Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 03225205 2023-12-21
"Method for sequentially constructing a conversion layer on components
comprising steel surfaces"
The invention relates to a method for the anti-corrosion pre-treatment of a
plurality of components in
series, in which the components of the series are at least partially formed of
iron and/or steel, and in
which the components of the series each initially undergo a first conversion
stage, followed by a
rinsing stage and a subsequent second conversion stage, wherein, in the
conversion stages,
respective acidic aqueous conversion solutions based on compounds of the
elements Zr and/or Ti
dissolved in water are brought into contact with the components, and,
additionally, copper ions are
contained in the conversion solution for the second stage.
In the anti-corrosion pre-treatment of components having surfaces made of the
materials iron, steel,
galvanized steel and/or aluminum, thin-film passivation based on amorphous
conversion layers
based on oxides and hydroxides of the elements Zr and/or Ti has become widely
established as an
alternative to phosphating, in the course of which crystalline coatings are
formed. Efforts to further
develop this type of conversion coating are essentially aimed at establishing
resource-saving and
chromium-free passivations that provide an excellent adhesive base for paint
systems applied
subsequently, wherein the aim is to achieve corrosion protection comparable to
trication zinc
phosphating. Especially in the case of amorphous thin films resulting from the
conversion treatment
of acidic aqueous solutions containing water-soluble compounds of the elements
Zr and/or Ti,
controlled film formation and growth of coatings with as few defects as
possible is of great
importance. In particular, it is difficult in this case to influence the
kinetics of film formation in the thin
diffusion film on the metal surface, in which an alkaline pH results in the
coating based on the
hydroxides and oxides of the elements Zr and/or Ti, in such a way that the
conversion of the
conversion treatment based mostly on fluoro complexes of the elements Zr
and/or Ti is as complete
as possible. This is to prevent fluorides from remaining in the thin film,
which can cause localized film
defects in contact with corrosive media. EP 1 455 002 Al therefore reports
that reducing the
proportion of fluorides in the conversion coating can result in an improved
corrosion behavior and
paint adhesion to a subsequent electrodeposition coating. To effectively
reduce the fluoride content
in the conversion coating, EP 1 455 002 Al proposes to add magnesium, calcium,
an Si-containing
compound, zinc, or copper to the conversion solution and alternatively, or in
combination, to dry the
conversion coating or post-rinse it with an alkaline aqueous composition.
Furthermore, in the prior art there are efforts to improve the quality of the
conversion coating via a
sequential structure of the coating. EP 2 318 566 Al, for example, shows that
cascading the rinsing
water of the conversion treatment into a pre-rinse before the actual
conversion treatment is
advantageous for the formation of amorphous coatings based on the elements Zr
and/or Ti, in
particular on steel surfaces, which protect against corrosion. According to EP
2 318 566 Al, a first
slight conversion of the surface takes place during the pre-rinse, which is
advantageous for the
subsequent construction of the actual conversion layer. According to the
teaching of EP 2 971 234
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Al, a sequential layer structure by means of conversion in successive wet-
chemical individual steps
carried out independently of one another is also used to improve paint
adhesion to correspondingly
pre-treated steel surfaces. It describes a two-step process for the build-up
of a conversion coating
based on elements of the secondary groups III b/lVb of the periodic table, in
particular on the element
Zr, consisting of acidic fluoride-containing solutions, which is particularly
suitable for a subsequent
electrodeposition coating and can be carried out on various metal substrates.
Proceeding from this prior art, it is the object of the present invention to
provide alternative methods
for providing conversion coatings with as few defects as possible for a wide
variety of metals, which
then have improved protection against corrosive delamination after paint layer
build-up. The method
should be able to be carried out with as few resources as possible and should
be particularly suitable
for the treatment of components in series. Compared to the prior art, a
significant improvement in
corrosion protection and paint adhesion, at least on the surfaces of steel
and/or iron, should also be
achieved in a stable manner during the pre-treatment of a series of components
to improve process
quality.
