EP2694296B1 - Optically variable security feature - Google Patents

Description

The present invention relates to a printed product with a security element and a method for producing such a printed product with a security element. The invention relates in particular to the production of a printed product with a forgery-proof optical element which, if possible, cannot be copied by an alleged forger without the copy being recognizable.

Nowadays there is an increased tendency for high-quality and particularly expensive products to be copied very often. In addition to the economic damage that the manufacturer of the original products suffers as a result, the fact that these copies are usually of a lower quality is also a problem. A buyer who purchases such an inferior copy thinking they have bought an original product will be disappointed by the poor quality of the product. However, since the buyer cannot immediately tell that it is a copy and not the original manufacturer's product, they will attribute the inferior quality to the original manufacturer. In addition to the economic damage, the original manufacturer also suffers considerable image damage.

If the copy is also a product that is used in a safety-relevant area, such as a spare part for a vehicle brake or the like, there is also a considerable risk to life and limb for the buyer of such an inferior copy.

Therefore, the manufacturers of high-quality original products are careful that potential buyers can quickly and easily distinguish an original product from an alleged copy. For example, open optical security features are available for this purpose, which on the one hand can be checked quickly without additional tools, but on the other hand at least with the currently available technical means available cannot easily be copied without the copy being recognizable.

Such an optical security feature is, for example, a hologram that is applied to a product or to the packaging of a product. On the one hand, however, such holograms are relatively expensive to produce. On the other hand, it would also be possible for an alleged counterfeiter to have access to a certain number of such holograms, who can then attach them to his copies.

Another security feature that is easily perceptible optically is a so-called "latent image". In this context, this means a security feature applied by printing that gives a different optical impression depending on the orientation of the viewing angle and incidence of light. This is achieved in that a printing process, preferably intaglio printing, simultaneously produces a relief-like surface structure in addition to the application of color. Areas with a large number of lines running in parallel are created in the relief, with there being in principle two different types of areas which differ in the orientation of the lines running in parallel. As in figure 1 shown, the lines of one area are perpendicular to the lines of the other area. Depending on the orientation towards the viewer and the incidence of light, one or the other area appears brighter. If the orientation of this latent image is changed, this effect is reversed and the area that originally appeared light suddenly becomes the darker area. The difference in brightness results from the different shadows cast by the line structures, which are aligned transversely to the incidence of light.

These security features are now very well known and widespread. Among other things, this means that suspected counterfeiters also have relatively easy access to the know-how required to produce such security features. Thus, there is a risk that these security features taken alone can already be imitated by alleged counterfeiters in a short time.

Another security feature that counterfeiters will probably not have access to for a long time is the use of optically variable colors with a tilting effect. These are printing inks with special color pigments that create a different color impression depending on the viewing angle. The variations in the perceived color impression are primarily based on interference caused by the special pigments in the printing ink.

The document U.S. 2004/195823 A1 discloses a background image portion and at least one message image portion printed on a surface of a base member. The background image part has a first line drawing arranged in a first direction and printed with a specular gloss ink to have an ink layer thickness. The message image part has a second line drawing arranged in a second direction and printed with the ink having the specular gloss to maintain the ink layer thickness.

The manufacture and sale of these color effect pigments are subject to very strict restrictions. The pigments are therefore only available to selected printers and are therefore not legally available to an alleged counterfeiter. Nevertheless, it cannot be ruled out that an alleged counterfeiter could come into possession of a certain amount of such color pigments.

It is therefore the object of the present invention to provide an overt security feature that is easily perceptible optically and has a very high security standard. It should continue to be possible to produce this security feature as cost-effectively and efficiently as possible.

This object is achieved by a printed product with an optical security feature according to claim 1, which comprises a printing material on which a first line structure of a plurality of raised parallel running parallel to the printing material are applied in a screen printing process and one of the first line structure different possess alignment; wherein the printing ink for printing the first line structure contains color pigments with a tilting effect, wherein the ratio of line spacing, which relates to the distance between two immediately adjacent line centers, to the line width of the raised lines of the first line structure is at least 1.5, that the first and the second line structure has a height of at least 5 microns, that the printing ink for printing the first line structure contains at least 30 percent by weight of color pigments with a tipping effect, and that the printed product also has at least partial background printing on the printing material, with the first and the second line structure being printed on the background printing and with the background printing having a dark, preferably black color is executed.

