Working Report, 20/2006 – Substitution of cobalt driers in wood coatings

Substitution of cobalt driers in wood coatings

1 Introduction

Within the paint and varnish industry there is today a trend to reduce any use of dangerous substances. One issue is to reduce the use of cobalt driers in air-drying systems, due to cobalt in these compounds among others is appearing on the list of dangerous substances /1/ as being possible carcinogenic. The addition of driers to oxidative drying products, including alkyds, is essential in order to achieve satisfactory drying of these coatings. Today most oxidative drying products still contain cobalt driers, despite their environmental and health drawbacks, and even though there is a wide spread interest in the paint trade to substitute cobalt driers. The reason is that Co-driers are the most efficient driers available and that they are quite difficult to substitute.

Extensive substitution work has already been done to replace cobalt driers /2/. The work has shown that it is very difficult to find a general replacement for cobalt driers, but the work also indicated that some alternative drier products, especially manganese driers, could give a satisfactory drying time in some types of oxidative products. How successful a replacement of Co-driers will turn out depends partly on the alternative drier but also to a great extent on the nature and content of oxidative drying binder in the coating. The substitution of cobalt in high solids products is known to be especially problematic due to the high amount of oxidative drying binder. A thorough examination of the connection between drying time, binder type, and binder amount is desirable when using cobalt-free drier systems. This project was therefore initiated. The drying potential of several alternative driers, both manganese and vanadium based, has been evaluated in different alkyd binders with known variations.

By examining the influence on the drying of both the (alternative) driers and the alkyd, the possibilities in the substitution process of Co-driers will hopefully no longer only be a question of substituting the drier itself in existing coatings, but also modifying the alkyd binder to enhance the drying as much as possible when using alternatives driers.

The project and hence this report is divided into the following areas:

Selection of raw materials, hereunder contact to suppliers
Technical evaluation of the influence of the alkyds and the drier systems respectively on the technical properties
Optimization of product properties based on the choice of alkyd and drier system respectively

A working committee including Dyrup, EnPro, Sasol Servo and Cray Valley was established in the beginning of this project. Before the practical work was started a meeting between Dyrup, EnPro, Sasol Servo and Cray Valley was arranged to discuss what variables with regard to drying that were relevant to investigate, what samples that were needed and to create a basis for a detailed project plan. A second meeting was held were the screening results were discussed. The industrial partners have thus been involved during the whole project.

The practical work and technical evaluations was performed by Dyrup and EnPro ApS.

The Danish Environmental Protection Agency has contributed to the costs of this project,

We thank all participants for their contributions with regard to samples, planning and discussions.

June 2005