Substrates secure against unauthorized copying and their production

The invention relates to substrates bearing visible information that is secure against unauthorized copying obtained by applying information in the form of combinations of at least one emitting colorant and at least one reflecting colorant that are selected to exhibit similar or identical hues when viewed, with no cognizance being taken of fluorescence, and are applied in such a manner that their color fields touch, wherein the color loci of the two colorants correspond to one of the trichromatic colors yellow, magenta, or cyan and the reflecting colorant is an organic or inorganic pigment.

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 .lambda..sub.max), in the reflectance
 spectrum is &lt;150 nm, preferably &lt;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 patterns may be produced.
 The invention further provides a process for producing 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 hue upon viewing with no cognizance being taken of
 fluorescence are similar or identical, and at the same time the colour
 loci of the two colorants correspond to one of the trichromatic colours
 yellow, magenta or cyan and the reflecting colorant is an organic or
 inorganic pigment, characterized in that the information is applied in
 such a manner by means of the colorant combination that the various colour
 fields touch.
 Colorant pairs useful in the process according to the invention have
 already been described above.
 The process according to the invention may be carried out for example in
 various techniques. These include intaglio printing, flexographic
 printing, offset printing, gravure printing, screen printing, ink-jet
 printing, thermal transfer printing, electrophotography, etc. However, it
 is also possible for colour and/or printed films to be applied to the
 substrate, for example by adhering.
 One possible way of the invention consists for example in printing paper
 with the emitting and the reflecting colorant in the form of a pattern in
 which the areas printed with the various colorants should touch. The
 printing ink includes for example the colorants as colour pigments
 (reflecting and/or emitting colorants) or as dye-pigmented plastics
 powders or polymer dispersions (emitting colorant) in binders customary
 for printing inks.
 Examples of useful plastics powders are polyacrylonitrile, polyesters,
 polycarbonate, epoxy resin, melamine-formaldehyde resins; examples of
 useful dispersions are styrene-acrylates, polyurethanes or polyureas.
 Instead of paper it is similarly possible to print other materials, for
 example nonwovens, polymeric films or platelets.
 As well as the colorants according to the invention, the substrates may
 also include other colorants, for example in printed form, in order that
 the desired design may be conferred on the substrate to be secured.
 After printing, the substrates may be coated with a transparent film or a
 lacquer. These may include for example UV absorbers or other light
 stabilizers. The photostability of the colorants may be enhanced in this
 way.
 The substrate according to the invention is secure in all paper techniques
 for generating colour copies of originals. These are for example
 electrophotography (colour copiers), photography, lithography via
 corresponding colour separations (print preparation), digital electronic
 scanning, for example based on CCD, possibly followed by electronic data
 processing and any desired printing process (laser printers or LED
 printers based on photoconductive drums, ink-jet printers, thermal
 transfer, diffusion or sublimation printers, AgX printers.
 If the scope for varying possible hues in the present invention is to be
 increased, it is further possible to modify the colorant combination for
 example by adding a reflecting colorant selected from the group consisting
 of magenta and cyan to the emitting as well as to the reflecting colorant
 component of the colorant combination.
 The invention therefore further 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 two colorants whose colour loci
 correspond to the trichromatic colour yellow, the reflecting colorant
 being an organic or inorganic pigment, have added to them a reflecting
 colorant whose colour locus corresponds to the trichromatic colour magenta
 or cyan.
 The added colorant is preferably a colorant of the trichromatic colour
 cyan.
 The reflecting colorant to be added is preferably likewise an inorganic or
 organic pigment, especially an organic pigment.
 The emitting colorant of this aspect of the invention is preferably a
 mixture of a fluorescent yellow and a nonfluorescent magenta or cyan. The
 reflecting colorant of this aspect of the invention is preferably a
 mixture of a nonfluorescent yellow and a nonfluorescent magenta or cyan.
 The substrate according to the invention particularly preferably includes
 colorant pairs where the absorption band of the yellow fluorescent
 colorant component prior to addition of the reflecting colorant is with no
 cognizance being taken of fluorescence ideally completely identical to the
 absorption band of the standard printing colour yellow and the yellow
 component of the reflecting colorant mixture corresponds to the yellow
 standard printing colour. The magenta and cyan components of the emitting
 and reflecting colorant mixtures each preferably correspond to the
 magenta-colour and the cyan-colour standard printing colour respectively
 and are nonemitting.
 The emitting and reflecting colorant mixtures preferably include the same
 amount of the magenta or cyan component.
 The colorant combination of the trichromatic colour yellow is otherwise
 subject to the preferred ranges indicated above.
 Particular preference is given to a colorant combination of this embodiment
 of the invention which is characterized in that the emitting and the
 reflecting colorant are each a mixture of a colorant of the trichromatic
 colour yellow and of the trichromatic colour magenta in a mixing weight
 ratio of 300:1 to 50:1, preferably 200:1 to 100:1.
 Preference is likewise given to a colorant combination of this embodiment
 of the invention which is characterized in that the emitting and the
 reflecting colorant are each a mixture of a colorant of the trichromatic
 colour yellow and of the trichromatic colour cyan in a mixing weight ratio
 of 300:1 to 2:1, preferably 100:1 to 10:1.
 The abovementioned mixing ratios are to be understood as applying in the
 case of identical or approximately identical colour strengths for the
 components emitting yellow, reflecting yellow and reflecting magenta or
 emitting, yellow, reflecting yellow and reflecting cyan. The ratios must
 be appropriately converted in the case of colour strength differences.
 If, for example, the emitting yellow component is only half as strong in
 colour as the reflecting yellow component, then the emitting colorant
 mixture is subject to mixing ratios of for example emitting yellow to
 reflecting cyan of 600:1 to 4:1, preferably 200:1 to 20:1, subject to the
 proviso that the cyan component is approximately as strong in colour as
 the reflecting yellow component. The same logic applies when the colour
 strengths of the yellow and cyan components differ. Such adaptations are
 necessary in particular when it is not pure colorants but preparations
 which are used.
 Such preparations are for example dispersions of colorants in suitable use
 media, for example oils, resins, binders, water, solvents or mixtures
 thereof.
 The preferred reflecting colorants to be added are the reflecting cyan and
 magenta colorants already mentioned above.
 In a substrate according to the invention, a pattern fabricated from one of
 the above colorant combinations according to the invention, if visible in
 the original, appears as a monochrome spot in the copy. For this a
 plurality of colorant combinations can be used simultaneously in order
 that complex colour patterns may be produced.
 A particular embodiment of the invention further provides a process for
 producing substrates bearing visible information applied thereto and
 secure against unauthorized copying, which is characterized in that the
 two colorants whose colour loci correspond to the trichromatic colour
 yellow, the reflecting colorant being an organic or inorganic pigment,
 have added to them a reflecting colorant whose colour locus corresponds to
 the trichromatic colour magenta or cyan.
 Colorant pairs useful in the process according to the invention are those
 already described above. Similarly, production and use corresponds
 essentially to the above description.

