Note: Descriptions are shown in the official language in which they were submitted.
WO 2021/170707
PCT/EP2021/054657
One-step pretreatment method of metallic substrates for metal cold forming
The present invention relates to method for pretreatment of a metallic
substrate for a
subsequent metal cold forming process, said method comprising at least steps
(1)
and (2) and optionally step (3), namely providing at least one substrate
having at
least one surface at least partially made of at least one metal (1),
contacting the at
least one surface of the substrate provided in step (1) with an aqueous
lubricant
composition (A) having a pH value below 2.0 and comprising besides water
oxalate
anions (al), thiosulfate anions (a2), chloride anions (a3), at least one film-
forming
polymer (a4), which is a homopolymer and/or copolymer being prepared by
polymerization of at least one ethylenically unsaturated monomer, at least one
wax
(a5), and fluoride anions and/or bifluoride anions (a6), and optionally drying
the
coating film obtained after having performed step (2), a pretreated metallic
substrate
obtainable by the aforementioned inventive method, a method of cold forming of
a
metallic substrate including a step of subjecting the inventive pretreated
metallic
substrate to a cold forming process, an aqueous lubricant composition (A) as
defined
above and a master batch for preparing the aqueous composition (A).
Background of the invention
Cold forming of metallic workpieces is conventionally achieved by rolling such
as
thread rolling, drawing, in particular sliding drawing or deep-drawing,
pressing,
stretch forming and/or cold upsetting of the workpieces in order to transform
them
into articles having a desired shape. Cold forming usually takes place at
temperatures below the recrystallization temperature of the metallic material
of the
workpiece subjected to cold forming, such as at temperatures below and up to
450 C. No external heating source is used in the method of cold forming.
Instead,
any heat development or temperature increase in general is caused solely by
frictional forces between the metallic workpiece and the work tools used
during
forming and due to internal friction forces generated by material flow in the
workpiece. Cold forming usually results in an increased pressure, e.g. for
steel, for
example in the range of from 200 MPa to 1 GPa and sometimes even up to 2 GPa.
The temperature of the workpieces to be cold formed is initially at ambient
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temperature, i.e. at approximately 10 to 32 C. In case the workpieces are pre-
heated
prior to forming, for example to a temperature in the range from 650 to 1250
C, the
forming process is no longer a "cold forming" process, but rather a "semi-hot"
forming, a hot forming or a forging process.
If the metallic workpieces are cold formed to shaped articles with a
comparably only
low degree of deformation rather low forces for the cold forming process to
take
place are needed. For this purpose, conventionally non-reactive forming oils
are
applied to the workpieces. At higher degrees of deformation, however, usually
at
least one coating film such as a conversion coating film is applied onto the
workpieces prior to the cold forming process, which functions as separating
layer
between the workpiece and the tools used in order to prevent a cold welding
during
the cold forming. The conversion coating film used as separating layer in this
case
can also function as lubricant film if no additional coating film is applied
on top of it.
Such processes are, e.g., disclosed in DE 1 179 437, DE 1 196 467 and EP 0 233
503 Al:
DE 1 179 437 relates to a pretreatment of wires of iron or steel for a
subsequent cold
forming. An oxalate coating is applied for this purpose onto the wires. The
coating is
zo obtained by making use of a solution containing inter alia oxalic
acid and an alkenyl
phosphonic acid such as vinyl phosphonic acid in monomeric form.
DE 1 196 467 also relates to a pretreatment of metal substrates for a
subsequent
cold forming. An oxalate coating is applied for this purpose onto the wires.
The
coating is obtained my making use of a solution containing inter alia oxalic
acid and
polyvinyl phosphonic acid and/or a copolymer comprising vinyl phosphonic acid
in
the form of monomeric units.
EP 0 233 503 Al relates to a pretreatment method for facilitating a subsequent
cold
forming of stainless steel substrates. An oxalate coating is applied for this
purpose to
the substrate. The coating is obtained by making use of an aqueous solution
containing inter alia oxalic acid, fluoride and nitrate anions as well as a
water-soluble
polymer. The solution used is essentially free of any chloride anions and
preferably is
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free of thiosulfate anions as well as the presence of these anions is
undesired
according to EP 0 233 503 Al.
Alternatively, it is also possible and known in the prior art that not only
the conversion
coating film applied onto the metallic substrates can be solely used at the
same time
as lubricant film, but that rather an additional lubricant composition is
further applied
onto the conversion coating film to form a lubricant film on top of this film
in order to
(further) reduce the frictional resistance between the surface of the
workpiece and
the tools and to avoid the occurrence of cold welding. Different kinds of
conversion
coating films can be used for this purpose, in particular phosphate or oxalate
coating
films, which are applied from corresponding phosphate or oxalate containing
aqueous acidic compositions. In addition, different kinds of lubricant
compositions are
known in the prior art. For example, aqueous lubricant compositions such as
soaps
or soap solutions, e.g. based on alkali or earth alkali stearate, polymer
dispersions,
solid lubricants such as MoS2 and/or graphite, and/or oil-based lubricants can
be
used for forming corresponding lubricant films. Processes of this kind are,
e.g.,
disclosed in EP 0 232 929 Al, WO 94/16119 Al, WO 2009/095373 Al, WO
2009/095375 Al, WO 2009/095374 Al and JP S56 72090 A.
EP 0 232 929 Al relates to a two-step pretreatment method for facilitating a
subsequent cold forming of stainless steel substrates. In a first step an
oxalate
coating is applied onto the substrate by making use of a solution containing
inter alia
oxalic acid, hydroxyl ammonium sulfate as well as a water-soluble polymer. EP
0 232
929 Al teaches that the use of chloride and fluoride anions in the oxalating
solutions
should be avoided. Afterwards, in a second step a lubricant is applied onto
the
oxalate coating. Metal soaps are named as suitable lubricants in EP 0 232 929
Al.
WO 94/16119 Al discloses a liquid aqueous composition for forming a conversion
coating on metal surfaces in a first step for a subsequent cold forming
process. The
composition comprises an organic cationic polymer and may further comprise
oxalate
anions. In a second step a lubricating film can be applied onto the conversion
film by
making use of inter alia oil-based lubricants and/or soaps.
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WO 2009/095373 Al discloses a two-step pretreatment method for facilitating a
subsequent cold forming of metal substrates. In a first step a phosphate layer
on the
surface of the workpiece is formed by using an aqueous acidic phosphatizing
solution
containing Ca, Mg and/or K cations. In a second step, an aqueous alkaline
lubricant
composition containing organic polymers is applied.
WO 2009/095375 Al and WO 2009/095374 Al both disclose a method for the
preparation of metallic workpieces for cold forming. A lubricant coating layer
is
applied onto the metallic surface of the workpieces optionally bearing a
conversion
coating layer as separating layer by contacting the surface with an aqueous
lubricant
composition comprising at least one water-soluble, water-containing or water-
binding
oxide and/or silicate and an organic polymer in case of WO 2009/095375 Al or
by
contacting the surface with an aqueous lubricant composition comprising at
least two
waxes and an organic polymer in case of WO 2009/095374 Al.
JP S56 72090 A relates to a two-step pretreatment method for facilitating a
subsequent cold forming of steel substrates. An oxalate coating is applied for
this
purpose onto the substrates in a first step. The oxalate coating is obtained
by making
use of a solution containing inter alia oxalic acid and a water-soluble
organic titanium
compound as well as a polyvinyl pyrrolidone. In a second step, a lubricant is
applied
onto the oxalate coating. Metal soaps and solid lubricants are named as
suitable
lubricants in JP S56 72090 A.
There are, however, several drawbacks as far as the processes known in the
prior art
are concerned. First of all, both for ecologic reasons and in order to avoid
the
formation of undesired phosphorous-induced delta ferrite on the substrate, it
is
desired to not use phosphate coating films as conversion coating films such as
the
conversion coating films applied in the process disclosed in WO 2009/095373
Al, but
to rather only use phosphate-free systems. As far as the lubricant
compositions
known from the prior art are concerned, oil-based lubricant compositions in
general
lead to a higher VOC-content, since considerable amounts of oil can evaporate
during their use. In addition, oil-based lubricant systems may cause safety
issues, as
they are flammable and must be stored at flash points >150 C as hazardous
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materials. For these reasons, the use of oil-based lubricant formulations is
undesired.
Solid lubricants such as lubricants based on MoS2 and/or graphite are only
feasible
for heavy cold forming with extensive degrees of deformation and thus, such
lubricants are of limited use only. Furthermore, sulfide present in such
lubricant films
5 often has a detrimental effect in particular on stainless steel. The use
of aqueous
lubricant compositions is thus more desirable both for ecologic and economic
reasons than using solid and/or oil-based lubricants.
The conventional aqueous lubricant compositions of the prior art are, however,
usually alkaline compositions such as the (metal) soaps and soap solutions
disclosed
in EP 0 232 929 Al, WO 2009/095373 Al, WO 2009/095375 Al, WO 2009/095374
Al and JP S56 72090 A, which are for example based on alkali or earth alkali
stearate. Such alkaline lubricant composition baths often have only comparably
short
lifetimes and thus have to be renewed rather frequently. This, of course, is
disadvantageous both from an ecological view (higher amounts of water and of
the
constituents present in the compositions have to be used) and an economic view
(higher energy costs and changeover time). In contrast to these aqueous
alkaline
lubricant compositions used for providing a lubricant layer on the prior to be
applied
conversion coating layer, the compositions used for generating said
aforementioned
zo conversion coating layer are acidic compositions - as already mentioned
herein-
before. For performing such a two-steps pretreatment process usually two
different
open treatment baths are employed, into which the metallic workpieces are
dipped,
namely a first bath containing the aqueous acidic conversion coating
composition
and a second bath containing the aqueous alkaline lubricant composition. It is
essential, however, to include a rinsing and/or neutralization step between
these two
dipping steps in order to remove any excessive acid present onto the workpiece
after
having it removed from the first acidic bath and before having dipped it into
the
second alkaline bath in order to preserve the life of the two baths and in
particular of
the second bath as long as possible. It is, however, disadvantageous for
economic
and ecological reasons to have to necessarily carry out such a rinsing and/or
neutralization step. Simple mixing or combining the conventional aqueous
acidic
compositions such as phosphate and/or oxalate compositions for providing the
conversion coating layer with the conventional aqueous alkaline compositions
for
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providing the lubricant layer is not possible as these compositions are not
miscible
with each other and consequently an undesired phase separation would be
observed. Moreover, most of the known organic polymer dispersions used for
preparing conventional aqueous alkaline lubricant compositions are unstable in
an
acidic environment. Therefore, it is not always possible to simply use acidic
versions
of the known aqueous alkaline lubricant compositions.
EP 3 290 544 Al relates to an acidic water-based lubricating coating agent
having a
pH value of 2.0 to 6.5, which inter alia contains a chemical conversion
component
such as oxalic acid and a lubricating component such as a lipophilic
lubricating
component including an oil or a soap. The coating agent may further comprise a
water-based resin as a binder component. EP 3 290 544 Al further discloses a
one-
step pretreatment method of metal substrates for a subsequent cold forming.
JP S54 5847 A relates to a lubricant composition for facilitating the cold
forming of
metals. The lubricant contains oxalic acid and at least one constituent
selected from
water-soluble organic titanium compounds, vinyl pyrrolidone homopolymers and
vinyl
pyrrolidone copolymers. The lubricant composition may further contain a
lubricating
aid.
In addition, the conventional pretreatment processes for cold forming known in
the
prior art not always result in a sufficiently high coating weight of the
lubricant layer
formed on the workpiece or - if a separating layer such as a conversion
coating layer
is also present underneath the lubricant layer - in a sufficiently high
coating weight of
the lubricant layer and said separating layer combined. This may result in
only
insufficient adhesion properties of the layer(s) to the metallic substrate.
Further, this
can result in an ineffective separation of the tool from the workpiece after
and during
cold forming and in an only ineffective reduction of the coefficient of
friction or even in
an undesired cold welding, as an only insufficiently high amount of the
coating
layer(s) as measured by their coating weight remains present on the workpieces
during the cold forming process.
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Thus, there is a need for simplifying the conventional surface pretreatment
processes
for metal cold forming that make use of aqueous lubricant compositions both
for
economic reasons and for ecological reasons, in particular to provide an
improved
technology for the water-based pretreatment of metallic substrates for the
cold
forming process that requires fewer treatment steps and makes use of aqueous
acidic lubricant compositions. At the same time such a simplified pretreatment
must
still lead to sufficiently high coating weights of the coating layer(s) formed
on the
metallic substrates in order to both ensure a good adhesion to the substrate
and an
effective reduction of the coefficient of friction during cold forming and to
prevent cold
welding.
