Note: Descriptions are shown in the official language in which they were submitted.
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
Coated aluminum strip and method for manufacturing
The invention relates to a method for manufacturing a strip
made of aluminum or an aluminum alloy as well as to a coated
aluminum or aluminum alloy strip, a formed metal part made of
said aluminum or aluminum alloy strip and an apparatus for
carrying out the inventive method.
Retortable and corrosion resistant aluminum or aluminum alloy
strips are used for the manufacturing of packages like cans
or cup-like food packages. In particular, foodstuffs often
contain ingredients which can cause corrosion of aluminum or
an aluminum alloy used for manufacturing the package of the
grocery, for example a food can. Thus, the aluminum or the
aluminum alloy of i.e. a food can has to be protected against
corrosion. Commonly this is done by a coating which is
applied onto the aluminum strip prior to forming the food
package. Such a food package is known for example from the
German patent application DE 40 30 646 Al. However, the
conventional food package has several problems. On the one
hand, when the coated aluminum strip or aluminum alloy strip
is formed to the food package part i.e. by deep drawing the
corrosion protecting coating sometimes shows damages. Thus,
the corrosion protecting layer has to be provided with a
greater thickness in order to prevent cracks or damages
during deep drawing for example. On the other hand coating of
a food package after deep drawing of the aluminum strip is
expensive.
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
2
High resistance against corrosion induced by the contact with
corrosion active media like water or rain is also a challenge
with architectural sheets, which are used for example as
facade sheets at the outer surface of buildings. For the
architectural sheets it is very important that they do not
change their appearance in the presence of aggressive
substances incorporated in the air in cities or near
industrial factories for years. Additionally, these sheets
are formed by roll forming, bending, or drawing and are
subjected to cutting processes, which leads to problems in
the vicinity of locally high sheet deformation degrees or in
the vicinity of cut edges. In particular coated architectural
sheets have the problem that corrosion might lift up the
coating which deteriorates the appearance of the sheets
dramatically.
Therefore, it is an object of the present invention to
provide a method for manufacturing an aluminum strip or an
aluminum alloy strip, which provide a much better corrosion
behavior. Furthermore, it is an object of the present
invention to provide such an aluminum or aluminum alloy
strip, a formed metal part made of the aluminum or aluminum
alloy strip as well as an apparatus for carrying out the
inventive manufacturing method.
According to a first teaching of the present invention the
above mentioned object is solved by a method for
manufacturing a strip made of aluminum or an aluminum alloy
comprising the steps of:
- degreasing and anodizing the surface of the strip by
immersing the strip in an acid electrolyte bath and
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
3
applying AC current, optionally followed by a desmutting
step and
- applying a passivation layer on the surface of the strip
by a no-rinse coil coating process.
It was found out by the invention that an aluminum strip or
an aluminum alloy strip which has been applied to the
aforementioned manufacturing steps offers a very good
corrosion resistant and additionally a very good adhesion for
an additional top coating which allows making i.e. food
packages by deep drawing the aluminum strip without damaging
the top coating during the deep drawing step. Also
architectural sheets can be manufactured from these above
mentioned aluminum or aluminum alloy strips comprising an
improved corrosion resistance. The optional desmutting step
improves application of the passivation layer after immersing
in the electrolyte bath. Degreasing and anodizing the surface
of the aluminum or aluminum alloy strip by immersing the
strip in an acidic electrolyte bath and applying AC-current
leads to an artificially grown oxide layer which provides a
very good corrosion resistant compared to the natural oxide
layer which is built up after manufacturing, i.e. after
rolling. The passivation layer on the other hand provides a
very good adhesion for a top coating since adhesion
properties of an artificially grown oxide layer are usually
low. Thus, i.e. retortable food packages can be manufactured
with an aluminum alloy strip, which has a very good
resistance against filling goods and a very high adhesion for
a top coating. Additionally, coated architectural sheets take
benefit of the inventive manufacturing steps in that they
have a much better corrosion resistance and the improved
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
4
adhesion of a coating on the inventively manufactured strip
contrary to conventional architectural sheets.
In order to improve the corrosion resistance according to an
embodiment of the present invention during the degreasing and
anodizing step a new oxide layer with a thickness of 50 nm to
300 nm is built on the surface of the strip. Preferably an
oxide layer of 50 nm to 160 nm is built since it allows
achieving the intended corrosion resistance combined with
satisfying manufacturing speeds.
According to a next embodiment the degreasing and anodizing
of the surface of the strip and optionally the desmutting of
the strip are carried out inline with applying the
passivation layer on the strip. Carrying out the
manufacturing strips inline means that the manufacturing
steps are made without coiling and decoiling the metal strip
between those steps. This allows to optimize productivity of
the inventive method as well as to reduce production time and
expenses to manufacture such aluminum or aluminum alloy
strips.
According to a next embodiment of the present invention said
degreasing and anodizing step is carried out with a sulfuric
acid at a concentration of 10 wt.-% to 25 wt.-% as
electrolyte with a temperature of 65 C to 90 C by applying an
AC-current density of 2 to 25 A/dm2 for an immersing time of
the strip of 1.5 s to 10 s. It has been found out that the
mentioned range of parameters regarding the electrolyte bath,
the concentration of the sulfuric acid, the temperature range
and the density of the AC-current as well as the immersing
time provides the possibility to increase the manufacturing
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
speed. These parameters allow high speed growth of the
intended corrosion inhibiting oxide layer as well as an
effective removal of surface contaminations of the aluminum
strip which are caused by the manufacturing process like cold
5 rolling. In particular good results has been achieved by an
AC-current with a frequency of 50 Hz and a current density of
4 to 22 A/dm2 with a temperature of 75 to 85 C with a
sulfuric acid comprising 15 wt.-% as a concentration and a
contact time of 3 to 6 s.
The passivation layer is according to a next embodiment based
on a chromate-free passivation or a zirconium or titan
passivation. A chromate-free passivation as well as the
passivation layer based on a zirconium or titan passivation
has the advantage that during production less harmful
materials are used.
A very high accuracy of the thickness of the passivation
layer is achieved in that the passivation layer is coated by
using roller coaters.
According to a next embodiment of the present invention the
applied passivation layer has a thickness of 2 to 10 g/m2, in
particular 4 to 7 g/m2 of the wet film which allows achieving
the desired adhesion properties of the aluminum or aluminum
strip.
To ensure a precise control of the thickness of the
passivation layer according to a further embodiment of the
present invention applying the passivation layer is
controlled by an inline measurement.
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
6
Furthermore, according to a next embodiment after applying
and drying the passivation layer of the strip at least one
further coating is applied onto the passivation layer of the
strip. As already outlined the adhesion properties of a
passivation layer on the strips are very good in particular
for polymer coatings or lacquered coatings. In particular
during forming processes like deep drawing it has been shown
that such an additional coating is not damaged during forming
of the aluminum strip to a formed metal part like i.e. a cup-
like food package or a coated architectural sheets, since the
adhesion properties of the manufactured aluminum strips are
very good. This applies in particular for a single-layer
varnish top coatings and polymer coatings.
According to a further embodiment the degreasing and
anodizing step and the step of applying the passivation layer
are carried out inline with applying of a further coating
onto the passivation layer. The expenses to manufacture an
aluminum strip of which formed metal parts for grocery
packages or coated architectural sheets can be manufactured
are decreased significantly. Additionally, the quality of the
top coating is increased significantly, so that the following
production steps like forming, drawing, roll forming, bending
can be accomplished with very low defective products.
According to a next teaching of the present invention the
above mentioned object is solved by an aluminum or aluminum
alloy strip manufactured by the inventive method comprising
an anodic oxide layer with a thickness of 50 to 300 nm,
preferably 50 to 160 nm and a chromate-free passivation layer
on the oxide layer. As already outlined such an aluminum or
aluminum alloy strip comprises a very good corrosion
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
7
resistance because of the artificially grown oxide layer on
top of the aluminum layer and as well as very good adhesion
properties for a top coating which allows to produce formed
metal parts like food packages or coated architectural
sheets. Nevertheless, this applies to all coated formed metal
parts made of aluminum or an aluminum alloy strip.
According to a next embodiment the strip additionally
comprises an organic coating on top of the passivation layer,
wherein preferably the organic coating is a lacquer,
preferably a single-layer varnish or a polymer coating.
Organic coatings protect the aluminum layer additionally from
the influence of the corrosive parts of for example groceries
or corrosive components in the environment. The aluminum or
aluminum alloy strip comprising the additional organic
coating can be easily manufactured to formed metal parts for
example by deep drawing, such as cup-like food packages or
architectural sheets. Both comprise very good properties with
respect to the corrosion resistance. Coatings for
architectural sheets are based on for example polyurethane,
polyamide, polyester, high durable polyester PVDF-systems
etc..
In order to provide the different desired properties with
regard to the mechanical strength, formability and
recyclability according to an embodiment the aluminum or
aluminum alloy strip comprises an aluminum alloy of the type
AA1xxx, AA3xxx, AA5xxx or AA8xxx. For food packages the
thickness of the strips are preferably between 0,05 mm to 1
mm. However, architectural sheets preferably have a thickness
of between 0,15 mm and 2 mm.
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
8
Furthermore, the above mentioned object is solved by a formed
metal part made of an aluminum or aluminum alloy strip
manufactured according to the present invention. The formed
metal parts according to the present invention comprise a
high resistance against damages of the top coating during
forming operations of the metal parts. The inventive formed
metal part can be manufactured with a very low ratio of
defective products.
Preferably according to another embodiment the formed metal
part is a package for groceries or an architectural sheet.
The packages for groceries have to provide different
properties like formability, high corrosion resistance and a
top coating which should be biocompatible. Preferably, these
top coatings are made of a polymer resin or a lacquer more
preferably a single-layer varnish. Due to the good adhesion
properties of the aluminum or aluminum alloy strip of the
present invention comprising the artificial oxide layer and
the passivation layer a package for groceries made of the
inventive aluminum or aluminum strip can be produced with
lower expenses and insures a very high level of package
quality. The architectural sheet has to provide a very good
corrosion resistance as well as very good adhesion properties
for the top coating which is applied commonly on both sides
of sheet. Typical architectural sheets are façade components,
roller shutters and façade structural components which are in
permanent contact with water, i.e. rain and the humidity of
the air.
Finally the above mentioned object is solved by an apparatus
for carrying out the inventive manufacturing method
comprising:
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
9
- an uncoiler for uncoiling a strip made of aluminum or
aluminum alloy,
- means for degreasing and anodizing the strip by
immersing the strip into a bath of an acid electrolyte
and means to apply an AC current to the strip,
- optionally means for desmutting the anodized strip,
- means to apply a no-rinse passivation on the strip
surface,
- means to dry the passivation layer on the strip and
- a recoiler for recoiling the strip.
With the inventive apparatus it is possible to manufacture a
coated aluminum strip with the inventive manufacturing method
without coiling and decoiling the strip between the step of
degreasing and anodizing and the application of the
passivation layer. With the aforementioned apparatus it is
possible to provide a coil of an aluminum or aluminum alloy
strip comprising an anodic oxide layer with the thickness of
50 nm to 300 nm, preferably 50 nm to 160 nm and comprising a
passivation layer, in particular a chromate-free passivation
layer on top of the anodic oxide layer. Means to dry the
passivation layer allow a quick coiling of the passivated
aluminum strip. The optional means for desmutting the
anodized strip allow a quick preparing of the aluminum strip
for the application of the passivation layer in the next
manufacturing step. Such a coil can be coated easily with a
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
top coating for a desired package, wherein the coating can be
adapted to the particular application like food packages or
architectural sheets.
5 Furthermore, according to a next embodiment of the inventive
apparatus the apparatus comprises additionally means to coat
the strip with a top coating on the passivation layer. An
organic coating on the passivation layer may serve to improve
the properties for forming food packages by deep drawing as
10 well as providing additionally a protection for corrosion.
The inventive method, aluminum strip, formed metal part and
apparatus for manufacturing such an aluminum strip according
to further embodiments are described below in connection with
the drawings. The drawings show in
Fig. 1 a schematical sketch of the different
manufacturing steps of an embodiment,
Fig. 2 an embodiment of an inventive apparatus for
manufacturing a coated aluminum or aluminum
alloy strip,
Fig. 3a, b) a comparison between a conventional formed
metal part and an inventive formed metal part
according to a further embodiment,
Fig. 4 a microscopic sectional view of an inventive
embodiment after degreasing an anodizing step,
Fig. 5a, b) a perspective view and a sectional view of an
embodiment of an architectural sheet and
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
11
Fig. 6) a further embodiment of an architectural sheet
in the form of a roller shutter in a
perspective view.
At first Fig. 1 shows in a schematical view the different
manufacture steps A, B, C, D and E on the right side and on
the left side sectional views of the strip resulting from
step B, C, D and E and with respect to step A a sectional
view of an aluminum or aluminum alloy strip with which the
shown embodiment starts with.