EXAMPLES
 Example 1
 Two offset printing plates were produced in known manner, one bearing the
 word "ORIGINAL" as positive, the other as negative. An offset printing
 press was then used to print the word "ORIGINAL" onto paper by means of
 the first printing plate using a printing ink produced from 900 g of the
 pigment preparation BO-115 "Lemon Yellow".RTM. from Sinloihi, Tokyo,
 Japan, a polymer powder coloured with a fluorescent dye and 100 g of
 linseed oil. In a second printing process, the second printing plate was
 used together with the printing ink Novavit HKS 3N.RTM. "Yellow" from K &
 E (Karst & Eichinger) Stuttgart to print a rectangular field around the
 word "ORIGINAL", so that there was finally a rectangular yellow area which
 contained the word "ORIGINAL" in fluorescent yellow without gap. This word
 was readily visible and legible to the human eye.
 This print was copied on a colour copier. The copy showed a yellow
 rectangle in which the word "ORIGINAL" was no longer visible, since it had
 been reproduced in the same hue as the surrounding rectangle.
 The original print and the copy have the following calorimetric data:

L* a* b*
 Original print "ORIGINAL" 97.4 -20.7 96.0
 Rectangle 85.6 3.4 94.2
 Copy "ORIGINAL" 86.4 -6.9 76.2
 Rectangle 86.3 -6.9 76.5
 Example 2
 Example 1 was repeated, except that the word "ORIGINAL" was printed using a
 printing ink produced from 900 g of the pigment preparation BO-117
 "Pink".RTM. from Sinloihi, Tokyo, Japan, a polymer powder colour with a
 fluorescent dye and 100 g of linseed oil. The surrounding rectangle was
 printed with the printing ink Novavit.RTM. HKS 27K "Magenta" from K & E
 (Karst & Eichinger) Stuttgart. This finally produced a rectangular
 magenta-colour area which contained the word "ORIGINAL" in fluorescent red
 without gap. This word was readily visible and legible to the human eye.
 This print was copied on a colour copier. The copy showed a magenta-colour
 rectangle in which the word "ORIGINAL" was no longer visible, since it had
 been reproduced in the same hue as the surrounding rectangle.
 On reading the print with a scanner and printing it out via an inkjet
 printer, this likewise produced a magenta-colour rectangle in which the
 word "ORIGINAL" was no longer visible, since it had been reproduced in the
 same hue as the surrounding rectangle.
 The original print, the copy and the inkjet printout have the following
 calorimetric data:

L* a* b*
 Original print "ORIGINAL" 61.6 85.7 -10.3
 Rectangle 53.4 67.2 -16.7
 Copy "ORIGINAL" 51.7 58.2 -27.4
 Rectangle 51.6 55.3 -20.0
 Inkjet printout "ORIGINAL" 49.1 51.2 2.2
 Rectangle 48.8 51.3 4.4
 Example 3
 Example 1 was repeated to produce in conventional manner two flexographic
 printing plates which again featured the word "ORIGINAL" once positively
 and once negatively.
 The first printing plate was then used together with the aqueous pigment
 preparation SP-15 "Lemon Yellow".RTM. from Sinloihi, Tokyo, Japan, a
 polyacrylic resin colour with a fluorescent dye, to print the word
 "ORIGINAL" onto paper. In a second printing process, the second printing
 plate was used together with the 1:10 water-diluted aqueous polymer
 dispersion of Pigment Yellow 74 (LEVANYL.RTM. Yellow 5GN-LF from Bayer AG,
 Leverkusen) to print a rectangular field around the word "ORIGINAL", to
 finally produce a rectangular yellow area which contained the word
 "ORIGINAL" in fluorescent yellow without gap. This word was readily
 visible and legible to the human eye.
 This print was copied on a colour copier. The copy showed a yellow
 rectangle in which the word "ORIGINAL" was no longer visible, since it had
 been reproduced in the same hue as the surrounding rectangle.
 Lightfastness: "ORIGINAL": 3
 Rectangle: 4
 The original print and the copy have the following colorimetric data:

L* a* b*
 Original print "ORIGINAL" 86.3 -40.4 44.2
 Rectangle 71.0 -21.1 29.2
 Copy "ORIGINAL" 70.6 -24.6 31.8
 Rectangle 70.7 -25.3 28.0
 Example 8
 Example 7 was repeated except that the two mixtures of aqueous pigment
 dispersions, instead of 0.05 part, contained only 0.1 part of the aqueous
 pigment dispersion of Pigment Blue 15:3, LEVANYL.RTM. Blau G-LF from Bayer
 AG, Leverkusen.
 This gave a rectangular green area containing the word "ORIGINAL" in
 fluorescent green. This word was readily visible and legible to the human
 eye.
 This print was copied on a colour copier. The copy showed a green rectangle
 in which the word "ORIGINAL" was no longer visible, since it had been
 reproduced in the same hue as the surrounding rectangle.
 The original print and the copy have the following calorimetric data:

L* a* b*
 Original print "ORIGINAL" 78.8 -44.8 38.3
 Rectangle 66.2 -23.3 21.7
 Copy "ORIGINAL" 62.6 -30.5 25.0
 Rectangle 67.1 -27.8 19.6
 Example 9
 Example 7 was repeated, except that the following two mixtures of aqueous
 pigment dispersions were used:
 For the word "ORIGINAL": Mixture of 10 parts of the aqueous pigment
 preparation SP-15 "Lemon Yellow" from Sinloihi, Tokyo, Japan, a
 polyacrylic resin coloured with a fluorescent dye and 0.01 part of an
 aqueous pigment dispersion of Pigment Red 122, BAYSCRIPT.RTM. Magenta
 VP-SP 25012 from Bayer AG, Leverkusen.
 For the surrounding rectangle: Mixture of 1 part of a pigment dispersion of
 Pigment Yellow 74, LEVANYL.RTM. Yellow 5GN-LF from Bayer AG, Leverkusen,
 0.01 part of an aqueous pigment dispersion of Pigment Red 122,
 BAYSCRIPT.RTM. Magenta VP-SP 25012 from Bayer AG, Leverkusen, and 9 parts
 of water.
 This gave a rectangular yellowish orange area which contained the word
 "ORIGINAL" in fluorescent yellowish orange. This word was readily visible
 and legible to the human eye.
 LEVANYL.RTM. Yellow 5GN-LF is 10 times as high as SP-15 "Lemon Yellow" and
 1.5 times as strong in colour as BAYSCRIPT.RTM. Magenta VP-SP 25012.
 This print was copied on a colour copier. The copy showed a yellowish
 orange rectangle in which the word "ORIGINAL" was no longer visible, since
 it had been reproduced in the same hue as the surrounding rectangle.
 The original print and the copy have the following colorimetric data: