Security Printing

Abstract

The use of a modified reduced indium tin oxide to provide a security image wherein the modified reduced indium tin oxide is obtained by heating indium tin oxide in a reducing atmosphere at a temperature of from 300 to 500° C.; and contacting the reduced indium tin oxide with an organophosphorus compound.

Claims

1. A method of producing a modified reduced indium tin oxide comprising: heating indium tin oxide in a reducing atmosphere at a temperature of from 300 to 500° C.; and contacting the reduced indium tin oxide with an organophosphorus compound.

2. The method of claim 1 wherein tin is present in the reduced indium tin oxide in an amount of from 5 to 15 mol%.

3. An article comprising a substrate which carries a modified reduced indium tin oxide prepared according to the method of claim 1 on a surface thereof.

4. The article according to claim 3 selected from a group consisting of: packaging; a label; an identification document; a credit card or other bank card; a ticket or voucher; and a certificate.

5. An article according to claim 3 which is a banknote.

6. An article according to claim 3, wherein the reduced indium tin oxide forms a security image on the surface of the substrate.

7. A polymer composition or a polymer precursor composition comprising particles of a modified reduced indium tin oxide prepared according to the method of claim 1 .

8. An ink composition having dispersed therein particles of a modified reduced indium tin oxide prepared according to the method of claim 1.

9. A method of manufacturing an article, the method comprising providing a substrate; and applying an ink composition of claim 8 onto a surface of the substrate.

10. A method of manufacturing an article, the method comprising the steps of: (i) heating indium tin oxide in a reducing atmosphere at a temperature of 300 to 500° C.; (ii) contacting the reduced indium tin oxide obtained in step (i) with an organophosphorus compound; (iii) incorporating the modified reduced indium tin oxide obtained in step (iii) into an ink composition; and (iv) applying the ink composition obtained in step (iii) onto a surface of a substrate.

11. An article according to claim 3, wherein the difference in colour between the substrate with and without the security image comprising the reduced indium tin oxide (dE) is less than 2.

12. The method of claim 1, wherein the colour of the reduced indium tin oxide is such that it has an L* measurement of at least 50.

13. A method of detecting a genuine article, said method comprising applying infrared radiation to the article and detecting absorption of said infrared radiation; wherein the article comprises a substrate which carries modified reduced indium tin oxide on a surface thereof and wherein the modified reduced indium tin oxide is obtained according to the method of claim 1.

14. A method of assessing the quality of an article of the second aspect, the method comprising measuring at a locus of the article which carries the modified reduced indium tin oxide, the absorption A.sub.1 of at least one wavelength of λ.sub.1 of radiation in the infra-red range and comparing the absorption with a known standard.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0175] FIG. 1 shows a graph of the reflectance of the compound of Example 9, intaglio printing ink mixed with the pigment of Example 4.

[0176] FIG. 2 shows a graph of the reflectance of the compounds of Examples 1 and 8.

[0177] The invention will now be further described with reference to the following non-limiting examples.

[0178] Examples 1 to 7 describe the preparation of modified reduced indium tin oxide materials of the invention.

[0179] Example 8 describes the synthesis of a reduced indium tin oxide according to the prior art.

[0180] In each case the colour and infrared absorbing properties of the materials obtained were measured using standard techniques.

Example 1

[0181] 100 g of yellow indium tin oxide prepared according to known methods was taken and fired in the tube furnace in forming gas (5%H2/95%N2) at a flow rate of 0.2-0.3L/min and 1 bar pressure from the cylinder. Temperature was 350° C. After 12 hours the gas supply was 20 switched to 100% N2 (with the same flow rate) whilst the kiln cooled overnight. The resulting powder was dispersed in 500 ml DI water under stirring. 5 gr of Butylphosphate were added to the dispersion. Stirring was continued for 1 hour and the dispersion was then dried at 120° C. overnight.

[0182] The resulting powder showed following properties: [0183] L-value: 57,3 [0184] a-value: -6,5 [0185] b-value: –9,6 [0186] NIR Absorption at 1500 nm: 55 % at 5% level in Intaglio ink Print on banknote paper

Example 2

[0187] Yellow indium tin oxide powder was mixed with around 50% of a 25% isopropanol solution i.e. 30 50 g of solution containing 12.5 g of isopropanol + 37.5 g water mixed with 100 g of powder to give damp slurry. This was fired in a nitrogen atmosphere at 300 to 500° C. for 4 to 5 hours. After cooling the resultant material was contacted with 5 gr Butylphosphate dissolved in 5 gr of Isopropanol. Following the homogenisation the powder was dried at 100° C. in air.

[0188] The resulting powder showed following properties: [0189] L-value: 65 [0190] a-value: -5 [0191] b-value: –10 [0192] NIR Absorption at 1500 nm: 35 % at 5% level in Intaglio ink Print on banknote paper

Example 3

[0193] Yellow indium tin oxide powder was mixed with around 50% of a 25% isopropanol solution i.e. 30 50 g of solution containing 12.5 g of isopropanol + 37.5 g water mixed with 100 g of powder to give damp slurry. The slurry was further treated with an 50% alcoholic solution of Trioctylphosphate. The resulting paste was fired in a nitrogen atmosphere at 300 to 500° C. for 4 to 5 hours. The product was milled to give a fine blue powder.

[0194] The resulting powder showed following properties: [0195] L-value: 62 [0196] a-value: -5,1 [0197] b-value: –10,3 [0198] NIR Absorption at 1500 nm: 30 % at 5% level in Intaglio Ink Print on banknote paper

Example 4

[0199] 100 g of yellow indium tin oxide prepared according to known methods was taken and fired in the tube furnace in forming gas (5%H2/95%N2) at a flow rate of 0.2-0.3 L/min and 1 bar pressure from the cylinder. Temperature was 400° C. After 12 hours the gas supply was 20 switched to 100% N2 (with the same flow rate) whilst the kiln cooled overnight. The resulting powder was dispersed in 500 ml DI water under stirring. 10 gr of Octylphosphonic Acid were added to the dispersion. Stirring was continued for 1 hour and the dispersion was then dried at 120° C.

[0200] The resulting powder showed following properties: [0201] L-value: 64 [0202] a-value: -5,1 [0203] b-value: –12,2 [0204] NIR Absorption at 1500 nm: 70 % at 1% level in Intaglio ink Print on banknote paper

Example 5

[0205] 100 g of yellow indium tin oxide prepared according to known methods was taken and fired in the tube furnace in forming gas (5%H2/95%N2) at a flow rate of 0.2-0.3 L/min and 1 bar pressure from the cylinder. Temperature was 350° C. After 12 hours the gas supply was 20 switched to 100% N2 (with the same flow rate) whilst the kiln cooled overnight. The resulting powder was dispersed in 500 ml DI water under stirring. 5 gr of Butylphosphate were added to the dispersion. Stirring was continued for 1 hour and the dispersion was then dried at 120° C.

[0206] The resulting powder showed following properties: [0207] L-value: 64 [0208] a-value: -5,1 [0209] b-value: –12,2 [0210] NIR Absorption at 1500 nm: 55 % at 5% level in Intaglio Ink Print on banknote paper

Example 6

[0211] 100 g of yellow indium tin oxide prepared according to known methods was taken and fired in the tube furnace in forming gas (5%H2/95%N2) at a flow rate of 0.2-0.3 L/min and 1 bar pressure from the cylinder. Temperature was 400° C. After 12 hours the gas supply was 20 switched to 100% N2 (with the same flow rate) whilst the kiln cooled overnight. The resulting powder was dispersed in 500 ml DI water under stirring. 10 gr of a long chain, polyethoxylated octadecenol phosphate ester were added to the dispersion. Stirring was continued for 1 hour and the dispersion was then dried at 120° C.

[0212] The resulting powder showed following properties: [0213] L-value: 60,3 [0214] a-value: -6,2 [0215] b-value: –11,6 [0216] NIR Absorption at 1500 nm: 60 % at 1% level in Intaglio ink Print on banknote paper

Example 7

[0217] 100 g of yellow indium tin oxide prepared according to known methods was taken and fired in the tube furnace in forming gas (5%H2/95%N2) at a flow rate of 0.2-0.3 L/min and 1 bar pressure from the cylinder. Temperature was 400° C. After 12 hours the gas supply was 20 switched to 100% N2 (with the same flow rate) whilst the kiln cooled overnight. The resulting powder was dispersed in 500 ml DI water under stirring. 5 gr of long chain, polyethoxylated octadecenol phosphate ester were added to the dispersion. Stirring was continued for 1 hour and the dispersion was then dried at 120° C.

[0218] The resulting powder showed following properties: [0219] L-value: 62,1 [0220] a-value: -6,0 [0221] b-value: -10,6 [0222] NIR Absorption at 1500 nm: 65 % at 1% level in Intaglio ink Print on banknote paper

Example 8 - Comparative

[0223] 100 gr of yellow indium tin oxide prepared to known methods was taken and fired in a tube furnace in forming gas at a flow rate of 1 I/min. and 1 bar pressure. Temperature was 450° C. After 6 hours the gas supply was switched to Nitrogen and then the furnace was allowed to cool over night.

[0224] The resulting product was a fine dark-blue powder at a yield of 98%.

[0225] The colour analysis of the powder showed [0226] L-value: 46,1 [0227] a-value: -3,75 [0228] b-value: -9,63 [0229] NIR Absorption at 1500 nm: 70% at 5% level in Intaglio Ink Print on banknote paper

Example 9

[0230] 99 gr of an intaglio printing ink were mixed with 1 wt% of the pigment of Example 4 in a speed mixer. The printing ink was printed on banknote paper strips with an Orange Test Printing Machine. The dried paper strips were then analysed with NIR spectrocospy and the colour of the prints were measured.

[0231] The results are shown in Table 1 and FIG. 1.

TABLE-US-00001 Sample L a b Clear Ink print 89.71 -2.01 1.25 Example 4 1% print 91.00 -1.86 -0.06

Example 10

[0232] The visible and infrared spectra of powders prepared according to examples 1 and 8 were recorded, along with colour measurements.

[0233] The results are shown in FIG. 2 and table 2.

TABLE-US-00002 Sample L a b Example 8 46.14 -3.75 -9.63 Example 1 57.37 -6.5 -12.01