Note: Descriptions are shown in the official language in which they were submitted.
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Description
PHOSPHATE CONVERSION COATING COMPOSITION AND PROCESS
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a composition and process for forming a phosphate
con-
version coating on active metal surfaces in order to increase the corrosion
resistance of
s the surfaces, either as treated or after subsequent conventional overcoating
of the con-
version coating layer formed by an organic based protective coating such as a
paint or
lacquer. Unlike many of the other compositions known for this general purpose,
a com-
position according to this invention is well adapted to treating any of a
variety of base
metals, including at least steel and galvanized steel, zinc and zinc based
alloys, aium-
,o inum and aluminum based alloys, and magnesium and magnesium based alloys.
The
composition and method of the invention are therefore especially well adapted
to treating
objects having surfaces including more than one typE: of active metal to be
protected
against corrosion.
Statement of Related Art
~s This invention is an improvement of the invention described and claimed in
U.S.
Patent 5,143,562 of Sep. 1, 1992 to Boulos.
DESCRIPTION OF THE INVENTION
Obiect of the Invention
The major object of this invention is to achieve equally satisfactory
phosphating
zo quality as in U. S. Patent 5,143,562 with reduced amounts of sludge
compared to the ex-
amples in that patent.
General Principles of Description
Except in the claims and the operating examples, or where otherwise expressly
indicated, all numerical quantities in this description indicating amounts of
material or
zs 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
numerical limits
stated is generally preferred, however. Also, throughout the specification,
unless ex-
pressly stated io the contrary: percent, "parts of', and ratio values are by
weight; the de-
scription 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 speci-
fied in the description, and does not necessarily preclude chemical
interactions among
the constituents of a mixture once mixed; specification of materials in ionic
form implies
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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 specified in ionic form, to the extent
possible; other-
wise such counterions may be freely selected, except for avoiding counterions
that act
s adversely to the objects) of the invention; the terms "molecule" and "mole"
(which herein
means "gram mole") and their grammatical variations may be applied to ionic,
elemental,
or any other type of chemical entities defined by the number of atoms of each
type pres-
ent therein, as well as to substances with well-defined neutral molecules; the
first
definition of an acronym or other abbreviation applies to all subsequent uses
herein of the
same abbreviation and applies mutatis mutandis to normal grammatical
variations of the
initially defined abbreviation; the term "paint" includes all like materials
that may be
designated by more specialized terms such as lacquer, enamel, varnish,
shellac, and the
like; and the term "polymer' includes "oligomer", "homopolymer", "copolymer",
"terpoly-
mer", and the like.
~s Summary of the invention
A composition according to this invention is an aqueous liquid composition com-
prising, or preferably consisting essentially of, still more preferably
consisting of, water
and:
(A) a water soluble component providing in aqueous solution dissolved complex
tluor-
zo ide ions selected from the group consisting of tluoroborate (BF4 ),
fluorohafnate
(HfFs ~, fluorosificate (SiFs 2), fluorotitanate (TiFs Z), fluorozirconate
(ZrFs 2), and
mixtures thereof;
(B) a water soluble component providing in aqueous solution ions selected from
the
group consisting of fluoride (F-), bifluoride (HFz ), and mixtures thereof;
zs (C) a water soluble iron chelating agent component selected from molecules
each of
which contains at least two, and preferably at feast three, moieties selected
from
the group consisting of -COOH, -OH, and mixtures thereof;
(D) a water soluble component source of dissolved hydroxyiamine in aqueous
sofu-
tion;
(E) a water soluble source of dissolved phosphate ions; and
(F) a water soluble component providing in aqueous solution dissolved
oxidizing
agents selected from the group consisting of (i) nitroaromatic organic
compounds
and (ii) water soluble salts of molybdic acids; and, optionally, one or more
of the
following components:
~s (G) a component including one or more surfactants to promote cleaning of
the metal
surface to be treated;
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(H) a hydrotrope component to increase the solubility of the constituents of
compon-
ent (G); and
(J) a component of antifoam agent or agents,
wherein, in said aqueous liquid composition:
s - the ratio by weight of component (A) to component (B) is in the range from
0.3:1.0 to 1.6:1.0;
- the ratio of parts per thousand by weight (hereinafter usually abbreviated
