U.S. patent application number 10/006255 was filed with the patent office on 2002-06-06 for fluorescent micro-particles embedded in a pigmented fluorescent coating for optical document security.
This patent application is currently assigned to Spectra Systems Corporation. Invention is credited to Lilly, William D..
Application Number | 20020066543 10/006255 |
Document ID | / |
Family ID | 22964628 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020066543 |
Kind Code |
A1 |
Lilly, William D. |
June 6, 2002 |
Fluorescent micro-particles embedded in a pigmented fluorescent
coating for optical document security
Abstract
A security feature (1) that is used with a substrate (2). The
security feature includes a plurality of fluorescent
micro-particles (1A) that form a background component of the
security feature and a plurality of fluorescent discrete particles
(1B) that form a foreground component of the security feature. The
discrete particles are larger in size than the micro-particles and
are optically distinguishable from the micro-particles under at
least one illumination condition. In the preferred embodiment the
security feature is applied as a coating to the substrate, and the
security feature further includes a coating binder (1C) in which
the micro-particles and the discrete particles are contained. The
coating binder can be made of, for example, at least one of an ink
base, an adhesive, an epoxy, a varnish, a polymer solution, or a
dry material having binding properties. The coating binder may be
substantially transparent or substantially opaque. The discrete
particles are optically distinguishable from the micro-particles
under long wavelength ultraviolet light and/or under short
wavelength ultraviolet light. Under no or low magnification
conditions the security feature exhibits a generally uniform color
to the naked eye, while in one embodiment under higher
magnification conditions the discrete particles exhibit a first
color while the micro-particles of the background component exhibit
a second color, while in another embodiment the discrete particles
exhibit a first color while the micro-particles of the background
component exhibit a lack of color, while in a further embodiment
the micro-particles of the background component exhibit a first
color while the discrete particles exhibit a lack of color. The
security feature exhibits a fluorescent signature having attributes
given by at least one of particle count per unit area, specific
particle size range which may or may not differ by fluorescent
color, relative intensities of measured spectral emission peaks due
to foreground component particle fluorescence versus background
component micro-particle fluorescence and specific emission
wavelength values of measured spectral emission peaks due to
foreground component particle fluorescence versus background
component micro-particle fluorescence.
Inventors: |
Lilly, William D.;
(Providence, RI) |
Correspondence
Address: |
HARRINGTON & SMITH, LLP
1809 BLACK ROCK TURNPIKE
FAIRFIELD
CT
06432
US
|
Assignee: |
Spectra Systems Corporation
|
Family ID: |
22964628 |
Appl. No.: |
10/006255 |
Filed: |
December 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60254529 |
Dec 5, 2000 |
|
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Current U.S.
Class: |
162/140 ;
162/162 |
Current CPC
Class: |
D21H 21/48 20130101;
G07D 7/1205 20170501; B41M 3/144 20130101 |
Class at
Publication: |
162/140 ;
162/162 |
International
Class: |
D21H 027/00; D21H
017/67 |
Claims
What is claimed is:
1. A security feature that is used with a substrate, comprising: a
plurality of fluorescent micro-particles that form a background
component of said security feature; and a plurality of fluorescent
discrete particles that form a foreground component of said
security feature, said discrete particles being larger in size than
said micro-particles and being optically distinguishable from said
micro-particles under at least one illumination condition.
2. A security feature as in claim 1, wherein said security feature
is applied as a coating to said substrate, and further comprising a
coating binder in which said micro-particles and said discrete
particles are contained.
3. A security feature as in claim 2, wherein said coating binder is
comprised of at least one of an ink base, an adhesive, an epoxy, a
varnish, a polymer solution, or a dry material having binding
properties.
4. A security feature as in claim 1, wherein said discrete
particles are optically distinguishable from said micro-particles
under long wavelength ultraviolet light.
5. A security feature as in claim 1, wherein said discrete
particles are optically distinguishable from said micro-particles
under short wavelength ultraviolet light.
6. A security feature as in claim 1, wherein under no or low
magnification conditions the security feature exhibits a generally
uniform color to the naked eye, while under higher magnification
conditions the discrete particles exhibit a first color while the
micro-particles of the background component exhibit a second
color.
7. A security feature as in claim 1, wherein under no or low
magnification conditions the security feature exhibits a generally
uniform color to the naked eye, while under higher magnification
conditions the discrete particles exhibit a first color while the
micro-particles of the background component exhibit a lack of
color.
