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-particle 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 an electrically non-conductive silver nanoparticles-containing layer on a substrate, the method comprising: A) coating or printing an ink composition on a substrate, the ink composition comprising: a) a silver compound or a mixture of silver compounds; b) a compound selected from the group consisting of a compound of formula (I): ##STR00022## wherein n=1, 2 or 3, if n=3, RH, if n=1 or 2, R is substituted or unsubstituted C.sub.1-C.sub.18alkyl, or C.sub.6-C.sub.10aryl; and x=1 to 20; a compound of formula (II) ##STR00023## wherein R.sub.1, R.sub.2 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, and R.sub.3 is independently from R.sub.1 and R.sub.2 hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, acyl; a compound of formula (III): ##STR00024## wherein R.sub.1 and R.sub.2 do not simultaneously stand for hydrogen, and n stands for 1; a compound of formula (III): ##STR00025## wherein R.sub.4, R.sub.5 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, R.sub.6, R.sub.7 are, independently from each other and R.sub.4 and R.sub.5, hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or un substituted C.sub.5-C.sub.12 cycloalkyl, substituted or un substituted C.sub.6-C.sub.10 aryl, acyl, an oligo(alkylene glycol) chain, R.sub.4 and R.sub.5 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms; a compound of formula (IV): ##STR00026## wherein R.sub.8 is substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, wherein the alkyl, cycloalkyl and aryl groups may contain oxygen, nitrogen or sulfur atoms as heteroatoms; c) optionally a solvent, an organic binder, a reducing agent, a formulation stabilizer, or a mixture thereof; and B) heating the coated or printed substrate to a temperature of from 30 C. to 200 C. or applying electromagnetic radiation, wherein in formula (II) and (IIa) R.sub.1 and R.sub.2 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms.

2. A method according to claim 1, wherein the substrate is a plain substrate.

3. A method according to claim 1, wherein the substrate is a structured substrate.

4. A method for forming an optically variable image on a substrate, the method comprising: A) forming an optically variable image (OVI) on a discrete portion of the substrate, the forming 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 an OVI former; and a3) curing the curable composition treated in step a2); B) coating or printing an ink composition on at least a part of the cured OVI obtained in step a3), the ink composition comprising a) a silver compound or a mixture of silver compounds, b) a compound selected from the groups consisting of a compound of formula (I): ##STR00027## wherein n=1, 2 or 3, if n=3, RH, if n=1 or 2, R is substituted or unsubstituted C.sub.1-C.sub.18alkyl, or C.sub.6-C.sub.10aryl; and x=1 to 20, a compound of formula (II): ##STR00028## wherein R.sub.1, R.sub.2 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, R.sub.3 is independently from R.sub.1 and R.sub.2 hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, acyl; a compound of formula (IIa): ##STR00029## wherein R.sub.1 and R.sub.2 do not simultaneously stand for hydrogen, and n stands for 1; a compound of formula (III): ##STR00030## wherein R.sub.4, R.sub.5 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, R.sub.6, R.sub.7 are, independently from each other and R.sub.4 and R.sub.5, hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, acyl, an oligo(alkylene glycol) chain (e.g. PEG, PPG, number of monomer units 1-20), R.sub.4 and R.sub.5 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms; a compound of formula (IV): ##STR00031## wherein R.sub.8 is substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, wherein the alkyl, cycloalkyl and aryl groups may contain oxygen, nitrogen or sulfur atoms as heteroatoms; c) optionally a solvent, an organic binder, a reducing agent, a formulation stabilizer, or a mixture thereof; and C) heating the coated or printed substrate to a temperature of from 30 C. to 200 C. or applying electromagnetic radiation, wherein in formula (II) and (IIa) R.sub.1 and R.sub.2 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms.

