U.S. patent application number 11/765933 was filed with the patent office on 2007-11-29 for vacuum roll coated security thin film interference products with overt and/or covert patterned layers.
This patent application is currently assigned to JDS Uniphase Corporation. Invention is credited to Keith Hollingsworth, Roger W. Phillips, Vladimir P. Raksha.
Application Number | 20070273147 11/765933 |
Document ID | / |
Family ID | 33477004 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070273147 |
Kind Code |
A1 |
Phillips; Roger W. ; et
al. |
November 29, 2007 |
Vacuum Roll Coated Security Thin Film Interference Products With
Overt And/Or Covert Patterned Layers
Abstract
A security device for providing an image having a color shifting
region and a visual reference, comprises a substrate having a first
side and a second side, a patterned thin film layer on the first
side of the substrate for providing the visual reference, and a
coating of color shifting ink supported by the first or second side
of the substrate for providing the color shifting region of the
image, wherein the patterned thin film layer has windows therein,
and the color shifting ink is visible through the windows.
Inventors: |
Phillips; Roger W.; (Santa
Rosa, CA) ; Hollingsworth; Keith; (Healdsburg,
CA) ; Raksha; Vladimir P.; (Santa Rosa, CA) |
Correspondence
Address: |
ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST P.A.
1401 CITRUS CENTER 255 SOUTH ORANGE AVENUE
P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Assignee: |
JDS Uniphase Corporation
|
Family ID: |
33477004 |
Appl. No.: |
11/765933 |
Filed: |
June 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10891335 |
Jul 14, 2004 |
|
|
|
11765933 |
Jun 20, 2007 |
|
|
|
60487527 |
Jul 14, 2003 |
|
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|
Current U.S.
Class: |
283/94 |
Current CPC
Class: |
B42D 2035/24 20130101;
Y10T 428/24917 20150115; Y10T 428/2938 20150115; D21H 21/48
20130101; Y10T 428/2933 20150115; D21H 21/42 20130101; B42D 25/355
20141001; B42D 25/328 20141001; G02B 5/18 20130101; G07D 7/04
20130101; B42D 25/369 20141001; D21H 21/44 20130101 |
Class at
Publication: |
283/094 |
International
Class: |
G09C 5/00 20060101
G09C005/00 |
Claims
1. A security device for providing an image having a color shifting
region and a visual reference, comprising a substrate having a
first side and a second side, a patterned thin film layer on the
first side of the substrate for providing the visual reference, and
a coating of color shifting ink supported by the first or second
side of the substrate for providing the color shifting region of
the image, wherein the patterned thin film layer has windows
therein, and the color shifting ink is visible through the
windows.
2. A security device as defined in claim 1, wherein the patterned
thin film layer is a reflective layer.
3. A security device as defined in claim 2, wherein the coating of
color shifting ink is supported by the first side of the substrate
and wherein the coating is provided over the reflective layer.
4. A security device as defined in claim 2, wherein the coating of
color shifting ink is on the second side of the substrate, and
wherein the substrate is light transmissive.
5. A security device as defined in claim 4, further comprising a
protective layer of abrasion resistant lacquer coated over the
reflective layer.
6. A security device as defined in claim 4, further comprising a
spacer layer supported by the reflective layer and an absorber
layer supported by the spacer layer, wherein the reflective layer,
the spacer layer, and the absorber layer form an interference
structure having window portions, whereby an OV effect of the color
shifting ink is observed when the security device is viewed from
the second side, and an OV effect of the interference structure is
observed, in addition to the OV effect of the color shifting ink,
when the security device is viewed from the first side.
7. A security device as defined in claim 1, wherein the color
shifting region of the image is a foreground and the visual
reference is a non-color shifting background.
8. A security device as defined in claim 1, wherein the color
shifting region of the image is a background and the visual
reference is a non-color shifting foreground.
9. A security device as defined in claim 1, wherein the color
shifting ink is selected from the group consisting of an ink
containing mica based pigments, SecureShift.RTM. ink, OVI.RTM., an
ink containing diffractive pigments, a liquid crystal color
shifting ink, an ink with pigments formed of flat thin film optical
structures, and an ink with diffractive flakes.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application of U.S. application Ser.
No. 10/891,335, filed Jul. 14, 2004, by Phillips et al, entitled:
"Vacuum Roll Coated Security Thin Film Interference Products With
Overt And/Or Covert Patterned Layers," which claims priority from
U.S. provisional application No. 60/487,527, filed Jul. 14, 2003,
by Phillips et al, entitled: "Imaged Optical Foils," the
disclosures of which are incorporated herein.
BACKGROUND OF THE INVENTION
[0002] The use of security threads for protecting banknotes, credit
cards and other valuable documents is well known. A security thread
is a strip of material placed on the surface of a banknote document
or sheet such as banknote; alternatively a security thread may be
serpentined or woven into the banknote paper (a window type effect)
to confer additional security (authenticity) to the bank note.
