METHOD OF TAGGING A SUBSTRATE

Abstract

The present invention relates to a method of tagging a substrate with a covert, spectroscopically detectable security feature, wherein a liquid treatment composition comprising at least one acid is deposited onto a substrate, which comprises at least one external surface comprising a salifiable alkaline or alkaline earth compound.

Claims

1.-15. (canceled)

16. A method of verifying the authenticity of a product, comprising the following steps: I) providing a product with a tagged substrate comprising a covert, spectroscopically detectable security feature, II) recording a spectrum of the substrate by a spectroscopic method, and III) detecting the presence of the security feature by comparing the recorded spectrum with a library of spectra of tagged substrates, wherein the tagged substrate comprising the covert, spectroscopically detectable security feature is obtainable by a method comprising the following steps: a) providing a substrate, wherein the substrate comprises at least one external surface comprising a salifiable alkaline or alkaline earth compound, b) providing a liquid treatment composition comprising at least one acid, c) applying the liquid treatment composition onto at least one region of the at least one external surface to form at least one surface-modified region on or within the at least one external surface, and d) applying an opaque top layer over the at least one surface-modified region obtained in step c).

17. The method of claim 16, wherein the substrate comprises the salifiable alkaline or alkaline earth compound in the form of a filler material.

18. The method of claim 16, wherein the product is a branded product, a security document, a non-secure document, a decorative product, a drug, a tobacco product, an alcoholic drug, a bottle, a garment, a packaging, a container, a sporting good, a toy, a game, a mobile phone, a compact disc (CD), a digital video disc (DVD), a blue ray disc, 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 postage or tax stamp, a banknote, a certificate, a brand authentication tag, a business card, a greeting card, or a wall paper.

19. The method of claim 16, wherein the tagged substrate is suitable for use in security applications, in overt security elements, in covert security elements, in brand protection, in microlettering, in micro imaging, in decorative applications, in artistic applications, or in packaging applications.

20. The method of claim 16, wherein the at least one external surface of step a) is in the form of a laminate or a coating layer comprising the salifiable alkaline or alkaline earth compound.

21. The method of claim 16, 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 laminates or composites thereof.

22. The method of claim 16, wherein the substrate is selected from the group consisting of paper, cardboard, containerboard, or plastic.

23. The method of claim 16, wherein (i) the at least one external surface and the substrate of step a) are made from the same material.

24. The method of claim 16, 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, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium magnesium carbonate, calcium carbonate, ground calcium carbonate, a precipitated calcium carbonate, a surface-treated calcium carbonate, or mixtures thereof.

25. The method of claim 16, wherein the salifiable alkaline or alkaline earth compound is selected from lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium magnesium carbonate, calcium carbonate, or mixtures thereof.

26. The method of claim 16, 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 organosulphur 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.

27. The method of claim 16, 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 mixtures thereof.

28. The method of claim 16, wherein the at least one acid is phosphoric acid and/or sulphuric acid.

29. The method of claim 16, 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, quantum dots, or a mixture thereof.

30. The method of claim 16, wherein the liquid treatment composition comprises the acid in an amount from 0.1 to 100 wt.-%, based on the total weight of the liquid treatment composition.

31. The method of claim 16, wherein the liquid treatment composition is applied in the form of a continuous layer, a pattern of repetitive elements, or repetitive combination(s) of elements, circles, dots, triangles, rectangles, squares, or lines.

32. The method of claim 16, wherein the opaque top layer is a top coat, a pigment layer, an overprint, a metal coating, a metal foil, a fibre layer, a laminate, a polymer foil, or a paper.

33. The method of claim 16, wherein the spectroscopic method is selected from the group consisting of infrared spectroscopy, X-ray spectroscopy, and combinations thereof.

34. The method of claim 16, wherein the spectroscopic method is selected from the group consisting of FTIR spectroscopy, X-ray diffractometry (XRD), energy dispersive X-ray spectroscopy (EDS), and combinations thereof.

35. The method of claim 16, wherein the spectroscopic method is selected from the group consisting of FTIR spectroscopy, energy-dispersive X-ray spectroscopy (EDS), and combinations thereof.

Description

DESCRIPTION OF THE FIGURES

[0243] FIGS. 1 to 5 show X-ray diffractograms of comparative substrates.

[0244] FIGS. 6 to 13 show X-ray diffractograms of tagged substrates according to the present invention.

