U.S. patent application number 09/194412 was filed with the patent office on 2002-01-31 for zinc phosphating with integrated subsequent passivation.
This patent application is currently assigned to Henkel Kommanditgesellschaft auf Aktien (Henkel KGaA). Invention is credited to GEKE, JUERGEN, KUHM, PETER, MAYER, BERND.
Application Number | 20020011281 09/194412 |
Document ID | / |
Family ID | 7795360 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011281 |
Kind Code |
A1 |
GEKE, JUERGEN ; et
al. |
January 31, 2002 |
ZINC PHOSPHATING WITH INTEGRATED SUBSEQUENT PASSIVATION
Abstract
A process for the phosphatizing of metal surfaces composed of
steel, zinc-coated steel or steel coated with zinc alloy, of
aluminum and/or of aluminum-magnesium alloys, characterized in that
the phosphatizing solution contains: 0.2 to 3 g/l of zinc ions, 3
to 50 g/l of phosphate ions, calculated as PO.sub.4, 0.001 to 4 g/l
of manganese ions, 0.001 to 0.5 g/l of one or more polymers
selected from polyethers, polycarboxylates, polymeric phosphonic
acids, polymeric phosphinocarboxylic acids and nitrogen-containing
organic polymers and one or more accelerators. Preferred polymers
are poly(vinylphenol) derivatives containing amino groups.
Inventors: |
GEKE, JUERGEN; (DUESSELDORF,
DE) ; KUHM, PETER; (HILDEN, DE) ; MAYER,
BERND; (DUESSELDORF, DE) |
Correspondence
Address: |
HENKEL CORPORATION
2500 RENAISSANCE BLVD
STE 200
GULPH MILLS
PA
19406
US
|
Assignee: |
Henkel Kommanditgesellschaft auf
Aktien (Henkel KGaA)
Duesseldorf
DE
|
Family ID: |
7795360 |
Appl. No.: |
09/194412 |
Filed: |
November 30, 1998 |
PCT Filed: |
May 20, 1997 |
PCT NO: |
PCT/EP97/02552 |
Current U.S.
Class: |
148/260 ;
148/262 |
Current CPC
Class: |
C23C 22/364 20130101;
C23C 22/182 20130101 |
Class at
Publication: |
148/260 ;
148/262 |
International
Class: |
C23C 022/07 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 1996 |
EP |
196 21 184.0 |
Claims
1. Process for the phosphatizing of metal surfaces composed of
steel, zinc-coated steel or steel coated with zinc alloy, of
aluminum and/or of aluminum-magnesium alloys, whereby the metal
surfaces, by means of spraying or dipping for a period of between 3
seconds and 8 minutes, are brought into contact with a
zinc-containing phosphatizing solution, characterized in that the
phosphatizing solution contains: 0.2 to 3 g/l of zinc ions; 3 to 50
g/l of phosphate ions, calculated as PO.sub.4; 0.001 to 4 g/l of
manganese ions; 0.001 to 0.5 g/l of one or more polymers selected
from polycarboxylates, polymeric phosphonic acids, polymeric
phosphinocarboxylic acids, nitrogen-containing organic polymers and
poly-4-vinylphenol compounds corresponding to the general formula
I: 11wherein n is a number between 5 and 100, x independently of
one another denote hydrogen and/or CRR.sub.1OH groups, in which R
and R.sub.1 denote hydrogen, aliphatic and/or aromatic groups
having 1 to 12 carbon atoms; and one or more accelerators selected
from: 0.05 to 2 g/l of m-nitrobenzoate ions; 0.05 to 2 g/l of
p-nitrophenol; 0.1 to 10 g/l of hydroxylamine in free or bound
form; 0.1 to 10 g/l of a reducing sugar, the phosphatizing solution
containing not more than 0.5 g/l nitrate and the weight ratio of
phosphate ions to zinc ions being within the range between 3.7 and
30.
2. Process according to claim 1, characterized in that the
phosphatizing solution contains in addition from 1 to 50 mg/l of
nickel ions and/or from 5 to 100 mg/l of cobalt ions.
3. Process according to one or both of claims 1 and 2,
characterized in that the phosphatizing solution contains in
addition from 0.2 to 1.5 g/l of lithium ions.
4. Process according to one or more of claims 1 to 3, characterized
in that the phosphatizing solution contains in addition fluoride in
quantities of up to 2.5 g/l of total fluoride, whereof up to 1 g/l
is free fluoride, in each case calculated as F.sup.-.
5. Process according to one or more of claims 1 to 4, characterized
in that the phosphatizing solution contains as accelerator from 0.1
to 10 g/l of hydroxylamine in free or bound form.
6. Process according to one or more of claims 1 to 5, characterized
in that the phosphatizing solution contains the organic polymers in
a concentration of between 0.01 and 0.1 g/l.
7. Process according to one or more of claims 1 to 6, characterized
in that the organic polymers are selected from homopolymeric or
copolymeric compounds which contain amino groups and which contain
or consist of structural units corresponding to the general formula
(II): 12and hydrolysis products thereof, wherein R.sup.1 and
R.sup.2 are identical with one another or different and can
represent hydrogen or alkyl having 1 to 6 carbon atoms.
8. Process according to one or more of claims 1 to 6, characterized
in that the organic polymers are selected from homopolymeric or
copolymeric compounds which contain amino groups and include at
least one polymer, which is selected from the group consisting of
a), b), c) or d), wherein: a) comprises a polymeric material which
has at least one unit corresponding to the formula: 13wherein:
R.sub.1 to R.sub.3, independently for each of the units, are
selected from the group comprising hydrogen, an alkyl group having
1 to 5 carbon atoms or an aryl group having 6 to 18 carbon atoms;
Y.sub.1 to Y.sub.4, independently for each of the units, are
selected from the group comprising hydrogen,
--CR.sub.11R.sub.5OR.sub.6, --CH.sub.2Cl or an alkyl or aryl group
having 1 to 18 carbon atoms or Z: 14but at least a fraction of
Y.sub.1, Y.sub.2, Y.sub.3 or Y.sub.4 of the homopolymeric or
copolymeric compound or material must be Z; R.sub.5 to R.sub.12,
independently for each of the units, are selected from the group
comprising hydrogen, an alkyl, aryl, hydroxyalkyl, aminoalkyl,
mercaptoalkyl or phosphoalkyl group; R.sub.12 can also be
--O.sup.(-) or --OH; W.sub.1, independently for each of the units,
is selected from the group comprising hydrogen, an acyl group, an
acetyl group, a benzoyl group; 3-allyloxy-2-hydroxy-propyl;
3-benzyloxy-2-hydroxypropyl; 3-butoxy-2-hydroxypropyl;
3-alkyloxy-2-hydroxypropyl; 2-hydroxyoctyl; 2-hydroxyalkyl;
2-hydroxy-2-phenylethyl; 2-hydroxy-2-alkylphenylethyl; benzyl;
methyl; ethyl; propyl; alkyl; allyl; alkylbenzyl; haloalkyl;
haloalkenyl; 2-chloropropenyl; sodium; potassium;
tetraarylammonium; tetraalkylammonium; tetraalkylphosphonium;
tetraarylphosphonium or a condensation product of ethylene oxide,
propylene oxide or a mixture or a copolymer of the same; b)
comprises a polymeric material having at least one unit
corresponding to the formula: 15wherein: R.sub.1 to R.sub.2,
independently for each of the units, are selected from the group
comprising hydrogen, an alkyl group having 1 to 5 carbon atoms or
an aryl group having 6 to 18 carbon atoms; Y.sub.1 to Y.sub.3,
independently for each of the units, are selected from the group
comprising hydrogen, --CR.sub.4R.sub.5OR.sub.6, --CH.sub.2Cl or an
alkyl or aryl group having 1 to 18 carbon atoms or Z: 16but at
least a fraction of Y.sub.1, Y.sub.2, or Y.sub.3 of the end product
must be Z; R.sub.4 to R.sub.12, independently for each of the
units, are selected from the group comprising hydrogen, an alkyl,
aryl, hydroxyalkyl, aminoalkyl, mercaptoalkyl or phosphoalkyl
group; R.sub.12 can also be --O.sup.(-) or --OH; W.sub.2,
independently for each of the units, is selected from the group
comprising hydrogen, an acyl group, an acetyl group, a benzoyl
group; 3-allyloxy-2-hydroxypropyl; 3-benzyloxy-2-hydroxypropyl;
3-alkylbenzyloxy-2-hydroxypropyl; 3-phenoxy-2-hydroxypropyl;
3-alkylphenoxy-2-hydroxypropyl; 3-butoxy-2-hydroxypropyl;
3-alkyloxy-2-hydroxypropyl; 2-hydroxyoctyl; 2-hydroxyalkyl;
2-hydroxy-2-phenylethyl; 2-hydroxy-2-alkylphenylethyl; benzyl;
methyl; ethyl; propyl; alkyl; allyl; alkylbenzyl; haloalkyl;
haloalkenyl; 2-chloropropenyl or a condensation product of ethylene
oxide, propylene oxide or a mixture of the same; c) comprises: a
copolymeric material, wherein at least a part of the copolymer has
the structure: 17and at least a fraction of the said part is
polymerized with one or more monomers which, independently for each
unit, are selected from the group comprising acrylonitrile,
methacrylonitrile, methyl acrylate, methyl methacrylate, vinyl
acetate, vinyl methyl ketone, isopropenyl methyl ketone, acrylic
acid, methacrylic acid, acrylamide, methacrylamide, n-amyl
methacrylate, styrene, m-bromostyrene, p-bromostyrene, pyridine,
diallyldimethylammonium salts, 1,3-butadiene, n-butyl acrylate,
tert-butylaminoethyl methacrylate, n-butyl methacrylate, tert-butyl
methacrylate, n-butyl vinyl ether, tert-butyl vinyl ether,
m-chlorostyrene, o-chlorostyrene, p-chlorostyrene, n-decyl
methacrylate, N,N-diallylmelamine, N,N-di-n-butylacrylamide,
di-n-butyl itaconate, di-n-butyl maleate, diethylaminoethyl
methacrylate, diethylene glycol monovinyl ether, diethyl fumarate,
diethyl itaconate, diethylvinyl phosphate, vinylphosphonic acid,
diisobutyl maleate, diisopropyl itaconate, diisopropyl maleate,
dimethyl fumarate, dimethyl itaconate, dimethyl maleate, di-n-nonyl
fumarate, di-n-nonyl maleate, dioctyl fumarate, di-n-octyl
itaconate, di-n-propyl itaconate, N-dodecyl vinyl ether, acidic
ethyl fumarate, acidic ethyl maleate, ethyl acrylate, ethyl
cinnamate, N-ethylmethacrylamide, ethyl methacrylate, ethyl vinyl
ether, 5-ethyl-2-vinyl pyridine, 5- ethyl-2-vinylpyridine-1 oxide,
glycidyl acrylate, glycidyl methacrylate, n-hexyl methacrylate,
2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, isobutyl
methacrylate, isobutyl vinyl ether, isoprene, isopropyl
methacrylate, isopropyl vinyl ether, itaconic acid, lauryl
methacrylate, methacrylamide, methacrylic acid, methacrylonitrile,
N-methylolacrylamide, N-methylolmethacrylamide,
N-isobutoxymethylacrylamide, N-isobutoxymethylmethacrylamide,
N-alkyloxymethylacrylamide, N-alkyloxymethylmethacrylamide,
N-vinylcaprolactam, methyl acrylate, N-methylmethacrylamide,
.alpha.-methylstyrene, m-methylstyrene, o-methylstyrene,
p-methylstyrene, 2-methyl-5-vinylpyridine, n-propyl methacrylate,
sodium p-styrenesulfonate, stearyl methacrylate, styrene,
p-styrenesulfonic acid, p-styrene sulfonamide, vinyl bromide,
9-vinylcarbazole, vinyl chloride, vinylidene chloride,
1-vinylnaphthalene, 2-vinylnaphthalene, 2-vinylpyridine,
4-vinylpyridine, 2-vinylpyridine-N-oxide, 4-vinylpyrimidine,
N-vinylpyrrolidone; and W.sub.1 , Y.sub.1 to Y.sub.4 and R.sub.1 to
R.sub.3 are as described under a); (d) comprises a condensation
polymer made from the polymeric materials (a), (b) or (c), a
condensable form of (a), (b), (c) or a mixture of the same being
condensed with a second compound selected from the group consisting
of phenols, tannins, novolak resins, lignin compounds, together
with aldehydes, ketones or mixtures thereof, in order to prepare a
condensation resin product, the condensation resin product forming,
by the addition of "Z" to at least a part of itself by further
reaction of the resin product with 1) an aldehyde or ketone, (2) a
secondary amine, a final adduct which may react with an acid.
9. Process according to claim 8, characterized in that at least a
fraction of the groups Z of the organic polymer possesses a
polyhydroxyalkylamine functionality which originates from the
condensation of an amine or of ammonia with a ketose or aldose
which has 3 to 8 carbon atoms.
10. Process according to claim 8, characterized in that the organic
polymer is a condensation product of a polyvinylphenol, having a
molar mass within the range of 1,000 to 10,000, with formaldehyde
or paraformaldehyde and with a secondary organic amine.
11. Process according to claim 10, characterized in that the
secondary organic amine is selected from methylethanolamine and
N-methylglucamine.
12. Process according to one or more of claims 1 to 8,
characterized in that the organic polymers are selected from
substituted polyalkylene derivatives: 18wherein: R.sup.1, R.sup.2,
R.sup.3 independently of one another can be hydrogen or a methyl or
ethyl group; x denotes 1, 2, 3 or 4; and Y denotes a substituent
which contains at least one nitrogen atom, which is incorporated
into an alkylamino group or into a mononuclear or polynuclear
saturated or unsaturated heterocyclic compound.
13. Process according to claim 12, characterized in that R.sup.1,
R.sup.2, R.sup.3 each denote hydrogen and that x equals 1.
