Electrochemical characterisation of multilayer organic coatings

The protective properties of eight high performance commercial multilayer organic coatings for aeronautical use (based on polyurethane, epoxy and polyurethane-compatible epoxy resins) on anodised 2024-T3 Al alloy were evaluated in neutral aerated 3.5% NaCl aqueous solution using the electrochemical impedance spectroscopy (EIS) technique. The investigation was performed on specimens supplied and prepared from Alenia in accordance with their technical specifications. Results obtained in this paper show that all coating systems exhibit excellent protective properties even after prolonged immersion in the test solution (one year). Although the dielectric properties of all multilayer coatings are quite similar, EIS was proved to be able to discriminate among them, making possible a rank of these protective systems to prevent or to reduce corrosion. Capacitance measurements performed on the same coatings allow their behaviour to be forecasted.     

呋喃树脂—丙烯酸酯聚氨酯互穿网络防腐涂料的研究

呋喃树脂涂料具有优良的防腐蚀性能，但质地较脆，附着性较差。用丙烯酸酯聚氨酯对其改性，形成互穿网络（ＩＰＮ）结构，可提高涂层的柔韧性和附着性，同时保持其优良的防腐蚀性能。文中讨论了ＩＰＮ形成过程中两种交联反应时间的匹配方法和丙烯酸酯聚氨酯用量对涂料性能的影响，并比较了改性前后的涂料性能。     

The influence of aluminium surface pretreatment on the corrosion stability and adhesion of powder polyester coating

One of the most important factors in corrosion prevention by protective coatings is the coating adhesion loss under environmental influence. Thus, adhesion strength is often used when characterizing protective properties of organic coatings on a metal substrate. In order to improve the adhesion of organic coating the metal substrate is often pretreated in some way. In this work, the adhesion of polyester coatings on differently pretreated aluminium surface (by anodizing, with and without sealing, by phosphating and by silane film deposition) was examined. The dry and wet adhesion of polyester coatings were measured by a direct pull-off standardized procedure, as well as indirectly by NMP test. It was shown that under dry test conditions all polyester coatings showed very good adhesion, but that aluminium surface pretreated by silane film showed superior adhesion. The overall increase of wet adhesion for polyester coating on aluminium pretreated by silane film was maintained throughout the whole investigated time period. The different trends in the change of adhesion of polyester coatings were observed for different aluminium pretreatments during exposure to the corrosive agent (3% NaCl solution). The highest adhesion reduction was obtained for polyester coating on aluminium pretreated with phosphate coating. The corrosion stability of polyester coated aluminium was investigated by electrochemical impedance spectroscopy in 3% NaCl solution. The results confirmed good protective properties of polyester coating on aluminium pretreated with silane film, i.e. greater values of pore resistance and smaller values of coating capacitance were obtained in respect to other protective systems, whereas charge-transfer resistance and double-layer capacitance were not measurable during 2 months of exposure to a corrosive agent.     

Performance of paint systems with polyurethane topcoats, proposed for atmospheres with very high corrosivity category

The EN ISO Standard 12944-5 describes the types of paint and paint systems commonly used for corrosion protection of steel structures. In this work four paint systems, applied on steel, including polyurethane topcoats, recommended for atmospheres with high corrosivity (C5 category), codified by 1–4, were studied. Systems 1 and 4 include zinc rich primers and epoxy/polyamide intermediates, system 2 has solvent free epoxy/polyamide primer and intermediate and, system 3 is a hybrid system with vinyl–acrylic water based primer and a high solids epoxy/polyamide intermediate. Systems 2–4 have acrylic–polyurethane topcoats and, the topcoat of the system 1 was identified as an aliphatic polyurethane.

According to EN ISO 12944-6, water condensation and neutral salt spray tests were performed. Three exposure times were considered taking into account the durability ranges of paint systems: low, medium and high, respectively. The paint systems were complementary submitted, during 30 days, to ultraviolet radiation with water condensation test according to ASTM G 154. At the same time, natural exposure was conducted in the marine atmosphere of Sines, with very high corrosivity (>C5).