This object is achieved by a method for the sequential build-up of a
conversion coating in two
treatment steps that are interrupted by a rinsing stage, wherein the
conversion solutions each contain
water-soluble compounds of the elements Zr and/or Ti and copper ions are
additionally contained in
the second conversion stage.
Specifically, the present invention relates to a method for the anti-corrosion
pre-treatment of a
plurality of components in series, in which the components of the series are
at least partially formed
of iron and/or steel, and in which the components of the series each undergo
the successive method
steps i)-iii) and at least the surfaces of iron and/or steel of the components
are successively brought
into contact with the respectively provided aqueous solutions (1)-(111):
i) a first conversion stage providing an aqueous conversion solution (1)
having a pH in the range
of 2.5 to 5.0, comprising at least 0.10 mmol/kg of compounds of the elements
Zr and/or Ti dissolved
in water and free fluoride;
ii) a rinsing stage providing an aqueous rinsing solution (II) having a pH
in the range of 5.0 to
10.0 and a concentration of compounds of the elements Zr and/or Ti dissolved
in water reduced by
at least a factor of 5 compared to the aqueous conversion solution (1) and
containing less than
0.25 mmol/kg of free fluoride;
iii) a second conversion stage providing an aqueous conversion solution
(111) having a pH in the
range of 2.5 to 5.0, comprising at least 0.10 mmol/kg of compounds of the
elements Zr and/or Ti
dissolved in water and at least 15 pmol/kg of copper ions dissolved in water.
Anti-corrosion pre-treatment of the components in series is when a large
number of components are
brought into contact with treatment solution provided in the respective
treatment stages of the method
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according to the invention and conventionally stored in system tanks, the
individual components
being brought into contact successively and thus at different times. In this
case, the system tank is
the container in which the treatment solution is located for the purpose of
anti-corrosion pre-treatment
in series.
When, in the context of the present invention, reference is made to the pre-
treatment of a component
composed of a metallic material, in particular on the surfaces of the
materials iron and steel to be
subjected to the pre-treatment according to the invention, all materials
containing the respective
element to an extent of more than 50 at.% are thus included. An anti-corrosion
pre-treatment always
affects the surfaces of the component and thus of the metallic materials. The
material can be a
uniform material or a coating. According to the invention, galvanized steel
grades consist both of the
material steel and of the material zinc, it being possible for surfaces of
steel to be exposed at the
cutting edges and cylindrical grinding points of, for example, an automobile
body which is made of
galvanized steel, in which case according to the invention there is pre-
treatment of the material steel.
Insofar as the concentration of an active component or compound is referred to
in the context of the
present invention as the amount of substance per kilogram, this is the amount
of substance based
on the weight of the respective total composition.
The components pre-treated according to the present invention can be three-
dimensional structures
of any shape and design that originate from a manufacturing process, in
particular also including
semi-finished products, such as strips, sheets, rods, pipes, etc., and
composite structures assembled
from said semi-finished products, in particular automobile bodies, the semi-
finished products
preferably being interconnected by means of adhesion, welding and/or flanging
to form a composite
structure.
With regard to the method steps, a solution (1)-(111) is considered to be
"provided" in the sense of the
method according to the invention if it is either prepared or held ready for
contacting as defined in
the respective treatment stage (i)-(iii) or is implemented during contact as
defined.
The multi-stage pre-treatment according to the present invention, in
comparison with a conversion
treatment by one-time contacting with an acidic aqueous solution containing
compounds of Zr and/or
Ti dissolved in water and free fluoride ("conventional single-stage conversion
layer formation"),
provides defect-free conversion layers with a low fluoride content and a
significantly reduced
tendency to corrosive delamination of a subsequently built up paint system.
The combination of a
first conversion stage and a second conversion stage, which takes place after
the rinsing stage in a
conversion solution containing copper ions dissolved in water, is
indispensable for this, and the mere
reduction of the fluoride content in the conversion coating after the first
conversion stage by means
of the rinsing stage, which takes place with a rinsing solution containing
substantially no free fluoride
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ions (Le., less than 0.25 mmol/kg, preferably less than 0.10 mmol/kg, very
particularly preferably less
than 0.05 mmol/kg of free fluoride), is not sufficient, in particular not for
sufficient performance in
terms of corrosion protection on the steel and/or iron surfaces of the
components of the series.
