Note: Descriptions are shown in the official language in which they were submitted.
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The present inVentiOn relates to corrosion-resis-
tant coating materials such as primers and the like and
to methods of preparing the same, being more particularly
concexned with increasing the anti-corrosive effect of
~hose primers or other coatings having electrochemically
active metal film additives and/or oxygen and moisture
diffusion barrier additives.
Though the present invention will be dascribed
in connection with the illustrative example of primer
coatings, i.t is to be understood that the invention is
applicable in the coating field genexally, wherever the
same phenomena are desired; and, more particularly, in
-~ the area of anti-corrosion coating~ For many years or-
ganic and inorganic primers have been used, for example,
in the painting of metal and the like for several func-
tions of purposes, includin~ (1) a base for a final top
coat, ~2) an anti-corrosive layer resistant to atmospheric
pollution, (3) bonding to substrates, and (4) fox film
strengthening. In connection with anti-corrosive applica-
tions, the attack by oxygen and moisture often causes
; rusting o~ exposed metal surfaces. Atmospheric pollution
containing sulphur dioxide and other gases similarly attacks
exposed surfaces. While it is the function of an effective
anti-corrosive primer to upgrade the protection by the
coating to such vapors or conditions, the fact is that
the problem of long life for such protective coatings still
exists in the art and is still the subject of much research
and de~elopment activity in view of the importance and high
co~t involved.
As described, for example, in Metal Finishins
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Guidebook Directory, published by Metals and Plastics Pub-
lications, Inc., Westwood, N.J. 1972, commencing with p.586,
there has been prior usage of electrochemically active anti-
corrosive additives, such as zinc dust or other elemental zinc
in high concentration; and also zinc chromate (sometimes known
as zinc yellow), the higher lead oxides such as so-called
red lead, and basic lead silico-chromates. These types of -
anti-corrosive additives may be used in high concentration
to provide a protective surface that prevents attack of the
metal or other surface on which the coaking is applied.
Some of the above additives and others, such as red iron
oxide, operate significantly as o~ygen and moisture diffusion
barriers that provide some protection to the underlying metal
or other surface. Current trends have limited the uses of-
some of these materials, particularly those involving lead,
however, as possible health hazards. Unfortunately, more-
over, bridges and other outdoor structures, particularly
I those in ocean and related environments, subject to salt
spray or other serious atmospheric and environmental abuse,
have to be scraped and repainted every few years at great
expense and inconvenience despite the use of such primers
as undercoats.
Numerous approaches have been tried and are still
being tried to improve this situation and better salve this
problem, including upgrading the paint materials with
alkyd epoxy, chlorinated rubber, silicone, vinyl and poly-
urethane resins and the like; but these have not adequately
solved the problem. As described in an article entitled
"Stainless Steel Paints", appearing in Metal Finishing,
Yebrgary, 1967, comme=ci=q with pa9e 6-, it has bee= sug~
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gested that the anti-corrosive pigments of corrosion in-
hibitive primers might be combined with conventional stain~
less steel particle pigments, such as those marketed under
the trademark "Stay-Steel" by Chas. Pfizer & Co., into a
one-coat primer top coat that might offer stainless steel
reinforcement. In practice, however, it has not been
found that such proposal, with conventional stainless
steel particles so admixed into a single coat, has actually
served significantly to improve the difficulty. The above~
mentioned article points out that such a single coat proposal,
had not heretofore in practice been able fully to achieve
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the desired results.
Underlying the present invention, however, is the
unexpected discovery that, if stainless steel particles are
rather critically geometically reshaped and dimenisoned, and
appropriately admixed, they can indeed be dispersed in anti-
corrosive primer binders as a single coat, with a rather re-
markable synergistically obtained improved protection per-
formance.
The present invention, therefore, has as one of its
primary objectives the provision of a new and improved corrosion
resistant coating material that employs such critically
dimensioned stainless steel material, and improved methods of
preparing the same, greatly to improve the protective charac-
teristîcs of a single coatine and the like.
