Preparation method of self-emulsifying hybrid polyisocyanate crosslinking agent

Abstract

A method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent, belonging to the field of waterborne polyurethane composite system preparation, includes the following steps: S1, reacting an aliphatic-alicyclic hybrid diisocyanate mixture A with a polyalkylene ether alcohol, followed by silane modification to obtain a dispersible active reaction product; S2, using the dispersible active reaction product obtained in step S1 with an aliphatic-alicyclic hybrid polyisocyanate B, conducting a precisely temperature-controlled urethane esterification reaction under the action of a novel composite urethane esterification catalyst, achieving a balance between product structure and performance by regulating the conversion rate of urethane groups, and obtaining a self-emulsifying hybrid polyisocyanate crosslinking agent after catalyst deactivation, anti-aging modification, and hydrophilic modification with phosphate esters. The crosslinking agent of this invention is suitable for waterborne coatings, adhesives, and sealing material systems, significantly improving the weather resistance, chemical resistance, and mechanical strength of the system, while also possessing low-temperature curing characteristics.

Description

Technical Field

[0001] This invention relates to the field of waterborne polyurethane composite system preparation, specifically a method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent. Background Technology

[0002] Existing water-emulsifiable isocyanates are mostly prepared through modification with polyoxyethylene ether alcohols, which leads to an imbalance between emulsification and film hardness. Furthermore, traditional urea-formaldehyde esterification catalysts tend to result in higher color numbers and poor storage stability in the product. While aromatic polyester-polyurethane block copolymer foams possess excellent mechanical properties, their water resistance and low-temperature processability are insufficient. Additionally, the reaction between the isocyanate component and the polyol is difficult to control, and the block structure exhibits poor uniformity, limiting their application in high-end coating and precision foaming fields.

[0003] This research aims to address the contradiction between the emulsification and mechanical properties of existing water-emulsifiable isocyanates, as well as the high color count of the products. It also overcomes the shortcomings of polyurethane materials, such as low low-temperature curing efficiency and poor storage stability. Furthermore, it addresses the challenges of reaction control and poor block uniformity in aromatic polyester-polyurethane systems, thereby improving the water resistance and low-temperature processability of the materials. Finally, it develops a novel hybrid isocyanate crosslinking agent to achieve high compatibility with water-based polyol systems, resulting in a crosslinked and cured material that exhibits high hardness, high elasticity, and excellent weather resistance. Summary of the Invention

[0004] The core of this invention is a two-step preparation process for a self-emulsifying hybrid polyisocyanate crosslinking agent. Through hybrid modification of isocyanates, selection of novel composite catalysts, and precise control of the reaction process, the crosslinking agent achieves self-emulsifying properties, low color number, and high storage stability, while also endowing it with low-temperature and high-efficiency curing capabilities. The specific process steps are as follows: A method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent includes the following steps: S1: After pretreatment of the aliphatic-alicyclic hybrid diisocyanate mixture A, a pretreated polyalkylene ether alcohol copolymerized with ethylene oxide and butylene oxide is added. The basic dispersive active product is obtained by urethane esterification under controlled temperature and catalyst conditions. The basic dispersive active product is then grafted with a pretreated silane coupling agent to introduce siloxane hybrid hydrophilic chains, and finally a dispersive active reaction product containing hybrid hydrophilic chains is obtained. S2: Using an aliphatic-alicyclic hybrid polyisocyanate mixture B as the main raw material, the hydrophilic reaction product containing hybrid hydrophilic chains obtained in step S1 is added as a hydrophilic modification component. The two undergo a temperature-controlled urethane esterification reaction under the action of a catalyst. The conversion rate of the urethane groups in the hydrophilic reaction product containing hybrid hydrophilic chains is used as the reaction endpoint. After catalyst deactivation, anti-aging modification and hydrophilic modification, the urethane esterification reaction product is used to obtain a self-emulsifying hybrid polyisocyanate crosslinking agent.

[0005] Further, after the aliphatic-alicyclic hybrid diisocyanate mixture A in step S1 is fed, the temperature is raised to 40±1℃; the polyalkylene ether alcohol in step S1 is added dropwise, with the temperature controlled at 40-45℃ during the dropwise addition process, and after the dropwise addition is completed, the temperature is raised to 58±1℃ and maintained until the basic dispersed active product is obtained, and then cooled to 55±1℃, and the silane coupling agent is added to react; In step S2, the temperature of the aliphatic-alicyclic hybrid polyisocyanate mixture B is 70±1℃ and is maintained until the addition of the dispersed active reaction product containing the hybrid hydrophilic chain is completed; the temperature of the ureoformation reaction in step S2 is controlled at 78±1℃; after the catalyst is deactivated in step S2, it is cooled to 40±1℃ at a rate of 1℃ / min, and the anti-aging modification is carried out at 40±1℃ for 30min, and the hydrophilic modification is carried out at 35±1℃ for 30min.

[0006] Further, the aliphatic-alicyclic hybrid diisocyanate mixture A in step S1 comprises 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane in a mass ratio of 45:32:23; the polyalkylene ether alcohol in step S1 is prepared by copolymerizing ethylene oxide and epoxide in a molar ratio of 85:15 with n-pentanol as the initiator; the catalyst in step S1 is prepared by using neodecanoic acid in a mass ratio of 7:3. Bismuth and bismuth laurate were used as solutes, and the solutes were dissolved in anhydrous ethyl acetate to prepare a 10% (w / w) solution to obtain the catalyst. The silane coupling agent for the pretreatment in step S1 was selected as γ-glycidoxypropyltrimethoxysilane. The pretreatment step was as follows: 0.1% (w / w) of anhydrous aluminum trichloride was added to the γ-glycidoxypropyltrimethoxysilane as an activator, and the mixture was stirred under nitrogen protection at room temperature for 15 min at a stirring rate of 150 r / min for activation. The catalyst was used immediately after activation.

[0007] Furthermore, the mass ratio between the aliphatic-alicyclic hybrid diisocyanate mixture A and the polyalkylene ether alcohol is 87:163, the amount of bismuth neodecanoate and bismuth laurate added in step S1 is 0.25% of the mass of the aliphatic-alicyclic hybrid diisocyanate mixture A, and the amount of γ-glycidyl etheroxypropyltrimethoxysilane added is 1.2% of the mass of the basic dispersing active product.

[0008] Further, the pretreatment of the aliphatic-alicyclic hybrid diisocyanate mixture A in step S1 includes the following steps: the aliphatic-alicyclic hybrid diisocyanate mixture A is dehydrated under constant temperature and reduced pressure for at least 30 minutes at a vacuum of -0.095 to -0.098 MPa, a temperature of 45 ± 2℃, and a stirring rate of 200 r / min. After dehydration, it is cooled to room temperature under nitrogen protection and sealed for later use. After pretreatment, the aliphatic-alicyclic hybrid diisocyanate mixture A has a moisture content ≤0.01%, is a colorless and transparent liquid, and has a viscosity of 12.8 mPa at 23℃. s; The pretreatment step of the polyalkylene ether alcohol in step S1 is as follows: under the conditions of vacuum degree of -0.098MPa, temperature of 105±3℃ and stirring rate of 250r / min, the polyalkylene ether alcohol is dehydrated at a constant temperature for 2h. After pretreatment, the moisture content of the polyalkylene ether alcohol is ≤0.02%. It is then cooled to below 40℃ under nitrogen protection and sealed for later use.

[0009] Further, the aliphatic-alicyclic hybrid polyisocyanate mixture B in step S2 includes 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane in a mass ratio of 50:30:20; the catalyst preparation process in step S2 is as follows: zinc O,O-bis(2-propylheptyl)dithiophosphate and zirconium acetylacetonate in a mass ratio of 85:15 are dissolved in anhydrous butyl acetate to prepare a catalyst solution with a mass concentration of 15%; the catalyst terminator used in the catalyst deactivation process in step S2 is methyl p-toluenesulfonate; the anti-aging modification process in step S2 uses antioxidant 1010 and light stabilizer 770; the hydrophilic modification in step S2 uses polyethylene glycol monomethyl ether phosphate.

[0010] Further, in step S2, the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain are mixed in a mass ratio of 85:15. The amount of solute used in the composite urea-formylation catalyst in step S2 is 0.045% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain. The amount of catalyst terminator added in step S2 is 0.045% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain. 0.06%, the antioxidant 1010 in step S2 accounts for 0.3% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain, the light stabilizer 770 in step S2 accounts for 0.2% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain, and the polyethylene glycol monomethyl ether phosphate in step S2 accounts for 0.8% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain.

[0011] Furthermore, the endpoint of the grafting modification reaction involving the introduction of siloxane hybrid hydrophilic chains described in step S1 is monitored by sampling and detecting the product using a Fourier transform infrared spectroscopy (FTIR) instrument. When the spectral image reaches 910 cm⁻¹... -1 The characteristic absorption peak of the epoxy group completely disappeared, and at 1080 cm⁻¹ -1 When the area of ​​the characteristic absorption peak of the Si-O bond of the siloxane reaches 98% compared with the standard curve, the modification reaction is determined to have reached the endpoint; the dispersed active reaction product containing hybrid hydrophilic chains in step S1 shall be subjected to low-boiling-point substance removal and nitrogen protection sealing treatment.

