New reds hit the market: Dr Gerd Koen et al explain how two innovative rubine pigments take DPP...

For thousands of years, natural raw materials were the only source for dyeing textiles paints. In Europe in 1800, about 30 substances for generating colours were traded, including exotic raw materials, such as indigo from India, redwood from Brazil, and a range of tropical resins and oils. It

Although these early synthesised pigments featured bright colours, the resistance to light and weather of most of the colours was disappointing. With the technological progress of the 20th century, however, entirely new materials conquered the world, and colorants had to keep up with them.

The production methods and conditions of use of automotive coatings or plastics, for example, required pigments for coloration that offered special fastness.

The solution was the development of high-performance organic pigments, which are convincing across the board: with brilliant shades yet extremely stable in high temperatures and chemicals of different kinds, and resistant against sunlight, wind, and weather.

DPP pigments are versatile in their applications. One of the most important high-performance pigments for red shades is diketopyrrolopyrrole pigments (DPP pigments). Chemically spoken, the basic composition of DPP pigments consists of two annellated five-membered rings, both of which contain one carboxylic acid amide group.

DPP pigments were discovered in 1974 by the American chemist Donald G. Farnum and developed at Ciba SC. Ever since, the market for the high-performance red pigments has grown continuously; today it is estimated at 2,000 metric tonns worldwide.

With DPP pigments, shades from orange red to vibrant red and red-purple can be generated. The pigments stand out by their versatility and their balanced properties, which allows them to be used in many applications.

Today the DPP pigment with the Colour Index P. R. 254 is the most important pigment for single-coloured red automotive coatings. DPP pigments are equally suited for industrial and powder coatings, and they are increasingly used for the pigmentation of architectural paints. Applications in plastics include the coloration of polyolefin and all sorts of consumer goods. Only after the protective patents expired in 2003, did Clariant have the opportunity to produce these high-tech pigments.

Highly automated plant

In view of the patent expiration, Clariant built a new facility especially for the production of DPP pigments. The plant was inaugurated in October 2004 after less than 18 months of construction. The production process was integrated into the existing HPP 1 facility at Clariant's site in Frankfurt-Hochst, Germany. The process engineering at the plant can be divided into the following steps:

1. Production of an amylate solution for the following pigment synthesis

2. Pigment synthesis: reaction of ester with nitrile, resulting in the formation of an alcohol

3. Finishing of the raw pigment with heat and solvents for quality optimisation

4. Filtration: separation of the solid pigment from the liquid reaction suspension; removal of salts and other by-products

5. Drying of the wet pigment paste

6. Confectioning: grinding and packaging of the pigment powder.

Parallel to each individual step, the solvents are recycled and reused in the process. The yield is in the range of the production of polycyclic pigments and corresponds to the latest technology levels.

In the construction of the new plant, 15,000 metres of pipes were used, which connect 119 different installations. The plant includes 1,100 measuring points and 41,000 metre of cables, which guarantee optimal process control and monitoring, as well as the compliance with the highest safety standards.

Currently the highly automated plant is laid out for an initial production capacity of 200 metric tons annually but it can be adapted to market needs at any time, providing Clariant with the infrastructure to supply the market with the needed amount of high-end red pigments in the long-term.

Vibrand red

Initially five pigments will be produced at the new DPP plant. They are a high-performance addition to the portfolio of the Pigments & Additives Division and perfectly fit in the existing range of products. In the range of Colour Index 254 the Pigments & Additives Division is adding three high-performance pigments.

Hostaperm Red D2G 70 is especially suited for the pigmentation of OEM automotive finishes and refinishes, as well as plastics coloration. Hostaperm Red D3G 70 is recommended for industrial coatings and printing inks. PV Fast Red D3G is a high-value pure red pigment that was specially developed for polyolefin coloration and food packaging. This brand will shortly be also available as a non-dusting and easy-dosing granule under the trade name DrizPearls[R] Red D3G. Two innovative rubine red DPP pigments

In addition to the three red pigments, two innovative rubine pigments with significantly improved properties for coatings will also be manufactured at the new plant: Hostaperm Rubine D3B and Hostaperm Rubine D3B-WD.

