Note: Descriptions are shown in the official language in which they were submitted.
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WO 2004/059034 PCT/EP2003/014577
PROCESS FOR PROVIDING A THIN CORROSION INHIBITING COATING ON A METALLIC
SURFACE
FIELD OF THE INVENTION
This invention relates to a process for coating the surface of a metallic
coil,
part or wire with an aqueous acidic phosphating solution containing
predominantly
alkali metal ions andlor ammonium ions as well as in many cases phosphate
ions. It
relates further on to a phosphating solution to be used in this process for
generating
excellent corrosion inhibiting coatings on metallic surfaces. In some
instances such
coating may be used for coldforming of the metallic part. Such solutions are
called
alkali metal phosphating solutions or, if used on iron-rich surfaces, iron
phosphating
solutions.
The invention is particularly concerned with a coating resp. conversion
coating
on aluminum, aluminum alloy, iron alloy like steel and stainless steel,
magnesium
alloy, zinc or zinc alloy as well as with a process, a concentrate and a
solution for the
formation of a phosphating coating on surfaces of these metallic materials.
Such coating solution is especially suitable for the generation of
pretreatment
coatings on substrate surfaces which will be coated in a second step with at
least one
organic film, especially at least one film like a thin electrocoating lacquer
layer, a
paint layer, a silane-rich layer and/or an adhesive layer. Alternatively, the
coating
may be used for a'treatment like a passivation without being covered with a
further
coating like a paint layer.
BACKGROUND OF THE INVENTION
Processes for the production of alkali metal phosphating coatings, especially
prior to a lacquering, are described in relatively few cases in comparison to
zinc
phosphating or manganese phosphating where there is a huge number of
publications. Fresh solutions for alkali metal phosphating that had not yet
been used
show typically only a very low or even practically no content of aluminum,
iron and
zinc. The fresh aqueous acid alkali metal phosphating solutions contain ions
of at
least one type of alkali metal ions and/or ammonium ions as well as phosphate
ions.
Because of the pickling effect of such acidic solutions on metallic surfaces,
the ions
CONFIRMATION COPY
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2
of the dissolved metals like aluminum, iron and zinc as well as traces of
other alloy
constituents of the pickled metallic materials will .be enriched during the
ongoing
phosphating process in the phosphating solution. Typically, the main phases of
the
alkali metal phosphating coatings are the corresponding phosphates, oxides
and/or
hydroxides of the metallic constituents of the metallic base material(s).
Alkali metal phosphating solutions resp. coatings are called iron phosphating
solutions resp. coatings if used on iron alloy surfaces like steel. The same
corresponds to aluminum and aluminum alloys where such solutions resp.
coatings
are described as aluminum phosphating solutions resp. coatings. Often surfaces
of
very different metallic materials may be coated in the same alkali metal
phosphating
bath at the same time or one after the other whereby the ions of the different
metals/alloys of the basic materials will be collected in the bath. Such
coatings are -
in contrast to coatings of the so called zinc-, zinc-manganese- or manganese-
phosphating, mostly or totally amorphous or extraordinarily fine-grained.
Alkali metal phosphatings are described in Werner Rausch: The Phosphating
of Metals, ASM International, Finishing Publications Ltd., Teddington, England
1990
(especially pages 94 - 100, 120 - ~ 30) in detail and are called the "non-
coating
phosphating" or in other publications "amorphous phosphating". The term "non-
coating phosphating" is misleading, as there will be coatings generated
although
such coatings will be significantly thinner than created during e.g. zinc
phosphating or
zinc-manganese phosphating. The very thin alkali metal phosphating coatings
are
not, poorly or - if coloured or grey - well visible; the coatings may be only
visible by
colours caused by physical effects, by their kind of grey appearance and/or by
their
matte appearance. The alkali metal phosphating solution contains always a
certain
content of at least one alkali metal like sodium, potassium and/or of
ammonium. The
alkali metal phosphating coatings are typically - in contrary to the well and
coursely
crystalline coatings of the so-called "coating-forming phosphatings" - more or
less
amorphous and show under the scanning electron microscope typically no
crystalline
grain shapes.
The alkali metal phosphating coatings are mostly poor, nearly free or totally
free of manganese and zinc, if there will not be manganese and/or zinc rich
surfaces.
to be pretreated or treated. They are typically poor, nearly free or totally
free of
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3
chromium, cobalt, copper, nickel, tin and/or other heavy metals. The phases
mainly
generated and/or precipitated during iron phosphating, which is performed by
contacting iron-rich metallic surfaces with an alkali metal phosphating
solution, are
iron phosphates, iron oxides and iron hydroxides like e.g. vivianite and/or
magnetite.
The contents of the ions dissolved from the metallic surface and then carried
in the
alkali metal phosphating solution, especially of aluminum, chromium, copper,
iron,
magnesium, tin, titanium, resp. zinc are relatively low as such compounds
resp.
cations are normally not added to the bath, but are only or nearly only
present
because of the pickling effect of the aqueous acidic alkali metal phosphating
solution
to the metallic surfaces of the parts, sheets, strips or wires to be . coated.
Such
contents will precipitate and generate the coating primarily containing
phosphates,
oxides and/or hydroxides of the metals' content in the solution further on,
there may
be traces or even low contents of such ions caused by impurities by pickling
the bath
containers and connecting tubes as well as by dragging in from earlier steps
of the
process succession.
A significant difference of the alkali metal phosphating process in comparison
to phosphating processes of the "coating-forming phosphating" is further that
the
cation(s) necessary for the coating formation during alkali metal phosphating
is/are
always present in a small percentage, mostly or totally dissolved from the
surtaces of
the metallic base substrates, whereby during e.g. zinc-, zinc-manganese-, zinc-
nickel- or zinc-manganese-nickel-phosphating there will be a relatively high
addition
_ of e.g. zinc so that zinc is contained mostly in a content of more than 0.3
g/L resp.
often of more than 1 g/L in the phosphating solution. This high zinc content
is often
caused by addition of zinc compounds of at least 40 %, mostly more than 60 %,
often
even more than 80 % of the total content to the bath, whereas only the
remaining
content is mostly generated by the pickling effect to ~zinciferous surfaces.
The
coatings generated by zinc-, zinc-manganese-, zinc-nickel- or zinc-manganese-
nickel-phosphating show typically the predominantly zinc and/or manganese
containing phases hureaulithe, phosphophyllite, scholzite andlor hopeite in
significant
crystalline shapes.
The coatings of alkali metal phosphating show significant other properties as
such from zinc-rich phosphatings: They have mostly a coating thickness in the
range
from 0.1 to 0.8 pm resp. only a coating weight in the range from 0.2 to 1.3
g/m2. In
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4
contrary to the mostly dull grey appearing zinc-rich phosphating coatings, the
much
thinner alkali metal phosphatings are mostly transparent or show iridescent
colours
related to their extremely thin thickness. Then they show the colours of
"higher
orders" and may be e.g. nearly transparent, yellowish, golden, reddish, a bit
violet,
greenish or often bluish, partly iridescent. Only in the case that the alkali
metal
phosphating coatings should have a higher coating weight, especially more than
0.7
and perhaps up to about 1.3 g/m~, they may show a more matte-grey appearance.
Especially aluminum-rich alkali metal phosphatings may occur silvery or
silvery-
iridescent.
The alkali metal phosphating coatings may be prepared without any later
generation of e.g. at least one paint layer and/or another organic paint-like
layer.
Then this coating process may be called a treatment. If the phosphating
coatings
should be used for a protection against corrosion for a limited time, then the
coatings
may be called a passivation. But they can be used under at least one paint
layer
and/or another organic paint-like layer like a primer, a lacquer, a silane
layer, a base
coat and/or a topcoat andlor respectively together with an adhesive and may
then be
called a pretreatment.
In general, alkali metal phosphating coatings are produced prior to painting
by
contacting the aqueous acidic phosphating solution which contains typically at
least
one mono- andlor orthophosphate and afterwards by electrocoating the
phosphated
metallic surfaces and/or often by powder painting e.g. of the parts of the
metallic
construction that are well accessible from outside like radiators and car
bodies.
