Substrates secure against unauthorized copying and their...

Details Substrates secure against unauthorized copying and their... Substrates secure against unauthorized copying and their...

2000-03-29

2001-10-16

Lam, Cathy (Department: 1775)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S029000, C428S199000, C428S211100, C428S916000, C283S072000, C283S902000

Reexamination Certificate

active

06303213

ABSTRACT:

The invention relates to substrates secure against unauthorized copying and processes for their production.
There is a long-felt need for effective security against unauthorized copying. The literature contains a whole series of different proposals. Most of them are based on colouring the background of the original in order that the contrast may be reduced. Since the human eye and the sensor in the machine have different sensitivities for lightness values of colours, it has been attempted to darken the background during copying to a relatively larger extent for the sensor than for the eye. Not only reflecting dyes, in particular reds, but also fluorescent dyes have been mentioned for this purpose.
The introduction of colour copiers has further aggravated the problem. colours provide rapidly discernible information and are therefore widely used for marking, identifying, coding of articles, etc. A particular problem is the counterfeiting of securities, identity cards or the like by means of colour copies.
This problem is solved in DE-A-4,236,143 by a colorant combination of an emitting and a reflecting colorant whose hue is similar or identical in retroreflective light.
It was found that, surprisingly, a substrate whose two colorants correspond to one of the trichromatic colours yellow, magenta or cyan and are distinctly more stable to the action of light permits universal use.
The invention provides substrates bearing visible information applied thereto which are secure against unauthorized copying and to which the information was applied using a colorant combination of at least one emitting and at least one reflecting colorant such that their hues upon viewing with no cognizance being taken of fluorescence are similar or identical, in such a manner that the various colour fields touch, characterized in that the colour loci of the two colorants then correspond to one of the trichromatic colour yellow, magenta or cyan and the reflecting colorant is an organic or inorganic pigment.
The trichromatic colour in question are preferably yellow or magenta.
The reflecting colorant is again preferably an organic pigment.
The trichromatic colour are defined by the following parameters in the CIELAB system at medium depth of shade:
nonfluorescent
fluorescent
Yellow:
L*
80 to 90
 95 to 105
a*
−10 to +10
−01 to −25
b*
 40 to 100
 20 to 100
Magenta
L*
45 to 60
70 to 90
a*
40 to 70
45 to 90
b*
−10 to −30
−10 to −25
Cyan
L*
45 to 60
a*
−20 to −40
b*
−30 to −50
Preferably, the b* value in the Lab system of the yellow emitting colorant is 20 to 100, that of a magenta-coloured emitting colorant is −30 to −10 and that of a cyan-coloured emitting colorant is −50 to −30.
Particularly preferably, the b* values of the emitting colorant differ by less than 10 units from the b* value of the reflecting colorant.
The substrate according to the invention preferably includes pairs of colourants whose colour locus in the context of the above-recited CIELAB ranges comes very close to one of the standard printing colour yellow or magenta under DIN 16539. Particularly preferably the substrate includes colorant pairs where the absorption band of the fluorescent colorant is with no cognizance being taken of fluorescence virtually completely identical to the absorption band of a standard printing colour (yellow, magenta) and the reflecting colorant corresponds to such a standard printing colour. Preferably their absorption maxima in the reflectance spectrum are not more than 30 nm apart, especially not more than 20 nm apart. Preference is given to colorant pairs whose full width at half maximum value, i.e. the spectral width of the longest-wavelength band at half maximum absorbance (E/2 at &lgr;
max
), in the reflectance spectrum is <150 nm, preferably <100 nm. In the case of soluble fluorescent dyes, the full width at half maximum value of the absorption spectrum in solution can be applied.
Methods for measuring reflectance spectra are generally known, for example from colour Physics for Industry, Roderick McDonald, ed., Society of Dyers and colourists, 1987, especially pages 152-169. Similarly the measurement of reflectance spectra of fluorescent colorants is known and permits for example not only the measurement of the reflectance inclusive of the emission due to fluorescence but also the pure reflectance with elimination of the contributions due to fluorescence (pages 152-169). It is this last method of measurement which is meant when the colour loci and reflectance curves of the colorant pair are compared “with no cognizance being taken of fluorescence”.
Such colorant combinations are independent of the type of copying machine in their colour effect. They are also independent of the type of copying process.
The substrate according to the invention preferably further includes colorant pairs whose lightfastness is ideally identical, preferably differing by less than one point on the 8-point wool scale according to DIN 54004. Useful colorant combinations are in particular colorant combinations which do not change their shade, or change their shade in similar manner, on illumination. Preferably the lightfastness of the two colorants is at least 2, especially at least 3, on the 8-point wool scale according to DIN 54004.
Useful pigments include all colo pigments, preferably organic colour pigments.
Preferred reflecting colorants are:
C.I. Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 17, Pigment Yellow 74, Pigment Yellow 150, Pigment Red 2, Pigment Red 48:2, Pigment Red 57, 57: 1, Pigment Red 122, Pigment Violet 19 and Pigment Violet 23.
Preference is likewise given to pigments obtained from cationic or anionic reflecting dyes by precipitation as insoluble lakes of these dyes with appropriate counterions, for example calcium, barium (in the case of anionic dyes) or molybdatophosphate, tungstenatophosphate, molybdatosilicate, tungstenatosilicate or the anions of organic carboxylic and sulphonic acids (in the case of cationic dyes). Useful dyes for this purpose include for example C.I. Basic Yellow 29, Basic Yellow 99 and Basic Red 46.
Examples of preferred emitting colorants are:
C.I. Direct Yellow 131, Disperse Yellow 36, Disperse Yellow 58, Disperse Yellow 82, Disperse Yellow 199, Disperse Yellow 202, Solvent Yellow 98, Basic Yellow 40, Acid Yellow 184, Acid Yellow 215, 215:1, Acid Yellow 226, Acid Yellow 227, Acid Red 50, Acid Red 52, Acid Red 189, Disperse Red 227, Disperse Red 303, C.I. 45 160, C.I. 45 175, C.I. 45 170, C.I. 73 300, and also polymer powders or polymer dispersions coloured with these dyes, for example polymer powders or polymer dispersions based on polyacrylonitrile, polyacrylate, polymethacrylate, polystyrene or their copolymers with each other or with other polymerizable monomers such as, for example, butadiene, maleic anhydride, methallylsulphonic acid, styrenesulphonic acid, acrylamidopropanesulphonic acid, etc., polyesters, polyamide, polycarbonate, epoxy resins, melamine-formaldehyde resins, polyurethanes, polyureas, styrene-acrylates, and also lakes of these dyes with appropriate counterions, for example calcium, barium (in the case of anionic dyes) or molybdatophosphate, tungstenatophosphate, molybdatosilicate, tungstenatosilicate or the anions of organic carboxylic and sulphonic acids (in the case of cationic dyes).
The reflectance colorant may be composed of a plurality of colorants, making it possible to exactly conform the hue to the reflectance spectrum without fluorescence of the emissive partner.
Similarly, the fluorescence colorant may consist of mixtures which are preferably made up in such a way that no absorption occurs within the emission band.
In a substrate according to the invention, a pattern fabricated from a colorant combination according to the invention, if visible in the original, appears as a monochrome spot in the copy. For this a plurality of colorant combinations may be used simultaneously in order that complex colour patte

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