U.S. patent application number 11/861393 was filed with the patent office on 2008-01-24 for diffractive surfaces with color shifting backgrounds.
This patent application is currently assigned to JDS UNIPHASE CORPORATION. Invention is credited to Richard L. Bonkowski, Patrick K. Higgins, Charles T. Markantes, Roger W. Phillips.
Application Number | 20080018965 11/861393 |
Document ID | / |
Family ID | 23379584 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080018965 |
Kind Code |
A1 |
Phillips; Roger W. ; et
al. |
January 24, 2008 |
Diffractive Surfaces With Color Shifting Backgrounds
Abstract
A security article includes a light transmissive substrate
having a first surface and an opposing second surface, with the
first surface having an embossed region with an optical diffraction
pattern or a holographic image pattern. A color shifting optical
coating is formed on the substrate such as on the opposing second
surface, with the optical coating providing an observable color
shift as the angle of incident light or viewing angle changes. The
security article can be used in a variety of applications and
products to provide for enhanced security measures such as
anticounterfeiting.
Inventors: |
Phillips; Roger W.; (Santa
Rosa, CA) ; Bonkowski; Richard L.; (Santa Rosa,
CA) ; Higgins; Patrick K.; (Windsor, CA) ;
Markantes; Charles T.; (Santa Rosa, CA) |
Correspondence
Address: |
ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST P.A.
1401 CITRUS CENTER 255 SOUTH ORANGE AVENUE
P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Assignee: |
JDS UNIPHASE CORPORATION
|
Family ID: |
23379584 |
Appl. No.: |
11/861393 |
Filed: |
September 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11849589 |
Sep 4, 2007 |
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11861393 |
Sep 26, 2007 |
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10706142 |
Nov 12, 2003 |
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11849589 |
Sep 4, 2007 |
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09351102 |
Jul 8, 1999 |
6761959 |
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10706142 |
Nov 12, 2003 |
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Current U.S.
Class: |
359/2 |
Current CPC
Class: |
Y10T 428/2457 20150115;
B42D 25/373 20141001; B42D 25/29 20141001; G03H 2250/42 20130101;
B42D 25/36 20141001; Y10T 428/24479 20150115; B42D 25/324 20141001;
B42D 25/328 20141001; G03H 1/02 20130101; Y10T 428/24802 20150115;
G03H 2250/12 20130101; G03H 1/0256 20130101; B42D 25/369 20141001;
Y10T 428/24355 20150115; G03H 1/0244 20130101; G03H 1/0011
20130101; B42D 2035/24 20130101 |
Class at
Publication: |
359/002 |
International
Class: |
G03H 1/00 20060101
G03H001/00 |
Claims
1. A security article comprising: a light transmissive substrate
having a first surface and an opposing second surface, said first
surface having a diffraction grating pattern or a holographic image
pattern formed thereon; and a color-shifting multilayer optical
film structure formed on said diffraction grating pattern or said
holographic image pattern formed on said first surface of said
light transmissive substrate, so as to conform to the shape
thereof, said color-shifting multilayer optical film structure
being defined by a reflector layer formed directly on said
diffraction grating pattern or said holographic image pattern
formed on said first surface of said light transmissive substrate,
a dielectric layer formed directly on said reflector layer, and an
optical absorber layer formed directly on said dielectric layer and
having a first surface thereof opposite a second surface thereof
formed directly on said dielectric layer, said first surface of
said reflector layer replicating said diffraction pattern or said
holographic image pattern formed on said first surface of said
light transmissive substrate; and wherein said color-shifting
multilayer optical film structure provides color shifting with
change of viewing angle or angle of incident light.
2. A security article as defined in claim 1, wherein the first
surface of the absorber layer has the diffraction pattern or
holographic image pattern replicated and formed therein.
3. A security article as defined in claim 1, wherein a layer of the
color-shifting multilayer optical film structure is segmented.
4. A security article as defined in claim 2 wherein a layer of the
color-shifting multilayer optical film structure is segmented.