Typically, today alkali metal phosphating processes are carried out with
solutions that contain alkali metal and/or ammonium and at least one type of
phosphate, mostly orthophosphate, as well as always at least one accelerator,
thereby showing a pH value during operating in the range of 4 to 6. These
aqueous
acidic solutions are contacted to the metallic surfaces typically at
temperatures in the
range from 48 to 72 °C. Their typical coating weights are in the range
from 0.3 to 1
g/m2. The coatings of today are rich in at least one phosphorus compound, show
mostly bluish or light grey coloured coatings and often a coating weight in
the range
from 0.5 to 1.5 g/m2.
CA 02511361 2005-06-21
28. OKT. 2004 13:18 DN PATENTA$TE I LUNG " ~ " '- NR. 931-" 'S. '7r ~ - - - - -
-
_5
DE A1-1 OD 06 338 describes a typical process for iron phosphating where
there has been added a small amount of copper ions to solutions of a pH value
in the
range from 3.5 to 6.5 at a temperature in the range from 30 to 70 °C
and especially at
a pH value of about 4.8 of about 55 °C. DE-A1-1 942 156 teaches an
alkali metal
phosphating process by using a high pressure spraying method fior contacting
the
metallic surtaces with solutions of a temperature of 60 °C and of a pH
value in the
range from 3 tv 5.5, especially of a pH value of 4. DE-A1-1 914 052 concerns
an
alkali metal phvsphating process by using a rollcvating application with a
solution
containing 5 tv 20 g!L of phosphate ions and 3 tv '12.5 g/L of chlorate at a
temperature of 54.5 to fi0 °C with an extraordinarily unconventional pH
value in the
range of 1 to 3.5 contacting a coif less than 30 seconds and squeegeeing. EP-
B7-0
968 320 protects a process for an alkali metal phosphating for radiators by
using a
surfactant rich solution of a pH value in the range from 4 to 6 at a
temperature in the
range from 35 to 60 °C and espeaally of at least 50 °G. FR-A-
1.155_705 refers to an
alkali metal phvsphating process by using an ammonium silicon hexafluvride and
nitrvguanidine containing solution of a pH value in the range from 3 tv 6 at a
temperature~in the range from 50 tv ?6 °C. GB A 1 388 435 reports an
alkali metal
phvsphating process by using a free fluoride and chlorate containing solution
of a pH
value in the range from 3 to 6 at a temperature in the range from 50 tv 80
°G,
especially used with a pH value in fihe range from 3.65 to 4.4. US A
~,,G65,23'J
discloses an alkali metal phvsphatirlg process by using a fluoride containing
solution
of a pH value in the range from 3 to 5.8 at a temperature in the range from 60
to 82
°C, especially used with a pH value in the range from 4.25 to 5.5.
EP 0 471 606 A2 describes methods of surface-treating aluminum or its alloys
by applying aqueous compositions containing niobium andlor tantalum together
with
fluoride and optionally with titanium andlor zirconium as well as with
phosphate. The
phosphate addition of 0.01 to 0.5 g/L shall be used as pH-adjusting agent:
These
compositions shall help tv avoid the blackening of cans during the treatment
in
boiling water
EP 0 721 155 A1 teaches processes for the preparation of surfaces of iron yr
steel for painting by applying aikali metal phosphating solutions containing
_-. dihydr_o~elrphosphate=and-nitrobenzvlsulfonate=that-show-pH-in-the-range-f
-ro-,m-4_-2 ' _ ., -
to 6.
~AM~NDEL SHEET;
Empf.zeit:~8/10/2004 13:16 ~ - ~"~~.~:~» -:337 P.017
CA 02511361 2005-06-21 E~'~',~'."~Gl,~"~~ .
..~ 28.OKT.2004 13:18 DN PATENTABTEILUNG NR.931 S. '~/g ~-
_~~_
DE '1942 'I56 A7 discloses processes for the treatment of metal surtaces,
especially of iron and steel surFaces, by applying alkali metal phosphate
resp.
ammonium phosphate and benzoate containing solutions at a pH in the range from
3
to 5_5 at high pressures and at temperatures of about 60 °C.
It was an object uF the invention tv propose an alkali metal phosphating
process with very stable bath conditions and with excellent coating
appearances and
coating qualities using at least one accelerator like nitroguanidine_ It was
further an
object to propose a phosphating process with an improved corrosion resistance
in
comparison to typical alkali metal phospha~ng processes used today. Further
on, it
was an object to propose an alkali metal phosphating process ~khat is stable,
well
suited for industrial application for coils, parts and wires as welt as easier
and
cheaper in comparison to actually used processes.
Astonishingly, it has been observed that it is possible tv uphosphate" a
metallic
surface with an unusually low or even with a zero phosphate content. Even
other
~~11UIENDED SHEET,
Fm~af ,aP; t W~/ ~ QI~C104 13:17 i.... , ~"~~., .", ,;; ~7 P .018
CA 02511361 2005-06-21 3 Ep(~'~' '~,G1,~'T~'
,.... 28.OKT.2U04 13:18 DN PATENTABTEILUNG NR. 931 S, yvy ..
OZ 0271 WO-A
s
acids than phosphorus containing acids could be used without a loss of the
quality of
the coatings' properties. Nevertheless, the term °phosphating" is used
here for all
kinds of coating processes and coatings independent if they contain phosphorus
yr
not
SUMMARY OF THE INVENTION -
According to the present invention, there is provided a process for coating
metallic surfaces with a phosphating coating by contacting metallic surfaces
at a
temperature not above 4.5 °C and at a pH value less than 3.5 with an
aqueous acidic
alkali metal phosphating solu6vn or dispersion containing:
At least one compound of at least one phosphorus containing acid andlor at
least one of their derivatives like esters and salts in a total content of aR
kinds of
acids and all their derivafiives like esters and salts together of less than
20 g/L
calculated on mole base as orthophosphate, whereby the content of such
phosphorus containing~cvmpvundsrons is at feast 50 °~ by weight in
comparison to
all such compoundslions and
afi least one ion selected from the group consisting of at least one alkali
metal
ion and ammonium ion, .
whereby the phosphating svtufivn or dispersion is free of chrornates,
molybdates, niobates, tantalates and tungstates,
whereby the phosphafiing cvafing has a coating composition with a
phosphorus content of not more than 8 atomie% as measured by Secondary Neutral
Mass Spectroscopy (SNMS) and
whereby the phosphating coating has a coating weight in the range from 0.01
to CI_5 glm2_
According to the present invention, there is provided a phvsphating coating on
- - ---- ~-
a metallic surface prepared by contacting metallic surtace5 with an aqueous
aadic
alkali metal phosphating solution or dispersion having a coating thickness of
not mere
than 0_'15 pm and having a good corrosion protection for the protected
metallic
material.
K\sust~an4\aZOZ~71 _do~
AlllIEI~JI~Ep '~I-'IEET',
Empf .zeit:~8/10I~004 13:17 ' --= - ~ ~:~~~~=~-.~"-:.337 P.019 , ,
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WO 2004/059034 PCT/EP2003/014577
7
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been found that for steel panels treated with an alkali metal
phosphating
solution based on a conventional composition, dried and later on painted with
a
polyester paint, show a corrosion inhibiting effect as measured by salt spray
(fog) test
clearly depending of the pH value of the alkali metal phosphating solution. At
a pH
value of the solution of about 7, the salt spray (SS) evaluation showed
results of
about 5, at a pH value of about 5 SS values of about 2.5 and at a pH value of
about
2.5 SS (mm creep from scribe) values of about 1.5 or even less. Further
details
thereto are found in the examples.
Tests were performed to identify the phases of different alkali metal
phosphating coatings, but there was no X-ray diffraction result to be able to
identify
the phases. Therefore, it is believed that the thin coatings are amorphous or
nearly
amorphous.
Then, the element content of the coatings was analysed by X-ray
Photoelectron Spectroscopy (XPS), which may be used successfully as routine
measurement method for controlling the different coatings, but which is an
insufficient
precise measurement method for such coatings to identify the element content
dependent from the depth of the coating. Only the upper 8 nm from the surface
into
the depth could be analysed and therefore there is an influence of surface
impurities.
