Note: Descriptions are shown in the official language in which they were submitted.
~3 ~2 -~
-- 1 --
The present invention relates to a process
for the passivating postrinsing of conversion layers OD
metal surfaces, particularl~ of steel, galva~ized steel,
5 . zi~c allog-coated steel and/or ~luminum i~ praparation
for a painting or an application of adhesive, which
postrinsing is effected by means of chromium-~ree aqueous
solutions, and also relates to the use of such process
for the preparation for a subsequent electro-dipcoating,
particularly a cathodic electro-dipcoating, and for the
postrinsing of metal surfaces provided with certain con- ~:
version layers.
The phosphating process is industrially
used on a large scale to prepare metal surfaces for a
subsequ~nt paintingO The resulting phosphate layers effect,
inter alia, an improved adhesion of the paint films on
the metal, they increase the resistance to cor:~sion ~nd
reduce migration under paint due to
.... . . . ... ..... .....
'
~ ~ ~ 7 ('IJ ~
locational defects in the paint film. Similar
effects are produced by other conversion layers, parti-
cularly by the chromate layers formed by colorless, yellow
or green chromating processes, and by the layers formed
by means of Ti- or Zr-based solutions. ~he protection
afforded by such conversion layers can further be improved
by an aqueous passivating postrinsing.
The passivating postrinsing age~ts
based on hexavalent and/or trivalent chromium ha~e
good properties from the aspect of application technology
but the toxicity of the trivalent and particularly of
the hexavalent chromium compounds is undesirableO
US-A-4,37~,000 discloses a chromium-
free postrinsing agent based on polyvinylphenol but that
agent must be used in a comparatively high concentration
so that its use will result in an undesired pollution of
the sewage and will particularly give rise to a high
oxygen demand for its decomposition.
It is known from US-A-3,695,942 to
use a soluble zirconium compound for an aftertret~tment of
conversion layers. In addition to zirconium, the post-
rinsing agents contain cations consisting of alkali and
ammonium. An explicit warning has been made against the
presence of cations of alkaline earth metals. ~hese post-
rinsing agents are used at a pH value from 3 to 805
but will not produce the same quality as the chromium-
'
,", ,
,
7 ,, ~ ?~1
containing agents.
US-A-3,895,970 desdribes acid aqueous
postrinsing agents for phospha-te layers, which agents
are based on simple or complex fluorides, and out of
the group of the zirconium compounds mentions chromium-
zirconium fluoride and zirconium fluoride. With the ex-
ception of chromium-zirconium fluoride, the products ~ :
mentioned in that patent specification will meet only
moderate requirements. But chromium-zirconium fluori~e
has the above-mentioned disadvantage that it is toxic~
In accordance with an earlier proposal,
phosphated metal surfaces are rinsed with aqueous solu-
tions which contain aluminum fluorozirconat with an Al:
Zr:F mole ratio of (0.15 to 0.67) : 1 : (5 to 7) whereas
the total concentration of Al + Zr + ~ is 0.1 to 2.0 g/l
and the pH value is adjusted to 3 to 5. That postrinsing
. .
distinguishes by resulting in a very high quality pro~e.
It is an object of the invention to
provide for a passivatin~ postrinsing o~conversion layers
on metals before a painting or before an application of
adhesives a process which is free of the disadvantages
of the known processes and results in a further improve-
ment over the earlier proposal and distinguishes by
resulting in a high corrosion resistance a~'in a very
strong adhesion of paint and adhesive and will virtually
not pollute the environment.
~ ($ 2 .~
~o accomplish that object the process of
the kind first hereinbefore is carried out in such a
manner in accordance with the invention in that the
metal surfaces provided with conversion layers are
rinsed with an aqueous solution which contains Ce(IV)
and/or Ce(III) in a total amount of 0.01 to 1.0 g/l
and has a pH value from 3 -to 6.
