Cobalt free paint driers: ADDITOL® dry CF series

Air-drying paints have long played a pivotal role in the architectural coatings sector. Traditionally, Cobalt has been a staple drying agent for these paints, but its associated complications are nudging the industry towards other options. Europe’s impending cobalt regulations are intensifying the search for reliable alternatives to Cobalt.

Oxidation is key for the paint’s hardening and provides it with lasting durability. The synergy of these stages ensures alkyd paints perform as intended, with the balance between solvent evaporation and oxidation is crucial for a durable paint film.

Below is a brief overview of the chemistry of the paint drying process. It shows the importance of the autoxidation sequence, especially in alkyds:

The drying process of alkyd paints is a complex interplay of reactions. From oxygen uptake to hydroperoxide formation and the intricate auto-polymerization process. Metal driers drive these mechanisms, influencing drying speed and the end performance of the paint.

Comprehending these fundamental principles enables paint formulators and manufacturers to fine-tune their products, ensuring optimal drying times, enhanced performance and superior finishes across applications.

Selecting the correct transition metals as primary paint driers is crucial for optimizing paint performance and quality. However, the role of auxiliary drying metals is essential in fine tuning specific requirments of the paint drying process.

Cobalt, both as an element and in the form of various soaps such as borate neodecanoate complexes or neodecanoic acid complexes, has raised significant health concerns, particularly in relation to DIY paints available in home markets. These materials mentioned fall under Category 2, as per the H361 sanctions outlined in the European CLP regulation.

Moreover, Cobalt is anticipated to be reclassified as a carcinogenic material, falling under Category 1B classification (CMR) once the relevant progress is made in REACH and ECHA. This development presents another challenge as it would limit the permissible dosage of Cobalt in ready-to-use formulations to below 0.1 percent.

Extensive testing conducted in allnex in-house labs revealed that formulating paints with a Cobalt content lower than 0.1 percent is unfeasible. This reclassification would discourage paint manufacturers from using Cobalt in their formulations, leading to its phase-out in the EU. Other countries including the USA and China also have ambitions to eliminate Cobalt from future oxidative paint driers.

Cobalt polymers comply with current regulations such as CLP and CMR. However, from a marketing and sustainability standpoint, having cobalt as an atom in the polymer is a disadvantage. Another drawback is that higher dosages of Cobalt polymer are required to achieve the same efficiency as cobalt metal, leading to increased formulation costs.

Iron complex driers are well-suited for waterborne alkyd paints, but compatibility becomes challenging in solventborne high solid alkyd paints. Furthermore, Iron has a negative impact on the anti-corrosion performance of waterborne systems as it promotes corrosion. It’s important to note that both the first-generation Iron and Manganese replacement driers experience performance loss as the paint ages.

Manganese exhibits good color retention and acceptable discoloration rates, making it suitable for undercoats and primers. However, it may not perform as effectively in top coats.

In summary, while alternatives to cobalt exist, each option comes with its own set of advantages and limitations. Careful consideration is necessary to choose the most appropriate replacement based on the specific requirements of the paint application.

Allnex has developed innovative solutions that eliminate the need for cobalt by utilizing manganese as a complex metal in combination with a specific composition of various complexing partners, accelerators and ligands.

Additol® Dry CF100 and CF103 are both cobalt-free. These products incorporate a patented multi-acceleration system that addresses the initial drying stage (known as set-dry) by compensating for the inherent weaknesses of Manganese. These paint driers exhibit an exceptionally rapid polymerization rate, reducing the risk of skin formation and minimizing the need for anti-skin additives.

For applications requiring a high film build, allnex offers co-designed auxiliary driers ADDITOL® dry CF200 and CF300. These can be combined with Lithium, Barium and Zirconium to enhance the performance of the primary paint driers. This combination is beneficial for WB and HS systems, including UHS formulations. It has been successfully used in heavy-duty coatings and mid-duty corrosion protection, specifically in direct-to-metal applications.

By utilizing these innovative solutions from Allnex, manufacturers can effectively eliminate the use of cobalt while achieving superior drying performance in various coating applications. The choice of materials in the transition away from cobalt is ultimately in the hands of our customers and formulation partners. Our experts offer guidance throughout different stages of the cobalt exit process.

