FIELD OF THE INVENTION
This invention relates generally to hot-stamping and more
particularly, to the hot-stamping of an optical device with a hot-stamp adhesive
having optical effect flakes to a substrate or article.
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims priority from
U.S. provisional application No. 60/744,842 filed on April 14, 2006
U.S. provisional application No. 60/779,484 filed on March 6, 2006
U.S. provisional application No. 60/832,826 filed on July 24, 2006
U.S. provisional application No. 60/861,608 filed on November 29, 2006
. All patents and patent applications mentioned heretofore and hereafter
are incorporated herein by reference, for all purposes.
This application is related to
11/273,985 filed November 15, 2005
, which is a continuation-in-part application of patent application serial
10/666,318 filed on September 18, 2003
, now issued as
6,987,590 on January 17, 2006
entitled "Patterned Reflective Optical Structures";
US provisional application number 60/673,080
filed on April 20, 2005 entitled "Patterned Reflective Optical Structures";
US provisional application number 60/729,907 filed October 25, 2005
entitled "Patterned Optical Structures With Enhanced Security Feature"
which are all incorporated therein by reference for all purposes.
BACKGROUND OF THE INVENTION
The term Chromagram used hereafter is meant to include
optical structures that have a patterned or windowed substrate together with special
effect coatings or layers supported by or supporting the patterned or windowed substrate.
Chromagrams of various designs are described in
US Patent Application publication number 20060285184
, and used as security devices or for enhancing the security of products
and for their aesthetic appeal.
One type of Chromagram is an optical structure that exhibits
the effects of surface relief patterns, such as holograms or diffractive gratings,
together with a pattern such as alphanumeric characters, bar codes, or graphical
or pictorial designs, and additional optical effects in the regions around such
pattern. Such structures are described in
United States Patent application publication number 20060077496
in the name of Argoitia et al. published April 13, 2006, referred to hereafter
as '496. Another Chromagram-type structure is described in
United States Patent application 20050128543
in the name of Phillips et al. In '496 patterned substrates having windowed
regions that one can see through, are coated with optically variable (OV) coatings
or optically variable inks that can be seen through the windows. For all intents
and purposes, all references described heretofore or hereafter are incorporated
herein by reference.
By use of the term "patterned" layer, it is meant that
a reflective, opaque, or partially transmissive layer is applied over a substrate
which may be planar or have a surface relief pattern therein, in a manner that forms
a desired "pattern" or design. By way of non-limiting examples, the patterned reflective
layer can be formed in the shape of letters, numerals, bar codes and/or graphical
or pictorial designs.
One type of the surface relief pattern is a demetalized
(demet) hologram described in
US Patents 5,314,767
. To enhance the security of holograms and to prevent contact copies being
made, a technique was developed for making holograms by a process of demetallization.
Demetalized holograms and patches are used in passports and ID cards to protect
photographs and data.
Although not limited thereto, this invention primarily
relates to types of Chromagrams, made with optical and, or, magnetic effect hot
stamp adhesive having flakes and/or colorant therein. Heretofore, a desirous quality
of adhesives used to bond two substrates together, wherein one substrate is to be
seen through the other, has been for the adhesive to be substantially transparent
and having required bonding properties. Therefore the goal has been to have an adhesive
that "appears" to be as invisible as possible, and substantially matched in refractive
index to the substrates with which it is bonding, thereby substantially un-affecting
light passing therethrough.
Hot stamp transfer foils have been provided in conjunction
with hot stamp machines to affix images onto various substrates such as paper, plastic
film and even rigid substrates. Hot stamping is a dry process. One commercially
available machine for hot stamping images onto substrates is the Malahide E4-PK
produced by Malahide Design and Manufacturing Inc. Machines of this type are shown
and described on the Internet at www.hotstamping.com. Simplistically, in
a hot-stamping process, a die is attached to the heated plate which is pressed against
a load roll of hot stamping foil to affix the foil to an article or substrate. A
roll on transfer process could also be used in this invention. In this case, the
article substrate and the adhesive (UV or heat activated) is brought together at
a nip to effect the transfer of the hot stamp layer to the article substrate.
An image is typically formed by utilizing a metal or silicone
rubber die into which the desired image has been cut. This die is placed in the
hot stamping machine and is used to press the image into hot stamp foil utilizing
a combination of heat and pressure. The back side of the foil is generally coated
with a dry heat activated, thermo set adhesive, for example an acrylate based adhesive.
Upon the application of heat, the adhesive becomes tacky in regions of the heated
image and adheres to the paper or plastic substrate.
Hot stamping is described or mentioned in the
United States patents 5,002,312
, in the name of Roger Phillips of Flex Products Inc. of Santa Rosa Ca.
Additional details of a hot stamping process may be found on
pages 440-445 of the Modem Plastics Encyclopedia, 1979-1980
United States patent 5,059,245
describes forming an optical coating upon a substrate wherein the optical
coating in one embodiment comprises optically variable flakes applied within a carrier
as paint or ink which is then dried or cured upon the substrate.
Optical effect flakes in an adhesive may have one or more
predetermined optical characteristics; for example, flakes may be optically variable
changing color with a change in angle of incident light, or flakes may be diffractive,
or may have covert symbols therein or thereon, or the flakes may simply be reflective
or absorptive. In some instances, optical effect flakes have a combination of optical
effects, for example they may be diffractive and color shifting, or they may be
diffractive and reflective, or diffractive and highly absorptive depending upon
the desired effect. Furthermore flakes having different optical effects may be mixed
together in desired ratios. Pigments that may be added include those based on interference,
for example mica based pigments, Fabry Perot type pigments, liquid crystal type
pigments, including those that color shift with viewing angle, non- shifting pigments
like gold and nickel, and other metallic flakes. Dyes and or other pigments may
be added to the adhesive to modify the colors of the interference and /or diffractive
pigments, including covert platelets, known as charms or taggants, and other shaped
particles. The examples of covert flakes include, but not limited to, charms or
taggants as taught in
United States patent application publication number 2006/0035080
incorporated herein by reference, shaped pigments as disclosed in
United States patent application publication number 20060035080
, magnetic flakes, fluorescent pigments, standard UV activated to form
visible light, or specialized anti-Stokes materials UV activated to form visible
Heretofore, in instances when a layer of material such
as an ink coated substrate having optically variable flakes therein was hot stamped
to another substrate or object, prior to hot stamping, a heat-activated adhesive
layer, typically 2-20 microns thick, was applied to the substrate or object to adhere
the layer of material to the substrate or object by applying suitable heat and pressure.
In relation to Figs. 1a and 1b,
US Patent 7,029,745
teaches a method of affixing a security article, such as security article
30, to a carrier substrate 66 through a hot-stamping process. Fig. 1a 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
release layer 62 allows security article 30, including substrate 24, absorber layer
18, dielectric layer 20 with optical interference pattern 15, and reflector layer
22, to be released from carrier structure 64 during the hot-stamping process.
