Polyurea modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel and preparation method thereof

Abstract

The application discloses a polyurea modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel and a preparation method thereof, and belongs to the technical field of polymer composite coating materials. The coating is composed of 60-80 parts of polyurea modified water-soluble acrylic resin, 20-40 parts of epoxy resin and the like, and forms an interpenetrating network structure through two-stage curing. A state is an uncured composite coating, is uniform in dispersion, environment-friendly and stable in storage; B state is an activated state after being baked at 120-180 DEG C for 1-2 min, has a plate surface hardness (2H-3H), no fluidity, an adhesion of 1 level and is suitable for lamination processing; and C state is a completely cured state after being baked at 220-250 DEG C for 20-30 min, has an impact resistance of 50-55 kg·cm, a bonding strength of 6.2-6.8 MPa and a salt spray resistance of 110-130 h. The application solves the problems of phase separation, curing conflict and interface weakening of a traditional coating and is suitable for industrial protection.

Description

Technical Field

[0001] This invention relates to the field of polymer composite coating materials technology, specifically to a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel and its preparation method. Background Technology

[0002] In the fields of industrial protection and high-end equipment coatings, waterborne epoxy-acrylic composite coatings have been widely studied due to their combination of the high adhesion strength of epoxy resin and the weather resistance of acrylic resin. However, existing technologies suffer from three major drawbacks: First, the hydrophobicity of epoxy resin (dense epoxy group structure) and the hydrophilicity of acrylic resin (containing carboxyl and hydroxyl polar groups) during physical blending lead to significant differences in interfacial tension, easily causing microphase separation and forming a dispersed phase. This severely damages the coating uniformity and consequently reduces mechanical properties. Second, during the curing process, the carboxyl groups of acrylic resin undergo a neutralization reaction with epoxy curing agents (such as amines). This reaction consumes some of the curing agent, resulting in a decrease in the crosslinking density of the epoxy resin, which severely impairs the coating's hardness and chemical resistance. Third, the acrylic and epoxy phases are only physically intertwined, resulting in low interfacial bonding strength. Under humid and hot environments, interfacial delamination is highly likely to occur.

[0003] Existing technologies often use silane coupling agents (such as KH-560) to treat the interface. Although this improves the interfacial adhesion, it only solves the physical compatibility problem and cannot change the curing conflict between the acrylic carboxyl groups and the epoxy curing agent. Furthermore, phase separation regions still exist after curing. Currently, there are also methods to prepare acrylic / epoxy composite particles through core-shell emulsion polymerization. However, the core-shell structure is prone to cracking during high-temperature curing, leading to premature cross-linking of the epoxy resin and making stepwise curing impossible. Summary of the Invention

[0004] The purpose of this invention is to provide a polyurea-modified water-soluble acrylic / epoxy resin composite coating for non-oriented silicon steel and its preparation method. Through the synergistic innovation of molecular structure design and two-stage curing process, the phase separation, curing conflict and interface weakening problems of traditional composite coatings are solved.

[0005] To achieve the above objectives, the present invention provides a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel, comprising the following components by weight: 60-80 parts of polyurea-modified water-soluble acrylic resin, 20-40 parts of epoxy resin, 5-10 parts of blocked isocyanate curing agent, 2-4 parts of aminosilane coupling agent, 0.5-1.5 parts of wetting agent, 0.3-0.8 parts of defoamer, 0.2-0.6 parts of leveling agent, and 20-40 parts of deionized water.

[0006] This invention also provides a method for preparing the above-mentioned polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel, specifically including the following steps: S1. Synthesis of polyurea-modified water-soluble acrylic resin; S2. Preparation of composite coating: Take polyurea modified water-soluble acrylic resin, epoxy resin and deionized water, then add wetting agent, defoamer and leveling agent, disperse at 1200 rpm for 30 min to obtain component A; Component B was prepared by mixing and pre-reacting a blocked isocyanate curing agent with an aminosilane coupling agent at 40°C for 15 min. After mixing component A and component B and allowing it to mature for 20 minutes, the mixture is filtered through a 200-mesh filter to obtain a composite coating. S3. Two-stage curing process: The prepared composite coating is applied to the surface of the non-oriented silicon steel substrate and cured in two stages. The first stage of curing is carried out by baking at 120-180℃ for 1-2 minutes, and the second stage of curing is carried out by heating to 220-250℃ for 20-30 minutes to strengthen the bonding between the two phases.

