New Clear Part I: Understanding
Scratch-Resistant Clear Coats
By Kevin Farrell
There has been much talk recently regarding the newer scratch-resistant clear coats. Some are very new and some are a few years old already. However, they are here
to stay, and auto manufacturers will be producing more and more cars with this newer clear-coat technology. In this series of articles, we will try to demystify the technology, and offer some advice on wet sanding and buffing the scratch-resistant clears.
Although not bulletproof, the scratch-resistant clears do hold up well to light scratches, stay cleaner (as they do not let as much dirt penetrate the surface), and some of them actually “heal” or remove light scratches when left out in direct sunlight. It may seem that these clear coats will put detailers out of business, but that’s not the case. They still need care and they will still need to be buffed out when imperfections get deeper into the surface.
A LITTLE CHEMISTRY
I hated chemistry as a student. It was confusing and really kind of boring. So in an effort to educate and not have you turn the page out of sheer boredom, I will try to keep this simple. When a clear coat is being applied, it needs to react with something to become the hard, shiny finish that you see on most new cars. Some manufacturers use a 2K or two-component system that starts to react and crosslink when the two components are mixed together. If you combine this with heat or baking in an oven, the clear coat crosslinks faster and to a higher degree, creating a hard and tough surface.
The problem many car manufacturers had years ago when they were using a different version of a harder clear coat called a Melamine clear, was that it was very brittle and was susceptible to stone chips. It also did not weather very well. If the vehicle was in a climate with drastic temperature changes, it would have problems with its elasticity and it could eventually crack. It also was not very etch resistant, meaning that acid rain would penetrate the surface and etch the clear, as would bird droppings, tree sap, etc. So this version of clear coat gave way to softer versions that had more elasticity, more gloss, more etch resistance, retained a better gloss over a longer period of time, and held up better to weathering. The downside with the softer clear coats was scratching and marring. They just do not hold up very well to any kind of scratches.
But now, with the newer technology, we are back to harder, more scratch-resistant clear coats that meet the car manufacturers’ requirements on everything previously mentioned.
Okay, here’s the technology. I needed David Ghodoussi of Optimum Polymer Technologies, the people I work with at BMW North America, and other paint chemists to “dumb this down” for me so that I could follow. Hopefully I’m passing it on in simple-to-understand language.
Many of us have heard that most clear coats use a polyurethane technology. It’s basically a form of plastic, but with more elastic capabilities. The way they get there is to combine an isocyanate (difficult to understand and no need
to explain) with an acrylic polyol (also difficult to understand and no need to explain). These two components make up the 2K in the two-component clear. However, the new scratch-resistance technology adds something — a hydrogen bond. The hydrogen bond allows some thermo plastic flow making the clear more flexible to relieve stress, prevent chipping or cracking, and also to actually “self heal” — kind of repair itself. What helps in the hardness of this clear coat is the level of crosslinking of the two components as well as baking it to further increase the hardness. Many of the scratch-resistant clears are baked at about 280 to 290 degrees for about 20 minutes to achieve full curing and crosslinking. A factory-baked scratch-resistant clear coat can sometimes be very hard and truly a challenge to buff and/or wet sand.
These clear coats have a tighter crosslink density. Think of it like tying your shoes. If your shoes are loosely tied, there will be larger gaps between the laces and a greater distance between the
two halves of your shoe. The shoe will also be very loose. If you pull your laces really tight, there will be very little distance between the halves, and the shoe will be much tighter. This also creates more surface tension. The surface becomes harder as a structure and much more difficult to penetrate. This is another reason why these clear coats are more difficult to scratch, etch, or mar. It’s also a reason why they seem to stay cleaner. Dirt cannot penetrate as easily, and that keeps the surface brighter and cleaner.
Some versions of these clear coats are called reflow scratch-resistant clears. I didn’t quite understand this terminology — “reflow” to me means that any heat I create will soften the clear. You may ask, as did I, how can a clear coat that is supposed to “reflow” and be more elastic also be hard and scratch resistant at the same time? I assumed a technology such as this would make it softer, much like the clear coats of the 90s and early 2000s.
IN A REFLOW CLEAR
| The 3-series BMW on the left has a medium-hard version of scratch-resistant clear coat. The BMW on the right has a non-scratch-resistant clear coat. You can’t tell by looking at a vehicle what type of clear coat it has.
I am sure some of you are as chemistry-challenged as I am, so hopefully I’m keeping this explanation of how it works simple. When the two components mix, they start to crosslink and that adds structure and strength. The urethane structure gives the coating good chemical and weather resistance, as well as hardness, toughness, and elasticity. A unique aspect of polyurethane chemistry is that the hydrogen bonding acts as an additional crosslink, but also allows for the thermoplastic flow to relieve stress, not chip, and enables self-healing of minor (yes, minor) scratches.
The basic structure of a polyurethane clear coat features a soft segment, based on the polyol, which gives it flexibility and elasticity. There is also a hard segment that has high urethane density, which gives the coating hardness and toughness.