The paint adhesion, before and after artificial ageing, was evaluated by cross-cut test and, for the systems with dry thickness greater than 250 μm, by pull-off test. Visual inspections were carried out.

For the exposure in UV radiation test chamber and at test site, gloss reduction, colour change and chalking were measured. Chemical changes on polyurethane topcoats exposed in the UV radiation test chamber were studied by Fourier transform infrared spectroscopy (FTIR).

In spite of the higher aesthetic degradation by UV radiation, of the aliphatic polyurethane topcoat of the system 1 relatively to the acrylic–polyurethane topcoats of the other systems, system 1 with ethyl silicate zinc rich primer and epoxy intermediate, was the one that presented the best corrosion protection when exposed in artificial and natural salty environments. At the test site, the worst anticorrosive behaviour seems to be presented by the system 2 with two coats of solvent free epoxy paint.     

Development and characterization of silicone/phosphorus modified epoxy materials and their application as anticorrosion and antifouling coatings

Epoxy resin is chosen for our present study owing to its exceptional combination of properties such as easy processing, high safety, excellent solvent and chemical resistance, toughness, low shrinkage on cure, good electrical, mechanical and corrosion resistance with excellent adhesion to many substrates. This versatility in formulation made epoxy resins widely applied for surface coatings, adhesives, laminates, composites, potting, painting materials, encapsulant for semiconductor and insulating material for electric devices. There are numerous paint/coating systems based on epoxy resin available for corrosion and fouling prevention. They however are not completely satisfactory in field applications, where high corrosion, fouling and flame resistance are required. The demand for epoxy resin as corrosion/fouling resistant coatings is restricted mainly due to its inferior characteristics like poor impact strength, high rigidity, and moisture absorbing nature besides inadequate flame retardant properties. It is for this reason that silicones and phosphorus-based compounds are used as modifier in this work by intercrosslinking network mechanism (ICN) to obtain epoxy resin with desired properties ideally suitable for field applications for preventing corrosion and fouling with flame retardantancy. The present work involves the development of solvent free silicone/phosphorus modified epoxy coating systems, since solvent free coating systems are widely used for numerous applications due to their lower cost per unit film thickness, freedom from fire and pollution hazard and ability to provide better performance. For the development of coating systems, epoxy resin (X) serves as base material, hydroxyl terminated polydimethylsiloxane (HTPDMS) as modifier, γ-aminopropyltriethoxysilane (γ-APS) as crosslinking agent and dibutyltindilaurate (DBTDL) as catalyst. Polyamidoamine (A), aromatic amine adducts (B) and phosphorus-containing diamine (C) were used as curing agents. The study also describes the evaluation of corrosion resistant behaviour of unmodified epoxy and siliconized epoxy coatings by potentiodynamic polarization method, electrochemical impedance spectroscopy (EIS), salt-spray and antifouling tests. The results are discussed.     

Adhesion and corrosion resistance of epoxy primers used in the automotive industry

One of the most important factors in corrosion prevention by protective coatings is the loss of adhesion of the coating under environmental influence. Thus, adhesion strength is often used when characterizing protective properties of organic coatings on a metal substrate. In this work, the adhesion of different epoxy primers (pigment-free, zinc-rich and chromate-based) was examined on steel. Both the dry and wet adhesion strengths of organic primers were measured directly by a pull-off standardized procedure, as well as indirectly by the NMP test. The corrosion stability of coated samples was investigated by electrochemical impedance spectroscopy. It was shown that under dry test conditions all the samples showed very good adhesion. However, different trends in adhesion for different primers during exposure to the corrosive agent (3% NaCl solution) were observed. The lowest adhesion values were obtained for chromate-based epoxy primer; however, the change in adhesion of this protective system during immersion in 3% NaCl solution for 25 days was the smallest of all investigated samples. Electrochemical impedance measurements in 3% NaCl solution confirmed good protective properties of pigmented epoxy primers on steel, i.e., greater values of pore resistance and charge-transfer resistance, and smaller values of coating capacitance and double-layer capacitance, were obtained for these protective systems.     

