U.S. patent application number 10/705610 was filed with the patent office on 2004-05-27 for optically variable security devices.
Invention is credited to Bonkowski, Richard L., Higgins, Patrick K., Markantes, Charles T., Phillips, Roger W..
Application Number | 20040101676 10/705610 |
Document ID | / |
Family ID | 23943041 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040101676 |
Kind Code |
A1 |
Phillips, Roger W. ; et
al. |
May 27, 2004 |
Optically variable security devices
Abstract
A security article 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
holographic image pattern or an optical diffraction pattern
thereon. A color shifting optical coating is formed on the
substrate such as on the interference pattern or on the opposing
second surface of the substrate, with the optical coating providing
an observable color shift as the angle of incident light or viewing
angle changes. Various processes can be utilized to form the
security article, such as vacuum coating processes, lamination,
laser scribing, and laser imaging. The security article can be
affixed to a variety of objects through various attachment
mechanisms, such as pressure sensitive adhesives or hot stamping
processes, 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: |
HOLME ROBERTS & OWEN, LLP
299 SOUTH MAIN
SUITE 1800
SALT LAKE CITY
UT
84111
US
|
Family ID: |
23943041 |
Appl. No.: |
10/705610 |
Filed: |
November 10, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10705610 |
Nov 10, 2003 |
|
|
|
09489250 |
Jan 21, 2000 |
|
|
|
Current U.S.
Class: |
428/323 |
Current CPC
Class: |
B42D 25/29 20141001;
Y10T 428/24479 20150115; B42D 25/23 20141001; B42D 25/355 20141001;
G03H 1/0252 20130101; G03H 2250/10 20130101; G03H 2250/42 20130101;
G03H 2250/40 20130101; Y10T 428/24942 20150115; B32B 27/36
20130101; B42D 25/24 20141001; B42D 25/425 20141001; B42D 25/47
20141001; B42D 25/00 20141001; B42D 25/455 20141001; B42D 25/378
20141001; G03H 1/0244 20130101; G03H 2250/36 20130101; B42D 25/36
20141001; G03H 2250/34 20130101; B42D 25/328 20141001; Y10T 428/25
20150115; G03H 1/0256 20130101; B42D 25/21 20141001; B42D 25/41
20141001 |
Class at
Publication: |
428/323 |
International
Class: |
B32B 005/16 |
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
1. A security article, comprising: (a) a light transmissive
substrate having a first surface and an opposing second surface,
the first surface having an optical interference pattern associated
therewith, said optical interference pattern comprises
microstructures having dimensions in the range from about 0.1
microns to about 10 microns; and (b) a color shifting multilayer
optical coating overlying the second surface of the substrate.
2. The security article of claim 1, wherein the microstructures
have dimensions in the range from about 0.1 microns to about 1
micron.
3. The security article of claim 1, wherein the color shifting
multilayer optical coating comprises: an absorber layer overlying
the second surface of the substrate; a dielectric layer overlying
the absorber layer; and a reflector layer overlying the dielectric
layer.
4. The security article of claim 1, wherein the color shifting
multilayer optical coating comprises: an absorber layer overlying
the second surface of the substrate; a dielectric layer overlying
the absorber layer; and an absorber layer overlying the dielectric
layer.
5. The security article of claim 1, wherein the color shifting
multilayer optical coating comprises alternating layers of low and
high index of refraction dielectric layers.
6. The security article of claim 1, wherein the color shifting
multilayer optical coating comprises a plurality of multilayer
color shifting flakes dispersed in a polymeric medium.
7. The security article of claim 1, further comprising a laser
ablated image formed in said optical coating.
8. The security article of claim 1, further comprising an adhesive
layer laminating said optical coating to said second surface of the
substrate.
9. The security article of claim 1, wherein said security article
is in the form of a security thread.
10. The security article of claim 1, further comprising an adhesive
layer overlying the optical coating for securing the security
article to an object.
11. The security article of claim 1, wherein the optical
interference pattern is formed on said light transmissive
substrate.
12. The security article of claim 1, wherein the optical
interference pattern is on a layer secured to the light
transmissive substrate.
13. A security article comprising: (a) a light transmissive
substrate having a first surface and an opposing second surface,
the first surface having an optical interference pattern associated
therewith; (b) a color shifting multilayer optical coating
overlying the second surface of the substrate; and (c) a laser
ablated image formed in said optical coating.
14. The security article of claim 13, wherein the optical
interference pattern comprises microstructures having dimensions in
the range from about 0.1 microns to about 10 microns.
15. The security article of claim 13, wherein the optical
interference pattern comprises microstructures having dimensions in
the range from about 0.1 microns to about 1 micron.
16. The security article of claim 13, wherein the color shifting
multilayer optical coating comprises: an absorber layer overlying
the second surface of the substrate; a dielectric layer overlying
the absorber layer; and a reflector layer overlying the dielectric
layer.
17. The security article of claim 13, wherein the color shifting
multilayer optical coating comprises: an absorber layer overlying
the second surface of the substrate; a dielectric layer overlying
the absorber layer; and an absorber layer overlying the dielectric
layer.
18. The security article of claim 13, wherein the color shifting
multilayer optical coating comprises alternating layers of low and
high index of refraction dielectric layers.
19. The security article of claim 13, wherein the color shifting
multilayer optical coating comprises a plurality of multilayer
color shifting flakes dispersed in a polymeric medium.
20. The security article of claim 13, further comprising an
adhesive layer laminating said optical coating to said second
surface of the substrate.
21. The security article of claim 13, wherein said security article
is in the form of a security thread.
22. The security article of claim 13, further comprising an
adhesive layer overlying the optical coating for securing the
security article to an object.
23. The security article of claim 13, wherein the optical
interference pattern is formed on said light transmissive
substrate.
24. The security article of claim 13, wherein the optical
interference pattern is on a layer secured to the light
transmissive substrate.
25. A security article comprising: (a) a light transmissive
substrate having a first surface and an opposing second surface,
the first surface having an optical interference pattern associated
therewith; and (b) a color shifting multilayer optical coating
overlying the second surface of the substrate, and (c) an adhesive
layer laminating said optical coating to said second surface.
26. The security article of claim 25, wherein the optical
interference pattern comprises microstructures having dimensions in
the range from about 0.1 microns to about 10 microns.
27. The security article of claim 25, wherein the optical
interference pattern comprises microstructures having dimensions in
the range from about 0.1 microns to about 1 micron.
28. The security article of claim 25, wherein the color shifting
multilayer optical coating comprises: an absorber layer overlying
the second surface of the substrate; a dielectric layer overlying
the absorber layer; and a reflector layer overlying the dielectric
layer.
