Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED PHOSPHATING OPERATION
BACKGROUND OF THE INVENTION
This invention relates to the well known general field of phosphate conversion
coating of metals and more particularly to phosphate coatings formed from a
liquid
phosphating composition that contains both zinc and at least one of nickel,
cobalt,
and manganese as layer forming cations. The coatings formed from such a
phosphating composition normally contain both zinc and at least the one(s) of
nickel,
cobalt, and zinc also present in the phosphating compositions. These coatings
may
also contain iron, particularly if a ferriferous substrate such as ordinary
(non-stainless)
steel is being phosphated.
Almost all phosphating compositions and processes are subject to the
formation of "sludge", a solid phase that separates spontaneously from the
liquid
phosphating composition as the latter is used. The major components of sludge
are
water-insoluble phosphates, usually of more or less the same type(s) that
constitute
the desired conversion coating. Although some attempts have been made to re-
use
sludge, in most commercial operations it still represents an economically
significant
cost of phosphating, because the anions and cations incorporated into the
sludge
generally must be replenished along with the ions from the phosphating
composition
that actually form the desired phosphate conversion coating. Sludge generally
either
sinks to the bottom of any container in which it forms or floats on the liquid
phosphating composition from which it forms and therefore can be easily
removed
from the liquid phosphating composition by filtering or skimming if desired or
needed.
Sludge also is usually only weakly adherent to metal surfaces, and if it does
accumulate on them can be readily removed by brushing, water flush, or the
like.
A phenomenon less common than sludging that is sometimes observed in
commercial phosphating is the formation of an adherent scale on process
equipment,
such as squeegee rolls, immersion heaters and heat exchangers, that must be
kept
in contact with the phosphating compositions during their use in order to
maintain
optimum conditions for phosphating. No phosphate conversion coating of these
items
of process equipment is desired, and the objects are generally made of non-
metals
such as rubber for squeegee rolls or of metals such as stainless steel on
which
normal phosphate conversion coatings do not spontaneously form. Nevertheless,
when these objects, especially if their surfaces are hot, are maintained in
contact with
liquid phosphating compositions for extended periods of time, a relatively
hard,
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adherent, and diff icult to remove scale develops over the part of the surface
in contact
with the phosphating composition. Such scale is usually a heat insulator, so
that even
a relatively thin coating of the scale substantially impedes the heat
transfer, between
the metal and the phosphating compositions, that is a major reason for
maintaining
many of the metal surfaces in contact with the phosphating composition in the
first
place. On some other surfaces, such as squeegee rolls, the scale can interfere
with
the intended operation of the process equipment in other ways. The scale must
therefore be periodically removed, often as much as every few hours of
operation,
and scale must usually be removed primarily by hand labor. Its removal
therefore is
often very costly.
In many commercial phosphating operations, particularly continuous
operations such as those usually used to phosphate large metal coils, there is
a large
fixed capital cost of the equipment used for the phosphating, so that it is
economically
important to obtain the phosphate coatings rapidly, thereby diminishing the
fixed cost
per item of production by distributing this cost over more items. In most
instances,
phosphating reactions proceed more rapidly at higher rather than lower
temperatures.
A high phosphating temperature is therefore desirable to minimize fixed costs
per
production item, but if the high temperature causes more rapid scaling as it
usually
does when the phosphating composition used has a tendency to form scale, the
cost
of scale removal may destroy the economic benefit of faster phosphating.
Phosphating compositions with a high total concentration of cations of
divalent
nickel, divalent cobalt, and/or divalent manganese (these three types of
cations being
hereinafter usually jointly referred to as "NCM") along with zinc, as taught
in U. S.
Patent 4,681,641 of July 21, 1987 to Zurilla et al., often provide better
corrosion
resistance to the metal substrates covered with them than do almost any other
kind
of commonly used phosphating. However, they are also more prone to sludging
and,
when the total NCM content is very high, are much more prone to scaling than
almost
any other type of commonly used phosphating process.
Accordingly, a major object of this invention is to provide high NCM
phosphating compositions and/or processes that produce less sludge and/or
scaling
than previously used high NCM phosphating, particularly when the processes are
operated at high temperatures.
Except in the claims and the operating examples, or where otherwise
expressly indicated, all numerical quantities in this description indicating
amounts of
material or conditions of reaction and/or use are to be understood as modified
by the
word "about" in describing the broadest scope of the invention. Practice
within the
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numerical limits stated is generally preferred. Also, throughout this
description, unless
expressly stated to the contrary: percent, "parts of', and ratio values are
bvweight; the
term "polymer" includes "oligomer", "copolymer", and "terpolymer"; the
description of a group or class of materials as suitable or preferred for a
given
purpose in connection with the invention implies that mixtures of any two or
more of
the members of the group or class are equally suitable or preferred;
description of
constituents in chemical terms refers to the constituents at the time of
addition to any
combination specified in the description or of generation in situ by chemical
reactions
specified in the description, and does not necessarily preclude other chemical
in-
teractions among the constituents of a mixture once mixed; specification of
materials
in ionic form additionally implies the presence of sufficient counterions to
produce
electrical neutrality for the composition as a whole (any counterions thus
implicitly
specified should preferably be selected from among other constituents
explicitly speci-
fied in ionic form, to the extent possible; otherwise such counterions may be
freely se-
lected, except for avoiding counterions that act adversely to the objects of
the inven-
tion); the term "paint" and all of its grammatical variations are intended to
include any
similar more specialized terms, such as "lacquer", "varnish", "electrophoretic
paint",
"top coat", "color coat", "radiation curable coating", or the like and their
grammatical
variations; and the term "mole" and its grammatical variations may be applied
to ele-
mental, ionic, and any other chemical species defined by number and type of
atoms
present, as well as to compounds with well defined molecules.
BRIEF SUMMARY OF THE INVENTION
It has surprisingly been found that the presence of iron cations (particularly
ferric cations) in an otherwise conventional high NCM zinc phosphating
composition
reduces the formation of scale and/or sludge, even when the phosphating
composition is maintained at a high temperature.
