METHOD FOR EMBOSSING HOLOGRAMS

Abstract: In a method for producing a material embodying an interference pattern, for example a holographic image, the interference pattern is introduced into a transparent release layer (2) situated on a plastic basefilm (1), by forming said pattern in the release layer (2), applying the substrate (11) onto the finished release layer (2) and removing the substrate (11) together with the release layer (2) from the plastic base film (1). In a first embodiment, the plastic base film (1) is embossed with the interference pattern and the transparent release layer (2) is then applied to the embossed side of the plastic base film (1). In a second embodiment, the transparent release layer (2) is applied to the plastic base film (1) and the transparent release layer is then embossed with the interference pattern.

Description: Method for embossing holograms, The invention relates to a method for producing a material embodying an interference pattern, for example a holographic image, in which the interference pattern is introduced into a transparent layer situated on a plastic basefilm, a substrate being applied onto the opposite side of the transparent layer and the plastic base film being removed. In this known method, a plastic basefilm is clad with a wax-based release layer which is in its turn clad with a lacquer layer which is finally metallized. The metallized lacquer layer is then printed with a hologram. As an alternative, the unmetallized lacquer layer can be printed with a hologram and then be metallized. Finally, the metallized lacquer layer is glued to a substrate and the plastic base film is removed so that the holographic image becomes visible. This may involve 2- dimensional, 3"dimensional holograms, and also 2D/3D holograms. This known method is beset by a number of disadvantages. As the first disadvantage, mention is made of the fairly high costs associated with this method. All these stem from the fairly large number of layers which have to be applied to one another. The finished product, for example a sheet printed with holographic images, is consequently fairly expensive. This method is therefore less suitable for producing wide strips of sheet-type material such as, for example, luxury packaging paper. The object of the invention is therefore to provide a method as described above which is less expensive. This is achieved by the coating plastic base film with a release layer, forming the interference pattern by printing said pattern in the finished release layer, and removing the substrate together with the release layer from the plastic base film. According to the invention, a saving is now achieved by omitting the step of applying a separate wax-based layer to the release layer. Surprisingly, the lacquer- based release layer appears to form an excellent medium for introducing a holographic image into it. Preferably, a material which can be printed at relatively low pressure and temperature is chosen for the release layer. As a result, a further advantage is obtained with respect to the prior art in which fairly high temperatures and pressures are necessary to introduce the holographic image. A good example of a method in which a metal layer is applied to any object without, however, holographic images being produced in the process is described in European Patent No. 3*^.392. The method according to the invention proves to be capable of being used in an excellent manner on the sheet-type composite structure described in said patent. In this way, for example, sheet-type luxury packaging material which is printed with holographic images can be produced in a relatively cheap manner. Therefore, reference is made to EP-A-3439 with respect to the materials which are suitable for the process according to the present invention. From US-A- i J75δ296 a method for forming a laminate with a holographic pattern is known according to which a hologram master is coated with a radiation-curable resin. Therefore, the holographic pattern is introduced into the resin upon coating the master with the resin. This method has the disadvantage of the additional step of curing and cross-linking the resin on the master, which makes a seperate release layer necessary. According to a first variant of the embodiment of the method according to the invention, the plastic base film is holographically printed with the aid of a printing device, such as an impression cylinder, embodying the negative of the interference pattern and the transparent release layer is then applied to the printed side of the plastic base film in a manner such that the interference pattern is imaged in the transparent release layer. When the transparent release layer is applied to the printed side of the plastic base film, the release layer is also shaped in accordance with the holographic image. In this variant of the embodiment, it is particularly attractive to use a plastic base film which can be used a number of times in the production process such as is described in said European Patent No. 3*^.392. In that case, the plastic base film has only to be printed once with a hologram, while a large number of products having a holographic image can nevertheless be obtained by transferring the holographic image on the plastic base film in all cases directly to the transparent release layer. The expensive printing device, for example an impression cylinder, is therefore saved and it is only necessary to provide it once for a good impression in the plastic base film in order to obtain a large number of holographic imprints with a correspondingly high quality. As the second variant of the embodiment, it is also possible that the transparent release layer is applied to the plastic base film and the transparent release layer is then printed with the aid of a printing device, such as an impression cylinder, embodying the negative of the interference pattern. In this case, the release layer has then to be printed separately in each case with the impression cylinder which embodies the negative of the holographic image. Furthermore, it is possible, according to the invention, that after the plastic base film on the release layer has been removed, a second transparent release layer provided with an interference pattern, for example a holographic image, and situated on a second plastic base film is applied by means of a transparent glue, after which the second plastic base film is removed. In this way two holographic images can be applied above each other. However, the lowermost holographic image in the direction of observation will be partly covered by the uppermost one. In general, it will not, however, be a problem if the foreground provided by the uppermost holographic image is somewhat more blurred than the rearmost one. The temperature and pressure during the printing of the holograms can be significantly reduced if the release layers are plasticized. This also affects the service life of the plastic base film advantageously. As examples of plasticizers for plasticizing the release layer, mention is made of phthalates, citrates, phosphates, adipates, azelates, sebacates, ditridecyl phthalates and polymeric plasticizers of polyethers and polyurethanes. The method according to the invention is suitable for producing objects such as credit-cards etc. The holographic pattern or other interference pattern produced affords a high degree of safety against falsifications. Moreover, two or more such patterns may be applied one on top of the other, making the appearance of a cord even more difficult to falsify. According to an alternative embodiment, the transparent layer is also clad with a reflecting layer such as a metal layer, after which the substrate is being glued onto the reflecting layer. This embodiment is highly suitable for producing the luxury packaging paper indicated above. The invention will now be explained further with reference to two exemplary embodiments. Figure 1 shows the first step of the method according to the invention, in which a holographic image is introduced into a release layer. Figure 2 shows the second step of the invention, in which the release layer is metallized. Figure 3 shows the third step of the method according to the invention, in which a substrate is glued to the metal layer. Figure 4 shows the fourth step of the invention, in which the plastic base film is removed. Figure 5 shows an alternative for the method step according to Figure 4. Figure 6 shows an additional step for applying a second release layer embodying a holographic image. Figure 7 shows another variant In the method step shown in Figure 1, an assembly comprising a plastic base film 1 and a release layer 2 is passed between the nip of two pressure rollers 3*» 4 situated opposite each other. The pressure roller 4 is provided with a holographic image which is introduced into the release layer 2. Said release layer 2 may, for example, be plasticized with W2 (DSM) or Priplast (Unichema) . As shown in Figure 2, the printed release layer is then provided in vacuo with a metal layer in a known manner, a metal vapour being deposited on the release layer 2 from a crucible 6. Then a glue layer 8 is applied to the metal layer by means of a roller 9 which is partly immersed in the glue stock 10. The sheet-type substrate 11 is applied to the glue layer and finally, as shown in Figure 4, the assembly comprising release layer 2, metal layer 5» glue layer 8 and substrate 11 is passed over the roller 12. In this process, the plastic base film 1 is stripped off the transparent release layer 2, exposing the holographic image. As shown in the variant of Figure 5. the plastic base film 1 may, however, also be passed over the roller 12 and consequently be stripped off the said assembly. Figure 6 shows that a second holographic image can be laminated onto the finished substrate embodying a holographic image. In this process, an assembly comprising a second plastic base film 18 and a second release layer provided with a holographic image is applied with the rollers 14, 15 to the first release layer 2 by means of a transparent glue layer 20. Then the second plastic base film 18 is also removed. The second release layer 19 is not itself metallized. In this way, two holographic images above each other become visible, the metal layer 5 reflecting the light incident through the two release layers 2, 19. It is conceivable to apply still more release layers to one another. However, in that case the light yield decreases ever further so that the number of release layers with transparent glue layers between them must not become too large. Figure 7 shows still another variant of the method. In this case, only the plastic base film is passed between a pressure roller pair 16, 17- A holographic image is applied during this process to the plastic base film by means of the pressure roller 17, after which the release layer 2 comes to rest on the holographic image formed in this -way. In this process, the release layer takes on the form of the holographic image in the plastic base film 1. If the plastic base film is ' of a quality such that it can be used several times, said plastic base film 1 of course only needs to be passed once between the roller pair 16, 17. As soon as the holographic image has been introduced into the plastic base film, it then no longer needs to be passed through between the nip of the rollers 16 and 17 during further use and the release layer 2 can be applied directly to it in all cases. The release layer 2 may be applied while it is still fluid. After solidification by evaporation of the solvent, the substrate may be applied onto the finished release layer. The method according to the invention offers great advantages in producing sheet-type material such as luxury packaging paper. It is, however, also conceivable to print cheap CDs by this method. It is also possible to bring about other optical effects such as diffraction patterns and Fresnel lenses. Finally, it is also possible to colour the release layer in order to obtain special effects.