14. Process according to claim 12 or 13, characterized in that the
organic polymers contain one or more of the following structural
units: 19
15. Process according to one or more of claims 1 to 6,
characterized in that the organic polymers are polymeric sugar
derivatives containing amino groups.
16. Process according to claim 15, characterized in that the
polymeric sugar derivatives contain the following structural
groups: 20
Description
[0001] This invention relates to processes for the phosphatizing of
metal surfaces using aqueous, acid phosphate solutions containing
zinc ions, manganese ions, phosphate ions and up to 0.5 g/l of
organic polymers. This invention also relates to the use of such
processes as pre-treatment of metal surfaces for a subsequent
coating, in particular an electrocoating or a powder coating. The
process may be used for the treatment of surfaces of steel,
zinc-coated steel or steel coated with zinc alloy, of aluminum,
aluminum-magnesium alloys, aluminized steel or steel coated with
aluminum alloy, and avoids the passivating rinse required
hitherto.
[0002] The phosphatizing of metals seeks to produce on the metal
surfaces firmly adhering metal phosphate layers, which alone
already improve the resistance to corrosion and in combination with
paints or other organic coatings contribute to a considerable
increase in the paint adhesion and in the resistance to loss of the
paint during corrosive stress. Such phosphatizing processes have
been known for a long time. The low-zinc phosphatizing processes,
wherein the phosphatizing solutions have comparatively low contents
of zinc ions of, for example, from 0.5 to 2 g/l, are particularly
suitable for pretreatment prior to coating, in particular
electrocoating. An important factor in these low-zinc phosphatizing
baths is the weight ratio of phosphate ions to zinc ions, which is
generally above 8 and may be up to 30.
[0003] It has become apparent that phosphate layers having
distinctly improved properties of corrosion protection and paint
adhesion may be formed by the concomitant use of other polyvalent
cations in the zinc phosphatizing baths. By way of example,
low-zinc processes with an addition of, for example, from 0.5 to
1.5 g/l of manganese ions and, for example, from 0.3 to 2.0 g/l of
nickel ions find wide application as so-called trication processes
for the pretreatment of metal surfaces for coating, for example,
for the cathodic electrocoating of car bodywork.
[0004] As nickel and the alternatively used cobalt are classified
as critical from the aspects both of toxicology and of waste water
technology, there is a need for phosphatizing processes which have
a level of performance similar to that of the trication processes,
but which function with considerably lower concentrations of nickel
and/or cobalt in the baths and preferably without these two
metals.
[0005] From DE-A 20 49 350 a phosphatizing solution is known which
contains as essential constituents from 3 to 20 g/l of phosphate
ions, from 0.5 to 3 g/l of zinc ions, from 0.003 to 0.7 g/l of
cobalt ions or from 0.003 to 0.04 g/l of copper ions or preferably
from 0.05 to 3 g/l of nickel ions, from 1 to 8 g/l of magnesium
ions, from 0.01 to 0.25 g/l of nitrite ions and from 0.1 to 3 g/l
of fluoride ions and/or from 2 to 30 g/l of chloride ions. Hence,
this process is a zinc-magnesium phosphatizing, with the
phosphatizing solution containing in addition the ions of one of
the metals cobalt, copper or, preferably, nickel. Such a
zinc-magnesium phosphatizing has not succeeded in gaining technical
acceptance.
[0006] EP-B 18 841 describes a zinc phosphatizing solution
accelerated by chlorate/nitrate, containing inter alia from 0.4 to
1 g/l of zinc ions, from 5 to 40 g/l of phosphate ions, as well as,
optionally, at least 0.2 g/l, preferably from 0.2 to 2 g/l, of one
or more ions selected from nickel, cobalt, calcium and manganese.
The optional manganese, nickel or cobalt content is therefore at
least 0.2 g/l. Nickel contents of 0.53 g/l and 1.33 g/l are given
in the Examples.
[0007] EP-A 459 541 describes phosphatizing solutions which are
substantially free from nickel and which contain, in addition to
zinc and phosphate, from 0.2 to 4 g/l of manganese and from 1 to 30
mg/l of copper. DE-A 42 10 513 discloses nickel-free phosphatizing
solutions which contain in addition to zinc and phosphate, from 0.5
to 25 mg/l of copper ions and, as an accelerator, hydroxylamine.
These phosphatizing solutions optionally-contain-in addition-from
0.15 to 5 g/l of manganese.
[0008] German Patent Application DE 196 06 017.6 describes a
phosphatizing solution reduced in heavy metals, which contains from
0.2 to 3 g/l of zinc ions, from 1 to 150 mg/l of manganese ions and
from 1 to 30 mg/l of copper ions. This phosphatizing solution may
optionally contain up to 50 mg/l of nickel ions and up to 100 mg/l
of cobalt ions. Lithium ions in quantities of between 0.2 and 1.5
g/l are another optional constituent.
[0009] German Patent Application DE 195 38 778.3 describes the
control of the layer weight in phosphate layers by the use of
hydroxylamine as accelerator. The use of hydroxylamine and/or
derivatives thereof to influence the shape of the phosphate
crystals is known from a number of published patents. EP-A 315 059
mentions, as a particular effect of the use of hydroxylamine in
phosphatizing baths, the fact that, on steel, the phosphate
crystals still form in a desired columnar or nodular shape if the
zinc concentration in the phosphatizing bath exceeds the range
conventional for low-zinc processes. Hence it becomes possible to
operate the phosphatizing baths at zinc concentrations of up to 2
g/l and using weight ratios of phosphate to zinc as low as 3.7.
More details regarding advantageous combinations of cations in
these phosphatizing baths are not provided, but nickel is used in
all cases in the Examples given in the patent. Nitrates and nitric
acid are also used in the Examples, although the description
advises against the presence of nitrate in larger quantities. The
required hydroxylamine concentration is given as 0.5 to 50 g/l,
preferably 1 to 10 g/l. The maximum concentration of
hydroxylammonium sulfate in the Examples is 5 g/l, from which the
calculated hydroxylamine content is 2.08 g/l. (Hydroxylammonium
sulfate contains 41.5 wt. % of hydroxylamine.) The phosphatizing
solution is applied to the steel surfaces by spraying. The document
does not mention the problems involved in a dipping process, which
lead to phosphate layers having distinctly higher layer weights,
which are undesirable as a foundation for a subsequent coating.
[0010] WO 93/03198 discloses the use of hydroxylamine as
accelerator in tricationphosphatizing baths having zinc contents of
between 0.5 and 2 g/l and nickel and manganese contents each of
from 0.2 to 1.5 g/l, with definite weight ratios between zinc and
the other divalent cations also having to be maintained. These
baths also contain from 1 to 2.5 g/l of a "hydroxylamine
accelerator", which according to the description means salts of
hydroxylamine, preferably hydroxylamine sulfate. If this stated
quantity is calculated as free hydroxylamine, then hydroxylamine
contents of between 0.42 and 1.04 g/l are provided.
