Study: The status quo of water-based polyurethane anti-corrosion coatings

China Coatings Online News
With the increasing awareness of environmental protection and the increasing control of volatile organic substances (VOC/TVOC) and harmful air pollutants (HAPs) in various countries, the world paint industry in the 21st century is walking in the fast lane of "water-based", "solvent-free" and "green" development. Corrosion is a phenomenon that changes or loses the original properties of a material due to chemical or electrochemical changes in the material and the medium in its surrounding environment. According to relevant statistics, the annual economic losses caused by metal corrosion account for 2% to 4% of gdp income, about six times the economic losses of natural disasters such as earthquakes, floods and typhoons. In recent years, while continuously improving the anti-corrosion paint corrosion performance, but also rapidly to the "water-based" direction of development. Polyurethane anti-corrosion coatings are the most common coating varieties after other anti-corrosion coatings, and their dosing is second only to acetic resin coatings. Among them, water-based polyurethane anti-corrosion coatings are becoming the leader in water-based anti-corrosion coatings, it not only has excellent physical properties, but also has excellent resistance to strong acids, strong alkalis, anti-aging, salt spray resistance (>480h), salt-resistant water (>480h) and other chemical properties, in the field of water-based anti-corrosion coatings has been rapidly developed. However, water-based polyurethane because of water as a dispersant, containing hydro-based groups, its coating film water resistance is poor, lower cross-linking density than solvent-based coatings, is not conducive to preventing corrosive factors into the substrate. Therefore, in order to achieve corrosion resistance, water-based polyurethane needs to be modified. In this paper, the classification, revision and research progress of water-based polyurethane anti-corrosion coatings are reviewed, and the future development prospects are looked forward to.1, water-based polyurethanepolyurethane is short for polyurethane, generally defined as polyurethane in the polymer chain containing duplicate urethane bonds of the structural unit of the polymer compound. China is a major producer of coatings industry in the world, with a total coating output of about 150 million t in 2014 and a polyurethane coating output of about 1.45 million t, up 3.6% YoY. Polyurethane coatings are a more common category, can be divided into two-group polyurethane coatings and single-group polyurethane coatings. Water-based polyurethane is a new polyurethane system that replaces organic solvents with water as a dispersion medium, also known as water-dispersed polyurethanes, water-based polyurethanes, or water-based polyurethanes. In view of its unique chemical structure, the excellent performance of water-based polyurethane coatings is given: 1) coating film wear resistance and strong adhesion;2) coating film anti-corrosion performance is excellent, oil-resistant, acid-alkali salt-resistant, industrial-resistant exhaust gas;3) coating film soft and hard adjustable, construction temperature range is wide;4) good resistance to high and low temperature, from -40 degrees C to 300 degrees C can have the corresponding varieties.2, water-based polyurethane anti-corrosion coating classification (1) single-group water-based polyurethane anti-corrosion coatingDue to the excessive amount of emulsifying agent, the film-forming performance is poor, resulting in limited application of the resulting coating. Single-group water-based polyurethane is a type of environmentally friendly coating with water as a dispersant and simple construction method. Water-based polyurethane coatings with cross-linking makeover have good storage stability, film-coating properties, water resistance, solvent resistance and aging resistance, and are similar to the performance of traditional solvent-based polyurethane coatings.。 Son Suk-Hye and others first introduced the pyridine base into the polyurethane molecular chain segment, and then neutralized with triethylamine into salt, synthesized a self-emulsified water-based polyurethane coating, and discussed the degree of neutralization and the effect of the nihine-based content on the performance of water-based polyurethane. With the increase of the degree of mesoth and the content of the carboxyl, the size of latex particles is reduced from 47nm to 27nm, and the stability of the emulsion is improved.Yang Dongya, etc., using isofone diocyanate (IPDI) or toluene-2, 4-diocyanate (TDI), polyether polyol (GE220) and dihydroxymethylate (DMPA) as raw materials, synthesizes single-part water-based polyurethane by pre-polymer, adjusts its NCO/OH value and DMPA content, and studies its stability and changes in physical properties after film. The results showed that when the ratio of NCO/OH substances was 1.8:1.0 and DMPA:GE220 was 2:1, the average particle size of emulsion was 30.6nm, the particle size distribution index was 0.306, and the water absorption rate of water-based polyurethane was 14.81%, and its physical properties after film-forming were optimal.Zhao Jing, etc., synthesized a new polyurethane