Tamper-proof medium for thermal printing

Abstract

The present invention relates to method of manufacturing a tamper-proof medium for thermal printing, wherein a liquid treatment composition comprising at least one acid is deposited on a substrate which comprises a thermochromic coating layer comprising at least one halochromic leuco dye.

Claims

1. A method of manufacturing a tamper-proof medium for thermal printing, the method comprising the following steps: a) providing a substrate, wherein the substrate comprises on at least one side a thermochromic coating layer comprising at least one halochromic leuco dye, b) providing a liquid treatment composition comprising at least one acid, and c) applying the liquid treatment composition onto at least one region of the thermochromic coating layer in form of a preselected pattern, wherein the thermochromic coating layer further comprises a salifiable alkaline or alkaline earth compound and the salifiable alkaline or alkaline earth compound is at least partially converted into a corresponding acid salt when the liquid treatment composition is applied.

2. The method of claim 1, wherein the substrate is selected from the group consisting of paper, cardboard, containerboard, plastic, cellophane, textile, wood, metal, glass, mica plate, and nitrocellulose.

3. The method of claim 1, wherein the at least one halochromic leuco dye is colourless.

4. The method of claim 1, wherein the at least one halochromic leuco dye is selected from the group consisting of arylmethane phthalide dyes, quinone dyes, triarylmethane dyes, triphenylmethane dyes, fluoran dyes, phenothiazine dyes, rhodamine lactam dyes, spiropyran dyes, and mixtures thereof.

5. The method of claim 1, wherein the thermochromic coating layer comprises the at least one halochromic leuco dye in an amount from 1 to 60 wt.-%, based on the total weight of the thermochromic coating layer.

6. The method of claim 1, wherein the thermochromic coating layer further comprises a colour developing agent.

7. The method of claim 1, wherein the at least one acid is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid, sulphamic acid, tartaric acid, phytic acid, boric acid, succinic acid, suberic acid, benzoic acid, adipic acid, pimelic acid, azelaic acid, sebaic acid, isocitric acid, aconitic acid, propane-1,2,3-tricarboxylic acid, trimesic acid, glycolic acid, lactic acid, mandelic acid, acidic organosulfur compounds, acidic organophosphorus compounds, HSO.sub.4.sup.−, H.sub.2PO.sub.4.sup.− or HPO.sub.4.sup.2−, being at least partially neutralized by a corresponding cation selected from Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.2+ or Ca.sup.2+, and mixtures thereof.

8. The method of claim 1, wherein the liquid treatment composition further comprises a dye, a solvent-soluble dye, a pigment, a fluorescent dye, a phosphorescent dye, an ultraviolet absorbing dye, a near infrared absorbing dye, a thermochromic dye, a halochromic dye, metal ions, transition metal ions, lanthanides, actinides, magnetic particles, quantum dots, or a mixture thereof.

9. The method of claim 1, wherein the liquid treatment composition comprises the at least one acid in an amount from 0.1 to 100 wt.-%, based on the total weight of the liquid treatment composition.

10. The method of claim 1, wherein the preselected pattern is a continuous layer, a pattern, a pattern of repetitive elements, a repetitive combination(s) of elements, a guilloche, a one-dimensional bar code, a two-dimensional bar code, a three-dimensional bar code, a QR-code, a dot matrix code, a security mark, a number, a letter, an alphanumeric symbol, a logo, an image, a shape, a signature, a design, or a combination thereof.

11. The method of claim 1, wherein the liquid treatment composition is applied by spray coating, inkjet printing, offset printing, flexographic printing, screen printing, plotting, contact stamping, rotogravure printing, spin coating, slot coating, curtain coating, slide bed coating, film press, metered film press, blade coating, brush coating, stamping and/or a pencil.

12. A tamper-proof medium for thermal printing obtainable by a method according to claim 1.

13. The tamper-proof medium of claim 12, wherein the tamper-proof medium is a branded product, a security document, a non-secure document, a decorative product, a packaging, a container, a compact disc (CD), a digital video disc (DVD), a blue ray disc, a sticker, a label, a seal, a tag, a poster, a passport, a driving licence, a bank card, a credit card, a bond, a ticket, a postage stamp, tax stamp, a banknote, a certificate, a brand authentication tag, a business card, a greeting card, a voucher, a tax banderol, a point-of-sale receipt, a plot, a fax, a continuous recording sheet or reel, or a wall paper.

