The surface finishing industry is in the midst of profound change, triggered by increasingly strict regulatory requirements for the handling of hazardous substances, in particular hexavalent chromium [Cr(VI)]. The chromium trioxide used in chrome plating is coming under increasing scrutiny due to its carcinogenic effects and significant environmental impact. Comprehensive restrictions on the use of Cr(VI) have now been imposed and the industry has been obliged to switch to safer alternatives such as trivalent chromium electrolytes [Cr(III)]. The challenge and complexity of the transition is exacerbated by additional regulations, e.g. for per- and polyfluoroalkyl substances (PFAS).
With these new regulatory requirements, the development of Cr(VI)-free technologies that also do not contain PFAS is becoming increasingly important. Solutions developed by MKS' Atotech fulfill the legal requirements and meet the high performance standards of surface finishing. The ability of the entire industry to continuously adapt and improve its environmental footprint is becoming increasingly important to ensure future sustainability.
Stricter EU regulations on Cr(VI) drive change to alternatives
Cr(VI), traditionally used as a source of chromium, is a known carcinogen and poses a significant risk to the environment and health. In order to minimize these risks, the EU is pushing for stricter regulations that could severely restrict the use of this substance and require its complete substitution in the long term. This is forcing the industry to research and implement alternatives such as trivalent chromium [Cr(III)]. A significant milestone was the commissioning of the European Chemicals Agency (ECHA) by the European Commission to draw up a proposal for the further restriction of Cr(VI) substances. The regulation of chromium trioxide [Cr(VI)] by the European REACH regulation, in particular its inclusion in Annex XIV in 2013, has already had a significant impact on the electroplating industry. Since September 21, 2017, the use of Cr(VI) has to be authorized and unauthorized uses have been prohibited since then. The ongoing CTAC sub-authorization thus continues to allow decorative and electroplated coatings on plastics under strict conditions (use 3). Even if a complete ban on Cr(VI) is not formulated for 2024, the dependence on this substance makes the industry uncertain, as the official restriction process has not yet been completed and further tightening is on the horizon.
MKS' Atotech: Cr(VI)-free and non-PFAS-based electroplating technology
MKS' Atotech has developed Cr(VI)-free processes for decorative electroplating and plastic coating. One example of this is the Covertron 600 system (Fig. 1), which is used to stain ABS and ABS/PC substrates. This process uses no chromium at all, yet delivers a stain finish that meets conventional benchmarks and therefore satisfies the visual and cosmetic requirements of the industry. Covertron 600 is already used in various production facilities worldwide and has successfully passed extensive OEM thermocycling tests. It offers very good adhesion and is compatible with a wide range of plastics, including ABS and ABS/PC. Its high selectivity in coating 2K and 3K components makes it a versatile solution that meets the demanding requirements of modern manufacturing processes.
Fig. 1: Atotech components coated with the Covertron 600 process
TriChrome process: Advanced Cr(VI)-free solutions
The TriChrome processes from MKS' Atotech offer a Cr(VI)-free alternative to traditional bright chrome plating without compromising on aesthetics or durability. TriChrome Plus is specifically designed for high plating speeds and is characterized by high corrosion resistance, proven in challenging tests such as the CaCl2/Russian Mud test. And TriChrome Ice offers a chrome surface that is visually comparable to Cr(VI) coatings. IMO anodes ensure throwing power and corrosion resistance.
The TriChrome family (Fig. 2) also includes a series of dark, modern shades that respond to current design trends. TriChrome Smoke 2 comes in a warm, light gray shade, while TriChrome Shadow offers a slightly darker, cold gray shade. TriChrome Titan allows for a deep, neutral gray, TriChrome Graphite an even darker, warm gray and TriChrome Phantom delivers the darkest gray in the series. These surfaces have been approved by numerous original equipment manufacturers (OEMs) in the automotive industry and are used in their series production.
Fig. 2: The TriChrome processes offer a Cr(VI)-free alternative to traditional bright chrome plating
Strategies to reduce the environmental impact
In view of global efforts to achieve sustainability targets, the development of appropriate technologies is increasingly coming into focus. OEMs committed to ambitious carbon neutrality targets are increasingly looking for surface finishing solutions that not only minimize their environmental footprint but also meet the technical and aesthetic requirements of the industry.
Environmental impact of surface finishing technologies
Assessing the environmental impact of surface finishing technologies plays a key role in the overall environmental impact of industries with high material consumption, such as steel, aluminum, polymers, electronics, tires and glass. In the automotive sector in particular, the demand for transparency in processes is becoming increasingly important. Due to the number of studies, standardized approaches are becoming increasingly important. At present, their absence and the inconsistent assessment methods within the automotive industry are leading to considerable inconsistencies in reporting and interpretation. These discrepancies present companies with major challenges, especially if they want to meet both legal requirements and OEM-specific sustainability targets.
