Note: Descriptions are shown in the official language in which they were submitted.
CA 02303183 2000-03-09
WO 99/12661 PCTIUS98/18001
PRETREATMENT BEFORE PAINTING OF COMPOSITE METAL STRUCTURES
CONTAINING ALUMINUM PORTIONS
BACKGROUND OF THE INVENTION
For many reasons, such as weight, rigidity or recyclability, aluminum is
increasingly used in vehicie construction. In the context of this invention
the expression
"aluminum" refers not only to pure aluminum but also to aluminum alloys whose
main
component is aluminum. Examples of commonly used alloying elements are
silicon,
magnesium, copper, manganese, chromium and nickel, the total proportion by
weight
of these alloying elements in the alloy normally not exceeding 10 %. Whereas
engine
and gear parts, wheels, seat frames, etc. already contain large amounts of
aluminum,
the use of aluminum in bodywork construction is presently still restricted to
parts such
,o as hoods, rear trunk lids, inner door parts and various small parts as well
as truck
cabins, side walls of transporters or attachments to minivans. Overall,
worldwide less
than 5 % of the metal surface of automobile bodies is made of aluminum. The
increased
use of aluminum in this sector is being intensively investigated by the
aluminum and
automobile industries.
is This invention relates to a process for the corrosion-prevention
pretreatment be-
fore painting of composite metal structures that contain aluminum and/or
aluminum alloy
portions in addition to steel and/or galvanized steel portions. The process is
particularly
intended for use in automobile manufacturing. In automobile manufacturing, car
bodies
or car body parts that contain structurai portions of aluminum and/or its
alloys in addition
20 to structural portions of steel and/or galvanized steel are subjected to a
conversion-
chemical pretreatment before they are painted. In this connection a cathodic
electro-dip-
coating is conventionally used at the present time as the first painting
stage. The pro-
cess according to the invention is particularly suitable as a pretreatment for
this stage.
The process differs from previous conventional pretreatment processes in auto-
25 mobile manufacturing in that a surface-covering zinc phosphate layer is
deposited in a
first step on th,e steel and/or galvanized steel surfaces, without coating the
aluminum
surfaces to any appreciable extent. A second step comprises a treatment with a
solution
that does not excessively attack the previously formed zinc phosphate layer,
and indeed
preferably even enhances its corrosion-prevention action, and which
simultaneously
1
CA 02303183 2000-03-09
WO 99/12661 PCT/US98/18001
forms a surface layer on the aluminum surfaces.
A two-stage process is thus involved, whose first stage comprises a
conventional
zinc phosphating. It is a necessary crondition, of course, that a zinc
phosphating solution
is used that does not form a layer on aluminum. Such zinc phosphating
solutions are
known in the prior art and are referred to by the way of example hereinafter.
In the sec-
ond stage solutions with constituents that are effective to form a protective
layer on
aluminum are used. In this connection the nature and concentration of these
solutions
should be chosen so that on the one hand a layer is reliably formed on the
aluminum
surfaces, but on the other hand the crystalline zinc phosphation layers formed
on the
iron and/or zinc surfaces are not excessively damaged.
The aim of phosphating metals is to produce firmly adhering metal phosphate
layers on the metal surface that per se already improve the corrosion
resistance, and
in conjunction with paints or other organic coatings contribute to a
substantial
improvement of the coating adhesion and resistance to creepage under corrosive
stress.
,s Such phosphating processes have been known for a long time. For the
pretreatment
before painting, especially before electro-dipcoating, low zinc phosphating
processes,
in which the phosphating solutions contain reiatively small concentrations of
zinc ions,
for example 0.5 to 2 grams per liter, hereinafter usually abbreviated as
"g/{", are
particularly suitable. A basic parameter in these low zinc phosphating baths
is the
weight ratio of phosphate ions to zinc ions, which is normally above 8 and may
reach
values of up to 30.
It has been found that phosphate layers with substantially improved corrosion-
prevention and paint adhesion properties can be formed by the co-use of other
polyvalent cations in the zinc phosphating baths. For example, low zinc
processes with
the addition of, e.g., 0.5 to 1.5 g/I of manganese ions and, e.g., 0.3 to 2.0
g/I of nickel
ions are widely used as so-called "tri-cation" processes for preparing metal
surfaces for
painting, for example for cathodic electro-dipcoating of car bodies.
Since nickel and its altemative cobalt also are classed as hazardous from the
toxicological and effluent treatment aspects, efforts are being made at the
present time
to find phosphating processes that are just as effective as the tri-cation
processes but
employ significantly lower bath concentrations of nickel and/or cobalt and
preferably
even dispense with these two metals altogether.
EP-A-459 541 describes phosphating solutions that are essentially free of
nickel
and that contain, in addition to zinc and phosphate, 0.2 to 4 g/I of manganese
and 1 to
30 milligrams per Iiter, hereinafter usually abbreviated as "mg/I", of copper.
From DE-A-
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WO 99/12661 PCT/US98/18001
42 10 513 nickel-free phosphating solutions are known that contain, in
addition to zinc
and phosphate, 0.5 to 25 mg/I of copper ions as well as hydroxylamine as
accelerator.
These phosphating solutions optionally also contain 0.15 to 5 g/I of
manganese.
German patent application DE 196 06 017.6 describes a phosphating solution,
with a decreased heavy metal concentration, which contains 0.2 to 3 g/1 of
zinc ions, 1
to 150 mg/I of manganese ions, and 1 to 30 mg/i of copper ions. This
phosphating
solution may optionally contain up to 50 mg/I of nickel ions and up to 100
mg/I of cobalt
ions. A further optional constituent is lithium ions in amounts of between 0.2
and 1.5 g/l.