As shown in Fig. 1b, a release layer 62 and carrier structure
64 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. Sometimes the release stays with
the substrate 62. 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
In the field of hot-stamping, a plurality of commercially
available adhesives have been developed to provide required adhesion of foils to
same and other materials, under heat and pressure. Although these heat-activated
adhesives have performed their intended function, they have not provided additional
functions now perceived to be highly useful.
For example, the inventors of this invention have discovered
that these dry heat activated adhesives can be applied to a substrate and can be
preloaded or premixed into the adhesive with special optical effect flakes, such
as magnetic flakes, magnetically alignable flakes, magnetic flakes with color shifting
properties, color shifting flakes, color switching flakes, diffractive flakes and
or covert flakes bearing indicia also known as charms.
It is an object of this invention to provide a hot stamp
adhesive, that has therein, special effect flakes, and wherein the flakes can be
seen through one or more layers the adhesive is bonding. It was not anticipated
that acceptable adhesion would result when optically variable pigment was added
to the hot stamp adhesive. The adhesive could also be printed in a pattern so as
to affect a patterned transfer even though a flat die would be used to make the
hot stamp transfer. Printing the adhesive rather than having an image in the die
of the hot stamper results in a better transferred image with higher definition
without "fringe" often seen in foil type transfers. Fringe refers to the ragged
edges of the foil image when hot stamped onto surface of paper, for example. The
problem is evident often in the hot stamp transfer of the letter "A" where the triangle
of the letter "A" is covered with foil.
It is an object of the invention, to provide a Chromagram
where the provision of a discrete special effect layer is obviated, by adding special
effect flakes to a hot-stamp adhesive for to bond two objects together. This makes
for a product that easier to manufacture and reduces manufacturing costs.
It is an object of this invention to hot stamp a substrate
to another substrate or object, wherein optical effect adhesive bearing optical
effect flakes is solely used as an adhesive.
Security threads have been known for some time.
US Patent No. 4,186,943 to Lee
describes a windowed security thread that is contained within the banknote
paper. Lee uses diachronic coatings, in all- dielectric optical stack, having a
symmetrical design so that the same reflected and transmitted color and color shift
is seen from either side of the paper through elongate windows of the paper substrate.
In one embodiment, paper is removed at various points over the embedded security
thread to allow the thread to be more clearly seen. Furthermore, unfortunately,
counterfeiters have at their disposal from the packaging field commercially available
transparent film made from hundreds of alternating layers of polymeric films that
display similar color shifting and reflection and transmission characteristics as
found in '943. See http://www.ptonline.com/articles/200603fa1.html. This
makes foils based on all-dielectric suspect as an anti-counterfeit system.
Patent application publication number
US20060255586 by Lazzerini
describes a security device composed of holographic regions with a continuous
metal layer of aluminum but with variations in its thickness. In co-pending application,
WO2004014665 by Lazzerini
, the method of "thinning" the deposited aluminum is by chemical etching
after some areas of the aluminum are protected by a transparent ink adapted to preserve
the aluminum by the attacks of acid substances. The aluminum is thinned from an
optical density of 1.8, transmission of 1.6%, down to 0.7 optical density or about
20% transmission, in the "A" portion, item 3 of the '586 patent application. In
other words, the aluminum is opaque in areas other than the "A" portion and only
semi-transparent in the "A' areas. The use of magnetic elements in register with
the holographic elements is mentioned but does not indicate the nature of the magnetic
elements. Another version of the invention uses color shifting ink between the backing
layer of Polyethylene Terephtalate (PET) and the continuous aluminum metal layer.
The type of color shifting ink is not defined - they could be mica based transparent
color shift with angle pigments, or liquid crystal color shift inks both of which
are transparent - in our invention the pigment is opaque). At any rate, Lazzerini
does not teach a color shift material based on Optically Variable Adhesive (OVA),
does not have color shift from both sides of the security thread, does not have
covert charms, and has no-demet areas in the holographic regions and does not have
magnetic elements confined within the color shift pigment.
US Patent No. 7,054,042 to Holmes et al
, hereinafter referred to as '042, disclosed a device employing a demet
hologram with a thin film color shifter underneath. The use of a thin film interference
filter has a large drawback in terms of color control because the methods employed,
vacuum deposition methods, particularly, those that are of such running speeds to
make them commercially viable has at best a plus/minus 2% error on the dielectric
layer thickness. For a Fabry Perot structure as discussed in '042, a typical design
would be Al opaque/Low index ie. MgF2/absorber Cr 3nm. With a 2% variation for a
4 QW optical thickness at 550nm, this thickness variation translates into a delta
E color of 27 units and at 6 QW optical thickness at 550nm translates into a delta
E color of 31. From a practical point of view, this color variation makes the distinction
between the genuine product and a counterfeit problematical. The only hope to improve
the color of a foil with a vacuum process is to have extensive editing which only
leads to high a high expensive product.
US Patent No. 5,700,550 to Uyama
teaches the use of an all dielectric optical stack on a holographic forming
layer, which has even less control of color than '042, since the structure disclosed
by Uyama has five layers of alternating ZnS and MgF2 or TiO2 and SiO2. Each layer
is subject to a 2% variation which would result in even larger color variation.
Uyama also requires that the device be placed on a black background otherwise if
placed on a white substrate the transmissive nature of his device will result in
light beams combining from light reflecting from the substrate back through the
device with the reflected light beam from the interference stack to produce white
light again. Even if the substrate (i.e. currency paper were colored) the light
recombination would give low chroma.
The aim of this invention is to eliminate the drawbacks
of the prior art so that a new security device having the desired characteristics
of a thread for banknotes or other paper documents or even a plastic document have
a layered system of counterfeit deterrence that can be manufactured with high quality
of color control, along with visible and covert features as well protection for
durability on both sides of the device while maintaining a minimum thickness. Therefore,
the problem that is being addressed is to provide a new security thread with enhanced
features that can easily be assembled. The problem is solved by giving the viewer
security features that can be remembered, that has a distinct color shift and covert
features for machine or forensic analysis.
It is an object of the invention to provide a simplified
mutli-layered security device using an optically variable adhesive (OVA).
It is an object of the invention, to provide a thin asymmetric
security thread displaying different optical effects when viewed from different
It is another object of the invention, to provide a thin
security device with high chroma and high color control.
It is another object of the invention, to provide a thin
security thread comprising a demet hologram and covert taggents therein.
It is another object of this invention, to provide a hot
stamp image with multilayer security features.
SUMMARY OF THE INVENTION
In accordance with this invention a structure for providing
an optical effect is provided, comprising a first substrate and a second substrate
affixed to the first substrate by an adhesive alone, wherein the adhesive comprises
an energy activated binder having a plurality of particles distributed therein or
thereon for providing the optical effect detectable through the first substrate.
