Base Coat Clear Coat (BC / CC) Paint System
Original equipment manufacturers (OEM) supply a specification to their paint suppliers that establishes a minimum film thickness necessary to ensure paint durability and enable them to provide a guarantee
• E-Coat ~33 µ (1.3 Mil) - an anticorrosion coat applied to both sides of the steel to prevent corrosion
• Primer ~18 µ (0.7 mil) - Initial protection layer with texture to assist the pigment layer in bonding to the metal beneath
• Base Coat ~15 µ (0.6 mil) - The basecoat is usually 0.5 to 1 mil thick
• Clear Coat ~48 µ (1.9 mil) - The clear coat provides gloss plus physical protection from the elements, including ultraviolet (UV) radiation, which is situated in the upper 1.0 – 1. 25µ (0.04 - 0.05 mil)
All paint has three major components: a pigment for colour and hiding powder; a binder that holds the pigment to the surface; and a carrier to maintain the pigment and binder in liquid form.
Polishing alleviates a myriad of paint surface problems. But use abrasive polishes wisely to maintain paint condition and to resolve surface damage problems. But know when to seek alternative methods of damage control and avoid over polishing with harsh, abrasive polishes.
Clear Coat
A clear coat system consists of one or more primer layers, a flat colour layer and a glossy, clear top layer. The primer is a corrosion inhibitor and a bonding agent for the bare metal and the colour layer. It prevents corrosion and provides a stable substrate for the colour and clear coats. The colour layer is applied to the primer and is typically very thin. Its only purpose is to provide colour. The clear coat is two to three times the thickness of the colour layer, adding to the appearance of paint depth and offering additional protection.
Specific gravity [: the specific gravity of water is 1.0 if an object or liquid has a specific gravity greater than one, it will sink. If the specific gravity of an object or a liquid is less than one, it will float]
Density (or specific gravity); different materials usually have different densities, so density is an important concept as less dense fluids float on more dense fluids if they do not mix, causing it to rise to the top (we have Archimedes to thank for this discovery)
OEM paint specifications usually require the addition of ultraviolet absorber technology in their clear coat systems for protection against photo degeneration (sun fading).
Titanium dioxide, also known as Titanium oxide or Titania, chemical formula TiO2 is the naturally occurring oxide of titanium, when used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. It has a wide range of applications, from the ultra violet protection of automobile paint to sunscreen to food colouring.
There are a couple things that should be realized; auto paint or chemical companies don't state the amount of ultra violet protection is in their clear coat, nor do they tell you what the specific ultra violet stabilizing chemical is in most cases.
Most automotive ultra violet (UV) absorbers are very durable and exhibit a 5 year half-life, meaning that every five years the concentration is reduced by 50% percent.
UV absorbers have a greater specific gravity than clear coat resin (1.15 g/ml for instance) which is heavier than water (0.80 g/ml) and much higher than the solvents used so there is reason to believe that it migrates throughout the clear coat. On the other hand fumed silica (CeramiClear) is low (less than 1.0 g/ml) and therefore migrates to the top of clear coat as the solvents evaporate and the paint cross-links and hardens.
Modern Isocyanate resins (clear coat) finishes are so good today that they lull people into thinking that vehicle paint has protection and shine when in reality there is not really much there, the clear coat that has a thickness of ~25.4 µ (micron). As a point of reference a sheet of copy paper is 89 µ.
A micron (µ) is a metric unit that equals one millionth of a meter, or 1/1000 of a millimetre. A micron is much smaller than a Mil. A human hair is about 2 Mil (50 µ) thick and individual bacteria are 0.1 mil (2.5µ). There are 25.4 millimeters in an inch and a micron is 1/1000 of a millimetre.
Using the micron (metric) measurement system gives you a much better idea of paint thickness as the numbers used are so much smaller. Most detailers are or should be aware of how thin clear coat paint is and it puzzles me why people over-polish paint causing it to fail prematurely
Abrasive Polishing
Polishing alleviates a myriad of paint surface problems. But use abrasive polishes wisely to maintain paint condition and to resolve surface damage problems. But know when to seek alternative methods of damage control and avoid over polishing with harsh, abrasive polishes.
There are two considerations; how much clear coat and how much ultra violet protection can be removed, they are not interchangeable. The following is the maximum allowable clear coat reductions the major USA car manufacturers will allow before the paint warranty becomes void-0.5 Mil (12µ)
Order of Magnitude (~ Thickness)
• Standard printer copy paper 7.5 µ (0. 3 Mil)
• A standard sandwich bag 28µ(1.1 Mil)
• Dollar ($1) bill 73.5µ(2.9 Mil)
0.2 Mil (0.5 µ) is the maximum paint that they are allowed to remove on the assembly line at the factory during their paint sanding and polishing process to remove dirt nibs. This number is based on testing carried out at both General Motors (GM) and Chrysler testing centres.
