Oxidation [: the loss of electrons or an increase in oxidation state by a molecule, atom, or ion]
Photo degradation [: decomposition of a compound by radiant energy] a common reaction is oxidation.
Ultra violet (UV) radiation exposure leads to gloss and colour instability (photo degradation or photo-oxidation) and surface fading stains. But before UV light can cause harm, it must first be absorbed. If it is not turned into heat or transferred to a nearby stabilizer molecule called a quencher, it breaks weak chemical bonds. This is the beginning of UV damage.
Some materials absorb UV radiation more readily than other materials. Materials that readily absorb (UV) radiation are quickly damaged...rubber, vinyl, gel coat fibreglass, and many other plastics.
When radiation is absorbed, it starts to break (cleave) weak chemical bonds, which leads to photochemical degradation (bleaching, (fading), discolouration, chalking, brittleness and cracking) all indications of UV deterioration. The bond cleavages resulting from UV absorption cause the formation of “radicals.” Each free radical can trigger a chain of reactions (in the presence of air), leading to more bond cleavages and destruction. These oxidising chain reactions require no further UV exposure, just the presence of air
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.
Photo-oxidation of polymers
Photo-oxidation (sometimes incorrectly described as oxidation) is the degradation of a polymer surface in the presence of ozone. This is a consequence of ultra violet (UV) radiation, which instigates a chemical change that reduces the polymer's molecular weight. As a consequence of this change the material becomes more brittle, with a reduction in its tensile, impact and elongation strength. Discolouration and loss of surface smoothness accompany photo-oxidation. Infra red (IR) radiation or high surface temperature significantly increases the effect of photo-oxidation by drying.
Clear Coat Oxidation - Failure
Acids enter the breach formed in the clear coat and attack the resin binder system, which accelerates the degrading of the paint film surface, eventually leading to oxidation and/or failure.
Ultra violet (UV) radiation is known to contribute to the chemical modification (oxidation) or drying out the polymers and the resin binder system of exposed paint surfaces resulting in loss of gloss. However (clear coat failure) results in colour change, chalking, flaking and eventually destruction of the paint film
Oxidation can appear as a dull and somewhat hazy, or `chalky' appearance to the paint surface, a paint film surface that is adequately protected with wax or a sealant actually has a lower surface temperature than one that is not.
A dark coloured vehicle parked in the sun can attain a surface temperature in excess of 200° F With both types of paint system the application of a Carnauba wax provides a sacrificial and easily renewable barrier against airborne contaminants, which means the wax is compromised not the paint system
The clear coat layer is extremely thin (1.5 – 2.0 Mils) it is not a solid coating and is to some extent porous, the top most layer of clear coat paint contains ultra violet (UV) protection. Oxygen interacts with substances in the paint layer (i.e. mica flakes as in metallic paints) and trigger the oxidation reaction. It's just that the amount of oxidation taking place is minimal in comparison to single stage paint.
An automobile with an oxidized clear coat paint finish can be restored up to the point that clear coat failure begins (blotchy white / gray areas).Paint oxidation is the result of ultra violet (UV) radiation drying out the polymers and its resin binder system of exposed paint surfaces resulting in loss of gloss (clear coat failure) colour change, chalking, flaking and eventually destruction of the paint film
Removing oxidation necessitates thinning the clear coat, and therefore successful paint renovation will be dependent upon how much paint thickness there is. Sometimes a non-invasive chemical paint cleaner like Werkstat Prime Strong, a water-based cleaner for removing contaminants from paint surface maybe all that is necessary
Ultra violet (UV) protection is added in the final coating; this tends to migrate towards the upper level of the clear coat this is why it’s important to check how much of the paint surface you are removing with an abrasive polish. Take measurements with a paint thickness gauge (PTG) or take the vehicle to a body shop and have the paint thickness measured. If the car has sufficient paint thickness you should be able to make it look very good with the right polishes
Two stage paint system- (base, colour and clear coat) - a clear-coat finish does not oxidize in the true sense of the word (meaning that the pigments and resins mix together and the pigments are exposed to the sun's ultra-violet rays, which causes them to dry out or oxidize. The clear coat is applied to protect against this but the finish will become ‘dull’ by using harsh (abrasive) or if acidic car washing solutions as used in ‘touch less’ car washing systems, or from industrial airborne pollutants compromising the clear coat allowing the suns heat to dry out (oxidize) the paint.
· Wash the paint surface and dry thoroughly
· Clean the paint with chemical paint cleaner (Werkstat Prime Strong, Autoglym Paint Renovator or Klasse All-In-One) using an orange foam pad at speed #4, this may take 2-3 applications
· Apply a paint surface protection
Single stage paint systems (base and colour coat) – without a clear coat to provide protection, primarily a hostile environment will attack the paint surface causing microscopic gaps and valleys (micro fissures) and it becomes compromised both chemically; by industrial fallout (IFO) acid rain, brake /rail dust and etc., and by ultra violet (UV) heat radiation, which causes it to dry out and/or fail, further causing the clear coat to expand and often separate from the base coat, allowing environmental pollutants to penetrate.
Single stage is easier to correct than most clear coats, as a general rule use a more aggressive pad before moving up the scale in an abrasive polish.
Optimum's Hyper Polish and / or Hyper Compound used with a Microfiber pads are very effective at removing oxidation from single stage paint
For highly oxidized paint systems (or Nitrocellulose lacquer)
· Wash the paint surface and dry thoroughly
· Clean the paint with chemical paint cleaner (Werkstat Prime Strong) using an orange foam pad at speed #4, this may take 2-3 or more applications
· If you need a more abrasive polish; use a high speed rotary and try Optimum Hyper or Menzerna Power Gloss with a LC White polishing foam pad, if the results are not satisfactory then step up by to going to a LC Orange (light) cutting foam and then if needed a LC Yellow cutting foam pad.
· Once the oxidation has been removed use a decontamination system (C.Quartz IronX)
· Apply an oil rich product to stabilize the paints binder system (3M Imperial Hand Glaze) apply a thick coat and allow to dwell time for 12-24 hours before buffing, repeat as necessary until surface has an ‘oily’ sheen.
· Remove residue with 1:10 solution of isopropyl alcohol and distilled water
Finally apply a coating (Opti-Coat™) a pre-polymer that cross links and forms a semi-permanent continuous film on the surfaces it is applied to similar to a single component Isocyanate that forms a clear coating finish.
1. “Clear Coat Thickness and UV Protection Removed by Polishing” - http://www.autopia.org/forum/car-detailing/136818-clear-coat-uv-protection-removal.html#
2. “Environmental Damage” - http://www.autopia.org/forum/car-detailing/136393-environmental-damage.html#
3. “Nanoskin Surface Prep Towel” - http://www.autopia.org/forum/autopia-detailing-wiki/141207-nanoskin-surface-prep-towel.html
4. “Oxidation or Clear Coat Failure?” - http://www.autopia.org/forum/autopia-detailing-wiki/141208-oxidation-clear-coat-failure.html
5. “Paint Thickness Gauge (PTG)” - http://www.autopia.org/forum/guide-detailing/137139-paint-thickness-gauge-ptg.html#post1454624
6. UV Radiation Damage – http://www.autopia.org/forum/guide-detailing/136963-ultra-violet-uv-radiation-damage.html?daysprune=100