as "ppt")
of the stoichiometric equivalent as fluoride ions of component (B) to ppt of
the
stoichiometric equivalent as citric acid of component (C) is in the range from
~0 0.30:1.0 to 8.0:1.0;
- the ratio of ppt of component (C) to ppt of component (D) is in the range
from
0.010:1.0 to 6.0:1.0;
- the ratio by weight of component (D) to component (E) is in the range from
0.05:1.0 to 5.0:1.0; and
,s - the ratio of the concentration in ppt of component (E) to the
concentration in
gram-moles per kilogram (hereinafter usually abbreviated as "M') of component
(F) is in the range from 2000:1.0 to 20,000:1.0 if component (F) is made up of
water soluble salts of molybdic acids or mixtures thereof and is in the range
from
400:1.0 to 4000:1.0 if component (F) is made up of p-nitrobenzene sulfonic
acid,
Zo water soluble salts thereof, or mixtures thereof,
wherein the improvement comprises selecting component (C) from citric acid and
its
water soluble salts:
A process according to this invention comprises at a minimum a step of contact-
ing a metal surface to be treated with a composition according to the
invention for a suffi-
Zs dent time to form on the metal surface a detectable conversion coating. The
composi-
tions according to this invention, when they contain adequate amounts and
types of sur-
factant component (G) as is usually preferred, are especially well suited to
treating metal
surfaces that have not been subjected 1o any prior chemical cleaning or
conventional
"activation" (e.g., contact with a suitably prepared aqueous dispersion of
colloidal titanium
compounds), but conventional metal surface cleaning andlor activation steps
before
contact between the metal to be treated and the compositions according to the
invention
may be used if desired as part of a process according to this invention.
A process according to the invention also may, and usually preferably does, in
clude conventional steps subsequent to the contact between the metal surface
to be
~s treated and the compositions according to the invention. These subsequent
steps, e.g.,
may inGude rinsing with water, using reactive post treatments, such as with
compositions
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according to the teachings of U. S. Patent 4,963,596 or with chromate
containing so-
lutions, and painting or otherwise protecting the surface with an outer
coating of an or-
ganic based solid material.
Description of Preferred Embodiments of the Invention
s With increasing preference in the order given and with independent
preference
for each noted component, compositions according to the invention contain no
more than
4, 0.9, 0.5, 0.2, 0.07, or 0.01 grams per liter (hereinafter "g/l_") of
cottons selected from
the group consisting of Zn'2, Ni'z, Mn'Z, Co'Z, Cu'Z, Fe'2, Ca'2, Mg'2, and
all metal cottons
with a valence of 3 or higher.
Prefer-ed sources for component (A) as described above are the acids and the
alkali metal and ammonium salts having the anions noted. In a composition
ready for use
in a process according to this invention (briefly denoted hereinafter as a
"working compo
sition"), it is preferred, with increasing preference in the order given, that
the concentra
tion of component (A), calculated as the anions) present, be in the range from
0.05 to
~s 1.0, 0.10 to 0.70, or 0.30 to 0.50 ppt.
However, for economy in shipment, it is often preferable to prepare a
concentrat-
ed composition according to the invention that is suitable for dilution with
water, optionally
with addition of acid or base for pH control at the same time as dilution of
the concentrat-
ed composition, to prepare, at the point of use, a working composition with a
concentra-
zo tion of component (A) in the range given above and of other components in
the ranges
given below. In such a concentrate, the concentrations of all components
except water
preferably are in the range from 5 to 100, more preferably from 12 to 50, or
still more
preferably from 20 to 25, times the concentrations of the same components in a
working
composition.
is For component (B) described above, the most preferred source is
hydrofluoric
acid, and ammonium and alkali metal fluorides and bitluorides are otherwise
preferred
among other acceptable sources. In a working composition, it is preferred,
with increas
ing preference in the order given, that the concentration of component (B),
calculated as
its stoichiometric equivalent of fluorine atoms, be in the range from 0.1 to
2.0, 0.2 to 0.8,
0 or 0.4 to 0.7 ppt.
For component (C) described above, only citric acid and/or its salts are used.
In
a working composition, it is preferred that the total concentration of citric
acid and/or its
stoichiometric equivalent for any citrate salts present be at least, with
increasing prefer-
ence in the order given, 0.0010, 0.0015, 0.0025, 0.0050, 0.010, 0.020, 0.030,
0.040,
~s 0.050, 0.060, 0.070, 0.080, 0.090, or 0.097 ppt and independently
preferably be not more
than, with increasing preference in the order given, 0.45, 0.40, 0.35, 0.30,
0.25, 0.20,
0.17, 0.15, 0.13, or 0.11 ppt of the total composition.
