Making the world a brighter place with innovative pigments

Paul Boughton

Colour has always played an important part in people's lives. As far back as cave drawings, pigments were the medium used to express a state of mind, to decorate and communicate.

After the dawn of the new millennium, a renewed emphasis was placed on the joy of colour. Objects and buildings, and indeed our entire surroundings, are becoming more and more colourful. New applications require new types of pigments, which in turn call for new technologies. At the same time, tighter legalisation dictates environmentally safe procedures.
The search for innovative solutions to the two demands of market forces and environmental law leads to the development of innovative colours.

The correct pigment choice

Choosing the correct pigment for an individual application is what makes a successful coating. Gloss, colour space, durability, chemical resistance and aesthetic appeal are all influenced by the choice of pigment. In simple terms, pigments can be classified as inorganic and organic. The inorganics include extenders, titanium dioxide, coloured, functional, metallic and effect pigments. Organic pigments are split into three categories of classical, high value and high performance types.
All pigments however, share a common characteristic in that they are insoluble in the application medium. Pigments are marketed as powders or pigment preparations. Pigments in powder form need to be dispersed to at least their outer limits to achieve gloss, stability and colour, but pigment preparations merely need to be stirred into the bulk medium and homogenised. The basic characteristics of organic and inorganic pigments can be seen in Table 1.
The application behaviour of pigments is not only determined by their chemical composition. Important physical parameters, such as crystal modification, mean particle size, surface treatment, particle size distribution, shape, specific surface area, surface character, optical properties, rheology and dispersion characteristics also have a decisive influence on their subsequent area of use.
For this reason pigment manufacturers must regulate their process in such a way that the resulting products, though of the same chemical composition, exhibit individual physical properties. The product must be optimised from the beginning of the development process onwards, and the end use must always be kept in mind.

Significant developments

The main developments in classical pigments took place during the first half of the 20th century and very little has changed since. In the second half of the century, more chemically advanced pigments have been developed to comply with more demanding applications.
A large number of inorganic pigments are still extracted from the earth's crust, and contain impurities that are expensive to remove. For example, natural iron oxides, including raw sienna and burnt umber, are probably the oldest pigments in use today. Synthetic equivalents are available, but they tend to have different properties from those of their natural counterparts. The most recent significant development in organic pigment technology was diketo-pyrrolo-pyrrole chemistry (DPP) in the 80s. The advantages of this type of pigment are excellent weather resistance and heat stability, with generally intrinsic high colour strength and high saturation. These high performance pigments are often used for automotive coatings, which must be of the highest quality.

Getting the best properties

To obtain the best pigment properties, and as a result, produce the ideal paint, a number of factors must be taken into account. One of the main properties of a pigment is ease of dispersion. As the particle size is reduced during dispersion, more surface area is exposed, resulting in increased viscosity. Ease of dispersion is becoming an increasingly important differentiator for paint manufacturers. A pigment that has the same or similar characteristics as a competing product is more attractive if the rheology of the ill-base is lower at equal pigment loading. Furthermore, higher pigment loading enables paint manufacturers to make a mill-base of more highly concentrated pigment levels, allowing them to reduce this expensive manufacturing process an additional benefit, VOC emission levels are reduced.
Another important issue in pigment selection is its performance in both water based and solvent based paint systems. Ideally the pigment should perform well in both, but in reality, this is not always possible.
A pigment that performs well in one manufacturer's system may not work in another, depending on the technology used.
The modern pigment manufacturer is faced with the challenge of developing pigments that are compatible with both systems, because regulations concerning VOC emissions from paint applications and manufacturing facilities are becoming increasingly stringent and it is all too likely that further legalisation will be imposed on the industry.
Water-based coatings have been around for many years, but because of tougher government regulations they are rapidly gaining importance in today's finishing industry. Many current users of solvent based coatings will be forced to switch to a more compliant coating in the future. Many of these manufacturers and end users will switch to water-based coatings, trying to make use of as much of their existing equipment as possible.
It is possible to change from solvent-based to ater-based systems. However, even though ater-based coatings are basically applied in the same way as solvent-based, certain factors must be taken into account. The system's metal components must be compatible with water-based materials because of the risk of rusting and corrosion over time when in contact with water. All components, including pumps, valves and piping, as well as the atomiser itself, have to be made of materials that are compatible with water-based coatings.

Low-emission alternatives

As legalisation tightens, environmentally compatible solutions become even more important. Besides ater-based systems, powder coatings are also becoming increasingly popular. They do not produce VOC emissions and are therefore environmentally safe. The powder is applied electrostatically onto the object and then cured, making the use of solvents redundant.
This technology has advanced by leaps and bounds in recent years, and today low film builds can be achieved. Problems with control of film builds can arise and scientists are currently working on this area. Results appear promising.
Lower VOC levels and cost savings are also the driving forces behind the development of UV cured coatings. The coatings are applied to the substrate and then cured with ultraviolet radiation.
UV curing is one of the most rapidly growing technologies in the coatings, graphic arts, adhesives and related industries. The system allows a dramatic increase in production line speeds and produces coatings with superior environmental resistance and better gloss. They also have excellent stain and adhesion resistance.