It should be understood the second substrate can be any
object to which the first substrate can be affixed, for example by hot stamping.
In accordance with another aspect of the invention, a method
of forming an article for providing an optical effect is provided comprising the
BRIEF DESCRIPTION OF THE DRAWINGS
- a) providing a first substrate having at least a first optical effect;
- b) coating the first substrate with a carrier vehicle having optical effect
particles therein or thereon, wherein the particles provide a second optical effect
detectable through the first substrate; and
- c) hot stamping the coated first substrate to a second substrate or article
so that the carrier vehicle is solely used as an adhesive in the hot stamping.
Exemplary embodiments of the invention will now be described,
in conjunction with the drawings, in which:
Fig. 1a is a schematic view of a security article before
hot-stamping, according to the prior art.
Fig. 1b is a schematic view of a security article shown
in Fig. 1a hot-stamped to a carrier substrate, according to the prior art.
Fig. 2 is a cross-sectional view of a foil in accordance
with the invention shown before transfer to an object wherein a substrate having
a patterned Al layer has a dry hot stamp adhesive bottom layer having optically
variable pigment (OVP) or optically variable magnetic pigment dispersed within the
Fig. 3 is cross-section of a Chromagram with optically
variable adhesive after hot stamp transfer onto a paper or cardboard substrate.
Fig. 4 is a plurality of different views of a same banknote
having a hologram bonded to a note substrate having optically variable adhesive
as the hot stamp adhesive.
Fig. 5 is a cross-sectional view of a Chromagram with optically
variable adhesive and high index layer before hot stamp transfer.
Fig. 6 is a cross-sectional view of a Chromagram with optically
variable patterned adhesive.
Fig. 7 is a cross-sectional view of a tamper evident device
before hot stamping.
Fig. 8 is a cross-sectional view of the tamper evident
device shown in Fig. 7, after hot stamping.
Fig. 9 is a cross-sectional view of the tamper evident
device shown in Fig. 7, after attempted removal.
Fig. 10a is a cross-sectional view of a Chromagram structure
showing color shift hot stamp adhesive with an over-layer of adhesive containing
Fig. 10b Security thread constructed from OVA and roll-on
transfer of demet hologram using two different OVA layers.
Fig. 11 is a cross-sectional view of a Chromagram structure
showing patterned aluminum with a color shift hot stamp adhesive and a separate
top layer of adhesive containing covert platelets.
Fig. 12a is a cross-sectional view of a Chromagram structure
according to one embodiment of the present invention.
Fig. 12b is a cross-sectional view of a Chromagram with
an adhesive between an optically variable (OV) foil and demet hologram.
Fig. 12c is a cross-sectional view of a Chromagram with
a clear adhesive between the foil and demet hologram, wherein the adhesive contains
covert flakes or a low concentration of optically variable flakes or optically variable
Fig. 12d is a cross-sectional view of a Chromagram with
Fig. 13 is a cross-sectional view of a thin color shifting
Figs. 14 and 15 are graphs used to calculate formulas for
estimation of the amount of deposited pigment.
Figs. 16 and 17 are graphs depicting reflectance scans
of hot stamp transferred images.
Fig. 18 is graphical representation of the subtractive
Fig. 19 is a graph of cross web optical density measurements.
Fig. 20 is a photograph of a security device applied to
a casino chip through a hot stamp transfer adhesive process.
Fig. 21 is a cross-sectional view of a refined "synthetic
thread" wherein multiple optical effects are produced by a layered security system.
Fig. 22 is a set of photographs of a security thread according
to the present invention.
Fig. 23 is a cross-sectional view of a Laminate Security
Thread using OVA according to one embodiment of the present invention.
Fig. 24 is a cross-sectional view of a security thread
wherein at least three layers of adhesive are used to laminate two substrates.
Fig. 25 is a cross-sectional view of a security thread
wherein a substrate is laminated using two different OVA's.
For the purpose of this application, the term "energy activated
adhesive" or "energy activated binder", means a bonding substance that requires
an energy source for curing. The energy activated adhesives include, but are not
limited to, hot stamp adhesives, UV activated adhesives, thermoplastic and thermoset
adhesives, paint-based polymeric compositions, varnishes, and staining compositions.
By way of example, an adhesive is selected from the group of: polymethacrylate,
polyacrylate, polyamide, nitrocellulose, alkyd resin, polyvinyl alcohol, polyvinyl
acetate, and polyurethane.
The methods of activating the adhesives include hot stamping,
UV curing, applying heat, or a beam of electrons. For brevity, an energy activated
adhesive, possibly with special flakes therein, is referred to as "an adhesive"
hereinbelow where it does not lead to confusion.
As was described heretofore, in the background of the invention,
the field of hot stamping and more particularly, hot stamping of one optical coating
or substrate with another is well known. For example, coated substrates bearing
images, logos or other indicia are hot stamped onto lottery cards, passports, banknotes,
driver's licenses, poker chips, and a variety of other articles and substrates are
Although commercially available hot stamp adhesives are
known to perform their intended function, the inventors of this invention serendipitously
discovered that some cured paints having optically variable flakes therein serve
adequately as hot stamp adhesives. Note, that the paint is no longer a paint but
is now an adhesive thereby obviating the requirement or step of adding an adhesion
layer of material to a paint layer having optically variable properties. Furthermore,
the added benefit of having special effect flakes within the hot stamp adhesive
provides enhanced structures. As well overall thinner structures may result from
this method, as well as structures with a patterned adhesive layer, and structures
comprising more than one layers of adhesive providing different optical effects,
for example having charms in one layer, and OVP in another.
The adhesive may be printed into patterns or flood coated
over the entire surface. If patterned, the product becomes more tamper proof since
the product cannot be physically removed in one piece. Attempts to remove the device
by dissolving the adhesive using solvents would also be detrimental since the solvent
would also attack the hardcoat/release which in turn would destroy the device, making
The flakes may vary considerably in size, but are preferably
at least 5 microns in diameter or across their surface. Flakes can be optically
variable flakes, color-shifting flakes, thin film light interference flakes, diffractive
flakes, reflective flakes, light absorbing flakes, covert flakes, flakes bearing
symbols or indicia, flakes that are uniform in shape, and magnetic flakes, color
shift pigments, such as thin film metal-dielectric, all dielectric, mica based pigments,
liquid crystal pigments etc.
The inventors also discovered that flake material such
as optically variable, diffractive, absorptive, or reflective flakes or flakes having
other properties such as covert features, can be added directly to conventional
hot stamping adhesives prior to curing to provide both the benefits of adhesion
and the optical effects which the added flakes exhibit.
Some of the devices described in this application comprise
a light transmissive or essentially transparent substrate, which may be made of
Polyethylene Terephtalate (PET), Oriented Polypropylene (OPP) or other suitable
plastic material. By way of example, a PET layer has a thickness of 6-25 microns.