5. A security article as defined in claim 3 wherein the reflector
layer is segmented.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/849,589 filed Sep. 4, 2007, entitled "A Security Device
Having A Segmented Layer" which is a continuation of U.S.
application Ser. No. 10/706,142 filed Nov. 12, 2003, entitled
"Methods For Forming Security Articles Having Diffractive Surfaces
And Color Shifting Backgrounds" which is a divisional of U.S.
application Ser. No. 09/351,102 filed on Jul. 8, 1999, entitled
"Diffractive Surfaces With Color Shifting Backgrounds," which are
incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention is related generally to thin film
optical coatings for use in producing security articles. More
specifically, the present invention is related to the production of
diffractive surfaces such as holograms or gratings having color
shifting or optically variable backgrounds which can be used as
security articles in a variety of applications.
[0004] 2. The Relevant Technology
[0005] Color shifting pigments and colorants have been used in
numerous applications, ranging from automobile paints to
anti-counterfeiting inks for security documents and currency. Such
pigments and colorants exhibit the property of changing color upon
variation of the angle of incident light, or as the viewing angle
of the observer is shifted. The primary method used to achieve such
color shifting colorants is to disperse small flakes, which are
typically composed of multiple layers of thin films having
particular optical characteristics, throughout a medium such as
paint or ink that may then be subsequently applied to the surface
of an object.
[0006] Diffraction patterns and embossments, and the related field
of holographs, have begun to find wide-ranging practical
applications due to their aesthetic and utilitarian visual effects.
One very desirable decorative effect is the iridescent visual
effect created by a diffraction grating. This striking visual
effect occurs when ambient light is diffracted into its color
components by reflection from the diffraction grating. In general,
diffraction gratings are essentially repetitive structures made of
lines or grooves in a material to form a peak and trough structure.
Desired optical effects within the visible spectrum occur when
diffraction gratings have regularly spaced grooves in the range of
hundreds to thousands of lines per millimeter on a reflective
surface.
[0007] Diffraction grating technology has been employed in the
formation of two-dimensional holographic patterns which create the
illusion of a three-dimensional image to an observer. Furthermore,
the use of holographic images on various objects to discourage
counterfeiting has found widespread application.
[0008] There currently exist several applications for surfaces
embossed with holographic patterns which range from decorative
items, such as gift wrap, to security documents, such as bank notes
and credit cards. Two-dimensional holograms typically utilize
diffraction patterns which have been formed on a plastic surface.
In some cases, a holographic image which has been embossed on such
a surface can be visible without further processing; however, it is
generally necessary, in order to achieve maximum optical effects,
to place a reflective layer, typically a thin metal layer such as
aluminum, onto the embossed surface. The reflective layer
substantially increases the visibility of the diffraction pattern
embossment.
[0009] Unfortunately, there exists a substantial incentive for
counterfeiters to reproduce the holograms which are frequently used
in credit cards, bank notes, and the like. One of the methods used
to reproduce holograms is to scan a laser beam across the embossed
surface and optically record the reflected beam on a layer of a
material such as a photopolymerizable polymer. The original pattern
can subsequently be reproduced as a counterfeit. Another method is
to remove the protective covering material from the embossed metal
surface by ion etching, and then when the embossed metal surface is
exposed, a layer of metal such as silver (or any other easily
releasable layer) can be deposited. This is followed by deposition
of a layer of nickel, which is subsequently released to form a
counterfeiting embossing shim.
[0010] Due to the level of sophistication of counterfeiting
methods, it has become necessary to develop more advanced security
measures. One approach, as disclosed in U.S. Pat. Nos. 5,629,068
and 5,549,774 to Miekka et al., is the application of inks, such as
metallic flake inks, metallic effect inks, or inks with pigments
formed of optical stacks, upon the embossed surface in lieu of a
thin metal layer. In another approach, disclosed in U.S. Pat. Nos.
5,624,076 and 5,672,410 also to Miekka et al., embossed metal
particles or optical stack flakes are used to produce a holographic
image pattern.
[0011] Another problem with the holographic images as described
above is that they require direct specular illumination in order to
be visualized. This means that for best viewing results, the
illuminating light must be incident at the same angle as the
viewing angle. Therefore, diffuse light sources, such as ordinary
room lights or viewing by an overcast sky, when used to illuminate
the holographic image, do not reveal much of the visual information
contained in the hologram, and what is typically seen is only a
silver colored reflection from the embossed surface.
[0012] It would therefore be of substantial advantage to develop
improved security products to provide enhanced viewing qualities in
ordinary room light and which are usable in various security
applications to make counterfeiting more difficult.
SUMMARY AND OBJECTS OF THE INVENTION
[0013] It is a primary object of the invention to provide a
security article have color shifting properties which increases the
difficulty of counterfeiting in a variety of applications.
