SECURITY ELEMENT

Abstract

The present invention relates to security, or decorative elements, comprising a transparent, or translucent substrate, which may contain indicia or other visible features in or on its surface, and on at least part of the substrate surface, a first layer, comprising transition metal particles having an average diameter of from 5 nm to 500 nm and a binder, on at least part of the first layer a second layer, comprising an organic material and having a refractive index of from 1.2 to 2.3 and having a thickness of from 20 to 1000 nm, wherein the transition metal is silver, copper, gold and palladium, wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 20:1 to 1:2 in case the binder is a polymeric binder, or wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 5:1 to 1:15 in case the binder is an UV curable binder. The security or decorative element show a certain color in transmission and a different color in reflection and a color flop on the coating side. The color in reflection and the color flop of the security or decorative elements are controlled by adjusting the refractive index and thickness of the second layer.

Claims

1. A security, or decorative element, comprising a transparent, or translucent substrate, which may contain indicia or other visible features in or on its surface, and on at least part of the substrate surface, a first layer, comprising transition metal particles having an average diameter of from 5 nm to 500 nm and a binder, on at least part of the first layer a second layer, comprising an organic material and having a refractive index of from 1.2 to 2.3, and having a thickness of from 20 to 1000 nm, wherein the transition metal is selected from the group consisting of silver, copper, gold and palladium, wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 20:1 to 1:2 in case the binder is a polymeric binder, or wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 5:1 to 1:15 in case the binder is an UV curable binder.

2. The security element, or decorative element according to claim 1, wherein the transition metal particles are in the form of nanoplatelets and have an average diameter of from 20 nm to 500 nm, and an average thickness of from 2 to 40 nm.

3. The security or decorative element according to claim 1, wherein the organic material is a polymeric binder and is selected from the group consisting of poly(vinyl alcohol) (PVA), nitro cellulose, vinyl chloride, vinyl acetate copolymers, vinyl, acrylic, urethane, polythyleneterephthalate, terpene phenol, polyolefin, silicone, cellulose, polyamide, polyester and rosin ester resins.

4. The security or decorative element according to claim 1 wherein the organic material is an UV cured binder.

5. The security or decorative element according to claim 4, wherein UV cured binder comprises (a) 0.02 to 20.0% by weight of photoinitiator, (b) 99.0 to 1.0% by weight of a binder (unsaturated compound(s) including one or more olefinic double bonds), (c) optionally 0 to 98.9% by weight of solvent wherein the sum of components a) and b) and c) adds up to 100%.

6. The security or decorative element according to claim 1, wherein the second layer comprises inorganic nanoparticles.

7. The security or decorative element according to claim 1, wherein the transition metal is silver.

8. The security or decorative element according to claim 7, wherein the silver particles are in the form of nanoplatelets and have an average thickness of 8 to 25 nm and an average diameter of 15 to 40 nm, the security or decorative element shows a brown, or orange color in transmission and the reflection color and the color flop of the security or decorative element are controlled by adjusting the refractive index and thickness of the second layer.

9. The security or decorative element according to claim 7, wherein the silver particles are in the form of nanoplatelets and have an average thickness of 8 to 25 nm and an average diameter of 30 to 70 nm, the security or decorative element shows a red, or magenta color in transmission and the reflection color and the color flop of the security or decorative element are controlled by adjusting the refractive index and thickness of the second layer.

10. The security or decorative element according to claim 7, wherein the silver particles are in the form of nanoplatelets and have an average thickness of 8 to 25 nm and an average diameter of 50 to 150 nm, the security or decorative element shows a turquoise, or blue color in transmission and the reflection color and the color flop of the security or decorative element are controlled by adjusting the refractive index and thickness of the second layer.

11. The security or decorative element according to claim 1, comprising on at least part of the substrate surface the first layer, comprising the transition metal particles, on part of the first layer the second layer in a defined shape selected from the group consisting of a symbol, a stripe, a geometrical shape, a design, lettering, an alphanumeric character, the representation of an object or parts thereof.

12. The security or decorative element according to claim 1, wherein the substrate comprises in or on its surface an optically variable image.

13. The security or decorative element according to claim 1, which comprises on at least part of the second layer a third layer which is partially transparent, or which comprises on at least part of the second layer a third layer in a defined shape selected from the group consisting of a symbol, a stripe, a geometrical shape, a design, lettering, an alphanumeric character, the representation of an object or parts thereof, which is transparent.

