Narrow particle size high crystallinity nonionic aqueous polyurethane and method of making same

Abstract

The application relates to a narrow-particle-diameter high-crystallinity nonionic waterborne polyurethane and a preparation method thereof, and belongs to the technical field of high polymer materials. Through a synergistic process of temperature gradient control + stepwise chain extension + high-temperature curing, the prepared nonionic waterborne polyurethane has the advantages of narrow particle diameter, high crystallinity, neutrality and non-corrosion, the particle diameter range is only 10-30 nm, the most frequent particle diameter is about 25 nm, the surface is smooth and free of particle feeling after film forming, the gloss reaches more than 95%, and the solvent wear resistance is improved by more than 40%; the nonionic waterborne polyurethane can be used in high-end furniture high-gloss coating, electronic device packaging, leather finishing and the like, and has a wide application range; and the industrialized mass production has high performance stability between batch processes at room temperature, no neutralizing agent is added in the process, and the process and product are more environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a narrow-particle-size, highly crystalline nonionic waterborne polyurethane and its preparation method. Background Technology

[0002] Nonionic waterborne polyurethane (WPU), as an environmentally friendly material that achieves water dispersibility through hydrophilic nonionic segments, has a wide range of applications in coatings, leather finishing, textile finishing, adhesives and electronic packaging because its system has no residual ions, extremely low volatile organic compound (VOC) content, and exhibits good adhesion and compatibility with various polar substrates (such as wood, plastics, leather, fabrics and even electronic components).

[0003] However, despite the aforementioned advantages, current mainstream nonionic waterborne polyurethane products still have significant shortcomings in key performance indicators, severely restricting their promotion and in-depth application in demanding high-end applications (such as high-gloss surface coatings for high-end furniture and protective encapsulation for precision electronic devices). These performance bottlenecks are mainly reflected in the following two interrelated aspects: First, the large particle size and wide distribution affect film quality and appearance. Existing nonionic WPU emulsions have particle sizes concentrated between 80nm and 150nm, but with a wide distribution and a high polydispersity index (PDI). This wide particle size distribution leads to uneven particle packing during film formation, making it difficult to form a dense and smooth microstructure. The direct consequence is that the cured coating surface is prone to microscopic roughness, increasing diffuse reflection of light and significantly reducing the coating's gloss, transparency, and visual fullness, failing to meet the requirements of high-end finishes for extremely high surface smoothness and high gloss. Second, the low crystallinity in the hard segment region restricts the physicochemical properties of the coating. The macroscopic properties of WPU (such as hardness, abrasion resistance, solvent resistance, and mechanical strength) largely depend on the orderly arrangement and crystallinity of its hard segment microdomains formed through hydrogen bonding. Existing nonionic WPU products typically lack effective guidance and optimization of the ordered aggregation and crystallization process of hard segments in their synthesis, resulting in generally low crystallinity of the hard segments in the final product. The loose structure and insufficient order of the hard segment microdomains directly weaken the cohesive strength and effectiveness of the cross-linking network in the coating, leading to poor abrasion and scratch resistance, and weak resistance to common solvents (such as alcohols and esters), making it difficult to meet the durable protection and long-lasting standards required for high-end applications.

[0004] Currently, the industry generally adopts a relatively extensive process mode of "single-temperature prepolymerization - one-step chain extension - room temperature curing". In this mode, room temperature curing is difficult to promote the orderly aggregation of hard segments and cannot precisely control the particle growth process: too high a prepolymerization temperature can easily lead to premature agglomeration of hard segments, while too low a temperature will result in insufficient prepolymerization reaction; one-step chain extension causes uneven distribution of hard segments, and room temperature curing further aggravates the problems of wide particle size and low crystallinity. In view of the inherent limitations of the existing preparation methods in terms of process route, this invention provides a narrow particle size, high crystallinity nonionic waterborne polyurethane and its preparation method. Summary of the Invention

[0005] To overcome the limitations of existing technologies, this application obtains a nonionic waterborne polyurethane with both narrow particle size and high crystallinity through synergistic regulation of "temperature gradient control + stepwise chain extension + high-temperature stirring and curing". The polyurethane also has solvent-resistant scrubbing properties, realizing the application of nonionic waterborne polyurethane in high-end fields.