[0014] Another object of the invention to provide a security
article with a distinctive pattern that is readily observable over
a wide range of viewing angles in diffuse lighting conditions.
[0015] Another object of the invention is to provide a security
article with a holographic pattern that has enhanced visibility and
contrast to provide for viewing under diffuse lighting conditions
without the need for direct specular light.
[0016] Another object of the invention to provide a security
article that can be manufactured at low cost compared to prior
security products.
[0017] To achieve the forgoing objects and in accordance with the
invention as embodied and broadly described herein, a security
article is provided which includes a light transmissive substrate
having a first surface and an opposing second surface, with the
first surface having an optical interference pattern such as a
diffraction grating pattern or a holographic image pattern. A color
shifting optical coating is formed on the substrate, with the
optical coating providing an observable color shift as the angle of
incident light or viewing angle changes. In one embodiment, the
color shifting optical coating is formed on the second surface of
the substrate opposite from the optical interference pattern, and
includes an absorber layer formed adjacent to the substrate, a
dielectric layer formed on the absorber layer, and a reflector
layer formed on the dielectric layer. Alternatively, this
multilayer optical coating can be formed on the same side of the
substrate as the interference pattern.
[0018] In another embodiment, the color shifting optical coating is
applied to the substrate in the form of a paint or ink which
includes a polymeric medium and a plurality of color shifting
multilayer optical interference flakes dispersed in the polymeric
medium. In other embodiments, the color shifting optical coating is
coextruded with a light transmissive embossed substrate to form
adjacent layers or is dispersed in the form of interference flakes
in the substrate material prior to forming the substrate.
[0019] The security article of the invention can be used in a
variety of applications to provide for enhanced security measures
such as anticounterfeiting. The security article can be utilized in
the form of a label, a tag, a ribbon, a security thread, and the
like, for application in a variety of objects such as security
documents, monetary currency, credit cards, merchandise, etc.
[0020] These and other aspects and features of the present
invention will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more fully understand the manner in which the
above-recited and other advantages and objects of the invention are
obtained, a more particular description of the invention will be
rendered by reference to specific embodiments thereof which are
illustrated in the appended drawings. Understanding that these
drawings depict only typical embodiments of the invention and are
not therefore to be considered as limiting of its scope, the
invention will be described and explained with additional
specificity and detail through the use of accompanying drawings in
which:
[0022] FIG. 1A is a schematic depiction of a security article
having a color shifting optical coating according to one embodiment
of the present invention;
[0023] FIG. 1B is a schematic depiction of a security article
having a color shifting optical coating according to an alternative
embodiment of the present invention;
[0024] FIG. 2A is a schematic depiction of a security article
having a color shifting optical coating according to another
embodiment of the present invention;
[0025] FIG. 2B is a schematic depiction of a security article
having a color shifting optical coating according to an alternative
embodiment of the present invention;
[0026] FIG. 3 is a schematic depiction of a security article
according to yet another embodiment of the present invention;
[0027] FIG. 4 is a schematic depiction of a security article
according to a further embodiment of the present invention;
[0028] FIG. 5 is a schematic depiction of the security article of
FIG. 1A with a release layer formed thereon;
[0029] FIG. 6 is a schematic depiction of the security article of
FIG. 1A attached to a carrier substrate;
[0030] FIG. 7 is a schematic depiction of the security article of
FIG. 1B with a release layer formed thereon; and
[0031] FIG. 8 is a schematic depiction of the security article of
FIG. 1B attached to a carrier substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The present invention is directed to security articles
having diffractive surfaces with color shifting backgrounds that
produce enhanced visual effects. The configuration of the security
articles is such that a combination of either holographic or
diffraction grating patterns with color shifting films or layers
decreases the possibility of counterfeiting. Furthermore, the
article of the invention allows a user to more easily view the
image or diffraction effect in diffuse light without the need for
direct specular light.
[0033] Generally, the configuration of the security articles of the
present invention is such that the combination of a light
transmissive substrate, having an interference pattern on the
surface thereof, with color shifting optical coatings provides
security features that make forgery or counterfeiting of an object
difficult.
