Note: Descriptions are shown in the official language in which they were submitted.
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Method for Coating Metallic Surfaces,
Substrates Coated with Same and Use of Same
The invention relates to a method for coating metallic surfaces with a
conversion layer,
optionally colored, in particular for replacing an alkaline phosphating
treatment, such as,
for example, iron phosphating, substrates with metallic surfaces coated
accordingly, as
well as the use of these coated substrates.
Methods for producing alkali phosphate coatings, in particular as pretreatment
layers
before painting, have been described in isolated cases. Fresh, unused alkali
phosphate
solutions usually have little or no aluminum, iron and zinc content. In
addition to ions of
at least one alkali metal and/or ammonium, the aqueous acidic alkali phosphate
solutions also contain phosphate ions and, because of the pickling effect of
these
solutions on the metallic surfaces, they also have ion contents from the
metals
dissolved out of the metallic surfaces such as aluminum, iron and/or zinc as
well as
traces of alloy constituents of the partially pickled metallic materials. The
main phases
formed in the alkali phosphate layer during alkali phosphating are the
corresponding
phosphates, oxides and/or hydroxides of the metals from the surfaces of the
basic
substrates to be treated.
Alkali phosphate solutions and/or coatings are also referred to as iron
phosphate
solutions and/or coatings in use on iron and steel materials. Alkali phosphate
coatings
are also referred to in general as layers of the so-called "non-layer-forming
type of
phosphating" according to Werner Rausch: Die Phosphatierung von Metal/en [The
Phosphating of Metals], Saulgau 1988 (see pages 109-118 in particular). This
terminology is misleading because layers are also formed here, but they are
much
thinner than the other phosphate layers, such as the various types of zinc
phosphating,
for example. The alkali phosphate solution always contains an elevated amount
of at
least one alkali metal, for example, sodium and/or ammonium.
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Alkali phosphating can usually be performed in a simple and economical manner,
but
high quality alkali phosphate coatings provide only limited corrosion
protection, even
after the second subsequent corrosion treatment, usually a) the corrosion
protection is
no better than, i.e., no less than 3 mm below-surface corrosion, tested in the
salt spray
test according to DIN 50021 NSS for 500 hours on a powder enamel coating,
based on
epoxy-polyester powder coating with a thickness of 60 to 80 pm on cold rolled
steel
plate and/or usually b) the corrosion protection is no better than, i.e., no
less than, 4 mm
below-surface corrosion in the salt spray test according to DIN 50021 NSS for
500
hours with a wet enamel coating, based on a polyurethane-isocyanate enamel of
60 to
80 pm thickness on a cold rolled steel plate and usually c) paint adhesion of
better than,
i.e., no less than CT 3 on a cross-cut test after 240 hours of testing in the
condensate
climate test according to DIN EN ISO 2409 with a powder enamel coating, based
on
epoxy-polyester powder enamel 60 to 80 pm thick on a cold rolled steel plate.
Therefore, in alkali phosphating, it is usually necessary to apply an
additional second
conversion layer and in most cases even at least one more subsequently applied
enamel layer. Such multistep methods are not only particularly complex but
also require
additional baths and/or treatment zones as well as optionally also additional
rinse steps
and/or drying steps, in addition to being cost-intensive and time-consuming.
The paint
adhesion with the alkali phosphate coating is frequently also inadequate, so
that then
there must be an additional conversion coating, for example, based on
zirconium
hexafluoride and/or silane before applying the enamel. The coating process
becomes
especially complex and expensive in this way. The high phosphate content in
alkali
phosphating is also a disadvantage because phosphate in wastewater must be
disposed of in a complex process.
Alkali phosphating is frequently applied in multiple steps, so that primarily
only a
cleaning is performed in the first step, and the layer is performed in the
second step.
Next the layer is rinsed and/or rerinsed.
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The object of the invention was to discover aqueous compositions that could be
applied
easily and would have the most environmentally friendly composition possible
and
would also yield greater corrosion protection than high quality alkali
phosphate coatings.
This object is achieved with a method for coating metallic surfaces with an
aqueous
acidic conversion composition, which is a solution or dispersion that is
characterized in
that it contains:
a total of 0.01 to 1 g/L of TiF62+, ZrF62+ and/or HfF62+ in the form of ions,
calculated as ZrF62+,
0 or 0.01 to 1 g/L of Fe2+, Mn and/or Zn ions, at least one type of which may
be
present in the concentration range of 0.01 to 1 g/L,
wherein preferably Mn and/or Zn ions are present,
0 or 0.01 to 2 g/L of an organic polymer and/or an organic copolymer, which is
stable at a pH <6.5, based on the solids content,
0 or 0.01 to 2 g/L of particulate Si02 with an average particle diameter <0.3
pm,
measured on a scanning electron microscope and based on the solids content,
approx. 0 or 0.01 to 10 g/L of at least one surfactant,
approx. 0 or 0.05 to 10 g/L of ions selected from the group consisting of
carbonate, nitrate and sulfate, converted to NO3, even if C032+ or S042+ is
present and
0 or 0.001 to 2 g/L of carboxylate and/or sulfonate anions which cause little
or no
impairment of the layer formation, calculated as the corresponding anions,
wherein the molybdate content, calculated as Mo042+ and/or the P-containing
oxyanion content calculated as P043+ is <0.1 g/L or approx. 0 g/L each and
wherein the aqueous acidic composition has a pH in the range of 2.5 to 6.5 and
preferably in the range of 3.0 to 5.5.
The ions of TiF62+, ZrF62+ and/or HfF62+ are largely equivalent and
interchangeable in
the aqueous acidic conversion composition but the ions of ZrF62+ often yield
the best
properties of the conversion coating produced with them. It is preferable here
that in the
case of a cation content of the aqueous conversion composition of only Fe2+
ions,
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based on the total Fe2+, Mn and Zn ion content, that this content originates
at least in
part from an intentional additive.
The ions of manganese and zinc as well as, to a limited extent, also those of
Fe2+ are
largely equivalent and interchangeable in the aqueous acidic conversion
composition,
but in many cases the ions of manganese and/or zinc yield the best properties
of the
conversion coating produced with them. They preferably contain 0 or 0.01 to
0.3 g/L or
0.02 to 0.15 g/L of Fe2+ ions as well as 0.01 to 1 g/L of Mn ions and/or 0.01
to 1 g/L or
0.1 to 0.6 g/L of Zn ions. It especially preferably contains 0.1 to 0.6 g/L or
0.2 to 0.4 g/L
of Mn ions and/or 0.1 to 0.6 g/L or 0.2 to 0.4 g/L of Zn ions.
Adding an organic polymer and/or an organic copolymer may contribute toward a
further
improvement in the properties of the conversion coating produced therewith and
then it
may optionally be possible to omit a subsequent enamel coating. If the enamel
coating
is omitted, then we speak of blank corrosion protection.
Addition of extremely fine particulate Si02 may have a positive effect similar
to that of
adding an organic polymer and/or an organic copolymer but often with the
difference
that the layer formation and thus the coating are even more uniform.
Fundamentally at least one nonionic, anionic, cationic and/or zwitterionic
surfactant may
be added. Addition of at least one nonionic surfactant is especially preferred
here.
The ions of manganese and zinc as well as to a limited extent also those of
Fe2+ are
largely equivalent and interchangeable in the aqueous acidic conversion
composition
but the ions of manganese and/or zinc often yield the best properties of the
corrosion
coating produced with them. The coating preferably contains 0 or 0.01 to 0.3
g/L or 0.02
to 0.15 g/L of Fe2+ ions and 0.01 to 1 g/L of Mn ions and/or 0.01 to 1 g/L or
0.1 to
0.6 g/L of Zn ions. It especially preferably contains 0.1 to 0.6 g/L or 0.2 to
0.4 g/L of Mn
ions and/or 0.1 to 0.6 g/L or 0.2 to 0.4 g/L of Zn ions.
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Addition of an organic polymer and/or an organic copolymer may contribute
toward an
even further improvement in the properties of the conversion coating produced
therewith and it may optionally allow the omission of a subsequent enamel
coating. If an
enamel coating is omitted, this is known as bare metal corrosion protection.
Addition of extremely fine particulate Si02 may have an effect similar to that
of adding
an organic polymer and/or an organic copolymer but often with the difference
that layer
formation and thus coating are even more uniform.
Fundamentally at least one nonionic, anionic, cationic and/or zwitterionic
surfactant may
be added. Addition of at least one nonionic surfactant is especially preferred
here.
Anions selected from the group consisting of carbonate, nitrate and sulfate
are often
added by addition of cations in the form of water-soluble salts. Nitrates are
especially
preferred here.
Addition of carboxylate anions, for example, in the form of acetic acid and/or
a
manganese carboxylate is fundamentally possible as an alternative or as an
addition to
these ions and is often suitable for preventing or reducing the amount of the
anions of
mineral acids. It is fundamentally possible to use all types of carboxylic
acids and their
derivatives, such as the salts and esters, which are water soluble are and are
stable in
the pH value range, which do not have any complex substance composition, which
form
anions in water, which do not interfere the formation of a layer, depending on
the type
and quantity of anions, and which optionally form complexes with alkali and/or
alkaline
earth metal ions, which are not involved in the formation of the layer.
These include in particular aliphatic carboxylic acids and mono-, di- and/or
polycarboxylic acids such as hydroxycarboxylic acids, for example. When adding
carboxylate anions, care should be taken to ensure that they do not interfere
with the
formation of the layer because citrate, for example, and certain other
individual
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complexing agents may interfere with the formation of a layer, depending on
the type
and quantity of anions.
Addition of at least one sulfonic acid such as methane sulfonic acid,
amidosulfonic acid
and/or one of their derivatives, for example, may be favorable here in order
to act as an
accelerator and/or as an additional counterion.
Addition of molybdate has proven successful only when very small amounts are
added.
Addition of oxyanions that contain phosphorus, for example, orthophosphate,
condensed phosphates and phosphonates, is to be avoided in particular because
of the
possible burden on wastewater and possibly also because of a greater
production of
sludge, which can result in complicated disposal of the wastewater and/or
sludge. In
particular in the case of P-containing oxyanions, it is preferable not to add
any P-
containing oxyanions because of reasons involving environmental safety and the
need
to avoid the expensive disposal associated with phosphorus, and it is
preferably
necessary to be sure that no P-containing oxyanions are entrained into the
process.
In the case of the method according to the invention, it is preferable for the
aqueous
acidic composition to additionally contain:
0.03 to 5 g/L of the sum of ions of lithium, sodium and/or potassium,
0 or 0.05 to 5 g/L of ammonium ions,
approx. 0 or 0.05 to 0.3 g/L of the sum of Co and/or Ni ions,
0 or 0.01 to 0.8 g/L of chlorate calculated as CI03-, nitrite, calculated as
NO2
and/or peroxide, calculated as H202,
0 or 0.01 to 0.5 g/L of free fluoride, calculated as F and
0 or 0.01 to 0.2 g/L of vanadate ions, calculated as V043-.
In most cases, it is fundamentally impossible to entirely avoid the presence
of some
lithium, sodium, potassium and/or ammonium content to achieve charge
equalization
and to avoid adding only polyvalent cations, such as heavy metal ions. Of the
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monovalent cations, sodium ions in particular are especially preferred. They
are largely
equivalent in the aqueous acidic conversion composition and can be used
interchangeably and are often necessary for regulating the pH.
As in many coating processes, here again, the addition of cobalt and/or nickel
is
advantageous to achieve better corrosion protection, although these elements
are
problematical with respect to environmental safety and occupational hygiene.
It is sometimes necessary to add at least one accelerator, in particular to
add a chlorate,
nitrite and/or peroxide. However, it is important to add a suitable amount,
for example,
an NO2 content of much less than 1 g/L. When adding at least one accelerator,
the
formation of a layer may be accelerated and the properties of the coating
produced in
this way can be improved. Overdosing of accelerator should be avoided so as
not to
interfere with the formation of a layer, as in the case of Example B40.
Addition of
nitroguanidine has not proven to be advantageous.
The complex fluoride content alone often leads to a lower free fluoride
content. Addition
of at least one fluoride may lead to a slightly higher free fluoride content.
The free
fluoride content, which is favorable for substrate surfaces that contain
aluminum in
particular, is often in the range of 0.01 to 0.5 g/L, calculated as F.
Addition of at least one vanadium compound can significantly increase the
corrosion
protection.
The possibility cannot be ruled out that additional element concentrations of
the metallic
surfaces of the substrates and of the installation may enter the bath due to
the pickling
effect of the aqueous acidic conversion composition and may optionally even
accumulate in the bath composition, in particular Fe2+ ions and alloying
elements and
their ions.
On the other hand, the possibility is usually also not ruled out in the case
of today's
coating methods and installations that amounts of ions and substances from
other areas
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of the installation such as a cleaning step used in the past, for example, may
perhaps
be entrained in small amounts, even despite the use of a water rinse. Amounts
of alkali
metals, ammonium, complexing agents, surfactants, anionic contaminants of the
cleaning bath and/or additional impurities and/or ions in particular may be
entrained into
the bath composition according to the invention in this way. However, it is
not absolutely
necessary to provide a separate previous cleaning step so that the input of
foreign ions
can be mostly ruled out by means of a chemical treatment solution. In the best
case, a
cleaning step may be performed with water containing a surfactant but without
any
builder content.
On the one hand, the cleaning may be performed before the corrosion coating
step, so
that the cleaning is performed prior to contacting the substrate with the
aqueous
composition. On the other hand, the aqueous composition may also contain at
least one
surfactant in addition to or instead of this cleaning step, so that the
cleaning and
conversion coating are (also) performed in the same process step.
Preferably little or none of the following are intentionally added to the
aqueous
conversion composition: 0.1 g/L carboxylic acids, phosphates, phosphonates
and/or
compounds and/or ions of calcium, chromium, chromate, cobalt, copper,
magnesium,
molybdenum, nickel, vanadium and/or tin and/or silane, silanol, siloxane,
polysiloxane.
Silane, silanol, siloxane and polysiloxane refer to silane, silanol, siloxane
and/or
polysiloxane because in water and in coating starting with a silane, for
example, it can
very rapidly yield silanols and/or siloxanes, which can sometimes also yield
polysiloxanes, depending on the chemical definition of each.
The aqueous acidic conversion composition of alkaline earth metals such as
calcium
and/or magnesium is preferably a total of no more than 0.2 g/L to prevent
precipitation
in the presence of fluorides if possible.
The following variants are especially preferred:
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The acidic aqueous conversion composition has a pH in the range of 2.5 to 6.5
and
contains consists of or essentially of a total of:
Variant A:
0.01 to 1 g/L of TiF62+, ZrF62+ and/or HfF62+ in the form of ions, calculated
as ZrF62+ and
0 or 0.01 to 1 g/L of Fe2+, Mn and/or Zn ions, such that at least one species
of these
ions is present in the content range from 0.01 to 1 g/L, as well as optionally
0.01 to 2 g/L
of particulate Si02 with an average particle diameter <0.3 pm, based on the
solids
content, and/or optionally 0.01 to 10 g/L of at least one surfactant and with
a phosphate
content <0.1 g/L PO4.
Variant B:
0.01 to 1 g/L of TiF62+, ZrF62+ and/or HfF62+ in the form of ions, calculated
as ZrF62+,
0 or 0.01 to 1 g/L of Fe2+, Mn and/or Zn ions, of which at least one species
of these ions
is present in the content range of 0.01 to 1 g/L, and 0.01 to 2 g/L of organic
polymer
and/or copolymer which is stable at a pH <6.5, based on the solids content,
and optionally 0.01 to 2 g/L of particulate Si02 with an average particle
diameter <0.3
pm, based on the solids content,
and optionally 0.01 to 10 g/L of at least one surfactant,
and optionally 0.05 to 10 g/L of anions, selected from the group consisting of
carbonate,
nitrate and sulfate, converted to NO3, even if C032+ or S042+ is present and
optionally 0.001 to 2 g/L of carboxylate and/or sulfonate anions, which cause
little or no
impairment of the layer-forming process, calculated as the corresponding
anions,
wherein the molybdate content, calculated as Mn042+ and/or the P-containing
oxyanion
content, calculated as P043+ is <0.1 g/L or approx. 0 g/L.
Variant C:
0.01 to 1 g/L of TiF62+, ZrF62+ and/or HfF62+ in the form of ions, calculated
as ZrF62+,
0 or 0.01 to 1 g/L of Fe2+, Mn and/or Zn ions, of which at least one species
of these ions
is present in the content range from 0.01 to 1 g/L, and a molybdate content,
calculated
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as Mo042+ in the range of 0.01 to <0.5 g/L plus optionally 0.01 to 2 g/L of
organic
polymer and/or copolymer which is stable at a pH <6.5, based on the solids
content,
and optionally 0.01 to 2 g/L of particulate Si02 with an average particle
diameter <0.3
pm, based on the solids content,
and optionally 0.01 to 10 g/L of at least one surfactant,
and optionally 0.05 to 10 g/L of anions, selected from the group consisting of
carbonate,
nitrate and sulfate, converted to NO3, even if C032+ or S042+ is present and
optionally 0.001 to 2 g/L of carboxylate and/or sulfonate anions which cause
little or no
impairment of the layer-forming process, calculated as the corresponding
anions,
wherein a molybdate content, calculated as Mn042+ is in the range of 0.01 to
<0.5 g/L
and the P-containing oxyanion content, calculated as P043+ is <0.1 g/L or
approx. 0 g/L.
