An environment-friendly functional diluent, a preparation method thereof and application thereof in a modified amine epoxy curing system

Abstract

This invention discloses an environmentally friendly functional diluent, its preparation method, and its application in modified amine epoxy curing systems. By mass fraction, it comprises 23%–39% hyperbranched polyether polyol, 16%–34% diisocyanate, 33%–41% cashew phenol glycidyl ether, 0.01%–0.1% polymerization inhibitor, and 0.05%–0.5% organotin catalyst. The diluent has a star-shaped structure with hyperbranched polyether as the core, polytetrahydrofuran ether as flexible segments, and cashew phenol glycidyl ether as end groups. It has an epoxy value of 0.25 eq / 100g–0.35 eq / 100g, a viscosity of 300 mPa·s–600 mPa·s at 25°C, and a VOC content of 5 g / L–8 g / L. The preparation method involves first reacting diisocyanate with hyperbranched polyether polyol to generate an isocyanate-terminated intermediate, then capping it with cashew phenol glycidyl ether, followed by purification by vacuum distillation and short-path molecular distillation. When used in low-viscosity cashew phenol modified amine curing agent systems, this diluent effectively dissipates the internal stress during the curing of high-film-thickness coatings, preventing coating cracking while maintaining rapid surface drying and long-term salt spray resistance.

Description

Technical Field

[0001] This invention relates to specialized diluents, and more particularly to an environmentally friendly functional diluent, its preparation method, and its application in modified amine epoxy curing systems. Background Technology

[0002] Epoxy resin coatings are two-component systems, containing epoxy resin and a curing agent. The active groups in the curing agent molecules undergo a cross-linking reaction with the epoxy groups in the epoxy resin molecules to form a solid coating film with a three-dimensional network structure. Due to their excellent adhesion, chemical corrosion resistance, and mechanical strength, epoxy resin coatings are widely used in special heavy-duty anti-corrosion engineering, marine engineering, and other special protection fields. As the defense industry continues to increase its requirements for equipment protection performance, it is usually necessary to increase the coating thickness. However, high film thickness coatings will generate huge internal stress during rapid curing, which can easily lead to coating cracking and peeling.

[0003] Chinese patent CN102633992A discloses a low-viscosity cashew phenol modified amine curing agent, which can achieve rapid curing in low-temperature and humid environments. However, when this curing agent is applied to high-thickness coatings with a single-coat thickness of more than 500 μm, the traditional diluent used in conjunction with it has the following technical problems: the compatibility between traditional small-molecule diluents and cashew phenol curing agents is limited, resulting in insufficient storage stability after mixing. Furthermore, the diluent forms brittle cross-linking points after curing, making the coating prone to cracking under the shrinkage internal stress generated by the rapid curing of high-thickness coatings. Small-molecule diluents migrate to the bottom of the coating during thick film construction, leading to incomplete bottom curing and a decrease in the coating's impact resistance. Although linear polyether grafted diluents improve compatibility to some extent, their linear segments have limited ability to dissipate internal stress in high-thickness coatings, and the coating still cracks in a 3 mm bending test.

[0004] Existing technologies disclose various hyperbranched polyether epoxy diluents. These diluents reduce system viscosity through hyperbranching, thus improving coating toughness to some extent. However, the molecular backbone of low-viscosity cashew phenol-modified amine curing agents contains a large number of C15 long alkyl chains, exhibiting low polarity and low surface energy. The molecular skeleton of existing general-purpose hyperbranched epoxy diluents is mainly composed of high-polarity polyethers or polyesters. When these two are mixed, it is difficult to achieve molecular-level miscibility, tending to form a macroscopically uniform but microscopically phase-separated dispersion system. At the same time, during the curing process, general-purpose diluents preferentially react with low-viscosity cashew phenol-modified amine curing agents, forming a locally highly crosslinked, diluent-rich phase, further exacerbating the phase separation. Therefore, there is an urgent need to develop a hyperbranched diluent specifically adapted to long-chain cashew phenol curing systems, possessing high internal stress dissipation capacity, excellent workability, and corrosion resistance, to solve the cracking problem of high-thickness special anti-corrosion coatings. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides an environmentally friendly functional diluent, its preparation method, and its application in modified amine epoxy curing systems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: an environmentally friendly functional diluent, comprising the following raw materials by mass fraction: Hyperbranched polyether polyol 23%–39%, diisocyanate 16%–34%, cashew phenol glycidyl ether 33%–41%, polymerization inhibitor 0.01%–0.1%, organotin catalyst 0.08%–0.3%; The diluent has a star-shaped structure, which includes a hyperbranched polyether core, a polytetrahydrofuran ether flexible segment, and a cashew phenol glycidyl ether end group; the cashew phenol glycidyl ether end group has an epoxy group, which can undergo a crosslinking reaction with a low-viscosity cashew phenol modified amine curing agent. The diluent has an epoxy value of 0.25 eq / 100g to 0.35 eq / 100g, a viscosity of 300 mPa·s to 600 mPa·s at 25°C, and a volatile organic compound content in the range of 5 g / L to 8 g / L. The hyperbranched polyether polyol has a pentaerythritol or trimethylolpropane as the core and polytetrahydrofuran ether as the branch chain, with a functionality of 3 to 6 and a number-average molecular weight of 800 g / mol to 2000 g / mol.

[0007] In a preferred embodiment of the present invention, the diisocyanate is at least one selected from isophorone diisocyanate, hexamethylene diisocyanate, or dicyclohexylmethane diisocyanate; The polymerization inhibitor is at least one of hydroquinone, p-hydroxyanisole, or 2,6-di-tert-butyl-p-cresol. The organotin catalyst is at least one of dibutyltin dilaurate, stannous octoate, or dibutyltin diacetate.

[0008] In a preferred embodiment of the present invention, the cashew phenol glycidyl ether has an epoxy value of 0.50 to 0.60 eq / 100g and is prepared by reacting cashew phenol with epichlorohydrin under alkaline conditions.

[0009] A method for preparing an environmentally friendly functional diluent, comprising: S1: Mix diisocyanate with organotin catalyst, heat to 40℃~50℃, add hyperbranched polyether polyol dropwise, and after the addition is complete, heat to 55℃~65℃ and react for 2h~4h to obtain isocyanate-terminated hyperbranched polyether intermediate; monitor the NCO value of the system using the di-n-butylamine method, and determine the reaction endpoint when the NCO value drops to 95%~100% of the theoretical value; S2: Add a polymerization inhibitor to the intermediate obtained in S1, heat to 60℃~70℃, add cashew phenol glycidyl ether dropwise, and after the addition is complete, heat to 75℃~85℃ and continue the reaction for 3h~5h; use Fourier transform infrared spectroscopy to monitor the NCO characteristic peak at wavenumber 2270cm-1, and when the peak disappears, it is determined to be the reaction endpoint. S3: The reaction product obtained in step S2 is subjected to vacuum distillation at 120℃~140℃ and pressure of -0.098MPa~-0.095MPa to remove low-boiling substances, and the intermediate product is obtained by filtration. S4: The intermediate product filtered from S3 is purified by short-path molecular distillation at a temperature of 150℃~170℃ and a system vacuum of 20Pa~30Pa.

[0010] In a preferred embodiment of the present invention, step S1 is carried out under inert gas protection, and the molar ratio of isocyanate groups to hydroxyl groups in hyperbranched polyether polyol is 2.1 to 2.2:1.

