Method for creating a hidden pattern

Abstract

The present invention relates to a method for creating a hidden pattern on a substrate, wherein a liquid treatment composition comprising at least one acid is deposited by inkjet printing onto a substrate, which comprises at least one external surface comprising a salifiable alkaline or alkaline earth compound.

Claims

1. A method for creating a hidden pattern on an assembly, which is invisible when viewed at a first angle relative to a surface of the assembly, and visible when viewed from a second angle relative to the surface of the assembly, the method comprising the following steps: a) providing an assembly, wherein the assembly comprises (i) a substrate comprising at least one external surface of the substrate, (ii) the substrate and a laminate, or (iii) the substrate and a coating layer, wherein the at least one external surface, the laminate or the coating layer comprises a salifiable alkaline or alkaline earth compound, b) providing a liquid treatment composition comprising at least one acid, and c) applying the liquid treatment composition onto the at least one external surface, the laminate or the coating layer in a form of a preselected pattern by inkjet printing to form a hidden pattern created by reaction of the at least one acid of the liquid treatment composition with the salifiable alkaline or alkaline earth compound, wherein the liquid treatment composition is applied in a form of drops having a volume of less than or equal to 1000 pl, and at a drop spacing of less than or equal to 1000 m.

2. The method of claim 1, wherein the assembly comprises a laminate comprising the salifiable alkaline or alkaline earth compound or a coating layer comprising the salifiable alkaline or alkaline earth compound.

3. The method of claim 1, wherein the substrate is selected from the group consisting of paper, cardboard, containerboard, plastic, non-wovens, cellophane, textile, wood, metal, glass, mica plate, marble, calcite, nitrocellulose, natural stone, composite stone, brick, concrete, and tablet, any laminate of said group, and any composite of said group.

4. The method of claim 1, wherein the substrate is paper, cardboard, containerboard or plastic.

5. The method of claim 1, wherein the assembly comprises a laminate or a coating layer, and the laminate or coating layer and the substrate of step a) are made from the same material.

6. The method of claim 1, wherein the salifiable alkaline or alkaline earth compound is an alkaline or alkaline earth oxide, an alkaline or alkaline earth hydroxide, an alkaline or alkaline earth alkoxide, an alkaline or alkaline earth methylcarbonate, an alkaline or alkaline earth hydroxycarbonate, an alkaline or alkaline earth bicarbonate, an alkaline or alkaline earth carbonate, or any mixture thereof.

7. The method of claim 1, wherein the salifiable alkaline or alkaline earth compound is lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium magnesium carbonate, calcium carbonate, or any mixture thereof.

8. The method of claim 1, wherein the salifiable alkaline or alkaline earth compound is calcium carbonate.

9. The method of claim 1, wherein the salifiable alkaline or alkaline earth compound is ground calcium carbonate, a precipitated calcium carbonate, a surface-treated calcium carbonate, or any mixture thereof.

10. 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, and any mixture thereof.

11. 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, oxalic acid, boric acid, suberic acid, succinic acid, sulphamic acid, tartaric acid, and any mixture thereof.

12. The method of claim 1, wherein the at least one acid is phosphoric acid and/or sulphuric acid.

13. The method of claim 1, wherein the liquid treatment composition further comprises 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, magnetic particles, or any mixture thereof.

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

15. The method of claim 1, wherein the liquid treatment composition comprises the acid in an amount from 3 to 60 wt.-%, based on a total weight of the liquid treatment composition.

16. The method of claim 1, wherein the preselected pattern is a one-dimensional bar code, a two-dimensional bar code, a three-dimensional bar code, a security mark, a number, a letter, an alphanumeric symbol, a logo, an image, a shape or a design.

17. The method of claim 1, wherein the liquid treatment composition is applied in a form of drops having a volume of from 100 pl to 10 fl.

18. The method of claim 1, wherein the liquid treatment composition is applied in a form of drops at a drop spacing of from 1 m to 500 m.