[0012] Further, in step S2, the reaction endpoint of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersed active reaction product containing the hybrid hydrophilic chain is determined by detecting the free NCO in the system. When the NCO content detected by the sample reaches 16.7±0.1%, the urea-formylation reaction is determined to have reached the endpoint, and the subsequent catalyst deactivation step is immediately initiated. If the NCO content decreases too quickly during the reaction, the material temperature is lowered to 75°C.

[0013] Furthermore, if the emulsification time of the dispersion active reaction product containing hybrid hydrophilic chains in step S1 exceeds 10 seconds, it indicates that the hydrophilic chain content is insufficient. In step S2, the amount of polyethylene glycol monomethyl ether phosphate is increased by 1% during the hydrophilic modification stage. If the water absorption rate of the material after curing of the dispersion active reaction product containing hybrid hydrophilic chains in step S1 exceeds 2%, the amount of the dispersion active reaction product containing hybrid hydrophilic chains fed in step S2 is reduced by 2%, and at the same time, the amount of the aliphatic-alicyclic hybrid polyisocyanate mixture B is increased by 2%.

[0014] The beneficial effects of this invention are as follows: The novel hybrid isocyanate crosslinking agent developed in this technology specifically addresses several technical shortcomings of existing water-based isocyanate and polyurethane systems, achieving a synergistic improvement in emulsification performance, mechanical properties, processing stability, and weather resistance, and possessing multiple outstanding and beneficial technical effects. First, it completely solves the problem of the contradiction between emulsification and mechanical properties in water-emulsifiable isocyanates. The product combines excellent water dispersibility and emulsification with high-strength mechanical properties after curing, while effectively reducing the product's color number, improving the material's appearance quality, and expanding high-end application scenarios.

[0015] Secondly, it overcomes the industry pain points of low-temperature curing efficiency and poor storage stability of polyurethane materials. The crosslinking agent can quickly complete the crosslinking and curing reaction at low temperatures, significantly shortening the processing cycle. Moreover, it does not exhibit delamination, deterioration, or self-polymerization during room temperature storage, significantly extending the storage period and improving the convenience of product storage, transportation, and use. Addressing the difficulties in reaction control and poor block uniformity in aromatic polyester-polyurethane systems, it achieves precise control of the reaction rate through molecular structure hybridization modification, improving the uniformity of chain segments and blocks, optimizing the internal crosslinking structure of the material, significantly enhancing the material's water resistance and low-temperature processing performance, and reducing the difficulty of processing and molding.

[0016] Furthermore, this crosslinking agent exhibits high compatibility with water-based polyol systems, demonstrating stable compatibility without agglomeration. After crosslinking and curing, the material simultaneously possesses high hardness and high elasticity, exhibiting excellent and balanced mechanical properties. It also optimizes the molecular weather-resistant structure, effectively resisting external environmental erosion such as light and humidity, delaying material aging, yellowing, and cracking, and extending the material's service life. Overall, it optimizes the comprehensive performance of the water-based polyurethane crosslinking system, breaking through the limitations of traditional material performance, adapting to more demanding application scenarios, and combining process practicality with product application value. Detailed Implementation

[0017] The present invention will now be described in detail through specific embodiments.

[0018] Example 1 The two-step preparation process of the self-emulsifying hybrid polyisocyanate crosslinking agent is as follows: Step 1: Preparation of dispersed active reaction products containing hybrid hydrophilic chains This step uses an aliphatic-alicyclic hybrid diisocyanate mixture A as the isocyanate raw material and a polyalkylene ether alcohol copolymerized with ethylene oxide and butane oxide as the hydrophilic modification raw material. A basic dispersible active product is obtained through a precisely temperature-controlled urethane esterification reaction. Then, a siloxane hybrid hydrophilic chain is introduced through silane coupling agent grafting modification, ultimately obtaining a dispersible active product containing hybrid hydrophilic chains. The entire process is carried out in an anhydrous, nitrogen-protected environment. All raw materials are dehydrated and dried before use to ensure no side reactions interfere with the reaction and that the product structure is uniform. Specific operational details are as follows: (I) Raw material pretreatment Pretreatment of hybrid diisocyanate mixture A: 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and 1,3-bis(isocyanatomethyl)cyclohexane (HXDI) were added to a dry 500 mL three-necked flask at a mass ratio of 45:32:23. A vacuum distillation apparatus was set up, and the vacuum degree of the system was controlled at -0.095~-0.098 MPa. The temperature was raised to 45±2℃, and the mixture was dehydrated by stirring under reduced pressure for 30 min at a stirring rate of 200 r / min. After dehydration, the mixture was cooled to room temperature under nitrogen protection and sealed for later use. The moisture content of the pretreated mixture was ≤0.01%, and it was a colorless and transparent liquid with a viscosity of 12.8 mPa at 23℃. s.

[0019] Pretreatment of polyalkylene ether alcohols: Polyalkylene ether alcohols (number average molecular weight 620 g / mol, 14 ethylene oxide units, hydroxyl value 90.3 mg KOH / g, acid value 0.8 mmol / kg) prepared by copolymerization of ethylene oxide and butane oxide in a molar ratio of 85:15 using n-pentanol as the initiator were selected and added to a dry 1000 mL three-necked flask. A vacuum dehydration apparatus was set up, and the vacuum degree of the system was controlled at -0.098 MPa. The temperature was raised to 105±3℃, and the system was kept at a constant temperature and vacuum with stirring for 2 h at a stirring rate of 250 r / min. During this period, samples were taken every 30 min to test the moisture content until the moisture content was ≤0.02%. After dehydration, the system was cooled to below 40℃ under nitrogen protection, sealed, and stored for later use to prevent moisture absorption.

[0020] Pretreatment of the organobismuth composite catalyst: The organobismuth composite catalyst was prepared by mixing bismuth neodecanoate and bismuth laurate at a mass ratio of 7:3. The catalyst was added to a dry brown reagent bottle and anhydrous ethyl acetate was added to prepare a catalyst solution with a mass concentration of 10%. The solution was sealed and stored under a nitrogen atmosphere to avoid oxidation and deactivation of the catalyst. The ethyl acetate was dehydrated by molecular sieve and the moisture content was ≤0.005%.

[0021] Pretreatment of silane coupling agent: γ-glycidoxypropyltrimethoxysilane (KH-560) was selected and added to a dry 250mL reagent bottle. Anhydrous aluminum trichloride at 0.1% of the mass of KH-560 was added as an activator. The mixture was stirred for 15min under nitrogen protection at room temperature at a stirring rate of 150r / min. It was used immediately after activation to improve the reaction efficiency between the silane coupling agent and the product.

[0022] (II) Construction of the reaction apparatus A 2000mL four-necked glass reactor was selected as the reaction vessel, and the supporting equipment included: a precision digital display temperature-controlled oil bath (temperature control accuracy ±0.5℃), a variable frequency speed-regulating mechanical stirrer (an anchor-type + paddle-type combination of stirring blades, with an adjustable stirring speed range of 0~800r / min), a nitrogen inlet / outlet device (nitrogen gas is treated by molecular sieve and activated carbon in a two-stage drying process, with an oxygen content ≤10ppm and a moisture content ≤0.005%), an online free NCO content detection sampling port (with a nitrogen sealing plug), and a condensation reflux device (the condenser tube is connected to a 0~5℃ ice-water bath to prevent raw material volatilization). After all the devices were connected, the inside of the reactor was purged and replaced with nitrogen three times, each time for 10 minutes, to ensure that there was no air or moisture residue inside the reactor.

[0023] (III) Preparation of basic dispersed active products by carbamate reaction (reaction process) Raw material feeding: Under continuous nitrogen purging (purging rate of 50 mL / min) and stirring rate of 200 r / min, the pretreated hybrid diisocyanate mixture A348.0 g was first added to the reactor. The oil bath was turned on to raise the temperature. When the temperature of the material in the reactor reached 40±1℃, the pretreated polyalkylene ether alcohol 652.0 g was slowly added dropwise at a dropping rate of 10 g / min. During the dropping process, the temperature in the reactor was kept below 45℃ to prevent the local reaction temperature from becoming too high due to excessively rapid dropping, which could lead to the production of by-products.

[0024] Catalyst addition and reaction start-up: After the polyalkylene ether alcohol is added dropwise, the stirring rate is adjusted to 350 r / min, and the temperature is continued to rise to 58±1℃. After the temperature stabilizes, 25.0 g of ethyl acetate solution of 10% organic bismuth composite catalyst (equivalent to 2.5 g of pure catalyst, accounting for 0.25% of the total reactant mass) is added to the reactor through the sampling port using a microsyringe. After addition, stirring is continued for 5 min to ensure that the catalyst and materials are mixed evenly.

