Modified polyurethane fluorine-free waterproofing agent with high peel strength and preparation method thereof

Abstract

This invention discloses a modified polyurethane fluorine-free waterproofing agent with high peel strength and its preparation method, belonging to the field of functional polymer coating materials technology. By introducing a core process step of low-temperature crystallization pre-orientation under a specific temperature window, a "thermally hydrophobic and internally energy-storing" core-shell structure with thermoresponsive characteristics is successfully constructed in the modified polyurethane emulsion micelles, thereby achieving excellent initial water repellency. During high-temperature hot-pressing, the shell melts and the active groups in the core layer are released and migrated, forming a strong chemical bond with the adhesive. This solves the fundamental technical contradiction in the field of fluorine-free waterproofing agents where waterproofing and peel strength are difficult to balance.

Description

Technical Field

[0001] This invention relates to the field of functional polymer coating materials technology, and in particular to a modified polyurethane fluorine-free waterproofing agent with high peel strength and its preparation method. Background Technology

[0002] The application of functional coating materials on flexible substrates is an important research direction in the field of new materials. Among them, waterproofing finishing of textiles is one of the key finishing processes to improve the added value of fabrics. For a long time, fluorinated waterproofing agents have been widely used due to their excellent water and oil repellency properties. However, with the increasing global environmental awareness and the increasingly stringent control over persistent organic pollutants such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), the development of environmentally friendly, biodegradable, and completely fluorine-free CO waterproofing agents has become an inevitable trend in the dyeing and printing auxiliaries industry.

[0003] Currently, fluorine-free waterproofing agents on the market mainly include silicone-based, alkane-based, and modified acrylate-based agents. While silicone-based and long-chain alkane-based waterproofing agents can impart excellent initial water repellency to fabrics, they generally suffer from a serious application drawback: excessively low surface tension leads to extremely poor interfacial adhesion. In the production of outdoor sportswear, waterproof-finished fabrics often need to be hot-pressed with thermoplastic polyurethane (PU) or polytetrafluoroethylene (PTFE) films, or undergo subsequent coating processes. Because these waterproofing agents, when used as coating materials, form an excessively smooth and chemically inert hydrophobic film on the fabric surface, adhesives such as PUR hot melt adhesives cannot effectively wet and anchor, resulting in a significant decrease in the peel strength of the laminated fabric. This makes it highly susceptible to delamination and blistering, commonly referred to in the industry as slippage.

[0004] To address the peel strength issue, the industry has attempted to use polyurethane as a film-forming matrix due to its excellent film-forming toughness and adhesion. To impart waterproofing properties to polyurethane, existing technologies typically employ long-chain alkyl modification methods, introducing long-chain fatty alcohols or organosilicon segments into the polyurethane molecular chain through copolymerization or end-capping. However, current synthesis processes often utilize conventional one-step methods or random copolymerization, resulting in a random statistical distribution of hydrophobic and polar adhesive groups along the molecular chain.

[0005] This disorder in molecular structure leads to severe functional incompatibility: on the one hand, under normal fabric conditions, some polar groups are exposed on the surface, disrupting the continuity of the low surface energy layer, making it difficult to achieve a high waterproof rating and resulting in poor washability; on the other hand, during high-temperature lamination, the randomly distributed giant hydrophobic side chains produce a significant steric hindrance effect, obscuring potential reactive sites and hindering the chemical crosslinking of the adhesive with the polyurethane skeleton.

[0006] Therefore, how to construct a smart modified polyurethane waterproofing agent that can maintain the enrichment of hydrophobic groups on the surface to achieve high water repellency under normal conditions and release active groups to achieve high peel strength under hot processing conditions without using fluorine is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] This invention overcomes the shortcomings of the prior art and provides a modified polyurethane fluorine-free waterproofing agent with high peel strength and its preparation method.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent, comprising the following steps: S1. Diisocyanate, high molecular weight polyol and hydrophilic chain extender are reacted in an organic solvent to prepare isocyanate-terminated polyurethane prepolymer; S2. Add long-chain hydrophobic modifier and blocking agent to the prepolymer of step S1 and react to introduce hydrophobic segments and blocked isocyanate groups into the polyurethane molecular chain to obtain a modified prepolymer solution. S3. Adjust the temperature of the modified prepolymer solution obtained in step S2 to the preorientation temperature. And at this temperature, the mixture is kept at a constant temperature and stirred to carry out a conditioning treatment, which induces the orderly arrangement of long-chain hydrophobic segments at the micro-phase interface. S4. Add a neutralizing agent to the solution after step S3 to carry out a neutralization and salt formation reaction, then add water to carry out shear emulsification, remove the solvent by vacuum distillation, and obtain the modified polyurethane fluorine-free waterproofing agent. Among them, the pre-orientation temperature mentioned in step S3 The following relationship must be satisfied: ; In the formula, The melting point of the long-chain hydrophobic modifier described in step S2.