8. A security feature as in claim 1, wherein under no or low
magnification conditions the security feature exhibits a generally
uniform color to the naked eye, while under higher magnification
conditions the micro-particles of the background component exhibit
a first color while the discrete particles exhibit a lack of
color.
9. A security feature as in claim 1, wherein said security feature
exhibits a fluorescent signature having attributes given by at
least one of particle count per unit area, specific particle size
range which may or may not differ by fluorescent color, relative
intensities of measured spectral emission peaks due to foreground
component particle fluorescence versus background component
micro-particle fluorescence and specific emission wavelength values
of measured spectral emission peaks due to foreground component
particle fluorescence versus background component micro-particle
fluorescence.
10. A security feature as in claim 1, wherein said discrete
particles have a size in the range of about 10 microns to about 20
microns in diameter.
11. A security feature as in claim 1, wherein said micro-particles
have a size in the range of about 0.2 microns to about 2 microns in
diameter.
12. A security feature as in claim 1, wherein an average size of
said discrete particles is greater by a factor of at least five
than an average size of said micro-particles.
13. A security feature as in claim 1, wherein an average size of
said discrete particles is greater by a factor of at least one
order of magnitude than an average size of said
micro-particles.
14. A security feature as in claim 2, wherein said coating binder
is substantially transparent.
15. A security feature as in claim 2, wherein said coating binder
is substantially opaque.
16. A security feature as in claim 1, wherein said discrete
particles are optically distinguishable in a first way from said
micro-particles when viewed under short wavelength ultraviolet
light, and are optically distinguishable in a second way from said
micro-particles when viewed under long wavelength ultraviolet
light.
17. A reader system comprising a plurality of light sources and a
magnification optics coupled to an imaging system, said reader
system comprising a controller for illuminating a security feature
using said plurality of light sources, said security feature
comprising a plurality of fluorescent micro-particles that form a
background component of said security feature and a plurality of
fluorescent discrete particles that form a foreground component of
said security feature, said discrete particles being larger in size
than said micro-particles and being optically distinguishable from
said micro-particles when illuminated by at least one of said
plurality of light sources, said controller cooperating with said
imaging system for resolving a fluorescent signature of said
security feature, said fluorescent signature having attributes
given by at least one of particle count per unit area, specific
particle size range which may or may not differ by fluorescent
color, relative intensities of measured spectral emission peaks due
to foreground component particle fluorescence versus background
component micro-particle fluorescence and specific emission
wavelength values of measured spectral emission peaks due to
foreground component particle fluorescence versus background
component micro-particle fluorescence.
18. A reader system as in claim 17, wherein said security feature
is applied as a coating to a substrate using a coating binder in
which said micro-particles and said discrete particles are
contained.
19. A method for reading a security feature, comprising steps of:
operating a reader system having a plurality of light sources and
magnification optics coupled to an imaging system for illuminating
the security feature using said plurality of light sources, said
security feature comprising a plurality of fluorescent
micro-particles that form a background component of said security
feature and a plurality of fluorescent discrete particles that form
a foreground component of said security feature, said discrete
particles being larger in size than said micro-particles and being
optically distinguishable from said micro-particles when
illuminated by at least one of said plurality of light sources; and
responsive to the illuminating, resolving a fluorescent signature
of said security feature, said fluorescent signature having
attributes given by at least one of particle count per unit area,
specific particle size range which may or may not differ by
fluorescent color, relative intensities of measured spectral
emission peaks due to foreground component particle fluorescence
versus background component micro-particle fluorescence and
specific emission wavelength values of measured spectral emission
peaks due to foreground component particle fluorescence versus
background component micro-particle fluorescence.
20. A method as in claim 19, and comprising a preliminary step of
applying said security feature as a coating to a substrate using a
coating binder in which said micro-particles and said discrete
particles are contained.
Description
TECHNICAL FIELD
[0001] These teachings relate generally to the use of fluorescent
pigments and materials and, in particular, to the use of
fluorescent pigments in applications where it is desired to provide
authentication and/or security function for documents, banknotes,
financial instruments and the like.