[0011] As a rule, to improve the corrosion protection produced by
the phosphate layer, a so-called "passivating rinse", also termed
post-passivation, is carried out in practice. Treatment baths
containing chromic acid are still widely used for this purpose. For
reasons of industrial safety and environmental protection there is
a tendency to replace these chromium-containing passivating baths
by chromium-free treatment baths. To this end, for example, organic
reactive bath solutions containing complexing substituted
poly(vinylphenols) are known. Such compounds are described, for
example, in DE-C 31 46 265. Particularly effective polymers of this
type contain amine substituents and may be obtained by a Mannich
reaction of poly(vinylphenols) with aldehydes and organic amines.
Such polymers are described, for example, in EP-B 91 166, EP-B 319
016 and EP-B 319 017. Polymers of this type are also used for the
present purposes and so these four disclosures are incorporated
herein by reference. The passivating rinse solutions may also
contain polymers having amino groups, the amino group being joined
directly to the polymer chain without any intervening aromatic
ring. Polymers of this type, which may likewise be used according
to the present invention, are described in DE-A 44 09 306.
[0012] In combination with a passivating rinse, the low-zinc
phosphatizing baths used at present meet the corrosion protection
standards set for automobile manufacture. This order of procedure
has the disadvantage, however, that the passivating rinse is a
separate treatment step which prolongs the production time and
increases the space requirement of the pre-treatment line.
[0013] An object of the present invention is to provide a
phosphatizing solution which satisfies the corrosion protection
standards in the automobile industry and in the case of which the
passivating rinse may be omitted. Hence the space requirement of
the pretreatment line is decreased and the production time may be
shortened.
[0014] The addition of polyacrylic acids to phosphatizing solutions
is already known from the literature. An example which may be
mentioned is the article by J. I. Wragg, J. E. Chamberlain, L.
Chann, H. W. White, T. Sugama and S. Manalis: "Characterization of
Polyacrylic Acid Modified Zinc Phosphate Crystal Conversion
Coatings", Journal of Applied Polymer Science, Vol. 50, 917-928
(1993). Here, however, model zinc phosphatizing solutions which
were investigated clearly differ from those currently used in
practice. They have higher contents of zinc; moreover, the widely
used manganese and the accelerators generally used at present are
absent. They are not, therefore, a model for the low-zinc
phosphatizing solutions used according to the present
invention.
[0015] The above object is fulfilled by a process for the
phosphatizing of metal surfaces composed of steel, zinc-coated
steel or steel coated with zinc alloy, and/or of aluminum, wherein
the metal surfaces, by means of spraying or dipping for a period of
between 3 seconds and 8 minutes, are contacted with a
zinc-containing phosphatizing solution, characterized in that the
phosphatizing solution contains:
[0016] 0.2 to 3 g/l of zinc ions;
[0017] 3 to 50 g/l of phosphate ions, calculated as PO.sub.4;
[0018] 0.001 to 4 g/l of manganese ions;
[0019] 0.001 to 0.5 g/l of one or more polymers selected from
polyethers, polycarboxylates, polymeric phosphonic acids, polymeric
phosphinocarboxylic acids and nitrogen-containing organic
polymers;
[0020] and
[0021] one or more accelerators selected from:
[0022] 0.3 to 4 g/l of chlorate ions;
[0023] 0.01 to 0.2 g/l of nitrite ions;
[0024] 0.05 to 2 g/l of m-nitrobenzene-sulfonate ions;
[0025] 0.05 to 2 g/l of m-nitrobenzoate ions;
[0026] 0.05 to 2 g/l of p-nitrophenol;
[0027] 0.005 to 0.15 g/l of hydrogen peroxide in free or bound
form;
[0028] 0.1 to 10 g/l of hydroxylamine in free or bound form;
[0029] 0.1 to 10 g/l of a reducing sugar.
[0030] The zinc concentration is preferably between about 0.3 and
about 2 g/l, particularly between about 0.8 and about 1.6 g/l. Zinc
contents above 1.6 g/l, for example, between 2 and 3 g/l, are of
only slight advantage to the process and on the other hand, may
increase the amount of sludge produced in the phosphatizing bath.
Such zinc contents may be established in an operating phosphatizing
bath if, during the phosphatizing of zinc-coated surfaces,
additional zinc enters the phosphatizing bath as a result of
corrosion by acid. Nickel ions and/or cobalt ions within the
concentration range of about 1 to about 50 mg/l for nickel and
about 5 to about 100 mg/l for cobalt, in combination with as low as
possible a nitrate content, of no more than about 0.5 g/l, improve
corrosion protection and paint adhesion compared with that of
phosphatizing baths containing no nickel or cobalt or having a
nitrate content of more than 0.5 g/l. Hence a favorable compromise
is reached between the performance of the phosphatizing baths, on
the one hand, and the requirements of waste water technology
regarding the treatment of the rinse water, on the other.
[0031] In phosphatizing baths reduced in heavy metals, the
manganese content may be within the range of about 0.001 to about
0.2 g/l. Otherwise, manganese contents of about 0.5 to about 1.5
g/l are usual.
[0032] From German Patent Application 195 00 927.4, it is known
that lithium ions within the quantitative range of about 0.2 to
about 1.5 g/l improve the corrosion protection attainable using
zinc phosphatizing baths. Lithium contents within the quantitative
range of 0.2 up to about 1.5 g/l, particularly of about 0.4 to
about 1 g/l, also have a favorable effect on the corrosion
protection attained in the phosphatizing process with integrated
post-passivation according to the present invention. In addition to
the cations mentioned above, which become incorporated into the
phosphate layer or at least have a favorable effect on the crystal
growth of the phosphate layer, the phosphatizing baths generally
contain sodium ions, potassium ions and/or ammonium ions for the
adjustment of the free acid. The concept of free acid is familiar
to the person skilled in the art of phosphatizing. The method
chosen in this document for determining the free acid and the total
acid is given in the Examples. Free acid and total acid are
important control variables for phosphatizing baths, as they have a
large influence on the layer weight. Values for the free acid of
between 0 and 1.5 points in phosphatizing of parts and, in the case
of continuous phosphatizing, up to 2.5 points, and values for the
total acid of between about 15 and about 30 points are within the
usual technical range and are suitable in accordance with the
present invention.
[0033] In phosphatizing baths which are to be suitable for
different substrates it has become conventional to add free
fluoride and/or fluoride bound in complex compounds in quantities
of up to 2.5 g/l of total fluoride, up to 1 g/l thereof being free
fluoride. The presence of these quantities of fluoride is also of
advantage in the phosphatizing baths according to the present
invention. In the absence of fluoride, the aluminum content of the
bath is not to exceed 3 mg/l. In the presence of fluoride, owing to
the formation of complexes, higher Al contents are tolerated,
provided that the concentration of the uncomplexed Al does not
exceed 3 mg/l. The use of fluoride-containing baths is therefore
advantageous when the surfaces being phosphated consist at least
partly of aluminum or contain aluminum. In these cases, it is
beneficial not to use fluoride bound in complex compounds, but to
use only free fluoride, preferably in concentrations of 0.5 to 1.0
g/l.
[0034] For the phosphatizing of zinc surfaces it is not absolutely
necessary that the phosphatizing baths contain so-called
accelerators. For the phosphatizing of steel surfaces, however, it
is necessary that the phosphatizing solution contain one or more
accelerators. These accelerators are common in the prior art as
components of zinc phosphatizing baths. They are understood as
including substances which, by being reduced themselves, chemically
bind the hydrogen formed as a result of the attack by the acid on
the metal surface. Oxidizing accelerators also have the effect of
oxidizing to the trivalent state the iron(II) ions released by
corrosive attack on steel surfaces, so that they may be
precipitated as iron(III) phosphate.
[0035] The phosphatizing baths according to the present invention
may contain as accelerators one or more of the following
components:
[0036] 0.3 to 4 g/l of chlorate ions;
[0037] 0.01 to 0.2 g/l of nitrite ions;
[0038] 0.05 to 2 g/l of m-nitrobenzene-sulfonate ions;
[0039] 0.05 to 2 g/l of m-nitrobenzoate ions;
[0040] 0.05 to 2 g/l of p-nitrophenol;
[0041] 0.005 to 0.15 g/l of hydrogen peroxide in free or bound
form;
[0042] 0.1 to 10 g/l of hydroxylamine in free or bound form;
[0043] 0.1 to 10 g/l of a reducing sugar.
[0044] In the phosphatizing of zinc-coated steel, it is necessary
that the phosphatizing solution contain as little nitrate as
possible. Nitrate concentrations of 0.5 g/l are not to be exceeded,
as at higher nitrate concentrations there is the danger of a
so-called "white specking". By this is meant white, crater-like
voids in the phosphate layer. Moreover, the paint adhesion on
zinc-coated surfaces is impaired.
[0045] The use of nitrite as accelerator leads to technically
satisfactory results, particularly on steel surfaces. For reasons
of industrial safety (danger of the evolution of nitrous gases), it
is, however, advisable to dispense with nitrite as accelerator. For
the phosphatizing of zinc-coated surfaces, this is also advisable
on technical grounds, as nitrate may be formed from nitrite and
this, as explained above, may lead to the problem of white specking
and to lowered paint adhesion on zinc.
[0046] Particularly preferred accelerators are hydrogen peroxide
for reasons of environmental acceptability and hydroxylamine for
the technical reasons involving the possibility of simplified
formulations for make-up solutions. The joint use of these two
accelerators is not advisable, however, as hydroxylamine is
decomposed by hydrogen peroxide. If hydrogen peroxide in free or
bound form is used as accelerator, concentrations of from 0.005 to
0.02 g/l of hydrogen peroxide are particularly preferred. Hydrogen
peroxide may be added as such to the phosphatizing solution. It is
also possible, however, to add hydrogen peroxide in bound form as
compounds which yield hydrogen peroxide as a result of hydrolysis
reactions in the phosphatizing bath. Examples of such compounds are
persalts, such as perborates, percarbonates, peroxosulfates or
peroxodisulfates. Other suitable sources of hydrogen peroxide are
ionic peroxides, such as alkali metal peroxides. A preferred
embodiment of the present invention involves the use of a
combination of chlorate ions and hydrogen peroxide in phosphatizing
by a dipping process. In this embodiment, the concentration of
chlorate may be, for example, 2 to 4 g/l and the concentration of
hydrogen peroxide may be 10 to 50 ppm.
[0047] The use of reducing sugars as accelerator is known from U.S.
Pat. No. 5,378,292. According to the present invention, they may be
used in quantities of between about 0.01 and about 10 g/l,
preferably of between about 0.5 and about 2.5 g/l. Examples of such
sugars are galactose, mannose and, in particular, glucose
(dextrose).
[0048] Another preferred embodiment of the present invention
involves the use of hydroxylamine as accelerator. Hydroxylamine may
be used as a free base, as a hydroxylamine complex, as an oxime,
which is a condensation product of hydroxylamine and a ketone, or
in the form of hydroxylammonium salts. If free hydroxylamine is
added to the phosphatizing bath or to a phosphatizing bath
concentrate, it will be present largely in the form of
hydroxylammonium cations owing to the acid character of these
solutions. If it is used in the form of hydroxylammonium salt, the
sulfates and phosphates are particularly suitable. In the case of
the phosphates, the acid salts are preferred owing to the better
solubility thereof. Hydroxylamine or the compounds thereof are
added to the phosphatizing bath in quantities such that the
calculated concentration of the free hydroxylamine is between 0.1
and 10 g/l, preferably between 0.3 and 5 g/l. Here it is preferred
that the phosphatizing baths contain hydroxylamine as the only
accelerator, possibly together with at most 0.5 g/l of nitrate.
Accordingly, in a preferred embodiment, phosphatizing baths are
used which contain none of the other known accelerators, such as
nitrite, oxo anions of halogens, peroxides or
nitrobenzene-sulfonate. A positive side effect is that
hydroxylamine concentrations above about 1.5 g/l lower the risk of
rust formation on inadequately flooded areas of the structural
parts being phosphatized.
[0049] During the application of the phosphatizing process to steel
surfaces, iron passes into solution in the form of iron(II) ions.
If the present phosphatizing baths do not contain substances which
oxidize iron(II), the divalent iron is converted into the trivalent
state solely as a result of atmospheric oxidation, so that it may
precipitate as iron(III) phosphate. This is the case, for example,
when hydroxylamine is used. Consequently, the iron(II) contents
which may build up in the phosphatizing baths are significantly
greater than those in baths containing oxidizing agents. In this
case, iron(II) concentrations of up to 50 ppm are normal, with
values of up to 500 ppm also being possible for a short period in
the course of production. These iron(II) concentrations are not
detrimental to the phosphatizing process according to the present
invention. When hard water is used, the phosphatizing baths may in
addition contain the hardness-producing cations Mg(II) and Ca(II)
in a total concentration of up to 7 mmol/l. Mg(II) or Ca(II) may
also be added to the phosphatizing bath in quantities of up to 2.5
g/l.
[0050] The weight ratio of phosphate ions to zinc ions in the
phosphatizing baths may vary within wide limits, provided it is
between 3.7 and 30. A weight ratio of between 10 and 20 is
particularly preferred. For the purpose of stating the phosphate
concentration, the total phosphorus content of the phosphatizing
bath is regarded as being present in the form of phosphate ions
PO.sub.4.sup.3-. In the calculation of the weight ratios,
therefore, no account is taken of the fact that, at the pH of
phosphatizing baths, which are generally in the range of about 3 to
about 3.6, only a very small part of the phosphate is actually
present in the form of the triply negatively charged anions. At
these pH values, it is more probable that the phosphate exists
mainly as a singly negatively charged dihydrogen phosphate anion,
together with smaller quantities of undissociated phosphoric acid
and doubly negatively charged hydrogen phosphate anions.
[0051] The organic polymers used according to the present invention
preferably have molecular weights (which may be determined, for
example, by gel permeation chromatography) of about 500 to about
50,000, in particular from about 800 to about 20,000.
[0052] The phosphatizing baths preferably contain the organic
polymers in a concentration of between about 0.01 and about 0.1
g/l. At lower concentrations, the required passivating effect
diminishes. Higher concentrations do not increase the effect
substantially and therefore become increasingly uneconomic.
[0053] The polymers which may be used according to the present
invention may be members of various chemical types. Common to them,
however, is that they carry oxygen atoms and/or nitrogen atoms
either in the polymer chain or in the side groups. The simplest
polymers of this type are polyalkylene glycols, for example,
polyethylene glycol or polypropylene glycol, which preferably have
a molecular weight of from 500 to 10,000. Polymeric carboxylic
acids, such as homo- or co-polymers of acrylic acid, methacrylic
acid and maleic acid, are likewise suitable, as also are polymeric
phosphonic acids or polymeric phosphinocarboxylic acids. An example
which may be given is a polyphosphinocarboxylic acid which may be
regarded as acrylic acid-sodium hypophosphite copolymer and is
available on the market as "Belciene.RTM. 500" from the FMC
Corporation, Great Britain.
[0054] The organic polymers may also be selected from homo- or
co-polymeric compounds containing amino groups and containing or
consisting of structural units corresponding to the general formula
(I): 1
[0055] and hydrolysis products thereof, wherein R.sup.1 and R.sup.2
are the same or different and may represent hydrogen or alkyl
having 1 to 6 carbon atoms, for example methyl, ethyl, n-propyl,
iso-propyl, n-butyl, iso-butyl, t-butyl, amyl, n-hexyl, isohexyl or
Diclohexyl.sup.1. .sup.1This word has not been translated, because
it has been determined that the original a mistake and therefore
has no proper translation.
[0056] A comprehensive list of such polymers may be found in DE-A
44 09 306, which disclosure is incorporated herein by reference.
Specific examples are hydrolysis products of homo- and co-polymers
of N-vinyl-formamide, N-vinyl-N-methyl-formamide,
N-vinyl-acetamide, N-vinyl-N-methylacetamide,
N-vinyl-N-ethylacetamide, N-vinyl-propion-amide and
N-vinyl-N-methyl-propionamide, with N-vinylformamide being
preferred, as it is very readily hydrolysable. Suitable comonomers
are monoethylenically unsaturated carboxylic acids having 3 to 8
carbon atoms, as well as the water-soluble salts of these
monomers.
[0057] The organic polymers may also be selected from
poly-4-vinylphenol compounds corresponding to the general formula
(II): 2
[0058] wherein:
[0059] n represents a number between 5 and 100,
[0060] x independently represents hydrogen and/or CRR.sub.1OH
groups, wherein R and R.sub.1 represent hydrogen, aliphatic and/or
aromatic groups having 1 to 12 carbon atoms.
[0061] These polymers are described as separate rinsing solutions
in DE-C 31 46 265. According to this specification,
poly-4-vinylphenol compounds of the type wherein at least one x
represents CH.sub.2OH are particularly suitable. A method for the
preparation thereof is given in the above-mentioned document.
[0062] Particularly preferred is the use of organic polymers
selected from homo- or copolymeric compounds containing amino
groups and including at least one polymer selected from the group
consisting of (a), (b), (c) or (d), wherein:
[0063] (a) comprises a polymeric material which has at least one
unit corresponding to the formula: 3
[0064] wherein:
[0065] R.sub.1 to R.sub.3 for each of the units are independently
selected from the group consisting of hydrogen, an alkyl group
having 1 to 5 carbon atoms or an aryl group having 6 to 18 carbon
atoms;
[0066] Y.sub.1 to Y.sub.4 for each of the units are independently
selected from the group consisting of hydrogen,
--CR.sub.11R.sub.5OR.sub.6, --CH.sub.2Cl or an alkyl or aryl group
having 1 to 18 carbon atoms or Z below: 4
[0067] but at least a fraction of Y.sub.1, Y.sub.2, Y.sub.3 or
Y.sub.4 of the homo- or co-polymeric compound or material must be
Z;
[0068] R.sub.5 to R.sub.12 for each of the units are independently
selected from the group consisting of hydrogen, an alkyl, aryl,
hydroxyalkyl, aminoalkyl, mercaptoalkyl or phosphoalkyl group;
[0069] R.sub.12 may also represent --O.sup.(-1) or --OH;
[0070] W.sub.1 for each of the units is independently selected from
the group consisting of hydrogen, an acyl group, an acetyl group, a
benzoyl group; 3-allyloxy-2-hydroxy-propyl;
3-benzyloxy-2-hydroxy-propyl; 3-butoxy-2-hydroxy-propyl;
3-alkyloxy-2-hydroxy-propyl; 2-hydroxy-octyl; 2-hydroxy-alkyl;
2-hydroxy-2-phenylethyl; 2-hydroxy-2-alkyl-phenylethyl; benzyl;
methyl; ethyl; propyl; alkyl; allyl; alkylbenzyl; haloalkyl;
haloalkenyl; 2-chloropropenyl; sodium; potassium;
tetraarylammonium; tetraalkylammonium; tetraalkylphosphonium;
tetraarylphosphonium or a condensation product of ethylene oxide,
propylene oxide or a mixture or a copolymer of the same;
[0071] (b) comprises:
[0072] a polymeric material having at least one unit corresponding
to the formula: 5
[0073] wherein:
[0074] R.sub.1 to R.sub.2 for each of the units are independently
selected from the group consisting of hydrogen, an alkyl group
having 1 to 5 carbon atoms or an aryl group having 6 to 18 carbon
atoms;
[0075] Y.sub.1 to Y.sub.3 for each of the units are independently
selected from the group consisting of hydrogen,
--CR.sub.4R.sub.5OR.sub.6, --CH.sub.2Cl or an alkyl or aryl group
having 1 to 18 carbon atoms or Z: 6
[0076] but at least a fraction of Y.sub.1, Y.sub.2, or Y.sub.3 of
the end product must be Z; R.sub.4 to R.sub.12 for each of the
units are independently selected from the group consisting of
hydrogen, an alkyl, aryl, hydroxyalkyl, aminoalkyl, mercaptoalkyl
or phosphoalkyl group; R.sub.12 may also be --O.sup.(-) or OH;
[0077] W.sub.2 for each of the units is independently selected from
the group consisting of hydrogen, an acyl group, an acetyl group, a
benzoyl group; 3-allyloxy-2-hydroxy-propyl;
3-benzyloxy-2-hydroxy-propyl; 3-alkyl-benzyloxy-2-hydroxy-propyl;
3-phenoxy-2-hydroxy-propyl; 3-alkyl-phenoxy-2-hydroxy-propyl;
3-butoxy-2-hydroxy-propyl; 3-alkyloxy-2-hydroxy-propyl;
2-hydroxy-octyl; 2-hydroxy-alkyl; 2-hydroxy-2-phenylethyl;
2-hydroxy-2-alkyl-phenylethyl; benzyl; methyl; ethyl; propyl;
alkyl; allyl; alkyl-benzyl; haloalkyl; haloalkenyl;
2-chloro-propenyl or a condensation product of ethylene oxide,
propylene oxide or a mixture of the same;
[0078] (c) comprises:
[0079] a copolymeric material, wherein at least a part of the
copolymer has the structure: 7
[0080] and at least a fraction of the said part is polymerized with
one or more monomers which for each unit are independently selected
from the group consisting of acrylonitrile, methacrylonitrile,
methyl acrylate, methyl methacrylate, vinyl acetate, vinyl methyl
ketone, isopropenyl methyl ketone, acrylic acid, methacrylic acid,
acrylamide, methacrylamide, n-amyl methacrylate, styrene,
m-bromostyrene, bromostyrene, pyridine, diallyl-dimethylammonium
salts, 1,3-butadiene, n-butyl acrylate, t-butylaminoethyl