5. 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 said substrate surface, an electrically non-conductive silver layer prepared by a coating or printing process comprising: A) coating or printing an ink composition on the substrate, the ink composition comprising: a) a silver compound or a mixture of silver compounds, b) a compound selected from the groups consisting of a compound of formula (I): ##STR00032## wherein n=1, 2 or 3, if n=3, RH, if n=1 or 2, R is substituted or unsubstituted C.sub.1-C.sub.18alkyl, or C.sub.6-C.sub.10aryl, and x=1 to 20; a compound of formula (II): ##STR00033## wherein R.sub.1, R.sub.2 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, R.sub.3 is independently from R.sub.1 and R.sub.2 hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, acyl; a compound of formula (IIa): ##STR00034## wherein R.sub.1 and R.sub.2 do not simultaneously stand for hydrogen, and n stands for 1; a compound of formula (III): ##STR00035## wherein R.sub.4, R.sub.5 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, R.sub.6, R.sub.7 are, independently from each other and R.sub.4 and R.sub.5, hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, acyl, an oligo(alkylene glycol) chain (e.g. PEG, PPG, number of monomer units 1-20), R.sub.4 and R.sub.5 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms; a compound of formula (IV): ##STR00036## wherein R.sub.8 is substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, wherein the alkyl, cycloalkyl and aryl groups may contain oxygen, nitrogen or sulfur atoms as heteroatoms; c) optionally a solvent, an organic binder, a reducing agent, formulation stabilizer, or a mixture thereof, and B) heating the coated or printed substrate to a temperature of from 30 C. to 200 C. or applying electromagnetic radiation, wherein in formula (II) and (IIa) R.sub.1 and R.sub.2 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms.

6. The element according to claim 5, which is adapted to function as a security element for the prevention of counterfeit or reproduction, on a document of value, right, identity, a security label or a branded good.

7. The method according to claim 1, wherein the ink composition comprises at least one binder comprising 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 mixtures thereof.

8. The method according to claim 1, comprising printing the ink composition on the substrate by offset or by gravure printing.

9. The method according to claim 1, further comprising applying a protective top coat.

10. The method according to claim 1, wherein the steps A) and B) are repeated 1 to 5 times resulting in a multilayer metallic structure.

11. A security product obtained by the method of claim 1.

12. The security product according to claim 11, which is in the form of banknotes, credit cards, identification documents like passports, identification cards, drivers licenses, or other verification documents, pharmaceutical apparel, software, compact discs, tobacco packaging and other products or packaging prone to counterfeiting or forgery.

13. The method according to claim 1, wherein the ink composition comprises at least one reducing agent selected from the group consisting of polyphenols and their derivatives; formic acids and it's salts; oxalic acid and it's salts; aldehydes; acetals and hemi-acetals; ascorbic acid; hydroxylamine and it's derivatives; hydrazine and its derivatives; alkyl and aryl phosphines; tin hydrides and silanes.

14. The method according to claim 1, wherein step B) is carried out by exposure to UV light.

15. A security product obtained by the method of claim 1, wherein the silver layer comprises an upper and a lower part.

16. A coating or printing ink composition, comprising: a) a silver compound or a mixture of silver compounds; b) a compound selected from the groups consisting of: a compound of formula (I): ##STR00037## wherein n=1, 2 or 3, if n=3, RH, if n=1 or 2, R is substituted or unsubstituted C.sub.1-C.sub.18alkyl, or C.sub.6-C.sub.10aryl, and x=1 to 20; a compound of formula (II): ##STR00038## wherein R.sub.1, R.sub.2 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, R.sub.3 is independently from R.sub.1 and R.sub.2 hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, acyl; a compound of formula (IIa): ##STR00039## wherein R.sub.1 and R.sub.2 do not simultaneously stand for hydrogen, and n stands for 1; a compound of formula (III): ##STR00040## wherein R.sub.4, R.sub.5 are independently hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, R.sub.6, R.sub.7 are, independently from each other and R.sub.4 and R.sub.5, hydrogen, substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, acyl, an oligo(alkylene glycol) chain, R.sub.4 and R.sub.5 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms; a compound of formula (IV) ##STR00041## wherein R.sub.8 is substituted or unsubstituted C.sub.1-C.sub.18 alkyl, substituted or unsubstituted C.sub.5-C.sub.12 cycloalkyl, substituted or unsubstituted C.sub.6-C.sub.10 aryl, wherein the alkyl, cycloalkyl and aryl groups may contain oxygen, nitrogen or sulfur atoms as heteroatoms, c) optionally a solvent, an organic binder, a reducing agent, a formulation stabilizer, or a mixture thereof, wherein in formula (II) and (IIa) R.sub.1 and R.sub.2 may be connected in a form of a saturated or unsaturated ring, optionally containing heteroatoms.

