U.S. patent application number 12/135710 was filed with the patent office on 2008-12-11 for wet on wet method and chrome-free acidic solution for the corrosion control treatment of steel surfaces.
This patent application is currently assigned to Henkel AG & Co. KGaA. Invention is credited to Sophie Cornen, Franz-Adolf Czika, Patrick Droniou, Stefan Frey, Silvia Hohagen, Jens Kromer, Peter Kuhn.
Application Number | 20080302448 12/135710 |
Document ID | / |
Family ID | 37836909 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080302448 |
Kind Code |
A1 |
Frey; Stefan ; et
al. |
December 11, 2008 |
WET ON WET METHOD AND CHROME-FREE ACIDIC SOLUTION FOR THE CORROSION
CONTROL TREATMENT OF STEEL SURFACES
Abstract
A process for anticorrosion treatment of bare metal surfaces
comprising steel surfaces, wherein the bare metal surfaces are
contacted with an acidic aqueous solution of a fluoro complex of at
least one element M selected from the group B, Si, Ti, Zr and Hf,
at least one further component which is selected from among: a
buffer system for the pH range from 2.5 to 5.5, nitrate ions,
copper ions, silver ions, vanadium or vanadate ions, bismuth ions,
magnesium ions, zinc ions, manganese ions, cobalt ions, nickel
ions, tin ions, aromatic carboxylic acids with at least two groups
containing donor atoms, or derivatives of such carboxylic acids,
and silica particles with an average particle size of below 1
.mu.m; and contains no more than 1 mg/l of an organic polymer with
allylamine or vinylamine monomers; the metal surfaces are then
rinsed with water and thereafter are coated with a cathodically
depositable electro-dipcoating.
Inventors: |
Frey; Stefan; (Deidesheim
Deutschland, DE) ; Kromer; Jens; (Duesseldorf,
DE) ; Hohagen; Silvia; (Wuppertal, DE) ;
Cornen; Sophie; (Duesseldorf, DE) ; Droniou;
Patrick; (Colombes, FR) ; Kuhn; Peter;
(Hilden, DE) ; Czika; Franz-Adolf; (Neuss,
DE) |
Correspondence
Address: |
HENKEL CORPORATION
1001 TROUT BROOK CROSSING
ROCKY HILL
CT
06067
US
|
Assignee: |
Henkel AG & Co. KGaA
Duesseldorf
DE
|
Family ID: |
37836909 |
Appl. No.: |
12/135710 |
Filed: |
June 9, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2006/011696 |
Dec 6, 2006 |
|
|
|
12135710 |
|
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Current U.S.
Class: |
148/274 ;
148/22 |
Current CPC
Class: |
C09D 5/44 20130101; C23C
22/83 20130101; C09D 5/4488 20130101; C23C 22/368 20130101; B05D
7/14 20130101; C23C 22/44 20130101; B05D 1/007 20130101; B05D 7/51
20130101; C25D 5/36 20130101; C25D 13/20 20130101; C23C 22/34
20130101; C23C 22/73 20130101 |
Class at
Publication: |
148/274 ;
148/22 |
International
Class: |
C23C 22/34 20060101
C23C022/34; C23C 30/00 20060101 C23C030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2005 |
DE |
102005059314.3 |
Claims
1. A process for anticorrosion treatment of bright metal surfaces,
which are at least in part steel surfaces, comprising: 1)
contacting metal surfaces that are not yet coated with an
anticorrosion coating, said surfaces comprising at least one steel
surface, with an acidic aqueous solution of a fluoro complex of at
least one element M selected from the group consisting of B, Si,
Ti, Zr and Hf; wherein: a) the aqueous solution comprises no more
than 1 mg/l of an organic polymer with allylamine or vinylamine
monomers; b) the aqueous solution comprises a buffer system for the
pH range from 2.5 to 5.5; c) the aqueous solution comprises at
least one component selected from the group consisting of: nitrate
ions, copper ions, silver ions, vanadium ions, vanadate ions,
bismuth ions, magnesium ions, zinc ions, manganese ions, cobalt
ions, nickel ions, tin ions, aromatic carboxylic acids having at
least two groups containing donor atoms, derivatives of said
carboxylic acids, and silica particles having an average particle
size of less than 1 .mu.m; 2) rinsing the metal surfaces after step
1); and 3) coating the metal surfaces with a cathodically
depositable electro-dipcoating.
2. The process according to claim 1, wherein the aqueous solution
further comprises additional organic polymers that do not contain
allylamine or vinylamine monomers, in an amount of less than 2000
mg/l, said polymers having thickening and/or dispersing properties
and/or anticorrosion activity.
3. The process according to claim 1, wherein the aqueous solution
comprises no more than 1 mg/l of organic polymer.
4. The process according to claim 1, wherein the element M is
selected from the group consisting of Si, Ti, Zr and Hf, the
aqueous solution contains on average at least 1 fluorine ion per
ion of the element M and the fluoro complex is present in an amount
such that concentration of the element M is from 1 to 5000
mg/l.
5. The process according to claim 1, wherein the aqueous solution
comprises 0.1 to 300 mg/l copper ions and/or silver ions.
6. The process according to claim 1, wherein component c) comprises
at least one component selected from the group consisting of
hydroxycarboxylic acids, aminocarboxylic acids, nitrocarboxylic
acids, carboxylic acids with at least two carboxyl groups, and
derivatives of said acids.
7. The process according to claim 1, wherein the aqueous solution
comprises 10 to 1000 mg/l of silicon in the form of silica
particles with an average particle size of less than 1 .mu.m.
8. The process according to claim 1, wherein after having been
brought into contact with the aqueous solution and before being
coated with the cathodically depositable electro-dipcoating, the
metal surface is not dried.
9. A process for anticorrosion treatment of bright metal surfaces,
which are at least in part steel surfaces, comprising: 1)
contacting metal surfaces that are not yet coated with an
anticorrosion coating, said metal surfaces comprising at least one
steel surface, with an acidic aqueous solution of a fluoro complex
of at least one element M selected from the group consisting of B,
Si, Ti, Zr and Hf; wherein: a) the aqueous solution comprises no
more than 1 mg/l of organic polymer; b) the aqueous solution
comprises 10 to 1000 mg/l of silicon in the form of silica
particles with an average particle size of less than 1 .mu.m, c)
the aqueous solution comprises at least one component selected from
the group consisting of: nitrate ions, copper ions, silver ions,
vanadium ions, vanadate ions, bismuth ions, magnesium ions, zinc
ions, manganese ions, cobalt ions, nickel ions, tin ions, a buffer
system for the pH range from 2.5 to 5.5, aromatic carboxylic acids
having at least two groups containing donor atoms, and derivatives
of said carboxylic acids; 2) rinsing the metal surfaces after step
1); and 3) coating the metal surfaces with a cathodically
depositable electro-dipcoating.
10. The process according to claim 9, wherein the element M is
selected from the group consisting of Si, Ti, Zr and Hf and the
aqueous solution contains on average at least 1 fluorine ion per
ion of the element M.
11. The process according to claim 9, wherein the aqueous solution
comprises 0.1 to 300 mg/l copper ions and/or silver ions.
12. The process according to claim 11, wherein the aqueous solution
contains a buffer system for the pH range from 2.5 to 5.5.
13. The process according to claim 9, wherein after having been
brought into contact with the aqueous solution and before being
coated with the cathodically depositable electro-dipcoating, the
metal surface is not dried.
14. An acidic, chromium-free aqueous solution of a fluoro complex
of at least one element M selected from the group consisting of B,
Si, Ti, Zr and Hf, said aqueous solution having a pH value in the
range from 2 to 5.5, and comprising: a) a buffer system for the pH
range from 2.5 to 5.5, b) one or more components selected from:
copper ions, silver ions, tin ions, bismuth ions, aromatic
carboxylic acids with at least two groups containing donor atoms,
and derivatives of said carboxylic acids.
15. The aqueous solution according to claim 14, wherein the aqueous
solution further comprises silicon in the form of silica particles
with an average particle size of less than 1 .mu.m and has an
organic polymer content of no more than 1 mg/l; the fluoro complex
being present in a quantity such that the concentration of the
element M is in a range from 1 to 5000 mg/l.
