Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
The present invention relates to inkless
fingerprinting systems used for identification pur-
poses. More specifically, it relates to compositions,
systems, and methods of generating instant, stable
fingerprints on various substrates without the need of
conventional inks and specially treated surfaces, and
without the use of any chemical or mechanical post-
treatment of the fingerprint or the surface on which
the fingerprint was made.
As used herein the term "fingerprints" also encom-
passes "footprints" such as those taken of newly-born
infants and placed on birth records. Also, the term
"inkless" means the absence of colored pigments such as
carbon black and as being distinct from printing inks
as such term is now understood in this art.
The fingerprint patterns or ridge endings and ridge
separations are highly individualized and are not
altered with time. The comparison of fingerprint pat-
terns has long been accepted as an absolute means of
20 identifying individuals in a multitude of criminal and
non-criminal situations.
In order for a fingerprinting identification system
to be commercially acceptable it must be extremely
stable and reliable, i.e., the prints must be distinct
and clear and must be easily readable by the human eye
and by automated fingerprint reading systems which are
finding increased usage especially with a number of law
enforcement agencies. Furthermore, the prints must
form instantaneously, and must possess a high degree of
stability toward exposure to extreme atmospheric con-
ditions such as temperature, humidity and light.
Preferably, the systems must be simple and aestheti-
cally inoffensive.
Traditionally, fingerprints have been made with
printing or writing types of ink, usually comprising
finely ground carbon black particles dispersed in a
liquid vehicle. The carbon black dispersion is ordi-
narily applied to a flat and firm surface, the excess
dispersion removed, transferred to the surface of the
object to be fingerprinted or identified, and sub-
sequently transferred to the surface of the substrate
where the final print is to be made. Such a procedureis cumbersome, time consuming and results in severe
soiling of the hands and clothing of everyone involved
in the fingerprinting process.
During the past several years inkless
fingerprinting systems have been proposed such as
disclosed in U.S. Patent No. 3,831,552 involving the
use of magnetizable powders. Other proposed inkless
systems utilize the chelation of specific metal salts
such as sodium vanadate with organic acids as described
in U.S. Patent No. 2,082,735, or various methods of
reacting 8-hydroxyquinoline with metal salts, and pre-
ferably ferric chloride, as described in U.S. Patents
Nos. 3,960,632, 4,262,623, and 4,379,178. Addition-
ally, U.S. Patent No. 4,232,083 discloses the use of
metal complexing compounds having a plurality of ligand
groups with transitional metal salts of oleophilic,
organic acids to form dark images which can be useful
in fingerprinting -:ystems.
The inkless fingerprinting systems known heretofore
possess varying degrees of undesirable properties.
Some are mechanically too complex to find commercial
application and others, especially those relying upon
metal-chelation reactions, are usually too slow and the
image of the fingerprint does not appear instan-
taneously and in some cases it takes long periods of
time before the print develops its full intensity.
Oftentimes, these slow-forming inkless fingerprinting
systems can be rendered completely inoperable if
fingerprinting is attempted in substantially lower
than ambient temperature as would be the case in an
outdoor environment in geographic locations with extre-
mely cold climates.
All of the known inkless fingerprinting systems
require at least two separate steps. That is, the
incorporation of one of the reactive components in one
medium such as a fingerprinting pad and the chemical or
mechanical pre-treatment of the .substrate, usually
paper, where the final fingerprint appears. In some
cases, the fingerprint is treated chemically or mecha-
nically after it is made in order to develop its
desired color and color intensity.
SUMMARY OF THE INVENTION
It has now been discovered that totally self-
contained, inkless fingerprinting system can be pro-
vided which systems produce clear and extremely stable
fingerprints on a number of substrates without
requiring a separate treatment of the substrate. The
fingerprints of the present invention are formed
instantaneously, they possess extremely high color
intensity and are stable even after prolonged periods of
exposure to atomospheric conditions.