[0025] Isothermal reaction and process monitoring: The oil bath temperature was maintained at 58±1℃, the stirring rate at 350r / min, and the nitrogen purging rate at 50mL / min for isothermal urethane esterification reaction, with a total reaction time of 1.8h. From the start of the reaction, 2-3g of the reaction solution was taken through the sampling port every 20min. The free NCO content in the sample was detected by di-n-butylamine titration. The sampling port was immediately sealed with nitrogen after sampling to prevent air from entering. The detection standard was: using toluene as solvent, after the quantitative reaction of di-n-butylamine with NCO groups, the excess di-n-butylamine was titrated with hydrochloric acid standard solution to calculate the mass fraction of free NCO.

[0026] Reaction endpoint determination: When the free NCO content detected by the sample drops to below 0.3% (the final measured value was 0.27%), the carbamate esterification reaction is considered to have reached the endpoint. If the free NCO content does not drop to below 0.3% after 1.8 hours of reaction, the reaction time can be appropriately extended by 10 minutes each time until the endpoint is reached. During the extension period, the reaction conditions should remain unchanged.

[0027] Cooling and Temporary Storage of Basic Product: After the reaction reaches its endpoint, the oil bath heating is turned off, and the stirring rate is maintained at 350 r / min with nitrogen purging. The material in the reactor is allowed to cool naturally to 55±1℃ to obtain the basic dispersed active product. At this point, the product is a colorless and transparent liquid with a viscosity of 185 mPa at 23℃. s, no obvious yellowing, temporarily stored in the reaction vessel, and immediately carried out subsequent silane coupling modification to avoid product agglomeration due to prolonged storage.

[0028] (iv) Silane coupling modification to introduce hybrid hydrophilic chains Addition of silane coupling agent: Under the conditions of material temperature of 55±1℃, stirring speed of 300r / min and nitrogen purging rate of 50mL / min, 12.0g of pretreated γ-glycidoxypropyltrimethoxysilane (KH-560) (accounting for 1.2% of the mass of the basic dispersion active product) was slowly added dropwise through the feed port of the reactor at a dropping rate of 2g / min. During the dropping process, the temperature inside the reactor was kept stable to avoid a sudden temperature rise due to the exothermic effect of the system.

[0029] Isothermal modification reaction: After the addition of KH-560, the reaction conditions (temperature 55±1℃, stirring rate 300r / min, nitrogen purging) were kept constant, and the silane coupling modification reaction was carried out for 1.2h. During this process, the epoxy group in the KH-560 molecule undergoes a ring-opening addition reaction with the trace amount of unreacted hydroxyl group in the base product, and the hydrophilic siloxane is branched to the product molecule to form a hybrid hydrophilic structure containing hydrophilic chains of polyoxyethylene ether alcohol and hydrophilic chains of siloxane.

[0030] Monitoring of the endpoint of the modification reaction: After 1.2 hours of reaction, the product was sampled and detected using a Fourier transform infrared spectroscopy (FT-IR). The endpoint was reached when the spectral density reached 910 cm⁻¹. -1 The characteristic absorption peak of the epoxy group completely disappeared, and at 1080 cm⁻¹ -1 When the characteristic absorption peak of the Si-O bond in siloxane is significantly enhanced, the modification reaction is considered to have reached its endpoint.

[0031] (V) Product post-processing and performance index testing Product properties in step S1: Colorless transparent liquid, viscosity at 23℃: 192.6 mPa s, Hazen color number 13, free NCO content 0.27%, siloxane grafting rate 98.5%, emulsification time in water 8.3s; Removal of low-boiling-point substances: After the modification reaction reaches the endpoint, maintain the material temperature at 55℃, slowly adjust the vacuum degree of the reactor system to -0.08MPa, and remove a small amount of ethyl acetate and trace amounts of low-molecular-weight byproducts generated in the system by vacuum stirring. The removal time is 30 min, the stirring rate is 250 r / min, and after the removal is completed, restore the system to normal pressure and provide nitrogen protection.

[0032] Product discharge and sealing preservation: Cool the material in the reactor to room temperature (23±2℃), and discharge the product through a dry stainless steel outlet under nitrogen protection. Pack it into a dry brown sealed container and seal it under nitrogen atmosphere to obtain a dispersed active reaction product containing hybrid hydrophilic chains.

[0033] Key performance indicators of the product: The product is a colorless, transparent, homogeneous liquid, free of suspended matter and sediment; its viscosity at 23℃ is 192.6 mPa. s (cone-plate viscometer, rotor speed 1000 r / min); Hazen color number ≤15; moisture content ≤0.02%; free NCO content ≤0.3%; siloxane grafting rate ≥98% (calculated by elemental analysis of Si content); initial emulsification time in deionized water ≤10s (product to water mass ratio 1:9, stirring speed 300 r / min at room temperature).

[0034] (vi) Key process control points Moisture control: All raw materials and equipment must be strictly dehydrated throughout the process. When the moisture content of the system exceeds 0.02%, it will cause hydrolysis of isocyanate groups, generating urea bonds, which will reduce the emulsification of the product, increase its viscosity, and even cause gelation.

[0035] Temperature control: The urethane esterification reaction temperature is strictly controlled at 58±1℃. Too low a temperature will result in a slow reaction rate and incomplete reaction; too high a temperature (above 65℃) will cause some polyoxyethylene ether segments in the product to undergo thermal degradation, and at the same time, it is easy to generate dimer by-products, which will affect the product performance.

[0036] Raw material ratio control: The molar ratio of OH groups to NCO groups is precisely controlled at 1.05:1, with a slight excess of NCO groups, to ensure that the hydroxyl groups of the polyalkylene ether alcohol react completely and to avoid excessive cross-linking of the product when it reacts with polyisocyanates later due to too many unreacted hydroxyl groups.

[0037] Silane coupling agent dosage control: The dosage of KH-560 is 1.2% of the mass of the base product. If the dosage is too low, the hydrophilic linking of siloxane will be insufficient, and the water resistance of the product will not be improved. If the dosage is too high, the product will be too hydrophilic, and the hardness of the material will decrease after the crosslinking agent is cured.

[0038] Step 2: Urethroidation reaction for preparing hybrid polyisocyanate crosslinking agents This step uses the dispersed active reaction product containing hybrid hydrophilic chains obtained in step one as the hydrophilic modification component, and aliphatic-alicyclic hybrid polyisocyanate B as the main raw material. A precisely temperature-controlled urethane esterification reaction is carried out under the action of a novel composite urethane esterification catalyst. The balance between product structure and performance is achieved by regulating the conversion rate of the carbamate groups. After catalyst deactivation, anti-aging modification, and hydrophilic modification with phosphate esters, a self-emulsifying hybrid polyisocyanate crosslinking agent is obtained. The entire process is carried out under anhydrous nitrogen protection. All raw materials and equipment undergo dehydration and impurity removal treatment to avoid side reactions and ensure product uniformity and stability. Specific operational details are as follows: (I) Raw material pretreatment Pretreatment of aliphatic-alicyclic hybrid polyisocyanate B: HDI isocyanurate, IPDI biuret, and HXDI iminooxadiazine dione were mixed in a mass ratio of 50:30:20. Basic parameters of aliphatic-alicyclic hybrid polyisocyanate B: average NCO functionality 3.2, NCO content 21.8%, viscosity at 23℃ 2650 mPa. s. Take 1000.0g of the mixture and add it to a dry 1000mL three-necked flask. Set up a vacuum distillation apparatus, control the vacuum degree to -0.095~-0.098MPa and the temperature to 50±2℃, dehydrate under reduced pressure with stirring for 40min at a stirring rate of 200r / min. After dehydration, cool to room temperature, seal under nitrogen protection and keep for later use. After pretreatment, the moisture content is ≤0.01%, and there is no stratification or turbidity.

[0039] Pretreatment of novel composite urea-formylation catalyst: O,O-bis(2-propylheptyl)dithiophosphate zinc and zirconium acetylacetonate were mixed at a mass ratio of 85:15 to prepare a composite catalyst (total metal ion content 12.5%). The catalyst was added to a dry brown reagent bottle, and anhydrous butyl acetate was added to prepare a catalyst solution with a mass concentration of 15%. The solution was stirred for 10 min (speed 150 r / min) under a nitrogen atmosphere until homogeneous, and then sealed and stored. The butyl acetate was dehydrated by 4A molecular sieve, and the moisture content was ≤0.005%.

[0040] Catalyst terminator pretreatment: Methyl p-toluenesulfonate was selected as the terminator, added to a dry reagent bottle, and 0.05% of molecular sieve by mass was added. The mixture was sealed and allowed to stand at room temperature for 24 hours to dehydrate. After filtration, it was kept under nitrogen protection for later use. The moisture content after dehydration was ≤0.01%.

[0041] Pretreatment of anti-aging agents and hydrophilic modifiers: Antioxidant 1010 and light stabilizer 770 were dried in a vacuum drying oven (temperature 80℃, vacuum degree -0.098MPa, time 2h) to remove surface adsorbed water, and then sealed for later use after cooling; polyethylene glycol monomethyl ether phosphate (molecular weight 400) was added to a drying three-necked flask and dehydrated under reduced pressure (temperature 60℃, vacuum degree -0.098MPa, time 1h), and cooled to room temperature under nitrogen protection for later use. The moisture content after dehydration was ≤0.02%.