[0245] FIGS. 14 and 15 show X-ray diffractrograms of comparative substrates.

[0246] FIG. 16 shows an SEM/EDS analysis of a tagged substrate according to the present invention.

[0247] FIG. 17 shows an SEM/EDS analysis of a tagged substrate according to the present invention.

[0248] FIG. 18 shows an SEM/EDS micrograph of a cross-section of a tagged substrate according to the present invention.

[0249] FIG. 19 shows an SEM/EDS micrograph of a cross-section of a tagged substrate according to the present invention.

[0250] FIGS. 20 to 24 show FTIR spectra of comparative substrates and tagged substrates according to the present invention.

[0251] FIG. 25 shows FTIR spectra of comparative substrates.

[0252] FIGS. 26 to 29 show graphs of LA-ICP-MS measurements of comparative substrates and tagged substrates according to the present invention.

[0253] FIG. 30 shows FTIR spectra of a comparative substrate and a tagged substrate according to the present invention.

[0254] FIG. 31 shows FTIR spectra of calcium hydrogenphosphate and tagged substrates according to the present invention.

[0255] FIGS. 32 and 33 show an SEM/EDS analysis of a tagged substrate according to the present invention.

[0256] FIGS. 34 and 35 show SEM/EDS micrographs of a cross-section of a tagged substrate according to the present invention.

EXAMPLES

[0257] In the following, measurement methods implemented in the examples are described.

1. Methods

Scanning Electron Microscope (SEM) Micrographs

[0258] The prepared 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.

X-Ray Diffraction (XRD) Analysis

[0259] The prepared 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 θ-θ goniometer, and a VÅNTEC-1 detector. Nickel-filtered Cu Kα radiation was employed in all experiments. The profiles were chart recorded automatically using a scan speed of 0.7° per minute in 2θ (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).

[0260] Quantitative analysis of the diffraction data, i.e. the determination of amounts of different phases in a multi-phase sample, has been performed using the DIFFRAC.sup.suite software package TOPAS (XRD LTM_7604). This involved modelling the full diffraction pattern (Rietveld approach) such that the calculated pattern(s) duplicated the experimental one.

[0261] Semi-Quantitative (SQ) calculations to estimate the rough mineral concentrations were carried out with the DIFFRAC.sup.suite software package EVA. The semi-quantitative analysis was performed considering the patterns relative heights and I/I.sub.cor values (I/I.sub.cor: ratio between the intensities of the strongest line in the compound of interest and the strongest line of corundum, both measured from a scan made of a 50-50 by weight mixture).

Energy-Dispersive X-Ray (EDS) Analysis

[0262] The prepared samples were examined by a Sigma VP field emission scanning electron microscope (Carl Zeiss AG, Germany). The backscattered electron images were recorded in COMPO-Mode with a chamber pressure of about 50 Pa in order to visualize differences in the chemical composition of the sample. The heavier the atomic weight of the elements present, the brighter the particle appears in the image.

[0263] The energy-dispersive X-ray images were recorded with an Oxford X-Max SDD-detector (Silicon Drift Detector) 50 mm.sup.2 (Oxford Instruments PLC, United Kingdom) and chamber pressure about 40-90 Pa (40-60 Pa for surfaces/approx. 90 Pa for cross-sections). Dot-mappings and EDS-analysis were taken with the energy dispersive x-ray detector (EDS). The EDS-detector determines the chemical elements of a sample and can show the position of the elements in the sample.

Fourier-Transform Infrared (FTIR) Analysis

[0264] The FTIR spectra of the samples were recorded by a Spectrum One™ FTIR spectrometer, commercially available from PerkinElmer, Inc., USA. The ATR crystal was a 3 bounce diamond/zinc selenide crystal. The scan speed was 0.2 cm/s, the resolution was 4.0 cm.sup.−1, the range was 4 000 to 550 cm.sup.−1. 10 scans per spectrum were made. The analysis of the bands was done by comparing to reference material and/or a data library.

2. Materials

Substrate

[0265] S1: Commercially available paper, pre-coated with a coating layer containing the pigments calcium carbonate, kaolinite, and talc. An X-ray diffraction spectrum of this paper is shown in FIG. 1 and a quantitative Rietveld analysis can be found in Table 2 (data are presented in % and are normalized to 100% crystalline material). [0266] S2: Commercially available, eucalyptus fiber-based, uncoated paper having a basis weight of 90 g/m.sup.2 and containing 36 wt.-% calcium carbonate as filler (based on total dry paper weight) and a minor amount optical brightener. A FTIR spectrum of said paper is shown in FIG. 30 (sample 18).