The measurement of the content of phosphorus and other elements in the coating
was performed by X-ray Photoelectron Spectroscopy with an instrument 5700LSci
of
Physical Electronics, with an X-ray source of monochromatic aluminum, a power
source of 350 Watts, an analysis region of 2 x 0.8 mm, an exit angle of 65
°, a charge
correction for C-(C,H) in C 1s spectra at 284.8 eV and a charge neutralization
by
electron flood gun.
Finally, the element content of the coatings was analysed by Secondary
Neutral Mass Spectroscopy (SNMS) with an INA3 electron gas - SNMS apparatus of
Leybold, which is a precise measuring method to identify the element content
dependent from the depth of the coating of such thin ~ alkali metal
phosphating
coatings. The samples were sputtered with Ar ions of 1040 eV energy and at a
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WO 2004/059034 PCT/EP2003/014577
8
current density of about 1.2 mA/cm2. An area of 5 mm diameter Divas sputtered
and
analysed. During the measurement, the atoms of the upper surface layer
evaporated
and the next atom layers of below were analysed, until the total coating was
removed
in the sputtered area during the analysis. In 10 seconds of sputtering, about
10 nm of
the upper part of the coating were removed. The measurement method could only
be
calibrated to a certain amount to the composition of the analysed coatings.
The
results showed a minor dependency of the surface roughness which was
considered
in the evaluation.
For both analyses, XPS and SLAMS, the same four samples of cold rolled steel
panels were analysed:
1 ) an only cleaned, but not coated panel,
2) a typical conventional iron phosphating coating according to the state of
the art as produced in today practice by first cleaning and then contacting
the
panel with an iron .phosphating solution containing phosphate, sodium and
chlorate at a pH value of 4.5 at a temperature of 50 °C generating a
coating of
about 0.16 to 0.22 pm thickness,
3) a very thin yellow iron phosphating coating according to the invention
generated after having cleaned the panel by contacting it with an iron
phosphating solution containing phosphate, sodium and 0.2 g/L nitroguanidine
at a pH value of 3.0 with a value for total acid of 6 points at a temperature
of
37 °C with a coating of about 0.02 to 0.1 pm thickness,
4) a thin bluish iron phosphating coating according to the invention
generated after having cleaned the panel by contacting it with an iron
phosphating solution containing phosphate, sodium and 0.2 g/L nitroguanidine
at a pH value of 3.0 at a temperature of 37 °C with a coating of about
0.06 to
0.12 pm thickness, but the value for total acid had fallen below 3 points.
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9
Table 1: Element content of the samples 1 ) to 4) as measured by XPS in
atomic%:
Sample Fe Mn Zn Na K Mg 0 N P
1 ) control10.8 1.5 1.0 2.3 < 0.1 0.4 41.8 0.9 0.5
~
2) cony. 7.2 0.3 0.3 1.3 0.1 0.1 50.2 1.2 10.8
3) yellow13.6 0.1 0.7 0.2 n.d. 0.2 56.3 0.8 1.0
4) bluish1 6.1 0.3 0.7 n.d. n.d. 0.2 57.2 0.5 1.8
~ I ~ I ~ I
The results of table 1 show that there is a considerable difference in the
composition between the uncoated sample 1 ), the coated sample according to
the
state of the art 2) and the coated samples 3) and 4) according to the
invention.
The figures present the element distribution in atomic% as analysed by
Secondary Neutral Mass Spectroscopy (SNMS) depending from the depth of the
coating which was analysed from the surface (left) into the massive steel
material
(medium to right) in nm. Figure 1 for the cleaned, but not coated sample 1 )
shows the
impurity effect of the surface region and then the composition of the-cold
rolled steel
material. Figure 2 for sample 2) covered with a typical conventional iron
phosphating
coating of today indicates via the Fe content the thicleness of the iron
phosphating
coating. As shown in the following figures, the curves of the content of
oxygen and
phosphorus are - in the logarithmic graph - more or less proportional
("parallel")
There is a level in the upper and middle parts of the coating of about 30
atomic% of
Fe, of about 50 atomic% of O and of about 9 atomic% of P. Figures 3 and 4 for
the
samples 3) and 4) with the coating according to the invention do not show
clear
content levels. The coating of sample 4) which is some percent thicker than
the
coating of sample 3), indicates a content of about 50 atomic% of Fe, of about
35
atomic% of 0 and of about 6 atomic% of P in the upper parts of the coating.
Figure 5
represents the results of sample 5) that is comparable with sample 3) but
shows
higher surtace roughness data and therefore higher signal output. Figure 6
represents the results of sample 6) that is comparable with sample 4) but
shows
higher surtace roughness data and therefore higher signal output, too. Figure
7
represents the curves of the P content of the samples 1 ) to 4) in comparison,
but now
- as linear graph - showing clearly different phosphorus contents dependent
from
the depth analysed in the coating.
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WO 2004/059034 PCT/EP2003/014577
Therefore, it is clearly demonstrated that the composition~of the conventional
iron phosphating coatings is significantly different from the composition of
the iron
phosphating coatings according to the invention.
The surface roughness of all samples was measured with a white light
interferometer NT3300 of Wyko, each coated panel on three areas. For the
samples
1 ) to 4), the average data of Ra per panel varied between 0.89 and 1.02 pm,
the
average data of RZ per panel varied between 1.11 and 1.22 pm and the average
data
of Rt per panel varied between 6.17 and 7.25 pm. In comparison to the samples
3)
and 4), the samples 5) and 6) had been coated in the same manner and under
nearly
the same conditions, but they showed surface roughness data nearly twice as
high
as the samples 3) and 4): The average data of Ra per panel varied at about
1.79 pm,
the average data of RZ per panel varied at about 11.7 pm and the average data
of Rt
per panel varied in the range from 11.4 to 12.1 pm. Sample 3 ) has to be
compared
with sample 5) for the difference in surface roughness and element content;
similarly,
sample 4) has to be compared with sample 6). As the rougher surfaces enable a
higher amount of neutral parts measured than from more even surfaces, the more
even surfaces shall be used for the analytical investigation and evaluation.
Preferably, the P content is less than 8 atomic% in a depth of 0.05 pm below
the (original) surface of the alkali metal phosphating coating as analysed by
Secondary Neutral Mass Spectroscopy (SLAMS) or is less than 6 or even less
than 4
atomic% in a depth of 0.1 pm below the surface of the alkali metal phosphating
coating or is less than 3 or less than 2 atomic% in a depth of 0.1 pm below
the
surFace of the alkali metal phosphating coating. Preferably, the phosphating
coating
according to the invention has a thickness of not more or less than 0.15 pm,
more
preferred of not more than 0.12 pm, much more preferred of not more than 0.10
pm.
The process according to the invention may preferably be characterized in that
the temperature of the phosphating solution or dispersion may be during the
contacting of the metallic surfaces in the range from 10 to 42 °C or
less than 40 °C
and more preferred at least 15 °C or up to 38 or up to 35 °C.
The pH value may
preferably be selected in the range starting from 1.8 resp. reaching up to
3.3, more
preferred of at least 2 or up to 3.1, especially of at least 2.5 or up to 2.9.
The coating
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WO 2004/059034 PCT/EP2003/014577
11
weight may preferably be selected in the range from 0.03 to 0.4 g/m2, more
preferred
of at least 0.05 or up to 0.36.g/m2, most preferred of at least 0.1 or up to
0.32 g/m2.
As acids for use in the phosphating solution or dispersion, most organic and
inorganic acids as well as their water-soluble and/or water-dispersible
derivatives,
especially salts and/or esters, may be taken, but hydrochloric acid and
chlorides are
not recommended as they may cause significant crevice corrosion. There may be
even used mixtures a) of acids, b) of at least one acid with at least one of
salts and/or
with at least one of ethers or c) of at least one of salts andlor of at least
one of ethers.