[0009] In a preferred embodiment of the present invention, the isothermal stirring curing treatment in step S3 takes 30-60 minutes and the stirring rate is 200-400 rpm; during the curing treatment, the system remains a homogeneous transparent or semi-transparent fluid and no visible solid precipitation occurs.

[0010] In a preferred embodiment of the present invention, the long-chain hydrophobic modifier in step S2 is at least one of a straight-chain saturated fatty alcohol, a straight-chain saturated fatty amine, or an acrylate monomer containing a long-chain alkyl group with C16 to C22 carbon atoms; preferably octadecyl alcohol or behenyl alcohol.

[0011] In a preferred embodiment of the present invention, the blocking agent in step S2 is selected from at least one of methyl ethyl ketone oxime, sodium bisulfite, 3,5-dimethylpyrazole, caprolactam, or diethyl malonate. The amount of the blocking agent added results in a capping rate of 30% to 80% for the remaining isocyanate groups -NCO in the polyurethane prepolymer, with the remaining uncapped -NCO groups being consumed by long-chain hydrophobic modifiers or water in subsequent reactions.

[0012] In a preferred embodiment of the present invention, the polymeric polyol in step S1 is selected from one or more of polycarbonate diol, polycaprolactone diol or polytetrahydrofuran ether diol, and its number average molecular weight is 1000-3000; the polymeric polyol is preferably polycarbonate diol to provide bulk structural strength of the modified polyurethane.

[0013] In a preferred embodiment of the present invention, the organic solvent in step S1 is one or a mixture of acetone, butanone, or ethyl acetate; In step S3, the mass ratio of the organic solvent to the solid content of the modified prepolymer is (0.5~1.5):1 to ensure that the long-chain hydrophobic segments are in good condition. At a certain temperature, the molecular chains have sufficient degrees of freedom to align themselves.

[0014] In a preferred embodiment of the present invention, the diisocyanate in step S1 is one or more of isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, or hexamethylene diisocyanate.

[0015] In a preferred embodiment of the present invention, the hydrophilic chain extender mentioned in step S1 is preferably a diol containing a carboxyl group, specifically selected from one or both of 2,2-dimethylolpropionic acid or 2,2-dimethylolbutyric acid.

[0016] In a preferred embodiment of the present invention, the neutralizing agent in step S4 is triethylamine or N,N-dimethylethanolamine; The shear emulsification speed is 2000-5000 rpm, the emulsification time is 10-30 minutes, and the average particle size of the resulting emulsion is controlled at 80-150 nm.

[0017] A high peel strength modified polyurethane fluorine-free waterproofing agent, which is an aqueous coating composition, wherein the micelle particles have a core-shell structure, wherein long-chain hydrophobic groups are enriched in the shell layer and are in a crystalline state, and blocked isocyanate groups are enriched in the core layer. When the waterproofing agent is applied to a substrate and heat-treated at temperatures above 130°C, the shell layer crystallizes and melts, while the core layer's closed isocyanate groups are released and migrate to the surface.

[0018] This invention addresses the shortcomings of the prior art and has the following beneficial effects: This invention introduces a specific solvent-assisted low-temperature crystallization pre-orientation step before emulsification and dispersion. The modified prepolymer is placed in a specific narrow temperature range below the melting point of the long-chain hydrophobic monomer for isothermal curing. Utilizing the differences in solubility parameters and crystallization kinetics of different chain segments under specific thermodynamic conditions, the hydrophobic long chains are induced to migrate to the outer side of the micelles, forming a dense pre-crystallized layer. Simultaneously, the closed isocyanate groups are driven to contract towards the micelle core, constructing a clearly defined outer hydrophobic-inner energy-storing core-shell structure micelle. This unique microscopic phase separation structure endows the substrate surface with a thermoresponsive intelligent interface. Under normal temperature and low-temperature washing conditions, the outer dense hydrophobic crystalline layer effectively shields against moisture intrusion. However, under the high-temperature conditions of subsequent hot-pressing lamination of the substrate with TPU or PTFE films, the outer hydrophobic crystal melts and collapses, causing the protected closed isocyanate groups in the core to break free and rapidly unblock, exposing highly active isocyanate-NCO anchor points that chemically bond with the adhesive molecules. Compared with existing waterproofing agents prepared by one-step random copolymerization, this invention completely eliminates the random steric hindrance of hydrophobic groups on reactive groups, solves the slippage problem caused by the low surface energy of traditional fluorine-free waterproofing agents, and significantly improves the peel strength of the film while maintaining excellent water repellency, and even achieves extremely high adhesion strength that destroys the film material rather than the adhesive layer.