chaining agent with diethanolamine (DEA) and acetone acrylamide (DAAM) through Michel addition for use with isofolone diocyanate (DAAM) IPDI), polytetrahydrofuran glycol (PTMG1000), dihydroxymethylate (DMPA), trihydroxymethyl propane (TMP) polymerization, the production of ketone cross-linked water-based polyurethane emulsion. When the ratio of n (-NHNH2) to n (-CO-) was from 0 to 1:1, the absorption rate of the coating film dropped from 32.42% to 14.28%, and the hardness of the pencil was increased to 2H. The test of coating film thermal weight loss shows that the introduction of ketone crosslinking structure improves the thermal stability of coating film.the water resistance, mechanical properties and chemical resistance of single-component water-based polyurethane coatings compared to solvent-based two-component polyurethane coatings. The addition of curing agent to cross-link reaction between molecules, making a two-part water-based polyurethane coating is the best way to improve the performance of the coating film.(2) two-group water-based polyurethane anti-corrosion coatingstwo-group polyurethane coatings with low film temperature, strong adhesion, good wear resistance, high hardness and chemical resistance, weather resistance and other superior performance, widely used in industrial protection, wood furniture and automotive coatings and other fields. The two-component water-based polyurethane coating is mainly composed of a water-based polyol containing -OH and a low-viscosity polycyanate curing agent containing -NCO.Wang Guo, etc. on the basis of water-based polyurethane resin, the preparation of metal with two-part water-based polyurethane coating. Film pencil hardness of 2H, adhesion ≥1 level, alcohol resistance, high temperature and humidity, salt water resistance are qualified, VOC content of 135g/L (technical indicators≤200g/L). The results show that the physical and mechanical properties of the water-based coating film are superior, and the construction performance is good, which can be used on the metal device on a large scale.shili equal use of hydroxypropyl acrylic emulsion prepared the corresponding water-based two-part polyurethane coating, the paint has good construction performance and decorative protection function. Compared with traditional solvent-based coatings, the membraneization process of two-part water-based polyurethane coatings is more complex and the coating requirements are higher. Coating construction needs to be carried out in a relatively low humidity, low temperature environment, strictly in accordance with the process requirements to control the ratio of the various parts of the coating, and according to the construction time limit requirements of the coating as soon as possible in a relatively short period of time to complete the coating.3, water-based polyurethane anti-corrosion coatings modified water-based polyurethane coatings with excellent adhesion and flexibility and so on. However, due to its low cross-linking density, the comprehensive performance of water-based polyurethane coatings is still a certain gap compared to solvent-based polyurethane (PU), so it is necessary to use certain methods to change the water-based polyurethane coatings, so as to improve the performance of water-based polyurethane coatings. (1) resin modified water-based polyurethane anti-corrosion coating Randhir Parmar and other epoxy resin and acrylic copolymer first sealed with acetylene, and then with isocyanate prepolymer reaction prepared water-based polyurethane coating. The results of DSC test show that the thermal stability of synthetic water-based polyurethane coatings is improved, the scratch hardness is increased to 2600g, and their acid-resistant, water-resistant and salt-resistant water properties are better than those of ordinary water-based polyurethane coatings. Heyu equal to the ionic acid monoglyceride modified water-based polyurethane emulsion as the base material, organic modified zinc orthophosphate as anti-corrosion pigment, the preparation of aluminum alloy water-based polyurethane anti-corrosion coating, and studied the amount of monoglycerides, rust-proof pigments and pigments The effect of the quality ratio on the performance of the coating, the adhesion of the coating film is the largest at 1.2, 12.8MPa, the salt spray test (500h) is 1.2 when the coating film is not rust-free, and foaming within 2mm in one way at scratches. The results show that when the mass score of monoglyceride is 20% and the face-based ratio is 1.2, the anti-corrosion performance of the coating film is optimal, the adhesion with the aluminum alloy substrate is strong, and there is potential application value in aluminum alloy truck. Tang Yu to bisphenol A type epoxy resin as a modifier, prepared polyester polyols as a soft segment of water-based polyurethane, and with infrared spectroscopy, particle size analyzer, contact angler and thermal weight analyzer and other means of the epigenetic means of emulsion and coating analysis, research shows that: emulsion stability is better, the average particle size of 26.67nm; The hardness of the coating pencil is 2H, the water absorption rate is only 2.4%, the heat resistance, corrosion resistance is improved, and the coating film comprehensive performance is excellent. 。 