Description

EXAMPLES

Example 1

Preparation of Coating Solution, containing Terminal Alkyne and Ag Ions

[0207] 1.67 g of silver (I) acetate is dispersed in 3.34 g of 1-methoxy-2-propanol with stirring and cooled to 0 C. 1.67 g of propoxylated propargyl alcohol, prepared according to Example 2 of EP 0 239 770 B1, is added in one portion and the mixture is stirred for 30 min at room temperature upon which time the silver acetate completely dissolves. The reaction mixture is filtered through 1.5 m filter and stored at +5 C. for further experiments.

Example 2a

Preparation of a Highly Reflective One Layer Coating

[0208] 1 g of the solution, obtained in the Example 1, is diluted with 4 g of 1-methoxy-2-propanol and this solution is coated onto PET foil, using the wire bar 0 (4 m wet thickness). The coating is dried at room temperature and then heated to 130 C. for 30 seconds to obtain a highly reflective surface coating.

Example 2b

Preparation of Highly Reflective Multi-Layer Coating

[0209] 1 g of the solution, obtained in the Example 1, is diluted with 4 g of 1-methoxy-2-propanol and this solution (solution 1) is coated onto PET foil, using the wire bar 0 (4 m wet film thickness). The coating is dried at room temperature and then heated to 130 C. for 30 seconds. The obtained dry coating is overcoated with solution 1, using a wire bar 0 (4 m wet film thickness) and then heated to 130 C. for 30 seconds to build a multi-layer coating providing a high reflectivity.

Example 3

Optical Data of the Reflective Coatings from Examples 2a and 2b

[0210]

TABLE-US-00001 TABLE 1 Reflexion maximum of the coated films measured over white by means of a spectrophotometer MCS 501 UV-NIR incl. MCS 511 NIR 1.7 (Zeiss) Reflexion maximum Wavelength Sample from example 2a 41.7% 584 nm Sample from example 2b 44.0% 705 nm

TABLE-US-00002 TABLE 2 Coloristical data of the coated films measured over white by means of a spectrophotometer MCS 501 UV-NIR incl. MCS 511 NIR 1.7 and a software Aspect Plus (Zeiss) L* a* b* Sample from example 2a 69.34 3.85 11.3 Sample from example 2b 53.58 16.45 16.66

Example 4

Conductivity of the Reflective Coatings

[0211] The sheet resistance of the coating, formed in Example 2a, is measured by four-point probe method to give a value of 1.5*10.sup.10 /sq.

Example 5

Preparation of Coating Solution, containing Terminal Alkyne (3-methyl-1-pentyne-3-ol), Ag Ions and additional Reducing Agent (2,3,4-trihydroxyacetophenone)

[0212] 110 mg (0.5 mmol) of silver trifluoroacetate is dissolved in 1.5 g of dry ethanol and 49 mg (0.5 mmol) 3-methyl-1-pentyne-3-ol are added with stirring, followed by addition of 42 mg (0.25 mmol) of 2,3,4-trihydroxyacetophenone. Finally, 0.34 g of 1-methoxy-2-propanol are added with stirring and the obtained clear solution is used to produce metallic nano-particle layers.

Example 6

Preparation of Coating Solution, containing Terminal Alkyne (3-methyl-1-pentyne-3-ol), Ag Ions, additional Reducing Agent (2,3,4-trihydroxyacetophenone) and a Binder (Hydroxypropyl Cellulose)

[0213] 220 mg (1 mmol) of silver trifluoroacetate are dissolved in 3 g of dry ethanol and 98 mg (1 mmol) 3-methyl-1-pentyne-3-ol was added with stirring, followed by addition of 84 mg (0.5 mmol) of 2,3,4-trihydroxyacetophenone. 0.68 g of 1-methoxy-2-propanol are added, followed by 10.8 mg of hydroxypropyl cellulose (Mw=ca. 1000000). The mixture is stirred at room temperature until dissolution of hydroxypropyl cellulose and the obtained clear solution is used to produce metallic nano-particle layers.