[0019] This invention selects C16-C22 long-chain alkyl groups as the hydrophobic framework and, combined with the aforementioned pre-orientation process, ensures that the long-chain alkyl groups are not randomly curled on the surface of the emulsion particles, but rather arranged in a highly ordered crystalline array. This highly ordered arrangement significantly reduces the surface energy after film formation, making it difficult for water droplets to wet and spread on the substrate surface, exhibiting an excellent lotus leaf effect similar to fluorinated waterproofing agents. Simultaneously, because the hydrophobic segments are firmly grafted onto the polyurethane backbone through chemical bonds, and the self-crosslinking reaction triggered by the unsealing of the isocyanate during baking further locks in this orientation structure, this invention overcomes the problem of poor waterproofing durability caused by the migration of hydrophobic components from the surface to the interior or their detachment during washing in traditional paraffin emulsions or physically blended waterproofing agents. This endows the finished substrate with highly efficient water-repellent protection even after multiple standard water washes.

[0020] Furthermore, the precise definition of the pre-orientation temperature window in this invention is not only key to microstructure control but also the core of the process for ensuring emulsion stability. Within this temperature range, the hydrophobic segments are in a liquid crystal or mesocrystalline state, between complete melting and complete crystallization. This retains the degrees of freedom required for molecular chain rearrangement and orientation while avoiding demulsification or stratification caused by excessive crystallization of hydrophobic segments due to excessively low temperatures. This subsequent shear emulsification process in the mesocrystalline state can form nanoemulsions with extremely narrow particle size distribution and uniform core-shell structure. This avoids the problems of unclear phase fusion caused by high-temperature direct emulsification or coarse particle size caused by low-temperature emulsification in existing technologies, significantly improving the centrifugal stability and thermal storage stability of the waterproofing agent, making it less prone to precipitation or oil drift during long-distance transportation and long-term storage. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a flowchart of a method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0024] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0026] Application Overview: The core technical contradiction that this invention aims to solve lies in the natural physical paradox between minimizing and moderately maximizing surface energy in the field of high-end textile finishing.

[0027] In existing technological systems, the industry generally adopts static surface modification strategies to replace traditional C8 fluorocarbon chemicals. Whether it's an organosilicon system based on siloxane bonds or a paraffin system based on long-chain alkanes, the essence of the technology is to construct a chemically inert, low-surface-tension cured film on the surface of the substrate fibers. While this one-size-fits-all static structure successfully imparts excellent hydrophobicity to the substrate, its serious negative effect lies in creating a difficult-to-insurmount interfacial barrier. When the substrate needs subsequent lamination or coating processing, the polar adhesive cannot effectively wet and spread on such a smooth and inert surface, resulting in a lack of necessary anchoring points between the adhesive and the fibers, thus causing severe interlayer slippage. This manifests macroscopically as extremely low peel strength, often less than 5 N / cm, making the finished garments prone to bubbling and delamination during washing or strenuous exercise, severely limiting the application of fluorine-free waterproofing agents in high-end outdoor jackets and protective clothing.

[0028] To break this deadlock, this invention abandons the traditional chemical synthesis approach of searching for a single universal monomer and instead proposes a physical morphology breakthrough based on a dynamic response mechanism in the time-temperature dimension. Utilizing the self-assembly characteristics of polymer segments under specific solvent and temperature fields, this invention employs a unique solvent-assisted low-temperature pre-orientation process to construct a metastable core-shell structure with thermoresponsive properties before emulsion micelle formation. This structure resembles a smart microcapsule: driven by the crystallization force of long-chain alkyl groups at a specific temperature range, it forces them to migrate outward and form a dense, ordered hydrophobic shell responsible for shielding moisture at room temperature; simultaneously, it utilizes polarity differences to compress highly active, closed isocyanate groups into the micelle core, where they remain dormant. When the application scenario switches to the high-energy state of hot pressing, the outer crystallization melts, and the active core groups are instantly released and chemically bonded to the adhesive. This design allows a single additive to intelligently switch between a water-repellent mode and an adhesive mode according to changes in the external energy field. Example 1