DE 195 38 778 describes controlling the coating weight of phosphate layers by
the use of hydroxyiamine as accelerator. The use of hydroxylamine and/or its
com-
pounds in order to influence the form of the phosphate crystals is known from
a number
of publications. EP-A-315 059 discloses as a special effect of the use of
hydroxylamine
in phosphating baths the fact that on steel the phosphate crystals still occur
in the
desired columnar or nodular form, even if the zinc concentration in the
phosphating bath
exceeds the conventional range for low zinc processes. In this way it is
possible to
operate the phosphating baths with zinc concentrations up to 2 g/I and with
weight ratios
of phosphate to zinc of as low as 3.7. The required hydroxylamine
concentration is
given as 0.5 to 50 g/i, preferably 1 to 10 g/l.
WO 93/03198 discloses the use of hydroxylamine as accelerator in tri-cation
phosphating baths with zinc contents of between 0.5 and 2 g/I and nickel and
manganese contents of in each case 0.2 to 1.5 g/I, specific weight ratios of
zinc to the
other divaient cations having to be maintained. In addition, these baths
contain I to 2.5
g/I of a"hydroxyfamine acceterator', which according to the description
denotes salts of
hydroxyiamine, preferably hydroxylamine ammonium sulfate.
In order to improve the corrosion prevention produced by the phosphate layer,
a so-called passivating post-rinsing, also termed post-passivation, is
generally employed
in this technology. Treatment baths containing chromic acid are still widely
used for this
purpose. For reasons of work safety and environmental protection there is a
tendency,
however, to replace these chromium-containing passivating baths by chromium-
free
treatment baths. Organo-reactive bath solutions containing complexing
substituted poly-
(vinylphenols) are known for this purpose. Examples of such compounds are
described
in DE-C-31 46 265. Particularly effective polymers of this type contain amine
substituents and may be obtained by a Mannich reaction between
poly(vinylphenols)
and aidehydes 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
within
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WO 99/12661 PCT/US98/18001
the scope of the present invention, and accordingly the contents of the
immediately
aforementioned four documents, except to any extent that may be inconsistent
with any
explicit teaching herein, are hereby incorporated herein by reference. The use
of such
polyvinyl phenol derivatives for the surface treatment of aluminum is known,
for
example, from the aforementioned EP-B-319 016.
WO 90/12902 discloses a chromium-free coating for aluminum, the aluminum
surfaces being contacted with a treatment solution that has a pH in the range
from about
2.5 to about 5.0 and contains, in addition to polyvinyl phenol derivatives,
also phosphate
ions as well as fluoro acids of the elements zirconium, titanium, hafnium and
silicon.
US-A-5 129 967 discloses treatment baths for a no-rinse treatment (termed
there
as "dried in place conversion coating") of aluminum, containing:
(a) 10 to 16 g/I of polyacrylic acid or copoiymers of acrylic acid,
(b) 12 to 19 g/I of hexafluorozirconic acid,
(c) 0.17 to 0.3 g/1 of hydrofluoric acid, and
1s (d) up to 0.6 g/I of hexafluorotitanic acid.
EP-B-8 942 discloses treatment solutions, preferably for aluminum cans,
containing:
(a) 0.5 to 10 g/! of polyacrylic acid or an ester thereof,
(b) 0.2 to 8 g/I of at least one of the compounds H2ZrFs, HZTFe and H2SiFg,
the pH
of the solution being below 3.5,
as well- as an aqueous concentrate to -replenish the treatment solution, -
containing*, (a) 25 to 100 g/I of polyacrytic acid or an ester thereof,
(b) 25 to 100 g/I of at least one of the compounds H2ZrF8, HZTiFe and H2SiF6,
and
(c) a source of free fluoride ions that yields 17 to 120 g/I of free fluoride.
DE-C-19 33 013 discloses treatment baths with a pH above 3.5, which besides
complex fluorides of boron, titanium or zirconium in amounts of 0.1 to 15 g/l,
measured
as its stoichiometric equivalent as boron, titanium, or zirconium as
appropriate, addition-
ally contain 0.5 to 30 g/I of oxidizing agent, especially sodium meta-
nitrobenzenesulfon-
ate. DE-C-24 33 704 describes treatment baths to improve paint adhesion and
perma-
nent corrosion prevention on, inheralia, aluminum, which may contain 0.1 to 5
g/I of poly-
acrylic acid or its salts or esters as well as 0.1 to 3.5 g/I of ammonium
fluorozirconate,
calculated as Zr02. The pH of these baths may vary over a wide range. The best
re-
sults are generally obtained when the pH is between 6 and 8. US-A-4 992 116 de-
scribes treatment baths for the conversion treatment of aluminum with pH
vaiues be-
tween about 2.5 and 5, which contain at least three components:
as (a) phosphate ions in the concentration range between 1.1x10'5 to 5.3x10'3
mole/I,
4
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WO 99/12661 PCT/US98/18001
corresponding to I to 500 mg/I,
(b) 1.1x10-5 to 1.3x10'3 mole/liter, hereinafter usually abbreviated as
"mole/I", of a
fluoro acid of an element of the group Zr, TI, Hf and Si (corresponding to 1.6
to
380 mg/i of each element) and
(c) 026 to 20 g/I of a polyphenol compound obtainable by reacting
poly(vinylphenol)
with aldehydes and organic amines.
A molar ratio of fluoro acid to phosphate of about 2.5:1 to about 1:10 should
be main-
tained.