水基标识涂料在夹布胶管上的应用研究

夹布胶管受其条件限制,在运输、存贮、安装及使用过程中经常发生弯曲形变,涂料在涂覆后,形状需随胶管的形变而发生变化,由于目前采用的聚氨酯涂料在固化后具有脆性大、延展力小等弊端,无法随胶管的形变而继续附着,进而发生脱落现象。为此开展高弹性水基涂料的研究,以改善涂层与胶管的附着力。叙述了对高弹性水基聚氨酯涂料进行模拟涂覆夹布胶管的试验过程及试验结果,并通过对试验结果的分析,证实了PUA-I水基聚氨酯涂料可以满足工艺要求。     

Polyurethane/Polysiloxane Ceramer Coatings: Evaluation of Corrosion Protection

A series of polyurea and polyurethane ceramer coatings were formulated using hexamethylene diisocyanate (HDI) isocyanurate, alkoxysilane‐functionalized HDI isocyanurate, tetraethyl orthosilicate (TEOS) oligomers and cycloaliphatic polyesters. The coatings were prepared as a function of alkoxysilane‐functionalized HDI isocyanurate and TEOS oligomers concentration. Also, the effect of acid catalyst was investigated. The corrosion resistance of polyurea or polyurethane ceramer coating systems were evaluated using a prohesion chamber on aluminium alloy 2024‐T3 substrate. The polyurethane ceramer coatings were compared with the chromate pretreatment and the epoxy‐polyamide primer containing the chromate pigment. In addition to prohesion, the interface between the coating and substrate was characterized using X‐ray photoelectron spectroscopy (XPS). The prohesion data showed that the corrosion was inhibited by the TEOS oligomers. However, high concentrations of TEOS oligomers and acid catalyst produced blistering in the polyurea/polysiloxane ceramer coatings. The prohesion data also showed that the corrosion protection of ceramer coatings performed as well as the chromate pretreatment and competitively with the epoxy primer. From the XPS and prohesion data, a self assembling silicon oxide layer at the metal‐coating interface was proposed.     

Recent advances in aqueous two-component systems for heavy-duty metal protection

Although waterborne coatings have successfully replaced their solventborne counterparts in a variety of areas, their use generally has been limited to applications with relatively modest performance requirements. Recently, advances in technology have allowed for the design of waterborne coatings with performance suitable for more demanding applications. The emergence of two-component waterborne polyurethane coatings exemplifies this trend. These coatings can provide performance similar to that of solventborne 2-pack urethanes, but with much lower VOC. The chemistry of these coatings is discussed, in light of its relevance to some of the technical challenges, e.g., pot life and CO₂-gassing in thick films, unique to these systems. The use of 2-pack waterborne urethane topcoats in combination with low VOC waterborne acrylic/epoxy primers and intermediate coats is also described. Such multiple coat systems offer the promise of long term corrosion protection in severe industrial and marine environments, coupled with very low VOC.     

三乙醇胺的附着增强作用

试验了三乙醇胺对聚氨酯涂料在聚酯烘烤涂层表面上的层间附着力的增强作用,并考查了其对涂层性能的影响。结果表明,加入三乙醇胺的烘烤型聚酯中涂层表面,未经打磨就喷涂聚氨酯面漆,层间附着力完全达到要求,不会明显影响聚酯中涂层的物理机械性能     

Anticorrosive epoxy/clay nanocomposite coatings: rheological and protective properties