Typical dimensions of a hot stamp thread are a width of 1-5 mm, a
thickness of 3-4 .mu.m; windowed polyester terephthalate (PET)
based threads have a thickness of about 0.5 mil or 12.5 microns. By
way of example, one of the earliest forms of security threads
consisted of reflective foil transferred by hot stamping to the
surface the banknote (GB 2119312 A). This reflective foil prevented
reproduction of counterfeit banknotes by printing processes such as
from printing presses, PC printers and copiers. Holograms
(EP-A-0624688), holographic features along with thermo chromic
features (GB 2347646), opaque coatings having characters and
patterns readable by transmitted light in combination with
luminescent substances (U.S. Pat. No. 6,474,695), repeating
patterns of magnetic/magnetic indicia or metal dots (W02103624),
laser etching fine lines and text with a laser (German
"Auslegeschrift" no. 22 05 428) and (WO02101147), printing
micro-characters on a metalized transparent plastic with clear acid
resistant inks followed by acid etching of the unprinted areas to
produce shiny micro-characters on a transparent base (U.S. Pat. No.
4,652,015), bonded nucleic acid molecules so that complementary
nucleic acid molecules can bind to the molecules already attached
to the document (DE 10122836), and optically variable security
elements using liquid crystal material (EP0435029) have all been
used to make security threads. However, these aforementioned
threads either take too much time to make and or have other
associated problems; for example, it is found that laser etching
takes too long to be cost effective, etching by use of chemicals
requires multiple steps and is not considered to be
environmentally-friendly; holograms can be readily copied, and in
many instances the features of the threads are not readily seen by
eye by the average person and machines are required to read
them.
[0003] A method to pattern a single layer of metal or carbon in a
vacuum chamber was advanced in U.S. Pat. No. 4,022,928 by Piwcyzk.
Piwcyzk used various methods to apply a perfluoropolyether known as
FOMBLIN.TM. or Krytox.TM. to a substrate requiring a pattern for a
vacuum deposited layer. The perfluoropolyether inhibited the
deposition of the depositing material to a web or plastic
substrate. Application of this fluid was by spray or vacuum
evaporation in combination with a selected removal process as with
a laser or an electron beam. A printing method was also described.
Printing techniques including relief printing such as letterpress
or flexography, planographic printing such as offset lithography,
and gravure, and screen-printing such as silkscreen process
printing were disclosed.
[0004] Subsequently, Ronchi in U.S. Pat. No. 4,749,591 incorporated
herein by reference, and in PCT application WO 8700208(A1))
advanced this printing process by applying the inhibiting oil,
FOMBLIN, to a vacuum roll coater where patterning thin films on
plastic substrates was desired.
[0005] Ronchi in U.S. Pat. No. 4,749,591 only discloses applying a
single layer of metal, for example, aluminum as is shown in FIG. 1,
deposited as a vacuum thin film layer. A demetallized aluminum
layer in the case of a security thread embedded into a banknote can
easily be forged by simply using a metallized polyester that is
subsequently patterned by one of the above methods. In an attempt
to copy a security thread having a single layer manufactured by
Ronchi's technique, patterning by photolithography in combination
with a caustic etchant, or by any of the aforementioned processes
or even by using a silver pencil to simulate the security thread
could be used. Security threads having multi-layer films where one
of more of the layers are patterned has not previously been
considered. A major impediment to providing several thin film
layers, was residual oil remaining on the images and on
non-patterned areas of the web. This residual oil was detrimental
to further thin film coating since left over oil would cause
"ghosting"; a process whereby the inhibiting oil is transferred to
the back side of plastic film when roll coating, which in turn
causes inhibiting oil to be transferred further down the web on the
front side. Left over inhibiting oil also causes adhesion failures
to subsequent thin film layers.
[0006] "Ghosting" and the ability to remove residual inhibiting oil
is overcome by this invention. By way of this advance, for the
first time, patterned multilayer optical stacks could be
conveniently manufactured in a cost effective way on a security
thread, by roll coating. In particular, a new optically variable
security thread that had a high pattern resolution was made that
contained readable text or graphic images where covert features
such a magnetic signatures could also be incorporated.
[0007] It is an object of this invention, to provide a security
thread having optically variable features such as an optically
variable pattern that can be seen against a background that is
distinguishable from the pattern, or from which the pattern stands
out.
[0008] It is a further object of this invention, to provide a
relatively simple, inexpensive method of manufacture of a
multilayer patterned security thread for use within or upon a web
or sheet, for example on currency, documents or packaging for
providing authentication thereof.
SUMMARY OF THE INVENTION
[0009] In accordance with this invention there is provided, a
security thread for embedding within or upon a sheet or document,
comprising:
[0010] an elongate substrate having a first side and a second
side;
[0011] an optically variable structure deposited on one of the
first and second side of the elongate substrate, wherein the
optically variable structure comprises a thin film interference
structure which has the appearance of a plurality of separated
interference filters arranged side-by-side and spaced from one
another having visible color shifting properties in the form of a
visible pattern of visually separated distinguishable indicia
against one of a foreground and background of a different
color.