16. The aqueous solution according to claim 14, wherein the aqueous
solution contains no more than 1 mg/l of organic polymers that
contain allylamine or vinylamine monomers.
17. The aqueous solution according to claim 16, wherein the aqueous
solution further comprises additional organic polymers that do not
contain allylamine or vinylamine monomers, in an amount of less
than 2000 mg/l, said polymers having thickening and/or dispersing
properties and/or anticorrosion activity.
18. The aqueous solution according to claim 14, wherein the aqueous
solution additionally contains 10 to 500 mg/l nitroguanidine or 0.1
to 5000 mg/l of nitrate ions.
19. The process according to claim 14, wherein component b)
comprises at least one component selected from the group consisting
of hydroxycarboxylic acids, aminocarboxylic acids, nitrocarboxylic
acids, carboxylic acids with at least two carboxyl groups, and
derivatives of said acids.
20. An acidic, chromium-free aqueous solution of a fluoro complex
of at least one element M selected from the group consisting of B,
Si, Ti, Zr and Hf, said aqueous solution having a pH value in the
range from 2 to 5.5, and comprising: a) no more than 1 mg/l of
organic polymer; b) 10 to 1000 mg/l of silicon in the form of
silica particles with an average particle size of less than 1
.mu.m; and c) one or more components selected from among: copper
ions, silver ions, tin ions, bismuth ions, buffer systems for the
pH range from 2.5 to 5.5, aromatic carboxylic acids with at least
two groups containing donor atoms, and derivatives of said
carboxylic acids.
21. The aqueous solution according to claim 20, wherein the aqueous
solution contains a quantity of fluoro complex such that the
concentration of the element M is in the range from 5 to 1000
mg/l.
22. The aqueous solution according to claim 20, wherein the aqueous
solution additionally contains 10 to 500 mg/l nitroguanidine or 0.1
to 5000 mg/l of nitrate ions.
23. The aqueous solution according to claim 20, wherein the aqueous
solution comprises from 0.1 to 300 mg/l of copper and/or silver
ions and 50 to 500 mg/l of silicon in the form of silica particles
with an average particle size of below 1 .mu.m.
24. The aqueous solution according to claim 20, wherein the aqueous
solution contains on average at least 1 fluorine ion per ion of the
element M and, in the fluoro complex, the element M is selected
from the group consisting of Si, Ti, Zr and Hf.
25. The aqueous solution according to claim 20, wherein, in the
fluoro complex, there are six fluorine ions per ion of the element
M and the aqueous solution also contains 1 to 1000 mg/l of fluoride
ions which are not attached to the element M.
26. An aqueous concentrate which, on dilution with water by a
factor of between 10 and 100, and optional adjustment of pH, gives
rise to an aqueous solution according to claim 20.
27. A process for the anticorrosion treatment of bright metal
surfaces, wherein the metal surfaces are brought into contact with
an aqueous solution according to claim 20.
Description
[0001] This application is a continuation under 35 U.S.C. Sections
365(c) and 120 of International Application No. PCT/EP2006/011696,
filed 6 Dec. 2006 and published 14 Jun. 2007 as WO 2007/065645,
which claims priority from German Application No. 102005059314.3,
filed 12 Sep. 2005, each of which is incorporated herein by
reference in its entirety.
[0002] The present invention relates to a novel product for the
anticorrosion treatment of metal surfaces. In addition, a process
is provided for the anticorrosion treatment of metal, in
particular, steel surfaces. The anticorrosion treatment is
primarily intended as a pre-treatment for a subsequent cathodic
electro-dipcoating.
[0003] Anticorrosion agents that involve an acidic aqueous solution
of fluoro complexes have been known for some considerable time.
They are increasingly employed as a replacement for chromating
processes that due to the toxicological properties of chromium
compounds are less and less used. Generally, solutions of fluoro
complexes of this type contain additional anticorrosion agents that
further improve the corrosion protection and paint adhesion.
[0004] DE-A-19 33 013, for example, describes in one embodiment a
treatment solution that is an aqueous solution of ammonium
hexafluorozirconate, sodium nitrate, cobalt nitrate and sodium
m-nitrobenzene sulfonate and has a pH of 5.2. The solution can be
used to treat zinc-, steel- or aluminum surfaces. EP-A-1 571 237
describes a treatment solution and treatment methods for iron-,
zinc-, aluminum- and magnesium-containing surfaces. This solution
has a pH in the range of 2 to 6 and contains 5 to 5000 ppm
zirconium and/or titanium as well as 0.1 to 100 ppm free fluoride.
In addition, the solution can further contain components selected
from chlorate, bromate, nitrite, nitrate, permanganate, vanadate,
hydrogen peroxide, tungstate, molybdate or each of the
corresponding acids. Organic polymers can also be present. After
the treatment with a solution of this type, the metal surfaces can
be rinsed with a further passivating solution. EP-A-1 405 933
discloses a composition that contains at least one metal from the
group Ti, Zr, Hf and Si as well as a fluoride ion source for the
treatment of iron and/or zinc surfaces, wherein defined conditions
concerning the concentration ratios of both components are set. In
addition, this solution can contain the same additional active
substances as in EP 1 571 237. Metal ions selected from the group
Ag, Al, Cu, Fe, Mn, Mg, Ni, Co and Zn can be present as further
components. DE-A-100 10 758 discloses a treatment solution
containing complex fluorides of Ti, Zr, Hf, Si and/or B as well as
organic polymers particularly for zinc, aluminum and/or magnesium
surfaces. The solution can also contain one or more of the metals
Mn, Ce, Li, V, W, Mo, Mg, Zn, Co and Ni. Further potential
additives are compounds that are known phosphatization accelerators
for the phosphatization layer formation. WO 95/14539 describes
treatment solutions for metal surfaces, particularly for aluminum,
which contain complex fluorides of Ti, Zr, Hf, Si, Ge, Sn or B as
well as organic hydroxycarboxylic acids containing at least 2
hydroxyl groups (wherein the hydroxyl groups of the carboxylic acid
groups are not counted) per carboxylic acid group. A specific
example of such an acid is gluconic acid.
[0005] In all these documents, mention is made--either in general
terms in the description or specifically in the embodiments--that
the metal surfaces treated with the stated solution are dried prior
to their being coated with an additional organic coating, such as
for example a varnish. However, especially for the manufacture,
pre-treatment and painting of automobile body work, because of the
short cycle times and the shortest possible length of the
pre-treatment line, it is desired that the pre-treated body work be
fed into the dip coating bath without being dried, i.e. while still
wet. Accordingly, a drying step, in which the pre-treatment layer
can be, for example, chemically modified and/or hardened by
dewatering, is not desired. Therefore, during the pre-treatment, an
anticorrosion layer has to be produced--without a drying step--and
which possesses the required corrosion protection and adhesion to
paint, prior to the application of a first organic paint layer.
[0006] A coating process that meets these specifications is
described in EP-A-1 433 876. Here, the treatment of steel, zinc and
aluminum surfaces for example, is carried out with a solution that
contains Zr, Ti and/or Hf as well as fluoride ions and additionally
a water-soluble polyvinylamine or polyallylamine resin. In the sole
embodiment that describes the painting of a still wet, pre-treated
metal surface, an aqueous solution of fluorozirconic acid,
polyallylamine, zinc nitrate, silica and ascorbic acid is employed.
It is predicted here, that the organic polymer is a significant
component in regard to the corrosion protection and the adhesion to
paint. However, the presence of organic polymers in pre-treatment
solutions is frequently undesirable as they can lead to
difficulties in the waste water treatment.
[0007] Surfaces of zinc, aluminum and galvanized steel can be
pre-treated with very differently formulated aqueous solutions of
fluoro complexes, and the previously stated requirements can be
satisfied. One drawback of the prior art is that with steel
surfaces that have not been pre-treated, the previously stated
requirements can only be satisfied up to now with a layer-forming
zinc phosphatization. Compared with the standard of the
layer-forming zinc phosphatization, a pre-treatment with aqueous
solutions of fluoro complexes shows significant disadvantages in
regard to corrosion protection and adhesion to paint when the
pre-treated surfaces are not dried before painting.