14. A method of producing the security or decorative element according to claim 1, comprising the steps of a) providing the substrate having a surface, which surface may contain indicia or other visible features; b) applying, on top of at least part of the said substrate surface the first layer, comprising transition metal particles having an average diameter of from 5 nm to 500 nm and the binder, c) applying on at least part of the said first layer the second layer, comprising the organic material and having a refractive index of from 1.2 to 2.3, and a thickness of from 20 to 1000 nm, wherein the transition metal is selected from the group consisting of silver, copper, gold and palladium, wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 20:1 to 1:2 in case the binder is a polymeric binder, or wherein the weight ratio of transition metal particles to binder in the first layer is in the range from 5:1 to 1:15 in case the binder is an UV curable binder.

15. A product, comprising the security or decorative element according to any of claims 1 to 13.

16. Use of the security or decorative element according to any of claims 1 to 13 for the prevention of counterfeit or reproduction, on a document of value, right, identity, a security label or a branded good.

17. The security or decorative element according to claim 1, wherein the second layer has a refractive index from 1.3 to 1.7 and a thickness from 30 to 600 nm.

18. The security or decorative element according to claim 5, wherein the UV cured binder comprises (a) 0.05 to 10.0% by weight of photoinitiator, (b) 97.0 to 3.0% by weight of a binder, and (c) 0 to 96.9% by weight of solvent wherein the sum of components a) and b) and c) adds up to 100%.

Description

EXAMPLES

[0188] TEM analysis of dispersions and coatings was performed on EM 910 instrument from ZEISS in bright field mode at an e-beam acceleration voltage of 100 kV. At least 2 representative images with scale in different magnification were recorded in order to characterize the dominant particle morphology for each sample.

[0189] The “average diameter” is the number mean diameter of the particles which was determined from TEM images as maximum dimension of nanoplatelets, oriented parallel to the plane of the image, using Fiji image analysis software, based on the measurement of at least 100 randomly selected particles.

[0190] The “average thickness” is the number mean thickness of the particles which was measured manually as the maximum dimension of nanoplatelets, oriented perpendicular to the plane of the image, from a TEM image, based on the measurement of at least 20 randomly selected particles.

Example 1

[0191] Ag nanoplatelets (having an average thickness of about 18 nm and an average diameter of about 45 nm (dispersion 1 g, 40% dry content w/w) in 1-methoxy-2-propanol is added to a solution of nitrocellulose in 1-methoxy-2-propanol (4 g, 5% dry content w/w) and vigorously mixed. The resulting composition is applied onto PET foil (Melinex 506) by means of wired hand-coater #1 and the coating is dried. The resulting coating shows magenta color in transmission and greenish-metallic color in reflection when observed from coating side and from PET substrate side.

[0192] This coating is overcoated with the solution of poly(vinyl alcohol) (Mw 13,000-23,000, 87-89% hydrolyzed) in water (3, 5, or 7% w/w concentration) by means of wired hand-coater #1 or #2.

[0193] The obtained 2-layer security or decorative elements exhibit intensive angle-dependent colors in reflection on the coating side and an angle-independent greenish-metallic color in reflection when observed from the PET substrate side. The transmission color of the security or decorative elements with and without overcoating is essentially the same; i.e. differs by not more than 5 ΔE*.sub.ab units. All the samples were visually assessed for the color flop upon tilting.

[0194] The thickness of the poly(vinyl alcohol) layer is determined as described below.

[0195] A small part (˜5 mm×10 mm) of the coated PET foils is sputter-coated with a gold layer (˜80 nm) for protection. Cross-sections were prepared by an Ultra-Microtome. The PET foils with the prepared cross-section area are fixed on aluminum holders by means of a carbon adhesive. The prepared sample cross-sections are analyzed using scanning electron microscope and image analysis software. The thickness of the poly(vinyl alcohol) layer between silver nanoparticle film and gold layer is measured on 6 different positions for each cross-section using image analysis software. The determined mean poly(vinyl alcohol) film thickness values are listed in Table 1 together with the standard deviation and corresponding color flops.

TABLE-US-00004 TABLE 1 Measured thicknesses of poly(vinyl alcohol) layer and corresponding color flops Poly(vinyl Measured mean Color flop alcohol) Wired thickness of (normal Sam- solution rackle poly(vinyl alcohol) incidence to ple concentration, hand- layer ± standard 60° from name % w/w coater deviation, nm normal) A 3 1  83 ± 11 Blue to magenta B 3 2 124 ± 16 Magenta to yellow C 5 1 133 ± 17 Yellow to blueish-green D 5 2 282 ± 19 Magenta to green E 7 1 192 ± 30 Blue to magenta F 7 2 495 ± 33 Magenta to green

[0196] The synthesis of the silver nanoplatelets used in Example 1 is described in Example 1 of PCT/EP2019/078469.