29. The security article of claim 25, wherein the color shifting
multilayer optical coating comprises: an absorber layer overlying
the second surface of the substrate; a dielectric layer overlying
the absorber layer; and an absorber layer overlying the dielectric
layer.
30. The security article of claim 25, wherein the color shifting
multilayer optical coating comprises alternating layers of low and
high index of refraction dielectric layers.
31. The security article of claim 25, wherein the color shifting
multilayer optical coating comprises a plurality of multilayer
color shifting flakes dispersed in a polymeric medium.
32. The security article of claim 25, further comprising a laser
ablated image formed in said optical coating.
33. The security article of claim 25, wherein said security article
is in the form of a security thread.
34. The security article of claim 25, further comprising an
adhesive layer overlying the optical coating for securing the
security article to an object.
35. The security article of claim 25, wherein the optical
interference pattern is formed on said light transmissive
substrate.
36. The security article of claim 25, wherein the optical
interference pattern is on a layer secured to the light
transmissive substrate.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application of U.S. application Ser.
No. 09/489,250, filed Jan. 21, 2000 and entitled "Optically
Variable Security Devices," which is incorporated herein by
reference, and to which priority is claimed.
[0002] This application is related to U.S. application Ser. No.
09/351,102, filed Jul. 8, 1999, and entitled "Diffractive Surfaces
with Color Shifting Backgrounds."
[0003] This application is related to U.S. application Ser. No.
10/688,357, filed Oct. 17, 2003, and entitled "Security Articles
having Diffractive Surfaces and Color Shifting Backgrounds."
BACKGROUND OF THE INVENTION
[0004] 1. The Field of the Invention
[0005] 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.
[0006] 2. The Relevant Technology
[0007] 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.
[0008] 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.
[0009] 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.
Three-dimensional holograms have also been developed based on
differences in refractive indices in a polymer using crossed laser
beams, including one reference beam and one object beam. Such
holograms are called volume holograms or 3D holograms. Furthermore,
the use of holographic images on various objects to discourage
counterfeiting has found widespread application.
[0010] There currently exist several applications for surfaces
embossed with holographic patterns which range from decorative
packaging 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.
[0011] Every type of first order diffraction structure, including
conventional holograms and grating images, has a major shortcoming
even if encapsulated in a rigid plastic. When diffuse light
sources, such as ordinary room lights or an overcast sky, are used
to illuminate the holographic image, all diffraction orders expand
and overlap so that the diffraction colors are lost and not much of
the visual information contained in the hologram is revealed. What
is typically seen is only a silver colored reflection from the
embossed surface and all such devices look silvery or pastel, at
best, under such viewing conditions. Thus, holographic images
generally 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.
[0012] Since the use of security holograms has found widespread
application, there exists a substantial incentive for
counterfeiters to reproduce holograms which are frequently used in
credit cards, banknotes, and the like. Thus, a hurdle that security
holograms must overcome to be truly secure, is the ease at which
such holograms can be counterfeited. One step and two step optical
copying, direct mechanical copying and even re-origination have
been extensively discussed over the Internet. Various ways to
counteract these methods have been explored but none of the
countermeasures, taken alone, has been found to be an effective
deterrent.
[0013] 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.
[0014] Due to the level of sophistication of counterfeiting
methods, it has become necessary to develop more advanced security
measures. One approach, disclosed in U.S. Pat. Nos. 5,624,076 and
5,672,410 to Miekka et al., embossed metal particles or optical
stack flakes are used to produce a holographic image pattern.
[0015] A further problem with security holograms is that it is
difficult for most people to identify and recollect the respective
images produced by such holograms for verification purposes. The
ability of the average person to authenticate a security hologram
conclusively is compromised by the complexity of its features and
by confusion with decorative diffractive packaging. Thus, most
people tend to confirm the presence of such a security device
rather than verifying the actual image. This provides the
opportunity for the use of poor counterfeits or the substitution of
commercial holograms for the genuine security hologram.
[0016] In other efforts to thwart counterfeiters, the hologram
industry has resorted to more complex images such as producing
multiple images as the security device is rotated. These enhanced
images provide the observer with a high level of "flash" or
aesthetic appeal. Unfortunately, this added complexity does not
confer added security because this complex imagery is hard to
communicate and recollection of such imagery is difficult, if not
impossible, to remember.
[0017] It would therefore be of substantial advantage to develop
improved security products which provide enhanced viewing qualities
in various lighting conditions, especially in diffuse lighting, and
which are usable in various security applications to make
counterfeiting more difficult.
SUMMARY AND OBJECTS OF THE INVENTION
[0018] It is a primary object of the invention to provide a
security article having color shifting properties which increases
the difficulty of counterfeiting in a variety of applications.
[0019] 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.
[0020] Another object of the invention is to provide a security
article with an optical interference pattern such as a holographic
pattern that has enhanced visibility and contrast to provide for
viewing under diffuse lighting conditions without the need for
direct specular light.
[0021] To achieve the foregoing 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
holographic image pattern or an optical diffraction pattern
thereon. A color shifting optical coating is formed on the
substrate such as on the interference pattern or on the opposing
second surface of the substrate, with the optical coating providing
an observable color shift as the angle of incident light or viewing
angle changes. Various processes can be utilized to form the
security article, such as vacuum coating processes, organic
coatings, lamination, laser scribing, and laser imaging.
[0022] The color shifting optical coating can be varied in
different embodiments of the invention. For example, the optical
coating can be a multilayer optical interference film such as a
three layer optical stack of absorber-dielectric-reflector, or
alternating layers of low and high index of refraction dielectric
layers. In addition, the optical coating can be formed from a
plurality of multilayer optical interference flakes dispersed in a
polymeric medium such as a color shifting ink.
[0023] In other embodiments, various security articles are formed
by laminating a prelaminate structure including a color shifting
optical coating, which can optionally be laser imaged by ablation,
to a substrate embossed with an optical interference pattern.
[0024] In another method of the invention, a color shifting optical
coating is formed on a master shim so as to conform to the shape of
an optical interference pattern on the shim. A carrier substrate
layer is affixed to the optical coating and is removed along with
the optical coating from the shim to produce a security article
with the interference pattern replicated in the optical
coating.
[0025] The security article of the invention can be affixed to a
variety of objects through various attachment mechanisms, such as
pressure sensitive adhesives or hot stamping processes, 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 to a
variety of objects such as security documents, monetary currency,
credit cards, merchandise, etc.
[0026] 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
[0027] 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:
[0028] FIG. 1 is a schematic depiction of a security article
according to one embodiment of the present invention;
[0029] FIG. 2 is a schematic depiction of a security article
according to another embodiment of the present invention;
[0030] FIG. 3 is a schematic depiction of a security article
according to a further embodiment of the present invention;
[0031] FIG. 4 is a schematic depiction of a security article
according to another embodiment of the present invention;
[0032] FIG. 5 is a schematic depiction of a security article
according to yet another embodiment of the present invention;
[0033] FIG. 6 is a schematic depiction of a security article
according to a further embodiment of the present invention;
[0034] FIG. 7 is a schematic depiction of a security according to
another embodiment of the present invention;
[0035] FIG. 8A is a schematic depiction of a security article
according to a further embodiment of the present invention;
[0036] FIG. 8B is an enlarged sectional view of the security
article of FIG. 8A;
[0037] FIG. 9 is a schematic depiction of a security article
according to another embodiment of the present invention;
[0038] FIG. 10A is a schematic depiction of a prelaminate structure
used to form a security article according to an additional
embodiment of the present invention;
[0039] FIG. 10B is a schematic depiction of a security article
formed from the prelaminate structure of FIG. 10A;
[0040] FIG. 11 is a schematic depiction of a security article
according to another embodiment of the present invention;
[0041] FIG. 12 is a schematic depiction of a security article
according to an alternative embodiment of the present
invention;
[0042] FIG. 13 is a schematic depiction of a security article
according to an additional embodiment of the present invention;
[0043] FIG. 14 is a schematic depiction of a security article
according to another embodiment of the present invention;
[0044] FIG. 15 is a schematic depiction of a hot stamping process
used to form one embodiment of a security article according to the
invention;
[0045] FIG. 16 is a schematic depiction of a hot stamping process
used to form another embodiment of a security article according to
the invention;
[0046] FIGS. 17A and 17B are diagrams showing the geometries of
various viewing conditions used in measuring the optical
characteristics of a security article of the invention;
[0047] FIG. 18 is a graph showing the spectral profiles for a
security article of the invention;
[0048] FIG. 19 is a graphical representation of the CIE Lab color
space showing trajectory of color for a security article of the
invention;
[0049] FIG. 20 is a graph showing the off-gloss spectral profiles
for a security article of the invention;
[0050] FIG. 21 is a graph showing the on-gloss spectral profiles
for a security article of the invention;
[0051] FIG. 22 is a graph showing the on-gloss spectral profiles
for a security article of the invention;
[0052] FIG. 23 is a photomicrograph of a thin film optical stack
used in a security article of the invention; and
[0053] FIGS. 24A and 24B are photomicrographs showing holographic
relief at the top of a thin film optical stack used in a security
article of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0054] 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 optical interference
patterns such as holographic or diffraction grating patterns with
color shifting foils or inks decreases the possibility of
counterfeiting. Furthermore, the articles of the invention allow a
user to more easily view the image or diffraction effect in diffuse
light without the need for direct specular light.
[0055] 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. The present invention combines the performance features
of light interference effects with the diffractive effects of a
diffractive surface such as a hologram. The security articles allow
for ready identification by the average person while still
preserving complex optical patterns, thus overcoming disadvantages
of conventional holographic technology.
[0056] The various embodiments of the invention, described in
further detail below, can be formed using three basic
constructions. One involves substituting the aluminum reflector of
a hologram or other diffractive surface with a thin film optical
interference stack. This construction builds the hologram structure
right into the optical interference stack. In this case, the
optical coating is vacuum deposited directly onto the embossed
surface. The second construction adds a thin film color shifting
foil or ink to the side of a substrate opposite of the embossing.
Whether foil or ink is used, the interference effect can be based
on a metal-dielectric-absorber interference structure, or
all-dielectric optical designs. The third approach involves
laminating a color shifting optical coating structure, which can be
digitally imaged by laser ablation, reflective pattern etching, or
chemical etching by photolithography, to a diffractive surface such
as a hologram.
[0057] Referring to the drawings, wherein like structures are
provided with like reference designations, FIG. 1 depicts a
security article 10 according to one embodiment of the present
invention. The security article 10 includes a light transmissive
substrate 12 having an optical interference pattern 14 such as an
embossed image on an outer first surface thereof. A color shifting
optical coating 16 is formed on an opposing second surface of
substrate 12 and is discussed in further detail below. The
combination of substrate 12 and color shifting optical coating 16
forming security article 10 provides a security feature that
reduces the possibility of duplication, forgery and/or
counterfeiting of an object having security article 10 thereon.
[0058] The optical interference pattern 14 formed on the outer
surface of light transmissive substrate 12 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, Kinegram.RTM. devices (i.e., holograms with
changing imagery as the angel of view is changed), Pixelgram.RTM.
devices (i.e., a hologram with multiple holographic pixels arranged
in a spatial orientation that generates one holographic image),
zero order diffraction patterns, moire patterns, or other light
interference patterns based on microstructures having dimensions in
the range from about 0.1 .mu.m to about 10 .mu.m, preferably about
0.1 .mu.m to about 1 .mu.m, and various combinations of the above
such as hologram/grating images, or other like interference
patterns.
[0059] The particular methods and structures that form optical
interference pattern 14 are known by those skilled in the art. For
example, embossing the light transmissive substrate to form an
interference pattern such as a hologram 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.
[0060] The Kinegram.RTM. device is a two-dimensional,
computer-generated image (available from OVD Kinegram Corp. of
Switzerland) in which the individual picture elements are filled
with light-diffracting microstructures. These microstructures are
extremely fine surface modulations with typical dimensions of less
than one micrometer.
[0061] Generally, moldable thermoformable materials are used to
form light transmissive substrate 12 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, cellulose diacetate and cellulose
triacetate, polypropylene, polydicyclopentadiene, mixtures or
copolymers thereof, and the like. In one preferred embodiment,
light transmissive substrate 12 is substantially composed of a
transparent material such as polycarbonate. The substrate 12 is
formed to have a suitable thickness of about 3 .mu.m to about 100
.mu.m, and preferably a thickness of about 12 .mu.m to about 25
.mu.m. In addition, substrate 12 can be made of one layer or
multiple layers of substrate materials. Generally, substrate 12
should have a lower melting point or glass transition temperature
than the optical coating, while being transparent.
[0062] In one method, substrate 12 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. Alternatively, the diffractive surface
can be made by passing a roll of plastic film coated with an
ultraviolet (UV) curable polymer, such as PMMA, through a set of UV
transparent rollers whereby the rollers set a diffractive surface
into the UV curable polymer and the polymer is cured by a UV light
that passes through the UV transparent rollers.
[0063] As shown in FIG. 1, the color shifting optical coating 16 is
a multilayer optical interference stack or foil that includes an
absorber layer 18, a dielectric layer 20, and a reflector layer 22.
The absorber layer 18 can be deposited on light transmissive
substrate 12 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 30-300 .ANG.
Angstroms (.ANG.), and preferably a thickness of about 50-100
.ANG..