Wet-sanding, compounding and polishing the amount of paint removed with a mild abrasive was ~ 0.1 mil (0.25 µ) this does not mean that the clear coat will fail if you remove 0.5 Mil (12µ)
There are many factors involved and each car plant may have a unique paint system that is designed for their specific needs and the thickness varies from one plant to another so there is no way to make such generalizations. One thing is for sure that if you keep removing clear coat, at some point you will experience strikethrough
The clear coat provides gloss plus physical protection from the elements, including ultraviolet (UV) radiation, which affects the upper level of a cured clear coat. Most car manufacturers will only allow ~ 25% of the clear-coat thickness to be removed without voiding the paint warranty and long-term durability problems becoming an issue. That means that if you started off with 50µ of clear coat (this will vary by vehicle manufacturer) you would only be able to remove <12 a="" and="" having="" p="" paint="" possibly="" re-paint="" the="" voiding="" warranty="" without="">
Most light surface marring is ~1.27 µ (0 .05 Mils) a surface scratch that can catch your fingernail is ~1.01 µ (~ 0.04 Mils) Using a medium abrasive polish and a rotary polisher will remove approximately ~ 2.5 - 3µ (~ 0. 98 – 0.12 Mil) from the paint surface. To remove a scratch you need to level the paint to its lowest part, so if a scratch is 1 µ that’s the amount of paint (and UV protection) you need to remove to eliminate it. Note: 25.4 µ (micron) = 1 Mil
Using an Abrasive
Using a medium abrasive polish and a rotary polisher will remove approximately 2.5 - 3µ (0. 1 Mil) from the paint surface, which is typically four passes at 1500-1800 RPM; however many variables such as polish/compound and speed / pressure used that may affect the paint removed)
A paint thickness reading of 4 Mil < ( 100 µ (Microns) is reasonably safe for polishing. 3 – 3.5 Mil ( 80-90 µ) I wouldn't use anything stronger than > 2000 grit polish, 2.75 – 3.0 Mil (70-80 µ) > 2500 grit polish and under 2.75 Mil (70 µ) use a glaze. The readings tend to vary from panel to panel and are thinner towards the panel edges.
• 200µ + can be expected on older cars that have been hand painted or a re-painted vehicle
• 100 – 200µ 4 – 8 Mil - normal paint thickness
• 80 – 100 µ - 3 – 4 Mils, thin paint
• 80 µ < - less than 3 Mil, very thin paint
These numbers are offered as a guide only, as there are too many variables to provide any more than an approximation.
CeramiClear Coating
PPG’s CeramiClear clear coat is the first automotive clear coat to use nano particle technology in the final coating applied to car bodies, protecting the colour coat while providing a durable, glossy appearance. With the help of the nano-technology developed at the beginning of the 1980s, scientists have been able to alter the molecular structure of the binding agent and integrate tiny, microscopic ceramic particles. These each have a diameter of less than 20 nanometers, which makes them tens of thousands times thinner than a human hair.
During the electrostatic paint application process, it is sprayed just like a Melamine or Silane 2K clear; the key is what happens during the cross linking or curing of the clear. The hard "ceramic" particles rise to the top, just as the ultra violet (UV) inhibitors do, and concentrate there and the binding agent particles float around freely at first in the liquid paint. Removing the top layer of clear coat it has been observed by some detailers that the paint is less dense (softer) and paint removal is no longer a linear process
Clear Coat
The clear coat is the coating layer that forms the last interface to the environment. It carries the biggest part of the technological performance and must be able to resist ultra violet radiation, environmental etch, bird droppings, car wash machines and other outside influences.
Be cognizant that clear coat thickness and composition will vary in accordance with the OEM assembly plant, paint specification, paint type (solvent or waterborne) and paint supplier and any additives used i.e. ultra violet stabilizers, Isocyanate hardener and catalysts
Base Coat Clear Coat – two stage paint; base (colour) coat and clear coat were adopted as an automotive industry standard in 19982, clear coat paint was originally used to protect metallic paints that are subject to oxidation and provide depth of colour.
BC_CC paint systems do not oxidize in the same way as single stage paint does, but they are subject to clear coat failure. They are applied over the primer and covered by the clear coat layer to protect it from the environment.
There exist three main base coat systems in the paint shops of the automotive industry worldwide: medium solids (MS) high Solids (HS) Water-based (waterborne) (WB) paints are essentially low solids paints (up to 60% waterborne solvent), but they are legal because de-ionized water is used as the solvent, as opposed to volatile organic compounds (VOC).
The main purposes of the solvent are to adjust the curing properties and viscosity of the paint. It is volatile and does not become part of the paint film. It also controls flow and application properties, and affects the stability of the paint while in liquid state. Its main function is as the carrier for the non-volatile components
Photo degradation
[: decomposition of a compound by radiant energy] a common reaction is oxidation.
Today’s water-based products have a number of obvious environmental benefits, but some are more susceptible to photo degradation (fading) over time, a significant drawback. In addition, because of ozone depletion, higher levels of solar ultra violet (UV) radiation now reach the surface of the earth. This further contributes to the rate of fading.
Polymers use in auto paint, plastics and vinyl, where they are routinely exposed to sunlight; the UV radiation adversely the mechanical properties of these materials, often causing structural failure, which limits their useful life.