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For component (D) the most preferred source is hydroxylamine sulfate (briefly
de-
noted hereinafter as "HAS"), but many other sources are satisfactory. In a
working com-
position, it is preferred, with increasing preference in the order given, that
the con-
centration of component (D), calculated as its stoichiometric equivalent of
hydroxylamine
s (H2NOH), be in the range from 0.1 to 10, 0.5 to 6, or 0~.5 to 2.0, g/L.
For component (E) the most preferred source is orthophosphoric acid (H3P04)
and/or its alkali metal and ammonium salts. The acid itself and all anions
produced by
its partial or total ionization in aqueous solution are considered part of
component (E) as
described herein. In a working composition, it is preferred, wish increasing
preference in
the order given, that the concentration of component (E), calculated as its
stoichiometric
equivalent as phosphoric acid (H3P04), be in the range: from 3 to 30, 7 to 15,
or 5 to 12,
g/L.
In one embodiment of the invention, the most preferred sources of component
(F)
are water soluble salts of one of the molybdic acids, most preferably of
HZMoO,. This
,s component provides a dark blue colored conversion coating that is easy to
detect visually
and gives good corrosion protection, adequate for many purposes. This
embodiment is
generally preferred by users who do not wish to quantitatively monitor the
thickness of
the coating produced. In a working composition of this embodiment, it is
preferred, with
increasing preference in the order given, that the total concentration of (F)
be in the
so range from 0.00002 to 0.02, 0.0002 to 0.02, or 0.002 to 0.02 M of total
molybdate salts.
In another embodiment of the invention, which produces the maximum possible
corrosion resistance, paranitrobenzene sulfonic acid andlor its water soluble
salts,
especially the sodium salt, are the most preferred source of component (F).
The conver-
sion coating layer produced by this embodiment is often difficult to detect
visually, but the
is thickness of the coating can be readily determined by the quantitative
methods known to
those skilled in the art, which generally involve weighing a sample of the
coating before
and after using an appropriate stripping solution composition to remove the
conversion
coating. In a working composition according to this embodiment, it is
preferred, with in-
creasing preference in the order given, that the concentration of component
(F) be in the
range from 0.0001 to 0.1, 0.001 to 0.1, or 0.01 to 0.1 M.
In a working composition, it is preferred, with increasing preference in the
order
given, that the concentration of component (G) be in the range from 0 to 5.0,
1.5 to 3.0,
or 1.5 to 2.0, g/L. Preferred chemical types for component (G) are
polyethoxylated alco-
hols with about 12 - 22 carbon atoms in the alcohol portion, other modified
polyethers of
~s the aliphatic or aromatic types, and salts of complex organic phosphate
esters.
A hydrotrope is defined generally as a substance that increases the solubility
in
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water of another material chat is only partially soluble. Hydrotrope component
(H) is
needed in the compositions according to this invention only if the amount of
component
(G) desired in the compositions is so large as to exceed the limit of ready
solubility in the
absence of a hydrotrope. In such cases, adequate solubility to produce an
optically clear
s and homogeneous composition as preferred can generally be achieved by use of
a
hydrotrope. A hydrotrope for this invention is preferably an ammonium or
alkali metal salt
of a sulfonate of toluene, xylene, or cumene, or a mixture of two or more such
salts. The
most preferred hydrotrope is sodium xylene sulfonate. A water soluble complex
organo-
phosphate ester or acid ester may often be advantageously added as an
auxiliary hy-
,o drotrope. In a working composition, it is preferred, with increasing
preference in the order
given, that the concentration of component (H) be in the range from 0 to 2.0,
0.4 to 1.2,
or 0.6 to 0.8, g/L.
Preferred chemical types for component (J) are (i) aliphatic petroleum
distillates
modified with hydrophobic silica andlor (ii) polyethoxylated alcohols. Block
copolymers
,s of ethylene oxide and propylene oxide may also be used. The amount used, if
needed,
should be sufficient to reduce the foaming of the composition to an acceptable
level.
