U.S. patent application number 15/035037 was filed with the patent office on 2016-09-08 for optically variable devices, their production and use.
The applicant listed for this patent is BANK OF CANADA. Invention is credited to Andrea Victoria Firth, Steven Paul Mcgarry, Alasdair Patrick Rankin.
Application Number | 20160258114 15/035037 |
Document ID | / |
Family ID | 53040739 |
Filed Date | 2016-09-08 |
United States Patent
Application |
20160258114 |
Kind Code |
A1 |
Firth; Andrea Victoria ; et
al. |
September 8, 2016 |
Optically Variable Devices, Their Production and Use
Abstract
Disclosed herein are devices that change their appearance and/or
physical properties when under an external influence, and methods
for their production and use. Such devices may be used as features
of any type of items, documents, billboards, posters, display
devices, advertisements and other items etc. and may be adapted to
include decipherable content. Such devices also afford new
techniques for a user to check quickly and easily whether the item
is a legitimate or a counterfeit copy, either by hand-manipulation
of the device, or with the assistance of an additional screening
tool.
Inventors: |
Firth; Andrea Victoria;
(Ottawa, CA) ; Mcgarry; Steven Paul; (Ottawa,
CA) ; Rankin; Alasdair Patrick; (Ottawa, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BANK OF CANADA |
Ottawa |
|
CA |
|
|
Family ID: |
53040739 |
Appl. No.: |
15/035037 |
Filed: |
November 6, 2014 |
PCT Filed: |
November 6, 2014 |
PCT NO: |
PCT/CA2014/051068 |
371 Date: |
May 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62056090 |
Sep 26, 2014 |
|
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|
61901592 |
Nov 8, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 5/24 20130101; B42D
25/355 20141001; G07D 7/005 20170501; B32B 2307/414 20130101; B32B
2255/205 20130101; B42D 25/23 20141001; G02F 2001/094 20130101;
B32B 27/40 20130101; B42D 25/369 20141001; G02F 1/09 20130101; B42D
25/47 20141001; B32B 27/322 20130101; B42D 25/24 20141001; B32B
2307/20 20130101; B32B 2590/00 20130101; G02B 5/008 20130101; B32B
2551/00 20130101; B32B 27/304 20130101; B42D 25/36 20141001; G02B
26/00 20130101; B32B 2457/20 20130101; B32B 2307/41 20130101; B42D
25/29 20141001; B82Y 20/00 20130101; B32B 9/005 20130101; B42D
25/351 20141001; G02F 1/0136 20130101; G02F 1/167 20130101; B32B
2307/40 20130101; G02B 26/02 20130101; B42D 25/364 20141001; B42D
25/445 20141001; B32B 7/12 20130101; G02F 1/0131 20130101; B32B
27/283 20130101; B32B 25/12 20130101; B32B 2307/412 20130101; B32B
27/06 20130101; B32B 2255/20 20130101; D21H 21/48 20130101; B32B
2307/208 20130101; B32B 29/002 20130101; B42D 25/46 20141001 |
International
Class: |
D21H 21/48 20060101
D21H021/48; G02B 26/00 20060101 G02B026/00; G02B 5/00 20060101
G02B005/00; B42D 25/36 20060101 B42D025/36; B82Y 20/00 20060101
B82Y020/00 |
Claims
1. An optically variable device, the device comprising: a control
element or layer; one or more responsive optical element(s); the
control element or layer and the responsive optical element(s)
moveable in the device relative to one another upon application of
an external influence upon the device, to change the distance of
separation of the control element or layer from the responsive
optical element(s), the control element or layer and/or the
responsive optical element(s), comprising a material with a surface
plasmon resonance that is influenced by proximity of the material
to the other of the control element/layer or the responsive optical
element(s); the relative movement and/or a resulting change of
surface plasmon resonance of the material causing a detectable or
perceivable change in the optical properties of the device.
2. The optically variable device of claim 1, wherein the material
comprises an electrically conductive material.
3. The optically variable device of claim 2, wherein the responsive
optical elements are conductive particles, conductive
nanoparticles, nonconductive particles, or nonconductive
nanoparticles.
4. The optically variable device of claim 1, wherein the responsive
optical element comprises a thin-film reactive layer at least a
portion of which comprises a responsive optical material.
5. The optically variable device of claim 1, wherein the responsive
optical elements are caused to undergo at least partial rotation
and/or translation when the device is exposed to the external
influence, the responsive optical elements optionally undertaking
such rotation and/or translation in fluid retained within the
device.
6. The optically variable device of claim 1, wherein the responsive
optical elements comprise a plurality of particles encapsulated in
a discrete layer from the control layer, the thickness of which is
varied by the external influence, thereby to increase and/or
decrease a distance of the particles from the control layer.
7. The optically variable device of claim 1, wherein the device
comprises a responsive optical layer comprising the responsive
optical elements, and a spacer layer between and attached to the
control layer and the responsive optical layer, the thickness of
which is varied by a degree of the external influence.
8. The optically variable device of claim 1, wherein the optical
properties of the device and/or any change of such properties, is
macroscopic, microscopic, observable in visible light conditions or
beyond visible light conditions.
9. The optically variable device of claim 1, wherein the responsive
optical elements, and/or the control layer, is/are present only
upon discrete portions or areas of the device so that the device
includes content that is detectable or visible in the presence
and/or the absence of the external influence.
10. The optically variable device of claim 1 wherein the responsive
optical elements form, or are present in, a responsive optical
layer, and wherein the responsive optical layer and/or a spacer
layer if present comprises a deformable material, changeable
between a relaxed state, and a compressed state when the external
stimulus in the form of increased mechanical pressure upon the
device, resulting in a change in the distance of the responsive
optical element(s) from the control layer, and thus a change in the
optical properties of the responsive optical layer.
11. The optically variable device of claim 10, wherein the
responsive optical layer and/or the spacer layer if present
comprises at least one adhesive material selected from the group
consisting of acrylated urethanes, methacrylate esters,
mercapto-esters and UV curable adhesives, optionally applied by
Gravure printing.
12. The optically variable device of claim 10, whereupon removal or
reduction of mechanical pressure, the responsive optical layer
and/or the deformable spacer layer if present of said device
relaxes from said compressed state to said relaxed state,
optionally-in a time of from 0.001 to 120 seconds.
13. The optically variable device of claim 10, wherein the
deformable spacer layer has a non-uniform thickness when in said
relaxed and/or said compressed state, such that different
responsive optical elements or parts of the responsive optical
layer exhibit different optical properties in the relaxed and/or
compressed state according to their distances from the control
layer, thereby to provide content to the device upon increased or
decreased mechanical pressure upon the device.
14. An optically variable device, the device comprising: two or
more responsive optical elements responsive to changes in their
relative positions through the interaction of mutual surface
plasmon resonance, each element having altered detectable or
perceivable optical properties in the device according to its
distance from at least one other responsive optical element, due to
an altered degree of exposure to the surface plasmon resonance of
at least one other responsive optical element; the responsive
optical elements being moveable within the device in terms of their
spacing relative to one another, in response to an external
influence, to cause a change in perceivable or detectable optical
properties of the responsive optical elements, resulting a change
of perceivable or detectable optical properties of the device.
15. The optically variable device of claim 14, wherein the
responsive optical elements comprise an electrically conductive
material.
16. The optically variable device of claim 14, wherein the
responsive optical elements are conductive particles, conductive
nanoparticles, nonconductive particles, or nonconductive
nanoparticles.
17. The device of claim 1, wherein the external influence upon the
responsive optical elements further causes a user-detectable
tactile surface change in the device, when the device is exposed to
said external influence.
18. A variable device that undergoes a user-detectable tactile
change, the device comprising: a control element or layer; one or
more responsive element(s); the control element or layer and the
responsive element(s) moveable in the device relative to one
another upon application of an external influence upon the device,
to change the distance of separation of the control element or
layer from the responsive element(s), the control element or layer
and/or the responsive element(s), comprising a material with a
surface plasmon resonance that is influenced by proximity of the
material to the other of the control element/layer or the
responsive element(s); the relative movement and/or a resulting
change of surface plasmon resonance of the material causing a
detectable or perceivable change in the physical properties of the
device.
19. The variable device of claim 18, wherein the user-detectable
change comprises a change in the thickness, texture, prominence, or
appearance of the device.
20. A method of changing the appearance of an item or document
comprising, including the device according to claim 1 as a feature
of the item or document.
21. An item or document comprising: a core material; and at least
one device of claim 1 affixed to at least one side or surface of
the document or item.
22. The item or document of claim 21, wherein the core material
comprises at least one material selected from the group consisting
of paper, polymer, plastic, and combinations or hybrids
thereof.
23. The document of claim 21, further comprising a portion to be
contacted with the device, thereby to cause a change in the optical
or physical properties of the device resulting from the contact by
and/or pressure applied by the portion.
24. The document of claim 23, wherein the portion is pressed
against the optically variable device, and the device comprises
intaglio printing, thereby to provide a raised, optionally
patterned, region as a pressure template to achieve the change in
optical properties of the device.
25. The document of claim 24, wherein the portion to be pressed
against the optically variable device comprises a transparent or
translucent window in the document, such that any change in the
visible appearance of the device can be observed through the window
as the mechanical pressure is applied.
26. A method for checking whether a security document is a
legitimate or counterfeit document, the security document
comprising at least one device of claim 1 on at least one side
thereof, the method comprising the steps of: applying an external
influence to at least one device; and checking whether the external
influence causes a perceivable or detectable change in the device,
wherein an appropriate change is indicative that the security
document is a legitimate document.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the field of devices that can
undergo a change either in terms of their optical or physical
properties, as well as methods for their production and use. Such
devices may, for example, be used as display devices or screens, or
be used for authentication of items or security documents of value,
including documents which may be subject to counterfeiting, such as
passports, banknotes, credit cards, cheques, identification cards
or certificates, and other articles.
BACKGROUND TO THE INVENTION
[0002] Interactive display devices are known, which can undergo a
change in optical appearance in response to some form of external
stimulus. Typically, such devices comprise a layered or
multi-layered structure where user manipulation of the device, or a
user-initiated external influence upon the device, causes a change
in appearance of the device, or at least a portion thereof.
[0003] However, there remains a need in the art for variable
devices, optionally in the form of a display screens or thin-layer
devices, that can undergo some form of observable or detectable
optical or physical change when under an external influence. The
need extends to display devices with relatively simple or more
complex content, that are single use or that can repeatedly undergo
the same change in optical or physical characteristics. Ideally,
though not necessarily, there is a need for such devices that can
be manufactured in a relatively simple and inexpensive manner. The
need for such devices extends into multiple disciplines, including
but not limited to interactive media material, advertisements,
magazines, books or other paper items with user-manipulated
content, advertizing billboards, and authentication devices for
security documents such as passports, credit cards and bank notes
to help prevent counterfeit.
[0004] In particular, there is a need for such devices that are
typically flat or planar in nature so that optionally they can take
the appearance of being flush with a planar substrate to which they
are applied, even including (but not limited to) devices that are
amenable to folding, bending or crumpling without significant
damage or affect upon the functionality of the device, thus to
improve robustness and longevity of the device when located within
or mounted upon a rigid or non-rigid substrate.
SUMMARY OF THE INVENTION
[0005] It is an object of the invention, at least in selected
embodiments, to provide a variable device at least a portion of
which can undergo a change in optical appearance or physical
characteristics in response to an external influence.
[0006] It is another object of the invention, at least in selected
embodiments, to provide a method to check whether an item or
document is a legitimate or counterfeit version.
[0007] Certain exemplary embodiments provide an optically variable
device, the device comprising:
[0008] a control element or layer;
[0009] one or more responsive optical element(s);
[0010] the control element or layer and the responsive optical
element(s) moveable in the device relative to one another upon
application of an external influence upon the device, to change the
distance of separation of the control element or layer from the
responsive optical element(s), and therefore to change a degree of
influence of the control element or layer upon the responsive
optical element(s), to cause a change of perceivable or detectable
optical properties of the device.
[0011] Certain other exemplary embodiments provide a variable
device that undergoes a user-detectable tactile change, the device
comprising:
[0012] a control element or layer;
[0013] one or more responsive element(s);
[0014] the control element or layer and the responsive element(s)
moveable in the device relative to one another upon application of
an external influence upon the device, to change the distance of
separation of the control element or layer from the responsive
element(s), and therefore to change a degree of influence of the
control element or layer upon the responsive optical element(s), to
cause a change of perceivable or detectable physical properties of
the device.
[0015] Certain other exemplary embodiments provide an optically
variable device, the device comprising:
[0016] a control element or layer;
[0017] one or more responsive optical element(s);
[0018] the control element or layer and the responsive optical
element(s) moveable in the device relative to one another upon
application of an external influence upon the device, to change the
distance of separation of the control element or layer from the
responsive optical element(s),
[0019] the control element or layer and/or the responsive optical
element(s), comprising a material with a surface plasmon resonance
that is influenced by proximity of the material to the other of the
control element/layer or the responsive optical element(s);
[0020] the relative movement and/or a resulting change of surface
plasmon resonance of the material causing a detectable or
perceivable change in the optical properties of the device.
[0021] Certain other exemplary embodiments provide an optically
variable device, the device comprising:
[0022] optically variable device, the device comprising:
[0023] two or more responsive optical elements responsive to
changes in their relative positions through the interaction of
mutual surface plasmon resonance, each element having altered
detectable or perceivable optical properties in the device
according to its distance from at least one other responsive
optical element, due to an altered degree of exposure to the
surface plasmon resonance of the at least one other responsive
optical element;
[0024] the responsive optical elements being moveable within the
device in terms of their spacing relative to one another, in
response to an external influence, to cause a change in perceivable
or detectable optical properties of the responsive optical
element(s), resulting a change of perceivable or detectable optical
properties of the device.
[0025] Certain other exemplary embodiments provide a variable
device that undergoes a user-detectable tactile change, the device
comprising:
[0026] a control element or layer;
[0027] one or more responsive element(s);
[0028] the control element or layer and the responsive element(s)
moveable in the device relative to one another upon application of
an external influence upon the device, to change the distance of
separation of the control element or layer from the responsive
element(s),
[0029] the control element or layer and/or the responsive
element(s), comprising a material with a surface plasmon resonance
that is influenced by proximity of the material to the other of the
control element/layer or the responsive element(s);
[0030] the relative movement and/or a resulting change of surface
plasmon resonance of the material causing a detectable or
perceivable change in the physical properties of the device.
[0031] Certainly other exemplary embodiments provide an optically
variable device, the device comprising:
[0032] a control element or layer comprising a material that is
permanently or temporarily electrically charged or polarized such
that an electric field emanates from the material;
[0033] one or more responsive optical element(s);
[0034] the control element or layer and the responsive optical
element(s) moveable in the device relative to one another upon
application of an external influence upon the device, to change the
distance of separation of the control element or layer from the
responsive optical element(s), and therefore to change the strength
of the electric field impinging upon the responsive optical
element(s) from the electrically charged or polarized material of
the control element or layer;
[0035] the relative movement and/or the change of the strength of
the electric field impinging upon the responsive optical element(s)
causing a change of perceivable or detectable optical properties of
the device.
