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Abstract

The present invention relates to a method of manufacturing a substrate with an embedded, UV-visible pattern, wherein a liquid treatment composition comprising at least one acid is deposited onto a substrate, which comprises at least one optical brightener and optionally a filler, wherein the filler comprises 0 to 60 wt.-% of a salifiable alkaline or alkaline earth compound, based on the total weight of the substrate.

Claims

1. A method of manufacturing a substrate with an embedded, UV-visible pattern, the method comprising the following steps: a) providing an uncoated substrate comprising at least one optical brightener and a filler, wherein the filler comprises from 0 to 60 wt.-% of a salifiable alkaline or alkaline earth compound, based on the total weight of the substrate, 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 substrate in form of a preselected pattern to form an embedded, UV-visible pattern.

2. The method of claim 1, wherein the filler comprises the salifiable alkaline or alkaline earth compound in an amount of at least 1 wt. %, based on the total weight of the substrate.

3. The method of claim 1, wherein the optical brightener is present in an amount of at least 0.001 wt. %, based on the total weight of the substrate.

4. The method of claim 1, wherein the optical brightener is selected from the group consisting of stilbene derivates, pyrazolin derivates, cumarin derivates, benzoxazol derivates, naphthalimide derivates, pyrene derivates, derivatives of diaminostilbenedisulfonic acid, derivatives of diaminostilbenetetrasulfonic acid, derivatives of diaminostilbenehexasulfonic acid, 4,4-diamino-2,2-stilbenedisulfonic acid, 4 4-bis(benzoxazolyl)-cis-stilbene, 2 5-bis(benzoxazol-2-yl)thiophene, 5-[(4-anilino-6-methoxy-1,3,5-triazin-2-yl)amino]-2-[(E)-2-[4-[(4-anilino-6-methoxy-1,3,5-triazin-2-yl)amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate (leucophor PC), and mixtures thereof.

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

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, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium magnesium carbonate, calcium carbonate, is a ground calcium carbonate, a precipitated calcium carbonate, a surface-treated calcium carbonate, or mixtures thereof.

7. The method of claim 1, wherein the salifiable alkaline or alkaline earth compound is in form of particles having a weight median particle size d.sub.50 from 15 nm to 200 m.

8. 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., HPO.sub.4.sup.2, being at least partially neutralized by a corresponding cation selected from Li, Na.sup.+, K.sup.+, Mg.sup.2+ or Ca.sup.2+, and mixtures thereof.

9. 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, lanthanides, actinides, magnetic particles, quantum dots, or a mixture thereof.

10. The method of claim 1, 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.

11. 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 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.

12. 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, reverse (counter-rotating) gravure coating, slot coating, curtain coating, slide bed coating, film press, metered film press, blade coating, brush coating, stamping and/or a pencil.

13. The method of claim 1, wherein the method further comprises a step d) of applying a protective layer above the embedded, UV-visible pattern.

14. A substrate comprising an embedded, UV-visible pattern, obtainable by a method according to claim 1.

15. A product comprising a substrate according to claim 14, wherein the product is a branded product, a security document, a non-secure document, a decorative product, a perfume, 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, a voucher, a tax banderol, or a wall paper.

16. The substrate of claim 14, wherein the 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, in visual applications, in packaging applications, or in track and trace applications.

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

18. The method of claim 1, wherein the salifiable alkaline or alkaline earth compound is in form of particles having a weight median particle size d.sub.50 from 100 nm to 10 m.

19. The method of claim 1, wherein the at least one acid is selected from the group consisting of sulphuric acid, phosphoric acid, boric acid, suberic acid, sulphamic acid, tartaric acid, and mixtures thereof.

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

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows an image of a substrate comprising an embedded, UV-visible pattern in form of a logo and a number series under ambient light.

(2) FIG. 2 shows an image of a substrate comprising an embedded, UV-visible pattern in form of a logo and a number series under ambient light with addition of UV light having a wavelength of 366 nm.

(3) FIG. 3 shows fluorescence spectra of a comparative substrate without any optical brightener or filler, and comparative substrate comprising calcium carbonate but no optical brightener.

(4) FIG. 4 shows fluorescence spectra of a comparative substrate and a substrate according to the present invention comprising an optical brightener.

(5) FIG. 5 shows fluorescence spectra of a comparative substrate and a substrate according to the present invention comprising an optical brightener and calcium carbonate.

EXAMPLES

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

1. Methods

(7) Photographs

(8) Images of the prepared samples were recorded with an EOS 600D digital camera equipped with a Canon Macro, EF-S 60 mm, 1:2.8 USM (Canon, Japan). UV light with a wavelength of 366 nm was provided by UV hand lamp NU-4, serial no. 10 31 002 H466.1 with a 366 nm, 4 watt tube (Herolab GmbH Laborgerte, Germany).

(9) Fluorescence Spectroscopy

(10) The prepared samples were examined with a LS 45 Fluorescence Spectrometer (PerkinElmer Inc., USA).

(11) CIE Lab Coordinates, Whiteness and Gloss

(12) The CIE lab coordinates of the prepared samples were recorded with a Techkon SP810 lambda densitometer (Techkon GmbH, Germany).

(13) The whiteness of the prepared samples was measured with a Techkon SpectroDens Premium densitometer (Techkon GmbH, Germany).

(14) The gloss of the prepared samples was measured at an incident angle of 85 (haze gloss) using a BYK-Gardner hazemeter (BYK-Gardner GmbH, Germany).

2. Materials

(15) Optical Brightener

(16) Tetrasulphonated optical brightener (Leucophor UHF), commercially available from Archroma Paper, Switzerland.

(17) Filler

(18) Precipitated calcium carbonate (d.sub.50=1.8 m, d.sub.98=8 m), commercially available from Omya AG, Switzerland. The precipitated calcium carbonate was provided in form of an undispersed, aqueous suspension having a solids content of 17 wt.-%.

(19) Liquid Treatment Composition

(20) 41 wt.-% phosphoric acid, 23 wt.-% ethanol, and 36 wt.-% water (wt.-% are based on the total weight of the liquid treatment composition).

3. Examples

Example 1Preparation of Paper Substrates

(21) 60 g (dry) pulp (100% eucalyptus 30 SR) were diluted in 10 dm.sup.3 tap water. Subsequently, the filler, if present, was added in an amount so as to obtain an overall filler content of 20 wt.-%, based on the final paper weight, and the optical brightener, if present, was added in an amount so as to obtain an overall content of 12 kg/ton, based on the final paper weight. The suspension was stirred for 30 minutes. Subsequently, 0.06% (based on dry weight) of a polyacrylamide derivate (Percol 1540, commercially available from BASF, Germany) was added as a retention aid and sheets of 80 g/m.sup.2 were formed using the Rapid-Kothen hand sheet former. Each sheet was dried using the Rapid-Kothen drier. The composition of the produced paper substrates is given in Table 1 below.

(22) TABLE-US-00001 TABLE 1 Compositions of prepared paper substrates (*based on the final paper weight). Substrate Filler amount [wt.-%*] Optical brightener [kg/t*] 1 (comparative) 2 12 3 (comparative) 20 4 20 12

Example 2Preparation of Embedded, UV-Visible Pattern

(23) A preselected pattern in form of a logo and a number series was created on substrates 1 to 4 prepared in Example 1 by applying the liquid treatment composition. 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 printhead having a drop volume of 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 10 pl and using different drop spacings. The optical properties of the prepared substrates were tested by determining the CIE lab coordinates, the whiteness, and the gloss at 850. The results are compiled in Table 2 below.

(24) TABLE-US-00002 TABLE 2 Optical properties of substrates with embedded, UV-visible pattern and comparative substrates. Amount of liquid treatment composition 4 ml/m.sup.2 6.3 ml/m.sup.2 11 ml/m.sup.2 Drop spacing 50 m 40 m 30 m Substrate 4 L 94.04 94.07 94.06 93.64 a 1.32 1.33 1.09 1.04 b 3.53 3.55 3.22 3.13 Whiteness (CIE) 104.2 103.8 101.4 100.8 Gloss (85) 2.0 2.1 2.3 2.6 Substrate 3 (comparative) L 93.67 93.66 93.32 93.39 a 0.14 0.13 0.15 0.15 b 1.12 1.12 1.02 0.96 Whiteness (CIE) 83.6 83.8 83.6 83.7 Gloss (85) 2.3 2.4 2.3 2.3 Substrate 2 L 90.69 90.31 90.33 90.62 a 1.64 1.23 1.21 1.14 b 4.63 3.77 3.61 3.32 Whiteness (CIE) 102.7 97.5 97 94.9 Gloss (85) 2.7 2.7 2.9 3.0 Substrate 1 (comparative) L 90.61 90.42 90.39 90.15 a 0.17 0.18 0.19 0.18 b 1.22 1.25 1.23 1.23 Whiteness (CIE) 77.6 76.2 75.6 76.5 Gloss (85) 3.0 2.8 2.9 2.9

(25) As can be gathered from Table 2, there is an observable change in CIE whiteness for the inventive substrates 2 and 4, which is due to the fact that the excitation light of the used densitometers contains some UV light (D65 standard light source). FIGS. 1 and 2 show images of the substrate 4, which was printed with 11 ml/m.sup.2 liquid treatment composition and a drop spacing of 30 m. While in FIG. 1, which was recorded at ambient light illumination, the printed logo and number series is not visible, the same is clearly visible in FIG. 2, which was recorded in the presence of UV light having a wavelength of 366 nm (the darker appearance of the image compared to FIG. 1 is a result of the greyscale conversion of the originally blue appearance of the surface caused by the UV light).

(26) FIGS. 3 to 5 show fluorescence spectra of printed substrates 1 to 4. As can be gathered from FIG. 4 the fluorescence main peak is decreased when the inventive substrate 2 containing the optical brightener is printed with the liquid treatment composition. FIG. 5 shows that the fluorescence main peak is increased when the inventive substrate 4 containing the optical brightener and the filler is printed with the liquid treatment composition. No change in fluorescence was observed for comparative substrates 1 and 3 (see FIG. 3).

(27) Thus, the results confirm that by using the method of the present invention substrates with embedded patterns can be prepared, wherein the pattern is invisible at ambient light but detectable under UV light.