[0006] To achieve the above technical effects, this application provides the following technical solution:

[0007] First, this application provides a method for preparing narrow-particle-size, highly crystalline nonionic waterborne polyurethane, comprising the following steps:

[0008] S1. Mix carbon dioxide-based polyol and isophorone diisocyanate, heat to 90-120℃ and stir to react, to obtain the prepolymer product;

[0009] S2. Cool the prepolymer to below 55°C, add the hydrophilic monomer and stir until completely dispersed;

[0010] S3. Heat the mixture of S2 to 70-95℃ and add a chain extender to continue the reaction;

[0011] S4. Cool the mixture of S3 to below 55°C, emulsify with water, and then add the diluted solution of the chain extender dropwise to carry out the reaction.

[0012] S5. Stir and mature the emulsion system of S4 at 75-90℃ for 1-5 hours to obtain the nonionic waterborne polyurethane.

[0013] Further, the mass ratio of the carbon dioxide-based polyol and isophorone diisocyanate in S1 is 60-80:25-40; preferably 65-78:30-40; more preferably 70-75:30-35. The relative amounts of the carbon dioxide-based polyol providing -OH and the diisocyanate providing -NCO in the reaction directly determine the polymer chain structure. Excess carbon dioxide-based polyol will lead to a large number of polyurethane chains being capped with hydroxyl groups, resulting in weakened hard segment crystallinity and decreased heat resistance, abrasion resistance, and solvent resistance. When diisocyanate is in excess, in addition to forming urethane bonds, excessive -NCO will lead to over-crosslinking, thereby restricting chain segment movement and inhibiting the orderly arrangement and crystallinity of the hard segments.

[0014] In one embodiment, the mass ratio of the carbon dioxide-based polyol to the isophorone diisocyanate is 75:35.

[0015] Furthermore, the weight-average molecular weight of the carbon dioxide-based polyol is 1000-3000, preferably 2000-2500.

[0016] Furthermore, the isophorone diisocyanate has an -NCO content of ≥37.5%.

[0017] Furthermore, the isophorone diisocyanate used in S1 needs to be dehydrated. This application does not impose strict requirements on the dehydration method; an exemplary dehydration method is to place the isophorone diisocyanate under vacuum drying at 40-50°C for 1-3 hours.

[0018] Furthermore, an organic Bi catalyst is added to S1, with the amount added accounting for 0.15-0.45% of the mass of isophorone diisocyanate, preferably 0.28-0.35%; in one embodiment, the amount of the organic Bi catalyst accounts for 0.32% of the mass of isophorone diisocyanate.

[0019] Furthermore, the organic Bi catalyst includes, but is not limited to, at least one of bismuth-2-ethylhexanoate (bismuth octanoate), bismuth neodecanoate, bismuth acetate, bismuth benzoate, bismuth citrate, bismuth lactate, and bismuth phthalate.

[0020] Furthermore, the reaction temperature in S1 is 95-115℃, preferably 98-105℃; the reaction time is 2-8h, preferably 4-5h. Under these prepolymerization temperature and time conditions, the reaction between isophorone diisocyanate and carbon dioxide-based polyol is more stable, effectively suppressing side reactions and yielding a linear prepolymer with uniform molecular weight distribution and stable terminal -NCO content. This provides a crucial foundation for subsequent stepwise chain extension to construct regular hard segment structures and for obtaining emulsions with narrow particle size distributions through high-temperature shear emulsification.

[0021] Further, the hydrophilic monomer is trimethylolpropane polyethylene glycol monomethyl ether; the hydroxyl value is 40-68 mg KOH / g, more preferably 54-60 mg KOH / g. Trimethylolpropane polyethylene glycol monomethyl ether has polyethylene glycol monomethyl ether segments and trimethylolpropane core reaction sites. The polyethylene glycol monomethyl ether segments have moderate hydrophilicity and can provide appropriate steric hindrance to prevent particle aggregation, which is conducive to the formation of a narrow particle size distribution emulsion. During emulsification and film formation, the trimethylolpropane can provide cohesive crosslinking points, enhance the network structure inside and between particles, and improve the stability of the emulsion. Further specifying its hydroxyl value avoids excessively low hydroxyl values, which would cause the prepolymer to be overly hydrophilic and destroy the hard segment crystals; and avoids excessively high hydroxyl values, which would lead to difficulties in emulsification, poor emulsion stability, large and wide particle size distribution, and easy precipitation.