Paint Thickness
A paint thickness reading of > 100 µ (Microns) is reasonably safe for polishing. 80-90 µ, I wouldn't use anything stronger than< 2000 grit polish, 70-80 µ <2500 70="" a="" and="" any="" are="" edges="" from="" glaze.="" grit="" p="" panel="" polish="" readings="" seams.="" tend="" the="" thinner="" to="" towards="" under="" use="" vary="">
• 200µ + can be expected on older cars that have been hand painted or a re-painted vehicle
• 100 – 200µ - average paint thickness
• 80 – 100 µ - thin paint
• < 80 µ - very thin paint
Paint Removed by Polish or Compound
Using a medium abrasive polish and a rotary polisher will remove approximately 2.5 - 3µ (0. 1 Mil) from the paint surface, which is typically four passes at 1500-1800 RPM; however many variables such as polish/compound and speed / pressure used and etc that may affect the amount of paint and ultra violet protection removed
If you have reservations about the amount of paint surface removed or the amount of paint remaining the use of a paint thickness gauge (PTG) is arbitrary. There comes a point when you must judge wither removing a scratch will compromise the clear coat and / or UV protection, if so you’ll have to ‘live’ with the imperfection
.
Paint thickness will often depend upon the OEM paint specification, which can vary by vehicle assembly plant. It’s interesting to note that painters must now demonstrate proficiency with an electronic paint thickness gauge in order to become certified to perform paint refinish warranty work for General Motors Corp. (GM) vehicles
Order of Magnitude (Thickness)
• Standard printer copy paper 76µ (3Mil) thick.
• A standard sandwich bag 28µ(1.1 Mil)
• Dollar ($1) bill 73.5µ(2.9 Mil)
These numbers are offered as a guide only, as there are too many variables to provide any more than an approximation.
Notes:
1. The elongation (elasticity) of paint enables it to move in tandem with the metal as it expands and contracts due to environmental temperature fluctuations; for this reason note the paint temperature when taking readings as they can vary in accordance to the surface temperature.
2. Measure your paint thickness in a very cold environment, then measure it when the paint surface is hot to the touch, you may find it varies by as much as a 2µ(microns)
Paint Insurance
The newer coatings available like synthetic polymers are a cross-linking thermoplastic, its cross-linking process attaches the polymer with covalent bond that becomes part of the surface of the material it is attached to, which in effect becomes a secondary protection for the clear coat, in fact a relatively inexpensive (when compared to repainting) renewable sacrificial coating.
Silica (AQuartz) or reactive resin hydrophobic coatings (OPT Opti-Coat™); think paint sealant that has greater durability and scratch resistance (9H) something that also provides a self-cleaning protection, with a durability on a timescale measured in years rather than months, these coatings add a measurable protection of 2-3 µ microns to the clear coat.
Opti-Coat™ is not a nano particle; it is rather a pre-polymer that cross links and forms a continuous film on the surfaces it is applied to, similar to a single component Isocyanate that forms a clear coat finish. It is very resistant to alkaline car wash concentrates as used by car wash spas and tunnel wash companies
The coating is very low maintenance and requires cleaning less often than conventional paint protection products. Provided the surface is kept free of abrasive grime, bird excrement or other acids, the coating should last for around two years. Coating longevity will be improved if the paint surface is cleaned on a regular basis, and only with either normal pH car care concentrate shampoo or a citrus degreaser.
After Care
To enable a vehicle to maintain its value original paint that is in good condition is an asset. People are
keeping their vehicles an average of nearly nine years.
Making you client aware of how to wash and dry a paint surface while inflicting the least amount of damage will help to avoid the need to overly polish the clear coat to remove scratches and the subsequent loss of both clear coat and ultra violet paint protection.
The main point of this article is to inform detailer that there is a very limited amount of clear coat and to keep them from over polishing and unnecessarily removing their clear coat and ultra violet (UV) protection.
Providing this kind of value added-value services will enhance your reputation and enable you to become the source for both ethical service and high quality work. As with the successful sale of any product, educating the customer is the key.
Summary
The main premise of this article is inform detailers that there is a very limited amount of clear coat available and to keep them from unnecessarily removing their clear coat. New polymer technologies are now available to add clear coat to the existing layer without the need for an expensive re-paint and at a fraction of the cost.
Depending on the resin technology, these clear coats can be more resistant to scratch and marring, more resistant to chemical etching, and more resistant to oxidation, therefore minimizing the need for polishing. Even if you have to polish it off at some point, you can always add a new layer without removing the thin layer of factory clear and avoiding the possibility of premature failure of the paint system and the need to repaint.
Bibliography
1. UV Protection and Coatings for Plastics in the Automobile Industry - Paint & Coatings Industry (PCI) - http://www.pcimag.com/…/uv-protection-and-coatings-for-plas…
2. “Protecting UV-absorbing Clear Coats from Sunburn," Polymers Paint Colour Journal, February 2000
References
1. Distribution of Stabilizers in Multi-Layer-Coatings and Plastic Coatings - 3rd International Coatings for Plastic Symposium, Troy, MI, June 2000.
2. Potential Reasons for Yellowing of Coatings over Plastic Substrates - 4th International Coatings for Plastic Symposium, Troy, MI, June 2000
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