[0008] Applicants have discovered this problem can be solved if the
aqueous solution of a fluoro complex contains certain additional
components. Consequently, in a first aspect, the present invention
relates to a process for the anticorrosion treatment of bright
metal surfaces, which are at least in part steel surfaces, wherein
the metal surfaces are brought into contact with an acidic aqueous
solution of a fluoro complex of at least one element M selected
from the group B, Si, Ti, Zr and Hf, are rinsed with water and
thereafter coated with a cathodically depositable
electro-dipcoating, characterized in that
a) the aqueous solution contains no more than 1 mg/l of an organic
polymer with allylamine or vinylamine monomers (a first organic
polymer), b) the aqueous solution additionally contains at least
one further component which is selected from among: nitrate ions,
copper ions, silver ions, vanadium or vanadate ions, bismuth ions,
magnesium ions, zinc ions, manganese ions, cobalt ions, nickel
ions, tin ions, buffer systems for the pH range from 2.5 to 5.5,
aromatic carboxylic acids with at least two groups containing donor
atoms, or derivatives of such carboxylic acids, silica particles
with an average particle size of below 1 .mu.m, c) after having
been brought into contact with the aqueous solution of the fluoro
complex and before being coated with the cathodically depositable
electro-dipcoating, the metal surface is not dried.
[0009] In this context, "steel surfaces" are understood to mean
surfaces of steel, which are not top-coated with an additional
metal, such as for example zinc or its alloys with nickel or
aluminum. "Bright" metal surfaces are understood to mean metal
surfaces, which are not yet coated with an anticorrosion coating.
Accordingly, the process according to the invention concerns the
first or sole treatment step, which produces an anticorrosion layer
that in turn can serve as the basis for a subsequent coat of paint.
Therefore, it is not a post-treatment of a previously produced
anticorrosion layer, such as for example a phosphate layer.
SUMMARY OF THE INVENTION
[0010] It is an object of the invention to provide a process for
the anticorrosion treatment of bright metal surfaces, which are at
least in part steel surfaces, wherein the metal surfaces are
brought into contact with an acidic aqueous solution of a fluoro
complex of at least one element M selected from the group B, Si,
Ti, Zr and Hf, are rinsed with water and thereafter coated with a
cathodically depositable electro-dipcoating,
characterized in that A) the aqueous solution contains no more than
1 mg/l of an organic polymer with allylamine or vinylamine
monomers, B) the aqueous solution contains a buffer system for the
pH range from 2.5 to 5.5, C) the aqueous solution additionally
contains at least one further component which is selected from
among: nitrate ions, copper ions, silver ions, vanadium or vanadate
ions, bismuth ions, magnesium ions, zinc ions, manganese ions,
cobalt ions, nickel ions, tin ions, aromatic carboxylic acids with
at least two groups containing donor atoms, or derivatives of such
carboxylic acids, silica particles with an average particle size of
below 1 .mu.m, D) after having been brought into contact with the
aqueous solution of the fluoro complex and before being coated with
the cathodically depositable electro-dipcoating, the metal surface
is not dried.
[0011] It is also an object of the invention to provide a process
for the anticorrosion treatment of bright metal surfaces, which are
at least in part steel surfaces, wherein the metal surfaces are
brought into contact with an acidic aqueous solution of a fluoro
complex of at least one element M selected from the group B, Si,
Ti, Zr and Hf, are rinsed with water and thereafter coated with a
cathodically depositable electro-dipcoating, wherein
A) the aqueous solution contains no more than 1 mg/l of an organic
polymer with allylamine or vinylamine monomers, B) the aqueous
solution additionally contains at least one further component which
is selected from among: nitrate ions, copper ions, silver ions,
vanadium or vanadate ions, bismuth ions, magnesium ions, zinc ions,
manganese ions, cobalt ions, nickel ions, tin ions, a buffer system
for the pH range from 2.5 to 5.5, aromatic carboxylic acids with at
least two groups containing donor atoms, or derivatives of such
carboxylic acids, silica particles with an average particle size of
below 1 .mu.m, C) after having been brought into contact with the
aqueous solution of the fluoro complex and before being coated with
the cathodically depositable electro-dipcoating, the metal surface
is not dried, characterized in that the aqueous solution contains
no more than 1 mg/l of an organic polymer differing from the above
which contains no allylamine or vinylamine monomers and which is
selected from among: a) polymers or copolymers of unsaturated
alcohols or the esters or ethers thereof, b) polymers or copolymers
of unsaturated carboxylic acids, organophosphonic acids,
organophosphinic acids or in each case the salts, esters or amides
thereof, c) polyamino acids or proteins or in each case the salts,
esters or amides thereof, d) carbohydrates or the esters or ethers
thereof, e) polyamines, in which the nitrogen atoms are
incorporated into the polymer chain, f) polyethers, g)
polyvinylphenols and the substitution products thereof, h) epoxy
resins, amino resins, tannins, phenol-formaldehyde resins, i)
polymers and copolymers of vinylpyrrolidone.
[0012] It is a further object of the invention to provide the
aforementioned processes wherein the aqueous solution contains no
more than 1 mg/l of an organic polymer differing from the above
which contains no allylamine or vinylamine monomers and which, at a
concentration of no more than 50 g/l, has thickening or dispersant
properties.
[0013] It is a further object of the invention to provide a process
characterized in that the aqueous solution contains no more than 1
mg/l of organic polymer.
[0014] It is a further object of the invention to provide the
aforementioned processes characterized in that the aqueous solution
contains a quantity of fluoro complex such that the concentration
of the element M is in the range from 1 to 5000 mg/l, preferably in
the range from 5 to 1000 mg/l and in particular in the range from
10 to 500 mg/l.
[0015] It is a further object of the invention to provide the
aforementioned processes characterized in that, in the fluoro
complex, the element M is selected from among the group Si, Ti, Zr
and Hf and in that the aqueous solution contains on average at
least 1, preferably at least 3, in particular at least five
fluoride ions per ion of the element M. In one embodiment, in the
fluoro complex, there are six fluorine ions per ion of the element
M and in that the aqueous solution furthermore also contains 1 to
1000 mg/l of fluoride ions which are not attached to the element
M.
[0016] It is a further object of the invention to provide the
aforementioned processes characterized in that the aromatic
carboxylic acid is selected from among hydroxycarboxylic acids,
aminocarboxylic acids, nitrocarboxylic acids and carboxylic acids
with at least two carboxyl groups, or derivatives thereof.
[0017] It is a further object of the invention to provide the
aforementioned processes characterized in that the aqueous solution
contains 10 to 500 mg/l nitroguanidine.
[0018] It is a further object of the invention to provide the
aforementioned processes characterized in that the aqueous solution
contains 0.1 to 5000 mg/l of nitrate ions.
[0019] It is a further object of the invention to provide the
aforementioned processes characterized in that the aqueous solution
contains 0.1 to 300 mg/l, preferably 1 to 30 mg/l of copper and/or
silver ions.
[0020] It is a further object of the invention to provide the
aforementioned processes characterized in that the aqueous solution
contains 0.1 to 1000 mg/l of the stated aromatic carboxylic acid or
derivatives thereof.
[0021] It is a further object of the invention to provide the
aforementioned processes characterized in that the aqueous solution
contains 10 to 1000 mg/l, preferably 50 to 500 mg/l of silicon in
the form of silica particles with an average particle size of below
1 .mu.m.
[0022] It is a further object of the invention to provide the
aforementioned processes characterized in that the aqueous solution
contains a buffer system for the pH range from 2.5 to 5.5.
[0023] It is a further object of the invention to provide the
aforementioned processes characterized in that, after having been
brought into contact with the aqueous solution of a fluoro complex
and before being coated with the cathodically depositable
electro-dipcoating, the metal is rinsed with an aqueous solution
which contains one or more components selected from among compounds
or salts of the elements cobalt, nickel, tin, copper, titanium and
zirconium and/or among water-soluble or water-dispersible organic
polymers.