Embodiments of the invention include working aqueous liquid compositions
suitable for contacting directly with metal surfaces to provide conversion
coatings
thereon; liquid or solid concentrates that will form such working aqueous
liquid com-
positions upon dilution with water, optionally with addition of other
ingredients;
processes of using working aqueous liquid compositions according to the
invention as
defined above to form protective coatings on metal surfaces and, optionally,
to further
process the metal objects with surfaces so protected; protective solid
coatings on
metal surfaces formed in such a process, and metal articles bearing such a
protective
coating.
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In one embodiment, there is provided an improved phosphating operation wherein
metal
substrates are either
A. contacted in a bath A with a working phosphating composition A comprised of
water, dissolved phosphate anions, dissolved NCM cations, and dissolved zinc
cations, wherein said bath A additionally contains at least one piece of
process
equipment having a surface, and wherein a hard, adherent, solid scale forms on
said surface when said surface is in contact with said working phosphating
composition A for an extended period of time; or
B. continually passed at a rate of speed in excess of 100 meters per minute
through
a bath B containing a working phosphating composition B comprised of water,
dissolved phosphate anions, dissolved NCM cations and dissolved zinc cations,
wherein a replenisher composition comprised of zinc cations is periodically
added to said working phosphating composition and wherein sludge forms in
bath B following such addition of the replenisher composition;
the improvement comprising said working phosphating composition A or said
working
phosphating composition B comprising a concentration of dissolved zinc cations
that is not
greater than 0.08 wt.%, wherein the weight ratio of dissolved zinc cations to
dissolved NCM
cations is not more than 0.5:1.00, and maintaining a level of dissolved ferric
cations in said
working phosphating composition A or said working phosphating composition B
which is
effective to either reduce the amount of scale forming on said surface or
reduce the amount
of sludge forming in bath B in said working phosphating composition A or
working
phosphating composition B, wherein working phosphating composition A or
working
phosphating composition B is maintained at a temperature of at least 66 C.
In another embodiment, there is provided a phosphating operation comprising:
contacting metal substrates comprised of a material selected from the group
consisting
of galvanized steel, zinc-magnesium alloys and zinc-aluminum alloys in a bath
with a working
phosphating composition comprised of water and:
a) 0.2 to 20% dissolved phosphate anions:
b) at least 4.3 ppt dissolved nickel cations; and
c) 0.010 to 2.0% dissolved zinc cations;
and having a ratio of zinc cations:NCM cations that is at least 0.03:1.00 and
not greater than
0.9:1.00;
while maintaining said working phosphating composition at a temperature of at
least 50 C,
wherein said bath additionally contains at least one piece of process
equipment having a surface
and wherein a hard, adherent scale forms on said surface when said surface is
in contact with
said working phosphating composition for an extended period of time, and while
maintaining a
level of dissolved ferric ions in said working phosphating composition which
is at least 40% of the
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saturation level for ferric ions in the working phosphating composition such
that powdery scale
removable by brushing forms instead of said hard, adherent scale.
In yet another embodiment, there is provided a phosphating operation
comprising
continually passing metal substrates comprised of a material selected from the
group consisting
of galvanized steel, zinc-magnesium alloys and zinc-aluminum alloys at a speed
of at least 100
meters per minute through a bath containing a working phosphating composition
comprised of
water and:
a) 0.2% to 20% dissolved phosphate anions;
b) 0.3 to 1.5% dissolved NCM cations; and
c) 0.010 to 2.0% dissolved zinc cations
wherein portions of a replenisher composition comprised of zinc cations and a
source of ferric
cations are periodically added to said working phosphating composition at a
rate sufficient to
maintain a concentration of ferric cations which is at least 40% of the
saturation level for ferric
cations in said working phosphating composition.
In yet another embodiment, there is provided a composition suitable for use in
replenishing a working phosphating composition, said composition comprising
water and:
a) a concentration of dissolved phosphate anions that is at least 15% and not
more than 50%;
b) a concentration of dissolved NCM cations that is at least 1.2% and not more
than 5.0%;
c) a concentration of dissolved zinc cations that is at least 4.0% and not
more than 15%; and
d) a concentration of dissolved iron cations that is at least 0.02%
In yet another embodiment, there is provided a composition suitable for use in
replenishing a working phosphating composition, said composition comprising
water and:
a) a concentration of dissolved phosphate anions that is at least 13% and not
more than 50%;
b) a concentration of dissolved NCM cations that is at least 4.2% and not more
than 8.0%;
c) a concentration of dissolved zinc cations that is at least 0.5% and not
more than 4.0%;and
d) a concentration of dissolved iron cations that is at least 0.02%.
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DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED
EMBODIMENTS
A working composition according to the invention preferably comprises water
and the following components:
(A) dissolved phosphate anions;
(B) dissolved NCM cations;
(C) dissolved zinc cations; and
(D) dissolved iron cations.
One or more of undissolved iron cations and the following components may also
be
present in the working composition:
(E) a phosphating accelerator that is not part of any of components
(A) through (D) as recited immediately above;
(F) dissolved fluoride ions that are not part of any of components
(A) through (E) as recited immediately above;
(G) an acidity adjustment agent that is not part of any of
components (A) through (F) as recited immediately above; and
(H) sludge conditioner that is not part of any of components (A)
through (G) as recited immediately above.
In a composition according to the invention, component (A) preferably, at
least
for economy, is sourced to a composition according to the invention by at
least one
of orthophosphoric acid and its salts of any degree of neutralization.
Component (A)
can also be sourced to a composition according to the invention by
pyrophosphate
and other more highly condensed phosphates, including metaphosphates, which
tend
at the preferred concentrations for at least working compositions according to
the
invention to hydrolyze to orthophosphates. However, inasmuch as the condensed
phosphates are usually at least as expensive as orthophosphates, there is
little
practical incentive to use condensed phosphates, except possibly to prepare
extremely highly concentrated liquid compositions according to the invention,
in which
condensed phosphates may be more soluble.