[0007] Preferably, the polyurea block in the polyurea-modified water-soluble acrylic resin accounts for 8-15% of the solid content of the modified acrylic resin. The polar groups of the polyurea block reduce interfacial tension through hydrogen bonding, improving the compatibility between acrylic and epoxy resins and preventing phase separation. Within this range, it can balance the flexibility and hardness of the coating, optimize coating density, reduce the penetration of corrosive media, and improve corrosion resistance. Below 8%, the polyurea hydrogen bond network is insufficient, resulting in limited improvement in toughness; above 15%, it leads to increased resin hydrophobicity and compromises water-soluble stability.

[0008] Preferably, the epoxy resin is waterborne bisphenol A type epoxy E-44 with an epoxy value of 0.44 mol / 100g. The bisphenol A type epoxy structure has high strength and hardness, providing mechanical support for the coating. The epoxy groups react to form a network structure, improving the coating performance. This epoxy value ensures a balance between hardness and toughness after curing; excessively high oxygen content can easily lead to embrittlement, while excessively low oxygen content can easily lead to insufficient hardness.

[0009] Preferably, the blocked isocyanate curing agent is methyl ethyl ketone oxime-blocked isophorone diisocyanate trimer or caprolactam-blocked hexamethylene diisocyanate trimer.

[0010] Preferably, the aminosilane coupling agent is one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0011] Preferably, the wetting agent is fatty alcohol polyoxyethylene ether-9; the defoamer is polydimethylsiloxane emulsion; and the leveling agent is polyether-modified polydimethylsiloxane.

[0012] Preferably, in step S1, the synthesis step of the polyurea-modified water-soluble acrylic resin is as follows: (1) Pre-emulsification: Mix acrylic acid, methyl methacrylate and butyl acrylate in a mass ratio of 3:4:3, add deionized water and emulsifier and pre-emulsify for 30 min; (2) Free radical polymerization: Under nitrogen protection, the temperature was raised to 75°C, and a redox initiator was added dropwise for 4 hours to obtain an acrylic copolymer; (3) Polyurea modification: Add the polyurea prepolymer with terminal -NCO groups and continue to react at 80℃ for 2h. Add ammonia to adjust the pH to 7-8 to obtain the modified resin.

[0013] Preferably, the emulsifier is DNS-86, and the redox initiator is a mixture of potassium persulfate and sodium metabisulfite, wherein the mass ratio of potassium persulfate to sodium metabisulfite is 1:0.3.

[0014] Preferably, the initiator accounts for 0.8% of the total mass of acrylic acid, methyl methacrylate, and butyl acrylate; and the polyurea prepolymer with terminal -NCO groups accounts for 5%-15% of the total mass of acrylic acid, methyl methacrylate, and butyl acrylate.

[0015] The composite coating for non-oriented silicon steel of this invention achieves performance optimization through the synergistic effect of polyurea-modified acrylic resin and epoxy resin. The polyurea block introduces a strong hydrogen bond network, significantly improving toughness, wear resistance, and chemical resistance; the carboxyl groups in the acrylic copolymer are neutralized by ammonia to form water-soluble salt groups, ensuring an environmentally friendly dispersion system. The epoxy resin provides high crosslinking density, contributing to hardness, adhesion, and corrosion resistance. The flexibility of acrylic compensates for the brittleness of epoxy, while the polyurea block acts as an interfacial bridge, enhancing the compatibility of the two phases through hydrogen bonding.

[0016] The curing system employs a combination of blocked isocyanate and aminosilane coupling agent. The blocked isocyanate partially deblocks at high temperatures, releasing -NCO groups that react with the hydroxyl groups of the acrylic resin to form an initial cross-linking network. The aminosilane plays a dual role: its amino groups participate in the curing of the isocyanate to form chemical bonds, and its alkoxy groups hydrolyze to form Si-O-Me covalent bonds with the metal substrate, significantly improving coating adhesion and moisture resistance. Wetting agents reduce surface tension and promote substrate spreading, defoamers inhibit bubble formation, and leveling agents optimize surface leveling. These components synergistically enhance the coating's performance.