[0029] like Figure 1 As shown, a method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent includes the following steps: S1. Diisocyanate, high molecular weight polyol and hydrophilic chain extender are reacted in an organic solvent to prepare isocyanate-terminated polyurethane prepolymer; S2. Add long-chain hydrophobic modifier and blocking agent to the prepolymer of step S1 and react to introduce hydrophobic segments and blocked isocyanate groups into the polyurethane molecular chain to obtain a modified prepolymer solution. S3. Adjust the temperature of the modified prepolymer solution obtained in step S2 to the preorientation temperature. And at this temperature, the mixture is kept at a constant temperature and stirred to carry out a conditioning treatment, which induces the orderly arrangement of long-chain hydrophobic segments at the micro-phase interface. S4. Add a neutralizing agent to the solution after step S3 to carry out a neutralization and salt formation reaction, then add water to carry out shear emulsification, remove the solvent by vacuum distillation, and obtain the modified polyurethane fluorine-free waterproofing agent. Among them, the pre-orientation temperature mentioned in step S3 The following relationship must be satisfied: ; In the formula, The melting point of the long-chain hydrophobic modifier described in step S2.

[0030] Transforming the theoretical concept of microphase separation into a feasible industrial solution requires bridging the enormous technological gap between kinetic freezing and thermodynamic equilibrium.

[0031] In conventional polyurethane synthesis processes, polymer chains in good solvents typically exhibit a randomly coiled, coiled structure, meaning that hydrophobic and hydrophilic groups are mixed and entangled. If emulsification with water is performed directly after the reaction, the movement of polymer chain segments is instantly frozen due to the sudden change in water polarity and the rapid drop in temperature. At this point, long-chain hydrophobic groups often do not have time to migrate to the surface and are instead randomly locked inside the micelles, while polar blocking groups may be exposed on the surface. This disordered structure results in hydrophobic groups not being on the surface, leading to poor waterproofing, and the blocking groups being embedded, resulting in poor adhesion.

[0032] The specific challenge of this invention lies in how to create an extremely narrow thermodynamic window within a limited timeframe prior to emulsification through precise process control. Within this window, long-chain hydrophobic groups must be endowed with sufficient segmental mobility to overcome viscous resistance and move towards the outer edge of the micelles, while simultaneously utilizing lattice energy to confine excessive thermal motion and prevent a return to a disordered state. Furthermore, macroscopic precipitation caused by localized over-crystallization must be avoided. This requires extremely precise equilibrium control of the system's solubility parameters, crystallization kinetics, and phase transition behavior.

[0033] Preferably, in step S1, IPDI is selected as the hard segment of the diisocyanate to provide skeletal support and rigidity for the molecule; Preferably, polycarbonate diol (PCDL) is selected as the soft segment of the polymer polyol to impart flexibility and hand feel to the film after formation. Preferably, the hydrophilic chain extender is DMPA, which is introduced into the carboxyl group to provide a hydrophilic center for subsequent water dispersion.

[0034] Specifically, the "reaction" in step S1 refers to the stepwise addition polymerization of isocyanate groups (-NCO) and hydroxyl groups (-OH) under the action of a catalyst to form urethane bonds. This stage is carried out using conventional methods, usually at 75-90°C, until the -NCO content reaches the theoretical value, forming a reactive prepolymer backbone.

[0035] Preferably, the long-chain hydrophobic modifier added in step S2 is octadecyl alcohol, which mainly utilizes the reaction of its terminal hydroxyl groups with some -NCO at the end of the main chain to graft long-chain alkyl groups with low surface energy characteristics onto the polyurethane chain ends; unlike physical blending, chemical grafting ensures that the hydrophobic agent is washable and does not fall off.

[0036] Preferably, the blocking agent subsequently added is methyl ethyl ketone oxime. The urethane bond formed between the blocking agent and -NCO is stable at room temperature, but reversibly dissociates at high temperature, thereby temporarily sealing and protecting the remaining highly active -NCO groups.