Problem
It has been therefore an object underlying the present invention to provide a
simplified surface pretreatment method for metal cold forming that make use of
an
aqueous lubricant composition both for economic reasons and for ecological
reasons, in particular to provide an improved technology for the water-based
pretreatment of metallic substrates for the cold forming process that requires
fewer
treatment steps and makes use of aqueous acidic lubricant compositions. At the
zo same time, however, such a simplified pretreatment must still lead to
sufficiently high
coating weights of the coating layer(s) formed on the metallic substrates in
order to
both ensure a good adhesion to the substrate and an effective reduction of the
coefficient of friction during cold forming and to prevent any cold welding.
Solution
This object has been solved by the subject-matter of the claims of the present
application as well as by the preferred embodiments thereof disclosed in this
specification, i.e. by the subject matter described herein.
A first subject-matter of the present invention is a method for pretreatment
of a
metallic substrate for a subsequent metal cold forming process, said method
comprising at least steps (1) and (2) and optionally step (3), namely
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(1) providing at least one substrate having at least one surface at
least partially
made of at least one metal,
(2) contacting the at least one surface of the substrate provided in step
(1) with an
aqueous lubricant composition (A) having a pH value below 2.0, wherein the
aqueous lubricant composition (A) comprises besides water
(al) oxalate anions,
(22) thiosulfate anions,
(a3) chloride anions,
(a4) at least one film-forming polymer, which is a homopolymer and/or
copolymer being prepared by polymerization of at least one ethylenically
unsaturated monomer,
(a5) at least one wax, which is different from constituent (a4), and
(a6) fluoride anions and/or bifluoride anions,
and
(3) optionally drying the coating film obtained after having performed step
(2).
A further subject-matter of the present invention is a pretreated metallic
substrate
obtainable by the inventive method.
A further subject-matter of the present invention is a method of cold forming
a
metallic substrate, characterized in that it comprises a step of subjecting
the inventive
pretreated metallic substrate to a cold forming process.
A further subject-matter of the present invention is an aqueous lubricant
composition
(A) as defined hereinbefore in connection with the inventive pretreatment
method.
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A further subject-matter of the present invention is a master batch to produce
the
inventive aqueous composition (A) by diluting the master batch with water and
if
applicable by adjusting the pH value.
It has been surprisingly found that all constituents present in aqueous
lubricant
composition (A) can be formulated as and into an acidic composition at a pH
value
below 2Ø It has been in particular surprisingly found that composition (A)
is stable
under such acidic conditions and that in particular the at least one film-
forming
polymer present in composition (A) is stable in such an acidic environment.
This
surprisingly has the advantage that composition (A) can be used in the
inventive
method both as lubricant composition and as a conversion coating composition
in a
single step only and that, consequently, it is not necessary to either apply
any
conversion coating composition or any lubricant coating composition in an
additional
step and that it is also no longer necessary to perform a rinsing step after
step (2).
Thus, the method can be simplified which has economic and ecologic advantages.
It has been further surprisingly found that baths containing the acidic
aqueous
lubricant composition (A) have comparably long lifetimes, in particular longer
lifetimes
that bath containing conventional alkaline aqueous lubricant compositions.
This, of
zo course, has economic and ecologic advantages.
In addition, it has been surprisingly found that the coating layer obtained
from
applying composition (A) adhered firmly on the substrate and showed good
lubricant
properties. Thus, the substrate pretreated by the inventive method can be
subsequently subjected to a metal cold forming process, in particular with
high speed
drawing. In the cold forming of substrates such as stainless steel it has been
found
that a coating layer obtained from application of composition (A) to the
substrate can
be efficiently subjected to a drawing step for the purpose of metal cold
forming.
Furthermore, it has been surprisingly found that the coated metallic
substrates
obtained by the inventive method bear a sufficiently high coating weight of
the
coating layer(s) formed on the metallic substrates obtained from applying
composition (A). The resulting coating layer(s) is/are homogenous, thick and
adhered
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firmly on the surface of the substrate. It has been found that such a high
coating
weight not only ensures a good adhesion to the substrate, but also an
effective
reduction of the coefficient of friction during cold forming and to prevent
any cold
welding. It has been surprisingly found that inter alia selecting a pH value
of
5 composition (A) below 2.0 results in formation of a comparably thick
conversion
coating layer, which in turn is advantageous for the subsequent metal cold
forming
process. This in particular applies to metal substrates, which are at least
partially
made of stainless steel. In case of higher pH values, the formed conversion
coating
layers are not sufficiently thick.
It has been further surprisingly found that the conversion coating layers
formed are
homogeneous, in particular when using metal substrates, which are at least
partially
made of stainless steel. It has been found that inter alia the presence of
fluoride
and/or bifluoride and chloride and thiosulfate anions have been found as being
advantageous in this regard.
Moreover, it has been surprisingly found that coated metal workpieces obtained
from
the inventive method have a good corrosion resistance. Further, it has been
found
that no stable foams have been formed during the inventive surface treatment
process.
In addition, it has been further found that the coating film obtained after
step (2) or
optionally after step (3) is a combined conversion and lubricant coating film.
Thus the
coating film obtained combines the properties of a conversion layer and a
lubricant
layer. The lubricant coating film can be present on top of the conversion
coating film.
Surprisingly, the combined layers can be separated and adjusted in part. For
example, a longer treatment time in step (2) results in a thicker conversion
layer, i.e.
in a higher layer thickness of the conversion layer, calculated as coating
weight,
whereas a higher concentration of the at least one wax (a5) and optionally of
the at
least one constituent (a4) leads to a thicker lubricant layer, i.e. a higher
layer
thickness of the lubricant layer, calculated as coating weight. In this way, a
combined
conversion and lubricant layer tailored to the respective conditions of cold
forming
can be produced.
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Detailed description of the invention
The term "comprising" in the sense of the present invention, in particular in
connection with the inventive method, the inventive composition (A) and the
master
batch used to prepare the composition (A), preferably has the meaning
"consisting
or. In this case, for example, with regard to the inventive composition (A),
in addition
to the mandatory constituents therein (constituents (al) to (a6) and water)
one or
more of the further optional components mentioned hereinafter may be contained
in
the composition. The same principle applies with respect to the composition
(A) used
in the inventive method and the master batch. All components/constituents can
be
present in each case in their preferred embodiments mentioned hereinafter. The
same applies to the further subject-matters of the present invention.
Inventive pretreatment method
The inventive method is a method for pretreatment of a metallic substrate for
a
subsequent metal cold forming process. The inventive method comprises at least
steps (1) and (2) and optionally additionally step (3). The inventive method
may
further comprise one or more additional steps.
Step (1)
In step (1) of the inventive method at least one substrate having at least one
surface
at least partially made of at least one metal is provided.
The surface of the substrate used is at least partially made of at least one
metal, i.e.
at least one region of said surface is made of at least one metal. The surface
can
consist of different regions comprising different metals. Preferably, the
overall surface
of the substrate is made of at least one metal. More preferably, the substrate
consists
of at least one metal.
Preferably, the at least one metal is selected from the group consisting of
aluminum,
aluminum alloys, zinc, steel including cold rolled steel, hot rolled steel,
galvanized
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steel (zinc plated steel) including hot-dip galvanized steel (hot zinc dipped
steel) or
electrolytically galvanized steel, stainless steel, steel alloys including
stainless steel
alloys, magnesium and/or zinc-magnesium alloys and/or zinc-iron alloys and
mixtures
thereof. In particular, the metal is ferrous and most preferably is steel.
Most preferred
is stainless steel and/or alloys thereof.
Preferably, the at least one surface of the substrate is at least partially
made of
stainless steel, more preferably the substrate as such is made of stainless
steel.
As substrates e.g. strips, sheets, slugs, wires, wire coils, more complicated
shaped
parts, sleeves, profiles such as hollow or solid profiles, tubes, discs,
discs, rods, bars
or cylinders can be used.
Optional steps (la) and (I b)
The surfaces to be substrates provided in step (1) may be cleaned by means of
an
acidic, alkaline or pH-neutral cleaning composition and/or etched before
treatment
with the acidic aqueous composition (A) in step (2) as it will be outlined
hereinafter:
Prior to step (2) of the inventive method one or more of the following
optional steps
can be performed, preferably in this order:
Step (la): cleaning, preferably by making use of an alkaline aqueous
cleaning
composition, and optionally subsequently rinsing the surface of the
substrate provided in step (1), and
Step (1 b): subjecting the surface of the substrate to acidic pickling,
i.e., etching,
and subsequently rinsing the surface of the substrate.
Preferably, both steps (la) and (1 b) are performed. Rinsing included in step
(la) is
preferably performed with deionized water or tap water. Preferably, the acidic
pickling
is performed by making use of hydrochloric acid, hydrofluoric acid, sulphuric
acid,
nitric acid and/or phosphoric acid.
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Most preferably, at least step (lb) is performed, in particular by making use
of
hydrofluoric acid and/or nitric acid for pickling, in particular when the
substrate is at
least partially made of stainless steel.
Step (2)
In step (2) of the inventive method the at least one surface of the substrate
provided
in step (1) is contacted with, preferably dipped into, an aqueous lubricant
composition
(A) having a pH value below 2.0, wherein the aqueous lubricant composition (A)
comprises besides water oxalate anions as constituent (al), thiosulfate anions
as
constituent (a2), chloride anions as constituent (a3), at least one film-
forming polymer
as constituent (a4), which is a homopolymer and/or copolymer being prepared by
polymerization of at least one ethylenically unsaturated monomer, at least one
wax
as constituent (a5) and fluoride anions and/or bifluoride anions as
constituent (a6).
The treatment procedure according to step (2), i.e. the "contacting", can, for
example,
include a spray coating and/or a dip coating procedure. The composition (A)
can also
be applied by flooding the surface or by roll coating or even manually by
wiping or
brushing. However, dipping is preferred. In this case, the substrate used is
dipped
into a bath containing the composition (A).
Preferably, contacting step (2) is performed by at least partially dipping the
substrate
into a bath containing the aqueous lubricant composition (A) having a bath
temperature in the range of from 20 to 95 C, preferably of from 30 to 90 C,
in
particular of from 45 to 85 C, most preferably of from 50 to 75 C.
The treatment time, i.e. the period of time the surface is contacted with the
aqueous
composition (A) used in step (2) is preferably from 15 seconds to 20 minutes,
more
preferably from 30 seconds to 10 minutes, and most preferably 45 seconds to 5
minutes, as for example 1 to 4 minutes.
Preferably, no rinsing step is performed after having carried out step (2).
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Composition (A)
The term "aqueous" with respect to composition (A) in the sense of the present
invention preferably means that the composition (A) is a composition
containing at
least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 70 wt.-
% in
particular at least 80 wt.-%, most preferably at least 90 wt.-% or 95 wt.-% or
98 wt.-%
or 99 wt.-% or even 100 wt.-% of water, based on its total content of organic
and
inorganic solvents including water. Thus, the composition (A) may contain at
least
one organic solvent besides water - however, in an amount significantly lower
than
the amount of water present. Preferably, composition (A) is free of organic
solvents.
Thus, preferably water is the only solvent/diluent present.
Preferably, composition (A) contains water in an amount of at least 50 wt.-%,
more
preferably of at least 60 wt.-%, even more preferably of at least 70 wt.-% and
still
more preferably of at least 80 wt.-%, in each case based on the total weight
of
composition (A).
Preferably, composition (A) has a pH value below 1.9, preferably below 1.7, in
particular a pH value in a range of from 0.1 to 1.5, most preferably in a
range of from
0.5 to 1.5.
Preferably, composition (A) is present in the form of a solution or
dispersion, in
particular in the form of a solution, preferably at a temperature of at least
40 C, in
particular at least 50 C.
Preferably, composition (A) is free of phosphate anions. This means that at
least on
purpose no phosphate is added to composition (A). In case of subsequent heat
treatment of sensitive components such as the hardening and tempering of
screws
otherwise phosphorus-induced delta-ferrite may be formed, which may lead to
disadvantageous material properties.
Preferably, composition (A) is free of silicone, i.e. free of siloxanes and/or
polysiloxanes. This means that at least on purpose no silicone is added to
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composition (A). The presence of silicones may be disadvantageous when
applying
coating materials such as paint to the substrate after having performed a
subsequent
cold forming.
5 Preferably, composition (A) has a solid content in the range of from 0.1
to 25 wt.-%,
more preferably in the range of from 0.2 to 20 wt.-%, even more preferably in
the
range of from 0.3 to 15 wt.-%, still more preferably in the range of from 0.4
to 12
wt.-%, in each case based on the total weight of composition (A).
10 The sum of all components/constituents present in composition (A) adds up
to 100
wt.-%.
Since composition (A) comprises (al) oxalate anions it represents an oxalating
composition, which is suitable of forming a conversion coating on the surface
of a
15 substrate. Since composition (A) also comprises (a5) at least one wax
and at least
one film-forming polymer (a4) it also represents a lubricant composition,
which is
suitable of forming a lubricating coating on the surface of a substrate.
