Bar code printing and scanning using wax based invisible fluorescent inks

Wax based invisible inks have been discovered that emit light at various wavelengths in the visible region when they are excited by UV light. This allows lower layer clear text information to be written on an object with a regular, visible ink and an upper layer bar code to be written over the lower layer text information with an ink that is invisible to the naked eye. This allows the lower layer text information and upper layer bar code to contain more information than conventional bar codes. These inks allow printing and decoding invisible bar codes over printed information with visible inks. The detection by fluorescence of these invisible inks provides a high signal to noise ratio and no interference with the visible printed information.

CROSS REFERENCE TO RELATED APPLICATIONS 
Reference is made to commonly assigned patent application Ser. No. 
08/347,740, U.S. Pat. No. 5,542,971, filed herewith entitled "Bar Code 
Using Luminescent Invisible Inks" in the names of Judith Auslander and 
William Berson, U.S. Pat. No. 5,502,304, filed herewith entitles "Bar Code 
Scanner For Reading Luminescent Invisible Inks" in the names of William 
Berson and Judith Auslander and Ser. No. 08/547,629, U.S. Pat. No. 
5,525,798, filed herewith entitled "Bar Code Scanner For Reading A Lower 
Layer Luminescent Invisible Ink That Is Printed Below A Upper Layer 
Luminescent Invisible Ink" in the names of William Berson and Judith 
Auslander. 
FIELD OF THE INVENTION 
The invention relates generally to the field of encoding marks and more 
particularly to bar codes. 
Background of the Invention 
Bar codes have been used in a wide variety of applications as a source for 
information. Typically bar codes are used at a point-of-sale terminal in 
merchandising for pricing and inventory control. Bar codes are also used 
in controlling personnel access systems, mailing systems, and in 
manufacturing for work-in process and inventory control systems, etc. The 
bar codes themselves represent alphanumeric characters by series of 
adjacent stripes of various widths, i.e. the universal product code. 
A bar code is a set of binary numbers. It consists of black bars and white 
spaces. A wide black bar space signifies a one and a thin black bar or 
space signifies a zero. The binary numbers stand for decimal numbers or 
letters. There are several different kinds of bar codes. In each one, a 
number, letter or other character is formed by a certain number or bars 
and spaces. 
Bar code reading systems or scanners have been developed to read bar codes. 
The bar code may be read by having a light beam translated across the bar 
code and a portion of the light illuminating the bar code is reflected and 
collected by a scanner. The intensity of the reflected light is 
proportional to the reflectance of the area illuminated by the light beam. 
This light is converted into an electric current signal and then the 
signal is decoded. 
Conventional bar codes are limited in the amount of information they 
contain. Even two dimensional bar codes such as PDF-417 and Code-1 are 
limited to a few thousand bytes of information. The ability to encode 
greater information density is limited by the resolution of available 
scanning devices. 
The prior art has attempted to use colored bar codes to convey additional 
information. However, color printing is inherently analog and the 
fastness, reproducibility and selective delectability of colored bar code 
imprints as well as the impractically of reproducibly calibrating 
detection systems, prohibit their use for the digital encoding of 
additional information. 
Bar codes have been affixed to many different types of documents, so that 
they may be read by a machine, thereby reducing labor costs. Documents 
that include bar codes have been issued by governmental agencies, 
financial institutions, brokerage houses, etc., that authorize the holder 
of such documents to perform authorized tasks or grant rights to the 
holder of such a document. Examples of such documents are drivers 
licenses, entry access badges, identification cards, etc. In issuing such 
documents, it is desirable to have them of a convenient size, while 
including information necessary for identifying the holder of the document 
and the rights conferred. Thus, oftentimes, there is not enough room to 
include the bar code with all of the information one would want to include 
in the bar code. 
Another problem encountered by the prior art when bar codes were affixed to 
documents is that the bar codes were not to difficult to forge and could 
be easily copied, hence there was unauthorized use of the documents to 
which the bar codes were affixed. 
SUMMARY OF THE INVENTION 
This invention overcomes the disadvantages of the prior art by providing an 
invisible ink for printing bar codes on documents, including 
identification cards, mail pieces and drivers licenses, etc. The visible 
clear text printing is underneath the bar code and may be read. The 
invisible transparent bar code is printed with a UV excited pigment 
emitting in either the red or green regions of the visible. The 
formulation and choice of the pigment provides for a high signal to noise 
ratio in the scanner in that the detector is blind to the illumination 
source, but sensitive to the emitted signal. 
The invisible inks of this invention may be used in thermal transfer 
printing or in hot melt ink jet. 
The invisible inks used are based upon wax dispersions or solutions of 
invisible pigments in typical thermal transfer vehicles such as wax 
mixtures. 
The invisible fluorescent inks can contain organic pigments such as: 
derivatives benzoxazine and benzoxazinone or complexes of rare earth 
elements with ligands containing .beta. diketones of the general formula: 
##STR1## 
where R.sub.1 and R.sub.2 are identical radicals or different and can be: 
alkyl with C.sup.1 -C.sub.18 or halogenated alkyl of the same length, 
alkoxy, phenyl, substituted phenyl, furyl, substituted furyl, thienyl, 
substituted thionyland. Other printing technology and vehicle that can be 
used is the hot melt ink jet. Another ligand type is represented by the 
formula: 
##STR2## 
where: R.sub.3 is an alkyl group C.sub.1 -C.sub.18 or an halogenated alkyl 
with the same length. R4, R5, R6 and R7 are identical groups or different. 
(Another ligand that can be used is the dipicolinic acid). An example of 
ligand that bonds through Nitrogen ion is 2.2' bipyridine. 
##STR3## 
Where M is a L.sub.n.sup.3+ ion or any rare earth ion and X is an anion 
such as Cl or NO.sub.3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In order to better understand that which separates this invention from the 
prior art consider the following. Refer to the drawings in detail, and 
more particularly to FIG. 1 a prior art bar code 11 is printed on an 
object 12. Bar code 11 has a data track 13 and a clock track 14. A black 
bar 15 would indicate a binary one in the data track and a white space 16 
would indicate a zero in the data track. A black bar 17 would indicate a 
binary one in the clock track and a white space 18 would indicate a binary 
zero in the clock track. 
The information contained in bar code 11 is illuminated by light source 19, 
reflected by bar code 11 and read by scanner 20. 
Thus, FIG. 1 illustrates the amount of information that may be contained in 
a prior art black and white bar code. 
FIG. 2 is a drawing of the bar code of this invention. Lower layer clear 
text information 21 is printed on object 25 with a visible ink. Object 25 
is any surface known in the art in which inks may be printed on i.e.; 
paper, envelopes, cardboard, plastic, etc. 
An upper layer bar code 31 is printed over clear text information 21. Bar 
code 31 is printed with an invisible ink. Bar code 31 has a data tract 33 
and a clock track 34. A dark bar 36 or space containing ink would indicate 
a binary one in the data track and an empty space 37 or space containing 
no ink would indicate a zero in the data track. A dark bar 38 or space 
containing ink would indicate a binary one in the clock track and an 
empty, space or space containing no ink would indicate a binary zero in 
the clock track. 
It will be obvious to one skilled in the art that bar code 31 may be 
printed with an invisible ink on object 25 even though no clear text 
information 21 is printed on object 25. 
The inks that are used to print clear text information 21 and bar code 31 
may be applied using non impact printing methods i.e. thermal transfer, 
hot melt ink jet, etc. All the various mixtures of wax performing in these 
two technologies: thermal transfer or hot melt ink jet can be used. The 
inks used to print clear text information 21 and 31 are similar and may 
have similar reflectance wavelengths to the emission wavelength of the ink 
used to print bar code 31. The ink that is used to print bar code 31 is 
invisible to the naked eye and can be excited by ultra violet light. 
Examples of the ink that is used to print bar code 31 is based on wax 
dispersions or solutions of organic fluorescent pigments such as 
derivatives of benzoxazine and benzoxazinone and organic complexes of, 
rare earth elements (acetonates), such as: europium, gadolinium and 
terbium acetonates. 
The advantages of using the above luminescent pigments are that they are 
spectrally well defined and can be mechanically read at a high speed 
without physical contact. The luminescent excitation is obtained by UV 
radiation. The luminescent signals are relatively insensitive to the 
environment i.e., dirt, temperature, etc. The light fastness values are 
good for most practical applications and the inks have a high degree of 
specificity due to their discrete emission spectra. 
The invisible inks used are based on complexes of rare earth elements with 
an atomic number higher than 57 such as: Eu, Tb, Sm, Dy with various 
chelating agents providing chromophore ligands that absorb in the 
ultraviolet and the blue region of the spectra such as: p acetone and its 
derivatives etc. The luminescent emission in these complexes is due to 
inner transitions such as: .sup.5 D.sub.0 .fwdarw..sup.7 F.sub.1 and 
5D.sup.0 .fwdarw..sup.7 F.sub.2 for Europium. All of the above chelates of 
rare earth metals show a strong ultraviolet absorption in the ultraviolet 
region of the spectra. Through an internal conversion and systems 
interference part of this energy is transferred to the rare earth ion 
which is excited to the electronic level of luminescence. 
The ink that is used to print clear text information 21 is a regular ink 
which absorbs in the visible range of the spectrum between (400-700 nm) 
and has a print contrast signal with a background of more than 0.4. An 
example of the above ink is any black ink that is currently being used in 
an ink jet printer, i.e. the desk jet printer manufactured by Hewlett 
Packard. 
The general composition of the ink that is used to print bar code 31 is 
based on wax dispersions or solutions of invisible organic fluorescent 
pigments such as derivatives of benzoxazine and benzoxazinone or complexes 
of rare earth elements with ligands containing .beta. diketones. 
The main spectral emission characteristics of the pigments have to match 
the spectral response of the scanner's detector and conversely the scanner 
should be blind to the incident illumination of the excitation source. 
This eliminates the effects of spurious reflections which tend to lower 
the signal to noise ratio and degrade the detection efficiency. 
In the first implementation, the excitation light source is chosen to be in 
the UV range of 350-380 nm and the emission of the pigment is chosen to be 
in the range of either the red or the green visible. The detector is 
relatively insensitive in the UV range and may be made blind to the 
350-380 nm. by the addition of a filter. 
Particle size of the pigment must be selected to enhance the contrast 
between the detected signal and the background, therefore to give 
sufficient emission for adequate signal (adequate fluorescence quantum 
yield). Particle size which are read too small will have insufficient 
signal. Also, the particle size should be sufficiently small in order to 
provide a stable dispersion. 
The spectral characteristics are shown in FIG. 5. The average particle life 
of the organic pigments used herein is 1.5-2.8.mu.. 
The ink vehicle must be also chosen for compatibility so that the 
fluorescent emission is not absorbed. 
EXAMPLE 1 For Thermal Transfer Ink 
______________________________________ 
Manufacturer 
Ingredient (Trade Name) WT (gms) 
______________________________________ 
Lumilux Yellow CD 799 
Riedel de Haen 5.00 
Polyethylene wax-molecular 
(Polywax 500) 64.1 
weight 500, melting 
Petrolite 
point 88.degree. C. 
urethane derivative of 
(WB-17) 
synthetic wax Bareco Div., Petrolite 
7.2 
carnauba wax Strahl & Patsch Inc. 
8.2 
Ethyl Vinyl Acetate Polymer 
Dupont 15.5 
Ink properties 
Excitation 360 nm 
Emission 525 nm 
______________________________________ 
The ink was applied to a polyethylene tetraphthalate film with the results 
discussed below. 
The inks of the instant invention exhibit good adhesion to a thermal ribbon 
film and to a non-porous surface, such as plastic, when applied thereto in 
a thermal printing operation. These inks have the characteristics of a low 
melting point which results in good transferability, good flexibility for 
non-flaking, high hardness that yields high mechanical abrasion resistance 
and prevents smudging of the final print, water fastness, high light 
fastness and good contrast properties. The inks were found to have good 
slip and are free of blocking characteristics. 
The ink vehicle must be also chosen for compatibility so that the 
fluorescent emission is not absorbed. 
EXAMPLE 2 For Thermal Transfer Ink 
______________________________________ 
Manufacturer 
Ingredient (Trade Name) WT (gms) 
______________________________________ 
Lumilux Green CD 702 
Riedel de Haen 10 
Polyethylene wax-molecular 
(Polywax 500) 59.1 
weight 500, melting 
Petrolite 
point 88.degree. C. 
urethane derivative of 
(WB-17) 
synthetic wax Bareco Div., Petrolite 
7.2 
carnauba wax Strahl & Patsch Inc. 
8.2 
Ethyl Vinyl Acetate Polymer 
Dupont 15.5 
______________________________________ 
The main spectral emission characteristics of the fluorescent pigments used 
are: either organic of the benzoxazine or benzoxazione type, or inorganic 
such as silicates or terbium or europium. 
EXAMPLE 3 
______________________________________ 
Manufacturer 
Ingredient (Trade Name) 
WT (%) 
______________________________________ 
Benzoxazinone Riedel de Haen 
5 
derivative 
Lumilux Green CD 702 
Riedel de Haen 
wax emulsion Michelson 126 
Michelson 90 
Igepal 530 GAF 5 
Ink properties 
Emission peak 522 nm 
______________________________________ 
EXAMPLE 4 
______________________________________ 
Manufacturer 
Ingredient (Trade Name) 
WT (%) 
______________________________________ 
Benzoxazinone Riedel de Haen 
7 
derivative 
Lumilux Green CD 797 
Riedel de Haen 
wax emulsion Michelson 126 
Michelson 90 
Igepal 530 GAF 3 
Ink properties 
Emission peak 535 nm 
______________________________________ 
The invention is the ink, printing system and scanner for printing 
invisible or transparent bar-codes on documents, including identification 
cards, mail and drivers licenses. The visible clear text printing is 
underneath the bar-code and may be read. The invisible, transparent 
bar-code is printed with a UV-excited pigment emitting in either the red 
or green regions of the visible. The formulation and choice of pigment 
provides for a high signal-to-noise ration in the scanner in the detector 
is blind to the illumination source, but sensitive to the emitted signal. 
In production of drivers licenses, identification cards and other valuable 
documents, it is desirable to apply the use of bar-codes, especially 
encrypted bar-codes. 
The operation using the luminescent characteristics of the rare earth 
complexes are used as binary characteristics for their absence or 
prescience or they can be used at various intensities. The advantage is 
that the signal to noise ratio is extremely high for the invisible ink 
that allows a precision that can not be attained by identification of 
visible contrast. 
The invisible inks can be used also by varying the intensity and therefore 
encoding more information, but in this case the parasite signals can not 
be eliminated such as in the case of binary signals. 
The information contained in clear bar code 31 may be read by utilizing 
light sources 41. Source 41 is utilized to illuminated bar code 31. Source 
41 is a ultraviolet source that emits light between 240-400 nm. Detector 
44 is utilized to sense bar code 31. 
Detector 44 senses the emitted light from bar code 31. Detector 44 may be a 
photo diode or photo transistor. 
FIG. 3 is a graph of the emission of the invisible green ink used to print 
bar code 31 which was excited at 360 nm. 
FIG. 4 is a graph of the emission of the invisible red ink used to print 
bar code 31 which was excited at 360 nm. 
FIG. 5 is a graph showing the spectral characteristics of detector 44. 
The above embodiments have been given by way of illustration only, and 
other embodiments of the instant invention will be apparent to those 
skilled in the ad from consideration of the detailed description. 
Accordingly, limitations on the instant invention are to be found only in 
the claims.