EP2572807B1 - Method for producing an aluminium film with integrated safety characteristics - Google Patents

Description

The invention relates to a method for producing an aluminum foil with integrated security features, wherein an aluminum foil is rolled in several cold rolling passes to a thickness of less than 150 microns, and at the same time on both surface sides of the aluminum foil, a texturing running in the rolling direction.

Medical products, which are usually packaged using aluminum foil, are often targets for counterfeiting. Counterfeit-proof features should therefore be as close as possible to the medical product, i. the direct application of security features during the production process of primary packaging offers the best prerequisite for this.

It was therefore - as usual with banknotes - trying to provide packaging materials for the pharmaceutical industry with holograms. It has been shown that even holograms, although their production is relatively expensive, can be falsified.

According to the WO 03/104890 A1 Therefore, a specially structured area on a film surface is proposed as a security feature. The structuring takes place by rolling the film surface.

Special rolling processes are for example from US Pat. No. 6,187,455 B1 or the JP 57 007303 A known.

However, the rolling parameters must be set precisely, otherwise an undesirable deformation of the film surface can take place.

The invention aims to remedy this situation.

According to the invention, a method of the type mentioned is proposed, which is characterized in that at least two aluminum foils, a loose composite is formed, which is supplied in a last cold roll pass a pair of work rolls, wherein at least one roll surface in the rolling direction by grinding produced relief-like surface structure depending on the contrast and the subject was reduced in a range of 10 to 50% based on the average surface roughness to form a motif for a security feature, which is transferred to the roll surface facing surface side of the aluminum foils, after which the loose composite of aluminum foils is separated.

Further embodiments of this method are disclosed according to subclaims 2 to 5.

The invention will be described below with reference to a possible embodiment for carrying out the invention and with reference to the FIGS. 1 to 8 explained in more detail.

It shows FIG. 1 a pair of work rolls for carrying out the method according to the invention, FIG. 2 a detailed view of a work roll and its surface design, FIG. 3 the Striebeckkurve for documentation of the relevant process parameters in the nip and FIG. 4 the procedure for producing the integrated security features. FIGS. 5 to 8 show possible embodiments for the integrated security feature.

The manufacturing process of the aluminum foil 1 with integrated security features 6 initially consists of the sub-processes continuous casting, homogenizing, hot rolling, cold rolling and subsequent annealing above the recrystallization temperature. This is followed by the process of film cold rolling. In this case, the aluminum foil 4 is rolled in several cold rolling passes to a thickness of less than 150 .mu.m, wherein at the same time on both surface sides 4a, 4b of the aluminum foil extending in the rolling direction texturing 5a, 5b, see FIG. 4b , This structured roughness formed in the direction of travel leads to a directed reflection of the incident light, so that the surface sides 4a and 4b have a glossy appearance due to this directed reflection.

For the last Walzstich is converted, see FIG. 1 such as FIG. 4a , wherein a pair of work rolls 9 is used, in which at least one roll surface has a motif 6 'for the security feature. This motif 6 'is produced insofar as the relief-like surface structuring 11a produced in the rolling direction by grinding is reduced in a range of 10 to 50%, based on the average surface roughness, in a contrast- and subject-dependent manner. This can be done for example under the action of laser beams, see FIGS. 2b . 2c and 4c , For the last cold roll pass, a loose composite 8 is formed, for example, from two glossy aluminum foils 4 via a release agent 7, see FIGS. 1 and 4b , This loose composite 8 is the closed nip 9 ', which is formed between the two work rolls 10, 11, respectively. The motive for the security feature 6 is now transferred to the surface side 4a of the aluminum foil facing the work roll. In the area of the security feature 6 of the aluminum foil 1 - see Fig. 4d - Now arises a dull, random texturing, which stands out visibly from the remaining, shiny-appearing surface area 2a with directed texturing 3. In the area of the security feature 6, due to this random texturing, a diffuse reflection of the incident light occurs, so that the area of the security feature 6 appears dull. The side facing away from the roll surface surface side 2b of the aluminum foil 1 is characterized by the release agent 7 and by the second aluminum foil - for reasons of clarity with 4 '- covered. The contact sides of the two films are characterized by the rolling marks of the previous one Walzstichs and by the doubled rolling newly created roughness, which is mainly aligned transversely to the direction. Due to the random texturing of these surfaces, diffuse scattering occurs. After cold rolling, the loose composite of the aluminum foil 1 produced according to the invention with the integrated security feature 6 and the aluminum 4 'are separated. The aluminum foil 4 'has a directed structuring 5'a on its surface side 4'a, so that this surface side appears shiny, whereas the second surface side 4'b has a random structure and therefore has a matte surface.