Briefly stated, the present invention comprises a liquid
composition for use in making fingerprints comprising the
reaction product of at least one leuco or non-leuco
chromogenic compound and at least one color-developing
substance in a liquid vehicle that is a solvent for said
chromogenic compound and reaction product and a solvent or
dispersant for said color-developing substance.
In accordance with another aspect of the invention there
is provided a fingerprinting system comprising means capable
of releasably retaining a liquid and a liquid composition
releasably retained in said means, said liquid composition
comprising the reaction product of at least one leuco or non-
leuco chromogenic compound at least one color-developing
substance, metallic ions, ammonia, and a liquid vehicle that
is a solvent for said chromogenic compound and reaction
product and a solvent or dispersant for said color-developing
substance.
The invention also comprises a fingerprinting system as
hereinafter described.
DETAILED DESCRIPTION
The essential components of the instant fingerprinting
compositions are the chromogenic compounds, color-developing
substances, and the liquid vehicle.
The chromogenic compounds are leuco dye intermediates
which possess the unique property of being colorless in
neutral or alkaline media, but become colored when they react
,.~
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6a
with an acidic or electron accepting substance. These dyes
are, ~E se, well known and examples thereof which can be used
in this
7 ~ 7~
invention are crystal violet lactone (CVL), dilactones,
benzoyl leuco methylene blue (BLMB), derivatives of
bis-(p-di-alkylaminoaryl) methane, xanthenes, indolyls,
auramines, fluorans and bisfluorans such as those
described in U.S. Patents Nos. 2,981,733, 2,981,738,
3,669,711, 3,681,390, 3819,396, 3,821,010 and
4,302,393. Additional'ly, non-leuco, oil-soluble dyes
such as Keystone Aniline's Keysolv Black RBM, Keysolv
Yellow R, DuPont's Oil Orange B Liquid, Oil Blue B
Liquid Dye, Oil Red B Liquid, Oil Yellow Liquid, and
Oil Green Liquid Dye, may be used in this invention.
The preferred dyes of the present invention, however,
are the leuco chromogenic compounds.
There is a multitude of known electron-accepting
color-developing substances capable of reacting with
the leuco chromogenic compounds, which can be used in
the present invention, and which have been described in
the prior art. Among such electron-accepting substan-
ces are acidic clays such as montmorillonites, kaolins,
bentonites and attapulgites, low molecular weight
phenol-aldehyde condensation products (novolaks) and/or
their metal salts as disclosed in U.S. Patents Nos.
3,427,180, 3,672,935, and 3,723,156, and derivatives of
s~ f~
arolnatic carboxyl c acids and/or their metal salts as
disclosed in U.S. Patents Nos. 3,488,207, 3,864,146,
3,871,900, 3,934,070,3,983,292, 4,303,719, and
4,372,583. Specific examples of such color-developing
materials usable in the present invention are:
3-phenyl salicylic acid, 3,5-di-tertiary butyl salicy-
lic acid, octyl salicylic acid, 2-hydroxy-1-benzyl-3-
naphthoic acid, 2-hydroxy-4-methyl-5-isobutyl
thiobenzoic acid, 3,3'-thiobis (2-hydroxy-5-methyl)
benzoic acid, 2-hydroxy-5-butyl sulfonyl benzoic acid,
condensation products of salicylic acid and salicylic
acid derivatives, United Catalyst's Copisil, a mont-
morillonite c].ay, low molecular weight condensation
products of p-phenyl phenol with formaldehyde,
p-cyclohexyl phenol-formaldehyde condensation product,
and p-tertiary-amylphenol-formaldehyde condensation
product.
Critical to the instant invention are the careful
selection of the type and amount of the chromogenic
compounds, their controlled coupling with the various
color-developing substances, and the physical and chem-
ical properties of the solvent. The type of chromoge-
nic compound selected will determine the hue or color
-- lP~ r'~
of the final print or image and the amount of the chro-
mogenic compound must be balanced with the amount of
the color-developing substance used to ensure the
desired final intensity, speed, and stability of the
final print or image. The solvent used with any par-
ticular combination of chromogenic compound(s) and
color-developing substance(s) must possess good
solvating or dispersing properties for the components
to be dissolved and/or dispersed in the solvent, give
good flow properties for easy and complete transfer of
the composition f.om the pad to the finger and from the
finter to the substrate, and have a low evaporation
rate for prolonged shelf-life in the fingerprinting
pad. Moreover, the acidity; or lack of it, of the
solvent used can affect the exact hue of the final
print or image depending upon the chromogenic compound
used.