The stated object is also achieved by a method for producing a printed product with an optical security feature according to claim 7, which comprises the following steps: providing a printing material;screen printing a first line structure from a plurality of raised, mutually parallel, spaced lines, wherein the printing ink for printing the first line structure contains color pigments with a tipping effect;screen printing a second line structure consisting of a plurality of raised, mutually parallel, spaced lines, wherein the first line structure is formed in such a way that the ratio of line spacing, which affects the distance between two immediately adjacent line centers relates to the line width of the raised lines of the first line structure is at least 1.5, that the first and the second line structure have a height of at least 5 micrometers, that the printing ink for printing the first line structure contains at least 30 percent by weight color pigments contains a tilting effect, and that the printed product also has at least partial background printing on the printing material, the first and the second line structure being printed on the background printing and the background printing being executed with a dark, preferably black color.

It is the special approach of the present invention, two independent, open To combine security features into a common security feature. The security feature according to the invention should be able to be produced in a single work step. For this purpose, on the one hand, the "latent image" security feature is modified in such a way that it can be produced with an alternative printing method instead of the conventionally used intaglio printing. Thus, a relief-like structure is not pressed into the printing material itself, but rather the required differences in height are placed on the printing material by means of a printing ink that is applied in a raised manner. At the same time, pigments with a color shift effect are added to the printing ink. In this way, two independent optical security features are firmly connected.

The interlocking of two initially independent security features results in a particularly strong, new type of security feature. This new type of security feature is also an open security feature, since it can be visually perceived and checked in a simple manner without additional aids. Therefore, the verification can be performed by almost anyone and at any convenient time.

The printing ink for printing the second line structure preferably also contains color pigments with a tilting effect. The security feature has an additional security aspect in the entire area of the latent image due to the tilting effect of the optically variable color used.

According to the invention, at least partial background printing is first applied to the printing material. At least one of the first or the second line structure is then printed onto this background printing. Both line structures, the first and the second line structure, are preferably printed onto the background printing. In this way, on the one hand, the contrast and thus the tilting effect of the latent image can be significantly increased. In addition, background printing also enables the surface of the printing material to be refined, so that the line structures can be printed with significantly better quality. According to the invention, dark colors such as black are used.

The first and the second line structure preferably have a height of at least 10 micrometers. The higher the printed lines of the first and second line structures are, the better the tilting effect of the latent image is.

In a preferred embodiment, the printing varnish for the first and the second line structure is cured after printing. Curing by thermal, ultraviolet or infrared radiation has proven to be particularly advantageous.

In a very specific embodiment, the printed product comprises at least a third line structure made up of a plurality of raised lines running parallel to one another, which are applied to the printing material in a printing process. In this case, the third line structure has a different alignment from the first and the second line structure.

Due to the fact that the printing ink for printing the first line structure contains at least 30 percent by weight of color pigments with a tilting effect, a high quality of the impression of the optically variable colors can be guaranteed with the security feature according to the invention.

• Figur 1: eine schematische Darstellung eines erfindungsgemäßen Sicherheitsmerkmals in einer Draufsicht;
• Figur 2: eine schematische Darstellung eines erfindungsgemäßen Sicherheitsmerkmals im Querschnitt;
• Figur 3: eine schematische Darstellung eines alternativen Ausführungsbeispiels eines erfindungsgemäßen Sicherheitsmerkmals in einer Draufsicht;
• Figur 4: eine schematische Darstellung eines weiteren alternativen Ausführungsbeispiels eines erfindungsgemäßen Sicherheitsmerkmals in einer Draufsicht;
• Figur 5: eine schematische Draufsicht einer alternativen Ausführungsform mit sich berührenden, ineinander greifenden Liniengruppen; und
• Figur 6: eine schematische Draufsicht einer weiteren alternativen Ausführungsform mit sich berührenden, ineinander greifenden Liniengruppen.

The raised lines of the first line structure preferably have a width of at least 130 micrometers. The ratio of line spacing to line width of the raised lines of the first line structure is at least 1.5. With these parameters, an excellent effect of the security features used can be achieved on the one hand. On the other hand, these parameters also enable a reliable production-related setting for the production of the security features in a printing process. The structure of a security feature according to the invention is described below with reference to the figures. show:

• figure 1 1: a schematic representation of a security feature according to the invention in a plan view;
• figure 2 : a schematic representation of a security feature according to the invention in cross section;
• figure 3 1: a schematic representation of an alternative exemplary embodiment of a security feature according to the invention in a plan view;
• figure 4 1: a schematic representation of a further alternative exemplary embodiment of a security feature according to the invention in a plan view;
• figure 5 Fig. 1 is a schematic plan view of an alternative embodiment with touching, interlocking line groups; and
• figure 6 FIG. 1: a schematic plan view of a further alternative embodiment with touching, interlocking line groups.

