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 nanoparticle layers, which are produced directly on a substrate as part of a coating or printing process. The layers show different colours in transmittance and reflectance. The layers do not show the typical conductivity of metallic layers, since the particles are essentially discrete particles which are not sintered. 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 show also different colours in reflection and transmission, an extremely bright optically variable image (OVD image) and high purity and contrast. Depending on the thickness of the layer a more or less intensive metallic aspect appears.

Claims

1. A method for forming a silver nanoparticles-containing layer on a substrate, the method comprising: A) optionally forming an optically variable device (OVD) on a discrete portion of the substrate; B) applying a composition on at least part of the substrate, optionally on at least part of the OVD obtained in step A), or both, to obtain a coating; and C) exposing the coating to heat, irradiating the coating with electromagnetic radiation, or both, to form a highly reflective layer comprising silver nanoparticles, wherein the composition comprises: b1) a silver metal precursor, b2) an acid, b3) optionally a solvent, b4) an optionally substituted polyhydric phenol, and b5) optionally a polymeric binder.

2. The method according to claim 1, wherein the silver metal precursor is selected from the group consisting of: a compound of formula R.sup.11C(═O)OAg, wherein R.sup.11 is a C.sub.1-C.sub.8alkyl group, wherein part of the hydrogen atoms may be replaced by F and/or Cl, a compound of formula R.sup.12C(═O)CH═C(—OAg)—R.sup.13, wherein R.sup.12 and R.sup.13 are independently of each other a C.sub.1-C.sub.8alkyl group, wherein part of the hydrogen atoms may be replaced by F, or an optionally substituted phenyl group, a compound of formula R.sup.14OC(═O)CH═C(—OAg)—R.sup.15, wherein R.sup.14 is a C.sub.1-C.sub.8alkyl group and R.sup.15 is a C.sub.1-C.sub.8alkyl group, wherein part of the hydrogen atoms may be replaced by F, and mixtures thereof.

3. The method according to claim 1, wherein the acid is selected from the group consisting of monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, difluoroacetic acid, trifluoroacetic acid, pentafluoropropionic acid, heptafluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid and 1,1,1,5,5,5-hexafluoroacetylacetone, and mixtures thereof.

4. The method according to claim 1, wherein the composition comprises a solvent selected from the group consisting of water, an alcohol, an ether, a ketone, an ether-alcohol, a polar aprotic solvent, and mixtures thereof.

5. The method according to claim 1, wherein the composition comprises a polyhydric phenol, which is tannic acid or a compound of formula (I): ##STR00014## wherein: R.sup.1 can be the same, or different in each occurrence and is a hydrogen atom, a halogen atom, a C.sub.1-C.sub.18alkyl group, a C.sub.1-C.sub.18alkoxy group, or a group —C(═O)—R.sup.3, R.sup.3 is a hydrogen atom, a C.sub.1-C.sub.18alkyl group, anunsubstituted or substituted aminogroup, or a C.sub.1-C.sub.18alkoxy group, and n is a number of 1 to 4, m is a number of 2 to 4, and the sum of m and n is 6.

6. The method according to claim 5, wherein the polyhydric phenol is a compound of formula (Ia): ##STR00015## wherein: R.sup.1 is a hydrogen atom, or a group of formula —C(═O)—R.sup.3, and R.sup.3 is a hydrogen atom, a C.sub.1-C.sub.18alkyl group, a C.sub.1-C.sub.18alkoxy group, or an unsubstituted or substituted aminogroup.

7. The method according to claim 1, wherein the composition comprising a polymeric binder selected from the group consisting of a nitrocellulose, an ethyl cellulose, a cellulose acetate, a cellulose acetate propionate (CAP), a cellulose acetate butyrate (CAB), a hydroxyethyl cellulose, a hydroxypropyl cellulose, an alcohol soluble propionate (ASP), a vinyl chloride, a vinyl acetate copolymer, a vinyl acetate, a vinyl, an acrylic, a polyurethane, a polyamide, a rosin ester, a hydrocarbon-containing binding, an aldehyde-containing binder, a ketone-containing binder, a urethane-containing binder, a polyethyleneterephthalate, a terpene phenol, a polyolefin, a shellac and mixtures thereof.

8. The method according to claim 1, comprising: a1) applying a curable composition to at least a portion of the substrate; a2) contacting at least a portion of the curable composition with OVD former; and a3) curing the curable composition treated in step a2) by the OVD former.

9. A security or decorative element, comprising a substrate, which may contain indicia or other visible features in or on its surface, and on at least part of the substrate surface, a silver layer obtained by the method of claim 1.

10. The security or decorative element according to claim 9, wherein the silver layer is coated with a protective layer.

11. An article, comprising the security or decorative element of claim 9.

12. A coating or printing ink composition, comprising: b1) a silver metal precursor, b2) an acid, b3) optionally a solvent, b4) a polyhydric phenol, and b5) optionally a polymeric binder.