[0012] This invention provides a security thread providing security
to a sheet, document or packaging, wherein thread has a visibly
optically variable structure thereon that is visible from at least
one side of the sheet; although the optically variable structure
may be a continuous plurality of layers forming a large Fabry-Perot
cavity or interference filter, by providing a patterned layer in
front of the Fabry-Perot cavity, the interference filter appears to
be separate spaced filters. In another embodiment plural separated
filters are provided which similarly appear as separated optically
variable structures.
[0013] In accordance with this invention there is provided, a sheet
having a security thread embedded therein or disposed thereon, the
security thread comprising:
[0014] a substrate having a first side and a second side;
[0015] a plurality of separated n-layered Fabry-Perot cavities
deposited upon the first side of the substrate, side-by-side,
wherein the Fabry-Perot cavities are spaced from one another,
wherein each n-layered Fabry-Perot cavity is a thin film
interference filter having visible color shifting properties; said
plurality of cavities being arranged along the substrate to form a
visible pattern as a result of the color shifting properties.
[0016] In accordance with another aspect of this invention there is
further provided, a security thread for imbedding within or
disposing upon a sheet, wherein the security thread comprises a
plastic web upon which is deposited layers of thin film color
shifting coatings forming side-by-side, spaced apart interference
filters, wherein the interference filters are seen as patterns
against a background of a different color.
[0017] In accordance with one embodiment of this invention, a
continuous Fabry Perot structure having plural layers defining one
or more cavities can be applied to one side of a web or substrate.
On a second side of the web, a pattern of aluminum or some other
material visibly distinguishable from the Fabry Perot structure can
be applied using an oil ablation process. Visually when one views
the thread from the patterned aluminum side, the portions absent
aluminum show as optical variable regions, and the portions with
aluminum present show as contrasting aluminum regions. Hence in
this embodiment, the continuous Fabry-Perot structure reveals to
the viewer from the patterned side, plural side-by-side spaced FP
cavities since the aluminum masks portions providing the
pattern.
[0018] In accordance with yet another aspect of the invention there
is provided a method for forming an optically variable device
comprising the steps of:
[0019] patterning a reflective layer on a web substrate having a
first side and a second side using an oil-ablation technique to
form a patterned reflective layer;
[0020] removing oil residue from the first side of the web and
depositing thin-film layers on the web substrate to form the
optically variable device.
[0021] In accordance with another aspect of the invention there is
further provided a method of patterning metal comprising the steps
of:
[0022] applying a non-wetting oil to selected portions of a first
surface of a web substrate to create an oil pattern;
[0023] depositing metal on the first surface of the web substrate
wherein the non-wetting oil ablates depositing metal from the oil
pattern; and
[0024] removing oil residue using a first glow discharge applied to
the first surface of the web and a second glow discharge applied to
a second surface of the web.
[0025] In accordance with another aspect of the invention there is
provided a machine-readable security device, comprising a web
having disposed thereon, a patterned layer of magnetic material
sandwiched between two metal layers.
[0026] In accordance with the invention a machine-readable security
device is also provided wherein a security thread includes a
magnetic material patterned thereon using an oil-ablation
process.
[0027] The use of an oil ablation process is a preferred
embodiment, allowing the coating and removal of a rolled on pattern
within a coating chamber to yield a patterned web having a visible
patterned interference structure. Notwithstanding, it is within the
scope of this invention to use of other materials having similar
properties to oil, wherein its removal is compatible with the
coating of subsequent layers in situ. Alternatively, but less
preferably, a water soluble polymer coating that can later be
removed by washing is possible, however temporary coatings of this
sort are not as useful as the application of oil, which can be
removed within the deposition chamber.
[0028] This invention circumvents difficulties encountered in wet
chemical etching methods for patterning by providing a novel
security thread that is optically variable either in reflection or
transmission with text or other patterns by using an all-dry
process, in-line, in a vacuum roll coater. The human eye can
readily see the optical performance of the thread as a color shift
as the thread is tilted back and forth. Either the text or pattern
is optically variable against a transparent or shiny reflective
background, or alternatively the background is optically variable
against the text or patterns that can be easily viewed in
transmission. Furthermore, the thread and its pattern can be
distinguished from the background of the sheet, which carries it.
Alternatively, the thread can be viewed in reflection where the
imagery appears to be colored or optically variable using foil or
color shifting ink against a reflective background of aluminum or
other colored metal such as copper, or an optically variable, or a
non-optically variable thin film optical stack. Alternatively an
embodiment of the invention provides the inverse or negative image
of the above-mentioned structures. The optically variable optical
stacks can take the form described in U.S. Pat. Nos. 4,705,356;
4,838,648; 5,135,812; 5,214,530; 5,278,590; 5,278,590; 6.157,489;
6,241,858; 6,243,204; 6,241,858; 6,569,529; and 6,699,313 to
Phillips, an inventor of this invention. In addition, mica based
interference pigments such as TiO.sub.2 or Fe.sub.2O.sub.3 coated
micas can be used as the color shifting pigments in the color
shifting inks.
[0029] Various embodiments of this invention are described and
shown in detailed description and accompanying figures. The thread
can either be windowed into the banknote in much the same manner as
that found in European patent application EP1258334 A3 in the names
of Cunningham, and Brian or can be applied across the surface of
the banknote.
