Overview of Water-Based Coatings

An Overview of Water-Based Coatings With increasing industrialisation in our lives, metal consumption is also steadily rising. The process by which metals gradually deteriorate through chemical and/or electrochemical reactions with their environment is termed "corrosion." Corrosion is a destructive phenomenon that not only damages the appearance of metals but also causes equipment failure and creates significant economic losses (Figure 1). Metal susceptibility to corrosion causes serious economic losses worldwide. Research findings show that the total annual cost of corrosion in the United States is USD 276 billion, and in the United Kingdom, 3.1% of Gross Domestic Product is spent on corrosion-related problems (Hou, et al., 2017).   One of the most effective and economical methods for protecting metal surfaces is the inhibition of corrosion through the use of organic coatings. The role of organic coatings here is to provide a physical barrier protecting the metal layer from the corrosive environment. However, volatile organic compounds (VOCs)* present in the structure of organic coatings cause significant harm to the environment and to people. To overcome this situation, numerous regulations have been introduced, and the paints and coatings industry has been included within their scope. Legal requirements imposed on environment-compatible coating processes have resulted in more extensive research into suitable coating materials (powder coatings, water-based paints, etc.) over the past 20 years. Consequently, water-based organic coatings have become an inevitable trend in the sector. Today, anticorrosive water-based paints not only reduce solvent consumption but also play an important role in metal protection (Gangopadhyay, 2018, Mohamed, Wan et al 2017, Zhu et al, 2017). However, the market introduction of water-based coatings has been challenging due to generally lower performance characteristics compared to solvent-based products. Additionally, the production costs of water-based resins and coatings are higher than their solvent-based counterparts, which can be viewed as a barrier to their rapid growth (Heilen, 2014). Despite the development and overcoming of challenges faced by water-based and powder paints and their increasing use in industry, nearly half of coatings in industrial processes in Germany remain in traditional form (solvent-based materials, etc.). From a European perspective, solvent processing industries and the paints and coatings industry are now the leading sources of organic compounds and solvent emissions. European parliament members responded to this reality by issuing an EU directive in 1999 (Council Directive 1999/13/EC of 11 March 1999) to force even small and medium-sized enterprises to implement stricter measures to prevent emissions. In the EU, the main VOC Solvent Emissions Directive was amended by Article 13 of Directive 2004/42/EC, the Paints Directive. On the other hand, in accordance with Turkey's EU accession process, Turkey has reached the implementation stage of the aforementioned legislation within the framework of a harmonisation and coordination programme. Within this scope, efforts are being made to monitor developments in systems that will minimise emissions, to reduce solvent ratios in paints or to transition to paints containing no organic solvents wherever possible (Heilen, 2014). According to a report prepared by Global Paint and Coatings Industry Market Analysis (2019-2024), the global paints and coatings market reached USD 164 billion in value in 2019. By volume, architectural paints hold the largest share at 52%, while industrial paints account for 48%. The paints industry in Turkey holds significant economic importance within the basic chemicals sector. Research was conducted on Europe's largest paint manufacturer companies by considering company turnover, export share and number of employees, and Yaşar Holding from Turkey entered the list at 22nd position (Web1). Approximately 600 small and medium-sized enterprises operate throughout Turkey. The Turkish paints industry, with a production of 724,000 tonnes and reaching an economic value of approximately USD 1.57 billion, holds approximately 2% of the world market. The decorative segment accounts for the largest market share at 50%. Water-based paints comprise approximately 86% of decorative paint production (Polisan Holding Activity Report, 2020). The share of water-based technologies used in plastic coatings has been reported at 23%. In the transportation sector, water-based 2K PU coatings are used in interior applications, while 1K base coats are applied to exterior surfaces. Most OEM sectors have considered and/or evaluated the implementation of water-based coatings, but have not yet fully realised them due to application difficulties, changing viscosity profiles, and poor appearance and performance characteristics. However, OEMs have no preference regarding whether component suppliers use solvent-based or water-based coatings as long as finished product specifications are met. Some OEMs can use a water-based base coat together with a solvent-based primer and either water-based or solvent-based topcoat. With continuous developments in water-based coating technology, water-based paints today account for 8% of heavy-duty services, 23% of wood coatings, 36% of general industrial coatings, 37% of drum and plastic coatings, 68% of automotive (OEM) coatings and 90% of architectural coatings (Heilen, 2009). In research conducted by market research company Grand View Research, it is reported that significant growth in consumption is expected due to increasing demand for water-based systems in the maritime, coil, wood, metal packaging, printing inks and electronics industries (Cynthia Challener). On the other hand, China is regarded by some industry stakeholders as a key growth market for water-based coatings in the coming years (Heilen, 2014). In 2020, a water-based ceramic alloy coating developed with cutting-edge world-leading technology specifically for multi-functional surface protection by EALEAN Technology Co., Ltd. (China) won the "Jung Technical Innovation" award (Web2). KANAT Paints & Coatings, operating in Turkey since 1986 in the paints sector, has specialised in the production of protective coatings and general industrial paints over the years. It operates with a customer-focused approach and maintains a broad R&D team that follows developments in the sector. It is beginning to establish its position in the sector through its R&D and customer work on water-based paints. The challenges encountered in the development of water-based paints are fundamentally based on certain key differences between water-based and solvent-based paints. The raw materials of water-based paints have significantly different properties compared to conventional solvent-based systems. The fundamental reason for this is the physical properties of water. Water's heat of evaporation is considerably higher compared to many solvents. Due to strong hydrogen bonding, water evaporation is much more difficult than most organic solvents. Water, being a highly polar solvent, also has high surface tension. This complicates the wetting and stabilisation of pigments/fillers and requires the use of surfactants in the process. At the same time, various surface defects due to water's high surface tension and poor adhesion on substrates where surface cleaning is not properly performed can be encountered. In these cases, the use of surface wetting agents and adhesion additives is important. Dispersing agents provide excellent electrostatic stabilisation for inorganic pigments and fillers in water-based paints but cannot reduce surface tension at the solid-liquid interface (particle/binder + particle/water). For this reason, dispersing agents and wetting agents must be used together in water-based paint systems (Figure 2). Unlike solvent-based paints, which typically use polymeric dispersing and wetting agents, water-based paints are formulated using polyphosphates and polyacrylic acid salts. Foam suppressants and air release agents are indispensable components of formulation, especially for airless applications (Lane, 2003; Heilen, 2014, Yetiş, 2019).   Another fundamental characteristic of water-based paints is the dispersed/emulsified structure of the resins. Surfactants are used to stabilise binders in this structure, but these materials cause a rapid increase in viscosity with increased solid content and lead to various effects such as phase inversion and coalescence requirements during film formation (Lane, 2003). When these emulsifiers remain in the dry film, they can also reduce water and corrosion resistance. Water-based paints are also susceptible to microbial infections during production and while stored as packaged products. Exposure to various physical and chemical events such as high temperature and humidity facilitates microbial contamination and can cause serious problems. Consequently, the use of biocides, which consist of groups of chemical agents with various antimicrobial mechanisms of action, is important (La Rosa et al., 2008). Besides these, due to the negative effect of moisture and temperature on film formation and quality of water-based paints, paints must be applied in temperature and humidity-controlled cabinets. Considering all the characteristics mentioned above, water-based coatings, which can be prepared today in both 1K and 2K forms, demonstrate performance levels comparable to conventional solvent-based systems. Through studies conducted, the basic properties expected from paint—such as hardness, moisture and chemical resistance—have been raised to a level that meets the demands of the industrial paint market. Performance can be further improved through fine adjustments to paint formulations. From an economic perspective, the transition to water-based coatings has begun to become increasingly attractive for both paint manufacturers and end users. *According to EU Directive 2004/42, VOCs are defined as follows: "Volatile organic compound (VOC) means any organic compound having at an initial boiling point less than or equal to 250°C or a vapour pressure of 0.01 kPa or more at 101.3 kPa standard pressure."  

