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.
Cause
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
Effect
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.
Paint oxidation
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.
Relevant Articles
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
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