[0011] In a preferred embodiment of the present invention, in step S2, the reaction temperature is controlled at 78°C to 82°C, and the reaction time is controlled at 3.5h to 4.5h.

[0012] In a preferred embodiment of the present invention, in step S1, the amount of the organotin catalyst added is 0.1% to 0.3% of the total mass of the reaction system.

[0013] In a preferred embodiment of the present invention, in step S3, the filtration uses a filtration device with a pore size of 1μm to 3μm.

[0014] An environmentally friendly functional diluent is used in a modified amine epoxy curing system, specifically in epoxy anti-corrosion coatings for special engineering projects. The epoxy anti-corrosion coating is prepared by compounding component A and component B. Component A comprises bisphenol A type epoxy resin E51 and the diluent according to any one of claims 1-3, and component B is a low-viscosity cashew phenol modified amine curing agent.

[0015] In a preferred embodiment of the present invention, the amount of the diluent added to component A of the epoxy anti-corrosion coating is 8% to 15% by mass fraction; the mass ratio of component A to component B is 1:0.8 to 1.2.

[0016] This invention addresses the shortcomings of the prior art and has the following beneficial effects: This invention provides a diluent specifically for low-viscosity cashew phenol modified amine curing agents. This diluent has a star-shaped molecular structure with a hyperbranched polyether as the core, polytetrahydrofuran ether as flexible segments, and cashew phenol glycidyl ether as end groups. When this diluent is added to E51 epoxy resin at a mass ratio of 8%–15%, a 500 μm thick coating prepared in conjunction with the low-viscosity cashew phenol modified amine curing agent exhibits a surface drying time of 2.3–2.7 hours, passes a 3 mm bending test, and shows no cracks under both normal and reverse impact (50 cm·kg). The coating also shows no abnormalities after a 2400-hour neutral salt spray test. Compared to existing small-molecule and linear diluents, the diluent provided by this invention maintains rapid surface drying performance while solving the cracking problem of high-thickness coatings under bending and impact conditions, and preserving the long-term corrosion resistance of the coating.

[0017] The diluent has a cashew phenol glycidyl ether end group, which shares the same C15 alkyl chain structural unit as the low-viscosity cashew phenol modified amine curing agent. This ensures molecular-level compatibility between the diluent and curing agent after mixing, preventing the diluent from migrating to the bottom of the coating during thick film application. In contrast, when cashew phenol glycidyl ether is used directly as a diluent, the coating cracks after bending at 6 mm and experiences severe impact cracking. The coating of this invention shows no cracks even after impact, and the bottom is uniformly cured. By grafting the cashew phenol glycidyl ether end group to the end of the hyperbranched molecular backbone, the structural advantage of compatibility with the curing agent is retained, while overcoming the defect of insufficient crosslinking at the bottom caused by the migration of small molecule monomers, thus eliminating the problem of impact cracking caused by migration.

[0018] The diluent's molecular structure includes a hyperbranched polyether core, flexible polytetrahydrofuran ether segments, and urethane bond connecting units. The hyperbranched core generates a space-occupying effect in the cross-linked network, reducing the density of the cross-linked network. The flexible polytetrahydrofuran ether segments absorb part of the curing shrinkage energy through a microphase separation mechanism. The urethane bonds dissipate stress during the stress process through the reversible dissociation and recombination of hydrogen bonds. In the prior art, hyperbranched polyether diluents with terminal epoxy groups lacking urethane bonds cracked in the 4mm bending test and showed microcracks in the normal impact test. This invention, through the synergistic effect of the hyperbranched core, polytetrahydrofuran ether segments, and urethane bonds, enables a 500μm thick coating to remain crack-free in both the 3mm bending and normal and reverse impact tests, achieving effective dissipation of internal stress under high film thickness conditions.

[0019] This invention combines the compatibility advantages of cashew phenol glycidyl ether end groups with the stress dissipation advantages of hyperbranched star structures in a single diluent molecule. Simultaneously, it selects polytetrahydrofuran ether, which exhibits superior hydrolysis resistance compared to polyethylene glycol and polypropylene glycol, as a flexible chain segment. The synergistic effect of these structural units enables the diluent to achieve the following technical effects in a low-viscosity cashew phenol-modified amine curing system: maintaining a coating life of 2.3 to 2.7 hours at 25°C, meeting the application requirements of a 2 to 3 hour spray interval at 25°C; a 500 μm thick coating passing a 3 mm bending test; no cracks under 50 cm·kg positive and negative impact conditions; and no abnormalities in the coating after 2400 hours of neutral salt spray testing. Attached Figure Description

[0020] 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 preferred embodiment of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0022] 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.

[0023] Application Overview: In existing technologies, to shorten the construction interval, the coating needs to have a fast surface drying speed at room temperature. However, accelerating the curing speed will cause significant volume shrinkage in the thickness direction of the coating, resulting in the accumulation of large shrinkage internal stress within the coating. Especially when the single-pass film thickness reaches 500μm or more, the accumulated internal stress exceeds the coating's own strength limit. Although using small molecule diluents can reduce the viscosity of the system, small molecule diluents form brittle cross-linked regions after curing, which cannot effectively dissipate internal stress and instead exacerbate the risk of coating cracking. Using linear polyether grafted diluents can improve the coating toughness to some extent, but its stress dissipation mechanism is chain segment slip, which has limited effect on dispersing concentrated internal stress under high film thickness conditions. In addition, for long carbon chain curing agent systems represented by cashew phenol modified amine, existing diluents have insufficient compatibility with this type of curing agent, and small molecule diluents tend to migrate to the bottom of the coating during thick film construction, resulting in a decrease in the cross-linking density at the bottom of the coating.

[0024] This invention constructs a diluent molecular architecture with a star-shaped molecular structure and applies it to an epoxy resin coating system using a low-viscosity cashew phenol-modified amine curing agent as the curing component. The hyperbranched core of this diluent generates a space-occupying effect in the crosslinking network, reducing the density of the crosslinking network. The flexible polytetrahydrofuran ether segments absorb some of the curing shrinkage energy through a microphase separation mechanism. The cashew phenol glycidyl ether end groups are homologous to the C15 alkyl segments of the target curing agent, achieving molecular-level homogeneity during curing. Compared to existing diluents, the diluent provided by this invention exhibits uniform curing at the bottom of the coating after being added to the epoxy resin system, overcoming the technical defect of existing diluents migrating to the bottom of thick films.

[0025] like Figure 1 As shown, a method for preparing an environmentally friendly functional diluent includes: S1: Mix diisocyanate with organotin catalyst, heat to 40℃~50℃, add hyperbranched polyether polyol dropwise, and after the addition is complete, heat to 55℃~65℃ and react for 2h~4h to obtain isocyanate-terminated hyperbranched polyether intermediate; monitor the NCO value of the system using the di-n-butylamine method, and determine the reaction endpoint when the NCO value drops to 95%~100% of the theoretical value; S2: Add a polymerization inhibitor to the intermediate obtained in S1, heat to 60℃~70℃, add cashew phenol glycidyl ether dropwise, and after the addition is complete, heat to 75℃~85℃ and continue the reaction for 3h~5h; monitor the wavenumber at 2270cm using Fourier transform infrared spectroscopy. -1 The NCO characteristic peak is observed, and the disappearance of this peak is considered the end point of the reaction. S3: The reaction product obtained in step S2 is subjected to vacuum distillation at 120℃~140℃ and pressure of -0.098MPa~-0.095MPa to remove low-boiling substances, and the intermediate product is obtained by filtration. S4: The intermediate product filtered from S3 is purified by short-path molecular distillation at a temperature of 150℃~170℃ and a system vacuum of 20Pa~30Pa.