However, by operating within the parameters
disclosed herein, one skilled in this art can by
routine eXperimentatioll determine for any particular
chromogenic compound the most suitable color-developing
substance and solvent and proportions thereof to give
the desired final hue or color and a final print having
the desired intensity and stability.
The solvents used in the present invention must
possess good solvating characteristics for the dyes and
the color-developing substances to enable and enhance
the reaction between the two materials, except when the
color-developing substance is an activated clay or a
similar pigment in which case only dispersability of
the color developer in the solvent is required.
Additionally, the solvents to be used in the self-
contained fingerprinting systems of the instant inven-
tion must have low evaporation rates for prolonged
shelf life in the pad, good flow properties for rapid
and complete transfer from the pad to the finger and
from the finger to the substrate, be clear in color to
avoid interference with the final hue of the
fingerprint, and exhibit no adverse toxicological
effects. Exemplary of the solvents in this invention
are alkylated phenols such as monoisobutyl biphenol and
monoisopropyl biphenol, chlorinated paraffins, alky-
lated naphthalenes, partially hydrogenated terphenylssuch as Monsanto's HB-40, soya bean oil, cottonseed
oil, coconut oil, ester alcohols such as Eastman
Kodak's Texanol, alkylated glycol ethers and ether ace-
* Trade Mark
tates such as Eastman Xodak's Ektasolve series, andcombinations thereof~
In accordance with this invention, fingerprints of
almost any color can be produced; the preferred color,
however, is black.
In one mode of this invention, the self-contained,
inkless fingerprinting solution is prepared by
dissolving the leuco dye in a solvent and subsequently
reacting them with amounts of the electron-accepting or
color-developing substance sufficient to acidify the par-
ticular dye used; a stoichiometric amount usually being suf-
ficient, by dissolving or dispersing such color-developing
substances in the same solution containing the leuco dyes.
The dye and color-developer react under ambient conditions
of temperature and pressure. A fingerprinting system,
usually comprising a container housing means capable of --
releasably retaining a fluid (such as any conventional felt
or blotter material pad now conventionally used for
fingerprinting) is impregnated with the self-contained
inkless solution. Clear and stable fingerprints can be made
with this pad without soiling the fingers; the solution is
removed from the finger when the finger is applied to the
substrate, usually paper, on which the print is to be
* Trade ~ark
.. ... .
-
S
retained.
In another mode of the present invention, the self-
contained, inkless fingerprinting solution is prepared
by sequentially dissolving the leuco dye(s) and the
color developer(s) in the same solvent and adding small
amounts of metallic ions such as zinc, cadmium, nickel,
aluminum, magnesium, and manganese in the form of salts
to the solution prior to impregnating the pad. The
addition of the metallic ions seems to catalyze the
dye-color developer reaction and significantly increase
the intensity and the rate of appearance of the final
fingerprint. Furthermore, since the metallic ions
themselves are electron-accepting species they can act
as the sole color-developing substances in this inven-
tion. It is preferable, however, to use them in com-
bination with one or more of the other color-developing
substances described earlier.
In still another mode of this invention, it has
been surprisingly found that when the self-contained,
inkless fingerprinting solution is produced by co-
reacting in the same solvent the leuco dyes, the color-
developing substances and the metallic ions and
followed by the addition of small amounts of aqueous or
13
liquid ammo~ia, ti~e color of the solution fades signi-
ficantly an~ yet the solution produces fingerprints
extremely rapidly of high intensity and stability.