An aluminum alloy strip made of the aluminum alloys of type
AA1xxx, AA3xxx, AA5xxx or AA8xxx is the starting point of the
inventive manufacturing process. The thickness of the strip
depends on the application. In general the thicknesses of the
aluminum or aluminum alloy strip is between 0,05 mm and 2,5
mm, preferably for food packages between 0,05 mm and 1,0 mm
and for architectural sheets between 0,15 mm and 2,0 mm. As
shown the aluminum alloy strip 1 prior to step A with
comprises on top of the aluminium alloy strip 1 a first layer
2 which is the natural oxide layer of the strip comprising
additionally undesirable contaminations. The oxide layer and
the contaminations present in the surface of the aluminum or
aluminum alloy strip result from the rolling process of the
strip. Such a strip is uncoiled in the step A and is provided
to a degreasing and anodizing step B. The degreasing an
anodizing step is preferably carried out with a sulfuric acid
at a concentration of 10 wt.-% to 25 wt.-%, preferably 12
wt.-% to 17 wt.-% as an electrolyte with a temperature of
65 C to 90 C by applying an AC-current density of 2 to 25
A/dm2, preferably 4 to 22 A/dm2 for an immersing time of the
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
12
strip of 1.5 s to 10 s, preferably 3 to 6 s. As shown on the
left side of step B the aluminum alloy strip 1 now comprises
an artificially grown anodic oxide layer 3 on top of the
surface of the aluminum strip 1. Compared to the naturally
given oxide layer with a thickness of 5 nm to 10 nm the
degreased and anodized aluminum or an aluminum alloy strip
comprises an oxide layer with a thickness of 50 nm to 300 nm,
preferably 50 nm to 160 nm. Due to the thickness of the oxide
layer the aluminum below the oxide layer is protected
effectively against corrosion. In the present drawings the
thicknesses of the different layers are not true to scale.
Such a strip is now provided to the next manufacturing step C
according which a passivation layer 4 is applied on top of
the oxide layer 3. However, optionally a desmutting step B'
can be applied to the degreased and anodized strip in order
to provide an optimized surface for applying the passivation
layer.
Although the present embodiment shows that the passivation
layer 4 is applied on both sides of the aluminum strip 1 it
is possible that only on one side a passivation layer is
applied to the aluminum strip. The passivation layer has a
thickness of 2 to 10 g/m2 of the wet film before drying the
no-rinse passivation layer. In particular it is
advantageously to apply a passivation layer which is
chromate-free or a zirconium or titan passivation. The
zirconium or titan passivation is one particular chromate-
free passivation. With a chromate-free passivation layer the
use of harmful substances during production can be avoided.
Architectural sheets as well as food packages take benefit of
the improved adhesion properties caused by the passivation
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
13
layer of the strip in the view of the adhesion of the top
coating.
After applying the passivation layer in manufacturing step C
the aluminum strip or aluminum alloy strip may be recoiled
because after passivation the aluminum strip or aluminum
alloy strip can be stored in step C' in order to optimize
production capacity. After storage in step C' or subsequently
after step C the strip is coated in the next manufacturing
step D with a top coating on top of the passivation layer. As
shown on the left side of step D the sectional view of the
aluminum alloy strip 1 shows that the strip now comprises an
outer layer 5 which may be an organic coating 5 consisting of
a lacquer, i.e. a one-layer varnish or for example of a
polymer coating.
According to step E the aluminum alloy strip 1 of step D can
be easily manufactured to a cup like food package as shown on
the left side of step E. As can be realized by the sectional
view in Fig. 1 at step E the coated aluminum strip according
to step D is preferably formed into a food package or an
architectural sheet by deep drawing or other forming
techniques, like roll forming or the like. In step E the
strip may be cut into sheets first and is formed subsequently
to food package or architectural sheet. However, it is also
possible to form first the product by forming the strip and
than cutting the strip into separate products.
The advantage of the inventive aluminum or aluminum alloy
strip is that during deep drawing or other forming steps to
build a food package or architectural sheet 6 as shown on the
left side to step E the top coating 5 of the aluminum or
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
14
aluminum alloy strip is not damaged. This is caused by the
good adhesion properties of the passivation layer
manufactured by said no-rinse step.