[0026] In the process of constructing a star-shaped diluent molecular structure using hyperbranched polyether polyols and cashew phenol glycidyl ether, the key technical challenges include: the epoxy groups in the cashew phenol glycidyl ether molecule are prone to ring-opening polymerization at higher temperatures and in the presence of a catalyst; the epoxy groups undergo side reactions during the end-capping stage, causing the epoxy value of the product to deviate from the design range, affecting the reactivity matching of subsequent cross-linking reactions; the NCO groups of diisocyanates are sensitive to moisture, and trace amounts of moisture in the system will react with NCO to form urea bonds and release carbon dioxide, causing the actual usable amount of NCO to deviate from the theoretical value, thus affecting the end-capping rate of the intermediate and the molecular structural integrity of the final product; the functionality of hyperbranched polyether polyols is 3-6, and when its multiple hydroxyl groups react with isocyanate intermediates, if the feeding sequence or reaction conditions are not properly controlled, excessive intermolecular cross-linking can easily occur, forming a gel.

[0027] Source of materials: Hyperbranched polyether polyol, core: pentaerythritol, branches: polytetrahydrofuran ether (PTMEG), functionality 4, Mn=1200, industrial grade, purchased from Shandong Lanxing Dongda Chemical Co., Ltd., product model HY-1200; when this model of product is unavailable, those skilled in the art can prepare hyperbranched polyether polyols with the same core structure, similar molecular weight and functionality according to the above synthesis method. The specific preparation steps are as follows: Add 100.0g pentaerythritol to a 2L jacketed stainless steel high-pressure reactor, seal the reactor, turn on the vacuum pump to -0.098MPa, then introduce high-purity nitrogen to atmospheric pressure, repeat this process 3 times, and finally maintain a slight positive pressure of 0.02MPa of nitrogen in the reactor. Start stirring and pressurize the mixture of 100.0g tetrahydrofuran and 10.0g propylene oxide into the reactor, followed by the addition of 1.5g boron trifluoride diethyl ether complex. Set the stirring speed to 200 rpm. Turn on the jacket heating and raise the temperature of the material in the reactor to 45°C. Maintain the temperature and stir for 1 hour to completely dissolve the solid pentaerythritol and form active centers. Start the dropping pump and begin dropping 900.0g tetrahydrofuran into the reactor, setting the dropping time to 10.0 hours. After the addition is complete, adjust the heating system to raise the reaction system to 65°C; continue the reaction at 65°C for 7.0 hours to allow the monomer to fully open the ring and graft onto the end of the branch chain. After the reaction is complete, cool down to 30°C, and slowly add 5wt% sodium hydroxide aqueous solution while stirring. Use a precision pH meter to monitor the pH dynamically. Stop adding when the pH of the system reaches 7.5; turn on the vacuum system, adjust the pressure inside the vessel to -0.095MPa, and raise the temperature to 110°C for vacuum distillation to recover the unreacted tetrahydrofuran monomer until no more liquid drips from the condenser; continue vacuum drying at 110°C and -0.095MPa for 2.0 hours to remove trace amounts of moisture. Filter through a precision filter with a 5-micron pore size to remove the salt solids produced by neutralization, and obtain a transparent to slightly yellow viscous liquid, which is the hyperbranched polyether polyol product.

[0028] Isophorone diisocyanate (IPDI), industrial grade, purity ≥99.5%, purchased from BASF, Germany; Cashew phenol glycidyl ether (CGE), industrial grade, epoxy value 0.55 eq / 100g, purchased from Nanjing Tianlu Nanotechnology Co., Ltd. p-Hydroxyanisole, industrial grade, purity ≥99.0%, purchased from Sinopharm Chemical Reagent Co., Ltd. Dibutyltin dilaurate (DBTDL), industrial grade, purity ≥98.0%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Nitrogen, industrial grade, purity ≥99.99%, oxygen content ≤10ppm, moisture content ≤5ppm; E51 epoxy resin, industrial grade, epoxy value 0.51eq / 100g, purchased from Sinopec Baling Petrochemical Branch. The preparation method of the low-viscosity cashew phenol modified amine curing agent is as follows: In a 500ml four-necked reaction flask equipped with a stirrer, condenser, thermometer, dropping funnel, and nitrogen purging tube, 198g of cashew phenol was added. The reaction was carried out under continuous stirring and N2 gas purging. 68.4g of methylcyclopentanediamine was added dropwise while maintaining the temperature at 30℃. After the addition was completed, the temperature was maintained at 30℃. Then, 48g of 37% formaldehyde aqueous solution was added dropwise. After the addition was completed, the temperature was raised to 82℃ and maintained for 4.5h. Acrylonitrile, the chain terminator, was added, and dehydration was carried out under reduced pressure. The theoretical dehydration amount was 40.5g, and the actual water output was 38g. After cooling, the low-viscosity cashew phenol modified amine curing agent was obtained.

[0029] Huntsman 3275 curing agent, industrial grade, purchased from Huntsman Chemicals Ltd. Butyl glycidyl ether (BGE), industrial grade, epoxy value 0.62 eq / 100g, purchased from Shandong Xinheng Chemical Co., Ltd. Polyethylene glycol diglycidyl ether (PEGDGE, Mn=400), industrial grade, epoxy value 0.50 eq / 100g, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0030] Equipment used: The rotary evaporator, model RE-52AA, was purchased from Shanghai Yarong Biochemical Instrument Factory. The short-path molecular distillation apparatus, model FMD-100, was purchased from Shanghai Shensheng Technology Co., Ltd. The filtration device is a microporous membrane filter with a pore size of 1 / 3μm, purchased from Hangzhou Wowa Technology Co., Ltd.

[0031] In step S1, diisocyanate and organotin catalyst are mixed, heated to 40℃~50℃, and hyperbranched polyether polyol is added dropwise. After the addition is complete, the temperature is raised to 55℃~65℃ and reacted for 2h~4h to obtain a terminal isocyanate-based hyperbranched polyether intermediate. The NCO value of the system is monitored using the di-n-butylamine method. When the NCO value drops to 95%~100% of the theoretical value, it is determined to be the reaction endpoint. The reaction is carried out under inert gas protection, and the molar ratio of diisocyanate to hyperbranched polyether polyol is 2.1~2.2:1.

[0032] Specifically, diisocyanate and organotin catalyst are added to a reactor, and nitrogen gas is introduced to replace the air in the reactor three times. After the replacement is completed, the nitrogen gas is kept under slight positive pressure protection, and the temperature is raised to 40℃~50℃. Under stirring conditions, hyperbranched polyether polyol is slowly added dropwise to the reactor, and the dropwise time is controlled to be 1h~2h. The amount of organotin catalyst added is 0.1%~0.3% of the total mass of the reaction system.

[0033] Cashew phenol glycidyl ether is prepared by a ring-opening and ring-closing reaction of cashew phenol and epichlorohydrin under alkaline conditions. During the process, some cashew phenol molecules undergo a 1:2 addition reaction with epichlorohydrin to generate a diepoxy byproduct containing secondary hydroxyl groups. At the same time, secondary hydroxyl groups remain in the intermediate molecules that are not completely closed. The secondary hydroxyl content of commercially available industrial-grade cashew phenol glycidyl ether is 0.02 eq / 100g to 0.05 eq / 100g. The hydroxyl value is determined by the phthalic anhydride method in GB / T12008.3-2009 "Plastic Polyether Polyols Part 3: Determination of Hydroxyl Value".