The figures show the structure according to the invention only schematically. For better clarification, the actual proportions were not taken into account. The schematic representations of the figures do not represent any limitations of the structure according to the invention.

figure 1 shows schematically the basic structure of the security feature "latent image" as it is implemented in the method according to the invention. A label is shown which is provided with a security feature. A plurality of raised lines 11 are applied to a printing material 1 in the left-hand area 10 . The lines 11 in this area are horizontal. In the area 20 to the right, several raised lines 21 are also applied. These lines 21 are vertical. Thus, the orientation of line 11 is offset by 90° to the orientation of lines 21.

figure 2 shows schematically a section along the line 1-1 'through such in figure 1 shown structure. The raised structure of the lines can be clearly seen.

If such a structure is now illuminated by a light source from direction A in figure 1 illuminated, the raised lines 11 in the left-hand area 10 cast a clear shadow in the gaps between the individual lines 11, the gaps therefore appear rather dark. In contrast, in the right-hand area 20 the intermediate spaces between the lines 21 are well illuminated by the light source and therefore appear brighter.

If, on the other hand, the structure is illuminated by a light source from direction B, the spaces between the lines 11 appear rather light, while the spaces between the lines 21 appear rather dark. The optical impression in the areas 10 and 20 therefore varies depending on the incidence of light and viewing direction.

In order to produce a structure for such a security feature without directly changing the surface of the printing material 1, as would be the case with the conventional production of a latent image in intaglio printing, the raised line structures 11 and 21 are printed on the printing material 1 in the method according to the invention printed in relief. In principle, all printing methods that can apply a corresponding printing ink in the required thickness to the printing material 1 are suitable for this purpose. Application by screen printing has proven to be inventive here.

The lines 11 of the area 10 are applied to the printing material 1 in a first printing process, for example. The lines 21 of the area 20 are then subsequently applied to the printing material 1 in a further second printing process. The printing processes differ, for example, in the orientation of the measures with which the raised structures are produced.

Line heights of preferably at least 5 to 10 μm, or preferably at least 30 μm, have been found to achieve a readily perceptible optical change when varying the incidence of light and the viewing angle. Line heights of up to 100 µm would be desirable, but are very difficult to achieve with the methods that are technically available today.

In practical test series, very good results with regard to the perceptibility of the security features could be achieved with line heights of approximately 26 microns.

In principle, all colors with which a desired line height can be achieved can be used as printing ink for the production of such raised line structures 11 and 21 . Typically, the ink for raised lines 11 and 21 is runny or at least viscous in process. In order to convert the printing ink into a solid state as quickly as possible after printing, the printed lines 11 and 21 should harden as quickly as possible. Methods in which a corresponding printing ink is activated after printing are particularly suitable for this purpose, so that a chemical or physical curing is initiated. For example, after printing, the printing ink can be irradiated with microwave rays, for example infrared or ultraviolet light, and curing can take place as a result. Since no substances are generally released into the environment during this process, the volume of the lines printed is also not reduced, which has an advantageous effect on the desired maximum possible height of the lines.

In principle, printing inks with a solvent that evaporates into the environment after printing can also be used. However, it must be taken into account that the volume of the lines and thus also the line height are reduced as a result of the evaporation of the solvent. This also slightly reduces the impression of the optical variation when the latent image security feature is tilted.

In order to increase the security effect of a latent image produced in this way, color pigments with a so-called tilting effect (optically variable color pigments) are additionally added to the printing ink for producing the raised lines 11 and 21 for a security feature according to the invention.

These color pigments with a tilting effect, which are used to produce so-called optically variable colors, are small, multi-layered platelets. If light hits such a small plate, the light is partly reflected and partly transmitted at the individual layers. In the interaction with the individual light components, which are thus reflected on different layers of a small plate, interferences arise that lead to variable color impressions depending on the viewing angle. Depending on the structure of the individual plates, the changing color impression varies.

By adding such color pigments with a tilting effect to the printing ink for the construction of the lines for the latent image, a combination of two initially separate security features is thus generated. It is particularly advantageous that the printing ink for the lines of the latent image can be printed exactly as before, without requiring additional work steps in the printing process would be. This is a significant benefit, especially in terms of print preparation time and production costs.

According to the invention, mixing a proportion of at least 30 percent by weight of optically variable color pigments into the printing ink has proven to be effective. Otherwise, the impression of a color variation can be significantly impaired, especially with low line heights.

