Note: Descriptions are shown in the official language in which they were submitted.
CA 02819772 2015-03-09
PROCESS FOR THE MANUFACTURE OF AN ALUMINUM FOIL
WITH INTEGRATED SECURITY FEATURES
The invention relates to a process for the manufacture of an aluminum foil
with
integrated security features as well as to an aluminum foil with integrated
security features
manufactured by this process.
Medical products, which are generally packaged with the help of aluminum foils
are
often a target for forgeries. Forgery-proof features should therefore be as
close as possible to
the medical product, which means the direct application of security features
during the
manufacturing process of primary packaging offers the best conditions herefor.
It was therefore attempted - as is common with banknotes ¨ to provide
packaging
materials for the pharma industry with holograms. It was however discovered
that even
holograms, although their manufacture is relatively complex, can be forged.
This is where the invention is to provide a remedy.
In accordance with the invention, a process of the above-mentioned type is
suggested,
whereby an aluminum foil in several cold roll reduction passes is rolled to a
thickness of less
than 150 p.m and whereby at the same time a texturing extending in rolling
direction is created
on both faces of the aluminum foil, whereby a loose composite is formed from
at least two
such aluminum foils, which is guided in a final rolling pass to a working
roller pair, in which
on at least one roller surface the relief type surface structuring produced by
grinding is
reduced, depending on contrast and motif in the range of 10-50% relative to
the average depth
of roughness for the formation of a motif for a security feature which is
transferred to the
outer face of the aluminum foil facing the roller surface, after which the
loose composite of
aluminum foils is separated.
Disclosed herein is a method for manufacturing an aluminum foil with
integrated
security features, wherein an aluminum foil is rolled down to a thickness of
less than 150 lam
in several cold-rolling passes and wherein a texturing extending in the
rolling direction is
simultaneously produced on both sides of the aluminum foil. A loose bond of at
least two of
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CA 02819772 2015-03-09
these aluminum foils is produced and in a last cold-rolling pass fed to a pair
of working rolls,
in which a relief-like surface structuring produced in the rolling direction
by means of
grinding is reduced on at least one roll surface in dependence on the contrast
and in
dependence on the motif in a range between 10 and 50% referred to the average
peak-to-
valley height in order to realize a motif for a security feature that is
transferred onto the side
of the aluminum foil facing the roll surface, whereupon the loose bond of the
aluminum foils
is separated.
In an embodiment, the last cold-rolling pass is carried out with a closed roll
gap. In
this embodiment, a mixed friction range may be adjusted with the parameters
coefficient of
friction, dynamic rolling oil viscosity, rolling speed and roll pressure based
on the Striebeck
curve, and in that longitudinal tensile stresses, which act against the
deformation stress of the
aluminum foils, are simultaneously exerted upon the aluminum foil in the
closed roll gap.
In a further embodiment, the relief-like surface structuring produced on the
roll
surface in the rolling direction may be reduced with respect to its average
peak-to-valley
height by means of laser beams for the last cold rolling pass.
In an embodiment, the motif for the security feature is not inadvertently
pressed
through onto the other side of the aluminum foil due to a separating agent on
the aluminum
foils used.
In yet another embodiment, the physical and/or chemical properties of the
aluminum
foils are also preserved in the end product due to the tribological conditions
in the closed roll
gap.
The invention further relates to an aluminum foil with integrated security
features,
which is manufactured according to the process of the invention and which has
security
features to an extent of at most 30% per unit of surface.
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CA 02819772 2013-06-03
The invention is further described in the following by way of a possible
exemplary
embodiment for the realization of the invention as well as by way of Figures 1-
8.
Figure 1 shows a working roller pair for the execution of the process in
accordance
with the invention. Figure 2 shows a detailed view of one working roller as
well as its
surface design, Figure 3 shows the Stribeck curve for the documentation of the
relevant
process parameters in the roller gap and Figure 4 shows the process sequence
of the
process for the manufacture of the integrated security features. Figures 5-8
show possible
embodiments of the integrated security feature.