Whatever its source, the concentration of component (A) in a working
composition according to the invention, measured as its stoichiometric
equivalent as
P04-3 anions with the stoichiometry based on equal numbers of phosphorus
atoms,
preferably is at least, with increasing preference in the order given, 0.2,
0.4, 0.6, 0.70,
0.75, 0.80, 0.84, 0.86, 0.88, 0.90, or 0.92 % and independently preferably is
not more
than, with increasing preference in the order given, 20, 10, 6.5, 5.0, 4.0,
3.5, 3.0, 2.0,
1.8, 1.6, or 1 .4
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Component (B) of dissolved NCM cations is preferably sourced to the
composition as at least one nitrate or phosphate salt (which may of course be
prepared by dissolving the elemental metal and/or an oxide or carbonate
thereof in
acid), although any other sufficiently soluble salt of the NCM cations may be
used.
The entire NCM cations content of any water-soluble NCM salt dissolved in a
composition according to the invention is presumed to be NCM cations in
solution,
irrespective of any coordinate complex formation or other physical or chemical
bonding of the NCM cations with other constituents of the composition
according to
the invention. Independently of their source, the concentration of NCM cations
in a
working composition according to the invention preferably is at least, with
increasing
preference in the order given, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18
or 0.20 % and
independently preferably is not more than, with increasing preference in the
order
given, 1.5, 1.0, 0.8, 0.70, 0.60, 0.55, 0.50, or 0.47 %. If the concentration
of NCM is
too low, the improved corrosion resistance associated with a "high NCM"
phosphating
composition will not usually be achieved, while if this concentration is too
high, the
cost of the composition will increase inordinately without any corresponding
increase
in performance. Among the NCM cations, nickel is most preferred because it is
at
least slightly more effective in imparting high alkaline corrosion resistance
than cobalt
or manganese.
Zinc cations for component (C) are preferably sourced to a composition
according to the invention from at least one zinc phosphate salt, at least one
zinc
nitrate salt, and/or by dissolving at least one of metallic zinc, zinc oxide,
and zinc
carbonate in a precursor composition that contains at least enough phosphoric
and/or
nitric acid to convert the zinc content of the oxide to a dissolved zinc salt.
However,
these preferences are primarily for economy and availability of commercial
materials
free from amounts of impurities that adversely affect phosphating reactions,
so that
any other suitable source of dissolved zinc cations could also be used. As for
NCM,
the entire zinc content of any salt or other compound dissolved or reacted
with acid in
a composition according to the invention is to be presumed to be present as
cations
when determining whether the concentration of zinc cations satisfies a
concentration
preference as noted below.
In any working composition according to the invention, the concentration of
zinc cations preferably is at least, with increasing preference in the order
given, 0.010,
0.020, 0.030, 0.040, 0.045, or 0.049 % and independently preferably is not
more than,
with increasing preference in the order given, 2.0, 1.5, 1.2, 1.0, 0.80, 0.70,
0.60, 0.55,
0.50, 0.45, 0.40, 0.36, or 0.33 %. In the first of two alternative especially
preferred
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embodiments of the invention, one in which the NCM cations concentration is
higher
than the zinc cations concentration: the concentration of zinc cations
additionally
preferably is not greater than, with increasing preference in the order given,
0.20,
0.15, 0.10, 0.08, or 0.06 %; and, independently, the ratio of zinc cations to
NCM
cations preferably is at least, with increasing preference in the order given,
0.03:1.00,
0.05:1.00, 0.07:1.00, 0.09:1.00, or 0.11:1.00 and independently preferably is
not more
than, with increasing preference in the order given, 0.9:1.00, 0.7:1.00,
0.5:1.00,
0.40:1.00, 0.35:1.00, 0.30:1.00, 0.25:1.00, 0.20:1.00, or 0.15:1.00. In the
second of
these two alternative especially preferred embodiments of the invention, one
in which
the concentration of zinc ions is greater than the concentration of NCM ions:
the
concentration of zinc cations additionally preferably is at least, with
increasing
preference in the order given, 0.075, 0.10, 0.15, 0.20, 0.23, 0.25, 0.27,
0.29, or 0.31
percent; and, independently, the ratio of zinc cations to NCM cations
preferably is at
least, with increasing preference in the order given, 1.10:1.00, 1.20:1.00,
1.30:1.00,
1.35:1.00,1.40:1.00,1.45:1.00, 1.50:1.00,1.55:1.00, or 1.58:1.00 and
independently
preferably is not more than, with increasing preference in the order given,
7:1.00,
5:1.00, 3.0:1.00, 2.7:1.00, 2.5:1.00, 2.3:1.00, 2.1:1.00, 1.9:1.00, or
1.7:1.00.
Component (D) of iron cations is preferably sourced to a phosphating
composition according to the invention by a source of iron(III) ions, most
preferably
ferric nitrate although other water-soluble sources of ferric ions may be
used. The
solubilities of ferric phosphate and of ferric hydroxide are rather low in the
presence
of preferred amounts of other constituents of a preferred phosphating
composition
according to this invention, and it is in certain embodiments of the invention
preferred
to maintain the dissolved iron(III) cations at their saturation value by
supplying an
excess of ferric salt, most of which remains undissolved unless and until some
of the
dissolved ferric ions are removed from the composition by drag-out,
precipitation as
sludge, or the like. It should be noted that the solubilities of ferric salts
are affected
by pH. At relatively low pH levels (high acidity) such as are typically
present in the
concentrate compositions of the present invention (replenisher or make-up),
the ferric
salt will generally be more soluble than at higher pH levels. Precipitation of
a portion
of the ferric salt dissolved in a replenisher or make-up concentrate will thus
commonly
be observed when the concentrate is diluted in the working phosphating
composition.