BACKGROUND
[0002] Coatings containing fluorescent pigments are currently used
to create threads, fibers, and other security structures that are
incorporated into the manufacture of banknote, financial, and legal
document papers. These structures may be though of as security
features that serve as optical authentication devices, as well as
to prevent document counterfeiting. Such coatings may also be
applied to product packaging to identify authentic products and
deter product counterfeiting. The fluorescence of such coatings is
typically not apparent when illuminated with ordinary ambient light
sources, but becomes visible when excited by an ultraviolet light
source.
[0003] Reference can be had to the following U.S. Pat. Nos.:
5,903,340, "Optically-Based Methods and Apparatus for Performing
Document Authentication", by N. M. Lawandy and T. J. Driscoll; and
4,863,783, "Security Paper", by N. A. Milton. Reference can also be
had to European Patent Application 0 219 743 A1, "Security Paper
Containing Vesiculated Beads, by R. H. Hamilton; and to French
Patent No.: 2 478 695, "Antifalsification Paper with Luminescent
Particles, its Method of Production and Method of Producing Said
Particles" (Aussedat Rey).
[0004] For example, Milton describes a paper that contains 30-500
micron size granules of 3-5 micron size pigment particles that are
chemically bound together by a cross-link binder. In order to
provide contrast between the pigment and the background during
inspection the granules are essentially free of finer
particles.
[0005] In French Patent No.: 2 478 695 a paper is provided that
includes luminescent particles that are a 30-50 micron size
conglomerate of 3-5 micron size pigment particles. The particles
may emit different wavelengths when exposed to UV radiation, and
combinations of colors are said to enable the papers to be
personalized. In addition to the use of the fluorescent particles,
the paper may also contain colored fibers and other conventional
means of identification.
[0006] A problem that has not been adequately addressed by the
prior art lies in complicating the task of the counterfeiter or
forger by increasing the complexity of the optically-based security
feature.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0007] The foregoing and other problems are overcome, and other
advantages are realized, in accordance with the presently preferred
embodiments of these teachings.
[0008] In accordance with the teachings of this invention there are
provided non-apparent fluorescent microscopic particles that are
present within a coating for the purposes of increasing a maximum
number of unique fluorescent emission combinations, also referred
to herein as unique fluorescent signatures, for secreting these
signatures from ready discovery, and for increasing the difficulty
of creating counterfeit documents and product packaging.
[0009] These teachings are an advancement over the prior art since
their use complicates the task of the counterfeiter or forger by
increasing the complexity of an optically-based security feature.
These teachings provide a security paper and substrate with an
efficient multi-level encoding mechanism using particles containing
pigment that emit light with different wavelengths and/or that emit
or do not emit light depending on the characteristics of the
stimulus. The use of light emitting particles within at least two
different size regimes increases the complexity of the security
feature and furthermore increases the amount of information that
can be encoded by the light emitting particles.
[0010] Disclosed herein is a security feature that is used with a
substrate. The security feature includes a plurality of fluorescent
micro-particles that form a background component of the security
feature and a plurality of fluorescent particles that form a
foreground component of the security feature. The particles are
larger in size than the micro-particles and are optically
distinguishable from the micro-particles under at least one
illumination condition. For example, the particles may have a size
in the range of about 10 microns to about 20 microns in diameter
and the micro-particles may have a size in the range of about 0.2
microns to about 2 microns in diameter. In general, and further by
example, an average size of the particles is greater by a factor of
at least five than an average size of the micro-particles, or the
average size of the particles is greater by a factor of at least
one order of magnitude than the average size of the
micro-particles.
[0011] In the preferred embodiment the security feature is applied
as a coating to the substrate, and the security feature further
includes a coating binder in which the micro-particles and the
particles are contained. The coating binder can be made of, for
example, at least one of an ink base, an adhesive, an epoxy, a
varnish, a polymer solution, or a dry material having binding
properties.
[0012] The coating binder may be substantially transparent or
substantially opaque. The particles are optically distinguishable
from the micro-particles under long wavelength ultraviolet light
(320-380 nm range, peaking at .about.365 nm) and/or under short
wavelength ultraviolet light (180-280 nm range, peaking at
.about.254 nm). Under no or low magnification conditions the
security feature exhibits a generally uniform color to the naked
eye, while in one embodiment under higher magnification conditions
the discrete particles exhibit a first color while the
micro-particles of the background component exhibit a second color,
while in another embodiment the discrete particles exhibit a first
color while the micro-particles of the background component exhibit
a lack of color, while in a further embodiment the micro-particles
of the background component exhibit a first color while the
discrete particles exhibit a lack of color. In the presently
preferred embodiment the security feature exhibits one of many
possible unique fluorescent signatures having attributes given by
at least one of particle count per unit area, specific particle
size range which may or may not differ by fluorescent color,
relative intensities of measured spectral emission peaks due to
foreground component particle fluorescence versus background
component micro-particle fluorescence and specific emission
wavelength values of measured spectral emission peaks due to
foreground component particle fluorescence versus background
component micro-particle fluorescence. In the preferred, but not
limiting embodiment, the discrete particles are invisible or nearly
invisible to the naked eye.
[0013] Also described is an automatic reader system for resolving
and identifying the various spectral and spatial properties of the
security feature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing and other aspects of these teachings are made
more evident in the following Detailed Description of the Preferred
Embodiments, when read in conjunction with the attached Drawing
Figures, wherein:
[0015] FIG. 1 is graph showing an exemplary emission spectrum for a
yellow-red system film;
[0016] FIG. 2A shows the film system of FIG. 1 as seen by the naked
eye (magnification 1.times.), while FIG. 2B shows a microscopic
view of the film system (magnification 100.times.);
[0017] FIG. 3 is a system-level block diagram of a reading system
for stimulating the particles contained within a substrate and for
reading the resulting emission(s) of light.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] This invention provides a novel approach for enhancing the
security of documents, packaging and other substrates by including
non-apparent fluorescent microscopic particles into a coating
and/or directly into the substrate, for the purposes of increasing
the number of unique fluorescent signatures possible, for secreting
these signatures from ready discovery, and for increasing the
difficulty factor in creating counterfeit documents and product
packaging. While described herein in the general context of
paper-based documents, such as legal documents (e.g., deeds and
contracts) and financial documents (e.g., currency, stock
certificates, bonds and letters of credit), these teachings may be
employed with any of a number of different types of documents.
These teachings may also be employed with other than paper-based
substrate materials, where the term "substrate" should be broadly
construed to include any type of substrate material that is
suitable for being printed on, including ceramic, polymeric,
plastic and plastic-containing substrate materials.
[0019] There are a number of possible embodiments of these
teachings. These embodiments include, but are not limited to, the
following embodiments shown by way of Examples A through I.
EXAMPLE A
[0020] Particles excited by Long Wavelength Ultraviolet (Long UV)
light emit a fluorescent color X (for example, yellow, where the
particles contain a 2-5 percent mixture of a fluorescent pigment of
the benzothiazolyl family embedded in a clear, hard plastic matrix,
or of similar construct using fluorescent pigments of other colors)
and have a specific size range (for example, about 10 microns to
about 20 microns in diameter). These particles are also referred to
herein as discrete particles. A coating binder may be comprised of,
for example, an ink base, an adhesive, an epoxy, a varnish, a
polymer solution, or a dry powder material having binding
properties. The coating binder contains a Long UV fluorescent
pigment having an emission color Z (for example, a red fluorescent
pigment such as a Europium chelate), with the pigment being milled
into the coating to a much smaller particle size range (for
example, 0.5 micron to 2.0 microns, also referred to herein as
micro-particles), or being fully dissolved into the coating. This
background field pigment loading in the coating may range from
2-20% by weight, with a preferred loading at about 10% (wet basis),
so to result a dry basis loading of about 10-30%. For example, the
average size of the discrete particles can be greater by a factor
of at least five than the average size of the micro-particles.
Further by example, the average size of the discrete particles can
be greater by a factor of at least one order of magnitude than the
average size of the micro-particles. The preferred loading of the
discrete particles in a given film may vary between about 0.2-10%
(wet basis) so to result in a dry basis loading of about 0.2-30%.
Such wide variation of this attribute contributes to the large
number of possible unique signatures within any single color
combination or other single embodiment of the security feature,
where such attribute is measurable as discrete particle count per
unit area of coated or co-manufactured substrate.
[0021] The 10-20 micron sized discrete particles are combined and
mixed with the coating binder and its micro-particles, or the
discrete particles and the micro-particles could be added together
into the coating binder, or they can be added in either order into
the coating binder, and then mixed. In any case, the resulting
liquid or solid phase coating material containing the discrete
particles and the micro-particles is applied as a thin film to a
substrate of interest. The coating material can be applied by
painting on, rolling on, spraying on, through commercial printing
techniques, or by any suitable application process, such as by
writing the coating material onto the substrate using a pen or a
marker (e.g., a felt-tip type marker) that contains the coating
material.