[0030] Such threads as described in accordance with this invention
cannot be accurately reproduced by way of being photocopied,
photographed, or printed since these technologies do not possess
optically variable effects. Furthermore, in the case of optically
variable foil, the optics of copiers prevents even the face color
at normal incidence from being imaged; since just a black image
results as the reflective surface of the optically variable thread
causes the light to miss the entrance optics of the copier. In
addition, the intricate design of the text, having a resolution
down to 60 microns, would prevent any counterfeiter from using
scissors to simulate this security device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Exemplary embodiments of the invention will now be described
in conjunction with the drawings in which:
[0032] FIG. 1 is a diagram illustrating a prior art device wherein
a layer of patterned aluminum on a PET substrate or web.
[0033] FIG. 2 is a cross sectional view showing an embodiment of
the invention wherein interference structures are shown created by
layer of patterned aluminum on a PET web covered with a spacer
layer of MgF2 capped by a Cr layer, the three layers forming a
plurality of optical interference structures, side-by-side having
windows, therebetween.
[0034] FIG. 3 is a cross sectional view of a layered structure with
patterned aluminum on one side of a PET web, an optically variable
foil coating on the same side of the PET web, and a different
optical coating on the other side of the PET web.
[0035] FIG. 3b is a cross sectional view similar to that of FIG. 3,
with the addition of an embossing of the plastic layer.
[0036] FIG. 4 is a diagram of an embodiment illustrating a
patterned magnetic layer on a PET web.
[0037] FIG. 5 shows an embodiment of the invention wherein a
patterned magnetic layer is sandwiched between two layers of
aluminum on a PET web.
[0038] FIG. 6 shows an embodiment with a patterned aluminum layer
on one side of a PET web and an optically variable foil with a
hidden magnetic layer on the same side of the PET web.
[0039] FIG. 7 is an illustration showing a patterned aluminum layer
deposited on a plastic substrate over-coated with color shifting
ink on one side of a PET web.
[0040] FIG. 8 shows the effect of positive and negative patterned
aluminum layer over-coated with color shifting ink layer on one
side of a PET web.
[0041] FIG. 9 is a diagram of an embodiment of the invention
wherein a patterned aluminum layer is deposited on one side of a
PET web and a color shifting ink layer is coated on the opposite
side of the PET web.
[0042] FIG. 10 is a cross sectional view illustrating a patterned
aluminum layer deposited on one side of a PET web over-coated with
a protective layer of abrasion resistant lacquer and a color
shifting ink on the opposite side of the PET.
[0043] FIG. 11 shows a patterned aluminum layer over-coated with a
Fabry-Perot design on one side of a PET web and coated with a
second different Fabry-Perot design on the second side of the
PET.
[0044] FIG. 12 is a cross sectional view of a patterned aluminum
layer on one side of the PET web and a continuous optical structure
on the second side of the PET.
[0045] FIG. 13 shows a patterned colored shifting foil and one side
of the PET and a printed layer of ink (black or complimentary color
to the color shifting foil) on the second side of the PET.
[0046] FIG. 14 is a cross sectional view showing a Fabry-Perot
design on a PET web where the dielectric spacer layer is
patterned.
[0047] FIG. 15 is a cross sectional view showing a Fabry-Perot
design on a PET web where the absorber layer is patterned.
[0048] FIG. 16 is a diagram, which illustrates a simplified coater
according to an embodiment of the invention.
[0049] FIG. 17 is a diagram which illustrates a cleaning
arrangement within the coating chamber to remove residual
"inhibiting oil".
[0050] FIG. 18 is a view of a one dimensional magnetic bar code
pattern hidden within the aluminum layers, wherein the Al layers
are conveniently shown in this figure to be transparent so that the
bar code can be seen.
[0051] FIG. 19 shows a two-dimensional magnetic bar code pattern
hidden within the aluminum layers.
[0052] FIG. 20 is a photograph which shows the resolution of a text
symbol in a patterned optically variable security thread.
[0053] FIG. 21 is a photograph of a patterned optically variable
thread embedded into a bank note in a windowed type format.
[0054] FIG. 22 is a photograph showing the text of the patterned
optically variable thread in a bank note viewed in
transmission.
[0055] FIG. 23 shows a graphic security label formed from a
patterned optically variable foil structure on a pressure sensitive
adhesive-releasable label paper stock.