[0064] 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 sub-oxides, metal sulfides, metal nitrides,
metal carbides, metal phosphides, metal selenides, metal silicides,
and combinations thereof, as well as carbon, germanium, ferric
oxide, metals mixed in a dielectric matrix, and the like.
[0065] The dielectric layer 20 can be formed on absorber layer 18
by a conventional deposition process such as PVD, chemical vapor
deposition (CVD), plasma enhanced chemical vapor deposition
(PECVD), 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/.lambda., where .lambda. 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.
[0066] 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.
[0067] Suitable low refractive index materials for dielectric layer
20 include silicon dioxide (SiO.sub.2), aluminum oxide
(Al.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.
[0068] The reflector layer 22 can be 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 .ANG., and preferably a thickness of
about 500-1000 .ANG.. 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 .ANG.. Thus, metals such as
chromium, nickel, titanium, vanadium, cobalt, and palladium, or
cobalt-nickel alloys, could also be used at an appropriate
thickness for reflector layer 22.
[0069] 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.
[0070] As shown in FIG. 1, security article 10 can also optionally
include an adhesive layer 24 such as a pressure sensitive adhesive
on reflector layer 22. The adhesive layer 24 allows security
article 10 to be easily attached to a variety of objects such as
credit cards, certificates of authenticity, bank cards, banknotes,
visas, passports, driver licenses, immigration cards, and
identification cards, as well as containers and other
three-dimensional objects. The adhesive layer 24 can be composed of
a variety of adhesive materials such as acrylic-based polymers, and
polymers based on ethylene vinyl acetate, polyamides, urethane,
polyisobutylene, polybutadiene, plasticized rubbers, combinations
thereof, and the like. Alternatively, a hot stamping process,
examples of which are discussed in further detail below, can be
utilized to attach security article 10 to an object. By using an
absorber/dielectric/reflect- or design for color shifting optical
coating 16, such as shown in FIG. 1, 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 well as variations in angles
of incident light. As a result, the variation in colors with
viewing angle increases the difficulty to forge or counterfeit
security article 10. Furthermore, the thin film interference color
shifting coating changes the diffractive colors, either
suppressing, modifying or enhancing certain colors depending on the
inherent color shifts of the diffractive and thin film structures.
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.
[0071] 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.
[0072] FIG. 2 depicts a security article 30 according to another
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 12
formed with an optical interference pattern 14 on an outer first
surface thereof, and a color shifting optical coating 16 formed on
an opposing second surface of substrate 12. The optical coating 36
is a multilayer film that includes an absorber layer 18, a
dielectric layer 20 thereon, and another absorber layer 38, but
does not include a reflector layer. This multilayer film
configuration is disclosed in U.S. Pat. No. 5,278,590 to Phillips
et al., which is incorporated by reference herein. Such a film
structure allows optical coating 36 to be transparent to light
incident upon the surface thereof, thereby providing for visual
verification or machine readability of information below optical
coating 36 on a carrier substrate (not shown). An adhesive layer 24
such as a pressure sensitive adhesive can be optionally formed on
absorber layer 38 if desired to allow attachment of security
article 30 to an appropriate surface of an object.
[0073] FIG. 3 depicts a security article 40 according to a further
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 12
formed with an optical interference pattern 14 on an outer first
surface thereof, and a color shifting optical coating 46 formed on
an opposing second surface of substrate 12. The optical coating 46
however, is a multilayer optical stack that includes all dielectric
layers. Suitable optical stacks for optical coating 46 that include
all dielectric layers are disclosed in U.S. Pat. Nos. 5,135,812 and
5,084,351 to Phillips et al., the disclosures of which are
incorporated herein by reference. Generally, optical coating 46
includes alternating layers of low and high index of refraction
dielectric layers which can be composed of various materials such
as those discussed above for dielectric layer 20. The all
dielectric stack of optical coating 46 enables security article 40
to be transparent to light incident upon the surface thereof. An
adhesive layer 24 such as a pressure sensitive adhesive can be
formed on optical coating 46 if desired.
[0074] FIG. 4 depicts a security article 50 according to a further
embodiment of the present invention. The security article 50
includes elements similar to those discussed above with respect to
security article 10, including a light transmissive substrate 12
formed with an optical interference pattern 14 on an outer first
surface thereof, and a color shifting optical coating 56 applied to
an opposing second surface of substrate 12. The color shifting
optical coating 56 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.
[0075] The color shifting flakes of optical coating 56 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.
[0076] 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 color shifting 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 color shifting 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.
[0077] 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 by reference herein.
[0078] The color shifting ink or paint utilized to form optical
coating 56 on security article 50 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 56 can be formed on security article
50 by coextruding a polymeric material containing color shifting
flakes, with the plastic material used to form substrate 12 having
interference pattern 14.
[0079] An adhesive layer 24 such as a pressure sensitive adhesive
can optionally be formed on optical coating 56 as desired to allow
attachment of security article 50 to an appropriate surface of an
object.
[0080] In another embodiment of the invention shown in FIG. 5, a
security article 60 includes elements similar to those discussed
above with respect to security article 10, including a light
transmissive substrate 12 formed with an optical interference
pattern 14 on an outer first surface thereof. A color shifting
optical coating 66 is provided in the form of a foil that is
laminated to a second opposing surface of substrate 12 by way of an
adhesive layer 62. The laminating adhesive may be composed of a
pressure sensitive adhesive, polyurethanes, acrylates, natural
latex, or combinations thereof. The optical coating 16 includes an
absorber layer 18, a dielectric layer 20 thereon, and a reflector
layer 22 on dielectric layer 20. The optical coating 16 is formed
on a carrier sheet 64 prior to being laminated to substrate 12. For
example, the optical coating 16 can be deposited in a vacuum roll
coater onto a transparent plastic carrier sheet such as PET prior
to lamination.
[0081] In alternative embodiments of security article 60, the
optical coating can take the form of a multilayer structure having
absorber and dielectric layers with no reflector layer such as in
optical coating 36 of security article 30, or can take the form of
an all dielectric optical stack such as in optical coating 46 of
security article 40. In addition, the optical coating of security
article 60 can take the form of a color shifting ink or paint layer
such as in optical coating 56 of security article 50.
[0082] FIG. 6 depicts a security article 70 according to a further
embodiment of the present invention. The security article 70
includes elements similar to those discussed above with respect to
security article 60, including a light transmissive substrate 12
formed with an optical interference pattern 14 on an outer first
surface thereof. A color shifting optical coating 76 is provided in
the form of a foil that is laminated to a second opposing surface
of substrate 12 by way of an adhesive layer 62. The optical coating
76 includes an absorber layer 18, a dielectric layer 20, and a
reflector layer 22, which are formed on a carrier sheet 64 prior to
being laminated to substrate 12. The optical coating 76 further
includes an essentially optically inactive interlayer 78 that is
shear sensitive. The interlayer 78 is formed between dielectric
layer 20 and reflector layer 22 by a conventional coating process
and is composed of a very thin layer (e.g., about 50-200 .ANG.) of
vapor deposited material such as polytetrafluoroethylene,
fluorinated ethylene propylene (FEP), silicone, carbon,
combinations thereof, or the like. The interlayer 78 makes it
impossible to peel off security article 70 in an undamaged state
once it has been applied to an object.