Pigment

[0267] Ground calcium carbonate (d.sub.50: 0.7 μm, d.sub.98: 5 μm), pre-dispersed slurry with solids content of 78%, commercially available from Omya AG, Switzerland, under the tradename Hydrocarb 90.

Binder

[0268] Styrene-acrylate latex (Acronal S728), commercially available from BASF, Germany.

Liquid Treatment Compositions

[0269] L1: 33.3 vol.-% phosphoric acid (85%), 33.3 vol.-% ethanol (95%, technical grade), and 33.4 vol.-% water (vol.-% are based on the total volume of the liquid treatment composition). [0270] L2: 16.7 vol.-% sulphuric acid (95-98%), 16.7 vol.-% ethanol (95%, technical grade), 66.6 vol.-% water (vol.-% are based on the total weight of the liquid treatment composition).

3. Examples

3.1. Example 1

[0271] Tagged substrates were produced by applying one of the liquid treatment compositions L1 and L2 onto substrate S1. This was done by applying the treatment composition continuously onto the substrate S1 at room temperature within a distance from the external surface of about 15 cm, using an air brush attached to the in-house pressure line. The air brush was operated at a pressure of 2 bar. The type and amount of applied liquid treatment composition is indicated in Table 1 below. After the liquid treatment composition has dried, the obtained surface-modified region was over-coated with an opaque top layer formulation comprising the pigment and the binder mentioned above. The coating was carried out with laboratory tabletop rod coater (K202 Control Coater, RK PrintCoat Instruments Ltd., United Kingdom). The composition of the coating formulation was 100 pph pigment and 8 pph binder, wherein the “pph” values are weight based. For a coat weight of 14 g/m.sup.2, the solids content of the coating formulation was 65 wt.-%, based on the total weight of the coating formulation, and for a coat weight of 7 g/m.sup.2, the solids content was 42 wt.-%, based on the total weight of the coating formulation. The prepared samples were dried under hot air at 150° C. after coating.

[0272] The obtained opaque top layer had a white colour and a final binder concentration of 8 wt.-%, based on the total weight of pigment. The layer weights of the produced top layers are indicated in Table 1 below.

[0273] In addition, comparative samples without a surface modification and with or without an opaque top layer have been prepared. The prepared tagged substrates and comparative substrates are listed in Table 1 below.

TABLE-US-00001 TABLE 1 Prepared tagged substrates and comparative substrates. liquid Applied amount of liquid coat weight top treatment treatment composition layer Sample composition [ml/m.sup.2] [g/m.sup.2]  1 — — — (comparative)  2 L1 2 — (comparative)  3 L1 6 — (comparative)  4 L2 2 — (comparative)  5 L2 6 — (comparative)  6 L1 2 14  7 L1 6 14  8 L2 2 14  9 L2 6 14 10 L1 2  7 11 L1 6  7 12 L2 2  7 13 L2 6  7 14 — — 14 (comparative) 15 — —  7 (comparative)

[0274] The obtained tagged substrates and comparative substrates were analysed by X-ray diffractometry, energy-dispersive X-ray spectroscopy, FTIR spectroscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

Results of X-Ray Diffractometry

[0275] FIGS. 1 to 15 show X-ray diffraction spectra and qualitative phase analysis of the spectra of samples 1 to 15. Comparison of the measured spectra with ICDD reference patterns revealed that all samples consisted of calcite, kaolinite and talc. The treated substrates contained additional phases, which were formed by the application of the liquid treatment compositions. The results are summarized in Table 2 below.