[0037] The mechanism for achieving low-temperature crystallization pre-orientation in step S3 is the core of this invention. In selected organic solvents, both the hard and soft segments of the polyurethane backbone typically exhibit good solubility, displaying a stretched state; however, the solubility of the inserted long-chain alkyl groups in acetone is extremely sensitive to temperature. At high temperatures, they are compatible with the solvent; however, within the limits defined in this invention... Within a certain temperature range, the solvent becomes a "poor solvent" for long-chain alkyl groups. According to the Flory-Huggins solution theory, at this point, in order to reduce the Gibbs free energy of the system, the long-chain alkyl groups will tend to be repelled from the solvent phase, resulting in microphase separation.

[0038] Preferably, a temperature range is set. Within this temperature range, the solvated long-chain hydrophobic segments are in a special "lyotropic liquid crystal state".

[0039] If higher At this point, the chain segments are in intense thermal motion, and the long-chain alkyl groups are in a state of random thermal motion, unable to form an ordered orientation; If lower At this point, if the crystallization driving force is too strong, long-chain alkyl groups will rapidly form a three-dimensional long-range ordered lattice, resulting in the precipitation of macroscopic solids. During emulsification, this will form coarse particles, which will destroy the stability of the emulsion.

[0040] Preferably, the isothermal stirring curing is not a simple static setting, but a thermodynamic self-assembly process. During the 30-60 minute curing period, the system utilizes the plasticizing effect of the organic solvent to grant hydrophobic long-chain segments mesoscopic degrees of freedom of movement. Since the solvent is a poor solvent for long-chain alkyl groups, the long-chain alkyl groups tend to undergo phase separation and migrate to the outer interface of the droplet, where they pre-crystallize and arrange themselves using van der Waals forces. Simultaneously, the highly polar urethane hard segments and blocked isocyanate groups are repelled and contract towards the droplet core. This process successfully completes the internal arrangement and assembly of the micelles before emulsification.

[0041] The mechanism by which emulsification and dispersion in step S4 is achieved is a structural locking process.

[0042] Preferably, neutralization and salt formation refers to the acid-base neutralization reaction of neutralizing the carboxyl groups on the chain extender with alkali to generate ammonium carboxylate salt, which causes the originally hydrophobic polymer chain to carry a charge and form a hydrophilic center, which is a chemical prerequisite for subsequent dispersion in water.

[0043] Preferably, adding water for shear emulsification utilizes high-speed shear force to disperse the oil phase into nano-sized droplets.

[0044] In step S3, a dense pre-crystallized layer forms at the interface due to the hydrophobic long chains. This hard shell acts as a protective layer under the high shear forces of emulsification, preventing the encapsulated isocyanate groups from directly contacting water and avoiding side reactions. After final desolvation under reduced pressure, the resulting aqueous emulsion particles perfectly retain the core-shell structure, laying the structural foundation for subsequent applications.

[0045] Source of materials: Isophorone diisocyanate (IPDI): Product No. I109582, purity 99%, isomer mixture, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Polycarbonate diol (PCDL): Model T5652, number average molecular weight Mn=2000, purchased from Asahi Kasei Corporation, Japan; 2,2-Dimethylolpropionic acid (DMPA): Product No. B104539, purity 98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Octadecyl alcohol: Product number O105099, purity >98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Behenyl alcohol: Product number D113391, purity >98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; 2-Butanone oxime: Product number B105233, purity >99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Triethylamine (TEA): Product No. T103285, purity 99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Acetone: Catalog No. 10000418, analytical grade (AR), purchased from Sinopharm Chemical Reagent Co., Ltd.

[0046] To further verify the effectiveness of the above method and the critical significance of the core parameters, specific comparative experiments are conducted below.

[0047] Experimental Example 1: S1. In a four-necked flask equipped with a mechanical stirrer, a condenser, and a nitrogen inlet tube, add 44.4 g of isophorone diisocyanate, 100 g of polycarbonate diol, 6.7 g of dimethylolpropionic acid, and 80 g of acetone solvent. Heat to 80°C and react for 2.5 hours under nitrogen protection. Titrate the NCO value until it reaches the theoretical value.

[0048] S2, cool to 60℃, add octadecanol ( =58℃) 13.5g, react for 1 hour, at which point the octadecyl alcohol hydroxyl group is completely reacted; then add 4.3g of butanone oxime, continue to keep warm for 0.5 hours, until the infrared spectrum shows that the -NCO peak part is weakened but the characteristic peak is retained.