The amount of free fluoride in the relevant stages of the pre-treatment
according to the invention can
be determined potentiometrically by means of a fluoride-sensitive measuring
electrode at 20 C in
the relevant provided solution after calibration with fluoride-containing
buffer solutions without pH
buffering.
The conversion layer formation in method steps i) and iii) is carried out by
means of conversion
solutions that produce an amorphous oxide/hydroxide coating based on the
elements Zr and/or Ti
and accordingly contain compounds of the elements Zr and/or Ti dissolved in
water. The term
"dissolved in water" comprises molecularly dissolved species and compounds
that dissociate in
aqueous solution and form hydrated ions. Typical representatives of these
compounds are titanyl
sulfate (TiO(SO4)), titanyl nitrate (TiO(NO3)2) and/or hexafluorotitanic acid
(H2TiF6) and salts thereof
or ammonium zirconium carbonate ((NH4)2ZrO(CO3)2) and/or hexafluorozirconic
acid (H2ZrF6) and
salts thereof. The compounds dissolved in water are preferably selected from
fluoro acids and/or
fluoro complexes of the elements Zr and/or Ti in the conversion stages. The
conversion layer
formation based on the fluoro acids and/or fluoro complexes of the element Zr
is particularly
preferred, because conversion layers of this kind provide improved paint
adhesion.
Furthermore, it is advantageous for the formation of an extremely homogeneous
and compact
amorphous conversion layer if the pH of the conversion solution is not set to
be acidic in order to
keep the pickling rate as low as possible during the growth of the conversion
layer, in particular in
the first conversion stage. Overall, it is therefore preferred for both
conversion stages in method steps
(i) and (iii) that the pH is in each case above 3.0, more preferably above
3.5, particularly preferably
above 4.0, but preferably below 4.5, because otherwise the precipitation of
sparingly soluble
hydroxides of the elements Zr and/or Ti in the interior of the solution can
only be kept under control
in a narrow process window during the serial treatment of a plurality of
components.
An embodiment of the method according to the invention is particularly
preferred in which the
predominant part of the layer formation is already carried out in the first
conversion stage and the
second conversion stage only serves to remedy defects in the conversion
coating formed in the first
stage by deposition of a relatively small additional coating on the elements
Zr and/or Ti, which is
supported by the local cementation of copper at point defects in the
conversion layer. Surprisingly, it
has been found in this context that deposition of Zr and/or Ti beyond the
required degree in the
second conversion stage in turn significantly worsens the corrosion protection
properties. This
applies in particular to the surfaces of iron and/or steel of the components
pre-treated according to
the invention.
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Accordingly, a method according to the invention is preferred in which the
contacting with the
conversion solution (i) in the first conversion stage in method step (i) takes
place at least for a period
of time during which a coating of at least 20 mg/m2 is produced on the
surfaces of steel and/or iron,
but the contacting is preferably not for so long that a coating of more than
150 mg/m2, more preferably
more than 100 mg/m2, very particularly preferably more than 80 mg/m2 in each
case based on the
elements Zr and/or Ti results on these surfaces.
Now, as already explained above, in connection with such a coating brought
about in the first
conversion stage, it is advantageous for corrosion protection and paint
adhesion, in particular on the
surfaces of steel and/or iron, and it is therefore also preferred if the
contacting with the conversion
solution (III) in the second conversion stage in method step (iii) does not
continue until there is an
increase in the coating of more than 15 mg/m2, particularly preferably more
than 12 mg/m2, very
particularly preferably more than 10 mg/m2, on the surfaces of steel and/or
iron, but the contacting is
preferably carried out at least for such a period of time that the coating on
these surfaces is increased
by at least 2 mg/m2 in each case based on the elements Zr and/or Ti.