Impact on the supply chain and legal framework
The demand for sustainable supply chains has further intensified due to stricter regulations and laws. These regulations increasingly cover the entire product life cycle, from raw material extraction to end use by the customer. The lack of harmonization of life cycle assessment methods poses significant challenges for companies, especially if they operate in different regions and have to comply with different regulatory requirements. As a result, OEMs and Tier 1 suppliers are demanding increasingly specific metrics to determine greenhouse gas emission figures, such as kilograms ofCO2 equivalent per square meter (kg CO2e/m2) of manufactured parts. This paradigm shift not only affects Tier 1 suppliers, but also has far-reaching implications for the entire supply chain. Suppliers of specialty chemicals and other materials used in surface treatment are also affected.
Sustainability in the electroplating industry
MKS' Atotech already provides data on its entire product portfolio. The calculation methodology is based on a comprehensive analysis that covers the entire value chain. It takes into account the composition of the products, the production processes and the raw materials used. MKS' Atotech uses a variety of data sources, including the company's own databases and, if necessary, also uses modeling techniques for specialty chemicals that are not available in conventional databases. Finally, energy consumption and packaging are included in the life cycle calculations.
Cradle-to-gate and gate-to-gate methods
Comprehensive assessments are used to precisely quantify the environmental impact of products. The cradle-to-gate approach covers the entire life cycle of a product from raw material extraction, material and energy supply to chemical production, packaging and delivery to the customer.
Methodology - calculation process
For the methodology, MKS' Atotech worked together with an independent project partner. The methodology covers the assessment of all production stages, including raw materials and specialty chemicals, with the entire supply chain being of key importance. Aspects assessed include raw materials. Despite existing data from literature and databases, the chemical industry does not currently provide all the necessary information on every substance in the supply chain. It is therefore necessary to model certain specific raw materials. Key factors such as transportation, primary products, energy supply and the detailed chemical processes involved in the production of raw materials and their intermediate products are taken into account. In addition to the primary products, by-products and internal recycling are also tracked. While the influence of plant construction and infrastructure is often considered negligible, other factors such as waste heat, waste water, waste and exhaust air are carefully calculated. These energy flows are assessed either in terms of their recycling potential or their environmental impact.
This complex process is currently essential, but will be facilitated in the future by expanded databases and greater knowledge of chemical suppliers, allowing for an even more accurate and complete analysis.
Calculating the carbon footprint
The method for quantifying environmental impact compares different surface finishing technologies, including Cr(VI) coatings, Cr(VI)-free alternatives, lacquers and physical vapor deposition (PVD). In the case of electroplating, the calculation includes detailed data on the chemicals used, in particular the raw materials, and their consumption over time. A particular focus is on metals such as copper, nickel, palladium and chromium. As most of the metals used, apart from copper, are assumed to be primary materials, the recycling of nickel, palladium and chromium is included in future assessments.
A virtual coating plant is used to estimate energy consumption, assuming a standard cycle time. Components such as rectifiers, racks, filters, cooling and heating systems and exhaust air management are explicitly taken into account. The generation of waste and waste water is also included in the calculations, whereby the removal is not taken into account. Other variables such as reject rates, rack occupancy, throughput and average layer thickness are also included in the analysis to ensure a precise and comprehensive assessment.
Technologies in competition with chrome: coatings and PVD
As announced, the methodology also includes the evaluation of competing technologies such as coatings and physical vapor deposition (PVD). When analyzing paint systems, a three-layer structure is assumed, consisting of a primer, a water-based basecoat and a solvent-based topcoat. The evaluation is carried out virtually using a simulation of a modern plant located in Europe. Curing is considered in gas-fired ovens and other energy-intensive processes. Important assumptions such as reject rates, rack occupancy and overspray are based on current literature and expert knowledge to ensure that the life cycle assessment is realistic. A three-layer structure is also assumed for the PVD process, comprising a water-based primer, the PVD coating and a solvent-based top coat. This comprehensive analysis allows a detailed comparison of the environmental impact of paints and PVD technologies compared to traditional chrome coatings.
Cr(VI)-free solutions for plastic coating
The development of Cr(VI)-free solutions for plastic coating follows a precise methodology. The first step is plastic pre-treatment, which aims to prepare the plastic for optimum adhesion of the metal layer and to ensure its conductivity. This step is crucial for the quality of the coating, although it is often not visible in the end product. The next step is the application of the decorative coating, where multiple layers of metal are applied to provide the desired appearance and the required corrosion resistance. Typically, this process involves plating with copper, nickel and chromium. Trivalent chromium (TriChrome) is used as a sustainable alternative to hexavalent chromium. Each of these steps is modeled in detail to capture the overall environmental impact. This includes raw material consumption, energy consumption and waste. This comprehensive approach enables a precise comparison between traditional and innovative surface finishing technologies.
