Due to the proposed limitations, diisocyanates have always been the focus of attention, and alternative crosslinking mechanisms have been sought in the focus of research and development. We talked with Lars Ossenschmidt, Worlée-Chemie's Technical Services Manager for Paints, Architectural and Industrial Coatings, on this issue and methods.

Polyurethane: Alternative cross-linking mechanism. Image source: roostler-Fotolia

What is the current status of the tightening of isocyanate labels?

Lars Ossenschmidt: Like any other hazardous substances, isocyanates should be handled safely by the user. REACH has proposed to limit mixtures containing diisocyanates. In order to deal with it correctly, it is recommended to conduct multi-level user training.

Given that these products are used in so many different fields, it may be necessary to train a large number of users. This expected complexity is prompting users to explore alternative products. Due to the excellent properties of the polyurethane used, it is of course difficult to find products with comparable or even superior properties. Our silane-functional polyurethanes contain urethane and urea groups to bridge this gap because they provide excellent performance without the need for isocyanates for cross-linking.

What alternative cross-linking mechanisms is Worlée developing?

Ossenschmidt: Since 2015, we have been considering the topic of alternative cross-linking mechanisms. In this case, we have studied various possibilities, but finally decided to stick to the sol/gel silane process. The reason is the necessary availability of raw materials, the basic applicability of the technology and the ease of implementation in our production process.

In addition to being able to use our knowledge in the synthesis of basic polyols, it soon became apparent that it makes sense to further strengthen the polymer backbone through urethane groups.

Can you talk about the balance between drying and processing time?

Ossenschmidt: The classic 2K polyurethane coating consists of the first coating component, which contains polyols with hydroxyl or amine groups. The second component is the corresponding isocyanate. The two components are mixed before application and then can react with each other. This reaction occurs within a certain period of time and is accompanied by an increase in viscosity. Depending on the reactivity, fast-drying coating systems can be obtained, however, their processing time is also very short, that is, their viscosity rises rapidly. The processing time here is usually between 1 and 24 hours.

Our silane-functional polyurethanes allow a certain degree of disconnection between drying time and processing time. After adding the catalyst, the reaction can start. This requires the silane groups to be hydrolyzed by moisture and decompose the blocking agent. This is an equilibrium reaction that only occurs quickly after application, not in the container.

It is possible to formulate coatings that exhibit very fast drying and crosslinking, but still have a long processing time. The typical processing time is between 24 hours and several weeks.

Which application areas are the solutions suitable for?

Ossenschmidt: As a manufacturer of adhesives and additives, we basically have a broad product portfolio suitable for various applications and cooperate with a large number of customers. Since our silane-functional polyurethane can be based on different polyols, such as polyester, alkyd resin, acrylate, etc., it can certainly cover a wide range of applications. Currently, these products range from industrial wood coatings and high-quality industrial topcoats for construction machinery and vehicles, to glass and tile coatings, paints, varnishes and wood oils.

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