The concentration of dissolved iron cations in a working phosphating
composition according to the invention preferably is at least, with increasing
preference in the order given, 40, 60, 80, or 100 % of its saturation level,
which is
believed to correspond to about 10 parts of dissolved iron per million parts
by weight
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of total phosphating composition (this unit of concentration being freely used
hereinafter for any constituent of a phosphating composition and being
hereinafter
usually abbreviated as "ppm"). In order to assure maintenance of the most
preferred
fully saturated concentration of dissolved iron cations, it is preferred to
provide to a
phosphating composition according to the invention an amount of total ferric
salt that
contains at least, with increasing preference in the order given, 20, 30, 40,
50, or 60
ppm of iron cations.
In at least certain embodiments of the invention, however, it may be desirable
to limit the amount of total ferric salt provided to the phosphating
composition. At very
high levels of total ferric salt, excessive sludging and/or scaling may take
place. For
this reason, it may be advantageous to provide to the phosphating composition
an
amount of total ferric salt that contains not more than, with increasing
preference in
the order given, 700, 600, 500, 400, 200 or 100 ppm of iron cations.
Optional component (E) of conversion coating accelerator preferably is
present in a composition according to the invention, because without this
component
the coating formation rate usually is slower than is desired. The accelerator
when
present in a working composition according to the invention preferably is
selected
from the group consisting of: 0.3 to 4 parts of chlorate ions per thousand
parts of total
phosphating composition, this unit of concentration being freely used
hereinafter for
any constituent of the composition and being hereinafter usually abbreviated
as "ppt";
0.01 to 0.2 ppt of nitrite ions; 0.05 to 2 ppt of m-nitrobenzene sulfonate
ions; 0.05 to
2 ppt of m-nitrobenzoate ions; 0.05 to 2 ppt of p-nitrophenol; 0.005 to 0.15
ppt of
hydrogen peroxide in free or bound form; 0.1 to 10 ppt of hydroxylamine in
free or
bound form; 0.1 to 10 ppt of a reducing sugar; and 1 to 30 ppt of nitrate
ions. Nitrate
ions are preferred within this group and are most preferably used without any
of the
other accelerators in this group. Nitrate ions are preferably sourced to the
composition by at least one of nitric acid and its salts. When nitrate ions
are present
in a working composition according to the invention, their concentration more
preferably is at least, with increasing preference in the order given, 1.5,
2.0, 2.5, 3.0,
3.3, 3.6, 3.9, 4.1, or 4.3 ppt and independently preferably is not more than,
with
increasing preference in the order given, 25, 20, 17, 15, 13, 11, or 9.0 ppt.
(If the
concentration of nitrate is too high, the danger of emissions of noxious
oxides of
nitrogen from the phosphating composition is increased.)
The presence of optional component (F) of dissolved fluoride in a composition
according to the invention is also preferred, because without it the danger of
forming
the small surface blemishes known in art as "white specking", "seediness", or
the like
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is increased when phosphating zinciferous surfaces, and there is also less
likelihood
of obtaining the most desired crystal morphology. More preferably, this
fluoride is
sourced to the composition in two differing forms: "uncomplexed fluoride"
supplied
by hydrofluoric acid and/or one of its salts (which may be partially or
totally
neutralized); and "complexed fluoride" supplied to the composition by at least
one of
the acids HBF4, H2SiF6, H2TiF6, H2ZrF6, and H2HfF6i and their salts (which
also may
be partially or totally neutralized). Among this group, H2SiF6 and its salts
are most
preferred, the acid itself being usually preferred for economy and ready
commercial
availability.
When both uncomplexed and complexed fluorides are present in a working
phosphating composition according to the invention and the concentration of
NCM in
the phosphating composition is greater than the concentration of zinc measured
in the
same mass-based units: the concentration of uncomplexed fluoride in the
phosphating composition preferably is at least, with increasing preference in
the order
given, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, or 0.16 ppt and independently
preferably is not more than, with increasing preference in the order given,
2.0, 1.5,
1.0, 0.8, 0.6, '0.40, 0.35, 0.30, 0.25, 0.23, 0.21, 0.19, or 0.17 ppt;
independently, the
concentration of complexed fluoride in the phosphating composition preferably
is at
least, with increasing preference in the order given, 0.04, 0.08, 0.12, 0.16,
0.20, 0.24,
0.28, 0.31, 0.33, 0.35, or 0.37 ppt and independently preferably is not more
than, with
increasing preference in the order given, 4.5, 3.5, 2.5, 2.0, 1.5, 1.0, 0.90,
0.80, 0.70,
0.60, 0.50, 0.45, or 0.40 ppt; and, independently, the ratio of uncomplexed
fluoride to
complexed fluoride preferably is at least, with increasing preference in the
order
given, 0.05:1.00, 0.10:1.00, 0.15:1.00, 0.20:1.00, 0.25:1.00, 0.30:1.00,
0.35:1.00,
0.39:1.00, 0.41:1.00, or 0.43:1.00 and independently preferably is not more
than, with
increasing preference in the order given, 4:1.00, 2.0:1.00, 1.5:1.00,
1.00:1.00,
0.80:1.00, 0.70:1.00, 0.65:1.00, 0.60:1.00, 0.55:1.00, 0.50:1.00, 0.48:1.00,
0.46:1.00,
or 0.44:1.00.
When both uncomplexed and complexed fluorides are present in a working
phosphating composition according to the invention and the concentration of
NCM in
the phosphating composition is less than or equal to the concentration of zinc
measured in the same mass-based units: the concentration of complexed fluoride
in
the phosphating composition preferably is at least, with increasing preference
in the
order given, 0.25, 0.50, 1.0, 1.5, 1.8, 2.0, 2.2, or 2.4 ppt and independently
preferably
is not more than, with increasing preference in the order given, 20, 15, 10.0,
7.0, 5.0,
4.0, 3.5, 3.2, 2.9, 2.7, or 2.5 ppt; independently, the concentration of
uncomplexed
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fluoride in the phosphating composition preferably is at least, with
increasing
preference in the order given, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40,
0.45, 0.50,
0.54, 0.57, or 0.59 ppt and independently preferably is not more than, with
increasing
preference in the order given, 7.0, 6.0, 5.0, 4.5, 3.5, 2.5, 2.0, 1.5, 1.00,
0.90, 0.80,
0.70, 0.65, or 0.60 ppt; and, independently, the ratio of uncomplexed fluoride
to
complexed fluoride preferably is at least, with increasing preference in the
order
given, 0.02:1.00, 0.04:1.00, 0.06:1.00, 0.08:1.00, 0.10:1.00, 0.12:1.00,
0.14:1.00,
0.16:1.00, 0.18:1.00, 0.20:1.00, 0.22:1.00, or 0.24:1.00 and independently
preferably
is not more than, with increasing preference in the order given, 2.0:1.00,
1.5:1.00,
1.00:1.00, 0.80:1.00, 0.50:1.00, 0.45:1.00, 0.40:1.00, 0.35:1.00, 0.32:1.00,
0.29:1.00,
0.27:1.00, or 0.25:1.00.