19. The method of claim 1, wherein the method further comprises a step d) of applying a protective layer and/or a printing layer above a region comprising the hidden pattern.

20. An assembly comprising a hidden pattern obtained by the method according to claim 1.

21. The assembly of claim 20, wherein the hidden pattern differs from the at least one external surface, the laminate, or the coating in one or more of surface roughness, gloss, light absorption, electromagnetic radiation reflection, fluorescence, phosphorescence, magnetic property, electric conductivity, whiteness and brightness.

22. The assembly of claim 20, wherein the hidden pattern comprises a security feature and/or a decorative feature.

23. The assembly of claim 20, wherein the hidden pattern comprises a one- dimensional bar code, a two-dimensional bar code, a three-dimensional bar code, a security mark, a number, a letter, an alphanumeric symbol, a logo, an image, a shape or a design.

24. A product comprising the assembly according to claim 20, wherein the product is a branded product, a security document, a non-secure document, or a decorative product, a perfume, a drug, a tobacco product, an alcoholic drug, a pharmaceutical product, a dietary product, a bottle, a garment, a packaging, a container, a sporting good, a toy, a game, a mobile phone, a CD, a DVD, a blue ray disk, a machine, a tool, a car part, a sticker, a label, a tag, a poster, a passport, a driving licence, a bank card, a credit card, a bond, a ticket, a tax stamp, a banknote, a certificate, a brand authentication tag, a business card, a greeting card, or a wall paper.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a scanning electron microscope (SEM) micrograph of a surface comprising a coating layer, which was inkjet printed with a liquid treatment composition with different drop spacings using a drop volume of 10 pl. The numbers in the figure indicate the drop spacing in m for the particular printed area.

(2) FIG. 2 shows a scanning electron microscope (SEM) micrograph of a surface comprising a coating layer, which was inkjet printed with a liquid treatment composition with different drop spacings using a drop volume of 1 pl. The numbers in the figure indicate the drop spacing in m for the particular printed area.

(3) FIG. 3 shows a scanning electron microscope (SEM) micrograph of a surface comprising a coating layer and a hidden pattern in form of a logo.

(4) FIG. 4 shows an optical microscope picture of a surface comprising a coating layer and a hidden pattern in form of a logo.

(5) FIG. 5 shows an optical microscope picture of a surface comprising a coating layer and a hidden pattern in form of a logo.

(6) FIG. 6 shows an optical microscope picture of a surface comprising a coating layer and a hidden pattern in form of a logo.

(7) FIG. 7 shows a photograph of a packaging box, which comprises hidden patterns illuminated with top ambient light.

(8) FIG. 8 shows a photograph of a packaging box, which comprises hidden patterns illuminated with ambient light at an angle of 35 relative to the surface of the substrate.

(9) FIG. 9 shows a photograph of a packaging box, which comprises hidden patterns illuminated with ambient light at an angle of 20 relative to the surface of the substrate.

(10) FIG. 10 shows a photograph of two dietary supplement tablets, wherein the right tablet comprises a hidden pattern, illuminated with top ambient light.

(11) FIG. 11 shows a photograph of two dietary supplement tablets, wherein the right tablet comprises a hidden pattern, illuminated with ambient light at an angle of 20 relative to the surface of the tablet.

(12) FIG. 12 shows a photograph of a printed substrate comprising a hidden pattern and an offset overprint, illuminated with ambient light at an angle of 20 relative to the surface of the substrate.

(13) FIG. 13 shows a photograph of a printed substrate comprising a hidden pattern and a rotogravure overprint, illuminated with ambient light at an angle of 20 relative to the surface of the substrate.

EXAMPLES

(14) 1. Measurement Methods

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

(16) Scanning Electron Microscope (SEM) Micrographs

(17) The prepared patterned samples were examined by a Sigma VP field emission scanning electron microscope (Carl Zeiss AG, Germany) and a variable pressure secondary electron detector (VPSE) with a chamber pressure of about 50 Pa.