In this way, the layer structure in the conversion stages of the method
according to the invention for
anti-corrosion pre-treatment is optimally coordinated.
Preferred embodiments of the method according to the invention are shown and
explained below
with respect to the individual treatment stages and the method execution,
which are particularly
advantageous with respect to the object on which the invention is based.
First conversion stage:
In the first conversion stage, it is necessary to produce a conversion coating
based on
oxidic/hydroxidic compounds of the elements Ti and/or Zr as homogeneously as
possible, while at
the same time satisfying the requirements for process economy. The treatment
time required for this
purpose, Le., the duration of contacting with the conversion solution at a
temperature in the range of
10-60 C, should be in the range of 10 seconds to 300 seconds. In order to
ensure this, a method
according to the invention is preferred in which, in the conversion solution
(I) of the first conversion
stage in method step i), the proportion of compounds of the elements Zr and/or
Ti dissolved in water
is preferably at least 0.15 mmol/kg, more preferably at least 0.25 mmol/kg,
particularly preferably at
least 0.30 mmol/kg. For reasons of process economy, the content of compounds
of the elements Zr
and/or Ti dissolved in water should be significantly below 10.0 mmol/kg,
particularly preferably below
5.0 mmol/kg.
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However, a proportion of free fluoride is necessary in any case, depending on
the type and surface
properties of the metallic substrates, in particular the steel substrates, and
the required pickling rate.
In principle, it is advantageous, and therefore preferred, if in the
conversion solution (I) of the first
conversion stage in method step i), the proportion of free fluoride is at
least 0.5 mmol/kg, particularly
preferably at least 1.0 mmol/kg, and very particularly preferably at least 1.5
mmol/kg. However, for
reasons of process economy and to prevent rust formation on the surfaces of
steel and/or iron,
especially after the rinsing stage, the proportion of free fluoride should
preferably be less than
8.0 mmol/kg, particularly preferably less than 6.0 mmol/kg, very particularly
preferably less than
5.0 mmol/kg.
A good balance of pickling rate and layer formation can be achieved if the
quotient A in the conversion
solution (I) of the first conversion stage in method step i) is according to
formula (1)
= ,F / mM
,/Me/mM (1)
where F/mM and Me/mM are the free fluoride (F) or reduced zirconium and/or
titanium concentration
(Me) reduced by the unit of the concentration in mmol/kg, is greater than
0.80, preferably greater
than 1.20, particularly preferably greater than 1.60, so that such conversion
solutions are preferred
according to the invention.
Suitable sources of free fluoride in the first conversion stage of method step
i) of the method
according to the invention are hydrofluoric acid and the water-soluble salts
thereof, such as
ammonium bifluoride and sodium fluoride, as well as complex fluorides of the
elements Zr, Ti and/or
Si, in particular complex fluorides of the element Si. In a phosphating
process according to the
second aspect of the present invention, the source of free fluoride is
therefore preferably selected
from hydrofluoric acid and its water-soluble salts and/or complex fluorides of
the elements Zr, Ti
and/or Si. Salts of hydrofluoric acid are water-soluble within the meaning of
the present invention if
their solubility in deionized water (-K < 1pScm-1) at 60 C is at least 1 g/L,
calculated as F.
Rinsing stage:
The rinsing stage in method step ii) of the method for sequential conversion
coating according to the
invention serves on the one hand for the complete or partial removal or
dilution of soluble residues,
particles and active components that are carried on the component in an
adhering manner from the
preliminary wet-chemical method step i). On the other hand, the removal of
soluble residues should
also specifically bring about the soluble fluoride species contained in the
conversion coating, thus
conditioning the first conversion coating for a subsequent passivating
deposition of oxidic/hydroxidic
Zr and/or Ti compounds and the cementation of copper in the second conversion
stage. It has been
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found that the rinsing solution does not have to contain substantially any
active components based
on metal or semi-metal elements, which are consumed merely by the metal
surfaces of the
component being brought into contact with the rinsing liquid by deposition.