The manufacturing process for the aluminum foil 1 in accordance with the
invention with integrated security features 6 consists first of all of the sub-
processes of
strand casting, homogenization, hot rolling, cold rolling and subsequent
annealing above
the recrystallization temperature. This is followed by the foil cold rolling
process. The
aluminum foil 4 is thereby rolled out in several cold rolling passes to a
thickness of less
than 150 [tm, by which simultaneously on both outer faces 4a, 4b of the
aluminum foil a
texturing 5a, 5b is created in rolling direction, as shown in Figure 4b. This
structured
roughness formed in rolling direction leads to a directed reflection of the
incident light, so
that because of this directed reflection the outer faces 4a and 4b have a
glossy appearance.
The process is modified for the last rolling pass as shown in Figure 1 as well
as
Figure 4A, whereby a working roller pair 9 is used in which at least one
roller surface has
a motif 6' for the security feature. This motif 6' is produced in that the
relief-like surface
structuring 11 a which is produced in rolling direction by grinding, is
reduced depending
on the contrast and motif in the range of 10-50% relative to the average
roughness depth.
This can be carried out, for example, by the action of laser beams as shown in
Figures 2b,
2c and 4c. For the last cold rolling step, a loose composite 8 is formed, for
example, from
two glossy aluminum foils 4 by way of a release agent 7, as shown in Figures 1
and 4b.
This loose composite 8 is fed into the closed roller gap 9', which is formed
between the
two working rollers 10, 11. The motif for the security feature 6 is now
transferred onto the
outer surface 4a of the aluminum foil which is directed towards the working
roller. A
random texturing which appears dull is now formed in the region of the
security feature 6
of the aluminum foil 1 ¨ see Figure 4d ¨ which is visibly distinguished from
the remaining
outer surface region 2a with glossy appearance and directed texturing 3.
Because of this
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CA 02819772 2013-06-03
random texturing, a diffused reflection of the incident light occurs in the
region of the
security feature 6, so that the region of the security feature 6 appears dull.
The outer
surface 2b of the aluminum foil 1 which is directed away from the roller
surface is covered
by the release agent 7 as well as the second aluminum foil ¨ referred to as 4'
for reasons of
clarity. The contact sides of the two foils are identified by the roller
grooves of the
proceeding rolling step and by way of the roughness newly generated during the
coupled
rolling, which roughness is primarily directed transverse to the rolling
direction. A
diffused scattering occurs because of the random texturization of these
surfaces. After the
cold rolling, the loose composite of the aluminum foil 1 with integrated
security feature 6,
manufactured in accordance with the invention, and the aluminum foil 4' is
separated.
The aluminum foil 4' has on its outer surface 4'a directional structuring 5'a,
so that this
outer surface appears glossy, whereas the second outer surface 4'b has a
random
structuring and therefore provides a dull surface.
However, when both working rollers are provided with a motif 6', a further
aluminum foil 1 with integrated security feature 6 is produced in place of the
aluminum
foil 4'.
The foil rolling process underlying the process in accordance with the
invention belongs to
the subcategory "flat rolling" and is defined especially through process end
products with
a thickness of 20 Jim. The cold rolling process in this thickness range
requires the specific
application of surface roughness values on the tools in combination with the
procedural
liquid which create the tribologic conditions in the rotor cap required for
the plastic
deformation.
Reference is made to the Stribeck curve ¨ see Figure 3 ¨ for the documentation
of
the process parameters relevant for the procedure. The co-efficient of
friction is
represented on the X axis and the function of speed, pressure and viscosity is
represented
on the Y axis. The mixed friction range is required for the cold rolling of
foils. In a
region of little lubrication, a continuous contact with the rolled material
occurs: a
reduction of the material in this region is not possible and leads in the
following to poor
surface properties and damage of the roller. In a region of hydrodynamic
lubrication ¨ see
in this respect Reference no. 14 in Figure 2a ¨ the working roller 11 starts
to float so that a
directed control of the rolling process and especially of the reduction of the
material
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thickness is no longer possible. The range of mixed friction can thereby be
adjusted by
varying the parameters V. P and N.
Only in the mixed friction range is it possible to generate longitudinal and
pressure
tensions which load up the material past the shape change resistance in order
to thereby
lead to a reshaping, which means reduction of the material thickness. The
adjustment of
the parameters of the rolling oil 12, which are required for the reshaping
process, namely
viscosity, pressure, stability, lubricant effect, is carried out by the
precise selection of a
base oil, namely a kerosene-like, highly refined hydrocarbon with an exactly
defined
viscosity and by the addition of about 5 volume percent rolling oil additives
which on the
one hand bring the pressure stability of the medium to a specific level but
also
significantly influence the friction conditions in the roller gap 9'.
The coordination of these parameters represents the basic requirement for the
process in accordance with the invention. These parameters are therefore
permanently
monitored and readjusted. In the concrete application, the concentration of
the rolling oil
additives is measured directly through sampling from the buffer container of
the roller
rack and maintained within an exactly defined range by way of additive
adjustment. For
exact dosage control, the processing liquid is sprayed onto the working
rollers 10, 11 by
way of a nozzle beam.
The mixed friction conditions in the roller gap 9' are required, since only a
defined
friction coefficient enables the application of longitudinal tension stress.
This longitudinal
tension stress acts against the deformation strength and is during the foil
rolling the
essential factor for the achievement of the deformation resistance. A
thickness reduction
without this longitudinal tension stress is not possible from a technical
point of view.
During cold rolling with a closed roller gap the reduction resulting from the
process and thereby the band thickness in the roller output is controlled by
way of the
primary parameter of entry tension, since it acts against the deformation
resistance of the
aluminum foil 4. After achievement of the maximum entry tension, the roller
speed is
used as the secondary control parameter in order to vary the lubricant film
thickness
(hydrodynamic lubricant input).
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During cold rolling, a mixed friction condition is desired which is
characterized by
the simultaneous occurrence of boundary friction and liquid friction. During
liquid
friction, which is the hydrodynamic lubrication 14, both surfaces are
completely separated
from one another. The transferred shear stress depends on the dynamic
viscosity of the
lubricant and the speed differential between the working roller and the
aluminum foil. In
contrast, during the boundary friction both surfaces are separated only by a
lubricant layer
which is only a few molecule layers thick, whereby the viscosity of the
lubricant plays
only a subordinate role. The ratio between boundary friction and liquid
friction over the
length of the roller gap depends on the layer thickness of the input lubricant
and the
roughness of the working roller and the aluminum foil
The mechanism for influencing the lubricant film thickness 13 depends on the
hydrodynamic lubricant input, the input of lubricant into the roughness
valleys 1Ib as well
as the attachment of lubricant particles, see Figure 2b.
The hydrodynamic lubricant input 14 primarily occurs in the input zone to the
roller gap 9'. The input zone thereby forms a wedge shaped gap 12, whereby the
working
roller 11 and the aluminum foil 4 as limiting surfaces during their movement
in direction
of the wedge tip pull along lubricant 13 in the form of a film, see Figure 2a.
The
hydrodynamic pressure buildup thereby caused in the rolling oil is dependent
for the
rolling speed, the viscosity of the lubricant and the geometry of the roller
gap. As soon as
the yield criterion for the aluminum foils 4 is fulfilled, they are
plastically deformed and
the layer thickness of the lubricant present at this location is pulled into
the roller gap 9'.
In the roller gap 9', lubricant is input into the surface depressions, the so-
called
roughness valleys 11b, on the working roller 11 and the aluminum foil 4, see
Figure 4c.
This process depends, apart from the oil storage volume of the surfaces, also
on the
orientation of the surface structure. This mechanism can be used for the
directed change
of the friction conditions and in the following serves to create a changed
surface texture
because of the liquid friction generated. This occurs because of the missing
contact with
the working roller and the thereby missing texturing in rolling direction.
Boundary layers are formed on the surface of the working roller and the
aluminum
foil, which are carried into the roller gap 9', because of physiosorption and
chemisorption
of lubricant components, for example surface active additives. This mechanism
is
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CA 02819772 2013-06-03
influenced by the roller material and the rolled material as well as the
chemical
composition of the rolling oil 12 and its temperature. Since the temperature
and the
composition of the rolling oil 12 with respect to the accretion of lubricant
components in
the process in accordance with the invention are not different from the
conventional cold
rolling process, this mechanism is not further discussed.
However, it is the combination of the above effects, which by way of directed
and
partial destruction of the ground-in structure of the working roller makes it
possible to
bring the lubricant film thickness and the associated changes of the
tribologic conditions in
the roller gap from the mixed friction range in the region of the motif into
the
hydrodynamic range. This leads to a floating of the working roller and a
random texture is
generated which differentiates barely measurable in the measured roughness but
is
optically clearly distinguished because of the reflection properties of the
remaining surface
regions which through the partial contact with the working roller have a
structured surface
in rolling direction.
The produced aluminum foil 1 with integrated security features 6 is copied
with
optical processes in several passes for the purposes of analysis. For the
clear illustration
of the surface structure, representative foil samples are produced in the
format A4. For the
measurement of the surface structure of the tools required for the
manufacture, epoxy resin
imprints of the surface are produced and measured by way of a reflected light
microscope
and infinite focus.
It is now possible with the help of this analytical process to carry out an
optical
identification for confirmation of the security features 6 produced in
accordance with the
invention. Figure 5 shows the illustration of a security feature 6 consisting
of the lettering
security in combination with the illustration of a staff of Asclepius
customary in the
medical industry. Of course, the latter is here illustrated only by way of
example and
without claim to any exclusionary rights. At any rate, it is important to
point out that the
outer surface illustrated in Figure 5b, which during the rolling process was
directed away
from the roller surface, includes no undesired negative print motifs
whatsoever of the
previously mentioned security feature.
A fantasy illustration of a security feature 6 is shown in Figure 6 whereby in
the
section b, see Figure 6b, it is apparent that in the region of the security
feature 6 a dull
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surface is present while in the respectively bordering surface regions the
structuring 3 in
longitudinal direction continues to be maintained, whereby the surface appears
glossy.
Figure 7 also shows an image taken by way of scanning electron microscopy of a
security feature 6. In the region of the security feature, the surface is
dull, whereby in the
bordering surface regions the surface appears glossy. The detailed views
according to
Figures 7a or 7b show that this different effect is caused by the surface
being rough in the
region of the security feature 6 while it is structured in longitudinal
direction in the
bordering regions.
This applies analogous to the image shown in Figure 8 of an aluminum foil 1
manufactured in accordance with the invention with the integrated security
feature 6
Security taken according to the infinitive focus analysis. From the
illustrations of Figure
8a, 8b, 8c and 8d, it is also apparent that a random texturing is present in
the region of the
security feature 6, whereas in the bordering regions a directed structuring 13
is present.
In summary, the following essential differentiating features for the exact
identification of the process in accordance with the invention are listed:
- Direct application of the security feature 6 and simultaneous with
the reduction
of the thickness of the aluminum foil 4; thus, no additional processing step
is
required;
- High operating efficiency through high speeds during the manufacture of
the
aluminum foil in accordance with the invention;
- More complicated imitation due to the complexity of the basic
process;
- Clear association of the process with the rolling process because of the
form
and placement of the surface structuring 3;
- No possibility of removal of the security features 6 without
destruction of the
surface of the aluminum foil;
- No strikethrough of the security feature 6 the back side of the aluminum
foil 1;
- No changes of the physical and/or chemical properties of the aluminum
foil 4
such as roughness, foldability, stretch, tensile strength and wettability;
- Change of the surface configuration in the range of the fourth
order,
measurable by way of the average roughness depth RZ;
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- No significant change of the arithmetic mean roughness index RA in
the region
of the security feature 6;
- No shape change in the range of the first degree (shape changes
such as
unevenness or out of roundness), second degree (waviness) or third degree
(grooves).
In the cold rolling used in accordance with the invention, optical features,
such as
the security feature 6 are applied by the directed application of differing
surface textures
of the aluminum foils in the range of the fourth order. No significant
difference in the
roughness depth can be determined, but a difference in the type of texturing
of grooves
and scaling is achieved. A change of the shape of the aluminum foil is not
detectable so
that a strikethrough to the foil backside does also not occur.
The graphic relief type shaping of flexible packaging materials with the help
of
conventional manufacturing processes and finishing technologies, for example
embossment (impression processes) are significantly differentiated from the
process in
accordance with the invention with respect to the starting material,
technology and
manufacturing processes while as the optical or mechanical properties of the
end product,
since in an impression process the motif to be embossed often strikes though
in an
undesired manner to the backside of the embossed material.
During the rolling in the course of the process in accordance with the
invention, the
surface structure of the aluminum foil 4 is changed during the mechanical
working,
whereby it is made possible to develop on the surface one or more security
features 6. An
imitation by way of conventional finishing technologies is not possible or is
easily
identifiable as such. The manufacture and the further processing of the
aluminum foil 1 in
accordance with the invention with integrated security features 6 is, with
respect to the
number of manufacturing steps, not distinguished from the processing of
conventional,
rolled aluminum foils and can thereby be easily implemented in the
conventional
manufacturing process for pharma products.
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