Europe Reports

Advances are being made in UV curing technology

By Sean Milmo | March 19, 2007

A new plasma technology is allowing topcoats of automobiles to be UV cured.

Ciba Specialty Chemicals claims that it is close to commercializing with two equipment manufacturing partners a plasma technology which allows the UV curing of the topcoats of automobiles. It believes that the breakthrough could radically change methods for applying OEM coatings.

The three companies have been doing development work on the process in a pilot unit for over a year. These trials have been so successful that Ciba reckons the technology can move to the next stage of full-scale application on a car production line. It is planning to demonstrate the process at the European Coatings Show in Nrenberg, Germany, in May.

"We are in close contact with a big German car manufacturer, which may start the process on a small-series model in late 2008 or early 2009," said Hermann Angerer, head of Ciba's coating effects operation at the company's annual result press conference in Basel, Switzerland, in February. "We believe this is a technology which could revolutionize coatings in the OEM industry."

The main obstacle to the introduction of UV curing in painting of car bodies is that conventional radiation curing systems have to be applied to flat substrates. With three-dimensional surfaces, large areas cannot be reached by the UV light waves.

In other sectors like wood coatings, 3D curing with UV radiation has been achieved by using different sources of energy than lamps. Approximately 18 months ago, Tikkurila, Kemira's coatings business, introduced in partnership with BASF a process for 3D curing of furniture with UV from inert carbon dioxide (CO2).

UV curing of coatings on automobile bodies has posed a major challenge because of their shape and size and the need for speed in a fast moving OEM paint shop.

With its two partners Roth & Rau AG and Duerr Group, both of Germany, Ciba has developed a technology in which ionized plasma gas in a vacuum chamber provides the source of the UV radiation. The plasma is induced by microwaves to discharge intense UV waves which surround the car body uniformly. As a result, unlike with conventional UV systems, there are no shadow zones.

Because of its versatility in the structure and modification of surfaces, the plasma process has the added benefit of not only curing the coating but of also upgrading its properties.

"This is a manufacturing process which is a big improvement on the conventional long drying line for heat curing of top coatings," explained Angerer. "The car body can move in and out of the plasma vacuum within a matter of minutes.

"It also considerably improves the properties of the coatings in terms of scratch and chemicals resistance with which the results are really outstanding," he added. "Car companies will not have to worry so much about the need to gain more scratch resistance from their coatings."

Another attraction for automobile manufacturers is that plasma curing has low energy use with reduced CO2 emissions and a low level of other pollutants because it avoids the use of solvents.

"Car companies want their paint shops to be more environmentally friendly," said Martin Riediker, Ciba's chief technology officer. "They don't want coatings which emit volatile organic compounds (VOCs) and they want water-based or solvent-free systems which in the final stages can be UV cured. Our innovation enables them to replace the traditional heat-curing process for top coats with a technology which has lower costs and energy consumption and overall is more ecologically compliant."

Roth & Rau, based at Hohenstein-Ernstthal, develops and manufactures equipment for the application of plasma and ion beam technologies. One of its main activities is the making of plasma process equipment for the photovoltaic sector, in particular systems for the plasma enhanced chemical vapor deposition (PECVD) of silicon nitride anti-reflective coatings of solar cells.

It has been providing technologies with microwave-sourced high plasma densities and low process pressures. These can combine a high degree of ionization with low ion energy so that there is little possibility of damage to substrate surfaces. The new plasma curing system for automobile coatings has had in the pilot stage a microwave-excited process gas with a low pressure of only 0.06 millibars.

Duerr Group, Stuttgart, is one of the world's leading suppliers of products and systems for automobile manufacturing, including the building and design of paint shops and final assembly plants.

Ciba is providing the chemistry for the curing of the coatings, derived from its long experience with additives for UV radiation, in particular photoinitiators. "In addition we are supplying the UV absorbers and the light stabilizers for the curing of what will be mainly acrylic-based coatings," said Angerer.

The strategy of the three partners will be to provide the technology to automobile manufacturers under a licensing arrangement which would also cover the supply of equipment and coatings additives.

In addition to the progress with the plasma curing system, Ciba also revealed that it is introducing to the market a new high performance pigment based on the technology for the red diketopyrrolo-pyrrole (DPP) class of pigments, which the company first discovered and developed over 20 years ago. The patents on the technology have recently expired so that Ciba's brilliant red DPP pigments are being exposed to strong competition from major rivals like Clariant and from Chinese producers. The main color of the new DPP pigment is orange but it also has a dark rubine red variation. The pigment has high levels of light, weather and solvent fastness.

"The big advantage of the pigment is that it is protected by patent although it is DPP-based," said Angerer. "It also shows how we are able to rejuvenate our portfolio of colors."

A major market for the new pigment will be OEM coatings in which Ciba says the plasma curing technology will enhance its performance, although it is not disclosing yet how this can be achieved technologically.

The introduction of the new pigment and the plasma curing system should together considerably bolster Ciba's position in the automobile coatings market after it lost its exclusive rights to the red DPP colorant.

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