Thus, the rinsing liquid
can simply be municipal water or deionized water, or, if necessary, a rinsing
liquid that can
additionally contain redox-active compounds ("depolarizers") to optimize the
conditioning of the metal
surface accessible at point defects, or additionally surface-active compounds,
such as non-ionic
surfactants or anionic surfactants, to optimize wettability with the rinsing
solution.
It is therefore essential for the fulfillment of the purpose of the rinsing
stage that the aqueous rinsing
solution (II) provided in the rinsing stage has a concentration of compounds
of the elements Zr and/or
Ti dissolved in water, which is reduced in comparison with the aqueous
conversion solution (I) at
least by a factor of 5, preferably at least by a factor of 10, particularly
preferably at least by a factor
of 20, very particularly preferably at least by a factor of 50, and in this
case comprises less than
0.25 mmol/kg, preferably less than 0.10 mmol/kg, particularly preferably less
than 0.05 mmol/kg of
free fluoride and preferably less than 0.10 mmol/kg of compounds of the
elements Zr and/or Ti
dissolved in water. In this case, the continuous reduction of soluble fluoride
species in the conversion
coating can also be achieved by bringing it into contact with rinsing
solutions that contain a reduced
concentration diluted by a factor of 5, for example by more than a factor of
100, of compounds of the
elements Zr and/or Ti dissolved in water, can also be achieved in that the
rinsing stage comprises a
plurality of immediately successive rinsing steps, but preferably, for reasons
of process economy,
not more than three rinsing steps, with rinsing solutions (II) that contain at
least one concentration,
reduced by a factor of 5, of compounds of the elements Zr and/or Ti dissolved
in water.
In view of the goal pursued with the rinsing stage, which is to bring about
conditioning for the
subsequent passivating deposition of oxidic/hydroxidic Zr and/or Ti compounds
and the cementation
of copper, it is advantageous and therefore preferred according to the
invention if the rinsing
solution(s) (II) of the rinsing stage contain(s) a total of less than 50
pmol/kg, preferably a total of less
than 15 pmol/kg, of metal ions of the elements copper, nickel and cobalt that
are dissolved in water.
According to the invention, the pH of the rinsing solution is in the range of
5.0 to 10Ø However, it
has been found that alkaline rinsing solutions can be disadvantageous in that
alkalinity is introduced
into the second conversion stage, which must be compensated for there by
resharpening with acidic
substances and additionally promotes the precipitation of active components
and thus sludge
formation. Accordingly, it is preferred according to the invention if the
aqueous rinsing solution (II),
preferably at least the rinsing solution of the final rinsing step of the
rinsing stage, has a pH above
6.0, but below 9.5, particularly preferably below 8.5 in method step (ii).
In a further aspect, it was possible to show that the conditioning of the
surfaces of steel and/or iron
provided with a first conversion layer for the subsequent passivating
deposition of oxidic/hydroxidic
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Zr and/or Ti compounds and the cementation of copper in the second conversion
stage is promoted
by the fact that redox-active compounds that inhibit the formation of hydrogen
on metal surfaces
(referred to as "depolarizers") are added to the rinsing solution. In a
preferred embodiment of the
method according to the invention, the aqueous rinsing solution (II) of the
rinsing stage in method
step (ii) therefore additionally contains at least 0.1 mmol/kg, more
preferably at least 0.5 mmol/kg,
particularly preferably at least 1 mmol/kg, but preferably no more than 10
mmol/kg, particularly
preferably no more than 6 mmol/kg of a depolarizer selected from nitrate ions,
nitrite ions,
nitroguanidine, N-methylmorpholine N-oxide, hydrogen peroxide in free or bound
form,
hydroxylamine in free or bound form, reducing sugars, preferably selected from
nitrite ions,
nitroguanidine, hydroxylamine in free or bound form, hydrogen peroxide in free
or bound form,
particularly preferably selected from nitrite ions.