At present, allnex provide waterborne formulations that contain emulsified Cobalt materials. These serve as an intermediate stage in the cobalt exit strategy. Moving forward, we have phase two Cobalt polymeric driers that offer an alternative to traditional Cobalt-based solutions. These polymeric driers help bridge the gap between Cobalt-containing and Cobalt-free materials.

Above you can see the Cobalt-free materials in green. These materials represent the ultimate goal in our Cobalt exit strategy, providing effective alternatives without compromising performance or regulatory compliance. We remain committed to supporting our partners in making informed choices that align with their specific needs and regulatory requirements.

One of the crucial testing results pertains to the loss of dry effect over time. When a painted surface is left on the shelf, the driers in the formulation tend to absorb onto pigments. Interestingly, this absorption is particularly prominent with Titanium dioxide and inorganic pigments. This leads to a noticeable decline in drier performance.

Through our testing, we observed a significant disparity in drier performance between freshly produced paints and those subjected to elevated temperature storage for three weeks. This discrepancy underscores the importance of having robust drier performance in paints that have been stored for extended periods.

The specific test we conducted involved a modern high solid, long oil white alkyd paint (a paint system known for its unique characteristics). The paint was co-accelerated with Calcium and Zirconium, demonstrating the effect of our new driers on enhancing performance and maintaining efficacy even after prolonged shelf storage. By addressing the issue of dry effect loss, we strive to provide our partners with driers that deliver consistent and reliable performance throughout the paint’s lifespan.

When it comes to air drying alkyd paints, there are several crucial conditions and requirements for the drier. Here is a summary of the key factors:

Set dry and through drying: The drier must exhibit excellent performance in the initial set drying stage and the subsequent through drying stage, which is responsible for the paint’s hardness development.

Discoloration: As white exterior paint systems are commonly used, it is important for the drier to minimize any discoloration effects, ensuring the desired color stability over time.

Skin formation: Prevention of skin formation is crucial, as it eliminates the need for anti-skin additives. Future formulations should aim to minimize or eliminate this issue.

Compatibility: The drier should be compatible with both waterborne and solvent-based systems, allowing for versatile application across various paint formulations.

Anti-corrosion effect: Considering that many paint systems are applied directly to metals, the drier should provide effective anti-corrosion properties, enhancing the durability and protection of the surface.

Post-storage performance: The drier should maintain its effectiveness, ensuring that the paint retains its quality and performance even after being stored for an extended period.

Modern requirements: Meeting industry standards, such as low VOC or near-zero VOC content and a high flashpoint for safe handling, is essential. These aspects cater to environmentally friendly practices and ensure safe usage, particularly in applications like inks.

By utilizing the new Cobalt free driers with specific ligands, most of the requirements and conditions can be effectively addressed. These innovative developments offer superior performance compared to existing technologies. They provide a reliable and sustainable solution for air drying alkyd paints.

To the left is a brushable glossy white paint formulation. This formulation utilizes Additol CF-100 as the primary paint drier, along with a small amount of calcium as a sacrificial drier, which is a commonly used practice in the industry.

To the right is a modern direct-to-metal glossy anti-corrosion monolayer paint formulation. For this formulation, Additol CF-100 serves as the primary paint drier. To accommodate higher film thickness, we incorporate a Lithium/Zirconium mix as a secondary drier.

These guiding formulations demonstrate the effectiveness of the new Cobalt-free paint driers in achieving desired paint properties and performance. By incorporating these, formulators can create high-quality coatings that meet specific requirements.

Dosages play a crucial role for our customers, and the good news is that our Cobalt-free driers can be added at any stage of the process. The dosage requirements are remarkably low compared to Cobalt or Cobalt polymer driers. In fact, our Cobalt free paint driers require approximately 10 times lower dosages.

Formulators can achieve multiple benefits. Firstly, it helps reduce the overall cost of the formulation. Additionally, these driers contribute to improved paint performance. The use of Cobalt-free driers is particularly advantageous in the world of alkyd high-solid formulations, where slightly higher dosages may be required.

The ECOWISE™ CHOICE range of Cobalt-free driers offer a cost-effective solution, while maintaining excellent performance. The ADDITOL® dry CF range from allnex is the ideal choice for formulators seeking to optimize their formulations.

Let’s answer some of the most frequently asked questions about drying metals:

The following article is from a webinar between Daria Samonova (Corporate communications manager, allnex) and Bernard Hirschmann (Director of Global Business Development & Innovation for Additives, allnex). For the full presentation, please see the video above.