[0034] Referring to the drawings, wherein like structures are
provided with like reference designations, FIG. 1A depicts a
security article 10 according to one embodiment of the present
invention. The security article 10 includes a light transmissive
substrate 14 formed with an optical interference pattern 15 on an
outer first surface thereof. A color shifting optical coating 16 is
formed on an opposing second surface of substrate 14 and is
discussed in further detail below. The combination of substrate 14
and color shifting optical coating 16 forming security article 10
provide a security feature that reduces the possibility of
duplication, forgery and/or counterfeiting of an object having
security article 10 thereon.
[0035] The optical interference pattern 15 formed on the outer
surface of light transmissive substrate 14 can take various
conventional forms including diffraction patterns such as
diffraction gratings, refraction patterns, holographic patterns
such as two-dimensional and three-dimensional holographic images,
corner cube reflectors, or other like interference patterns. The
particular methods and structures that form optical interference
pattern 15 are known by those skilled in the art. For example,
embossing the light transmissive substrate to form an interference
pattern thereon can be done by well known methods, such as
embossing the surface of a plastic film by pressing it in contact
with a heated nickel embossing shim at high pressure. Other methods
include photolithography, molding of the plastic film against a
patterned surface, and the like.
[0036] Generally, moldable materials are used to form light
transmissive substrate 14 and include, for example, plastics such
as polyethylene terephthalate (PET), especially PET type G,
polycarbonate, acrylics such as polyacrylates including polymethyl
methacrylate (PMMA), polyacrylonitrile, polyvinyl chloride,
polystyrene, polypropylene, polynaphthalene terephthalate (PNT),
mixtures or copolymers thereof, and the like. It is preferred that
light transmissive substrate 14 be substantially composed of a
transparent material such as polycarbonate. The substrate 14 is
formed to have a suitable thickness of about 5 .mu.m to about 100
.mu.m, and preferably a thickness of about 12 .mu.m to about 25
.mu.m. In addition, substrate 14 can be made of one layer or
multiple layers of substrate materials.
[0037] In one embodiment, substrate 14 can be produced from a
thermoplastic film that has been embossed by heat softening the
surface of the film and then passing the film through embossing
rollers which impart the diffraction grating or holographic image
onto the softened surface. In this way, sheets of effectively
unlimited length can be formed with the diffraction grating or
holographic image thereon.
[0038] As shown in FIG. 1A, the color shifting optical coating 16
is a multilayer optical interference film that includes an absorber
layer 18, a dielectric layer 20, and a reflector layer 22. The
absorber layer 18 is deposited on light transmissive substrate 14
by a conventional deposition process such as physical vapor
deposition (PVD), sputtering, or the like. The absorber layer 18 is
formed to have a suitable thickness of about 30-150 Angstroms, and
preferably a thickness of about 50-100 Angstroms. The absorber
layer 18 can be composed of a semi-opaque material such as a grey
metal, including metals such as chromium, nickel, titanium,
vanadium, cobalt, and palladium, as well as other metals such as
iron, tungsten, molybdenum, niobium, aluminum, and the like.
Various combinations and alloys of the above metals may also be
utilized, such as Inconel (Ni--Cr--Fe). Other absorber materials
may also be employed in absorber layer 18 including metal compounds
such as metal fluorides, metal oxides, metal sulfides, metal
nitrides, metal carbides, metal phosphides, metal selenides, metal
silicides, and combinations thereof, as well as carbon, germanium,
cermet, ferric oxide, metals mixed in a dielectric matrix, and the
like.
[0039] The dielectric layer 20 is formed on absorber layer 18 by a
conventional deposition process such as PVD, reactive DC
sputtering, RF sputtering, or the like. The dielectric layer 20 is
formed to have an effective optical thickness for imparting color
shifting properties to security article 10. The optical thickness
is a well known optical parameter defined as the product .eta.d,
where .eta. is the refractive index of the layer and d is the
physical thickness of the layer. Typically, the optical thickness
of a layer is expressed in terms of a quarter wave optical
thickness (QWOT) that is equal to 4.eta.d/.lamda., where .lamda. is
the wavelength at which a QWOT condition occurs. The optical
thickness of dielectric layer 20 can range from about 2 QWOT at a
design wavelength of about 400 nm to about 9 QWOT at a design
wavelength of about 700 nm, and preferably 2-6 QWOT at 400-700 nm,
depending upon the color shift desired. Suitable materials for
dielectric layer 20 include those having a "high" index of
refraction, defined herein as greater than about 1.65, as well as
those have a "low" index of refraction, which is defined herein as
about 1.65 or less.
[0040] Examples of suitable high refractive index materials for
dielectric layer 20 include zinc sulfide (ZnS), zinc oxide (ZnO),
zirconium oxide (ZrO.sub.2), titanium dioxide (TiO.sub.2), carbon
(C), indium oxide (In.sub.2O.sub.3), indium-tin-oxide (ITO),
tantalum pentoxide (Ta.sub.2O.sub.5), ceric oxide (CeO.sub.2),
yttrium oxide (Y.sub.2O.sub.3), europium oxide (Eu.sub.2O.sub.3),
iron oxides such as (II)diiron(III) oxide (Fe.sub.3O.sub.4) and
ferric oxide (Fe.sub.2O.sub.3), hafnium nitride (HfN), hafnium
carbide (HfC), hafnium oxide (HfO.sub.2), lanthanum oxide
(La.sub.2O.sub.3), magnesium oxide (MgO), neodymium oxide
(Nd.sub.2O.sub.3), praseodymium oxide (Pr.sub.6O.sub.11), samarium
oxide (Sm.sub.2O.sub.3), antimony trioxide (Sb.sub.2O.sub.3),
silicon carbide (SiC), silicon nitride (Si.sub.3N.sub.4), silicon
monoxide (SiO), selenium trioxide (Se.sub.2O.sub.3), tin oxide
(SnO.sub.2), tungsten trioxide (WO.sub.3), combinations thereof,
and the like.
[0041] Suitable low refractive index materials for dielectric layer
20 include silicon dioxide (SiO.sub.2), aluminum oxide
(A1.sub.2O.sub.3), metal fluorides such as magnesium fluoride
(MgF.sub.2), aluminum fluoride (AlF.sub.3), cerium fluoride
(CeF.sub.3), lanthanum fluoride (LaF.sub.3), sodium aluminum
fluorides (e.g., Na.sub.3AlF.sub.6 or Na.sub.5Al.sub.3F.sub.14),
neodymium fluoride (NdF.sub.3), samarium fluoride (SmF.sub.3),
barium fluoride (BaF.sub.2), calcium fluoride (CaF.sub.2), lithium
fluoride (LiF), combinations thereof, or any other low index
material having an index of refraction of about 1.65 or less. For
example, organic monomers and polymers can be utilized as low index
materials, including dienes or alkenes such as acrylates (e.g.,
methacrylate), perfluoroalkenes, polytetrafluoroethylene (Teflon),
fluorinated ethylene propylene (FEP), combinations thereof, and the
like.
[0042] The reflector layer 22 is formed on dielectric layer 20 by a
conventional deposition process such as PVD, sputtering, or the
like. The reflector layer 22 is formed to have a suitable thickness
of about 300-1000 Angstroms, and preferably a thickness of about
500-1000 Angstroms. The reflector layer 22 is preferably composed
of an opaque, highly reflective metal such as aluminum, silver,
copper, gold, platinum, niobium, tin, combinations and alloys
thereof, and the like, depending on the color effects desired. It
should be appreciated that semi-opaque metals such as grey metals
become opaque at approximately 350-400 Angstroms. Thus, metals such
as chromium, nickel, titanium, vanadium, cobalt, and palladium, or
cobalt-nickel alloys (which would be magnetic), could also be used
at an appropriate thickness for reflector layer 22.
[0043] In addition, reflector layer 22 can be composed of a
magnetic material such as a cobalt-nickel alloy, or can be formed
of a semitransparent material, to provide for machine readability
for security verification. For example, machine readable
information may be placed on a backing underlying the optical
coating, such as personal identification numbers (PINS), account
information, business identification of source, warranty
information, or the like. In an alternative embodiment, reflector
layer 22 can be segmented to allow for partial viewing of
underlying information either visually or through the use of
various optical, electronic, magnetic, or other detector devices.
This allows for detection of information below optical coating 16,
except in those locations where reflector segments are located,
thereby enhancing the difficulty in producing counterfeits.
Additionally, since the reflector layer is segmented in a
controlled manner, the specific information prevented from being
read is controlled, providing enhanced protection from forgery or
alteration.