methacrylate, n-butyl methacrylate, t-butyl methacrylate, n-butyl
vinyl ether, t-butyl vinyl ether, m-chlorostyrene, o-chlorostyrene,
p-chlorostyrene, n-decyl methacrylate, N,N-diallyl-melamine,
N,N-di-n-butylacrylamide, di-n-butyl itaconate, di-n-butyl maleate,
diethylaminoethylmethacrylate, diethylene glycol monovinyl ether,
diethyl fumarate, diethyl itaconate, diethylvinyl phosphate,
vinyl-phosphonic acid, diisobutyl maleate, diisopropyl itaconate,
diisopropyl maleate, dimethyl fumarate, dimethyl itaconate,
dimethyl maleate, di-n-nonyl fumarate, di-n-nonyl maleate, dioctyl
fumarate, di-n-octyl itaconate, di-n-propyl itaconate, N-dodecyl
vinyl ether, acidic ethyl fumarate, acidic ethyl maleate, ethyl
acrylate, ethyl cinnamate, N-ethylmethacrylamide, ethyl
methacrylate, ethyl vinyl ether, 5-ethyl-2-vinyl-pyridine,
5-ethyl-2-vinyl-pyridine-1 oxide, glycidyl acrylate, glycidyl
methacrylate, n-hexylmethacrylate, 2-hydroxy-ethyl methacrylate,
2-hydroxy-propyl methacrylate, isobutyl methacrylate, isobutyl
vinyl ether, isoprene, isopropyl methacrylate, isopropyl vinyl
ether, itaconic acid, lauryl methacrylate, N-methylolacrylamide,
N-methylol-methacrylamide, N-isobutoxy-methylacrylamide,
N-isobutoxy-methylmethacrylamide, N-alkyloxy-methylacrylamide,
N-alkyloxy-methylmethacrylamide, N-vinyl-caprolactam,
N-methyl-methacrylamide, .alpha.-methyl-styrene, m-methyl-styrene,
o-methylstyrene, p-methyl-styrene, 2-methyl-5-vinyl-pyridine,
n-propyl methacrylate, sodium p-styrene sulfonate, stearyl
methacrylate, styrene, p-styrene sulfonic acid, p-styrene
sulfonamide, vinyl bromide, 9-vinyl-carbazole, vinyl chloride,
vinylidene chloride, 1-vinyl-naphthalene, 2-vinylnaphthalene,
2-vinyl-pyridine, 4-vinyl-pyridine, 2-vinyl-pyridine N-oxide,
4-vinyl-pyrimidine, N-vinyl-pyrrolidone; and W.sub.1, Y.sub.1 to
Y.sub.4 and R.sub.1 to R.sub.3 are as described under (a); (d)
comprises a condensation polymer of the polymeric materials (a),
(b) or (c), a condensable form of (a), (b), (c) or a mixture of the
same being condensed with a second compound selected from the group
consisting of phenols, tannins, novolak resins, lignin compounds,
together with aldehydes, ketones or mixtures thereof, in order to
prepare a condensation resin product, the condensation resin
product forming, by the addition of "Z" to at least a part of
itself by further reaction of the resin product with 1) an aldehyde
or ketone, (2) a secondary amine, a final adduct which may react
with an acid.
[0081] Methods for preparing such polymers are described in the
publications EP-B 319 016 and EP-B 319 017 already cited. Polymers
of this type may be obtained from The Henkel Corporation, Parker
Amchen Division, USA, under the tradenames Parcolene.RTM. 95C,
Deoxylyte.RTM. 90A, 95A, 95AT, 100NC and TD-1355--CW.
[0082] In this connection particularly preferred polymers are those
wherein at least a fraction of the groups Z of the organic polymer
possesses a polyhydroxy-alkylamine functionality which originates
from the condensation of an amine or of ammonia with a ketose or
aldose having 3 to 8 carbon atoms. The condensation products may,
if desired, be reduced to amine.
[0083] Further examples of such polymers are condensation products
of a polyvinylphenol with formaldehyde or paraformaldehyde and with
a secondary organic amine. Here it is preferable to start from
polyvinylphenols having a molecular weight of about 1,000 to about
10,000. Particularly preferred condensation products are those
wherein the secondary organic amine is selected from
methylethanolamine and N-methylglucamine.
[0084] Within the stated concentration ranges the organic polymers
are stable in the phosphatizing baths and do not lead to
precipitation. They also show no adverse effects on the layer
formation and hence do not lead, for example, to the manifestation
of passivation, which may inhibit the growth of the phosphate
crystals, on the metal surface.
[0085] The organic polymers may also be selected from substituted
polyalkylene derivatives containing the structural units: 8
[0086] wherein R.sup.1, R.sup.2, R.sup.3 may independently
represent hydrogen or a methyl or ethyl group, x represents 1, 2, 3
or 4, and Y represents a substituent which contains at least one
nitrogen atom and is incorporated in an alkylamino group or in a
mono- or poly-nuclear saturated or unsaturated heterocyclic
compound.
[0087] Here, those polymers are preferred wherein R.sup.1, R.sup.2,
R.sup.3 each represent hydrogen. Preferably, x represents 1.
Accordingly, substituted polyethylenes are particularly preferred
polymers. Organic polymers which contain one or more of the
following structural units are particularly preferred: 9
[0088] In a further preferred embodiment, the organic polymers are
polymeric sugar derivatives containing amino groups. An example of
these are chitosans, which may contain, for example, the following
structural group: 10
[0089] It is valid for all organic polymers containing nitrogen
that, at the pH of the phosphatizing solution, at least some of the
nitrogen atoms are protonated and therefore carry a positive
charge.
[0090] Phosphatizing baths are generally distributed in the form of
aqueous concentrates, which are adjusted in situ to the
concentration to be used by the addition of water. For reasons of
stability, these concentrates may contain an excess of free
phosphoric acid so that, on dilution of the bath concentration, the
value of the free acid is initially too high and the pH is too low.
The value of the free acid is lowered to the required range by the
addition of alkalies such as sodium hydroxide, sodium carbonate or
ammonia. It is also known that the content of free acid may
increase with time while the phosphatizing bath is in use, as a
result of the consumption of layer-forming cations and possibly as
a result of decomposition reactions of the accelerator. In these
cases, it is necessary to re-adjust the value of the free acid to
the required range by adding alkali from time to time. This means
that the contents of alkali metal or ammonium ions in the
phosphatizing baths may fluctuate within wide limits and, in the
course of the period that the phosphatizing baths are in use, the
free acid tends to increase owing to dealkalization. The weight
ratio of alkali metal ions and/or ammonium ions to, for example,
zinc ions may accordingly be very low in the case of freshly
prepared phosphatizing baths, for example, it may be <0.05 and
in extreme cases may even be 0, while it generally rises over time
as a result of bath maintenance procedures, so that the ratio
becomes greater than 1 and the values may reach up to 10 and above.