In a working composition, it is preferred, with increasing preference in the
order
given, that the concentration of free acid be in the range from 0.0 to 2.0,
0.0 to 1.0, or 0.2
to 1.0, "points" and that the concentration of total acid be in the range from
3 to 12, 5 to
zo 10, or 6.0 to 9.0, "points". "Points" are defined for this purpose as the
number of millilit-
ers (hereinafter "ml") of 0.1 N NaOH solution required to titrate a 10 ml
sample of the
composition, to a phenolphthalein end point for total acid and a bromthymol
blue end
point for free acid. Independently, it is preferred that the pH value of a
working composi-
tion according to the invention be in the range from 3.0 to 7.0, 4.2 to 5.9,
or 4.5 to 5.5.
zs For concentrated compositions according to the invention, it is more useful
to
characterize the preferred embodiments in terms of ratios of ingredients
rather than
specific concentrations as noted above for the working compositions.
Specifically, it is
preferred, with increasing preference in the order given for each ratio, that:
- the ratio by weight of component (A) to the stoichiometric equivalent as
tluoride
~o ions of component (B) be in the range from 0.3:1.0 to 1.6:1.0, from 0.5:1.0
to
1.3:1.0, or from 0.6:1.0 to 0.9:1.0;
- the ratio of ppt of the stoichiometric equivalent as fluoride ions of
component (B)
to ppt of the stoichiometr~c equivalent as citric acid of component (C) be at
least,
with increasing preference in the order given, 0.35:1.0, 0.45:1.0, 0.55:1.0,
3s 0.65:1.0, 0.75:1.0, 0.85:1.0, 0.95:1.0, 1.05:1.0, 1.15:1.0, 1.25:1.0,
1.35:1.0,
1.45:1.0, 1.55:1.0, 1.60:1.0, or 1.65:1.0 and independently preferably be not
more
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than, with increasing preference in the order given, 7.0:1.0, 6.0:1.0,
5.5:1.0,
5.0:1.0, 4.5:1.0, 4.0:1.0, 3.5:1.0, 3.1:1.0, 2.7:1.0, 2.4:1.0, 2.2:1.0,
2.00:1.0,
1.90:1.0, 1.85:1.0, 1.80, or 1.75:1.0;
- the ratio of ppt of the stoichiometric equivalent as citric acid of
component (C) to
s ppt of component (D) be not less than, with increasing preference in the
order
given, 0.040:1.0, 0.070:1.0, 0.100:1.0, 0.130:1.0, 0.160:1.0, 0.190:1.0,
0.220:1.0,
0.250:1.0, 0.280:1.0, 0.310:1.0, 0.340:1.0, 0.360:1.0, 0.390:1.0, 0.420:1.0,
0.440:1.0, or 0.460:1.0 and independently preferably be not more than, with in-
creasing preference in the order given, 5.0:1.0, 4.5:1.0, 4.0:1.0, 3.5:1.0,
3.0:1.0,
~0 2.5:1.0, 2.0:1.0, 2.0:1.0, 1.5:1.0, 1.0:1.0, 0.80:'1.0, 0.70:1.0, 0.60:1.0,
0.55:1.0,
or 0.50:1.0;
- the ratio by weight of component {D) to component (E) be in the range from
1:8
to 1:80, from 1:12 to 1:59, or from 1:21 to 1:40;
the ratio of the concentration in g/L of component (E) to the total
concentration
~s in M of nitrobenzene sulfonic acid and its salts, if .at least one of these
ingredients
is present in the composition, be in the range from 400:1 to 4000:1, from
860:1
to 2565:1, or from 1400:1 to 1800:1 and the ratio of the concentration in g/L
of
component (E) to the total concentration in M of molybdate salts, if at least
one
of these ingredients is present in the composition, be in the range from
2000:1 to
zo 20,000:1, from 4300:1 to 12,825:1, or from 70t)0:1 to 9000:1.
In determining these ratios, the components are to be measured in the same
manner and
units as described above for measuring the concentrations of the same
components in
working solutions.
