Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2021/198429
PCT/EP2021/058640
Method for forming a black-passivation layer on a zinc-iron alloy and black-
pas-
sivation composition
Field of the Invention
The present inventions refers to a method for forming a black-passivation
layer on a zinc-
iron alloy and a black-passivation composition for depositing a black-
passivation layer
on such, wherein the black-passivation composition comprises one or more than
one
blackening agent selected from the group consisting of formula (I) and formula
(II) as
described hereinafter.
Background of the Invention
To protect metallic substrates from corrosive environmental influences,
different meth-
ods are available according to the prior art. To apply a protective
coating/layer of a metal
or metal alloy on the metallic substrate is a widely used and established
method. A well
know principle is the deposition of a zinc or zinc-nickel coating/layer on
metallic sub-
strates, such as iron metal substrates. Such coating/layers are often called
conversion
coatings/conversion layers. Such conversion coatings/conversion layers
typically com-
prise reaction products (which are insoluble in aqueous media over a wide pH
range) of
the metallic substrate with a respective conversion treatment solution. In
order to further
increase the corrosion resistance, such conversion coatings/conversion layers
are addi-
tionally passivated with a passivation layer by contacting it with a
passivation composi-
tion. Such passivation compositions and respective methods are known in the
art.
Besides a zinc and zinc-nickel coating/layer, other alloys are becoming more
prominent
such as zinc-iron. Since nickel becomes more and more questionable in regard
to envi-
ronmental and health issues, less critical alternatives are desired.
In many cases the passivation composition furthermore modifies the color of
the conver-
sion coating/conversion layer, for example into a bluish or even dark black
color. De-
pending on the application, such a color modification is often very much
desired for op-
tical reasons, in particular in the automotive field.
However, for certain conversion coatings/conversion layers a suitable color
modification
caused by means of passivation compositions is either not available at all,
provides an
insufficient color modification, deteriorates corrosion resistance upon color
modification,
1
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
or requires sophisticated passivation compositions, which are demanding to
handle. This
is particular true for zinc-iron conversion coatings/conversion layers, e.g.
substrates pro-
tected with a zinc-iron layer. Blackening of same without compromising the
corrosion
resistance is still a demand.
EP 1 816 234 B1 refers to an aqueous passivating coating composition for zinc
or zinc
io alloys and method for using same.
CN 104651823 A refers to a cobalt-free, environmentally friendly trivalent
chromium
black passivation liquid, comprising tungsten disulfide particles as
blackening agent.
CN'823 is silent with respect to zinc iron alloys.
WO 97/13888 Al refers to a non-chromate containing, corrosion-inhibiting
coating corn-
position capable of protecting a wide variety of metal surfaces.
WO 02/49960 A2 refers to specific tripolyphosphates, mixtures thereof, and
their use as
anti-corrosion agents and as biocides (anti-microbial agents) and, where
applicable, as
encrustation-inhibiting agents.
EP 3 360 989 Al refers to a method for electrolytically passivating an
outermost chro-
mium or outermost chromium alloy layer to increase corrosion resistance
thereof.
US 2004/0170848 Al refers to a corrosion inhibiting composition for coating an
article or
substrate such as a metal, metal coating, chromated metal coating, and the
like com-
prises a film-forming compound such as a wax or a polymer, and a sulfide salt
or thio
compound or a derivative of a thio compound. US'848 is silent with respect to
blackening.
Although black-passivation compositions are described in the art, there is an
ongoing
demand to improve blackening of zinc-iron conversion coatings/conversion
layers.
Objective of the present Invention
It was therefore the objective of the present invention to provide a method
for forming a
black-passivation layer particularly on a zinc-iron alloy with improved
blackening quality
and without compromising corrosion resistance. Furthermore, a respective black-
pas-
sivation composition is needed too.
It is furthermore the objective to overcome the disadvantages mentioned above
and to
provide in particular a method (along with a respective composition), which is
easy to
handle and avoids sedimentation by being substantially free of particles.
Summary of the Invention
2
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
The objectives mentioned above are solved by a method for forming a black-
passivation
layer on a zinc-iron alloy, the method comprising the steps:
(a) providing a substrate comprising the zinc-iron alloy,
(b) providing a black-passivation composition for depositing the black-
passivation
layer on the zinc-iron alloy, the composition comprising
(i) one or more
than one blackening agent selected from the group consisting
of
formula (I),
R1
/N R3
R2
\
(I),
wherein
R1 and R2 are independently selected from the group consisting of hydro-
gen and Cl to C5 alkyl,
R3 is selected from the group consisting of sulfonic acid, carboxylic acid,
alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and
n is 2, 3, 4, or 5,
and formula (II),
N y S R4
=
(II),
wherein
3
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
R4 is selected from the group consisting of sulfonic acid, carboxylic acid,
alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and
m is 1, 2, 3, 4, or 5, and
(ii)
one or more than one species of metal ions selected from the group consist-
ing of trivalent chromium, titanium, and zirconium, and
(c) contacting
the substrate with said black-passivation composition such that the
black-passivation layer is formed on the zinc-iron alloy.
By utilizing said one or more than one blackening agent, a very good
blackening of a
zinc-iron alloy is obtained along with good corrosion resistance. Moreover,
the method
of the present invention is simple and can be easily carried out. Our own
experiments
have furthermore shown that the blackening obtained by means of the method of
the
present invention and the respective black-passivation composition of the
present inven-
tion is highly specific for zinc-iron alloys. Own experiments confirm that
zinc alone and
zinc nickel alloys are not blackened. Further details are given in the
examples section
below in the text.
