Over Polishing Paint
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.
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. 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 environmental etch, bird
droppings, car wash machines and other outside influences.
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, most if not all car
manufacturers also use ultraviolet-light-blocking technology in their clear
coat systems for protection against sun fading.
Solvent-based vs. Water-based
The clear coat is the final original equipment
manufacturers coating applied to a vehicle to protect the (colour) base coat
from ultra violet radiation, while providing both depth and a durable, glossy
appearance, originally designed to protect metallic paints, but is now applied
to all colours, with a few exceptions
Most
of the newer clear coats are using a paint matrix system in which the clear
coat chemically adheres to the base coat to prevent clear coat failure or
delamination.
The
paint data sheet (PDS) states spray clear coat over base coat within 24 hours.
If you are not able to clear coat within this time, wait for at least 48 hours
and apply another coat of base coat followed by the clear coat
Clear coat .is simply paint without pigmentation (colour) added
and is formulated with resin and solvent, quality is a result of the resin
solvent ratio.
Resins can be either acrylic, enamel, or urethane
(poly-urethane) some are a combination, acrylic/urethane, acrylic is the least
expensive resin and urethane the most expensive, the other determining factor
is the amount of that resin, high solids should mean a larger percentage of
resin and lesser percentage of solvent but there are rules as to what a high
solids clear coat should be.
Most automotive paint used was a solvent-based Nitrocellulose
lacquer coating, which required oil-based products that contained solvents to
keep them from becoming brittle and cracking The oil-based paint,
nitrocellulose lacquer or enamel and older technology paints on classic
vehicles requires oils to keep them from becoming too brittle and cracking,
water-based high solid/low solvent and urethane paints only require protection
(as opposed to ‘feeding’)
In the 60's, the pinnacle of customized cars, a thick topcoat of
clear, solvent-based Nitrocellulose lacquer coating was the final finish to a
customized car. European auto manufacturers (notably BMW and Mercedes
– Benz) began working with clear coats in an attempt to provide
greater depth and gloss to the paint system.
In the 70s both
Japanese and European began using a paint that contained mica chips (metallic
paints) in an acrylic paint with a clear coat. This top layer of the paint film
system comprising clear polyurethane or urethane paint that provides an
outstanding hardness, premium gloss, distinctness of image and long lasting
colour retention and a hard protective layer, which contained ultra violet (UV)
protection. The US later embraced both the metallic paints and clear coat
technology, but the clear coats applied to late 70s US vehicle often failed
within two to three years due to quality issues
In 1980 the US Government
began to get involved with the paint process used by auto makers, namely the
volatile organic compounds (VOC) content of the petroleum based paints and
solvents being used.
The allowable emission
limits of VOC were subjected to dramatic cutbacks. Volatile organic compounds
(VOCs) are organic chemical compounds that have high enough vapour pressures
under normal conditions to significantly vaporize and enter the atmosphere
1982
a two stage paint; base (colour) coat and clear coat were adopted as an
automotive industry standard, sometimes abbreviated as BC/CC, although some OEM
continued to offer some models with a single stage paint finish. The clear coat
is the final original equipment manufacturers coating applied to a vehicle to
protect the (colour) base coat from ultra violet radiation, while providing both
depth and a durable, glossy appearance, originally designed to protect metallic
paints, but is now applied to all colours, with a few exceptions.
The Chrysler Corporation was
one of the first manufacturers to use clear coat system finish throughout their
entire North American passenger car line. Ford utilizes the clear coat finish
on about 95% of their vehicles. They are a leader in the use of tinted clear
coat finishes.
Almost
all original equipment manufacturers' (OEM's) automotive paint systems manufactured
from 1990 on (with the exception of single stage paint systems) used today have
a pigmented base coat protected by a thin layer of clear coat, that contains
polymeric resin or binder, UV inhibitors, and generally one or more silicone
additives. The base coat is comprised primarily of pigments or colorants held
in place by a polymeric resin (binder).
The US later embraced both
the metallic paints and clear coat technology, but the clear coats applied to
late 70s US vehicle often failed within two to three years due to quality
issues
Solvent-based paints - are categorized by the ratio of solids
(resins, pigments, binders, etc.) to liquids (solvents) In the US manufacturers
are required to use high solids paints, with a ratio of about 60% solids to 40%
solvent. In order to produce a better flow rate a higher percentage of solvents
is required, however due to recent volatile organic compound (VOC) limit
restrictions; the 60/40 percentage cannot be exceeded. These restrictions stem
from the Environmental Protection Agency (EPA) limits on volatile organic
compound (VOC), which are in almost all solvents.
In
other countries, these restrictions either don't exist or are more lenient,
allowing manufacturers to use low solids paints (as low as 30% solids to 70%
solvent), which tend to have a smoother appearance. To combat these
restrictions paint companies are developing new technologies.
High or low solid, is a ratio of paint
to solvents - High is 60/40) that leaves more material (coverage) once paint
has cured. Low is (30/70, which means the paint contains more solvents, once
they have out-gassed (evaporated) leaves a thinner coat (paint thickness)
Mechanical Properties
Tensile strength [: quantifies how much
stress the material will endure before suffering permanent deformation]
The urethane used for
automobile paint is classified as a semi-solid , micro structured permeable
membrane, due to its micro-fissures, or pores’, being a thermosetting polymer
it remains flexible, whilst retaining its tensile strength, to enable it to
expand and contract to follow temperature fluctuations (elongation). Some
chemicals penetrate in easily, others stay on top dependent upon molecule size.
Paint Systems
A paint resin system comprises a binder,
which as its name implies holds the paint molecules and various other
components (additives} together and a film former, which creates a dense
surface. Various solvents are used, one as a carrier system, one holds the
paint together and the final solvent that evens out the paint to create a
smooth, glossy surface( this solvent has the most bearing on the ripple effect
(orange peel). These solvents are responsible for the paints density (hard or
soft) the paint becomes,
Single stage paint system - until
1970 most cars were painted with solid colour paint as the only top coat layer The problem with single stage paints is oxidation. Clear
coat paint was first used on production cars in the US in the early ‘80s. While initially these coatings were based on
alkyd resins and were not very durable, later they came to be based on thermoplastic
acrylic enamels, which had slightly better outdoor durability.
At the same time, aluminium
pigments were used to give a metallic effect, but its durability was not
sufficient, which then led to the introduction of base coat–clear. It proved
difficult to get the metallic to lay evenly and get decent gloss with minimum
orange peel. Since most of the metallic floats close to the surface sanding and
polishing can cause problems with single stage metallic. Some OEM vehicles
still use single stage paint (notably; White, Red and Black) and rarely other
colours
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 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 surfacer 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).