[0036] Certain other exemplary embodiments provide a variable
device that undergoes a user-detectable tactile change, the device
comprising:
[0037] a control element or layer comprising a material that is
permanently or temporarily electrically charged or polarized such
that an electric field emanates from the material;
[0038] one or more responsive element(s);
[0039] the control element or layer and the responsive elements)
moveable in the device relative to one another upon application of
an external influence upon the device, to change the distance of
separation of the control element or layer from the responsive
element(s), and therefore to change the strength of the electric
field impinging upon the responsive element(s) from the
electrically charged or polarized material of the control element
or layer;
[0040] the relative movement and/or the change of the strength of
the electric field impinging upon the responsive elements causing a
change of perceivable or detectable physical properties of the
device.
[0041] Certain other exemplary embodiments provide an optically
variable device, the device comprising:
[0042] a control element or layer comprising a magnetic material
that is permanently or temporarily magnetic, such that a magnetic
field emanates from the material;
[0043] one or more responsive optical element(s);
[0044] the control element or layer and the responsive optical
element(s) moveable in the device relative to one another upon
application of an external influence upon the device, to change the
distance of separation of the control element or layer from the
responsive optical element(s), and therefore to change the strength
of the magnetic field impinging upon the responsive optical
element(s) from the magnetic material of the control element or
layer;
[0045] the relative movement and/or the change of the strength of
the magnetic field impinging upon the responsive optical
element(s), causing a change of perceivable or detectable optical
properties of the device.
[0046] Certain other exemplary embodiments provide a variable
device that undergoes a user-detectable tactile change, the device
comprising:
[0047] a control element or layer comprising a magnetic material
that is permanently or temporarily magnetic, such that a magnetic
field emanates from the material;
[0048] one or more responsive element(s);
[0049] the control element or layer and the responsive element(s)
moveable in the device relative to one another upon application of
an external influence upon the device, to change the distance of
separation of the control element or layer from the responsive
element(s), and therefore to change the strength of the magnetic
field impinging upon the responsive element(s) from the magnetic
material of the control element or layer;
[0050] the movement of the responsive element(s) and/or the change
of the strength of the magnetic field impinging thereupon, causing
a change of perceivable or detectable tactile properties of the
device.
[0051] Further exemplary embodiments provide for a use of any
variable device as described herein, as a feature of an item or
document.
[0052] Further exemplary embodiments provide for an item or
document comprising:
[0053] a core material; and
[0054] at least one device as described herein affixed to at least
one side or surface of the core material, or at least partially
embedded into the core material, such that the device is at least
partly visible or detectable from said at least one side.
[0055] Further exemplary embodiments provide for a method for
producing a variable device, the method comprising the steps
of:
[0056] providing a control element or layer;
[0057] optionally providing a spacer layer on at least portions of
the control element or layer;
[0058] providing one or more responsive elements optionally in the
form of a responsive layer, upon preselected portions of the
control element or layer or the spacer layer if present, the
responsive element(s) responsive to changes in their distance from
the control layer, the control element or layer and the responsive
element(s) moveable relative to one another in response to an
external influence thereby to cause a change in optical and/or
physical properties of the device.
[0059] Further exemplary embodiments provide for a method for
checking whether an item is a legitimate or counterfeit item, the
item comprising at least one device as described herein on at least
one side thereof, the method comprising the steps of:
[0060] applying an external influence to at least one device;
and
[0061] observing/detecting whether the external influence causes a
change in the optical and/or physical properties of the device,
wherein an appropriate change is indicative that the item is a
legitimate (and not counterfeit) item.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1a illustrates a top plan view of a document
incorporating an example optically variable device.
[0063] FIG. 1b illustrates a cross-sectional view of a document
incorporating an example optically variable device, taken along
line A-A' in FIG. 1a.
[0064] FIG. 1c illustrates a cross-sectional view of a document
incorporating an example optically variable device, taken along
line A-A' in FIG. 1a, under mechanical pressure.
[0065] FIG. 2a illustrates a top plan view of a document
incorporating an example optically variable device.
[0066] FIG. 2b illustrates a cross-sectional view of a document
incorporating an example optically variable device, taken along
line A-A' in FIG. 2a.
[0067] FIG. 2c illustrates a cross-sectional view of a document
incorporating an example optically variable device, taken along
line A-A' in FIG. 2a, under mechanical pressure.
[0068] FIG. 3a illustrates a cross-sectional view of a document
incorporating an example optically variable device associated with
a device for checking a legitimacy of the document.
[0069] FIG. 3b illustrates a cross-sectional view of the same
document and an optically variable device associated with a device
for checking a legitimacy of the document as FIG. 3a, except that a
potential difference is applied across the optically variable
device.
[0070] FIG. 4a illustrates a cross-sectional view of a document
incorporating an example optically variable device associated with
a device for checking a legitimacy of the document.
[0071] FIG. 4b illustrates a cross-sectional view of the same
document and an optically variable device associated with a device
for checking a legitimacy of the document as in FIG. 4a, except
that a potential difference is applied across the optically
variable device.
[0072] FIG. 5a illustrates a top plan view of a document
incorporating an example optically variable device.
[0073] FIG. 5b illustrates a cross-sectional view of a document
incorporating an example optically variable device, taken along
line A-A' in FIG. 5a.
[0074] FIG. 6a illustrates a top plan view of a document
incorporating an example optically variable device.
[0075] FIG. 6b illustrates a cross-sectional view of a document
incorporating an example optically variable device, taken along
line A-A' in FIG. 6a.
[0076] FIG. 7a illustrates a top plan view of a document
incorporating an example optically variable device.
[0077] FIG. 7b illustrates a cross-sectional view of a document
incorporating an example optically variable device, taken along
line A-A' in FIG. 7a.
[0078] FIG. 8a illustrates a cross-sectional view of an example
optically variable device.
[0079] FIG. 8b illustrates a cross-sectional view of the example
optically variable device shown in FIG. 8a under mechanical
pressure.
[0080] FIG. 9a illustrates a cross-sectional view of an example
optically variable device.
[0081] FIG. 9b illustrates a cross-sectional view of the example
optically variable device shown in FIG. 9a under mechanical
pressure.
[0082] FIG. 10 illustrates a method for producing an example
optically variable device as described herein.
[0083] FIG. 11 illustrates a method for checking the legitimacy of
a security document incorporating an optically variable device as
described herein.
[0084] FIG. 12 illustrates a Mie scattering calculation of
multipole excitation for silver spheres having radii of 50 nm and
100 nm, excited by 400 nm plane wave propagating along the Z axis
and polarized along the X-axis. The scattered field in response to
the dipole and quadrupole components is plotted within the XZ
plane. a) Dipole mode distribution of incident wave and orientation
of incident plane wave b) Dipole scattering by 50 nm sphere c)
Dipole scattering by 100 nm sphere d) Quadrupole mode distribution
of incident wave e) Quadrupole scattering of 50 nm sphere f)
Quadrupole scattering of 100 nm sphere.
[0085] FIG. 13 schematically illustrates an optically variable
device structure with deformable nanoparticle film over a
conductive metal film. Near-field interaction with image charges
results in shift in surface plasmon resonance wavelength.
[0086] FIG. 14 (a) schematically illustrates a metal nanoparticle
suspended over a conductive metal film at distance d (b)
illustrates calculated reflectance from an array of 10 nm spherical
silver particle in proximity to an underlying conductor at various
distances d, with 20% surface coverage.
[0087] FIG. 15: illustrates reflectance changes due to near field
interaction for (a) 40 nm spheres, (b) oblate spheroid (40
nm.times.20 nm) and (c) oblate spheroid (40 nm.times.10 nm).
Surface concentration of 20% was used in all cases; (d)
relationship between primary resonance peak and distance to the
underlying substrate.
[0088] FIG. 16 provides a graph to show reflectance spectra for
test device structures having variable distance between
nanoparticle film and underlying aluminum reflector: a)
hemispherical silver island films (inset) Photograph of the silver
island film samples for spacer thicknesses of 200 nm and 2.5 nm b)
40 nm.times.10 nm nanoplates with data vertically offset to further
illustrate resonance shifts.
[0089] FIG. 17: a) Process overview for a flexible optically
variable device structure using: (b)-(c) silver island films and
(d)-(e) silver nanoplates. A thin photoresist layer was applied to
the region shown in figure (d) and (e) to provide a reference when
comparing the two images.
[0090] FIG. 18 schematically illustrates an exemplary device (in
cross-section) that includes two charged layers.
[0091] FIG. 19 provides a graph to show voltage drop across the
active layer shown in FIG. 19 as a function of the width of the
variable gap.
[0092] FIG. 20 schematically illustrates an exemplary device (in
cross-section) that includes one charged layer and a ground plane
electrode.
[0093] FIG. 21 provides a graph to show voltage drop across the
active layer shown in FIG. 20 as a function of the width of the
variable gap.
[0094] FIG. 22 schematically illustrates an electret structure
using patterned positive and negative charge regions.
[0095] FIG. 23 provides a graph to illustrate lateral electrical
field strength vs `vertical` position within the device of FIG.
22.
[0096] FIG. 24 illustrates schematically a simulation model to
assess sufficient force can be generated to manipulate particles in
accordance with select devices disclosed.
[0097] FIG. 25 compares simulation calculations for the model shown
in FIG. 24 for a) a model that employs magnets, with b) a model
that employs electrets.
DEFINITIONS
[0098] Authentication/security device or feature: refers to any
device or feature that may be added to any item or document (e.g.
security document) for the purposes of making that item or document
more difficult to copy or replicate. An authentication device is
one example of a variable device as described herein. Compressed
state: generally refers to a condition of a layer of a device as
described herein in which the thickness of at least a portion of
the layer is reduced or lessened compared to a "relaxed state" (see
below), either as a result of pressure upon the layer (if the layer
is deformable), or increased or decreased electrical potential
difference across the layer (if the layer is composed of a
piezoelectric material), or as a result of any other suitable
external influence. For greater certainty, in selected embodiments
in which a layer is deformable, the expression "compressed state"
refers to a state, shape or thickness of a layer upon application
thereto of a mechanical force or pressure, or in the presence of an
increased mechanical force or pressure, relative to a relaxed
state, to compress or squash the layer such that the thickness of
at least a portion of the layer is reduced. In selected embodiments
a compressed state is a state that is different to a relaxed state
in which the mechanical force or pressure is reduced or absent. A
compressed state may be a single state in response to a fixed
degree of force or pressure, or may pertain to a range of degrees
of deformation in response to a range of degrees of mechanical
force or pressure. Moreover, the amount of pressure or force
required for a layer to adopt a compressed state may vary according
to a degree of deformability of the layer. In further selected
embodiments in which a layer comprises a piezoelectric material, a
"compressed state" refers to a state, shape or thickness of a
piezoelectric layer upon application thereto, or removal therefrom,
of an electrical potential difference, or in the presence of an
increased or decreased electrical potential difference, relative to
a relaxed state, to decrease the thickness or configuration of the
layer or at least a portion thereof relative to a relaxed state by
virtue of the response of the piezoelectric material to the change
in electrical potential difference. Such a compressed state may be
a single state in response to a fixed degree of electrical
potential difference, or may pertain to a range of degrees of
states, shapes or thicknesses in response to a range of degrees of
electrical potential difference. Moreover, the amount of electrical
potential difference required for a piezoelectric layer to adopt a
compressed state may vary according to the piezoelectric properties
of the layer. Regardless of whether the layer is mechanically
deformable, piezoelectric, or another material able to undergo a
change of thickness or configuration, the layer may be sufficiently
thin when adopting a compressed state (compared to a relaxed state)
to cause adjacent layers disposed or adhered to either side of the
layer to interact in some way or to cause elements of the layer to
interact with an adjacent layer, such that when adopting the
compressed state one or both of the adjacent layers changes its
optical appearance compared to the relaxed state, or the elements
of the layer itself change their optical appearance. Likewise, the
layer may be sufficiently thick when in a relaxed state (compared
to a compressed state) to cause adjacent layers disposed or adhered
to either side of the layer to interact to a lesser degree, or not
to interact at all, such that when adopting a relaxed state one or
both of the adjacent layers, or element(s) of the layers, changes
its optical appearance compared to the compressed state.
Alternatively, the layer may be sufficiently thick when in a
relaxed state that elements of the layer are unable to interact
with one or more adjacent layers due to the distance of the
element(s) from the adjacent layers. Control element or layer:
refers to any element or layer of a device as described herein,
which has inherent properties that permit the control element or
layer to exert an influence over other layer(s) of the device, or
elements thereof, regardless of whether the control layer is or is
not directly in contact with such other layer, layers or elements
thereof. As used herein, reference to a "control layer" may where
appropriate also refer to a "control element" that is not
necessarily in the form of a layer but may take some other form,
shape or configuration. Otherwise the expressions "control layer"
and "control element" are essentially interchangeable in terms of
their function in the devices disclosed herein. In selected
embodiments, for example, a control element or layer may comprise
materials suitable to emit some field such as a magnetic or
electric field, wherein the proximity or distance of the control
layer from the other layer or layers (or elements of the other
layer or layers) affects the strength of the field imposing upon
those other layer or layers, and thus the impact of the control
layer upon those other layer or layers (or elements thereof). For
example, the strength of such a field from a control layer will
normally decrease with distance from the control layer. In this
way, a control layer may exert an increased or decreased influence
upon such other layers, and preferably alter the optical appearance
or other physical characteristics of such other layers (or elements
thereof), depending upon its distance from the other layers (or
elements thereof). In other examples a control layer, and layer or
elements to be controlled, may interact by way of surface plasmon
resonance (e.g. conductive nanoparticles), wherein again the
distance of the control layer from the other layer(s) or their
components influences the optical and/or physical properties of the
other layer(s) or their components. For greater certainty, a
"control element" refers to any element that functions in the same
manner as a "control layer" but without necessarily adopting the
form, shape, or configuration of a planar or thin layer, but
instead refers to any element of any shape or size that has the
capacity to "control" the optical or physical characteristics of
one or more responsive elements responsive to changes in their
distance from the control element. Core material: refers to any
material used to form the main substrate, structure or sheet of any
item or document as described herein. In select embodiments, the
material may be formed into a sheet or member, and may be composed
of a substance selected from but not limited to paper, a plastic, a
polymer, a resin, a fibrous material or the like, or combinations
thereof. In selected embodiments the core material is of a material
suitable for application thereto, either directly or indirectly, of
an optically variable device of the types disclosed herein. The
optically variable device, or elements thereof, may be applied or
attached to the core material in any manner including the use of
adhesive materials or layers, such as glues, or by overlaying an
adhesive substance, film, varnish or other material over the top of
the device or components thereof. The core material may be smooth
or textured, fibrous or of uniform consistency. Moreover, the core
material may be rigid or substantially rigid, or flexible, bendable
or foldable as required by the document. The core material may be
treated or modified in any way in the production of the final
document. For example, the core material may be printed on, coated,
impregnated, or otherwise modified in any other way.
Deform/deformable: any reference to deformation encompasses any
change in shape, configuration or thickness of a layer (e.g. an
optically responsive layer or spacer layer as defined herein) upon
application to the layer or a part thereof of a mechanical force or
pressure of any type from any implement (including a finger, plate,
or any other item including another portion of a security document
or device) by hand manipulation or any mechanical force generated
by a machine or lever. Deformable layer/deformable spacer layer:
refers to any layer formed from any material that (1) can be
deformed in any way either permanently or temporarily such that the
thickness of the layer can be changed between a relaxed state
absent an external influence or under less external influence and a
compressed state under an external influence or increased external
influence, and either (2a) has suitable properties such that when
the layer separates a control layer and a responsive layer as
described herein, a change in the visual appearance or other
physical properties of the responsive layer occurs in at least one
of the relaxed and compressed states compared to the other of those
states, or (2b) when the deformable layer is a responsive layer
comprising responsive elements, the change of thickness of that
deformable layer changes a distance of the responsive elements from
a control layer so that the optical appearance or physical
properties of the responsive elements becomes altered. Preferably a
deformable layer is reversibly deformable such that the layer can
be transitioned between compressed and relaxed states multiple
times upon repeated application and removal of the external
influence, or repeated increase and decrease of external influence
upon the layer, either directly or indirectly through other layers.
The degree of deformability of a deformable layer (in other words
the capacity of the layer to be reduced in thickness upon
application of mechanical pressure) may be established according to
the material used to form the layer. Denser materials may be less
inclined to deform compared to less dense materials under the same
degree of mechanical pressure. Moreover, a deformable layer may
optionally comprise a material comprising voids, pores or cavities
preferably too small to be visible to the naked eye, but sufficient
to provide space for the remainder of the material of the
deformable layer to press into when under mechanical pressure.
Examples of materials suitable for use in the formation of
deformable layers include but are not limited to flexible materials
such as natural rubbers, elastomers, latexes, urathanes,
polydimethylsiloxanes and their derivatives (such as Dow Corning's
Sylgard 184 commonly used in as a deformable substrate for the
technique of micro-contact printing). Furthermore, a deformable
layer may optionally comprise or consist of an adhesive material
such as but not limited to: acrylated urethanes, methacrylate
esters, mercapto-esters and UV curable materials. A deformable
layer may be applied under any conditions and in any way. In
selected embodiments the layer is applied by printing such as by
Gravure printing. Deformable layers are not limited to those that
are deformable in response to external influence such as mechanical
pressure: other such layers may deform in response to other
external influence such as but not limited to heat, light,
potential difference. In selected embodiments, a deformable layer
may comprise one or more of piezomagnetic materials,
magnetostrictive materials, piezoelectric materials. Regardless of
the material of the deformable layer or deformable spacer layer,
the layer may consist of any deformable material or material that
can be caused to change its thickness, shape or configuration.
Alternatively the layer may comprise any deformable material
combined with non-deformable materials, or may comprise
compressible voids, pockets, compartments, vesicles or pores
comprising any material, liquid or gas. In some embodiments the
layer may be comprised mostly of a gas or gases (e.g. air) with
supporting "posts", "columns" or "supports" to maintain one or more
voids, pockets or compartments in an open state absence an external
influence such as mechanical pressure. Electrostatic layer/layer
from which emanates an electric field: refers to a control layer
that comprises a material that inherently exhibits, or can be
caused to exhibit, electrostatic properties resulting from charge
distribution in the material of the layer. Such materials may
comprise, for example, a material selected from but not limited to:
a polymer, a plastic, a resin, silica, PTFE, and derivatives
thereof. Electrostatic layers may in addition comprise or
alternatively comprise an electrets or piezoelectric material.
External influence: refers to any influence, force, energy or
object that does not form part of or is not derived or derivable
from an optically variable device as described herein, but which
nonetheless is able to impact upon or influence the device so as to
change the optical or other physical properties of the device by
causing a change in the dimensions of thickness of one or more
layers or elements of the device, or to otherwise cause movement of
one or more responsive elements relative to a control layer or
element. An external influence may be selected from, but is not
limited to: some form of user-derived manipulation of an (e.g.
optically) variable device or a document to which the device is
applied, or an external influence upon the variable device or a
document to which the device is applied from some form of external
device adapted to induce the variable device to under an optical or
physical change. An external influence may be quite simple, in the
form of mechanical pressure from any finger, digit or implement
upon an optically variable device, or an increased or decreased
potential difference across the device, or any other means to
affect a device as described herein. Item: refers to any object,
document, substrate or material to which a device as described
herein is applied, either permanently or temporarily. For example,
in selected embodiments the item may be subject to counterfeit
risks, such that the presence of a device as described herein
affixed to the item may be indicative that the item is legitimate
and not counterfeit. Magnetic layer: refers to a control layer that
comprises a material that inherently exhibits, or can be caused to
exhibit, magnetic properties resulting from charge distribution
and/or orientation in the material of the layer. Such magnetic
properties may occur because the layer comprises a permanent
magnet, or a permanently magnetic material, an electromagnet or an
electromagnetic material. Such magnetic materials may comprise, for
example, a material selected from but not limited to: Co, Fe,
Fe.sub.2O.sub.3, FeOFe.sub.2O.sub.3, NiOFe.sub.2O.sub.3,
CuOFe.sub.2O.sub.3, MgOFe.sub.2O.sub.3, MnBi, Ni, MnSb
MnOFe.sub.2O.sub.3, Y.sub.3Fe.sub.5O.sub.12, CrO.sub.2, MnAs, Gd,
DyEuO, NdFeB, SmCo, and SmCo.sub.5, magnetic liquids etc. Moveable:
refers to responsive elements being moveable relative to a control
layer, wherein "moveable" encompasses a change in distance
(translation) and/or orientation of the responsive elements
compared to the control element or layer. Optical properties:
refers to the electromagnetic radiation reflected, transmitted,
emitted or otherwise received from a device or element that is
visible to the naked eye of an observer, or as observable to an
observer with the assistance of a screening or scanning tool. For
example, where the optical properties of a device or element, or a
change in such properties, are detectable only using incident UV or
other beyond visible electromagnetic radiation, a corresponding
screening tool may be one that emits UV radiation and directs the
radiation onto the device or element under analysis. The optical
properties of any device or element thereof as herein described may
be caused, influenced or occur due to the material properties of
the device or element, the degree of reflection, transmission,
absorption, refraction or other modification of electromagnetic
radiation incident thereupon, and may also depend upon the
orientation, shape, structure, nanoscale properties, or other
material properties of the device or element when taken alone or in
combination with other devices, elements or device components.
Responsive optical element: refers to any element, feature, layer,
particle, molecule, component, portion, vesicle, pixel, compartment
or other discrete aspect embedded or otherwise forming a part of an
optically or physically variable device as disclosed herein, or a
layer thereof, the position of which, and the distance and/or
orientation of which relative to a control element or layer, can be
changed according to other features of the device, wherein such a
change in the position or distance of the responsive optical
element from the control element or layer causes a change in the
optical appearance or optical properties of the responsive optical
element. Such optical changes may be permanent or reversible,
visible to the naked eye or visible with the assistance of a
screening tool or device. In select embodiments, a responsive
optical element may be a single element and/or comprise the
entirety of an optically responsive layer. Thus, in select
embodiments, a responsive optical element refers to either a single
or multiple elements of any type and configuration that can under
an optical change according to its/their proximity to a control
layer, and thus according to an increased or decreased influence of
the control layer. A responsive optical element may comprise a
single uniform or non-uniform layer of material that itself
undergoes the optical change, or may pertain to a plurality of
discrete compartments or particles embedded, suspended or
incorporated into an optically responsive layer which themselves
undergo an optical
change under an increased or decreased level of an external
influence. For example, such responsive optical elements may
comprise solid particles, conductive nanoparticles, encapsulated
particles optically containing a liquid, or compartments or pixels
in a layer each optionally containing particles. In selected
embodiments, the optically variable devices disclosed herein are of
a thin-film configuration, or generally thin and flat yet flexible
such that they are amenable to application to a flexible, thin
substrate such as paper or polymer sheets. In some of these
embodiments the devices may have a thickness of less than 1000
.mu.m, less than 100 .mu.m, less than 10 .mu.m or less than 1
.mu.m. Select forms of responsive optical elements may include
those that undergo a change of orientation upon user-manipulation
of a related device may comprise for example "flakes" of material;
for example optical interference structures comprising laminate
Bragg-stacked or Fabry-Perot structures. A "responsive element"
without recitation of the term "optical" refers to an element that
otherwise corresponds to an "responsive optical element" but which
may undergo a change that is not optical, visually discernable or
detectable, but some other change such as a change in physical
properties depending upon proximity of the responsive element to a
control element or layer. Optically responsive layer: refers to any
layer forming part of an optically variable device as described
herein, that is responsive to an influence exerted upon the
optically responsive layer by a control layer, such that an
increased influence by the control layer gives rise to a change in
optical appearance or properties of the optically responsive layer
(or responsive optical elements thereof) compared with a decreased
influence by the control layer. Such a change in optical appearance
or properties may be apparent to the naked eye, or may only be
apparent to a human with the assistance of some form of viewing
device, for example to magnify a portion of the optically
responsive layer, or to apply to the layer some form of
electromagnetic radiation that is beyond the visible light range.
Thus, an optically responsive layer may comprise any structure,
components, materials or elements that undergo a change in
appearance for example under increased or decreased influence of a
magnetic or electric field, or plasmon resonance, for example
caused by a change in the proximity of the source of the field or
resonance relative to the optically responsive layer (or responsive
optical elements thereof). Examples of such structures, components
or materials suitable for use in optically responsive layers may
include, but are not limited to, materials that contain freely
suspended or flowable magnetic or electrostatic nanoparticles,
optionally contained within fluid-filled compartments. Optically
variable device: refers to any device as disclosed herein at least
comprising: a control layer (or one or more control elements); one
or more responsive optical element(s) such as responsive optical
elements that are responsive to changes in their distance from the
control layer or control element(s), and moveable in response to an
external influence to increase and/or decrease a distance of the
element(s) from the control layer or control element(s), thereby to
cause a change in optical appearance or other physical properties
of the device. In selected embodiments, optically variable devices
comprise at least two layers including a control layer and an
optically responsive layer comprising the responsive optical
element or elements. The responsive optical element could also be
in the form of a single layer making up the optically responsive
layer, or alternatively may be a layer comprising discrete elements
or particles that make up the responsive optical elements as
described herein. In select embodiments, the optically responsive
layer may itself undergo a change in conformation, shape or
thickness in response to an external influence, thus to alter a
proximity of the optically responsive layer (or elements thereof)
to the control layer. Alternatively, or in addition, a spacer layer
may be present between the control layer and the responsive layer,
the thickness, shape or configuration of which may be altered in
response to the external influence, thus to alter a proximity of
the responsive layer (or elements thereof) to the control layer.
Other embodiments of optically variable devices are also described.
Perceivable or detectable change (of optical and/or physical
properties of a device): refers to any change that occurs to a
device as described herein, that may be perceived by the user of a
device (through sight, touch etc.) or which is detected for example
by a user of the device with the assistance of a screening tool. To
provide just one example, a change of optical properties of a
device might occur only in the beyond visible spectrum of
electromagnetic radiation, in which case a user of the device may
choose to employ a UV screening tool to detect a corresponding
change in optical properties. Piezoelectric layer: refers to any
layer formed from any material that: (1) can undergo a change of
shape, thickness, configuration or form, either permanently or
temporarily, under conditions of an electrical potential
difference, an increased electrical potential difference, or
decreased electrical potential difference, by virtue of the
piezoelectric properties of the materials of the layer. For
example, the thickness of the layer may be changeable between a
`relaxed` state absent electrical potential difference, (or under
less electrical potential difference) and a `compressed` state
under increased electrical potential difference, and (2) has
suitable optical properties such that when the layer separates a
control layer and an optically responsive layer as described
herein, a change in the thickness of the layer causes a change in
the optical properties of the optically responsive layer resulting
from a change in the proximity of the optically responsive layer
relative to the control layer. Alternatively, a piezoelectric layer
may form part or all of a control layer or an optically responsive
layer. Preferably the piezoelectric layer is reversibly changeable
such that the layer can be transitioned between relaxed and
compressed states multiple times upon repeated application and
removal of the electrical potential difference, or repeated
increase and decrease of electrical potential difference. The shape
or thickness change of the piezoelectric layer (for example the
capacity of the layer to be reduced or increased in thickness
depending upon electrical potential difference) may be established
according to the material used to form the layer. For example,
different polymers or crystals may be less or more inclined to
change shape or thickness compared to other materials under the
same degree of electrical potential difference. Examples of
materials suitable for use in the formation of piezoelectric layers
include but are not limited to ferroelectric and pyroelectric
materials such as poly(vinylidene fluoride) (PVDF) and its
copolymer with trifluoroethylene P(VDFTrFE). The piezoelectric
layer may alternatively be made of materials in polyvinylidene
difluoride (PVDF) or PVDF derivatives. In one example, the
piezoelectric layer may be made of poly (vinylidene
fluoride-trifluoroethylene) (P(VDF-TrFE)) or poly(vinylidene
fluoride/tetrafluoroethylene) (P(VDF-TeFE)). In other examples, the
piezoelectric layer may be made of a blend of a material in PVDF or
PVDF derivatives and at least one of lead zirconate titanate (PZT)
fibers or particles, polymethylmethacrylate (PMMA), or poly(vinyl
chloride) (PVC). Inorganic materials that can deposited by vacuum
deposition or sol gel process including lead zirconate titanate
(PZT) and barium titanate, and zinc oxide may also be used. Further
examples of materials suitable to used as a component material for
the piezoelectric layer include, but are not limited to, those
disclosed in Chu et al. (2006) Science, Vol. 313, pages 334-336,
and Bauer et al. Dielectrics and Electrical Insulation, IEEE
Transactions Publication Date: October 2006 Volume: 13 Issue: 5,
pages: 1149-1154, both of which are incorporated herein by
reference. Furthermore, a piezoelectric layer may optionally
comprise or consist of an adhesive material such as but not limited
to: acrylated urethanes, methacrylate esters, mercapto-esters and
UV curable materials. A piezoelectric layer may be applied under
any conditions and in any way. In selected embodiments the layer is
applied by printing such as by Gravure printing. Moreover, the
piezoelectric properties of a piezoelectric layer may be imparted
to the layer either before, during or after its application or
formation upon a reflector or absorber layer, in accordance with
the teachings herein. In one example of a piezoelectric layer, when
an electric field having the same polarity and orientation as the
original polarization field is placed across the thickness of a
single sheet of piezoceramic, the piece expands in the thickness or
"longitudinal" direction (i.e. along the axis of polarization). At
the same time, the sheet contracts in the "transverse" direction
(i.e. perpendicular to the axis of polarization). When the field is
reversed, the motions are reversed. Sheets and plates utilize this
effect. The motion of a sheet in the thickness direction may at
least in some embodiments be extremely small (in the order of tens
of nanometers). For example, in accordance with the security
devices and documents disclosed herein a thickness change in the
order of tens of nm may be suitable for operation or optical change
of the device since it will represent a 5-8% change in thickness
for the spacer layer. On the other hand, since the length dimension
is often substantially greater than the thickness dimension, the
transverse motion is generally larger (on the order of microns to
tens of microns). The transverse motion of a sheet laminated to the
surface of a structure can induce it to stretch or bend, a feature
often exploited in structural control systems. A piezoelectric
layer may also be used to provide an electrically charged layer for
use as a control layer. Polymer core material: refers to any
polymer or polymer-like substance suitable to form a core material
in the form of a sheet-like configuration to be formed or cut into
a size suitable for use in various items and documents. The polymer
core material may be a substantially uniform sheet of polymer
material, or may take the form of a laminate structure with layers
or polymer film adhered together for structural integrity, such as
disclosed for example in international patent publication
WO83/00659 published Mar. 3, 1983, which is incorporated herein by
reference. A polymer core material may also comprise a material
that includes a polymer in combination with other materials such as
plastic or paper to form a hybrid core material. Reflected light:
refers to light incident upon a surface and subsequently `bounced`
or otherwise reflected by that surface such that the reflected
light is visible to the naked eye or detectable by a suitable
means. The degree of light reflection may vary according to the
surface, and the degree of light that is not reflected by the
surface because it is scattered by, diffracted by, absorbed by, or
transmitted through the surface and the material of the substrate.
Relaxed state: in selected embodiments that employ a deformable
layer, the expression "relaxed state" refers to a state, shape or
thickness of a deformable layer absent an external influence, or as
a result of a reduced external influence, upon the layer. For
example, if the external influence comprises a mechanical force or
pressure upon the layer, then a relaxed state may be present under
a reduced mechanical force or pressure relative to that applied to
achieve a `compressed` state. In selected embodiments a relaxed
state is any state that is different to a compressed state in which
a mechanical force or pressure is present or increased upon the
layer relative to a relaxed state. Such a relaxed state may be a
single state in response to a fixed degree of force or pressure (or
no force or pressure), or may pertain to a range of degrees of
deformation in response to a range of degrees of mechanical force
or pressure. Moreover, the amount of pressure or force required for
a deformable layer to adopt a relaxed state may vary according to a
degree of deformability of the layer. In further selected
embodiments in which a layer is a piezoelectric layer comprised of
a piezoelectric material, a "relaxed state" refers to a state,
shape or thickness of a piezoelectric layer upon removal of an
electrical potential difference, or in the presence of an decreased
electrical potential difference, relative to a compressed state, to
change, alter, increase, or decrease the state, shape, thickness or
configuration of the layer in at least a portion thereof relative
to a compressed state. In selected embodiments a relaxed state is a
state that is different to a compressed state in which the
electrical potential difference is present or increased. Such a
relaxed state may be a single state in response to a fixed degree
or absence of electrical potential difference, or may pertain to a
range of degrees of states, shapes or thicknesses in response to a
range of degrees of electrical potential difference. Moreover, the
amount of electrical potential difference required for a
piezoelectric layer to adopt a relaxed state may vary according to
the piezoelectric properties of the layer. Regardless of whether a
layer is mechanically deformable or piezoelectric or other type,
the layer may be sufficiently thin in said compressed state
(compared to the relaxed state) to cause an adjacent layer (e.g. a
magnetic layer and an optically responsive layer) disposed or
adhered to either side of the layer, or elements in that layer, to
interact in some way with another layer present, such that when
adopting the compressed state one of the adjacent layers (or
elements thereof) changes its optical appearance compared to the
relaxed state. Likewise, the layer may be sufficiently thick when
in a relaxed state (compared to a compressed state) to cause an
adjacent layer disposed or adhered to either side of the layer, or
elements of that other layer, to interact to a lesser degree, or
not to interact at all, such that when adopting a relaxed state one
of the adjacent layers (or elements thereof) changes its optical
appearance compared to the compressed state. The same applies if a
deformable, piezoelectric material is used to form an optically
responsive layer optically responsive layer as described herein,
optionally with embedded or included responsive optical elements:
the thickness of the optically responsive layer optically
responsive layer as influenced by an external influence may change,
thus changing the distance of the responsive optical elements to an
adjacent control layer. Responsive element: encompasses responsive
optical elements as described herein, as well as any other feature
or element of a device as described herein that can undergo a
user-detectable e.g. physical change upon user-manipulation of the
devices as described herein. For example, responsive elements may
alternatively comprise, but are not limited to, tactile elements
that undergo a change in texture, thickness or contour that are
detectable by touch of the user. Security document: refers to any
document, item or article of manufacture of any importance or
value, which might be subject to or susceptible to counterfeit
copying. In selected embodiments, a security document may include
features or devices intended to show that the document, item or
article is a genuine and legitimate version, and not a counterfeit
copy of such a document, item or article. For example, such
security documents may include security features such as those
disclosed herein. Such security documents may include, but are not
limited to, identification documents such as passports, citizenship
or residency documents, drivers' licenses, bank notes, cheques,
credit cards, bank cards, and other documents, as well as labeling
or other security features, for items of monetary value such as
designer clothing, accessories, or any other branded products where
it is desired to indicate or demonstrate the authenticity or
legitimacy of the product compared to a counterfeit copy. Such
security features may be permanently or removably incorporated
therein depending upon the nature of the document, item or article,
and the intended end user. Spacer layer: refers to any layer that
spaces a first layer on one side of the spacer layer from another
second layer on a side of the spacer layer opposite to the first
layer. Any spacer layer herein described may comprise or consist of
any deformable layer or deformable spacer layer as herein
described. Regardless of the material of the spacer layer, the
layer may optionally consist of any deformable material or material
that can be caused to change its thickness, shape or configuration.
Alternatively the layer may comprise any deformable material
combined with non-deformable materials, or may comprise
compressible voids, pockets, compartments, vesicles or pores
comprising any material, liquid or gas. In some embodiments the
layer may be comprised mostly of a gas or gases (e.g. air) with
supporting "posts", "columns" or "supports" to maintain one or more
voids, pockets or compartments in an open state
absence an external influence such as mechanical pressure.
Transmitted light: refers to light that is incident upon a surface,
layer or multiple layers, of which a portion of the light is able
to pass through and/or interact in some way with the surface, layer
or layers by transmission. Light may be transmitted through a layer
or layers by virtue of the layer or layers not being entirely
opaque, but instead permitting at least a portion (e.g. 0-99%) of
the incident light to be transmitted through the layer or layers in
view of the layer or layers exhibiting at least some degree of
translucency. Window: refers to a region or portion of a security
document in which a component of a security device is exposed for
visual inspection, because there is little or no translucent or
opaque material to obscure the view of the exposed portions. A
window may be present even if there are transparent or translucent
layers, for example of film, to cover the security device or
components thereof, because the exposed portions of the security
device are still visible, at least in part, through the film. In
further selected embodiments as disclosed herein `window` refers to
one or more portions of a security device as disclosed herein in
which a masking layer does not extend across the entire surface of
a security device, such that portions of the security device are
exposed for visual inspection in reflective light. A window may
also refer to a clear or transparent or translucent region of a
substrate, for example for viewing therethrough other parts of a
security document when the document is folded or manipulated.
DETAILED DESCRIPTION OF THE INVENTION
[0099] Disclosed herein are devices that are useful for a broad
range of applications including, but not limited to, displays for
devices and documents, magazines, books or other items with
user-manipulated content, and advertizing billboards. In further
applications, the devices may be used as authentication devices for
any items such as for example security documents such as passports,
credit cards and bank notes to help prevent counterfeit. In
selected embodiments the devices may be especially amenable to
large-scale production, and yet include materials and/or structural
configurations that are difficult to replicate without prior
knowledge of the nature of the component materials and their
dimensions. Herein described are devices that, at least in selected
embodiments, comprise laminate or layered structures that, at least
in selected embodiments, give rise to a wide range of optical
variability, including colour-changes, appearance of content
including text and images, or even moving images according to the
application and configuration of the device. In other embodiments
the devices may exhibit changes in texture or contour (or other
changes sensed for example by the touch of a user) in addition to
or instead of optical variability. The invention encompasses the
devices themselves, their structures, as well as methods for their
manufacture and their use.
[0100] In selected embodiments the devices may include a material
that is deformable in some way, wherein the deformation of the
material causes a change in the proximity and/or orientation of one
or more responsive elements relative to a control element or layer,
or relative to one another, which in turn causes a change in the
properties of the responsive element(s) that is detectable by a
user or observer of the device in some way.
[0101] In particular, the inventors have endeavoured to develop
devices that exhibit user-sensed features that can be altered or
selectively activated according to user-manipulation of the device,
either by hand and/or with the assistance of a screening tool or
device. To this end some of the devices disclosed herein comprise
at least one layer of material that can be deformed, squashed,
expanded or caused in some other way to change in thickness upon
application to the device of an external influence such as
mechanical pressure, or some other influence such as a change in
potential difference across the device. Such deformation or change
enables the device to adopt alternative optical or other properties
according to whether the material of the layer is in a `relaxed`
state under reduced external influence or absent the external
influence, or alternatively whether the material of the spacer
layer is in a `compressed` state under increased degrees of the
external influence (at least compared to a relaxed state). In any
embodiments described below or herein, any reference to responsive
optical elements or layers, or any references to changes in optical
properties, may be substituted with alternative means to achieve
changes in physical properties of the devices disclosed.
[0102] Thus, the optically variable devices disclosed herein at
least in selected embodiments may comprise at least one layer of
any material, wherein at least a portion of the layer undergoes a
change in thickness once an external influence of some kind is
imposed upon, or increased upon, the layer, either directly or
through other layers. Such external influences may include, but are
not limited to, mechanical forces and pressures upon the layer
(especially where the layer comprises a deformable material) or the
application of a potential difference or increased potential
difference across the layer (for example where the layer comprises
a piezoelectric material).
[0103] In selected embodiments of the devices disclosed herein, the
layer may include a spacer layer that at least in part separates,
or is otherwise disposed between, other layers of the device,
wherein the other layers may be caused to interact in some way with
one another depending upon the thickness of the spacer layer. For
example, one of the other layers may comprise a "control layer"
juxtaposed with or adhered to the spacer layer, wherein the control
layer affects one or more other layers of the device, or components
of those layers, according to its relative proximity to those other
layers or components.
[0104] In selected embodiments, responsive optical elements may be
in the form of, or be part of, an optically responsive layer (or
other responsive layer), which may be juxtaposed with or adhered to
the spacer layer, on an opposite side of the spacer layer compared
to the control layer, thus to form a layered or laminate structure
with the spacer layer separating the control and optically
responsive layers. The optically responsive layer may comprise any
material, structure or form that can undergo any change in
appearance when under the influence of the control layer.
Therefore, the optically responsive layer may adopt a particular
appearance upon visual inspection thereof (or upon inspection with
the aid of a viewing device or tool) when the spacer layer adopts a
relatively thick or "relaxed" configuration. However, when the
spacer layer is caused to become thinner by some external
influence, the optically responsive layer is brought into closer
proximity with the control layer. This in turn may cause the
optically responsive layer to be exposed to an increased influence
from the control layer, which in turn may be sufficient for the
optically responsive layer to exhibit alternative optical
properties upon visual inspection thereof (or upon inspection with
the aid of a viewing tool or device).
[0105] Thus selected embodiments, which will become more apparent
from the foregoing examples, may comprise devices with three
layers: a control layer, a spacer layer, and an optically
responsive layer, which interact with one another in a specific
manner. However, the invention is not limited in this regard: other
embodiments may simply include optically variable devices
comprising:
[0106] a control element or layer; and
[0107] one or more responsive optical element(s) responsive to
changes in their spatial separation from the control layer, the
control element or layer and the responsive optical element(s)
moveable relative to one another in response to an external
influence to increase and/or decrease a distance of the element(s)
from the control layer, thereby to cause a change in optical
appearance of the element(s) resulting a change of optical
appearance of the device.
[0108] Such embodiments may include, for example, two-layer devices
comprising a control layer and responsive optical elements that
form or form part of an optically responsive layer, wherein the
optically responsive layer itself can be caused to undergo a change
of shape, thickness or configuration in response to an external
influence sufficient to change a proximity of the optically
responsive layer, or elements thereof, relative to the control
layer, so that the device undergoes an optical change.
[0109] Optionally, the responsive optical element or elements may
comprise a thin-film reactive layer, at least a portion of which
comprises an optically responsive material. In this way, a single
layer of thin-film material that is able to change its appearance,
at least in part, depending upon its proximity or distance from the
control layer. However, in other embodiments the responsive optical
element or elements may comprise a plurality of particles,
molecules or compartments encapsulated in an optically responsive
layer discrete from the control layer, wherein the thickness of the
optically responsive layer is altered by the external influence,
thereby to increase and/or decrease a distance of the particles,
molecules or compartments containing them from the control layer,
which in turn causes a change in the appearance of the particles,
molecules or compartments containing them, and thus the appearance
of the optically responsive layer.
[0110] Optionally, any of the optically variable devices disclosed
herein may comprise an optically responsive layer comprising the
responsive optical element or elements, and a spacer layer between
and attached to the control layer and the optically responsive
layer, the thickness of which is dependent upon an external
influence. In this way the appearance of the spacer layer may be
altered by the external influence causing a change in the proximity
or distance of the responsive optical element(s) from the control
layer.
[0111] The embodiments disclosed herein are not limited with regard
to the nature of the control element or layer, nor the spacer layer
(if present) nor the optically responsive layer or elements thereof
that `respond` to the relative proximity of the control element or
layer. Indeed, further embodiments encompass any layers or
components thereof that, when positioned appropriately, react in
some way to cause an optical change in the responsive optical
element(s) either individually or when viewed collectively in the
device, or an optically responsive layer comprising such elements,
resulting from the change in the spatial separation of the
element(s) from the control layer. Moreover, the embodiments
described herein are not limited to the use of one or more
responsive optical elements or layers comprising them that undergo
a visual change that can be detected by a human eye. Indeed,
selected embodiments may comprise responsive optical elements or
layers that undergo a microscopic change of optical properties
and/or a change that is only visible with the aid of a viewing
device or tool, such as may be required under conditions of
electromagnetic radiation beyond visible light. Selected
embodiments will also become more apparent from the foregoing.
[0112] Therefore, the optical properties of the responsive optical
elements, or an optically responsive layer comprising such
elements, and/or any change of such optical properties, may be
macroscopic, microscopic, or observable in visible light conditions
or beyond visible light conditions.
[0113] The embodiments disclosed herein are also not limited in
terms of the nature of the control layer, and the way it exhibits
an influence over the optical properties of the responsive optical
element(s) or an optically responsive layer comprising such
element(s). Selected embodiments involve magnetism.
[0114] For example, selected embodiments provide an optically
variable device, the device comprising:
[0115] a control element or layer comprising a magnetic material
that is permanently or temporarily magnetic, such that a magnetic
field emanates from the material;
[0116] one or more responsive optical element(s);
[0117] the control element or layer and the responsive optical
element(s) moveable in the device relative to one another upon
application of an external influence upon the device, to change the
distance of separation of the control element or layer from the
responsive optical element(s), and therefore to change the strength
of the magnetic field impinging upon the responsive optical
element(s) from the magnetic material of the control element or
layer;
[0118] the relative movement and/or the change of the strength of
the magnetic field impinging upon the responsive optical
element(s), causing a change of perceivable or detectable optical
properties of the device.
[0119] For example, an optically variable device as described
herein may include a control element or layer composed at least in
part of a magnetic material from which emanates a magnetic field.
In such embodiments, the responsive optical element(s) (or
optically response layer comprising such elements) may comprise a
material or structure the optical properties of which depend upon a
strength of the magnetic field impinging thereupon from the
magnetic material of the control layer. Upon manipulation of the
device, a user in some way (e.g. by hand or with the aid of an
external device or tool, or some other external influence) may
change the proximity or distance of the responsive optical
element(s) (or optically responsive layer comprising such elements)
to the control layer, which in turn alters the strength of the
magnetic field impinging upon the responsive optical elements
sufficient to change their optical properties. Optionally, the
control layer comprises a permanent magnet, or a permanently
magnetic material. Alternatively, the control layer may comprise an
electromagnet or an electromagnetic material. For example,
electromagnets and electromagnetic materials may be energized by
any means such an external microwave source. Electromagnetics may
for example be integrated into selected versions of the devices in
connection with an internal or integrated battery, such as a
printed battery.
[0120] In further examples, the magnetic material of the control
layer may be selected from one or more of: Co, Fe, Fe.sub.2O.sub.3,
FeOFe.sub.2O.sub.3, NiOFe.sub.2O.sub.3, CuOFe.sub.2O.sub.3,
MgOFe.sub.2O.sub.3, MnBi, Ni, MnSb MnOFe.sub.2O.sub.3,
Y.sub.3Fe.sub.5O.sub.12, CrO.sub.2, MnAs, Gd, DyEuO, NdFeB, SmCo,
and SmCo.sub.5.
[0121] When the optically variable device comprises a control layer
itself comprised of a magnetic material, the responsive optical
element(s) may comprise any layer or structure that undergoes a
change of optical properties when the magnetic field impinged
thereupon from the control layer is altered, for example in terms
of an increased or decreased flux density.
[0122] In alternative embodiments to those involving magnetism, the
control layer may comprise an electrically charged material from
which emanates an electric field. Moreover, the responsive optical
element(s) (or optically response layer comprising such element(s))
may comprise a material or structure the appearance of which
depends upon a strength of the electric field impinging thereupon
from the electrically charged material of the control layer. In
this way, a change in the thickness of the spacer layer may alter
the strength of the electric field impinging upon the optically
responsive layer sufficient to cause a change in the optical
properties of the responsive optical element(s) (or optically
response layer comprising such elements).
[0123] For example, related exemplary embodiments may provide an
optically variable device, the device comprising:
[0124] a control element or layer comprising a material that is
permanently or temporarily electrically charged or polarized such
that an electric field emanates from the material;
[0125] one or more responsive optical element(s);
[0126] the control element or layer and the responsive optical
element(s) moveable in the device relative to one another upon
application of an external influence upon the device, to change the
distance of separation of the control element or layer from the
responsive optical element(s), and therefore to change the strength
of the electric field impinging upon the responsive optical
element(s) from the electrically charged or polarized material of
the control element or layer;
[0127] the relative movement and/or the change of the strength of
the electric field impinging upon the responsive optical element(s)
causing a change of perceivable or detectable optical properties of
the device.
[0128] For example, in any embodiments involving an electric field,
the control layer may comprise any material that is able to obtain,
retain, or adopt an electric charge or polarization by any means.
For example, electrically insulating materials may be suitable that
exhibit, or can be caused to adopt, a positive or negative electric
charge sufficient to generate the electric field. In selected
embodiments, such control layers may comprise at least one of: a
polymer, a plastic, a resin, silica, and derivatives thereof, an
electret or piezoelectric material. Moreover, for such embodiments
the responsive optical element or elements may comprise
electrochromic, electrostatic, polarizable or polarized, optionally
encapsulated particles, particles with a permanent or induced
dipole moment, or other suitable materials that are able to change
their appearance, orientation or configuration in the device
according to their distance from a control element or layer that
produces an electric field. Examples may include, but are not
limited to, freely-rotatable optionally polarizable particles or
molecules, embedded liquid crystal microcapsules, electrochromic
materials (e.g. with optional charge transfer between active
materials and an ion reservoir), or Janus particles. In some
examples, the control element or layer may comprise at least one
of: a polymer, a plastic, a resin, silica, PTFE, and derivatives
thereof.
[0129] In yet further embodiments of the optically variable
devices, surface plasmon resonance and corresponding interaction
between a control layer and responsive elements can result in
changes in the optical properties of the device.
[0130] For example, certain exemplary embodiments provide an
optically variable device, the device comprising:
[0131] a control element or layer;
[0132] one or more responsive optical element(s);
[0133] the control element or layer and the responsive optical
element(s) moveable in the device relative to one another upon
application of an external influence upon the device, to change the
distance of separation of the control element or layer from the
responsive optical element(s),
[0134] the control element or layer and/or the responsive optical
element(s), comprising a material with a surface plasmon resonance
that is influenced by proximity of the material to the other of the
control element/layer or the responsive optical element(s); the
relative movement and/or a resulting change of surface plasmon
resonance of the material causing a detectable or perceivable
change in the optical properties of the device.
[0135] In just one example, surface plasmon resonance may cause
migration and/or rotation of conductive nanoparticles suspended in
gas and/or liquid-encapsulated in vesicles or compartments in an
optically responsive layer, whereupon a change in the distance of
the conductive nanoparticles from the control layer results in an
optical change in the optically responsive layer caused by the
migration and/or rotation. For example, the control element or
layer may comprise an electrically conductive material, and
optionally the responsive optical elements may comprise conductive
particles, conductive nanoparticles, nonconductive particles, or
nonconductive nanoparticles.
[0136] In any of the embodiments described, the responsive optical
elements may optionally be caused to undergo at least partial
rotation and/or translation when the device is exposed to the
external influence, the responsive optical elements optionally
undertaking such rotation and/or translation in fluid retained
within the device. For example a device may comprise charged
particles suspended in a fluid (including gases, liquids and
mixtures thereof), wherein the particles can be caused to move
(migrate and/or rotate) by electrophoresis or other induced
migration in the liquid in response to their exposure to an
increased magnetic or electric field, or surface plasmon resonance,
caused by a change in a spatial separation of the responsive
element(s) from the control element or layer.
[0137] In any of the embodiments described, the responsive optical
elements may be encapsulated in a discrete layer (e.g. optically
responsive layer) from the control layer, the thickness of which is
varied by the external influence, thereby to increase and/or
decrease the distance of separation of the particles and the
control element or layer. Alternatively, or in addition, a spacer
layer may be present between the control element or layer and the
responsive optical element(s), which itself may vary in thickness
according to the external influence.
[0138] The capacity of an optically responsive layer and/or a
spacer layer (if present) to alter its thickness or configuration
may be achieved via any means, and via the use of any materials
that can be caused to adopt an altered thickness in response to any
external influence. For example, in selected embodiments a
deformable layer may comprise any deformable material, changeable
between a relaxed state with no or less mechanical pressure upon
the layer, and a compressed state upon increased mechanical
pressure upon the layer, wherein the reduction in thickness of the
layer may be sufficient to cause a change of optical properties of
the responsive optical element or elements present in the device.
For example, a deformable layer may optionally comprise at least
one adhesive material selected from acrylated urethanes,
methacrylate esters, mercapto-esters and a UV curable adhesives.
Such adhesive materials may not only assist in the adhesion of the
layers forming the optically variable device, but also may provide
materials with desirable deformability when under mechanical
pressure or stress.
[0139] In other embodiments, a deformable layer may be formed on
the control layer, or indeed another layer, by a printing technique
such as Gravure printing. In this way, the deformable layer may be
applied on only select portions of the device, or on select
portions in different thicknesses, thus to provide a pattern, or
content, to the device before and/or after the application of
mechanical pressure. Thus, a deformable spacer layer may have a
non-uniform thickness when in said relaxed and/or said compressed
state, such that different parts of the responsive optical element
or elements (or an optically responsive layer comprising such
elements) exhibit different optical properties in the relaxed
and/or compressed state according to their distances from the
control layer.
[0140] If an optically responsive layer or a spacer layer (any
layer) comprises a deformable material then it may be deformable
only once such that it does not regain its original shape and form
once the mechanical pressure has been removed. However, in other
embodiments a deformable layer may be resiliently deformable so
that it may cycle multiple times between compressed and relaxed
states. Moreover, once the mechanical pressure is removed the
deformable layer may relax to its original shape and form (prior to
the application of mechanical pressure) very slowly or very quickly
depending upon the application. For example, the spacer layer may
transform from a compressed to a relaxed state in from 0.000001 to
1000 seconds, preferably from 0.001 to 120 seconds.
[0141] Selected materials for a deformable layer may include a
plurality of pores or voids that reduce in volume when mechanical
pressure is applied to the device thereby to assist compression of
the deformable spacer layer from a relaxed state to a compressed
state. Such pores or voids may be small or microscopic, or comprise
voids or compartments in the layer that comprise the majority of
the volume of the layer, with posts, columns or supports of
material defining the voids or compartments.
[0142] In still further embodiments of the optically variable
devices, a spacer layer (if present) or an optically variable layer
may comprise a piezoelectric material changeable between a relaxed
state and a compressed state upon a change in electrical potential
difference across the device, resulting in a change in optical
properties of the device. For example, a piezoelectric layer may
adopt a relaxed state absent any electric potential difference
across the layer.
[0143] Optionally, a spacer layer (if present) or an optically
variable layer may comprise a piezoelectric material, comprising a
crystal or polymer, and optionally at least one adhesive material
selected from acrylated urethanes, methacrylate esters,
mercapto-esters and a UV curable adhesives.
[0144] As with any deformable layer, any piezoelectric layer may
optionally be formed by any printing technique such as Gravure
printing. For example, selected piezoelectric layers may have a
non-uniform thickness when in said relaxed and/or said compressed
state, such that different parts of the optically responsive layer
exhibit different optical properties according to their distances
from the control layer.
[0145] Still further embodiments provide an optically variable
device, the device comprising:
[0146] two or more responsive optical elements responsive to
changes in their relative positions through the interaction of
mutual surface plasmon resonance, each element having altered
detectable or perceivable optical properties in the device
according to its distance from at least one other responsive
optical element, due to an altered degree of exposure to the
surface plasmon resonance of the at least one other responsive
optical element;
[0147] the responsive optical elements being moveable within the
device in terms of their spacing relative to one another, in
response to an external influence, to cause a change in perceivable
or detectable optical properties of the responsive optical
elements, resulting a change of perceivable or detectable optical
properties of the device. In such embodiments, the external
influence may for example cause the two or more responsive optical
elements to organize into an array of elements, or to become
disorganized in the device, depending upon the presence or degree
of the external influence upon the device, thereby giving rise to a
change of optical appearance of the device. For example, the
external influence may cause a change in the separation of two or
more elements resulting in a change of optical appearance of the
device.
[0148] In such embodiments, the external influence may optionally
cause a change in the orientation of two or more elements,
resulting in a change of optical appearance of the device.
Optionally the elements are conducting particles.
[0149] Optionally the elements are nanoparticles.
[0150] Optionally the elements are conducting nanoparticles.
[0151] Optionally the elements are a combination of conducting and
non-conducting particles.
[0152] Still further example devices may undergo a physical,
tactile change rather than, or in addition to, an optical change.
In any of the embodiments described herein that refer to responsive
optical elements or layers, or which refer to an optical change of
the device, any reference to optical responsiveness or optical
changes may be substituted by physical changes to the device (e.g.
that can be detected by touching or feeling the device). For
example other embodiments encompass a variable device that
undergoes a user-detectable tactile change, the device
comprising:
[0153] a control element or layer;
[0154] one or more responsive element(s);
[0155] the control element or layer and the responsive element(s)
moveable in the device relative to one another upon application of
an external influence upon the device, to change the distance of
separation of the control element or layer from the responsive
element(s), and therefore to change a degree of influence of the
control element or layer upon the responsive optical element(s), to
cause a change of perceivable or detectable physical properties of
the device.
[0156] For example, the user-detectable change may comprises a
change in the thickness, texture, or prominence of the device or
portions thereof, optionally combined with a change in the optical
properties or appearance of the device.
[0157] Still further embodiments provide for a use of any device
described herein, as a feature of any type of item or document.
Such documents may be selected from, but are not limited to, paper
document, books, magazines, advertisements, billboards,
identification documents such as passports, citizenship or
residency documents, drivers' licenses, bank notes, cheques, credit
cards, bank cards, and other documents, as well as labeling or
other security features, for items of monetary value such as
designer clothing, accessories, or any other branded products where
it may be desired to indicate or demonstrate the authenticity or
legitimacy of the product compared to a counterfeit copy.
[0158] Thus, in further embodiments there are provided any "items"
comprising:
[0159] a core material; and
[0160] at least one device as described herein affixed to at least
one side of the core material, or at least partially embedded into
the core material, such that the device is at least partly visible
or detectable from at least one side of the core material.
Depending upon the application, the core material may comprise at
least one material selected from the group consisting of: paper,
polymer, plastic, and combinations or hybrids thereof, and any
other suitable core materials.
[0161] In selected embodiments, the item may further comprise a
portion to be contacted with the device, thereby to cause a change
in the optical or physical properties of the device resulting from
a change in distance of the responsive element(s) from the control
layer of the device. For example, in the case of a security
document, a portion of the document may be adapted to be pressed
against an optically variable device, and may optionally comprises
intaglio printing, thereby to provide a raised, optionally
patterned, region as a pressure template to achieve the change in
visible appearance of the device. Alternatively, or additionally,
the portion to be contacted or pressed against the optically
variable device may comprise a transparent or translucent window in
the document, such that any change in the visible appearance of the
device can be observed through the window.
[0162] Certain exemplary embodiments will now be described with
reference to the accompanying figures. For simplicity, selected
embodiments will be described in terms of a relaxed state absent an
external influence, and a compressed state in the presence of an
external influence. However, no embodiment is limited in this
regard and any a transition between relaxed and compressed states
may be achievable by altering the degree of external influence
being applied to the device (rather than completely applying or
completely removing the external influence). Further, the examples
will be described principally with reference to optically variable
devices. However, any such devices may alternatively (or
additionally) exhibit changes in the physical properties, texture
or feel of the device. It should also be noted that the
accompanying figures illustrate exemplary embodiments in a
schematic fashion: the thickness of the layers shown relative to
one another, or the relative thicknesses of layers in relaxed or
compressed states, are not shown to scale but exaggerated from
typical working embodiments to facilitate an understanding of
certain aspects of the invention.
[0163] It should also be noted that some of the examples shown in
select figures are described with reference to a `magnetic control
layer` from which emanates a magnetic field, wherein `magnetic
control elements` undergo an optical or physical change depending
upon their distance from the magnetic control layer. Other
embodiments are described and illustrated with reference to plasmon
or electrets devices. However, each of the embodiments illustrated
would also be applicable to other forms of control elements/layers,
and their respective response elements/layers.
[0164] Turning first to FIG. 1 there is shown in FIG. 1a a top-plan
view of a document shown generally at 9 comprising a core substrate
10. In FIG. 1b there is shown a cross-section through the same
document along lines A-A' in FIG. 1a, with an optically variable in
direct contact with the core substrate 10 of the document.
[0165] In FIG. 1 the core substrate 10 may comprise any suitable
material or combination of materials, but in this example comprises
a polymer such as PET having a thickness of about 12 .mu.m.
Attached to the PET is an optically variable device shown generally
at 11, comprising three distinct layers. A control layer 12 is in
direct contact with the core substrate 10, and comprises any
material or structure with an ability to impose an influence upon
one or more other layers of the optically variable device
(depending upon proximity as described below). In the example shown
in FIG. 1 the control layer comprises a vacuum-deposited layer of a
metallic material with magnetic properties, and having a thickness
of about 200 nm.
[0166] In contact with the control layer 12 is a deformable spacer
layer 13, which in this instance generally covers the control layer
12. In the embodiment shown in FIG. 1, also present is an optically
responsive layer 14 adhered to the deformable spacer layer, wherein
the optically responsive layer comprises any material or structure
that can undergo an optical change according to its relative
proximity (distance) from the control layer. For example, the
optically responsive layer may comprise one or more responsive
optical elements (not shown) which themselves individually undergo
an optical change. The embodiment illustrated in FIG. 1b shows how
the optically responsive layer 14 is spaced from the control layer
12 by deformable spacer layer 13.
[0167] FIG. 1b illustrates the device 11 upon substrate 10 in a
relaxed state absent any mechanical force upon the device. In the
relaxed state the thickness of the deformable spacer layer 13 as
shown in the embodiment is about 400 nm: a thickness sufficient to
distance the optically responsive layer from the control layer such
that any magnetic field emanating from the control layer is
insufficient (i.e. insufficient magnetic flux density) to influence
the appearance of the optically responsive layer, thus giving rise
to a certain optical appearance of the optically responsive layer
14 shown by arrow 15 schematically illustrating reflected light
from the optically responsive layer 14, derived from incident light
shown with a large arrow.
[0168] In contrast, FIG. 1c illustrates the same device 11 upon the
same substrate 10, but with a mechanical force denoted by arrows 16
applied to the device to cause the deformable spacer layer to be
deformed from the relaxed state, thereby to adopt a compressed
state. In the compressed state the thickness of the deformable
spacer layer 13 is less (e.g. 250 nm) than in the relaxed state
shown in FIG. 1b. The compression is sufficient to bring the
optically responsive layer 14 into closer proximity to the control
layer 12, such that a magnetic field emanating from the control
layer impinges upon the optically responsive layer sufficiently
(e.g. with increased magnetic flux density) to cause the optically
responsive layer to adopt an alternative optical appearance, as
illustrated schematically by dashed arrow 17 showing an alternative
reflected light from the optically responsive layer 14.
[0169] FIG. 2 illustrates an alternative embodiment similar to FIG.
1, but in which discernible optical features are only apparent upon
the device when the device adopts a relaxed state absent mechanical
pressure. Specifically, FIGS. 2a and 2b illustrate a device similar
in appearance to that shown in FIGS. 1a and 1b, except that in a
relaxed state absent any mechanical pressure incident light upon
the device is reflected 18 so that image 19 (see FIG. 2a) can be
seen on the device by virtue of the optical properties of the
optically responsive layer. For example, the optically responsive
layer 14 may include ink or toner compositions in the form of
magnetic particles in liquid that, depending upon the strength of a
magnetic field impinging thereupon from the control layer 12, are
able to form image 19. In FIGS. 2a and 2b, absent mechanical
pressure upon the device, the spacer layer is thick enough (e.g.
600 nm) to prevent the magnetic field emanating from control layer
12 from influencing the appearance of optically responsive layer
14.
[0170] However, as shown in FIG. 2c, application of mechanical
pressure denoted by arrows 16 causes deformation of the deformable
spacer layer 13 such that it is compressed to adopt a thickness of
400 nm in a compressed state. In this way, the control layer 12 and
the optically responsive layer 14 may be brought into closer
proximity with one another, such that the magnetic field emanating
from the control layer has a stronger influence upon the optically
responsive layer, which in turn causes image 19 to change or
disappear from view according to the configuration of the
device.
[0171] Whilst the embodiments illustrated in FIGS. 1 and 2 include
spacer layers comprising a deformable material, any suitable
materials may be used for the spacer layers providing the spacer
layer can be caused to undergo a change of thickness in response to
some form of external influence. For example, with reference to
FIGS. 1 and 2, spacer layer 13 may alternatively comprise a
piezoelectric material that can undergo a change of thickness when
a potential difference is placed and/or removed from across the
device (or an increased or decreased potential difference is
present). FIG. 3 illustrates one such embodiment.
[0172] In FIG. 3a there is shown a core material of a security
document 10 in contact with a security device or optical
interference structure 11 as herein described and illustrated in
previous figures, but including a piezoelectric material rather
than a material that is deformable by mechanical pressure. As
shown, wire 21 connects power supply 22 to control layer 12
comprising a magnetic material, such that control layer 12
effectively functions as a bottom electrode. Furthermore, wire 23
connects power supply 22 to a top electrode 24, itself in contact
(both physical and electrical contact) with optically responsive
layer 14. In this way, top electrode 24 effectively acts in concert
with optically responsive layer 14 to provide a top electrode
component. The top electrode 24 may comprise any material, and be
applied by any means. For example, transparent top electrodes may
be applied by sputtering over the top of a metallic optically
responsive layer, and may comprise materials such as but not
limited to a polyethylene dioxythiophene (PEDOT) dispersion sold by
HC Stark under the trade name Baytron P.TM..
[0173] In FIG. 3a the power supply is shown to provide 0 volts of
electrical potential difference. FIG. 3b, in contrast, illustrates
the same arrangement as FIG. 3a except that power supply 22 now
provides an electrical potential difference of from 10-100 volts.
This in turn causes piezoelectric layer 13 to shift from a
`compressed` state to a `relaxed` state, and thus adopt an
increased thickness of 400 nm: sufficient to induce a change in the
optical appearance of the optically responsive layer 14, due to its
greater spatial separation from control layer 12. Removal of the
electrical potential difference from power supply 22 would cause
the device to revert to the `compressed` state shown in FIG. 3a.
Thus, application of an electrical potential difference in this
embodiment causes an increase in thickness of piezoelectric spacer
layer 13. Other embodiments are not limited in this regard:
different piezoelectric spacer layers may be configured to achieve
alternative changes of state: e.g. compressed to relaxed and back,
or decreased thickness, in response to an increased potential
difference.
[0174] FIG. 4 illustrates the same arrangement as FIG. 3, except
that the wires 21 and 23 (and electrode 24) are absent, replaced,
by an electrode-free design in which the electric field generated
by an electrical potential difference in itself sufficient to cause
the piezoelectric spacer layer to transition between a compressed
and relaxed state. In FIG. 4a there is shown a core material of a
security document 10 together with optically variable device 11.
Whilst the core material 10 rests upon bottom plate 26 it insulates
control layer 12 from direct electrical contact with the bottom
plate 26. Top plate 27 is spaced (e.g. by air) from optically
responsive layer 14. In the absence of an electrical potential
different the piezoelectric spacer layer 13 remains in a compressed
state. However, as shown in FIG. 4b application of a higher
electrical potential difference of 1000 volts across electrodes 26
and 27 causes the piezoelectric layer to transition from a relaxed
state to a relaxed state by virtue of the external electrical field
generated. This in turn results in the generation of sufficient
electrical potential across the piezoelectric layer for the
transition to occur from the compressed to the relaxed state, such
that the piezoelectric layer adopts a thickness of 400 nm:
sufficiently thick to result a change of optical properties of the
optically responsive layer 14, as denoted by arrows 28, 29
schematically showing reflected light from the optically responsive
layer 14.
[0175] The embodiment illustrated in FIG. 4 may present a useful
practical embodiment of the invention, since the electrodes 26 and
27 may form part of a device for checking the legitimacy of, for
example, bank notes. A person wishing to verify the legitimacy of a
bank note may simply slide or guide the note by hand into the
device between two concealed plates, and observe an optical change
in the associated security device without need to connect
electrodes to the bank note. Thus, the procedure for checking the
bank note may be as simple as current procedures involving a UV
lamp. Further, if the optical change is visible for example only in
beyond-visible light (e.g. UV) then a corresponding lamp may also
be incorporated into the bank note verification device.
[0176] FIGS. 5 to 7 illustrate how content may be included in
selected optically variable devices disclosed herein. The
embodiments will be described to include a deformable spacer layer,
although it will be apparent from the above that any type of spacer
layer may be used in substitution of a deformable spacer layer,
including piezoelectric or other layers that can change in
thickness in response to an external influence. Importantly, FIGS.
5 to 7 do not provide an exhaustive review of means or
configurations to include content in the optically variable devices
disclosed herein, as will become apparent from other figures.
[0177] In FIG. 5 there is shown an authentication device 11 again
comprising layers 12, 13, and 14 as for FIGS. 1 to 4, except that
the triple-layer structure has only been completed in certain areas
by deformable spacer layer 13a, 13b, 13c and optically responsive
layer 14a, 14b, 14c. In contrast, FIG. 6 provides in effect a
negative of the embodiment illustrated in FIG. 5, with deformable
spacer layer 13' and absorber layer 14'. In selected embodiments,
such patterns may be achieved by the use of a spacer layer material
that is amenable to being printed upon control layer 12 such as by
Gravure printing, or alternatively other techniques known in the
art may be employed to produce patterns, such as but not limited to
vacuum deposition and wet etching techniques. If the spacer layer
is adhesive or tacky, then the layer may be contacted with material
suitable to form the optically responsive layer, for example
located via a release layer on a web, such that the material
adheres to the spacer layer and is released from the web, thus to
complete the laminate structure of the device. Regardless, the
spacer layer may have any properties and thickness as required to
achieve as desired loss, gain or change of optical properties as
the device transitions between a relaxed and compressed state, as
described with reference to FIGS. 1 to 3.
[0178] FIG. 7 illustrates an alternative optically responsive
device shown generally at 11 including content in the form of
numbers 1, 2 and 3 as shown in FIG. 7a. FIG. 7b illustrates a
cross-section through the device along line A-A' in FIG. 7a. The
portions of the device that include numbers 1, 2, and 3 comprise a
deformable spacer layer 13a, 13b, 13c, which is thicker than the
deformable spacer layer 13' of the remainder of the device. As a
result, whether in a relaxed or compressed state, the numbers 1, 2
and 3 are visible by virtue of the alternative optical properties
of the device provided by the differences in the thickness of the
spacer layer 13a, 13b, 13c relative to layer 13'. For example, in a
relaxed state the portion of the device comprising areas other than
those forming number 1, 2, and 3 may comprise a spacer layer 13'
having a thickness of 400 nm: sufficiently thin to cause the
control layer 12 to impose an influence upon the optical appearance
of optically responsive layer 14'. In contrast, in the relaxed
state the portions comprising number 1, 2, and 3 may have a spacer
layer with a thickness of 650 nm: sufficiently thick to prevent the
control layer 12 from influencing the optical appearance of
optically responsive layer 14a, 14b, 14c. Upon application of
mechanical pressure (or some other suitable external influence),
all spacer layers present may be reduced in thickness by 250 nm.
This would result in those areas of the device excluding numbers 1,
2, and 3 to adopt a spacer layer having a thickness of 150 nm:
sufficiently thin to provide some form of enhanced level of
interaction between the control layer 12 and optically responsive
layer 14', whereas the spacer layer of the numbers 1, 2, and 3 may
be reduced to 400 nm: suitable to provide at least some interaction
between respective portions of control layer 12, and optically
responsive layer 14a, 14b, 14c. Thus, in such embodiments, the
number 1, 2 and 3 may be caused to "disappear" from view, or
alternatively adopt an alternative appearance whilst remaining
visible to a user in both relaxed and compressed states. Any
variants to alter the optical properties of the various regions of
the device in the relaxed and/or compressed state are encompassed
by the invention.
[0179] In other embodiments only selected portions of the device
may include a deformable spacer layer (or some other spacer layer
that can change its thickness), whereas other portions may comprise
any `regular` spacer layer that cannot change in thickness in
response to an external influence. In such embodiments, the
portions that include a regular spacer layer and the portions that
include a deformable spacer layer may optionally have spacer layers
having the same or near identical thicknesses either when the
portions comprising a deformable spacer layer adopt a relaxed or
compressed state. In this way the content may only become visible
to a user upon application or removal of mechanical pressure (or
other external influence), to transition select portions of the
device to an alternative state (relaxed or compressed) suitable to
provide a difference in the relative spacer layer thicknesses of
the regions comprising the deformable spacer layer compared to the
regions comprising the regular non-deformable spacer layer. For
example with reference to FIG. 7a, the device may comprise numbers
1, 2 and 3 each having a regular non-deformable spacer layer,
surrounded by other regions having a deformable spacer layer with
the same thickness as the regular non-deformable spacer layer only
when in one of the relaxed or compressed states. For example,
application of mechanical pressure to the device may alter the
thickness only of the deformable spacer layer present in the
regions surrounding numbers 1, 2 and 3 with a resulting optical
difference (gain, loss or change in optical properties) compared to
the regions comprising numbers 1, 2 and 3. If the mechanical
pressure causes the regions surrounding numbers 1, 2 and 3 to adopt
optical properties more different to those of the numbers then this
may result in the numbers 1, 2 and 3 becoming more obvious so that
they `appear` to a user upon visual inspection of the device when
pressure is applied. In alternative embodiments, the numbers 1, 2
and 3 may be visible to a user only when the regions surrounding
the numbers are in a relaxed state, due to a different thickness of
the deformable spacer layer in the regions surrounding the numbers
compared to the regions comprising the numbers, wherein the numbers
may be caused to `disappear` when a user applies pressure to the
device to bring the regions comprising the deformable spacer layer
into a compressed state, such that the thickness of the deformable
spacer layer is then comparable to the thickness of the regular
non-deformable spacer layer. Of course, it will be appreciated that
further variants of such embodiments may be used, including use of
a deformable spacer layer in the regions of the device forming the
numbers, with a regular non-deformable spacer layer in the other
regions of the device.
[0180] Different thicknesses of the deformable spacer layer may be
produced for example by a single Gravure printing step using a
template with varying thicknesses of spacer layer material, or by
multiple rounds of Gravure printing of the spacer layer material.
The embodiments encompassed herein are not limited in this regard,
and any means to generate any form of optically variable device,
with any type of content, is included within the scope of the
invention, the device or structure including, at least in selected
embodiments, at least portion comprising a spacer layer giving rise
to a change in optical properties upon application of, or increase
in, or decrease in, and external influence applied to the
device.
[0181] Any of the optically variable devices disclosed herein may
comprise a deformable spacer layer that can be permanently or
temporarily altered (in terms of its thickness) to produce an
observable change in the optical properties of the device.
Preferably, the change can be repeated on several, or many
occasions by virtue of the capacity of the deformable layer
material to be repeatedly transitioned or cycled between relaxed
and compressed states. Most materials suitable for this application
may be compressed relatively quickly so the optical change can be
observed without delay. However, consideration must also be given
to the relaxation time for the layer; that being the time it takes
for the layer to transition back to the relaxed state from the
compressed state after removal of the external influence. The
invention encompasses the use of any deformable material for any
suitable layer giving rise to any relaxation time, although a
relaxation time of from 0.001 to 120 seconds would be desired, with
a degree of relaxation close to 100% compared to a previous relaxed
state. This would allow a user or scanning tool to "check" for an
optical change in a device, or repeatedly cycle an optically
variable device, without having to wait very long before another
check can be made. The deformability of the layer, and the degree
of external influence required to cause deformation and transition
from a relaxed to a compressed state, may be adjusted according to
the materials used. Furthermore, a deformable spacer layer may
optionally include a plurality of pores or voids that reduce in
volume when the external influence is applied to the device thereby
to assist compression of the spacer layer from a relaxed state to a
compressed state.
[0182] Further embodiments of the optically variable devices
encompass 2-layer devices in which the optically responsive layer
itself can undergo a change of thickness in response to an external
influence. In such embodiments, the need for a spacer layer that
can be deformed or otherwise caused to change in thickness is
effectively reduced or eliminated. The relative simplicity of
2-layer devices thus presents an advantage for some
applications.
[0183] An example 2-layer device is illustrated with reference to
FIG. 8. For the sake of illustration, the optically variable device
11 is shown independent of any substrate: the device 11 may for
example be intended as a separate display item without need for
application to a particular object or material. With reference
first to FIG. 8a, which provides a cross-sectional view, the device
11 includes control layer 20, which comprises an electret or
piezoelectric material suitable to generate an electric field.
Affixed to control layer 20 is optically variable layer 21.
Optically variable layer 21 comprises a deformable but otherwise
non-flowable material 22, into which are embedded optically
variable elements, which in the example illustrates are in the form
of liquid filled compartments 23 (shown as being spherical in FIG.
9, but which may comprise any shape or form). Each compartment 23
comprises a liquid suspension of electrostatic particles 24 (a
collection of particles is shown schematically as 24 in each
compartment 23; individual nanoparticles are not shown in FIG. 8 as
they may be micro or nanoparticles). In FIG. 8a the electrostatic
particles are substantially located on the control layer-side of
the compartments 23--for example the electrostatic particles 23 may
be located in this position due to the effects of gravity or
thermal agitation.
[0184] FIG. 9b illustrates the same device as FIG. 9a in
cross-section, but in contrast to FIG. 9a a mechanical force is
applied illustrated schematically by arrows 25. The effect of the
mechanical force deforms or otherwise squashes the optically
responsive layer 21 (comprised mainly of deformable material 22),
so that compartments 23 are pressed into a closer proximity with
electrostatic control layer 20. Thus, electrostatic particles 23,
by virtue of their closer proximity, are influenced by the electric
field emanating from control layer 20, and are repelled such that
they migrate to a side of the compartments 23 opposite the side
facing the control layer as shown: the force of repulsion by the
field being greater than the force of gravity or thermal agitation
acting upon the particles. The migration of the electrostatic
particles in turn provides a change in the optical appearance of
the device 11, at least when observed from `above` the device (i.e.
when viewing a side opposite the control layer 20).
[0185] Thus, FIG. 8 illustrates one embodiment in which two layers
are sufficient to provide a device in accordance with select
embodiments of the invention. Of course, further embodiments may
involve two-layer devices that utilize magnetic fields or plasmon
resonance characteristics of materials to provide the desired
visual effect. Alternatively, a visual change may be induced by
rotation of particles in fluid as an alternative to particle
migration.
[0186] FIG. 9 schematically illustrates an alternative 3-layer
embodiment in which the optically responsive layer includes
compartments with particles that react in alternative ways. In FIG.
9a there is shown a device 11 comprising a control layer 30, which
for the sake of this example comprises a metallic layer generating
a magnetic field. Immediately juxtaposed to the control layer 30 is
deformable spacer layer 31. Immediately juxtaposed to deformable
spacer layer 31 is optically responsive layer 32 comprised of a
plurality of adjacent fluid-filled compartments 33. Each of the
fluid-filled compartments 33 includes in suspension bi-coloured,
polarized magnetic particles 34. In FIG. 9a the particles 34 are
shown under the influence of gravity such that particles 34a in
compartment 33a are oriented with their darker side facing towards
control layer 30, whereas particles 34b, 34c in compartments 33b,
33c are oriented in an opposite manner with their lighter side
facing control layer 30.
[0187] FIG. 9b illustrates the same optically responsive device to
that shown in FIG. 9a under an external influence of mechanical
pressure. In FIG. 9b mechanical pressure is applied to the device
as illustrated schematically by arrows 35. The effect of the
mechanical pressure 35 is to force deformable spacer layer 31 to
adopt a squashed or deformed configuration such that it is thinner
than in FIG. 9a. As a result, optically responsive layer 32 is
brought into closer proximity with control layer 30, and as a
result particles 34 are brought sufficiently close to control layer
30 that they are more influenced by the increased magnetic flux
density of the magnetic field emanating from magnetic control layer
30, causing the particles effectively to reverse their orientation
compared to FIG. 9a. Under the influence of the magnetic field,
particles 34a in compartment 33a orientate themselves such that
their lighter side faces the control layer 30, whereas particles
34b, 34c in compartments 33b, 33c orientate themselves such that
their darker sides now face away from the control layer 30. It
follows that an observer or user of the device will observe a
change in the appearance of the compartments when mechanical
pressure is applied to the device. If the compartments are arranged
in the form of pixels, then one image may be apparent to a user
absent mechanical pressure, but an alternative image (or a negative
of the initial image) may be apparent when mechanical pressure is
applied to the device. Whilst this embodiment has been described
and illustrated with reference to magnetic forces and magnetic
particles, any other control layer and responsive optical elements
(or optically responsive layer) may be used, including for example
the use of electrostatics or plasmon resonance. In further related
embodiments, the spacer layer may be eliminated or absent to
provide a 2-layer device, and layer 32 comprised of a deformable
material such that its deformation has a similar effect to bring
particles 34 sufficiently close to control later 30 to induce
movement.
[0188] It is important to note that content may optionally be
incorporated into any of the embodiments herein described by the
use of non-uniform layers, wherein a non-uniform layer includes
varied material types and constituents across the layer. For
example, some devices may comprise a control layer in which only a
portion of the control layer includes material that generates a
magnetic field, an electric field, or that has a surface plasmon
resonance suitable to influence an optically responsive layer.
Likewise, in addition to or instead of the content in the control
layer, the optically responsive layer may itself be non-uniform
such that only portions of the layer are able to "respond" to the
proximity of the control layer. For example, only portions of the
optically responsive layer may include responsive optical elements,
or may include various amounts, densities of the responsive optical
elements compared to other portions of the layer. Alternatively,
different portions of the optically responsive layer may comprise
different types of responsive optical elements, including for
example those that give rise to different colour or reflectance
changes. Thus, changes in the optical appearance of an optically
variable device as described herein may be localized to specific
regions of the device, or alternative optical changes may be
generated in different regions of the device. As discussed
elsewhere, a spacer layer, if present, may additionally or
alternatively be non-uniform in terms of its constituents and/or
thickness to add further content to the device.
[0189] The embodiments disclosed herein may further include
optically variable devices that undergo different changes in
appearance according to a degree or level of external influence
being applied to the device. In just one example, significant
mechanical pressure may be applied to an optically variable device,
such that the deformable layer or layers of the device `relax` over
a period of time, perhaps 1 second to 20 minutes in length. The
optical appearance of the device may depend upon the degree of
relaxation of the deformable layers, such that the optical
properties of the optically responsive layer change as the
deformable layers are, for example, 20% relaxed, 40% relaxed, 60%
relaxed, 80% relaxed and 100% relaxed. Thus, as the deformable
layer or layers continue to relax from a compressed to a
fully-relaxed state, a progressive change in the appearance of the
device may be observed. Such embodiments clearly present the option
for select devices to present changing or even moving images,
depending upon a number of stages of relaxation, and a speed of
relaxation, of the device.
[0190] Further exemplary embodiments encompass a use of any
optically variable device as herein described, as a feature of an
item, document or display.
[0191] Further exemplary embodiments provide for an item or
document comprising:
[0192] a core material; and
[0193] at least one optically variable device as herein described,
affixed to at least one side of the core material, or at least
partially embedded into the core material, such that the optically
variable device is at least partly visible in reflected light from
said at least one side. The core material may comprise any material
suitable for the production of a document, but in selected
embodiments may comprise at least one material selected from the
group consisting of: paper, polymer, and plastic, and combinations
or hybrids thereof.
[0194] The optically variable devices described herein may be
incorporated onto or into the core material of the document via any
appropriate means, and may take any form or shape suitable for the
document or item to which they are applied. For example, the device
may take the form of a thread either laminated or adhered into
position upon the core material or the document, or woven into the
core material in a manner known in the art. The device may be
entirely visible on the document, or may be only partially visible
through `windows` formed either by the threading of the device
through the core material of the document, or by masking of select
portions of the device by way of a masking material.
[0195] Optionally, the document may further comprise a portion to
be pressed against the optically variable device, thereby to cause
a change in the visible appearance of the device. For example, the
document may be folded over to align the portion so that it can be
pressed against the device, thereby to alter a thickness of at
least one of the optically variable layer or the spacer layer (if
present) to cause a change in the visible appearance of the device.
Optionally, the portion to be pressed against the optically
variable device comprises intaglio printing, thereby to provide a
raised, optionally patterned, region as a pressure template to
achieve the change in visible appearance of the device. In this
way, the raised, printed portions may exert increased pressure upon
the device compared to adjacent unraised portions, thereby to
achieve a desired pattern of mechanical pressure upon the device,
and a resulting pattern of optical variation in the device.
Alternatively, the portion to be pressed against the optically
variable device may comprise simply a transparent or translucent
window in the document, such that folding of the document and
alignment of the window with the device, followed by mechanical
pressure by the window on the device, causes a change in the
appearance of the device visible through the window.
[0196] Further exemplary embodiments relating to FIG. 10 provide
for a method for producing an optically variable device, the method
comprising the steps of:
[0197] in step 100 providing a control layer;
[0198] in step 101 optionally providing a spacer layer upon
preselected portions of the control layer, the thickness of which
can be altered by an external influence; and
[0199] in step 102 providing a responsive layer upon preselected
portions of control layer or the spacer layer if present, the
responsive layer comprising responsive element(s) responsive to
their distance from the control layer, so that the optical and/or
other physical properties of the responsive layer are dependent
upon the thickness of the spacer layer if present, and/or upon the
thickness of the responsive layer, as influenced by the external
influence;
[0200] wherein the steps 100, 101 and 102 may be performed in any
order.
[0201] In further embodiments, illustrated with reference to FIG.
11, there are provided methods for checking whether a security
document is a legitimate or counterfeit document, the security
document comprising at least one device as described herein,
visible or touchable on at least one side thereof, the method
comprising the steps of:
[0202] in step 110 applying an external influence to at least one
device; and
[0203] in step 111 observing or otherwise detecting whether the
external influence causes a change in the appearance or physical
properties of the device, wherein any change is indicative that the
security document is a legitimate document. Optionally, in step
110, the external influence may comprise increased or decreased
mechanical pressure upon the device, or application of an increased
or decreased potential difference across the device. Optionally,
step 111 of checking comprises inspection (visual or physical) of
the device upon application and/or removal of the external
influence.
[0204] Alternatively, step 110 of applying comprises pressing a
portion of the security document against the optically variable
device. Optionally, the portion of the security document comprises
intaglio printing as a pressure template for said mechanical
pressure. Optionally, the portion comprises a transparent or
translucent window in the document so that a change in the
appearance of the device may be observed through the window as said
mechanical pressure is being applied.
[0205] The following examples provide further illustrate of certain
exemplary embodiments, which are in no way intended to be limiting
with respect to the scope of the appended claims.
Example 1
Tunable Plasmonic Devices
[0206] This example discloses efforts by the inventors to fabricate
a flexible pressure sensitive device based on near-field coupling
between silver nanoparticles and an underlying conductor. Visually
apparent color changes can be realized with minimal change in
separation owing to the high fields localized to the particle's
surface. The use of soft and compliant materials enables actuation
of the device at low strain.
[0207] With improvements to the synthesis of nanoparticles and
fabrication techniques for nanotechnology, opportunities for
plasmonic devices are expanding. Simultaneously, increasing demand
for responsive materials has fuelled continued investigation.
[0208] Among their potential uses, conductive nanoparticles can be
employed as sensitive optical devices, having a response that is
highly dependent on their surroundings. Furthermore, their high
optical cross-section at resonance imparts significant absorbance
for even a sparse monolayer of particles. For these reasons, they
have been used as optical sensors.sup.1,2 and as sensitizers for
Surface-Enhanced Raman Spectroscopy.sup.3 (SERS) and
fluorescence..sup.4,5 To date, however, the particles have
generally been restricted to use in static configurations. Only
more recently have efforts turned towards dynamic tuning of the
nanoparticle configuration..sup.6
[0209] By actively controlling the coupling distance, a dynamic
optically tunable device has been realized by the inventors. A
random distribution of conductive nanoparticles is simultaneously
easier to manufacture than ordered structures while maintaining
high absorbance. A layered device structure offers design
flexibility by disentangling the nanoparticle deposition from the
coupling interaction. With suitably designed inks, such an approach
could also be attractive for printable devices. Potential
applications of interest would include touch responsive materials,
pressure sensors, and low complexity reflective displays.
[0210] In this example, the simulation and fabrication of a simple
device structure having a tunable resonance is disclosed, which
relies on the coupling of silver nanoparticles to an underlying
metal film. A polydimethysiloxane (PDMS) elastomer substrate was
coated with nanoparticles and subsequently suspended over a
flexible aluminum coated substrate. A spacer layer has been used to
maintain a gap in its unactuated state. With applied pressure, the
gap is reduced and the nanoparticles are brought into close
proximity with the underlying metal film, resulting in a large
shift in the observed optical absorbance.
[0211] To better understand the response of a nanoparticle in
proximity to a conductive film, it is instructive to first consider
the behaviour of isolated particles. Although a wide range of
techniques exist for modelling a variety of geometries,.sup.15 we
will restrict the discussion here is restricted to spherical
particles.
[0212] In an approach that is similar to the decomposition of a
signal's spectral content by Fourier analysis, a particle's
response to incident light can be uniquely expanded into a series
of orthogonal modes by Vector Spherical Harmonics..sup.16 With this
technique, scattering by a spherical particle can be expressed
as
E s = n = 1 .infin. E n [ ia n N n ( r , .phi. , .theta. ) - b n M
n ( r , .phi. , .theta. ) ] ##EQU00001##
where a.sub.n and b.sub.n are scattering coefficients specific to
particle geometry, as calculated using Mie theory,.sup.16 and
E.sub.n represents the contribution of the incident field to a
given multipole mode. An incident plane wave, for instance, can be
decomposed into a series of orthogonal multipole field
distributions such that E.sub.n=i.sup.nE.sub.0(2n+1)/n(n+1).
[0213] FIG. 12 illustrates the near field responses of two
individual silver nanospheres due to an incident plane wave with a
wavelength of 400 nm. Although the incident wave has significant
dipolar and quadrupolar amplitudes, each particle preferentially
responds to one mode and has a total effective extinction
cross-section of
C ext = 2 .pi. k 2 n = 1 .infin. | E n E 0 | 2 n 2 ( n + 1 ) 2 2 n
+ 1 Re { a n + b n } ##EQU00002##
[0214] Although the scattering coefficients a.sub.n and b.sub.n are
fixed for a given particle, total extinction can be controlled by
altering the spatial distribution of the incident field. If, for
example, the dipolar component in FIG. 12 were to be attenuated, a
much smaller extinction cross-section could be anticipated for the
50 nm sphere. By contrast, the total extinction cross-section of
this particle is much less sensitive to changes in higher order
modes. By selectively enhancing or attenuating specific multipole
modes, tuning of the localized surface plasmon resonance peak or
excitation of dark plasmon modes are possible. In practice, this
can be accomplished by using highly focused light sources.sup.17,18
or by introducing additional surfaces or nanostructures which
modulate the local electric field distribution..sup.19,20
[0215] A tunable optical device, as illustrated in FIG. 13, can be
achieved with the addition of a conductive film in close proximity
to an array of suspended nanoparticles. Here, the extinction of the
structure is influenced by interaction of the particle with
incident, reflected, and scattered waves. Where the underlying
conductor can be approximated as a perfect electric conductor
(PEC), the system can be analytically modelled and understood by
replacing the film with an image particle..sup.14 In this view, the
interaction dynamics between the object and image particle are
similar to those of aggregated particles..sup.21,22
[0216] As with isolated particles, changes in resonance for this
structure arise due to changes in the local field and originate,
primarily, from the particle's near-field being reflected back onto
itself. As the distance between the particle and substrate
decreases, coupling is rapidly enhanced, owing to the exponential
character of the near-field. A second effect, which can be
exploited in some circumstances, is due to the standing wave
between the incident and reflected plane waves of the source. At
the PEC surface, the electric field is reduced to zero due to
destructive interference between the two waves. For very small
particles, the low field intensity near the surface gives rise to a
lower optical response.
[0217] These effects have been explored using a commercial finite
element analysis tool (COMSOL) for flexibility in the simulation of
both spherical and non-spherical particles. The calculated results
illustrate reflectance from an array of silver particles in close
proximity to a PEC substrate. For the purposes of this example, an
incident plane wave propagating normal to the surface was used as
the source. Interpolation of tabulated material data.sup.23 was
used for modelling silver permittivity.
[0218] Commonly exploited for anti-reflection coatings, standing
waves occur due to interference between incident and reflected
plane waves. For very small particles, such interference effects
can be exploited using a deformable structure to modulate the
optical density. In an unactuated state, the particles are
separated from the substrate and have large optical density at
resonance. In response to a stimulus--for instance, electrical or
mechanical--a decreasing gap results in decreased optical density
due to the reduced field strength experienced by the particles, as
shown in FIG. 14. Visual contrast between these two states is
possible due to the significant absorbance generated, even by a
single layer of nanoparticles. In FIG. 14b, a surface concentration
of only 20% imparts significant losses to the reflected signal when
particles are separated from the film.
[0219] The absence of observed shifts in the resonance peak
indicates that, for very small spheres (less than 10 nm), the
contribution of near-field coupling is not significant even at 5 nm
of separation. Near-field interaction would be observed as
separation becomes further reduced. By this point, however, the low
field experienced by the particle gives rise to small optical
activity in this structure.
[0220] For larger or non-spherical particles, the optical
absorption of the structure at these distances is dominated by near
field interaction between the particle and reflected image field.
In contrast to very small spheres, such particles are more
responsive to changes in the spatial distribution of the exciting
field. Furthermore, owing to the exponential character of the
near-field, this behaviour is highly sensitive to changes in
distance. The interaction can therefore be nearly extinguished with
minimal increase in separation between the structures. In selected
embodiments, such sensitivity may be highly desirable for
manufacturing a responsive device.
[0221] Illustrated in FIG. 15 are the optical responses for a
selection of spheroids in proximity to an underlying metallic film.
Of particular note is the enhanced responsiveness of ellipsoidal
particles compared to spherical particles. The explanation lies in
their differing response to higher order multipole excitation. As
distance decreases, the contribution of high order multipoles to
the optical response is of increasing influence. Ellipsoids have a
much larger response to high-order excitation than do spheres of
similar size and can therefore be expected to produce larger
shifts.
[0222] As an intermediate step towards a responsive device, test
structures were constructed by forming silver nanoparticles at
well-defined distances from an aluminum reflector. In these
samples, spacer layers having variable thicknesses were created
using SiO2 films deposited by e-beam evaporation. Film thicknesses
were monitored during deposition using a quartz crystal
microbalance and confirmed by single beam ellipsometry at 632
nm.
[0223] Near-field induced shifts were studied using two different
nanoparticle films. The first, shown in FIG. 16a, are silver island
films formed by annealing of e-beam evaporated silver.sup.24,25,26;
the second, in FIG. 16b, are silver nanoplates (0.02 mg/mL silver
nanoplate concentration, nanoComposix), applied by self-assembly
using an electrostatic linker between the particles and the
substrate..sup.27
[0224] Fabrication of silver island films was achieved by
deposition and annealing of a thin 7 nm silver film deposited on
the spacer layer. In a nitrogen ambient at elevated temperatures,
the film undergoes a dewetting process due to poor adhesion with
the spacer oxide. The resulting structure comprises a randomly
distributed array of hemispherical islands. These islands feature a
resonant absorption, whose peak frequency is dependent on their
size and packing density. As demonstrated in FIG. 16a, when in
close proximity to an underlying aluminum film, the resonance peak
undergoes a significant shift. Although, these island films are
simple to manufacture, limited options exist for tuning the
detwetting process. A variety of alternatives are available by
instead adsorbing synthesized nanoparticles onto the surface.
[0225] The self-assembled layer of silver nanoplates was produced
by first oxidizing a polydimethylsiloxane (PDMS) surface with an O2
plasma followed by adsorption of polyethylenimine (PEI) (1% in DI
water) from solution over a 24 hour period. With the
polyelectrolyte layer in place, the sample was immersed for 4 hours
into the silver nanoplate suspension. Adhesion of the nanoplates to
the surface relied on electrostatic interaction between the
positively charged PEI molecules and the negative surface charge of
the polyvinylpyrrolidone (PVP)-capped silver particles.
[0226] The particle-coated PDMS surface was subsequently placed in
contact with the aluminum/SiO 2 test structures for measurement. As
illustrated in FIG. 16b, no changes in the reflected signal are
observed over distances spanning nearly five orders of magnitude
(from 1 mm to 25 nm). Instead, a shift in resonance is observed
only when the particles are very close. In addition to the observed
shift, there is also a decrease in the optical density of the film.
As these particles are very thin--approximately 10 nm in
thickness--this phenomenon can be understood by revisiting the
calculated results from FIG. 14 for very small particles. When in
close proximity to the underlying conductor, the exciting field in
the vicinity of these thin plates is very low, resulting in a
similarly small absorbance.
[0227] A rudimentary flexible structure, outlined in FIG. 17a, was
realized by deposition of silver nanoparticles or island films onto
a deformable PDMS elastomer. The silver particles were applied to
the cured PDMS films either by e-beam & annealing or by
self-assembly, as described previously.
[0228] The resulting PDMS/silver assembly was subsequently
suspended over a flexible aluminized Mylar substrate. For these
tests, a simple adhesive support layer was used to maintain a gap
between the two films in their unactuated state. In addition, a
diffusing film was incorporated within the stack in order to
scatter the otherwise specularly reflected light. As shown in FIG.
17, observable color changes are achieved under applied mechanical
strain.
[0229] Although silver nanoparticles were used in both cases, the
difference in their shape yields unique responses. The synthesis of
nanoparticles has greatly matured in recent years and a diverse
range of geometries can now be realized. By selecting from a
variety of materials and particle geometries, a broad palette of
colors and responses would be achievable.
[0230] Plasmonic nanostructures are undergoing continual
investigation and development. An ever increasing assortment of
synthesized particles and improved fabrication techniques has
greatly expanded potential applications for such devices.
[0231] In this example, a simple and flexible optically variable
device and corresponding theoretical considerations were discussed.
Actuation of a deformable bridge structure allowed for variation of
near-field coupling under the application of pressure. The optical
response of conductive nanoparticles is highly sensitive to changes
in close proximity, thus only small perturbations of the structure
are required to achieve large optical responses. By coupling
between layers rather than between precisely aligned particles,
simplified deposition techniques can be used to apply the
nanoparticle layer over large areas.
Example 2
Embodiments and Studies that Employ Electrets
[0232] FIG. 18 schematically illustrates one embodiment in the form
of a layered device comprising two charged layers, and a variable
gap inbetween. One of the charged layers effectively functions as a
control layer, and the other charged layer functions as the
optically responsive layer. This forms a device comprising
negatively and positively charged electret layers separated by a
variable gap. As illustrated the variable gap is absent any
material, but in accordance with the present teachings the gap may
comprise for example a spacer layer that becomes deformed or
squashed when the device is subjected to mechanical pressure. The
region of the device labed as "active" comprises the optically
responsive layer, which itself is composed of reversible
electro-responsive materials responsive to electric field changes
caused by changes in the proximity of the negatively charged
control layer. For example, the "active" optically responsive layer
may comprise polarisable bichromal janus spheres, or charged
electrophoretic materials. A voltage drop across the active layer
causes a flip between positive and negative charges present by
changing the width or dimensions of the variable gap, for example
by at least one micron.
[0233] FIG. 19 illustrates potential drop across the "active"
optically responsive layer due to changes in gap thickness. Voltage
is positive in an un-actuated state and negative when the variable
gap is narrowed. This is achieved by rearrangement of charge
distribution within "virtual" ground planes. Virtual grounds can be
achieved by making the ground plane significantly larger than the
active color change device area. The embodiment affords an
opportunity to enable repeated voltage switches and optical
changes, if the device can be "reset" by resorting the size of the
variable gap between the charged layers.
[0234] FIG. 20 schematically illustrates an alternative device
arrangement comprising a single charged layer of electro-optical
materials (labelled "active" layer) with a negative charge adjacent
the variable gap. The electroptical materials provide an observable
response with increased electrical field (e.g. liquid crystal,
polymer dispersed liquid crystal, suspended particles). Compared to
the device of FIG. 18 the second charged layer is replaced with a
ground plane on the opposite side of the variable gap.
[0235] As illustrated by the graph in FIG. 21, the observed voltage
drop across the active region can be controlled by adjusting the
gap thickness. The voltage drop can be driven from large to small
by reducing the gap, as seen in FIG. 21. Voltage is much larger in
un-actuated state than when mechanical pressure is applied, which
is achieved by forcing .sup..about.0 V on the "virtual ground
plane". An effective virtual ground can be achieved by making the
ground plane electrode significantly larger than the active color
change device area. As with the device of FIG. 18, the device of
FIG. 20 may be suitable for repeated switching between optical
states by repeatedly reducing and increasing the size of the
variable gap. For example, where mechanical pressure provides the
external influence to change the optical appearance of the device,
a deformable or squashable spacer layer between the "active"
optically responsive layer and the ground plane electrode (i.e. in
the variable gap) may provide the desired resilience for repeated
cycles of observable optical changes.
[0236] FIG. 22 schematically illustrates another device that
employs electrets/electrostatics, and employs and electret
structure using patterned positive and negative charge regions. The
electrical field vectors are illustrated with arrows in the surface
plot shown. Moving the active layer vertically modulates the
electric field impinging upon the layer as shown in FIG. 23. This
embodiment is useful for materials/particles that rotate or migrate
under an electric field (eg: polarizable particles, electrophoretic
materials).
[0237] The graph in FIG. 23 thus illustrates lateral electric field
strength vs vertical position within device. As one moves away from
the patterned charges, the field strength decreases. Beyond a
certain distance, the torque/charges associated with the electric
field are smaller than the movement imparted by random motion
and/or gravity. The direction of the field line and their value can
be tuned by altering the pitch between charge regions or
incorporation of ground planes.
[0238] This embodiment further illustrates that patterning of a
control layer or (optically) responsive layer with different
electric charges, magnetic charges, or materials with different
plasmon resonances enables further content, characters, images and
the like to be incorporated into the devices as herein disclosed,
including both simple/increased transformations of images or moving
images as the external influence is applied/increased or
removed/decreased from the device.
Example 3
Comparison of Numeric Simulations for Electrets and Magnetic
Dipoles
[0239] In each simulation, an array of charged or magnetized
particles was spaced apart from an array of smaller platelets, as
shown in FIG. 24. The force induced by the electric/magnetic field
on these platelets was compared to gravitational forces. This was a
check to ensure that sufficient force could be generated to
manipulate the particles given the anticipated constraints on the
strength of the electrets/magnets that could be realized. The
structure was simulated for varying gap thickness to determine the
point where gravational effects overcome the electric/magnetic
forces.
[0240] Corresponding results are shown in FIG. 25a for magnetic
model results and FIG. 25b for electrets model results. For the
magnetic model results (FIG. 25a) the descending curve illustrates
the average force on four centre platelets, and the straight line
graph indicates the force of gravity on a single platelet
(F.sub.g=1.5 pN). The forces are observed to `cross` at around 42
.mu.m separation distance. For the electret model results (FIG.
25b) the descending curve illustrated the average force on four
centre platelets, and the straight line graph indicates the force
of gravity on a single platelet (F.sub.8=1.5 pN). The forces are
observed to `cross` at around 53 .mu.m separation distance. The
results thus illustrate the induced force relative to gravity as
the gap thickness increased. These data demonstrate that there is
sufficient force in this structure to influence an underlying
"color change" particle, and illustrates the feasibility to
generate movement of particles with a device comprising an assembly
of magnets or electrets.
[0241] Whilst various embodiments of optically variable devices,
items incorporating such devices, documents, as well as methods for
their production and use, are described and illustrated herein, the
scope of the appended claims is not limited to such embodiments,
and the invention encompasses further embodiments readily
obtainable in view the teachings presented herein.
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