The preparation of epoxy/clay nanocomposites (NCs) and their insertion into coatings are of great importance since the NCs could enhance the protective performances. In this study, epoxy NCs with 1–10 wt% of nanoclay Cloisite 30B (C30B) were prepared by the sonication-assisted solution method. The rheological measurements of epoxy/C30B suspensions revealed non-Newtonian, shear-thinning behavior of the uncured NCs, with an increase in the viscosity, yield stress, and shear modules with increasing organoclay content, while the dispersion effectiveness of C30B decreased. A significant enhancement of the rheological parameters was observed at the second percolation threshold (4.1 vol%) due to the formation of a continuous network of 45-layer-thick tactoids. Although NCs with 1–3 wt% C30B exhibited slightly reduced mechanical and adhesion properties compared with the cured reference epoxy resin, the epoxy primer and topcoat based on NC with 1 wt% C30B generally displayed improved impact resistance and maintained flexibility, pendulum hardness, and good adhesion properties. Two-layer coating systems, i.e., NC-based primers and topcoats, had higher corrosion stability in a salt spray chamber compared to the unmodified system.     

新型环氧硅酸酯防腐涂料的研制

将环氧树脂和硅酸酯预聚物通过催化缩合反应,制得环氧硅酸酯涂料,兼有有机和无机涂料的优点,具有高硬度、高耐磨、高附着力、优异的抗渗性、抗溶剂溶胀、抗介质氧化等性能。本文介绍了环氧硅酸酯树脂的合成以及环氧硅酸酯新型防腐涂料的制备。     

不同表面处理条件下复合涂层体系失效过程的EIS特征

研究了不同表面处理条件下环氧富锌/环氧云母氧化铁/氯化橡胶涂层体系的电化学阻抗谱特征。利用Bode图、涂层吸水率、涂层电阻及特征频率的变化评价了表面处理对涂层防护性能的影响。结果表明,基材表面状态不同的复合涂层体系吸水率相对稳定阶段所持续的时间长短顺序为：手工打磨>表面锈蚀>表面未处理,与涂层的防护寿命长短、涂层/基材间的黏附力大小顺序一致。此外,不论基材表面处理程度如何,当涂层体系的特征频率增加到1400 Hz左右时,涂层电阻均发生较快降低,吸水率发生较大增长,涂层失去防护作用。     

Coatings prepared from waterborne polyurethane dispersions obtained with polycarbonates of 1,6-hexanediol of different molecular weights

Waterborne polyurethane dispersions (PUDs) were synthesized with polycarbonates of 1,6-hexanediol of different molecular weight (500–3000 Da) and their properties, adhesion (Hatch adhesion) and coatings on stainless steel properties (Pencil hardness, Persoz hardness, gloss at 60°, chemical resistance, yellowness index) were characterized. The hatch adhesion of the polyurethane coatings to stainless steel was very good and decreased slightly by increasing the molecular weight of the polycarbonate of 1,6-hexanediol. Both the Pencil and Persoz hardness values of the coatings increased by increasing the hard segments content in the polyurethane, i.e. by decreasing the molecular weight of the polycarbonate of 1,6-hexanediol, whereas the gloss and the yellowness index were lower for the coatings obtained with the polycarbonate of 1,6-hexanediol of molecular weight of 500 Da. Very good chemical resistance against ethanol for all polyurethane coatings on stainless steel plates was obtained but for long time of ethanol in contact with the coating surface the chemical resistance decreased, more markedly for the polyurethane coating obtained with the polycarbonate of 1,6-hexanediol of higher molecular weight. In summary, the segmented structure of the waterborne polyurethane dispersion determined the properties of the polyurethane coatings obtained from them.     

纳米改性工业防腐蚀涂料的研制与应用

介绍了纳米改性工业防腐蚀涂料的制备工艺,包括纳米浓缩浆、纳米改性环氧封闭漆、纳米改性环氧云铁中间漆以及纳米改性含氟聚氨酯面漆等系列产品的制备与表征。测试结果表明,纳米材料在纳米浆及涂料中获得了良好分散,纳米改性复合涂层(即喷铝涂层+纳米改性环氧封闭漆+纳米改性云铁中间漆+纳米改性含氟聚氨酯面漆)的物理机械性能以及耐久性均得到显著提高,产品在实际工程应用中也取得了可喜成果。该纳米改性工业防腐蚀涂料具有良好的应用前景。     