With all three variants, it is preferable for M and/or Zn ions to be added,
while the Fe2+
ion content is pickled out of the iron-rich metallic substrate preferably by a
pickling effect
of the acidic conversion composition. The coating is optionally then enameled
at least
once.
An aqueous acidic conversion composition which is a solution or dispersion
containing
the following is especially preferred:
a total of 0.01 to 1 g/L of TiF62+, ZrF62+ and/or HfF62+ in the form of ions,
calculated as ZrF62+,
0 or 0.01 to 1 g/L of Mn and/or Zn ions, at least one type of these ions being
present in the concentration range of 0.01 to 1 g/L,
0 or 0.01 to 0.3 g/L of Fe2+ ions,
wherein preferably Mn and/or Zn ions are present,
0 or 0.01 to 1 g/L of an organic polymer and/or an organic copolymer which is
stable at a pH of <6.5, based on the solids content,
0 or 0.01 to 1 g/L of particulate Si02 with an average particle diameter of
<0.3 pm, measured with a scanning electron microscope and based on the solids
content,
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approx. 0 or 0.01 to 6 g/L of at least one surfactant,
approx. 0 or 0.05 to 6 g/L of anions selected from the group consisting of
carbonate, nitrate and sulfate, converted to NO3, even if C032+ or S042+ is
present and
0 or 0.001 to 1 g/L of carboxylate and/or sulfonate anions, which have little
or no
negative effect on the formation of a layer, calculated as the corresponding
anions,
wherein the molybdate content, calculated as Mo042+ and/or the P-containing
oxyanion content, calculated as P043+ each amounts to <0.1 g/L or approx. 0
g/L, and
wherein the aqueous composition has a pH in the range of 2.5 to 6.5 and
preferably in the range of 3.0 to 5.5.
The aqueous acidic composition especially preferably contains, consists of or
essentially comprises:
0.01 to 5 g/L of the total of ions of lithium, sodium and/or potassium,
0 or 0.05 to 5 g/L of ammonium ions,
approx. 0 or 0.05 to 0.2 g/L of the total of Co and/or Ni ions,
0 or 0.01 to 0.4 g/L of chlorate, calculated as CI03-, nitrite, calculated as
NO2
and/or peroxide, calculated as H202,
0 or 0.01 to 0.5 g/L of free fluoride, calculated as F and
0 or 0.01 to 0.1 g/L of vanadate ions, calculated as V043-.
The bath composition according to the invention may preferably also be
prepared by
diluting one or two concentrates with water by a dilution factor in the range
of 5:1 to
40:1. The second concentrate may contain a surfactant, for example, and may
also be
aqueous. Fluoride may also be added as a monofluoride, a bifluoride and/or in
the form
of the corresponding acids. The free fluoride content is often in the range of
0.01 to
0.2 g/L.
For the aqueous acidic conversion composition, it is preferably possible to
work with
municipal water having a conductance of approx. 200 to 600 pS/cm, for example,
or
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with deionized water for the batch as well as for supplementing the liquid
level in the
bath as well as for the first rinse after the conversion coating.
After this first rinse step, a deionized rinse using deionized water is
necessary as a
standard only as a final rinse to prevent drying of the salt load, which can
result in
inferior corrosion protection.
The paint adhesion and anticorrosion effect on hot-dip galvanized (HDG) steel
plate
tend to be somewhat inferior to that on cold rolled steel (CRS) plate. If the
zinc content
in the aqueous acidic conversion composition is decreased or even omitted
entirely,
then the properties of the coating on hot-dip galvanized steel plate are often
improved.
An Fe2+ ion content often has no negative effect on the properties of the
coating, but it
has been found that Fe2+ ions are gradually oxidized to Fe3+ and form a sludge
sediment in the bath. It is therefore preferable for the aqueous acidic
conversion
composition to have a manganese and/or zinc ion content.
A surfactant-containing aqueous composition can help to either further improve
the
cleaning effect after degreasing and/or pickling or to at least omit the
degreasing step
before conversion coating, so that it is possible to perform the cleaning in a
one-pot
process.
With the method according to the invention, it is preferable for at least one
substrate
having metallic surfaces to be brought in contact with the aqueous composition
for a
period of time in the range of 1 second to 10 minutes, in particular 0.5 to 10
minutes in
treatment of parts. A period of time in the range of 1 to 10 minutes is
especially
preferred, in particular in dipping, or preferably 0.5 to 6 minutes, in
particular in
spraying. Thus even with these compositions the same treatment times may be
used as
in alkali phosphating, which facilitates switching from alkali phosphating
installations to
the conversion coating according to the invention, because in alkali
phosphating, 3 to 5
minutes are frequently also used. Alternatively, the composition according to
the
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invention may also be applied to strip steel metal if it is still rinsed with
water after the
strip coating (rinse process). In strip coating, the metal strip is preferably
brought in
contact with the aqueous composition over a period of time in the range of 1
second to
2 minutes.
With the method according to the invention, it is preferable for the substrate
having
metallic surfaces to be a temperature in the range of 5 to 90 C, preferably in
the range
of 15 to 70 C or 30 to 60 C when brought in contact with the aqueous
composition. On
the other hand, it is also preferable for the aqueous composition to have a
temperature
in the range of 35 to 70 C or 45 to 60 C when brought in contact with the
substrate
having metallic surfaces. Then the temperatures used with these compositions
may be
the same as those as in alkali phosphating, where temperatures of 50 to 55 C
are often
used.
This object is also achieved with a coated substrate having metallic surfaces
that have
been coated according to the invention.
It is preferable here for the coating thereby produced to have a layer
thickness of 0.3 to
3 pm and/or for the total of the application of zirconium, measured as an
element and/or
titanium in the conversion coating, to be in the range of 1 to 300 mg/m2 or
preferably in
the range of 15 to 150 mg/m2, measured by X-ray fluorescence analysis (RFA).
It is also preferable for the coating produced in this way to be colored,
iridescent or
gray. Interference colors of the first order or of a higher order or colors in
which the
interference color has superimposed on it the color of ions preferably occur
with the
coating produced in this way. These colors are similar to those which are
obtained in
alkali phosphate coating. The colors often help to approximately estimate the
thickness
and to some extent even the uniformity and/or quality of a coating. If this is
even
possible at a greater distance of viewing, then it is especially advantageous
with a
coating process.
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For particularly high quality application purposes in particular, it is
preferable for the
conversion coating thereby produced according to the invention to next be
rinsed with
water or with an aqueous after-rinse solution, in particular one containing
silane, an
organic polymer and/or an organic copolymer and optionally also to be
enameled. The
after-rinse may be performed using aqueous after-rinse solutions, for example,
Gardolene D95, which contains a phenolic resin or Gardolene D6890, based on
silane.
The aqueous after-rinse solution especially preferably contains at least one
a) cation
selected from alkaline earth metal cations, aluminum cations, titanium
cations, yttrium
cations and heavy metal cations, b) an organic polymer and/or an organic
copolymer, c)
silane, silanol, siloxane and/or polysiloxane and/or d) a complex fluoride,
where
"complex fluoride" also stands for the corresponding fluorine-containing acid.
In
particular aminosilanes with one, two or even more amino groups and/or bis-
silyl silanes
are the preferred silanes here.
In a particularly preferred process according to the invention, a coating is
applied with
an aqueous acidic composition according to the invention, then optionally
rinsed with
water thereafter and/or optionally rerinsed thereafter with an aqueous
composition, and
the at least one coating prepared in this way is then enameled at least once.
In a particularly preferred process according to the invention, a coating is
applied using
an aqueous acidic composition according to the invention, based on 0.01 to 1
g/L of
TiF62+, ZrF62+ and/or HfF62+ or only ZrF52+ in the form of ions, calculated as
ZrF62+ and 0
or 0.01 to 1 g/L of Fe2+, Mn and/or Zn ions, of which at least one species of
these ions is
present in the content range from 0.01 to 1 g/L, as well as optionally 0.01 to
2 g/L of
particulate Si02 with an average particle diameter <0.3 pm, based on the
solids content
and/or optionally 0.01 to 10 g/L of at least one surfactant, which is
essentially
phosphate-free and essentially phosphonate-free, then the coating is
optionally rinsed
with water and/or optionally thereafter rerinsed with an aqueous composition,
based on
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zirconium complex fluoride, silane and/or organic polymer copolymer, which is
stable at
a pH of <6.5, and the at least one coating produced in this way can next be
enameled at
least once. Because of the surfactant content in the aqueous acidic
composition
according to the invention, it may optionally be possible to omit a previous
cleaning
step.
The conversion coating thereby produced according to the invention may contain
no
organic polymer and no organic copolymer, preferably without subsequent
rinsing with
water or preferably with an aqueous after-rinse solution, in particular one
that contains
silane, an organic polymer and/or an organic copolymer, then dried and
optionally also
enameled.
Alternatively, if the conversion coating produced in this way according to the
invention
contains an organic polymer and/or an organic copolymer, preferably be used
without
coating it with a primer, enamel or adhesive.
The conversion coating produced in this way according to the invention may
optionally
also be coated preferably at least once with a primer, enamel or adhesive,
optionally
after at least one rinsing with water and/or with an aqueous after-rinse
solution. Thus,
the same treatment steps, sequences and methods as in alkali phosphating may
be
successfully used, as needed, even with these compositions.
The coating produced in this way may in an excellent manner represent a
substitute for
an alkali phosphate coating such as an iron phosphate coating, for example.
The at least one substrate having metallic surfaces coated according to the
invention is
preferably used as an architecture element, as a container, as a construction
or
connecting element, as a profile element, as a heating body element, as a
molding body
with a complex shape and/or as a component in construction, energy technology,
automotive engineering, equipment design, household appliances or mechanical
engineering.
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It was surprising that excellent coatings, which have an excellent corrosion
resistance,
excellent paint adhesion and in most cases also a definite color are obtained
with the
aqueous conversion compositions according to the invention. The corrosion
resistance
on steel surfaces is almost as good as that of a high quality zinc phosphating
and is
thus definitely superior to the corrosion resistance of a high quality alkali
phosphating
treatment without having used an after-rinse solution subsequently to improve
the
properties of the coating. When using an additional after-rinse solution, the
corrosion
resistance of a high quality zinc phosphating can even be achieved.
It was also surprising that an excellent substitute for alkali phosphating can
be obtained
in a comparatively simple process, which is simple and environmentally
friendly and in
some cases even yields fully similar results.
The composition according to the invention and the process according to the
invention
are particularly advantageous in the chemical pretreatment of surfaces of
various steel
substrates, which are used in the metal-working industry, where it is possible
to perform
a cleaning in one step and at the same time to apply a conversion layer that
can be
enameled, which is why this three-step treatment process of cleaning with
conversion
coating, rinse with tap water and rinsing with deionized water is fully
sufficient. In
particular the bath analysis is very simple to handle because an accurate
determination
of anions and cations is rarely necessary since the pH and the conductivity
usually
provide sufficient information about the chemical condition of the bath.
The process according to the invention can be used to produce a colored,
iridescent,
gray or colorless (as in the case of B40) passivation layer (without
enameling) or a
colored, iridescent, gray or colorless (as in the case of B40) conversion
coating (with
enameling). A passivation layer per se is also a coating produced by
conversion.
Therefore, the term "conversion coating" in the sense of this patent
application also
includes the term "passivation layer," if or as long as no enamel layer has
been applied
even in the claims, for example.
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The process according to the invention may be used as a substitute for an
alkali
phosphating process or in isolated cases may even be used to replace a zinc
phosphating process. The products produced with the inventive process may be
used in
a variety of ways, in particular as architectural elements, as containers, as
construction
elements or connecting elements, as profile elements, as heating elements, as
molded
parts having a complex shape and/or as components in construction engineering,
energy technology, automotive engineering, equipment manufacture, household
appliance manufacture or mechanical engineering and, for example, as heating
elements, as frames, as sheets, as linings, as angles or as components in the
interior of
motor vehicles or aircraft.
Examples and comparative examples
The subject matter of the invention will now be explained in greater detail on
the basis
of exemplary embodiments. These examples were carried out using the
substrates,
process step, substances and mixtures discussed below.
The following standard sheet metal plates were used: Gardobond C of cold
rolled
steel, CRS, from St14 DC05, Gardobond HDG/5 from the corresponding hot-dip
galvanized steel or Gardobond F from AA 5005 from AlMg1 from Chemetall GmbH
for
coating. Unless otherwise indicated, standard Gardobond C plates were used.
Aqueous conversion compositions corresponding to those listed in Table 1 were
prepared using as the surfactant a nonionic surfactant of the Gardobond
additive
H7438 which ensured an additional cleaning of the metal surface. The alkaline
potassium hydroxide-stabilized Si02 dispersion Gardobond additive H7157 from
Chemetall GmbH had a solids content of 20% and an average particle size of 0.2
pm.
The polymer dispersion 1 AC 2773, based on acrylate from Alberdingk had a
solids
content of 53%. The copolymer dispersion 2 VA 294 VP containing acrylate from
Alberdingk had a solids content of 47%. The acrylate-containing copolymer
dispersion
3 AS 2084 VP from Alberdingk had a solids content of 53%. Copolymer, Si02
particles
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and/or surfactant were added separately to the previously prepared aqueous
conversion
composition toward the end of the mixing process. In individual experiments
ammonium
molybdate was added.
The plates were conversion coated at 55 C for 3 minutes with a cleaning
effect. Then
they were rinsed once with process water and then with deionized water before
drying
the coated plates at 120 C in a drying cabinet for at least 10 minutes. When
using a
different temperature, no definite difference in quality was observed.
Next, one and only one enamel layer was applied to the conversion coated
plates.
Either an epoxy-polyester powder coating of Interpon 700 from Akzo Nobel
Power
Coatings GmbH was applied in a layer thickness of 60 to 80 pm, or a wet
coating of
Alexit Monolayer, based on polyurethane and isocyanate from Mankiewicz, was
applied in a layer thickness of 60 to 80 pm or Cathoguard 350, a black
cathodic dip
coat from BASF, was applied in a layer thickness of 20 pm.
The enamel adhesion of the enameled samples was determined in the cross-cut
method according to DIN EN ISO 2409 before and after 240 hours of alternating
climate
test. The corrosion resistance of the enameled samples was determined in the
salt
spray test according to DIN 50021 over 500 hours in the neutral salt spray
test NSS in
which case a single enamel layer was applied ¨ unlike what is customary in the
Asian
and North American markets.
The layer weight was measured in mg/m2 using X-ray fluorescence analysis for
an
application of elemental zirconium. The element zirconium is often the
indicator element
for the quality of the coating, wherein different applications of metal to
zirconium were
deposited using the same aqueous composition but different metal substrates.
In the Comparative Examples VB1 and VB2, the examples according to the
invention
were compared with high quality alkali phosphating, which is widely used
internationally
on Gardobond C plates made of cold rolled steel: the typical procedure in
alkali
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phosphating, which is also known as iron phosphating, when used on iron and
steel
materials, was performed using Gardobond WH = Gardobond A 4976 on steel
surfaces at 55 C for 3 minutes, rinsing with deionized water and optionally
with a
subsequent after-rinse for 5 minutes with a Gardolene D 6800 after-rinse
based on
ZrF6 before drying for at least 10 minutes in a drying cabinet at 120 C.
Table 1. Overview of the compositions of the aqueous baths and the properties
of the
respective coated samples and the coatings
=
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Content in g/L VB1 VB2 VB3 VB4 VB5 VB6
B1 B2 B3 64
Iron phosphating GB A 4976 A 4976 - - -
- - - -
,
Zr as H2ZrF6- - 0.50 1.00 0.05 0.30
0.30 0.30 0.30 0.30
Mn _ _ -
0.15 0.15 0.15 0.15
Zn _ _ - - -
0.15 0.15 0.15 0.15
Surfactant: GBA H7438 4 4 3 3 3 3
3 3 3 3
pH 5.4 5.4 4.8 4.8 4.8 4.8
3.5 4.2 4.8 5.4
After-rinse with
Gardolene D6800/6 - yes - - - -
- - - - 1 P
Color of the layer lightly light
light "
blue blue
light blue
golden blue* golden
golden blue yellow F
blue
purple
purple purple
.
yellow yellow
yellow "
.
Layer weight of Zr
,
0 7 41 77 55 46
79 105 134 81 ,
mg/m2 2
,
Enamel adhesion in the cross-cut test after 240 hours of condensate climate
test according DIN EN ISO 2409:
In wet paint 60-80 pm GT 4 GT 1 GT 0 GT 0 GT 0-1 GT 0
GT 0 GT 0 GT 0 GT 0
In powder coating
GT 3 GT 2
GT 0
60-80 pm
Corrosion resistance in a salt spray test according to DIN 50021 500 h NSS in
mm:
In wet paint 60-80 pm 8.0 3.0 3.0-4.5 2.0-3.0 1.0-2.5 .
2.0 0.0-2.0 1.0 2.0-2.5 3.0
In powder coating
5.0 2.0
1.0-2.0
60-80 pm
In cathodic dip coating
1.0-2.0
* unevenly blue
'
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Content in g/L B9 B10 B11 B12 B13 B14
B15 VB16 B17 B18
Zr as H2ZrF6 0.30 0.30 0.30 0.30 0.30 0.30
0.30 - 0.30 0.30
Mn 0.05 0.15 0.50 -
0.025 0.15 0.50 0.15
Zn - 0.05 0.15 0.50
0.025 0.15 0.50 0.15
NH4 molybdate as Moat -
- - -
- 0.02
Surfactant: GBA H7438 , 3 3 3 3 3 3
3 3 3 3
pH 4.8 4.8 4.8 4.8 4.8 4.8
4.8 4.8 4.8 4.8
Color of the layer light light golden
light golden golden
golden golden yellow to golden golden
blue golden
golden
yellow to yellow to P
yellow yellow
purple yellow 0
yellow yellow blue
yellow blue blue "
l0
_______________________________________________________________________________
________________________________________ 00
Layer application Zr
.
,
44 59 96 55 60 112
46 63 88 112 '
mg/m2
"
c,
Enamel adhesion in the cross-cut test after 240 hours in the condensate
climate test according DIN EN ISO 2409:
,
IV
In wet paint 60-80 pm GT 0 GT 0 GT 0 GT 0 GT 0 GT 0
GT 0 GT 0 GT 0 GT 0 "
Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS
in mm:
In wet paint 60-80 pm 2.5 1.0-2.0 2.5 2.0 2.0-2.5 2.5-
3.0 2.0 0-3.0 4.0 0-2.5
'
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Content in g/L B19 B20 B21 B22 B23
B24 B25 B26 B27 B28
Zr as H2ZrP6 0.30 0.30 0.30 0.30 0.30
0.30 0.30 0.30 0.30 0.30
Ti as H2TiF6 - - 0.02 0.20 0.50 -
- - -
Mn 0.15 0.15 0.15 0.15 0.15
0.15 0.15 0.15 0.15 0.15
Zn 0.15 0.15 0.15 0.15 0.15
0.15 0.15 0.15 0.15 0.15
NH4 molybdate as Mo04 0.08 0.33 - - -
-
Polymer dispersion 1 - - - -
0.10 0.50 1.00 3.00
-
Copolymer dispersion 2 - - - - - -
- - 0.10
Surfactant: GBA H7438 3 3 3 3 3 3
3 3 3 3 P
pH 4.8 4.8 4.8 4.8 4.8
4.8 4.8 4.8 4.8 4.8
,
Color of the layer golden golden golden
golden golden golden
yellow to yellow to yellow to yellow yellow to
yellow to
yellow to
yellow to yellow to blue to
purple
blue
purple purple purple
purple purple purple purple
Layer application Zr
76 29 68Zr, 10Ti 1Zr, 18Ti
1Zr, 23T1 102 98 123 102 126
mg/m2
Enamel adhesion in the cross-cut test after 240 hours condensate climate test
according DIN EN ISO 2409:
In wet paint 60-80 pm GT 0 GT 0 GT 0 GT 4-5 GT 0
GT 0 GT 0 GT 0 GT 0 GT 0
Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS
in mm:
In wet paint 60-80 pm 2.5 >10 1.0-2.0 1.5 1.0 0.5-
1.5 0-0.5 1.5 0 0-1.5
'
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Content in g/L B29 B30 B31 B32 B33 B34
B35 B36 B37 B38
Zr as H2ZrF6 0.30 0.30 0.30 0.30 0.30 0.30
0.30 0.30 0.30 0.30
Mn 0.15 0.15 0.15 0.15 0.15 0.15
0.15 0.15 0.15 0.15
Zn 0.15 0.15 0.15 0.15 0.15 0.15
0.15 0.15 0.15 0.15
Si02 nanoparticles - - -
- 0.20 1.00 5.00
Copolymer dispersion 2 0.50 1.00 3.00- - -
- - - -
Copolymer dispersion 3 - - 0.10 0.50 1.00
3.00 - - -
Surfactant: GBA H7438 3 3 3 3 3 3
3 3 3 3
pH 4.8 4.8 4.8 4.8 4.8 4.8
4.8 4.8 4.8 4.8 P
Color of the layer blue to blue to yellow to yellow to
yellow to yellow to yellow to purple yellow to golden
purple purple purple purple purple
purple purple purple yellow .7.
Layer application Zr
,
'
115 126 99 116 98 104 81 126
102 71 0
mg/m2
,
,
rõ
rõ
Enamel adhesion in the cross-cut test after 240 hours condensate climate test
according DIN EN ISO 2409:
In wet paint 60-80 pm GT 0 GT 0 GT 0 GT 0 GT 0 GT 0
GT 0 GT 0 GT 0 GT 0
Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS
in mm:
In wet paint 60-80 pm 0-3.0 0-1.0 0-1.0 0-1.0 1.5 1.5
5.0 0-2.0 0-3.0 0-1.0
-
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Content in g/L B39 B40 B41 B42 B43 B44
B45 B46 B47 B48
Metallic substrate CRS CRS CRS CRS HDG/5 AA 5005
CRS CRS CRS CRS
In comparison with
- - - -
B3, VB2 B3 B3 B3
example
Zr as H2ZrF6 0.30 0.30 0.30 0.30 0.30 0.30
0.30 0.30 0.30 0.30
Mn 0.15 0.15 0 0 0.15 0.15
0.15 0.15 0.15 0.15
Zn 0.15 0.15 0 0 0.15 0.15
0.15 0.15 0.15 0.15
Fe2+ - 0.20 ** 0.80 ** - -
- -
NO2 as NaNO2 0.10 1.00 - - -
- - - - p
Surfactant: GBA H7438 3 3 3 3 3 3
- - - - N,
-
.3
pH 4.8 4.8 , 4.9 4.9 4.8 4.8
5.2 5.2 5.2 5.2 .7.
N,
After-rinse with
Gardolene Gardolene Polymer
0 Oxsilane dispersion
- - - - - -
9810/3 1:
06800/6
D6890 0.1 gIL
Color of the layerblue to blue to yellowish
blue golden golden golden golden
purple invisible
purple purple iridescent
iridescent yellow yellow yellow yellow
Layer application Zr
127 1 101 94 20 50 90 70 70
75
mg/m2
Enamel adhesion in the cross-cut test after 240 hours in the condensate
climate test according DIN EN ISO 2409, optionally after an after-rinse at:
Wet paint 60-80 pm GT 0 GT 3 GT 0 GT 0 GT 0-1 GT 0
- - - -
Powder coating 60-80 pm _ _ _ - GT 0-1 GT 0
- - - -
KTL + automotive
- - - - - -
GT 0-1 GT 0-1 GT 0 GT 0-1
engineering
Corrosion resistance in the salt spray test according to DIN 50021 500 h NSS
in mm, optionally after an after-rinse with:
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Wet paint 60-80 pm 0-1.0 4.5 2.5 3.0
0.0-2.0 _
Powder coating 60-80 pm 2-10 0 *
1.0-2.0
KTL + automotive
4.0
3.5 2.5 2.5
engineering
* same value also at 1000 h in the NSS salt spray test ** amounts added
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These examples illustrate that excellent coatings which have an excellent
corrosion
resistance, an excellent paint adhesion and usually also a distinct color are
obtained by
using the aqueous conversion compositions according to the invention. The
corrosion
resistance on steel surfaces is almost as good as that of the high quality
zinc
phosphating and is therefore far superior to the corrosion resistance of a
high quality
alkali phosphating (e.g., B3 in comparison with VB1).
In the comparative example VB2, the coating properties were determined only
after an
additional second conversion treatment ¨ unlike the examples according to the
invention. The paint adhesion on steel surfaces is almost as good as that with
a high
quality zinc phosphating and is thus very definitely superior to a high
quality alkali
phosphating. In addition, the aqueous conversion compositions according to the
invention have a very environmentally friendly composition, are advantageous
from the
standpoint of occupational health and are phosphate-free.
If an after-rinse solution was used, for example, such as solution with a
silane content,
an organic polymer content and/or an organic copolymer content after the
corrosion
conversion coating according to the invention and after at least one rinsing
with water,
then paint adhesion to steel surfaces achieved in this way is at least as good
as that
with a high quality zinc phosphating and a corrosion resistance at least as
good as that
of a high quality zinc phosphating was also achieved.
On the whole, it has been found that the aqueous acidic conversion
compositions
according to the invention are excellent for replacement of alkali phosphating
on a
variety of types of metallic substrate surfaces and not only for iron
phosphating on iron
and steel surfaces. A multimetal capability in the treatment has even been
found so that
a mix of different types of metallic surfaces can be treated either
simultaneously or in
succession in the same bath.
If ZrF6 is replaced by TiF6, there may optionally be a minor impairment in
corrosion
protection when used on steel in particular.
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When only zinc was used as the heavy metal cation, high quality coatings were
obtained even when the zinc content of the coatings remained unexpectedly
extremely
low. When using only manganese as the heavy metal cation, high quality
coatings were
obtained although the manganese content of the coatings was also unexpectedly
extremely low. If manganese and zinc were used at the same time, minor
impairments
were observed in some cases in comparison with the use of only one of these
types of
heavy metal cations.
When using only Fe2 as a heavy metal cation or in addition to Mn and/or Zn
ions, high
quality coatings were also obtained. Fe2+ can be resupplied from the bath of
substrate
surfaces containing iron through a reaction-induced pickling process. However,
the iron
is then frequently oxidized to Fe3+ due to the circulation of the bath and is
then
withdrawn from the bath as a reactive constituent. Despite the addition of
Fe2+, a
steady-state Fe2+ concentration is often established in the range of 0.025 to
0.1 g/L
Fe2+, as also occurs in Examples B41 and B42.
In the case of longer-lasting coatings with a plurality of substrates, for
example, the
main elements and some of the alloying elements are removed by pickling in the
aqueous acidic conversion composition and can accumulate in the bath
composition to
some extent, so in that case there are frequently more cations in the bath at
the same
time and can have subordinate effects on their properties, in particular
affecting the
composition of the coating.
If no heavy metal cations at all were added in Comparative Examples VB3 and
VB4, in
most cases inferior coatings were obtained. Zn and Mn are deposited only in
insignificant immeasurable quantities, based on measurements by X-ray
fluorescence
analysis, in contrast with Zr. However, Zr is the main component of the layer
and may
be present as Zr(OH)F, for example. Zn often acts as a fluoride scavenger in
the
interface between the metal and the coating, so that less fluoride can be
incorporated
into the layer, which is understood to mean leads to better properties, based
on the
information available to the present applicant. Zn and Mn are components of
the layer
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only in relatively small amounts and can therefore be detected analytically
with some
accuracy only by means of photoelectron spectroscopy XPS/ESCA.
The properties of the coatings to be produced are then the best when the Zr
layer is the
thickest in comparative tests. However, the Zr layer varies with different
grades of steel
and also in the case of the same grade of steel with different surface
properties.
In the experiments, a nonionic surfactant that was added further improved the
cleanliness of the metallic surface of the standard plates of CRS Gardobond C
that
were used. The prior cleaning step may therefore be omitted. If the addition
of the
surfactant was omitted by comparison with the former, the properties of the
coating
were fundamentally the same but the risk that the metallic surfaces would not
be
cleaned adequately was increased, and this may also have a negative influence
on the
properties of a layer.
In the case of larger amounts of molybdenum added, the possibility of a slight
separation of the coating must be considered.
Addition of an organic polymer, an organic copolymer and Si02 nanoparticles
have
proven to be particularly successful. It should be noted here that when
amounts in
excess of 0.5 g/L are added, there is no foaming and there are no
encrustations on
spray nozzles and walls to cause interference.