[0022] Furthermore, the mass ratio of the carbon dioxide-based polyol, isophorone diisocyanate, and hydrophilic monomer is 65-78:30-40:20-35.

[0023] In one embodiment, the mass ratio of the carbon dioxide-based polyol, isophorone diisocyanate, and hydrophilic monomer is 70-75:32-37:25-30.

[0024] Furthermore, the stirring speed in S2 is 300-600 rpm, and the stirring time is 10-60 min.

[0025] Further, the chain extender is 1,4-butanediol, and the amount added is 2-6% of the mass of the prepolymer product, preferably 3-5%.

[0026] Furthermore, the stirring speed of the S3 reaction is 300-600 rpm, preferably 400-500 rpm; the stirring reaction time is 20-60 min, preferably 30-40 min.

[0027] Furthermore, the amount of water added in S4 is 1-3 times the mass of the prepolymer product, preferably 1.5-2 times; the water temperature is 50-55℃ to avoid particle agglomeration caused by temperature difference.

[0028] Furthermore, in S4, the emulsification stirring speed is 800-1000 rpm, and the stirring time is 25-35 min. This speed range can provide suitable shear energy for prepolymer dispersion; when the speed is below 800 rpm, the dispersion is insufficient, resulting in large emulsion particle size and wide distribution; when the speed is above 1000 rpm, excessive shear and the generated frictional heat will destroy the emulsion stability and may trigger side reactions.

[0029] Furthermore, the chain extender is isophorone diamine, and the amount added is 2-5% of the mass of the prepolymer product, preferably 3-4%.

[0030] Furthermore, the mass concentration of the diluted chain extender is 8-15%, the dropping rate is 1-2 drops / second, and the stirring reaction time after dropping is 10-20 min. The introduction of isophorone diamine, through the formation of strong hydrogen bonds and highly regular urea bond hard segments, synergistically enhances the crystallization driving force and crystallization quality of the hard segment microregions with the isophorone diisocyanate hard segments, fundamentally improving the crystallization driving force and crystallization quality of the hard segment microregions.

[0031] Furthermore, the curing temperature is 78-82℃, and the stirring speed is 300-400 rpm. These conditions simultaneously meet the dual requirements of molecular chain motion and colloidal stability. Appropriate stirring ensures uniform dispersion of latex particles throughout the curing process, maintaining a narrow particle size distribution. A suitable curing temperature provides the optimal thermodynamic environment for the hard segments formed after chain extension, allowing for sufficient rearrangement and crystallization, ultimately achieving high film durability. If the curing temperature is too low or the stirring speed is too slow, the crystallinity of the nonionic waterborne polyurethane hard segments will be insufficient; if the temperature is too high or the stirring speed is too fast, it may lead to increased side reactions or damage to the latex particle structure.

[0032] Secondly, this application provides a narrow-particle-size, highly crystalline nonionic waterborne polyurethane obtained according to the above preparation method.

[0033] Furthermore, the nonionic waterborne polyurethane has a particle size range of 10-30 nm, a most frequent particle size of 25 nm, and a maximum frequency of 38%.

[0034] Furthermore, the nonionic waterborne polyurethane exhibits a high-intensity characteristic peak at 2θ = 18.30°.

[0035] Furthermore, the pH value of the nonionic waterborne polyurethane is 7.0-7.2.

[0036] The beneficial effects of this invention are:

[0037] 1. The nonionic waterborne polyurethane emulsion of this application breaks through the existing technical bottleneck in particle size, with a particle size range of only 10~30nm and the most frequent particle size of about 25nm, which is much smaller than the capped nonionic waterborne polyurethane on the market (80-150nm). The particles are uniformly dispersed (no agglomeration in SEM image), and the surface is smooth and free of particles after film formation, with a gloss of over 95%.

[0038] 2. The nonionic waterborne polyurethane prepared in this application has significantly improved crystallinity. Through the synergistic process of temperature gradient control, stepwise chain extension and high-temperature stirring and curing, the orderly aggregation of hard segments is promoted. The XRD shows the highest intensity characteristic peak at 2θ=18.30°, and the wear resistance is improved by more than 40% (withstanding 50 ethanol wiping cycles without damage). This solves the problems of low crystallinity and insufficient mechanical properties of existing products.