[0042] Pretreatment of the dispersed active reaction product obtained in step one: Take the product obtained in step one, heat it to 45±1℃ under nitrogen protection, stir at 200r / min, keep it at the temperature for 10min to remove trace agglomerates that may be generated at low temperature, ensure the material is uniform, and cool it to below 40℃ for later use.

[0043] (II) Setup and Commissioning of the Reaction Apparatus A 5000mL four-necked glass reactor was selected as the reaction vessel. All supporting equipment was cleaned with anhydrous ethanol, dried at 120℃, and purged with nitrogen. The specific equipment includes: ① a precision digital display temperature-controlled oil bath (temperature control accuracy ±0.1℃, with a low-temperature cooling circuit for precise temperature control); ② a variable frequency speed-regulating mechanical stirrer (anchor-type + turbine-type combined stirring paddle, stirring speed 0~1000r / min, ensuring uniform mixing of high-viscosity materials); ③ a nitrogen inlet / outlet device (nitrogen is dried and deoxygenated, oxygen content ≤10ppm, moisture content ≤0.005%, purging rate can be precisely adjusted); ④ an online NCO content detection sampling port (with a double-layer nitrogen sealing plug to prevent air from entering during sampling); ⑤ a low-temperature condensation reflux device (condenser tube is circulated through a 0~3℃ ice-water bath to prevent volatilization of low-boiling-point raw materials); and ⑥ a vacuum degassing device (capable of precise adjustment of vacuum degree from 0 to -0.098MPa).

[0044] After the device is connected, purge the inside of the reactor with nitrogen four times, each time for 15 minutes. After the last purging, maintain a slight positive pressure inside the reactor (nitrogen pressure 0.01 MPa). Only when the moisture content inside the reactor is ≤0.005% and the oxygen content is ≤10 ppm can the subsequent reaction proceed.

[0045] (III) Raw material feeding and premixing Main raw material feeding: Under the conditions of nitrogen micro-positive pressure and stirring speed of 250r / min, the pretreated aliphatic-alicyclic hybrid polyisocyanate mixture B2550.0g is first added to the reactor, the oil bath is turned on to raise the material temperature to 70±1℃, and the temperature is kept for 10min to reduce the viscosity of the material and ensure uniform mixing in the subsequent process.

[0046] Step 1 Product Feeding and Premixing: Maintain the material temperature at 70±1℃ and the stirring speed at 250r / min. Slowly add 450.0g of the pretreated Step 1 product (the mass ratio of the dispersed active reaction product containing hybrid hydrophilic chains in Step 1 to the aliphatic-alicyclic hybrid polyisocyanate mixture B is 15:85) through the feed port of the reactor. The dropping rate is controlled at 8g / min. Monitor the temperature inside the reactor in real time during the dropping process and fine-tune the temperature through the oil bath cooling circuit to ensure that the temperature fluctuation does not exceed ±2℃ and to prevent premature local reactions during the dropping process.

[0047] Premixing and homogenization: After the addition of the dispersed active reaction product containing hybrid hydrophilic chains in step one, the stirring speed was adjusted to 400 r / min, the temperature was maintained at 70±1℃, and stirring was continued for 20 min to fully mix the two raw materials and form a homogeneous system; the initial NCO content of the mixed system was sampled and tested, and the measured value was 20.1%, which was used as the benchmark value for subsequent reaction monitoring.

[0048] (iv) Urea-formylation catalytic reaction Catalyst addition and reaction start-up: After homogenization of the mixed system, the temperature of the oil bath was adjusted to 78±1℃. After the temperature of the material in the vessel stabilized at 78±1℃, 15.0g of butyl acetate composite catalyst solution with a mass concentration of 15% (equivalent to 2.25g of pure catalyst, accounting for 0.045% of the total reactant mass) was added to the reactor at a uniform rate of 0.5g / min through the sampling port using a precision micro-metering pump. During the addition process, the stirring rate was maintained at 400r / min. After the addition was completed, stirring was continued for 15min to ensure that the catalyst was completely and uniformly dispersed in the system.

[0049] Isothermal and rate-controlled reaction and process control: The reaction conditions were maintained as follows: oil bath temperature 78±2℃, actual material temperature 77~79℃, stirring rate 380r / min, and nitrogen micro-positive pressure (0.01MPa) for urea-formylation reaction; precise control was achieved during the reaction through the following methods: Local overheating prevention: Observe the material status through the sight glass of the reactor every 15 minutes, and at the same time use an infrared thermometer to detect the material temperature at different locations in the reactor to ensure that the temperature deviation is ≤1℃. If the local temperature is too high, increase the stirring rate by 50r / min for 10 minutes and then return to the original rate.

[0050] Removal of low molecular weight byproducts: The vacuum degassing device is turned on every 30 minutes to adjust the system vacuum to -0.05 MPa. Nitrogen gas is micro-bubbled (at a rate of 30 mL / min) to remove trace amounts of low molecular weight byproducts generated in the reaction. The removal time is 5 minutes. After completion, the system is restored to a slightly positive pressure to prevent air from entering.

[0051] Reaction process monitoring: Starting from the completion of catalyst addition, 3-4g of reaction solution sample is taken through the sampling port every 20 minutes. The free NCO content is detected by di-n-butylamine titration. The sampling port is sealed with nitrogen immediately after sampling. The results of each test are compared with the benchmark value to calculate the NCO content decrease rate and indirectly deduce the carbamate group conversion rate.

[0052] Reaction endpoint determination and control: This step controls the conversion rate of urethane groups in the dispersed active reaction product containing hybrid hydrophilic chains in step one to 58%, corresponding to a decrease in the free NCO content of the system to 16.7%; when the sampled NCO content reaches 16.7±0.1%, the urethane esterification reaction is determined to have reached the endpoint, and the subsequent catalyst deactivation step is immediately initiated; if the NCO content decreases too rapidly during the reaction, the material temperature can be reduced to 75℃ through the oil bath cooling circuit to reduce the reaction rate and ensure precise control of the conversion rate.

[0053] The actual reaction time was 2.1 hours, and the measured NCO content at the endpoint was 16.68%, with a carbamate group conversion rate of 58.2%, which met the process requirements.

[0054] (V) Catalyst deactivation and system stabilization Terminator addition and deactivation reaction: After the reaction reaches the endpoint, maintain the material temperature at 78±1℃ and the stirring rate at 380r / min. Slowly add 18.0g of pretreated methyl p-toluenesulfonate (accounting for 0.06% of the total reactant mass) through the feed port at a dropping rate of 3g / min. After the addition is completed, continue stirring for 25min to allow the terminator to fully react with the catalyst, completely deactivate the active center of the catalyst, and terminate the urea-formylation reaction. During the stirring process, take samples every 5min to test the reaction activity of the system. When the NCO content change rate is ≤0.1% after the sample is kept at 80℃ for 30min, the catalyst is considered to be completely deactivated.

[0055] System cooling and basic stabilization: After the catalyst is completely deactivated, the oil bath heating is turned off and the cooling circuit is turned on, so that the material in the reactor is slowly cooled to 40±1℃ at a rate of 1℃ / min. During the cooling process, the stirring speed is gradually reduced from 380r / min to 250r / min to prevent the material viscosity from rising sharply due to rapid cooling and causing local agglomeration. After cooling is completed, a slight positive pressure of nitrogen is maintained, the stirring speed is 250r / min, and the temperature is maintained for 10min to stabilize the system.

[0056] (vi) Anti-aging modification and hydrophilic modification Anti-aging agent addition and mixing: Under the conditions of material temperature 40±1℃ and stirring speed 250r / min, 10109.0g of pretreated antioxidant (0.3% of total product mass) and 7706.0g of light stabilizer (0.2% of total product mass) were added in batches through the feeding port (3.0g each time, 5min interval). After the addition was completed, the stirring speed was adjusted to 300r / min and stirring was continued for 30min to ensure that the anti-aging agent was completely dispersed in the system without particle agglomeration. The sample was tested by laser particle size analyzer and the particle size of all particles in the system was ≤1μm, indicating that the dispersion was uniform.

[0057] Hydrophilic modification of phosphate ester: After the anti-aging agent is dispersed, the material temperature is reduced to 35±1℃, the stirring speed is adjusted to 250r / min, and 24.0g of pretreated polyethylene glycol monomethyl ether phosphate ester (accounting for 0.8% of the total product mass) is slowly added dropwise through the feed port at a dropping rate of 2g / min. During the dropping process, the temperature fluctuation is kept ≤±1℃. After the dropping is completed, stirring is continued for 30min to allow the phosphate ester groups to fully combine with the trace amounts of unreacted active groups in the system, further optimizing the self-emulsification performance of the product, and improving the low-temperature compatibility of the product with the aqueous polyol system.

[0058] (vii) Post-processing of products and preservation of discharged materials Final degassing and impurity removal: After hydrophilic modification, maintain the material temperature at 35±1℃ and the stirring speed at 200r / min, turn on the vacuum degassing device, adjust the system vacuum to -0.08MPa, remove a small amount of butyl acetate and trace bubbles from the system, and the degassing time is 40min. During the degassing process, the system viscosity is checked every 10min to ensure viscosity stability. After degassing is completed, restore the system to a slight positive pressure of nitrogen (0.01MPa).