North America predominantly uses HS, whereas
water-based clear coat is the preferred technology in Europe
Paint Test- using
a cleaner wax and a clean micro fibre towel on a clean paint surface, lightly
abrade the surface, if the towel shows the paint colour it’s single stage
paint, if not it’s a base coat-clear coat paint
Clear Coat Formulation
IUPAC definition [: a thermosetting resin as a petrochemical in a soft solid or viscous
state that changes irreversibly into an infusible, insoluble polymer network by
curing. Curing can be induced by the action of heat or suitable radiation,
and/or both. There are various kinds of thermosetting plastics. A cured
thermosetting resin is called a thermoset]
A thermosetting polymer (urethane or plastic), also
known as a thermoset, is a petrochemical material that irreversibly cures. The cure may be induced by heat, generally
above 200 °C (392 °F), through a chemical reaction, or suitable irradiation. Thermoset materials are usually liquid or
malleable prior to curing and designed to be molded into their final form
Solvent-based paints are categorized by the ratio
of solids (resins, pigments, binders, etc.) to liquids (solvents) In the US
manufacturers are required to use high solids paints, with a ratio of about 60%
solids to 40% solvent.
In order to produce a better flow rate a higher
percentage of solvents is required, however due to recent volatile organic
compound (VOC) limit restrictions; the 60/40 percentage cannot be exceeded.
A
company selling clear coat with 10% solids could also produce a clear coat with
29% and call it high solids however
Spies Hecker sells clear with 65% solids but doesn’t call it high solids. The
solvent also drives price since solvent is refined just as gasoline is and the
higher the refinement the higher the cost.
Drying
times will also be mostly determined from% of resin content; acrylics dry
quickly, urethanes dry slowly. Painter’s use a small tip for high solids and a
large tip for low solids
There are three major paint suppliers to the
automotive industry PPG Automotive Coatings, DuPont Chemicals,
and BASF Aktiengesellschaft, they have all have focused on
creating super-hard clear coats. These "rigid" clears are more
resistant to chemical etching which makes them less susceptible to acid rain
spots and owner induced swirls from washing and drying improperly.
The
disadvantage of rigid clears is their susceptibility to chip when struck by
stones or road debris; they also require a more abrasive polish to enable paint
repairs. It should be noted that some car manufacturers use a harder clear coat
then others, regardless of the cars paint colour (GM Corvette,
VW, and Audi etc.)
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. Most car
manufacturers also use ultraviolet-light-blocking technology in their clear
coat systems for protection against sun fading.
If you look at the vehicles on the road today that
have a clear coat, they look great for a while, but scratches in the surface
will cause white marks to appear, and dents smudge the finish, reducing the
clarity of the top coat, which in turn affects both the depth of shine and
paint colour showing through.
It doesn’t take long before the finish looks dull
and lifeless because the clear coat isn’t reflecting light as it once did. A
better finish can have a dramatic impact on the residual value of vehicles, and
it certainly doesn’t hurt customer satisfaction.
The statement that “a sealant has no benefit to the
paint ‘because’ there is a clear coat, is baffling, as clear coat is a
polyethylene paint but without colour pigmentation, its applied to provide the
colour coat (base coat) with shine, if a clear coat did not need an ultra
violet protection (UV) applied, there would be no such thing as clear coat
failure due to oxidation or any of a myriad of clear coat problems.
Typical OEM Paint Thickness
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.
Almost
all automotive paint systems today are clear coat systems unless stated
otherwise. 2K paint is an epoxy type paint consisting of the base plus a
catalyst to start the chemical reaction that the paint needs to cure. It
consists of 2 components: (a) base coat (colour) and (b) clear coat.
Clear coat paint was originally
formulated to protect the base coat from UV damage. Once vehicle mfg. started
to use metallic paint a clear coat was necessary to cover the metallic flakes
as they are subject to oxidation. The clear coat serves two functions (1) To provide gloss and depth (2) To provide physical protection from the elements for
the base coat (including ultra violet (UV) protection
Automotive coating
technology is becoming more and more complex requiring educated and skilled
technicians to work on them. As the materials used are constantly changing we
must maintain our knowledge base and adopt our methodologies to keep up with
emerging technologies
Clear Coat Thickness
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 ~50 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. One (µ) micron is roughly 1/80th of the
thickness of a human hair. There are 25.4 millimeters in an inch and a micron
is 1/1000 of a millimetre. Using the micron measurement gives you a much better
idea of paint thickness because it's so much smaller.
The
following are the maximum allowable clear coat reductions the major USA car
manufacturers will allow before the paint warranty becomes void; 0.3 Mil- x10 -3 inch (8µ)
(Source – Technical Service Bulletin’s
(TSB)
The
clear coat provides gloss plus physical protection from the elements, including
ultraviolet (UV) radiation, which is in 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
mfg.) you would only be able to remove 12µ without voiding the paint warranty and
possibly having a re-paint (Note: this may vary by vehicle
mfg.).
There
is ultra violet (UV) protection all the way through the paint, but the majority
of it migrates to the top of cross-linked clear coat along with the thinner
solvents and particles, the paint is also less dense (softer) below this
level. Therefore removing clear coat
ultra violet protection is not a linear process; by removing a small percentage
of the clear coat paint tends to remove a larger percentage of the ultra violet
(UV) inhibitors.
Benzotriazole is fairly
water-soluble, not readily degradable and has limited sorption tendencies,
which is used in some paint formulations to provide ultra violet protection. It
has a specific gravity of 1.17 g/ml, which is heavier than water (0.98 g/ml) and
much heavier than solvent (0.80 g/ml)
There is ultra violet (UV)
protection all the way through the paint,
vehicle manufacturers also add ultra violet protection to the base coat
to minimize the transfer due to density,
the majority of it migrates to the top as the paint cross-links, along with the thinner solvents and
particulates, the paint is also somewhat softer below this level. The amount of migration will vary with the
formulation of the paint, and which ultra violet protection chemical is used.
With a clear coat thickness
of ~49µ and knowing that most of the ultra violet protection is in the
top 50% (~24.5µ); therefore, limiting UV protection removal to ~25 % means that approximately 6.125µ< can be removed before the ultra violet protection
is compromised. Once you remove too much clear coat you'll have no paint
UV protection other than what you apply with a LSP (providing
it contains UV protection.
Be cognizant that ultra
violet protection removal is not a liner process; and the first paint
renovation will remove the most UV protection, therefore the above are probably
conservative estimates. Two variables need to be established; how much clear
coat is available and how much clear coat can be removed without compromising
the paint systems long-term durability / paint warranty
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 edge.
- 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
Some vehicle manufacturing
assembly plants only apply one coat of clear paint to door jambs and no clear
coat to the engine compartment or the trunk areas.
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 that may affect the
paint removed)
If
you have reservations about the amount of paint surface removed or the amount
of paint coating 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 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
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)
Scratches from car-washing
(especially High Street Tunnel Washes) account for the majority of scratches to
painted car surfaces.
PPG
Automotive Coatings - PPG CeramiClear™ Clear Coat is applied as a final coating over a
traditional clear coat, and has an approximate thickness of 7.5 µ (0.5
Mil) the upper region contains the paint systems ultra violet (UV) protection
PPG
Enviracryl® Powder Clearcoat - is an environmental friendly
technology, as it does not emit any organic solvent during its application. Powder
clear coat exhibit: hydrophobicity of the paint, which results in: lower water
permeability, the higher cross-link density is better, scratch resistance is
higher, this can be related to higher cross-link density and elasticity of the
polymer network and better UV durability of the resin matrix.
Nissan
Scratch Guard Coat - contains a newly developed high elastic resin that helps
prevent scratches from affecting the inner layers of a car’s painted surface.
With “Scratch Guard Coat” a car’s scratched surface will return to its original
state anywhere from one day to a week, depending on temperature and the depth
of the scratch.
Nissan has approved CeramiClear™ D8105 Scratch
Resistant Clearcoat from PPG Automotive Refinish
for the refinish repair of its new Scratch Guard paint system.
The water-repellent paint
also has a higher resistance to scratches compared with conventional clear
paints. A vehicle painted with Scratch Guard Coat will have only one-fifth the
abrasions caused by a car-washing machine compared with a car covered with
conventional clear paint.
Generally
speaking the clear coat makes up 50% of the total paint thickness. The paint
system is split 50-25-25% please note
that this is a very general approximation
Measure the inside of door;
this will give you an approximation of the paint system minus the clear coat.
The difference between readings inside the door and on the exterior paintwork
gives the thickness of the clear coat) it should be noted that some vehicles do
have a clear coat)
Ultra
violet protection is mixed through the clear coat upon application; however as
part of the curing process, the majority of the UV Blockers migrate toward the
topmost layer.
.As
a point of reference a sheet of copy paper is 3.5Mil (89µ) a surface scratch that will `catch'
your fingernail is approximately 0.004 Mil (0.01µ) deep will usually require wet sanding
and refinishing.
Ultra Violet (UV) Radiation
Ultra violet (UV) radiation is
unrelenting, and can never be totally eliminated. It affects human skin, the
paint and headlights of motor vehicles and aircraft as well as the gel coats of
boats, and trailers. This process is called oxidation.
It also affects paint,
plastic, rubber, and vinyl, just to name a few.
Paint turns dull, then chalky. Rubber seals
and bumpers turn white, dry out, and become hard as a rock. Vinyl trim will
also turn white and eventually crack. Hard plastic (headlights, air dams, side
mirrors, trim) react similarly to paint.
Clear Coat and UV Protection Removal
Modern
clear coat paint 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. One (µ) micron is roughly
1/80th of the thickness of a human hair. 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.
There
are two considerations; how much clear coat and how much ultra violet
protection can be removed, they are not interchangeable. The following are the
maximum allowable clear coat reductions the major USA car manufacturers will
allow before the paint warranty becomes void; 0.3 Mil (8 µ) (Source - Technical Service Bulletin (TSB)
The
clear coat provides gloss plus physical protection from the elements, including
ultraviolet (UV) radiation, which is in 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 <12µ without voiding the paint warranty and
possibly having a re-paint (Note: this may vary by vehicle
mfg.).
CeramiClear - in 2002, PPG introduced the first
scratch resistant clear coat to the automotive marketplace. Since then, scratch
resistant clear coats have rapidly become the standard in the automotive
industry.
It 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.
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 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 surfacer 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). North
America predominantly uses HS, whereas water-based clear coat is the preferred
technology in Europe
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
Density (or specific
weight); 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 (we have Archimedes to
thank for this discovery)
If the average density of an
object is less than that of water, which is 1.000 g/ml, it will float in and if
it is more than water's it will sink. Most organic solvents have a lower
density ~0.8 g/ml than water, which means they are lighter and will form a
separate layer on top of water.
Benzotriazole is fairly
water-soluble, not readily degradable and has limited sorption tendencies,
which is used in some paint formulations to provide ultra violet protection. It
has a specific gravity of 1.17 g/ml, which is heavier than water (0.98 g/ml)
and much heavier than solvent (0.80 g/ml)
There
is ultra violet (UV) protection all the way through the paint, but the majority
of it migrates to the top as the paint of cross-links along with the thinner
solvents and particulates, the paint is also less dense (softer) below this
level. The amount of migration will vary
with the formulation of the paint, and which ultra violet protection chemical
is used.
With a clear coat thickness
of ~49µ and knowing that most of the ultra violet protection is in the
top 50% (~24.5µ); therefore, limiting UV protection removal to ~25 % means that approximately < 6.125µ can be removed before the ultra violet
protection is compromised. Once you remove too much clear coat you'll have no paint
UV protection other than what you apply with a LSP (providing
it contains ultra violet inhibitors).
Be cognizant that ultra
violet protection removal is not a liner process; and the first paint
renovation will remove the most UV protection, therefore the above are probably
conservative estimates. Two variables need to be established; how much clear
coat is available and how much clear coat can be removed without compromising
the paint systems ultra violet protection, its long-term durability and / or
the paint warranty
Polishing
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.
If
you have reservations about the amount of paint surface removed or the amount
of paint coating remaining the use of a paint thickness gauge (PTG) is
arbitrary
These numbers are offered as a guide
only, as there are too many variables to provide any more than an
approximation.
Note: 1 µ (micron) is 1/1000th of a millimetre or 0.0393700787 Mil or 0.001 of an inch
·
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
Paint Identification
Detailer’s
should know and be able to identify a two-stage paint finish. To test a car to find out if
it has a clear coat or a single stage finish you should use a chemical paint cleaner
and a white micro
fibre towel, if you're working on a white car then you'll want to use a dark
colour micro fibre towel because if the car is in fact a single stage paint
then you won't be able to see the white or silver pigment you're removing on
white cloth, so use a dark colour cloth when testing white cars. To
check rub the surface using a medium to heavy pressure and wipe off. If there
is no paint colour on the cloth it has a clear coat finish.
It' also important to check
for paint type on a number of different panels, and if you want to be 100% sure
then check all the panels as it’s possible to have one type of paint on one
panel (repainted) and another type of
paint on a different panel.
Volatile
Organic Compound (VOC)
These restrictions stem from the (US) Environmental
Protection Agency (EPA) limits on volatile organic compound (VOC), which are in
almost all solvents. In other countries, these restrictions either don't exist
or are more lenient, allowing manufacturers to use low solids paints (as low as
30% solids to 70% solvent), which tend to have a smoother appearance. To combat
these restrictions paint companies are developing new technologies.
High or low solid, is a ratio of paint to solvents
- High is 60/40) that leaves more material (coverage) once paint has cured. Low
is (30/70, which means the paint contains more solvents, once they have
out-gassed (evaporated) leaves a thinner coat (paint thickness)
Waterborne paints, for example, are essentially low
solids paints (up to 60% solvent), but they are legal because de-ionized water
is used as the solvent, as opposed to volatile organic compounds (VOC). In
addition to the low solids aspect, waterborne paints have many other neat
properties that help improve the performance and appearance.
The isocyanate group reacts with the hydroxyl
functional group to form a urethane linkage. If a diisocyanate is reacted with a
compound containing two or more hydroxyl groups (a polyol), long polymer chains
are formed, known as polyurethanes. Clear coats are two part systems (either a
Urethane, or a good quality non-yellowing isocyanate polyurethane and an epoxy)
A 2K paint means that the product requires 2 components to be mixed together to
make the product usable.
Resin and an activator / hardener, a solvent based
urethane is applied in two layers; it also contains UV inhibitors. Clear coat
is not armour plating, Urethane /
Polyurethane paint is porous but by adding UV blockers it provides a level of
protection for the colour pigmentation of the base (colour) coat, but it must
be protected, and the most durable protection is a polymer sealant.
Durability is really a very real concern for car
owners today. With the increase in airborne pollution and other environmental
factors, a car's finish is subject to serious damage.
Acid rain; jet fuel fallout; industrial fallout;
hard water, not to mention high acidic bird droppings; insect residue; tree sap
all are very dangerous to a paint finish if not removed immediately. By adding
UV blockers to the clear coat you have a new level of protection for the
pigments in the base coat.
Density
The mass density or density
of a material is defined as its mass per unit volume. The symbol most often
used for density is ρ (the Greek letter rho). In some cases (for instance, in
the United States oil and gas industry), density is also defined as its weight
per unit volume; although, this quantity is more properly called specific
weight.
Different materials usually have different densities, so density is an
important concept regarding buoyancy, purity and packaging. Osmium and iridium
are the densest known metal elements at standard conditions for temperature and
pressure but not the densest materials.
Density (specific weight);
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 (we have Archimedes to thank for this discovery) Most organic solvents
have a lower density than water, which means they are lighter and will form a
separate layer on top of water.
Acidic pollutant protection
Bird excrement comprises;
ammonia and urine as white crystals of uric acid (pH 3.0 - 4.5) a small organic
compound, which is produced by the breakdown of protein during digestion, and
is excreted by reptiles and birds.
Uric acid is also the end
product of nitrogen catabolism in birds Ammonia is a mixture of nitrogen gas
and hydrogen gas; with moisture as a catalyst it becomes Ammonium Hydroxide,
which is caustic.
Heat
and water act as a catalyst; a vehicle paint surface temperature of >90.oF
creates a very aggressive reactivity of the Alkaline, Uric Acid and Ammonia.
This will cause surface etching, so they should be removed without delay, at
lower temperatures (> 40.oF or less) there’s no reactivity and
therefore little or no etching.
The
latest nanotechnology PPG CeramiClear™ Clear Coat or the newer nanotechnology,
although they are highly resistant to chemicals, detergents, scratches and
ultra violet radiation (UV) will only offer limited resistance to acid etching.
Organic or inorganic protective coatings, with the exception of Acrylic
polymers, offer very limited resistance to acidic pollutants (acid rain, bird
excrement, industrial fallout, hydrazine and etc.).
The
most effective deterrent, once the paint film surface has been decontaminated,
is to apply an Acrylic poly amino siloxane or polyethylene-acrylic (Klasse, Jeff Werkstatt or
Duragloss #105 Total Performance Polish) are sulfonic acid-based so they hold up better to acidic pollutants
(acid rain, bird excrement, and etc.) there is no cross-linking capability with
this technology, and they cannot be layered, however, they form an anchor with
the paint by etching, which gives this type of polymer its durability and they
are heat resistant up to 350.0F.
For
added protection apply an organic wax over the polymer sealant or
nanotechnology coating as this will act as a sacrificial barrier The best way
to avoid clear coat etching is by removing the wax along with the environmental
acid, as soon as it’s noticed; but given enough time acid will compromise the
clear coat whatever its protection.
Ultra a Violet Radiation
Ultra violet radiation
consist of wavelengths that have a two-fold effect; UV-A (ultra violet heat)
and UV-B (ultra violet light)
They are known to contribute
to the chemical modification of exposed paint surfaces resulting in loss of
gloss, colour change, chalking, flaking and eventually destruction of the clear
coat paint film by oxidation UVR protection is a sacrificial / renewable
component; this is due to the UV protection layer (stabilizers) being degraded
by exposure to the elements (sun, sand, road or sea salt, and etc.) it is also
water miscible, so it is imperative that you renew it and needs to be
re-applied on a regular basis (dependent upon location climatic condition)
There is no such thing as a permanent UV stabilizer, it a matter
of physics, not chemistry. Ultra violet protection is a sacrificial and
necessarily renewable protection. Acrylic polymers and polyurethane
polymer
are slow to absorb UV light and accordingly resistant to photo degradation.
Ultra Violet Photo-oxidation
UV
radiation is a paint film surface's greatest enemy, causing more damage than
any other airborne contaminant and affecting both the interior and exterior of
a vehicle. The light in this spectral range is responsible for photo-degradation
Oxidation is the result of the paint
molecules drying out, hence the powdery look; is indicative of clear coat failure.
It is also a ‘natural protection for some metals as it provides a ‘barrier’
against infra-red (heat) radiation heat. Photo degradation results in
discoloration, fading, embitterment, cracking, chalking and/or loss of
mechanical properties.
Chalking gel coat fibreglass, yellowing plastics, fading
and weakening fabrics and sunburned skin are all familiar problems caused by UV
radiation. Infrared radiation (IR) infrared radiation is a light source that
transmits heat that when combined with a UV (light) radiation source will cause
oxidation by drying out the material.
Before
ultra violet radiation 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 light more readily than other materials.
Materials
that readily absorb ultra violet radiation are quickly damaged...rubber, vinyl,
gel coat fibreglass, and many other plastics. Acrylic is slow to absorb UV-b
radiation and accordingly resistant to photo degradation.
1.
Infrared Radiation
Infrared Radiation (IR)
infrared radiation represents part of the ultra violet solar spectrum
(approximately 55%-60%). The remaining heat source comes from visible and ultra
violet light Infrared radiation (IR) infrared radiation is a light source that
transmits heat that will cause oxidation by drying out materials, like the
paint (binder) resin system, the plasticizers in vinyl, moisture evaporation of
leather and the elasticity of rubber causing these materials to dry out and
become brittle and compromise their structural integrity
Dependent upon interior
colour at a 90.oF ambient; Interior (Light) 104 - 135.oF
(Dark) 220 – 275.oF,
Steering wheel – 160.oF
- Dashboard 182.oF - Seats 165.oF (dependent upon colour,
material and colour, actual results may
vary depending on time in sun, make of car, size of windows and direction (sun
Azimuth or angle) in which car is parked.
Heat alone will not cause
photosynthesis (fading) although it will dry the resin (binder system) in
paint; leading to oxidation. It will also dry out the oils and plasticizers in
vinyl and other materials. It will dehydrate leather and may lead to structural
damage (this is especially relevant to open top convertibles)
Ultra violet penetration of
auto glass; UV radiation is present in the sun’s rays throughout the year in
varying amounts. Ordinary auto window glass filters out about 37% of UV-A
radiation.
Ultra violet penetration of
auto glass; UV radiation is present in the sun’s rays throughout the year in
varying amounts. Ordinary auto window glass filters out about 97% of the UV-B
radiation, the cause of photosynthesis (fading)
2.
Ultra violet radiation
UV- B radiation is known to
contribute to the chemical modification, photosensitise (fading) of exposed
paint surfaces resulting in loss of gloss, colour change, chalking, flaking and
along with infrared heat radiation (IR) infrared radiation eventually the
destruction of the clear coat paint film.
Ultra violet radiation (UV)
and environmental contaminant exposure leads to gloss and colour instability
(photosynthesis) and surface 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 light more readily
than other materials.
Materials that readily
absorb UV light are quickly damaged...rubber, vinyl, gel coat fibreglass, and
many other plastics. Acrylic is slow to absorb UV light and accordingly very
resistant to photo degradation.
Ultra violet penetration of
auto glass; UV radiation is present in the sun’s rays throughout the year in
varying amounts. Ordinary auto window glass filters out about 97% of the UV-B
radiation, the cause of photosynthesis (fading)
Ultra Violet Protection
[: organically modified
silica or organically modified silicate, used in a matrix material for
UV-protection coating]
UV protection is a
sacrificial / renewable component; this is due to the UV protection layer being
degraded by exposure to the elements (sun, sand, road or sea salt, and etc.) it
is also water miscible, so it is imperative that you renew it and needs to be
re-applied on a regular basis (dependent upon location climatic condition)
Providing protection from
ultra violet radiation (UV) is very important to avoid photo synthesis (colour
fading) particularly in an open-air roadster/convertible (303™
Aerospace Protectant, pH 9.5) UVR protection is a sacrificial / renewable component;
this is due to the UV protection layer being degraded by exposure to the
elements (sun, sand, road or sea salt, and etc.)
No product on the market
retains UV protection effectiveness more than 2-3 months; so it is imperative
that you renew it and needs to be re-applied on a regular 45 to 60 day basis
(dependent upon location climatic condition)
To determine a sunscreen's sun protection factor (SPF) testers
chose 20 sun-sensitive people and measure the amount of UV rays it takes them
to burn without sunscreen. Then they redo the test with sunscreen. The
"with sunscreen" number is divided by the "without
sunscreen" number, and the result is rounded down to the nearest five.
This is the sun protection factor (SPF)
Some
car care manufacturers are using an SPF number to rate the ultra violet (UV)
protection of their paint protection products, I would be interested as to how
these numbers were arrived at.
303™ Aerospace Protectant – Application; use on a clean surface (there are only mild cleaning agents in this product) spray product onto a damp
micro fibre cloth folded in four; the surface to be protected should not be
wet, just damp.
Buff
surface with a fresh clean micro fibre towel to ensure the protected surface is
dry (this product does not air-dry) After application allow 60 minutes for
product to cure, then using a 100% cotton cloth to lightly buff surface
Streaking (No, not the kind you see at Rugby
matches) always ensures that you are not using too much product; a thin layer
is all that's required. Be sure also that both your surface and the applicator
is clean and has not become saturated. In general, a quick wipe down with a
microfiber towel should remove the excess and eliminate it
Ultra Violet Radiation Stabilizers
Are a group of chemical
agents with the ability to counteract or neutralize the harmful effects of UV radiation?
Competitive absorbers provide protection by converting UV light to heat so it
can dissipate harmlessly. Other UV stabilizers work differently, but all UV
stabilizers are consumed as they do their job. In a way, they serve as
sacrificial molecules, taking the abuse from the UV light instead of the
material they are protecting.
Two
important points-
a)
Ultra violet radiation protection is
a sacrificial / renewable component; this is due to the UV protection layer
being degraded by exposure to the elements (sun, sand, road or sea salt, and etc.)
so it is imperative that you renew it or your surfaces will degrade.
b)
Ultra violet radiation stabilizers
have to be periodically renewed or replenished if continuing protection is to
be achieved, there is no such thing as a permanent UV stabilizer, it a matter
of physics, not chemistry.
Clear Coat Failure
Ultra violet (UV) radiation is known to contribute
to the chemical modification (drying out the polymers and its resin binder
system) of exposed paint surfaces resulting in loss of gloss, color change,
chalking, flaking and eventually destruction of the paint film
Oxidation - is the result of some of the
top layer of polymer drying out; once the air borne contaminates and
pollution compromises the paint surface they accelerate the oxidation (reduction)
or paint failure process, which leads to bleaching (fading), discoloration,
chalking, brittleness and cracking - all indications of UV deterioration.
Clear coat failure-
is the result of ultra violet radiation drying out
both the polymer paint and its resin binder system, causing structural failure;
the paint take on a dull grey cloudy
appearance, then as time progresses this is accompanied by paint delamination
(flaking) Once a paint surface structural integrity is compromised like this it
usually means the paint requires replacement (re-painting)
The clear coat is the final original equipment
manufacturers coating applied to a vehicle to protect the (base) colour coat
while providing both depth and a durable, glossy appearance, originally designed
to protect metallic paints, but is now applied to all colours. Any product applied on top of the clear coat
needs to be transparent otherwise both the paint colour and its depth of shine
will be muted.
It’s also worth noting that the UV absorbents
migrate to the top of the clear coat, so one you remove too much clear 0.5 mil (12µ) you'll have no
paint ultra violet protection other than what you apply with a LSP
1. Ultra violet
radiation is the prime cause of clear coat failure, infrared (IR)
infrared radiation represents part of the ultra violet solar spectrum
(approximately 55%-60%). The remaining heat source comes from visible and ultra
violet light Infrared radiation (IR) infrared radiation that transmits heat
that will cause oxidation by drying out materials, like the paint (binder)
resin system, the plasticizers in vinyl, moisture evaporation of leather and
the elasticity of rubber causing these materials to dry out and become brittle
and compromise their structural integrity
2. Ultra violet light; UV radiation is
known to contribute to the chemical modification, photosensitise (fading) of
exposed paint surfaces resulting in loss of gloss, colour change, chalking,
flaking and along with infrared heat radiation (IR) infrared radiation
eventually the destruction of the clear coat paint film.
3. Acid
Rain, as previously mentioned penetrates the clear coat surface and breaks
down the chemical bond between the Clearcoat and the basecoat colour.
Again,
this will cause a delamination between the layers since once the chemical bond
is destroyed; only the weaker mechanical bond remains. Like the above reason, usually
occurs predominately on top surfaces for obvious reasons.
A polyurethane paint (high solid / low solvent)
clear coat can absorb moisture; as water molecules are smaller than a
cross-linked clear coats molecule. Acid rain can permeate and break down the chemical bonds
between the clear coat and the basecoat. This will also cause delamination
between the layers since once the chemical bond is destroyed; only the weaker
mechanical bond remains.
So be careful of the contents in car wash
concentrates, sealant and waxes (i.e. low pH acids, high pH alkaline,
Dimethyl Silicone (DMS) or solvents that contain butyl, heptanes, and xylene or
hydrocarbon aliphatic solvents. (See
also MSDS, Potential of Hydrogen (pH)
Oxidation is sometimes confused with clear coat
failure; the clear coat finish can become ‘dull’ by using harsh (abrasive) or
if a high alkaline car washing solution as used in ‘touch less’ car washing
systems, or from industrial airborne pollutants compromising the clear coat
allowing the suns heat to dry out and oxidize the paint .
There comes a point when you must judge wither
removing a scratch will compromise the clear coat and if so you’ll have to
‘live’ with the imperfection. Check the paint with a PTG to see how much paint
there is available before attempting repairs
Clear coat that is too thin loses its ability to adhere effectively
(delaminating) to the underlying paint layer and will flake off
Hardness is defined as - the ability to resist
local deformation (or penetration) from externally applied pressure. Hardness
is directly related to the tensile strength of a material; stronger materials
are generally harder (be cognizant that hardness is not related to a materials scratch resistance)
Today’s paints, unfortunately, rank somewhere near
the bottom of the scale of hardness when compared to all the materials your
paint can possibly come in contact with, bear this in mind. That’s why a micro
thread in an otherwise soft towel will scratch your paint with enough applied
pressure. (See also Mors (paint) Hardness Scale)
Note -
Heat makes solids softer; cold makes them harder. Keep that in mind when
detailing (especially polishing) your car in the sun or on a really, really hot
day.
When polishing a clear coat ‘spot’ surface
temperature should be limited to 100.oF (138. oC) as isocyanates
urethane starts to soften at a ‘spot’ temperature of 115.oF, just
like any other plastic material, polishing at this or elevated temperatures
will cause scratches to be driven deeper into the surface due to urethane
expansion and foam / wool pad friction on the softened paint surface.
Information
resource- Heat Vs
Urethane Coatings, The Society of Automotive Engineers (SAE) article
Almost all original equipment manufacturers'
(OEM's) automotive paint systems manufactured from 1990 on (with the exception
of single stage paint systems) used today have a pigmented base coat protected
by a thin layer of clear coat, that contains polymeric resin or binder, UV
inhibitors, and generally one or more silicone additives.
The base coat is
comprised primarily of pigments or colorants held in place by a polymeric resin
film (binder) (See also Oxidation, Clear Coat Delamination)
Oxidation -
Reduction
[: oxygen is added to a molecule with an electron being displaced, which
in turn dries the paints binder system. If
the car's outer finish is not protected the oxygen molecules in the air will
eventually start interacting with the paint. As the oxygen burns up the free
radicals contained in the paint, the finish becomes duller and duller]
Because electrons are neither created nor destroyed
in a chemical reaction, oxidation and reduction are linked. It is impossible to
have one without the other.
Ultra violet (UV-B) radiation is known to
contribute to the chemical modification of exposed paint surfaces resulting in
loss of gloss, color change, chalking, flaking and eventually destruction of
the paint film
Once the air borne contaminates and pollution
compromises the paint surface they accelerate the oxidation (reduction) or
paint failure process, which leads to bleaching (fading), discoloration,
chalking, brittleness and cracking - all indications of UV deterioration. Once
a paint surface structural integrity is compromised like this it usually means
the paint requires replacement (re-painting)
Basically the chemical
integrity of the paint has been degraded by both ultra violet (UV) and infrared
(IR) radiation, stress, environment fall out and etc. Oxidation really amounts
to a weakening of the resins that bind paint, which results in the micro-pores
becoming exposed and a larger area of paint becomes oxidized. The paint top
surface loses its reflective ability and becomes ‘chalky’; this is a sign that
the structural integrity (mechanical strength) of the paints matrix has become
compromised.
On
average, a high solid clear coat will absorb approximately one pint of water
when the vehicle is subjected to a heavy rain or a car wash. If there is a
"clouding" of the clear, simply applying isopropyl alcohol (IPA) to
the area, allowing it to dwell time and with a heat gun or hair dryer, heat the
area (do not exceeding 100.oF spot temperature) The IPA acts as a
"drying" agent, and when combined with the heat the moisture will
evaporate
Once the paint has been
breached in this manner, polishing may remove minor oxidation but use caution
as you are further ‘thinning’ the paint, applying waxes and polishes temporarily wets the surface making it
appear better. The oils and other components do not have the ability to repair
the resin binders but rather cover up the problem for a short period of time.
A chalk like appearance on the paint surface or
small triangular marks (crow’s feet) or other similar marks on the paint
surface - basically the chemical integrity of the paint has been degraded by
ultra violet (UV) radiation, stress, environment fall out and etc.
Oxidation
really amounts to a weakening of the resins that bind paint, which results in
the micro-pores becoming exposed and a larger area of paint becomes oxidized.
Once the paint has been breached in this manner, applying waxes and polishes
temporarily wets the surface making it appear better.
The oils and other components do not have the
ability to repair the resin binders but rather cover up the problem for a short
period of time.
What happens when paint oxidizes?
Acids enter
the breach formed in the paint surface and attack the resin binder system,
which accelerates the degrading of the paint film surface, eventually leading
to oxidation and/or failure. 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.
Think of these polymer matrixes as being chains of
molecules which get their strength from the bonds that hold them together, they
have one unalterable characteristic...they are chains that are only as strong
as their weakest link. That’s why the reactivity is so important in urethanes.
Reactivity is the chemical process that makes those
linkages; break the link at any point and you begin to weaken the chain that
gives a coating its protective capabilities. Un-reacted bonds are “weak links”
from the beginning.
Thermal, photo- degradation, mechanical, chemical,
and biological degradation bring about changes in physical properties in
polymers. They disturb or weaken the links that give the chain its integrity.
There are other stress agents like airborne pollution, salt, sand, abrasion,
solvents, biological contaminants, acidic or alkaline substances, chlorides,
etc. that also add stress.
But, as damaging as they are, they are only
contributory elements leading to polymer bond failure, or as some call it
“polymer unzipping” because of the similarity to a zipper being unfastened.
Ultra violet radiation, moisture migration and how they interact with each
other.
Let’s start with sunlight induced damage known UV
radiation Perhaps you’ve read about how “free radicals” are bad for you and how
anti-oxidants of whatever kind (foods, vitamins, and supplements) will control
them and prevent damage to your body. Well, the same free radicals apply to
paint as well.
First understand polymer backbones are made up of
multiple elements. Key among these is hydrogen and oxygen. When the coating
absorbs photons of UV-B radiation from sunlight, some of the energy “excites”
the binder’s molecules to a higher energy level and causes bond cleavage, like
a hot knife through the molecule’s heart. The result is free radicals.
Free
radicals are simply scavengers trying to steal an electron from a weaker
molecule that has one. They react with oxygen in the air to create oxygen
radicals, which then attack the polymer backbone. In so doing, hydrogen atoms
break from the coating to form hydrogen radicals and more free radicals. This
is where a vicious cycle begins.
The free radicals combine with oxygen again to form
a chain reaction. More and more molecular links break; leading eventually to
failure of the coating’s properties. Remember the demonstration of a nuclear
chain reaction, where they had a room full of mousetraps all loaded with a
ping-pong or golf ball. They threw a ball into the room and triggered a chain
reaction. It took a slow motion camera to see clearly all the balls going off
everywhere with increasing intensity. There you have, in its simplest form, the
chain reaction that is photo-oxidation.
Moisture accelerates this degradation through a
chemical process called hydrolysis. Once again, the process involves hydrogen
when the splitting of a bond causes a reaction between the hydrogen from the
coating and the hydroxide from the water (H2O). Finally, the infrared heat
energy from the sun comes into play, expanding and contracting the coating
during a 24-hour cycle, causing accelerating stress fatigue degradation. High
temperatures also accelerate the process of link breakage outlined in photo-oxidation.
All
these stress factors lead to one additional form of degradation, the porosity
of the coating film. It’s like having an umbrella attacked with hairpins. The
holes created are small and relatively insignificant until they become so
numerous that the integrity of the umbrella (coating) is compromised.
Once
moisture, with all the contaminants it can bring along, and oxygen (that’s why
they call it oxidation) gain access to the coating’s weak underbelly, the
coating’s protective barrier (whether clear coated or not), is attacked from
inside and under to devastating effect. An oxidizer- is any compound that spontaneously
emits oxygen either at room temperature or under slight heating.
Many chemical compounds
react vigorously at ambient temperatures as the oxidizing process takes place.
Oxidation is caused by environmental pollutants (acid rain, ozone, industrial
pollutants, hydrocarbons, etc.) the suns heat, which also causes paint colour
fading from ultraviolet radiation (UVR) inclement weather or the use of harsh
detergents, all of which attack the paints binder system(resin)
It starts as a chemical
reaction that causes the resin binder system to overheat and dry out, leaving
microscopic surface imperfections and micro fissures in the paint film surface
that are vulnerable to deterioration. Once the air borne contaminates and
pollution compromises the paint surface they accelerate the oxidation
(reduction) or paint failure process.
Clear Coat Paint Delamination
[: the separation of a material into
layers in a direction approximately parallel to the surface.]
Extreme temperature
fluctuations can cause the clear coat and the basecoat to delaminate. Basically the clear coat elasticity will
react at differing rates during extreme temperature swings. This actually
happens more often on areas of the surface where snow, ice, or frost
accumulates. It can also be accelerated in areas that are subjected to rapid
heat application, such as the engine hood, especially when the engine is
subjected to strain i.e. towing another vehicle
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 (IR)
infrared radiation, which cause them to dry out; this is not oxidation, but
clear coat failure.
The clear coat, which
contains ultra violet (UV) protection 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 the paints resin binder 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, oxygen interacts with substances in the paint layer (i.e. 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.
For oxidized paint try the
following (this is only a temporary ‘fix’)
•
Wash the paint surface and dry thoroughly
•
Clean the paint with chemical paint cleaner (Klasse
All-In-One) using an Lake County (LC) orange foam pad at speed #4, this may take 2-3
applications
•
If a chemical paint cleaner doesn’t remove the oxidation use a
(LC) purple foamed wool (PFW) pad and Menzerna Power Gloss (POS
34A) or Meguiar’s M105, clean or replace with a clean pad as the
oxidized paint will load the pad
•
A foam pad will transfer kinetic (friction) heat to the paint
and may exasperate the problem
·
Using Gloss It EVP Pad Prime will help maintain
sufficient oil lubrication for the polish
•
Wet-sanding will remove ‘oxidation’ debris, which may remove too
much clear coat
•
Once the oxidation has been removed use a decontamination system
(Aquartz Iron Cut)
•
Apply an oil rich product to stabilize the paints binder system
(3M Imperial Hand Glaze) apply a thick coat and
allow to dwell for 12-24 hours before buffing, repeat as necessary until
surface has an ‘oily’ sheen.
•
Remove residue and apply a polymer coating (Opti-Coat™) for
protection.
•
Try to keep vehicle paint surface away from UV heat radiation
•
Keep paint surface waxed on a regular basis.
Temporary remedy – wash and dry the surface, and then use a chemical paint cleaner
(Klasse AIO) Check the paint thickness and there is
sufficient thickness polish the surface (Meguiar’s
M105) Apply a coating (Opti-Coat™) for
protection
Single-stage paint
systems (base and colour coat) – (note-single
stage paint is usually very ‘soft’) 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 UV heat radiation, which causes it to dry out and/or fail, causing the
clear coat to expand and often separate from the base coat, allowing
environmental pollutants to penetrate.
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.
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. 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 colour 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
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. Start with a
Lake County (LC) Orange (light) cutting foam pad with Optimum Polish or
Menzerna Intensive Polish (IP) you may also want to try an LC yellow cutting
foam pad.
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.
Products-
•
Carnauba wax – Pinnacle Souverän Paste, Menzerna
Finishing Touch Glaze, or Autoglym Super Resin Polish,
•
Polymer sealant-Zaino ZFX + Z3 for Regular (for
single stage) Zaino ZFX + Z2 for Regular (for clear coat paint)
Polish - Optimum Hyper or Menzerna Intensive Polish (IP)
Paint System Solvents
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
There is ultra violet (UV)
protection all the way through the paint, but the majority of it migrates to
the top as the paint of cross-links along with the thinner solvents and
particulates, the paint is also less dense (softer) below this level. Therefore removing clear coat ultra violet
protection is not a linear process; by removing a small percentage of the clear
coat paint tends to remove a larger percentage of the ultra violet (UV)
inhibitors
Density (specific weight);
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 (we have Archimedes to thank for this discovery) Most organic solvents
have a lower density than water, which means they are lighter and will form a
separate layer on top of water.
There
is ultra violet (UV) protection all the way through the paint, but the majority
of it migrates to the top as the paint of cross-links along with the thinner
solvents and particulates, the paint is also less dense (softer) below this
level. Therefore removing clear coat
ultra violet protection is not a linear process; by removing a small percentage
of the clear coat paint tends to remove a larger percentage of the ultra violet
(UV) inhibitors.
With a clear coat thickness
of ~49µ and knowing that most of the ultra violet protection is in the
top 50% (~24.5µ); therefore, limiting UV protection removal to ~25 % means that approximately < 6.125µ can be removed before the ultra violet
protection is compromised. Once you remove too much clear coat you'll have no paint
UV protection other than what you apply with a LSP (providing
it contains ultra violet inhibitors).
Be cognizant that ultra
violet protection removal is not a liner process; and the first paint
renovation will remove the most UV protection, therefore the above are probably
conservative estimates. Two variables need to be established; how much clear
coat is available and how much clear coat can be removed without compromising
the paint systems ultra violet protection, its long-term durability and / or
the paint warranty
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 and="" grit="" polish="" span="" under="">70
µ use a glaze. The readings tend to vary from panel to panel and are
thinner towards the panel edges and any seams.
·
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
Environmental Damage
The rate of environmental
exposure that negatively effects (clear coat) paint varies widely with ambient
conditions (UV
radiation, Environmental Fall-out, paint protection used, etc.) but an
approximation of 0.005Mil (0.13µ) per annum is about average; protective
coatings polymer sealants, wax, etc.), being renewable are meant to be
sacrificial (it is subjected to oxidation, thereby by saving the clear coat)
This barrier is all that
stands between the environmental contaminants (ultra violet radiation, acid
rain, ozone, industrial pollution, rain, road dirt and tar, etc.) and the paint
film surface and this renewable barrier is probably less than 0.000001-inch (0.0254
µ) thick. An applied paint protection product is the entire
barrier that provides protection for automotive paintwork besides the clear
coat paint.
Paint Removed by Polish / Compound
Removing more than 0.3 mil (8 µ) of
clear coat will cause premature paint film failure as UV protection percolates
to the top of the clear coat, there is UV protection all the way through the
paint, but the majority of it rises to the top with the thinner solvents and
particles. As a point of reference a sheet of copy paper is 3.5Mil (89µ) a
surface scratch that will `catch' your fingernail is approximately 0.004 Mil (0.01µ)
deep will usually require wet sanding and refinishing.
Using a medium abrasive
polish and a rotary polisher will remove approximately 0. 1 Mil (3µ)
from the paint surface (typically 4 passes at 1500-1800 RPM) but there are many variables such as
polish/compound and speed / pressure used that may affect the paint removed)
There comes a point when you must judge wither removing a scratch will
compromise the clear coat and if so you’ll have to ‘live’ with the
imperfection.
If you have reservations
about the amount of paint surface removed or the amount of paint coating
remaining the use of a paint thickness gauge (PTG) is arbitrary
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.
These numbers are offered as a guide only, as there are too many
variables to provide any more than an approximation.
Paint Thickness Gauge (PTG)
These paint thickness
numbers are much too small to guess, a paint thickness gauge should be used to
measure clear coat both before and after polishing or compounding a paint
system. Using a paint thickness gauge acts as an insurance against ‘break-though’
of a clear coat, which would entail a re-paint. Original paint has a better
resale value than a re-painted vehicle, plus they will lose the use of their
vehicle for some days.
Take measurements with a
paint and coating thickness gauge and mark them on a template so that you have
a reading of before / after polishing. Take readings on each panel left – right
every 2- 4 inches, then drop down 2-inches and repeat.
[When the clear coat is breached, it very quickly is GAME OVER
for the pigmented paint below. So, what process explains why paint fades,
oxidizes, discolours or chalks?
In fact, incomplete reactivity is the “dirty little secret” of
the industry. They are always trying to get it better, but so far haven’t.
Think of these polymer matrixes as being chains of molecules which get their
strength from the bonds that hold them together (like links in a chain used to
pull a heavy object). Whether simple or complex, they have one unalterable
characteristic...they are chains that are only as strong as their weakest link.
That’s why the reactivity is so important in urethanes.
Reactivity is the
chemical process that makes those linkages. Break the link bond at any point
and you begin to weaken the chain that gives a coating its protective
capabilities. Un-reacted bonds are “weak links” from the beginning. Don’t
misunderstand quality polyurethanes from any name manufacturer are good
coatings, just not as good as some might like you to believe. ]
Paint Thickness Template http://s3.photobucket.com/albums/y88/TOGWT/?action=view¤t=carplan9br-3.jpg
If you use a car outline
template and mark the paint thickness, you can advise the customer of any
potential problems and you’ll also have a permanent record of the vehicle’s
paint surface, which can be used as a reference each time the car is polished.
Vehicles left outside absorb
radiation and can experience temperature swings of 20.oF; solvents, resins,
polymer and other ingredients in paint expand when they are heated, so
dependent upon paint surface temperature, you will obtain differing paint
thickness readings.
Clear Coat Failure (photo-oxidation)
Cause and Effect - Ultraviolet
(UV-B) Radiation - is vehicles paint and interior surface's greatest enemy,
causing more damage than any other airborne contaminant and affecting both the
interior and exterior of a vehicle. The light in this spectral range is
responsible for photo degradation.
Photo
degradation results in discoloration, fading, embitterment, cracking (crow’s
feet) chalking and/or loss of mechanical properties
Chalking
gel coat fibreglass, yellowing plastics, fading and weakening fabrics and
sunburned skin are all familiar problems caused by ultra violet radiation; UV-B
light is responsible for photosensitised fading. UV-A Infrared radiation is a
light source that transmits heat that when combined with a UV-B source will
cause oxidation by drying out the material.
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 light more readily than other materials.
Materials
that readily absorb UV light are quickly damaged...rubber, vinyl, gel coat
fibreglass, and many other plastics. Acrylic is slow to absorb UV light and
accordingly very resistant to photo degradation.
Competitive
absorbers (i.e. the carbon black in tyres) provide protection by converting UV
light to heat so it can dissipate harmlessly. All UV stabilizers are consumed
as they do their job. In a way, they serve as sacrificial molecules, taking the
abuse from UV light instead of the material they are protecting.
When UV
light is absorbed, it starts to break (cleave) weak chemical bonds, which leads
to bleaching (fading), discoloration, chalking, brittleness and cracking - all
indications of UV deterioration
When a
clear coat area appears to have an opaque ‘white or grey chalky’ or ‘cloudy’
look, this is the resin or paint binder system, which is indicative of clear
coat failure, sometimes due to;
Other causes- (a) Polishing the clear
coat too often or using an aggressive abrasive polish / compound that has
compromised the clear coat down to the colour (base) coat (sanding through)
this can be checked with a paint thickness gauge. Clear coat that is too thin loses
its ability to adhere effectively (delaminating) to the underlying paint layer
and will flake off. Moderate to light polishing will remove approximately 0.000025
Inches (0.635 Microns)
(b) Clear coat failure
becomes noticeable when a section becomes opaque as it reflects less gloss than
surrounding areas; this can be ascertained very clearly with an inspection
light. More often than not this condition cannot be corrected by buffing or
levelling the surface, it requires the refinishing of the paint system
Clear Coat Repaint
Surface preparation – use a
silicone and grease remover, use 2000 grit finishing paper and backing block to
provide a key for the paint. Spray the clear, apply thin coats (4-5) and allow
24 hours for the paint to cure and then use suitable (2500-3000) finishing grit
paper. Wipe down surface with Prep Sol and then use a Tack cloth, then polish
with a finishing polish and a foam pad.
Spray Max 2K Rapid Cut-In
Spot Clear coat (PN 3680061 - a two
component premium urethane clear coat for panel repairs, with excellent
resistance to chemical, weather, fuel and abrasive wear (12oz aerosol can)
Professional paint results, sprays like a spray gun - http://www.autobodytoolmart.com
Bibliography
1.
An Examination of What Paint Is, How It Degrades and What to Do
When It Does -By William Rice Evolution
2.
Automotive Paint and Protectant Technology, Gene Praschan and
David Ghodoussi
3.
Auto Painting: Basic of Basics - http://www.hotrodders.com/forum/basic-basics-how-do-i-paint-my-car-myself-44210.html
4.
Automotive Paint Handbook: Paint Technology for Auto Enthusiasts
and Body Shop Professionals - John Pfanstiehl
5.
UV Protection and Coatings for Plastics in the Automobile
Industry (P&CI) - http://www.pcimag.com/Articles/Cover_Story/da32fd89f66a7010VgnVCM100000f932a8c0
Information resource-
2.
PPG website on paint problems- http://bit.ly/4JAaVa
3.
Akzonoble Paints - http://www.akzonobelcarrefinishes.net/
4.
DuPont™ Automotive Coatings
5.
Glasurit, Advice on Paint and Paintwork Defects -
http://www.glasurit.com/Service/
6.
PPG Automotive Refinish Product Catalogue - http://bit.ly/4wMYuH
7.
Automotive Body Repair News (ABRN) -
http://www.abrn.com/abrn/
8.
Benjamin Moore Paints-http://www.benjaminmoore.com/
9.
A new perspective on paint defect return - Jason Rose from
Meguiar’s
10.
PCI Paint & Coating Industry Newsletters
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