It should be understood that when the description of a device contains only one
substrate, a second substrate can be a protective coat, a release coat, or any document
or object to which the first substrate can be affixed, by way of example a paper
document or a free standing plastic film.
An optical stack, also referred to as an interference stack,
comprises a reflective layer, an absorber, and a dielectric layer between the reflective
layer and the absorber, as it is known in the art. A reflective layer can be made
of any metal that has a reflectance over 20%, preferably aluminum. By way of example,
a dielectric layer is made of MgF2 or other transparent material as known
in the art.
An absorber can be a grey metal with a ratio of n/k about
1, where n is the real part of the refractive index and k is the imaginary part
of the reflective index, for example Cr, Ti, or Ni, or can be a non-selective absorber
across the visible spectrum like TiN, or can be a cermet, as described in the article
Influence of Nanosized Metal Clusters on the Generation of Strong Colors and
Controlling of their Properties through Physical Vapor Deposition (PVD)" by R. Domnick
et al., 49th Annual Technical Conference Proceedings (2006), Society of Vacuum Coaters
, incorporated herein by reference. By way of example, a cermet material
comprises silver islands in a dielectric matrix.
Some of the devices disclosed in the present application
comprise a diffractive structure, which may be any relief including a hologram,
a demetallized hologram, a kinegram, and a zero order diffractive structure or a
simple grating structure. An embossable resin can be made of such materials as type
G PET, Polycarbonate, polyvinyl chloride or polymethacrylate. An embossable layer
may be combined with hardcoat/release layer. An embossing may be either patterned
or continuous. A demet layer can be made of Al, Cu, Ni, and other metals and metal
alloys that has been patterned by demetallization. Various techniques may be used
to pattern the metal layer, such as chemical etching or oil ablation in vacuum,
both done in registration with the relief image. A high refractive index layer can
be made of ZnS, TiO2, ZrO2, etc.
In one embodiment of this invention, dye particles are
added to the adhesive to modify the optically variable effect. Optionally, the adhesive
layer is transparent or semi-transparent and concentration of the pigment particles
is adjusted so that when a security article is hot stamped to a printed document,
the insignia printed on the document is visible through the security article.
In one embodiment of this invention, colorless reflective
flakes are added to the adhesive, so that the flakes appear to have color, reflecting
the color of the dye in the adhesive or paint or ink used as adhesive, wherein the
ink is preferably made of acrylic or urethane carrier with flakes therein.
Another embodiment of this invention is a single layer
of adhesive with particles providing an optical effect therein. By way of example,
the particles are color-shifting flakes. This structure can be used to join two
objects together, wherein one of the objects is light-transmissive to make visible
optical effects provided by the adhesive.
In another embodiment of the present invention, reflective
flakes bearing symbols or text, as described in co-pending
US Patent Application publication number 20060035080
, are added to the adhesive. These symbols stand out against a colored
background when viewed under a microscope using reflected light.
In another embodiment of the present invention, a security
device comprises two adhesive layers: a first layer of adhesive is dye-free and
has reflective flakes therein; a second layer of adhesive is colored with a dye,
so that the dye mutes or enhances the reflectance of the first layer, depending
from which side the security device is viewed.
In other embodiments of the present invention fluorescent
dyes activated by UV or up-conversion pigments that fluoresce when IR activated,
for example by two photon absorption, are added to the adhesive as a covert feature.
Nano-particles or transparent conductive particles, for example Indium Tin Oxide
(ITO) flakes, can also be added to the adhesive for covert features.
In a less preferred embodiment of the present invention,
an adhesive is first applied to a substrate and then optically variable pigment
(OVP) particles are added to the adhesive, for example, sprinkled or scattered by
an air jet onto the adhesive surface, optionally followed by more adhesive so that
a semitransparent layer of OVP is seen in the transferred product.
Although a stamping die may be utilized in some embodiments
having an image formed therein, alternatively an image may already be created in
the form of a de-metalized hologram. In this instance, a flat hot-stamp die is utilized
to transfer the image. The transferred image may be a square or other shape as defined
by the flat hot die or by the area of the adhesive.
An alternative to the hot-stamping an adhesive onto a demetalized
(demet) hologram, is to print a UV activated adhesive containing the OVP particles,
bring a laminating sheet containing the demet hologram onto the adhesive and then
cure the adhesive by shining the UV light or e-beam radiation through the transparent
backing to the adhesive sheet or e-beam radiation though the demet hologram using
the e-beam curing step. UV will not work through the areas of the hologram that
are not demet unless the width of the non demet areas are very narrow, estimated
to be less than 2 microns, so that the UV can cure the adhesive by coming in at
Fig. 2 shows a structure in accordance with one embodiment
of the present invention. An embossed hologram layer 100 has an Al layer 102 thereon.
The opaque Al coating 102 is patterned to form windows or gaps. Both the opaque
Al regions 102 and gaps therebetween are coated with optically variable adhesive
104 having therein optically variable flakes 105, which can be magnetic pigment
flakes shifting color with viewing angle. A resin layer 106 is formed to allow the
embossing of relief surface 100, and a release (or hardcoat) layer 108 is coated
onto the removable carrier substrate 110, typically PET 10-25 microns in thickness.
In another embodiment, the release and hardcoat/resin layers are combined into one
Fig. 3 shows the structure of Fig. 2 hot stamped to a paper
or cardboard substrate 112. When the PET layer 110 is removed and the structure
is viewed from the top looking down through the hard coat 108, through the holographic
patterned Al layers, color shifting coating is seen through the windows. What makes
this structure particularly ideal is the synergy that is attained by combining special
effect pigments in the adhesive material, obviating the requirement for an additional
thick color shifting layer. The overall thickness is less than 20 microns, typically
around 10 microns.
Fig. 4 is a photograph of a portion of a Chinese note,
wherein the structure shown in Fig. 2 is hot stamped to the banknote paper. This
structure includes a hologram made by Hologram Industries of Paris, France, and
provides color shifting effects, i.e. different colors can be seen from different
angles. For example, a square background changes its color from indigo, pointed
by arrow 301, through violet - arrow 302, to hot pink color, pointed by arrow 303.
The hot-stamped (HS) product has higher chroma than its
ink counterpart because the flakes settle fast in the low viscosity formulation
adhesive against a smooth substrate. Printed OVP has a lower chroma because one
is looking at the side of the ink that was pulled away from the applicator. When
a string of ink breaks, clumps of ink flow out a relatively rough surface compared
to interface between a plastic substrate and ink. This is why the HS has better
chroma than a printed surface.
The device shown in Fig. 4 has at least five security elements:
1) a hologram with a double image - the number "25" in the center of the hologram
appears at one angle and disappears at other angles, 2) an image of Venus de Milo
that is easily remembered. 3) the hologram has a demetallized Al layer in a lace
pattern, 4) a color shift, and 5) covert images seen at 100X or higher magnification.
