ProXL
ProXL
In the automotive refinishing industry, a clear coat is a transparent paint finish used as a topcoat on car body panels or components that have previously been painted.
In this blog post, we start by looking at why we apply a clear coat on top of car paint (also known as the colour coat). We then talk about the different types of clear coat and how application and performance determine why one type of clear coat may be chosen above others.
There are two reasons why it’s common practice to apply a clear coat lacquer after a colour coat: aesthetics and protection.
The composition of a clear coat is designed to add depth and lustre to any car paint finish. This is particularly noticeable when a clear coat is used on metallic and pearlescent paint finishes.
When special paint effects such as colour blends are applied to car bodywork, this can sometimes result in inconsistencies in the microscopic finish of the paint surface. A clear coat applied over these effects ensures a uniform finish over the entire panel or car body.
Clear coats are also used to modify the gloss level of the finished result, ranging from an extremely high gloss to a satin or even totally matte finish.
While originally only used for finishing plastic car parts such as bumpers and trim, a matte finish for the entire vehicle has become popular.
A clear coat gives triple protection to the colour coat on a car – mechanical, chemical and climatic.
Without the clear coat’s protective layer, the relative softness of a colour coat makes it more susceptible to light scratches and chips, which can be harder to repair if they are in the colour coat. Clear coats are generally harder, with good anti-scratch properties, and if the clear coat is blemished it can often be lightly sanded and recoated without disturbing the colour coat.
Clear coats – particularly 2K (two-component) clear coats – also provide excellent resistance to chemicals that vehicles are exposed to, including traffic film and fuels, tar specks and road salt, detergents and other car cleaning chemicals.
The climate is also harsh on car body finishes, with the most destructive element being the ultraviolet (UV) radiation that naturally occurs in sunlight. Many clear coats contain ingredients that help to block the harmful effects of this radiation, in a similar way to sunblock for our skin.
A 1K clear coat contains only resin solids dissolved in solvents. As the solvents evaporate on contact with air the solids congeal and harden. Generally speaking, 1K clear coats are easier to apply.
2K clear coats also contain resin solvents and solvents but are mixed with a chemical hardener immediately before use. This causes a chemical reaction that permanently hardens the clear coat, resulting in a harder, more chemically resistant finish.
While clear coats are traditionally solvent-based, environmental and health concerns have driven technological advances in water-based clear coats which contain lower amounts of volatile organic compounds (VOC) than solvent-based clear coats.
A relatively new innovation, UV-cure clear coats are VOC-free and remain workable for longer periods as they rely on concentrated UV light to cure, rather than air evaporation or chemical reaction.
All clear coats consist of solids and liquids. The liquids – often solvent or water-based – evaporate during the drying process, leaving the clear resin solids as the finished topcoat. If a clear coat has a higher solids content the topcoat will be thicker after drying and fewer coats will need to be applied to reach the required total thickness.
UHS clear coats contain the highest levels of solids and therefore offer excellent coverage and short drying times. Their lower solvent content also means they comply with environmental legislation regarding volatile organic compound (VOC) emissions. Many UHS clear coats require a low-viscosity hardener to maintain good flow during spraying.
With a lower percentage of solids present, HS clear coats tend to flow more easily than UHS clear coats but are also more likely to need additional coats to build the required thickness.
MS clear coats have the lowest proportion of solids. This means they require multiple layers to achieve the required thickness, but on the plus side they are easier to apply.
While most clear coats are versatile in their use, differences in their formulation mean that some are a better choice than others in certain applications.
As we have already seen, the high solids content of UHS clear coats allows them to reach the required thickness with fewer coats.
Fast and ultra-fast drying clear coats are more commonly used for partial or spot repairs rather than full body resprays. They can often reduce or eliminate the need for heat-accelerated drying, reducing energy usage.
For more information, advice or details on the ProXL clear coat product range, call 01634 823900 or contact us via our online contact form.