[0039] 3. The preparation method of this application has high process controllability. When the nonionic waterborne polyurethane is mass-produced industrially, the batch-to-batch performance error is <5%, which is far superior to commercial products (error of about 10%). Moreover, no neutralizing agent is required, and it is environmentally friendly with low VOC.

[0040] 4. The nonionic waterborne polyurethane of this application has the advantages of narrow particle size, high crystallinity, neutrality and non-corrosiveness, and can be used in high-end furniture high-gloss coating, electronic device packaging, leather finishing and other scenarios. It has a wide range of applications and high market conversion value. Attached Figure Description

[0041] Figure 1 Particle size distribution diagram of the nonionic aqueous polyurethane emulsion prepared in Example 1.

[0042] Figure 2 XRD pattern of the nonionic aqueous polyurethane emulsion prepared in Example 1. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] Unless otherwise specified, each drop of the raw material added in this application is approximately 0.05 g. The carbon dioxide-based polyol used was purchased from Asahikawa Chemicals Sales (Suzhou) Co., Ltd., model XCP-4000B. The isophorone diisocyanate (IPDI) used has an -NCO content ≥37.5%; it needs to be dehydrated by vacuum drying at 40°C for 1 hour before use. The hydrophilic monomer trimethylolpropane polyethylene glycol monomethyl ether (TMP-mPEG) has a hydroxyl value of 56±2 mg KOH / g and a moisture content ≤0.5%, and was purchased from Guangzhou Jiafucheng Materials Technology Co., Ltd. The organic Bi catalyst is NIAX MC-710.

[0045] Example 1

[0046] This embodiment provides a narrow-particle-size, high-crystallinity nonionic waterborne polyurethane, the preparation method of which includes the following steps:

[0047] S1. By mass, 75 parts of carbon dioxide-based polyol (Mw=2000) and 35 parts of isophorone diisocyanate were added to a four-necked flask and mixed evenly. 10 drops of organic Bi catalyst were slowly added along the inner wall of the flask and stirred for 10 min. The temperature was raised to 100°C and stirred at 350 rpm for 4 h to carry out the prepolymerization reaction to obtain the prepolymer product.

[0048] S2. Turn off the heating and cool the prepolymer product to 50°C at a cooling rate of 2°C / min. Add 25 parts of the hydrophilic monomer trimethylolpropane polyethylene glycol monomethyl ether, adjust the stirring speed to 350 rpm, and stir for 20 min to ensure that the hydrophilic monomer is completely dispersed in the prepolymer product without local agglomeration.

[0049] S3. Continuously purge nitrogen gas into the four-necked flask (flow rate 0.5 L / min) and heat the mixture from S2 to 80°C. Slowly add 4 parts of chain extender 1,4-butanediol to the four-necked flask, adjust the stirring speed to 450 rpm, and continue stirring for 35 min to ensure the chain extension reaction is complete.

[0050] S4. Turn off the heating and allow the mixture from S3 to cool naturally to 50°C. While maintaining a stirring speed of 450 rpm, add 200 parts of deionized water at 50°C (conductivity ≤10 μS / cm). Then adjust the stirring speed to 900 rpm and emulsify for 30 min. After emulsification, add 4 parts of a diluted solution of isophorone diamine and 30 parts of deionized water at a rate of 1.5 drops / second, and stir for 15 min to complete the stepwise chain extension reaction.

[0051] S5. Heat the closed emulsion system of S4 to 80°C and mature it for 2 hours with a stirring speed of 350 rpm. After completion, allow it to cool naturally to room temperature to obtain the nonionic waterborne polyurethane.

[0052] Testing revealed that the nonionic waterborne polyurethane particle size range of this embodiment is 10~30nm, with the most frequent particle size at 25nm and the maximum frequency at 38% (see appendix). Figure 1 This demonstrates that the proposed method can produce nonionic waterborne polyurethane with smaller particle size and a narrower particle size distribution range; (Attached) Figure 2 The XRD results show that the characteristic peak intensity is the highest (18000 a.u.) at 2θ=18.30°, indicating that the nonionic waterborne polyurethane of this application also has excellent crystallization properties.