Sources / References

Cynthia Challener. (2017). Waterborne Industrial Coatings: Regulatory Changes Slowly Driving Shift to Waterborne, CoatingsTech | Vol. 14, No. 10 | October 2017 Gangopadhyay, S., & Mahanwar, P. A. (2018). Recent developments in the volatile corrosion inhibitor (VCI) coatings for metal: a review. Journal of Coatings Technology and Research, 15(4), 789-807. Goldschmidt, A., & Streitberger, H. J. (2003). BASF handbook on basics of coating technology. William Andrew. Heilen,W. (2009). Additives for Waterborne Coatings, European Coatings Tech Files, e-book, ISBN: 978-3-86630-800-8 Hou, B., Li, X., Ma, X., Du, C., Zhang, D., Zheng, M., ... & Ma, F. (2017). The cost of corrosion in China. npj Materials Degradation, 1(1), 1-10. Lane, B. C. (2003). Additives in water-borne coatings (No. 290). Royal Society of Chemistry. La Rosa, F. R., Giese, E. C., Dekker, R. F. H., Pelayo, J. S., & Barbosa, A. M. (2008). Microbiological contamination of water-based paints from an industry in the state of Paraná, Brazil. Ciências Exatas Ciências Exatas e Tecnológicase da Terra, Londrina, 29, 85-92. Mohamed, H. A. (2010). New waterborne paints with different binders and corrosion inhibition application. Journal of coatings technology and research, 7(1), 85-89. Polisan Holding Activity Report, 2020 Wan, H., Song, D., Li, X., Zhang, D., Gao, J., & Du, C. (2017). A new understanding of the failure of waterborne acrylic coatings. RSC advances, 7(61), 38135-38148. Yetiş, S. (2019). WATERBORNE COATINGS-Expert Voices-Solvents meet their Waterloo. European Coatings Journal, (11), 14-15. Zhu, K., Li, X., Li, J., Wang, H., & Fei, G. (2017). Properties and anticorrosion application of acrylic ester/epoxy core–shell emulsions: effects of epoxy value and crosslinking monomer. Journal of Coatings Technology and Research, 14(6), 1315-1324. Web 1: https://endustriyel.dyo.com.tr/kurumsal/dyodan-haberler/dyo-avrupanin-en-buyuk-boya-ureticileri-arasinda Web 2: https://www.european-coatings.com/articles/archiv/waterborne-coatings-a-steady-growing-business Web 3: https://www.ealeancoating.com/news/congratulations-ealean-shenzhen-winning-the-2020-coatings-industry-jung-technical-innovation-award.html

 

Dr. Suna Koçyiğit

R&D Specialist Engineer Water-Based Paints KANAT Paints & Coatings