. The reaction temperature was adjusted to 80℃, and 40.0 g of isophorone diisocyanate and 0.1 g of dibutyltin dilaurate were added according to the formula. The reaction was continued for 2 hours. After the reaction was completed, a mixture of 7.0 g of 1,4-butanediol and 25.0 g of acetone was added dropwise, and the reaction was continued at 80℃ for 2 hours. Finally, the temperature was lowered to 38℃, acetone was added to reduce the viscosity of the prepolymer, and then 3.3 g of triethylamine was added to neutralize the reaction for 30 minutes to obtain the NCO-terminated polyurethane prepolymer. After transferring the synthesized polyurethane prepolymer to a dispersion tank, 280.0 g of deionized water was poured in while the stirring speed was increased to 6500 r / min. Emulsification and shearing were performed for 10 min to disperse and emulsify the prepolymer via phase inversion. Then, a mixture of 4.0 g of 4,4-diaminodicyclohexylmethane and 10.0 g of acetone was added dropwise to initiate a post-chain extension reaction. The reaction was carried out at a stirring speed of 4200 r / min for 20 min. The stirring speed was then reduced to approximately 2000 r / min and stirred for another 30 min before discharging. A small amount of acetone was removed under vacuum. The mixture was allowed to stand for 24 h and then filtered through a 200-mesh filter. A waterborne polyurethane with a solid content of 32.8% was obtained.

[0037] Example 3

[0038] In a four-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 40.0 g of PH200 (2000 molecular weight), 35.0 g of polypropylene glycol (PPG) (2000 molecular weight), 6.0 g of dimethylolpropionic acid, and 6.0 g of Ymer. TM N120 was heated to 118℃. After the raw materials melted, the vacuum degree inside the reactor was controlled at 0.09 MPa for 2 hours for dehydration. The reaction temperature was then adjusted to 82℃, and 46.0 g of isophorone diisocyanate and 0.1 g of dibutyltin dilaurate were added according to the formula. The reaction was continued for 2.5 hours. After the reaction was completed, a mixture of 8.0 g of 1,4-butanediol and 25.0 g of acetone was added dropwise, and the reaction was continued at 82℃ for 1.5 hours. Finally, the temperature was lowered to 40℃, acetone was added to reduce the viscosity of the prepolymer, and then 4.4 g of triethylamine was added to neutralize the reaction for 30 minutes to obtain the NCO-terminated polyurethane prepolymer. After transferring the synthesized polyurethane prepolymer to a dispersion tank, 280.0 g of deionized water was poured in while the stirring speed was increased to 7000 r / min. Emulsification and shearing were performed for 15 min to disperse and emulsify the prepolymer via phase inversion. Then, a mixture of 5.9 g of 4,4-diaminodicyclohexylmethane and 10.0 g of acetone was added dropwise to initiate a post-chain extension reaction. The reaction was carried out at a stirring speed of 4500 r / min for 20 min. The stirring speed was then reduced to approximately 2000 r / min and stirred for another 30 min before discharging. A small amount of acetone was removed under vacuum. The mixture was allowed to stand for 24 h and then filtered through a 200-mesh filter. A waterborne polyurethane with a solid content of 33.3% was obtained.

[0039] Example 4

[0040] In a four-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 45.0 g of PH200 (2000 molecular weight), 48.0 g of polypropylene glycol (PPG) (2000 molecular weight), 7.4 g of dimethylolpropionic acid, and 6.7 g of Ymer. TMN120 was heated to 120℃. After the raw materials melted, the vacuum degree inside the reactor was controlled at 0.1 MPa, and dehydration was carried out for 1.5 hours. The reaction temperature was adjusted to 85℃, and 60.0 g of isophorone diisocyanate and 0.2 g of dibutyltin dilaurate were added according to the formula. The reaction was continued for 3 hours. After the reaction was completed, a mixture of 11.2 g of 1,4-butanediol and 25.0 g of acetone was added dropwise, and the reaction was continued at 85℃ for 2 hours. Finally, the temperature was lowered to 42℃, acetone was added to reduce the viscosity of the prepolymer, and then 5.3 g of triethylamine was added to neutralize the reaction for 30 minutes to obtain the NCO-terminated polyurethane prepolymer. After transferring the synthesized polyurethane prepolymer to a dispersion tank, 340.0 g of deionized water was poured in while increasing the stirring speed to 7000 r / min. Emulsification and shearing were performed for 15 min to disperse and emulsify the prepolymer via phase inversion. Then, a mixture of 7.4 g of 4,4-diaminodicyclohexylmethane and 10.0 g of acetone was added dropwise to initiate a post-chain extension reaction. The reaction was carried out at a stirring speed of 5000 r / min for 20 min. The stirring speed was then reduced to approximately 2000 r / min and stirred for another 30 min before discharging. A small amount of acetone was removed under vacuum. The mixture was allowed to stand for 24 h and then filtered through a 200-mesh filter. A waterborne polyurethane with a solid content of 34.3% was obtained.

[0041] Comparative Example 1 without the addition of a nonionic hydrophilic chain extender

[0042] In a four-necked flask equipped with a stirrer, thermometer, and reflux condenser, 45.0 g of PH200 (2000 molecular weight), 48.0 g of polypropylene glycol (PPG) (2000 molecular weight), and 8.5 g of dimethylolpropionic acid were added. The mixture was heated to 120°C, and after the raw materials melted, the vacuum in the reactor was controlled at 0.1 MPa for 1.5 h for dehydration. The reaction temperature was adjusted to 85°C, and 60.0 g of isophorone diisocyanate and 0.2 g of dibutyltin dilaurate were added according to the formula. The reaction was continued for 3 h. After the reaction was completed, a mixture of 11.2 g of 1,4-butanediol and 25.0 g of acetone was added dropwise, and the reaction was continued at 85°C for 2 h. Finally, the temperature was lowered to 42°C, acetone was added to reduce the viscosity of the prepolymer, and then 6.3 g of triethylamine was added to neutralize the reaction for 30 min to obtain an NCO-terminated polyurethane prepolymer. After transferring the synthesized polyurethane prepolymer to a dispersion tank, 340.0 g of deionized water was poured in while increasing the stirring speed to 7000 r / min. Emulsification and shearing were performed for 15 min to disperse and emulsify the prepolymer via phase inversion. Then, a mixture of 7.4 g of 4,4-diaminodicyclohexylmethane and 10.0 g of acetone was added dropwise to initiate a post-chain extension reaction. The reaction was carried out at a stirring speed of 5000 r / min for 20 min. The stirring speed was then reduced to approximately 2000 r / min and stirred for another 30 min before discharging. A small amount of acetone was removed under vacuum. The mixture was allowed to stand for 24 h and then filtered through a 200-mesh filter. A waterborne polyurethane with a solid content of 33.6% was obtained.

[0043] Comparative Example 2: Addition of water-soluble chain extender

[0044] In a four-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 42.0 g of PH200 (2000 molecular weight), 40.0 g of polypropylene glycol (PPG) (2000 molecular weight), 4.7 g of dimethylolpropionic acid, and 5.7 g of Ymer. TM N120 was heated to 114℃. After the raw materials melted, the vacuum degree inside the reactor was controlled at 0.1 MPa, and dehydration was carried out for 1.5 hours. The reaction temperature was adjusted to 80℃, and 40.0 g of isophorone diisocyanate and 0.1 g of dibutyltin dilaurate were added according to the formula. The reaction was continued for 2 hours. After the reaction was completed, a mixture of 7.0 g of 1,4-butanediol and 25.0 g of acetone was added dropwise, and the reaction was continued at 80℃ for 2 hours. Finally, the temperature was lowered to 38℃, acetone was added to reduce the viscosity of the prepolymer, and then 3.3 g of triethylamine was added to neutralize the reaction for 30 minutes to obtain the NCO-terminated polyurethane prepolymer. After transferring the synthesized polyurethane prepolymer to a dispersion tank, 280.0 g of deionized water was poured in while increasing the stirring speed to 6500 r / min. Emulsification and shearing were performed for 10 min to disperse and emulsify the prepolymer via phase inversion. Then, a mixture of 3.3 g of isophorone diamine and 10.0 g of water was added dropwise to initiate a post-chain extension reaction. The reaction was carried out at a stirring speed of 4200 r / min for 20 min. The stirring speed was then reduced to approximately 2000 r / min and stirred for another 30 min before discharging. A small amount of acetone was removed under vacuum. The mixture was allowed to stand for 24 h and then filtered through a 200-mesh filter. A waterborne polyurethane with a solid content of 32.8% was obtained.

[0045] Experimental results testing and analysis:

[0046] Performance testing methods for the products obtained in the above embodiments:

[0047] 1. Water absorption rate test of adhesive film

[0048] Preparation of the film: Weigh an appropriate amount of the prepared waterborne polyurethane emulsion and spread it evenly on a polytetrafluoroethylene plate. Place it horizontally and let it dry naturally at room temperature for 3 days. After the film is formed, put it in a 50℃ oven to dry to constant weight and put it in a desiccator for later use.

[0049] Determination of water absorption rate: Cut the film into 2cm×2cm samples, weigh them on an analytical balance, and record the weight as M0. Then, soak them in deionized water for 24 hours, remove them, blot the surface moisture with filter paper, and weigh them again, recording the weight as M1. Calculate the water absorption rate of the latex film using the following formula:

[0050] Water absorption rate W / % = (M1 - M0) / M0 × 100%

[0051] 2. Emulsion particle size test:

[0052] Particle size and its distribution were determined by dynamic light scattering (DLS, Malvern, ZS-Nano-S) at 25 °C. The prepared waterborne polyurethane emulsion was diluted with deionized water to 0.1 wt%, and the average particle size, particle size distribution and zeta potential of the diluted waterborne polyurethane were measured. The results were the average of three tests.

[0053] 3. Ion stability:

[0054] Add 5 ml of the prepared aqueous polyurethane emulsion to a 10 ml graduated test tube using a dropper, then slowly add 1 ml of 1% NaCl solution or 1 ml of 0.1% CaCl2 solution. After thorough mixing, place the tube on a test tube rack and observe whether the emulsion breaks down, precipitates, or flocculates after 24 hours.

[0055] 4. Storage stability

[0056] Storage stability was simulated using a centrifuge-accelerated sedimentation experiment. Equal masses of the prepared aqueous polyurethane emulsion were placed in centrifuge tubes, which were then symmetrically placed in a centrifuge and centrifuged at 3000 rpm for 15 minutes. The presence or absence of stratification was observed; if no stratification occurred, the emulsion was considered to have a 6-month storage stability period.

[0057] Table 1. Particle size changes before and after chain extension of waterborne polyurethane emulsion.

[0058]

[0059] As can be seen from Table 1, the waterborne polyurethane prepared using non-water-soluble hydrophobic chain extenders has a smaller particle size after chain extension with the addition of nonionic hydrophilic monomers. This indicates that using anionic-nonionic hydrophilic monomers as hydrophilic chain extenders can endow waterborne polyurethane with stronger self-emulsifying and dispersing capabilities, which is beneficial for the non-water-soluble hydrophobic diamine chain extender to enter the interior of the waterborne polyurethane prepolymer emulsion particles for reaction, thereby obtaining waterborne polyurethane with smaller particle size.

[0060] Table 2. Appearance, stability, and water absorption of waterborne polyurethane emulsions

[0061]

[0062]

[0063] Table 2 shows that the waterborne polyurethane emulsions obtained by adding nonionic hydrophilic monomers all have high transparency and good Ca2+ resistance. 2+ Na +Stability. Compared to waterborne polyurethanes prepared using water-soluble hydrophobic chain extenders, waterborne polyurethanes prepared using insoluble hydrophobic chain extenders have lower water absorption rates. This indicates that insoluble hydrophobic chain extenders can introduce stronger hydrophobic segments during the post-chain extension reaction, thus more effectively reducing the penetration of water molecules.

[0064] Table 3. Stress (tensile strength) and strain (elongation at break) of waterborne polyurethane before and after immersion in water.

[0065]

[0066] Table 3 shows that the stress change of waterborne polyurethane prepared using a non-water-soluble hydrophobic chain extender was not significant after soaking in water for 24 hours. This indicates that using a non-water-soluble hydrophobic chain extender can not only reduce the penetration of water molecules into the polyurethane but also effectively improve the hydrolytic stability of the waterborne polyurethane. However, when no nonionic hydrophilic monomer is added, the waterborne polyurethane emulsion prepared has a large particle size and poor stability due to the uneven post-chain extension reaction process, resulting in poor hydrolytic stability.

[0067] Based on the above test results, the waterborne polyurethane emulsion prepared by this invention has the advantages of excellent electrolyte stability, average particle size of 30-40 nm, low water absorption and excellent hydrolytic stability, non-toxicity, safety and environmental protection, simple process, stable and easy operation, and convenient product transportation and use.