Preferably, at least one acid is used like orthophosphoric acid, diphosphoric
acid, monophosphoric acid, at least one of phosphonic acids, e.g. especially
at least
one with at least one aliphatic and/or aromatic group each, especially at
least one of
diphosphonic acids, phosphonous acid, phosphorous acid, molybdatophosphoric
acid, tungstophosphoric acid and/or at least one of its derivatives like
esters) and/or
salt(s), especially at least one of monoester(s), of diester(s) and/or ofi
triester(s) of a
phosphorus containing acid like orthophosphoric acid, more preferred mixed
with at
least one phosphorus containing acid.
Preferably, at least one sulfur containing acid and/or at least one of its
derivatives like esters) and/or salts) is used like sulfuric acid, sulfamatic
acid, at
least one of sulfonic acids like nitrosulfonic acid resp. at least one of
their derivatives
like esters) and/or salt(s).
Preferably, at least one nitrogen containing acid and/or at least one of its
derivatives like esters) and/or salts) is used like nitric acid, at least one
acid having
at least one nitro andlor at least one amino group resp. at least one of its
derivatives
like esters) and/or salt(s).
Preferably, at least one organic acid and/or at least one of its derivatives
like
esters) and/or salts) is used like at least one of aromatic organic acids,
hydroxocarboxylic acids, oxo acids, peracids and/or oxocarboxylic acids resp.
at least
one of its derivatives like esters) and/or salts) especially like acetic acid,
benzoic
acid, citric acid, formic acid, gluconic acid, hydroxy acetic acid, lactic
acid, malic acid,
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WO 2004/059034 PCT/EP2003/014577
12
oxalic acid, succinic acid, tartaric acid and/or its water-soluble and/or
water-
dispersible derivatives) like esters) and/or salts) may be used.
Any acid, derivative of it, acid mixture andlor mixture with at least one of
its
derivatives like esters) and/or salts) may be used, especially at least one or
any
mixture that is able to show a pH value e.g. of about 2.4, of about 2.9, of
about 3.4, of
about 3.9 and/or of about 4.4 and that is able to generate - at least together
with the
cations present - a thin coating, but a high amount of hydrochloric acid and
of
chloride is not favourable to be used because of its very strong corroding
effect. Of
these acids and derivatives, especially phosphoric acid and dissolved
phosphate
esters/salts are especially favourable. To accelerate the phosphating process,
reducing and/or oxidizing accelerators may be added, but must not be applied.
Such
accelerators) may be favourable to enhance the process, the coating quality
andlor
to influence the oxidation situation.
In the process according to the invention, the phosphating solution or
dispersion contains in many, but not all cases at least one accelerator like
such on
the base of chlorate, guanidine, of an organic compound with at least one
nitro group
like nitroguanidine and/or nitrobenzenesulfonic acid and its derivatives, of
hydrogen
peroxide, hydroxylamine, nitrate and/or of other nitrogen containing
accelerators;
more preferred are' nitroguanidine, nitrobenzenesulfonic acid and/or its
derivatives)
like salt(s). All accelerators together show a content in the range from 0.005
to 10
gIL, preferably in the range from 0.01 to 6 g/L, more preferred in the range
from 0.02
to 3 gIL, especially preferred of at least 0.03 or up to 1 g/L, most preferred
of at least
0.05 or up to 0.7 gIL.
Astonishingly it was observed that it is possible to use the process according
to the invention without addition of any accelerator. The quality of the
accelerator-free
phosphating solutions or dispersions as well as the coating procedure and the
quality
of the resulting coatings was the same as with a content of at least one
accelerator. It
may,only happen that the pickling rate of the accelerator-free solution or
dispersion is
a bit reduced so that the coating rate is lowered and the contacting time has
to be
increased by a small amount.
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In the process according to the invention, an amount of Fe2+ ions may be
added to the phosphating solution or dispersion, preferably in the range from
0.01 to
1 gIL, more preferred in the range from 0.02 to 0.8 gIL, specifically
preferred in the
range from 0,03 to 0.5 g/L, most preferred of at least 0.05 or up to 0.3 g/L.
The
addition may be a dissolved iron phosphate. This addition helps in some cases,
especially for nonferrous metal surfaces like such of hot-dip-galvanized (HDG)
or
electrogalvanized materials (EG), to generate a better corrosion inhibiting
performance.
In case of the - especially accelerator-free - coating of steel surfaces, it
is
favourable to take care that the phosphating solution or dispersion does not
contain
more than about 0.5, 1 or 1.5 g/L of Fe2+ ions, depending on the actual
phosphating
conditions; the iron content may then be lowered by addition of an oxidizing
agent -
which may be in some cases an accelerator - and/or by using a cation exchange
material, e.g. an adequate resin.
In favourable embodiments, the phosphating solution or dispersion contains
free fluoride, preferably in the range from 0.01 to 1 g/L, and/or complex
fluoride,
especially of aluminum, boron, silicon, titanium and/or zirconium, preferably
each in
the range from 0.01 to 1 g/L. In such cases, it is more preferred that the
content of
each of free fluoride resp. of each of the complex fluorides) lies in the
range from
0.02 to 0.8 g/L, specifically preferred in the range from 0.03 to 0.5 g/L,
most preferred
of at least 0.05 or up to ~0.3 g/L. The content of free fluoride and/or of the
at least one
complex fluoride enhances the pickling effect, especially on galvanized
metallic
surfaces as well as on aluminum-rich surfaces as oxide contents may be easier
removed from the metallic surface; further on, it improves the performance and
the
quality of the corrosion inhibition and paint adhesion of the thereof formed
coating for
all metallic material bases.
In the process according to the invention, an amount of POa. ions may be
added to the phosphating solution or dispersion preferably in the range from
0.1 to 18
gIL, more preferred in the range from 0.5 to 15 g/L, especially preferred of
at least 1
and/or up to 12 ~g/L, most preferred of at least 2 g/L and/or up to 9 g/L of
P04 ions.
The phosphate content may provide the necessary acidity for the primary
pickling
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14
effect. It also may help in some cases to remove the excess heavy metal
content like
an iron content out of the solution, that may predominantly or totally be a
result of the
pickling. The orthophosphoric acid may be added as acid, as monoacid and/or as
poly acid salt of an alkali metal and/or of an ammonium group or in a small
amount
as an iron phosphate. Instead or partially instead of orthophosphoric acid,
its esters)
and/or its salt(s), a phosphonic acid and/or other phosphorus containing acid
and/or
at least one of their salts and/or esters may be added to the solution or
dispersion,
especially at least one water-soluble ester of phosphoric acid.
In the process according to the invention, the phosphating solution or
dispersion may contain an amount of S04 ions in the range from 0.1 to 10 or 18
g/L,
preferably of at least 0.5 and/or up to 15 g/L, more preferred in the range
from 1 to 12
g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of SOa. ions.
The sulfate
content may provide the necessary acidity for the primary pickling effect. The
sulfuric
acid may be added as acid or as sulfate of an alkali metal and/or of an
ammonium
group or in a small amount as an iron sulfate. Especially a mixture of at
least one
phosphorus containing acid and/or its salts) and/or its esters) with at least
one
sulphur containing acid and/or its salts) and/or its esters) may be added to
the
solution or dispersion; preferably, the content of such phosphorus containing
compounds should be at least 50 % by weight of all such acids, salts and
esters.
In the process according to the invention, the phosphating solution or
dispersion may contain an amount of NOs ions in the range from 0.1 to 18 or to
10
gIL, preferably of at least 0.5 andlor up to 15 g/L, more preferred of at
least 1 and/or
up to 12 g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of N03
ions.
The nitrate content may provide the necessary acidity for the primary pickling
effect.
The nitric acid may be added as acid, as nitrate of at least one alkali metal
and/or
ammonium or in a small amount as an iron nitrate. Especially a mixture of at
least
one phosphorus containing acid and/or its salts) and/or its esters) with at
least one
nitrogen containing acid and/or its salts) and/or its esters) may be added to
the
solution or dispersion; preferably, the content of , such phosphorus
containing
compounds should be at least 50 % by weight of all such acids, salts and
esters.
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In the process according to the invention, the phosphating solution or
dispersion may contain an amount of groups, ions and compounds together of
organic acids) and/or of its derivatives) in the range from 0.1 to 10 or 18
g/L,
preferably of at least 0.5 and/or up to 15 g/L, more preferred in the range
from 1 to 12
g/L, much more preferred of at least 2 g/L andlor up to 9 g/L of such groups,
ions and
compounds.