The quality of the security feature increases even if only some of the raised lines contain the color pigments with a tilting effect. For example, it is possible that only the lines 11 of an area 10 are provided with such color pigments, and the lines 21 of another area 20 are printed with a color without such special optically variable color pigments. Of course, it is also possible for all of the raised lines 11 and 21 to be produced with a printing ink that contains the corresponding color pigments. The relatively large height of the raised lines 11 and 21 for the construction of the latent image proves to be particularly advantageous for the effect of the optically variable colors. The effect of the optically variable colors also becomes more apparent the higher the color application.

The distance D of the individual lines 11 or 21 from one another and also the width LW of the individual lines depend on the character of the image to be displayed. Due to the different requirements resulting from the constraints of the two security features latent image and optically variable color, as well as the general conditions for printing the raised structures, partially opposing conditions have to be taken into account. The distance D between the lines is, for example, the distance between two repeating structures of the lines that correspond to one another, for example the distance between the line centers of two directly adjacent lines.

For example, small line widths are advantageous for a latent image that is as clear as possible, while larger line widths are desirable for a reproduction by printing.

In order to generate a security feature according to the invention from a latent image and optically variable ink, it has proven to be particularly suitable for production by printing technology to select a line width LW of at least 130 μm. The ratio of line spacing D to line width LW is designed in such a way that a value of at least 1.5 is not fallen below. This means that the distance D should be at least 195 µm for the minimum desired line width LW of 130 µm. The actual specifications of the structure can vary depending on the size and content of the security feature.

Almost any printable material is suitable as the printing material on which the above-described raised lines 11 and 21 are printed. It is a particular advantage if the material for the printing material 1 has a surface that is as smooth as possible. The printing material 1 should also absorb as little of the printing ink as possible, so that at best the entire volume of the applied printing ink is available for the raised line structures 11 and 21 on the surface of the printing material 1. A highly absorbent substrate would absorb a significant part of the printed color, which means that less color substance would be available for the formation of the raised line structures of the latent image.

Therefore, for example, very particularly plastic films of any kind, such as those made from polyethylene or polyvinyl chloride, are very well suited as printing materials or as substrates to be printed or substrates to be printed. However, other plastic films which have the properties described above are also suitable for printing with the security feature according to the invention. Furthermore, papers, in particular papers with a coated surface, are also very suitable.

In order to increase the tilting effect of the latent image before the raised line structures 11 and 21 are printed, the surface of the printing material 1 is also coated with background printing 30 . A corresponding structure with background printing 30 is in figure 3 shown. According to the invention, a dark color, for example dark blue or red, is selected for the background printing. Background printing in black has also proven particularly advantageous. The background printing 30 preferably has a matt or matt-glossy character.

By coating the printing material 1 with a background print 30, the surface of the printing material 1 can also be finished at the same time. This means that even initially relatively rough surfaces of a printing material are given a smooth surface by the coating, and it is therefore very easy to print the raised lines 11 and 21. Furthermore, by applying surface printing, the suction effect of the printing material can also be reduced, which has a positive effect on the expected line height of the printed lines.

In the previous exemplary embodiments, the raised lines 11 and 21 are aligned perpendicularly to one another, i.e. they extend at least approximately at a 90° angle to one another. In addition, the effect of a latent image, possibly with a slightly weakened effect, can also be achieved with lines that are at an angle other than 90° to each other. For example, lines that run at an angle of approximately 60° or 45° to one another would also be possible.

The previously shown structure of a latent image from two groups of lines does not represent any limitation. figure 4 Figure 13 shows another embodiment in which the latent image is built up from three raised line groups 111, 121 and 131. In principle, latent images with the three line groups shown here or even more are possible. As a result, a far greater variability of the tilting effect is achieved and a higher security level of the security feature according to the invention is achieved.

Line group 111 has a parallel raised line orientation in which all lines are at an acute angle to a reference line, such as a horizontally oriented line. The angle is 45°, for example. Line group 121 comprises a number of parallel raised lines perpendicular to the reference line. The group of lines 131 comprises a number of raised lines running parallel to one another and having an obtuse angle to said reference line, for example 135°.

Either all line groups 11, 21 and 31 or 111, 121, 131 can be produced from printing inks with optically variable color pigments, or only one or two of the line groups are provided with such color pigments. Here, too, the security level of the security feature generated in this way can be significantly increased through the use of the optically variable color pigments with a tilting effect.