[0034] In step S1, the isocyanate group in the diisocyanate molecule preferentially undergoes a nucleophilic addition reaction with the hydroxyl group in the hyperbranched polyether polyol to generate a carbamate bond. Under the reaction temperature and feed ratio specified in step S1, only one isocyanate group in the diisocyanate molecule participates in the above reaction, while the other isocyanate group remains in a free state, ultimately yielding a terminal isocyanate group hyperbranched polyether intermediate. Furthermore, the hydroxyl value of each batch of cashew phenol glycidyl ether is determined before feeding, and the number of molar hydroxyl groups after determination is used as the basis for calculating the amount of diisocyanate used.

[0035] After the addition was complete, the reaction system was heated to 55℃~65℃ and the reaction continued for 2h~4h. During the reaction, samples were taken every 30min, and the NCO value of the reaction system was determined using the di-n-butylamine method. When the NCO value dropped to 95%~100% of the theoretical value, heating was stopped, and the terminal isocyanate group hyperbranched polyether intermediate was obtained. The principle of the di-n-butylamine method is that the isocyanate groups in the sample react with excess di-n-butylamine to generate substituted urea. The remaining di-n-butylamine is back-titrated with a standard hydrochloric acid solution, and the NCO value is calculated based on the amount of hydrochloric acid consumed. The NCO value is defined as the mass of isocyanate groups contained in 100g of sample, in g / 100g.

[0036] Multiple hydroxyl groups in a hyperbranched polyether polyol molecule undergo nucleophilic addition reactions with an isocyanate group in a diisocyanate molecule to form a urethane bond. An excess of diisocyanate is added, ensuring that each branch of the hyperbranched polyether polyol molecule is attached to an isocyanate group, yielding a terminal isocyanate-based hyperbranched polyether intermediate. The isocyanate groups in this terminal isocyanate-based hyperbranched polyether intermediate undergo nucleophilic addition reactions with the hydroxyl groups in cashew phenol glycidyl ether. An excess of cashew phenol glycidyl ether is added to ensure complete reaction of all isocyanate groups, yielding a terminal epoxy-based star-shaped diluent.

[0037] The trace amounts of unreacted cashew phenol residue contained in industrial-grade cashew phenol glycidyl ether undergo an addition reaction with the isocyanate group and participate in the end-capping reaction in step S2. Under the reaction conditions of 55℃~65℃ in step S1, only one isocyanate group in the diisocyanate molecule participates in the reaction, while the other remains in a free state, waiting to react with the secondary hydroxyl group of cashew phenol glycidyl ether in step S2.

[0038] The molar ratio of isocyanate groups in diisocyanate to hydroxyl groups in hyperbranched polyether polyol is controlled at 2.1–2.2:1. This drives the reaction equilibrium toward the end-capping product, preventing unreacted cashew phenol glycidyl ether from affecting the product molecular structure in subsequent steps. Furthermore, it compensates for the consumption of NCO groups by trace amounts of water in the system, ensuring that an NCO group remains in the intermediate molecule after the end-capping reaction, which can be used in step S2.

[0039] Organotin catalysts reduce the activation energy of the reaction between isocyanate groups and hydroxyl groups, thereby increasing the reaction rate. The amount of organotin catalyst added is 0.1% to 0.3% of the total mass of the reaction system. Within this range, the reaction can be completed within 3 to 5 hours, while avoiding the impact of catalyst residue on the storage stability of the product.

[0040] Meanwhile, the upper limit of the reaction temperature in step S1 is controlled at 65℃. When the reaction temperature exceeds 65℃, the difference in reactivity between the two NCO groups and the hydroxyl group of the diisocyanate decreases, and the probability of the two NCO groups participating in the reaction at the same time increases, which can easily lead to the occurrence of bilateral end-capping or intermolecular chain extension side reactions of the diisocyanate. Excessive temperature will accelerate the thermally initiated ring-opening polymerization of the epoxy group, causing the epoxy value of the product to deviate from the design range.

[0041] The temperature during the dropwise addition stage is controlled at 40℃~50℃. Dropwise addition at a lower temperature helps to control the rate of heat release and prevent side reactions caused by local overheating. After the dropwise addition is completed, the temperature is raised to 55℃~65℃ to ensure that the remaining NCO groups and secondary hydroxyl groups in the system react completely and shorten the total reaction time.

[0042] When the NCO value drops to 95%–100% of the theoretical value, the NCO groups available for the end-capping reaction in the system have been basically consumed, and the end-capping reaction has reached its endpoint. The theoretical value is the NCO concentration value calculated based on the amount of feed, assuming that only one NCO group in the diisocyanate participates in the reaction. Using this endpoint determination criterion can avoid the reaction from going too far and causing the remaining NCO groups to be consumed.

[0043] The theoretical NCO value is calculated as follows: the initial NCO value is the ratio of the mass of all isocyanate groups in the diisocyanate to the total mass of the reaction system; the number of moles of isocyanate groups consumed in the reaction is equal to the number of moles of hydroxyl groups in the hyperbranched polyether polyol; the ratio of the mass of the remaining isocyanate groups to the total mass of the reaction system is the theoretical NCO value.

[0044] The calculation logic for the theoretical value of NCO is as follows: Initial NCO value = (mass of diisocyanate × NCO content in diisocyanate) ÷ total mass of reaction system × 100%; Theoretical NCO value = (Initial total NCO mass - Total NCO mass consumed) ÷ Total mass of reaction system × 100% × (1 - Moisture correction factor - Impurity correction factor).

[0045] The moisture correction factor is the ratio of the mass of moisture in the system to the mass of diisocyanate multiplied by 4.35; the impurity correction factor is the ratio of the mass of impurities that can react with isocyanate groups in the system to the mass of diisocyanate multiplied by 2.0; the moisture content of the system is determined by Karl Fischer method, and the impurity content is determined by gas chromatography.

[0046] In step S2, a polymerization inhibitor is added to the intermediate obtained in S1, the temperature is raised to 60℃~70℃, and cashew phenol glycidyl ether is added dropwise. After the addition is complete, the temperature is raised to 75℃~85℃ and the reaction continues for 3h~5h. The wavenumber is monitored at 2270cm using Fourier transform infrared spectroscopy. -1 The reaction is considered complete when the characteristic peak of NCO is detected and disappears. The reaction temperature is controlled at 78℃~82℃ and the reaction time is controlled at 3.5h~4.5h.

[0047] Specifically, the role of the polymerization inhibitor is to suppress the thermal ring-opening polymerization of the epoxy groups of cashew phenol glycidyl ether at a reaction temperature of 75-85℃, ensuring that the epoxy value of the product remains stable within the design range.

[0048] After the addition is complete, the reaction system is heated to 75℃~85℃ and the reaction continues for 3h~5h. During the reaction, samples are taken every 30min and scanned using a Fourier transform infrared spectrometer, monitoring the wavenumber at 2270cm⁻¹. -1 The intensity change of the characteristic absorption peak of the isocyanate group was measured. When the characteristic absorption peak disappeared, the reaction was determined to have reached the endpoint, and heating was stopped to obtain the crude product of hyperbranched polyether modified cashew phenol diluent.

