The EU directive (2004/42/CE) limiting the volatile organic compound (VOC) (which have a boiling point of less than 250 ° C in normal air pressure) emissions of construction coatings will come into force in two phases, the first in 2007 and the second in 2010. This directive will categorize paint products according to their area of use, and the strict VOC specifications for the paints will cause some products to either disappear from the market or be modified to meet the new limitations. These specifications do not affect the colorant itself, but the coloured, ready-to-use paints instead. This in fact puts more demand on the colorant producers, who have to meet both the paint legislation requirements and anticipate the modifications to the paint products. The main objective is that the colorant should not affect the paint properties or increase the VOC content of the paint.

VOC Limitations

Table 1 describes some of the VOC limitations according to the EU directive for paints and varnishes. As we can see from this table, the strictest limit for waterborne paints is 30 g/L, while for solventborne paints, categorized as trim paints, it is 300 g/L. Since waterborne, low-VOC or totally VOC-free paints are already dominating the interior paint sector, there is only slight or no pressure to effect changes in this area. In general, solventborne paints are more critical, especially alkyds, where the VOC directive is forcing paint manufacturers to lower the VOC content or go to waterborne applications. Therefore, changes in paint composition are expected, and this is also a challenge for colorant producers.

In addition to this VOC directive, there are also several market-specific requirements and eco-labels that will set even stricter limits, not just for VOCs, but for several other raw materials such as biocides and formaldehyde as well. One example of a local eco label is Blaue Engel in Germany.

Solutions From Colorants

Conventional colorant technologies, where glycols are used, are seen as reliable and easy-to-use technologies. Equalling this performance in low- or zero-VOC colorants is possible not only by concentrating on colorant technology development, but also by modifying the environment where the colorants are used, including, for example, the tinting machines and biocides used in them. Universal colorants, which are suitable for both water- and solventborne decorative paints, have for a long time been the preferred option for point-of-sale tinting, due to their simplicity of usage at the shop level. VOC-free, universal colorant technologies have existed for more than 10 years. These colorant technologies are well accepted in northern and central Europe and are also supported by several innovations from the tinting machine technologies, such as humidifiers. The main concern about continuing with these technologies is maintaining the wide application area, which ranges from masonry products to interior and exterior paints and alkyds. The anticipated changes in the alkyd area might affect the suitability of the colorant for these new or modified alkyd paints.

In some cases, universality is seen as a compromise; colorants can have an effect on paint properties, especially if the paint is not well adjusted to the colorants. These changes in paint properties are mainly seen in the solventborne paints, where colorants can prolong the drying time of the paint and change the gloss level or film hardness. In addition, some other product groups, such as masonry paints, may also require special colorants due to the requirements for water repellence, for example. Product-specific technologies are also preferred if the paint producer has decided to focus on certain paint products (e.g., only waterborne paint).

The development of alkyd colorants that meet the 300 g/L limit faces big challenges, since the paints are still under development. First, the colorant has to be compatible with the paint products and, secondly, the colorant rheology has to be good in order to be used in the tinting equipment.

CPS Color has developed a new version of the alkyd colorant technology that meets the VOC requirement for 2007 (400 g/L). This new alkyd range consists of 12 colorants and is based on alkyd resin and aromatic-free solvents.

In addition to this, some colorant versions containing even lower amounts of VOC (less than 300 g/L, thereby meeting the 2010 limit) have been developed and tested.

Test Results

CPS Color tested four different colorant technologies in several alkyd paints. The properties tested were:

• compatibility of colorant with the paint;
• effect of colorant addition on paint drying;
• effect of colorant addition on paint film hardness;
• effect of colorant addition on paint gloss.

The results presented in Figures 1-4 are based on phthalo blue and yellow oxide colorant. However, several other colorants and alkyd paints have also been tested. The colorant technologies tested were:

1. Conventional, glycol-containing universal;
2. VOC-free, universal;
3. Alkyd, based on aromatic-free solvents; and
4. Alkyd, low VOC, based on aromatic-free solvents
a. Phthalo blue has less than 400 g/L VOC
b. Yellow oxide has less than 300 g/L VOC.

The colorant additions used in the test series were: 10 vol% in clear base paint and 2 vol% in white base paint. The compatibility of the colorant with the paint was found to be good in all the test cases, and the addition of colorants had no significant impact on drying times.

Film Hardness

Figures 1 and 2 show the effect of colorant addition on paint film hardness. Alkyd 1 is a conventional alkyd paint with a relatively high VOC content. Alkyd 6 meets the 2010 requirement with a VOC content of less than 300 g/L.

All the colorants have quite similar effects on paint film hardness. As can be seen in Figures 1 and 2, the film hardness of Alkyd 4 is the most affected, and all the colorants have an effect on that paint.

Gloss

All the colorants have quite similar effects on paint gloss level. As Figures 3 and 4 show, the biggest changes in gloss level are seen in Alkyd 3 and 5.

Conclusion and Future Challenges

There is a clear need for both universal and product-specific colorants. VOC-free universal colorant technologies are well proven and widely used. The new alkyd colorant technology with low-VOC content behaves in a similar manner to conventional alkyd colorant technology.

One of the challenges for colorant producers is to keep up with the changes in paints, while ensuring that colorant technologies are suitable for both current and future needs.

This paper was presented at the Nürnberg Congress held during the European Coatings Show, Nürnberg, Germany, May, 2007 and organized by the Vincentz Network. See events@coatings.de.