Claims: CLAIMS 1. Method for producing a material embodying an interference pattern, for example a holographic image, in which the interference pattern is introduced into a transparent layer situated on a plastic basefilm, a substrate being applied onto the opposite side of the transparent layer and the plastic base film being removed, characterized by coating the plastic base film with a release layer, forming the interference pattern in the release layer, applying the substrate onto the finished release layer, and removing the substrate together with the release layer from the plastic base film. 2. Method according to Claim 1, wherein the plastic base film is printed with the aid of a printing device, such as an impression cylinder, embodying the negative of the interference pattern and the transparent release layer is then applied to the printed side of the plastic base film in a manner such that the interference pattern is imaged in the transparent release layer. 3. Method according to Claim 2, wherein the plastic base film is used a number of times after it has been printed for imaging the interference pattern in a number of release layers. 4. Method according to Claim 1, wherein the transparent release layer is applied to the plastic base film and the transparent release layer is then printed with the aid of a printing device, such as an impression cylinder, embodying the negative of the interference pattern. 5- Method according to one of the preceding claims, wherein, after the plastic base film on the release layer has been removed, a second transparent release layer provided with an interference pattern, for example a holographic image, and situated on a second plastic base film is applied by means of a transparent glue, after which the second plastic base film is removed. 6. Method according to one of the preceding claims, wherein the release layer is plasticized with a plasticizer. 7- Method according to one of the preceding claims, wherein the transparent layer is also clad with a reflecting layer such as a metal layer, after which the substrate is being glued onto the reflecting layer.

Inventors: VAN DER LAAN EDWARD JOHANNES, VAN SUYLEKOM GIJSBERTUS, VAN DER LAAN, EDWARD, JOHANNES, VAN SUYLEKOM, GIJSBERTUS
Applicants: LEER KONINKLIJKE EMBALLAGE, KONINKLIJKE EMBALLAGE INDUSTRIE VAN LEER B.V.
Application year: 1990
Main classification: B29C59
IPC codes: B29C43, B29C59, G03H1