[0022] The net visual effect to the naked eye, or under low
magnification, is a single emission color Y (orange), which is the
visually averaged combination of the yellow and red fluorescent
emissions. However, inspection of the coating film under higher
magnification reveals the presence of the discrete particles having
the fluorescent color X (yellow in this example) disposed within a
field comprised of micro-particles having fluorescent color Z (red
in this example). If the coating binder is itself transparent, a
thin film of this coating is translucent to transparent
(substantially transparent) when viewed under ordinary ambient
light by the naked eye.
[0023] An emission spectrum (as seen by the naked eye) of such a
yellow-red system film is shown in FIG. 1. A drawing representing
the appearance of the same film (as viewed by the naked eye vs.
through a microscope) is shown in FIGS. 2A and 2B. FIG. 2B shows
the micro-particles 1A, discrete particles 1B, and the coating
binder 1C.
EXAMPLE B
[0024] Discrete particles excited by either Long or Short UV light
emit a fluorescent color X (for example, blue) and have a specific
size range (for example, 10 microns to 20 microns). The coating
binder can be any one described above in Example A. The coating
contains a Long UV/Short UV color-shifting background pigment blend
having Long UV emission color X (for example, a blue emitting
pigment of the stilbene family) and Short UV emission color Z (for
example, an inorganic red emitting pigment such as Uveda.TM. YO
obtained from United Mineral Corporation). Such a blend of
background pigments may contain a ratio of between 1:5 and 1:10
Long UV: Short UV pigments. The blend is milled into the coating to
a final size range (micro-particles of, for example, 0.5 micron to
2.0 microns) smaller than the discrete particles, then the discrete
particles and micro-particles are added and thoroughly mixed into
the coating (solution or dry powder). When a thin film of this
coating is excited under Long UV light and viewed either by the
naked eye or under high magnification, the net appearance is a flat
field having emission color X (blue). Outlines of the discrete
particles are visible under magnification. When the film is excited
under Short UV light and viewed by the naked eye the net appearance
is a flat field having emission color Y (violet). When viewed under
high magnification, however, the presence of discrete particles
having fluorescent color X (blue) standing in a field of
fluorescent color Z (red) is revealed. If the coating binder used
is transparent, this coating is translucent to transparent when
viewed under ordinary ambient light by the naked eye.
EXAMPLE C
[0025] Discrete particles excited by Long UV light emit fluorescent
color X (for example, blue), and when excited by Short UV light
emit a different fluorescent color Y (for example, red) and have a
specific size range (for example, 10 microns to 20 microns). The
coating binder can be any one described in above in Example A. The
coating contains a Long UV background pigment having emission color
Z (for example, yellow), but having very little or no emission when
excited by a Short UV light source. Again, the background pigment
is milled into the coating and has a smaller size range
(micro-particles of, for example, 0.5 micron to 2.0 microns) than
the particles. The discrete particles and micro-particles are added
and thoroughly mixed into the coating (solution or dry powder).
When a thin film of this coating is excited under Long UV light and
viewed by the naked eye, the net appearance is a flat field having
emission color W (green, in this case). When viewed under high
magnification the presence of the discrete particles having
fluorescent color X (blue) standing in a field of fluorescent color
Z (yellow) is revealed, similar to Example A above. However, when
this film is excited under Short UV light and viewed by the naked
eye the net appearance is a disperse field having emission color Y
(red). When viewed under high magnification the presence of
discrete particles having fluorescent color Y (red) standing in a
non-fluorescing background field is revealed. If the coating binder
used is transparent, this coating is translucent to transparent
when viewed under ordinary ambient light by the naked eye.
EXAMPLE D
[0026] In this example the discrete particles emit Long UV color X
(for example, yellow), but do not fluoresce under Short UV
excitation. The coating binder can be any one described in above in
Example A. The coating contains a Long UV/Short UV color-shifting
background pigment having Long UV emission color Y (for example,
blue) and Short UV emission color Z (for example, red). Again, the
background pigment is milled into the coating and has a smaller
size range (micro-particles of, for example, 0.5 micron to 2.0
microns) than the particles. The particles and micro-particles are
added and thoroughly mixed into the coating (solution or dry
powder). When a thin film of this coating is excited under Long UV
light and viewed by the naked eye, the net appearance is a flat
field having emission color W (green, in this case). When viewed
under high magnification the presence of discrete particles having
fluorescent color X (yellow) standing in a field of fluorescent
color Y (blue) is revealed, similar to Example A above. However,
when this film is excited under Short UV light and viewed by the
naked eye the net appearance is a disperse field having emission
color Z (red). When viewed under high magnification the presence of
discrete particles having no fluorescence (dark spots) standing in
a background field of fluorescent color Z (red) is revealed. If the
coating binder used is transparent, this coating is translucent to
transparent when viewed under ordinary ambient light by the naked
eye.
EXAMPLE E
[0027] In this example non-fluorescing discrete particles were
selected that may be opaque, translucent, or transparent, and have
a specific size range (for example, 10 microns to 20 microns). The
coating binder can be any one described in above in Example A, and
the background pigment may be as described above in either Example
A or Example B. When a film of this coating is excited under Long
UV light and viewed by the naked eye the net appearance is a flat
field having Long UV emission color X (for example, green). When
viewed under high magnification the presence of discrete particles
having no fluorescence (dark spots) standing in a background field
of fluorescent color X (green) is revealed. If the background
pigment is as described in Example B, and the film is excited under
Short UV light, when viewed by the naked eye the net appearance is
a flat field having Short UV emission color Y (for example,
orange). When viewed under high magnification the presence of
discrete particles having no fluorescence (dark spots) standing in
a background field of fluorescent color Y (orange) is revealed. If
the coating binder used is transparent, this coating is translucent
to transparent when viewed under ordinary ambient light by the
naked eye.
EXAMPLE F
[0028] Fluorescent discrete particles were selected having emission
properties as described in any of Examples A, B, C or D, and have a
specific size range (for example, <10 microns). A transparent
coating binder is used, such as one of those described in Example
A, but the coating contains no background pigment. When a film of
this coating is excited under appropriate (Long and/or Short, per
particle properties) UV light and is viewed by the naked eye the
net appearance is a disperse field having emission color X (for
example, green). When viewed under high magnification the presence
of discrete particles having fluorescent color X (green) standing
in transparent background field is revealed. When viewed under
ordinary ambient light by the naked eye, this coating is
transparent (invisible).
EXAMPLE G
[0029] Fluorescent discrete particles were selected having emission
properties as described in any of Examples A, B, C, or D, and have
a specific size range (for example, <10 microns). A transparent
coating binder is used, such as described in Example A, and the
coating contains a non-fluorescent, substantially opaque background
pigment (for example, black). When a film of this coating is
excited under appropriate (Long and/or Short, per particle
properties) UV light and is viewed by the naked eye the net
appearance is a disperse field having emission color X (for
example, green). When viewed under high magnification the presence
of discrete particles having fluorescent color X (green) standing
in an opaque (black) background field is revealed. When viewed
under ordinary ambient light by the naked eye, this coating is
opaque (black).
EXAMPLE H
[0030] A mixture of two or more different fluorescent colored
discrete particles is used having emission properties as described
in any of Examples A, B, C, D or E, and having a predetermined size
range (which may or may not differ according to particle
fluorescent color). The coating binder can be as described in
Example A, and the coating may contain any fluorescent or other
background field pigment having properties as described in Examples
A, B, C, D, E, F, or G. When a thin film of this coating is excited
under appropriate (Long and/or Short, per particles and background
micro-particle properties) UV light and viewed by the naked eye,
the net appearance is a flat field having a single color (being the
sum of emission wavelengths and intensities as integrated by the
human eye). When viewed under high magnification, the presence of
discrete particles having various fluorescent colors is revealed.
The background pigment field color may or may not be of the same as
any one of the particle colors.
EXAMPLE I
[0031] In accordance with a further aspect of these teachings a
coating containing a binder as described in Example A, and
containing any fluorescent or other background field pigment having
properties as described in Examples A, B, C, D, E, F, or G, is
first applied as a base film and allowed to dry or cure. A second
coating, as described in Example F above, except that this coating
may instead contain discrete particles as described in Example H,
is applied as a thin film to the top surface of the base film. In
this case, the discrete particles are not embedded in the pigmented
base coating, but are surface mounted above the base coat. To the
naked eye, when illuminated under appropriate UV light source from
directly above, such binary coating system film appears as a flat
field having a single color (being the sum of emission wavelengths
and intensities as integrated by the human eye), but assumes a
speckled or disperse appearance as the incident angle of UV
illumination is changed. When viewed under high magnification, the
layer of discrete particles in the top coat will be at a shorter
focal length than the background pigment field color in the base
coat.
