Note: Descriptions are shown in the official language in which they were submitted.
' ' CA 02378935 2002-O1-10
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"A process for applying no-rinse products to continuous metal strips"
This invention relates to the field of corrosion-protective surface treatment
of metal
strips. It relates specifically to the application of so-called no-rinse
products, that is
products which are dried immediately after application without first being
rinsed with
water. This means that all non-volatile components in the treatment solution
being used
and products of the reaction with the metal surface remain on the metal. One
advantage
of this technique is that no product-polluted wash-water which has. to be
disposed of in a
costly manner is produced. Traditionally, the treatment solutions are applied
to the metal
strips via rollers having a hard surface, these being known as Chemcoaters or
Rollcoaters. An alternative to this method is the so-called spray/dip-squeeze
technology
in which the surface is briefly contacted with the treatment solution being
applied, by
spraying or immersion, after which the treatment solution is squeezed off
using rollers
and then the surface is dried.
A disadvantage of Chemcoaters is the high investment and operating cost. A
disadvantage of the spray/dip-squeeze method is that the wet-filrr~ thickness
depends on
the running time of the squeezing rollers, different rates of appli~~ation of
the film also
being obtained in the edge regions on changing the width. The coating on the
strip is
then uneven. Furthermore, since the wet film is very thin (generally thinner
than 2 Vim)
after being squeezed off, small changes in the wet film thickness are very
noticeable in
the final layer which is produced.
An object of the present invention is to provide an improved application
system for no-
rinse products which does not have the disadvantages mentioned above.
The present invention also provides a process for the chemical treatment of
metal strips,
wherein a treatment liquid is applied to the surface of one or both faces of
the metal
strips using an application roller and dried without an intermediate wash
process,
characterised in that a non-woven roller is used as the application roller.
CA 02378935 2002-O1-10
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Non-woven rollers, termed 'soft rolls', are currently used in the continuous
strip industry
as squeezing rollers. The surface of these rollers consists of a soft
covering, generally
made of a chemicals-resistant matted fibrous material. Examples .are polyamide
(nylon)
or polypropylene fibrous materials. In general, any fibres may bc: used which
have an
adequate absorption volume and adequate resistance to strongly acid or
alkaline
solutions. In the process according to the present invention, these rollers
may rotate in
the opposite direction to or the same direction as the metal strip.
The gap between the non-woven rollers is preferably adjusted as a function of
the
thickness of the metal sheeting in such a way that the treatment liquid is
applied to the
surface of the metal strips by the non-woven roller with a wet film thickness
of 1 to 10
Vim. This is the case, for example, using a gap width between 0.3 ~~nd 0.8 mm.
The roller
gap is preferably adjusted so that a wet film thickness of 2 to 6 pm
(corresponding to
ml/m2) is produced on the surface of the metal strips.
In accordance with the present process, any treatment solutions which are
suitable for a
no-rinse method may be applied. These treatment liquids are generally adjusted
to be
either acid (pH between 0 and 7) or alkaline (pH between 7 and l~l). The
composition of
the treatment solutions is generally selected so that a chemical reaction
occurs with the
metal surface. Large numbers of these types of treatment solutions are known
from the
prior art. The following may be mentioned by way of example:
Phosphatising solutions: acidic, phosphorus-containing solutions which produce
a
crystalline or amorphous layer of metal phosphate on the metal surface. These
solutions
generally contain zinc ions, frequently together with manganese andlor nickel
ions, as
canons.
Chromatising solutions: acidic solutions which contain Cr(VI) ions and
frequently also
Cr(111) ions.
CA 02378935 2002-O1-10
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Acid or alkaline passivating solutions: aqueous solutions which generally
contain
transition metal ions and which produce a corrosion-protective amorphous
(mixed)
oxide layer after drying.
Treatment solutions based on complex fluorides: generally acidic solutions of,
for
example, hexafluorozirconic acid, hexafluorotitanic acid, hexafluorosilicic
acid and also
the particular salts thereof.
Solutions or dispersions of organic film-formers, for example polyacrylates.
In this case,
the solution may contain inorganic reactive components, such as complex
fluorides, in
addition to the film-formers. An inorganic/organic polymeric mixed layer is
produced
therefrom.
These treatment solutions are currently used for treating a variety of
different substrates
in conventional application processes. They are adjusted to be appropriate for
the metal
surface being treated and are suitable, for example, for treating steel,
galvanised or alloy-
galvanised steel, alloy-aluminised steel and also for treating ;aluminum and
alloys
thereof. Accordingly, the process according to the present invention may be
used to treat
strips made from the materials mentioned, using these types of treatment
liquids.
The treatment solution may be applied to the surface of the non-woven rollers
in a
variety of ways. For example, it is possible to spray it onto the sur~_ace of
the non-woven
rollers via nozzles. As an alternative, it may be transferred to the surface
of the non-
woven rollers from a storage container, via transfer-rollers.
An alternative involves applying the treatment liquid to the surf~~ce of the
non-woven
rollers via the internal cavity in the non-woven rollers. This is possible
because the wall
of the non-woven roller may be designed to be permeable to liquids. Treatment
liquid
fed to the interior of the non-woven roller, for example, via a hollow roller
shaft, may
reach the surface thereof via holes in the wall of the roller.
CA 02378935 2002-O1-10
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The treatment solution is preferably applied to the metal strips at a
temperature from
about 15 to about 40°C, in particular between 20 and 30°C. Then
the metal strips are
dried without an intermediate wash process. The time betwec,n application of
the
treatment liquid by the non-woven roller and the start of drying should then
be not
shorter than 1 second and not longer than 15 seconds. Drying itsc;lf may be
performed,
for example, in a circulating air oven, as is conventionally the case in a no-
rinse process.
If production is interrupted, it is recommended that any treatment solution
remaining on
the non-woven roller be washed off. This may take place, for example, by
spraying with
water. If the non-woven roller is designed so that the surface is fecL with
treatment liquid
via the internal cavity, washing is preferably also performed via th~~
internal cavity of the
non-woven roller.
The process according to the present invention has the advantage that even
when
changing the width of the strips, uniform application of the treatment liquid
over the
entire width of the strip is facilitated. This avoids different regions of the
strips being
coated with different thicknesses.
CA 02378935 2002-O1-10
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Examples
Using a polypropylene non-woven roller from the Thomas Rolls Co., the
following
applications were achieved. The thickness of the sheeting being treated was
0.75 mm:
Ingredients in the pH Direction Gap Wet
'
Rate
of
treatment solution of (mm) film
application
(g/1): rotation
4.5 Mn; 3.5 Ti; 2.3 same 0.5 3 10 mg/m2
~m Ti
8.2 fluoride;
8.3 phosphate;
50.0 polyglucamine
derivative
(GranodineR 1455
Henkel KGaA)
reverse 0.6 4 13 mg/m2
um Ti
87.4 phosphate; 2.0 same 0.7 5 1.1 g/m2
4.4 ~m of
Ca; 3.1 Zn; 3.2 coating
Ni;
7.9 Mn; 0.3 Fe(II);
0.5 sulfate
(GranodineR 5893
Henkel KGaA)
reverse 0.6 4 0.9 g/mz
~m of
coating
6.2 Cr(III); 12.7 2.6 reverse 0.4 2 20 mg/mz
~m Cr
Cr(VI); 1.6
phosphate; 7.4 Si;
(GranodineR 1402
W
Henkel KGaA)
4.8 Zr; 5.9 fluoride;1.2 reverse 0.5 3 15 mg/mz
~m Zr
5.3 phosphate;
0.3 polyacrylic
acid
(AlodineR 778 Henkel
KGaA)