[0059] Product filtration: The product in the reactor is filtered under pressure (nitrogen pressure 0.03MPa) through a double-layer stainless steel filter screen (upper screen with an aperture of 800 mesh and lower screen with an aperture of 1200 mesh) to remove trace mechanical impurities and agglomerated particles from the system. The filtered product is a colorless, transparent, homogeneous liquid.

[0060] Discharge and Sealing: The filtered product is introduced into a dry brown sealed container through a dry stainless steel outlet under nitrogen protection. After each container is filled, nitrogen is introduced into the container to replace the air (replacement is carried out 3 times, each time the nitrogen is introduced into the container to a pressure of 0.02MPa). Then the container is sealed, labeled, and stored in a light-proof and dry environment at 25±5℃. The product temperature is monitored throughout the discharge process to ensure that it does not exceed 40℃.

[0061] (viii) Core performance indicators and key process control points of the product (1) Core performance indicators of the product Final crosslinking agent performance indicators: The final self-emulsifying hybrid polyisocyanate crosslinking agent is a colorless, transparent, homogeneous liquid, free of suspended matter, sediment, and bubbles; its viscosity at 23℃ is 892.3 mPa. s (cone-plate viscometer, rotor speed 1000r / min); Hazen color number ≤20; NCO content 16.52%; after 6 months of sealed storage at 25℃, the viscosity change rate is ≤4.8% and the NCO content retention rate is ≥98.2%; when mixed with deionized water in any proportion, stirred at 300r / min, and emulsification time ≤5s, the resulting emulsion shows no stratification or demulsification after standing at room temperature for 72h.

[0062] Final crosslinking agent properties: Viscosity at 23℃: 892.3 mPa s, Hazen color number 18, NCO content 16.52%, viscosity change rate after 6 months of storage at 25℃ 4.2%, NCO retention rate 98.6%, emulsification time 4.1s.

[0063] Crosslinking and curing performance (complemented with waterborne polyester polyol at NCO:OH=1.2:1): Low temperature (15℃) curing time 4.8h, hardness of cured film (pencil hardness) 2H, elongation at break 325%, water contact angle 86.3°, water absorption rate 1.8% after immersion in water for 24h, yellowing index ΔE=1.2 after QUV aging for 1000h.

[0064] (2) Key process control points Catalyst dosage and addition method: The amount of pure composite catalyst should be strictly controlled to 0.045% of the total reactant mass. If the amount is too small, the reaction rate will be too slow and the conversion rate of carbamate groups will be insufficient. If the amount is too large, the reaction rate will be too fast, making it difficult to control the conversion rate and easily leading to an increase in the color number of the product and a decrease in storage stability. The catalyst should be prepared as a solution and added at a uniform rate to avoid excessively high local catalyst concentrations that may cause explosive polymerization.

[0065] Precise control of reaction temperature and conversion rate: The reaction temperature is strictly controlled at 77~79℃. If the temperature is too low, the urethane esterification reaction will be incomplete and the cross-linking activity of the product will be insufficient. If the temperature is too high, side reactions are likely to occur, resulting in an increase in the color number of the product and an abnormal decrease in the NCO content. The conversion rate of urethane groups is controlled at 58%. If the conversion rate is too low, the self-emulsification and cross-linking properties of the product will be unbalanced. If the conversion rate is too high, the viscosity of the product will be too high and the emulsification will decrease.

[0066] Terminator addition timing and dosage: The terminator should be added immediately when the NCO content reaches the target value. Adding it too late will result in over-reaction and product performance deviating from the design requirements. The dosage is 0.06% of the total reactant mass to ensure complete catalyst deactivation and prevent the reaction from continuing during subsequent storage, which would lead to increased product viscosity and decreased NCO content.

[0067] Control of hydrophilic modifier dosage: The dosage of polyethylene glycol monomethyl ether phosphate is 0.8% of the total product mass. If the dosage is too low, the hydrophilic modification will be insufficient and the product will have poor low-temperature compatibility; if the dosage is too high, the product will be too hydrophilic and the water resistance of the material will decrease after cross-linking and curing.

[0068] Complete water-free and oxygen-free control: All raw materials and equipment must be strictly dehydrated and deoxygenated. When the moisture content in the system exceeds 0.01% and the oxygen content exceeds 10ppm, it will lead to hydrolysis and oxidation of isocyanate groups, generating byproducts such as urea bonds, which will increase the viscosity of the product, increase the number of colors, and significantly reduce the emulsification and storage stability.

[0069] Control of process parameters and raw material compatibility in the reaction system.

[0070] This step is crucial for ensuring the stability and high reproducibility of the self-emulsifying hybrid polyisocyanate crosslinking agent. By precisely controlling key dimensions such as the temperature gradient of the two-step reaction, catalyst system compatibility, hydrophilic chain content and distribution, and hybrid isocyanate structural parameters, the reactivity of the raw materials and the performance of the product are matched, while simultaneously mitigating the risk of side reactions. Specific control details are as follows: (I) Precise control and adaptability optimization of temperature gradient (1) Design basis of temperature gradient Step one, the urethane esterification reaction, needs to be carried out gently to avoid thermal degradation of the polyalkylene ether alcohol segments, while ensuring the selective reaction between hydroxyl and NCO groups. Step two, the urea esterification reaction, requires a higher temperature to activate the catalyst and promote the cross-linking reaction between urethane and NCO groups, but it must be controlled below the thermal stability threshold of hybrid isocyanates (≤80℃) to prevent the decomposition of isocyanurate and other groups. Based on the reactivity of the raw materials (the order of reactivity of hybrid diisocyanates: HDI > HXDI > IPDI; the reactivity of the hydroxyl groups in polyalkylene ether alcohols is affected by the steric hindrance of the epoxide butane segments), the temperature difference between the two steps is determined to be 20℃, forming a temperature gradient of "low-temperature selective reaction - high-temperature efficient cross-linking".

[0071] (2) Details of temperature control at each stage Step 1: Temperature Control Preheating stage: After the aliphatic-alicyclic hybrid diisocyanate mixture A is fed in, the temperature is raised to 40±1℃. This temperature can reduce the viscosity of isocyanate, which is convenient for subsequent ether alcohol dropwise mixing, and is also lower than the isocyanate self-polymerization reaction temperature (≥60℃), thus avoiding premature self-polymerization.

[0072] Dropping stage: The temperature of polyalkylene ether alcohol is controlled at 40~45℃ during the dropping process. It is adjusted in real time through the cooling circuit of the oil bath. The dropping rate is linked to the temperature (for every 2g / min increase in the dropping rate, the upper limit of the temperature is reduced by 1℃) to prevent the local NCO group concentration from being too high and causing a rapid reaction and exothermic reaction, which would lead to a sudden temperature rise (the maximum temperature fluctuation is allowed to be ±2℃).

[0073] During the isothermal reaction stage: the temperature is precisely controlled at 58±1℃. Temperature control accuracy is achieved through PID regulation of the oil bath (proportional coefficient Kp=2.5, integral coefficient Ki=0.1, derivative coefficient Kd=0.5). The actual temperature inside the vessel is recorded every 5 minutes. If the deviation exceeds 0.5℃, automatic cooling or heating compensation is initiated. If the temperature rises above 60℃ during the reaction, the stirring rate is immediately reduced by 50 r / min, and nitrogen purging is initiated at a rate of 80 mL / min for rapid heat dissipation. The original parameters are restored after the temperature recovers.

[0074] Cooling stage: After the urethane esterification reaction reaches its endpoint, the temperature is cooled to 55°C at a rate of 1.5°C / min for silane modification to avoid rapid cooling that could cause a sudden change in product viscosity and affect the dispersion of the silane coupling agent.

[0075] Step 2: Temperature Control Premixing stage: The aliphatic-alicyclic hybrid diisocyanate mixture B is heated to 70±1℃, at which temperature the viscosity of the polyisocyanate decreases to 1800 mPa. When mixing with the product from step one, reduce interfacial tension to ensure homogeneous mixing (the turbidity of the system after mixing is ≤5 NTU, which can be detected by an online turbidity meter).

[0076] Catalytic reaction stage: The temperature is stabilized at 78±2℃, and a "segmented temperature control" strategy is adopted: the temperature is controlled at 77±1℃ for the first 30 minutes of the reaction (induction period) to avoid rapid catalyst activation leading to runaway reaction; after 30 minutes of reaction (rapid reaction period), the temperature is raised to 79±1℃ to increase the reaction rate; in the later stage of the reaction (conversion rate ≥50%), the temperature is lowered to 78±1℃ to slow down the reaction rate and facilitate endpoint control.

[0077] Cooling stage: After catalyst deactivation, cool to 40°C at a rate of 1°C / min. Viscosity is monitored in real time during cooling (every 5 minutes). When the viscosity rises to 500 mPa... At time s, the stirring rate was simultaneously reduced from 380 r / min to 250 r / min to prevent excessive shear force from causing the product molecular chains to break.

[0078] (3) Emergency plan for handling abnormal temperatures If the temperature in step one unexpectedly rises above 65°C, immediately add 0.05% ethyl acetate as a cooling agent, and simultaneously turn on vacuum degassing (-0.06 MPa) to accelerate heat dissipation. After the temperature drops to 58°C, add 0.01% organic bismuth catalyst and extend the reaction time by 20 minutes to ensure that the hydroxyl groups react completely.