The present invention also concerns a respective black-passivation composition
as fur-
ther described below in the text as well as a respective use of said one or
more than one
blackening agent for blackening a zinc-iron alloy. Generally, features
described in regard
to the method of the present invention, in particular features described as
being pre-
ferred, apply likewise to the black-passivation composition of the present
invention, most
preferably to a black-passivation composition described as being preferred,
and apply
likewise to the use according to the present invention, most preferably to the
use de-
scribed as being preferred.
Detailed Description of the Invention
In the context of the present invention, ions of trivalent chromium refers to
chromium ions
with the oxidation number +3 (also called trivalent chromium ions) including
the free and
complexed form, respectively. Thus applies mutatis mutandis to the metal ions
of tita-
nium and zirconium, respectively.
In the context of the present invention, the term "black-passivation layer"
also denotes a
black-conversion layer.
The substrate
4
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferably, the black-passivation layer has a darkness value L* of 40 or
below, preferably
of 33 or below, most preferably of 25 or below, based on the CI ELAB color
space defini-
tion.
As mentioned above, the method of the present invention is highly specific for
a zinc-iron
alloy. Preferred is a method of the present invention, wherein in the zinc-
iron alloy the
io amount of iron ranges from 0.1 wt.-% to 30 wt.-%, based on the total
weight of the zinc-
iron alloy, preferably 0.6 wt.-% to 28 wt.-%, more preferably 2.1 wt.-% to 25
wt.-%, even
more preferably 3.5 wt.-% to 22 wt.-%, most preferably 4.9 wt-% to 18 wt.-%,
even most
preferably 6.1 wt.-% to 15 wt.-%. A very preferred amount of iron ranges from
4.9 wt.-%
to 30 wt.-%. In this very preferred range, an excellent blackening is easily
obtained.
The method of the present invention generally applies to a zinc-iron alloy.
Preferred is a
method of the present invention, wherein the zinc-iron alloy is present on the
substrate
as a layer, preferably as a layer resulting from a galvanization process, most
preferably
from a zinc-iron galvanization process. Thus, most preferred is a method of
the present
invention, wherein the zinc-iron alloy is distinct from the rest of the
substrate. In such a
way, the substrate is typically protected from corrosion.
Preferred is a method of the present invention, wherein the substrate
comprises iron.
This means that the substrate preferably comprises a base material, preferably
a ferrous
base material, more preferably steel, on which the zinc-iron alloy is
deposited. Thus, the
zinc-iron alloy is distinct from the rest of the substrate (i.e. is
represented by the base
material).
However, in a few cases, a method of the present invention is preferred,
wherein the
substrate comprises the zinc-iron alloy in a sense that the substrate itself
is made of a
zinc-iron alloy. In other words, preferably the base material is already the
zinc-iron alloy
and thus, the base material is the substrate.
Preferred is a method of the present invention, wherein the substrate is a
metal or metal
alloy substrate, preferably the substrate comprises iron, most preferably the
substrate
comprises iron and is different from the zinc-iron alloy.
Preferred is a method of the present invention, wherein the substrate is a
work piece
requiring anodic corrosion resistance, most preferably required due to
environmentally
caused corrosion.
5
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Typically, a preferred substrate is selected from the group consisting of
screws, bolts,
nuts, and automotive parts.
Preferred is a method of the present invention, wherein more than one
substrate is pro-
vided in step (a), preferably a plurality of substrates is provided in step
(a). This in par-
ticular applies if the substrate refers to screws, bolts, and nuts.
Preferred is a method of the present invention, wherein the substrate is
(preferably the
substrates are) provided in a barrel or fixed on a rack. Thus, the method of
the present
invention is applicable to both kinds.
The black-passivation composition
In the method of the present invention a black-passivation composition is
utilized, pref-
erably the black-passivation composition of the present invention (see text
further below).
Preferably, the black-passivation composition is also called a conversion
composition.
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is aqueous (i.e. comprises water), wherein preferably water has a
concentration of
more than 50 vol.- /0 based on the total volume of the black-passivation
composition,
more preferably of 75 vol.-% or more, most preferably of 90 vol.-% or more.
Very prefer-
ably, water is the only solvent.
Preferably, the black-passivation composition is a solution. Thus, preferred
is a method
of the present invention, wherein the black-passivation composition is
substantially free
of, preferably does not comprise, particles (including colloids).
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is acidic, preferably having a pH from 1.0 to 4.5, preferably from 1.2 to
4.0, more
preferably from 1.4 to 3.3, even more preferably from 1.5 to 2.8, most
preferably from
1.6 to 2.2.
As mentioned above, the black-passivation composition comprises one or more
than one
blackening agent as defined above.
As indicated by formula (I) and (II), respectively, the one or more than one
blackening
agent utilized in the black-passivation composition is an organic blackening
agent. Pre-
ferred is a method of the present invention, wherein the black-passivation
composition
is substantially free of, preferably does not comprise, an inorganic
blackening agent. An
inorganic blackening agent is for example disclosed in CN 104651823 A.
6
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion comprises at least one or more than one (preferably one) blackening agent
of for-
mula (I). According to own experiments, a blackening agent of formula (I)
provides ex-
cellent results (see examples below).
Only in some cases, a method of the present invention is preferred, wherein
the black-
passivation composition is substantially free of, preferably does not
comprise, a black-
ening agent of formula (II). This most preferably applies if the black-
passivation compo-
sition comprises already a blackening agent of formula (I).