If a phosphating composition according to the invention contains either
fluoride only in uncomplexed form or fluoride only in complexed form, then: if
the NCM
concentration is greater than the zinc concentration in the phosphating
composition,
the total fluoride content of the composition preferably is at least, with
increasing
preference in the order given, 0.10, 0.20, 0.30, 0.40, or 0.50 ppt and
independently
preferably is not more than, 5, 3, 2.0, 1.0, 0.8, or 0.6 ppt; but if the NCM
concentration
is less than or equal to the zinc concentration in the composition, the total
fluoride
content of the composition preferably is at least, with increasing preference
in the
order given, 0.5, 1.0, 1.5, 2.0, 2.5, or 2.9 ppt and independently preferably
is, with
increasing preference in the order given, not more than 20, 15, 10, 7, 5, or
3.1 ppt.
Independently of other preferences, if a phosphating composition according
to the invention contains dissolved fluoride of any type, the ratio of the
total dissolved
fluoride concentration to the dissolved zinc cations concentration, both
measured in
the same mass-based units, preferably is at least, with increasing preference
in the
order given, 0.2:1.00, 0.4:1.00, 0.6:1.00, 0.80:1.00, 0.87:1.00, or 0.92:1.00
and
independently preferably is not more than, with increasing preference in the
order
given, 5:1.00, 3:1.00, 2.0:1.00, 1.8:1.00, 1.6:1.00, 1.4:1.00, 1.20:1.00, or
1.10:1.00.
A phosphating composition according to this invention is necessarily acidic.
Its acidity is preferably measured for control and optimization by two
characteristics
familiar in the art as "points" of Free Acid (hereinafter usually abbreviated
as "FA")
and of Total Acid (hereinafter usually abbreviated as "TA"). Either of these
values is
measured by titrating a 10.0 milliliter sample of the composition with 0.100 N
strong
alkali. If FA is to be determined, the titration is to an end point of pH 3.8
as measured
by a pH meter or an indicator such as bromcresol green or bromthymol blue,
while if
TA is to be determined, the titration is to an end point of pH 8.0 as measured
by a pH
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meter or an indicator such as phenolphthalein. In either instance, the value
in points
is defined as equal to the number of milliliters of the titrant required to
reach the end
point.
A working phosphating composition according to this invention preferably has
an FA value that is at least, with increasing preference in the order given,
0.1, 0.3, 0.5,
0.7, 0.9, 1.1, 1.3, 1.5, 1.7 or 1.9 points and independently preferably is not
more than,
with increasing preference in the order given, 10, 8, 6.0, 5.0, 4.5, 4.0, 3.7,
3.5, 3.3, or
3.1 points. Also and independently, a working phosphating composition
according to
the invention preferably has a TA value that is at least, with increasing
preference in
the order given, 10, 13, 16, 19, 22, 25, or 27 points and independently
preferably is
not more than, with increasing preference in the order given, not more than,
with
increasing preference in the order given, 50, 45, 40, 38, 36, or 34 points. If
either the
FA or the TA value is too low, the phosphating coating formation will be lower
than is
usually desired, while if either value is too high there may be excessive
dissolution of
the substrate and/or suboptimal crystal morphology in the coating formed.
Ordinarily,
the FA and TA values can be brought within a preferred range by use of
appropriate
amounts of acidic sources of phosphate, nitrate, and/or complexed fluoride and
basic
sources of zinc and/or NCM, but if needed, optional component (G) preferably
is used
to bring the composition within a preferred range of both TA and FA. Alkali
metal
2 0 hydroxides, carbonates, and/or oxides are preferably used for this purpose
if alkalinity
is needed, and phosphoric acid and/or nitric acid is preferably used if
acidity is
needed.
Optional component (H) of sludge conditioner is not always needed in a com-
position according to the invention and therefore is preferably omitted in
such
instances. However, in many instances, at least one such conditioner may be
advantageously used, in order to make separation and collection of any sludge
that
forms easier. In any such instances, suitable material for these purposes can
be
readily selected by those skilled in the art. Preferred sludge conditioners
are shown
in the examples below.
For various reasons, almost always including at least a cost saving from elimi-
nation of an unnecessary ingredient, it is preferred that a composition
according to
this invention should be largely free from various materials often used in
prior art com-
positions. In particular, compositions according to this invention in most
instances
preferably do not contain, with increasing preference in the order given, and
with
independent preference for each component named, more than 5, 4, 3, 2, 1, 0.5,
0.25, 0.12, 0.06, 0.03, 0.015, 0.007, 0.003, 0.001, 0.0005, 0.0002, or 0.0001
% of
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each of (i) dissolved calcium cations, (ii) dissolved copper cations, (iii)
dissolved
aluminum, and (iv) dissolved chromium in any chemical form.
Preferred concentrations have been specified above for working compositions
according to the invention, but another embodiment of the invention is make-up
con-
centrate compositions that can be diluted with water only to produce a working
composition, and the concentration of ingredients other than water in such a
concentrate composition preferably is as high as possible without resulting in
instability of the concentrate during storage, in order to minimize the cost
of shipping
water from a concentrate manufacturer to an end user, who can almost always
provide water more cheaply at the point of use.
