Preparation Of High Performance Waterborne Coil Steel Coating

Because the coil steel is coated before forming processing,therefore,the coating needs to have excellent post-processing properties.At present,steel coil coatings are mainly solvent-based,although the environmental protection laws and regulations are increasingly strict,however,water-based steel coil coatings are in the process of industrial application resistance.The most critical factor is that the mechanical properties and anti-corrosion properties of waterborne coatings cannot reach the solvent-based technical index.Therefore,in this paper,the performance of water-based coil steel coating is improved through three approaches:the development of high-performance water-based coating resin,inorganic nanoparticle composite and wax emulsion addition.The purpose is to develop a water-based coil steel coating whose performance index can completely replace the solvent based coil steel coating.The following is the main work content of this paper:1.Preparation and properties of acrylic acid grafted epoxy phosphate ester waterborne resinIn this paper,epoxy phosphate ester was prepared by esterification of phosphoric acid using epoxy resin as raw material.Acrylic acid and its ester grafted epoxy phosphate ester waterborne resin（P-EPA）were prepared by solution polymerization.The introduction of functional phosphoric acid can give passive anodic protection to the metal surface of the coating.Functional groups such as epoxy and hydroxyl in the epoxy resin can give excellent adhesion and anti-corrosion properties to the coating.Acrylic resin can give the coating the ideal toughness.The results show that the viscosity and crosslinking activity of P-EPA aqueous resin is greatly affected by the molecular weight of the epoxy resin.The viscosity of P-EPA（E-12）prepared by low molecular weight E-12 is significantly lower than that of P-EPA（E-03）prepared by large molecular weight.At the same time,an important discovery was made:P-EPA（E-03）water-based resin has self-crosslinking property,that is,it can be thermocured into the film without an external curing agent such as amino resin.It is further revealed that the self-crosslinking mechanism of P-EPA（E-03）is the cross-linking reaction between the epoxide group,carboxyl group and hydroxyl group in the P-EPA chain at high temperatures.Electrochemical AC impedance（EIS）and XRD studies have revealed that P-EPA（E-03）coating has long-term anticorrosive properties due to its dense coating structure and the formation of Fe-phosphate passivation film between phosphate and Fe²⁺.2.Preparation and properties of P-EPA（E-12）nano composite coatings by inorganic nano silica compositeInorganic nano modification can improve the wear resistance,hardness,toughness and other mechanical and mechanical properties of the coating,and improve the chemical resistance of the coating.In this chapter,spherical nano-silica with a diameter of～10 nm was selected and its surface was modified by hydroxyethylation（HEM-SiO₂）to improve its compatibility with P-EPA/amino resin.The effects of the concentration of HEM-SiO₂ on the surface morphology,hydrophobicity,friction and mechanical properties of P-EPA coatings were investigated.The results show that compared with the P-EPA coating,the elastic modulus,wear resistance and hydrophobicity of the prepared nano-composite coating is significantly improved with the HEM-SiO₂ filling content of only 0.1-0.2 wt%.In particular,the wear rate of the nano-composite coating with 0.1 wt%HEM-SiO₂ nano-composite coating is reduced nearly 20 times.The resistance to friction and wear of the coating is significantly enhanced.The results of the Tafel curve,EIS and chemical resistance test showed that 0.1 wt%HEM-SiO₂ nanocomposite coating has the best anticorrosion performance.Which different coating soaked in 65℃ 3.5 wt%NaCl solution,soaking in 30 days after the blank coating electrochemical impedance Bode diagram of low-frequency impedance modulus |Z|_0.1Hz was 5.17×10⁵ Ω cm²,and add the 0.1 wt%HEM-SiO₂ nanocomposite coating the |Z|_0.1Hz was 1.23×10⁷ Ω cm²,by nearly two orders of magnitude.The excellent anti-corrosion performance of the HEM-SiO₂ nano-composite coating is because the surface of the nano-SiO₂ participates in the cross-linking reaction with the amino resin to form a denser coating.3.Effect of PE wax emulsion on coating properties of waterborne coil steelPolytetrafluoroethylene（PTFE）and polyethylene（PE）wax are often used as additives to improve the friction resistance of coatings because of their low surface energy.In this chapter,PE wax emulsion（AD-62）imported from Japan was used as a functional additive,and the effects of PE wax addition on hydrophobicity,friction resistance and T-bending mechanical properties of the coating were studied.The results show that the optimal additive dosage of AD-62 is 3 wt%of the solid content of the coating,and the friction coefficient of the modified coating is significantly reduced（from 0.5046 to 0.4429）compared with that of the unadded coating.The wear rate is reduced by 12 times,showing excellent friction resistance;the T-bend rating increased from 6T to 4T;The toughness of the coating is enhanced.SEM,XPS and other characterization methods revealed that the mechanism of PE wax improving coating properties is that the hydrophobic PE molecules tend to migrate to the coating surface.