Figure 1

Paint chemists are naturally influenced by the colour of the raw materials they use for their binder formulations. Therefore, yellowish or, even worse, brownish-coloured raw materials are perceived as inadequate to formulate many pale-shade coatings. The paint chemist could, therefore, not approach technical problems with an open mind. This is particularly the case for primer formulations that will be top-coated with pigmented coatings, thereby hiding the colour of the primer.

Table 1

Phenalkamine curing agents, derived from the cashew nutshell liquid1, are good performance products for protective coatings. Phenalkamine-based coatings are used successfully in marine, civil engineering and transportation primer paints. Despite their outstanding anti-corrosion properties, phenalkamine-based primers can be wrongly perceived as poor quality due to their colour. Even if some improvements were brought to that technology, the Gardner colour of commercial phenalkamines remains quite high (Table 1). A Gardner colour of 10 is regarded as too high compared to a conventional polyamide epoxy curing agent having a colour of about Gardner 7 (Figure 1).

Figure 2

New Very Light-Colour Phenalkamine

Recent development in phenalkamine technology has led to a new, very low-colour phenalkamine, even lower in colour than a commercial polyamide diluted with either 10 or 30 % xylene (Figures 1 and 2). Actually a 4 Gardner colour is achievable.

This new phenalkamine, named LX 5307, is a light-colour version of LITE 2001S90 from Cardolite. The colour improvement is illustrated in Figure 3. Cure speed of Cardolite LX5307 is identical to its counterpart LITE 2001S90 (Figure 4).

Figure 3

New Phenalkamine - Advantages/Disadvantages

The paint chemist can now formulate primer with phenalkamine having a very light colour. Properties of the primer will be exactly the same as by using the coloured versions.

Unfortunately, to make these low-coloured phenalkamines, one has to use a more sophisticated process, leading to higher production costs. As a consequence, the price of such products will be orders of magnitude higher than their coloured counterparts.

Figure 4

There is, therefore, a trade-off for the formulator: either to increase the formulation cost tremendously or to use higher-colour cheaper versions.

The question is: is it really necessary to use a low-colour curing agent for a primer? However, such innovation by a leader in the technology, if not at first sight very useful commercially, sets up the basis for future promising developments in -curing agent chemistry.