The process in accordance with the in-
vention call be applied to conversion layers of all
kinds which can be formed on metals, particu~ ly on
steel, galvanized and zinc alloy-coated steel, alumi-
nized steel, æinc, zinc alloys, aluminum and aluminum
alloys. These conversion layers include layers based
on phosphate, such as the phosphates of zinc, iron,
manganese, calcium7 zinc-mang~nese and zinc-calcium
and other mixed products containing two or more diva-
lent cations. It is particularlg suitable for phosphate
layers formed by low-zinc phosphating processes with
and without an addition of further cations, such as Mn,
Ni, Co, Mg~
~ he process in accordnce with the invention
may also be used to postrinse conversion layers v~hich
by means of solutions based on Ti or Zr have been formed
on surfaces of aluminum or aluminum alloys.Such solutions
may con-tain additional components consisting, e.g., o~
fluorides, phosphates, boron compounds and optional
.
.
,
,
passivating components, such as tannins. ~he process
may also be used to aftertreat cllromate coatings, such
as those of the kind mentioned hereinbefore, and of
conversion layers which are formed, e.g., on zinc or
zinc alloys by means of a solution that contains at
le~st two different polyvalent metal ions and complex-
ing agents and preferably has a pH value above 11.
The formation of the conversion layers
is succeedéd by a rinsing with water before the after-
treatment by the process in accordance with the inven-
tion, which is carried out, e.g., by dipping, spraying,
floodi~g or application by a roller is performed.
According to all test results the passi-
vating postrinsing in accordance with the invention im-
proves the resistance to corrosion at least to the same .
degree as a passivating pos-trinsing with the solutions
which contain Cr(III) and/or Cr(VI) and which are known
for their excellent effect.
According to a particularly preferred
embodiment of the invention the metal surfaces provided
with conversion la~ers are rinsed with an aqueous solu-
tion having a Ce concentration of 0.05 to 0.15 g/l.
~ ccording to a preferred feature of the
invention the metal surfaces provided with conversion
layers are rinsed with a solution which contains Ce(III)
and Ce(IV) in a weight rati.o of 9 to 2 parts Ce(III)
to 1 part Ce(IV). The use of a mixture of Ce(III)
and Ce(IV) within said range of weight ratios will
improve the resistance to corrosi.on to a h.igher d~gl~ae
than the use of the Ce eompound in only one degree of
oxidation.
~ further preferred feature of the
invention resides in that the metal surfaces provided
with conversion layers are rinsed with a solution into
which Ce(III) and/or Ce(IV) has been introduced as a
nitrate and/or as a sulfate. It will also be desirable
to introduce the Ce compound at least in part as a
fluoride, hex2~1uorozi~conate, hexaEluorotitanat~,
hexafluorosilicate, hexafluoroaluminate, tetrafluoro-
borate or as a salt of carboxylie aeids, hydroxyearboxylic
aeids and/or aminocarboxylic acids. Suitable carboxylic
acids are, e.g., acetie acid, oxylic aeid and malonic acid.
Sui.table hydro~yearboxylic acids are, e.~., glyeolie
acid, lactie acid, tartarie aeid, eitrie acid. Suitable
amino acids are, e.g.1 nitrilotriaeetie acid and ethylene- :~
diaminetetraacetic acid. The addition of Ce in the form
of compounds of the above-mentioned acids will improve
the solubility, particularly of Ce(IV).
hccording to a further desirable fea-
ture of the invention the metal surfaces provided wlth
conversion layers are rinsed with an aqueous solution
which addil;i.onall;y contains molybda-l;e and/or tungstat~.
Said compounds are particularly added in the form of
their alkali salts.
The pH value of the postrinsing solu-
tion is suitably adjusted with simple mineral acids,
such as nitric acid or hydrofluoric acid. If additives
which react alkaline are requirsd, it will be possible
to use volatile bases, such as ammonia, ethanolamine,
di- and triethanolamine. But according to a further de-
sirable embodiment of the invention the pH value is
adjusted with alkali hydroxides because alkali hydro-
xides, particularly sodium hydroxides, have over volatile
bases the advantage that a destabilisation o~ the
postrinsing solutions will not occur.
The afterrinsing solution for use
in the process in accordance with the invention is usu-
ally prepared by a dilution of a concentra-te.
~ ccording to a fur-th-r desirable feature
of the invention, the passivating postrinsing is suc-
ceeded by a postrinsing with de-ionized water to remove
any still adhering salts and/or salt solutions, which
mi~ht adversely affect the adhesion of paint and the
resistance -to corroslon.