However, if both work rolls are provided with a motif 6 ', a further aluminum foil 1 with integrated security feature 6 is produced instead of the aluminum foil 4'.

The film rolls underlying the process according to the invention belong to the subgroup "flat rolls", and are defined in particular by process end products having a thickness of 20 μm. The cold rolling process in this thickness range requires the specific use of surface roughness of tools in combination with process fluids to produce the tribological conditions required for plastic deformation in the roll nip.

For documentation of the process-relevant process parameters, see the Striebeck curve - see Fig. 3 - referred.

The abscissa shows the friction coefficient, the ordinate the function of speed, pressure and viscosity. For cold rolling of foils, the mixed friction area is required. In the area of low lubrication, there is constant contact with the rolling stock; a reduction of the material is not possible in this area, and subsequently leads to poor surface properties and damage to the roller. In the field of hydrodynamic lubrication - see also Reference 14 Fig. 2a - The work roll 11 "floats", so that a targeted control of the rolling process and in particular the reduction of the material thickness is no longer possible. By varying the parameters v, p and n, one can therefore set the range of mixed friction.

Only in the mixed friction region is it possible to generate longitudinal tensile and compressive stresses which stress the material via the deformation resistance and thus lead to a deformation, that is to say reduction of the material thickness. The adjustment of the parameters required for the forming process of the rolling oil 12, namely viscosity, pressure stability, lubricating effect, is achieved by the precise selection of a base oil, namely a kerosene-like, highly refined hydrocarbon with well-defined viscosity, and by adding about 5% by volume rolling oil additives, on the one hand bring the pressure stability of the medium to a certain level, but also significantly affect the friction conditions in the nip 9 '.

The tuning of these parameters is the basic requirement for the method according to the invention. Therefore, these parameters are permanently monitored and readjusted. In concrete application, the concentration of the rolling oil additives is measured directly by sampling from the buffer tank of the mill stand and kept in a well-defined area by means of additives. For precise metering, the process fluid is sprayed onto the work rolls 10, 11 by means of a nozzle bar.

The mixed friction conditions in the nip 9 'are required because only a defined coefficient of friction allows the application of longitudinal tensile stresses. These longitudinal tensile stresses counteract the yield strength and are the major factor in achieving film strain in film rolling resistance. A reduction in thickness without these longitudinal tensile stresses is from a technical point of view certainly not possible.

During cold rolling with a closed roll gap, the reduction resulting from the process and thus the strip thickness in the roll outlet are regulated by means of the primary parameter entry-tension (intake run), since these act against the deformation resistance of the aluminum foil 4. After reaching the maximum intake train, the secondary control parameter rolling speed is used to vary the lubricant film thickness (hydrodynamic lubricant intake).

In cold rolling, a mixed friction condition is sought, which is characterized by the simultaneous occurrence of boundary friction and fluid friction. In fluid friction, that is hydrodynamic lubrication 14, both surfaces are completely separated. The transferred shear stress depends on the dynamic viscosity of the lubricant and the speed difference between the work roll and the aluminum foil. By contrast, in boundary friction, the two surfaces are only separated by a layer of lubricant that is only a few molecules thick, with the viscosity of the lubricant playing only a minor role. The ratio between boundary friction and fluid friction over the length of the nip depends on the layer thickness of the drawn-in lubricant and the roughness of the work roll and the aluminum foil.

The mechanisms for influencing the lubricating film thickness 13 are determined by the hydrodynamic lubricant intake, the entry of lubricant into the roughness valleys 11 b and the attachment of lubricant particles influenced, see Fig. 2b ,

The hydrodynamic lubricant entry 14 takes place primarily in the inlet zone to the nip 9 '. In this case, the inlet zone forms a wedge-shaped gap 12, wherein the work roll 11 and the aluminum foil 4 entrain lubricant 13 in the form of a film as delimiting surfaces as they move in the direction of the wedge tip, see Fig. 2a , The resulting in rolling oil hydrodynamic pressure build-up depends on the rolling speed, the viscosity of the lubricant and the geometry of the nip. Once the flow condition for the aluminum foils 4 is met, they are plastically deformed and the layer thickness of the lubricant present at that point is drawn into the nip 9 '.

In the nip 9 'is in the surface depressions, the so-called roughness valleys 11 b, registered on the work roll 11 and the aluminum foil 4 lubricant, see Fig. 4c , This process depends not only on the oil storage volume of the surfaces but also on the orientation of the surface structure.

This mechanism can be used for the targeted change of the friction conditions, and subsequently serves to produce an altered surface texture due to the resulting fluid friction. This is done by the lack of contact of the work roll and the lack of texturing in the rolling direction.

On the surface of the work roll and the aluminum foil are formed by physisorption and chemisorption of lubricant components, such as. As surface-active additives, boundary layers, which are 9 'out in the nip. This mechanism is influenced by rolling and rolling stock 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 attachment of lubricant components in the process according to the invention do not differ from the conventional cold rolling process, this mechanism will not be discussed in detail.

However, the combination of the above effects makes it possible to bring the lubricating film thickness and the concomitant change in the tribological conditions in the nip from the mixed friction region in the region of the motif into the hydrodynamic region by means of targeted and partial destruction of the grinding structure of the work roll. This causes the work roll to float, resulting in a random texture which hardly differs measurably in the measured roughnesses, but because of the reflective properties it is visually distinct from the other surface areas, which have a patterned in the rolling direction surface by the partial contact with the work roll.

The manufactured aluminum foil 1 with integrated security features 6 is photographed for analysis purposes in several passes with optical methods. To illustrate the surface structure, representative foil samples in A4 format are produced. For the measurement of the surface structure of the tools required for the production, epoxy resin impressions of the surface are made and measured by means of incident light microscope and InfiniteFocus.

With the aid of this analysis method, it is now possible to carry out an optical identification for the detection of the safety marks 6 produced according to the invention. So shows Fig. 5 the representation of a security feature 6 consisting of the word security in connection with the usual in the medical industry representation of an Aesculapian. This is of course presented here as an example without any right of exclusion. In any case, it is important to note that the in Fig. 5b represented surface side, which was facing away from the roll surface during the rolling process, has no undesirable negative pressure motifs of the aforementioned security feature.

In Fig. 6 is a fanciful representation of a security feature 6 indicated, where in the section B, see Fig. 6b , it should be noted that in the area of the security feature 6, a matt surface, but in the respective adjacent surface areas, the structuring 3 is maintained in the longitudinal direction, whereby the surface appears shiny.

Likewise shows Fig. 7 a representation of a security feature taken by scanning electron microscopy 6. In the area of the security feature, the surface is dull, whereas in the adjacent surface areas the surface appears shiny. The detailed views according to FIGS. 7a and FIG. 7b show that this different effect is caused by the surface being rough in the area of the security feature 6, but longitudinally structured in the adjacent areas.

The same applies to the in Fig. 8 shown representation of an aluminum foil 1 according to the invention with integrated security feature 6 security after the infinitive focus analysis. Also from the respective representations according to 8a, 8b, 8c and 8d can be seen that in the area of the security feature 6 a random texturing, whereas in the adjacent area a directional structuring 13 is present.

• Aufbringung des Sicherheitsmerkmals 6 unmittelbar und gleichzeitig mit der Reduktion der Dicke der Aluminiumfolie 4; daher ist kein zusätzlicher Arbeitsschritt erforderlich,
• Hohe Wirtschaftlichkeit durch hohe Geschwindigkeiten bei der Herstellung der Aluminiumfolie 1,
• Erschwerte Imitation durch die Komplexität des Grundverfahrens,
• Eindeutige Zuordnung des Verfahrens zum Walzprozess aufgrund der Form und Anordnung der Oberflächenstrukturierung 3,
• Keine Möglichkeit der Entfernung der Sicherheitsmerkmale 6 ohne Zerstörung der Oberfläche der Aluminiumfolie 1,
• Kein Durchdrücken des Sicherheitsmerkmals 6 auf die Rückseite der Aluminiumfolie 1
• Keine Änderung der physikalischen und/oder chemischen Eigenschaften der Aluminiumfolie 4 wie Rauheit, Faltbarkeit, Dehnung, Zugfestigkeit und Benetzbarkeit,
• Änderung der Oberflächenbeschaffenheit im Bereich der 4. Ordnung, messbar über die mittlere Rautiefe Rz.
• Keine signifikante Änderung des arithmetischen Mittenrauwerts Ra im Bereich des Sicherheitsmerkmals 6
• Keine Formänderung im Bereich der 1. Ordnung (Formabweichungen wie Unebenheit oder Unrundheit), 2. Ordnung (Welligkeiten) oder 3. Ordnung (Rillen).

In summary, the following essential distinguishing features for the exact identification of the method according to the invention are listed:

• Application of the security feature 6 immediately and simultaneously with the reduction of the thickness of the aluminum foil 4; therefore no additional work step is required
• High efficiency due to high speeds in the production of aluminum foil 1,
• Complicated imitation due to the complexity of the basic procedure,
• Clear assignment of the process to the rolling process due to the shape and arrangement of the surface structuring 3,
• No possibility of removing the security features 6 without destroying the surface of the aluminum foil 1,
• No pushing of the security feature 6 on the back of the aluminum foil. 1
• No change in the physical and / or chemical properties of the aluminum foil 4 such as roughness, foldability, elongation, tensile strength and wettability,
• Change in surface quality in the 4th order range, measurable over the average surface roughness Rz.
• No significant change of the center-line arithmetic Ra in the area of the security feature 6
• No change of shape in the area of the 1st order (shape deviations such as unevenness or out-of-roundness), 2nd order (undulations) or 3rd order (grooves).

When used according to the invention cold rolling the optical features, such as the security features 6, introduced by targeted application of different surface textures of the aluminum foil in the 4th order. There is no significant difference in roughness depths, but a difference in the texture type of grooves and scales is achieved. A change in the shape of the aluminum foil 4 can not be determined, therefore, a push is not given on the back of the film.

The graphic relief-like design of flexible packaging materials using conventional manufacturing processes and finishing technologies, such as embossing (embossing) differ significantly from the inventive method in terms of the starting material, technology and the manufacturing process and the optical or mechanical properties of the final product, as in a Eindrückverfahren, Embossing motif is often pressed undesirably on the back of the stamped product.

During rolling in the course of the method according to the invention, the surface structure of the aluminum foil 4 is changed during the forming process, which makes it possible to design the surface with one or more security features 6. An imitation by common finishing technologies is not possible or as such easily identified. The production and further processing of the aluminum foil 1 with integrated security features 6 does not differ in terms of the number of production steps from the processing of conventional, hard-rolled aluminum foils and can thus easily be implemented in the production process customary for pharmaceutical products.

Claims (5)

1. A method for manufacturing an aluminum foil (1) with integrated security features (6), wherein an aluminum foil (4) is rolled down to a thickness of less than 150 µm in several cold-rolling passes, and wherein a texturing (5a, 5b) extending in the rolling direction is simultaneously produced on both sides (4a, 4b) of the aluminum foil, characterized in that a loose bond (8) of at least two of these aluminum foils (4) is produced and in a last cold-rolling pass fed to a pair of working rolls (9), in which the relief-like surface structuring (11a) produced in the rolling direction by means of grinding was reduced on at least one roll surface (11) in dependence on the contrast and in dependence on the motif in a range (6') between 10 and 50% referred to the average peak-to-valley height in order to realize a motif for a security feature (6) that is transferred onto the side (2a) of the aluminum foil facing the roll surface, whereupon the loose bond (8) of the aluminum foils (1, 4') is separated.
2. The method according to claim 1, characterized in that the last cold-rolling pass is carried out with a closed roll gap (9') and a mixed friction range is 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 (4) in the closed roll gap (9').
3. The method according to claim 1 or 2, characterized in that the relief-like surface structuring (11a) produced on the roll surface (11) in the rolling direction was reduced with respect to its average peak-to-valley height by means of laser beams for the last cold-rolling pass.
4. The method according to one of claims 1 to 3, characterized in that the motif (6') for the security feature (6) is not inadvertently pressed through onto the other side (2b) of the aluminum foil (1) due to a separating agent (7) on the aluminum foils (4) used.
5. The method according to one of claims 1 to 4, characterized in that the physical and/or chemical properties of the aluminum foils (4) are also preserved in the end product (1) due to the tribological conditions in the closed roll gap (9').

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