An alternative embodiment of the invention is shown in
Fig. 5 wherein a high refractive index layer 114 is coated between the optically
variable adhesive layer 104 and the Al patterned layer 102. The high refractive
index coating 114 of a material such as ZnS, TiO2 or ZrO2 is coated over the demetallized
holographic film. In this instance, the high index layer 114 allows the diffractive
or holographic surface 100 to be seen at the same time as the optically variable
adhesive 104. The high refractive index prevents an optical index match between
the adhesive and the embossing in the resin layer.
An alternative embodiment is shown in Fig. 6, wherein the
optically variable adhesive 104 is printed between the windows of the aluminum 102
so that the transferred device will be tamper evident. If one tries to remove the
device, it will break apart in regions defined by no adhesive and with adhesive.
According to another embodiment of the present invention
shown in Figs. 7 - 9, a device has a patterned release layer 108 on a substrate,
resin layer 106 with high adhesion to the substrate, and is coated continuously
across the windows and non-windows of demet aluminum layer 102 with an OVP adhesive
104 with flakes 105 therein. Fig. 7 shows the device before hot stamping it to carrier
66 which needs protection. In operation, the device is attached to the surface 66
as shown in Fig. 8, wherein adhesive 104 is activated by hot stamping. If someone
tries to detach the device from the carrier, the release layer 108 only releases
in a pattern, leaving a reverse pattern on the substrate 66. The result of such
attempt is shown in Fig. 9, wherein the broken jagged split of adhesive is pointed
by arrow 120. In effect, this device is a tamper evident security label.
The following embodiments of the present invention are
Chromagrams having two different layers of optically variable energy activated adhesive
for providing at least two different optical effects, wherein one of the adhesives
may contain covert taggant flakes, referred in the art as taggants or taggents.
In the embodiment shown in Fig. 10a, a Chromagram comprises
a hologram, that may be demetalized, or a high index layer, or other relief type
surface, and the adhesive made up of two discrete layers. One of the hot stamp adhesive
layers, layer 119, contains covert materials, in this instance covert flakes 118,
and the other hot stamp adhesive 104 contains optically variable pigment 105. This
invention provides a vehicle for efficient use of expensive covert materials. The
examples of covert flakes 118 include, but not limited to, charms or taggants as
United States patent application publication number 2006/0035080
incorporated herein by reference, shaped pigments, magnetic flakes, fluorescent
pigments, standard UV activated to form visible light, or specialized anti-Stokes
materials IR activated to form visible light. The covert materials are placed in
a thin layer of adhesive 119 covered by a layer of adhesive 104 containing color
shift pigments, such as thin film metal-dielectric, all dielectric, mica based pigments,
liquid crystal pigments etc. The covert materials are not visible under normal condition,
but easily detectable, for example, in UV light, or under a microscope, or by magnetic
or infrared detectors. Upon application of the Chromagram to a document or other
object requiring protection, the PET layer having a thickness of 12-25 microns,
typically 19 microns, is discarded leaving a very thin security device on the document,
no more than 20 microns thick.
An alternative embodiment of the invention is shown in
Fig. 11. A patterned Al layer 102 on a PET substrate is laminated to another PET
substrate that has been coated with optically variable adhesive. The aluminum pattern
may take the image of text, symbols, bar-codes or even photographic images. The
aluminum is patterned by means of a demet process (laser ablation, chemical etch,
or oil ablation of a flexographic print image in a vacuum machine). In the case
of photographic images produced by using the oil ablation process resolutions down
to 70 microns (≈180dpi) can be achieved. Oil ablation is the demet method
of choice since the patterned aluminum takes places in line, in vacuum, in one process
step. The optically variable adhesive comprises at least one of two discreet layers
of adhesive, one adhesive layer 104 contains color shift pigments 105 and another
adhesive layer 119 contains covert materials 118. This forms a security thread.
In this case, the thickness of the PET layers is about 5-10 microns each, so that
the overall thickness is 20 microns or less. This thickness limitation is necessary
for a security thread so that in a stack of banknotes one end of the stack is not
thicker than the other end.
In another embodiment of the present invention shown in
Fig. 10b, a two coat process is utilized to laminate two transparent substrates
together. First, a demet hologram is coated by successive layers of optically variable
adhesive: a first coat of an optically variable adhesive 130, either magnetic or
non-magnetic, and a second coat of a different optically variable adhesive 131.
By way of example, the first coating shifts color gold-to-green, and the second
coating shifts blue-to-red. Then a substrate 110, transparent or semi-transparent,
is laminated via a hot nip roller to the adhesive 130. After that, a second substrate
supporting the hologram (not shown) is removed leaving protective layer 106. The
final product has different color shifting effects dependent on which side it viewed
from. In yet other embodiments, one of the coatings is non-shifting, and/or contains
In reference to Fig. 11, an additional embodiment of this
invention is a structure wherein an optically variable adhesive is used to laminate
two pieces of transparent PET to produce a color shifting security thread. Looking
at one side of such a structure, in Fig. 11 from top down, one would see the image
formed by the demet hologram and a color shift in addition to the covert images
e.g. fluorescent. From the other side, one would only see a color shift if the opaque
pigments were used at high concentration. For example, interference based metal-dielectric
pigments at concentrations greater than 10% of pigment weight in total solids -pigment
plus adhesive produce such an effect. In this embodiment, a release layer is absent,
and the patterned metal layer and the covert images are optional.
In one embodiment of the present invention, an adhesive
with color shifting flakes therein is used as a laminate adhesive to make a security
thread that is thin and has qualities of an optically variable device (OVD). By
way of example, a 6-10 micron thick web is coated with the optically variable adhesive
(OVA), which is a thermoset adhesive or a moisture cure urethane adhesive with OV
particles therein, and laminated at a hot nip to another 6-10 micron thick web to
produce a laminate sheet. This sheet is then slit for security ribbons having 2-5mm
in width, which are typical widths used for currency. In essence, it creates a synthetic
foil due to the low viscosity of the adhesive during the first coating operation
and then again during the nip process. Both processes tend to align the flakes flat
with the web surfaces.
In one embodiment of the present invention a transparent
substrate, for example made of PET, with dye added to add or suppress colors of
the optically variable adhesive, disposed on the substrate, and printed information
is added to the substrate layer. Optionally, a demet Chromagram is roll nipped to
the adhesive layer.
According to another embodiment of the present invention,
the structure shown in Fig. 12a has resin layer 106, embossed with relief 100, but
has no release layer. Relief 100 is covered with demet aluminum 102 and two layers
of adhesive 104 and 119 with different flakes 105 and 118. By way of example, flakes
119 are covert flakes, taggants, and flakes 105 for providing a color-shifting effect.
Alternatively, substrate 110 itself can be an embossable layer. Such materials as
type G PET, Polycarbonate, polyvinyl chloride or polymethacrylate are suitable for
embossable substrate 110. This structure would be useful as a security label, so
that layer 104 would be attached to the outside of a box or package.