Generally preferred is a method of the present invention, wherein in the black-
passivation
composition the one or more than one blackening agent selected from the group
con-
sisting of formula (I) and formula (II) are the only blackening agents in the
black-pas-
sivation composition.
Preferred is a method of the present invention, wherein in the black-
passivation corn po-
sition the one or more than one blackening agent has a total concentration
ranging from
0.2 mmol/L to 100 mmol/L, based on the total volume of the black-passivation
composi-
tion, preferably from 0.3 mmol/L to 80 mmol/L, more preferably from 0.4 mmol/L
to 60
mmol/L, even more preferably from 0.8 mmol/L to 45 mmol/L, most preferably
from 1.6
mmol/L to 38 mmol/L.
In particular preferred is a method of the present invention, wherein the
black-passivation
composition comprises one or more than one (preferably one) blackening agent
of for-
mula (I) in a total concentration ranging from 0.4 mmol/L to 25.0 mmol/L,
based on the
total volume of the black-passivation composition, preferably from 0.6 mmol/L
to 20.0
mmol/L, more preferably from 0.8 mmol/L to 12.0 mmol/L, even more preferably
from 1.0
mmol/L to 10.0 mmol/L, most preferably from 1.2 mmol/L to 8.0 mmol/L. Most
preferably,
in combination with such a total concentration, compounds of formula (I) are
the only
blackening agents in the black-passivation composition utilized in the method
of the pre-
sent invention. Surprisingly, an excellent blackening was obtained even with a
compar-
atively low total concentration of compounds of formula (I) including a total
concentration
of 0.4 mmol/L. It is very desired to maintain a comparatively low
concentration of black-
ening agents such that the life-time of a respective black-passivation
composition is as
long as possible. A very preferred total concentration ranges from 0.4 mmol/L
to 8.0
mmol/L.
7
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein R1 and R2 are
independently
selected from branched and unbranched Cl to C5 alkyl, preferably unbranched Cl
to
C5 alkyl.
Preferred is a method of the present invention, wherein in R3 and R4 the salts
are inde-
pendently selected from the group consisting of ammonium salts and alkaline
salts, pref-
erably from the group consisting of ammonium, sodium, and potassium.
Preferred is a method of the present invention, wherein R1 and R2 are
independently
selected from the group consisting of hydrogen, methyl, ethyl, 1-propyl, 2-
propyl, 1-butyl,
2-butyl, and tert-butyl, preferably hydrogen, methyl, ethyl, 1-propyl, and 2-
propyl, most
preferably hydrogen and methyl.
Preferred is a method of the present invention, wherein at least one of R1 and
R2 is an
alkyl group, preferably as described above as being preferred.
Preferred is a method of the present invention, wherein n is 2, 3, or 4,
preferably 3.
In the method of the present invention, R3 is selected from the group
consisting of sul-
fonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and
esters
thereof.
Sulfonic acid preferably means -S03H, wherein "-" denotes the covalent bond
connect-
ing this group with the rest of the compound of formula (I). Carboxylic acid
preferably
means -COOH, wherein "-" denotes the covalent bond connecting this group with
the
rest of the compound of formula (I). Alkyl carboxylic acid preferably means a
saturated,
branched or unbranched alkyl comprising one or more than one (preferably two)
carbox-
ylic acid groups, more preferably means a saturated, branched or unbranched Cl
to C6
alkyl (preferably C2 to C4 alkyl) comprising one or more than one (preferably
two) car-
boxylic acid groups, even more preferably it comprises -C(COOH)(CH2)kCOOH,
wherein
"-" denotes the covalent bond connecting this group with the rest of the
compound of
formula (I) and k is an integer ranging from 1 to 5, most preferably it
comprises
-C(COOH)CH2COOH. Phosphonic acid preferably means -P03H2, wherein "-" denotes
the covalent bond connecting this group with the rest of the compound of
formula (I).
Preferably, the above mentioned regarding R3 applies mutatis mutandis to R4 in
formula
(II).
8
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein R3 comprises at least
sulfonic
acid, salts and/or esters thereof, preferably R3 comprises at least sulfonic
acid, salts
and/or esters thereof, and n is 3.
More preferred is a method of the present invention, wherein R3 is selected
from the
group consisting of sulfonic acid, carboxylic acid, phosphonic acid, and salts
thereof,
lo most preferably R3 comprises at least sulfonic acid and/or salts
thereof, preferably R3
comprises at least sulfonic acid and/or salts thereof, and n is 3.
Most preferred is a method of the present invention, wherein formula (1)
comprises the
compound 3-(N,N-Dimethylthiocarbamoy1)-thiopropanesulfonic acid, salts and/or
esters
thereof, preferably 3-(N, N-Dimethylthiocarbamoy1)-thi opropanesulfonic acid
and/or salts
thereof.
Preferred is a method of the present invention, wherein m is 2, 3, or 4,
preferably 3.
Preferred is a method of the present invention, wherein R4 comprises at least
sulfonic
acid, salts and/or esters thereof, preferably R4 comprises at least sulfonic
acid, salts
and/or esters thereof, and m is 3.
More preferred is a method of the present invention, wherein R4 is selected
from the
group consisting of sulfonic acid, carboxylic acid, phosphonic acid, and salts
thereof,
most preferably R4 comprises at least sulfonic acid and/or salts thereof,
preferably R4
comprises at least sulfonic acid and/or salts thereof, and m is 3.