As already explained, the rinsing stage can take place in a plurality of
successive rinsing steps if it is
ensured that the respective rinsing solutions (II) each have a pH in the range
of 5.0 to 10.0 and a
concentration of compounds of the elements Zr and/or Ti dissolved in water
that is reduced at least
by a factor of 5 in comparison with the aqueous conversion solution (I) and
contain less than
0.25 mmol/kg, preferably less than 0.10 mmol/kg, particularly preferably less
than 0.05 mmol/kg of
free fluoride. In a preferred embodiment, the contacting with the respectively
provided rinsing solution
in the rinsing stage of method step (ii) is carried out by dipping and/or
spraying, preferably dipping
and spraying, wherein dipping is preferably carried out first and then
spraying.
Second conversion stage:
The conversion of the metal surfaces of the component brought about in the
second conversion
stage serves, as has already been explained, primarily for the post-
passivating deposition of
oxidic/hydroxidic Zr and/or Ti compounds, so that, for reasons of process
economy, but also for
reliable compliance with the process window, relatively few active components
of Zr and/or Ti in the
conversion solution of the second conversion stage can be advantageous for
optimum corrosion
protection properties of the conversion layer constructed sequentially in the
method according to the
invention. Accordingly, a method according to the invention is preferred in
which the conversion
solution (III) of the second conversion stage in method step iii), the
proportion of compounds of the
elements Zr and/or Ti dissolved in water is less than 1.00 mmol/kg, preferably
less than
0.80 mmol/kg, more preferably less than 0/0 mmol/kg, particularly preferably
less than
0.60 mmol/kg.
In the second conversion stage, an amount of free fluoride is optional and it
should be noted that the
downstream conversion stage should not be set to be too mordanting at the same
time in order to
prevent the formation of local defects in the conversion coating.
Nevertheless, a small amount of free
fluoride may be useful for the cementation of the copper ions and the
accelerated post-passivating
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deposition of oxidic/hydroxidic Zr and/or Ti for a short process time window.
It is therefore preferred
if, in the conversion solution (III) of the second conversion stage in method
step iii), the proportion of
free fluoride is less than 3.00 mmol/kg, preferably less than 2.50 mmol/kg,
particularly preferably less
than 2.00 mmol/kg, but preferably at least 0.1 mmol/kg, more preferably at
least 0.2 mmol/kg, to
support the increase in the coating on Zr and/or Ti. Suitable sources of free
fluoride in the second
conversion stage in method step i) of the method according to the invention
are identical to those
which are mentioned in connection with the first conversion stage.
Corrosion protection and paint adhesion, which are not sufficiently achieved
until the second
conversion stage, can be optimized by the amount of copper ions contained in
the conversion
solution (III). It is found that in the conversion solution (III) of the
second conversion stage in method
step iii), preferably more than 40 pmol/kg, particularly preferably more than
50 pmol/kg, should be
contained. However, for reasons of process economy and for avoiding massive
cementation of
metallic copper, in particular when components are additionally pretreated
with surfaces of zinc, it is
preferred if no more than 500 pmol/kg, particularly preferably no more than
300 pmol/kg, and very
particularly preferably no more than 200 pmol/kg of copper ions dissolved in
water are contained in
the conversion solution (II). Suitable sources of copper ions dissolved in
water are water-soluble
salts, such as copper nitrate (Cu(NO3)2), copper sulfate (CuSO4) and copper
acetate
(Cu(CH3C00)2).
Method execution and substrates:
With regard to the execution of the method according to the invention, it has
been found that a
transfer of the components from a "wet-in-wet" stage both into the rinsing
stage and into the second
conversion stage is advantageous, firstly for the removal of soluble residues
from the first conversion
layer and, finally, for the passivating deposition of the oxidic/hydroxidic
compounds of the elements
Zr and/or Ti and the cementation of copper. According to the invention, for
reasons of process
economy, a method is also preferred in which no drying step takes place
between method steps (i)
and (iii).