Xu et al. prepare methyl acrylic ethyl acetate-coated water-based polyurethane resins with isofrone diocyanate (IPDI), polyether polyols (NJ-220), dihydroxymethylbutyric acid (DMBA), methyl acrylates (HEMA) as raw materials, and then water-based polyurethane coated with acrylates and acrylics. For active thinners, 2-hydroxy-2-methyl-1-benzene-1-acetone (HMPF) prepares UV-cured water-based polyurethane coatings for light-trigger agents, and explores the protective properties of coatings on metal surfaces. (2) the main anti-corrosion of water-based polyurethane coating nanoparticles modified by nanoparticles is to fill the shrink holes produced in the coating film process, increase the degree of cross-linking of the coating film, prevent corrosion factors from entering the substrate, improve the corrosion resistance of the coating film, protect the substrate; It also improves the mechanical, thermal and electrochemical properties of coatings. Li Wen and others prepared a water-based UV silicone-polyurethane anti-corrosion coating with water-based polyurethane acrylates, water-based epoxy acrylics, silicone emulsions, water-based polyurethanes, light triggers, anti-flash rust agents, pigments and fillers. The preparation method is: according to the ratio of each raw material, first water-based polyurethane acrylates, water-based epoxy acrylates, silicate emulsion, water-based polyurethane mixed evenly, and then in turn added light triggers, leveling agents, pigments and fillers and other components, dispersed evenly after grinding, grinding to a fineness of less than 30 m. The anti-corrosion coating has the advantages of good adhesion, good water resistance, good salt spray resistance, high hardness, good wear resistance, good gloss and good aging resistance. The preparation method is simple, easy to operate and low preparation cost. 。 Christopher and others prepared PVA modified graphene oxide (GO)/ZnO and PVA modified carbon black (CB)/ZnO nanocomposites, and then modified water-based polyurethane to synthesize low-carbon steel water-based polyurethane anti-corrosion coatings. The EIS results show that the polarization resistance increases with the content of PGZ and PCZ, and the polarization resistance of WPU/0.3% PGZ and WPU/0.3% PCZ is 56.85k?cm2 and 10.37k?cm2, respectively. By comparison, it is concluded that both WPU/0.3% PGZ and WPU/0.3% PCZ improve the corrosion protection of water-based polyurethane to some extent, but WPU/0.3% PCZ has better dispersion, stability and corrosion resistance than WPU/0.3% PCZ. 。 Christopher and others use oocylic acid-modified ZnO interface interactions with polymer substrates to improve the performance of water-based polyurethane coatings. The contact angle of unalgraded water-based polyurethane in water is 65.78 degrees. ZnO-modified water-based polyurethanes are more hydrophobic, with a contact angle of 75.78 degrees. The EIS results show that the polarization resistance increased with the ZnO content, from 0.758k?cm2 to 13.739k?cm2. Ionic acid modified ZnO nanoparticles can be better dispersed in water-based polyurethane coatings, and effectively prevent corrosive substances from entering the substrate, thus has excellent corrosion resistance. 。 Christopher and others use sonic degradation to modify ZnO with sodium alginate (SA) and litopic sulfonate (LS) to prepare biomolecules modified ZnO/water-based polyurethane coatings. The polarization resistors of 0.3% SA/WPU and 0.3% LS/WPU are 4.45k?cm2 and 21.51k?cm2, respectively. The results show that the corrosion resistance of ligand sulfonate/ZnO composite water-based polyurethane is better than that of sodium alginate/ZnO composite water-based polyurethane. 。 M Rashvand is used to mix nanoZnO with water-based polyurethane with a mass fraction of 3%, resulting in a water-based polyurethane nano-composite coating. ESI test shows that nano ZnO composite coating has better membrane resistance than ordinary water-based polyurethane coating. After 1080h salt spray resistance performance test, the thickness of the composite nanocoat is still as high as 2 to 3mm, which is basically no different from the traditional anti-corrosion coating. The results show that nano ZnO improves the protective properties of water-based polyurethane and has excellent corrosion resistance. 。 Li and so on will oxidize graphene, functional fossil ink and water-based polyurethane mixed to improve the corrosion resistance of water-based polyurethane, EIS tests show that its impedance module up to 109 ohm, 3.5% sodium chloride solution soaked 236h after the resistance mode is basically unchanged. Compared with ordinary water-based polyurethane, graphene correction performance effectively improves the corrosion resistance of water-based polyurethane. (3) other methods modified water-based polyurethane anti-corrosion coating passivation is a method to form a dense structure on the metal surface, thereby improving the corrosion resistance of the metal. The formation of passivation layer on metal surface can effectively organize corrosive substances into the metal and improve the corrosion resistance of the coating. 。 Yang and so on to water-based polyurethane, TiSO4, (NH2) 2CS, NH4F as raw materials, mixed after spraying on acetone treated metal sheet, and then immersed in HNO3,