[0049] S3. Precisely adjust the temperature of the reaction system to 53℃, that is... Maintain a stirring speed of 300 rpm and cure at a constant temperature for 45 minutes. Observation: At this time, the system appears as a translucent, uniform fluid with a bluish tint, and no visible solid particles precipitate, indicating that the system is in a stable mesocrystalline state.

[0050] S4. Quickly lower the temperature to 40℃, add 5.0g of triethylamine to neutralize for 5 minutes, then shear at 3000rpm and add 400g of deionized water dropwise over 10 minutes. After the addition is complete, continue shearing for 15 minutes.

[0051] Post-processing: Acetone was removed by vacuum distillation to obtain a modified polyurethane emulsion with a solid content of about 30%. The emulsion had a bluish appearance and good centrifugal stability.

[0052] Experimental Example 2: The procedure is exactly the same as in Experiment Example 1, except that the pre-orientation temperature in step S3 is adjusted to 55℃. This experiment aims to verify the effectiveness of the upper limit of the liquid crystal state window.

[0053] Experimental Example 3: The difference from Experimental Example 1 is that stearyl alcohol was replaced with an equimolar amount of behenol ( =70℃).

[0054] Accordingly, the pre-orientation temperature in step S3 is adjusted to 64℃, that is... This experiment aims to demonstrate the temperature formula proposed in this invention. It has universal applicability and can guide the process setting of raw materials with different melting points.

[0055] Comparative Example 1: The formula is exactly the same as that of Experimental Example 1, except that the low-temperature conditioning in step S3 is omitted, and after the reaction in step S2 is completed, it is directly heated at 75℃ (significantly higher). Triethylamine is added, followed by direct addition of hot water for emulsification. This simulates the "hot emulsification" process commonly used in existing technologies, where the molecular chains undergo intense thermal motion and the hydrophobic groups are in a random coil state.

[0056] Comparative Example 2: The formula is exactly the same as that in Experimental Example 1, except that the temperature for the conditioning in step S3 is set to 40℃. It is far below the lower limit.

[0057] Upon observation, after 15 minutes of the conditioning process, visible residue appeared on the inner wall of the flask, the system gradually became turbid, and a large amount of white flocculent precipitate appeared. After forcibly adding water to neutralize and emulsify, the resulting emulsion had extremely coarse particles, an opaque milky appearance, and after standing for 24 hours, obvious sedimentation and stratification appeared at the bottom.

[0058] Comparative Example 3: The difference from Experiment 1 is that instead of using methyl ethyl ketone (MEK) oxime as a blocking agent, the amount of octadecyl alcohol is increased to completely block all isocyanate groups in the prepolymer with octadecyl alcohol, so that the final product does not contain any potentially reactive -NCO groups. This experiment is used to demonstrate the decisive contribution of "blocked isocyanates" to peel strength.

[0059] The waterproofing agents obtained from Experimental Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. The test methods included: Particle size distribution (PDI) test of emulsion: The uniformity of micro-assembly of emulsion micelles was characterized by dynamic light scattering method. The emulsion to be tested was diluted with deionized water to a solid content of about 0.1 wt%, and tested using a laser particle size analyzer under constant temperature of 25℃. The instrument automatically outputs the average hydrated particle size and polydispersity index (PDI) according to the Stokes-Einstein equation. The PDI value directly reflects the monodispersity of the system. The lower the value, the narrower the micelle size distribution and the more regular the structure formed under the induction of pre-orientation process.

[0060] Crystallization melting enthalpy test: Differential scanning calorimetry was used to quantitatively verify the degree of ordered arrangement of long-chain alkyl groups. The emulsion was slowly dried in a vacuum drying oven at 40℃ to preserve its original thermal history structure. 5-10 mg of dried sample was packaged in an aluminum crucible and heated at a rate of 10℃ / min using a TA Q2000 instrument under nitrogen protection. The melting enthalpy was obtained by integrating the area of ​​the melting peak of the long-chain alkyl side chain in the 40-60℃ range of the single heating curve. The higher the enthalpy value, the more dense and complete the crystallization of the hydrophobic segments on the micelle surface.

[0061] Static water contact angle test: The wetting performance of the fabric surface is objectively evaluated using an optical contact angle meter. The treated fabric is laid flat on the sample stage, and 5 μL of deionized water is added to the fabric surface using a micro-syringe. The water-gas-solid three-phase contact angle is measured by the tangential method at 30 seconds after the droplet contacts the surface. Five tests are performed on different parts of the fabric, and the average value is calculated.