In one particular aspect the present invention provides
in a corrosion-resistant coating composition comprising a :
primer selected from the group consisting of organic and
inorganic binders and metallic particles dispersed therethrough;
the improvement comprising, as said particles, stainless steel
planar flakes of thicknes6 of the order of 1/3 of a micron and
of surface dimensions largely of the order of 10 to ~0 microns
and in amounts of at least 1 pound per U.S. gallon of primer.
In another particular aspect the present invention
provides in a method of increasing the corrusion-resistant effect
of anti-corrosive primer resins containing at least one of :
electrochemically active metal film additives and oxygen
moisture diffusion barriers; the improvement comprising adding
to the primer resin stainless steel planar flakes in amounts of ;~
at least one pound per U.S. gallon of primer resin, said flakes
having a thickness of the order of 1/3 of a micron and surface
dimensions largely of the order of 10 to ~Q microns, and
; dispersing said flakes through the primer resin to provide a
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supplemental protective surface that cooperates with such
metal film additives to increase the electrochemical protection
thereof and cooperates with said diffusion barriers to
provide a supplemental flake barrier.
Other and further objects will be explained hereinafter
and are more particularly delineated in the appended claims.
As above stated, it has been quite accidently discovered
that the use of stainless steel particles in extremely thin
planar flake form, as distinguished from the arbitary shape,
somewhat spherical or other discreet particle size, as in the
prior art stainless steel pigments, including those before-
mentioned, vastly improves the protective quality of primer
binders and similar coatings in a manner that cannot be
attained with stainless steel particles of the shapes and
sizes previously used.
When such prior art stainless steel pigments are added
to conventional red primers containing 2inc chromates, zinc
- oxide and red iron oxide, for example, and the same is applied
as a primer to steel surfaces and exposed to rigid salt spray
attack over prolonged periods of time, the coating has been
found seriously to blister and rust to about the same degree
as the primer alone without the added stainless steel particles.
When, however, the same amount of stainless steel was added
to and dispersed in the primer in exactly the same conditions
of test, but with the stainless steel in the form of planar
flakes of the above-mentioned rather critical dimensions and
configuration, vastly improved, and indeed in some cases,
negligible blistering and rusting results were obtained.
Specifically, using the before-mentioned anti-rust
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primer of the type marketed by Sears under No. 68~92, with
one pound of the said "Stay-Steel" stainless steel pigment per
gallon of primer, salt spray testing was conducted on steel
plates in accordance with ASTM Test Bi, B117 (100F at ~
salt spray). This same test was performed with exactly thç
same weight of stainless steel flakes having an average thick- -:
ness of 0.34 or 1/3 micron and surface climensions of the flakes
largely in the range of f.rom 10-40 microns ~with approximately
33% being in the range of 2Q-30 microns, about 14% from 30-40
.microns and about 30% between 10 and 20 microns), with the - ~ .
surface dimensions of the flakes being very large compared to
the minute thickness of the fla~es. Additionally, the .same
test was performed with the anti-corrosive primer alone absent ~ :.
of any type of stainless steel additive.
On a scale of 10 established by the said test, a~te~ ~: .
140 hours oE salt spray exposure, the plates coated with the
primer alone and with the primer and "Stay-Steel" particles -
showed the same degradation as follows: blistering down to 7; :
and rusting down to S. In connection with the primer contain- ;
lng the stainless steel planar flakes, however,~the blistering
was extremely slight, at 9; and the rasting was also slight, :
at 8. A~ter 290 hours of the salt spray exposure, the plates -:
with the primer alone showed a degradation of blistering to ~, :
and a rusting down to 3; being somewhat better than the primer ~ :
with the "Stay-Steel" particles, which degraded to.a blister- :
ing o~ 4 and a rusting of 3. The 290 hour test with the before
mentioned stainless steel planar flakes additive, however, still
: showed but slight blistering at 8, and very slight degradation
in rusting at 7.
Other salt spray tests with zinc chromate primer
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similarly showed remarkably improved rus-t inhibiting perfor-
mance in accordance with the invention.
It was further found that while improved results
could be obtained within a rather wide range of variation of
stainless steel flake additive proportions, if the weight were
reduced substantially below one pound of stainless steel addi-
tive per U. S. gallon of primer, the results were closer to
the performance of the primer alone; such that at least of the
order of approximately one pound of stainless steel flakes
.additive per gallon of primer has been determined to be desirable
for the more spectacular improvement results above delineated.
While there is no intention to be bound by theoretical
explanations, correct or incorrect, it being sufficient merely
to describe the construction that has been found to work in
practice, it may be helpful to consider what is believed to be
a possible explanation for this unexpected improved resul~. In
the case of anti-corrosive primer additives of the type that
form metallic film (such as el0mental zinc additives before-
mentioned and the like), it appears that those partioles
that contact the stainless steel flakes have a vastly im-
proved or enhanced electrochemical reaction beyond that attain-
able with the metallic film alone in the absence of saia
flakes, such that a more effective protective surface is
thereby attained. This, of course, is supplimental to the
inherent protection provided by the surface formed by the
planar flakes of stainless steel. In connection, moreover,
with anti-corrosive additives (such as iron oxide, lead oxide
and the like~, which appear to protect at least in part as a
result of forming an oxygen and moisture diffusion barrier,
the contacting of the same with the stainless steel f~lake
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barrier appears -to provide a supplemental and vastly improved
difEusion oarrier effect1 with the barriers cohering in im~
proved fashion.
A second example of efficacious use of the invention
is the use of substantially one pound of the said critically
dimensioned stainless steel planar flakes in a gallon of
Irco zinc chromate primer in an organic binder, where no
evidence o~ rust even started to appear until slightly over
300 hours of intense salt spray testing.
. As a further example, the successful tests first
described in connection with tbe Sears primer and its anti-
corrosive zinc chromate, zinc oxide and red iron oxide addi-
tives were conducted with the stainless steel planar flakes
of the critical shape and dimensions before detailed dis-
persed in the organic primer binder after the flakes had been
formed with mineral spirits into a paste. The paste was mixed
rapidly into the binder containing the anti-corrosive elements
above mentioned.
As still another example, the primer organic binder
with which the said stainless steel flakes are mixed =ay com-
prise a binder material seleoted from the group consisting o~
alkyd, epoxy, vinyl, silicone, chlorinated rubber, and poly- ;
urethane resins.
As still a further illustration, the binder receivlng
the stainless steel flakes may be inorganic, as of zinc alkali
silicates.
As other examples, in addition to the elemental zinc,
zinc chromate and zinc oxide pigment additives for anti-corro-
sion purposes, where health hazard restrictions are not appli-
cable, lead o~ide and lead silico-chromate may be used, as well
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as combinations of all of the above with the flakes.
As still another example, diffusion barrier supple-
mentation with the said stainless steel flakes may be attained
with iron oxide and lead oxide additives.
In all of the above cases, the conventional electro-
chemically actlve anti-corrosion metal film additives and/or
the diffusion barrier additives were employed in precisely the
conventional commercial proportions that have been used for
many years and are currently used in the conventional organic
and inorganic primer binders, such as the specific examples ,~
above referenced.
~ s before stated, while the invention is particularly
;-- efficacious in its application to a one-coat anti-corrosive
stainless steel additive coating, it is clearly applicable with '
other coatings wherein the improvement herein attained may be
desired. It should be noted that the invention in no way' ' -'
modifies the physical and other properti~es of the primer or
' other coating so that paint or oth~e~r,~r,e,at,ment may be applied
as in present-day operation. Further modifications will occur
to those skilled in this art and all such are considered to
fall within the spirit and scope of tha invention as defined
- in the appended claims.
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