[0049] The secondary hydroxyl group in the cashew phenol glycidyl ether molecule undergoes a nucleophilic addition reaction with the isocyanate group retained in the terminal isocyanate group hyperbranched polyether intermediate molecule obtained in step S1, generating a urethane bond; each hyperbranched polyether polyol molecule is connected to multiple terminal isocyanate group hyperbranched polyether intermediate molecules through urethane bonds, forming a star molecular structure with hyperbranched polyether as the core, polytetrahydrofuran ether as the flexible chain segment, and cashew phenol glycidyl ether as the terminal group.

[0050] The functionality of hyperbranched polyether polyols is 3 to 6, meaning that each hyperbranched polyether polyol molecule contains an average of 3 to 6 hydroxyl groups. The amount of cashew phenol glycidyl ether used is based on completely consuming the remaining isocyanate groups in the system, with an excess of 5% to 10% to ensure complete end capping. The hydroxyl groups on the hyperbranched polyether polyol molecules can fully react with the isocyanate intermediate molecules to form a complete star-shaped molecular structure.

[0051] If the amount of isocyanate intermediate is below this ratio range, some hydroxyl groups on the hyperbranched polyether polyol molecule will not participate in the reaction, leaving unreacted hydroxyl groups in the product, resulting in an incomplete product molecular structure. Furthermore, the residual hydroxyl groups may undergo side reactions with the curing agent during subsequent applications. If the amount of isocyanate intermediate is above this ratio range, there will be an excess of isocyanate groups in the system. The excess isocyanate intermediate will exist in the product in a free state, increasing the VOC content of the product.

[0052] The isocyanate group has a wavenumber of 2270 cm⁻¹ in the infrared spectrum. -1The characteristic stretching vibration absorption peak near the system is positively correlated with the concentration of isocyanate groups in the system. As the hydroxyl groups of the hyperbranched polyether polyol gradually react with the isocyanate groups, the concentration of isocyanate groups in the system continuously decreases, reaching 2270 cm⁻¹. -1 The intensity of the absorption peak decreases accordingly; when the absorption peak disappears, it indicates that all isocyanate groups in the system have been consumed by the reaction, and the chain extension reaction in step S2 has been completed.

[0053] The upper limit of the reaction temperature in step S2 is controlled at 85℃. If the polytetrahydrofuran ether segments are heated for a long time at temperatures above 85℃, the ether bonds in the main chain are prone to thermal oxidation and breakage, resulting in a decrease in the molecular weight of the segments and damage to the integrity of the flexible segments. The temperature during the dropping stage is controlled at 60℃~70℃. Dropping at a lower temperature is conducive to the stable release of reaction heat and prevents local overheating from causing thermal degradation of the polytetrahydrofuran ether segments or side reactions of the isocyanate groups. After the dropping is completed, the temperature is raised to 75℃~85℃ to ensure that the remaining isocyanate groups and hydroxyl groups in the system react completely.

[0054] In step S3, the reaction product obtained in step S2 is subjected to vacuum distillation at 120℃~140℃ and pressure of -0.098MPa~-0.095MPa to remove low-boiling substances, and the intermediate product is obtained by filtration. The filtration is carried out using a filter device with a pore size of 1μm~3μm.

[0055] Specifically, the crude product obtained after the reaction in step S2 is transferred to a rotary evaporator and subjected to vacuum distillation at a temperature of 120℃~140℃ and a pressure of -0.098MPa~-0.095MPa for 1h~2h. This process removes unreacted diisocyanate monomers and other low-boiling-point volatile components from the crude product. Trace amounts of low molecular weight impurities introduced from the raw material are also removed during the vacuum distillation process.

[0056] The selection of a temperature range of 120℃ to 140℃ is based on the following: diisocyanates have a high boiling point and require a high temperature to distill under normal pressure. However, under negative pressure conditions of -0.098MPa to -0.095MPa, the boiling point of diisocyanates decreases, and they can be effectively vaporized and removed from the system within the range of 120℃ to 140℃. At the same time, this temperature range is lower than the thermal decomposition temperature of the target product, thus avoiding damage to the molecular structure of the product during the distillation process.

[0057] After vacuum distillation, the distilled product is filtered while still hot through a filter with a pore size of 1μm to 3μm. The product has a lower viscosity at higher temperatures, which is beneficial for the filter medium to retain solid impurities and improve filtration efficiency. The pore size of the filter membrane in the filter device is selected to be 1μm to 3μm. This pore size range can effectively retain trace amounts of gel particles, catalyst residues and other mechanical impurities that may be formed during the reaction in step S2, while allowing the target product molecules to pass through smoothly.

[0058] In step S4, the intermediate product filtered in S3 is purified by short-path molecular distillation at a temperature of 150℃~170℃ and a system vacuum of 20Pa~30Pa.

[0059] Specifically, by controlling the distance between the condensation surface and the evaporation surface to be less than the mean free path of the target product molecules and greater than the mean free path of the low molecular weight impurity molecules, the low molecular weight impurities are preferentially evaporated and condensed and collected on the condensation surface, while the target product molecules are retained on one side of the evaporation surface due to their smaller mean free path, thereby achieving the separation of the target product from the low molecular weight impurities.

[0060] The target product is a hyperbranched polyether-modified cashew nut shell diluent with a number-average molecular weight in the range of 1500 g / mol to 3000 g / mol and a low vapor pressure. In contrast, the unreacted cashew nut shell glycidyl ether monomer, trace amounts of diisocyanate monomer, and other oligomerizing byproducts in the system have relatively small molecular weights and relatively high vapor pressures. Under high vacuum conditions of 20 Pa to 30 Pa, the low molecular weight components can evaporate and migrate to the condensation surface within a temperature range of 150 °C to 170 °C, while the target product, due to its high molecular weight and low vapor pressure, hardly evaporates and is thus retained.

[0061] Step S4 removes trace amounts of free monomers that could not be completely removed by vacuum distillation in step S3, reducing the volatile organic compound content of the product to 5 g / L to 8 g / L; and removes trace amounts of low molecular weight byproducts that may be generated in step S2, improving the uniformity of the product's molecular structure.

[0062] By employing a three-tiered molecular structure—hyperbranched core, PTMEG flexible chain, and cashew phenol glycidyl ether end group—a triple stress dissipation system is formed to solve the problem of internal stress cracking in high-thickness coatings. Carbamate bonds are introduced as stress dissipation units, utilizing their reversible hydrogen bond dissociation and recombination effects to improve the coating's bending and impact resistance. The same cashew phenol glycidyl ether end group as the curing agent is used to achieve molecular-level entanglement and perfect compatibility, avoiding incomplete curing at the bottom of thick films caused by small molecule migration. PTMEG, with its excellent hydrolysis resistance, is selected as the flexible chain segment, improving toughness while ensuring the coating's long-term salt spray resistance.

[0063] The application of an environmentally friendly functional diluent in a modified amine epoxy curing system involves applying a special diluent to an epoxy anti-corrosion coating for special engineering projects. The epoxy anti-corrosion coating is prepared by compounding component A and component B. Component A contains bisphenol A type epoxy resin E51 and a special diluent, while component B is a low-viscosity cashew phenol modified amine curing agent.

[0064] The amount of the special diluent added to component A by mass fraction is 8% to 15%, and the mass ratio of component A to component B is 1:0.8 to 1.2.

[0065] To prepare component A, bisphenol A type epoxy resin E51 is mixed with a special diluent and stirred until the system is uniform and transparent. Rust-inhibiting pigments, fillers, and additives are then added to the mixture and dispersed at high speed to a fineness of 30μm–50μm to obtain component A. During application, component A and component B are mixed according to the above mass ratio, stirred evenly, and then sprayed. A single coat achieves a dry film thickness of 500μm–600μm. The coating is cured by air drying at room temperature or by low-temperature baking. It fully cures by air drying for 7 days at 25℃ or by baking at 60℃ for 6 hours.