Driving forces

The European paint market is in a transitional phase. Large organisations are diversifying, either merging with or buying other companies in search of higher profit margins. Small to medium-size paint companies may seize the opportunity to move into niche areas passed over by the multinationals.
All businesses, large and small, are governed by the three overriding issues that determine success -- costs, technical quality and environmental impact.
Cost control is always a key factor for any company. High technical quality and performance are essential for success in this highly competitive market, and as legalisation becomes even more stringent, environmental issues take on an increasingly dominant role in the development of pigments. A balance between these three factors is crucial for the successful pigment and coatings manufacturer.

Pressure to innovate

The new millennium demanded a further component for success: Innovation. The paint and coatings market in Western Europe is forecast to grow by over twopercent, and new fields of application are constantly arising. Pigments and the technologies behind them have to keep up.
Developments from Engelhard include the new Cyclo luster pigments.
These are white pearlescent, titanium dioxide coated pigments delivering unique value, flexibility and styling options for powder- coating formulators. They help eliminate the potential build-up of pearl pigment on spray gun tips, which enables formulators to increase the amount of pearl pigment in their formulations by up to 10percent. This offers more flexibility to formulators attempting to match the colour of liquid coatings and new styling options in metallic anodised finishes. These pigments are offered in three different particle sizes, and as well as an interesting colour space they are designed for easy incorporation into formulations by dry blending under typical conditions used in the powder coating industry. Cyclo pigments have a surface treatment that provides better charge compatibility with multiple powder coating resins. This reduces separation concerns due to charging differences, tip build-up and spitting, which are typically seen when untreated Ti02 coated mica pigments are used in a dry blend powder application

Colours and trends

Developing a pigment is a major challenge. Colour trends have to be evaluated and put into practice quickly. Producing a quality coating for the automotive industry requires the highest technical skills, but at the same time producing the ain-colour' on schedule can mean the difference making a car the most popular in Europe and allowing a promising opportunity to slip by.
In automotive coatings there is a current trend towards atechno' colours, such as silvers, golds and red effects.
But the vehicle colour crown in Europe still rests securely with silver. The 2004 model year finds that silver ranked as the most popular vehicle colour for the sixth consecutive year, according to the annual global colour popularity survey conducted by PPG Industries. Silver topped all other colours among European vehicles produced in 2004 with 35.4percent, up from 33.6percent in 2003.
Silver also led global colour popularity with 38percent for the 2004 model year. Research conducted by PPG in France, Germany, Italy, Poland, Scandinavia, Spain, Portugal and the United Kingdom reveals that for the 2004 model year, blue was Europe's second most popular colour with 16.1 per cent of vehicles produced, followed by black at 12.5percent and white at 11percent. The naturals colour family -- which includes gold, copper, champagne and lighter shades of brown and yellow -- was featured on 9.2percent of vehicles, while red came in at 8.5percent and green at 7.2percent.

Globally, white was the second most popular vehicle colour in 2004 with 15.4percent, followed by black with 13.9percent, naturals at 9.3percent, blue with 8.9percent, red at 6.9percent, green with 6.3percent and others just over onepercent.
It is not just the automotive industry that needs to react promptly to current colour trends. Objects around us are becoming more and more colourful, creating new opportunities for the industrial and decorative market. Driven by ideas from fashion magazines and house design programmes on television, the general industrial and decorative paints sector is focusing more strongly on imaginative use of colour. In an effort to be different from their neighbours, consumers want to decorate their homes with deep, rich, novel colours.
The recently developed Lumina pigments from Engelhard offer exciting new effects. These pigments literally change colour when viewed from different angles. Engelhard's newest metallic-looking pigments, Lumina Russet and Copper special effect pigments, offer increased chromaticity, advanced colour purity, and more brilliance and hiding capability. They produce copper and rouge-tone looks through a tight mica particle-size distribution and an exclusive multilayer coating technology. Lumina Russet and Lumina Copper pigments are also available with Engelhard's proprietary CFS chrome-free treatment for exterior applications.

Meeting higher standards

For the general industrial and decorative paints sectors, new shades present a challenge, but the standards required for these types of coatings have become more stringent as well. While slight colour discrepancies and low performance in coatings for buildings, bridges and industrial machinery were tolerated in the past, today general industrial coatings must show more consistency. Coatings need to have good resistance to weather, chemicals and pollution, whilst still remaining affordable. Higher performance pigments are required.

Bright new future

Today's European market demands colourful, high tech, innovative and environmentally compatible coatings. The immense challenge for pigment chemists and paint manufacturers is to meet these demands whilst still remaining cost-effective. Colours for the future will be bold and user-friendly, driven by trends in fashion and new technologies.
Technical innovation in pigment production and use will produce exciting new colours that will make the world around us a brighter place.

Cornelius is based in Bishops Stortford, Hertfordshire.