[0079] If the temperature in step two is below 75℃, the reaction rate decreases (NCO content decreases by ≤0.3% every 20 minutes). Then, gradually increase the temperature to 78℃ (increase by 1℃ each time and hold for 10 minutes), while adding 5% of the composite catalyst solution to avoid insufficient conversion.

[0080] (II) Adaptability control of catalyst system (1) Basis for catalyst selection and dosage matching Step 1: Organic-bismuth composite catalyst: Bismuth neodecanoate and bismuth laurate (mass ratio 7:3) are selected. Bismuth neodecanoate has high catalytic activity (suitable for urethane esterification reactions from room temperature to 60°C), while bismuth laurate has greater steric hindrance, which can slow down the reaction rate. The combination of the two balances the "reaction efficiency - product uniformity". The amount used is 0.25% of the total reactant mass, calculated based on the molar number of hydroxyl groups in the polyalkylene ether alcohol (catalyst metal ion to hydroxyl molar ratio = 1:1000), which ensures that the hydroxyl conversion rate is ≥99% while avoiding catalyst residue that could lead to runaway subsequent urea-formaldehyde esterification reactions.

[0081] Step 2: Composite urea-formylation catalyst: O,O-bis(2-propylheptyl)dithiophosphate zinc is the main catalyst (high selectivity for urea-formylation reaction), and zirconium acetylacetonate is the co-catalyst (can form coordination with isocyanate groups, reducing the activation energy of the reaction). The two are combined (mass ratio 85:15) to suit the multi-group structure of hybrid polyisocyanates (the reactivity of isocyanurate and biuret groups differs). The amount used is 0.045% of the total reactant mass, dynamically adjusted according to the NCO content of the hybrid polyisocyanate (for every 0.5% fluctuation in NCO content, the catalyst amount fluctuates by 0.005%).

[0082] (2) Catalyst addition method and timing control Step 1 Catalyst: Prepare a 10% ethyl acetate solution. After the polyalkylene ether alcohol is added dropwise and the temperature is stabilized at 58°C, use a "segmented addition" method: first add 70% of the catalyst solution, and after reacting for 40 minutes, add the remaining 30%. This avoids excessively high initial catalyst concentration, which could lead to excessively rapid local reactions and a broadened molecular weight distribution of the product (target molecular weight distribution index PDI≤1.3, detected by GPC).

[0083] Step 2 Catalyst: Prepare a 15% butyl acetate solution. After the temperature of the mixed system stabilizes at 78℃, add it at a uniform rate (0.5g / min) using a micro-metering pump. During the addition process, increase the stirring rate to 400r / min to form a strong shear field, so that the catalyst is uniformly dispersed (catalyst particle size ≤0.5μm, detected by laser particle size analyzer), avoiding local catalyst enrichment that could lead to "hot spot reactions".

[0084] (3) Compatibility verification of catalyst and raw materials Catalyst compatibility with hybrid isocyanates: Preliminary experiments determined that when the IPDI content in the aliphatic-alicyclic hybrid diisocyanate mixture A exceeds 35%, the amount of organic bismuth catalyst needs to be increased by 0.02% to compensate for the decrease in reaction rate caused by the steric hindrance of the IPDI isocyanate groups.

[0085] Catalyst compatibility with polyalkylene ether alcohols: If the acid value of the ether alcohol exceeds 0.8 mmol / kg, 0.01% triethylamine should be added first to neutralize it before adding the catalyst to avoid the acid value being too high and inhibiting the activity of the bismuth catalyst.

[0086] (III) Precise regulation of hydrophilic chain content and distribution (1) Basis for regulating hydrophilic chain content The product from step one constitutes 15% of the final crosslinking agent by mass. This proportion is determined based on the balance between emulsification and water resistance. Experiments have shown that when the proportion is below 10%, the crosslinking agent emulsifies in water for more than 30 seconds, and the emulsion separates after 24 hours of standing. When the proportion is above 20%, the water contact angle of the cured material is below 70°, and the water resistance decreases significantly (water absorption exceeds 5% after 24 hours of immersion). A proportion of 15% ensures that the crosslinking agent emulsification time is ≤10 seconds, the water contact angle after curing is ≥85°, and the water absorption is ≤2%.

[0087] (2) Details of hydrophilic chain distribution regulation Distribution of hydrophilic chains in polyoxyalkylene ether alcohols: By controlling the molar ratio of OH to NCO in step one to 1.05:1, the hydroxyl groups of the polyalkylene ether alcohols were almost completely reacted, and the hydrophilic chains were uniformly grafted onto the hybrid diisocyanate molecules, avoiding the aggregation of unreacted hydroxyl groups (unreacted hydroxyl content ≤0.05%, detected by ¹H-NMR). Samples were taken every 40 minutes during the reaction, and the molecular weight distribution of the product was detected by gel permeation chromatography (GPC) to ensure that PDI ≤1.3, indicating uniform distribution of hydrophilic chains.

[0088] Distribution of hydrophilic chains in siloxanes: The amount of KH-560 used was 1.2% of the product mass from step one, determined based on the molar ratio (1:1.2) of the epoxy groups to the trace hydroxyl groups in the product. Excess KH-560 ensured complete reaction of the hydroxyl groups while avoiding excessive cross-linking of the siloxane segments, which could lead to product gelation. After the modification reaction, the characteristic peak of the Si-O bond (1080 cm⁻¹) was detected by FT-IR. - The peak area of ​​¹) is compared with the standard curve to ensure that the siloxane grafting rate is ≥98%.

[0089] Hydrophilic chain distribution of phosphate ester: The amount of polyethylene glycol monomethyl ether phosphate ester is 0.8% of the total product mass, determined based on the reaction molar ratio (1:1) of phosphate ester groups and trace amounts of urethane groups in the crosslinking agent. The grafting efficiency of phosphate ester groups is detected by potentiometric titration (≥95%) to avoid free phosphate ester groups affecting the storage stability of the crosslinking agent.

[0090] (3) Dynamic compensation of hydrophilic chain regulation If the emulsification time of the product in step one exceeds 10 seconds, it indicates that the hydrophilic chain content is insufficient. In step two, the amount of polyethylene glycol monomethyl ether phosphate can be increased by 0.2% during the hydrophilic modification stage. If the water absorption rate of the cured material exceeds 2%, it indicates that the hydrophilic chain content is too high. In this case, the proportion of the product in step one in step two can be reduced by 2%, and the amount of hybrid polyisocyanate can be increased accordingly.

[0091] (iv) Structural parameter regulation of hybrid isocyanates (1) The component ratio of hybrid isocyanates is adapted Step 1 involves an aliphatic-alicyclic hybrid diisocyanate mixture A: HDI, IPDI, and HXDI in a mass ratio of 45:32:23. This ratio is based on a balance between reactivity and product performance: HDI exhibits the highest reactivity, ensuring efficient urethane esterification; IPDI provides the alicyclic structure, enhancing product hardness; and HXDI combines aliphatic and alicyclic properties, improving product flexibility. Preliminary experiments confirmed that the tensile strength of the product in Step 1, under this ratio, is ≥8 MPa, and the elongation at break is ≥300%, meeting the requirements for subsequent crosslinking.

[0092] Step 2: Aliphatic-alicyclic hybrid diisocyanate mixture B: HDI isocyanurate, IPDI biuret, and HXDI iminooxadiazine dione in a mass ratio of 50:30:20. This ratio stabilizes the average NCO functionality of the polyisocyanate at 3.2, with an NCO content of 21.8%. The isocyanurate groups enhance crosslinking density and weather resistance, the biuret groups improve flexibility, and the iminooxadiazine dione groups balance reactivity and storage stability. If the NCO content of the hybrid polyisocyanate fluctuates by more than 0.5%, it is compensated by adjusting the proportions of each component (increasing the proportion of HDI isocyanurate by 5% for every 0.5% decrease in NCO content).

[0093] (2) Adaptive regulation of functionality and reactivity The average NCO functionality of the aliphatic-alicyclic hybrid diisocyanate mixtures A and B was controlled at 3.2 ± 0.1. It was determined by a combination of gel permeation chromatography (GPC) and chemical titration: GPC determined the distribution of different molecular weight fractions, and chemical titration determined the total NCO content. The weighted average functionality was calculated. If the functionality was below 3.1, 5% HDI isocyanurate (functionality 3.0) was added; if it was above 3.3, 5% IPDI biuret (functionality 3.0) was added.

[0094] Reactivity regulation: The reactivity order of different groups in the hybrid polyisocyanate is: biuret group > isocyanurate group > iminooxadiazine dione group. By activating the reactivity of isocyanurate and iminooxadiazine dione groups at the reaction temperature in step two (78±2℃), the three groups can participate in the ureoformation reaction in a synergistic manner, avoiding the overreaction of a single group that would lead to uneven product structure.

[0095] (v) Control of the compatibility between raw material purity and moisture content (1) Raw material purity requirements and pretreatment compatibility The aliphatic-alicyclic hybrid diisocyanate mixtures A and B have a purity ≥99.5% and a hydrolyzed chlorine content ≤0.01%, which are detected by gas chromatography (GC). If the hydrolyzed chlorine content exceeds the standard, it needs to be purified by vacuum distillation (temperature 80℃, vacuum degree -0.098MPa) to remove impurities and chlorinated products to avoid affecting the catalyst activity.

[0096] The number-average molecular weight deviation of polyalkylene ether alcohols is ≤±5%. It is detected by gel permeation chromatography (GPC). If the molecular weight is too high (above 650 g / mol), the amount of hybrid diisocyanate can be increased appropriately, and the molar ratio of OH to NCO can be adjusted to remain at 1.05:1. If the molecular weight is too low (below 590 g / mol), the amount of hybrid diisocyanate can be reduced, while keeping the molar ratio unchanged.

[0097] The purity of silane coupling agent KH-560 is ≥98%, and the epoxy value deviation is ≤±0.02mol / 100g. It is tested by hydrochloric acid-acetone titration. If the epoxy value is too low, the amount of KH-560 is increased by 0.2% to ensure sufficient reactive sites.

[0098] (2) Standards and measures for moisture control throughout the process Moisture control standards: The moisture content of all raw materials is ≤0.02% (polyalkylene ether alcohol, polyethylene glycol monomethyl ether phosphate) or ≤0.01% (hybrid isocyanate, catalyst, terminator); the total moisture content of the reaction system is ≤0.005%, which is detected in real time by an online Karl Fischer moisture analyzer (detection frequency every 15 minutes).

[0099] Moisture control measures Raw material pretreatment: Aliphatic-alicyclic hybrid diisocyanate mixtures A and B are dehydrated under reduced pressure at a temperature of 45~50℃ for 30~40 min, with a vacuum degree of -0.095~-0.098 MPa. After dehydration, they are immediately sealed with nitrogen and stored for no more than 24 hours. Polyalkylene ether alcohols are dehydrated under reduced pressure at a temperature of 105±3℃ for 2 hours to ensure a moisture content of ≤0.02%.

[0100] Equipment drying: After the reactor, condenser and other equipment are dried at 120℃ for 2 hours, they are purged with nitrogen and cooled to room temperature; the feed port and sampling port are equipped with dryers (filled with 4A molecular sieves) to prevent moisture from being introduced by the air.

[0101] Nitrogen protection: The nitrogen purging rate is 50±5 mL / min throughout the process, and a slight positive pressure (0.01±0.005 MPa) is maintained inside the vessel. If the pressure is lower than 0.005 MPa, nitrogen should be added immediately to prevent air from entering and causing moisture to react with isocyanate.

[0102] Abnormal handling: If the moisture content of the system is detected to exceed 0.005%, immediately start vacuum degassing (-0.08MPa) and increase the nitrogen purging rate to 100mL / min. Dehydrate for 10min and continue the reaction after the moisture content is restored. If the moisture content exceeds 0.01%, hybrid isocyanate needs to be added (addition amount = moisture excess × 1000) to compensate for the NCO groups lost by hydrolysis.

[0103] (vi) The linkage control logic of process parameters A linkage control model for "raw material parameters - process parameters - product performance" is established, with the following core logic: For every 5% fluctuation in the IPDI content in the aliphatic-alicyclic hybrid diisocyanate mixtures A and B, the reaction temperature in step one is adjusted by 1°C (the temperature increases by 1°C for every increase in IPDI content), while the catalyst dosage is adjusted by 0.02% to ensure a stable reaction rate.

[0104] For every 5 mg KOH / g fluctuation in the hydroxyl value of polyalkylene ether alcohol, the molar ratio of OH to NCO in step one is adjusted by 0.05 (the molar ratio increases by 0.05 as the hydroxyl value increases) to ensure a quantitative reaction between the hydroxyl group and the NCO group.

[0105] In step two, for every 0.5% fluctuation in the NCO content of the aliphatic-alicyclic hybrid diisocyanate mixture B, the catalyst dosage is adjusted by 0.005%, and the reaction temperature is adjusted by 1℃ (for every increase in NCO content, the temperature is decreased by 1℃) to avoid the reaction rate being too fast or too slow.

[0106] For every 1% decrease in the siloxane grafting rate of the product in step one below the target value, the amount of polyethylene glycol monomethyl ether phosphate in the hydrophilic modification stage of step two is increased by 0.1% to compensate for the insufficient hydrophilicity.

[0107] Example 2 In step one, the ratio of aliphatic-alicyclic hybrid diisocyanate mixture A (HDI:IPDI:HXDI) is 47:30:23. In step two, the proportion of the dispersible active reaction product containing hybrid hydrophilic chains is 14.5%, and the amount of polyethylene glycol monomethyl ether phosphate (as a percentage of the total product mass) is 0.78%. Product properties in step S1: Colorless transparent liquid, viscosity at 23℃: 189.7 mPa s, Hazen color number 12, free NCO content 0.25%, siloxane grafting rate 98.8%, emulsification time in water 7.9s; Final crosslinking agent properties: Viscosity at 23℃: 876.5 mPa s, Hazen color number 17, NCO content 16.73%, viscosity change rate after 6 months of storage at 25℃ 3.9%, NCO retention rate 98.9%, emulsification time 3.8s; Crosslinking and curing performance: curing time at 15℃ is 4.5h, hardness of cured film is 2H, elongation at break is 318%, water contact angle is 85.7°, water absorption rate is 1.7% after immersion in water for 24h, and ΔE=1.1 after QUV aging for 1000h. Example 3 In step one, the ratio of aliphatic-alicyclic hybrid diisocyanate mixture A (HDI:IPDI:HXDI) is 43:34:23. In step two, the proportion of the dispersible active reaction product containing hybrid hydrophilic chains is 15.3%, and the amount of polyethylene glycol monomethyl ether phosphate (as a percentage of the total product mass) is 0.83%. Step 1 Product Properties: Colorless and transparent liquid, viscosity at 23℃: 195.4 mPa s, Hazen color number 14, free NCO content 0.29%, siloxane grafting rate 98.2%, emulsification time in water 9.1s; Final crosslinking agent properties: Viscosity at 23℃: 912.7 mPa s, Hazen color number 19, NCO content 16.35%, viscosity change rate after 6 months of storage at 25℃ 4.5%, NCO retention rate 98.3%, emulsification time 4.3s; Crosslinking and curing performance: curing time at 15℃ is 5.1h, hardness of cured film is 2H+, elongation at break is 332%, water contact angle is 87.1°, water absorption rate is 1.9% after immersion in water for 24h, and ΔE=1.3 after QUV aging for 1000h. Example 4 In step one, the ratio of aliphatic-alicyclic hybrid diisocyanate mixture A (HDI:IPDI:HXDI) is 46:31:23. In step two, the proportion of the dispersible active reaction product containing hybrid hydrophilic chains is 14.8%, and the amount of polyethylene glycol monomethyl ether phosphate (as a percentage of the total product mass) is 0.79%. Step 1 Product Properties: Colorless and transparent liquid, viscosity at 23℃: 191.2 mPa s, Hazen color number 13, free NCO content 0.26%, siloxane grafting rate 98.6%, emulsification time in water 8.1s; Final crosslinking agent properties: Viscosity at 23℃: 885.1 mPa s, Hazen color number 18, NCO content 16.61%, viscosity change rate after 6 months of storage at 25℃ 4.1%, NCO retention rate 98.7%, emulsification time 4.0s; Crosslinking and curing performance: curing time at 15℃ is 4.7h, hardness of cured film is 2H, elongation at break is 322%, water contact angle is 86.5°, water absorption rate is 1.8% after immersion in water for 24h, and ΔE=1.2 after QUV aging for 1000h. Example 5 In step one, the ratio of aliphatic-alicyclic hybrid diisocyanate mixture A (HDI:IPDI:HXDI) is 44:33:23. In step two, the proportion of the dispersible active reaction product containing hybrid hydrophilic chains is 15.2%, and the amount of polyethylene glycol monomethyl ether phosphate (as a percentage of the total product mass) is 0.82%. Step 1 Product Properties: Colorless and transparent liquid, viscosity at 23℃: 193.8 mPa s, Hazen color number 14, free NCO content 0.28%, siloxane grafting rate 98.4%, emulsification time in water 8.8s; Final crosslinking agent properties: Viscosity at 23℃: 903.5 mPa s, Hazen color number 19, NCO content 16.43%, viscosity change rate after 6 months of storage at 25℃ 4.3%, NCO retention rate 98.5%, emulsification time 4.2s; Crosslinking and curing performance: curing time at 15℃ is 4.9h, hardness of cured film is 2H+, elongation at break is 328%, water contact angle is 86.9°, water absorption rate is 1.8% after immersion in water for 24h, and ΔE=1.2 after QUV aging for 1000h.

[0108] The comparison of the embodiments is shown in the table below:

[0109] Through experiments using five examples, the self-emulsifying hybrid polyisocyanate crosslinking agent prepared by the two-step method exhibited excellent stability and consistency in product performance, even with minor fluctuations (≤±5%) in key variables such as the aliphatic-alicyclic hybrid diisocyanate mixture A and the proportion of the dispersible active reaction product containing hybrid hydrophilic chains. In all examples, the Hazen color number of the crosslinking agent was ≤19, the viscosity change rate after 6 months of storage at 25℃ was ≤4.5%, the NCO retention rate was ≥98.3%, and the emulsification time with water was ≤4.3s. This completely solved the problems of high color number, poor storage stability, and insufficient emulsification of traditional isocyanate crosslinking agents. Crosslinking curing... Afterwards, the material cures at a low temperature of 15℃ for ≤5.1h, possessing both high hardness of 2H~2H+ and high elasticity of 318%~332%, a water contact angle ≥85.7°, a water absorption rate of ≤1.9%, and excellent weather resistance (QUV aging ΔE≤1.3). It successfully overcomes the defects of low low-temperature curing efficiency and the contradiction between water resistance and mechanical properties of polyurethane materials. At the same time, through hybrid modification and precise reaction control, it solves the problems of difficult reaction control and poor block uniformity in aromatic polyester-polyurethane systems, achieving high compatibility with water-based polyol systems. The comprehensive performance of the product meets the requirements of industrial applications, and the process has strong reproducibility, showing potential for large-scale production.

Claims

1. A method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent, characterized in that, Includes the following steps, S1: After pretreatment of the aliphatic-alicyclic hybrid diisocyanate mixture A, a pretreated polyalkylene ether alcohol copolymerized with ethylene oxide and butylene oxide is added. The basic dispersive active product is obtained by urethane esterification under controlled temperature and catalyst conditions. The basic dispersive active product is then grafted with a pretreated silane coupling agent to introduce siloxane hybrid hydrophilic chains, and finally a dispersive active reaction product containing hybrid hydrophilic chains is obtained. S2: Using an aliphatic-alicyclic hybrid polyisocyanate mixture B as the main raw material, the hydrophilic reaction product containing hybrid hydrophilic chains obtained in step S1 is added as a hydrophilic modification component. The two undergo a temperature-controlled urethane esterification reaction under the action of a catalyst. The conversion rate of the urethane groups in the hydrophilic reaction product containing hybrid hydrophilic chains is used as the reaction endpoint. After catalyst deactivation, anti-aging modification and hydrophilic modification, the urethane esterification reaction product is used to obtain a self-emulsifying hybrid polyisocyanate crosslinking agent.

2. The method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to claim 1, characterized in that, After the aliphatic-alicyclic hybrid diisocyanate mixture A in step S1 is fed, the temperature is raised to 40±1℃; the polyalkylene ether alcohol in step S1 is added dropwise, with the temperature controlled at 40-45℃ during the dropwise addition process. After the dropwise addition is completed, the temperature is raised to 58±1℃ and maintained until the basic dispersed active product is obtained. Then, it is cooled to 55±1℃ and the silane coupling agent is added to react. In step S2, the temperature of the aliphatic-alicyclic hybrid polyisocyanate mixture B is 70±1℃ and is maintained until the addition of the dispersed active reaction product containing the hybrid hydrophilic chain is completed; the temperature of the ureoformation reaction in step S2 is controlled at 78±1℃; after the catalyst is deactivated in step S2, it is cooled to 40±1℃ at a rate of 1℃ / min, and the anti-aging modification is carried out at 40±1℃ for 30min, and the hydrophilic modification is carried out at 35±1℃ for 30min.

3. The method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to claim 1, characterized in that, The aliphatic-alicyclic hybrid diisocyanate mixture A in step S1 comprises 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane in a mass ratio of 45:32:23; the polyalkylene ether alcohol in step S1 is prepared by copolymerizing ethylene oxide and epoxide in a molar ratio of 85:15 with n-pentanol as the initiator; the catalyst in step S1 is prepared by mixing bismuth neodecanoate in a mass ratio of 7:3 with... Bismuth laurate was used as a solute and dissolved in anhydrous ethyl acetate to prepare a 10% (w / w) solution to obtain the catalyst. The silane coupling agent for the pretreatment in step S1 was selected as γ-glycidoxypropyltrimethoxysilane. The pretreatment step was as follows: 0.1% (w / w) of anhydrous aluminum trichloride was added to the γ-glycidoxypropyltrimethoxysilane as an activator, and the mixture was stirred under nitrogen protection at room temperature for 15 min at a stirring rate of 150 r / min for activation. The catalyst was used immediately after activation.

4. The method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to claim 3, characterized in that, The mass ratio between the aliphatic-alicyclic hybrid diisocyanate mixture A and the polyalkylene ether alcohol is 87:

163. In step S1, the amount of bismuth neodecanoate and bismuth laurate added is 0.25% of the mass of the aliphatic-alicyclic hybrid diisocyanate mixture A, and the amount of γ-glycidyl etheroxypropyltrimethoxysilane added is 1.2% of the mass of the basic dispersing active product.

5. The method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to claim 1, characterized in that, The pretreatment of the aliphatic-alicyclic hybrid diisocyanate mixture A described in step S1 includes the following steps: The aliphatic-alicyclic hybrid diisocyanate mixture A is dehydrated under constant temperature and reduced pressure for at least 30 minutes at a vacuum of -0.095 to -0.098 MPa, a temperature of 45 ± 2℃, and a stirring rate of 200 r / min. After dehydration, it is cooled to room temperature under nitrogen protection and sealed for later use. The pretreated aliphatic-alicyclic hybrid diisocyanate mixture A has a moisture content ≤0.01%, is a colorless and transparent liquid, and has a viscosity of 12.8 mPa at 23℃. s; The pretreatment step of the polyalkylene ether alcohol in step S1 is as follows: under the conditions of vacuum degree of -0.098MPa, temperature of 105±3℃ and stirring rate of 250r / min, the polyalkylene ether alcohol is dehydrated at a constant temperature for 2h. After pretreatment, the moisture content of the polyalkylene ether alcohol is ≤0.02%. It is then cooled to below 40℃ under nitrogen protection and sealed for later use.

6. The method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to claim 1, characterized in that, The aliphatic-alicyclic hybrid polyisocyanate mixture B in step S2 includes 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane in a mass ratio of 50:30:

20. The catalyst preparation process in step S2 is as follows: zinc O,O-bis(2-propylheptyl)dithiophosphate and zirconium acetylacetonate in a mass ratio of 85:15 are dissolved in anhydrous butyl acetate to prepare a catalyst solution with a mass concentration of 15%. The catalyst terminator used in the catalyst deactivation process in step S2 is methyl p-toluenesulfonate. The anti-aging modification process in step S2 uses antioxidant 1010 and light stabilizer 770. The hydrophilic modification in step S2 uses polyethylene glycol monomethyl ether phosphate.

7. The method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to claim 6, characterized in that, In step S2, the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain are mixed in a mass ratio of 85:

15. The amount of solute used in the composite urea-formylation catalyst in step S2 is 0.045% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain. The amount of catalyst terminator added in step S2 is 0.0% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain. 6%, the antioxidant 1010 in step S2 accounts for 0.3% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain, the light stabilizer 770 in step S2 accounts for 0.2% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain, and the polyethylene glycol monomethyl ether phosphate in step S2 accounts for 0.8% of the mass of the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersion-active reaction product containing the hybrid hydrophilic chain.

8. A method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to any one of claims 1-7, characterized in that, The reaction end point of the graft modification of introducing the siloxane hybrid hydrophilic chain in step S1 is monitored by sampling the product for detection by a Fourier transform infrared spectrometer. When the characteristic absorption peak of the epoxy group at 910 cm -1 in the spectrum disappears completely, and the area of the characteristic absorption peak of the siloxane Si-O bond at 1080 cm -1 compared with the standard curve reaches 98%, it is determined that the modification reaction has reached the end point; the reaction product containing the hybrid hydrophilic chain in step S1 is subjected to low-boiling substance removal and nitrogen protection sealing treatment.

9. A method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to any one of claims 1-7, characterized in that, The endpoint of the reaction between the aliphatic-alicyclic hybrid polyisocyanate mixture B and the dispersed active reaction product containing the hybrid hydrophilic chain in step S2 is determined by detecting the free NCO in the system. When the NCO content detected by the sample reaches 16.7±0.1%, the urea-formylation reaction is determined to have reached the endpoint, and the subsequent catalyst deactivation step is immediately initiated. If the NCO content decreases too quickly during the reaction, the material temperature is lowered to 75°C.

10. A method for preparing a self-emulsifying hybrid polyisocyanate crosslinking agent according to any one of claims 1-7, characterized in that, If the emulsification time of the dispersion active product containing hybrid hydrophilic chains in step S1 exceeds 10 seconds, it indicates that the hydrophilic chain content is insufficient. In step S2, the amount of polyethylene glycol monomethyl ether phosphate is increased by 1% during the hydrophilic modification stage. If the water absorption rate of the material after curing of the dispersion active product containing hybrid hydrophilic chains in step S1 exceeds 2%, the amount of the dispersion active product containing hybrid hydrophilic chains fed in step S2 is reduced by 2%, and the amount of the aliphatic-alicyclic hybrid polyisocyanate mixture B is increased by 2%.

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