(18) Optical Microscope Pictures

(19) The prepared patterned samples were examined by a Leica MZ16A stereomicroscope (Leica Microsystems Ltd., Switzerland).

(20) X-Ray Diffraction (XRD) Analysis

(21) The samples were analysed with a Bruker D8 Advance powder diffractometer obeying Bragg's law. This diffractometer consisted of a 2.2 kW X-ray tube, a sample holder, a - goniometer, and a VNTEC-1 detector. Nickel-filtered Cu K radiation was employed in all experiments. The profiles were chart recorded automatically using a scan speed of 0.7 per minute in 2 (XRD GV_7600). The resulting powder diffraction pattern was classified by mineral content using the DIFFRAC.sup.suite software packages EVA and SEARCH, based on reference patterns of the ICDD PDF 2 database (XRD LTM_7603).

(22) 2. Materials

(23) Salifiable Alkaline Earth Compounds

(24) CC1: ground calcium carbonate (d.sub.50: 1.5 m, d.sub.98: 10 m), pre-dispersed slurry with solids content of 78%, commercially available from Omya AG, Switzerland. CC2: ground calcium carbonate (d.sub.50: 0.7 m, d.sub.98: 5 m), pre-dispersed slurry with solids content of 78%, commercially available from Omya AG, Switzerland. CC3: aragonitic precipitated calcium carbonate (A-PCC) (d.sub.50: 0.45 m, d.sub.98: 2 m), pre-dispersed slurry with solids content of 72%, commercially available from Omya AG, Switzerland. CC4: ground calcium carbonate (d.sub.50: 0.21 m, d.sub.98: 0.85 m), pre-dispersed slurry with solids content of 55%. CC5: ground calcium carbonate (d.sub.50: 0.5 m, d.sub.98: 3 m), pre-dispersed slurry with solids content of 78%, commercially available from Omya AG, Switzerland. KA1: pre-dispersed kaolin slurry with solids content of 72%, fineness: residue on a 45 m sieve (ISO 787/7), particles <2 m (Sedigraph 5120), commercially available from Omya AG, Switzerland.
Binders B1: Starch (C*-Film 07311), commercially available from Cargill, USA. B2: Styrene-butadiene latex (Styronal D628), commercially available from BASF, Germany. B3: Rheology modifier (Sterocoll FS), commercially available from BASF, Germany.
Surface-Coated Substrates S1: Impermeable polypropylene flexible film (basis weight: 62 g/m.sup.2), commercially available from Synteape/Yupo, Oji-Yuka Synthetic Paper Company Ltd., Japan. S2: Z-Offsetkarton, Z-Mail Supra, (basis weight: 170 g/m.sup.2), commercially available from Ziegler Papier, Switzerland.

(25) Surface-coated substrates were prepared by equipping substrate S1 or S2, respectively, with one or more coating layers having the composition indicated in Table 1 below. The coating was carried out with a tabletop K202 Control Coater (RK PrintCoat Instruments Ltd., Great Britain).

(26) TABLE-US-00001 TABLE 1 Composition of coating layers (wt.-% are based on the total weight of the mineral compound). Coating layer Mineral compound Binder A 100 wt.-% CC2 10 wt.-% B2 B 100 wt.-% CC1 6 wt.-% B1 3 wt.-% B2 0.05 wt.-% B3 C 70 wt.-% CC2 10 wt.-% B2 30 wt.-% KA1 D 100 wt.-% CC3 10 wt.-% B2 0.05 wt.-% B3 E 100 wt.-% CC4 10 wt.-% B2