DE-A-27 15 292 discloses treatment baths for the chromium-free pretreatment
of aluminum cans, which contain at least 10 parts per million by weight,
hereinafter
usually abbreviated as "ppm", of titanium and/or zirconium, between 10 and
1000 ppm
of phosphate, and a sufficient amount of fluoride, but at least 13 ppm, to
form complex
fluorides of the titanium and/or zirconium present, and have pH values of
between 1.5
and 4.
is WO 92/07973 discloses a chromium-free treatment process for aluminum, which
uses as essential components in acid aqueous solution 0.01 to about 18 wt. %
of HZZrFe
and 0.01 to about 10 wt. % of a 3-(N-C,-4alkyl-N-2-hydroxyethyl-aminomethyl)-4-
hydroxy-
styrene polymer. Optional components include 0.05 - 10 wt. % of dispersed
SiOz, 0.06
to 0.6 wt. % of a solubilizing agent for the polymer, as well as a surfactant.
The afore-
mentioned polymer is included among the "reaction products of
poly(vinylphenol) with
aldehydes and organic hydroxyl group-containing amines" described below and
that can
be used within the scope of the present invention.
In practice it has been found that in the joint phosphating of surfaces of
aluminum and those of steel and/or galvanized steel, technical compromises
have to be
accepted as regards the composition of the phosphating baths. Aluminum ions
released
from the aluminum surface by the etching and pickling action act as a bath
poison for
the phosphating solution and interfere in the formation of zinc phosphate
crystals on iron
surfaces. The dissolved aluminum must therefore be precipitated or masked by
appropriate measures. For this purpose free or complex-bound fluoride ions are
normally added to the phosphating baths.
The fluoride ions mask the aluminum ions by complex formation and/or
precipitate these ions as hexa-fluoroaluminates of sodium and/or potassium if
the
solubility products of the corresponding salts are exceeded. Furthermore free
fluoride
ions usually lead to an increased etching attack on the aluminum surfaces,
with the
result that a more or less closed and sealed zinc phosphate layer can form on
the latter.
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The joint phosphating of aluminum structural portions with those of steei
and/or
galvanized steel thus has the technical disadvantage that the phosphating
baths have
to be very accurately monitored as regards their fluoride content. This
increases the
control and monitoring work involved and may require stocking and metering
fluoride-
s containing solutions as separate replenishment solutions. Also, the
precipitated
hexafluonoaluminate salts increase the amount of phosphating sludge and raise
the cost
of its removal and disposal.
Accordingly there exists a need for pretreatment processes for complex
stmctural parts, for example autoniobile bodies, that contain besides aluminum
portions,
also steel and/or galvanized steel portions. The formulation range for the
phosphating
baths should be broadened and the control and monitoring work involved should
be
reduced. The result of the overall pretreatment should be the formation of a
conversion
layer on all exposed metal surfaces that is suitable as a corrosion-preventing
paint
substrate, especially before a cathodic electro-dipcoating.
SUMMARY OF THE INVENTION
This object is achieved by a process for the chemical pretreatment, before an
or-
ganic coating, of composite metal structures that contain aluminum or aluminum
alloy
portions together with steel, galvanized steel and/or alloy-galvanized steel
portions,
characterized by:
(I) treating in a first step the composite metal structure with a zinc
phosphating solu-
tion that forms on steel and on galvanized and/or alloy-galvanized steel a sur-
face-covering crystalline zinc phosphate layer having a coating weight in the
range from 0.5 to 5 g/m2, but without forming a zinc phosphate layer on the
aluminum portions;
and subsequently, with or without intermediate rinsing with water,
(II) contacting in a second step the composite metal structure with a
treatment solu-
tion that does not dissolve more than, with increasing preference in the order
given, 60, 50, 40, 30, 20, 15, 10, 8, or 6 % of the crystalline zinc phosphate
layer
formed on steel, galvanized and/or alloy-galvanized steel in step (I), but
does
produce a conversion layer on the aluminum portions.
The stipulation that no zinc phosphate layer is to be formed on the aluminum
portions
in the treatment step (a) is to be understood to mean that no closed and
seaied
crystalline layer is formed and that the mass per unit area of any deposited
zinc
phosphate does not exceed 0.5 grams per square meter, hereinafter usually
abbreviated
as "g/m2". In order to satisfy this condition, the phosphating baths may be
arbitrarily
6
CA 02303183 2007-08-08
7
formulated as long as specific conditions for the fluoride concentration are
observed.
These conditions may be found in EP-B-452 638. This document summarizes the
conditions under which
a closed zinc phosphate layer is formed on aluminum surfaces.
According to this disclosure the concentration of free fluoride ions for
example, measured in g/l, should
satisfy the condition that, at a specific temperature T (in C), it lies above
a value of 8/T. Since however
within the scope of the present invention no zinc phosphate layer should be
formed on aluminum in the
phosphating step (I), in contrast to the teaching of EP-B-452 638, at a
specific temperature T (in C) the
concentration of free fluoride ions (in g/1) in the phosphating solution must
be below 81T.
More particularly, the invention provides a process for chemical pretreatment
of a composite metal
structure that contains at least one aluminium or aluminium alloy portion
together with at least one steel,
galvanized steel or alloy-galvanized steel portion, said process comprising
steps of:
I) treating in a first step the composite metal structure with a zinc
phosphating solution, wherein
the zinc phosphating solution has a free acid value of between 0 and 2.5
points and contains an amount
of free fluoride, expressed in g/l, that is not greater than a quotient of the
number 8 divided by the solution
temperature in C for a sufficient time to thereby form on steel and on
galvanized and alloy-galvanized
steel a surface-covering crystalline zinc phosphate layer having a coating
weight in the range from 0.5 to
5 g/m2, but without forming a surface-covering zinc phosphate layer on the
aluminium portions;
and subsequently, with or without an intermediate rinsing with water,
II) contacting in a second step the composite metal structure with a treatment
solution, comprising
organic polymer, hexafluorotitanate and/or hexafluorozirconate ions, having a
pH of 2.5-10 and a
temperature in a range from 20 to 70 C such that the treatment solution does
not dissolve more than
60% of the crystalline zinc phosphate layer on steel, galvanized and/or alloy-
galvanized steel, but does
produce a conversion layer on the aluminum portions.
In another aspect, the invention provides a process for chemical pretreatment
of a composite metal
structure that contains at least one aluminium or aluminium alloy portion
together with at least one steel,
galvanized steel or alloy-galvanized steel portion, said process comprising
steps of:
I) treating in a first step the composite metal structure with a zinc
phosphating solution having a
free acid value of between 0 and 2.5 points and an amount of free fluoride,
expressed in g/l, that is not
greater than a quotient of the number 8 divided by the solution temperature in
C, at a temperature in a
range from 20 to 65 C for a time sufficient to deposit on the steel,
galvanized and alloy-galvanized steel
portion, a surface-covering crystalline zinc phosphate layer and deposit on
the aluminium portions only
widely scattered zinc phosphate crystals;
CA 02303183 2007-08-08
7A
and subsequently, with or without an intermediate rinsing with water,
II) contacting in a second step the composite metal structure with a treatment
solution,
comprising organic polymer, hexafluorotitanate and/or hexafluorozirconate
ions, having a pH of 2.5-10
and a temperature in a range from 20 to 70 C such that the treatment solution
does not dissolve more
than 60% of the crystalline zinc phosphate layer on steel, galvanized and/or
alloy-galvanized steel, but
does produce a conversion layer on the aluminum portions.
In yet another aspect, the invention provides a process for chemical
pretreatment of a composite metal
structure that contains at least one aluminium or aluminium alloy portion
together with at least one steel,
galvanized steel or alloy-galvanized steel portion, said process comprising
steps of:
I) treating in a first step the composite metal structure with a zinc
phosphating solution, wherein
the zinc phosphating solution has a pH in a range from 2.5 to 3.6 and a
temperature in a range from 20 to
65 C and contains an amount of free fluoride, expressed in g/l, that is not
greater than a quotient of the
number 8 divided by the solution temperature in C thereby forming on steel
and on galvanized and alloy-
galvanized steel a surface-covering crystalline zinc phosphate layer having a
coating weight in the range
from 0.5 to 5 g/M2, but without forming a zinc phosphate layer on the aluminum
portions;
and subsequently, with or without an intermediate rinsing with water,
II) contacting in a second step the composite metal structure with a treatment
solution,
comprising organic polymer, hexafluorotitanate and/or hexafluorozirconate
ions, having a pH of 2.5-10
and a temperature in a range from 20 to 70 C such that the treatment solution
does not dissolve more
than 60% of the crystalline zinc phosphate layer on steel, galvanized and/or
alloy-galvanized steel, but
does produce a conversion layer on the aluminum portions.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, in the phosphating step (I) a zinc phosphating solution which has
a pH in the range
from about 2.5 to about 3.6 and a temperature in the range from about 20 to
about 65 C, and which does
not contain more free fluoride in g/I than is specified by the expression 8/T,
"T' denoting the bath
temperature in C, is preferably used. Independently for each component
stated, this zinc phosphating
solution preferably also comprises:
0.3 to 3 g/I of Zn(II),
5 to 40 g/I of phosphate ions,
and at least one of the following accelerators:
0.3 to 4, or more preferably 1 to 4, g/I of chlorate ions,
CA 02303183 2007-08-08
7B
0.01 to 0.2 g/I of nitrite ions,
0.05 to 2, or more preferably 0.2 to 2, g/I of m-nitrobenzenesulfonate ions,
0.05 to 2 g/l of m-nitrobenzoate ions,
0.05 to 2g/I of p-nitrophenol,
0.001 to 0.15, or more preferably 0.001 to 0.070, g/l of hydrogen peroxide in
free or
bound form,
0.1 to 10 g/l hydroxylamine in free or bound form, and
0.1 to 10 g/I of a reducing sugar.
Experience shows that the corrosion prevention and paint adhesion of the
crystalline zinc
phosphate layers formed in such a phosphating bath are improved if the zinc
phosphating solution in step
(I) additionally contains one or more of the following cation concentrations:
0.001 to 4 g/I of manganese(II),
0.001 to 4 g/l of nickel(II),
0.002 to 0.2 g/I of copper(II),
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WO 99/12661 PCT/US98/18001
0.2 to 2.5 g/I of magnesium(11),
0.2 to 2.5 g/I of calcium(II),
0.01 to 0.5 g/I of iron(II),
0.2 to 1.5 g/I of lithium(I), and
0.02 to 0.8 g/I of tungsten(VI).
The zinc concentration is more preferably in the range between about 0.8 and
about 1.6 g/I. Zinc concentrations above 1.6 g/l, for example between 2 and 3
g/l, bring
only slight advantages for the process, but on the other hand can increase the
incidence
of sludge in the phosphating bath. Such zinc concentrations are adjusted in a
working
phosphating bath if during the phosphating of galvanized surfaces additional
zinc passes
into the phosphating bath through its etching action. Nickel and/or cobalt
ions in a
concentration range of in each case about I to about 50 mg/i for nickel and
about 5 to
about 100 mg/i for cobalt in combination with as low a nitrate content as
possible, not
more than about 0.5 g/l, improve the corrosion prevention and paint adhesion
compared
is to phosphating baths that do not contain nickel or cobalt or that have a
nitrate content
of more than 0.5 g/I. In this way a favorable compromise is reached between
the per-
formance of the phosphating baths on the one hand and the requirements of the
effluent
technology treatment of the rinse waters on the other hand.
With phosphating baths containing reduced amounts of heavy metals, the man-
ganese content may be in the range from about 0.001 to 0.2 g/l. Othennrise
manganese
contents of about 0.5 to about 1.5 g/I are conventional.
It is known from DE-A-195 00 927 that lithium ions in amounts of about 0.2 to
about 1.5 g/l improve the corrosion prevention that can be achieved with zinc
phosphat-
ing baths. Uthium concentrations in the range from 0.2 to about 1.5 g/I and in
particular
26 from about 0.4 to about 1 g/l also have a beneficial effect on the
resultant corrosion pre-
vention with the phosphating process according to the invention and subsequent
post-
treatment.
Apart from the aforementioned cations, which are incorporated into the
phosphate layer or at least positively influence the crystal growth of the
phosphate layer,
the phosphating baths as a rule also contain sodium, potassium and/or ammonium
ions
to adjust the free acid. The term "free acid" is well known to those skilled
in the art in
the phosphating field. The method chosen to determine free acid as well as the
total
acid in this step is specified in the examples. Free acid and total acid
represent an
important control parameter for phosphating baths, since they have a large
influence on
the coating weight. Free acid values of between 0 and 1.5 points in parts
phosphating,
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WO 99/12661 PCTIUS98/18001
or up to 2.5 points in coil phosphating, and total acid values of between
about 10, or for
immersion phosphating preferably about 15, and about 30 points lie in the
technically
normal range and are suitable within the scope of this invention.
For the phosphating of zinc surfaces it would not be absolutely necessary for
the
phosphating baths to contain so-called accelerators. For phosphating steel
surfaces it
is, however, necessary for the phosphating solution to contain one or more
accelerators.
Such accelerators are conventionally used in the prior art as components of
zinc phos-
phating baths. The term accelerators refers to substances that chemically
react with the
hydrogen produced on the metal surface by the etching action of the acid in
such a way
that they are themselves reduced. Oxidizing acceierators furthermore have the
effect
of oxidizing iron(ii) ions released by the etching action on steel surfaces to
the trivalent
oxidation state, so that they can precipitate out as iron (Ill) phosphate.
In step (II), solutions according to the prior art that produce a conversion
layer
on aluminum may be used. These solutions must not, however, excessively
dissolve
the crystatiine zinc phosphate layer formed in step (1). The pH of these
solutions should
therefore lie in the range from 2.5 to 10, preferably from 3.3 to 10.
Advantageously in
step (II) solutions are chosen containing components that additionally
passivate the
crystalline zinc phosphate layers. Such solutions are mentioned hereinafter by
way of
example. Within the scope of the process sequence according to the invention,
in step
(II) the metal structures are generally brought into contact with the
treatment solutions
by spraying or by dipping. The temperature of the treatment solution for step
(II) is pref-
erably chosen in the range from 20 to 70 C.
By way of example, in step (II) a treatment solution may be used that has a pH
in the range from about 5 to about 5.5 and that contains overall about 0.3 to
about 1.5
g/l of hexafluorotitanate and/or hexafluorozirconate ions. It may be
advantageous for
the corrosion protection of the crystalline zinc phosphate layer produced in
step (1) if this
treatment solution additionally contains about 0.01 to 0.1 g/I of copper ions
for step (II).
Moreover, a treatment solution may be used in step (II) that has a pH in the
range from 3.5 to 5.8 and that contains 10 to 500 mg/I of organic polymers
chosen from
poly-4-vinyiphenol compounds of the immediately following general formula (I):
9
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WO 99/12661 PCT/US98/18001
OH
x Y
-(CH-CH2)n--
wherein n is an integer between 5 and 100, each of X and Y independently of
each other
denotes hydrogen or a CRR'OH moiety in which each of R and R' independently is
hy-
drogen or an aliphatic or aromatic moiety with 1 to 12 carbon atoms.
For step (It) in particular those treatment solutions are preferred that
contain
polyvinylphenoi derivatives according to the teaching of EP-B-319 016. This
document
,s also discloses the preparation of such polyvinylphenol derivatives.
Accordingly, in step
(II) a treatment solution is preferably used that has a pH in the range from
3.3 to 5.8 and
contains 10 to 5000 mg/1 of organic polymers selected from homopoiymer or
copolymer
compounds containing amino groups, comprising at least one polymer selected
from the
group consisting of materials (a) and (p), wherein:
(a) consists of polymer molecules each of which has at least one unit
conforming to
the immediately following general formula (II):
W~
~
Y 2 0
3 Yt
a
Y4 RI
C
(
R 2 Rs
wherein:
- each of R2 through R4 is selected, independently of each other and
independently from one molecule of the component to another and from one to
another unit of any polymer molecule conforming to this formula when there is
CA 02303183 2000-03-09
WO 99/12661 PCT/US98/18001
more than one such unit in a single polymer molecule, from the group
consisting
of a hydrogen moiety, an alkyl moiety with from 1 to 5 carbon atoms, and an
aryl
moiety with from 6 to 18 carbon atoms;
each of Y' through Y4 is selected, independently of each other and
independently from one molecule of the component to another and from one to
another unit of any polymer molecule conforming to this formula when there is
more than one such unit in a single polymer molecule, except as noted further
below, from the group consisting of: a hydrogen moiety; a -CH2CI moiety; an
alkyl moiety with from 1 to 18 carbon atoms; an aryl moiety with from 6 to 18
carbon atoms; a moiety conforming to the general formula -CR12R130R14, where
each of R12 through R14 is selected from the group consisting of a hydrogen
moiety, an alkyl moiety, an aryl moiety, a hydroxyalkyl moiety, an aminoalkyl
moiety, a mercaptoalkyl moiety, and a phosphoalkyl moiety; and a moiety Z that
conforms to one of the two immediately following general formulas:
R 5 R5
+ /
I R7 I R7
C N o r C N\ R
J e R I 6 Ro
R R
where each of R5 through R is seiected, independently of each other
and independently from one molecule of the component to another and
from one to another unit of any polymer molecule conforming to this
formula when there is more than one such unit in a single polymer
molecule, from the group consisting of a hydrogen moiety, an alkyl
moiety, an aryl moiety, a hydroxyalkyi moiety, an aminoalkyl moiety, a
mercaptoalkyl moiety, and a phosphoalkyl moiety and R is selected from
the group consisting of a hydrogen moiety, an alkyl moiety, an aryl
moiety, a hydroxy or polyhydroxy alkyl moiety, an amino or polyamino
alkyi moiety, a mercapto or polymercapto alkyl moiety, a phospho or
polyphospho alkyl moiety, an -O` moiety, and an -OH moiety,
at least one of Y' through Y4 in at least one unit of each selected polymer
u molecule being a moiety Z as above defined; and
11
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- W' is selected, independently from one molecule of the component to another
and from one to another unit of any polymer molecule conforming to this
formula
when there is more than one such unit in a single polymer molecule, from the
group consisting of a hydrogen moiety, an acyl moiety, an acetyl moiety, a
benz-
oyl moiety; a 3-allyioxy-2-hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl
moiety, a 3-butoxy-2-hydroxypropyl moiety; a 3-alkyloxy-2-hydroxypropyl
moiety;
a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a 2-hydroxy-2-phenylethyl
moiety; a 2-hydroxy-2-alkyiphenyiethyi moiety; a benzyl, methyl, ethyl,
propyl,
unsubstituted afkyl, unsubstituted allyl, unsubstitued alkylbenzyl; halo or
polyhalo
alkyl, or halo or poly haloalkenyl moiety; a moiety derived from a
condensation
polymerization product of ethylene oxide, propylene oxide or a mixture thereof
by deletyng one hydrogen atom therefrom; and a sodium, potassium, lithium, am-
monium or substitued ammonium, or phosphonium or substituted phosphonium
cation moiety; and
((3) consists of polymer molecules each of which does not include a unit
conforming to
general formula (Ii) as given above but does include at least one unit
corresponding to
the immediately following general formula (III):
W s
1
0
Y4
y YS
Rt C
I 1 o
wherein:
- each Df. R1 and R". i.s selected, .independently of. each other.and
indep.endentlx....
from one molecule of the component to another and from one to another unit of
any polymer molecule conforming to this formula when there is more than one
such unit in a single polymer molecule, from the group consisting of a
hydrogen
moiety, an alkyl moiety with from I to 5 carbon atoms, and an aryl moiety with
from 6 to 18 carbon atoms;
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WO 99/12661 PCT/US98/18001
- each of Y' through Y6 is selected, independently of each other and
independently from one molecule of the component to another and from one to
another unit of any polymer molecule conforming to this formula when there is
more than one such unit in a single polymer molecule, except as noted further
s below, from the group consisting of: a hydrogen moiety; a-CHZCI moiety; an
alkyl moiety with from I to 18 carbon atoms; an aryl moiety with from 6 to 18
carbon atoms; a moiety conforming to the general formula -CR'ZR130R1 , where
each of R'Z through R" is selected from the group consisting of a hydrogen
moiety, an alkyl moiety, an aryl moiety, a hydroxyalkyl moiety, an aminoalkyl
moiety, a mercaptoalkyl moiety, and a phosphoalkyl moiety; and a moiety Z as
defined for material (a) above, at least one of Y' through Y' in at least one
unit
of each selected polymer molecule being a moiety Z as above defined; and
- W2 is selected, independently from one molecule of the component to another
and from one to another unit of any polymer molecule conforming to this
formula
when there is more than one such unit in a single polymer molecule, from the
group consisting of a hydrogen moiety, an acyl moiety, an acetyl moiety, a
benz-
oyl moiety; a 3-allyloxy-2-hydroxypropyl moiety; a 3-benzyioxy-2-hydroxypropyl
moiety; a 3-butoxy-2-hydroxypropyi moiety; a 3-alkyloxy-2-hydroxypropyl
moiety,
a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a 2-hydroxy-2-phenylethyi
moiety; a 2-hydroxy-2-alkylphenylethyl moiety; a benzyl, methyl, ethyl,
propyl,
unsubstituted alkyl, unsubstituted allyl, unsubstitued alkylbenzyl; halo or
polyhalo
alkyl, or halo or poiyhalo alkenyl moiety; a moiety derived from a
condensation
polymerization product of ethylene oxide, propylene oxide or a mixture thereof
by deleting one hydrogen atom therefrom; and a sodium, potassium, lithium, am-
monium or substitued ammonium, or phosphonium or substituted phosphonium
cation moiety;
the phrase "polymer molecute" in the above definitions of materials (a) and
(p) including
any electrically neutral molecule with a molecular weight of at least 300
daltons.
Oniinarily, primarily for reasons of economy, it is preferred to utilize as
materials
ao (a) andlor (R) predominantly molecules which consist entirely, except for
relatively short
end groups, of units conforming to one of the general formulas (I) and (II) as
described
above. Again primarily for reasons of economy, such materials are generally
prepared
by reacting homopolymers of p-vinyi phenol, for material (a), or phenol-
aldehyde con-
densation products, for material (R), with formaldehyde and secondary amines
to graft
moieties Z on some of the activated benzene rings in the materials thus
reacted.
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However, in some particular instances, it may be more useful to utilize more
chemically complex types of materials (a) and/or (p). For example, molecules
formed
by reacting a condensable form of a molecule belonging to component (a) or (p)
as
defined above, except that the molecule reacted need not initially satisfy the
requirement
for component (a) or (R) that each molecule contain at least one moiety Z,
with at least
one other distinct type of molecule which is selected from the group
consisting of
phenols, tannins, novolak resins, lignin compounds, aldehydes, ketones, and
mixtures
thereof, in order to prepare a condensation reaction product, which optionally
if needed
is then further reacted with (1) an aidehyde or ketone and (2) a secondary
amine to
introduce at least one moiety Z as above defined to each molecule, so that the
molecule
can qualify as material (a) or ((i).
Another example of more complex materials that can be utilized as material (a)
is material in which the polymer chains are. at least predominantly copolymers
of simple
or substituted 4-vinyl phenol with another vinyl monomer such as
acrylonitrile, metha-
1s crylonitrile, methyl acrylate, methyl methacrylate, vinyl acetate, vinyl
methyl ketone, iso-
propenyl methyl ketone, acryiic acid, methacrylic acid, acrylamide,
methacrylamide, n
amyl methacrytate, styrene, m-bromostyrene, p-bromostyrene, pyridine,
diallyidimethyl-
ammonium salts, 1,3-butadiene, n-butyl acrylate, t-butylamino-ethyl
methacrylate, n-
butyl methacrylate, t-butyl methacrylate, n-butyl vinyl ether, t-butyl vinyl
ether,
rs-chlorostyrene, Q-chlorostyrene, 2-chlorostyrene, n-decyl methacrylate, N,N-
dial-
lylmelamine, N,N-di-n-butylacrylamide, di-n-butyl itaconate, di-n-butyi
maleate, diethyla-
minoethyl 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,
26 di-n-nonyl fumarate, di-n-nonyi 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-ethyl methacryiamide, ethyl methac,ryiate, ethyl
vinyl ether,
5-ethyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine-1-oxide, glycidyl acrylate,
glycidyl
methacrylate, n-hexyl methacrylate, 2-hydroxyethyl methacryiate, 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-methyloi-
methacrylamide,
N-isobutoxymethylacryiamide, N-isobutoxy-methylmethacrylamide, N-
alkyloxymethylacrylamide, N-alkyl-oxymethylmethacrylamide, N-vinylcaprolactam,
meth-
yi acrylate, N-methylmethacrylamide, a-methylstyrene, m,-methylstyrene, Q-
methyl-
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WO 99/12661 PCT/US98/18001
styn3ne, p-methylstyrene, 2-methyl-5-vinylpyridine, a propyl methaccyiate,
sodium 2-sty-
renesulfonate, stearyi methacrylate, styrene, L)-styrenesulfonic acid, 2-
styrenesulfona-
mide, vinyl bromide, 9-vinyl carbazole, vinyl chloride, vinylidene chloride, 1-
vinyinaphtha-
lene, 2-vinyinaphthalene, 2-vinyipyridine, 4-vinylpyridine, 2-vinylpyridine N-
oxide, 4-vinyl-
pyrimidine, and N-vinylpyrrolidone.
The following preferences, primarily for reasons of economy, improved
corrosion
resistance, and/or increased water solubility, apply, independently for each
preference,
to the molecules of materials (a) and (p):
- each of R2 through R6, R'0, R", W', and W2, independently for each and from
one unit to another in the same or a different molecule, preferably is a
hydrogen
moiety,
- each of Y' through Y , independently for each and from one unit to another
in the
same or a different molecule, preferably is a hydrogen moiety or a moiety Z;
- each polymer motecuie contains a number of units corresponding to one of gen-
eral formulas (li) and (III) as defined above that is at least, with
increasing prefer-
ence in the order given, 2, 3, 4, 5, 6, 7, or 8 and independently preferably
is not
more-than-100, 75; 50, 40; 30; or 20;
- in the total of materials (a) and (p) in a composition used in step (II)
according
to the invention, the number of moieties Z has a ratio to the number of
aromatic
nuclei that is at least, with increasing preference in the order given,
0.01:1.0,
0.03:1.0, 0.05:1.0, 0.10:1.0, 0.20:1.0, 0.40:1.0, 0.50:1.0, 0.60:1.0,
0.70:1.0,
0.80:1.0, 0.90:1.0, or 0.95:1.0 and independently preferably is not more than,
with increasing preference in the order given, 2.0:1.0, 1.6:1.0, 1.50:1.0,
1.40:1.0,
1.30:1.0, 1.20:1.0, 1.10:1.0, or 1.00:1.0; and
- in the total of materials (a) and (p) in a composition used in step (II)
according
to the invention, the number of "polyhydroxy moieties Z", which are defined as
moieties Z in which at least one of R5 through Re in the general formulas
given
above for moieties Z has (i) from 3 to 8, or preferably from 4 to 6, carbon
atoms
and (ii) as many hydroxyl groups, each attached to one of the carbon atoms, as
one less than the number of carbon atoms in the R5 through R8 moiety, has a
ratio to the total number of moieties Z in the composition that is at least,
with
increasing preference in the order given, 0.10:1.0, 0.20:1.0, 0.30:1.0,
0.40:1.0,
0.50:1.0, 0.60:1.0, 0.70:1.0, 0.80:1.0, 0.90:1.0, or 0.98:1.0 (preparation of
such
materials is described in the references cited above).
Pofy(5-vinyl-2-hydroxy-N-benzyl)-N-methylglucamine is a specific polymer of
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CA 02303183 2000-03-09
WO 99/12661 PCT/US98/18001
most preferred type, which, in the acidic pH range which is to be established,
is present
at least in part as an ammonium salt.
Solutions may be used that do not contain any further active constituents,
apart
from the polyvinyl phenol derivative and an acid for adjusting the pH,
preferably phos-
phoric acid. Additions of further active constituents, in particular
hexafluorotitanate or
hexafluorozirconate ions, may however improve the layer formation on aluminum.
For
example, a solution may be used whose pH lies preferably in the range from
about 3.3
to about 5.8 and which contains as organic polymer about 100 to about 5000
mg/I of an
organic polymer in the form of a methylethanolamine derivative or N-
methylglucamine
derivative of polyvinyl phenol and in addition 10 to 2000 mg/I of phosphate
ions, 10 to
2500 mg/I of hexafluorotitanate or hexafiuorozirconate ions, and 10 to 1000
mg/I of
manganese ions.
Instead of the poiyvinyl phenol derivatives, whose preparation involves a
certain
expense, there may be used in step (II) solutions or dispersions of organic
polymers se-
Is lected from homopolymers and/or copolymers of acrylic acid and methacrylic
acid as
well as their esters. Preferably these solutions or dispersions have pH values
in the
range from about 3.3 to about 4.8 and contain about 250 to about 1500 mg/I of
organic
polymers. According to the teaching of EP-B-O 08 942 these polymer solutions
or
dispersions may additionally contain hexafluorotitanates, hexafluorozirconates
and/or
hexafluorosilicates.
Examples
A process sequence according to the invention was tested on sample metal
sheets of cold rolled steel (hereinafter usually abbreviated as "CRS"),
electrolytically gal-
vanized steel (hereinafter usually abbreviated as "ZE"), electrolytically zinc-
iron-coated
steel (hereinafter usually abbreviated as "ZFE") and on aluminum 6111. As is
conven-
tional in the automobile manufacturing sector, these metal sheets were first
of all
cleaned with alkali and activated with an activating solution containing
titanium
phosphate. The sheets were then dipped for 3 minutes in a phosphating bath at
a
temperature of 48 C having the following composition:
Zn=1.2g/I
Mn=0.8g/l
Ni=0.8g/t
PO43' 18 g/I
NOZ- = 110 ppm
Residual cations = Na'
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WO 99/12661 PCT/US98/18001
Free acid 1.1
Sealed phosphate layers having coating weights in the region of 2 g/m2 were de-
posited by this phosphating procedure on cold rolled steel, electrolytically
galvanized
steel and on electrolytically zinc-iron-coated steel. Scanning electron
microscopy
photographs showed that only widely-scattered zinc phosphate crystals had
formed on
the aluminum sheets.
As step (II) the sample sheets were treated with fully deionized water
(comparison tests) as well as with solutions of one of the following
compositions (a), (b),
and (c). These solutions had a temperature of 25 C and were sprayed for 30
seconds
,o onto the sample sheets. The sheets were then sprayed for 15 seconds with
fully
deionized water and blown dry with compressed air at room temperature. For the
corrosion prevention tests, they were coated with a triple layer paint
structure, applied
in the order shown: E-coat = PPG ED 5000, base coat = Dupont white 542 AB 839,
Clear coat = Dupont RK 8010. The corrosion resistance tests were carried out
according to the GM9540P-B process cycle of General Motors, which consists of
the
following steps:
1. (1.1) Spraying each panel with a salt spray solution (0.9 wt. % of table
salt, 0.1
wt. % of calcium chloride, 0.25 wt. % of sodium bicarbonate, with the balance
water) sufficiently to thoroughly wet the panel; (1.2) within 30 minutes after
spraying the panel, inserting it into an atmosphere controlled to remain at 25
C
and 30 - 50 % relative atmospheric humidity; (1.3) ninety minutes after
beginning
step (1.2), removing the panel from the controlled atmosphere in which it was
kept during step (1.2), then repeating steps (1.1) and (1.2) three times each.
Step 1 as a whole thus consumes 8 hours.
zs 2. 8 hours' condensate water test at 49 C and 95 - 100 % reiative
atmospheric
humidity;
3. 8 hours' dry storage at 60 C and <30 % relative atmospheric humidity;
4. At the week-end: oniy dry storage at 25 C and 30 - 50 % relative
atmospheric
humidity.
The steps 1 to 3 immediately above in each case form a cycle that is repeated
Mondays
through Fridays. Step 4 is not counted in the cycle number. The tests lasted
for 40
cycles (5 cycles per week corresponding to a test time of 8 weeks).
Table 1 below shows the compositions of the three post-rinse solutions, and
Tables 2 and 3 show the zinc phosphate coating etch amounts and the average
paint
creepages at the scribe (full scribe width) respectively.
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WO 99/12661 PCT/US98/18001
Table 1: POST-RINSE COMPOSITIONS
Ingredient Amount of Ingredient in:
Postrins+r - Posttrinmsola:(b); - Post-rinsersvUc:(c);
soln.(a), pH 3.5 pH 2.9
pH 2.7
Polvmer* 0.453 0.451 0.113
Phosphate 0.957 0.955 gli 0.239
H e x a f l u o r t i t a n a t e 19/1 19/1 0.25
0.39 0.39 0.1
" Po1y(5-vinyl-2-hydroxy-N-benzyl)-N-methylgiucamine
Table 2: ZINC PHOSPHATE COATING ETCHING Loss VALUES
Test Number Substrate Post-Rinse Solution Coating Loss,
Percent
Example 1 CRS (a) 69
Exmple 2 CRS 5
Example 3 CRS (c) 27
Example 4 ZE (a) 50
Exmplc 5 ZE 5
Example 6 ZE c 31
Exmplc 7 ZFE (a) 50
Example 8 ZFE 1
Exam le 9 ZFE (C) 25
Table 3: CORROSION TEST RESULTS
Test Number Substrate Post-Rinse Solution Paint Creepage,
Millimeters
C arison 1 CRS Deionized Water 9.6
E le 1 CRS (a) 8.8
Exam le 2 CR.S 3.1
Example 3 CRS c 4.2
Comparison 2 ZE Deionized Water 2.2
Example 4 ZE (a) 1.6
Example 5 ZE (b) 1.8
E le 6 ZE c 1.8
Comparison 3 ZFE Deionized Water 2.2
Exwnple 7 ZFE (a) 1.3
Example 8 ZFE 1.6
le 9 ZFE c 1.1
Com arism 4 A16111 Deionized Water 1.7
Example 10 A16111 (a) 0.9
Example 11 A16111 (b) 1.2
E ic 12 A16111 c 1.2
18