Example 7

Preparation of Coating Solution, containing Terminal Alkyne (3-methyl-1-pentyne-3-ol), Ag Ions, additional Reducing Agent (2,3,4-trihydroxyacetophenone), a Binder (Hydroxypropyl Cellulose) and an Acid (Trifluoroacetic Acid)

[0214] 220 mg (1 mmol) of silver trifluoroacetate are dissolved in 3 g of dry ethanol and 98 mg (1 mmol) 3-methyl-1-pentyne-3-ol are added with stirring, followed by addition of 84 mg (0.5 mmol) of 2,3,4-trihydroxyacetophenone. 0.68 g of 1-methoxy-2-propanol are added, followed by 10.8 mg of hydroxypropyl cellulose (Mw ca. 1,000,000 g/mol). The mixture is stirred at room temperature until dissolution of hydroxypropyl cellulose, then 100 mg of trifluoroacetic acid are added and the obtained clear solution is used to produce metallic nano-particle layers.

Example 8

Preparation of Coating Solution, containing Terminal Alkyne (1-decyne), Ag Ions and additional Reducing agent (2,3,4-trihydroxyacetophenone)

[0215] 110 mg (0.5 mmol) of silver trifluoroacetate are dissolved in 3 g of 2-methyltetrahydrofurane and 69 mg (0.5 mmol) of 1-decyne are added with stirring, followed by addition of 42 mg (0.25 mmol) of 2,3,4-trihydroxyacetophenone and the obtained clear solution is used to produce metallic nano-particle layers.

Example 9

Preparation of Highly Reflective One Layer Coatings from Examples 5, 6, 7 and 8

[0216] Solutions, obtained in Examples 5, 6, 7 and 8, are coated onto PET foil (Melinex 506), using the wire bar 1 (6 m wet thickness). The coatings are dried at room temperature and then parts of it are heated to 110 C. for 30 seconds and other parts are exposed to UV light (Aktiprint 18/9 device, Hg lamp, 200 W/cm.sup.2) to obtain highly reflective surface coatings.

Example 10

Optical Data of the Reflective Coatings from Examples 5 to 8

[0217]

TABLE-US-00003 TABLE 3 Optical data of the reflective coatings from example 5 to 8, measured over white background. Gloss at 20 is measured with glossmeter Zehnter 1120. Color charachteristics are measured with X-Rite SP68 Sphere Spectrophotometer. Example 5 Example 6 Example 7 Example 8 Heating Gloss 20 650 630 560 390 110 C. L* 69.9 75.2 72.6 69.5 C* 24.3 25.6 29.7 16.8 h 72.7 68.5 65.8 70 UV lamp Gloss 20 630 660 634 450 Curing L* 70.2 69 66.1 76.3 C* 44.3 41.7 37.6 31.8 h 61.9 59 54.9 64

TABLE-US-00004 TABLE 4 Optical data of the reflective coatings from example 5 to 8, measured over black background. Gloss at 20 was measured with glossmeter Zehnter 1120. Color charachteristics were measured with X-Rite SP68 Sphere Spectrophotometer. Example 5 Example 6 Example 7 Example 8 Heating Gloss 20 540 656 600 408 110 C. L* 61.5 68 63.3 54 C* 12.1 13.3 12.1 15.1 h 97.4 105.1 96 69.8 UV lamp Gloss 20 655 535 586 370 Curing L* 65.8 61.3 63.6 59.6 C* 15.4 12.4 12.5 14.9 h 97.9 107.2 118.2 100.7

[0218] FIGS. 1 and 2 show TEM-images of cross-sections of coated PET substrate from example 2a. In particular, the upper (i.e. darker) layer comprises most of the silver nanoparticles, and the second and lower layer, being in direct contact with the substrate, a PET foil, comprises further clearly smaller silver nanoparticles (in this case the dimensions are up to 12 nm). The total thickness of these two layers is 61-67 nm.