An embodiment of an inventive apparatus for carrying out the
inventive manufacturing process is shown in a schematical
view in Fig. 2. At first using an uncoiler 7 an aluminum or
an aluminum alloy strip 1 is uncoiled and provided to a
degreasing and anodizing step B in which the degreasing and
anodizing is carried out by using sulfuric acid under the
condition already outlined under manufacturing step B of Fig.
1. In step B' the aluminum or aluminum alloy strip 1 is
desmutted and optionally dried.
The aluminum strip or aluminum alloy strip 1 is than provided
to a device which carries out the manufacturing step C which
applies a passivation layer onto the surface of the strip by
using a no-rinse coil coating application. As indicated in
Fig. 2 application of the passivation layer is preferably
done by using roller coaters Cl and C2. Means to measure the
passivation layer thickness are not shown in Fig. 2 but are
advantageously used to control the thickness of the
passivation layer. In device 8 the no-rinse passivation layer
4 which is preferably a chromate-free passivation layer or a
zirconium or titan passivation layer is dried and in device 9
the aluminum strip is cooled again. In general it is possible
to coil the coated strip 1 now, because due to the passivated
surface of the strip it is possible to store a coil of the
strip with such a coating without problems.
According to the present embodiment shown in Fig. 2, however,
the aluminum or aluminum alloy strip 1 is provided inline to
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
a further coating step D in which a top coating 5 is applied
onto the aluminum strip or aluminum alloy strip. Preferably,
for applying the top coat a roller coater is used again.
However, depending from the particular coating other coating
5 methods can be applied, too. The top coat is than dried in
device 8' and the aluminum or aluminum alloy strip 1 is
cooled down in device 9' in order to prepare the aluminum
strip 1 for recoiling on recoiler 10.
10 Fig. 3a) and b) show photos of an exemplary embodiment Fig.
3a) and an inventive embodiment, Fig. 3b). The exemplary
embodiment Fig. 3a) comprises a top coating which is damaged
at a specific location of the deep drawn food package 11
shown in Fig. 3a) which is caused by a low adhesion of the
15 top coating on the surface of the aluminum alloy strip. As
shown in Fig. 3b) the deep drawn inventive embodiment does
not have any damages in the top coating of the food package
11.
Fig. 4 shows the anodic oxide layer 12 having a thickness of
nearly to 100 nm in a micro section. The combination of the
relatively thick anodic oxide layer of 50 nm up to 300 nm
which provides a very effective corrosion resistant together
with the use of a passivation layer applied by no-rinse coil
coating process allows to produce an aluminum strip or
aluminum alloy strip which provides very good corrosion
resistance combined with a good adhesion for top coatings.
Thus, aluminum or aluminum alloy strip according to the
present invention can be used very easily to manufacture food
packages or i.e. architectural sheets, which comprise
necessarily a top coating and which are formed by applying
forming operations to a coated strip or coated sheet.
CA 02890114 2015-04-29
WO 2014/067937 PCT/EP2013/072593
16
Finally, Fig. 5 shows an embodiment of an architectural sheet
13. The architectural sheet 13 comprises a plurality of
cuttings 14 and bended parts 13a. Preferably the cuttings are
made into the architectural sheet 13 after applying the
inventive method, thus the inventive method is applied to an
aluminum strip without cuttings. The strip is than coated
with a top coat which can be made of a polymer. Although,
cuttings are made into the architectural sheet after applying
the inventive method the inventive architectural sheet has a
good corrosion resistance due to the excellent corrosion
resistance and adhesion properties of the coated areas.
Furthermore, bending of the flat strip to a bended
architectural sheet as shown in Fig. 5b) does not change the
corrosion resistance, since the architectural sheet has
beside the corrosion resistance of the anodic oxide layer
very good adhesion properties for its top coating.
Another application of an architectural sheet is the roller
shutter 15 shown in Fig. 6. An inventive roller shutter made
from an aluminum alloy strip treated with the inventive
method offers higher corrosion resistance combined with a
very good adhesion of the top coating on the passivation
layer. In particular the good adhesion properties of the
passivation layer combined with the high corrosion resistance
of the anodic oxide layer leads to less defective goods
during production of the roller shutter 15, in particular
during rollforming of the coated strip. Furthermore, the
inventive roller shutter 15 comprises excellent corrosion
resistance even in the vicinity of cuttings of the roller
shutter (not shown in the drawings).