Further on, the phosphating solution or dispersion may contain an amount of
nitroguanidine andlor other accelerators on the base of guanidine like
acetatoguanidine, aminoguanidine, carbonatoguanidine, melanilinoguanidine,
nitratoguanidine and ureidoguanidine in the total range from 0.01 to 5 g/L,
preferably
in the range from 0.015 to 3 g/L, more preferred in the range from 0.01 to 1.2
g/L,
much more preferred of at least 0.02 g/L andlor up to 0.6 g/L of the guanidine
cornpound(s). IVitroguanidine had shown in several instances to give the best
results
of all accelerators tested. In comparison to the use of aminoguanidine, the
addition
of nitroguanidine was a small amount more favourable, especially for the
corrosion
inhibition.
In the process according to the invention, the phosphating solution or
dispersion may contain at least one surfactant, especially when cleaning and
phosphating is carried out with the same solution or dispersion, then
preferably with
an amount of all surfactants together in the range from 0.01 to 10 g/L. If
using at least
one surfactant in the phosphating solution, ifi is preferred to take care not
to generate
foam. In some cases, it may be favourable to add a defoamer. This total
surfactant
content may preferably vary in the range from 0.1 to 7 g/L, more preferred in
the
range from 0.3 to 5 g/L, much more preferred of at least 0.5 g/L and/or up to
3 glL of
surfactant(s). Especially in one-bath-processes, the cleaning and phosphating
may
be carried out in the same bath container with the same solution or
dispersion, so
that in the first time of contacting the metallic components with the
phosphating
solution or dispersion, the cleaning and pickling effect of the solution or
dispersion
may prevail, whereas in the further time of the contacting, the coating
process with
the phosphating coating formation may predominate. In general, nearly all
types of
surfactants resp. surfactant mixtures are suitable to be added to the
phosphating
solution or dispersion, especially surfactants resp. surfactant mixtures with
low-
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foaming or non-foaming properties and with a cloud-point in the range from 25
to 40
°C, whereby the surfactant mixtures may be free of further constituents
than
surfactants.
The phosphating solution is preferably free or nearly free of other heavy
metals than those being pickled out of the metallic surface, perhaps with the
exception of titanium and/or zirconium, especially in the presence of complex
fluoride(s). It is preferably free of chromates, molybdates and tungstates.
In the process according to the invention, the phosphating solution or
dispersion may contain at least one solvent like a propylene glycol and/or a
glycol
ether; further on it may contain at least one biocide, at least one
stabilizing agent for
a surfactant like a condensed sulfonic salt, at least one stabilizing agent
for the
accelerator like a fine-particular silicate-, clay- or clay-like material
and/or at least one
stabilizing agent for the solution or dispersion itself like a biopolymer. A
solvent may
be preferable for enhancing the cleaning effect of the metallic surface,
especially in
combination with at least one surfactant. It is favourable to use a guanidine
compound in the form of a suspension containing a stabilizing agent,
especially the
nitroguanidine.
In the process according to the invention, a phosphating coating is generated
showing mostly a colourless, faintly coloured, silvery, golden, yellowish,
yellowish-
brownish, yellowish-reddish andlor bluish colour. If the coating according to
the
invention is bluish, there seems to be often a phosphorus content of the
coating
being not as low as typical for such coatings and there are to be found often
corrosion inhibition results less than of excellence. This coating may in
several cases
be less intensively coloured or may show a less brighter and/or even a matter
appearance than conventional coatings. This coating may typically have a
coating
thickness in the range of up to 1 pm, mostly only up to 0.6 pm, often only up
to 0.3
pm.
In the process according to the invention, a clean, a cleaned and/or a pickled
metallic surface is contacted with the solution resp. dispersion. The metallic
surface
may be contacted with the solution resp. dispersion by immersing, spraying,
steam-
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phosphating, roll-coating and/or squeegeeing. All application varieties except
of
steam-phosphating are often used for coil coating. The coated metallic surface
is
dried after contacting it with the solution resp. dispersion or later on after
at least one
thereon succeeding rinsing step, preferably by air-drying, oven-drying and/or
infrared-
drying, especially at temperatures in the range from 20 to 250 °C.
There may be applied at least two coatings one after the other on the metallic
surface whereby at least one of them is applied with an alkali metal
phosphating
solution resp. dispersion and whereby at least one other coating may
optionally be
applied with a conversion coating solution like a zinc- and/or manganese-rich
phosphating.
In the process according to the invention, first an alkali metal phosphating
coating is generated on a metallic surface and then a coating selected from
the group
consisting of a conversion coating like a zinc- and/or manganese-rich
phosphating
coating, a stearate coating and an organic polymer coating is applied
thereon,.
especially for coldforming.
In the process according to the invention, a metallic surface consisting
essentially of metallic materials of aluminum, chromium, titanium and/or zinc
as well
as at least one alloy containing aluminum, chromium, copper like brass or
bronze,
iron, magnesium, tin, titanium and/or zinc alloys is covered with a coating of
a
phosphating solution or dispersion.
The coating prepared with a process according to the invention may be used
for the short-term passivation, for the pretreatment prior to at least one
succeeding
paint layer, layer of any other organic coating and/or adhesive coating, as a
lubricant
carrier or as one of the lubricating coatings prior to coldforming. The
lubricant resp.
lubricant carrier may be favourably be used for cans, for machining, for wire
drawing
and/or for lubricating the moving chains.
The process may be successfully varied by coating the thin phosphating
coating according to the invention with a final seal solution resp.
dispersion. The
results of the salt spray testings show that a second, third and/or fourth
coating on
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18
the metallic sun'ace generated by contacting the panels phosphated in such way
with
the final seal solution resp. dispersion enhance the corrosion resistance
significantly,
although such final seal coatings are very thin. Preferably, such final seal
coatings
may be generated with a final seal solution/ dispersion containing at least
one rare
earth element compound like a cerium compound, at least one resin component
like
acrylic acid and/or at least one silane.
The coating prepared with a process according to the invention may be used
for the corrosion inhibition and/or the lubrication of metallic surfaces,
especially for
use in aerospace industry, automobile industry, rail transportation,
shipbuilding, metal
forming, metal working like machining and/or grinding, in metallic container
and
especially can production, coil industry, for metal sheet applications, wire
production,
appliances, housings, machines and construction of buildings.
EXAMPLES
The following examples illustrate, in detail, embodiments of the invention.
The
following examples and comparison examples shall help to clarify the
invention, but
they are not intended to restrict its scope:
Group 1: Comparison Examples 1 to 6:
First tests were made in which an aqueous acidic solution as standard
chlorate and sodium metanitrobenzene sulfonate (SNBS) accelerated alkali metal
phosphating concentrate A containing
1.3 % by weight of phosphoric acid,
11.7 % by weight of monosodium phosphate,
1.0 % by weight of SNBS,
10.0 % by weight of sodium chlorate and
the rest being deionized water
was compared to another aqueous acidic solution of an alkali metal phosphating
concentrate B accelerated only on nitroguanidine containing
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1..3 % by weight of phosphoric acid,
11.7 % by weight of monosodium phosphate and
the rest being deionized water.
Starting from these concentrates, the baths with these solutions were
prepared at 3 % by volume for both formulations, this means for the solution A
3.58
% by weight resp. for the solution B 3.30 % by weight of the concentrate. To
the
solution B, 0.2 g/L nitroguanidine stabilized with a small content of clay-
like material
was further added. The pH value of both phosphating baths was adjusted to 4.5
resp.
to 2.8 with an addition of sodium hydroxide.
Panels of cold rolled steel (CRS) were cleaned with Okemclean~ at 3 % by
volume and 54.4 °C for 30 seconds by spraying. The panels were then
rinsed and
afterwards treated in the phosphating bath A or B for 60 seconds by spraying
at
various temperatures. This was followed by rinsing and drying with compressed
air.
The panels were finally painted with a Dupont TGIC polyester powder paint and
subjected to a salt spray (fog) test strictly according to ASTM B 117 for 336
hours for
the evaluation of the corrosion inhibiting properties strictly according to a
ASTM D
1654 rating, with 10 to be the best and 0 the worst.