Constituents (al), (a2) and (a3)
Preferably,
the oxalate anions (al) are present in the composition (A) in an amount in the
range
of from 2 to 500 g/I, more preferably of from 5 to 100 g/I, in particular of
from 10 to 50
g/I of oxalic acid, calculated in each case as oxalic acid dihydrate, and/or
the thiosulfate anions (a2) are present in the composition (A) in an amount in
the
range of from 0.01 to 25 g/I, more preferably of from 0.5 to 10 g/I, in
particular of from
1.0 to 5.0 g/I, calculated in each case as sodium thiosulfate, and/or
the chloride anions (a3) are present in the composition (A) in an amount in
the range
of from 0.1 to 25 g/I, more preferably of from 0.5 to 10 g/I, in particular of
from 1.0 to
5.0 g/I, calculated in each case as sodium chloride.
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In the sense of the present invention, "oxalic acid" also means the single and
double
deprotonated form of oxalic acid. Likewise, in the sense of the present
invention,
"oxalate" also means the single and double protonated form thereof, the double
protonated from being oxalic acid. Preferably, oxalic acid dihydrate is used,
as is it
cheap and less hygroscopic.
If, in connection with weight concentrations (e.g., gip, the term "calculated
as X" is
used, where X is a specific, specified chemical compound, this is to be
understood as
follows: If an alternative chemical compound (not X) it should be used in such
a
molar concentration as calculated for X, taking into account its molar mass,
from the
specific weight concentration (e.g. g/1) indicated in each case.
The content of cations and anions mentioned herein with respect to composition
(A)
can be monitored and determined by the means of ICP-OES (optical emission
spectroscopy with inductively coupled plasma). Said method is described
hereinafter
in detail. The content of free fluoride anions is, however, determined by
means of a
fluoride electrode.
zo Constituent (a4)
Composition (A) comprises at least one film-forming polymer, which is a
homopolymer and/or copolymer being prepared by polymerization of at least one
ethylenically unsaturated monomer as constituent (a4), which is different from
constituent (a5).
Preferably, the at least one film-forming polymer is water-soluble or water-
dispersible,
more preferably water-soluble. Preferably, the at least one film-forming
polymer is
soluble or dispersible, more preferably soluble, in composition (A).
Preferably, the at least one film-forming polymer (a4) is a homopolymer and/or
copolymer, said homopolymer and/or copolymer being prepared at least from at
least
one monomer bearing at least one vinyl group, preferably selected from the
group
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consisting of vinyl amine, vinyl alcohol, vinyl formamide, vinyl pyrrolidone,
vinyl
caprolactam, vinyl acetate and vinyl imidazole, preferably from at least one
monomer
selected from the group consisting of vinyl pyrrolidone and vinyl acetate, in
particular
from at least vinyl pyrrolidone. Exemplary polymers are Sokalan K 17P, from
BASF
SE, Germany and Lupamine 9030 from BASF SE, Germany.
Most preferred are polyvinyl pyrrolidone homopolymers and copolymers of vinyl
pyrrolidone and vinyl acetate.
In case the at least one film-forming polymer (a4) is a copolymer at least one
further
monomer bearing at least one ethylenically unsaturated group and being
different
from the above defined monomers can be used for preparing constituent (a4).
Preferably, such further monomers bears at least one (meth)acrylic group.
(Meth)acrylic groups include e.g. (meth)acrylate groups and (meth)acrylic acid
groups. The further monomer can be an ionomer. The further monomer can also be
ethylene, propylene, butylene, styrene etc. The term "(meth)acryl" means
"acryl"
and/or "methacryl". Similarly, "(meth)acrylate" means acrylate and/or
methacrylate.
Preferably, the at least one film-forming polymer (a4) has a weight average
molecular
zo weight (Mõ) in the range of from 1 000 to 100 000 g/mol, more preferably
of from 3
000 to 75 000 g/mol, even more preferably of from 5 000 to 50 000.
Determination of
M, is performed by gel permeation chromatography (GPC).
Preferably, the at least one film-forming polymer (a4) is present in the
composition
(A) in an amount in the range of from 0.05 to 20 wt.-%, more preferably in the
range
of from 0.10 to 15 wt.-%, even more preferably in the range of from 0.15 to 10
wt.-%,
still more preferably in the range of from 0.20 to 7.5 wt.-%, in particular of
from 0.25
to 5.0 wt.-%, in each case based on the total weight of the composition (A).
Constituent (a5)
Composition (A) comprises at least one wax as constituent (a5), which is
different
from constituent (a4).
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As the term "wax "already implies, the at least one wax is a solid substance
at room
temperature (23 C). A person skilled in the art is familiar with the term
"wax". Said
term is e.g. defined in by the German Society for Fat Science (DGF) within DGF
standard method M-I 1 (75) (2015). Preferably, the at least one wax used as
constituent (a5) satisfies this definition of a wax. Waxes according to this
definition
can be kneaded at 20 C, have a firm (solid) to brittle hardness, have a
coarse to fine
crystalline structure, are translucent to opaque in color but not glassy or
glass-like,
melt without decomposition at temperatures above 40 C, are slightly liquid
above
their melting point and have a low viscosity above their melting point, have a
highly
temperature-dependent consistency and solubility, and can be polished under
light
pressure. Preferably and according to the definition of the DGF (DGF standard
method M-I 1 (75)), a substance is not a wax if it does not meet more than one
of the
above properties.
Preferably, the at least one wax (a5) is water-soluble or water-dispersible,
more
preferably water-dispersible. Preferably, the at least one wax (a5) is soluble
or
dispersible in composition (A).
zo Preferably, composition (A) is obtainable by using an aqueous dispersion
or solution
of the at least one wax (a5) for its preparation.
Preferably, the at least one wax (25) has a melting point in the range of from
40 C to
170 C, more preferably in the range of from 50 C to 160 C, especially
preferred in
the range of from 50 C to 140 C.
Composition (A) preferably comprises more than one wax as constituent (a5).
Preferably, composition (A) comprises at least two, more preferably at least
three
different waxes as constituents (a5). Preferably, the at least two or at least
three
different waxes differ from each other at least in their melting temperature
(melting
point). Preferably, the difference between melting points of at least two of
the waxes
is at least 20 C.
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Preferably, the at least one wax (a5) is present in the composition (A) in an
amount in
the range of from 0.1 to 20 wt.-%, more preferably in the range of from 0.5 to
15 wt.-
%, even more preferably in the range of from 0.75 to 12.5 wt.-%, still more
preferably
in the range of from 1.0 to 10.0 wt.-%, in particular of from 1.5 to 9.0 wt.-
%, most
preferably in the range of from 2.0 to 7.5 wt.-%, in each case based on the
total
weight of the composition (A).