The bluish red pigments with the Colour Index 264 are highly transparent and offer excellent fastness properties. Compared to existing rubine pigments based on DPP chemistry, these pigments not only show more colour strength--the specially modified surface of Hostaperm Rubine D3B also improves the rheological properties (Table 1) and significantly increases the resistance to flocculation. The main areas of application are automotive effect shades, where the pigments are combined with aluminum bronzes or mica pigments. Table 2 summarises the technical data of the two pigments.

With the two new rubine pigments, Clariant is also pursuing the concept of twin pigments, taking DPP chemistry a step further in a new direction. While Hostaperm Rubine D3B is ideally suited for solvent-based coating systems, particularly for environmentally friendly high-solid coating systems, the same coloristic properties can be achieved with HostapermRubine D3B-WD in water-based systems.

The incentive to develop these twin pigments came from the fact that two fundamentally different automotive coating systems are being used worldwide: solvent-based high solids and aqueous base coats.

Due to the different pigment wetting and stabilisation, if conventional pigments are used, the results can differ significantly, depending on the coating technology. This can cause a problem if a shade of an aqueous OEM base lack needs to be recreated in a high-solid refinishing coating. In the past, the only solution was a tailored surface refinishing. The new twin pigments, on the other hand, come in two supply forms--one for solvent-based, and one for aqueous coating systems. They allow a simple transfer of a shade from one system to another.

Sophisticated printing

The high-performance DPP pigments are also suited for high-value printing applications where brilliant red shades with excellent fastness properties are needed. Important areas of application are: aqueous decorative gravure printing (decorative furniture panels, decorative laminate flooring), metal printing, packaging printing, and silkscreen printing.

Another area of application is the colour filters of Flat Panel Displays (LCD) in the new generation of television sets and displays. These pigments are currently in the introduction and development phase at Clariant, where they are being tailored to the requirements of each individual application.

Summary

With the addition of five new high-performance red pigments, including two rubine pigments with improved properties, the Pigments & Additives Division of Clariant shows its outstanding innovative power. A highly automated plant, built with the latest technology, gets Clariant ready to supply the market with high-performance red pigments for years to come. The potential of the new red pigments is far from being fully explored. The development of tailored DPP pigments for sophisticated printing jobs and colour filters, to be launched by Clariant in the near future, will be only one of many more innovations to come out of DPP chemistry.

Table 1. Hostaperm Rubine D3B- Rheological behaviour
in different binder systems.

Mill Base Vscosity (50/s)   Plate-Cone   Viscosimeter

Alkyd mekamine              0.32         Pas
Polyester                   0.23         Pas
High solid                  0.08         Pas

Table 2. Technical data Hostaperm Rubine D3b and Hostaperm
Rubine D3B -WD

                             Hostaperm         Hostaperm
C I Pigment Red 264          Rubine D3B        Rubine D3B-WD

Density                      1.40g/cm3         1.40g/cm3
Specific surface area        58m2/g            61m2g
Main article size            54nm              58nm
Fastness to acid             5                 5
Fastness to alkaline         5                 5
Heat resistance              200[degrees]C     200[degrees]
Colour depth 1               1:11.8 TiO2       1:11.8 TiO2
Colour depth 11              1:121 TiO2        1:118 TiO2
Fastness to solvent (PV)     5                 5
Fastness to butylglycole     4-5               4-5
Fastness to xylene           5                 5
Fastness to MEK              4-5               4-5
Fastness to butylacetate     4-5               4-5

Bernhard Ehrenreich, Clariant GmbH, Pigments & Additives Division, Head Marketing Printing Email: bernhard.ehrenreich@ clariant.com

Dr. Leonhard Unverdorben, Clariant GmbH, Pigments & Additives Division, Head Product Management HP Polycyclics Email: leonhard.unverdorben@ clariant.com

Jochen Ahrens, Clariant GmbH, Pigments & Additives Division, Head Marketing Plastic Email: jochen.ahrens@clariant.com

Dr. Gerd Konig, Clariant GmbH, Pigments & Additives Division, Head Technical Marketing Coating Email: gerd.koenig@clariant.com