Table 2: Composition of the coatings of the different groups
Contents in g/L P043- Na* CIOs NBS Nitro- Amino-
Examplesl guani- guanidine
Comparison Examples
dine Carbonate
108, 0.12 0.02 - - 0.02 -
61, 64, 67, 0.58 0.12 - - 0.2 -
70, 73, 76, 0.58 0.12 - - - 0.2
82, 84, 92, 1.16 0.25 - - 0.02 -
62, 65, 68, 1.16 0.25 - - 0.2
71, 74, 77, 1.16 0.25 - - - 0.2
83, 85, 95, 1.16 0.25 - - 0.6 -
106, ~ 3.01 0.64 - - 0.5 -
88, 91, 94, 97, 3.01 1.38 2.37 0.90 - -
1-3, 11-14, 19-22, 3.48 0.74 - - 0.2 -
27-30,
35-38, 51-53, 63,
86, 69,
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54-.56, 72, 75, 78, 3.48 0.74 - - - 0.2
4-6, 15-18, 23-26, 3.78 1.61 2.81 0. - -
31-34, 32
39-42, 79, 110, 111
107, 4.41 0.94 - - 0.8 -
86, 93, 96, 102, 5.80 1.23 - - 0.02 -
101, 5.80 1.23 - - 0.5 -
81, 87, 89, 90, 5.80 1.23 - - 0.6 -
Table 3: Coating weight and salt spray test ratings on CRS for a high pH value
dependent from the temperature of the coating solutions of differently
accelerated
alkali metal phosphating systems
Comp. Accelerator pH Tempe- Coating ASTM
Value rature Weight D 1654
Rating
for SaIt.Spray
Tests
( C) (g/m2) 550 h 1008 h
CE 1 Nitroguanidine4.5 54.4 0.18 6 6
C E " " 65.6 0.24 5 4
2
C E " ~ " 82.2 0. 34 --- 3
3
CE 4 Chlorate-SNBS4.5 54.4 0.32 3 0
CE 5 " " 65.6 0.52 0 1
C E " " 82. 2 0. 46 --- 1
6
The higher the values of the rating, especially after longer testing time, the
better the corrosion inhibition results. As the temperature increased in the
nitroguanidine-accelerated bath B, the coatings became more uniform and
changed
from grey-brown to blue. Lower temperature treatments and lower coating
weights
were correlated with a better salt spray performance. The nitroguanidine-
accelerated
system B showed a better and more homogeneous appearance of the coatings and a
better corrosion inhibition than the chlorate-SNBS-accelerated system A. The
coating
for the panels was homogeneous and went from blue to golden as the temperature
increased.
Group 2: Comparison Examples 11 to 42:
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21
The same base bath formulations were used for the following tests with. the
standard chlorate-SNBS-accelerated system A and with the nitroguanidine-
accelerated system B as in Group 1. Panels of cold rolled steel (CRS), hot
dipped
galvanized steel (HDG), electrogalvanized steel (EG) and aluminum alloy AA
6061
were cleaned with Gardoclean~ S 5206, rinsed, treated in the phosphating baths
A or
B and then rinsed and dried with compressed air. Based on Group 1, the
temperature
range covered was changed to lower temperatures used. The panels were finally
painted with IVlorton Corvel Black powder paint and subjected to salt spray
(fog) test
for 250 hours according to ASTM B 117. The creepage from scribe was measured
according to the rating from 0 to 10 according to ASTIVI D 1654; the higher
the SS
values, the better are the results.
Table 4: Salt spray test results for different metallic surfaces dependent
from the
temperature of the coating solutions of differently accelerated alkali metal
phosphating systems for a pH value of 4.5
Comp. Accelerator SubstrateTempera- Coating Salt Spray
ture ( Weight (g/m2)Test
C) Rating for
250 h
CE 11 NitroguanidineCRS 26.7 0.02 7
C E " " 43.3 0.14 ~ 2
12
CE 13 " " 54.4 0.26 3
CE 14 " " 65.6 0.33 3
CE 15 Chlorate-SNBSCRS 26.7 0.23 1
CE 16 " " 43.3 0.23 2
CE 17 " " 54.4 0.50 3
C E " " 65.6 0.27 2
18
CE 19 NitroguanidineHDG 26.7 - 3
CE 20 " " 43.3 - 2
CE 21 " " 54.4 - 3
C E " " 65. 6 - 1
22
CE 23 Chlorate-SNBSHDG 26.7 - 3
CE 24 " " 43.3 - 3
CE 25 " " 54.4 - 3
CE 26 ~ " " 65.6 - 4
CE 27 NitroguanidineEG 26.7 - 2
CE 28 " " 43.3 - 3
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22
CE 29 " " 54.4 - 2
CE 30 " " 65.6 - 0
CE 31 Chlorate-SNBSEG 26.7 - 4
C E " " 43. 3 - 3
32
C E " " 54.4 - 2
33
CE 34 " " 65.6 - 0
CE 35 NitroguanidineAA 6061 26.7 - 10
C E " " 43. 3 - 10
36
CE 37 " " 54.4 - 10
CE 38 " " 65.6 - 10
CE 39 Chlorate-SNBSAA 6061 26.7 - 10
CE 40 " " 43.3 - 10
CE 41 " " 54.4 - 10
CE 42 " " 65.6 - 10
The test Vresults of this test series show that the results are partially
better at
lower temperatures, but the results depend strongly from the metallic material
of the
surface contacted. Excellent results could be reached with all panels of the
aluminum
alloy. Nitroguanidine showed good corrosion inhibition results, whereby it was
very
astonishing that this could be gained with such a thin coating.
Again, all panels were homogeneous. For the invention, the CRS panels went
from grey-brown to blue as temperature increased. The HDG and EG panels
showed an etched appearance in all cases, but no colour. The aluminum panels
were shiny with no apparently visible coating. For the chlorate samples, the
CRS
panels went from blue to golden with increasing temperature, the HDG and EG
panels had an iridescent appearance and the aluminum panels had a transparent
light tan colour.
Group 3: Comparison Examples 43 to 44:
The cold rolled steel panels were treated with aqueous acidic phosphating
solutions C containing only a very tiny amount much less of 1 g/L of
phosphoric acid
only to adapt the pH value of the ready mixed solution to 2.5 resp. 4.5, 0.2
g/L
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23
nitroguanidine and 0.2 g/L aminoguanidine bicarbonate. If in all the examples
aminoguanidine was added, it was added as bicarbonate, although not always
indicated. The panels were cleaned with Gardoclean° S 5206 and rinsed
before the
nitro- and the aminoguanidine were added. The panels were contacted with the
phosphating solution for the test with a pH value of 2.5 at ambient
temperature and
for the test with a pH value of 4.5 at 49 °C. This was followed by
rinsing and drying
the panels with compressed air. The such coated panels had a golden appearance
and showed a homogeneous coating. The panels were then painted with a Ferro
TGIC polyester powder paint. Finally, the panels were checked for paint
adhesion by
cross hatch and direct impact. There was significant paint loss when these
tests were
performed and were not acceptable. The panels were then also subjected to salt
spray (fog) testing for 250 hours according to ASTM B 117. The panels had a
rating
of 0 per ASTM D 1654 for all cases after 250 hours, which is further on a bad
result.
As the solutions did not contain any alkali metal ions, nor ammonium ions,
they were
not buffered and lacked a significant content of acid.
Group 4: Comparison Examples 51 to 56:
The comparison examples illustrate the effect of low and very.-high pH values
of the phosphating solution using 0.2 g/L of nitroguanidine and 0.2 g/L of
aminoguanidine carbonate as accelerators and using the base bath solution B of
Group 1 containing 3 % by volume of the concentrate containing 1.3 % by weight
of
phosphoric acid, 11.7 % by weight of monosodium phosphate and the rest being
deionized water. The CRS panels were cleaned as in the previous examples.
Starting
with a very acidic bath, the addition of NaOH resulted in very high pH values.
The
panels were sprayed with this conversion coating solution for 60 seconds at
48.9 °C.
