Process for the preparation of metallic nano-particle layers and their use for decorative or security elements

Abstract

The present invention relates to a process for the preparation of thin silver nano-particles containing layers, which are produced directly on a substrate as part of a coating or printing process. The layers can show different colours in transmittance and reflectance. The invention further relates to decorative and security elements. When the layers are applied over a security element, such as a hologram, the obtained products may show different colours in reflection and transmission, an extremely bright optically variable image (OVD image). Depending on the thickness of the layer a more or less intensive metallic aspect appears.

Claims

1. A method for forming a highly reflective silver nanoparticle-comprising layer on a substrate, the method comprising: A) optionally forming surface relief microstructure on a discrete portion of the substrate; B) applying a composition on at least part of the substrate, and/or optionally at least part of the surface relief microstructure if the surface relief microstructure is formed in A), to obtain a coating, wherein the composition comprises b1) a metal complex of formula (I),
Ag.sup.+L.sup.−(I) wherein L.sup.− is a group of formula ##STR00028## wherein R.sup.1 is a perfluoroalkyl group, or a C.sub.1-C.sub.8alkyl group wherein a hydrogen atom is replaced by a fluorine atom; R.sup.2 is a perfluoroalkyl group, a C.sub.1-C.sub.8alkyl group, a C.sub.1-C.sub.8alkyl group wherein a hydrogen atom is replaced by a fluorine atom, a phenyl group which may optionally be substituted by at least one C.sub.1-C.sub.4alkyl or C.sub.1-C.sub.4alkoxy group, a C.sub.2C.sub.5heteroaryl group which may optionally be substituted at least one C.sub.1-C.sub.4alkyl or C.sub.1-C.sub.4alkoxy group, or a C.sub.1-C.sub.8alkoxy group; R.sup.3 is a hydrogen atom, a fluorine atom, a chlorine atom, or a C.sub.1-C.sub.8alkyl group; or R.sup.2 and R.sup.3 together form a cyclic or bicyclic ring, which may optionally be substituted by at least one C.sub.1-C.sub.4alkyl group, b2) a solvent, b3) a reducing agent, wherein the reducing agent is a 1,2-diol, or an aldehyde, b4) optionally a polymeric binder, and b5) optionally a dispersant, and C) heating the coating obtained in B) to a temperature below 120° C. and/or irradiating the coating with electromagnetic radiation, to form a highly reflective layer, comprising silver nanoparticles, wherein the highly reflective layer comprising silver nanoparticles is non-conductive, and wherein the highly reflective layer has a resistance of greater than 1*10.sup.3 Ω/sq as measured by a four-point probe method.

2. The method according to claim 1, wherein the metal complex of formula (I) is prepared in situ from a silver compound which is selected from silver oxide, silver hydroxide, silver complexes with non-fluorinated beta-diketones and beta-ketoesters and mixtures thereof, and a compound of formula wherein H.sup.+L.sup.− is as defined in claim 1.

3. The method according to claim 1, wherein the solvent is selected from alcohols, cyclic or acyclic ethers, ketones, ether-alcohols, esters, polar aprotic solvents, mixtures thereof and mixtures with water.

4. The method according to claim 1, wherein the reducing agent is glutaric dialdehyde.

5. The method according to claim 1, wherein the binder comprises nitrocellulose, ethyl cellulose, cellulose acetate, cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), hydroxyethyl cellulose, hydroxypropyl cellulose, alcohol soluble propionate (ASP), vinyl chloride, vinyl acetate copolymers, vinyl acetate, vinyl, acrylic, polyurethane, polyamide, rosin ester, hydrocarbon, aldehyde, ketone, urethane, polyethyleneterephthalate, terpene phenol, polyolefin, silicone, cellulose, polyamide, polyester, rosin ester resins, shellac or a mixture thereof.

6. The method according to claim 1, wherein A) is performed and comprises: a1) applying a curable composition to at least a portion of the substrate; a2) contacting at least a portion of the curable composition with surface relief microstructure; and a3) curing the curable composition treated in a2).

7. The method according to claim 1, wherein a protective coating is applied on the layer obtained in C).

8. A security, or decorative article, comprising a substrate which optionally comprises indicia or other visible features in or on a surface, and which comprises on at least part of the surface, a silver layer which is obtained by the method according to claim 1.