[0017] Polyurea-modified water-soluble acrylic resin is synthesized in three steps: pre-emulsification to form stable monomer droplets, followed by free radical polymerization initiated by a redox initiation system at 75°C. The low temperature condition avoids the degradation of the polyurea prepolymer with terminal NCO groups added later. Finally, the polyurea prepolymer with terminal NCO groups is added, and its terminal NCO groups react with the hydroxyl groups of the acrylic copolymer to form a polyurethane bond graft structure. After reacting at 80°C for 2 hours, ammonia is added to adjust the pH to 7-8, thereby ensuring that the polyurea nano-microdomains are dispersed in the resin and achieving a balance between toughening and water solubility.

[0018] The composite coating preparation process of the present invention includes state A (uncured state), state B (activated state), and state C (fully cured state).

[0019] State A corresponds to the process stage after obtaining the composite coating in step S2 and before coating. It is the stable state of the coating system before cross-linking reaction. It is uniformly dispersed, free of particulate impurities after filtration, and shows no stratification even after long-term storage following high-speed rotary dispersion, ensuring uniformity during coating. It is also environmentally friendly, using a water-soluble system containing 20-40 parts of deionized water, with no organic solvent evaporation, meeting modern industrial environmental protection requirements. Furthermore, it has good storage stability; after component A and component B are mixed evenly, gelation does not occur in a short time, exhibiting excellent application leveling properties and providing sufficient time for subsequent coating operations.

[0020] State B corresponds to the first stage of curing in step S3 (120-180℃, 1-2 min). At this point, the acrylic resin has completed self-crosslinking, and the epoxy resin is partially pre-cured, forming a solid coating with board surface hardness and no flowability, possessing the activity for lamination processing. It can be adapted to the lamination processing of non-oriented silicon steel, meeting the coating requirements of silicon steel parts of different shapes. It also has initial strength, as the carboxyl groups of the acrylic resin undergo a self-crosslinking reaction to form a skeleton structure, while the polyurea hydrogen bonds are initially constructed, giving the coating sufficient initial strength, toughness, and adhesion, without large-area peeling, and can protect the silicon steel surface during processing. In addition, it has excellent compatibility. The polar groups (-NH-CO-) of the polyurea blocks reduce the interfacial tension between acrylic and epoxy, and there is no acrylic-epoxy phase separation phenomenon, laying the foundation for subsequent complete curing to form a uniform structure.

[0021] State C corresponds to the second stage of curing in step S3 (220-250℃, 20-30min). The epoxy phase is deeply cross-linked and forms a dense interpenetrating network (IPN) structure with the acrylic phase. This is the final usable state of the coating. The covalent bonding between the aminosilane and the substrate is also completely completed at this stage. The resulting coating is free of voids, has a tight interface bond, and no interface delamination. The coating ultimately exhibits extremely high hardness, excellent impact resistance, strong bonding strength, and outstanding corrosion resistance, ensuring the stability of the coating for long-term use.

[0022] Therefore, the present invention provides a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel and its preparation method, which has the following beneficial effects: (1) This invention solves the compatibility problem by modifying polyurea. Polyurea blocks are introduced into the acrylic resin molecular chain. By utilizing their strong polarity and hydrogen bonding, they act as molecular bridges to effectively reduce the interfacial energy between acrylic resin and epoxy resin, suppress the phase separation trend during blending and curing, and lay the foundation for achieving a uniform IPN structure.