Comparison of technologies
When analyzing the environmental performance indicators of different surface finishing technologies such as electroplating, painting (three-layer system) and physical vapor deposition (PVD), both energy consumption and material input are decisive factors. However, the relative effects vary considerably between the technologies. In electroplating, energy consumption accounts for around 65% of total greenhouse gas emissions. This is primarily determined by electricity and gas consumption, with rectifiers in particular being the largest energy consumers. The remaining 35% is accounted for by material consumption, with plating with metals such as copper, nickel and chromium making up the majority.
In contrast, a three-layer coating system accounts for around 70 % of emissions from energy consumption, in particular from gas and the corresponding ovens. The material input is around 25%, mainly caused by the organic components in the paint. A further 5 % results from volatile organic compounds (VOCs), which are converted into carbon dioxide during the curing process.
PVD technology shows a similar pattern: energy consumption accounts for around 75% of emissions, with gas and ovens being the main sources. Material consumption accounts for around 20%, while volatile organic compounds account for 5% of GHG emissions. These comparisons illustrate the different priorities and challenges of the individual technologies in terms of energy and material efficiency.
Recyclability of coated components
Chrome-plated components are often misjudged in terms of sustainability, even though they offer significant environmental benefits thanks to their lasting material value and full recyclability. A closed-loop recycling process enables chrome-plated plastic components to be comprehensively recycled at the end of their life cycle. Old chrome-plated parts are efficiently transformed into new components, reducing waste and conserving valuable resources. This circular approach not only helps manufacturers to reduce their environmental footprint, but also strengthens the long-term sustainability of chrome-plated products.
Plastic components coated with PVD (Physical Vapor Deposition) or paint pose a challenge in terms of recyclability. In contrast to chrome-plated components, which can be fully recycled, the combination of plastic with PVD coatings or paint layers makes the recycling process considerably more difficult. These coatings adhere firmly to the plastic and are difficult to separate, which means that such components cannot usually be recycled. This creates additional waste and valuable resources are lost, which significantly increases the environmental footprint of these products compared to fully recyclable alternatives.
Potential for reducing the environmental impact
For all three surface finishing technologies - electroplating, painting and PVD - energy consumption is the key factor in greenhouse gas emissions. However, electroplating offers particularly promising opportunities to reduce greenhouse gas emissions through the use of renewable energy sources. Switching to a cleaner energy mix, where renewables replace fossil fuels, can reduce electricity emissions by up to 70%. With an electricity mix containing more than 60% renewables or nuclear energy, this reduction could be up to 90%.
In addition, material consumption in electroplating offers considerable potential for reducing greenhouse gas emissions. The use of recycled metals can significantly reduce the impact, especially in processes that use large quantities of metals such as copper, nickel and chromium.
Furthermore, Cr(VI)-free solutions in electroplating have shown that their greenhouse gas emissions are equivalent or even slightly lower than those of traditional Cr(VI) methods, depending on the specific process and materials used.
Energy and material contributions in electroplating
In electroplating, different process steps contribute differently to the overall energy and material footprint. Plastics pre-treatment, which accounts for around 10 % of total chemical-related emissions, is an early but significant step in the process. In comparison, the majority of the emissions, around 90%, come from decorative coating, which uses metals such as copper, nickel and chrome.
The rectifiers account for the highest energy consumption. In terms of material consumption, plastic pre-treatment accounts for around 20-25% of total material-related emissions, mainly due to pickling processes and the use of metals and salts. In contrast, decorative coating accounts for around 75-80% of material-related emissions. More than 90 % of this contribution is attributable to the metals and salts used, in particular copper, nickel and chromium. The amount of emissions is significantly influenced by the thickness of the applied metal layers.
Summary
The surface finishing industry is at a critical turning point where it will need to both adapt to increasingly stringent regulations on hazardous substances and meet sustainability targets. The trend towards innovative, sustainable technologies, such as Cr(VI)-free solutions, underlines the industry's commitment to environmental responsibility while maintaining performance.
With ambitious sustainability targets and a growing demand for transparent sustainability metrics, the need for harmonized assessment methods is becoming increasingly urgent. The successful transition to advanced technologies will not only reduce the health and environmental risks associated with traditional processes, but will also pave the way for a more sustainable future for surface finishing.
By integrating these changes, the industry can play a central role in achieving broader sustainability goals in the manufacturing industry, contributing to a cleaner and safer planet.
The article is based on the presentation "Carbon footprint and sustainability of plating on plastics" at Oberflächentage 2024.