[0024] It is an object of the invention to provide a composition
comprising an acidic, chromium-free aqueous solution of a fluoro
complex of at least one element M selected from among the group B,
Si, Ti, Zr and Hf with a pH value in the range from 2 to 5.5 for
the treatment of metal surfaces, characterized in that it
additionally contains
a) a buffer system for the pH range from 2.5 to 5.5, b) one or more
components selected from among: copper, tin ions, bismuth ions,
aromatic carboxylic acids with at least two groups containing donor
atoms, or derivatives of such carboxylic acids and for aqueous
solutions with an organic polymer content of no more than 1 mg/l
silicon in the form of silica particles with an average size of
below 1 .mu.m.
[0025] It is a further object of the invention to provide a
composition, characterized in that it contains a quantity of fluoro
complex such that the concentration of the element M is in the
range from 1 to 5000 mg/l, preferably in the range from 5 to 1000
mg/l and in particular in the range from 10 to 500 mg/l.
[0026] It is a further object of the invention to provide a
composition characterized in that, in the fluoro complex, the
element M is selected from among the group Si, Ti, Zr and Hf and in
that the aqueous solution contains on average at least 1,
preferably at least 3, in particular at least five fluoride ions
per ion of the element M.
[0027] It is a further object of the invention to provide a
composition characterized in that, in the fluoro complex, there are
six fluorine ions per ion of the element M and in that the aqueous
solution furthermore also contains 1 to 1000 mg/l of fluoride ions
which are not attached to the element M.
[0028] It is a further object of the invention to provide a
composition characterized in that the aromatic carboxylic acid is
selected from among hydroxycarboxylic acids, aminocarboxylic acids,
nitrocarboxylic acids and carboxylic acids with at least two
carboxyl groups, or derivatives thereof.
[0029] It is a further object of the invention to provide a
composition characterized in that it contains 0.1 to 1000 mg/l of
the stated aromatic carboxylic acid or derivatives thereof.
[0030] It is a further object of the invention to provide a
composition characterized in that it additionally contains 10 to
500 mg/l nitroguanidine.
[0031] It is a further object of the invention to provide a
composition characterized in that it additionally contains 0.1 to
5000 mg/l of nitrate ions.
[0032] It is a further object of the invention to provide a
composition characterized in that it additionally contains 0.1 to
300 mg/l, preferably 1 to 30 mg/l of copper and/or silver ions.
[0033] It is a further object of the invention to provide a
composition characterized in that it contains no more than 1 mg/l
of organic polymer.
[0034] It is a further object of the invention to provide a
composition, characterized in that it additionally contains 10 to
1000 mg/l, preferably 50 to 500 mg/l of silicon in the form of
silica particles with an average particle size of below 1
.mu.m.
[0035] It is an object of the invention to provide an aqueous
concentrate which, on dilution with water by a factor of between 10
and 100 and if necessary adjustment of the pH value, gives rise to
an aqueous solution as described herein.
[0036] It is an object of the invention to provide a process for
the anticorrosion treatment of bright metal surfaces, characterized
in that the metal surfaces are brought into contact with an aqueous
solution as described herein.
[0037] It is a further object of the invention to provide a process
characterized in that, after having been brought into contact with
the aqueous solution of a fluoro complex, the metal surface is
rinsed with an aqueous solution which contains one or more
components selected from among compounds or salts of the elements
cobalt, nickel, tin, copper, titanium and zirconium and/or among
water-soluble or water-dispersible organic polymers.
DETAILED DESCRIPTION
[0038] The treatment solution can contain aromatic carboxylic
acids, as one of the previously stated components, which have at
least two groups containing donor atoms in the molecule. Donor
atoms are those atoms that carry free electron pairs, by which they
can coordinate to transition metal ions. Typical donor atoms are
oxygen, nitrogen and sulfur atoms. The carboxylic group of the
aromatic carboxylic acid is therefore itself already a group that
contains donor atoms. An aromatic carboxylic acid with at least two
carboxylic groups in the molecule, therefore falls under the stated
definition. Those aromatic carboxylic acids, which carry, for
example at least one hydroxyl group, at least one amino group or at
least one nitro group in addition to the carboxylic group, also
fall under the definition. Examples of these carboxylic acids are
the various positional isomers of benzene dicarboxylic acid,
especially phthalic acid, or the various positional isomers of
hydroxy-, amino- or nitro-benzoic acid.
[0039] In general, such aromatic carboxylic acids are preferred, in
which at least two groups containing donor atoms are disposed in
such a way that through the donor atoms, 5-, 6- or 7-membered
chelate complexes with transition metal ions can be formed.
Particularly preferred aromatic carboxylic acids are therefore:
phthalic acid, salicylic acid, o-aminobenzoic acid or
o-nitrobenzoic acid. Instead of aromatic carboxylic acids
containing only a single benzene ring, the corresponding acids with
condensed ring systems can be used, for example the acids derived
from naphthalene or anthracene.
[0040] Derivatives of the stated aromatic carboxylic acids can also
be employed. Among these are meant those molecules, in which one or
more hydrogen atoms of the basic structure (e.g. hydrogen atoms on
the aromatic core, hydrogen atoms of the hydroxyl or amino groups
or hydrogen atoms of the carboxyl groups) are replaced by other
atoms or groups of atoms.
[0041] The aforementioned silica particles with an average particle
size of below 1 .mu.m are known under various generic names to the
person skilled in the art. They are called, for example, colloidal
silica, precipitated silica or pyrogenic silica. The average
particle size, which is preferably in the range of about 0.01 .mu.m
to about 1 .mu.m, can be determined by light scattering methods or
by electron microscopy.
[0042] In the process according to the invention, an aqueous
solution is added that on toxicological grounds is essentially free
of chromium (VI) compounds and preferably contains no chromium
compounds of any kind. Traces of chromium compounds, which can
arrive in the treatment solution by being leached out of stainless
steel containers, are not considered to render the solution
"chromium containing". In this context, treatment solutions
containing no more than 1 ppm, particularly no more than 0.1 ppm
chromium, are understood as "chromium free". The treatment
solutions to be employed according to the invention do not
represent phosphatization solutions, i.e. they do not lead to the
formation of an amorphous or crystalline phosphate layer. This is
achieved in that the treatment solutions preferably contain no more
than 1 g/l inorganic phosphate or phosphoric acid, calculated as
PO.sub.4.sup.3-. However, phosphate contents in the range of 10 to
500 mg/l, for example, can be tolerated and can even improve the
action of the treatment solution.
[0043] The stability of concentrates, from which the aqueous
treatment solutions to be used in the process according to the
invention can be manufactured by dilution with water, can be
improved by adding thickeners and/or dispersants. These thickeners
and/or dispersants are then also present in a suitably diluted
state in the ready for use aqueous treatment solution. Their
presence in the treatment solution can be tolerated, such that a
treatment solution of this type can be used in the process
according to the invention. Accordingly, the aqueous treatment
solution can be wherein it contains no more than 1 mg/l of another
organic polymer than such a polymer that does not contain
allylamine or vinylamine monomers, and that, at a concentration of
no more than 50 g/l, has thickening or dispersing properties.
Examples of such polymers are polymers or copolymers of unsaturated
carboxylic acids, carbohydrates or proteins.
[0044] Desirably, the aqueous treatment solution contains no more
than 1 mg/l of an organic polymer containing allylamine or
vinylamine monomers, preferably 0 to 1 mg/l. However, other
polymers can be present. Among these are the previously stated
polymers with thickening and/or dispersing properties. Apart from
these, the treatment solution can contain additional polymers with
known positive activity in anticorrosion treatment. Exemplary
polymers of this type (including those with thickening and/or
dispersing properties) are:
a) polymers or copolymers of unsaturated alcohols or the esters or
ethers thereof, b) polymers or copolymers of unsaturated carboxylic
acids, organophosphonic acids, organophosphinic acids or in each
case the salts, esters or amides thereof, c) polyamino acids or
proteins or in each case the salts, esters or amides thereof, d)
carbohydrates or the esters or ethers thereof, e) polyamines, in
which the nitrogen atoms are incorporated into the polymer chain,
f) polyethers, g) polyvinylphenols and the substitution products
thereof, h) epoxy resins, amino resins, tannins,
phenol-formaldehyde resins, i) polymers and copolymers of vinyl
pyrrolidone.
[0045] In so far as these types of polymer are present, their
concentration in the aqueous treatment solution is preferably less
than 2000 mg/l. On secondary technical grounds, such as for example
the simplification of the waste water treatment, it can be
advantageous to largely or completely dispense with the presence of
organic polymers in the aqueous treatment solution. Consequently, a
preferred embodiment of the present invention is wherein the
aqueous solution contains no more than 1 mg/l of organic
polymer.
[0046] The pH of the acidic treatment solution is preferably in the
range 2 to 5.5, particularly 3.5 to 5. The pH is preferably
adjusted to the stated acidic range by adding the fluoro complex at
least partially in the form of an acid. However, it can also be
adjusted by means of another acid, for example nitric acid.
According to the invention and according to this first aspect of
the invention, no measures are required, and preferably should be
even avoided, which would dry the metal surface after it has been
contacted with the aqueous solution of the fluoro complex and
before being coated with the cathodically depositable
electro-dipcoating. An unintentional drying can however occur
during a unit shutdown when the treated metal surface, for example
an automobile body or a part thereof, is exposed to air between the
bath containing the aqueous solution of the fluoro complex and the
electro-dipcoating bath. This unintentional drying is harmless,
however.
[0047] The additional components stated in feature b) are
preferably present in the following concentration ranges;
nitrate ions: 0.1 to 5000 mg/l, preferably 1 to 3000 mg/l, in
particular 10 to 1000 mg/l, copper-, silver-, cobalt- or nickel
ions: each 0.1 to 300 mg/l, preferably 1 to 30 mg/l, vanadium- or
vanadate ions: 1 to 2000 mg/l, preferably 5 to 500 mg/l (calculated
as vanadium), bismuth-, magnesium-, zinc-, manganese- or tin ions:
each 1 to 2000 mg/l, preferably 5 to 500 mg/l, buffer system for
the pH range 2.5 to 5.5: in sufficient quantity that the pH of the
solution does not change by more than 0.2 units when a 1 N acid or
base per liter solution is added, aromatic carboxylic acids
containing at least two groups containing donor atoms, or
derivatives of such acids: 0.01 to 1000 mg/l, preferably 1 to 500
mg/l, silicon in the form of silica particles with an average
particle size of less than 1 .mu.m: 10 to 1000 mg/l, preferably 50
to 500 mg/l
[0048] In the context of the present invention, when an "acid",
specifically a "carboxylic acid" is mentioned, then the free acid
and/or its anions are to be understood. The person skilled in the
art is aware that independently of whether the acid is added in the
form of a free acid or in the form of soluble salts in the given
concentration range, an equilibrium is reached between the free
acid and the salt form, which depends on the pK.sub.a of the acid
in question and the pH of the aqueous solution. Concentrations are
calculated as the free acid. The same is true, for example, for
H.sub.2ZrF.sub.6 or other acids, which are present in the aqueous
solution.
[0049] An acetic acid/acetate buffer is particularly suitable as
the buffer system for the stated pH range. A further suitable
buffer system is based on potassium hydrogen phthalate.
[0050] Preferably the aqueous solution contains a quantity of
fluoro complex such that the concentration of the metal M is in the
range from 1 to 5000 mg/l, preferably in the range from 5 to 1000
mg/l and in particular in the range from 10 to 500 mg/l. Zirconium
and/or titanium is particularly preferred as the metal M.
[0051] It is further preferred that in the fluoro complex the
element M is selected from the group Si, Ti, Zr and Hf, and in that
the aqueous solution contains on average at least 1, preferably at
least 3, in particular at least five fluoride ions per ion of the
element M. Here, the statement "on average" means the calculated
atom ratio of fluoride ions to M ions in the aqueous solution. The
stability of fluoro complexes of the stated metals M leads to the
expectation that if the aqueous solution contains less than six
fluoride ions per M ion, then the fluoride ions are almost
completely attached to the M ions in the form of fluoride
complexes. Therefore, in this case the fluoride is essentially
totally present as "complex fluoride".
[0052] However, the aqueous solution can also contain more fluoride
ions than is required for the complete formation of hexafluoro
complexes. In this case, one can assume that six fluoride ions are
present in the fluoro complex and that the excess fluoride ions are
present as so-called "free fluoride". They can be in the form of,
for example HF and/or water-soluble salts thereof. In one
embodiment of the present invention, six fluoride ions per ion of
the metal M (M selected from Si, Ti, Zr, Hf) are present in the
fluoro complex, and the aqueous solution still contains 1 to 1000
mg/l of fluoride ions which are not attached to the metal M, which
is desirably zirconium.
[0053] In a particularly preferred embodiment, the aqueous solution
contains at least 0.1 mg/l, preferably at least 1 mg/l and
particularly at least 10 mg/l of nitrate ions. The upper limit of
the nitrate concentration is chosen more from economic than
technical grounds, the economic grounds also including the costs of
the waste water disposal. The upper limit of the nitrate ion
concentration can be chosen, for example as 5000 mg/l, preferably
3000 mg/l and particularly 1000 mg/l. The aqueous solution can
contain copper ions and/or silver ions as additional components
according to feature b). They can be present instead of the nitrate
ions or be together with them. In this embodiment, the aqueous
solution preferably contains 0.1 to 300 mg/l, particularly 1 to 30
mg/l of copper ions and/or silver ions.
[0054] In a further preferred embodiment, the aqueous solution
contains at least one aromatic carboxylic acid, as defined above,
or derivatives thereof. Salicylic acid is particularly preferred.
The aromatic carboxylic acid can be present together with the
nitrate ions and/or the copper ions and/or the silver ions. It is
preferably present in a concentration of at feast 0.1 mg/l,
preferably at least 1 mg/l and particularly at least 10 mg/l. The
upper limit of the concentration is again more conditional on
economics than on technical concerns. For example, the upper
concentration level of the aromatic carboxylic acid can be 1000
mg/l, preferably 500 mg/l and especially 400 mg/l.
[0055] In a further preferred embodiment, the aqueous treatment
solution contains a buffer system for the pH range 2.5 to 5.5, as
already described.
[0056] Accordingly, preferably employable aqueous treatment
solutions contain at least one of the components described above in
more detail: nitrate ions, copper ions and/or silver ions, aromatic
carboxylic acids, silica particles with an average particle size of
below 1 .mu.m and/or a buffer system for the pH range 2.5 to 5.5.
Two or more of these components can also be present together. The
presence of further components in addition to the preferred stated
five can have a favorable effect on anticorrosion and paint
adhesion. For example, in addition to one or more of the five
previously stated components (nitrate ions, copper ions and/or
silver ions, aromatic carboxylic acids, silica particles, buffer
system), one or more of the following components can be present:
vanadium- or vanadate ions, cobalt ions, nickel ions, manganese
ions, tin ions, bismuth ions, magnesium ions and zinc ions. Their
preferred concentration ranges have already been given above. In
this regard, a treatment solution, which in addition to one of the
five stated preferred components (nitrate ions, copper ions and/or
silver ions, aromatic carboxylic acids, silica particles, buffer
system), contains both zinc ions as well as magnesium ions, is
particularly preferred.
[0057] Moreover, the aqueous treatment solution can additionally
contain aluminum ions. They can be introduced in the form of
soluble salts, for example in the form of the nitrates. In this
case, the aqueous treatment solution preferably contains 1 to 1000
mg/l, especially 10 to 500 mg/l of aluminum ions. Aluminum ions can
serve as "complexers" for excess free fluoride ions, as with these
they form stable fluoro complexes. Free fluoride ions are produced
in the aqueous treatment solution because the metal M, for example
zirconium, precipitates out, probably in the form of oxides, onto
the treated metal surface. In this way, the fluoride ions that were
originally attached to the metal M are released. The increased
pickling effect of the aqueous solution caused by free fluoride
ions can be reduced by the presence of the aluminum ions owing to
the complex formation.
[0058] In addition to the already stated components, the aqueous
treatment solution can contain compounds that are employed in layer
forming phosphatization as so-called "accelerators". These
accelerators have the property of capturing hydrogen atoms that are
produced by the pickling attack of the acids on the metal surface.
This reaction, also known as "depolarization", facilitates the
attack of the acidic treatment solution on the metal surface and
thereby accelerates the formation of the anticorrosion layer.
Accelerators, which are listed in the previously stated document
DE-A-199 33 189, can be employed, for example:
[0059] 0.05 to 2 g/l m-nitrobenzene sulfonate ions,
[0060] 0.1 to 10 g/l hydroxylamine in free or bound form,
[0061] 0.05 to 2 g/l m-nitrobenzoate ions,
[0062] 0.05 to 2 g/l p-nitrophenol,
[0063] 1 to 70 mg/i of hydrogen peroxide in free or bound form,
[0064] 0.05 to 10 g/l organic N-oxides,
[0065] 0.01 to 3 g/l, preferably up to 0.5 g/l nitroguanidine,
[0066] 1 to 500 mg/l of nitrite ions
[0067] 0.5 to 5 g/l chlorate ions.
[0068] It is known from the previously stated document EP-A-1 571
237 that after the treatment with the aqueous solution of a fluoro
complex, the treated metal surface is then rinsed with an aqueous
solution that contains one or more components selected from
compounds or salts of the elements cobalt, nickel, tin, copper,
titanium and zirconium and/or from water-soluble or
water-dispersible organic polymers. Corrosion protection and paint
adhesion are further improved by this final rinse. A final rinse of
this type also has a positive effect in the course of the process
according to the invention. Accordingly, the present invention also
includes a process variant, in which after having been brought into
contact with the aqueous solution of a fluoro complex and before
being coated with the cathodically depositable electro-dipcoating,
the metal surface is rinsed with an aqueous solution that contains
one or more components selected from among compounds or salts of
the elements cobalt, nickel, tin, copper, titanium and zirconium
and/or from among water-soluble or water-dispersible organic
polymers.
[0069] In the context of the experiments which led to the
previously described inventive process steps, it was clear that an
addition of one or more components selected from among tin ions,
bismuth ions, buffer systems for the pH range 2.5 to 5.5, aromatic
carboxylic acids or derivatives thereof, generally improved the
anticorrosion effect of aqueous solutions of fluoro complexes for
surfaces of steel, aluminum, zinc and galvanized steel. This is
true independently of whether the surfaces are dried or not between
the contact with this solution and a subsequent painting. These
types of treatment solution are therefore not only advantageously
employable in the context of the previously described inventive
process cycle, but also show a positive effect for anticorrosion
and paint adhesion of metal surfaces in general.
[0070] Accordingly, a second aspect of the present invention rests
on the provision of an acidic, chromium-free aqueous solution of a
fluoro complex of at least one element M selected from among the
group B, Si, Ti, Zr and Hf with a pH in the range from 2 to 5.5 for
the treatment of metal surfaces, wherein it additionally contains
one or more components selected from among: tin ions, bismuth ions,
buffer system for the pH range from 2.5 to 5.51 aromatic carboxylic
acids with at least two groups containing donor atoms, or
derivatives of such carboxylic acids.
[0071] The treatment solution can contain aromatic carboxylic acids
as one of the previously stated components, which have at least two
groups containing donor atoms in the molecule. Donor atoms are
those atoms that carry free electron pairs, by which they can
coordinate to transition metal ions. Typical donor atoms are
oxygen, nitrogen and sulfur atoms. The carboxylic group of the
aromatic carboxylic acid is therefore itself already a group that
contains donor atoms. An aromatic carboxylic acid with at least two
carboxylic groups in the molecule, therefore falls under the stated
definition. Those aromatic carboxylic acids, which carry, for
example at least one hydroxyl group, at least one amino group or at
least one nitro group in addition to the carboxylic group, also
fall under the definition. Examples of these carboxylic acids are
the various positional isomers of benzene dicarboxylic acid,
especially phthalic acid, or the various positional isomers of
hydroxy-, amino- or nitro-benzoic acid.
[0072] In general, such aromatic carboxylic acids are preferred, in
which at least two groups containing donor atoms are disposed in
such a way that through the donor atoms, 5-, 6- or 7-membered
chelate complexes can be formed with transition metal ions.
Particularly preferred aromatic carboxylic acids are therefore:
phthalic acid, salicylic acid, o-aminobenzoic acid or
o-nitrobenzoic acid. Instead of aromatic carboxylic acids
containing only a single benzene ring, the corresponding acids with
condensed ring systems can also be used, for example the acids
derived from naphthalene or anthracene.
[0073] Derivatives of the stated carboxylic acids can also be
employed. Among these are meant those molecules, in which one or
more hydrogen atoms of the basic structure (e.g. hydrogen atoms on
the aromatic core, hydrogen atoms of the hydroxyl or amino groups
or hydrogen atoms of the carboxyl groups) are replaced by other
atoms or groups of atoms.
[0074] For this second aspect of the present invention, the
previously made explanations to the essential or additional
facultative components are correspondingly valid:
[0075] An aqueous solution is added, which on toxicological
grounds, is essentially free of chromium (VI) compounds and
preferably contains no chromium compounds of any kind. Traces of
chromium compounds, which can arrive in the treatment solution by
being leached out of stainless steel containers, are not considered
to render the solution "chromate-containing". In this context,
treatment solutions containing no more than 1 ppm, particularly no
more than 0.1 ppm chromium, are understood as "chromium free". The
treatment solutions according to the invention do not represent
phosphatization solutions, i.e. they do not lead to the formation
of an amorphous or crystalline phosphate layer. This is achieved in
that the treatment solutions preferably contain no more than 1 g/l
inorganic phosphate or phosphoric acid, calculated as
PO.sub.4.sup.3-. However, phosphate contents in the range of 10 to
500 mg/l, for example, can be tolerated and can even improve the
action of the treatment solution.
[0076] The pH of the acidic treatment solution is preferably in the
range 2 to 5.5, particularly 3.5 to 5. The pH is preferably
adjusted to the stated acidic range by adding the fluoro complex at
least partially in the form of an acid. However, it can also be
adjusted by means of another acid, for example nitric acid.
[0077] The one or more essential components are preferably present
in the following concentrations:
tin ions: 1 to 2000 mg/l, preferably 5 to 500 mg/l, bismuth ions: 1
to 2000, preferably 5 to 500 mg/l, buffer system for the pH range
2.5 to 5.5: in sufficient quantity that the pH of the solution does
not change by more than 0.2 units when a 1 N acid or base per liter
solution is added, aromatic carboxylic acids: 0.1 to 1000,
preferably 1 to 500 mg/l.
[0078] In addition, this aqueous solution can contain one or more
of the following components:
nitrate ions: 0.1 to 5000 mg/l, preferably 1 to 1000 mg/l, copper-,
cobalt-, nickel- and/or silver ions: each 0.1 to 300 mg/l,
preferably 1 to 30 mg/l, vanadium- or vanadate ions: 1 to 2000,
preferably 5 to 500 mg/l (calculated as vanadium), magnesium ions:
1 to 2000, preferably 5 to 500 mg/l, manganese ions: 1 to 2000
mg/l, preferably 5 to 500 mg/l, zinc ions: 1 to 2000, preferably 5
to 500 mg/l,
[0079] In this regard, it can be preferred that the aqueous
solution contains both zinc ions as well as magnesium ions in
addition to at least one of the stated essential components (tin
ions, bismuth ions, buffer system for the pH range 2.5 to 5.5,
aromatic carboxylic acids or derivatives thereof). Moreover, the
presence of copper ions and/or silver ions is preferred.
[0080] An acetic acid/acetate buffer is particularly suitable as
the buffer system for the stated pH range. A further suitable
buffer system is based on potassium hydrogen phthalate.
[0081] Preferably the aqueous solution contains a quantity of
fluoro complex such that the concentration of the metal M is in the
range from 1 to 5000 mg/l, preferably in the range from 5 to 1000
mg/l and in particular in the range from 10 to 500 mg/l. Zirconium
and/or titanium is particularly preferred as the metal M.
[0082] It is further preferred that in the fluoro complex the
element M is selected from the group Si, Ti, Zr and Hf, and in that
the aqueous solution contains on average at least 1, preferably at
least 3, in particular at least five fluoride ions per ion of the
element M. Here, the statement "on average" means the calculated
atom ratio of fluoride ions to M ions in the aqueous solution. The
stability of fluoro complexes of the stated metals M leads to the
expectation that if the aqueous solution contains less than six
fluoride ions per M ion then the fluoride ions are almost
completely attached to the M ions in the form of fluoro complexes.
Therefore, in this case the fluoride is essentially totally present
as "complex fluoride".
[0083] However, the aqueous solution can also contain more fluoride
ions than is required for the complete formation of hexafluoro
complexes. In this case, one can assume that six fluoride ions per
M ion are present in the fluoro complex and that the excess
fluoride ions are present as so-called "free fluoride". They can be
in the form of, for example HF and/or water-soluble salts thereof.
Is one embodiment of the present invention, six fluoride ions per
ion of the metal M (M selected from Si, Ti, Zr, HD are present in
the fluoro complex, and the aqueous solution still contains 1 to
1000 mg/l of fluoride ions which are not attached to the metal "M",
which is desirably zirconium.
[0084] In the context of the second aspect of the present
invention, when an "acid", specifically a "carboxylic acid" is
mentioned, then the free acid and/or its anions are to be
understood. The person skilled in the art is aware that
independently of whether the acid is added in the form of a free
acid or in the form of soluble salts in the given concentration
range, an equilibrium is reached between the free acid and the salt
form, which depends on the .sub.pK.sub.a of the acid in question
and the pH of the aqueous solution. Concentrations are calculated
as the free acid. The same is true, for example, for
H.sub.2ZrF.sub.6 or other acids, which are present in the aqueous
solution.
[0085] In a further preferred embodiment in the second aspect of
the present invention, the aqueous solution contains at least one
aromatic carboxylic acid, preferably salicylic acid, or derivatives
thereof. This can be present together with the bismuth ions and/or
the buffer system. It is preferably present in a concentration of
at least 0.1 mg/l, preferably at least 1 mg/l and particularly at
least 10 mg/l. The upper limit of the concentration is again more
conditional on economics than on technical concerns. For example,
the upper concentration level of the aromatic hydroxycarboxylic
acid can be selected as 1000 mg/l, preferably 500 mg/l and
especially 400 mg/l.
[0086] In a further preferred embodiment in the context of the
second aspect of the invention, the aqueous treatment solution
contains a buffer system for the pH range 2.5 to 5.5, as already
described.
[0087] Moreover, the aqueous treatment solution can additionally
contain aluminum ions. They can be introduced in the form of
soluble salts, for example in the form of the nitrates. In this
case, the aqueous treatment solution preferably contains 1 to 1000
mg/l, especially 10 to 500 mg/l of aluminum ions. Aluminum ions can
serve as "complexers" for excess free fluoride ions, as with these
they form stable fluoro complexes. Free fluoride ions are produced
in the aqueous treatment solution because the metal M, for example
zirconium, precipitates out, probably in the form of oxides, onto
the treated metal surface. In this way, the fluoride ions that were
originally attached to the metal M are released. The increased
pickling effect of the aqueous solution caused by free fluoride
ions can be reduced by the presence of the aluminum ions owing to
the complex formation.
[0088] In addition to the already stated components according to
the second aspect of the invention, the aqueous treatment solution
can contain compounds that are employed in layer forming
phosphatization as so-called "accelerators". These accelerators
have the property of capturing hydrogen atoms that are produced by
the pickling attack of the acids on the metal surface. This
reaction, also known as "depolarization", facilitates the attack of
the acidic treatment solution on the metal surface and thereby
accelerates the formation of the anticorrosion layer. Accelerators
can be employed, for example, which are listed in the previously
stated document DE-A-1 99 33 189:
[0089] 0.05 to 2 g/l m-nitrobenzene sulfonate ions,
[0090] 0.1 to 10 g/l hydroxylamine in free or bound form,
[0091] 0.05 to 2 g/l m-nitrobenzoate ions,
[0092] 0.05 to 2 g/l p-nitrophenol,
[0093] 1 to 70 mg/l of hydrogen peroxide in free or bound form,
[0094] 0.05 to 10 g/l organic N-oxides
[0095] 0.01 to 3 g/l, preferably up to 0.5 g/l nitroguanidine
[0096] 1 to 500 mg/l of nitrite ions
[0097] 0.5 to 5 .mu.l chlorate ions.
[0098] Moreover, the treatment solution can contain polymers with
known positive activity in anticorrosion treatment. Examples of
this type of polymers are:
a) polymers or copolymers of unsaturated alcohols or the esters or
ethers thereof, b) polymers or copolymers of unsaturated carboxylic
acids, organophosphonic acids, organophosphinic acids or in each
case the salts, esters or amides thereof, c) polyamino acids or
proteins or in each case the salts, esters or amides thereof, d)
carbohydrates or the esters (including esters of xanthic acid) or
ethers thereof, e) polyamines, in which the nitrogen atoms are
incorporated into the polymer chain, f) polyethers, g)
polyvinylphenols and the substitution products thereof, h) epoxy
resins, amino resins, tannins, phenol-formaldehyde resins, i)
polymers and copolymers of vinyl pyrrolidone.
[0099] In so far as these types of polymer are present, their
concentration in the aqueous treatment solution is preferably less
than 2000 mg/l. On secondary technical grounds, such as for example
the simplification of the waste water treatment, it can be
advantageous to largely or completely dispense with the presence of
organic polymers in the aqueous treatment solution. Consequently, a
preferred embodiment of the present invention is wherein the
aqueous solution contains no more than 1 mg/l of organic polymer.
Under this condition, it is further preferred that the aqueous
solution additionally contains 10 to 1000 mg/l, preferably 50 to
500 mg/l of silicon in the form of silica particles with an average
particle size of less than 1 .mu.m. The stated silica particles
with an average particle size of less than 1 .mu.m are known under
various generic names to the person skilled in the art. They are
called, for example, colloidal silica, precipitated silica or
pyrogenic silica. The average particle size, which is preferably in
the range of about 0.01 .mu.m to about 1 .mu.m, can be determined
by light scattering methods or by electron microscopy.
[0100] According to the second aspect of the present invention, the
treatment solution can be manufactured at the place of use by
dissolving the stated components in water and adjusting the pH.
However, this procedure is unusual in practice. In practice,
instead of this, aqueous concentrates are usually provided to the
place of use, diluted with water and the pH optionally adjusted to
produce the ready-for-use treatment solution. Accordingly, an
aqueous concentrate belongs to the second aspect of the invention,
which on dilution with water by a factor of about 10 to about 100,
particularly by a factor of about 20 to about 50 and optionally
adjusted in pH, results in an acidic, chromium-free, aqueous
solution of fluoro complexes according to the previous
description.
[0101] For stabilization, the concentrates can contain polymers
with thickening and/or dispersing properties. Examples of such
polymers are polymers or copolymers of unsaturated carboxylic
acids, carbohydrates or proteins. They can be present in a
concentration of up to 50 g/l.
[0102] On stability grounds, concentrates of this type are often
adjusted such that on dilution with water, the pH is not directly
in the required range. In this case, after dilution with water, the
pH has to be corrected either downwards or upwards. A downwards
adjustment is made by adding an acid, wherein either the acid form
of the fluoro complex of the metal M or nitric acid is suitable. An
upwards adjustment of pH can be effected with any basic substance,
for example with a solution of alkali metal hydroxides or
-carbonates, ammonia or organic amines. However, basic compounds or
salts, for example metal oxides, -hydroxides or -carbonates, which
represent the possible active components in the treatment solution,
can also be added to increase the pH. For example, magnesium or
zinc oxides, -hydroxides or -carbonates can be used here.