An unpainted panel from each test was put into a 100 % humidity test
chamber for a water fog test according to ASTM D 1735 for 72 hours and
thereafter
the surface percentage of red rust was rated. The rest of the panels was
painted with
a Ferro TGIC polyester powder paint and was put into a salt spray test chamber
according to ASTM B 117 for 250 hours and for a copper accelerated acetic acid
salt
spray (fog) ~ test (CASS) test strictly according to General Motors
Engineering
Standards June 1997 for 72 hours. The salt spray test results and the CASS
test
results were measured in mm creep from the scribe. The panels from test 3 and
6 did
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24
not produce any visible coating and were therefore not further tested. The
nitroguanidine bath was not stable above a pH value of about 7.
Table 5: Results of the humidity, salt spray and CASS tests dependent from the
pH
value of the coating solutions of differently accelerated alkali metal
phosphating
systems
Comp. Accelerator pH valueHumidity Salt SprayCASS in
in in mm mm
CE 51 Nitroguanidine 2.8 10 - 25 0.1 0.2
C E " 7. 0 10 - 25 0.2 0.4
52
C E " 9.0 ---- --- ---
53
CE 54 Aminoguanidine 2.8 100 0.2 0.3
Carbonate
CE 55 " 4.5 40 0.1 < 0.1
C E " 6. 5 --- --- ---
56
The corrosion inhibition was only for sample CE 51 of a pH value of 2.8 good
and otherwise of medium quality. No coating weights were measured for this
group.
The coatings in all cases were homogeneous. Both coatings generated with the
nitro-
and aminoguanidine showed a golden colour at a low pH value and were blue at a
high pH.
Group 5: Examples and Comparison Examples 61 to 79:
Cold rolled steel panels were cleaned and rinsed as in the previous examples
and comparison examples. The phosphating baths were prepared with varying
amounts of the base bath formulations starting from Group 1 and varying the
accelerator concentrations of A and B. The conversion coating baths were
operated
at 26.7 °C and mostly at a pH value 4.5 for 60 second spraying. The
last comparison
example 79 was the standard chlorate-SNBS-accelerated alkali metal phosphating
as
outlined in Group 1, but only this was operated at a pH value of 4.5 and at a
temperature of 48.9 °C for 80 seconds of spraying. The salt spray
rating was
evaluated according to ASTM D 1654 after 500 hours salt spray (tog) test
according
to ASTM B 117.
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Table 6: Results of the salt spray test and the coating weight dependent from
the
accelerator amount of the coating solutions of differently accelerated alkali
metal
phosphating systems and of the pN value at a temperature of 26.7 °C; *
bath without
accelerator content
Ex./ Accelerator Accelera-Bath * pH CoatingSalt Spray
Comp. for (g/L)Concentra-Value Weight Rating
tion Vol. (g/m~) for
% 500 h
CE 61 Nitroguanidine0.02 0.5 4.5 0.06 0
C E " " 1 " 0.14 0
62
C E " " 3 " 0. 07 0
63
CE 64 " 0.2 0.5 " 0.16 0
CE 65 " " 1 " 0.13 0
C E " " 3 " 0.01 0
66
C E " 0.4 0.5 " 0.16 0
67
CE 68 " " 1 " 0.14 0
CE 69 " " 3 " 0.11 0
CE 70 Aminoguanidine0.2 0.5 " 0.11 0
Carbonate
CE 71 " " 1 " 0.30 0
E 72 " " 3 2.8 0.15 3
CE 73 " 0.1 0.5 4.5 0.03 2
CE 74 " " 1 " 0.19 0
E 75 " " 3 2.8 0.16 3
C E " 0. 05 0.5 4. 0. 03 2
76 5
C E " " 1 " 0.10 1
77
E78 " "~ 3 2.8 0.01 3
CE 79 Chlorate-SNBS " 3 -- 4.5 0.45 1
, , , _ - , _ , , ,
The examples according to the invention, E 72, E 75 and E 78, show
significantly better corrosion results than most of the other samples. The
coatings
were even, of a golden colour at a low pH value and of a blue colour at a high
pH
value for coatings generated with amino- resp. nitroguanidine.
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Group 6: Examples and Comparison Examples 81 to 97:
In this group, a so-called multimetal formulation was used. The bath solution
contained fluoride to treat cold rolled steel, hot dipped galvanized,
electrogalvanized
and aluminum. The base solution B of Group 1 was used by With an additional
content of free fluoride, whereby fihe content of all components of this bath
were
varied at a temperature of 38 °C.
A high number of solutions and tests was performed to generate data for
intensive studies with design of experiment evaluation. For these experiments,
the
metallic surfaces, the content of fluoride (50 - 200 mg/L), the content of
added Fe2+
(0 - 200 mg/L), the content of phosphate and sodium monophosphate together
(1.4 -
7.2 g/L), the content of nitroguanidine as the single accelerator (0.02 - 0.6
g/L) as
well as the pH value (2.8 - 4.5) were systematically varied within the
mentioned
limits, whereby only the examples according to the invention are listed in
table 7. In
comparison hereto, a chlorate-SNBS-accelerated solution of a pH value of 4.5
was
tested at 49 °C with CE 88, CE 91, CE 94 and CE 97, whereas the other
comparison
examples belong strictly to the data set as shown for the rest of the examples
according to the invention. The number of examples and comparison examples
tested was reduced for this overview, so that typical results are represented
here.
From these experiments, systematical calculations were performed and the
regions
of excellent resp. good resp. stable behaviour selected.
The panels were painted with a Ferro TGIC polyester powder paint of 38 to 51
pm thickness and were put into a salt spray (SS) test chamber according to
ASTM B
117 for 250 hours, whereby the test results were measured in mm creep from the
scribe. Further on, adhesion was tested according to ASTMD 3359, whereby 5B
means that no flaking did .occur in the cross-cut area which is the best
possible test
result, whereas e.g. 2B means that there is a certain amount of flaking in the
cross-
cut area.
Table 7: Results of the salt spray (fog) test dependent from the chemical
composition
of the phosphating solutions and from the pH value at a temperature of 32
°C; * bath
without accelerator content
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Ex.l Me- Bath Acce- Fluo-Fe2+ pH Adhe- SS SS
Comp tallic* lera- ride (mg Va- sion Rating Rating
~ Sur- Con- for (mg /L) lue ASTM for 240 for
face cen- (g/L) /L) 3359 h 500
tration h
(g/L)
E 81 CRS 7.2 0.6 200 0 2.8 5B 1 2.5
E 82 " ~ 1.4 0.02 50 200 " 5B 0.5 2
~
E 83 " 1.4 0.6 200 200 " 5B 0.5 1
E 84 " 1.4 0.02 200 0 " 4B 1 1.5
CE " 1.4 0.6 200 0 ~ 4.5 5B 2.5 4
85
I
E 86 " 7.2 0.02 200 200 2.8 5B 1 1.5
CE " 7.2 0.6 200 200 4.5 4B 4 9
87
CE " 4.1 4.4 310 0 4.5 2B 4.5 7
88
E 89 HDG 7.2 0.6 50 200 2.8 3B 3.5. 4
E 90 " 7.2 0.6 200 0 " 3B 4 5
CE " 4.1 4.4 310 0 4.5 2B 10 18
91
E 92 EG 1.4 0.02 50 200 2.8 5B 2 2.5
~
E 93 ,~ 7.2 0.02 200 200 " 5B 1.5 3
CE " 4.1 4.4 310 0 4.5 2B 3.5 4
94
E 95 AI 1.4 0.6 50 0 2.8 4B 0.5 0.5
6061 .
E 96 " 7.2 0.02 50 0 " 4B 0.5 0.5
CE " 4.1 4.4 310 0 4.5 4B 0.5 1
97
Nearly all of the examples according to the invention showed very good
corrosion inhibition results resp. for the corrosion-sensitive material HDG
even
excellent results compared with the results of the comparison examples. The
higher
the values of the adhesion tests, the better are the results. The coatings
were even in
all cases. CRS panels according to the invention were grey, HDG panels were
very
faint golden, EG panels were grey and aluminum panels were of no significant
colour.
For the control, the CRS panels were golden, EG and HDG panels were
transparent
and iridescent and aluminum panels were light blue.