Most preferred is a method of the present invention, wherein formula (II)
comprises the
compound 3-(2-Benzthiazolylthio)-1-propanesulfonic acid, salts and/or esters
thereof,
preferably 3-(2-Benzthiazolylthio)-1-propanesulfonic acid and/or salts
thereof.
The black-passivation composition utilized in the method of the present
invention com-
prises one or more than one species of metal ions selected from the group
consisting of
trivalent chromium, titanium, and zirconium. Although a significant blackening
of a zinc-
iron alloy can be observed already even without the presence of these metal
ions, i.e. in
the total absence of these and other transition metal ions, said metal ions
are in particular
beneficial in order to obtain a significant corrosion resistance besides the
blackening
effect. Although a certain corrosion resistance is in some cases present,
corrosion re-
sistance can be thus significantly further increased.
Preferred is a method of the present invention, wherein the one or more than
one species
of metal ions is selected from the group consisting of trivalent chromium and
titanium.
9
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
More preferred is a method of the present invention, wherein the one or more
than one
species of metal ions at least comprises trivalent chromium, most preferred
the one or
more than one species of metal ions is trivalent chromium. Own experiments
have shown
that excellent corrosion resistance results are obtained with trivalent
chromium ions.
Preferred is a method of the present invention, wherein the metal ions of
trivalent chro-
mium are from an organic and/or inorganic trivalent chromium ion source,
preferably
from an inorganic trivalent chromium ion source. A very preferred trivalent
chromium ion
source is an organic and/or inorganic trivalent chromium ion source. A
preferred organic
trivalent chromium ion source is trivalent chromium citrate. A preferred
inorganic trivalent
chromium ion source is trivalent chromium chloride hexahydrate.
Preferred is a method of the present invention, wherein said one or more than
one spe-
cies of metal ions has a total concentration ranging from 0.1 g/L to 30 g/L,
based on the
total volume of the black-passivation composition and based on the mass of the
free
ions, preferably from 0.2 g/L to 20 g/L, more preferably from 0.5 g/L to 14
g/L, even more
preferably from 0.8 g/L to 10 g/L, most preferably from 1.3 g/L to 6.0 g/L. A
very preferred
total concentration is ranging from 0.1 g/L to 4.0 g/L. If the total
concentration is signifi-
cantly below 0.1 g/L, in many cases a particular desired corrosion resistance
is not
achieved. In contrast, if the total concentration is significantly above 30
g/L, no further
benefit is identified and costs are typically inacceptable.
Since trivalent chromium ions are preferred, preferred is a method of the
present inven-
tion, wherein the metal ions of trivalent chromium have a total concentration
ranging from
0.1 g/L to 8.0 g/L, based on the total volume of the black-passivation
composition, pref-
erably from 0.2 g/L to 7.1 g/L, more preferably from 0.5 g/L to 6.1 g/L, even
more prefer-
ably from 0.8 g/L to 5.0 g/L, most preferably from 1.0 g/L to 3.5 g/L. Most
preferably, the
above mentioned total concentration for metal ions of trivalent chromium
applies with the
proviso that these ions are the only species of transition metal ions in the
black-pas-
sivation composition.
In the following a number of compounds and ions are listed that preferably are
not con-
tained in the black-passivation composition utilized in the method of the
present inven-
tion. Such compounds/ions are either not helpful for solving the objectives
mentioned in
the outline above or even have a detrimental effect and are therefore avoided.
In a few
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
cases the presence of further compounds/ions is inevitable upon utilizing the
black-pas-
sivation composition. Generally, it is preferred to utilize a comparatively
simple black-
passivation composition.
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is substantially free of, preferably does not comprise, hexavalent
chromium. This
io includes any compounds and ions comprising chromium with an oxidation
number of
(+VI). It is a very important objective that the method of the present
invention avoids any
utilization of hexavalent chromium due to its environmental and health issues.
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is substantially free of, preferably does not comprise, thioglycolic acid
and salts
thereof. However, in some cases a method of the present invention is
preferred, wherein
the black-passivation composition comprises thioglycolic acid and/or salts
thereof in ad-
dition to said one or more than one blackening agent selected from the group
consisting
of formula (I) and formula (II), as defined above. Although own experiments
(data not
shown) indicate that the mere presence of thioglycolic acid and/or salts
thereof in many
cases also cause a significant blackening, the obtained results are less good
compared
to the effect obtained with the blackening agents of formula (I) and (II).
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is substantially free of, preferably does not comprise, nickel ions,
preferably is sub-
stantially free of, preferably does not comprise, nickel.
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is substantially free of, preferably does not comprise, intentionally
added zinc ions.
If zinc ions are present in the black-passivation composition they are
released/dissolved
from the zinc-iron alloy upon utilizing the black-passivation composition.
Thus, preferred
is a method of the present invention, with the proviso that, if zinc ions are
present in the
black-passivation composition, they are released from the zinc-iron alloy. In
other word,
if zinc ions are present, the source is the zinc-iron alloy. After setting up
a respective
black-passivation composition no zinc ions are typically present. After
starting the
method of the present invention, the total concentration is very low. Upon
utilizing the
black-passivation composition the total concentration typically increases.
Thus, prefera-
bly, zinc ions are present in a total concentration of 10 g/L or below, based
on the total
volume of the black-passivation composition, preferably of 8 g/L or below,
most prefera-
bly of 5 g/L or below, after step (C) is carried out multiple times.
11
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is substantially free of, preferably does not comprise, silver ions,
preferably is sub-
stantially free of, preferably does not comprise, silver.
