AMS visits Ingersheim to speak to the company's technical director, EMEA, about the challenges facing coatings specialists in light of new body materials and the rise of electric and autonomous vehiclesWilliam BrunatNick Holt (NH): How much of a challenge will multi-material vehicles present in the future?William Brunat (WB): There are two areas that present a challenge. Firstly, the electro-coat pretreatment; we need to have a homogenous appearance and avoid inconsistent coating on different substrates. So we have to develop pretreatments that can clean and treat all the substrates [in vehicle structures]. Today, it is expected to be able to treat cold-rolled steel, hot-dip and electro-galvanised steel, and aluminium using the same dip tank.

Magnesium is another material that is likely to be used in the future and there have been some [coating] trials, but it is difficult as it’s not easy to remove the magnesium oxide or electro-coat the surface. So we need to adapt the treatments and coatings. Plastics are also a challenge. If they are part of the body-in-white then we need to be able to clean them and treat them without damaging the surface. Twenty years ago, we were only developing coatings to go on to bare steel and hot-dip galvanised surfaces – but not any more.

Also, the pretreatment coatings are moving away from phosphate-based formulations to thinner, zirconium-type chemistries such as Zircobond. These are more sensitive to the type of substrate, so we have to take this into account in the development process. The paint industry as a whole is dealing with the challenge of moving away from phosphate-based formulations, which generally offer a thicker coating compared to the newer, environmentally friendly formulations. For the electro-coats, the conductivity of the substrate plays a role; for example, when you move from a cold-rolled steel to galvanised steel you get a difference in surface conductivity. Some electro-coatings were prone to providing different thickness in these cases. So we had to completely reformulate for that.

The next big challenge for electro-coats will be CFRPs [carbon-fibre-reinforced plastics]; these are conductive but it’s hard to get a class-A surface [finish]. If you put 20 microns of electro-coat on it, you will still see the surface texture of the carbon fibre. It might require these parts to be primed and then mounted on the body. So there is work to be done on this.

That’s for the coatings, but the other big challenge with multi-material bodies is with the adhesives and sealants. These need to stick together all the different substrates and provide the correct mechanical performance. Cleaners are also involved in this because of the different types of protective oils and oxides that need to be removed, so it is very complicated.

"Twenty years ago, we were only developing coatings to go on to bare steel and hot-dip galvanised surfaces – but not any more"– William Brunat, PPG

NH: Are there any vehicles currently in production that are especially challenging in this respect?WB: A few years ago, you could have singled out a [small] number of vehicles but now the situation is much more stable. Ten years ago, when applying an electro coat to two different substrates it wasn’t unusual to get a coating of 15 microns on one and 25 microns on the other. Because of the developments we have made, the worst you might get now would be a difference of one or two microns. Because exterior panels can come from different suppliers, you need to ensure a consistent finish with the electro-coat. We have not only developed and adapted the formulations but also the application processes, for example with new voltage profiles for electro-coat.

NH: Do you collaborate closely with other companies regarding coatings and application processes?WB: We have regular meetings with the application technology companies to ensure that we are not developing paints that can’t be applied with the available technology and vice-versa. We also collaborate closely with the substrate suppliers (steel manufacturers, etc). We get samples of new steel grades – for example, press-hardened steel that has a special coating, not galvanised – and we are able to test coatings on the samples, and if there are any issues we can discuss the solutions together. It’s amazingly complex, with more vehicle launches, environmental constraints and controls on costs.

NH: PPG’s solution to the challenges of LIDAR-equipped vehicles uses a special primer and topcoat, but are primerless systems feasible in these cases?WB: In primerless (compact) systems, for most colours we use two-coat basecoats and we can still use these where reflectivity is a problem. The first basecoat would be white to be infrared-reflective, the second coat would be the modified colour but using an infrared-transparent pigment. The compact process is over ten years old and is now the standard in the industry; the next big step will be low-temperature curing, using temperatures down to 80-90°C. This will mean the chemistries will need to be different.

NH: Is the Performa data an IoT/I4.0 application for paintshops?WB: Yes, the idea is to collect data that is available but [currently] not being consistently processed or analysed. We then use a Six Sigma analytic tool to look for any ‘bad’ trends so we can optimise processes and become more proactive rather than reactive. Avoiding unnecessary downtime is vital and by combining material, application and paintshop expertise we can support improvements in the process.

Inside PPG Ingersheim

The process and application line is an important part of PPG's Ingersheim facility in Germany. It features a working paintbooth and curing oven very similar to the type used by vehicle-makers, but in this instance somewhat shorter in length and with paint robots on only one side of the booth. Application manager Sven Rell explains that PPG aims to recreate exactly the same environment used by its automotive customers so that the paint application tests (and results) are accurate in every way. To this end, the company has developed a special adapter which enables it to fit different air bells to the robots, helping to replicate exactly the paint application system used in any plant. This is challenging but key to customer support and product development.

One of the company's latest developments for automotive applications is an easy-clean clearcoat that acts to repel dirt and water from the paint surface leaving little or no residue, and which requires only a rinse with clean water to restore the shine. The idea is to create finish that requires less maintenance and keeps its appearance for longer. A crucial factor in this was the development of a new functionality in the resin structure of the coating.

PPG Ingersheim

The paint line at PPG Ingersheim is designed to replicate OEM working environments, to ensure accurate test results

A demonstration of this coating’s performance compared with the standard PPG scratch-resistant clearcoat shows a marked difference. A section of bodywork finished in the easy-clean clearcoat repels any liquids or dirt far more effectively than the standard finish. Although the company has developed this new coating to allow it to be easily integrated into existing OEM paintshop processes, it does potentially require some additional operations to be employed during the assembly phase. This product is still undergoing extensive field testing, for resistance to ultraviolet fading and to extend the lifecycle of the easy-clean properties.

According to Axel Nagel, manager for Technology Platform Clearcoat, the very property that enables it to resist liquids creates challenges with the adhesion of any components that need to be bonded to the painted body, such as windscreens. Affected areas require some additional form of process to allow the glue to stick, potentially adding further operations to the assembly process, and cost.

Preparing for electric and autonomous mobilityPPG is also developing environmentally friendly coatings for electric vehicle (EV) battery cells. Technical director William Brunat notes that all the coating layers on the surface of the average car together amount to around 300 sq.m, while a typical battery for a full EV has around 1,000 sq.m of coated surface. Currently, the internal structures of EV batteries use a toxic solvent (NMP) in the coating that is not environmentally friendly. The company claims that its new coating is NMP- and solvent-free and will improve the performance of the battery due to better adhesion and flexibility of this type of resin. It is said to help with the assembly of the battery, offering a more stable coating and increased durability of the electrodes, reducing the potential for delamination. Brunat also says that PPG is working on using graphene as a conductive element in these coatings in the future.

Interestingly, special coatings are also playing a part in autonomous vehicle technology in terms of visibility. Brunat explains that the LIDAR (light detection and ranging) systems employed to identify and localise other vehicles use a laser in the near-infrared spectrum (905nm) that is invisible. However, this light is not easily reflected by dark colours and if the laser light is not reflected back to the sensor, the vehicle’s systems cannot detect the dark-coloured vehicle. The issue is exacerbated by the fact that dark colours are a popular choice, apparently representing around a third of the vehicle parc. PPG’s solution is to use colour pigments that are near-infrared transparent, in addition to a near-infrared reflective white primer. The special dark pigments do not absorb the laser light, which is reflected back to the sensor by the white primer.

The company is also developing digital solutions. Performa is a new system that collects and analyses data from coating application processes in paintshops and helps to optmise the operations.