14. The tamper-proof medium for thermal printing according to claim 12, wherein the tamper-proof medium for thermal printing is suitable for use in security applications, in overt security elements, in covert security elements, in brand protection, in deviation prevention, in microlettering, in micro imaging, in decorative applications, in artistic applications, in visual applications, in packaging applications, in printing applications, in monitoring applications, or in track and trace applications.

15. The method of claim 1, wherein the substrate is selected from the group consisting of paper, cardboard, containerboard, and plastic.

16. The method of claim 1, wherein the thermochromic coating layer comprises the at least one halochromic leuco dye in an amount from 20 to 40 wt.-%, based on the total weight of the thermochromic coating layer.

17. The method of claim 1, wherein the thermochromic coating layer further comprises a colour developing agent in an amount from 1 to 80 wt.-%, based on the total weight of the thermochromic coating layer.

18. The method of claim 1, wherein the thermochromic coating layer further comprises a colour developing agent in an amount from 40 to 60 wt.-%, based on the total weight of the thermochromic coating layer.

19. The method of claim 1, wherein the at least one acid is phosphoric acid.

20. The method of claim 1, wherein the liquid treatment composition comprises the at least one acid in an amount from 10 to 50 wt.-%, based on the total weight of the liquid treatment composition.

21. The method of claim 1, wherein the thermochromic coating layer further comprises fillers, binders, or sensitizers.

22. The method of claim 1, wherein the salifiable alkaline or alkaline earth compound comprises calcium carbonate and the at least one acid is sulphuric acid or phosphoric acid.

23. The method of claim 1, wherein the thermochromic coating layer comprises calcium carbonate.

24. The method of claim 1, wherein the thermochromic coating layer comprises calcium carbonate and the at least one acid is selected from the group consisting of citric acid, oxalic acid, tartaric acid, and phosphoric acid.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1 shows magnifications of the substrates manufactured according to Example 1.

(2) FIG. 2 shows a tamper-proof medium for thermal printing manufactured according to Example 2, wherein a part of the original print was removed by an erasing liquid.

(3) FIG. 3 shows a magnification of the section highlighted in FIG. 2 before application of the liquid treatment composition.

(4) FIG. 4 shows a magnification of the section highlighted in FIG. 2 after application of the liquid treatment composition.

(5) FIG. 5 shows a magnification of the section highlighted in FIG. 2 after application of the erasing liquid.

(6) FIG. 6 shows a magnified infrared image of the section highlighted in FIG. 2 after application of the erasing liquid.

(7) FIG. 7 shows a magnified infrared image of a tamper-proof medium for thermal printing manufactured according to Example 3, wherein the original print was removed by an erasing liquid.

(8) FIG. 8 shows two tamper-proof media for thermal printing manufactured according to Example 4, wherein the left logo was printed with a liquid treatment composition comprising a red dye.

(9) FIG. 9 shows two tamper-proof media for thermal printing manufactured according to Example 4, wherein the left logo was printed with a liquid treatment composition comprising a red dye, and wherein the logos were partially removed by an erasing liquid.

EXAMPLES

(10) In the following, measurement methods implemented in the examples are described.

1. Methods and Materials

(11) Photographs

(12) Images of the prepared samples were recorded with the document detector PF-3000 (Ribao Technology, China).

(13) Substrates

(14) S1: Ticket of Münchner Verkehrs-und Tarifverbund (MVV), commercially bought from ticket machine in Munich, Germany. S2: Ticket of Deutsche Bahn AG (DB), commercially bought from ticket machine in Stuttgart, Germany. S3: Ticket of Schweizerische Bundesbahnen (SBB), commercially bought from ticket machine in Oftringen, Switzerland. The thermochromic coating layer of the ticket paper includes calcium carbonate as filler.
Liquid Treatment Composition L1: 41 wt.-% phosphoric acid, 24 wt.-% ethanol, and 35 wt.-% water (wt.-% are based on the total weight of the liquid treatment composition). L2: 41 wt.-% phosphoric acid, 24 wt.-% ethanol, 34 wt.-% water, and 1 wt.-% Amaranth red (wt.-% are based on the total weight of the liquid treatment composition).
Erasing Liquid

(15) Potassium hydroxide solution (1.0 M).

2. Examples

(16) Tamper-proof tickets were prepared by applying the liquid treatment composition onto the above-mentioned substrates in form of a preselected pattern (guilloche or logo “mosaiq”) with an inkjet printer (Dimatix DMP 2800, Fujifilm Dimatix Inc., USA) with varying droplet sizes between 1 and 10 pl (pico litre) at varying drop spacings between 10 to 40 am.

Example 1—Guilloche Pattern with Different Colour Intensities

(17) Guilloche patterns were printed on substrate S1 with different amounts of liquid treatment composition L1, wherein the amount was controlled by varying the droplet size and drop spacing:

(18) TABLE-US-00001 TABLE 1 Printing conditions and colour of printed guilloche pattern. Sample Droplet size [pl] Drop spacing [μm] Colour of pattern 1 10 30 black colour 2 1 30 grey colour 3 1 40 pale grey colour

(19) Magnifications of the different printed guilloche patterns are shown in FIG. 1. It is clearly visible from said figure that by the inventive method a coloured pattern can be formed on the thermochromic coating layer of a substrate. Furthermore, the colour intensity can be controlled by adjusting the droplet size and drop spacing.

Example 2—Erasing of Guilloche Pattern

(20) A guilloche pattern was printed on substrate S2 with a droplet size of 1 pl and a drop spacing of 30 m using liquid treatment composition L1. An image of the printed substrate is shown in FIG. 2, wherein the guilloche pattern is clearly visible on the bottom right.

(21) Subsequently, a part of the original thermal print within the guilloche pattern was gently wiped with a cloth soaked with the erasing liquid. Said treated area is highlighted in FIG. 2 by a dashed square. It can be gathered from FIG. 2 that said treatment resulted in an almost complete erasing of both the thermal print and the later added guilloche pattern.

(22) FIG. 3 shows a magnification of the original thermal print of substrate S2 in the section highlighted in FIG. 2 by the dashed square.

(23) FIG. 4 shows the same section after application of the liquid treatment composition. The guilloche pattern is clearly visible. FIG. 5 shows the same spot after it has been treated with the erasing liquid. Both the thermal print and the guilloche pattern formed by the inventive method have been almost completely erased. An infrared image of the same region is shown in FIG. 6.

(24) Thus, Example 2 confirms that by the inventive method a tamper-proof medium can be manufactured.

Example 3—Erasing of Thermal Print and Guilloche Pattern on Calcium Carbonate Containing Substrate

(25) A guilloche pattern was printed on substrate S3 with a droplet size of 1 pl and a drop spacing of 30 am using liquid treatment composition L1.

(26) Subsequently, a part of the original thermal print within the guilloche pattern was gently wiped with a cloth soaked with the erasing liquid. A magnified infrared image of treated area is shown in FIG. 7. It can be gathered from said figure that the treatment resulted in a complete erasing of both the thermal print and the later added guilloche pattern. Moreover, the application of the liquid treatment composition resulted in a build-up of a water-insoluble calcium phosphate salt, which cannot be removed.

(27) Therefore, by including a salifiable alkaline or alkaline earth compound filler into the thermal paper, an additional security feature can be created.

Example 4—Erasing of a Thermal Print and a Logo Created by a Liquid Treatment Composition Containing a Dye

(28) A logo was printed on substrate S1 with a droplet size of 10 pl and a drop spacing of am using liquid treatment composition L1. In addition, a logo was printed on substrate S1 under the same conditions using the liquid treatment composition L2, which contains a red dye.

(29) Images of the printed substrates are shown in FIG. 8, wherein the logo on the right side was printed with liquid treatment composition L1 and the logo on the left side was printed with liquid treatment composition L2.

(30) Subsequently, a part of the printed area was gently wiped with a cloth soaked with the erasing liquid. Said treated areas are highlighted in FIG. 9 by dashed squares. It can be gathered from FIG. 9 that the logo printed with liquid treatment composition L1 is almost completely erased (FIG. 9, right), while the logo printed with the liquid treatment composition L2 remains as a red print, and thus, is still visible (see FIG. 9, left).

(31) Therefore, by including a dye into the thermal paper, an additional security feature can be created.