Group 7' Examples and Comparison Examples 101 to 111:
In this group, only cold rolled steel panels were used and different
influences
were checked, even the influence of the bath temperature. The solutions were
free of
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fluoride and added Fe2+. All the other contents and conditions of the coatings
were
the same as in Group 6. Further on, the samples CE 109 and CE 110 were coated
with Bonderite~ 1000 (CE 109) for having an additional thin chromium final
seal
covering the phosphate coating resp. Cryscoat° 547 for having an
additional thin
non-chromium final seal covering the phosphate coating (CE 110) and the last
having
no additional final seal (CE 111 ) = each being coated in a typical manner.
These
coatings may be used as typical industry standards to get a comparison of
typical
conventional iron phosphating coatings of today.
Table 8: Results of the salt spray (fog) test on three CRS panels each
dependent
from the chemical composition of the coating solutions, the pH value, the
contacting
time and the temperature; * bath without accelerator content
Examples Bath ~ Acce- pH contac- tempe- SS rating
/Comp. Concen- leratorValue ting rature for 240
tration (g/L) time ( C) h
(g/L) (s) mm .creep
E 101 7.2 0.5 2.8 30 32 1
E 102 7.2 0.02 2.8 105 32 1.1
E 103 4.3 0.2 3.0 60 37 0.5
E 104 0.14 0.02 2.8 180 37 1.2
E 105 0.14 ~ 1.0 2.8 30 44 1.0
C E 106 3. 7 0. 5 4. 9 105 44 1. 6
C E 107 5.4 0. 8 6. 0 68 54 8.1
~
CE 108 0.14 0.02 4.9 180 60 ~ 9.3
I
CE109 - - - - - 0.2,0.5
CE 110 4.6 3.9 ~ 4.5 52 60 2
C E 111 4. 6 3. 9 4. 5 52 60 5
The examples according to the invention showed very good corrosion
inhibition results compared with the results of the comparison examples. The
comparison examples vary with respect to the corrosion inhibition quality
depending if
there is a further seal or not and especially if this final seal is a chromium
containing
layer. CE 109 showing such additional chromium containing layer covering the
phosphate layer should show the best corrosion inhibition properties.
Nevertheless, it
is astonishing that the best panels according to the invention were able to
reach the
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excellent corrosion inhibition properties of CE 109 which is the best industry
standard
material on the base of iron phosphate known in the art which in this case is
even
covered by a strongly further corrosion inhibiting final rinse layer.
The coatings were even in all cases. The colour changed from golden to blue
when either the pH or temperature was increased. The contact time, bath
concentration and accelerator concentration did not have any apparent effect
on the
appearance.
The results of the design of experiments showed clearly a broad region of
unusually stable working conditions for an alkali metal phosphating solution
below a
pH value of 3.5 and astonishingly very constant coating properties. The
phosphating
results on aluminum alloy 6061 were best at a F- content of less than 200 ppm
and at
a Fe2+ content less than 120 ppm. On hot dip galvanized steel (HDG), they were
best
at a F- content of less than 360 ppm and at a Fe2+ content of more than 80
ppm,
although the results were - as usual with HDG in such comparisons - worse than
for
the other metallic materials tested. On electrogalvanized steel (EG), they
were best
at a very low P04 content and at a F- content of less than 200 ppm. On
coldrolled
steel (CRS), they were best at a F- content of less than 250 ppm. During a
long
throughput study, it was confirmed that these working conditions as well as
the
coating properties could be maintained nearly without any variation for all
the time
without changing the bath, but with continuous replenishment.
The appearance of the coatings was at least as good as for comparable good
alkali metal phosphating coatings used in the market. As best accelerator
during all
these studies, nitroguanidine was identified. Further on, the alkali metal
phosphating
process with the slightly modified working conditions for the solutions
according to
the invention are well suited for industrial application of coils, parts and
wires. The
use of the phosphating solution at a significantly lower temperature than
today usual
for the contacting of metallic surfaces helps to reduce heating costs
considerably.
The herein proposed phosphating process is easier than the processes used
today
as it is quite sufficient to control only total and free acid content, but no
other
parameters of the bath within short time limits, as the bath behaviour is very
stable.
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Finally, this process is not only superior because less heating is needed and
therefor
is cheaper in comparison to actually used processes as there is a significant
lower
consumption of all chemical compounds of the solution than usual.
Group 8: Examples 112 to 119:
For this investigation, cold rolled steel panels supplied by Q Panel were used
as the
substrates. Table 9 below lists the bath composition for each variation. The
examples 117 to 119 were rinsed with a final seal instead of the rinsing with
DI water.
CrysCoat UItraSeal is a product of Chemetall Oakite based on water, silane and
alcohol. The pretreated panels were painted using TGIC polyester powder paint
supplied by Rohm & Haas. Single scribe panels were placed in salt spray
testing per
°ASTM B 117 for 240 hours. The panels were scraped with a metal spatula
and the
amount of paint loss from the scribe was measured in mm. All variations were
subjected to cross hatch adhesion per ASTM D 3359 and direct and reverse
impact
per ASTM D 2794. In all cases, the rating for the cross hatch adhesion testing
was
5B (no loss of adhesion) and for the direct and reverse impact, no cracking or
other
paint loss was seen up to 160 pounds/inch2 (1.84 kilogrammlmeter2). The panels
were pretreated as written below:
1. Gardoclean S 5206, 3 v/v% b.v., 120 -125 °F (49 - 52 °C), 60
second spray
2. Tap water rinse, ambient temperature, 30 second spray
3. Conversion coating, 86 - 92 °F (30 - 33 °C)
4. Tap water rinse, ambient temperature, 30 second spray
5. DI water rinse, 10 seconds or final seal, ambient temperature, 30
second immersion
6. Oven dry, 225 °F (107 °C), 5 - 10 minutes
Table 9: Chemical compositions of the examples 112 to 119 in g/L; Cerium
nitrate
addition calculated as Ce; CCU = CrysCoat UItraSeal; * bath of the final seal
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Ex. H3 LacticGl,yco-Nitro-NaOH Ce Acry- CCU pH
PO~ Acid lic guani- lic Value
Acid dine Acid
E112 2.2 2~.0 - 0.2 1.0 - - - 3.0
E113 2.2 - 1.7 0.2 1.8 - - ~ - 3.0
E114 4.6 - - 0.2 2.1 0.4 - - 2.9
E 11 4.6 - - 0.2 2.1 0.4 2.0 - 3.1
E116 4.3 - - 0.2 1.7 - - - 2.8
E117 4.3 - - 0.2 1.7 - - - ~ 2.8
E 117* - - - - - - - 1.6 2.85*
*
E118 4.3 - - 0.2 1.7 - - - 2.8
E118* - - - - - 2.0* - - 4.3*
E119 4.3 - - 0.2 1.7 - - - 2.8
E119* _ _ _ _ - 2.0* 2.0* - 2.9*
Table 10: Results of the salt spray (fog) test as well as visual appearance of
the
panels and coating weight of the coatings
Examples Further additionsSS rating Visual appearance Coating
of
for 240 panels weight
h
mm creep (g/m~)
E 112 Lactic acid 1.0 Even grey-tan colour0.02
E 113 Glycolic acid 1.2 Even grey-tan colour0.07
E 114 Ce nitrate 2.0 Even tan colour 0.01
E 115 Ce nitrate and 1.2 Mostly even, deep 0.14
acrylic acid golden colour
E 116 - 1.5 Even tan colour 0.06
E 117 - ; additional 0.3 Even tan colour 0.08
final
seal: CCU
E 118 - ; additional 0.3 Even light tan-grey0.01
final
seal: Ce nitrate colour
E 119 - ; additional 0.3 Patchy grey to 0.07
final tan
seal: Ce nitrate colour
and acrylic acid
The panels showed excellent thin coatings of more or less tan colour and good
or even excellent corrosion inhibition. In comparison hereto, the best
standard for an
iron phosphate coating coated with a chrome final seal reached a salt spray
test
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rating for 240 h of 0.2 mm creep. Within the scope of avoiding poisonous
chromium
compounds, the results are excellent.