[0044] By using an absorber/dielectric/reflector design for color
shifting optical coating 16, such as shown in FIG. 1A, high chroma
variable color effects are achieved that are noticeable to the
human eye. Thus, an object having security article 10 applied
thereto will change color depending upon variations in the viewing
angle or the angle of the object relative to the viewing eye. As a
result, the variation in colors with viewing angle increases the
difficulty to forge or counterfeit security article 10. By way of
example, the color-shifts that can be achieved utilizing color
shifting optical coating 16 in accordance with the present
invention include, but are not limited to, gold-to-green,
green-to-magenta, blue-to-red, green-to-silver, magenta-to-silver,
magenta-to-gold, etc.
[0045] The color shifting properties of optical coating 16 can be
controlled through proper design of the layers thereof. Desired
effects can be achieved through the variation of parameters such as
thickness of the layers and the index of refraction of each layer.
The changes in perceived color which occur for different viewing
angles or angles of incident light are a result of a combination of
selective absorption of the materials comprising the layers and
wavelength dependent interference effects. The interference
effects, which arise from the superposition of the light waves that
have undergone multiple reflections and transmissions within the
multilayered structure, are responsible for the shifts in perceived
color with different angles.
[0046] FIG. 1B depicts a security article 30 according to an
alternative embodiment of the present invention. The security
article 30 includes elements similar to those discussed above with
respect to security article 10, including a light transmissive
substrate 14 formed with an optical interference pattern on a
surface thereof, and a color shifting optical coating 16 that is a
multilayer film. The optical coating 16 is formed, however, on the
same side as the interference pattern on substrate 14 by
conventional deposition processes. The optical coating 16 includes
an absorber layer 18 on the interference pattern, a dielectric
layer 20 on absorber layer 18, and a reflector layer 22 on
dielectric layer 20. As shown in FIG. 1B, each of these layers
formed on substrate 14 conforms to the shape of the interference
pattern such as a holographic image.
[0047] FIG. 2A depicts a security article 40 according to another
embodiment of the present invention. The security article 40
includes elements similar to those discussed above with respect to
security article 10, including a light transmissive substrate 14
formed with an optical interference pattern 15 on an outer first
surface thereof, and a color shifting optical coating 16 formed on
an opposing second surface of substrate 14. The optical coating 16
is a multilayer film that includes an absorber layer 18 and a
dielectric layer 20 thereon, but does not include the reflector
layer. This allows optical coating 16 to be transparent to light
incident upon the surface thereof, thereby providing for visual
verification or machine readability of information below optical
coating 16 on a carrier substrate (not shown).
[0048] FIG. 2B depicts a security article 50 according to an
alternative embodiment of the present invention. The security
article 50 includes elements similar to those discussed above with
respect to security article 40, including a light transmissive
substrate 14 formed with an optical interference pattern on a
surface thereof, and a color shifting optical coating 16 that is a
multilayer film. The optical coating 16 is formed, however, on the
same side as the interference pattern on substrate 14 by
conventional deposition processes. The optical coating 16 includes
an absorber layer 18 on the interference pattern, and a dielectric
layer 20 on absorber layer 18. This allows optical coating 16 to be
transparent to light incident upon the surface thereof, providing
for visual verification or machine readability of information on a
carrier substrate.
[0049] FIG. 3 depicts a security article 60 according to a further
embodiment of the present invention. The security article 60
includes elements similar to those discussed above with respect to
security article 10, including a light transmissive substrate 14
formed with an optical interference pattern 15 on an outer first
surface thereof, and a color shifting optical coating 26 applied to
an opposing second surface of substrate 14. The color shifting
optical coating 26 is formed from a layer of color shifting ink or
paint that includes a polymeric medium interspersed with a
plurality of optical interference flakes having color shifting
properties.
[0050] The color shifting flakes of optical coating 26 are formed
from a multilayer thin film structure that includes the same basic
layers as described above for the optical coating 16 of security
article 10. These include an absorber layer, a dielectric layer,
and optionally a reflector layer, all of which can be composed of
the same materials discussed above in relation to the layers of
optical coating 16. The flakes can be formed to have a symmetrical
multilayer thin film structure, such as
absorber/dielectric/reflector/dielectric/absorber, or
absorber/dielectric/absorber. Alternatively, the flakes can have a
nonsymmetrical structure, such as absorber/dielectric/reflector.
The flakes are formed so that a dimension on any surface thereof
ranges from about 2 to about 200 microns.
