In the field of OEM paints, two technologies dominate today - waterborne basecoat systems and high-solid systems. Waterborne automotive OEM paints were first used at the beginning of the 1970s in some automobile production plants in the U.S. because of federal and state laws governing solvent emissions. Their chemical and physical properties were, however, not adequate in all climatic conditions, especially where water resistance is concerned. The reason for this was the fact that they were one-coat systems. Consequently, this technology fell out of favor in the United States and, in the search for ways of reducing solvent content, was replaced by NAD technology and later by high-solids NAD technology.

In Europe, ICI in the UK was the first company to tackle the development of waterborne paint systems in the early 1980s. This development was necessary in view of the low-solids two-coat systems used in the metallic sector, which had a basecoat with a solvent content of 80% and thus no longer met the more stringent legislative measures governing solvent reduction.

The revision of the clean air regulations governing solvent emissions was responsible for the introduction of waterborne paint technology in Germany. This technology was first used in the Bochum plant of Adam Opel AG in 1987 in the new painting line for metallic paints. Shortly afterwards came Volvo's switch to waterborne paints for metallics in Sweden.

In Europe, waterborne paint technology was given preference over high-solids technology. The reason for this was that the metallic effect achieved with waterborne paints is practically identical to that with the conventional low-solids systems. Initially, the use of waterborne systems was restricted to the metallic sector because it was still possible to meet the limit values of the clean air regulations with solid shades. Figure 1 shows the present situation concerning OEM technology in use in different parts of the world.

It can be clearly seen that in Europe waterborne technology has gained a high market share, keeping in mind that in Germany exclusively waterborne systems are applied.

In contrast, in the United States high-solid systems are still the majority, with 70%. In Japan, waterborne technology has just become an issue, but with increasing importance in the future. With the introduction of new technologies, new demands for the improvement of organic pigments concerning flow properties, flocculation stability and bleed resistance were raised.

Let us first look at the yellow organic pigments development history. Figure 2 clearly shows a never-ending story of development concerning the demands of the paint industry for nearly 100 years. Figure 3 shows possible improvement methods for either solventfastness and/or weatherfastness. Researchers were looking for new pigments, especially in the field of greenish- to medium-yellow pigments, because the existing organic pigments did not fulfill the demands for application in waterborne systems with respect to either bleed resistance or weatherfastness. This problem led to the development of a new product based on a new chromophore - Hostaperm Yellow H5G.

Looking at the existing green-shade yellows in the world market for automotive paints you see P.Y. 154, 151,138 and 109 having the highest consumption (Figure 4). Figure 5 shows the chemical structure of the newly developed pigment beside the above-mentioned products mainly for solid-shade applications.

Hostaperm Yellow H5G is based on a new coupling component including a new heterocyclic "quinoxalindione", which is responsible for the improvements. The existing pigments all had major restrictions when used in waterborne systems.

With P.Y.151 the pH value should never exceed 8.5 because of the free carboxylic acid group in the molecule. P.Y. 138 as well as P.Y. 109 must be considered borderline in terms of weatherfastness especially when used in pastel shades. P.Y. 154 has the requested durability but shows severe bleeding in the presence of the necessary cosolvents like butylglycol, which leads to a color shift when bleeding in the clearcoat, especially in lighter shades.

Only P.Y. 213 fulfills all the demands without restrictions for application in waterborne basecoat systems and high solids as well.

Figure 6 shows the existing greenish-yellow pigments for metallic application. The metal complex pigments P.Y. 129 and P.Y. 150 are very dull in solid-shade applications, whereas in combinations with aluminum flakes or mica pigments one can achieve very bright, greenish-yellow shades.

The suitability of P.Y. 129 in waterborne systems is restricted (Figure 7).

Next, I would like to cover the fastness to overpainting in greater detail. As already mentioned, waterborne basecoat systems are not completely solvent-free. They contain a few percent of hydrophilic solvents such as butylglycol, NMP or MP. These are more aggressive to pigments than xylene or butyl acetate, which are frequently used in solventborne systems. Usually, basecoat and clearcoat are applied "wet on wet"- the water of the basecoat has flashed off, but the solvent is still in the basecoat when the clearcoat is applied. During the subsequent baking cycle, the evaporating solvent carries some dissolved colored matter into the clearcoat. The degree of bleeding depends on solvent, its concentration, the diffusion resistance of the resin matrix and the temperature of the baking cycle (Figure 8).

When we looked at bleeding in waterborne basecoats, we adopted the wet-on-wet-method, but we applied a white, opaque, waterborne inter-coat between the basecoat and the clearcoat. This makes bleeding visible and it allows the colorimetric evaluation of bleeding. Bleeding is more obvious in pale shades than in deep shades, but our method also detects bleeding in deep shades, which would be hard to see otherwise. The method is to assess the color difference between Point A and Point B; for QC it is better to compare Point B with Point C.

Figure 9 shows the bleeding behavior of the mentioned products according to the described method at different baking temperatures. Figure 10 clearly shows the advantage of P.Y. 213, even at higher baking temperatures like 160 °C, over the other yellow pigments.

Pigment weatherfastness is one of the stringent demands for OEM applications. Figure 10 shows Florida exposure results in two different white reductions with TiO2 and a metallic application. This picture clearly shows the restrictions of P.Y. 138 and P.Y. 109 in paler shades or metallic applications when exposed in Florida. The latter-mentioned product shows severe darkening in deep shades and distinct fading in whiter reductions.

P.Y. 213 shows excellent opacity for a greenish-yellow pigment and a higher color strength than P.Y. 154. Heat stability of the new pigment is excellent - more than 200 °C depending on the system - so the product is ideally suited for powder or coil coating applications especially for long-term outdoor use. Figure 11 shows the overall performance of P.Y. 213.

This is what you might have expected from a new product designed to compete with the world's leading pigments. But it can do more - it opens new styling opportunities to the formulator of metallic shades. Normally, you would not think of using an opaque pigment in metallics. Everybody knows that if you use too much, you will kill the metallic effect, and if you use too little of the yellow pigment it is either not bright enough to color the aluminum or not good enough in weatherfastness. Hostaperm Yellow H5G has sufficient color strength and durability to be used at a 1:10 reduction level. Using it in metallics creates unique green to greenish-yellow shades, which give new life to this area of styling.

Figure 12 shows the color space coordinates of the mentioned high-performance yellow pigments.


Hostaperm Yellow H5G has been accepted by all major automotive OEM paint manufacturers. Major manufacturers of refinish paint decided to use this pigment as a key yellow pigment in their second-generation waterborne refinish systems. This was one example of our basic pigment research that led to the development of a new yellow, filling a gap in the line of existing pigments.


1 Geißler, G. Neue Hochecht und Wetterechte Organische Gelbpigmente, Farbe & Lack 83 (1977), No. 5, p. 391-401. 3 German Patent DE 197 33 307 (Clariant GmbH, Frankfurt).
4 Herbst,W. and Hunger, K. Industrielle Organische Pigmente, VCH, 2nd edition, 1995.
5 Geißler, G. "Von den Quellen der Farben", Hoechst brochure DP 7507, 1987.
6 Wang, D.; Schauer, T.; and Entenmann, M. Tendency to Bleeding for Organic Pigments, ECJ, (2000), No. 5, p. 52-58.
7 Europäisches Patent EP 911337 (Clariant Int. Ltd.).
8 XXV FATIPEC-Kongress Turin 2000, B.L. Kaul; Some Novel High Performance for High Value in use Coatings Application.
9 Wilker, G. New Pigment Developments for Automotive Coatings 21st Indian Paint Conference, Agra, Jan. 17 - 19, 2003.

This paper was presented at the 8th International Abrafati Congress, Sao Paulo, Brazil, September 3-5, 2003.