[0083] It should be understood that the shear interlayer as
described for security article 70 can be utilized if desired in the
other above described embodiments that utilize an optical coating
comprising a multilayer foil. For example, FIG. 7 depicts a
security article 80 that includes essentially the same elements as
those discussed above with respect to security article 10,
including a light transmissive substrate 12 having an optical
interference pattern 14, and a color shifting optical coating 86
having an absorber layer 18, a dielectric layer 20, and a reflector
layer 22. The optical coating further includes an essentially
optically inactive interlayer 88 that is formed between dielectric
layer 20 and reflector layer 22. An adhesive layer 24 such as a
pressure sensitive adhesive can optionally be formed on reflector
layer 22, or on an optional carrier sheet 64, such as a plastic
sheet, to allow attachment of security article 80 to an appropriate
surface of an object. In the latter case, the absorber layer would
be adhesively bonded to light transmissive substrate 12 since
carrier sheet 64 would carry the layers 18, 20, 88, and 22.
[0084] FIG. 8A depicts a security article 90 according to another
embodiment of the present invention in which the embossed surface
of a substrate carries the optical coating. The security article 90
includes elements similar to those discussed above with respect to
security article 10, including a light transmissive substrate 12
having an optical interference pattern 14 embossed on a surface
thereof, and a color shifting optical coating 96 that is a
multilayer film optical stack. The optical coating 96 is formed,
however, on the same side as the interference pattern on substrate
12 by conventional vacuum deposition processes. The optical coating
96 includes an absorber layer 18, a dielectric layer 20 under
absorber layer 18, and a reflector layer 22 under dielectric layer
20. Alternatively, the order of layer deposition can be reversed,
i.e., the absorber layer may be deposited first onto the optical
interference pattern, followed by the dielectric layer, and finally
the reflective layer. In this configuration, one can view the
interference pattern such as a modified hologram by viewing the
security article through light transmissive substrate 12.
[0085] Each of these layers of optical coating 96 formed on
substrate 12 preferably conforms to the shape of the underlying
interference pattern such as a holographic image, resulting in the
holographic structure being present at the outer surface of optical
coating 96. This is shown more clearly in the enlarged sectional
view of security article 90 in FIG. 8B. The vacuum processing
utilized in forming optical coating 96 or other multilayer coating
will maintain the holographic structure through the growing film so
that the holographic image is retained at the outer surface of
optical coating 96. This is preferably accomplished by a directed
beam of vapor essentially normal to the coated surface. Such
processing tends to replicate the initial structure throughout the
optical stack to the outer surface.
[0086] An adhesive layer 24 such as a pressure sensitive adhesive
can be optionally formed on a surface of substrate 12 opposite from
optical coating 96 to allow attachment of security article 90 to an
appropriate surface of an object.
[0087] It should be understood that in alternative embodiments of
security article 90, optical coating 96 can take the form of a
multilayer structure having absorber and dielectric layers with no
reflector layer such as in optical coating 36 of security article
30, or can take the form of an all-dielectric optical stack such as
in optical coating 46 of security article 40.
[0088] FIG. 9 depicts a security article 100 according to another
embodiment of the present invention which is formed from a master
shim 102 used to replicate an interference structure such as a
hologram in an optical stack. The master shim 102 is composed of a
metallic material such as nickel, tin, chromium, or combinations
thereof, and has a holographic or diffractive pattern 104 formed
thereon. An optical coating 106 is formed on pattern 104 by
conventional vacuum deposition processes such as physical vapor
deposition. The optical coating 106 includes a release layer (not
shown) directly deposited onto pattern 104, an absorber layer 18, a
dielectric layer 20 on absorber layer 18, and a reflector layer 22
on dielectric layer 20. The release layer may be composed of a
material such as gold, silicone, or a low surface energy material
such as FEP. The dielectric layer is preferably a low index
material such as MgF.sub.2 or SiO.sub.2 because of the stress
benefits provided. Each of these layers of optical coating 106 is
formed on master shim 102 so as to conform to the shape of the
underlying holographic or diffractive pattern 104. A receiver sheet
108 such as a plastic sheet with an adhesive (not shown) is
attached to reflector layer 22. The optical coating 106 can then be
stripped away from master shim 102 onto receiver sheet 108 for
attachment onto an object, leaving the holographic or diffractive
pattern replicated in optical coating 106.
[0089] In alternative embodiments of security article 100, optical
coating 106 can take the form of a multilayer structure having
absorber and dielectric layers with no reflector layer such as in
optical coating 36 of security article 30, or can take the form of
an all-dielectric optical stack such as in optical coating 46 of
security article 40.
[0090] In the following embodiments, various security articles are
formed by laminating laser imaged optical coating structures to
embossed substrates. Lamination provides the advantage of being
cost effective and secure since the two expensive security
components (i.e., the color shifting film and hologram) are kept
separate until laminated together. The laminated articles can
include either a color shifting foil or ink, which can be used as
the background underneath a holographic image, with the holographic
image capable of being seen only at selected angles. The hologram
is thus seen superimposed on a color shifting background that also
has an associated image.
[0091] In the embodiment illustrated in FIGS. 10A and 10B, a
security article 110 is provided with laser ablated images formed
in a color shifting optical coating 116. As shown in FIG. 10A,
optical coating 116 is formed on a carrier sheet 64 such as
transparent PET by conventional coating processes to form a
prelaminate structure 117. The optical coating 116 is formed by
depositing a reflector layer 22 on carrier sheet 64, followed by
deposition of a dielectric layer 20 and an absorber layer 18. A
laser ablated image 118 is then formed in optical coating 116 on
prelaminate structure 117 by a conventional laser imaging system
The laser ablated image 118 can take the form of digital images
(e.g., pictures of people, faces), bar codes, covert (i.e.,
microscopic) data and information, or combinations thereof. The
laser imaging can be accomplished by using a semiconductor diode
laser system such as those available from Presstek, Inc. and
disclosed in U.S. Pat. Nos. 5,339,737 and Re. 35,512, the
disclosures of which are incorporated by reference herein.
Alternatively, reflective pattern etching, or chemical etching by
photolithography can be utilized to form various images in the
optical coating.
[0092] The prelaminate structure 117 with laser ablated image 118
is then laminated to a a light transmissive substrate 12 having an
optical interference pattern 14, such as a diffractive or
holographic pattern on a surface thereof, as shown in FIG. 10B. The
prelaminate structure 117 is laminated to substrate 12 through
adhesive layer 62 at a surface opposite from interference pattern
14 to form the completed security article 110. Alternatively,
prelaminate structure 117 can be laminated on the embossed surface
of substrate 12. In the latter case, the device is viewed through
transmissive substrate 12. In such a case, a high index transparent
layer must be in place on the embossed surface so that index
matching between the adhesive and embossed surface does not occur.
Suitable examples of such a high index transparent layer include
TiO.sub.2 or ZnS.
[0093] It should be understood that prelaminate structure 117 can
be used as a final product if desired without subsequent lamination
to an embossed substrate. In this case, prelaminate structure 117
could be directly attached to an object by use of an adhesive or
other attachment mechanism. The prelaminate structure can also be
prepared by directly laser ablating a suitable optically variable
layer which has been directly deposited onto a holographic or
diffractive substrate.
[0094] FIG. 11 shows a security article 120 according to another
embodiment of the invention which includes elements similar to
those discussed above with respect to security article 110,
including a light transmissive substrate 12 having an optical
interference pattern 14 such as a holographic or diffractive
pattern, and a color shifting optical coating 126 that is laminated
to substrate 12 by an adhesive layer 62. The optical coating 126
includes an absorber layer 18, a dielectric layer 20, and a
reflector layer 22. The optical coating 126 is deposited on a
carrier sheet 64 to form a prelaminate structure prior to being
laminated to substrate 12. The prelaminate structure is subjected
to a laser imaging process such as described above for security
article 110 in order to form a laser scribed number 122 such as a
serial number for use in serialized labels.
[0095] FIG. 12 depicts a security article 130 according to a
further embodiment of the invention which includes elements similar
to those discussed above with respect to security articles 110 and
120, including a light transmissive substrate 12 formed with a
holographic or diffractive pattern, and a color shifting optical
coating 136 that is laminated to substrate 12 by an adhesive layer
62. The optical coating 136 includes an absorber layer 18, a
dielectric layer 20, and a reflector layer 22 as described above.
The optical coating 136 is deposited on a carrier sheet 64 to form
a prelaminate structure prior to being laminated to substrate 12.
The prelaminate structure is subjected to a laser imaging process
such as described above for security articles 110 and 120 in order
to form both a laser ablated image 118 as well as a laser scribed
number 122, thereby combining the features of security articles 110
and 120.
[0096] In an additional embodiment of the invention illustrated in
FIG. 13, a security article 140 includes elements similar to those
discussed above with respect to security articles 130, including a
light transmissive substrate 12 formed with an optical interference
pattern 4, and a color shifting optical coating 146 that is
laminated to a substrate 12 by way of an adhesive layer 62. The
optical coating 146 includes an absorber layer 18, a dielectric
layer 20, and a reflector layer 22 as described above, with optical
coating 146 being deposited on a carrier sheet 64 to form a
prelaminate structure prior to being laminated to substrate 12. The
prelaminate structure is subjected to a laser imaging process such
as described above for security article 130 in order to form both a
laser ablated image 118 as well as a laser scribed number 122. In
addition, a covert resistive layer 148 is formed on substrate 12
over interference pattern 14. The covert resistive layer 148 is
composed of a transparent conductive material such as indium tin
oxide (ITO), indium oxide, cadmium tin oxide, combinations thereof,
and the like, and provides enhanced features to security article
140 such as a defined electrical resistance. Such covert resistive
layers are described in U.S. patent application Ser. No.
09/094,005, filed Jun. 9, 1998, now U.S. Pat. No. 6,031,457, the
disclosure of which is incorporated herein by reference. The covert
resistive layer can be applied to other embodiments of the
invention if desired.
[0097] It should be understood that the above embodiments depicted
in FIGS. 10-13 could alternatively be laminated obversely such that
the embossed surface with a high index transparent dielectric layer
is adjacent to the laminating adhesive and optical coating. For
example, FIG. 14 depicts a security article 150 which includes
essentially the same elements as security article 130, including a
light transmissive substrate 12 with an optical interference
pattern 14, and a color shifting optical coating 156 that is
laminated to substrate 12 by way of an adhesive layer 62. The
optical coating 156 includes an absorber layer 18, a dielectric
layer 20, and a reflector layer 22. The optical coating 156 is
deposited on a carrier sheet 64 to form a prelaminate structure
prior to being laminated to substrate 12. The prelaminate structure
is subjected to a laser imaging process to form both a laser
ablated image 118 as well as a laser scribed number 122. As shown
in FIG. 14, the optical coating 156 is laminated to substrate 12 so
as to be adjacent to optical interference pattern 14 such as a
holographic or diffractive pattern.
[0098] In various alternative embodiments of the security articles
depicted in FIGS. 10-14, the optical coating can take the form of a
multilayer structure having absorber and dielectric layers with no
reflector layer such as in optical coating 36 of security article
30, or can take the form of an all-dielectric optical stack such as
in optical coating 46 of security article 40. In addition, the
optical coating of these security articles can take the form of a
color shifting ink or paint layer such as in optical coating 56 of
security article 50. Such alternative optical coatings would be
formed directly on carrier sheet 64 prior to laser imaging and
subsequent lamination.
[0099] It should be understood that the color shifting optical
coatings deposited directly on embossed substrates, such as shown
in the embodiments of FIGS. 1-4 and 7-9, can also be imaged if
desired, such as by laser ablation as discussed above.
[0100] The security articles of the invention can be transferred
and attached to various objects by a variety of attachment
processes. One preferred process is hot stamping, which is shown
schematically in FIGS. 15 and 16. A hot stamp structure 160
according to one embodiment is illustrated in FIG. 15 and includes
a carrier sheet 162 having a thermal release layer 164 on one
surface thereof. An embossed substrate 12 having an interference
pattern 14 plus a high index transparent layer (not shown) on
interference pattern 14 is attached to release layer 164 so that
the release layer is on the side opposite of the embossing. A color
shifting optical coating 166 which has been applied to substrate 12
as a solution coating of ink is interposed between substrate 12 and
a thermally activated adhesive layer 168.
[0101] Generally, carrier sheet 162 can be composed of various
materials such as plastics with various thicknesses which are known
by those skilled in the art. For example, when carrier sheet 162 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. Furthermore,
carrier sheet 162 can be part of various manufacturing belts or
other processing structures that assist in transferring the
security article to a desired object.