In the preceding figures, the areas of the individual line groups 11, 21 and, if applicable, 31 are shown separately from one another for better illustration. In practice, however, the different groups of lines intertwine, overlap or touch. Through the interlocking of the line structures, information can be formed in the form of a symbol, a number, lettering or the like. Two exemplary variants are this in the Figures 5 and 6 shown, in which the respective line groups 211 and 221 interlock. figure 5 illustrates the basic principle while figure 6 represents an excerpt from a practical security feature. Other embodiments of interlocking line structures are of course also possible.

In figure 5 the line group 211 is completely surrounded by the line group 221 on three of its sides, namely from above, from the right and from below with regard to the plane of the drawing. Only the edge of the line group 221 shown on the left is free and not surrounded by the line group 211 . There are also designs conceivable in which the line group 211 (not shown) completely around from is surrounded on all sides by lines of line group 221. With regard to the orientation of the lines of the first group of lines 211 to the lines of the second group of lines 212 is in figure 5 determine that the lines of one group are perpendicular to the orientation of the lines of the second group.

In figure 6 the lines of line group 221 run along a strip-like course within the lines of line group 211. For example, the strip for the lines of line group 221 begins at the top right, then runs to the left, is guided in a right-pointing arc, so that the orientation is almost reversed and the stripe again runs to the right to the edge of the latent image. Within the strip, the lines of the line group 221 are arranged parallel to one another.

In summary, the present invention relates to an overt optical security feature with a high security standard that can be produced relatively easily in a technical production process. The security features of optically variable inks with a tilting effect and the properties of a latent image are combined and intertwined. By generating the security feature in a printing process, the security feature can be implemented cost-effectively but with a very high security standard. The security feature produced in this way can be easily verified by any person at any time without additional aids.

Claims (11)

1. A printed product having an optical security feature, comprising:

   a printing substrate;

   a first line structure consisting of a plurality of raised, mutually parallel, spaced-apart lines which are applied to the printing substrate in a screen printing method; and

   a second line structure consisting of a plurality of raised, mutually parallel, spaced-apart lines which are applied to the printing substrate in a screen printing method and have an orientation which differs from that of the first line structure;

   the printing ink for printing the first line structure containing color pigments having a tilt effect,

   the ratio of a line spacing, which refers to the spacing of two immediately adjacent line centers, to a line width of the raised lines of the first line structure being at least 1.5, the first and the second line structure having a height of at least 5 micrometers, the printing ink for printing the first line structure containing at least 30 percent by weight of color pigments having a tilt effect and the printed product further comprising an at least partial-area background print on the printing substrate, the first and the second line structure being printed onto the background print and the background print being carried out with a dark, preferably black, color.
2. The printed product according to claim 1, wherein the printing ink for printing the second line structure contains color pigments having a tilt effect.
3. The printed product according to any of the claims 1 to 2, wherein the first and the second line structure have a height of at least 10 micrometers.
4. The printed product according to any of the claims 1 to 3, wherein the first and the second line structure are applied with a print varnish and the print varnish is cured by irradiation.
5. The printed product according to any of the claims 1 to 4, further comprising at least one third line structure consisting of a plurality of raised, mutually parallel lines, which are applied to the printing substrate in a printing method, wherein the third line structure has an orientation which differs from that of the first and the second line structure.
6. The printed product according to any of the claims 1 to 5, wherein the raised lines of the first line structure have a width of at least 130 micrometers.
7. A method for producing a printed product having an optical security feature, comprising the following steps:

   providing a printing substrate;

   screen printing a first line structure consisting of a plurality of raised, mutually parallel, spaced-apart lines, the printing ink for printing the first line structure containing color pigments having a tilt effect;

   screen printing a second line structure consisting of a plurality of raised, mutually parallel, spaced-apart lines,

   the first line structure being formed such that the ratio of a line spacing, which relates to the spacing of two immediately adjacent line centers, to a line width of the raised lines of the first line structure being at least 1.5, the first and the second line structure having a height of at least 5 micrometers, the printing ink for printing the first line structure containing at least 30 percent by weight of color pigments having a tilt effect and the printed product further comprising an at least partial-area background print on the printing substrate, the first and the second line structure being printed onto the background print and the background print being carried out with a dark, preferably black, color.
8. The method according to claim 7, wherein the printing ink for printing the second line structure contains color pigments having a tilt effect.
9. The method according to any of the claims 7 to 8, wherein the steps for printing the first and the second line structure each print lines with a height of at least 10 micrometers.
10. The method according to any of the claims 7 to 9, further comprising a step of curing the print varnish of the first and the second line structure.
11. The method according to any of the claims 7 to 10, further comprising a step of printing a third line structure consisting of a plurality of raised, mutually parallel lines, wherein the third line structure has an orientation which differs from that of the first and the second line structure.

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