Security elements and method for their manufacture

Abstract

The present invention relates to complex security elements based on recording materials for optical elements with refractive index modulation, in particular, holograms, which are subsequently coated with specific metallic nano-shaped metal particles, a method for their manufacture, in particular on a paper or on a plastic substrate and a security product obtainable using the security element. A further aspect of the invention is the use of such a security element for the prevention of counterfeit or reproduction of a document of value.

Claims

1. A security element, comprising: a) a substrate; b) a volume hologram formed in a refractive index modulated layer, which is obtained by holographically exposing a recording material to actinic radiation and thereon; and c) an embossed surface relief microstructure on at least a portion of the refractive index modulated layer, wherein the embossed surface relief microstructure comprises: platelet shaped transition metal particles, wherein the transition metal is Ag and/or Cu; and a binder, wherein the pigment to binder ratio is from 4:1 to 1:1000, the security element exhibits a gold color in reflection when viewed from the side of the embossed surface relief microstructure, a green color in reflection viewing the volume hologram from the unembossed reverse side, and a blue color in transmission, and wherein when the platelet shaped transition metal particles have a diameter from 15-40 nm and a height of 8-20 nm, the security element shows an angle dependent color change upon viewing from orange to blue, when the platelet shaped transition metal particles have a diameter from 30-70 nm and a height of 8-20 nm, the security element shows an angle dependent color change upon viewing from red to green, and when the platelet shaped transition metal particles have a diameter from 5-120 nm and a height of 7-17 nm, the security element shows an angle dependent color change upon viewing from blue to gold.

2. The security element according to claim 1, wherein the transition metal is Ag.

3. The security element according to claim 1, wherein the shaped transition metal particles comprise hexagonal, triangular, and/or truncated triangular prisms, wherein the prisms make up more than 20% of the total number of shaped transition metal particles.

4. The security element according to claim 1, wherein the binder is selected from the group consisting of nitrocellulose, ethyl cellulose, cellulose acetate, cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), alcohol soluble propionate (ASP), vinyl chloride, vinyl acetate copolymers, vinyl acetate, vinyl, acrylic, polyurethane, polyamide, rosin ester, hydrocarbon, aldehyde, ketone, urethane, polythyleneterephthalate, terpene phenol, polyolefin, silicone, cellulose, polyamide, polyester and rosin ester resins or is a photopolymerisable composition comprising an ethylenically unsaturated monomer and/or oligomer and a photoinitiator.

5. The security element according to claim 4, wherein the photoinitiator is selected from the group consisting of benzophenone, alpha-hydroxy ketone type compounds, alpha-alkoxy ketone type compounds, alpha-amino ketone type compounds, mono and bisacylphosphine oxide compounds, phenyiglyoxylate compounds, oxime ester compounds and onium salt compounds and mixtures thereof.

6. The security element according to claim 1, wherein the recording material of component b) is a photopolymerisable composition comprising an ethylenically unsaturated monomer and/or oligomer and a photoinitiator.

7. The security element according to claim 6, wherein the photoinitiator comprises an arylborate and a dye as sensitizer.

8. The security element according to claim 1, wherein both, the recording material of component b) and the coating of component c) are photopolymerisable compositions comprising an ethylenically unsaturated monomer and/or oligomer and a photoinitiator.

9. The security element according to claim 1, wherein the substrate comprises glass, plastic or paper.

10. A security product comprising a security element according to claim 1, wherein the security product is selected from the group consisting of banknotes, credit cards, identification documents, pharmaceutical apparel, software, compact discs, tobacco packaging and other products or packaging prone to counterfeiting or forgery.

11. A method for preventing counterfeit or reproduction, comprising applying the security element according to claim 1 on a document of value, right, identity, a security label or a branded good.

12. The security element according to claim 1, wherein the embossed surface relief comprises microstructures having dimensions in the range from about 0.01 microns to about 100 microns.

13. The security element according to claim 12, wherein the dimensions of the microstructures are in the range from about 0.1 microns to about 1 microns.

14. The security element according to claim 1, wherein the pigment to binder ratio is from 1:100 to 1:1000.

15. The security element according to claim 1, wherein the platelet shaped transition metal particles have a diameter from 15-40 nm and a height of 8-20 nm and the security element shows an angle dependent color change upon viewing from orange to blue.

16. The security element according to claim 1, wherein the platelet shaped transition metal particles have a diameter from 30-70 nm and a height of 8-20 nm and the security element shows an angle dependent color change upon viewing from red to green.

17. The security element according to claim 1, wherein the platelet shaped transition metal particles have a diameter from 5-120 nm and a height of 7-17 nm and the security element shows an angle dependent color change upon viewing from blue to gold.

18. A method for forming the security element of claim 1, the method comprising: a) depositing a recording material on a substrate; b) exposing the recording material to modulated actinic radiation carrying holo-graphic information, thereby producing a volume hologram; and c) coating the volume hologram at least in part with an embossed surface relief microstructure comprising: platelet shaped transition metal particles, wherein the transition metal is Ag and/or Cu; and a binder, wherein the pigment to binder ratio is from 4:1 to 1:1000, and wherein the platelet shaped transition metal particles have a diameter from 15-40 nm and a height of 8-20 nm and the security element shows an angle dependent color change upon viewing from orange to blue, the platelet shaped transition metal particles have a diameter from 30-70 nm and a height of 8-20 nm and the security element shows an angle dependent color change upon viewing from red to green, or the platelet shaped transition metal particles have a diameter from 5-120 nm and a height of 7-17 nm and the security element shows an angle dependent color change upon viewing from blue to gold.

19. The method according to claim 18, wherein the recording material, component b) has a thickness of from 0.1 m to 100 m in the dry or cured state.

20. The method according to claim 18, wherein the coating, component c) has a thickness of from 0.5 m to 50 m in the dry or cured state.

Description

(1) The definitions and preferences given above apply equally for all aspects of the invention.

(2) The following examples illustrate the invention.

(3) Preparation of Silver Platelets

(4) The preparation is carried out according to example 1 of WO 2011/064162. The precipitate is dispersed in any solvent of choice, and includes water, methanol, ethylacetate, cyclohexanone, methoxypropanol to obtain a dispersion containing 20% of silver platelets.

(5) The thus obtained platelets are used in the following application examples.

APPLICATION EXAMPLES

(6) Photopolymer Materials:

(7) Lumogen OVD Primer 301 is a commercial UV curable product of BASF SE.

(8) Irgacure 2100 is a commercial photoinitiator of BASF SE.

(9) 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

Application Examples

(10) The color coordinates of the volume hologram are measured in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d-(Measurement-d8 geometry)

(11) TABLE-US-00002 TABLE 1 Color Coordinates, Volume Hologram without coating (comparative) CIELab L* C* h Reflexion over white 91.5 8.1 89.8 Reflexion over black 49.7 19.4 147.7 Transmission 93.2 8.3 347.3

Example 1

UV Embossed Volume Hologram

(12) The composition of the UV lacquer is shown below:

(13) TABLE-US-00003 TABLE 2 UV varnish 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

(14) Photoinitiator Blend

(15) ##STR00026##

(16) UV Ink Preparation:

(17) 7 g UV varnish containing +5% Photoinitiator (% by weight, based on the total weight) are added to 3 g silver platelets dispersion (50% pigment in cyclohexanone) 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 a volume hologram manufactured according to WO2005/124456 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 1:5

(18) The color coordinates of the volume hologram are measured in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d-(Measurement-d8 geometry)

(19) TABLE-US-00004 TABLE 3 Color Coordinates, Volume Hologram with UV coating CIELab L* C* h Coated side Reflexion over white 37.7 16.9 345.3 Reflexion over black 33.1 14.7 23.7 Uncoated side Reflexion over white 46.8 17.1 167.9 Transmission 49.4 33.3 285.1

(20) Effect obtained: UV embossed gold hologram on surface and green volume hologram on reverse side of the PET film, blue color in transmission.

Example 2

Nitrocellulose Ink

(21) Ink Preparation:

(22) 28 g of nitrocellulose (DHM 10/25 IPA, 70% solids (Nobel Enterprises, UK)) are slowly added to 72.00 g of ethyl acetate (99-100% rein, Brenntag) in a 250 mL glass bottle and gently stirred until complete dissolution at room temperature. Solid content measurements are then performed and quantity of ethyl acetate is adjusted to achieve a value of 19.6% solid content in the varnish preparation. General procedure for metallic ink preparation: 10.0 g silver pigment dispersion (19.6% of the pigment particles obtained in ethylacetate) are added to 10 g above varnish in such a proportion as to adjust 1:1 the pigment to binder ratio. The obtained dispersion is stirred with a Dispermat at 800 rpm for 10 minutes affording a metallic ink which is coated by means of a wire bar 0 (4 micron wet ink thickness) on a volume hologram manufactured according to WO2005/124456 on PET film and air dried.

(23) The color coordinates of the volume hologram on film are measured in reflexion and in transmission using a Colorimeter Konica Minolta CM3610-d-(Measurement-d8 geometry)

(24) TABLE-US-00005 TABLE 4 Color Coordinates, Volume Hologram with Nitrocellulose coating CIELab L* C* h Coated side Reflexion over white 43.4 24.1 58.4 Reflexion over black 43.7 32.4 70.3 Uncoated side Reflexion over white 57.4 22.9 124.4 Reflexion over black 57.3 27.4 120.9 Transmission 16.8 61.1 299.9

(25) Effect obtained: Gold metallic color in reflexion on coated side of the volume hologram over white and over black, blue color in transmission and green volume hologram visible on uncoated side of the PET film.