13. The coating or printing ink composition according to claim 12, comprising: the silver metal precursor b1) selected from the group consisting of a compound of formula R.sup.11C(═O)OAg, wherein R.sup.11 is a C.sub.1-C.sub.8alkyl group, wherein part of the hydrogen atoms may be replaced by F and/or Cl, a compound of formula R.sup.12C(═O)CH═C(—OAg)—R.sup.13, wherein R.sup.12 and R.sup.13 are independently of each other a C.sub.1-C.sub.8alkyl group, wherein part of the hydrogen atoms may be replaced by F, or an optionally substituted phenyl group, a compound of formula R.sup.14OC(═O)CH═C(—OAg)—R.sup.15, wherein R.sup.14is a C.sub.1-C.sub.8alkyl group and R.sup.15 is a C.sub.1-C.sub.8alkyl group, wherein part of the hydrogen atoms may be replaced by F, and mixtures thereof; an acid b2) selected from the group consisting of monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, difluoroacetic acid, trifluoroacetic acid, pentafluoropropionic acid, heptafluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid and 1,1,1,5,5,5-hexafluoroacetylacetone, and mixtures thereof; a solvent b3) selected from the group consisting of water, an alcohol, a cyclic or acyclic ether, a ketone, a polar aprotic solvent, and mixtures thereof; and a polyhydric phenol of formula (Ia): ##STR00016## wherein: R.sup.1 is a hydrogen atom, or a group of formula —C(═O)—R.sup.3, and R.sup.3 is a hydrogen atom, a C.sub.1-C.sub.18alkyl group, a C.sub.1-C.sub.18alkoxy group, or an unsubstituted or substituted aminogroup.

14. A reflective layer formed from the coating or printing ink composition claim 12.

Description

EXAMPLES

Example 1

[0169] General Procedure:

[0170] 116 mg (0.5 mmol) of Ag.sub.2O was added to 2.5 g of 1-methoxy-2-propanol, followed by 171 mg (1.5 mmol) of trifluoroacetic acid and the mixture was stirred for 15 min at 25° C. for dissolution of Ag.sub.2O. After that, 0.5 mmol of compound X (see table 1, except for tannic acid, which was added in the amount of 85 mg (0.05 mmol)) was added with stirring, followed by addition of 1-methoxy-2-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 wire bar #1 (6 micrometers wet film). Coating was dried and cured in the oven at 95° C. for 30 sec. Gloss measurements were carried out using a glossmeter Zehntner 1110 (Table 1). Coloristic measurements were carried out using a spectrophotometer X-RITE SP68 at 10° observation angle over white background (Table 1).

TABLE-US-00001 TABLE 1 Coloristic and gloss properties for coatings, obtained in Example 1. Gloss L* C* h Sample (20° (over (over (over ID Structure of compound X angle white) white) white) 1.0 Melinex 506 227 — — — (blank PET substrate) 1.1 [00008] 400 65 27.1 64 1.2 [00009] 402 63.3 26.1 61.8 1.3 [00010] 569 66.5 17.4 73.9 1.4 [00011] 521 66.7 23 74.6 1.5 [00012] 628 73.2 8.5 84.1 1.6 [00013] 509 65.8 12.3 81.8 1.7 Tannic acid 335 69.9 34.2 63.9

[0171] 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 95° C.

Example 2

[0172] a) Two solutions were prepared:

[0173] Solution A: 11.5 g (50 mmol) Ag.sub.2O was added to 200 g of 1-methoxy-2-propanol, followed by addition of 14.8 g (130 mmol) of trifluoroacetic acid. The mixture was stirred until dissolution of Ag.sub.2O (approximately 10 min).

[0174] Solution B: 9.9 g (50 mmol) of ethyl gallate was dissolved in 200 g of 1-methoxy-2-propanol.

[0175] b) Solutions A and B from Example 2a) were mixed and the resulting mixture was printed onto PET foil (Melinex 506) by rotogravure using a 70 l/cm gravure cylinder at a speed of 10 m/min to 20 m/min and 120° C. drying temperature.

[0176] 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 (Tables 2 and 3).

TABLE-US-00002 TABLE 2 Gloss properties of the coatings, obtained in Example 2 Melinex Angle 10 m/min 20 m/min 506 20° 928 891 226 60° 426 409 202 85° 112 112 121

TABLE-US-00003 TABLE 3 Coloristic data of the coatings, obtained in Example 2 Speed 10 m/min 20 m/min L* 78.6 77.3 C* 17.7 18.3 h 71.6 70.2

[0177] As can be seen from the data in Tables 2 and 3, with a composition according to the present invention, a highly reflective (high gloss value at 20°) coating can be obtained with a printing speed of up to 20 m/min with a given drying chamber length. Increasing the drying chamber length to such as found in industrial printing mashines would allow for further increase of printing speed without losing the reflectivity.