环氧改性有机硅耐高温防腐涂料的研制

以环氧改性有机硅树脂作为漆基,制备了磷酸锌底漆、云母氧化铁中间漆以及不同颜色的面漆,研究了不同漆膜的耐热性以及以磷酸锌底漆加云母氧化铁中间漆复配不同颜色面漆所得复合涂层的耐热性和耐蚀性。结果表明,以磷酸锌底漆、云母氧化铁中间漆和氧化铬绿面漆复配所得的涂层具有较好的耐高温防腐蚀性能,该复合涂层在350°C烘烤3h后,耐冲击强度≥40kg·cm,附着力≤2级,柔韧性≤2mm。     

Laboratory evaluation of epoxy coatings with an adhesion promoter by impedance

The corrosion behaviour of glassflake epoxy coatings on steel substrate with and without an adhesion promoter was examined by electrochemical impedance spectroscopy. The impedance data show that an improvement in the protective behaviour of the coating is connected with a large increase in the resistance in the pores of the coating. These effects are probably due to an improvement in the initial, wet and recovered adhesion between glassflakes and epoxy binder. The results of pull-off adhesion tests are presented.     

Corrosion behaviour of epoxy coatings electrodeposited on galvanized steel and steel modified by Zn–Ni alloys

The electrochemical and transport properties and thermal stability of epoxy coatings electrodeposited on hot-dip galvanized steel and steel modified by Zn–Ni alloys were investigated during exposure to 3% NaCl solution. Zn–Ni alloys were electrodeposited on steel by direct and pulse current. From the time dependence of pore resistance, coating capacitance and relative permittivity of epoxy coating, diffusion coefficient of water through epoxy coating, D(H₂O) and thermal stability, it was shown that Zn–Ni sublayers significantly improve the corrosion stability of the protective system based on epoxy coating. Almost unchanged values of pore resistance were obtained over the long period of investigated time for epoxy coatings on steel modified by Zn–Ni alloys, indicating the great stability of these protective systems, due to the existence of the inner oxide phase layer and the outer layer consisting of basic salts.     

Study of degradation of organic coatings in seawater by using EIS and AFM methods

In this article, electrochemical behaviors and their topography observation for four organic coatings used in seawater, by using both electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) methods to study environment behaviors of different coatings as well as the effects of their film formation, pigments, and fillers on anticorrosion behaviors, were measured. The results show that polyurethane, epoxy, and chlorinated rubber coatings all present one capacitive loop in their tested EIS which contains phenomenally only one time constant, whereas alkyd coating presents two capacitive semicircle arcs. With two capacitive loops, the capacitive semicircle in the high frequency range represents barrier layer property, but the semicircle in the low frequency range represents corrosion reaction of metals under the film. Polyurethane coating used in seawater has well anticorrosion property in seawater immersion test. The appearance features of different layers are visible different between different layers of tested coatings at their surface topography. The property of polyurethane paint film coated on metal is better than other layers, and film of alkyd coating has many pits at its surface by observing the layer's images. AFM photos imaged have also been used to further detail surface topography for four organic coatings, and to approve effects of topography of these coatings on its electrochemical behaviors, from two views of both height and phase modes. It is beneficial to explain deeply the environment behaviors and degradation mechanism of organic coatings. To further study failure of these organic coatings and dynamic processes of corrosion of metal under the film, two equivalent circuit models, according to these tested EIS, have been suggested to explain the corrosive kinetics of these four coatings. To polyurethane, epoxy, and chlorinated rubber coatings used in seawater which have good protection effects for substrate metal, the diffusion process for water, from their layer's surface to interface of film/metal, is mainly controlled factor for degradation. However, the electrochemical reaction process has may become a control procedure for corrosion of alkyd coated metal. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

柔性环氧防腐涂料的制备

以聚醚聚氨酯改性环氧树脂和自制的固化剂为基料,添加适当的防锈颜填料及助剂,制备了一种柔性环氧防腐涂料,该涂料具有良好的机械性能、耐介质性能及防腐性能,而且涂层浸水后以及低温下的柔韧性保持率高,湿态附着力好。