I was able to understand this because of my hockey experience. Who knew? I play both ice and roller hockey. Obviously in roller hockey the skates have wheels. They are also made of a urethane, more like rubber (this will be important to remember when we get to wet sanding this stuff). They grade the wheels based on what surface you are skating on. Some wheels need to be very hard and some need to be softer for a particular surface. They grade the hardness or density of these wheels by a measure called durometer, a term I needed to understand to get the correct set of wheels on my skates. The higher the durometer or density, the harder the wheels will be. Some of the denser wheels are hard as a rock, and they take much longer to wear. They are more brittle and have much less flex. The softer wheels have a lower durometer. They wear very quickly, but have great grip.
Almost sounds like some of the different versions of clear coat, doesn’t it? Clear coats can be made with harder durometers or softer durometers and that will also determine the scratch resistance. All of this combined will give the clear coat a level of scratch resistance, yet at the same time it will have a “reflow” effect and make it self-healing. To fully understand the theory of scratch resistance, we must know what types of scratches this clear can self-repair or heal. Only a lighter scratch or a mar in the clear, which would be a typical wash scratch or small abrasion that does not result in whitening, will be able to be self-healed. When the clear coat gets a deeper scratch, it will show up as white. This is the chemistry in any clear coat. When the scratch is white, the clear coat has been “fractured.” This type of scratch will not be self-healing. A light mar or scratch that only “deforms” the clear coat can technically self-heal and repair itself (sometimes only to a certain degree) when heat is induced and it reaches a certain temperature. It will reflow and “theoretically” flex and contract and significantly improve the scratch or make it disappear.
A key scratch or a deep white scratch are examples of the clear coat being compromised and “fractured,” and thus not able to self-heal or reflow. More conventional buffing methods or possible wet sanding would be needed to improve or eliminate this type of scratch. But there is more. There is still another totally different type and chemistry of a scratch resistant clear coat.
CERAMI-CLEAR OR NANO-PARTICLE CLEAR
This is another clear coat that PPG developed for Mercedes a few years ago. This type of clear coat has slightly different technology and properties compared to the reflow and high-crosslinking scratch-resistant clear coats. In this system, PPG uses nano (very small) particles of ceramic, which is obviously a very hard material, to gain its scratch resistance. Here the nano particles of ceramic migrate to the very top portion of the clear coat, usually within the top 3 to 5 microns. It’s not a very dense layer, but is effective at giving the same type of scratch resistance to similar marrings as the other versions of scratch-resistant clear. In other versions of this clear coat, made by other paint manufacturers, a particle called “fumed silica” is commonly used and incorporated into the clear the same way.
This clear coat is very hard at the top where the hard nano particles migrate. However, once this layer is broken, the clear coat becomes much softer and has very little scratch resistance below. There is no consensus on which version of clear coat is better or, for that matter, which company makes the best version of a scratch-resistant clear coat.
HOW DOES THIS AFFECT CAR WASHING?
Cars with scratch-resistant clear coats are much easier to wash than cars without because of the clear coat’s extreme hardness and self-healing capabilities. The newer scratch-resistant clear coats have a higher surface tension and are much “tighter” and less porous, resulting in not as much dirt penetrating the paint. Much of this dirt will be easier to wash off in an automated wash, or by detailers who need to prep a car before detailing.
There should also be fewer claims of damage at automated washes as the clears are more scratch resistant and the chances of damaging this surface are far less. The clear coat is brighter — a good wash should make the overall appearance of the vehicle that much better and satisfy more customers in that regard.
So the good news about a much harder clear-coat surface is that it is easier to keep clean and will look cleaner after washing. This is what the car manufacturers were looking for while creating this new technology. However, car washes and detailers trying to wet sand or buff these clear coats, especially with an orbital buffer, will have a much harder time, as we will discuss in upcoming issues.
WHOSE CLEAR COAT IS THE HARDEST?
I wish I knew the answer. Both scratch-resistant clear coat versions on the market can be found in factory finishes as well as refinish products. Some are harder than others. The more confusing issue is that even within one company — that is using scratch-resistant clear coat across the board — some clears will be harder than others. Sometimes it’s tough to tell which brand a manufacturer is using. All auto manufacturers have several plants where their vehicles are built. Some of these plants use one brand of clear coat, while the rest use another. BMW uses at least three different brands of scratch-resistant clear coat on cars made in Germany. All have different characteristics and varying levels of hardness. The same is true at General Motors.
You may ask, “Why don’t they use just one brand?” or “Why are they all so different?” Having to work on so many different versions of clear coat just makes our jobs as detailers that much more
difficult. As long as a paint manufacturer meets or exceeds the factory specifications on scratch resistance, elasticity, gloss, etch resistance, etc., the various scratch-resistant clears are approved for use. Some of these clear coats may just meet the hardness requirement and scratch resistance spec, and some may far exceed the requirement. This leads to different paint systems that will not buff out the same way even though they are all termed scratch-resistant clear coats.
While a scratch-resistant clear coat will be harder to mar, it will still need correction at some point. This is where it becomes interesting. In upcoming issues of Auto Laundry News, we will discuss wet sanding and buffing of these scratch-resistant clear coats and why different methods and products may have to be used in the process.
Kevin Farrell owns and operates Kleen Car (www.kleencarauto.com), a full-service auto-detailing business located in New Milford, NJ. Kevin is also an instructor for a detailing program he developed for, and in conjunction with, BMW of North America. His background includes auto dealership experience and training through DuPont, General Motors, and I-Car.