[0053] Example 2

[0054] This embodiment provides a narrow-particle-size, high-crystallinity nonionic waterborne polyurethane, the preparation method of which includes the following steps:

[0055] S1. By mass, 65 parts of carbon dioxide-based polyol (Mw=2000) and 30 parts of isophorone diisocyanate were added to a four-necked flask and mixed evenly. 8 drops of organic Bi catalyst were slowly added along the inner wall of the flask and stirred for 10 min. The temperature was raised to 95°C and stirred at 300 rpm for 5 h to carry out the prepolymerization reaction to obtain the prepolymer product.

[0056] S2. Turn off the heating and cool the prepolymer product to 50°C at a cooling rate of 1°C / min. Add 20 parts of the hydrophilic monomer trimethylolpropane polyethylene glycol monomethyl ether, adjust the stirring speed to 300 rpm, and stir for 35 min to ensure that the hydrophilic monomer is completely dispersed in the prepolymer product without local agglomeration.

[0057] S3. Continuously purge nitrogen gas into the four-necked flask (flow rate 0.5 L / min) and heat the mixture from S2 to 75°C. Slowly add 5.7 parts of chain extender 1,4-butanediol to the four-necked flask, adjust the stirring speed to 500 rpm, and continue stirring for 20 min to ensure the chain extension reaction is complete.

[0058] S4. Turn off the heating and allow the mixture from S3 to cool naturally to 50°C. While maintaining a stirring speed of 450 rpm, add 100 parts of deionized water at 50°C (conductivity ≤10 μS / cm). Then adjust the stirring speed to 800 rpm and emulsify for 25 min. After emulsification, add 2 parts of a diluted solution of isophorone diamine and 23 parts of deionized water at a rate of 1 drop / second, and stir for 15 min to complete the stepwise chain extension reaction.

[0059] S5. The closed emulsion system of S4 is heated to 75°C and matured at a stirring speed of 350 rpm for 2 hours. After completion, it is naturally cooled to room temperature to obtain the nonionic waterborne polyurethane.

[0060] Example 3

[0061] This embodiment provides a narrow-particle-size, high-crystallinity nonionic waterborne polyurethane, the preparation method of which includes the following steps:

[0062] S1. By mass, 78 parts of carbon dioxide-based polyol (Mw=2000) and 40 parts of isophorone diisocyanate were added to a four-necked flask and mixed evenly. 15 drops of organic Bi catalyst were slowly added along the inner wall of the flask and stirred for 10 min. The temperature was raised to 115°C and stirred at 350 rpm for 3 h to carry out the prepolymerization reaction to obtain the prepolymer product.

[0063] S2. Turn off the heating and cool the prepolymer product to 50°C at a cooling rate of 2°C / min. Add 35 parts of the hydrophilic monomer trimethylolpropane polyethylene glycol monomethyl ether, adjust the stirring speed to 500 rpm, and stir for 20 min to ensure that the hydrophilic monomer is completely dispersed in the prepolymer product without local agglomeration.

[0064] S3. Continuously purge nitrogen gas into the four-necked flask (flow rate 0.5 L / min) and heat the mixture from S2 to 95°C. Slowly add 6 parts of chain extender 1,4-butanediol to the four-necked flask, adjust the stirring speed to 600 rpm, and continue stirring for 20 min to ensure the chain extension reaction is complete.

[0065] S4. Turn off the heating and allow the mixture from S3 to cool naturally to 50°C. While maintaining a stirring speed of 500 rpm, add 300 parts of deionized water at 50°C (conductivity ≤10 μS / cm). Then adjust the stirring speed to 1000 rpm and emulsify for 25 min. After emulsification, add 5.5 parts of a diluted solution of isophorone diamine and 45 parts of deionized water at a rate of 2 drops / second, and stir for 15 min to complete the stepwise chain extension reaction.

[0066] S5. The closed emulsion system of S4 is heated to 90°C and matured at a stirring speed of 500 rpm for 2 hours. After completion, it is naturally cooled to room temperature to obtain the nonionic waterborne polyurethane.

[0067] Comparative Example 1

[0068] This comparative example provides a commercially available nonionic waterborne polyurethane, FS-6A, purchased from Anhui Femtosecond New Materials Co., Ltd.

[0069] Comparative Example 2

[0070] This comparative example provides a nonionic waterborne polyurethane, the preparation method of which is basically the same as that of Example 1, the only difference being that the curing temperature of S5 is 50°C.