9. A method of preventing counterfeit or reproduction, of a document of value, right, and/or identity, a security label or a branded good, the method comprising contacting the document, the security label or the branded good with the security, or decorative article of claim 8.

10. The method according to claim 2, wherein the compound of formula H.sup.+L.sup.− is selected from: ##STR00029## ##STR00030## ##STR00031## ##STR00032## ##STR00033## and mixtures thereof.

Description

EXAMPLES

Example 1

General Procedure

(1) 116 mg (0.5 mmol) of Ag.sub.2O was added to 2.5 g of iso-propanol, followed by 1.2 mmol of one of the compounds X (see Table 1) and the mixture was stirred for 30 min at 25° C. for dissolution of Ag.sub.2O. After that, 46 mg (0.5 mmol) of glycerol was added, followed by addition of iso-propanol such as to adjust the Ag concentration in the mixture to 3% w/w. The mixture was filtered through 0.45 μm PTFE syringe filter and coated onto flexible PET-foil substrate (Melinex 506) using a wired rackle hand-coater #1. Coating was dried and cured in the oven at 85° C. for 20 sec. Gloss measurements were carried out using a glossmeter Zehntner 1110. Coloristic measurements were carried out using a spectrophotometer XRITE SP68 at 10° observation angle over white background.

(2) TABLE-US-00001 TABLE 1 Gloss and coloristic data obtained with samples from Example 1. Gloss L* C* h (20° (over (over (over Sample Structure of compound X angle) white) white) white) 0.0 Melinex 506 (blank substrate) 227 — — — 1.1 0 591 73.3 17.8 64.4 2.1 420 70.5 8.8 95.6 3.1 623 71.5 12.1 79.2 4.1 432 71.7 9.9 92.6 5.1 549 69.3 10.7 88.4

(3) As can be seen from the data in Table 1, higly reflective coatings can be obtained upon coating and curing the compositions of the present invention at a temperature as low as 85° C.

Example 2

(4) 116 mg (0.5 mmol) of Ag.sub.2O was added to 2.5 g of iso-propanol, followed by 1.2 mmol of one of the compounds X (see Table 2) and the mixture was stirred for 30 min at 25° C. for dissolution of Ag.sub.2O. After that, 200 mg of glutaric dialdehyde (50% solution in water, 1 mmol of dialdehyde) was added, followed by addition of iso-propanol such as to adjust the Ag concentration in the mixture to 3% w/w. The mixture was filtered through 0.45 μm PTFE syringe filter and coated onto flexible PET-foil substrate (Melinex 506) using a wired rackle hand-coater #1. Coating was dried and cured in the oven at 85° C. for 20 sec. Gloss measurements were carried out using a glossmeter Zehntner 1110. Coloristic measurements were carried out using a spectrophotometer X-RITE SP68 at 10° observation angle over white background.

(5) TABLE-US-00002 TABLE 2 Gloss and coloristic data obtained with samples from Example 2. Gloss L* C* h (20° (over (over (over Sample Structure of compound X angle) white) white) white) 0.0 Melinex 506 (blank PET substrate) 227 — — — 1.2 466 76.2 31.4 59.4 2.2 322 69.1 13.6 86.9 3.2 488 68.7 20.8 66.1

(6) As can be seen from the data in Tables 1 and 2, with a composition according to the present invention, a highly reflective (high gloss value at 20°) coating can be obtained.

Example 3

(7) 116 mg (0.5 mmol) of Ag.sub.2O was added to 2.5 g of iso-propanol, followed by 221 mg (1.2 mmol) of ethyl 4,4,4-trifluoro-3-oxo-butanoate and the mixture was stirred for 30 min at 25° C. for dissolution of Ag.sub.2O. After that, 18.4 mg (0.2 mmol) of glycerol was added, followed by addition of iso-propanol such as to adjust the Ag concentration in the mixture to 3% w/w. The mixture was filtered through 0.45 μm PTFE syringe filter and coated onto flexible PET-foil substrate (Melinex 506) using a wired rackle hand-coaters #1 and #2. Coating was dried and cured in the oven at 85° C. for 20 sec. Gloss measurements were carried out using a glossmeter Zehntner 1110.

(8) The following values for gloss at 20° angle were obtained:

(9) Hand-coater #1: Gloss (20° angle): 765

(10) Hand-coater #2: Gloss (20° angle): 1010