DETAILED DESCRIPTION
[0056] Referring now to FIG. 2 a layer of patterned aluminum 22 on
a PET web 20 is shown. This embodiment is not limited to the use of
aluminum as a reflector material and other reflecting materials,
for example another reflecting metal could be used instead of
aluminum. The PET web forms the base of the security thread upon
which the layers shown are deposited; however other materials, such
as other plastics could be used in place of PET. The aluminum
patterned layer 22 is covered by a spacer layer 24 of MgF2
deposited over the patterned aluminum and web which forms windows
28 in regions over the web absent the deposited aluminum; a layer
of absorber material 26, such as a thin layer of chromium, is
deposited over the spacer layer 24. An optical interference
structure is formed from the reflector/dielectric spacer/absorber
(R/D/Ab) stack over the remaining portions of the patterned metal,
but not over the portions of the web where the Al has been removed;
these portions were Al has been removed are referred to as window
portions. The optical interference structure(s) 21 can be color
filters that gives the patterned metal a particular appearance, or
one that gives the patterned metal a color-shifting, "optically
variable" appearance. The aluminum is patterned by printing an
image or pattern onto the plastic web 20 using the "inhibiting oil"
and then depositing a thin film of aluminum. Although the exact
mechanism by which the oil prevents the sticking of the vacuum
deposit to the substrate may not be entirely understood, the
process nevertheless works. Various theories have been proposed to
explain this phenomenon. One theory invokes the idea that the heat
of condensation of the depositing material turns the oil into a gas
and in effect ablates the metal away. Another explanation is that
the oil simply prevents nucleation of the depositing material and
hence the arriving material is scattered away.
[0057] In the embodiment shown in FIG. 2 the Al--MgF.sub.2--Cr
stacks each form a Fabry-Perot ("F-P")
absorber-spacer-reflector-type optically variable device ("OVD"),
which are not formed over the window portions of the web because
there is an absence of a Fabry-Perot structure in these areas. The
plastic web can be clear, tinted, translucent, or opaque, and the
materials chosen for the patterned metal layer and overlying thin
films are merely exemplary. After coating the thin-film layers, a
protective layer is optionally applied, such as a thin layer of
lacquer, not shown, or a thin (e.g. 0.5 mil) plastic film that is
adhered to the OVD using laminating adhesives.
[0058] FIG. 3 shows a layer structure, similar to that of FIG. 2 on
a front side of a web 30. Patterned aluminum is deposited after
using a roll-coater with inhibiting oil to apply a pattern of oil
to prevent permanent deposition onto predetermined regions of the
web 30 on a "front" side of a PET web. Layers 34 and 36 of
MgF.sub.2 and Cr are deposited over the front side to form optical
interference structures over the Al; the Al serves as a reflector
in the Fabry-Perot structure(s). Another optical structure 39, such
as a reflective layer, an optically variable (OV) layer, a magnetic
layer, either continuous or patterned, either sandwiched between
layers of aluminum or as a single layer or fluorescent layer is
formed on the "back" side of the web. In this embodiment, a
protective layer is optionally applied to both surfaces of the OVD.
The optical structure may be opaque or semi-transmissive.
[0059] In accordance with this invention, in the embodiment where a
magnetic layer is sandwiched in between the reflective layer, as is
described in U.S. Patent application number 2002/0160194A1 and WO
02090002(A2), in the name of the same inventor, a cover signature
is present. A number in digital code or as in a bar code may be
present, that is unseen by the naked eye, and may be fore
validating the serial number on the bill or the denomination for
example, $50.00.
[0060] In this embodiment, where a magnetic bar code is hidden
within the device, it exhibits the same reflective properties as
aluminum but has a magnetic signature that can be read with
appropriate magnetic detectors. The magnetic detection may be just
the presence of a magnetic material as in a magnetic image such as
a hidden bar code or a hidden logo, or may be a signal of digital
or analog recorded information.
[0061] In accordance with this invention, the thickness of the
magnetic layer is preferably between 0.1 and 1.0 microns in
thickness. In the prior art, it is known to use a thick layer for
example having a thickness of 12 to 13 microns. Notwithstanding,
this invention can provide a very thin layer that is detectable by
providing a continuous layer of magnetic metal or metal that is
detectable by magnets. Thinner layers are advantageous for use with
security threads to be imbedded in or on currency so that a large
stack of bills do not pile up at an angle when stacked.
Furthermore, providing thinner layers ensures that that overall
thickness of the thread remains relatively thin, which is desired.
Hence, the thickness of the magnetic layer should be less than 5
microns and preferably less.
[0062] In the simplest case, as shown in FIG. 4 a single layer 42
of magnetic material may be deposited onto the plastic web 40,
patterned by the oil imaging method, and then formed into a
security thread, label or hot stamp image. In more complicated
structures, the patterned magnetic layer 52 supported by a
substrate 50 is sandwiched between two layers of aluminum 54 and 56
as is shown in FIG. 5 or is sandwiched between two layers of
aluminum in a Fabry-Perot optical stack shown in detail in FIG. 6
wherein a substrate 60 has deposited thereon a patterned aluminum
layer 62; upon the layer 62 is a Cr layer 63 a dielectric layer 64,
and a magnetic layer 66 between two Al layers 65 and 67 upon the
dielectric layer 64. In the instance where only one side of a
security thread is visible, the magnetic layer 66 can be covered by
a single layer of aluminum 67 and need not be sandwiched between
two such layers.
[0063] Referring now to FIG. 5, a cross-sectional view is shown
wherein a plastic substrate 50 has deposited thereon a non-magnetic
layer 54 of aluminum. Of course other non-magnetic materials could
be used. A pattern of inhibiting oil is then applied to create a
predetermined bar-code pattern of oil dependent upon the design
upon the rollers that pick up the oil and coat the plastic web 50.