[0102] The release layer 164 is composed of a suitable material to
allow substrate 12 to be removed from carrier sheet 162 during the
hot stamping process. The release layer 164 may be a polymeric
material such as polyvinyl chloride, polystyrene, chlorinated
rubber, acrylonitrile-butadiene-styrene (ABS) copolymer,
nitrocellulose, methyl methacrylate, acrylic copolymers, fatty
acids, waxes, gums, gels, mixtures thereof, and the like. The
release layer 164 can have a thickness of about 1 .mu.m to about 25
.mu.m.
[0103] The thermally activated adhesive layer 168 can be composed
of various adhesive materials such as acrylic-based polymers,
ethylene vinyl acetate, polyamides, combinations thereof, and the
like. The adhesive layer 168 can have a thickness of about 2 .mu.m
to about 20 .mu.m.
[0104] During the hot stamping process, carrier sheet 162 is
removed by way of release layer 164 from substrate 12 after hot
stamp structure 160 has been pressed onto a surface of an object
169 to be hot stamped, with the security article composed of
substrate 12 and optical coating 166 being bonded to object 169 by
way of thermally activated adhesive layer 168. The object 169 may
be composed of various materials such as plastics, polyester,
leathers, metals, glass, wood, paper, cloth, and the like, e.g.,
any material surface that requires a security device. The bonding
of adhesive layer 168 against the surface of object 169 occurs as a
heated metal stamp (not shown), having a distinct shape or image,
comes into contact with object 169 which is heated to a temperature
to provide a bond between object 169 and adhesive layer 168. The
heated metal stamp simultaneously forces adhesive layer 168 against
object 169 while heating adhesive layer 168 to a suitable
temperature for bonding to object 169. Furthermore, the heated
metal stamp softens release layer 164, thereby aiding in the
removal of carrier sheet 162 from substrate 12 in the areas of the
stamp image to reveal the security article attached to object 169.
Once the security article has been released from carrier sheet 162,
the carrier sheet is discarded. When the security article has been
attached to object 169, the image produced by the security article
is viewed from substrate 12 toward optical coating 166.
[0105] A hot stamp structure 170 according to another embodiment is
illustrated in FIG. 16 and includes essentially the same elements
as hot stamp structure 160 discussed above. These include a carrier
sheet 162 having a thermal release layer 164 on one surface
thereof, and an embossed substrate 12 having an interference
pattern 14, with substrate 12 attached to release layer 164. A
color shifting multilayer optical coating 176 which has been
applied to substrate 12 as a direct vacuum coating is interposed
between substrate 12 and a thermally activated adhesive layer
168.
[0106] The hot stamping process for hot stamp structure 170 is the
same as that described above for hot stamp structure 160. The
carrier sheet 162 is removed by way of release layer 164 from
substrate 12 after hot stamp structure 170 has been pressed onto a
surface of an object 169, with the security article composed of
substrate 12 and optical coating 176 being bonded to object 169 by
adhesive layer 168.
[0107] It should be understood that various of the other
embodiments of the security article of the invention described
previously can be adapted for a hot stamping process.
[0108] Alternatively, a cold transfer process using a UV activated
adhesive can be utilized to attach the security articles of the
invention to various objects. Such a process is described in a
paper by I. M. Boswarva et al., Roll Coater System for the
Production of Optically Variable Devices (OVD's) for Security
Applications, Proceedings, 33rd Annual Technical Conference,
Society of Vacuum Coaters, pp. 103-109 (1990), the disclosure of
which is incorporated by reference herein.
[0109] 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, security labels, financial transaction cards,
monetary currency, credit cards, merchandise packaging, license
cards, negotiable notes, stock certificates, bonds such as bank or
government bonds, paper, plastic, or glass products, or other
similar objects. Preferred applications for the security articles
of the invention are in the following areas; 1) rigid substrate
security products, such as payment cards, "smart cards," and
identification cards; 2) laminated products, including driving
licenses, security passes, border crossing cards, and passports;
and 3) "one trip" security items such as tax stamps, banderoles,
package seals, certificates of authenticity, gift certificates,
etc.
[0110] The above applications share some common considerations. In
these applications, the holographic or other diffractive structure
is best presented and protected by a rigid substrate and overlay
lamination, or if these are not used, the application should be one
that does not require long circulation life and extensive handling.
An over-riding factor is that the application document must depend
on a limited array of security devices and a relatively non-skilled
observer must be able to easily authenticate the devices. Credit
cards, for example, usually depend on one major security device,
and secondary devices such as printing techniques, for their
authentication. The arsenal of tools available for banknote
security (watermarks, intaglio, special paper, threads, etc.)
cannot be applied to rigid opaque substrates. The security device
of the invention, therefore, can be a very cost-effective
"defensive shield" readily discerned by the public, and integrated
into the overall style of the security document.
[0111] The security devices of the present invention also have the
advantage of being suited to automated machine verification, while
at the same time preserving an easily remembered feature, namely, a
distinct color shift as the viewing angle is changed. Security can
be further heightened by the incorporation of digital information
that can be compared to the same image in photographic form. While
the creative computer hacker might find ways to simulate a simple
logo on a decorative holographic substrate, simulation of the color
shifting background using an ink-jet printer is not possible and
images cannot be created that appear only at certain viewing
angles.
[0112] While conventional holograms provide an element of
protection in document security, such holograms are difficult for
the lay person to authenticate decisively since they exhibit
eye-catching appeal, but do not naturally lead the observer into a
correct determination. Building on the eye-catching appeal of
holograms, the security articles of the invention add distinctive
elements which are both easy to authenticate and difficult to
replicate or simulate.
[0113] The following examples are given to illustrate the present
invention, and are not intended to limit the scope of the
invention.
EXAMPLE 1
[0114] 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
[0115] 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.
[0116] Alternatively, the aluminum layer can be deposited so that
it is essentially 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.
[0117] 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.
EXAMPLE 3
[0118] A security article was formed by laminating a laser imaged
optical coating structure to an embossed substrate according to the
present invention. The security article included four main parts:
1) A laser ablated image, 2) a laser ablated bar code or serial
number, 3) a multilayer color shifting thin film, and 4) a
holographic image.
[0119] The color shifting thin film was deposited in a vacuum roll
coater onto a clear polyester (PET) substrate that was 1 mil thick.
The thin film was formed by depositing a metal layer of aluminum on
the substrate, followed by a dielectric layer composed of magnesium
fluoride being deposited on the metal layer, and an absorber layer
composed of chromium being deposited on the dielectric layer.
Thereafter, the thin film was subjected to laser ablation using a
laser diode imaging system based on the Heidelberg Quickmaster
printing system to provide digital encoding. The imaging system
used a high-resolution diode laser array with a spot size of
approximately 30 microns. After the digital information had been
encoded into the thin film, a plastic film embossed with a hologram
was laminated to the thin film using a pressure sensitive adhesive
to produce the completed security article. The hologram word
"security" was placed upside down so as to place the embossed
surface close to the thin film as well as to protect the image. The
finished structure of the security article was similar to that
shown for the embodiment of FIG. 14 described above.
[0120] Upon visual inspection, the security article had three
distinct images as it was rotated back and forth. At normal
viewing, a profile of a woman's face created by laser ablation was
seen in a magenta color, which at high angle shifted to a green
color. This color shift was easy to see under various lighting
conditions and it is easy to recall this simple color shift. At an
intermediate angle, the hologram appeared with its multitude of
facets of color and images.
EXAMPLE 4
[0121] The security article of Example 3 was subjected to various
tests to measure its optical performance, which are described as
follows.
[0122] A. Instrumentation and Sample Orientation
[0123] A Zeiss GK/311M goniospectrophotometer using a xenon flash
lamp with angle adjustable fiber optics for both illumination and
reflectance was used to characterize the security article. Three
types of viewing conditions were examined, with the geometries
utilized shown in FIGS. 17A and 17B. These viewing conditions
included: a) set angle of illumination at 45 degrees, with the
angles of measurement being 5 degree increments from 65 through 155
degrees (FIG. 17A); b) off-gloss, with the angles of illumination
being 5 degree increments from 25 through 75 degrees and the angles
of measurement being 5 degree increments from 100 through 150
degrees (FIG. 17B); and c) on-gloss (specular), with the angles of
illumination being 5 degree increments from 25 through 80 degrees
and the angles of measurement being 5 degree increments from 100
through 155 degrees (FIG. 17B). Calibration for all these
geometries was made with a white tile. To test whether any
orientation effects were present, the security article was oriented
at 0, 90, 180 and 270 degrees with respect to the viewing optics
for each viewing condition.
[0124] B. Optical Results
[0125] The results of optical testing for the three viewing
conditions are described below. The measurements indicate that it
is possible to uniquely characterize the interference optically
variable effects separately from the diffractive effects.
[0126] 1. Set Angle of Illumination
[0127] In this configuration, the optical properties of the
hologram dominated the spectral response, but only in two
orientations, at 90.degree. and 270.degree. (i.e., at 90.degree. to
the grooves of the hologram). Inspection of the spectral profiles
shown in the graph of FIG. 18 show that the various diffractive
orders of the hologram predominate. Only at small and large angle
differences does the color shifting thin film show its spectra. A
comparison of the color trajectory in CIE Lab color space in FIG.
19 shows that the resultant color travel for the security device is
due mostly to the hologram. The chroma or color saturation of the
hologram is high as can be seen by the large excursions from the
achromatic point (a*=b*=0).
[0128] 2. Off-Gloss Geometry
[0129] In contrast to those spectral profiles found above, the
off-gloss measurements showed that in this geometry, the color
shifting thin film now dominated the optical response, irrespective
of sample orientation. While there was no evidence of optical
effects from the hologram in the 0.degree. orientation, combined
optical effects from the hologram and the thin film optical stack
were seen in the 90.degree. orientation. The spectral peaks arising
from the optical stacks were modified as shown in FIG. 20. The
spectral profiles are typical of metal-dielectric-absorber optical
stacks where the spectrum and the resultant color move to shorter
wavelengths as the view angle increases. It is interesting to note
that in this configuration, the brightness, L* moves from high to
low as the color changes from magenta-to-yellow. At the
0.degree./180.degree. orientation, the hologram showed no spectral
peaks.
[0130] 3. On-Gloss Geometry
[0131] In the on-gloss geometry, the security article showed two
distinct features: one at 0.degree., 180.degree. and one at
90.degree., 270.degree.. In the first orientation, the only optical
effect was the one typical from a color shifting thin film where
the color shifts to shorter wavelengths as the angle of incidence
is increased. FIG. 21 is a graph showing the on-gloss spectral
profiles for the security article at the first orientation. The
color shifts from magenta to green. Peak suppression occurs
progressively as the peaks move toward the shorter wavelengths.
This suppression is caused, in part, by the higher reflectance
values arising from the standard white tile as well as from the
security article itself. Theoretically, the spectra of the thin
film retain the same spectrum, but shift to shorter wavelengths as
the angle of incidence increases. It should be noted that the
on-gloss orientation at 0.degree., 180.degree. is well suited to
machine reading since the peaks are well defined for the optical
stack and are free of holographic features.
[0132] In the second orientation, the spectral peaks arising from
the optical stack, at the high angles of incidence, show large
optical interactions with the hologram. FIG. 22 is a graph showing
the on-gloss spectral profiles for the security article at the
second orientation.
[0133] C. Optical Microscopy
[0134] The security article was viewed on a Zeiss optical
microscope to see the digital features encoded into the color
shifting thin film. FIG. 23 is a photomicrograph of the digital
image (magnified 50.times.) in the thin film optical stack of the
security article. In FIG. 23, the digital dots (ablation holes),
where the entire optical stack is missing, have dimensions on the
order of about 100 microns. Each 100 micron pixel is actually made
up of 30 micron overlapping digital dots. Thus, it is possible to
write covert information with 30-100 micron pixel resolution, a
resolution below the eye detection limit. The cracking observed in
the coating is typical of dielectric films that have undergone
stress relief. These cracks do not have any detrimental effect
either on the optical properties or adhesion of the thin film.
EXAMPLE 5
[0135] A color shifting optical stack having a three-layer design
was formed on an embossed transparent plastic film by direct vacuum
coating of the optical stack onto a holographic surface to produce
a security article. During the fabrication process, the standard
aluminum layer was removed from a commercially available hologram
by a dilute solution of sodium hydroxide. After rinsing and drying,
the embossed surface was coated in vacuum with a layer of
semi-transparent metal, a layer of low index dielectric material,
and finally an opaque layer of aluminum, by physical vapor
deposition processes. This thin film optical stack was a
Fabry-Perot filter centered at 500 nanometers. The layers could be
coated in the opposite direction with a corresponding change in
which side of the plastic film was modified by the optical
stack.
[0136] When this construction was viewed through the plastic film,
a superposition of the hologram and the optical stack was seen. In
essence the rainbow of colors that were in the initial hologram
have been modified by the optical stack whereby some colors are
accentuated and some are suppressed. Actually, the hologram could
be viewed from both sides; on the aluminum side the original
hologram can be seen, and on the other side, the superposition of
the hologram and the optical stack can be seen through the plastic
film.
[0137] A close examination of the optical stack by scanning
electron microscopy (SEM) showed that the diffractive surface
pattern of the hologram was replicated up through the optical stack
so that the holographic image was preserved in the aluminum
surface. This is depicted in FIGS. 24A and 24B, which are
photomicrographs of SEM images (magnified 2000.times. and
6000.times., respectively) showing holographic relief at the top of
the optical stack of the security article.
[0138] 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.
* * * * *