In a process according to the invention, contact between the metal surface to
be
zs treated and a composition according to the invention may be accomplished by
spraying,
dipping, or any other convenient method or combination of methods. The
temperature
during contact between the metal treated and the composition according to the
invention
preferably is, with increasing preference in the order given, in the range
from 21 to 85,
25 to 70, or 30 to 65, °C. The time of contact preferably is, with
increasing preference
3o in the order given, in the range from 5 sec to 15 minutes (hereinafter
"min"), 15 sec to 10
min, or 30 sec to 5 min. The add-on mass of the phosphate coating formed
preferably
is, with increasing preference in the order given, in the range from 12 to
1600, 98 to 975,
or 285 to 700, milligrams per square meter (hereinafter sometimes abbreviated
as
"mglmz) of surface treated.
Further appreciation of the present invention may be had from considering the
fol-
lowing examples and comparative examples which are intended to illustrate, but
not limit,
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- the invention.
s
Examples and Comparison Examples
Concentrate compositions were prepared containing the following components
Parts Material
by
Wei4ht
105 50 % sodium hydroxide
154 75 % orthophosphoric acid
Variable ion sequestering agent - see table below
,0 35 40 % sodium xylene sulfonate
3.5 ANTAROXT"" LF-330
5.6 TRITONT"" DF-16
17.5 RHODAFACT"" RP-710
10.5 Hydroxylamine sulfate
,s 15.4 p-nitrobenzene sulfonic acid
4.9 70 % hydrofluoric acid
3.5 Sodium fluoroborate
The balance to a total of 1000 parts was water.
ANTAROXT"" LF-330 was commercially obtained from Rhone-Poulenc and is re-
zo ported by its supplier to be a modified linear aliphatic polyether
detergent and wetting
agent with low foaming tendency. TRITONT"" DF-16 was commercially obtained
from
Union Carbide Corp. and is reported by its supplier to be a modified
polyethoxylated
straight chain alcohol nonionic low foaming detergent. RHODAFACr"" RP-710 was
com-
mercially obtained from Rhone-Poulenc and is reported by its supplier to be a
complex
zs organic phosphate anionic detergent and emulsifier with hydrotropic effect
on low foam-
ing nonionic surfactants.
In preparing these concentrates, the sodium hydroxide was added to about 90
of the amount of water expected to be finally needed; the phosphoric acid was
added
next, with cooling until the temperature of the mixture fell to 43 °C
or below. Then the
~o sequestering agent, the principal hydrotrope, and the three surfactants
were added in
rapid succession and the mixture stirred until clear (about 15 min). The
hydroxylamine
sulfate and p-nitrobenzene sulfonic acid were then added, and 30 minutes of
additional
mixing was performed. Subsequently, the last two named ingredients were added,
fol-
lowed by another 30 minutes of mixing. The remaining water was then added, to
the ex-
35 tent necessary to achieve a total of 1000 parts by weight.
The concentrated compositions as described above were diluted with water to
produce a working composition containing 50 grams of the concentrated
composition per
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liter of the working composition. Each working composition had a pH value of
4.8 and
a total acidity as shown in Table 1 below.
Cold rolled carbon steel test panels, without any preliminary chemical
cleaning,
were immersed for 5 minutes each in a five liter volume of the above specified
working
s compositions at a temperature of 49 °C, rinsed in cold tap water, and
dried. A total of 25
rectangular panels, each about 30 x 15 centimeters in size, were used in each
composi-
tion, with no attempt at replenishment, and coating add-on masses per unit
area in grams
per square meter (hereinafter usually abbreviated as "glm2) were measured for
the first,
twelfth, and twenty-fifth panels in each composition. The solid sludge formed
in each
,o composition was then collected by filtration, dried, and weighed. The
sequestering agent
in the concentrated compositions, coating masses, and sludge amounts are shown
in
Table 1. As can be seen from the results in that Table, large concentrations
of citric acid
completely suppress sludge formation, but the coating masses achieved fall
rather
rapidly. Smaller amounts of citric acid give much more stable coating
performance, and
,s the amount of sludge is still considerably less than when gluconic acid is
used as the se-
questering agent.
TABLE 1
Property Measured Results
for:
Examples: Comparison
Ezamples:
1 Z; 1 2
Total Acid 10 10 9 10
Points
0.20 % 0.28 %
Sequestering citric 1_0 % none glu-
Agent acid conic
acid
1st Panel 0.81 0.59 0.73 0.73
Coating Masses,
g~m~ 12th Panel 0.81 0.27 0.68 0.66
25th Panel 0.81 0.:22 0.68 0.68
Dry Sludge 1.6 0.0 3.7 2.9
Mass, grams
9