This is especially true when the metallic ions employed
are zinc, cadmium, nickel, aluminum, tin, titanium,
magnesium, or manganese. While not completely
understood, a possible explanation for such a phenome-
non is the fact that some of these metallic elements
such as zinc and cadmium, for example, are known to
form hydroxyl and ammonia containing anion complexes
which can be described as [M(NH3)X)--, where M is the
metal and x is the complex co-ordination number of the
metal. These complexes are known to have limited sta-
bility, especially under hydrolytic conditions, and
lS this fact coupled with the "bleaching" effect of ammo-
nia toward leuco dyes (leuco dyes by definition are
colorless in neutral or alkaline media) could explain
this surprising and highly desirable behavior of the
inkless fingerprinting solutions of this invention
which contain ammonia and metallic ions. It can be
presumed that any other compound capable of forming
complexes of low stability in alkaline media with the
metallic iGns could be used in lieu of ammonia and
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14
still produce the same favorable effects in the instant
invention.
In still another mode of the present invention, the
inkless fingerprinting solution is prepared by sequen-
tially reacting the dissolved leuco dyes with the colordeveloper and the arlunonia complex of the metallic salt,
and subsequently dispersing in the solution small
amounts; about 5 to 20% by weight of inorganic
pigments. Inorganic pigments generally possess high
refractive indices and the incorporation of such
pigments into the inkless fingerprinting solution faci-
litates the automated reading of the fingerprints by
such instruments which rely upon high light refraction
and light scattering of the characters which are to be
recognized optically. For such purposes, a minor amount of
a printing ink; i.e., 1 to 5% by weight can also be added.
In still another mode of this invention, the
inkless fingerprinting solutions are produced by uti-
liz,ing non-leuco, oil-soluble dyes in the oleophilic
solvents already set forth above.
During the development of the present invention it
has also been found that the addition of small amounts
oE latexes (natural or synthetic) such as butadiene-
7~
15styrene, acrylic, polyvinyl acetate latexes and the
like, along with small amounts of coalescing aides such
as ester alcohols and alkylated glycol ether acetates
to the inkless fingerprinting solutions, greatly en-
hances the clarity of the fingerprints made; i.e,,there is a sharper image of the prints of the distal
ridges. This feature is especially important to the
present inkless fingerprinting system since the pro-
ducer of these self-contained pads will have no control
of the surface of the substrate on which the finger-
prints will be placed. The properties of paper sur-
faces, the most commonly used substrates for finger-
print taking, can vary widely depending upon type and
degree of surface treatment such as surface sizing
during paper manufacturing. This, in turn, can affect
greatly the degree of oil adsorption by the paper
fibers and the diffusion or spreading of the oil within
the fibers and thus affect the clarity of the finger-
print. The controlled addition of small amounts of
latex-coalescing aide mixtures to the inkless finger-
printing solutions, increases the viscosity of the
solution and reduces substantially the risk of pro-
ducing unclear fingerprints irrespective of the nature
~ ` ~ ~
1~~
16
and characteristics of the paper surface.
It has also been found during the development of
this invention that the addition of small amounts
(between 0.5% and 2.0% of the weight of the inkless
solution) of ultra violet absorbers such as nickel
bis(octyl phenol) sulfide, hydroxy benzophenones,
hydroxy benzotriazoles and the like, to the inkless
fingerprinting solutions can further improve the stabi-
lity of the fingerprints during prolonged exposures to
light.
The invention will be further described in connec-
tion with the examples that follow, which are set
forth for purposes of illustration only without
intending to limit the scope of the invention.
The following leuco dyes with their respective
designation in parentheses were used in the examples
and obtained from Ciba-Geigy: Pergascript Black
(I-BR), Pergascript Blue (I-2R), crystal violet lactone
(CVL), Pergascript Green (I-GD), Pergascript Red (I-6B), and
Pergascript Orange (I-5R); Benzoyl Leuco Methylene Blue
(BLMB) was obtained from Hilton Davis Chemical Company.
Unless otherwise noted, all percentages and parts are by
weight.
17
EXAMPLE 1
A self-contained inkless fingerprinting solution
was prepared by dissolving in 40 parts of Monsanto's
Hs-40 (a partially hydrogenated terphenyl), 2 parts
of I-BR, 0.35 parts of CVL, 0.25 parts of BLMB, and 1.2
parts of an oligomeric condensation product of 5-octyl
salicylic acid with formaldehyde. Following the disso-
lution of the dyes and the acid, 5.5 parts of a 16%
solution of zinc octoate in mineral spirits were added
and the total solution was agitated for 15 minutes.
A fingerprinting pad was impregnated with the solu-
tion of this example and black-colored fingerprints of
high intensity were made in the conventional manner on
a number of diEferent paper substrates using this
system. The solution deposited a slightly dark haze on
the finger prior to making the fingerprint, but the
haze disappeared after impressing the finger on the
substrate in making the fingerprint. The fingerprints
appeared instantaneously, exhibited good stability
during exposure to sunlight for prolonged periods of
time, and they possessed good clarity. The degree of
clarity, however, varied with changes in the surface
pre-treatment of the paper. For example, when
18
fingerprints were made on newsprint, a paper surface
this is not normally sized, they had a tendency to dif-
fuse or "feather" upon standing; this resulted in some
unclear fingerprints after a while.
COMPARATIVE EXAMPLE la
This example illustrates the invention wherein the
addition of small amounts of an alkaline substance
capable of formirg complexes of relatively low stabi-
lity with the metallic ions used can improve the
aesthetics of the self-contained inkless fingerprinting
system without interfering with its functionality.
Example l was repeated, but a small amount (about
0.4 milliliters) of aqueous ammonia was thoroughly
mixed with the self-contained inkless fingerprinting
solution for about fifteen minutes prior to
impregnating the pad. Equivalent results to those in
Example l were obtained with the exception that the
slight haze was completely eliminated from the finger
even prior to making the Eingerprint.
~OMPARATIVE EXAMPLE lb
_
This example illustrates the invention wherein the
addition of small amounts of latex along and coalescing
aide can significantly improve the sharpness of the
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19
fingerprints.
Example 1 was repeated, but 1.5 parts of a mixture
containing 90% Dow Chemical's latex 638 and 10% Eastman
Kodak's Texanol (ester alcohol) were added to the self-
contained inkless fingerprinting solution and allowedto mix for about one hour prior to impregnating the
pad. Equivalent results to those of Example 1 were
obtained with the exception that fingerprints made even
on newsprint were clear and maintained their clarity
indefinitely.
EXAMPLE 2
A pad was impregnated with a self-contained inkless
fingerprinting solution which solution was prepared as
follows: 4.8 parts of I-BR, 1.5 parts of CVL, 1.0 part
of I-6B, 110 part vf I-GD, 1.0 part of I-5R, 0.3 part
of nickel bis(octyl phenol) sulfide, and 5 parts of
3,5-di-tertiary butyl salicylic acid were dissolved in
30 parts of HB-40 and 30 parts of Texanol. Following
complete dissolution of the dyes and the acid, 1.0 part
of a 50% aqueous solution of zinc chloride, 16.5 parts
of a 16% solution of zinc octoate, 10 milliliters of
aqueous ammonium hydroxide, and 2.0 parts of Rohm and
Haas' acrylic copolymer e~ulsion E-2074 were added to
"f ~
the inkless fingerprinting solution and mixed for about
45 minutes.
Black-colored fingerprints with high degree of
clarity and stability were produced on a number of dif-
ferent paper substrates using this system.
EXAMPLE 3
Example 2 was repeated, but the 5 parts of
3,5-di-tertiary butyl salicylic acid were replaced with
5 parts of 5-octyl salcicylic acid. Equivalent results
were obtained.
EXAMPLE 4
Example 2 was repeated, but the 5 parts of
3,5-ditertiary butyl salicylic acid were replaced with
5 parts of 2-hydroxy-4-methyl-5-isobutyl thio benzoic
acid. Equivalent results were obtained.
EXAMPLE 5
Example 2 was repeated, but 5 parts of titanium
dioxide were thoroughly dispersed in the solution,
using a Waring blender, prior to the addition of the
acrylic copolymer emulsion. This resulted in an
increase in the viscosity of the solution compared to
that of Example 2, but the results obtained were
equivalent to those obtained in Example 2.
f ~
21
RXAMPLE 6
A fingerprinting pad containing an inkless printing
composition was prepared by first dissolving 5.0 parts
of I-BR, 1.0 part of CVL, 1.0 part of I-GD, 1.0 part of
I-5R, l.S parts of BLMB, 0.5 parts of I-6B and 0.5
parts of nickel bis(octyl phenyl) sulfide in a solution
containing 60 parts diethylene glycol monoethyl ether
acetate, 40 parts of HB-40, and 8 parts of a low mole-
cular weight p-phenylphenol-formaldehyde condensation
product. To this solution, 10 parts of a 16% solution
of zinc octoate and 5 milliliters of aqueous ammonia
solution were added along with 3.5 parts of Rohm and
Haas' Acryloid NAD-10 resin and mixed for about one
hour.
A pad was impregnated with this inkless
fingerprinting solution and fingerprints taken. The
re~ult was clear, dark green, almost black fingerprints
with good stability during prolonged exposures to
atmospheric conditions.
EXAMPLE 7
Example 6 was repeated, but the 8 parts of p-
phenylphenol-formaldehyde condensation product were
replaced with 7 parts of a low molecular weight conden-
22
sation product of p-tertiary-amylphenol with for-
maldehyde. The results were equivalent to those of
Example 4.
EXAMPLE 8
Example 6 was repeated with the exception that 6
parts of Huber's Hydrasperse-90, a kaolin clay, were
thoroughly dispersed in the solution prior to the addi-
tion of the 3.5 parts of the Acryloid NAD-10 resin.
The results were equivalent to those of Example 4.
EXAMPLE 9
A self-contained inkless fingerprinting solution
was prepared by dissolving 3.1 parts of I-BR, 1.0 part
of CVL, 3.3 parts of I-GD, 0. 8 parts of I-6B, 0.3 part
of BLMB and 0.3 part of nickel bis(octyl phenol) sulfide
15 in 92 parts of HB-40 which had dispersed in it 10 parts
of Copisil clay. Three parts of a mixture containing
90% Dow's latex 638 and 10% Eastman Kodak's Texanol
were added to the dispersion and allowed to mix for
about one hour.
A pad impregnatad with the solution of this example
was used to make black, clear fingerprints on a number
of various paper surfaces.
23
EXAMPLE 10
A self-contained inkless fingerprinting solution
comprising 3.0 parts of Keystone Aniline's Keysolv
Black RBM and 0.3 parts of Keysolv Yellow R, 0.3 parts
of DuPont's Oil Red B Liquid, and 60 parts of HB-40 was
prepared.
A pad impregnated with the solution gave clear,
purplish-black finyervrints on a number of paper
substrates.
EXAMPLE 11
A self~contained inkless fingerprinting solution
was prepared by d.issolving 4.0 parts of I-BR, 1.0 part
of CVL, 0.5 parts of BLMB, 0.3 part of nickel bis(octyl
phenol) sulfide and 2.5 parts of 5-octyl salicylic acid
in 80 parts of HB-40, 5 parts of monoisobutyl biphenol
and 5 parts of Texanol. Subsequently, 1.0 part of a
50% aqueous solution of zinc chloride, 7 parts of a 16%
solution of zinc octoate, 2.5 parts of aqueous ammonia
and 2.5 parts of Dow's latex 638 were added and allowed
to mix for about 30 minutes.
A pad saturated with the solution of this example
gave black, clear fingerprints with excellent stability
during prolonged exposures toward severe atmospheric
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24
conditions of light, temperature and humidity.
While the invention has been described in connec-
tion with a preferred embodiment, it is not intended to
limit the scope of the invention to the particular form
set forth, but, on the contrary, it is intended to
cover ~such alternatives, modifications, and equivalents
as may be included within the spirit and scope of the
invention as defined by the appended claims.