The application of the passivating
postrinsing solution to the metal surfaces provided
with a conversion layer is carried out in a usual manner,
e.g., by dipping, floodin~, s~aying and applicatiorl by
~ ~ ~ r~ 3 ~;
a roller. *he treating times lie between about 1 second
and 2 minutes. The application temperature may lie bet-
ween room temperature and about 80~. Temper~ures bet-
ween 20 and 50 C are usually preferred. For t~ prepa-
ration of -the postrinsing solutions it is preferable to
use water which ~s the lowest possible salt content,
pre`ferably de-ionized water. Water havin~ a hi~h salt
content cannot be used to prepare a bath.
'~he process in accordance with the
invention serves to prepare the metal surfaces coated
with a conversion layers for painting or for an applica-
tion of adhesives. It will improve the adhesion of the
organic films, improve the resis~nce of the organic
film against blistering under a corrosive action, and
inhibit the subsurface corrosion from the locations of
defects in the film. The process can be used for a prepa-
ration for powder coating and paintin~ with low-solvent
hight-solids paints and with paints comprising subst~ti-
ally water as a solvent. A particularly desirabl~ use of
the process in accordance with the invention is -the prepa-
ration of metal surfaces provided with conversion layers
for a subsequent elect,ro-dipcoating, particularly for a
cathodic electro-dipcoating~
'~he process can be used to special
advanta~e for the postrinsing of metal surfaces provided
with conversion layers which consist of phos~ate layers or
~ ~ ~3 ~
of layers formed by a chromium-free, acid process using
Zr and/or Ti~ F and optionally P04, or of complex metal
oxide layers.
The process in accor~nce with the
invention will be explained by way of example and more
in detail hereinafter.
_XA~ E 1
In a manganese-modified low-zinc
phosphating process, degreased sheets of steel~ electro-
lytically galvanized steel and AlMgSi were sprayed at
55C for 2 minutes. rrhe phospha-ting solution had the
following composition:
0.7 g/l Zn 0.04 g/l Fe(III)
1.0 g/l Mn 13 g/l Fe205
1.0 g/l Ni 2.1 g/l N0
2.9 g/l Na oO3 g/l F
0.15 g/l NH~ -7 g/b N02 .
Uni~ormly covering, finely crystalline
phosphate layers having a wei~ht of 2.5 to ~ g/m3 were
formed on the three metal substrates. The sheets were
subsequently rinsed with water and were then subjected
to a passivating postrinsing carried out by di~ping at
3~C for 1 minute. The final treatment consisted of a
spraying with de-ionized water.
'~he sheets were painted with a cathodic
electro-dipcoating primer, a filler and a top paint.
~ 7 ~ ~ ~
paint -10-
Each layer of the/coating was separately baked. The
total -thickness of the paint coating was about 90 ~m.
~ The sheets were scratched to the metal
substrate with a steel needle and were then subjected
to various tests. The results have been compiled in ~e :
following Tables 1 to 3.
To prepare the postrinsing agent in
~ccor~ nce with the invention, 0.081 g Ce(III) (intro-
duced as Ce(~03)3.6H20) and 0.020 g Ce(IV) (introduced as
Ce(S04)2.4H20) per liter were dissolved. Ce(IV) was sta-
bilized by an addition of 0.1 g/l fluoride in the form
of HF to the bath. The pH value was subsequently ad-
justed with ammonia -to 4.0 to 4O5 r~he slight turbidity
resulting from the preparation of the bath solution does
not affect the passivating properties of the postrinsing
agent.
The solutions used for comparison con- ~ -
tained:
1~ Cr(VI)/Cr(III) solution: 0.2 g/l CrO3 a~ :
0.0~7 g/l Cr(III)
The pH value was ad~usted to 3.5 to 400.
2. Al-zr-F solution: 0.014 g/l Al
0.14 G/l Zr, and
0.17 g/l F.
The pH value was also adjusted -to 3.5 to 4Ø
r7 r j ~,
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From the tables it is apparent that as
regards resistance to corrosion the results produced
by the process in accordence with the invention are at
least equivalent and in part even superior to those
produced particu~rly by the Cr(VI)/Cr(III) solution,
which is recognized for its strong effectO
2~ .3
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TABIE 1 Results on STEEL
Postrinsing Agent
Cr(~ III) Aluminum- Ce(N0 ) /Ce(SOL~)2
zirconium adjus~e~ with
fluoride NH3 to pH
.
pH value 3,5_4.0 3-5_L~o L~.o-4.5
~later of c(onden-
~ation test
conditions
DIN 50017 ~
cross-cutting ` .
DIN 53151 (Note)
Stone throw according
to VW, 12 cycles
Test under changing
conditions -:
VDA 621-415
Subsurface
corrosion, mm
: ~ Flaking of
paint, /a (1) (1) (1) :
~ ~-,:-
: GM-Scab Test
(20 cycles)
G~l 9511P
Subsurface corrosion 9
m~ 2 2 2
:
:
.;;g ~ ~h~ r~
q'ABLE 2 Results on GA~VANIZED Sl'EEL
Postri~sing A~ent
Cr~VI/-III) Aluminum- ae(N0 ) /Ce($o4)2
zirconium adjus~e~ with
fluoride NH3 to pH
pH value 3O5_400 '3.5_4.o 4 o_4 5
'~'a-ter of conden~
sation test
conditions
DIN 50017 ~
cross-cutting
DIN 53151 ~Note)
Stone throw according
to VW, 12 c~cles
~est under changing
conditions
VDA 621-415
Subsurface
corrosion, mm 5 6 2-5
Flaking of
paint, % (1-2) (1-2) (1-2)
GM-Scab Test
(20 cycles)
GM 9511p
Subsurface corrosion,
mm 1... 2 1... 2 1~oo2
~ $~3
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TABLE 3 Results on ALUMINUM
Postrinsing Agent
Cr(VI/-III) Aluminum- Ce(N0 ) /Ce(S~ 2
zirconium ad,jus~e~ with
fluoride ~H3 to pH
.. . . .. . . _
pH Value 3,5_400 305-4.0 4.0-405
Water of conden-
sation test
conditions
DIN 50017 +
cross-cutting :
DIN 53151 (Note) 0.5 005 o
.
Stone throw according -. :.
to VW, 12 cycles
Test under changing
conditions '-:;
~DA 621-415
Subsurface
corrosion, mm 0 0 0
Flaking of
paint, % (1) (1) (1)
GM-Scab Test
(20 cycles)
GM 9511P
Subsurface corrosion1
mm 0 0 0
,
~ ~3~ 2 -~
-15-
EXAMPI,E 2
Cleaned a~ degreased aluminum sheets to
be provided with a conversion coating were dipped for
lO seconds into a so].ution which was at a tempe.rat;ure o~
50C and had the following composition:
Ti O.lr~ g/l
F lo24 g/l
P205 0~09 ~/l
N~I4 o9l g/l
rTannin 0,11 g/l
Na 0.003 g/l
Biocide O.lO g/l
The sheets were subseque~tly rinsed with
water and subjected to a passivating postrin-lngO For that
purpose the sheets were dipped into the postrinsing
solution at 35C for 5 seconds and were subsequently
squeegeed to remove surplus solution. After the sheets
had been dried in a recirculating-air oven at 60C for
005 minute they were painted with a foodstuff-compatible
two-layer paint t which in its first layer cons;sted of an
epoxide-phenol re~in an-~n the second layer cGnsi^ted of
an organosol. The to-tal thickness of the paint coati.ng
was between lO and 15 ~mO
The treated sheets havinK a thickness of
about 0.25 mnl were subse~;uen-tly punched tc lorm round
disks 60 mm in diameter and by deep dr.lwing were formed
to CUp9, which were 26 mm in diameter and had a he~ht of
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`:
~ f~?t s? 7 ,~
--16--
25 mmO-
Said cups were subjected to a steri-
li~ing -test, in which they were subjected in a pressure
container for 40 minutes to the action of an aqueous
solution of 3% common salt, 1,~ citric acid and 0.5%
lactic acid at 121C. The defects subsequently detected
at the cups (spalling of paint, blisters) were rated
in accordance with a scale ranging from 1 (paint spalled
throughout the shell of -the cup = unusable) to 15 (no
paint defects = excellent).
The postrinsing solution (A) which was
employed contained 0.110 g/l Ce(III) (introduced as -
Ce(N03)3.6H20) and 0.020 g/l Ce(IV) (introduced as
Ce(S043204H20). The pH value had been adjusted to 4.0 to
4-5.
For comparison, postrinsing was also
effected with an aqueous solution of 0.6 g/l polyvinyl~
phenol at a pH value of about 5 (postrinsing solution B)
and with a solution which contained 0.014 gjl Al, 0.14 g/l
Zr, 0.17 g/l F and 0.016 g/l r~4 and had a pE value of
3.5 to 4.0 (postrinsing solution C).
. .
Test results of the sterilizing test
(Rating scale: 1 = unusable to 15 - excellent)
Postrinsing solu~ion Ratirlg
. _ . .. . . . . .
A (invention) 12-13
B (control) 6
C (control) 11
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A comparison of the tabulated data
shows that the process i~ accordance with the invention
results in distinctly better values, particularly when
compared with the control example in which a pos-trinsing
solution based on polyvinylphenol was employed.
X~LE 3
Cleaned and degreased sheets of hot-
galvanized steel were provided with a conversion coating
in that they were dipped for 30 seconds into a solution
which was at a temperature of 55C and had the following
composition:
ao2+ 0.3 g/l
Fe~+ 0.2 g/l
N03- 1.3 g/l
Sodium salt of
hexahydrohepta-
noic acid 202 g/l - ;
~aOH 27.4 g/l
l'he sheets were subsequently rinsed
with water and subjected to a passivating postrinsing.
For that purpose the sheets were dipped into the post-
rinsing solution at ~C for 5 seconds and were subse-
quently squeegeed to remove surplus solution. ~fter
a drying at 75C in a recirculating-air oven for 0.5
minute the pre-treated sheets were painted with an
epoxide primer and with an acrylate -top coat~ ~he total
- -18-
thickness of the paint coating amounted to about
25 ~um.
The treated sheets were subsequently sub-
jected to the following tests:
The adhesion of the paint ~as determined
in the ~ bend test, in which the sheets were bent through
180. ~he various radii of curvature were stated as n
times the thickness of the sheet metal (n = O, 1, 2 ...)
(Tn). The test result is stated as the percentage o~ the
area of the flaked paint in the entire curved surfaceO
were
Other treated sheets/provided by means
of a sheet me-tal needle with scratches extending to the
metal substrate and by means of sheet metal shears were
formed with a cut edge. The sheets were subsequently
subjected to the salt spray test in accordance with
DIN 50021 SS for 1008 hours. The test result is stated
as the subsurface corrosion under the paint in mm from
the scratch or the cut edge.
he postrinsing solution (1~) employed in
accordance with the inven-tion contained 0.110 ~/1 Ce(III)
(introduced as Ce(N03)3~6ll20) and 0.020 g/l Ce(IV)
(introduced as Ce(S04)2~4H20) and had a pH value of 4.0
to 4.50
For comparison, a postrinsin~ solution (B)
was ernployed, which contained 0.014 g/1 Al, 0.14 ~/1 Zr,
0.17 g/l F and 0.016 ~ ~4 and had a pH value ~f 3.5
.
r~ J ~ -
-19-
to 4.0~ and a postrinsing solution (C), ~hich contained
2.0 g/l Cr(VI), 0~8 g/l Cr(IIIj, 0.2 g/l F, and 0.3 g/l Zn.
The test resu].ts are stated in ~e following
tables.
Adhesion of Paint in ~-bent test
Flaked area (,0) in case of a
Pos~trinsing solution radius of curvature Tn
,.
~1 ~2 T3 T4
: A (invention) 100 5 10 ~5
B (control) 100 55 15 5
~ C (control) 100 80 30 5
:
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Resistance to corrosion in salt spray test
,
postrinsing sol~utionSubsurface corroslon (mm)a ter ~-
.. _
~t the scr~tch At the edge
A (invention) 0 - 1 6 - 8
B (control) <1 - 1 8 - 9
C (control) 1 - 3 9 - 10
A comparison of the tabulated data reveals
that in each case the process in accordance with the
invention gives at least equivalent or improved results,
particularly when compared with the con-trol process in
which a postrinsing solution based on Cr(VI)/Cr(III)
~20- .
was employed, which is recognized for its strong
effect as re~;ards the resi~tance to corrosionO
,
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