The magnetic layer 52 is subsequently deposited and magnetic
material only remains where no oil has been applied during the
vacuum coating and cleaning process. A final layer of non-magnetic
material 56 effectively sandwiches the magnetic layer 52 between
the two non-magnetic layers.
[0064] In an alternative embodiment now shown, one could use an
additional layer over a patterned layer to serve as a leveling
layer. This could be done by evaporating an organic smoothing layer
in vacuum and curing by cross linking as taught by Yializis in U.S.
Pat. No. 6,706,412. In the embodiment described in accordance with
this invention, the depth of the vacuum deposition layer is
considerably thinner than the thickness of the oil pattern; hence
in relation to the oil thickness of about 10,000 Angstroms the
small bumps of 1000 Angstroms or less for the vacuum deposited
layer would be negligible. Patterning for multilayers could take
place on unpatterned regions or even on previously patterned
regions.
[0065] FIG. 6 is a more complex structure than that of FIG. 5,
however the method of manufacture is essentially the same,
patterning and depositing subsequent layers.
[0066] In yet another embodiment of the invention the combination
of patterned thin film with color shifting ink including but not
limited to inks containing pearlescent type pigments based on
coated mica, SecureShift.RTM. colors (registered to Flex Products),
optically variable ink (OVI.RTM., registered to SICPA), inks based
on diffractive based pigments or liquid crystal color shifting inks
can be present. The pigment may be formed of flat thin film optical
structures or may be formed of diffractive flakes as described in
U.S. Pat. No. 6,692,830 and PCT patent application WO
03011980A1.
[0067] Referring now to FIGS. 7 and 8 an embodiment of the
invention is shown that utilizes color-shifting ink. In this
instance, the color shifting ink 75 is visible through the holes or
windows 76 in the patterned thin film 73. In the simplest case, a
patterned aluminum 73 is formed on a plastic film 70 such as
polyester terephthalate (PET) and the color shifting ink 75 is
coated over the patterned aluminum so that from the opposite side,
one sees a color shift with viewing angle through the text or
graphic images or appears as background around reflective text or
graphics.
[0068] In FIG. 8 is an illustration showing that the background can
be non-color shifting and foreground color shifting or vice
versa.
[0069] Alternatively the color shifting ink is coated onto the
surface opposite the patterned aluminum so that one views the
security device from the patterned aluminum side. In this instance,
the color shifting ink shows through the openings of the patterned
aluminum. As in embodiments described heretofore, the patterned
aluminum can have an additional protective layer placed upon it,
such as a scratch resistant lacquer or is laminated to a thin PET
sheet typically having a thickness of 0.5 mil or less. FIGS. 9 and
10 exemplify these structures.
[0070] In FIG. 9 a plastic web 90 has on an upper side thereof, an
optically variable structure 92, for example in the form of
optically variable ink, color shifting ink, optically variable
pigment or a thin film Fabry-Perot cavity structure. On a lower
side of the web, a patterned layer of aluminum 94 is shown. In FIG.
10 a color shifting ink layer 105 is disposed upon a plastic
substrate 100 and a patterned layer of aluminum 103 is deposited on
the lower side of the substrate 100 having a protective lacquer
coating 106 over it.
[0071] In one embodiment, the reflective layer is a layer of opaque
aluminum, so that the window portions of the patterned layer appear
reflective. The backside reflector does not typically form an OV
structure with the front side MgF2-Cr layers because the
intervening PET web is relatively thick for use as a spacer in a
Fabry-Perot structure in the visible range of light. The window
portions appear mirrored, while the front-side F-P structures
provide an OVD as is shown in FIG. 3.
[0072] Alternatively, the optical structure on the backside of the
web is an optical interference structure, such as a thin-film
absorber layer on the PET web, a spacer layer over the absorber
layer, and a reflective layer over the absorber layer, thus
creating a second F-P structure in addition to the F-P structures
on the frontside of the web as is shown in FIG. 11. A reflective
backside layer 112a is particularly desirable for security threads
with OVDs because the mirror-like background provides a good visual
reference to the color change of the frontside OVD. This reflective
backside layer also serves as a layer in the optically variable
structure defined by the two adjacent layers; a Cr layer 115a, a
dielectric layer 111a. FIG. 11 also shows a plastic substrate 110
having a patterned aluminum layer 112, followed by a dielectric
layer 111 having a layer of Cr 115 over top.
[0073] Alternatively, a layer of color shifting ink may be applied
to the backside of the web. The application of color shifting ink
to the backside of the web enables an optically variable (OV)
effect when the structure is viewed from either side. When viewed
from the backside, the OV effect of the color shifting ink is
observed. When viewed from the front side, the OV effect of the
color-shifting structures formed with the patterned Al layer is
observed, in addition to the OV effect of the color shifting
ink.