[0068] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for producing a waterborne polyurethane having good water resistance, characterized by, The preparation steps include the following: (1) After vacuum dehydration of polyol, anionic hydrophilic chain extender and nonionic hydrophilic chain extender containing polyoxyethylene side chain, polyisocyanate is added to carry out polymerization reaction to obtain polyurethane prepolymer; the nonionic hydrophilic chain extender is trimethylolpropane polyethylene glycol monomethyl ether. (2) The above polyurethane prepolymer is dispersed in water under high-speed stirring to obtain a prepolymer emulsion; (3) Add dropwise a mixture of non-water-soluble diamine chain extender containing hydrophobic chain segments and organic solvent to the prepolymer emulsion obtained in step (2), stir and react to obtain waterborne polyurethane with good water resistance; The non-water-soluble diamine chain extender containing hydrophobic linkages mentioned in step (3) includes one or a mixture of 3,5-diethyltoluene diamine, 4,4-diaminodicyclohexylmethane, 4,4-diaminodiphenylmethane, N,N-bis(sec-pentylcyclohexane)diamine, 2,4,4-trimethylhexamethylenediamine, 2-aminobenzamidotoluene diamine, and 3,5-dimethylthiotoluene diamine; The anionic hydrophilic chain extender mentioned in step (1) is one or more of carboxylic acid chain extenders and sulfonate chain extenders; the polyol is a polyether polyol and a polycarbonate polyol with a molecular weight of 1000-2000. The amounts of the polyol, polyisocyanate, anionic hydrophilic chain extender, nonionic hydrophilic chain extender, and post-chain extender added are respectively 50% to 60%, 25% to 32%, 2.5% to 5%, 2.5% to 5%, and 2% to 4% of the solid mass of the obtained waterborne polyurethane.

2. The production method according to claim 1, characterized by, The anionic hydrophilic chain extender is dimethylolpropionic acid; the polyether polyol is one or more of polytetrahydrofuran ether diol and polypropylene glycol; the polycarbonate polyol is one or more of aliphatic polycarbonate polyol and aromatic polycarbonate polyol. The polyisocyanate is at least one of hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

3. The production method according to claim 1 or 2, characterized by, In step (1), a catalyst is added to the polymerization reaction. The reaction is carried out at 75-85℃ for 2-3 hours. Then, a mixture of alcoholic small molecule chain extender and organic solvent is added dropwise, and the reaction continues for 1-2 hours. Finally, the temperature is lowered to 35℃-50℃, organic solvent is added to reduce the viscosity of the prepolymer, and then a neutralizing agent is added to react for 0.5±0.1 hours to obtain the polyurethane prepolymer.

4. The production method according to claim 3, characterized by, The alcohol-based small molecule chain extender is at least one of ethylene glycol, 1,4-butanediol, hexanediol, and diethylene glycol; the catalyst is at least one of dibutyltin dilaurate and stannous octoate. The neutralizing agent is at least one of triethylamine, triethanolamine, N,N-dimethylethanolamine, and diethanolamine; The amount of the alcohol-based small molecule chain extender and the catalyst added accounts for 3%~6% and 0.05%~0.1% of the solid mass of the obtained waterborne polyurethane, respectively.

5. The production method according to claim 1 or 2, characterized by, The molar ratio of NCO / OH in the waterborne polyurethane prepolymer in step (1) is 1.2~1.5; the vacuum dehydration conditions are to raise the temperature to 110~120℃, and after the raw materials melt, control the vacuum degree in the reactor to 0.08 MPa~1 MPa, and dehydrate for 1~2 hours; the organic solvent in steps (1) and (3) is acetone. The high-speed stirring speed in step (2) is 6000 r / min ~ 7000 r / min, and the stirring time is 5 min ~ 10 min; The stirring reaction in step (3) is carried out at a speed of 4000 r / min ~ 5000 r / min for 20 ± 10 min, then the stirring speed is reduced to 2000 ± 1000 r / min and the stirring reaction is continued for 30 ± 10 min; finally, the organic solvent is removed and the mixture is allowed to stand for 24 ± 12 h.

6. The waterborne polyurethane prepared by the method according to any one of claims 1 to 5.

7. The aqueous polyurethane of claim 6, wherein, The solid content of the waterborne polyurethane is 30% to 35%.

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