An Overview of Stoz: Chemical and Physical Fundamentals of Industrial Coating Systems

Industrial coatings are far more than decorative surfaces. They protect materials against corrosion, weathering, and mechanical stress while shaping the visual appearance of a product. Without modern coating systems, today’s high industrial quality standards would be nearly impossible to achieve.

However, coating technology is in a state of tension: on one hand, legislation and societal demands push for a reduction of volatile organic compounds (VOC), promoting the use of water-based systems. On the other hand, in day-to-day industrial practice, the well-established solvent-based systems remain indispensable due to their robustness, process reliability, and proven performance. As a specialist with nearly 100 years of experience, Stoz provides insights into the current state and trends in industrial coatings, surface technology, and corrosion protection.

Fundamentals of Coating Systems

At their core, industrial coating systems are divided into one-component (1K) and two-component (2K) systems.

1K Coatings: All ingredients are contained in a ready-to-use mixture. Curing occurs either physically through solvent evaporation or chemically by reacting with atmospheric oxygen or moisture. Their application is straightforward, though they cannot match the durability of more advanced systems.

2K Coatings: Here, the two components – resin and hardener – are mixed shortly before application. A subsequent chemical reaction forms a highly cross-linked film with excellent hardness, abrasion resistance, and chemical durability. These systems demand greater discipline during processing but are the top choice where maximum performance is required.

Baking Coatings: These coatings cure fully only under heat in an oven. Through the crosslinking of polyester or acrylic resins with amino resins (typically melamine), they create a highly cross-linked thermoset film with outstanding hardness, chemical resistance, gloss retention, and both process and end-performance. The ecological assessment must, however, factor in the energy consumption of the baking process.

Solvent-based baking coatings have long been the standard in automotive OEM finishes and coil coating. Their water-based equivalent, such as cathodic electrodeposition (CED/KTL), today coats virtually every car body during manufacturing.

Water-Based Systems

The development of water-based coatings has made significant strides. 1K water-based coatings, typically based on acrylic or polyurethane dispersions, are now widely used. They dry quickly, remain elastic, and resist yellowing, making them common in furniture and interior applications. However, they also have limitations: their block and scratch resistance is limited, they are sensitive to climate conditions, and high humidity or low temperatures can significantly extend drying times.

2K water-based coatings, often based on polyurethane or epoxy resins, mitigate many of these weaknesses. Offering excellent hardness, chemical resistance, and abrasion durability, they are increasingly used for demanding industrial floors, corrosion protection, and premium furniture finishes. However, their processing requires precise mixing ratios, has short pot life, and remains sensitive to climatic fluctuations.

The ecological advantage of water-based systems is nuanced. While VOC emissions are lower, water evaporation often requires longer or more energy-intensive drying. Furthermore, binders must be stabilized in water using additives – substances that are not always harmless. Therefore, the true ecological footprint of water-based coatings largely depends on process design and, above all, the longevity of the coating.

A special case is water-based baking coatings, especially cathodic electrodeposition (KTL), which has become the automotive industry standard thanks to its even, full-coverage corrosion protection on complex geometries. Its downsides include the high energy demand for baking and limited decorative properties.

Solvent-Based Systems

Solvent-based coatings remain the benchmark for technical stability and process reliability. 1K systems like traditional alkyd or acrylic coatings offer excellent flow, strong adhesion, and dependable application even under less-than-ideal climatic conditions. Acrylic resins are prized for their high UV stability and clarity, while alkyd resins are valued for elasticity and robustness, despite a tendency to yellow.

Solvent-based baking coatings, typically based on polyester or acrylic resins combined with melamine resins, cure at around 140–180 °C. The result is a highly cross-linked thermoset film with exceptional hardness, chemical resistance, and gloss retention. In automotive OEM coatings and coil coating, they remain indispensable. Their process reliability and decades of proven performance make them a standard that modern alternatives struggle to match.

The strength of solvent-based 2K coatings is even more pronounced. Polyurethane coatings are universal high-performance finishes with a unique combination of hardness, elasticity, and chemical resistance. Acrylic-PUR systems combine brilliance and lightfastness with the toughness of polyurethane crosslinking, making them irreplaceable in automotive manufacturing, aerospace, and high-end machinery. Epoxy coatings, on the other hand, are the gold standard in heavy-duty corrosion protection, tank linings, and pipelines, thanks to their unmatched adhesion and resistance to aggressive media.

From an environmental perspective, it’s worth noting that modern solvents are increasingly derived from renewable resources. Combined with their typically longer service life and fewer recoats required, the environmental footprint of solvent-based systems is often surprisingly favorable.

Trends and Developments

The goal is to align sustainability with industrial requirements. To this end, the industry has developed high-solid systems with higher solids content, reducing the amount of solvent needed and thereby VOC emissions, without compromising the strengths of solvent-based chemistry. Hybrid systems are also gaining importance by combining different binder types to achieve tailored properties. At the same time, bio-based resins and sustainable raw materials are becoming increasingly relevant.

At present, these innovative systems do not yet offer the same processing stability or final performance as established technologies. Water-based systems continue to gain market share but face practical limitations in many industrial applications. The push toward sustainability continues, however. Leveraging its expertise in R&D, Stoz tests innovations early and delivers customized solutions that ensure both cost-effectiveness and premium, sustainable industrial coatings.

Conclusion

Industrial coating systems reflect a balance between innovation, regulation, and technical realities. Water-based systems are an important step toward reducing emissions, but their ecological advantage is not always as clear-cut as it might seem, and their performance remains limited in certain applications.

By contrast, solvent-based systems have proven their strengths over decades and remain the benchmark for top-level performance, particularly in their two-component variants. Their extensive track record, long-lasting durability, and the growing use of bio-based solvents ensure that they will continue to play a crucial role in the future of industrial coating technologies.