(27) TABLE-US-00002 TABLE 2 Composition of substrates (in case two coating layers are present, the first one is the pre-coating being in contact with the substrate surface and the second one represents the external surface layer). Surface-coated Coating Coating layer thickness substrate Substrate layer [g/m.sup.2] 1 S1 A 10 2 S2 B (pre-coat) 20 C 15 3 S2 B (pre-coat) 20 D 15 4 S3 B (pre-coat) 20 E 15 S3: Double coated paper having a basis weight of 90 g/m.sup.2. The pre-coat of the double coated baseboard had a coat weight of 10 g/m.sup.2 and was composed of 100 pph CC1, and 6 pph B2. The top coat of the double coated baseboard had a coat weight of 8.5 g/m.sup.2 and was composed of 100 pph CC5, and 8 pph B2.
Liquid Treatment Compositions L1: 41 wt.-% phosphoric acid, 23 wt.-% ethanol, and 36 wt.-% water (wt.-% are based on the total weight of the liquid treatment composition). L2: 3.7 wt.-% sulphuric acid, 19.2 wt.-% ethanol, 77.1 wt.-% water (wt.-% are based on the total weight of the liquid treatment composition).
3. Examples

Example 1Inkjet Printing of Arrays

(28) A preselected pattern in form of an array was created on the surface-coated substrate 1 by applying either liquid treatment composition L1 or L2. The liquid treatment compositions were deposited onto the substrate by inkjet printing using a Dimatix Materials Printer (DMP) of Fujifilm Dimatix Inc., USA, with a cartridge-based inkjet printhead having a drop volume of either 1 pl or 10 pl. The print direction was from left to right, one row (line) at a time. The liquid treatment compositions were applied onto the substrates with a drop volume of 1 pl and 10 pl, respectively, and using different drop spacings. The results of said prints were inspected visually and are compiled in Tables 3 and 4 below.

(29) TABLE-US-00003 TABLE 3 Results of inkjet printing tests with different drop spacing using a drop volume of 10 pl and either liquid treatment composition L1 or L2. Drop Amount of liquid Amount of printed spacing treatment Surface acid per area [ml/m.sup.2] [m] composition [ml/m.sup.2] coverage L1 L2 5 400 Oversaturation 164 14.8 10 100 Oversaturation 41.0 3.70 15 44 Oversaturation 18.0 1.63 20 25 Full coverage 10.3 0.93 25 16 Full coverage 6.56 0.59 30 11 Small gaps 4.51 0.41 35 8.0 Small gaps 3.28 0.30 40 6.3 Gaps 2.58 0.23 50 4.0 Individual dots 1.64 0.15 60 2.8 Individual dots 1.15 0.10 70 2.0 Individual dots 0.82 0.07 80 1.6 Individual dots 0.66 0.06 90 1.2 Individual dots 0.49 0.04 100 1.0 Individual dots 0.41 0.04

(30) TABLE-US-00004 TABLE 4 Results of inkjet printing tests with different drop spacing using a drop volume of 1 pl and either liquid treatment composition L1 or L2. Drop Amount of liquid Amount of printed spacing treatment Surface acid per area [ml/m.sup.2] [m] composition [ml/m.sup.2] coverage L1 L2 5 40 Oversaturation 16.4 1.48 10 10 Overlapping 4.10 0.37 15 4.4 Full coverage 1.80 0.16 20 2.5 Full coverage 1.03 0.093 50 0.4 Individual dots 0.16 0.015

(31) FIGS. 1 and 2 show scanning electron microscope (SEM) micrographs of the substrates that were printed with liquid treatment composition L1. The numbers on the top of the figures indicate the drop spacing in m for a particular pattern. Said images clearly show that by varying the drop volume and the drop spacing filled areas, individual rows or individual dots can be prepared. In addition, FIG. 2 shows a magnified section of a surface area, wherein one single drop of the liquid treatment composition has been deposited. It can be seen from said magnification that the structure of the treated surface area differs from the surrounding surface structure.

(32) X-ray diffraction (XRD) measurements were performed on the printed areas of the substrates printed with liquid treatment composition L1, a drop volume of 10 pl and a drop spacing of 10, 15, 20, 25, and 30 m using rotatable PMMA specimen holder rings. Comparison of the measured data sets with ICDD reference patterns revealed that all samples consisted of calcite and additional phases, which were formed by the application of the liquid treatment composition. The results are summarized in Table 5 below.