[0103] A process for the anticorrosion treatment of bright metal
surfaces further belongs to the second aspect of the present
invention, wherein the metal surface is contacted with a previously
described aqueous solution according to the second aspect of the
invention.
[0104] Optionally, after contact with the aqueous solution of a
fluoro complex, the metal surface is then rinsed with an aqueous
solution that contains one or more components selected from
compounds or salts of the elements cobalt, nickel, tin, copper,
titanium and zirconium and/or from water-soluble or
water-dispersible organic polymers.
[0105] The term "bright" metal surface was explained further above
in connection with the first aspect of the present invention. This
explanation is also correspondingly valid for the second aspect of
the present invention.
[0106] Independently of whether the treatment of the metal surface
with the aqueous solution of a fluoro complex corresponding to the
process cycle according to the first aspect of the invention or
with an aqueous solution according to the second aspect of the
invention, the following is generally valid for this process
step:
[0107] The bright metal surface is contacted with the acidic,
aqueous solution of a fluoro complex for a period of 0.5 to 10
minutes, preferably for 1 to 5 minutes. This can be carried out by
dipping into the treatment solution or by spraying the treatment
solution. In this regard, the temperature of the aqueous solution
of a fluoro complex is preferably in the range 15 to 60.degree. C.,
especially in the range of 25 to 50.degree. C. After this contact,
rinsing is preferably carried out with water, especially fully
deionized water. After this, the previously described final rinse
can optionally follow. In this case, another rinse is subsequently
made with water.
[0108] In the process cycle according to the first aspect of the
present invention, the treated metal surfaces are transferred
without drying into a bath for the cathodic electro-dipcoating. One
can proceed in exactly the same way for the treatment with a
solution of fluoro complexes according to the second aspect of the
present invention. However, one can also dry the treated metal
surface before coating it with a cathodic electro-dipcoat or with
another coating, such as for example a powder coating.
[0109] The subsequent embodiments demonstrate the technical
advantages of the process according to the invention or the novel
aqueous treatment solutions according to the invention.
EXAMPLES
[0110] Sample sheets of cold rolled steel, as is used in the
automotive construction industry, were used as the substrate in the
following experiments. All process steps were carried out as dip
processes. Abbreviations: FD water=fully deionized water, RT=room
temperature, min.=minutes, CED=cathodic electro-dipcoating.
TABLE-US-00001 TABLE 1 General procedure Bath Treatment Process
step Bath composition Temp pH time Cleaning 3% Ridoline .RTM. 1562
+ 60.degree. C. Alkaline 5 min. 0.3% Ridosol .RTM. 1561,
commercially available alkaline cleaners from Henkel Corp. Rinse
Tap water RT 1 min. Rinse FD water RT 1 min. Pre- See Tables
30.degree. C. See 3 min. treatment (zirconium is added as Tables
H.sub.2ZrF.sub.6) Rinse FD water RT 0.5 min. Optional Drying
cabinet 50.degree. C. 60 min. drying (see Tables) CED
Electro-dipcoat "Cathoguard .RTM." 310 from BASF Corporation
[0111] Table 2 recites the bath composition for the pre-treatment
in the process cycle according to Table 1 with drying after
pre-treatment, and corrosion results. Climate change test was
according to VDA 621-415: average corrosion after 70 days in mm,
and stone impact damage after 70 days, scale from 0.5 to 5
according to DIN 55996-1 (the smaller the better).
TABLE-US-00002 TABLE 2 Climate change Climate change test: Bath
composition test: corrosion (mm) stone impact damage Comparative
Example 1: 3.4 4.5 150 mg/l Zr, pH 4 Example 1: 150 mg/l Zr + 1.6
4.0 50 mg/l salicylic acid, pH 4 Example 2: 150 mg/l Zr + 1.9 3.5
200 mg/l salicylic acid, pH 4 Comparative Example 2: 9.3 5.0 150
mg/l Zr + 200 mg/l citric acid, pH 4
Results:
[0112] Examples 1 and 2, according to the invention, prove the
favorable effect of an addition of salicylic acid, when the
pre-treatment layer is dried (second aspect of the invention). In
contrast, an addition of citric acid (Comparative Example 2) has a
rather negative result.
[0113] Table 3 recites the bath composition for the pre-treatment
in the process cycle according to Table 1 without drying after
pre-treatment ("wet on wet"), and corrosion results. Climate change
test was according to VDA 621-415: average corrosion after 35 days
in mm.
TABLE-US-00003 TABLE 3 Climate change test: Bath composition
corrosion (mm) Comparative Example 3: 150 mg/l Zr, pH 4 1.5 Example
3: 150 mg/l Zr, 400 mg/l nitrate (added as 1.3 nitric acid), 200
mg/l Si (added as colloidal silica), pH 4
Results:
[0114] Example 3 proves the favorable effect of an addition of
nitrate and silica, when the pre-treatment layer is not dried
(first aspect of the invention).
[0115] A new test solution was used in the procedure according to
Table 1 to compare panels that were dried after pretreatment to
those coated wet on wet. For this experiment, the following
treatment solution was employed for the pre-treatment (treatment
time: 5 min.), wherein panels for (Comparative Example 4) were
dried after pre-treatment and panels (Example 4) were not dried
after the pre-treatment and prior to dipcoating: 150 mg/l Zr, 400
mg/l nitrate (added as nitric acid), 200 mg/l Si (added as
colloidal silica), pH 3.8. The so pretreated panels were subjected
to a climate change test according to VDA 621-415: average
corrosion after 70 days in mm is shown in Table 4.
TABLE-US-00004 TABLE 4 Climate change test: corrosion Bath
composition (mm) Comparative Example 4: (with drying) 3.9 mm
Example 4: (without drying) 3.6 mm
Results:
[0116] Example 4 shows that in the presence of nitrate and silica,
better results are obtained without drying than with drying (first
aspect of the invention).
[0117] Table 5 recites the bath composition for the pre-treatment
in the process cycle according to Table 1 without drying ("wet on
wet"), after pre-treatment and corrosion results. Climate change
test was according to VDA 621-415: average corrosion after 70 days
in mm, and stone impact damage after 70 days, scale from 0.5 to 5
according to DIN 55996-1 (the smaller the better).
TABLE-US-00005 TABLE 5 Climate change Climate change test: test:
corrosion stone impact Bath composition (mm) damage Comparative
Example 5: 150 mg/l 3.1 4.5 Zr, pH 4 Example 5: 150 mg/l Zr + 20
mg/l 1.3 3.7 Cu, pH 4 Example 6: 150 mg/l Zr + 20 mg/l 1.1 3.2 Cu +
200 mg/l Si, pH 4
Results:
[0118] Example 5 proves that the addition of 20 mg/l of copper (as
Cu(NO).sub.3) to the conversion bath in the "wet on wet" process
yields significantly better infiltration values in the climate
change test. The further addition of 20 mg/l of silicon in the form
of colloidal silica (Example 6) yields a significant improvement in
the K-value in the stone impact test. Table 6 recites the bath
composition for the pre-treatment in the process cycle according to
Table 1 without drying ("wet on wet"), after pre-treatment and
corrosion results. Climate change test was according to VDA
621-415: average corrosion after 70 days in mm, and stone impact
damage after 70 days, scale from 0.5 to 5 according to DIN 55996-1
(the smaller the better).
TABLE-US-00006 TABLE 6 Climate change Climate change test: test:
corrosion stone impact Bath composition (mm) damage Example 7: 150
mg/l Zr + 0.9 3.7 20 mg/l Cu + 50 mg/l Si, pH 4 Example 8: 150 mg/l
Zr + 0.7 2.3 5 mg/l Cu + 50 mg/l Si + 50 mg/l nitroguanidine, pH
4
Results
[0119] Examples 7 and 8 in comparison show that the addition of the
accelerator nitroguanidine (50 mg/l) to the conversion bath
resulted in a further improvement in the climate change test in
regard to the corrosive paint infiltration and also significantly
smaller K-values in the stone impact damage test.
* * * * *