More particularly, in a concentrate composition according to this invention,
the
concentration of each ingredient other than water preferably is at least, with
increasing preference in the order given, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 or
times as great
as the preferred minimum amounts specified above for working compositions
according to the invention. In addition to the concentrations recited above, a
make-up
concentrate preferably has the same ratios between various ingredients as are
specified for working compositions above.
A phosphating composition according to the invention is preferably maintained
while coating a metal substrate in a process according to the invention at a
temperature that is at least, with increasing preference in the order given,
30, 40, 50,
55, 60, 62, 64, 66, or 68 C and independently preferably is not more than,
with
increasing preference in the order given, 95, 90, 85, 81, 79, or 77 C.
The specific areal density (also often called "add-on weight for mass]") of a
phosphate coating formed according to this invention preferably is at least,
with in-
creasing preference in the order given, 0.3, 0.6, 0.8, 1.0, 1.2, 1.4, or 1.6
grams of
dried coating per square meter of substrate coated, this unit of coating
weight being
hereinafter usually abbreviated as "g/m2,, , and independently preferably is
not more
than, with increasing preference in the order given, 10, 8, 6, 5.0, 4.5, 4.0,
or 3.5 g/m2.
The phosphate conversion coating weight may be measured by stripping the
conversion coating in a solution of chromic acid in water as generally known
in the art.
Before treatment according to the invention, metal substrate surfaces
preferably are conventionally cleaned, rinsed, and "conditioned" with a
Jernstedt salt
or an at least similarly effective treatment, all in a manner well known in
the art for any
particular type of substrate; and after a treatment according to the invention
the
composition according to the invention generally should be rinsed off the
surface
coated before drying.
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This invention is particularly advantageously, and therefore preferably, used
on zinciferous metal substrates, such as galvanized steel of all kinds and
zinc-
magnesium and zinc-aluminum alloys, or more generally any metal alloy surface
that
is at least 55 % zinc, and on such substrates there are two particularly
preferred
established areas of commercial operation in which this invention is
especially
advantageous and to which it is therefore highly preferably applied.
In the first of these areas:
the phosphating composition used:
-- contains at least, with increasing preference in the order given,
2.5, 3.0, 3.3, 3.6, 3.9, 4.1, 4.3, or 4.5 ppt of NCM cations; and
-- contains NMC and zinc cations in a ratio of zinc to NMC that
preferably is at least, with increasing preference in the order given,
0.03:1.00, 0.05:1.00, 0.07:1.00, 0.09:1.00, or 0.11:1.00 and
independently preferably is not more than, with increasing preference
in the order given, 0.9:1.00, 0.7:1.00, 0.5:1.00, 0.40:1.00, 0.35:1.00,
0.30:1.00, 0.25:1.00, 0.20:1.00, or 0.15:1.00; and
the phosphating composition is:
-- in contact during its use in phosphating with at least one
surface on which no phosphate coating or other solid coating forma-
tion is desired; and
-- maintained during its use at a temperature that preferably is at
least, with increasing preference in the order given, 50, 55, 60, 62, 64,
66, or 68 C.
Under such conditions, the formation of scale on the metal surfaces on which
no
coating is desired is usually a serious problem in the absence of iron in the
phosphating composition.
In the second established area of commercial operation in which this invention
is most particularly preferred (an area which is not at all necessarily
exclusive of the
first), the characteristic feature is a very rapid movement of the substrate
through the
phosphating composition during the phosphating process, a common condition in
high speed treatment of coils. When the relative speed of the substrate
through the
phosphating composition exceeds, with increasing preference in the order
given, 100,
125, 150, 160, 165, 170, 175, 180, or 185 meters per minute (this unit of
speed being
hereinafter usually abbreviated as "m/min"), it has surprisingly been found
that disso-
lution of zinc from the surface of the substrate, which can normally be relied
on to
provide a sufficient amount of zinc to compensate for the amount consumed as
zinc
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phosphate and make it unnecessary to add zinc in any replenisher for the
phosphating composition, is often not effective for this purpose. This is
severely
limiting, because in prior art practice with phosphating compositions that did
not
contain dissolved iron cations but were otherwise similar to those according
to this
invention, it has surprisingly been found that adding a conventional zinc
containing
replenisher is ineffective, inasmuch as most or all of the zinc content of the
replenisher added is rapidly precipitated as sludge. The presence of iron in a
composition according to the invention very greatly reduces the amount of
sludge
formed by adding a replenisher that contains a substantial concentration of
zinc, par-
ticularly if the replenisher itself also contains dissolved iron cations.
Furthermore, in prior art practice with phosphating compositions similar to
those of this invention except for the absence of iron in the prior art
compositions, it
has surprisingly been found that a high speed of the substrate through the
phosphating composition resulted in a crystal morphology in the coating formed
that
had inferior protective value, compared with a coating formed on the same
substrate
with the same phosphating when the motion of the substrate through the
phosphating
composition was lower. This adverse effect also can be eliminated in a process
according to this invention.
In any phosphating process according to this invention, as with all or almost
all other known phosphating processes, if the initially prepared phosphating
composition is to be used for a long period, it is preferred to maintain the
effectiveness of the process by adding a suitable replenisher to compensate
for any
changes in the concentrations of ingredients in the initially prepared
phosphating
composition that occur as a result of using the phosphating composition. The
optimum characteristics of a replenisher composition often depend on the
nature of
the substrate being coated and the relative speed of motion between the
phosphating
composition and the substrate being phosphated. For the second of the two
established areas of commercial operation in which this invention is most
particularly
preferred as noted above, a preferred replenisher composition preferably
comprises
water and the following concentrations of the following other components:
(R2A) a concentration of dissolved phosphate anions that is at least,
with increasing preference in the order given, 15, 17, 19, 21, 23, 25, or 27 %
and independently preferably is not more than, with increasing preference in
the order given, 50, 45, 40, 37, 34, 32, 30, or 28 %;
(R26) a concentration of dissolved NCM cations that is at least, with
increasing preference in the order given, 1.2, 1.4, 1.6, or 1.8 % and
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independently preferably is not more than, with increasing preference in the
order given, 5.0, 4.0, 3.0, 2.5, 2.3, 2.1, or 1.9 %;
(R2C) a concentration of dissolved zinc cations that is at least, with
increasing preference in the order given, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, or 5.2
%
and independently preferably is not more than, with increasing preference in
the order given, 15, 12, 10, 8.0, 7.0, 6.0, or 5.5 %; and
(R2D) a concentration of dissolved iron cations that is at least, with
increasing preference in the order given, 0.02, 0.04, 0.06, 0.08, or 0.10 %.