The anti-corrosion pre-treatment of the method according to the invention
relates to a method
execution for providing an amorphous conversion coating based on
oxidic/hydroxidic compounds of
the elements Zr and/or Ti, which provides an excellent paint adhesion primer
for subsequently
applied paint systems. Accordingly, it is preferred according to the invention
if, after the method step
(iii) with an intermediate rinsing step, but preferably without an
intermediate drying step, a coating of
the components is carried out using a paint system, preferably an
electrodeposition coating,
particularly preferably a cathodic electrodeposition coating.
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In this context, a rinsing step is used exclusively for the complete or
partial removal of soluble
residues, particles and active components that are carried over by adhering to
the component from
the previous wet-chemical method step (iii), from the component to be painted,
without metal-
element-based or semi-metal-element-based active components, which are already
consumed
merely by bringing the metal surfaces of the component into contact with the
rinsing liquid, being
contained in the rinsing liquid itself. Thus, the rinsing liquid can simply be
municipal water or
deionized water, or, if necessary, a rinsing liquid that contains surface-
active compounds to improve
the wettability with the rinsing liquid, which are preferably nonionic
surfactants that, in the case of a
subsequent electrodeposition coating to improve coverage, are in turn selected
in particular from
alkoxylated alkyl alcohols and/or alkoxylated fatty amines, which are
ethoxylated and/or
propoxylated, wherein the number of alkylene oxide units is preferably in
total no more than 20, more
preferably no more than 16, but more preferably at least 4, particularly
preferably at least 8, wherein
the alkyl group preferably comprises at least 10 carbon atoms, more preferably
at least 12 carbon
atoms, wherein an HLD value is realized in the range of 12 to 16, which is
calculated as follows:
HLB = 20-(1-MI/M)
where MI: molar mass of the lipophilic group of the non-ionic
surfactant
M: molar mass of the non-ionic surfactant.
A drying step in this context is a drying of the components caused by
controllable technical
precautions, for example by supplying heat or by means of directed air supply.
The contacting of the aqueous solutions (1)-(111) in method steps (i)-(iii)
with the components or
surfaces of steel and/or iron is not selective for the success of the method
according to the invention,
so that conventional methods, such as dipping, spraying and splashing, are
preferred. The same
applies with respect to the duration of the contacting in the respective
treatment stages, which in
each case is preferably in the range of 10-300 seconds, the temperature of the
conversion solutions
(1)-(11) during the contacting preferably being in the range of 10-60 C,
particularly preferably in the
range of 25-55 C, very particularly preferably in the range of 30-50 C.
With respect to the components, it is found that the method according to the
invention is well suited
for the anti-corrosion pre-treatment in series of materials composed of
different metallic materials,
the components of the series preferably also having surfaces of zinc and/or
aluminum in addition to
the surfaces of steel and/or iron. In addition to steel and iron, suitable
metallic materials whose
surfaces can be subjected to corrosion protection in the method according to
the invention are zinc,
electrolytic (ZE), hot-dip galvanized (Z) and alloy-galvanized (ZA), (ZF) and
(ZM), and aluminum-
coated (AZ), (AS) strip steel, as well as the light metals aluminum and
magnesium and their alloys.
Date Recue/Date Received 2023-12-21
CA 03225205 2023-12-21
Examples:
The advantages of a method sequence according to the invention are illustrated
below on the basis
of the anti-corrosion pre-treatment and cathodic electrodeposition coating of
individual sheets of steel
(CRS).
I. Alkaline degreasing for 90 seconds at 55 C by spray application
with a composition (pH
10.5) consisting of the following process chemicals from Henkel AG & KGaA:
- 20 g/L Bonderite C-AK 2011
- 1 g/L Bonderite C-AD 1270
II. Alkaline purification for 120 seconds at 55 C by dip application
with a composition (pH
11.0) consisting of the following process chemicals from Henkel AG & KGaA:
- 20 g/L Bonderite C-AK 2011
- 1 g/L Bonderite C-AD 1270
III. Rinsing with deionized water (lc < 1pScm-1) by dip application
IV. First conversion stage for 120 seconds at 35 C by dip application with
a composition (pH
4.0) consisting of the following process chemicals from Henkel AG & KGaA:
Variant (A) with 6 g/L of Bonderite M-NT 1800 gives:
- 30 mg/kg of Zr
- 4 mg/kg of copper
- 34 mg/kg of free fluoride
Variant (B) with 16.6 g/L of Bonderite M-AD 110, 15 g/L Bonderite M-NT 12001
MU
gives:
- 150 mg/kg of Zr
- 4 mg/kg of copper
- 33 mg/kg of free fluoride
V. Rinsing with deionized water (lc < 1 pScm-1) by dip application
VI. Second conversion stage for 30 seconds at 35 C by dip application with
a nitric acid
composition (pH 4.0) consisting of the following process chemicals from Henkel
AG & KGaA:
Variant (A) with 6 g/L of Bonderite M-NT 1800 gives:
- 30 mg/kg of Zr
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Date Recue/Date Received 2023-12-21
CA 03225205 2023-12-21
- 4 mg/kg of copper
- 27 mg/kg of free fluoride
Variant (B) with 30.0 g/L of Bonderite@ M-NT 1800 gives:
- 150 mg/kg of Zr
- 4 mg/kg of copper
- 29 mg/kg of free fluoride
Variant (C) with 2.5 g/L of Bonderite@ M-PT 54 NC gives:
- 150 mg/kg of Zr
- 17 mg/kg of free fluoride
VII. Rinsing with deionized water (lc < 1 pScm-1) in dip application
VIII. Drying with compressed air
IX. Cathodic dip coating with CathoGuard@ 800 (BASF Coatings AG) in a dry
film thickness
of?? g/m2
The proportion of free fluoride was adjusted by means of an aqueous solution
of ammonium bifluoride
and the adjustment of the pH with ammonium bicarbonate.
The pre-treated and electro-dip coated sheets were then aged for 6 weeks over
30 cycles according
to the VW PV 1210 alternating climate test and the scribe delamination after
aging was determined.
As a result, it is evident that the method according to the invention leads to
a significant improvement
in corrosion protection compared to a two-stage conversion treatment in which
no intermediate
rinsing step is carried out (Table 1: V3 vs. El). The presence of copper ions
in the second conversion
stage is also crucial for sufficient corrosion protection (Table 1: V4 vs.
E2). In addition, an increase
in layer weight of less than 10 mg/m2 of Zr in the second conversion stage or
a content of compounds
of the elements Zr in the second conversion stage dissolved in water proves
advantageous in
preventing corrosive delamination after electrodeposition (Table 1: E3 vs. E4
and El vs. E2).
Tab. 1
Layer weight* (mg/m2) after step...
Process sequence Alternating climate test
Ex. (IV) (VI)
(I-II-III-.. .-VII-VIII-IX)
U/21 (mm) Stone impact 2 (K) Zr Cu Zr Cu
V1 IV(A) 1.20 3 28 8
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Date Recue/Date Received 2023-12-21
CA 03225205 2023-12-21
V2 IV(B) 1.25 3 35 30 - -
V3 IV(A)-VI(A) 1.25 3 28 8 2 1
V4 IV(A)-V-VI(C) 140 3.5 28 8 16 -
V5 IV(B)-V-VI(C) 1A5 3.5 35 30 18 -
El IV(A)-V-VI(A) 0.80 2.5-3 28 8 4 1
E2 IV(A)-V-VI(B) 1.10 3 28 8 10 4
E3 IV(B)-V-VI(A) 0.90 2.5 35 30 2 0
E4 IV(B)-V-VI(B) 1.20 3 35 30 11 5
1 Corrosion and delamination
according to DIN EN ISO 4628-8
2 Stone impact test according to DIN EN ISO 20567-1
* Measured by means of X-ray fluorescence analyzer (Thermo Fisher
Scientific, NitonO XL3t
900) after compressed air drying of the sheet metal sections immediately after
the rinsing following
the conversion stage
13
Date Recue/Date Received 2023-12-21