[0062] NCO group retention rate test: The shielding and protection mechanism of the core-shell structure on the core active groups was verified by di-n-butylamine back titration. The theoretical NCO content in the prepolymer was calculated according to the formula. A quantitative amount of emulsion was dried at low temperature to form a film and then dissolved in an anhydrous solvent. Excess di-n-butylamine was added under the high temperature unsealing condition of 120℃ to make it react completely with the released NCO. Then, the remaining amine was back titrated with standard hydrochloric acid to calculate the actual NCO residue.

[0063] Peel strength test: conducted in accordance with GB / T 2790-1995.

[0064] Washability test: The treated fabric was washed 20 times in a standard washing machine with standard detergent at a water temperature of 40°C. After drying and equilibration, its static water contact angle was tested again.

[0065] The performance test results of each experimental example and comparative example are shown in the table below: Table 1. Test results of physicochemical properties and application effects of each experimental example and comparative example.

[0066] As can be seen from the above table, Example 1 exhibits an extremely narrow particle size distribution coefficient and a high enthalpy of fusion of 48.5 J / g, a stark contrast to Comparative Example 1. Comparative Example 1 employs a conventional high-temperature direct emulsification process. Due to the random thermal motion of molecular chains at high temperatures, it cannot form an ordered arrangement, resulting in an emulsion PDI as high as 0.358 and a enthalpy of fusion of only 15.6 J / g. This significant difference directly confirms the effectiveness of step S3 of this invention: at a specific temperature range, solvent-assisted mesocrystalline behavior successfully induces the formation of a highly dense and ordered crystalline array at the micelle interface of hydrophobic long-chain alkyl groups; this dense surface crystalline structure endows the fabric with excellent initial water repellency and superior washability, while Comparative Example 1, lacking this ordered structure, shows a significant decrease in both contact angle and washability.

[0067] The NCO group retention rate in Example 1 was as high as 92%, while that in Comparative Example 1 was only 45%. This is because the dense hydrophobic crystalline shell formed in step S3 of Example 1 acted as a physical barrier during the emulsification and dispersion stage, effectively preventing water molecules from penetrating into the micelle core, thereby avoiding the hydrolysis and consumption of highly active blocked isocyanate groups. Because most of the active crosslinking sites were retained, when the emulsion of Example 1 was film-formed and desealed by high-temperature hot pressing, the large number of NCO groups released could fully chemically bond with the adhesive molecules, achieving a peel strength as high as 16.5 N / cm. In contrast, Comparative Example 1 suffered a large loss of NCO due to its loose shell, resulting in a peel strength of only 6.8 N / cm. The results of Comparative Example 3 further confirmed the necessity of the chemical bonding mechanism from the opposite perspective; the physical adsorption of long-chain alkyl groups alone cannot meet the requirements for high-strength interlayer adhesion.

[0068] Example 1 ( ) All performance aspects are optimal; Example 2 ( Although the emulsion did not break down at the upper limit of the temperature window, the slightly stronger thermal motion resulted in a slightly lower enthalpy of fusion and PDI compared to Example 1, indicating that the microscopic order is extremely sensitive to temperature. When the temperature dropped to 40°C, outside the lower limit of the window, the crystallization driving force within the system became too strong, leading to macroscopic phase separation and precipitation, making it impossible to prepare a stable emulsion. This series of data fully demonstrates that the temperature range defined in this invention (…) to It is not a simple process optimization, but a necessary thermodynamic condition for achieving controllable self-assembly of polymer segments in the lyotropic liquid crystal state. It is the core technology for achieving simultaneous improvement in waterproofness and peel strength.

[0069] In summary, this invention successfully constructs a thermoresponsive "external hydrophobic-internal energy storage" core-shell structure in modified polyurethane emulsion micelles by introducing a core process step of low-temperature crystallization pre-orientation within a specific temperature window. This structure allows the waterproofing agent to achieve excellent initial water repellency under normal conditions through the dense crystalline arrangement of the outer long-chain alkyl groups. During high-temperature hot-pressing, it can form a strong chemical bond with the adhesive through shell melting and the release and migration of active groups in the core layer. This effectively solves the fundamental technical contradiction in the field of fluorine-free waterproofing agents—the difficulty in simultaneously achieving waterproofing and peel strength. Experimental data clearly demonstrate that the waterproofing agent prepared using this method achieves a peel strength of over 15 N / cm on the treated fabric, with the failure mode being membrane failure, while maintaining excellent initial waterproofing and wash resistance. The process parameters provided by this invention are clear and reproducible, offering a practical technical path for developing high-performance, intelligent, and environmentally friendly fluorine-free waterproofing agents.