Optionally, one or more of undissolved iron cations and the following
concentrations
of the following components may also be present:
(R2E) a concentration of nitrate ions that is at least, with increasing
preference in the order given, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, or 6.2 % and
independently preferably is not more than, with increasing preference in the
order given, 12, 10, 9.0, 8.0, 7.5, 7.0, 6.8, 6.6, or 6.4 percent;
(R2F) a concentration of dissolved uncomplexed fluoride ions that is
at least, with increasing preference in the order given, 0.05, 0.10, 0.15,
0.20,
0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, or 0.58 percent and independently
preferably is not more than, with increasing preference in the order given,
1.5,
1.2, 1.0, 0.90, 0.80, 0.70, 0.65, or 0.62 percent;
(R2G) surfactant that is not part of any of components (R2A) through
(R2F) as recited immediately above; and
(R2H) sludge conditioner that is not part of any of components (R2A)
through (R2G) as recited immediately above.
Preferred surfactant(s) and sludge conditioners are described in the working
examples.
For the first of the two established areas of commercial operation in which
this
invention is most particularly preferred as noted above, if the relative
motion between
the substrate being phosphated and the phosphating composition during
phosphating
is not as much as 100 meters per minute, a particularly preferred replenisher
compo-
sition preferably comprises water and the following concentrations of the
following
other components:
(R1 A) a concentration of dissolved phosphate anions that is at least,
with increasing preference in the order given, 13, 15, 17, 19, 21, 23, or 25
percent and independently preferably is not more than, with increasing
preference in the order given, 50, 45, 40, 37, 34, 32, 30, 28, or 26 percent;
(R2B) a concentration of dissolved NCM cations that is at least, with
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WO 01/96627 PCT/US01/19499
increasing preference in the order given, 4.2, 4.4, 4.6, or 4.8 % and
independently preferably is not more than, with increasing preference in the
order given, 8.0, 7.0, 6.0, 5.5, 5.3, 5.1, or 4.9 %;
(R2C) a concentration of dissolved zinc cations that is at least, with
increasing preference in the order given, 0.50, 0.60, 0.70, 0.80, 0.90, 1.00,
or
1.06 percent and independently preferably is not more than, with increasing
preference in the order given, 4.0, 3.0, 2.5, 2.0, 1.7, 1.5, 1.3, or 1.1
percent;
and
(R2D) a concentration of dissolved iron cations that is at least, with
increasing preference in the order given, 0.02, 0.04, 0.06, 0.08, or 0.10 %.
Optionally, one or more of undissolved iron cations and the following
concentrations
of the following components may also be present:
(R2E) a concentration of nitrate ions that is at least, with increasing
preference in the order given, 3.0, 3.5, 3.7, 3.9, 4.1, 4.3, 4.5, or 4.7 % and
independently preferably is not more than, with increasing preference in the
order given, 10, 8.0, 7.0, 6.5, 6.0, 5.7, 5.4, 5.2, 5.0, or 4.8 percent;
(R2F) a concentration of dissolved uncomplexed fluoride ions that is
at least, with increasing preference in the order given, 0.05, 0.10, 0.15,
0.20,
0.25, 0.30, 0.35, 0.40, 0.42, 0.44, 0.46, or 0.48 percent and independently
preferably is not more than, with increasing preference in the order given,
1.2,
1.0, 0.90, 0.80, 0.70, 0.60, 0.55, or 0.50 percent;
(R2G) surfactant that is not part of any of components (R2A) through
(R2F) as recited immediately above; and
(R2H) sludge conditioner that is not part of any of components (R2A)
through (R2G) as recited immediately above.
Preferred surfactant(s) and sludge conditioners are described in the working
examples.
The practice of this invention may be further appreciated by consideration of
the following, non-limiting, working examples, and the benefits of the
invention may
be further appreciated by reference to the comparison examples.
EXAMPLE AND COMPARISON EXAMPLE 1
In these tests, both working phosphating compositions were made from a con-
centrate with the ingredients shown in Table 1 below. The working compositions
each
contained 425 milliliters of this concentrate and 42 grams of sodium carbonate
in a
total volume of 6.0 liters. Example 1 also contained 4 grams of ferric nitrate
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WO 01/96627 PCT/US01/19499
nonahydrate crystals, but this ingredient was omitted from Comparison Example
1,
which was otherwise identical to Example 1 in concentrations of ingredients
other
than water. Both working phosphating compositions had FA values of 2.5. The TA
value was 31.1 for Example 1 and 30.9 for Comparison Example 1. Each working
composition was heated with one of two substantially identical heating
elements with
a surface of Type 316 stainless steel exposed to the working composition,
which was
maintained at 71 " 5 EC while conventionally cleaned and conditioned
galvanized
steel test panels were phosphated by immersion for 5 seconds each. The
appearance of the phosphated galvanized steel surfaces from Example 1 and
Comparison Example 1 was substantially identical in scanning electron
micrographs
at 1000 diameters magnification. However, after five hours of use, the
surfaces of the
two immersion heaters were very different. The heater in Example 1 according
to the
Table 1
Ingredient Concentration, as % of
the Total Composition, for
the Ingredient Shown at
Left:
75 % Solution of H3PO4 in water 21.4
Zinc Oxide 0.90
Solution in water of nickel nitrate that contains 13.7 40.7
% nickel and 30 % nitrate
Solution in water of nickel phosphate that contains 8.9
8.1 % nickel and 37 % phosphate
25 % Solution of H2SiF6 in water 2.52
70 % Solution of HF in water 0.40
Additional water Balance
invention had a powdery scale that was readily removed by brushing, while the
heater
in Comparison Example 1 was covered with a tightly adherent solid scale. About
3.5
grams of this solid scale was removed with considerable difficulty from the
heater in
Comparison Example 1, while only about 0.7 grams of scale could be removed
from
the heater in Example 1.