[0074] Turning now to FIG. 12, a PET web 120 is shown with
patterned aluminum 112 on the front side and an optical structure
on the backside. In one embodiment the optical structure is an
organic layer 128 containing Anti-Stokes material in the form of
powder. The Anti-Stokes layer fluoresces at a shorter wavelength
when illuminated at a longer wavelength. Many suitable materials
exist, and are typically applied to the backside of web as very
fine particles in a carrier. Powdered Anti-Stokes material is
available from STAR DUST TECHNOLOGIES. The particles are generally
light-colored, such as a cream or a light tan color, and fluoresce
in a color, such as blue, green, yellow, or orange when irradiated
with near IR light, which is outside the visible range. Thus, when
the window portions are irradiated with the near IR light, the
window portions fluoresce in a visible color. This can be used as a
covert security feature because the Anti-Stokes coating is not
easily seen by casual observation.
[0075] Alternatively, shown in FIG. 13, a patterned optically
variable foil comprising a patterned layer of aluminum 132, a
dielectric layer 131, and a Cr layer 135 may be formed on one side
of the PET and a printed layer of regular ink 136 is printed on the
second side of the PET substrate 130. The printed ink 136 is either
black in color or is a complimentary color to the normal (90
degree) color of the color shifting foil. In this case, the black
or complimentary color shows through the windows of the patterned
OVD or in the reversed image, the black or complimentary color
layer acts as a background for the color shifting patterned text.
For instance, a green to blue color shifting foil would have a
magenta printed ink on the second side of the PET; for example,
green and magenta are complimentary colors. In both instances, the
contrast between the printed ink layer and the color shifting foil
allows easy viewing in reflected light. A matching color could also
be printed so that the reflected colors of the text only show up at
other angles than the one at normal.
[0076] In an embodiment shown in FIG. 3b, the plastic web a plastic
film 30 has an embossed surface coated with an aluminum layer 32 on
the side opposite the patterned coating 34 so that the holographic
imagery or diffractive imagery shows through the holes 36.
[0077] FIG. 14 shows an OVD (optically variable device) formed on a
web 140 wherein a reflective layer 142, such as an Al layer is
deposited, and an overlying spacer layer, such as an MgF2 layer
144, is patterned, with the oil-"inhibiting" technique. An absorber
layer 146, such as a thin layer of Cr, is deposited over the
underlying layers to form OVDs where the reflective, spacer, and
absorber layers form an F-P structure. As with the OVD shown in
FIG. 3 wherein the optical structure on the backside is a
reflective layer, the embodiment shown in FIG. 14 may have highly
reflective regions proximate to the OVD structures that provide
visual references when observing the OVD. In another embodiment,
more dielectric layer material can be deposited onto the patterned
dielectric so that a color-shifting pattern is formed on top of a
different color-shifting pattern, once the final absorber layer has
been deposited.
[0078] FIG. 15 shows an OVD formed on a web 150 with reflective and
spacer layers 152 and 154 respectively formed on the web and an
overlying patterned absorber layer 156. The absorber layer is
patterned using the oil-ablation techniques. An OVD is formed where
the absorber material remains.
[0079] FIG. 16 shows a simplified coating machine according to an
embodiment of the invention. The coater includes an unwind roller
160a, a wind roller 160b, a printing head 162, an evaporation boat
164 and glow discharge elements 166a and 166b. In operation, the
printing head 162 receives the "inhibiting oil" oil from the
pick-up roller 168 and applies the oil to a PET web 170.
[0080] The oil has the property that it does not readily evaporate
in the vacuum of the roll coater, but readily evaporates when
subjected to the heat of condensation of the evaporating material.
In addition, the oil has the property that is does not spread on
the surface of the plastic web i.e. there is little, if any, dot
gain.
[0081] The oil must stick to the substrate but not spread beyond
the image area that is printed. Ideally, it should have an
interaction with the plastic web but not spread. If it spreads
beyond the image of the imprinting cylinder, the image will not be
faithfully reproduced. If the graphic images are in pixel form, it
is important that pixels are distinguishable from one another and
do not have edges or portions that run into each other. Such an
unwanted increase in pixel size is known as dot gain. For very thin
layers of oil it likely does not make any difference whether it is
wetting oil or non-wetting oil. However, it is preferable that oil
not bead up. If the oil was thick and non-wetting, it would simply
bead up and run off of the web and not maintain the printed image.
The spreading of one material on another is determined by the
respective surface energies, .gamma.A, .gamma.B and .gamma.AB,
where .gamma.A is the surface tension (ie. surface energy) of the
plastic web, .gamma.B is the surface tension of the oil and
.gamma.AB is the interfacial surface tension. Spreading is
determined by the equation S.sub.L/S=.gamma.A-.gamma.B-.gamma.AB,
where S.sub.L/S is the spreading coefficient. If S.sub.L/S is
positive, spreading will occur. In other words, .gamma.A is larger
than the sum of .gamma.B and .gamma.AB which means (.gamma.B plus
.gamma.AB) has a lower surface energy than .gamma.A. Thus, to
minimize energy, spreading will occur. Therefore, S.sub.L/S should
be negative so that spreading of the oil on the plastic substrate
does not occur. As mentioned above, spreading would be detrimental
since the dot gain would reduce the resolution from the original
print image on the patterned imaging roller. The oil also has a low
vapor pressure so that it does not evaporate after printing the
image onto the web. FOMBLIN or Krytox oils meet the spreading
criteria; however, other low vapor pressure oils may be used
depending on the substrate being used.