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is substantially free of, preferably does not comprise, nicotinic acid
and salts thereof.
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is substantially free of, preferably does not comprise, phytic acid and
salts thereof.
In most cases, preferred is a method of the present invention, wherein the
black-pas-
sivation composition is substantially free of, preferably does not comprise,
intentionally
added disulfides. This preferably means that the black-passivation composition
is sub-
stantially free of, preferably does not comprise, intentionally added ionic
disulfides and
compounds comprising a covalent disulfide. In turn, only in very rare cases a
method of
the present invention is preferred, wherein the black-passivation composition
comprises
disulfides, preferably ionic disulfides and/or compounds comprising a covalent
disulfide.
However, in general, the absence of such compounds is generally preferred.
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is substantially free of, preferably does not comprise, intentionally
added iron ions.
If iron ions are present in the black-passivation composition they are
released/dissolved
from the zinc-iron alloy upon utilizing the black-passivation composition.
After setting up
a respective black-passivation composition no iron ions are typically present.
After start-
ing the method of the present invention, the total concentration is very low.
Upon utilizing
the black-passivation composition the total concentration typically increases.
Thus, pref-
erably, iron ions are present in a total concentration of 1 g/L or below,
based on the total
volume of the black-passivation composition, preferably of 0.8 g/L or below,
most pref-
erably of 0.5 g/L or below, after step (C) is carried out multiple times.
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is substantially free of, preferably does not comprise, tungsten ions.
More preferred is a method of the present invention, wherein the black-
passivation com-
position is substantially free of, preferably does not comprise, tungsten.
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is substantially free of, preferably does not comprise, tungsten
disulfide particles,
preferably is substantially free of, preferably does not comprise, tungsten
disulfide.
12
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is substantially free of, preferably does not comprise, thiodiglycol.
Preferred is a method of the present invention, wherein the black-passivation
composi-
tion is substantially free of, preferably does not comprise, silicon dioxide,
silicates, a
silane, and a silane containing compound, preferably is substantially free of,
preferably
does not comprise, a silicon-containing compound. Only in very rare cases a
method of
the present invention is preferred, wherein the black-passivation composition
comprises
a silane and/or a silane containing compound. It is assumed that in some cases
the
presence of the silane and/or the silane containing compound positively
affects the cor-
rosion resistance of the black-passivation layer. However, in many cases an
excellent
corrosion resistance is already achieved even without the presence of a silane
and/or a
silane containing compound.
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is substantially free of, preferably does not comprise, cobalt ions,
preferably is sub-
stantially free of, preferably does not comprise, cobalt. The presence of
cobalt becomes
more and more an environmental issue. Only in very few cases, a method of the
present
invention is preferred, wherein the black-passivation composition comprises
cobalt ions
and/or cobalt containing compounds. The presence of cobalt typically increases
corro-
sion resistance of a heat-treated substrate with the black-passivation layer
obtained by
the method of the present invention.
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is further comprising
(iii) one or more than one species of halogen ions, and/or
(iv) one or more than one carboxylic acid and/or salts thereof.
Said halogen ions are typically the counter ions of the one or more than one
species of
metal ions selected from the group consisting of trivalent chromium, titanium,
and zirco-
nium.
Preferred is a method of the present invention, wherein the one or more than
one species
of halogen ions have a total concentration from 1 g/L to 18 g/L, based on the
total volume
of the black-passivation composition, preferably from 2 g/L to 15 g/L, even
more prefer-
ably from 3 g/L to 12 g/L, most preferably from 4 g/L to 10 g/L, even most
preferably from
6 g/L to 9 g/L.
13
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein the one or more than
one species
of halogen ions comprises chloride ions and/or fluoride ions. In some cases,
fluoride
preferably also serves as cornplexing agent for the metal ions, most
preferably if the one
or more than one species of metal ions is selected from the group consisting
of titanium
and zirconium. Bromide ions are preferably not comprised in the black-
passivation com-
position.
More preferably, the chloride ions have a total concentration from 1 g/L to 18
g/L, based
on the total volume of the black-passivation composition, preferably from 2
g/L to 15 g/L,
even more preferably from 3 g/L to 12 g/L, most preferably from 4 g/L to 10
g/L, even
most preferably from 6 g/L to 9 g/L. Most preferably, in the black-passivation
composition
chloride ions are the only species of halogen ions.
Said one or more than one carboxylic acid and/or salts thereof typically serve
as corn-
plexing agents for said one or more than one species of metal ions selected
from the
group consisting of trivalent chromium, titanium, and zirconium, most
preferably for metal
ions of trivalent chromium.
Preferred is a method of the present invention, wherein the one or more than
one c
comprises a dicarboxylic acid, a tricarboxylic acid, and/or salts thereof.
A preferred dicarboxylic acid and/or salts thereof comprises a C2 to C6
dicarboxylic acid
and/or salts thereof, preferably oxalic acid, malonic acid, and/or salts
thereof, most pref-
erably oxalic acid and/or salts thereof.
A preferred tricarboxylic acid and/or salts thereof comprises citric acid
and/or salts
thereof.
Preferred is a method of the present invention, wherein the one or more than
one car-
boxylic acid and salts thereof have a total concentration from 0.5 mmol/L to
120 mmol/L,
based on the total volume of the black-passivation composition, preferably
from 8 mmol/L
to 105 mmol/L, even more preferably from 15 mmol/L to 90 mmol/L, most
preferably from
30 mmol/L to 80 mmol/L, even most preferably from 45 mmol/L to 70 mmol/L. More
pref-
erably, the above total concentration applies with the proviso that the black-
passivation
composition comprises at least one or more than one dicarboxylic acid and/or
salts
thereof.
14
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Even more preferably, the oxalic acid and salts thereof have a total
concentration from
0.5 mmol/L to 120 mmol/L, based on the total volume of the black-passivation
composi-
tion, preferably from 8 mmol/L to 105 mmol/L, even more preferably from 15
mmol/L to
90 mmol/L, most preferably from 30 mmol/L to 80 mmol/L, even most preferably
from 45
mmol/L to 70 mmol/L. Most preferably, oxalic acid and salts thereof are the
only dicar-
lo boxylic acids and salts thereof in the black-passivation composition,
preferably the only
carboxylic acids and salts thereof in the black-passivation composition.
In some cases a method of the present invention is preferred, wherein the
black-pas-
sivation composition comprises citric acid and/or salts thereof, preferably in
a total con-
centration from 0.5 mmol/L to 120 mmol/L, based on the total volume of the
black-pas-
sivation composition, preferably from 8 mmol/L to 105 mmol/L, even more
preferably
from 15 mmol/L to 90 mmol/L, most preferably from 30 mmol/L to 80 mmol/L, even
most
preferably from 45 mmol/L to 70 mmol/L. In such cases, citric acid and salts
thereof are
preferably the only tricarboxylic acid and salts thereof in the black-
passivation composi-
tion, most preferably the only carboxylic acid and salts thereof in the black-
passivation
composition.
Preferred is a method of the present invention, wherein the black-passivation
cornposi-
tion is further comprising
(v) nitrate ions.
Nitrate ions preferably act as oxidizing agent in the black-passivation
composition.
Preferred is a method of the present invention, wherein the nitrate ions have
a total con-
centration ranging from 0.1 g/L to 20 g/L, based on the total volume of the
black-pas-
sivation composition, preferably from 0.4 g/L to 15 g/L, even more preferably
from 0.8
g/L to 11 g/L, most preferably from 1.2 g/L to 7 g/L, even most preferably
from 1.7 g/L to
4.5 g/L.
The contactind with the black-passivation composition (step (c))
In step (c) the substrate is contacted with the black-passivation composition,
preferably
as described above, more preferably as described above as being preferred.
Preferred is a method of the present invention, wherein in step (c) the black-
passivation
composition has a temperature in a range from 10 C to 80 C, preferably from 15
C to
65 C, even more preferably from 19 C to 45 C, most preferably from 22 C to 38
C. If
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
the temperature is significantly exceeding 80 C, in many cases an undesired
rapid dis-
solution (stripping) of the zinc-iron alloy is observed impairing the
corrosion resistance.
However, if the temperature is too low, in many cases the contacting in step
(c) is unde-
sirably long.
Preferred is a method of the present invention, wherein in step (c) the
contacting is per-
formed for a time period from 10 seconds to 200 seconds, preferably from 20
seconds
to 160 seconds, even more preferably from 40 seconds to 130 seconds, most
preferably
from 60 seconds to 100 seconds. If the time period is significantly exceeding
200 sec-
onds, in many cases an undesired rapid dissolution (stripping) of the zinc-
iron alloy is
observed impairing the corrosion resistance. However, if the time period is
too low, typi-
cally the blackening is insufficient and thus, the optical appearance is
negatively im-
paired.
Preferred is a method of the present invention, wherein step (c) is performed
without
applying an electrical current. Preferably, in step (c) the substrate is
dipped into the
black-passivation corn position.
Post-treatment
As shown in the examples below, an indeed very good corrosion resistance is
obtained
if after step (c) the substrate is further treated in order to increase
corrosion resistance.
Generally preferred is a method of the present invention, wherein the
substrate obtained
after step (c) of the method of the present invention is additionally treated
with a post-dip
composition and/or a sealer composition, preferably as outlined below, either
in this order
or in reversed order.
Preferred is a method of the present invention, wherein step (c) is followed
by step
(d)
contacting the substrate obtained after step (c) with a post-dip
composition such
that a post-dipped substrate is obtained.
Preferred is a method of the present invention, wherein the post-dip
composition is
acidic, preferably has a pH ranging from 3.0 to 6.8, more preferably from 3.5
to 6.5, even
more preferably from 4.0 to 6.3, most preferably from 4.3 to 6Ø
Preferred is a method of the present invention, wherein the post-dip
composition com-
prises trivalent chromium ions.
16
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein the sealer composition
is sub-
stantially free of, preferably does not comprise, compounds and ions
comprising hexa-
valent chromium.
Preferred is a method of the present invention, wherein the post-dip
composition com-
prises phosphate ions.
Preferred is a method of the present invention, wherein the post-dip
composition com-
prises one or more than one wetting agent.
Preferred is a method of the present invention, wherein the post-dip
composition com-
prises one or more than one complexing agent, preferably for the trivalent
chromium
ions.
Preferred is a method of the present invention, wherein in step (d) the post-
dip compo-
sition has a temperature in a range from 18 C to 60 C, preferably 20 C to 58
C, more
preferably from 28 C to 56 C, even more preferably from 33 C to 54 C, most
preferably
from 38 C to 50 C.
Preferred is a method of the present invention, wherein in step (d) the
contacting is per-
formed for a time period from 5 seconds to 200 seconds, preferably from 10
seconds to
140 seconds, even more preferably from 20 seconds to 100 seconds, most
preferably
from 30 seconds to 70 seconds.
Preferred is a method of the present invention, wherein step (d) is followed
by step
(e) contacting the substrate obtained after step (d) with a sealer
composition such that
a sealed substrate is obtained.
Preferred is a method of the present invention, wherein the sealer composition
is alka-
line, preferably has a pH of 9 or higher, more preferably in a range from 9.1
to 12, even
more preferably from 9.3 to 11, most preferably from 9.5 to 10.5.
Preferred is a method of the present invention, wherein the sealer composition
comprises
two or more than two organic compounds.
Preferred is a method of the present invention, wherein the sealer composition
is sub-
stantially free of, preferably does not comprise, trivalent chromium ions.
17
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
Preferred is a method of the present invention, wherein the sealer composition
comprises
at least one organic polymer, preferably comprising a polyurethane, a
polyalkylene (pref-
erably polyethylene), a polyfluoroalkylene (preferably
polytetrafluoroethylene) and/or a
polyacrylate.
Preferred is a method of the present invention, wherein the sealer composition
comprises
one or more than one wax.
Preferred is a method of the present invention, wherein the sealer composition
comprises
one or more than one silicon-containing compound, preferably at least one
silane and/or
at least one inorganic silicate. Preferably, the at least one inorganic
silicate is a colloid.
Preferred is a method of the present invention, wherein in step (e) the sealer
composition
has a temperature in a range from 15 C to 35 C, preferably 17 C to 30 C, more
prefer-
ably from 19 C to 27 C, most preferably from 21 C to 25 C.
Preferred is a method of the present invention, wherein in step (e) the
contacting is per-
formed for a time period from 5 seconds to 200 seconds, preferably from 10
seconds to
140 seconds, even more preferably from 20 seconds to 100 seconds, most
preferably
from 30 seconds to 70 seconds.
When performing steps (d) and (e) as outlined above in this order, not only a
very good
black-passivation layer is obtained but additionally also an excellent
corrosion re-
sistance, most preferably up to 480 hours, based on ISO 9227, 5% white rust
limit.
Preferred is a method of the present invention, wherein step (e) is followed
by step
(f) drying the substrate obtained after step (e).
Preferred is a method of the present invention, wherein step (f) is carried
out at a tem-
perature ranging from 55 C to 95 C, preferably 58 C to 90 C, more preferably
from 58 C
to 85 C, most preferably from 60 C to 80 C.
Preferred is a method of the present invention, wherein step (f) is carried
out for a time
period from 2 minutes to 20 minutes, preferably from 3 minutes to 16 minutes,
even more
preferably from 4 minutes to 13 minutes, most preferably from 6 minutes to 10
minutes.
Preferably, a drying step, preferably as defined above, is also carried out
after one or
more than one of the previous steps, e.g. after step (c), step (d), etc. Very
preferred is a
method of the present invention, wherein a drying step, preferably as defined
in step (f),
is carried out after step (d) and prior to step (e). This is very preferred
because in step
18
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
(d) the post-dip composition is acidic, wherein in step (e) the sealer
composition is alka-
line.
The present invention furthermore refers to a black-passivation composition
for deposit-
ing a black-passivation layer on a zinc-iron alloy, the composition comprising
(i) one or more than one blackening agent selected from
the group consisting
of
formula (I),
W
/N er R
R2 3
(I),
wherein
R1 and R2 are independently selected from the group consisting of hydro-
gen and Cl to C5 alkyl,
R3 is selected from the group consisting of sulfonic acid, carboxylic acid,
alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and
n is 1, 2, 3, 4, or 5,
and formula (II),
N S R4
=
(II),
wherein
R4 is selected from the group consisting of sulfonic acid, carboxylic acid,
alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and
19
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
rrl is 1, 2, 3, 4, or 5, and
(ii) one or more than one species of metal ions selected from
the group consist-
ing of trivalent chromium, titanium, and zirconium,
with the proviso that
the black-passivation composition is substantially free of, preferably does
not
comprise, nickel ions, cobalt ions, and tungsten ions.
In particular preferred is a black-passivation composition of the present
invention,
wherein the black-passivation composition is substantially free of
intentionally added zinc
ions, preferably does not comprise intentionally added zinc ions. Most
preferably, the
aforementioned regarding zinc ions in view of the method of the present
invention in
particular applies likewise to the black-passivating composition of the
present invention.
Preferably, the aforementioned regarding the black-passivation composition
utilized in
the method of the present invention (in particular what is defined as being
preferred)
applies likewise to the black-passivation composition of the present
invention. This ap-
plies in particular to compounds and ions not contained in the black-
passivation compo-
sition utilized in the method of the present invention.
The present invention furthermore refers to the use of one or more than one
blackening
agent selected from the group consisting of
formula (I),
W
/N er R
R2 3
(I),
wherein
R1 and R2 are independently selected from the group consisting of hydro-
gen and Cl to C5 alkyl,
R3 is selected from the group consisting of sulfonic acid, carboxylic acid,
alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
n is 1, 2, 3, 4, or 5,
and formula (II),
oNyst,),R4
(II),
wherein
R4 is selected from the group consisting of sulfonic acid, carboxylic acid,
alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and
m is 1, 2, 3, 4, or 5,
for blackening a zinc-iron alloy.
Preferably, the aforementioned regarding the one or more than one blackening
agent of
formula (I) and (II) (in particular what is defined as being preferred) used
in the black-
passivation composition which is utilized in the method of the present
invention applies
likewise to the use of the present invention.