[0071] Comparative Example 3

[0072] This comparative example provides a narrow-particle-size, highly crystalline nonionic waterborne polyurethane, the preparation method of which includes the following steps:

[0073] S1. By mass, 75 parts of carbon dioxide-based polyol (Mw=2000), 35 parts of isophorone diisocyanate and 25 parts of hydrophilic monomer trimethylolpropane polyethylene glycol monomethyl ether were added to a four-necked flask and mixed evenly. 10 drops of organic Bi catalyst were slowly added dropwise along the inner wall of the flask and stirred for 10 min. The temperature was raised to 100℃ and stirred at 350 rpm for 4 h to carry out the prepolymerization reaction to obtain the prepolymer product.

[0074] S2. Continuously purge nitrogen gas (flow rate 0.5 L / min) into a four-necked flask and heat the mixture of S2 to 80°C. Slowly add 4 parts of chain extender 1,4-butanediol into the four-necked flask, adjust the stirring speed to 450 rpm, and continue stirring for 35 min to ensure that the chain extension reaction is complete.

[0075] S3. Turn off the heating and allow the mixture from S2 to cool naturally to 50°C. While maintaining a stirring speed of 450 rpm, add 200 parts of deionized water at 50°C (conductivity ≤10 μS / cm). Then adjust the stirring speed to 900 rpm and emulsify for 30 min. After emulsification, add 4 parts of a diluted solution of isophorone diamine and 30 parts of deionized water at a rate of 1.5 drops / second, and stir for 15 min to complete the stepwise chain extension reaction.

[0076] S4. The closed emulsion system of S3 is heated to 80°C and matured at a stirring speed of 350 rpm for 2 hours. After completion, it is naturally cooled to room temperature to obtain the nonionic waterborne polyurethane (NI-WPU).

[0077] Performance testing methods and results:

[0078] I. Particle size test: The particle size of the nonionic waterborne polyurethane emulsions in each embodiment was tested using a ZETA potentiometer.

[0079] II. Film gloss: The gloss was determined using the method specified in the national standard GB / T 9754-2025, "Determination of gloss at 20°, 60°, and 85° for paints and varnishes".

[0080] III. Ethanol wiping resistance: The test was conducted according to the provisions of National Standard GB / T 23989-2009, Method A, for the test of solvent resistance of coatings.

[0081] IV. 120h Water Absorption Rate: Nonionic waterborne polyurethane emulsion was coated onto a clean quartz substrate using a spin coating method (3000 rpm, 30 s). The film was formed and cured for 72 h in a constant temperature and humidity environment (23±2℃, relative humidity 50±5%), with a film thickness controlled at (100±10) μm. The initial mass (m0) of the film sample was weighed using an analytical balance with an accuracy of 0.01 mg. Three samples were prepared in parallel for each group. The samples were completely immersed in deionized water at 23±1℃ with a conductivity ≤5μS / cm, sealed, and soaked for 120 h, ensuring the film sample was free of bubbles and folds. After soaking, residual moisture on the surface of the film sample was quickly wiped off with anhydrous ethanol, and the sample was allowed to stand for 30 s under inert gas protection. The mass (m1) after soaking was then measured. The water absorption rate was calculated according to the formula... Calculate the water absorption rate, and the results are expressed as mean ± standard deviation (retain 2 significant figures).

[0082] The test results are shown in Table 1-2.

[0083] Table 1. Performance comparison of nonionic waterborne polyurethane in Example 1 and the comparative example.

[0084] Performance indicators Example 1 Comparative Example 1 Performance improvement (Example 1 vs. Comparative Example 1) Comparative Example 2 Comparative Example 3 Particle size range / nm 10-30 80-150 -75% ~ -87% 45-85 55-90 Most frequent particle size / nm 25 100 -75% 65 72 XRD characteristic peak intensity / au 18000 8500 +111.8% / / Ethanol Scrub Resistance (Number of Scrubs) ≥50 ≤30 +66.7% ≤20 ≤22 Film gloss (60°) / % 96 85 12.9% 78 80 120h water absorption rate / % 60 ≥90 -33.3% ≥85 ≥88 Inter-batch performance error (three batches) / % <5 ≈10 -50% ≈12 ≈13

[0085] As can be seen from Table 1, the nonionic waterborne polyurethane emulsion prepared in this application has a particle size range of only 10~30nm, with the most frequent particle size being about 25nm, which is much smaller than the capped nonionic waterborne polyurethane on the market. The particles are more dispersed and uniform, more resistant to solvent scrubbing, and the film gloss and water absorption are also more excellent. Importantly, its crystallinity is excellent, which can solve the problem of insufficient mechanical strength of films in the prior art.

[0086] Table 2. Comparison of stability tests of different batches of nonionic waterborne polyurethane from Example 1

[0087] Test batch Particle size range (nm) Most frequent particle size (nm) XRD characteristic peak intensity (au) Ethanol resistance to wiping (number of times) Particle size change rate (%) after 3 months of storage Batch 1 10~28 24 17800 52 2.1 Batch 2 12~30 25 18200 50 1.8 Batch 3 11~29 26 17900 51 2.3

[0088] As shown in Table 2, this application, through the synergistic process of temperature gradient control, stepwise chain extension and high-temperature curing, can achieve a batch-to-batch performance error of less than 5% for industrially mass-produced nonionic waterborne polyurethane, which is far superior to commercial products (error of about 10%). It also exhibits excellent long-term stability, with no significant change in particle size after 3 months of storage, stable crystallinity, and no agglomeration, thus possessing high market application value.

[0089] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a narrow-particle-size, highly crystalline nonionic waterborne polyurethane, characterized in that, The preparation method includes the following steps: S1. Mix carbon dioxide-based polyol and isophorone diisocyanate, heat to 90-120℃ and stir to react, to obtain the prepolymer product; S2. Cool the prepolymer to below 55°C, add the hydrophilic monomer and stir until completely dispersed; S3. Heat the mixture of S2 to 70-95℃ and add a chain extender to continue the reaction; S4. Cool the mixture of S3 to below 55°C, emulsify with water, and then add the diluted solution of the chain extender dropwise to carry out the reaction. S5. Stir and mature the emulsion system of S4 at 75-90℃ for 1-5 hours to obtain the nonionic waterborne polyurethane. The weight-average molecular weight of the carbon dioxide-based polyol is 1000-3000, and the -NCO content of the isophorone diisocyanate is ≥37.5%; the hydrophilic monomer is trimethylolpropane polyethylene glycol monomethyl ether, and the hydroxyl value of trimethylolpropane polyethylene glycol monomethyl ether is 40-68 mg KOH / g. The mass ratio of the carbon dioxide-based polyol, isophorone diisocyanate, and hydrophilic monomer is 65-78:30-40:20-35. The emulsification stirring speed is 800-1000 rpm, and the stirring time is 25-35 min; The chain extender is isophorone diamine, and the amount added is 2-5% of the mass of the prepolymer product.

2. The preparation method according to claim 1, characterized in that, The mass ratio of carbon dioxide-based polyol and isophorone diisocyanate in S1 is 70-75:30-35; And / or, the weight-average molecular weight of the carbon dioxide-based polyol is 2000-2500; And / or, an organic Bi catalyst is also added to S1, the amount of which accounts for 0.15-0.45% of the mass of isophorone diisocyanate.

3. The preparation method according to claim 1, characterized in that, The reaction temperature in S1 is 95-115℃, and the reaction time is 2-8h; And / or, the stirring speed in S2 is 300-600 rpm, and the stirring time is 10-60 min; And / or, the stirring speed for the S3 reaction is 300-600 rpm, and the stirring reaction time is 20-60 min.

4. The preparation method according to claim 1, characterized in that, In S4, the amount of water added is 1-3 times the mass of the prepolymer product, and the water temperature is 50-55℃.

5. The preparation method according to claim 1, characterized in that, The mass concentration of the diluted chain extender is 8-15%, the dropping rate is 1-2 drops / second, and the stirring reaction time after dropping is 10-20 minutes.

6. The preparation method according to claim 1, characterized in that, The maturation temperature is 78-82℃, and the stirring speed is 300-400rpm.

7. A nonionic waterborne polyurethane prepared by the preparation method according to any one of claims 1-6, characterized in that, The nonionic waterborne polyurethane has a particle size range of 10-30 nm, a most frequent particle size of 25 nm, and a maximum frequency of 38%.

8. The nonionic waterborne polyurethane according to claim 7, characterized in that, The nonionic waterborne polyurethane has a high-intensity characteristic peak at 2θ=18.30°.

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