[0066] Example 1: S1: In a 1000mL four-necked flask equipped with a stirrer, thermometer, constant-pressure dropping funnel, reflux condenser, and nitrogen inlet tube, 214g of isophorone diisocyanate and 0.8g of dibutyltin dilaurate were added. Nitrogen gas was purged into the flask three times to replace the air. After replacement, a slight positive pressure of nitrogen was maintained, and the temperature was raised to 45°C. Under stirring, 262g of hyperbranched polyether polyol was slowly added dropwise. The hyperbranched polyether polyol had a pentaerythritol core and polytetrahydrofuran ether branches, with a number-average molecular weight of 1200g / mol and a functionality of 4. The dropping time was 1.5h. After the addition was completed, the temperature was raised to 60°C and the reaction was continued for 3h. Samples were taken every 30min during the reaction, and the NCO value of the system was determined using the di-n-butylamine method. When the NCO value dropped to 9.2%, heating was stopped, and the isocyanate-terminated hyperbranched polyether intermediate was obtained.

[0067] S2: Add 0.2 g of p-hydroxyanisole to the intermediate obtained in step S1, stir until homogeneous, and then heat to 65°C; under stirring, slowly add 260 g of cashew phenol glycidyl ether, which has an epoxy value of 0.55 eq / 100 g and a free cashew phenol content of 8%; the addition time is 2 h; after the addition is complete, heat to 80°C and continue the reaction for 4 h; during the reaction, take samples every 30 min and monitor the wavenumber at 2270 cm⁻¹ using a Fourier transform infrared spectroscopy. -1 The characteristic absorption peak of the isocyanate group is observed; when the absorption peak disappears, heating is stopped to obtain the crude product.

[0068] S3: Transfer the crude product obtained in step S2 to a rotary evaporator and distill under reduced pressure at 130℃ and -0.096MPa for 1.5h to remove low-boiling substances; after distillation, pass the product through a filter with a pore size of 3μm while it is still hot to obtain the initial product.

[0069] S4: Transfer the initial product obtained in step S3 to a short-path molecular distillation apparatus and perform molecular distillation purification at a temperature of 160°C and a system vacuum of 20Pa; collect the retained components to obtain a light yellow transparent liquid, which is the hyperbranched polyether modified cashew phenol diluent.

[0070] Taking the amount of feed in Example 1 as an example, the theoretical value of NCO is calculated as follows: 214g of isophorone diisocyanate, with a molecular weight of 222.3g / mol, and a total number of moles of isocyanate groups of 0.96mol×2=1.92mol; The amount of hyperbranched polyether polyol fed was 262g. The hyperbranched polyether polyol had pentaerythritol as the core and polytetrahydrofuran ether as the branch chain. The number average molecular weight was 1200g / mol, the functionality was 4, and the total number of hydroxyl groups was 0.873mol. The molar ratio of isocyanate groups to hydroxyl groups in hyperbranched polyether polyols is 1.92:0.873≈2.20:1, which is within the specified range of 2.1 to 2.2:1. In step S1, the isocyanate group and the hydroxyl group undergo a nucleophilic addition reaction in a stoichiometric ratio of 1:1, consuming 0.873 mol of isocyanate group. The remaining molar number of isocyanate groups after the reaction is 1.92 mol - 0.873 mol = 1.047 mol; The molar mass of the isocyanate group is 42.02 g / mol, and the mass of the remaining isocyanate group is 1.047 mol × 42.02 g / mol ≈ 44.0 g; The total mass of the reaction system in step S1 is 214g + 0.8g + 262g = 476.8g; The theoretical NCO value at the endpoint of step S1 is (44.0g ÷ 476.8g) × 100% ≈ 9.23%.

[0071] Considering the consumption of isocyanate groups by trace amounts of moisture and impurities in the system, the actual reaction endpoint is controlled when the measured NCO value drops to 95%–100% of the theoretical value, i.e., 8.77%–9.23%, at which point step S1 is considered complete.

[0072] Example 2: The difference from Example 1 is that in step S1, 203g of isophorone diisocyanate and 0.6g of dibutyltin dilaurate were added, and 255g of hyperbranched polyether polyol was added dropwise; in step S2, 0.15g of p-hydroxyanisole was added, and 280g of cashew phenol glycidyl ether was added dropwise. In step S1, the reaction temperature was 55℃, the reaction time was 2.5h, and heating was stopped when the NCO value dropped to 8.7%. In step S2, the reaction temperature was 78℃, and the reaction time was 4.5h.

[0073] In this embodiment, the theoretical NCO value of step S1 is 8.94%, and the actual reaction endpoint is controlled at 8.7%, which meets the requirement of 95% to 100%.

[0074] Example 3: The difference from Example 1 is that the hyperbranched polyether polyol in step S1 is replaced with a hyperbranched polyether polyol with trimethylolpropane as the core and polytetrahydrofuran ether as the branch chain, with a number average molecular weight of 1000 g / mol, a functionality of 3, and an amount of 230 g; 165 g of isophorone diisocyanate and 0.6 g of dibutyltin dilaurate are added in step S1; heating is stopped in step S1 when the NCO value drops to 8.2%.

[0075] In this embodiment, the theoretical NCO value of step S1 is 8.44%, and the actual reaction endpoint is controlled at 8.2%, which meets the requirement of 95% to 100%.

[0076] Example 4: The difference from Example 1 is that: 214g of isophorone diisocyanate in step S1 is replaced with 158g of hexamethylene diisocyanate, 0.2g of p-hydroxyanisole is replaced with 0.2g of hydroquinone; 0.8g of dibutyltin dilaurate in step S1 is replaced with 0.8g of stannous octoate; and heating is stopped in step S1 when the NCO value drops to 9.8%.

[0077] In this embodiment, the theoretical NCO value of step S1 is 10.04%, and the actual reaction endpoint is controlled at 9.8%, which meets the requirement of 95% to 100%.

[0078] Example 5: The difference from Example 1 is that: in step S1, 214g of isophorone diisocyanate is replaced with 246g of dicyclohexylmethane diisocyanate, 0.2g of p-hydroxyanisole is replaced with 0.2g of 2,6-di-tert-butyl-p-cresol; in step S1, 0.8g of dibutyltin dilaurate is replaced with 0.8g of dibutyltin diacetate; in step S1, heating is stopped when the NCO value drops to 8.1%.

[0079] In this embodiment, the theoretical NCO value of step S1 is 8.29%, and the actual reaction endpoint is controlled at 8.1%, which meets the requirement of 95% to 100%.

[0080] Example 6: The difference from Example 1 is that: 214g of isophorone diisocyanate in step S1 is replaced with 158g of hexamethylene diisocyanate; 0.8g of dibutyltin dilaurate in step S2 is replaced with 0.8g of dibutyltin diacetate; and heating is stopped in step S1 when the NCO value drops to 9.8%.

[0081] In this embodiment, the theoretical NCO value of step S1 is 10.04%, and the actual reaction endpoint is controlled at 9.8%, which meets the requirement of 95% to 100%.

[0082] Comparative Example 1: The difference from Example 1 is that commercially available butyl glycidyl ether was used as the diluent. The epoxy value of butyl glycidyl ether is 0.62 eq / 100g, its viscosity at 25°C is 180 mPa·s, and its volatile organic compound content is 420 g / L. This diluent was added to E51 epoxy resin at a mass ratio of 12%, and a 500 μm thick coating was prepared in conjunction with a low-viscosity cashew phenol modified amine curing agent.

[0083] Comparative Example 2: The difference from Example 1 is that commercially available linear polyethylene glycol diglycidyl ether was used as the diluent, with a number-average molecular weight of 400 g / mol, an epoxy value of 0.50 eq / 100g, a viscosity of 220 mPa·s at 25°C, and a volatile organic compound content of 85 g / L. This diluent was added to E51 epoxy resin at a mass ratio of 12%, and a 500 μm thick coating was prepared in conjunction with a low-viscosity cashew phenol modified amine curing agent.

[0084] Comparative Example 3: The difference from Example 1 is that a hyperbranched polyether diluent without urethane bonds was prepared, and the preparation method is as follows: In a 500 mL three-necked flask equipped with a stirrer, thermometer, and reflux condenser, 100 g of hyperbranched polyether polyol was added. The hyperbranched polyether polyol had a pentaerythritol core and polytetrahydrofuran ether branches, with a number-average molecular weight of 1200 g / mol and a functionality of 4. 200 mL of epichlorohydrin and 5 g of sodium hydroxide were added, and the mixture was heated to 80 °C and reacted for 6 h. After the reaction was complete, excess epichlorohydrin was recovered by vacuum distillation, the product was dissolved in toluene, washed with water until neutral, dried over anhydrous magnesium sulfate, filtered, and toluene was removed by vacuum distillation to obtain a terminal epoxy-terminated hyperbranched polyether diluent. The obtained diluent had an epoxy value of 0.35 eq / 100 g, a viscosity of 550 mPa·s at 25 °C, and a volatile organic compound content of 7.5 g / L. The diluent was added to E51 epoxy resin at a mass ratio of 12%, and a 500 μm thick coating was prepared in combination with a low-viscosity cashew phenol modified amine curing agent.

[0085] Comparative Example 4: The difference from Example 1 is that no diluent was added, and only E51 epoxy resin was used in combination with a low-viscosity cashew phenol modified amine curing agent to prepare a 500 μm thick coating.

[0086] Comparative Example 5: The difference from Example 1 is that commercially available cashew phenol glycidyl ether was used directly as a diluent; the epoxy value of cashew phenol glycidyl ether was 0.55 eq / 100g, the viscosity at 25°C was 85 mPa·s, and the volatile organic compound content was 15 g / L; this diluent was added to E51 epoxy resin at a mass ratio of 12%, and a 500 μm thick coating was prepared in combination with a low-viscosity cashew phenol modified amine curing agent. Comparative Example 6: The difference from Example 1 is that a hyperbranched polyether diluent without PTMEG flexible segments was used. The preparation method was the same as in Example 1, except that the hyperbranched polyether polyol was replaced with a hyperbranched polyether polyol with pentaerythritol as the core and polypropylene glycol as the branch, with a number average molecular weight of 1200 g / mol, functionality of 4, and an amount of 262 g; the epoxy value of the resulting diluent was 0.30 eq / 100 g, and the viscosity at 25°C was 440 mPa·s; this diluent was added to E51 epoxy resin at a mass ratio of 12%, and a 500 μm thick coating was prepared in combination with a low-viscosity cashew phenol modified amine curing agent.

[0087] Comparative Example 7: The difference from Example 1 is that step S4 is omitted, and the product obtained after step S3 is the final diluent.

[0088] Performance testing: The test methods are all based on current national standards or industry-standard methods, as detailed below: Epoxy value: GB / T1677-2023 "Determination of Epoxy Value of Plasticizers" Hydrochloric acid-acetone method; Viscosity: GB / T2794-2022 "Determination of Viscosity of Adhesives" Rotational viscometer method, measured under constant temperature conditions of 25℃±0.5℃, using a single-cylinder rotational viscometer or a cone-plate rotational viscometer; VOC content: GB / T34682-2017 "Determination of Volatile Organic Compounds (VOC) Content in Coatings Containing Diluents" Headspace Sampling Method; Surface drying time: GB / T1728-2020 "Determination of drying time of paint film and putty film", the endpoint of surface drying is determined when no fingerprint is left when lightly touching the surface of the paint film; Bending performance: GB / T6742-2007 "Paints and Varnishes Bending Test (Cylindrical Shaft)", film thickness 500μm, coating film thickness 500μm±20μm, test cylindrical shaft diameter 3mm, bending angle 180°, test at 23℃±2℃, the criterion for passing is that there are no visible cracks on the paint film surface; Impact performance: GB / T1732-2020 "Test Method for Impact Resistance of Coating Film", coating film thickness 500μm, using an impact tester with a weight of 1000g±1g and a punch diameter of 8mm±0.1mm, impact tests were conducted on the front and back of the test plate respectively. The maximum height (cm) that does not cause the coating film to break is used to represent the impact resistance of the coating film. The test results are recorded under the condition of the coating film under a normal impact of 50cm·kg and a reverse impact of 50cm·kg. Neutral salt spray resistance: Using a 50g / L±5g / L sodium chloride solution with a pH of 6.5~7.2, the salt spray deposition rate is 1mL / h~2mL / h per 80cm² collection area. The test chamber temperature is 35℃±2℃. After continuous spraying for 2400h, the test panels are removed, rinsed with deionized water, dried, and then the paint film surface is checked for abnormal phenomena such as rust, blistering, and peeling.

[0089] Testing equipment: The Fourier transform infrared spectrometer, model Nicolet iS50, was purchased from Thermo Fisher Scientific. The rotational viscometer, model NDJ-5S, was purchased from Shanghai Jingke Instrument Co., Ltd. The gas chromatograph, model GC-2014C, was purchased from Shimadzu Corporation; the paint film bending tester, model QTY-32, was purchased from Tianjin Materials Testing Machine Factory. The paint film impact tester, model QCJ, was purchased from Tianjin Materials Testing Machine Factory. The salt spray test chamber, model YWX / Q-250, was purchased from Wuxi Sunan Test Equipment Co., Ltd.

[0090] Table 1 - Test results of product performance and coating application performance of each embodiment

[0091] Table 2 - Test results of performance and coating application performance of each comparative example product

[0092] Comparative Example 4 did not add any diluent, and its epoxy value, viscosity, and VOC content were not measured.

[0093] Results analysis: As shown in Table 1, the epoxy values ​​of the diluents obtained in Examples 1 to 6 are all in the range of 0.25eq / 100g to 0.35eq / 100g, the viscosity of the diluents at 25°C is all in the range of 300mPa·s to 600mPa·s, and the content of volatile organic compounds is in the range of 5g / L to 8g / L.

[0094] The 500μm thick coating prepared by adding the diluent of each embodiment to E51 epoxy resin at a mass ratio of 12% and using a low-viscosity cashew phenol modified amine curing agent had a surface drying time of 2.3h to 2.7h, which met the construction requirements of 2h to 3h spraying interval at 25℃.

[0095] Examples 1-6 all achieved a 3mm bending pass, indicating that within the epoxy value and viscosity range defined in claim 1, the diluent can effectively dissipate the internal stress generated during the curing process of high film thickness coatings, and prevent the coating from cracking under bending deformation conditions.

[0096] Under a normal impact of 50 cm·kg, no cracks were found in Examples 1 to 6; under a reverse impact of 50 cm·kg, no cracks were found in Examples 1 to 6; and after 2400 hours of neutral salt spray testing, no abnormalities were found in the coatings of Examples 1 to 6.