Preferably, the at least one wax (a5) is selected from the group consisting of
cationic
waxes, cationically stabilized waxes and non-ionic waxes. A "cationically
stabilized
wax" is preferably a wax that is stabilized by cationic groups in acidic
medium such
as in the composition (A) or is stabilized by at least one cationic
surfactant.
Preferably, the at least one wax (a5) is stabilized by at least one
emulsifier. For
example, the at least one wax (a5) can be stabilized by a cationic emulsifier
(cationically stabilized) or can be stabilized by a non-ionic emulsifier (non-
ionically
stabilized). Examples of cationic emulsifiers are alkoxylated such as
ethoxylated
stearyl amine and/or polyalkoxylated such as polyethoxylated tallow amine.
Examples of non-ionic emulsifiers are alcohols including for example
diethylaminoethanol.
Preferably, the at least one wax (a5) is selected from the group consisting of
polyolefin waxes (including polyethylene waxes, in particular HDPE (high
density
polyethylene) and/or polypropylene waxes, natural waxes including plant and
animal
waxes such as montan waxes, bees waxes and/or carnauba waxes, paraffin waxes
(petroleum derived waxes) and mixtures thereof.
In this context, the term "olefin" mainly refers to alkenes typical of
polyolefins,
preferably alkenes with 2 to 8, especially alkenes with 2 to 6 and especially
alkenes
with 2 to 4 carbon atoms, especially those with a terminal double bond. In the
context
of this invention, preferred representatives are ethylene, propylene, 1-butene
and
isobutene. Ethylene and propylene are particularly preferred olefin monomers
in the
context of this invention. The term "polyolefin" is generally understood to
mean
homopolymers of a single type of olefin monomer (e.g. ethylene homopolymers)
or
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copolymers of at least two olefin monomers (e.g. polymers of mixtures
comprising or
consisting of ethylene, propylene, 1-butene and/or isobutene). Polyolefins
thus
contain one or more types of olefin monomers and are therefore homopolymers or
copolymers. However, they may also additionally contain one or more
ethylenically
5 unsaturated monomers other than olefin monomers, in particular
ethylenically
unsaturated monomers bearing carboxylic acid groups, polymerized or grafted.
If
different ethylenically unsaturated monomers with carboxyl groups or
carboxylic acid
anhydride groups are used for the purpose of polymerization or grafting of the
olefin
monomers, this is done in an amount such that the polyolefin wax as
constituent (a5)
10 containing carboxyl groups has an acid number in the range from 3 to 50,
preferably
from 5 to 40, particularly preferably from 8 to 35, very particularly
preferably from 10
to 25 and particularly preferably from 13 to 20 mg KOH/g. Polyolefin waxes are
preferably selected from the group consisting of oxidized polyethylene waxes,
oxidized polypropylene waxes, oxidized poly(ethylene-co-propylene) waxes and
15 oxidized ethylene-olefin copolymers, ethylene-(meth)acrylic acid
copolymers and
polymers of ethylene and/or propylene other than the abovementioned
copolymers,
which have been grafted, for example, with maleic anhydride (converted into
the
hydrolyzed form, and carrying free COOH groups). Of course, other
ethylenically
unsaturated acids such as acrylic acid can also be used for grafting.
The paraffin waxes used are preferably microcrystalline.
Exemplary waxes that are commercially available and that can be used are, e.g.
Aquacer 1041 from BYK Chemie, Germany, Aquacer 561 from BYK Chemie,
Aquacer 517 from BYK Chemie, WCikonile 0-33a from MCinzing Chemie and
Licowaxe KST from Clariant, Germany,
Constituent (a6)
Composition (A) further comprises at least one of fluoride anions and
bifluoride
anions as constituent (a6). Preferably, composition (A) comprises fluoride
anions as
constituent (a6), more preferably in combination with bifluoride anions.
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Preferably, fluoride anions and/or bifluoride anions are present in the
composition (A)
in each case independently of one another in an amount in the range of from
0.01 to
25 g/1, more preferably of from 0.5 to 10 g/1, in particular of from 1.0 to
5.0 g/1,
calculated as sodium fluoride in case of fluoride anions and as sodium
bifluoride in
case of bifluoride anions.
Optional further constituents
Optionally, composition (A) may comprise at least one furthers constituent
(a7). Said
at least one further constituent (a7) is preferably selected from the group
consisting
of thickeners, pigments, fillers, corrosion inhibitors, defoamers, surfactants
and
mixtures thereof. Constituent(s) (a7) may be present in amount of from 0.01 to
10
wt.-% in composition (A), based on the total weight of composition (A).
Examples of defoamers are polymer-based, silicone-free defoamers. If a
defoamer is
present, which is preferred, the amount of the at least one defoamer in
composition
(A) is preferably in a range of from 0.01 to 3 wt.-%, based on the total
weight of
composition (A).
Examples of corrosion inhibitors are morpholine, benzylamine, butindiol,
diisopropylamine nitrite, morpholine nitrite, 2-(2-heptadec-8-eny1-2-
imidazolin-1-
yl)ethanol, dicyclohexylamine nitrite, cyclohexylamine benzoate,
dicyclohexylamine
caprylate, guanadine chromate, hexamethyleneimine benzoate, dicyclohexylamine
benzoate, ethylaniline, mercaptobenzotriazole, pyridine, rosin amine,
phenylacridine,
hexamethylentetramin, nonylphenoxyacetic acid, succinic acid semi-ester and
butindiol. If a corrosion inhibitor is present the amount of the at least one
corrosion
inhibitor in composition (A) is preferably in a range of from 0.01 to 3 wt.-%,
based on
the total weight of composition (A).
Examples of thickeners are polysaccharide, polysiloxane, polyvinlyamide,
polyacrylamide and polyglycol.
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Examples of pigments and fillers are boron nitride, graphite and molybdenum
sulfide.
However, as in particular graphite and molybdenum sulfide are solid lubricants
and
their use is related to disadvantages as outlined in the introductory part,
preferably no
such pigments, in particular neither graphite nor molybdenum sulfide, is
present in
composition (A).
Examples of surfactants are fatty alcohol alkoxylates and especially fatty
alcohol
ethoxylates.
Optional step (3)
Optional step (3) of the inventive method is a step, wherein the coating film
obtained
after step (2) is optionally dried.
The drying step (3) may be preferably performed, e.g. at a temperature in the
range
of 15 C to 100 C, more preferably at a temperature in the range of 18 C to 95
C, in
particular at a temperature in the range of 20 C to 90 C.
Inventive pretreated substrate
A further subject-matter of the present invention is a pretreated metallic
substrate
obtainable by the inventive method.