[0070] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent, characterized in that, Includes the following steps: S1. Diisocyanate, high molecular weight polyol and hydrophilic chain extender are reacted in an organic solvent to prepare isocyanate-terminated polyurethane prepolymer; S2. Add long-chain hydrophobic modifier and blocking agent to the prepolymer of step S1 and react to introduce hydrophobic segments and blocked isocyanate groups into the polyurethane molecular chain to obtain a modified prepolymer solution. S3. Adjust the temperature of the modified prepolymer solution obtained in step S2 to the preorientation temperature. And at this temperature, the mixture is kept at a constant temperature and stirred to carry out a conditioning treatment, which induces the orderly arrangement of long-chain hydrophobic segments at the micro-phase interface. S4. Add a neutralizing agent to the solution after step S3 to carry out a neutralization and salt formation reaction, then add water to carry out shear emulsification, remove the solvent by vacuum distillation, and obtain the modified polyurethane fluorine-free waterproofing agent. Among them, the pre-orientation temperature mentioned in step S3 The following relationship must be satisfied: ； In the formula, The melting point of the long-chain hydrophobic modifier described in step S2.

2. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The isothermal stirring curing treatment in step S3 takes 30-60 minutes and the stirring rate is 200-400 rpm. During the curing treatment, the system remains a homogeneous transparent or semi-transparent fluid and no solids are visible to the naked eye.

3. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The long-chain hydrophobic modifier mentioned in step S2 is at least one of a straight-chain saturated fatty alcohol, a straight-chain saturated fatty amine, or an acrylate monomer containing a long-chain alkyl group, with carbon atoms of C16 to C22; preferably octadecyl alcohol or behenyl alcohol.

4. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The blocking agent in step S2 is selected from at least one of methyl ethyl ketone oxime, sodium bisulfite, 3,5-dimethylpyrazole, caprolactam, or diethyl malonate; The amount of the blocking agent added results in a capping rate of 30% to 80% for the remaining isocyanate groups -NCO in the polyurethane prepolymer, with the remaining uncapped -NCO groups being consumed by long-chain hydrophobic modifiers or water in subsequent reactions.

5. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The high molecular weight polyol mentioned in step S1 is selected from one or more of polycarbonate diol, polycaprolactone diol or polytetrahydrofuran ether diol, and its number average molecular weight is 1000~3000; the high molecular weight polyol is preferably polycarbonate diol to provide the bulk structural strength of the modified polyurethane.

6. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The organic solvent mentioned in step S1 is one or a mixture of acetone, butanone, or ethyl acetate; In step S3, the mass ratio of the organic solvent to the solid content of the modified prepolymer is (0.5~1.5):1 to ensure that the long-chain hydrophobic segments are in good condition. At a certain temperature, the molecular chains have sufficient degrees of freedom to align themselves.

7. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The diisocyanate mentioned in step S1 is one or more of isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, or hexamethylene diisocyanate.

8. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The hydrophilic chain extender mentioned in step S1 is preferably a diol containing a carboxyl group, specifically selected from one or both of 2,2-dimethylolpropionic acid or 2,2-dimethylolbutyric acid.

9. The method for preparing a high peel strength modified polyurethane fluorine-free waterproofing agent according to claim 1, characterized in that, The neutralizing agent mentioned in step S4 is triethylamine or N,N-dimethylethanolamine; The shear emulsification speed is 2000-5000 rpm, the emulsification time is 10-30 minutes, and the average particle size of the resulting emulsion is controlled at 80-150 nm.

10. A high peel strength modified polyurethane fluorine-free waterproofing agent, prepared by the preparation method according to any one of claims 1-9, characterized in that, The waterproofing agent is an aqueous coating composition in which the micelle particles have a core-shell structure, wherein long-chain hydrophobic groups are enriched in the shell and are in a crystalline state, and blocked isocyanate groups are enriched in the core. When the waterproofing agent is applied to a substrate and heat-treated at temperatures above 130°C, the shell layer crystallizes and melts, while the core layer's closed isocyanate groups are released and migrate to the surface.

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