[0097] Table 2 shows that Comparative Example 1 used butyl glycidyl ether as a diluent, with an epoxy value of 0.62 eq / 100g and a viscosity of 180 mPa·s, both exceeding the numerical range defined in claim 1. The resulting coating cracked in a 10 mm bending test, and showed severe cracking under both positive and negative impacts. Large-area corrosion was observed in a 2400-hour salt spray test. Comparative Example 2 used linear polyethylene glycol diglycidyl ether as a diluent, with an epoxy value of 0.50 eq / 100g and a viscosity of 220 mPa·s, also exceeding the numerical range defined in claim 1. The coating cracked in a 5 mm bending test, and showed cracking under both positive and negative impacts. Localized corrosion was observed in a salt spray test. This indicates that when the epoxy value and viscosity of the diluent do not fall within the range defined in this invention, the crack resistance and corrosion resistance of the coating under high film thickness conditions cannot meet the application requirements.

[0098] The hyperbranched polyether diluent without urethane bonds prepared in Comparative Example 3 had an epoxy value of 0.35 eq / 100g and a viscosity of 550 mPa·s. Although the epoxy value and viscosity fell within the range defined in claim 1, it cracked in the 4mm bending test, showed microcracks in the normal impact, cracked in the reverse impact, and showed local blistering in the salt spray test. This indicates that the diluent, which only has a hyperbranched structure and epoxy end groups but lacks urethane bonds as stress dissipation units, has significantly inferior mechanical and anti-corrosion properties compared to the products of Examples 1 to 6 of this invention. This proves that the presence of urethane bonds plays an irreplaceable role in the overall performance of the diluent.

[0099] Comparative Example 5 used cashew phenol glycidyl ether directly as a diluent, with an epoxy value of 0.55 eq / 100g and a viscosity of 85 mPa·s, both exceeding the numerical range defined in claim 1. The coating cracked in a 6 mm bending test, showed cracks upon normal impact, and severe cracking upon reverse impact. Local blistering was observed in the salt spray test. This indicates that even if the end-group structure is homologous to the target curing agent, the cracking problem of high-thickness coatings cannot be solved without the internal stress dissipation structure composed of hyperbranched nuclei and flexible segments.

[0100] Comparative Example 6 used a hyperbranched polyether diluent with polypropylene glycol as the branch, which did not contain PTMEG flexible segments. The epoxy value was 0.30 eq / 100g, and the viscosity was 440 mPa·s, both within the range defined in claim 1. It passed a 3mm bend test, showed no cracks upon normal impact, but microcracks appeared upon reverse impact. Localized blistering occurred during salt spray testing. These results indicate that the hydrolysis resistance of polypropylene glycol segments under long-term salt spray conditions is inferior to that of PTMEG segments.

[0101] 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. An environmentally friendly functional diluent, characterized in that, By mass fraction, it includes the following raw materials: Hyperbranched polyether polyol 23%–39%, diisocyanate 16%–34%, cashew phenol glycidyl ether 33%–41%, polymerization inhibitor 0.01%–0.1%, organotin catalyst 0.08%–0.3%; The diluent has a star-shaped structure, which includes a hyperbranched polyether core, a flexible polytetrahydrofuran ether segment, and a cashew phenol glycidyl ether end group; the hyperbranched polyether core and the flexible polytetrahydrofuran ether segment are covalently connected, and the flexible polytetrahydrofuran ether segment and the cashew phenol glycidyl ether end group are connected by a carbamate bond formed by diisocyanate. The diluent has an epoxy value of 0.25 eq / 100g to 0.35 eq / 100g, a viscosity of 300 mPa·s to 600 mPa·s at 25°C, and a volatile organic compound content in the range of 5 g / L to 8 g / L. The hyperbranched polyether polyol has a pentaerythritol or trimethylolpropane as the core and polytetrahydrofuran ether as the branch chain, with a functionality of 3 to 6 and a number-average molecular weight of 800 g / mol to 2000 g / mol.

2. The environmentally friendly functional diluent according to claim 1, characterized in that: The diisocyanate is at least one of isophorone diisocyanate, hexamethylene diisocyanate or dicyclohexylmethane diisocyanate; The polymerization inhibitor is at least one of hydroquinone, p-hydroxyanisole, or 2,6-di-tert-butyl-p-cresol. The organotin catalyst is at least one of dibutyltin dilaurate, stannous octoate, or dibutyltin diacetate.

3. The environmentally friendly functional diluent according to claim 1, characterized in that: The cashew phenol glycidyl ether has an epoxy value of 0.50–0.60 eq / 100g and is prepared by reacting cashew phenol with epichlorohydrin under alkaline conditions.

4. A method for preparing an environmentally friendly functional diluent, used to prepare the diluent according to any one of claims 1-3, characterized in that: include: S1: Mix diisocyanate with organotin catalyst, heat to 40℃~50℃, add hyperbranched polyether polyol dropwise, and after the addition is complete, heat to 55℃~65℃ and react for 2h~4h to obtain isocyanate-terminated hyperbranched polyether intermediate; monitor the NCO value of the system using the di-n-butylamine method, and determine the reaction endpoint when the NCO value drops to 95%~100% of the theoretical value; S2: Add a polymerization inhibitor to the intermediate obtained in S1, heat to 60℃~70℃, add cashew phenol glycidyl ether dropwise, and after the addition is complete, heat to 75℃~85℃ and continue the reaction for 3h~5h; monitor the wavenumber at 2270cm using Fourier transform infrared spectroscopy. -1 The NCO characteristic peak is observed, and the disappearance of this peak is considered the endpoint of the reaction. S3: The reaction product obtained in step S2 is subjected to vacuum distillation at 120℃~140℃ and pressure of -0.098MPa~-0.095MPa to remove low-boiling substances, and the intermediate product is obtained by filtration. S4: The intermediate product filtered from S3 is purified by short-path molecular distillation at a temperature of 150℃~170℃ and a system vacuum of 20Pa~30Pa to obtain a special diluent.

5. The method for preparing an environmentally friendly functional diluent according to claim 4, characterized in that: Step S1 is carried out under inert gas protection, and the molar ratio of isocyanate groups to hydroxyl groups in hyperbranched polyether polyol is 2.1 to 2.2:

1.

6. The method for preparing an environmentally friendly functional diluent according to claim 4, characterized in that: In step S2, the reaction temperature is controlled at 78℃~82℃ and the reaction time is controlled at 3.5h~4.5h.

7. The method for preparing an environmentally friendly functional diluent according to claim 4, characterized in that: In step S1, the amount of the organotin catalyst added is 0.1% to 0.3% of the total mass of the reaction system.

8. The method for preparing an environmentally friendly functional diluent according to claim 4, characterized in that: In step S3, the filtration uses a filtration device with a pore size of 1μm to 3μm.

9. The application of an environmentally friendly functional diluent in a modified amine epoxy curing system, characterized in that: The epoxy anti-corrosion coating used in special heavy-duty anti-corrosion projects is prepared by compounding component A and component B; component A contains bisphenol A type epoxy resin E51 and the diluent according to any one of claims 1-3, and component B is a low-viscosity cashew phenol modified amine curing agent.

10. The application of the environmentally friendly functional diluent according to claim 9 in a modified amine epoxy curing system, characterized in that: The amount of the diluent added to component A of the epoxy anti-corrosion coating by mass fraction is 8% to 15%; the mass ratio of component A to component B is 1:0.8 to 1.2.

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