[0051] Typically, the multilayer thin film structure is formed on a
flexible web material with a release layer thereon. The various
layers are deposited on the web by methods well known in the art of
forming thin coating structures, such as PVD, sputtering, or the
like. The multilayer thin film structure is then removed from the
web material as thin film flakes, which can be added to a polymeric
medium such as various pigment vehicles for use as an ink or paint.
In addition to the flakes, additives can be added to the inks or
paints to obtain desired color shifting results. These additives
include lamellar pigments such as aluminum flakes, graphite, mica
flakes, and the like, as well as non-lamellar pigments such as
aluminum powder, carbon black, and other colorants such as organic
and inorganic pigments, and colored dyes.
[0052] Suitable embodiments of the flake structure are disclosed in
a copending application Ser. No. 09/198,733, filed on Nov. 24,
1998, now U.S. Pat. No. 6,157,489 and entitled "Color Shifting Thin
Film Pigments," which is incorporated herein by reference. Other
suitable embodiments of color shifting or optically variable flakes
which can be used in paints or inks for application in the present
invention are described in U.S. Pat. Nos. 5,135,812, 5,171,363,
5,278,590, 5,084,351, and 4,838,648, the disclosures of which are
incorporated herein by reference.
[0053] For example, U.S. Pat. No. 5,135,812 discloses a symmetrical
optical multilayer film which is composed either of transparent
all-dielectric stacks, or transparent dielectric and
semi-transparent metallic layered stacks. In the case of an
all-dielectric stack, the optical coating is made of alternating
layers of high and low index of refraction materials. In U.S. Pat.
No. 5,278,590 to Phillips et al., a symmetrical three-layer optical
interference coating which can be formed into flakes is disclosed
and includes first and second partially transmitting absorber
layers that have essentially the same composition and thickness,
with a dielectric spacer layer located between the first and second
absorber layers. The dielectric layer is composed of a material
having a low index of refraction such as magnesium fluoride.
[0054] The color shifting ink or paint utilized to form optical
coating 26 on security device 60 can be applied by conventional
coating devices and methods known to those skilled in the art.
These include, for example, various printing methods such as silk
screen, intaglio, gravure or flexographic methods, and the like.
Alternatively, optical coating 26 can be formed on security device
60 by coextruding a polymeric material containing color shifting
flakes, with the plastic material used to form substrate 14 having
interference pattern 15.
[0055] FIG. 4 depicts a security article 70 according to another
embodiment of the present invention. The security article 70
includes a light transmissive substrate 14 formed with an optical
interference pattern 15 on an outer surface thereof. A color
shifting pigment is dispersed within substrate 14 and comprises a
plurality of multilayer optical interference flakes, such as those
described above with respect to security article 40. The flakes are
dispersed within the material that forms substrate 14 prior to
formation thereof. Preferably, the flakes are oriented so that they
lie parallel to the planar back surface of substrate 14 opposite
from the outer surface thereof in order to provide maximum color
shifting effects.
[0056] The various security articles as described above can be used
in a variety of applications to provide for enhanced security
measures such as anticounterfeiting. The security articles can be
utilized in the form of a label, tag, ribbon, security thread,
tape, and the like, for application in a variety of objects such as
security documents, monetary currency, credit cards, merchandise
packaging, license cards, negotiable notes, bank bonds, paper,
plastic, or glass products, or other similar objects.
[0057] The security articles of the invention can be transferred
and attached to various objects by a variety of conventional
processes. For example, the security articles can applied to an
object by use of a release layer. FIG. 5 shows security article 10
with a release layer 62 formed on substrate 14. The release layer
62 is of a suitable type to allow security article 10 to be removed
therefrom during the application process, such as by a hot-stamping
process. The release layer 62 may be a polymeric material such as
polyvinyl chloride, polystyrene, chlorinated rubber,
acrylonitrile-butadiene-styrene copolymer, nitrocellulose, methyl
methacrylate, acrylic copolymers, fatty acids, waxes, gums, gels,
and mixtures thereof. The release layer is coupled to a carrier
structure 64, which can be part of various manufacturing belts or
other processing structures that assist in transferring security
article 10 to the final structural element.
[0058] As shown in FIG. 6, the release layer is removed when
security article 10 has been applied to an object such as by
hot-stamping, and the security article is coupled to a carrier
substrate 66 by way of an adhesive layer 68. The carrier substrate
66 may take the form of the final structural object to which
security article 10 is to be bonded, such as those objects
discussed above. The materials forming carrier substrate 66 can be
selected from plastics, cellulose, composites, polyester films, PET
sheets, mylar sheets, cellophane, polypropylene, paper, rag/cotton,
combinations thereof, and the like. The material of adhesive layer
68 can be selected from acrylic-based polymers, UV activated
adhesives, ethylene vinyl acetate, polyamides, and the like.
[0059] FIGS. 7-8 depict the method and final structure of affixing
a security article, such as security article 30, to a carrier
substrate 66 through a hot-stamping process. FIG. 7 shows security
article 30 with a release layer 62 formed on one side of a light
transmissive substrate 24, such as an acrylic coating with an
interference pattern formed thereon. The substrate 24 may be
composed of other materials such as those discussed above relative
to substrate 14, including polystyrene, polyacrylonitrile,
polyvinyl chloride, and the like. The release layer 62 is formed on
the side opposite from optical coating 16 on the interference
pattern, and is attached to a carrier structure 64. The release
layer 62 allows security article 30, including substrate 24,
absorber layer 18, dielectric layer 20, and reflector layer 22, to
be released from carrier structure 64 during the hot-stamping
process.
[0060] Generally, carrier structure 64 can be composed of various
materials with various thicknesses which are known by those skilled
in the art. For example, when carrier structure 64 is formed of
PET, the thickness preferably ranges from about 10 .mu.m to about
75 .mu.m. Other materials and thickness ranges are applicable in
light of the teachings contained herein.
[0061] Furthermore, the thickness of light transmissive substrate
24, when taking the form of an acrylic material, can range from
about 3 .mu.m to about 20 .mu.m with an embossed surface.
[0062] Generally, substrate 24 should have a lower melting point or
glass transition temperature than the optical coating, while being
transparent.
[0063] Prior to hot-stamping, an adhesive layer 68 is formed on
reflector layer 22, with the adhesive layer having a thickness of
about 2 .mu.m to about 20 .mu.m. As shown in FIG. 8, the release
layer and carrier structure are removed when security article 30
has been applied to an object such as a carrier substrate 66 by
hot-stamping, with security article 30 being coupled to carrier
substrate 66 by way of adhesive layer 68. The bonding of adhesive
layer 68 against carrier substrate 66 occurs as a heated metal
stamp (not shown) comes into contact with carrier structure 64. The
heated metal stamp simultaneously forces adhesive layer 68 against
carrier substrate 66 while heating adhesive layer 68 to more
effectively bond to carrier substrate 66. Furthermore, the heated
metal stamp softens release layer 62 thereby aiding in releasing
security article 30 from carrier structure 64 which is subsequently
discarded. Once security article 30 has been attached to carrier
substrate 66, the image produced by security article 30 is viewed
from substrate 24 toward optical coating 16.
[0064] The following examples are given to illustrate the present
invention, and are not intended to limit the scope of the
invention.
EXAMPLE 1
[0065] Optical coatings composed of color shifting flakes in a
polymeric vehicle were formed by a drawdown process on light
transmissive substrates composed of PET films containing a
holographic image. The drawdown vehicle included two parts
lacquer/catalyst and one part color shifting flakes. The color
shifting flakes utilized had color shifting properties of
green-to-magenta, blue-to-red, and magenta-to-gold.
EXAMPLE 2
[0066] A color shifting optical coating having a three-layer design
was formed on an embossed transparent film to produce a security
article. The optical coating was formed on the flat surface of the
transparent film on the side opposite from the embossed surface.
The optical coating was formed by depositing an absorber layer
composed of chromium on the flat surface of the transparent film,
depositing a dielectric layer composed of magnesium fluoride on the
absorber layer, and depositing a reflector layer of aluminum on the
dielectric layer.
[0067] Alternatively, the aluminum layer can be deposited so that
it is transparent. This would allow printed information on an
object to be read underneath the optical coating. Further, the
reflector layer can alternatively be composed of a magnetic
material. Such a magnetic feature in the color shifting component
when added to the holographic component would give three
independent security features to the security article.
[0068] The embossed film and optical coating forming the security
article can be rigidly affixed to a carrier substrate, or can be
attached to a release layer so that the security article can be hot
stamped to a surface of an object. In addition, the hot stamped
image of the color shifting thin film can be in the form of a
pattern, as for example, dots, lines, logos, or other images. This
pattern of optically variable effects will add an even greater
degree of deterrence to counterfeiting.
[0069] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the forgoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *