The Field of the Invention
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 which may have color shifting, color switching, or optically variable
backgrounds and which have a magnetically alignable pigment thereon aligned in a
magnetic or electric field and which can be used as security articles in a variety
Background of the Invention
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 hue 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. Color switching pigments appear to change color for example from a
dark green to a light green, or from a light blue to a dark blue. Color switching
pigments are described in
United States patent 6,150,022
in the name of Coombs et al. Color switching pigments consist of bright
metal flakes that are substantially reflective disposed in a liquid carrier vehicle
that includes a dye. For example when a blue carrier vehicle is used, the flakes
have a range of color from light to dark blue when they switch color upon a change
in viewing angle.
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. For all intents and purposes, a diffraction
pattern, whether embossed, etched or inked, is be understood to be a marked region.
A marked region is to be understood to be a region having some form of indica thereon,
whether inked or stamped or etched. 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.
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.
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 to
coat a reflective layer upon the embossed surface, typically a thin metal layer
such as aluminum in order to achieve maximum optical effects. The reflective layer
substantially increases the visibility of the diffraction pattern embossment.
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
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.
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.
One method 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.
Due to the level of sophistication of counterfeiting methods,
it has become necessary to develop more advanced security measures. One approach,
U.S. Pat. Nos. 5,624,076
5,672,410 to Miekka et al.
, where embossed metal particles or optical stack flakes are used to produce
a holographic image pattern.
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
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.
In other efforts to thwart counterfeiters, the hologram
industry has resorted to using 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.
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.
Security articles having diffractive surfaces and color
shifting backgrounds are described
United States patent application numbers 20040105963 A1
. Such security devices include a transparent holographic substrate coated
with a color-shifting layer on the side opposite to the holographic embossing. The
color-shifting optical coating provides an observable color shift as the angle of
incident light, or viewing angle, changes. The color-shifting coating can be fabricated
by vacuum deposition of an optical interference structure onto the corresponding
surface of the substrate, by spraying of a paint containing color-shifting pigment,
or by printing ink as by flexographic, gravure or Intaglio means.
A patterned layer of a reflective material might be applied
over predetermined portions of the holographic substrate to form alphanumeric characters,
bar codes, pictorial or graphic designs as described in
WO 2005/026848 A2
. To produce such, a highly reflective material needs to be deposited on
the top of the holographic substrate and etched out from predetermined portions
of the substrate. As a result of demetalizing these areas of the substrate, where
the metal was etched out, they become essentially transparent and the holographic
effect there becomes almost invisible. In contrast, the portions of the substrate
where the reflective metal was left on the surface in different predetermined shapes,
maintain visible holographic properties.
Color-shifting coatings can be applied to such a demetalized
structure in different ways. It can be applied to the side of the substrate opposite
to the embossed side. In this manner the coating becomes visible through transparent
demetalized portions of the substrate. Alternatively the color-shifting coating
can be applied on the top of embossed side. The coating and patterned holographic
elements become visible through the transparent substrate when the substrate is
flipped over. This combination of hologram substrate and a color-shifting coating
is called a "chromagram". General concept of chromagrams can be readily understood
with reference to Figs. 1 through 5.
Demetalized holograms are more difficult to counterfeit
since one not only has to make the hologram but also demetalize an intricate pattern
in register with the holographic pattern.
It is an object of this invention, to provide an image
that can be used as a security device, that is very difficult for counterfeiters
to copy, and that can readily be authenticated.
It is a further object of the invention to provide a security
device that offers a high degree of security while at same time providing considerable
Summary of the Invention
In accordance with the invention, this object is achieved
by a security device as defined by the independent claims. The dependent claims
define preferred or advantageous embodiments.
In accordance with the invention there is provided a security
device having a first region coated with magnetically aligned pigment particles;
a second marked region different from the first printed region, wherein the magnetically
aligned pigment forms an image that appears to move with a change in viewing angle
or incident light, and wherein the second marked region serves as a frame of reference
against which the image appears to move.
In accordance with the invention there is further provided,
a security device having a first region coated with a magnetically aligned pigment
and a second different region having a diffraction grating thereon, wherein the
magnetically aligned pigment forms an image that appears to move with a change in
viewing angle or angle of incident light, and wherein the diffraction grating serves
as a frame of reference against which the image appears to move.
In accordance with the invention there is provided, a security
device comprising a patterned reflective optical structure having:
- a substrate having a diffraction grating therein or thereon;
- an at least partially reflective layer adjacent to or near the diffraction grating;
- a layer of field aligned pigment supported by the substrate.
In accordance with the invention there is provided, a security
device having a first region coated with a magnetically aligned pigment and a second
different region having a diffraction grating thereon, wherein the magnetically
aligned pigment forms an image that appears to move with a change in viewing angle
or angle of incident light, and wherein the diffraction grating serves as a frame
of reference against which the image appears to move, wherein the first region is
contained within boundaries of the second region, or, wherein the second region
is contained within boundaries of the first region, and wherein both the diffraction
grating and the magnetically aligned pigment can be seen from one side of the device.
In accordance with the invention there is provided, a security
device comprising a substrate having a surface that is partially embossed such that
embossed regions on said surface are separated by non-embossed regions forming windows
and a layer of magnetically aligned pigment above, below or within the windows and
visible through the windows, whereby diffractive effects are seen from the embossed
regions separate from effects seen from the magnetically aligned pigment seen through
or in the windows when the device is irradiated with light.
In accordance with the invention there is provided, a security
device that includes a layer having a diffractive region and a different layer having
a magnetically aligned pigment, wherein when the device is irradiated with light,
diffractive and kinematic effects are seen.
In accordance with a broad aspect of the invention there
is provided, a security device comprising a layer having a diffraction pattern therein
or thereon, and another layer formed of a color shifting coating wherein only some
regions of the color shifting coating are magnetically aligned.
Brief Description of the Drawings
Exemplary embodiments of the invention will now be described
in conjunction with the drawings in which:
- Fig. 1 is a security image formed in accordance with the prior art, wherein
an a polyester substrate is embossed with a pattern and wherein particular areas
- Fig. 2 is a cross section of the image of Fig. 1.
- Fig. 3 is a cross section of a security image similar to Fig.1 wherein an additional
layer of color shifting pigment has been deposited on the underside of the substrate.
- Fig. 4a is a plan view of the image of Fig. 3 having a diffraction grating and
color shifting coating under the grating.
- Fig. 4b is a cross sectional view of a structure wherein the grating or hologram
is embossed on the underside of the substrate and wherein a color-shifting coating
is directly next to the embossing.
- Fig. 5 is a plan view of the chroma shown in Fig. 4b.
- Fig. 6a is a plan view of an embodiment of the invention wherein a color-shifting
magnetically aligned layer is adjacent to the hologram or diffraction grating yielding
a chromagram that has optically-illusive color-shifting effects from the magnetically
aligned color-shifting pigment and diffractive effects from the hologram.
- Fig. 6b is a view of the embodiment shown in Fig. 6a whereby planes through
sections 11 and 12 taken in Fig. 6a are shown.
- Fig. 7a is a detailed cross-section of the chromagram shown in Fig. 6a taken
along line 11 in the plane shown in Fig. 6b.
- Fig. 7b is a detailed cross-section of the chromagram shown in Fig. 6a taken
along line 12 in the plane through line 12 shown in Fig. 6b.
- Fig. 8 is a plan view of a magnetic print and the graphical design for a security
thread used on banknotes.
- Fig. 9 is a more detailed view of a portion of Fig. 8.
- Fig. 10 is a cross-section as shown in Figs. 8 and 9 wherein the thread was
flipped over after curing of the ink and laminated with adhesive to the paper.
- Fig. 11 is a cross-sectional view of an alternative embodiment wherein the aligned
color shifting coating is deposited on an opposite side of the substrate from the
segmented diffraction grating.
- Fig. 12 is a cross-sectional view of an alternative embodiment wherein the color-shifting
coating 8 is applied to a non-embossed side on the substrate and and placed into
a field to align magnetic particles to form the 100 pattern; and after curing of
the ink the structure is laminated to a paper with adhesive.
- Fig. 13 is a demetalized holographic embossing overlap the magnetically formed
image to enhance its appearance having an aluminum metalized embossed frame and
metalized embossed contours in the shape of the letters AB.
- Fig. 14 is a cross-section of the substrate of Fig. 13
- Fig. 15 is an image in accordance with an embodiment of the invention wherein
color shifting magnetically aligned flakes are disposed under a hologram.
- Fig. 16 is a cross-sectional view of the image of Fig. 15.
- Fig. 17 is the cross-sectional view of the image of Fig. 15 shown tilted at
a different angle than Fig. 16.
- Fig. 18 is the image shown in Fig. 17.
- Fig. 19a is an image in accordance with an embodiment of this invention wherein
a bridge is shown having water thereunder, wherein the water appears to move relative
to the bridge as the image is tilted.
- Figs 19b through 19d are figures of different magnetic arrangements that can
be used to produce magnetic fields that can arrange the magnetically alignable pigment
so that it appears is if the water is moving upon tilting the image of Fig. 19a.
- Fig. 19e is a view of the image in Fig. 19a prior to adding the color-shifting
magnetic pigment and aligning the flakes in a magnetic field.
- Figs 20b through 20d are perspective views of the magnetic arrangements shown
in Figs. 19b through 19d respectively.
Referring now to Fig. 1 an image is shown having an embossed
pattern. A polyester substrate 1 is shown to have several different regions defining
specific features in the image. Region 2 is embossed and demetalized. This can readily
be seen in Fig. 2. Regions 3 and 4 are embossed and metalized with a highly reflective
coating of aluminum. The circle 5 and the star 6 were metalized with aluminum but
not embossed. Region 7 shown in Fig. 1 was not embossed or metalized. The frame
8 was metalized but non-embossed. The fine lines 2 in the pattern of Fig 1 were
barely visible because they were not coated with a reflective metal. The star 6
and the circle 5 exhibit a silver-like appearance. The patterns in regions 3 and
4 have a rainbow colored appearance because of the diffractive nature of the light
reflected from embossings on their surfaces.
Fig. 3 illustrates an improvement over the structure shown
in Fig. 2 wherein a color-shifting coating 9 can be applied to the hologram shown
in Fig. 1. The color-shifting coating 9 can be applied in two different ways, resulting
in two different chromagrams. It can be applied to the surface of the holographic
substrate that is opposite to the embossed side as shown in Fig. 3. In this instance
the chromagram has an appearance as shown in Figure 4a. The difference of this chromagram
with the hologram in Fig. 1 is that the region 7 in Figs. 3 and 4a has a color-shifting
According to another embodiment the color-shifting coating
9 can be applied on the top of embossing as shown in Fig. 4b. To view the effect
the coated substrate needs to be flipped over as shown. In this instance the embossing
2 disappears because the refraction indices of the transparent substrate and the
ink vehicle closely match one another. The chromagram has an appearance shown in
The images shown in Figs. 4a and 5 pictorially illustrate
the concept of the "chromagrams" as an optical structure, for example a hologram
or grating with a patterned demetalized layer of a reflective material applied over
certain regions of the structure and an active optical coating applied over the
patterned layer of reflective material and exposed portions of the surface of the
In accordance with this invention, it is proposed to use
a novel and inventive structure to form chromagrams for preventing of counterfeits
of valuable documents, credit cards, banknotes, and the like.
In accordance with an aspect of the invention, it is possible
to enhance the security properties of a patterned holographic structure by printing
a color-shifting magnetically alignable optically visible coating or a non-color
shifting magnetically alignable optically visible coating and applying a magnetic
field thereto to form in this layer either three dimensional patterns or three dimensional
informative signs or patterns with illusive optical effects. The coating should
be based on an ink containing platelet-like magnetic pigments for example as described
United States patent 6,808,806
, or in co-pending
United States patent applications serial numbers 20040051297
, incorporated herein by reference for all purposes. The term "magnetic
pigment" is used to mean a pigment that will align in a magnetic field. E-field
alignable pigments may be used in place of magnetic pigments when an electric field
is used to align the pigment. Field alignable pigments are pigments that have flakes
that will align in a magnetic or electric field. Of course permanent magnets or
electromagnets can be used to generate magnetic fields. In accordance with this
invention, the magnetic pigment can be color-shifting or non-color shifting. The
ink vehicle can be clear or dyed. To make a structure with the enhanced security
properties, the ink needs to be printed on the surface of the substrate as it was
done for the above mentioned described chromagrams. The substrate with a layer of
wet ink is moved into a magnetic field to form the illusory image. Preferably, the
field is shaped to a desired, desirable, or predetermined pattern. When the wet
ink is exposed to a magnetic or electric field, flat magnetic or e-field alignable
particles of the pigment align along magnetic lines of the field. This is shown
in Figs 6a, 6b and 7b.
Fig. 6b more clearly illustrates an extended view whereby
the planes along where the cross-section is taken can be viewed.
Turning now to Figs. 6a an image is shown having two section
lines 11 and 12 indicating cross-sections taken along lines 11-11 and 12-12. The
cross sectional drawing taken along line 11 is shown in Fig. 7a, and the cross-sectional
drawing taken along line 12 is shown in Fig. 7b.
UV or e-beam or thermal curing of the ink vehicle directly
within the field or shortly after its exposure to the field fixes magnetic particles
inside of the layer of the ink at their aligned positions. When the ink is illuminated
by the light source and observed with a naked eye or with an optical instrument
the differently aligned platelet-like shaped magnetic pigment particles reflect
incident light differently. One portion of the particles is so oriented with respect
to the substrate, to the light source and to the observer that it reflects coming
light rays right into the eye of the observer. Another portion of the particles
of the print reflects light rays in different directions because they are tilted
at different angles relative to the direction of the observer. When the substrate
with printed coating is tilted with respect to the light source or the observer
the first portion of the pigment particles does not reflect the light toward the
observer any more. These particles start to reflect the light in different direction
while the particles of the second portion start to reflect the light rays in the
direction of the observer. When particles are aligned gradually in the layer of
the ink, tilting of the substrate causes appearance of an illusive motion effect.
When particles are aligned along the lines of a magnet that was shaped in predetermined
pattern a portion of the printed layer repeats the shape of the magnet creating
an effect of three-dimensionality. In this region it appears as if the image comes
out of the substrate toward the observer.
Fig. 6a shows a chromagram fabricated according to the
procedure described in Figs. 4 and 5. The color-shifting coating 9 in this figure
was fabricated by printing of a color-shifting magnetic ink on the surface of a
partially demetallized hologram 3. After the printing was completed the hologram
with wet ink was placed in the magnetic field of a star shaped magnet and subsequently
cured with UV light. When viewed in the direction of the arrow as shown in Fig.
7a, the chromagram shows presence of the star 10 that has virtual height close to
The chromagram with the enhanced security feature has a
magnetically printed star around the star in hologram 2. It is generally important
that the magnetically introduced pattern of the print was a part of the graphical
design of the security article.
The magnetically formed image can be placed inside of a
holographic image. An example of such combination of a magnetic print and the graphical
design for a security thread of banknotes is illustrated in Figs. 8, 9 and 10. In
Fig. 10 a polyester substrate 81 which is partially aluminized has a layer of magnetically
aligned flakes thereunder as shown.
The security thread 81 is attached to the paper substrate
82 by traditional technology. The thread 81 is made from a thin transparent polyester
substrate, embossed in certain regions 83 with a shape of a rectangular frame 84
and the number100 inside of the frame 84. Both the frame 84 and the 100 in the region
83 are embossed with diffractive grooves 85 using known technology for forming holograms.
Due to the embossing, a rainbow-colored diffractive pattern
of the frame with the number 100 in the area 83 results. The embossed side of the
substrate was coated with a thin aluminum layer 86. Part of aluminum was etched
off the substrate leaving rectangular windows 87 of the same size as the frames
84 of embossed boxes in the area 83. Color-shifting ink 88 was applied to the embossed
and partially aluminum-coated side of the substrate 81. The substrate with the wet
ink 88 was placed in the magnetic field providing alignment of magnetic particles
in the shape 89 of the number 100 with the same size as the size of 100 in the holographic
part of the thread. The magnetically formed number 100 has a three-dimensional like
appearance. The thread was flipped over after curing of the ink and laminated with
adhesive 90 to the paper 82 with the color-shifting ink coated side as shown in
the cross-section of the chromagram in Fig. 10. The three-dimensional like magnetically
formed number 100 can be seen through the polyester substrate 81 in demetalized
boxes 87 as well as rainbow-colored holographic images of the number 100 can be
seen in holographic boxes 83.
Enhanced chromagrams can also be fabricated by an alternative
method. In contrast to the chromagrams in Fig. 9 and 10, the color-shifting coating
88 in this method can be applied to the non-embossed side on the substrate 81 as
shown in Figs. 11 and 12 and placed into the field to align magnetic particles to
form the 100 pattern 89. After curing of the ink 8 with aligned magnetic pigment,
the structure shown in Fig. 11 was turned over and laminated to the paper 82 with
adhesive 90 as shown in Fig. 12. The three-dimensional like magnetically formed
pattern 89 of the number 100 can be seen through the polyester substrate 81 in demetallized
windows 87 and the rainbow-colored holographic images of the number 100 surrounded
by the frame in the area 83.
The chromagrams in Figs. 6 through 12 described samples
when magnetically generated prints were placed either outside or inside of a demetallized
holographic image. In some cases demetallized holographic embossing may overlap
the magnetically formed image to enhance its appearance. Examples of such a chromagram
is shown in several figures below. Polyester substrate 131 in Fig. 13 has an aluminum
metallized embossed frame 132 and metallized embossed contours 133 of the sign 134
in the shape of AB. The regions 135, 136, 137, 138 and 139 are demetalized.
A cross-section of the substrate 1 with demetalized pattern
of Fig. 13 is shown in Fig. 14. Magnetic ink containing magnetically orientable
particles is separately printed in two areas on the top of the embossed substrate.
In exemplary embodiments gold to blue color-shifting ink was applied in one sample,
colored color switching non-color shifting ink vehicle was applied in another sample,
and magnetic diffractive ink was applied in another sample. While wet, each of the
prints was separately oriented in an applied magnetic field and separately cured.
The printed substrate was flipped over so as to face and receive incident light
rays with its non-embossed side and laminated to the paper 142 with the adhesive
133. Different orientation of magnetic pigment particles created color or contrast
difference in printed areas as shown in Fig 15. Layer 141 of the ink, in the background
areas 135, 138 and 139 are bright gold at a normal angle of observation. The sign
AB is blue at this angle while the frame 132 and contours 133 have rainbow-like
colors. Alignment of the pigment particles and the light rays reflection are shown
in the cross-section of the structure in Fig. 16.
The AB 134 was printed in the margins of the sign's
contour lines 133. A magnetic field applied to the layer 140 of the wet ink provided
alignment of the pigment particles as shown in Fig. 14. Layer 141 of the ink in
the background areas 135, 138 and 139 have different alignment of particles. The
particles here are almost parallel to the substrate.
Observations of the structure in Figs. 15 and 16 show that
the rays 144 incident from a distant light source penetrate the transparent polyester
substrate 131 and are reflected from the magnetic particles 145 of the pigment.
The direction of reflection of the light rays depends on two factors: alignment
of the particles dispersed in the cured ink vehicle and the observation angle. At
normal angle, as shown in Fig. 16, the light rays 144, reflected from the particles
in the background layer 141, shine in the direction 146 to the observer 147. The
observer sees a gold background layer 141 and sees this in areas 135, 138 and 139
in Fig. 15. The particles in the layer 140 of the sign AB are tilted at a
larger angle with respect to the viewer than the particles in the background layer
141. At this particular angle of observation the reflectance maximum of the particles
shifts to the region of shorter wavelengths and the light of short wavelengths shines
in the direction 148. The observer sees the sign AB as dark blue. The frame
132 and the contours 133 are rainbow-colored.
The tilt of the sample from the observer changes the observation
angle of the particles. Particles in the layer 140, that is, the sign AB, are at
a normal angle with respect to the observer while the particles in the background
layer 141 are tilted as shown in Fig. 17.
Now the particles in the layer 140 reflect yellow light
rays in the direction 146 and the observer sees the sign AB as gold in color.
Background particles in layer 141 reflect blue light in the direction 148 and the
observer sees dark blue background areas surrounding the sign AB as shown
in Fig. 18. The frame 132 and the contours 133 maintain the same rainbow colors.
In addition to the embodiments described above, an alternate
structure is shown in Fig. 19a, which combines a magnetically formed image and a
hologram, that has incredible appeal. The structures includes a transparent substrate
with embossed holographic pattern. Regions are coated with metal and other regions
are absent metal or demetalized. This is visible through the substrate and both
the holographic effect and the magnetically aligned coating effect are viewed.
It has been discovered that the presence of reference points
in an optically illusive image produces a very strong illusion of the depth within
an image. For example using a magnetically aligned pigment with a reference point
has significant advantages. The reference point could be anything located in close
proximity the printed layer that could be seen by the naked eye and which provides
awareness to the viewer of the location of the layer. The reference points include
printing, writing, dusting or splattering of paint on the top surface of the magnetically
oriented layer. Additionally, the surface of the printed layer could be textured
by cutting, scratching, etching, or the like; provided a textured surface on the
substrate so that a layer of the ink adhered thereto will have a textured surface;
a top coat containing particles visible to the naked eye such as flakes, specks,
etc. Turning now to Figs. 19a and 19e, an optically illusive image useful as a security
device to protect a substrate or contents of a package is shown. This image is printed
in a manner similar to the aforementioned images, however a fixed printed image
of a bridge 191 serves as a reference point juxtaposed with an optically illusive
kinematic image of water which appears to move relative to the bridge. The bridge
191 and other elements of this figure are shown as fixed images that do not have
optically illusive properties. In contrast, the water 193 underneath the bridge
appears to move as the image is tilted or the direction of incident light upon he
water 193 is varied. The contrast between a fixed portion of the image and a visually
perceived moving portion of the image enhances the illusion of movement of the water
193. The bridge 191 and surrounding other fixed elements in the figure provide a
frame of reference against which the water 193 under the bridge changes providing
the appearance of movement. The bridge is a partially demetalized hologram; the
landscape around the water can either be a transparent hologram coated with a high
index transparent material or a selectively demetalized hologram. The sky can be
a selectively demetalized hologram as well. The waves in the water 193 are printed
with magnetic pigment aligned in an applied field along magnetic lines. Exemplary
magnetic systems for alignment of particles to form the wave pattern are shown in
Figs 19b through 19d, wherein the image is seen in the substrate above the magnets.
Regions 194 in Fig. 19e are metalized. Region 195 is transparent.
Region 196 is a transparent hologram coated with high index material, whereby optically
variable ink can be seen through this area. Regions 194 are metalized. The water
shown in Fig. 19f is added to the image in Fig. 19e by printing magnetic ink in
the field shown absent water under the bridge in Fig. 19e and applying on of the
magnetic field generated from one of the aforementioned magnetic systems. Optically
variable ink is also applied to the sky region of the image and is not magnetically
oriented by a magnetic field; notwithstanding this region has a distinct color shift.
It is interesting to note that the same optically variable ink applied to the water
region and the sky region have very different visual effects. The water has an appearance
of moving waves having a kinematic effect as the flakes are magnetically oriented
and the sky has an a color shifting appearance with no kinematic effects; both the
sky and water regions are preferably printed simultaneously.
The inventors of this invention have found that the presence
of a hologram on the top or around a magnetically formed image generates a three-dimensionality
to the image. In accordance with this invention the diffractive pattern serves as
a frame of reference; that is, reference points relating to where things are with
respect to one another. Illusive or virtual depth of the disclosed optical device
depends on several constituent factors. The factors for the magnetically formed
pattern include magnetic pigment color and brightness, thickness of the layer of
the ink, sharpness of magnetically generated pattern, contrast ratio between the
background and the magnetically generated pattern. Factors for the hologram include
level of transmittance of the coated layer.
A diffractive pattern can be embossed in such a manner
that it would be invisible at normal angle of observation allowing viewing of a
magnetic print and become gradually highly visible at rotation of the print from
0° to 90° around the axis perpendicular to the surface of the diffractive
embossing. A transparent blazed-patterned diffractive grating laminated to a magnetically
formed image, is very good for this purpose.
Another significant advantage of using a transparent hologram
is an increased capacity of information that can be placed into the optical device.
A magnetically aligned image may form a pattern that would carry a particular amount
of information or text and the transparent hologram laminated on the top of magnetic
print would carry another amount of information or additional text. Both of these
difference sources of information could overlap one another providing multiple information
sources of different information covering a same viewing region, essentially increasing
the information storing capacity of a same viewing region.
Various other embodiments may be envisaged without departing
from the spirit and scope of the invention. For example, the light transmissive
substrate can be coated with a high index layer, and coated with magnetically aligned
pigment is any desired pattern and subsequently stamped with an embossed grating.
The bridge 191 in Fig. 19a is an image of an object capable
of casting a shadow. When such an object is printed whereby the print is a fixed
print and when magnetically aligned optically illusive pigment is applied near,
under or beside the fixed image of the object, the illusive magnetically aligned
pigment is perceived to be highly kinematic juxtaposed to the fixed print of the