TABLE-US-00002 TABLE 2 Results of quantitative Rietveld analysis of the prepared substrate samples. Data are presented in % and are normalized to 100% crystalline material. Sample Mineral 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Calcite 76 40 29 79 34 80 66 79 70 79 58 70 53 90 87 CaCO.sub.3 Kaolinite 17 18 18 8 12 8 7 7 6 9 10 10 7 7 9 Al.sub.2Si.sub.2O.sub.5(OH).sub.4 Talc 7 5 3 3 5 3 4 2 5 4 5 2 7 3 4 Mg.sub.3Si.sub.4O.sub.10(OH).sub.2 Calcium — 38 50 — — — — — — — — — — hydrogen phosphate hydrate Ca(H.sub.2PO.sub.4)2•H.sub.2O Brushite — — — — — 9 23 — — 8 27 — — Ca(HPO.sub.4)•2H.sub.2O Gypsum — — — 10 49 — — 12 19 — — 18 33 CaSO.sub.4

Results of Energy-Dispersive X-Ray (EDS) Spectroscopy

[0276] The results of the EDS analysis confirmed that all samples consisted of calcite, kaolinite and talc. Additional phases, which were formed by the application of the liquid treatment compositions, could be detected for the treated substrates. A map of the crystal phosphor-containing phases of sample 10 is shown in FIG. 16, wherein the phosphor-containing phases are highlighted in white. FIG. 17 shows a map of the crystal sulphur-containing phases of sample 15, wherein the sulphur-containing phases are highlighted in white. SEM pictures showing cross-sections of samples 10 and 15 are shown in FIGS. 18 and 19.

Results of FTIR Spectroscopy

[0277] The analysis of the measured FTIR spectra revealed that the samples which were treated with the liquid treatment compositions show characteristic phosphate or sulphate bands, respectively.

[0278] As can be gathered from the FTIR spectra of comparative samples 1, 2, and 3 shown in FIG. 20, the dihydrogenphosphate bands are clearly visible in samples 2, and 3, which were treated with the liquid treatment composition L1 containing phosphoric acid. The bands were identified on the basis of a reference spectrum of Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O, which is also shown in FIG. 20.

[0279] FIG. 21 shows the FTIR spectra of comparative samples 1, 4, and 5. The gypsum bands are clearly visible in samples 4, and 5, which were treated with the liquid treatment composition L2 containing sulphuric acid. The bands were identified on the basis of a reference spectrum of calcium sulphate dihydrate, which is also shown in FIG. 21.

[0280] FIG. 22 shows the FTIR spectra of comparative sample 1, and inventive samples 6 and 7. The inventive samples show medium to weak phosphate bands between 1 250 and 950 cm.sup.−1. FIG. 23 shows the FTIR spectra of comparative sample 1, and inventive samples 10 and 11. The inventive samples show medium to weak phosphate bands between 1 650 and 950 cm.sup.−1. FIG. 24 shows the FTIR spectra of comparative sample 1, and inventive samples 15 and 16. The inventive samples show characteristic gypsum bands at 1 119.5 cm.sup.−1 (the main gypsum bands typically occur between 1 100 and 1 130 cm.sup.−1).

[0281] A comparison of the FTIR spectra of comparative sample 1, and comparative sample 14, which contains an opaque top layer but has not been treated with a liquid treatment composition, is shown in FIG. 25.

[0282] The results of the IR band analysis are compiled in Table 3 below.

TABLE-US-00003 TABLE 3 Results of analysis of FTIR spectra. Sample phosphate band sulphate band other bands 1 — — cellulose and CaCO.sub.3 2 ++ — — (dihydrogen phosphate) 3 ++ — — (dihydrogen phosphate) 4 — +++ — (gypsum) 5 — +++ — (gypsum) 6 + — — 7 + — — 10 +++ — — 11 +++ — — 12 — + — (gypsum) 13 — + — (gypsum) (+++: strong band, ++: medium band, +: weak band).

Results of LA-ICP-MS

[0283] Inductively coupled plasma mass spectrometry combined with laser ablation was used to analyse samples 2, 6, 8, and 10.

[0284] A laser ablation unit (ESI NWR213 laser ablation system, Electro Scientific Industries, Inc., USA) with a He gas flow of 0.6 l/min was used to scan over a line length of ca 8500 μm, with a laser spot diameter of 60 g at a speed of 40 μm/s. The laser power was set on 40%. For inductively coupled plasma mass spectrometry (ICP-MS), a Perkin Elmer Elan DRC-e (PerkinElmer Inc., USA) was used to count the ions detected (phosphor and sulphur), using a total dwell time of 390 ms per cycle, a lens voltage of 6 V, and a nebulizer gas flow of 0.66 l/min.

[0285] The results of the LA-ICP-MS measurements are shown in FIGS. 26 to 29, which show the amount (number) of counted ions, as function of a scanned line (length in micrometers). For the samples 2, 6 and 10 detection was made for phosphor (see FIGS. 16, 27, and 29). For sample 8, detection was made for sulphur (see FIG. 28). The variation in detected counts per micrometer is due to the uneven distribution of the very small amount of the applied liquid treatment compositions. The LA-ICP-MS measurements confirm that the LA-ICT-MS method is capable of detecting the elements of the additional phases, which were formed by the application of the liquid treatment composition, at a high precision.

[0286] The results of the X-ray diffractometry, energy-dispersive X-ray spectroscopy, FTIR spectroscopy, and LA-ICT-MS confirm that by the inventive method a material modification can be created in a substrate, which can be detected by spectroscopic methods. Furthermore, due to the opaque top layer the created modifications are not visible to the naked eye, and, therefore, can be used as a covert security feature, which can only be traced with special equipment and knowledge on what to look for.

3.2. Example 2

[0287] Tagged substrates were produced by applying the liquid treatment composition L1 in an amount of 6 ml/m.sup.2 onto substrate S2. This was done by applying the treatment composition continuously onto substrate S2 at room temperature within a distance from the external surface of about 15 cm, using an air brush attached to the in-house pressure line. The air brush was operated at a pressure of 2 bar.

[0288] After the liquid treatment composition has dried, the obtained surface-modified region was over-coated with an opaque top layer formulation comprising the pigment and the binder mentioned above. The coating was carried out with laboratory tabletop rod coater (K202 Control Coater, RK PrintCoat Instruments Ltd., United Kingdom). The composition of the coating formulation was 100 pph pigment and 8 pph binder, wherein the “pph” values are weight based. The solids content of the coating formulation was 42 wt.-%, based on the total weight of the coating formulation, and the obtained coat weight was 7 g/m.sup.2. The prepared samples were dried under hot air at 150° C. after coating.

[0289] The obtained opaque top layer had a white colour and a final binder concentration of 8 wt.-%, based on the total weight of pigment.

[0290] The application of the liquid treatment composition L1 and the over-coating with the opaque top layer formulation was either carried out on the top side of substrate S2 (sample 16) or on the wire side of substrate S2 (sample 17).

[0291] The obtained tagged substrates (samples 16 and 17) and the untreated substrate S2 (comparative sample 18) were analysed by FTIR spectroscopy and energy-dispersive X-ray spectroscopy.

Results of FTIR Spectroscopy

[0292] The analysis of the measured FTIR spectra revealed that the samples which were treated with the liquid treatment composition L1 show characteristic phosphate bands.

[0293] As can be gathered from the FTIR spectra of samples 16 and 18 shown in FIG. 30, the inventive sample shows phosphate bands at 1213 cm.sup.−1, 1131 cm.sup.−1, 1057 cm.sup.−1, and 985 cm.sup.−1. The bands were identified on the basis of a reference spectrum of Ca(H.sub.2PO.sub.4).sub.2, which is shown in FIG. 31. Moreover, FIG. 31 confirms that the surface modifications could be successfully carried out on the top side as well as on the wire side of the uncoated paper substrate S2, and that the surface modification is easy to detect on each of the two sides.

Results of Energy-Dispersive X-Ray (EDS) Spectroscopy

[0294] The results of the EDS analysis confirmed that additional phases were formed by the application of the liquid treatment compositions, which can be detected by EDS spectroscopy. A map of the crystal calcium phase of inventive sample 16 is shown in FIG. 32, wherein the calcium-containing phases are highlighted in white, and a map of the crystal phosphor-containing phases of inventive sample 16 is shown in FIG. 33, wherein the phosphor-containing phases are highlighted in white. SEM pictures showing cross-sections of sample 16 are shown in FIGS. 34 and 35, wherein in FIG. 34 the calcium-containing phases are highlighted in white and in FIG. 35 the phosphor-containing phases are highlighted in white. It can be gathered from FIGS. 34 and 35 that crystal phases comprising calcium and phosphor are also formed in the opaque top layer.

[0295] The results of the FTIR spectroscopy and the energy-dispersive X-ray spectroscopy confirm that by the inventive method a material modification can be created in an uncoated substrate, which can be detected by spectroscopic methods. Furthermore, due to the opaque top layer the created modifications are not visible to the naked eye, and, therefore, can be used as a covert security feature, which can only be traced with special equipment and knowledge on what to look for.