In one embodiment of the present invention, a demet hologram
is first coated with charms in an adhesive, followed by an additional hit of adhesive
with OVP therein. This double hit method utilizes fewer charms and makes the charms
more visible, than known in the art methods, wherein charms are disposed throughout
the optically variable ink medium and many of the charms are screened out by the
overlaying OVP opaque particles. Preferably, the OV ink has an acrylic or urethane
In one embodiment of the present invention, the first adhesive
layer is discontinuous. By way of example, a first thin layer of adhesive carrier
with relatively low viscosity is printed onto a substrate in form of dots. The carrier
contains a high density of charms or other flakes therein, and is covered with a
second layer of less expensive adhesive providing an additional optical effect.
In another embodiment shown in Fig. 13, the structure is
composed of a PET layer 110, an optional resin layer 106 with embossing, a demet
Al layer 102, two layers of adhesive 104 and 119, and a protective hardcoat covering
layer 108, i.e. the protective hardcoat/release takes the place of the second PET.
In this way, the overall security thread type structure can be made quite thin,
for example, 15 microns even if a 9 micron PET is used for embossing or for depositing
an embossing lacquer/resin 106. By way of example, this structure is made by running
a PET with a demet hologram or a PET just with patterned Al, through a heated nip
against a releasable PET coated with the layers of adhesive containing the color
shift materials and the covert materials. The releasable PET is later discarded,
but hardcoat layer 108 stays with the final structure as shown. Alternatively, a
demet hologram on a PET substrate is processed serially through a number of gravure
print stations including two print stations for the adhesive 119 and 104 and a print
station for the protective hardcoat. Drying stations are placed between each print
In the embodiments described hereinafter, an OV foil has
a demet hologram in a region thereof with an OV adhesive between the foil and demet
In another embodiment shown in Fig. 12b, first substrate
222 is coated with a reflective layer 220a, a dielectric layer 220b and an absorber
layer 220c forming an optically variable color shifting foil 223. Substrate 212,
which can be a resin/hardcoat layer, is impressed with a hologram and partially
coated with a pattern of highly reflective aluminum 216 in register with the hologram,
for preventing light from passing therethrough. As a result, substrate 212 has one
or more regions 100 embossed and covered with demet aluminum. Substrate 212 optionally
has one or more regions 214 embossed but not covered with aluminum. Resin layer
212 is optionally covered with protective light transmissive layer 218 with opaque
indicia 219 printed thereon. The demet hologram is hot stamped or hot roll nipped
to the optical stack using clear hot stamp adhesive 230.
Shown in Fig.12d, a layer of adhesive with OV particles
can be used as shown in another embodiment shown in Fig. 2d. This embodiment is
similar to shown in Fig. 12b in many respects, however has a first substrate, preferably
made of PET, coated with a color shifting flakes 235 in a carrier 234, an adhesive
or acrylic- or urethane-based ink, hot stamped to the same upper structure as in
Fig. 12b. After the ink has dried and cured, thus forming a color shifting coating,
a hot stamp adhesive 230 is applied and cured. To form a Chromagram the coated first
substrate having the hot stamp adhesive 230 is bonded with a second substrate covered
with the same layers as in the embodiment shown in Fig. 12b.
In another embodiment shown in Fig. 12c, covert flakes
245 bearing indicia that cannot be seen with the unaided eye are mixed into the
hot stamp adhesive 240 and are used to bond the two structures together as in the
previous embodiments. In this embodiment both color shifting effects that can be
seen though the windows where the A1 coating is missing and with magnification the
covert flakes 245 can be seen and serve as a means of authentication. Instead of
covert flakes, optically variable flakes could be used at low concentrations so
that the OV foil colors are modified when viewing from the top.
This manufacturing process allows the first and second
substrates to be manufactured in two different facilities and stored in rolls to
be united later.
The present invention was reduced to practice as follows:
The adhesive was diluted to the correct strength by the addition of toluene and
applied using a reverse gravure coater equipped with in-line drying ovens. The applied
adhesive levels ranged from 1.5-10 g/sq m while the pigment applied was between
0.005 and 0.05 g/sq m for the covert pigment and 1 -10g/sq m for color shift OVP
pigment. Two optically variable pigments were chosen for a series of devices: a
red to green two period stack i.e. Ab/D/Ab/D/R/D/Ab/D/Ab and a Blue to Red a one
period optical stack i.e. Ab/D/R/D/Ab, where Ab is an absorber of Cr, D is a dielectric
of MgF2, and R is a reflector of aluminum. Two different covert charms
were used: a 10 micron square shaped pigment with a € symbol located in its
center and a 30 micron square shaped pigment with a $ sign in its center. The press
speed was about 20 feet/min for each.
Experiments were preformed by incorporating optically variable
pigment (OVP) into a commercially available hot stamp adhesive. The thickness for
hot stamp adhesive was between 3µm and 10 µm, with preferable range 3-
Formulas were developed to estimate pigment deposition
weight of applied pigment to hot-stamp adhesive (HSA) coating from their optical
density. It was found that in general the optical density of a pigment/HSA should
be approximately 0.3 or greater on a black background to obtain optical performance
that approaches coatings with an optical density of approximately 0.6 on a white
In test trials, a series of hot-melt adhesive and pigmented
hot melt adhesive blends were coated on 19µm polyester film with a release
layer and Chromagram layer.
The adhesive coating was carried out on a 10" wide solvent
roll coater with 100 feet of drying oven. The adhesive was applied by reverse roll
Pigments were blended into a commercial hot-melt adhesive
and stirred continuously until placed in the coating pan. Toluene was used to dilute
formulations to obtain the lower coating weight samples. The sample for percent
solids was taken from the adhesive just before it was added to the coating pan.
The adhesive application weight was obtained by weighing a known area of coated
web, removing the adhesive with solvent, drying the web, and weighing the web after
the adhesive was removed. Three samples across the web were taken for each coating
weight and averaged to obtain a coating weight for each sample. Anilox rolls were
cleaned after each sample was run. A 75 TH (Trihelical) Anilox roll was used for
the majority of the experiments. A 55 TH Anilox roll was used with two coatings
to increase the amount of deposited adhesive. '
The first 4 coatings were un-pigmented applications coated
at two different dilutions. These coatings were used to determine the optimum coating
weight for acceptable hot stamp transfer. It is known in the art that the adhesive
thickness can vary in a very broad range. By way of example, conditions that yielded
an un-pigmented adhesive thickness of 3µm - 3.5µm, calculated from g/m2
measurements, were chosen to yield the optimum adhesive coating thickness.
Each of the coated web samples was evaluated for stamping
performance and optical density. Hot stamp transfers were made of all the samples.
The optimum stamping conditions for transfer were found to be 100° C to 125°
C, 0.5-1.0 second dwell time, using the Kenson Hot Stamp Press with the 35 mm x
22 mm rectangular brass stamp. The pressure was adjusted to its lowest operational
point to minimize embossing of the evaluation samples. Very little fringing was
observed with any of the samples. Hot stamp transfers of each of the samples were
made onto the black and white areas of Leneta cards. The transfers were made at
100° C, 1.0 sec. dwell time. Reflectance scans and color variation measurements
were made over the black and white backgrounds for each transfer.
Optical densities were measured over the transparent areas
of the web.
Tables 1 and 2 summarize the adhesive coated web properties.
The optical density (OD) of the pigment-containing adhesive
was used to estimate the amount of pigment on the web. This was done to determine
if this could be used as a viable analytical procedure for setting a production
specification for the adhesive/pigment deposition. If the ratio of pigment to adhesive
is known for any formulation, the optical density of the adhesive coating could
be used to determine the amount of adhesive applied to any transparent web. The
optical density of the High Red vs. weight per unit area of High Red was plotted
in Fig. 15; this dependence was used to obtain the formula for High Red. All of
the optical densities vs. grams of pigment per m2 were plotted in a separate
graph shown in Fig. 14, and a second formula was obtained from this data set. The
formulas are very similar regardless of the differences in pigment weight per unit
area. It is likely that an offset exists in the total data set due to pigment settling
and the fact that 3 of the 4 pigments tested have similar pigment weight per unit
area. These factors may cause the formulas to yield slightly higher pigment weights
per unit area.
The resulting formulas for estimation of the amount of
deposited pigment are:
Grams of High Red deposited per sq meter = 0.135546396874281 X (OD coated film)
Table 3 compares the measured optical density of the coating
with the optical density value calculated using the above formula. Because of relatively
low variations between OD measured and OD calculated shown in Table 3, the optical
density of the adhesive coating can be used to determine the amount of adhesive
applied to any transparent web for a known ratio of pigment to adhesive.
Figs. 16 and 17 are reflectance scans of hot stamp transferred
images onto the white and black areas of Leneta cards, respectively. The data shown
in Figs. 16 and 17 was converted to absorbance, and the values of absorbance related
to the white areas were subtracted from the corresponding absorbance values related
to the black areas. Graphical representation of the subtractive absorbance data
is shown in Fig. 18. Samples that show the smallest variation between their black
and white absorbance values have the highest performance. The highest performance
samples are the samples with the highest pigment loading.
Cross web optical density measurements are displayed in
Fig. 19. There were 5 equally spaced measurements taken across each web. The data
indicated that the cross coating thickness varied by less that +/- 5% in all pigmented
In Table 4 of experimental data, "Charm L" stands for Low
concentration of charms and "Charm H" - for High concentration of charms.
Fig. 20 is a photograph of a security device applied through
a hot stamp transfer adhesive process as described before, in which covert flakes
bearing the € symbol and $ symbol are disposed within the adhesive material
over blue to red color shifting flakes in a second layer of adhesive. Here a poker
chip has a holographic image of Venus di Milo on a background of color shifting
flakes. The covert flakes can be seen with 100 times magnification but are not visible
without magnification. This embodiment combines color shifting, holographic effects
and covert symbols using adhesive bearing special effect flakes.
To produce the aforedescribed chips, the adhesive coated
rolls were slit down the length to a width of 3.25 inches so that two rolls of hologram/OVP
adhesive i.e. Chromagrams could be hot stamped two at a time. A Malahide hot stamping
machine, model, E4-PK, was used to transfer the Chromagrams to poker chips made
of acrylonitrile butadiene stryrene (ABS) copolymer. The die was made of silicone
rubber and was set at about 375° F.
Approximately 1000 impressions were continuously printed
at the production rate of 450-500 impressions per hour. The transfers had good adhesion
when scraped with a finger nail and there was very little fringing. The Chromagram
foil production performance was equivalent to commercial hot stamp foils. In practice,
the covert images would either show the denomination of the banknote, poker chip
or the logo, symbol of the bearer or company issuing such value based documents.
In the case of using transparent covert pigment and transparent
color shift pigment in a transparent adhesive, an additional security element is
introduced so that the observer will also be able to see printed information that
is on the document through the device.
Described hereinafter are embodiments of refined "synthetic
threads" wherein multiple optical effects are produced by a layered security system.
In reference to Fig. 21, a security thread comprises substrate
110, reflective layer 102b, optically variable adhesive layer 130, another layer
of adhesive 132 with charms therein, relief structure 100 covered with demet Al
layer 102a, and resin layer 106. Substrate 110 is preferably made of PET, however
oriented polypropylene (OPP) or other plastic materials can be used. The substrate
can also be dyed in a continuous color or could be patterned.
Reflective layer 102b is preferably made of Al, has windows
so that optical effect provided by layer 130 is visible though substrate 110 and
reflective layer 102b. Optionally, the windows in layer 102b are shaped as letters
or other insignia, so that a color shifting text can be seen though substrate 110.
Alternatively, instead of the patterned layer 102b being
internal to the structure, the substrate 110 could have the patterned layer of Al
facing outward while the internal interface of the PET is in contact with the layer
130. In the case where the reflective patterned Al faces the outside of the device,
an additional protective layer such a vacuum deposited SiO2 layer or an organic
resin protective layer may be placed over the reflective material.
Optically variable adhesive 130 is preferably made of color-shifting
adhesive, which can be controlled so that a color variation from one sample to another,
&Dgr;E, defined as the square root of the difference in hue squared plus the difference
in chroma squared plus the difference in brightness squared, is less than 1.0, using
color additive mixing of the optically variable pigments. However, in general a
&Dgr;E of being less than 3.0 is acceptable to the security field. This degree
of color control can not be achieved by optically variable foil since color control
by additive mixing is not possible. Optionally, other materials such as fluorescent
materials, phosphorescent and anti-stokes, dyes and other colorants can be added
to the OVA.
Adhesive layer 132 having charms, taggants or pigment flakes
therein, is substantially transparent to allow effects produced by OVA 130 to be
visible therethrough; adhesive material of layer 132 can be clear or colored. Either
the charms themselves are transparent or the concentration of the charms is sufficiently
low to allow visibility of adhesive layer 130.
Optionally, magnetic flakes, such as metal flakes or OV
flakes with a magnetic layer sandwiched between two layers of reflective material,
are added to adhesive within layers 130 and 132, possibly in combination with non-magnetic
optically variable flakes.
Relief structure 100, is embossed into the resin layer
106 covered with demet layer 102a, provides a demet holographic effect and includes
such features as a double image hologram, a zero order hologram , a kinegram or
other imagery based on grating technology. Demet layer 102a is patterned to provide
visibility of OVA layer, when the security thread shown in Fig. 21 is viewed from
the top. Layer 102a or 102b can be patterned with fine lines of lace-like pattern
for providing an additional counterfeit feature, and/ or with insignia 133a.
An image familiar to most people, such as famous statues
of David and Venus de Milo, famous buildings including Eiffel Tower and Great Wall
of China, famous people like Einstein, can be incorporated as a zero order diffractive
image, allowing the common person to recognize and remember the device and authenticate
it by combination of the image and the associated color shift.
The thread is protected from both sides, on one side by
substrate 110, and on the other - by a hardcoat /resin layer 106.
When the thread is viewed at one side, the top as shown
in Fig. 21, a color shifting effect of layer 130, a double image hologram or a zero
order hologram 100, a demet lace-like pattern of aluminum 102a with indicia 133a
and covert features such as "charms", are visible. When the thread is viewed from
another side, a color shifting pattern showing the color shifting background 130
in the windows of layer 102b, surrounded by reflective aluminum 102b, is visible.
Advantageously, the overall thickness of the aforedescribed
thread can be as low as 12µ, if the thread is made of 6 micron thick foil hot
stamped and/or laminated to a 6µ PET. Multiple security effects within such
a thin thread have previously not been achieved.
Another advantage of the aforedescribed thread is multiple
technologies used to manufacture this thread. This makes counterfeiting difficult
since the counterfeiter must have multiple skill sets to make a counterfeit. Holographic
structure, optically variable pigment and demet Al on the PET could be made in separate
and perhaps distant facilities and brought together at the point of currency manufacture
to make the final product. The OVA weds all the components together. The idea of
putting components together right before the security device is inserted into the
currency paper gives added security to the device since interception of one component
by during shipment gives the counterfeiting only one component of the overall device.
Optionally, said prefabricated components have matching symbols, for example in
the aluminum layer 102b and in the demet hologram 100 and 102a.
Moreover, fine lines of demet layer, such as lace-like
pattern, in the hologram make it very difficult for a counterfeiter to reproduce
the patterning using scissor, die cutting or even using photopolymers since precise
registration is required in the demet process to align the demet patterns to the
Additionally, the cost of putting text or other images
into the aluminum layer next to the PET is negligible since an oil ablation demet
in-line process in the vacuum roll coater can be used. Resolutions down to 70µ
can be achieved.
Such a security thread can be used in banknotes as a windowed
system where the thread is woven in and out the paper exposing itself in windows
on either side of the note. It can also be embedded with in the paper itself where
the paper is thin and transparent enough over the thread to still see the security
features. Checks, passports, other security paper documents and plastic documents
such a plastic based banknotes, credit cards and identity cards can utilize the
aforedescribed security thread; it also can be used as a tear thread in such items
as cigarette boxes and other secure packaging. In the case of paper documents, the
viewing from both sides is affected by the thread passing to the surface of each
side at regular or irregular intervals or at the same location if the paper is absent
at that location.
Fig. 22 shows photographs of the security thread described
in reference to Fig. 21.
Fig. 23 shows a Security Thread using OVA according to
another embodiment of the present invention. The thread comprises two light-transmissive
substrates, preferably made of PET, joined by OVA layer 104 having optically variable
flakes 105 and covert taggants 118 therein.
Another embodiment of the present invention shown in Fig.
24 is a security thread wherein at least three layers of adhesive are used to laminate
two substrates. The central layer OVA comprising a carrier 104 and pigment flakes
105, and two layers of adhesive with taggants 118 therein, the layers symmetrically
disposed between the two substrates..
Yet another embodiment is shown in Fig. 25, wherein a security
thread comprises substrate 110 laminated using two different OVA's. Relief structures
100 are covered with demetallized Al 102 and hardcoat / resin layer 106. To manufacture
such security thread, each side of a PET or other plastic substrate is hot stamped
or roll nipped with a Chromagram, which is a demet hologram with OVA, wherein two
OVAs differ in color and color shifting effect.
Prior art does not disclose such very thin security threads
with OVA providing a layered system of counterfeit deterrence as described in reference
to Figs. 21- 25.
In particular, in contrast to the aforementioned
US Patent No. 4,186,943
, our invention is asymmetric so that the thread appears different from
each side providing an additional security feature.
Also, our invention improves color variation in comparison
US Patent No. 7,054,042
, by mixing slightly different batches of optically variable pigment to
get exact color and color shift time after time at least to less and or equal to
a delta E of 1.0-3.0. Human perception can see color variation down to this level.
Table 5 shows the variation calculated for such a Fabry Perot thin film foil at
normal incidence using white light, for the design comprising an opaque Al layer,
a low index MgF2 layer, and a 3nm absorber layer made of Cr.
The construction of the thread disclosed in the present
application also provides a possibility to add covert materials (covert platelets
and other pigments) which can not be done with '042. Furthermore, although '042
mentions patterning of the opaque aluminum it does not result in color shifting
windows in the patterned aluminum as is the case for our invention. Removing some
of the aluminum of the Fabry Perot filter disclosed in '042, would result in clear
windows as the cavity of the Fabry Perot is destroyed. Furthermore, the device disclosed
in '042 is really for only viewing from one side.
In comparison to
US Patent No. 5,700,550
, the invention of the present application allows for high chroma and high
color control irrespective of the substrate color to which the device is affixed,
and teaches the addition of covert taggents into the device.
In comparison to
US patent Application publication number 2005/0127663
, this invention provides better color control of the OVA and thin gauge
PET as it can easily be rolled with an OVA.
While the particular invention has been described with
reference to illustrative embodiments, this description is not meant to be construed
in a limiting sense. It is understood that although the present invention has been
described, various modifications and combinations of the illustrative embodiments,
as well as additional embodiments of the invention, will be apparent to one of ordinary
skill in the art upon reference to this description without departing from the spirit
of the invention, as recited in the claims appended hereto.
It is therefore contemplated that the appended claims will
cover any such modifications or embodiments as fall within the true scope of the
grams solids per sq meter deposited
TOTAL % SOLIDS
CALC % PIGMENT IN SOLIDS
CALC g per sq meter deposited pigment only
CACL g per sq in deposited pigment only
ADHESIVE IN PAN NOT STIRRED
DURING RUN, LARGE AMOUNT OF SETTLING OBSERVED
ADHESIVE IN PAN STIRRED DURING; RUN, NO SETTLING OBSERVED
CALC g per sq meter deposited no pigment
grams pigment per 100 g adhesive solution
Caculated Adhesive Thickness in Microns
g per sq M deposited pigment only for CALC OD
CALC OD FROM GRAPH
ADHESIVE IN PAN NOT STIRRED
DURING RUN, LARGE AMOUNT OF SETTLING OBSERVED
ADHESIVE IN PAN STIRRED DURING RUN, NO SETTLING OBSERVED
CALC g/ sq M deposited pigment only
CALC OD FROM GRAPH
+/- Percent variation in OD measured vs. OD calculated
Table 5. Calculated Variation in Color for a 2% Variation in the Dielectric
Thickness of a Fabry Perot Structure.
&Dgr;E = Sq Root of (&Dgr;a*2 + &Dgr;b*2