[0032] The creation of a specific and unique fluorescence signature
in any of the above Examples A-I is accomplished through a balance
of pigment concentrations contained in the particles of the
foreground component of the security feature coating and the
micro-particles of the background component of the security feature
coating, the overall concentrations of particles and of the
background micro-particles, the excitation range(s) selected, and
the fluorescent color(s) selected, all within an appropriate
application thickness of the coating film.
[0033] Attributes of such fluorescent signature may include
particle count per unit area, specific particle size range (which
may or may not differ by fluorescent color for the case of Example
H), net spectral characteristic relative intensities of measured UV
emission peaks due to particle fluorescence vs. background pigment
fluorescence, specific emission wavelength values due to particle
fluorescence vs. background pigment fluorescence, and other
characteristics such as particle density(s) and background field
pigment concentration. For a given coating formulation, the values
of certain of these attributes will vary as a function of applied
film thickness.
[0034] Referring to FIG. 3, a security feature 1 as described above
in the Examples A-I is provided on a substrate 2 and may be coupled
with an automated reading device 10 to authenticate the presence of
the security feature 1 and/or to verify its specific fluorescent
signature. The reading device 10 can include an image collection
element 12, which may include a digital or video camera image
capture device 14, magnification optics 16, a physical standoff 16A
to readily establish a correct focal distance between the optics 16
and the target coating film of the security feature 1 on the
substrate 2, and appropriate UV target illumination source(s) 18
(Long UV) and 20 (Short UV). The reading device 10 also includes a
measurement element 22 that can include a spectrometer 24 and image
and spectral data processing elements 26, such as a real-time or
captured image display 28, a data link 30 to a computer 32 having a
memory 34, and image processing software 36 for evaluating the
target image and spectra, and for comparing their values with
signature-specific allowed value ranges. The memory 34 can store a
lookup table or other type of data structure 34A wherein various
authentic combinations of background and foreground colors,
particle sizes, particle densities and the like are stored.
[0035] As an example, a particular document may be provided with an
optical signature given by a thin film coating security feature
containing background micro-particles that fluoresce with a yellow
color when excited by Long UV, and that do not have any appreciable
fluorescent emission when excited by Short UV, and with discrete
particles of size about 20 microns that fluoresce with a red color
when excited by Long UV and with a yellow color when excited by
Short UV, where the particles have a density of about
10/mm.sup.2.
[0036] In this case the reading device 10 may be automatically
operated so as to first illuminate the coating with the Long UV
light source 18, and to detect the discrete yellow and red
emissions, then to illuminate the coating with the Short UV light
source 20, and to detect the discrete yellow emission (but of
smaller magnitude than the magnitude of the yellow emission due to
the background micro-particles when exited by the Long UV). The
output of the image capture device 14 may also be processed to
confirm that the red and yellow emissions originate from particles
having a size of about 20 microns and a density of about
10/mm.sup.2. If all of these criteria are satisfied then the
substrate maybe declared to be genuine or authentic, as the
security feature is validated against data stored in the data
structure 34A. A further test, or an initial test, may be one
performed by a human operator who verifies that the expected
color(s) are present under different Long and Short UV illumination
conditions. It can be appreciated that these teachings provide a
multi-dimensional security feature (e.g., excitation source
wavelength(s), emission wavelength(s), particle size(s), particle
density(s), and emission amplitude(s)).
[0037] While described in the context of the use of the two UV
sources (Long and Short) 18 and 20, a single tuneable output UV
source could be used. Also, these teachings can be employed with a
single UV source, e.g., either Long or Short, or with more than two
UV sources, for example one that covers at least the 280 nm to 320
mn between the Short UV and the Long UV ranges. Also, these
teachings are not restricted for use with only the described
pigments, particle and micro-particle sizes, ranges of particle and
micro-particle sizes and/or types of coating binders. Furthermore,
while described in the context of a coating that is applied to form
a thin film on the substrate 2, it is also within the scope of
these teachings to incorporate at least the micro-particles and the
particles into the substrate, such as by adding them during the
substrate manufacturing process.
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