The present invention is described in more detail by the following non-
limiting examples.
Examples
In the examples, various test passivation compositions were prepared with the
number-
ing as introduced in Table 1 below, each composition is aqueous and generally
com-
prises a species of metal ions; 6 g/L to 8 g/L chloride ions if chromium ions
were utilized;
50 mmol/L to 70 mmol/L oxalic acid if chromium ions were utilized or 10 mmol/L
to 300
mmol/L fluoride ions if titanium ions and zirconium ions were utilized,
respectively, as
complexing agents; approximately 1 g/L to 7 g/L nitrate ions; and one of the
following
compounds abbreviated as below:
DPS: 3-(N,N-DimethylthiocarbamoyI)-thiopropanesulfonate, sodium salt; also
known as
Raluplate DPS (CAS 18880-36-9; Raschig company); a compound of formula (I),
wherein R1 and R2 are methyl, R3 is the sodium salt of sulfonic acid, and n is
3;
ZPS: 3-(2-Benzthiazolylthio)-1-propanesulfonate, sodium salt; also known as
Raluplate
21
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
ZPS (CAS 49625-94-7; Raschig company); a compound of formula (II), wherein R4
is the
sodium salt of sulfonic acid, and m is 3;
SPS: Bis-(3-sulfopropyI)-disulfide, disodium salt, also known as Raluplate SPS
(CAS
27206-35-5; Raschig company); comparative example;
SPV: 1-(3-SulfopropyI)-2-vinylpyridinium betaine; also known as Raluplate SPV
(CAS
90552-35-5; Raschig company); comparative example;
MPS: 3-Mercaptopropanesulfonate, sodium salt; also known as Raluplate MPS (CAS
17636-10-1; Raschig company); comparative example;
DTO: Dithiooxamide; comparative example.
The specific compound and its respective total concentration is outlined in
Table 1 below.
Each test passivation composition has a pH of approximately 2.
In each example, as substrates a plurality of u-shaped iron plate specimens
(base ma-
terial) galvanized with a silver-like colored zinc-iron layer (Hiron-Zn/Fe for
high iron con-
tent and Protedur Plus for low iron content, respectively, each is a product
of Atotech;
for iron content see Table 1 below) was dipped for approximately 90 seconds in
the
respective test passivation composition, the compositions having a temperature
of ap-
proximately 22 C. In examples according to the invention, a blackening was
immediately
observed.
Afterwards the treated specimens were dried, and a post-dip composition
(acidic, com-
prising trivalent chromium phosphate) as well as a sealer composition
(alkaline, compris-
ing a wax and a silicon-containing compound) was applied. Subsequently, the
blacken-
ing quality was visually evaluated; the corrosion resistance according to ISO
9227.
Table 1:
No. % Fe blacken- [mmol/L] Species of [g/L] Blackening corrosion*
ing agent metal ions quality [h]
1-1 1.6 DPS 1.9 Cr(III) 3 ¨ 4## <72
1-2 15 DPS 3.8 Zr(IV) 0.5 ++ <24
22
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
1-3 15 DPS 1.9 Ti(IV) 0.3 120
1-4 15 DPS# 1.9 - 8" Cr(III) 3 ¨ 4 +++ 480
11-1 15 ZPS 32.0 Cr(III) 3 ¨ 4 ++ 240
Cl 15 SPS 14.1 Cr(III) 3 ¨ 4 n.d.
C2 15 SPV 22.0 Cr(III) 3 ¨ 4 n.d.
03 15 MPS 28.1 Cr(III) 3 ¨ 4 n.d.
04 15 DTO 41.6 Cr(III) 3 ¨ 4 n.d.
n.d.
"*" denotes: time until max. 5% white rust was observed,
"a" also tested on screws in barrel applications,
""tested in compositions with various concentrations,
"n.d." denotes not determined, typically because of no (sufficient)
blackening,
"+++" denotes an excellent blackening; no visual defects are noticeable all
over the spec-
lo imen,
"++" denotes still an acceptable blackening with only minor but still
acceptable visual
defects; the whole specimen is sufficiently black,
"+" denotes not anymore acceptable blackening with significant visual defects
and areas
of the zinc-iron layer,
"-" denotes no or almost no blackening, visual defects and large areas of the
zinc-iron
layer
In all examples according to the invention (i.e. examples 1-1, 1-2, 1-3, 1-4,
and 11-1) a
blackening of a zinc-iron alloy was obtained. Very good results were obtained
in exam-
ples 1-3 and 1-4, wherein example 1-4 provided these very good results even
over a corn-
paratively wide concentration range for DPS and chromium ions.
23
CA 03173505 2022- 9- 26
WO 2021/198429
PCT/EP2021/058640
In contrast, alternative compounds (comparative examples 01-03) provide no or
almost
no blackening of the zinc-iron alloy. Example C4 revealed that DTO was not
soluble at
all and, thus, could not be used for testing and is found unsuitable. If no
blackening was
obtained, corrosion resistance was not further tested because blackening was a
basic
requirement.
In further comparative examples, above test passivation compositions (in
particular ac-
cording to the present invention) were tested with said substrates but having
a zinc (no
zinc alloy) or a zinc-nickel alloy layer thereon. In each further example no
blackening
was obtained (i.e. evaluated as "-"). As a conclusion, the test passivation
compositions
utilized in the method of the present invention very specifically blacken zinc-
iron alloys.
24
CA 03173505 2022- 9- 26