[0023] (2) In the first stage of curing under state B, the polar groups (-NH-CO-) of the polyurea block form hydrogen bonds with acrylic acid and epoxy, reducing interfacial tension and completely inhibiting phase separation, laying a uniform foundation for the interpenetrating network structure under state C; the first stage curing temperature (120-180℃) is precisely matched with the crosslinking temperature of acrylic acid and the partial unsealing temperature of isocyanate, avoiding premature complete curing of epoxy resin, ensuring that the coating has no flowability to meet processing requirements, and retaining epoxy activity; under state B, the aminosilane alkoxy group is initially hydrolyzed and forms hydrogen bonds with the hydroxyl group of the silicon steel substrate, and the adhesion reaches level 0 in advance, avoiding coating peeling during stacking processing. In the second stage of curing, under state C, the acrylic crosslinking network and the epoxy crosslinking network interpenetrate with each other. The polyurea block acts as an interfacial bridge, forming hydrogen bonds and covalent bonds, increasing the crosslinking density, eliminating voids in the coating, and improving salt spray resistance. Furthermore, the high temperature (220-250℃) in the second stage completely deseals the isocyanate, and the released -NCO groups react simultaneously with the hydroxyl groups of acrylic acid and epoxy, strengthening both the acrylic network and increasing the epoxy crosslinking density, thus enhancing the bonding strength. In this state, the aminosilane alkoxy groups are completely hydrolyzed into silanol groups, which condense with the hydroxyl groups of the silicon steel substrate to form Si-O-Me covalent bonds. At the same time, the amino groups participate in the epoxy curing, forming a resin-coupling agent-substrate chemical chain, maintaining a grade 0 adhesion and solving the interfacial peeling problem.

[0024] (3) The present invention solves the interface weakening problem by using an aminosilane coupling agent. It can form a strong chemical bond by reacting with the resin system through the amino group; and it can form a stable Si-O-Me covalent bond with the metal substrate through the hydrolyzed silanol group, thereby building a strong chemical bridge at the resin-substrate interface, significantly improving adhesion, water resistance and corrosion resistance, solving the common interface failure problem of water-based coatings, and meeting the requirements of harsh environments such as marine and chemical industries.

[0025] (4) The present invention achieves the unity of environmental protection and high performance. The entire system uses water as the dispersion medium and has low VOC content. At the same time, through the above-mentioned structural and process innovations, the coating achieves a balance between environmental protection and high performance.

[0026] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the invention should be considered equivalent substitutions and are included within the scope of protection of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the scope of protection of the invention.

[0028] In this document, references to embodiments mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0029] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0030] Unless otherwise specified, all reagents, instruments, and equipment used in this invention are commercially available and commonly used by those skilled in the art, and all performance testing methods used are conventional testing methods.

[0031] Example 1 This embodiment provides a method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel, specifically including the following steps: S1. Synthesis of polyurea-modified water-soluble acrylic resin Pre-emulsification: Mix 30g acrylic acid, 40g methyl methacrylate and 30g butyl acrylate, add 50g deionized water and 3g DNS-86, stir and pre-emulsify for 30 minutes to obtain a pre-emulsified solution.

[0032] Free radical polymerization: The pre-emulsion was transferred to a reactor, protected with nitrogen, heated to 75°C, and 0.8g of initiator (potassium persulfate: sodium metabisulfite = 1:0.3) was added dropwise. The reaction was maintained at this temperature for 4 hours to obtain an acrylic copolymer.

[0033] Polyurea modification: 10g of polyurea prepolymer with terminal -NCO groups was added to the reactor, the temperature was raised to 80℃ and the reaction continued for 2h. Ammonia water was added dropwise to adjust the pH to 7-8 to obtain polyurea modified water-soluble acrylic resin.

[0034] S2, Formulation of Composite Coatings Take 70g of polyurea-modified water-soluble acrylic resin and 30g of waterborne epoxy E-44, mix them, add 30g of deionized water, then add 1.0g of fatty alcohol polyoxyethylene ether-9, 0.5g of polydimethylsiloxane emulsion and 0.4g of polyether-modified polydimethylsiloxane, disperse at 1200rpm for 30min to obtain component A.

[0035] 8g of caprolactam-blocked hexamethylene diisocyanate trimer was mixed with 3g of γ-aminopropyltriethoxysilane and pre-reacted at 40°C for 15min to obtain component B.

[0036] After mixing component A and component B and maturing for 20 minutes, the mixture is filtered through a 200-mesh filter to obtain a composite coating, which is denoted as state A.

[0037] S3. Two-stage curing process: The composite coating is applied to the surface of the non-oriented silicon steel metal substrate and a two-stage curing process is adopted. The first stage is baked at 180℃ for 2 minutes, which is recorded as state B. The second stage is heated to 230℃ and baked for 20 minutes. After cooling, the composite coating is obtained, which is recorded as state C.

[0038] Example 2 This embodiment provides a method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel, specifically including the following steps: S1. Synthesis of polyurea-modified water-soluble acrylic resin Pre-emulsification: Mix 30g acrylic acid, 40g methyl methacrylate and 30g butyl acrylate, add 55g deionized water and 3.2g DNS-86, stir and pre-emulsify for 30min to obtain a pre-emulsion.

[0039] Free radical polymerization: The pre-emulsion was transferred to a reactor, protected with nitrogen, heated to 75°C, and 0.8g of initiator (potassium persulfate: sodium metabisulfite = 1:0.3) was added dropwise. The reaction was maintained at this temperature for 4 hours to obtain an acrylic copolymer.

[0040] Polyurea modification: Add 8g of polyurea prepolymer with terminal -NCO groups to the reactor, heat to 80℃ and continue the reaction for 2h, add ammonia water to adjust the pH to 7-8, and obtain polyurea modified water-soluble acrylic resin.

[0041] S2, Formulation of Composite Coatings Take 60g of polyurea-modified water-soluble acrylic resin and 40g of waterborne epoxy E-44, mix them, add 40g of deionized water, then add 1.5g of fatty alcohol polyoxyethylene ether-9, 0.8g of polydimethylsiloxane emulsion and 0.6g of polyether-modified polydimethylsiloxane, disperse at 1200rpm for 30min to obtain component A.

[0042] Component B was prepared by mixing 10g of methyl ethyl ketone oxime-blocked isophorone diisocyanate trimer with 4g of γ-aminopropyltriethoxysilane at 40°C for 15min.

[0043] After mixing component A and component B and maturing for 20 minutes, the mixture is filtered through a 200-mesh filter to obtain a composite coating, which is denoted as state A.

[0044] S3. Two-stage curing process: The composite coating is applied to the surface of the non-oriented silicon steel substrate and a two-stage curing process is adopted. The first stage is baked at 180℃ for 1.5 min, which is recorded as state B. The second stage is heated to 250℃ and baked for 30 min. After cooling, the composite coating is obtained, which is recorded as state C.

[0045] Example 3 This embodiment provides a method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel, specifically including the following steps: S1. Synthesis of polyurea-modified water-soluble acrylic resin Pre-emulsification: Mix 30g acrylic acid, 40g methyl methacrylate and 30g butyl acrylate, add 58g deionized water and 2.8g DNS-86, stir and pre-emulsify for 30min to obtain a pre-emulsion.

[0046] Free radical polymerization: The pre-emulsion was transferred to a reactor, protected with nitrogen, heated to 75°C, and 0.8g of initiator (potassium persulfate: sodium metabisulfite = 1:0.3) was added dropwise. The reaction was maintained at this temperature for 4 hours to obtain an acrylic copolymer.

[0047] Polyurea modification: 15g of polyurea prepolymer with terminal -NCO groups was added to the reactor, the temperature was raised to 80℃ and the reaction was continued for 2h. Ammonia water was added dropwise to adjust the pH to 7-8 to obtain polyurea modified water-soluble acrylic resin.

[0048] S2, Formulation of Composite Coatings Take 80g of polyurea-modified water-soluble acrylic resin and 20g of waterborne epoxy E-44, add 20g of deionized water, then add 0.5g of fatty alcohol polyoxyethylene ether-9, 0.3g of polydimethylsiloxane emulsion and 0.2g of polyether-modified polydimethylsiloxane, disperse at 1200rpm for 30min to obtain component A.

[0049] Component B was prepared by mixing 5g of caprolactam-blocked hexamethylene diisocyanate trimer with 2g of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane at 40°C for 15min.

[0050] After mixing component A and component B and maturing for 20 minutes, the mixture is filtered through a 200-mesh filter to obtain a composite coating, which is denoted as state A.

[0051] S3, Two-stage curing process: The composite coating is applied to the surface of the non-oriented silicon steel substrate and a two-stage curing process is adopted. In the first stage, the coating is baked at 160℃ for 2 minutes. In the second stage, the temperature is raised to 220℃ and baked for 25 minutes. After cooling, the composite coating is obtained, which is denoted as state C.

[0052] Comparative Example 1 (without polyurea modification) In this comparative example, 70g of ordinary water-soluble acrylic resin was used instead of the polyurea-modified water-soluble acrylic resin in Example 1. All other steps were the same as in Example 1 and will not be repeated here.

[0053] Comparative Example 2 (Single-stage curing) The only difference between this comparative example and Example 1 is that the coating curing process is constant temperature baking at 200℃ for 30 minutes. The other raw material amounts, polyurea modified resin synthesis, and composite coating preparation are the same as in Example 1, and will not be repeated here.

[0054] Comparative Example 3 (using KH-560 coupling agent) The only difference between this comparative example and Example 1 is that the existing silane coupling agent KH-560 is used instead of γ-aminopropyltriethoxysilane in Example 1. The amounts of other raw materials used, the synthesis of polyurea modified resin, and the preparation of composite coatings are the same as in Example 1, and will not be repeated here.

[0055] The coatings in states B and C during the composite coating process in the above embodiments and comparative examples were tested and verified according to the following test standards.

[0056] Pencil hardness: tested according to GB / T6739-2006; Impact resistance: tested according to GB / T1732-2020 (impact hammer mass 1kg, impact height 50cm); Adhesion: tested according to GB / T9286-1998 (cross-cut test); Bond strength: tested according to GB / T5210; Salt spray resistance: tested according to GB / T1771-2007 (5% NaCl solution, 35℃); Flowability: visual observation (tilted at 45° and left to stand for 1h); Dry film thickness: coating thickness gauge (average of 5 random points); Water resistance (immersion in deionized water at 25℃ for 24h): GB / T1733-1993.

[0057] The test results of the coating in state B are shown in Table 1 below.

[0058] Table 1

[0059] As shown in Table 1, polyurea modification is the core factor in improving the overall performance of the B-state coating. Examples 1-3 exhibited a pencil hardness of 2H-3H and an impact resistance of 38-42 kg·cm (without cracking or peeling), while Comparative Example 1 had a hardness of only 2H and an impact resistance of 25 kg·cm (with fine cracks). This indicates that the soft-segment toughening and hard-segment reinforcement mechanism of the polyurea block can effectively improve the coating's damage resistance in the B-state. Examples 1-3 showed no flow deformation, while Comparative Example 1 showed slight flow (deformation within 0.5 mm of the edge). This is because the polyurea block constructs a preliminary cross-linked skeleton through hydrogen bonds, ensuring the coating's non-flowability required for laminate processing. Examples 1-3 showed no bubbling or whitening after 24 hours of immersion, maintained adhesion at grade 1, and showed no significant phase separation at the microscopic level. Comparative Example 1 showed localized whitening, reduced adhesion to grade 2, and significant phase separation (dispersed phase percentage ≥30%), confirming that the polyurea block can reduce the interfacial tension between acrylic and epoxy, simultaneously optimizing water resistance and compatibility.

[0060] The two-stage curing process is crucial for ensuring the compatibility of B-state coatings. Comparing Example 1 (two-stage curing) with Comparative Example 2 (single-stage curing), the advantages of the two-stage process are significant. Example 1 showed no flow deformation and no abnormalities in water resistance, while Comparative Example 2, due to single-stage curing, experienced uneven premature cross-linking of the epoxy, resulting in slight flow (deformation within 0.8mm of the edge) and localized blistering (≤3 blister / 10cm). 2 Example 1 shows no obvious phase separation at the microscopic level and an impact resistance of 42 kg·cm. Comparative Example 2 shows local phase separation (dispersed phase ratio ≥ 25%) and an impact resistance of only 28 kg·cm (micro-cracks at the edges). This shows that the logic of low-temperature preferential curing of acrylic acid in the two-stage process can avoid premature epoxy reaction and ensure the structural uniformity and processing adaptability of the B-state coating (such as morphological stability and impact resistance when stacked).

[0061] Aminosilane coupling agents (γ-aminopropyltriethoxysilane) are better suited for B-state interface strengthening than traditional KH-560. Example 1 showed no peeling after cross-cut adhesion and maintained Grade 1 adhesion after water resistance, while Comparative Example 3 showed edge peeling, slight whitening (area ≤8%) after water resistance, and adhesion reduced to Grade 2. Example 1 exhibited no micropores and suppressed phase separation, while Comparative Example 3 showed minute voids at the interface and a dispersed phase ratio ≥20%. This indicates that aminosilane coupling agents can pre-construct substrate-coating interface bonding through pre-hydrolysis of hydrogen bonds, while traditional KH-560 can only improve physical compatibility and cannot achieve the same interface strengthening effect.

[0062] The test results of the coating in state C are shown in Table 2 below.

[0063] Table 2 Performance Test Results

[0064] As shown in Table 2, Examples 1-3, due to the introduction of polyurea blocks, exhibited superior performance compared to Comparative Example 1 without polyurea modification. Specifically, Example 1 achieved an impact resistance of 55 kg·cm (without cracks), an 83% improvement over Comparative Example 1 (30 kg·cm, with cracks); its salt spray resistance time was 130 hours (without abnormalities), a 117% extension compared to Comparative Example 1 (48 hours, with blistering and rusting); and microscopic observation revealed no significant phase separation, forming a uniform interpenetrating network. Furthermore, Examples 2 and 3 both met performance standards (impact resistance ≥ 50 kg·cm, salt spray resistance > 110 hours). This indicates that the polyurea blocks optimize mechanical properties through a soft-segment toughening-hard-segment reinforcement mechanism, while simultaneously improving compatibility through polarity, representing the core innovation for comprehensive performance improvement.

[0065] Examples 1-3, employing a two-stage curing process, exhibited significantly superior performance compared to Comparative Example 2, which used a single-stage curing method. Specifically, Example 1, after gradient curing at 160℃ / 230℃, achieved an adhesion level of 1 (no peeling off during cross-cutting) and a salt spray resistance of 130 hours. Comparative Example 2, due to single-stage curing at 200℃, experienced premature synchronous cross-linking of the epoxy and acrylic phases, resulting in significant local phase separation. Its adhesion level dropped to 2 (local peeling), and its salt spray resistance was shortened to 72 hours (local blistering). This confirms the scientific logic of two-stage curing: the first stage at a low temperature ensures mild cross-linking of the acrylic phase to maintain fluidity, while the second stage at a high temperature promotes deep cross-linking of the epoxy under fluid dynamics, forcing the formation of a uniform IPN structure and preventing macroscopic phase separation. This demonstrates that the two-stage curing process is a key means of suppressing phase separation.

[0066] Examples 1-3 used aminosilane coupling agents and a two-stage curing process. The adhesion of all examples reached level 1 (no peeling after cross-cutting) and the corresponding bonding strength was also high (6.2-6.8 MPa). This is because the Si-O-Me covalent bonds and interpenetrating network structure formed by aminosilane simultaneously enhanced the anti-peeling ability and interfacial bonding force, which was much higher than that of comparative examples 1-3.

[0067] Comparing Example 1 with Comparative Example 3, which uses KH-560 coupling agent, the interface-enhancing advantage of aminosilane coupling agents can be observed. Example 1, using γ-aminopropyltriethoxysilane, achieved an adhesion grade of 1 and salt spray resistance of 130 hours. Comparative Example 3, where KH-560 only improves the interface through physical compatibility, experienced a drop in adhesion grade to 2 (edge ​​flaking) and a salt spray resistance shortened to 72 hours (slight rusting), with microscopic observation revealing interfacial voids. This indicates that aminosilane, through a dual effect of chemical bonding and substrate anchoring, can significantly improve coating adhesion and moisture resistance compared to traditional silane coupling agents.

[0068] Furthermore, Example 1 exhibits the best overall performance due to its balanced resin ratio (pencil hardness 3H, impact resistance 55 kg·cm, salt spray resistance 130h); Example 3, by increasing the polyurea content, achieves an impact resistance of 53 kg·cm and salt spray resistance of 120h, demonstrating a significant advantage in toughness; Example 2 shows a slight decrease in hardness (2H) but still meets the requirements, making it suitable for scenarios with slightly lower hardness requirements. All three examples collectively verify the universality and performance adjustability of the technical solutions.

[0069] In summary, this invention effectively solves the core defects of traditional composite coatings through the synergistic innovation of polyurea modification, two-stage curing, and aminosilane interface strengthening. Its significant advantages in mechanical properties, corrosion resistance, and interface stability provide a high-performance and environmentally friendly solution for industrial protection and high-end equipment coatings.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel, characterized in that, The product comprises the following components by weight: 60-80 parts of polyurea-modified water-soluble acrylic resin, 20-40 parts of epoxy resin, 5-10 parts of blocked isocyanate curing agent, 2-4 parts of aminosilane coupling agent, 0.5-1.5 parts of wetting agent, 0.3-0.8 parts of defoamer, 0.2-0.6 parts of leveling agent, and 20-40 parts of deionized water.

2. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel as described in claim 1, characterized in that, Specifically, the following steps are included: S1. Synthesis of polyurea-modified water-soluble acrylic resin; S2. Preparation of composite coating: Take polyurea modified water-soluble acrylic resin, epoxy resin and deionized water, then add wetting agent, defoamer and leveling agent, disperse at 1200 rpm for 30 min to obtain component A; Component B was prepared by mixing and pre-reacting a blocked isocyanate curing agent with an aminosilane coupling agent at 40°C for 15 min. After mixing component A and component B and maturing for 20 minutes, the mixture is filtered through a filter screen to obtain a composite coating. S3. Two-stage curing process: The prepared composite coating is applied to the surface of the non-oriented silicon steel substrate and cured in two stages. The first stage of curing is carried out by baking at 120-180℃ for 1-2 minutes, and the second stage of curing is carried out by heating to 220-250℃ for 20-30 minutes to strengthen the bonding between the two phases.

3. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 2, characterized in that, In polyurea-modified water-soluble acrylic resin, the polyurea block accounts for 8-15% of the solid content of the modified acrylic resin.

4. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 2, characterized in that: The epoxy resin is waterborne bisphenol A type epoxy E-44 with an epoxy value of 0.44 mol / 100g.

5. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 2, characterized in that: The blocked isocyanate curing agent is methyl ethyl ketone oxime-blocked isophorone diisocyanate trimer or caprolactam-blocked hexamethylene diisocyanate trimer.

6. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 2, characterized in that: The aminosilane coupling agent is one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

7. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 2, characterized in that: The wetting agent is fatty alcohol polyoxyethylene ether-9; the defoamer is polydimethylsiloxane emulsion; and the leveling agent is polyether-modified polydimethylsiloxane.

8. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 2, characterized in that: In step S1, the synthesis steps of the polyurea-modified water-soluble acrylic resin are as follows: (1) Pre-emulsification: Mix acrylic acid, methyl methacrylate and butyl acrylate in a mass ratio of 3:4:3, add deionized water and emulsifier and pre-emulsify for 30 min; (2) Free radical polymerization: Under nitrogen protection, the temperature was raised to 75°C, and a redox initiator was added dropwise for 4 hours to obtain an acrylic copolymer; (3) Polyurea modification: Add the polyurea prepolymer with terminal -NCO groups and continue to react at 80℃ for 2h. Add ammonia to adjust the pH to 7-8 to obtain the modified resin.

9. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 8, characterized in that: The emulsifier is DNS-86, and the redox initiator is a mixture of potassium persulfate and sodium metabisulfite, wherein the mass ratio of potassium persulfate to sodium metabisulfite is 1:0.

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10. The method for preparing a polyurea-modified water-soluble acrylic resin / epoxy resin composite coating for non-oriented silicon steel according to claim 8, characterized in that: The initiator accounts for 0.8% of the total mass of acrylic acid, methyl methacrylate, and butyl acrylate; the polyurea prepolymer with terminal -NCO groups accounts for 5%-15% of the total mass of acrylic acid, methyl methacrylate, and butyl acrylate.

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