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The Basic Elements
The
Basic Elements
1.
Binders: Polymer binders hold the lubricating particles
and hard fillers in place and enable them to adhere to a wide
variety of substrates. From these materials the coatings derive
most of their corrosion and thermal characteristics. The
first binder employed in Xylan was a thermosetting alloy, which
offered exceptional toughness and is stable to 290°C/550°F.
After more than two decades, this binder is still widely used
for industrial applications in which its superior properties
and flexible cure schedule make it very adaptable. This class
of binder is found in the 1000, 1600 and 1700 Series of Xylan
coatings. (See Whitford’s “Introduction to the Xylan
1000 Series.”)
Another
rugged polymer employed as a binder in Xylan is a high-temperature-stable
thermoplastic. It is extremely resistant to abrasion and corrosion,
and is a good choice for components that operate in the presence
of strong acids, bases or solvents. It is the binder used in
the Xylan 1300 Series coatings.
A
third class of binder is a lower-temperature thermoset. Although
not as tough as some polymers, it provides good corrosion protection,
an exceptional array of colors, plus economy. It is a part of
the Xylan 1400 Series coatings (used on saw blades and other
consumer products for release and corrosion protection).
2.
Lubricants: Small particles of materials such as polytetrafluoroethylene
(PTFE), molybdenum disulfide, and graphite, suspended in the
wear-resistant binder, reduce friction at the surface of the
coating. These materials tend to be soft (and, in the case of
PTFE, waxy). When coated parts rub together, the lubricants
smear along the surface of the coating, thereby reducing friction.
PTFE
is most commonly used in Xylan because it has the lowest coefficient
of friction, is stable and effective at high and low temperatures,
and is inert to chemical attack. Also, because of its waxy characteristic,
it is an excellent release agent.
Other
fluoropolymer lubricants include FEP and PFA, which are more
thermoplastic and therefore offer better melt/flow characteristics,
resulting in denser coatings that can give improved release.
Both FEP and PFA have excellent nonstick and good low-friction
properties. Both are stable in the presence of a wide range
of solvents and corrosives.
Each
offers certain properties required in specific applications,
FEP for its superb release characteristics and PFA for its outstanding
toughness in abrasive conditions.
Moly
is preferred for high-load, low-speed applications. Moly increases
the load-bearing capability and the wear resistance of coatings
that are filled with other lubricants (notably PTFE).
Note:
encapsulating moly in a matrix coating seems to eliminate its
characteristic sensitivity to oxygen and moisture. For these
reasons, Whitford employs this lubricant in Xylan 1052, designed
for high load applications. Graphite is used for applications
where temperatures are in excess of 260°C/500°F and
in wet service at lower temperatures. Its drawback is that it
has a higher coefficient of friction than PTFE or moly.
3.
Pigments/Fillers: Coatings are modified by pigments
and fillers to provide properties not inherent in the primary
formulation, making them harder, more corrosion resistant or
adding color. For example, Xylan can be made electrically conductive
by the addition of fillers such as carbon or metal particles.
The
3 principal fluoropolymers
used in Xylan coatings
PTFE
(polytetrafluoroethylene): Has the lowest coefficient
of friction of any known solid and is the fluoropolymer
most widely used in coatings. It feels waxy to the
touch. Also blends well with engineering polymer binders;
is inert to most chemicals and is approved for use
in food applications.
FEP
(fluorinated ethylene propylene): Has the best nonstick
and nonwetting characteristics of the three. It feels
oily to the touch and lacks the high-temperature stability
of PTFE. It's more resistant to corrosives than PTFE.
Approved for use on food contact applications. Has
excellent stability in waterborne coatings.
PFA
(perfluoroalkoxy): Has better release and non wetting
properties than PTFE but not as good as FEP. Its wear
characteristics are not as good as PTFE. Limited use
in food contact applications. Has nearly the temperature
capability of PTFE.
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4.
Carriers:
Solid components of coatings are suspended or dissolved in solvents
or water which enable them to be applied as a paint. The solvents
used as carriers for Xylan are chosen for curing performance,
ease of clean-up, economy and environmental safety.
Different application
systems (conventional air spray/siphon, electrostatic, HVLP,
airless, coil coating, dip/spin) require different carrier combinations
to achieve optimum coating performance. For instance, conventional
spray systems require relatively slow (less volatile) solvents
that enable coatings to level more uniformly on the substrate
after spraying.
Other application techniques,
such as dip/spin, may require fast (more volatile) carriers,
to “set” the coating film rapidly while parts are
being processed.
Because of the many formulation
options possible with Xylan coatings, they can be tailored to
provide a wide and differing range of properties — to
solve different problems. If you have unique requirements for
lubricity, hardness, noise dampening, corrosion protection, environmental
compliance — even electrical conductivity — these
coatings may be modified to meet your exact need.
Xylan
“firsts”
Whitford has frequently created special coatings to solve specific
problems, leading to the extensive range of Xylan coatings today.
In this process of solving problems, many “firsts”
have been achieved by Xylan:
- First
polymer coating to survive the rigors of internal diesel engine
application on piston skirts and journal bearings (for more
information, ask for Whitford’s “Automotive Report”).
- First
tough PTFE coating with a flexible cure schedule. You can
apply it to temperature-sensitive materials such as forged
aluminum or tempered steel without reannealing the parts,
or to many polymeric parts without thermally de-grading and/or
warping them.
- First
coating to be used by engine manufacturers to achieve a boost
in output power.
- First
coating to be used to dampen “piston slap” and
resultant wear in high RPM motorcycle engines.
- First
coating to be used as a dynamic seal on air conditioner rotor
vanes.
- First
coating to achieve a wear rate equal to bronze/steel bearings
impregnated with PTFE-lead.
- First
coating to effectively displace cadmium and zinc as a corrosion
barrier on small fasteners.
- First
and only self-lubricating coating to be used by NASA on storage
vault for moon rocks.
Related
Links:
For additional Whitford firsts see - "Company
Profile - A few firsts"
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