As a rule, low-zinc phosphatizing baths require additions of alkali
metal ions or ammonium ions in order that the free acid may be
adjusted to within the required range at the required weight ratio
of PO.sub.4.sup.3-:Zn of >8. Similar observations may also be
made regarding the ratios of alkali metal ions and/or ammonium ions
to other constituents of the bath, for example, to phosphate
ions.
[0091] In the case of lithium-containing phosphatizing baths it is
preferable to avoid using sodium compounds to adjust the free acid,
as the beneficial effect of lithium on the corrosion protection is
suppressed by excessively high sodium concentrations. In this case,
basic lithium compounds are preferably used for the adjustment of
the free acid. Alternatively, potassium compounds are also
suitable.
[0092] In principle, the form in which the cations giving rise to
or influencing the layer are introduced into the phosphatizing
baths is unimportant. Nitrates, are however, to be avoided, so as
not to exceed the preferred upper limit for the nitrate content.
The metal ions are preferably used in the form of those compounds
which do not introduce any foreign ions into the phosphatizing
solution. For this reason it is most advantageous to use the metals
in the form of the oxides or carbonates thereof. Lithium may also
be used as sulfate.
[0093] Phosphatizing baths according to the present invention are
suitable for the phosphatizing of surfaces composed of steel,
zinc-coated steel or steel coated with zinc alloy, aluminum,
aluminized steel or steel coated with aluminum alloy, as well as of
aluminum-magnesium alloys. Here the term "aluminum" includes the
aluminum alloys common in technology such as AlMg.sub.0.5Si.sub.14.
The aforesaid materials may, as is becoming increasingly common in
automobile manufacture, also be juxtaposed.
[0094] In this connection, parts of the bodywork may also consist
of already pre-treated material, as occurs, for example, in the
Bonazink.RTM. process. Here, the substrate material is first of all
chromed or phosphated and subsequently coated with an organic
resin. The phosphatizing process according to the present invention
then leads to a phosphatizing on damaged areas of this pre-treated
layer or on untreated reverse sides.
[0095] The present process is suitable for application by dipping,
spraying or spray/dipping. It may be used particularly in
automobile manufacture, where treatment times of between 1 and 8
minutes, particularly of 2 to 5 minutes, are conventional. However,
its use in continuous phosphatizing in steelworks, wherein the
treatment times are between 3 and 12 seconds, is also possible.
When continuous phosphatizing processes are used, it is advisable
to adjust the bath concentrations in each case within the upper
half of preferred range according to the present invention. For
example, the zinc content may be from 1.5 to 2.5 g/l and the
content of free acid from 1.5 to 2.5 points. Especially zinc-coated
steel and electrolytically galvanized steel in particular are
suitable as substrates for continuous phosphatizing.
[0096] As is also conventional in other known phosphatizing baths,
suitable bath temperatures, irrespective of the field of
application, are between 30 and 70.degree. C., with the temperature
range of between 45 and 60.degree. C. being preferred.
[0097] The phosphatizing process according to the present invention
is intended particularly for the treatment of the above-mentioned
metal surfaces prior to coating, for example, prior to a cathodic
electrocoating, such as is conventional in automobile manufacture.
It is also suitable as a pre-treatment prior to a powder coating,
such as is used, for example, for domestic appliances. The
phosphatizing process should be seen as an individual step in the
conventional industrial pre-treatment chain. In this chain, the
steps involving cleaning and degreasing, intermediate rinsing and
activation precede the phosphatizing process with the activation
generally being carried out by means of activating agents
containing titanium phosphate.
EXAMPLES
[0098] The phosphatizing processes according to the present
invention and comparison processes were tested on steel sheets ST
1405, which are used in automobile manufacture. The dipping process
carried out was the following procedure, conventional in the
manufacture of car bodywork:
[0099] 1. Cleaning by means of an alkaline cleaner (Ridoline.RTM.
1501, Henkel KGaA), formulation 2% in tap water, 55.degree. C., 4
minutes.
[0100] 2. Rinsing with tap water, room temperature, 1 minute.
[0101] 3. Activation by means of an activating agent containing
titanium phosphate (Fixodine.RTM. 950, Henkel KGaA), formulation
0.1% in demineralized water, room temperature, 1 minute.
[0102] 4. Phosphatizing using phosphatizing baths of the following
composition:
[0103] 1.0 g/l of Zn.sup.2+
[0104] 1.0 g/l of Mn.sup.2+
[0105] 0.1 g/l of Fe.sup.2+
[0106] 14 g/l of PO.sub.4.sup.3-
[0107] 0.95 g/l of SiF.sub.6.sup.2-
[0108] 0.2 g/l of F.sup.-
[0109] 1.7 g/l of (NH.sub.3OH).sub.2SO.sub.4
[0110] Polymers as in the Table.
[0111] In addition to the cations listed above, the nitrate-free
phosphatizing baths contained, if necessary, sodium ions for
adjusting the free acid.
[0112] The number of points of the free acid was 0.9 and that of
the total acid was 23; the pH was 3.35. The number of points of the
free acid means the required consumption in ml of 0.1 N sodium
hydroxide solution to titrate 10 ml of bath solution until a pH of
3.6 is attained. Similarly, the number of points of total acid
indicates the consumption in ml to attain a pH of 8.2.
[0113] 5. Rinsing with demineralized water
[0114] 6. Blowing dry using compressed air.
[0115] The mass per unit of surface ("layer weight") was determined
by dissolving in 5 % chromic acid solution in accordance with DIN
50942. It is shown in the Table.
[0116] The phosphated specimen sheets were coated with a cathodic
dipping paint from the firm BASF (FT 85-7042). The anticorrosive
action was tested in an alternating climate test by VDA 621-415
over 9 cycles. The result is included in the Table as the loss of
the paint at the scribe (half gap width).
1TABLE Phosphatizing baths and results of phosphatizing Loss of
Polymer Layer weight paint (Half No. (concentration) (g/cm.sup.2)
gap width) Comp. 1 Without polymer 3.7 1.9 Ex. 1 Polyethylene
glycol 3.2 1.7 Molecular weight 1000, 10 ppm Ex. 2 As Example 1, 50
ppm 3.9 1.5 Ex. 3 TD-1355-CW 3000*) 3.5 1.5 Ex. 4 As Example 3, 50
ppm 3.8 1.3 Ex. 5 TD-1355-CW 8600**) 3.7 1.4 Ex. 6 As Example 5, 50
ppm 3.2 1.1 *)Mannich reaction product of polyvinyl-phenol
(molecular weight 3000, determined by gel permeation
chromatography) with paraformaldehyde and glucamine (Parker Amchen,
USA) **)as above, molecular weight of the polyvinylphenol:
8600.
* * * * *