METHOD FOR MANUFACTURING SECURITY ELEMENTS AND HOLOGRAMS

Abstract

The present invention relates to a method for forming a surface relief microstructure, especially an optically variable image (an optically variable device) on a transparent or translucent substrate and a product obtainable using the method. A further aspect of the invention is the use for the prevention of counterfeit or reproduction of a document of value and a method of forming a coating showing an angle dependent color change.

Claims

1: A method for forming a surface relief microstructure, especially an optically variable image on a substrate comprising the steps of: A) applying a curable composition to at least a portion of a front side of the substrate wherein the substrate is transparent or translucent, and wherein the curable composition comprises: a1) an ethylenically unsaturated resin, a monomer or a mixture thereof; a2) a photoinitiator selected from the group consisting of a monoacylphosphine oxide compound and a bisacylphosphine oxide compound; and a3) a metal pigment which is in the form of platelet shaped transition metal particles having a longest dimension of edge length of from 5 nm to 1000 nm, and a thickness of from 1 nm to 100 nm, wherein the metal is Ag; B) contacting at least a portion of the curable composition with a surface relief microstructure; C) curing the composition with at least one UV lamp, which is arranged on a backside of the transparent or translucent substrate.

2: The method according to claim 1, wherein the lamp is a gallium or iron doped medium pressure mercury lamp.

3: The method according to claim 1, wherein the curable composition further comprises a second photoinitiator selected from the group consisting of a benzophenone compound, an alpha-hydroxy ketone, alpha-alkoxyketone, and alpha-aminoketone compound.

4: The method according to claim 1, wherein the curable composition comprises: (a) 5.0 to 0.6% by weight of the photoinitiator; (b) 94.9 to 11.9% by weight of the ethylenically unsaturated resin, monomer or mixture thereof; and (c) 0.1 to 87.5% by weight of the metal pigment, wherein the sum of components a) to c) adds up to 100%.

5: The method according to claim 1, wherein the shaped transition metal particles comprise hexagonal and/or triangular and/or truncated triangular prisms, which prisms make up more than 20% of a total number of shaped transition metal particles.

6: The method according to claim 1, wherein the transparent or translucent substrate is paper or a thermoplastic or crosslinked polymer.

7: The method according to claim 10 wherein the transparent or translucent substrate is a thermoplastic polymer selected from the group consisting of polyester, polyvinyl chloride (PVC), polyethylene, polycarbonate, polypropylene and polystyrene.

8: The method according to claim 1, wherein the surface relief microstructure is a shim which is a nickel sleeve; a nickel plate; an etched, or laser imaged metallic drum, or another material mounted on an opaque cylinder or metal cylinder containing an optical variable device (OVD image) on the surface.

9: The method according to claim 8, wherein the shim is a nickel plate mounted on an opaque cylinder or metal cylinder and containing the OVD in on the surface.

10: The method according to claim 1, wherein the surface relief microstructure is applied over an already existing security element.

11: A method for forming a coating showing an angle dependent color change on a substrate comprising the method according to claim 1.

12: The method according to claim 1, wherein the surface relief microstructure comprises microstructures having dimensions in the range from about 0.01 microns to about 10 microns.

13: The method according to claim 1, wherein the surface relief microstructure comprises microstructures having dimensions in the range from about 0.01 microns to about 1 micron.

14: The method according to claim 1, wherein the platelet shaped transition metal particles have a longest dimension of edge length of from 7 nm to 600 nm and a thickness of from 2 inn to 40 nm.

15: The method according to claim 1, wherein the platelet shaped transition metal particles have a longest dimension of edge length of from 10 nm to 500 nm and a thickness of from 3 nm to 30 nm.

Description

APPLICATION EXAMPLES

[0240] Photopolymer Materials:

[0241] Lumogen OVD Primer 301 is a commercial UV curable product of BASF SE.

[0242] Irgacure@ 2100 is a commercial photoinitiator of BASF SE.

[0243] Manufacture of a volume hologram, (reflexion hologram) is carried out according to WO2005/124456 Example 1, page 22 or on a film from Bayer, Bayfol HX or Dupont, Omnidex, Toppan, DNP

[0244] The composition of the UV lacquer is shown below:

TABLE-US-00002 UV lacquer % by weight Tripropylene glycol diacrylate (TPGDA) 1-25 Dipropylene glycol diacrylate (DPGDA) 30-45 Ethoxylated trimethylol propane triacrylate 10-50 (TMEOPTA) Reactive tertiary amine 1-15 Photoinitiator blend 5-9

TABLE-US-00003 Photoinitiator blend [00027] Bis(2,4,6-trimethylbenzoyl)- phenylphosphine oxide 9 parts [00028] 2,4,6-Trimethylbenzoyl-phenyl phosphinic acid ethyl ester 91 parts

Example 1 in UV Inks

[0245] UV ink preparation: 1 g UV varnish (Lumogen OVD Primer 301 +5% Irgacure 2100) are added to 20 g silver platelets dispersion (20% pigment in methanol) in a 50 mL glass bottle and gently stirred at room temperature. The obtained ink is coated by the means of a wire bar 0 (4 micron wet ink thickness) on PET film and air dried. The coated film is pressed against a shim containing the holographic structure and is cured under UV light (Aktiprint 18/2, 80 W/cm, 10 m/min) through the film. The PET film is peeled off the shim. The pigment to binder ratio of the ink corresponds to 4:1.

[0246] The color coordinates of the film are measured on the embossed surface in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d-(Measurement-d8 geometry)

TABLE-US-00004 CIELab L* C* h Reflexion over white 57.9 10.7 91.7 Reflexion over black 55.9 4.0 121.2 Transmission 40.3 5.6 276.2 Effect obtained: Metallic hologram visible on the embossed side of the PET film.

Example 2 in UV Inks

[0247] UV ink preparation: 6 g UV varnish (Lumogen OVD Primer 301 +5% Irgacure 2100) are added to 10 g silver platelets dispersion (20% pigment in methanol) in a 20 mL glass bottle and gently stirred at room temperature. The obtained ink is coated by the means of a wire bar 0 (4 micron wet ink thickness) on PET film and air dried. The coated film is pressed against a shim containing the holographic structure and cured under UV light (Aktiprint 18/2, 80W/cm, 10 m/min) through the film. The PET film is peeled off the shim. The pigment to binder ratio of the ink corresponds to 1:3.

[0248] The color coordinates of the film are measured on the embossed surface in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d-(Measurement-d8 geometry)

TABLE-US-00005 CIELab L* C* h Reflexion over white 44.9 13.5 83.4 Reflexion over black 46.5 20.8 86.3 Transmission 24.0 57.0 301.9 Effect obtained: Metallic hologram visible on the embossed side of the PET film.

Example 3 in UV Inks

[0249] UV ink preparation: 20 g UV varnish (Lumogen OVD Primer 301 +5% Irgacure 2100) are added to 1 g silver platelets dispersion (20% pigment in methanol) in a 50 mL glass bottle and gently stirred at room temperature. The obtained ink is coated by the means of a wire bar 0 (4 micron wet ink thickness) on PET film and air dried. The coated film is pressed against a shim containing the holographic structure and cured under UV light (Aktiprint 18/2, 80W/cm, 10 m/min) through the film. The PET film is peeled off the shim. The pigment to binder ratio of the ink corresponds to 1:100. The color coordinates of the PET film are measured on the embossed surface in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d- (Measurement-d8 geometry)

TABLE-US-00006 CIELab L* C* h Reflexion over white 69.6 17.6 254.4 Reflexion over black 40.5 3.2 355.5 Transmission 89.8 10.2 249.1 Effect obtained: Metallic hologram visible on two sides of the PET film.

Example 4 in UV Inks

[0250] UV ink in example 2 is coated by the means of a wire bar 0 (4 micron coating) on a UV casted hologram image A on PET , it is air dried and is subsequently pressed against a shim containing a holographic image B. It is cured under UV light (Aktiprint 18/2, 80 W/cm, 10 m/min) through the film. The PET film is peeled off the shim.

[0251] The color coordinates of the film are measured on the embossed surface in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d-(Measurement-d8 geometry)

TABLE-US-00007 CIELab L* C* h Reflexion over white 53.7 19.6 119.4 Transmission 13.2 15.1 283.9 Effect obtained: Metallic hologram image A and image B visible on each side of the PET film, blue color in transmission.

Example 5 in Waterborne UV Inks

[0252] UV ink preparation: 5 g UV varnish (Lumogen OVD Primer 301 +5% Irgacure 2100) mixed with 2 g distilled water are added to 20 g silver platelets (25% pigment in water) in a 50 mL glass bottle and gently stirred at room temperature.

[0253] The obtained ink is coated by the means of a wire bar 0 (4 micron wet ink thickness) on PET film and air dried. The coated film is pressed against a shim containing the holographic structure and cured under UV light (Aktiprint 18/2, 80 W/cm, 10 m/min) through the film. The PET film is peeled off the shim. The pigment to binder ratio of the ink corresponds to 1:1

[0254] The color coordinates of the film are measured on the embossed surface in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d-(Measurement-d8 geometry)

TABLE-US-00008 CIELab L* C* h Reflexion over white 38.1 5.5 19.6 Transmission 23.2 57.6 289.7 Effect obtained: Metallic hologram visible on the embossed side of the PET film.

[0255] Conclusion: The UV curable compositions of the instant invention provide none-leafing properties which are particularly suitable for coating on holograms or embossing holograms. The extremely small particles are filling the grating of the OVD and give rise to the same reflection (Optical Density 2 or higher) as a vapour metal deposited pigment.