(33) TABLE-US-00005 TABLE 5 Results of XRD measurements. Drop spacing [m] Mineral name Formula 10 15 20 25 30 Calcite CaCO.sub.3 23 22 38 39 55 Calcium phosphate CaP.sub.2O.sub.6 5 14 13 6 Calcium oxide hydrate CaO.sub.2(H.sub.2O).sub.8 17 16 5 Monetite (calcium CaHPO.sub.4 20 21 28 hydrogen phosphate) Calcium hydrogen Ca(H.sub.2PO.sub.4).sub.2H.sub.2O 77 73 5 4 2 phosphate hydrate Calcium phosphate hydrate Ca.sub.2P.sub.2O.sub.74H.sub.2O 5 7 3

(34) The results confirm that the surface of the surface-coated substrate was modified by the application of the liquid treatment composition L1 and that the hidden pattern comprises acid salts of the salifiable alkaline earth compound calcium carbonate. Since the area measured by XRD was a circle with a diameter of 6 mm, and the analysis goes through the substrate (not only the outermost surface is analysed), there is trend in a decreasing amount of remaining non-converted calcium carbonate (calcite) with a lower drop spacing (larger amount acid per area). With a higher amount of phosphoric acid per area, the phosphate containing compounds increase relatively.

Example 2Inkjet Printing of a Hidden Pattern in Form of a Logo

(35) Preselected patterns in form of a logo, two-dimensional bar code, and security marks were created on substrates 1 to 4 by applying liquid treatment composition L1. The liquid treatment composition was deposited onto the substrate by inkjet printing using a Dimatix Materials Printer (DMP) of Fujifilm Dimatix Inc., USA, with a cartridge-based inkjet printheads having a drop volume of 1 pl or 10 pl, respectively. The print direction was from left to right, one row (line) at a time. The liquid treatment composition was applied onto surface-coated substrate 1 with a drop volume of 1 pl and a drop spacing of 15 m, and onto surface-coated substrates 2 to 4 with a drop volume of 10 pl and a drop spacing of 30 m.

(36) The results of said prints were inspected by scanning electron and optical microscopy. A SEM micrograph of the created logo is shown in FIG. 3 and optical microscope images of the created logo are presented in FIGS. 4 to 6. As can be gathered from said images, the application of the liquid treatment composition results in a pattern on the surface-coated substrate, which clearly stands out on the remaining non-printed area.

(37) A picture of printed substrate 2 illuminated at top ambient light is shown in FIG. 7. As can be gathered from said figure, the hidden patterns are invisible for the human eye at an illumination angle of about 90 relative to the surface of the substrate. FIGS. 8 and 9 show the same printed substrate at an illumination angle of 355 and 205, respectively. These figures show that by decreasing the illumination angle the hidden logo (1), the hidden two-dimensional bar code (2), and the hidden security marks (3) become visible. For illumination a RB 5055 HF Lighting Unit (Kaiser Fototechnik GmbH & Co. KG, Germany) was used. The printed substrates were placed in the centre of the mid table of the lighting unit and were illuminated with one of the two lamps, wherein the distance between the substrates and the centre of the lamp was about 50 cm.

Example 3Inkjet Printing of a Hidden Pattern in Form of a Logo on a Tablet

(38) A preselected pattern in form of a logo was created on the surface of a commercially available effervescent calcium carbonate containing tablet (Calcium-Sandoz forte 500 mg, Hexal AG, Germany), by applying liquid treatment composition L1. The liquid treatment composition was deposited onto the tablet by inkjet printing using a Dimatix Materials Printer (DMP) of Fujifilm Dimatix Inc., USA, with a cartridge-based inkjet printheads having a drop volume of 10 pl. The print direction was from left to right, one row (line) at a time. The liquid treatment composition was applied onto the tablet with a drop volume of 10 pl and a drop spacing of 25 m.

(39) The result of said print was inspected visually. Pictures of the non-printed, original tablet (left tablet) and the printed tablet (right tablet) illuminated at top ambient light are shown in FIG. 10. As can be gathered from said figure, the hidden pattern is invisible for the human eye at an illumination angle of about 90 relative to the surface of the substrate. FIG. 11 shows the same tablets at an illumination angle of 205. This figure reveals that by decreasing the illumination angle the hidden logo on the right tablet become visibles. For illumination a RB 5055 HF Lighting Unit (Kaiser Fototechnik GmbH & Co. KG, Germany) was used. The printed tablets were placed in the centre of the mid table of the lighting unit and were illuminated with one of the two lamps, wherein the distance between the tablets and the centre of the lamp was about 50 cm.

Example 4Inkjet Printing of a Hidden Pattern and Offset Overprint

(40) Preselected patterns in form of a logo and squares were created on substrate S3 by applying liquid treatment composition L1. The liquid treatment composition was deposited onto the substrate by inkjet printing using a Dimatix Materials Printer (DMP) of Fujifilm Dimatix Inc., USA, with a cartridge-based inkjet printheads having a drop volume of 10 pl. The print direction was from left to right, one row (line) at a time. The liquid treatment composition was applied onto the substrate with a drop volume of 10 pl. The drop spacing of the squares was 25, 30, 40, 50 and 80 m and the drop spacing of the logo was 25 m.

(41) The patterns were overprinted with 100% coverage using a commercially available offset ink (Novavit X 800 Skinnex, Flint Group Germany GmbH, Germany) and the printer SeGan ISIT ink surface interaction tester (Segan, Great Britain) without the tack measuring unit.

(42) The result of said print was inspected visually. A picture of the printed substrate illuminated at an angle of 2005 is shown in FIG. 12. As can be gathered from said figure, the hidden pattern is visible for the human eye when viewed at said angle. At an illumination angle of about 90 relative to the surface of the substrate, the squares and the logo were invisible (not shown). For illumination a RB 5055 HF Lighting Unit (Kaiser Fototechnik GmbH & Co. KG, Germany) was used. The printed substrate was placed in the centre of the mid table of the lighting unit and were illuminated with one of the two lamps, wherein the distance between the substrate and the centre of the lamp was about 50 cm.

Example 5Inkjet Printing of a Hidden Pattern and Rotogravure Overprint

(43) Preselected patterns in form of a logo and squares were created on substrate S3 by applying liquid treatment composition L1. The liquid treatment composition was deposited onto the substrate by inkjet printing using a Dimatix Materials Printer (DMP) of Fujifilm Dimatix Inc., USA, with a cartridge-based inkjet printheads having a drop volume of 10 pl. The print direction was from left to right, one row (line) at a time. The liquid treatment composition was applied onto the substrate with a drop volume of 10 pl. The drop spacing of the squares was 30, 40 and 50 m and the drop spacing of the logo was 30 m.

(44) The patterns were overprinted with a rotogravure gradient 100% to 0% using a commercially available rotogravure ink (10-115395-5.1650, Siegwerk Druckfarben AG & Co. KGaA, Germany) and the laboratory gravure printing system Labratester I (nsm Novert Schlfli AG, Switzerland).

(45) The result of said print was inspected visually. A picture of the printed substrate illuminated at an angle of 205 is shown in FIG. 13. As can be gathered from said figure, the hidden pattern is visible for the human eye when viewed at said angle. At an illumination angle of about 90 relative to the surface of the substrate, the squares and the logo were invisible (not shown). For illumination a RB 5055 HF Lighting Unit (Kaiser Fototechnik GmbH & Co. KG, Germany) was used. The printed substrate was placed in the centre of the mid table of the lighting unit and were illuminated with one of the two lamps, wherein the distance between the substrate and the centre of the lamp was about 50 cm.