Frequent automatic brush washing can be detrimental to vehicle paintwork, the scratching and minor abrasions caused by rotating plastic brushes leading to considerable gloss reduction over time. Add road dust and grit into the watery mix and they literally take the shine off automotive topcoats.

Now, innovative, independent British paintmaker, HMG Paints of Manchester, has developed a self-healing topcoat system, which actually recovers from scratches and blemishes, restoring the original shine. Called Recover and believed to be unique in its formulation, this self-healing, highly scratch-resistant coating is ideal for the bus and coach market, where vehicles typically go through brush washes every day, as well as truck and automobile finishing and refinishing applications.

Recover is a clear 2-pack isocyanate cured polyurethane coating, which is spray applied over any HMG basecoat system, available in virtually any colour. Not only is this remarkable coating self-healing, it is also 'water clear', which means no slight yellowing effect, highly accurate shade matching and excellent colour retention.

"Most bus and coach operators are highly image conscious, as are many CV fleet owners, and like to have their vehicles looking pristine on the road," says HMG's Sales & Marketing Director, Stephen Falder. "We believe there is tremendous market potential for this product, which represents a genuine technical breakthrough, and have already trialled it successfully with bus companies and manufacturers. Experienced professionals looking at six month old paintwork actually believe it's newly resprayed. Yet there will be no significant cost premium on this two-component PUR coating."

As one of the last independent British manufacturers of automotive coatings and a leading supplier to the UK bus and coach industry, HMG Paints is continually researching and developing new paint systems at its Collyhurst Road site. In order to come up with a solution to an age-old market irritation, the degradation of gloss finishes caused by brush washes, the company's R&D department recently conducted extensive laboratory testing of scratch-resistant automotive clear coats, in the process developing the formulation for Recover.

Automotive clear topcoats are required to possess a number of performance characteristics, including toughness, durability and excellent resistance to chemicals and scratching. Market experience has shown that polyurethane (PUR) coatings based on aliphatic isocyanates are superior to conventional finishes in this respect, although even with these coatings there is traditionally a compromise, in that any increase in scratch resistance was generally accompanied by a decrease in chemical performance.

However, HMG's paint technicians reasoned that, given the many options for modifying the chemical structure of PUR coatings, there was a great deal of scope for further performance optimisation. The company then conducted an extensive series of tests to determine the detailed characteristics of scratch resistance at all stages of binder and coating development, using image analysis techniques and microhardness measurements.

Since existing studies showed that scratching of vehicle bodies in automatic brush washes is primarily caused by sandy dirt particles, this process was recreated in a laboratory brush wash simulator by adding quartz sand to the water and washing test panels coated with various 1K and 2K polyurethanes, then examining the results. Scratching subjects the coating to considerable localised mechanical stress and any recovery starts shortly after stress removal, due to the viscoelastic deformation behaviour of polymer networks, known as 'reflow'.

Such in-depth analysis led to the formulation of Recover, a flexible, yet tough and durable 2K PUR coating, which possesses optimum chemical and scratch resistance characteristics, as well as inherent self-healing or 'reflow' properties. This self-healing nature allows the paint film to recover and obscure any minor marks and scratches caused by mechanical washing, within a time period of anything from 5 minutes to an hour or so, depending on severity.

To demonstrate this effect, HMG has even produced sample Recover-coated panels, which technical and sales personnel can abrade with Scotchbrite pads and allow customers to see the coating recover before their eyes. HMG's Recover can be sprayed with conventional or HVLP equipment, then force cured at up to 60ºC, with drying times comparable to conventional 2K PUR coatings.

HMG Paints has also developed appropriate polishing techniques for this unique clear coat, in association with automotive specialists Autoglym, Farecla and 3M.

Further enquiries to:
HMG Paints
Riverside Works
Collyhurst Road
Manchester
M40 7RU
Telephone 0161 205 7631
email sales@hmgpaint.com