All preferred embodiments described above herein in connection with the
inventive
method of pretreatment are also preferred embodiments of pretreated substrate.
The
same applies, of course, to the embodiments of the substrate as such as
outlined
hereinbefore in connection with step (1) of the inventive method.
The coating film obtained after step (2) or optionally after step (3) is a
combined
conversion and lubricant coating film. Thus, the coating film obtained
combines the
properties of a conversion layer and a lubricant layer.
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Preferably, the pretreated metallic substrate obtainable by the inventive
method
contains a conversion coating film obtained by performing step (2) and further
contains a lubricant coating film on top of said conversion coating film also
obtained
by performing step (2). However, it is also possible that the coating film
obtained after
step (2) or optionally after step (3) is chemically heterogeneous.
Preferably, the coating film present on the surface of the substrate after
having
performed step (2) and optionally step (3) has a coating weight in a range of
from 1.0
to 40.0 g/m2, preferably in a range of from 5.0 to 35.0 g/m2, more preferably
in a
range of from 10.0 to 30.0 g/m2. The method for determining the coating weight
is
disclosed in the example section.
Inventive cold formind method
A further subject-matter of the present invention is a method of cold forming
a
metallic substrate, characterized in that it comprises a step of subjecting
the inventive
pretreated metallic substrate according to a cold forming process, preferably
by
drawing.
zo All possible cold forming processes known in the prior art can be
carried out, in
particular rolling such as thread rolling or beating, e.g. for nut or bolt
blanks,
drawing, in particular sliding drawing (tensile compression forming), e.g. of
welded or
seamless tubes, hollow sections, solid sections, wires or rods, e.g. during
wire
drawing or tube drawing, or deep-drawing, e.g. of strips or sheet metal,
pressing
such as cold extrusion (pressure forming), e.g. of hollow or solid bodies,
stretch
forming (forming to gauge block/final size) and/or cold upsetting, e.g. from
wire
sections to fasteners such as nuts.
The most common shaped bodies to be formed from the inventive pretreated
metallic
substrates are strips, sheets, slugs, wires, wire coils, more complicated
shaped parts,
sleeves, profiles such as hollow or solid profiles, tubes, discs, discs, rods,
bars or
cylinders.
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Preferably, the cold-formed substrate obtained after the cold forming process
still
bears at least part of the coating film obtained after having performed step
(2) and
optionally step (3): Due to the amount of the coating weight of the coating
film
obtained after step (2) or optionally step (3) present on the pretreated
substrate, said
coating film "survives" conventional cold forming processes. For example, this
leaves
at least 10 %, preferably at least 15 %, particularly preferred at least 20 %
of the
coating weight on a pretreated and cold formed substrate after cold forming,
in
particular if the substrate has undergone a drawing.
However, the coating film may be removed from the cold formed substrate, e.g.,
by
using an aqueous cleaning composition. Thus, after the cold forming process,
the
obtained substrate is preferably cleaned, in order to remove the conversion
and
lubricant coating film from the substrate, e.g. by means of alkaline cleaners,
acids or
pickling agents.
Inventive composition (A)
A further subject-matter of the present invention is an aqueous lubricant
composition
(A) as defined hereinbefore in connection with the inventive pretreatment
method.
All preferred embodiments described above herein in connection with the
inventive
method and the composition (A) used in step (2) thereof and the constituents
contained therein are also preferred embodiments of the inventive composition
(A).
Inventive master batch
A further subject-matter of the present invention is a master batch to produce
the
inventive aqueous composition (A) by diluting the master batch with water and
if
applicable by adjusting the pH value.
All preferred embodiments described above herein in connection with the
inventive
methods and the inventive composition (A) and the constituents contained
therein
are also preferred embodiments of inventive master batch.
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If a master batch is used to produce the aqueous composition (A) according to
the
present invention, the master batch typically contains the constituents of the
aqueous
composition (A) to be produced in the desired proportions, but at a higher
5 concentration. Such master batch is preferably diluted with water to the
concentrations of constituents as disclosed above to form the aqueous
composition
(A). If necessary, the pH value of the aqueous composition (A) may be adjusted
after
dilution of the master batch.
10 Of course, it is also possible to further add any of the optional
components to the
water, wherein the master batch is diluted or to add any of the optional
components
after diluting the master batch with water. It is however preferred that the
master
batch already contains all necessary components.
15 Preferably, the master batch is diluted with water and/or an aqueous
solution in the
ratio of 1:5,000 to 1:5, more preferred 1:1,000 to 1:10, most preferred in the
ratio of
1:300 to 1:10 and even more preferred 1:150 to 1:50 to produce composition
(A).
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METHODS
1. Total acid (TA)
The total acid (TA) is the sum of the divalent cations present as well as free
and
bound oxalic acids (the latter being oxalates). It is determined by the
consumption of
0.1 M NaOH using 10 to 15 drops of phenolphthalein water solution as test
indicator.
For this, 10 ml of the composition are pipetted into a suitable vessel, for
example a
300 ml Erlenmeyer flask and diluted with 50 ml of deionized water. It is then
titrated
with 0.1 M NaOH until a color change to red has taken place. The consumption
in ml
per 10 ml of the diluted composition corresponds to the total acid score (TA).
2. Solid content
The non-volatile fraction (solids or solid content) is determined in
accordance with
DIN EN ISO 3251 (date: June 2019). This involves weighing out 1 g of sample
into
an aluminum dish which has been dried beforehand and drying the dish with
sample
in a drying cabinet at 130 C for 60 minutes, cooling it in a desiccator, and
then
reweighing. The residue, relative to the total amount of sample employed,
corresponds to the nonvolatile fraction.
3. ICP-OES
The amounts of certain elements in a sample under analysis is determined using
inductively coupled plasma atomic emission spectrometry (ICP-OES) according to
DIN EN ISO 11885 (date: September 1,2009).
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EXAMPLES
The following examples further illustrate the invention, but are not to be
construed as
limiting its scope.
1. Inventive lubricant composition
Inventive example II
An acid stable aqueous polymeric lubricant composition 11 was prepared in a
high-
speed mixer with stirring. The composition of this lubricant is given in Table
1.
Table 1: Composition of lubricant example 11
Constituent Amount [wt.-`36]
Polymer 1 0.73
Aqueous wax dispersion 1 (40 wt.-% solids) 6.63
Aqueous wax dispersion 2 (40 wt.-% solids) 1.60
Wax 3 0.55
Defoamer 0.18
Oxalic acid dihydrate 4.93
Sodium chloride 1.95
Sodium hydrogen fluoride 0.84
Titanium dioxide 0.14
Sodium thiosulfate 0.07
Sodium fluoride 0.01
Deionized water 82.37
100.0
Polymer 1 is a polyvinyl pyrrolidone homopolymer. A commercial product
available
from BASF SE has been used.
zo Aqueous wax dispersion 1 contains a polypropylene wax, which is
commercially
available from BYK Chemie. Aqueous wax dispersion 2 contains a
microcrystalline
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wax, which is commercially available from Michelman. Wax 3 is a montan wax,
which
is dispersible in aqueous medium.
The composition has a pH value below 2Ø
Comparative example Cl
The commercially available product Gardobonde AS 4200, which is an oxalating
treatment solution containing oxalic acid, chloride and/or fluoride anions,
and sodium
thiosulfate, has been used as comparative composition Cl.
Comparative examples C2, C3, C4 and C5
A number of further comparative compositions, namely compositions C2, C3, C4
and
C5, were prepared. Composition C2 was identical to lubricant example 11, but
no
sodium chloride was used for its preparation. Composition C3 was identical to
lubricant example 11, but no sodium thiosulfate was used for its preparation.
Composition C4 was identical to lubricant example 11, but no sodium chloride
and no
sodium thiosulfate were used for its preparation. Composition C5 was identical
to
zo lubricant example 11, but its pH was adjusted to be >3.
2. Inventive method
2.1 Oxalating treatment and lubricating treatment in a single step by making
use of
inventive composition 11
As metal workpiece the following substrate 51 was used:
Sheet made of 1.0 mm stainless steel (material-No.: 1.4571).
The workpiece was dipped in a cleaning bath with a 50 g/L aqueous cleaning
solution
of Gardocleane 351 available from Chemetall GmbH at 90 C for 10 min. and then
rinsed by cold tap water for 1 min. Afterwards, the surface purified workpiece
was
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then pickled by using an aqueous solution containing 20 wt.-% nitric acid and
4 wt.-%
hydrofluoric acid at room temperature (23 C) for 1 min. and subsequently
rinsed by
cold tap water for 1 min.
Then, in a single step, the workpiece was dipped into a bath containing
lubricant
example 11 at 65 C for 10 min.
Finally, the coated workpiece obtained was dried with air at 85 C.
No solid foams were formed during this process. The resulting sludge in the
reaction
bath of 11 was powdery and similar to the sludge formed in an oxalating bath
containing Gardobonde AS 4200 from Chemetall GmbH (composition Cl, cf. item
2.2) and could be easily removed from the reaction bath.
2.2 Treatment with commercially available oxalating solution Cl in a single
step
Substrate S1 as described hereinbefore was used as workpiece.
The workpiece was treated as follows:
The workpiece was dipped in a cleaning bath with a 50 g/L aqueous cleaning
solution
of Gardocleane 351 available from Chemetall GmbH at 90 C for 10 min. and then
rinsed by cold tap water for 1 min. Afterwards, the surface purified workpiece
was
then pickled by using an aqueous solution containing 20 wt.-% nitric acid and
4 wt.-%
hydrofluoric acid at room temperature (23 C) for 1 min. and subsequently
rinsed by
cold tap water for 1 min.
Then, in a single step, the workpiece was dipped into a bath containing
Gardobonde
AS 4200 at 65 C for 10 min.
Finally, the coated workpiece obtained was dried with air at 85 C.
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2.3 Treatment by making use of comparative compositions C2, C3, C4 and C5
A substrate Si was treated in the same manner as described hereinbefore in
item
2.1 except in that one of compositions C2, C3, C4 and C5 was used instead of
11.
5
3. Properties of the coated substrates
3.1 Coated substrate obtained from the 1-step-process as outlined in item 2./
The resulting coating layer of the coated workpiece is homogenous, thick and
adhered firmly on the treated surface of the workpiece. The top coating layer
formed
by the method is a polymer lubricant layer and the bottom coating layer formed
is an
oxalate coating layer. Coating layers properties are observed using SEM
technology.
The bottom oxalate coating layer on the stainless-steel surface was proven to
be a
sufficiently closed coating layer on the surface of the metal workpiece.
The coating weights on the substrate were determined using the following test
method:
The coated workpiece was weighted. Then, the polymer lubricant coating layer
was
washed with boiling xylene in order to detach it and subsequently with boiling
water.
The workpiece was then dried and weighted. The oxalate coating layer was
washed
with an alkaline solution containing NaOH, triethyl amine and EDTA (PL 83 from
Chemetall GmbH) in order to detach it. Finally, the workpiece was rinsed with
water,
dried and weighted once again.
The resulting coating weights are listed in Table 2.
Table 2: Coating weights on substrate surfaces (substrate S1 ) in g/m2
Substrate Polymer lubricant coating Oxalate coating weight
Total [g/m2]
weight [g/m2] rgini2)1
Si 7.5 10.6
18.1
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The coated substrate shows very good lubricating properties and is very
suitable for
cold forming, even with high drawing speeds, and for cold extrusion. The
coating
layers adhere firmly on the metal surface of the substrates, even after cold
forming.
After metal cold forming, the remaining coating adhered still firmly on the
metal
surface and the remaining coating layer can be washed using aqueous alkalic
cleaner, e.g. Gardocleae S 5171 with Gardobonde Additive H 7375 from Chemetall
GmbH, or aqueous acidic cleaner, e.g. Gardobone Additive H 7132 with
Gardobond Additive H 7390 from Chemetall GmbH.
3.2 Coated substrate obtained from the 1-step-process as outlined in item 2.2
The resulting oxalate coating layer on stainless steel is closed and
homogenous.
The coating weight on the substrate was determined using the following test
method:
The oxalated workpiece was weighted. The oxalate coating layer was washed with
an alkaline solution containing NaOH, triethyl amine and EDTA (PL 83 from
Chemetall GmbH) in order to detach it. Finally, the workpiece was rinsed with
water,
zo dried and weighted once again. The resulting oxalate coating weight is
10 g/m2.
The coated substrate shows no lubricating properties at all and is thus as
such not
suitable for cold forming. For this the oxalate coated stainless-steel
substrate has to
be subjected to lubrication in an additional process step.
3.3 Coated substrates obtained from the 1-step-processes as outlined in item
2.3
In case of having used comparative composition C2 the resulting coating layer
of the
coated workpiece was found to have an inferior homogeneity compared to the
coated
workpiece obtained from having used composition 11. An even inferior
homogeneity
was observed when comparative composition C3 was used. In case of having used
comparative examples C4 and C5 no coating layer at all was found to have been
formed on the substrate.
CA 03168959 2022- 8- 22