A preferred replenisher for use with a high nickel-low zinc phosphating
composition as used in Example 1 contains the ingredients shown in Table 2
below.
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EXAMPLE 2 AND COMPARISON EXAMPLES 2.1 AND 2.2
In all of these examples, the substrate was also conventionally cleaned and
conditioned galvanized steel, but in these examples the steel was passed
rapidly
through the phosphating composition rather than being immersed in it. In both
the
Comparison Examples, the phosphating composition contained the ingredients
shown
in Table 3 below. In Comparison Example 2.1, the phosphating composition was
replenished with a conventional replenisher that did not contain zinc or iron,
and the
speed of the substrate through the phosphating composition was varied. A
minimum
coating weight of 1.5 g/m2 is required for this operation and was readily
achieved at
substrate speeds up to 182 m/min. However, when the speed was raised to 199
m/min, satisfactory coating weights could not be maintained.
In Comparison Example 2.2, it was attempted to restore satisfactory coating
characteristics by adding a substantial concentration of zinc to the
replenisher
previously used. This attempt was unsuccessful. As soon as the replenisher
began
to be added, the phosphating composition became turbid and eventually obvious
sludging began.
Table 2
Ingredient Concentration, as % of
the Total Composition, for
the Ingredient Shown at
Left:
75 % Solution of H3PO4 in water 29.3
Zinc Oxide 1.30
Solution in water of nickel nitrate that contains 13.7 15.9
% nickel and 30 % nitrate
Solution in water of nickel phosphate that contains 8.9
8.1 % nickel and 37 % phosphate
Solid anhydrous NaH2PO4 3.0
35 % Solution of HF in water 1.46
Solid Fe(N03)3. 91-120 0.76
Additional water Balance
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Table 3
Ingredient Concentration, as % of the Total
Composition, for the Ingredient
Shown at Left:
Phosphate anions 9.2
Zinc cations 3.2
Nickel cations 2.0
Nitrate anions 4.4
Complex fluoride from H2SiF6 2.4
Uncomplexed fluoride from HF 0.59
Additional water Balance
The coating characteristics did not improve, presumably because substantially
all of
the zinc cations added in the replenisher were precipitated as zinc phosphate.
In Example 2 according to the invention, a phosphating composition was used
that contained the same ingredients for Comparison Example 1 except that 0.062
percent of iron cations was added to the composition as ferric nitrate
nonahydrate, not
all of which dissolved. The replenisher used had a composition including iron
and
zinc, as shown in full in Table 4 below. With these operating conditions,
required
coating weights and other coating characteristics were easily achieved for a
period
of twelve hours at a substrate speed of 199 m/min, and little or no turbidity
and/or
sludge formation was observed. The xanthan gum, urea, and sulfonate salt
present
in this composition are all sludge modifiers.
18
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Table 4
Ingredient Concentration, as % of
the Total Composition,
for the Ingredient Shown
at Left:
75 % Solution of H3PO4 in water 37.5
Zinc Oxide 6.5
Solution in water of nickel nitrate that contains 13.7 13.1
% nickel and 30 % nitrate
70 % Solution in water of nitric acid 3.5
35 % Solution of HF in water 1.8
Solid Fe(NO3)3 9 HZO 0.76
Xanthan gum 0.10
Prilled urea 0.05
Sodium 2-ethylhexyl sulfonate 0.08
Additional water Balance
EXAMPLES 3, 3.1 AND 3.2
To further demonstrate the influence of the total amount of ferric salt on
sludge
and scale formation, three phosphating baths were prepared using varying iron
levels
TM,'.
as described in Table 5. The baths were built up using BONDERITE 1421 make up
(available from the Surface Technologies division of Henkel Corporation,
Madison
Heights, Michigan, U.S.A.) and differing amounts of ferric nitrate
nonahydrate. Hot
dipped G70 galvanized steel test panels (supplied byACT) were cleaned with
PARC
1200 cleaner (available from the Surface Technologies division of Henkel
Corporation) (14 point, 60 C, 10 seconds), then rinsed with hot water (10
seconds),
TM
and treated with PARCOLENE' AT conditioner (available from the Surface
Technologies division of Henkel Corporation) at 28 C prior to immersion in the
phosphating baths (77-80 C, 5 sec.). Coating weights were measured by
stripping
using ammonium dichromate, in accordance with conventional practice. Scaling
and
sludging were evaluated by visual inspection of the reaction vessel and the
amount of
scale deposited.on the immersion heating device over the course of the
phosphating
operation (approximately 6 hours). At 75 ppm and 7.5 ppm Fe (III) (Examples 3
and
19
CA 02413646 2008-05-20
3.2, respectively), acceptable levels of scaling and sludging were observed.
Severe
sludge and scale formation occurred when operating at 750 ppm Fe (III)
(Example
3.1). The phosphating baths for Examples 3 and 3.2 had precipitate present,
which
suggests that the baths were saturated with ferric salt. Although Example 3.2
(7.5
ppm Fe (III)) gave optimum results (no sludging, minimal scaling), in
commercial
operation it would be preferable to operate at a somewhat higher Fe (III)
level due to
the problems associated with trying to precisely maintain a very low
concentration of
Fe (III), as a relatively minor decrease in the Fe (III) level (e.g., where
the level
approaches 0 ppm) could lead to severe sludging and scaling problems.
Table 5
Example Fe (III), ppm Coating Weight, g/m Sludge Scale
3 75 1.98 Minimal Minimal
3.1 750 1.95 Pronounced Pronounced
3.2 7.5 2.07 None Minimal