[0082] In operation, the web is advanced to the evaporation boat,
which deposits Al or other material on the surface of the web.
Process conditions are controlled so that the heat of condensation
of the Al vaporizes the oil where it underlies the Al, removing the
Al from the regions that previously had oil. An alternate
explanation is that the oil prevents nucleation of the depositing
aluminum, i.e. the aluminum does not stick and re-evaporates into
the chamber. However, even though the process occurs under vacuum,
it was discovered that either products of oil breakdown and/or
residual oil (generally "oil residue") may be present on some
portions of the web, including the backside of the web after vacuum
deposition. Such residue can degrade the optical performance of
OVDs subsequently formed on the web and prevents acceptable
adhesion of subsequent then film layers. It is very difficult to
even detect the presence of such residue, absent forming an OVD and
evaluating its optical performance. Ghosting, smearing, and other
undesirable effects were observed when thin-film OVD structures
were deposited on webs with patterned Al without some cleaning of
this residual oil. The Al was deposited and patterned in one vacuum
coater, and the OVDs were deposited in another vacuum coater. It
was found that oil residue removal can be performed in the Al
coater after patterning, in the OVD coater before deposition, or
that a single vacuum roll coater can be used to deposit and pattern
the Al and to deposit the OVD layers, with an intervening
cleaning.
[0083] A glow discharge cleaning technique was used to successfully
remove oil residue. Several types of glow discharge cleaning
techniques were evaluated, as well as other cleaning techniques. A
glow discharge cleaning technique using argon gas was tried, but
did not adequately clean the residue of the oil used in the
patterning process. IR heaters were used before coating, but oil
transfer still occurred, presumably because oil transfer between
layers of the web occurred. For example, oil residue on the
frontside of the web will be transferred to the backside of the web
on the wind roll. In an in-line process that coats the OVD before
layers of the web are wound together, frontside cleaning of residue
may be sufficient. However, with the oil used in this example, it
is believed that some amount of cross-contamination occurred during
the patterning process, and cleaning both the fontside and the
backside was performed, as shown in FIG. 17.
[0084] Many additional features of the coater are omitted, such as
tensioning rollers and chamber dividers. Similarly, the web may be
held against a drum during the Al deposition/patterning.
[0085] FIG. 17 shows a simplified depositing apparatus for cleaning
a patterned web. The patterned web 170 comes off the unwind roller
170b and along a series of tension rollers. The backside of the web
is cleaned at a first station with a first glow bar 171, shown as
being unshrouded. The frontside of the web is cleaned at a second
station 172 further along the web with a glowbar that is shrouded.
The shroud is optionally omitted if the glow discharge does not
affect other system components. Similarly, cleaning the backside of
the web might not be necessary in all embodiments. Oxygen was
provided to the glowbar shroud, but could be provided at other
locations of the chamber. The oxygen provided at the shroud
diffused to the region of the first glowbar to create the cleaning
discharge. A chamber divider 179 keeps material from the OV
source(s) from depositing on the tension rollers and other system
components. The web is tensioned against a coating drum 178 during
deposition of the OV layers. A glow discharge using O.sub.2 as the
precursor was found to work well to clean the web of oil residue.
Other precursors may be preferred for other oils or liquids, or
even for this type of oil residue. In a particular embodiment, a
web of PET about 8.5 inches wide was transported through a glow
discharge cleaning stage at a speed of 0.5 meters/second. The total
current to the backside glowbar and the frontside glowbar was 100
mA and the glowbars were operated at 2,200 Volts. Pure O.sub.2 was
provided to the shroud of the frontside glowbar to create a chamber
pressure of 5.times.10.sup.-3 Torr to remove the residual oil from
both sides of the patterned web. An OVD that was formed on the
patterned web after cleaning in this fashion showed good optical
characteristics, suitable for use in commercial applications.
FURTHER DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0086] The invention is generally directed toward methods and
apparatus for manufacturing imaged foils, as well as security
articles including optically variable foils and security labels. In
a particular embodiment, an optically variable foil is produced
using an all vacuum in-line process.
[0087] A substrate consisting of 0.25 to 5 mil PET, preferably
0.5-1.0 mil (1 mil=25.4 microns) is first patterned on the web,
width 2''-60'' or more, with a positive or negative image with
perfluorinated polyether as described in US publication
"Proceedings of the Fourteenth International Conference on Vacuum
Web Coating, Oct. 25-27, 2000 by Aerre Machine. A printing station
similar to that described in U.S. Pat. No. 4,749,591 was used and
is incorporated herein as a reference. However, the printing method
is not necessarily limited to that described in U.S. Pat. No.
4,749,591. For example, other printing techniques may be used
include ink-jet printing, flexographic printing, gravure printing
or lithographic printing, or even dot matrix printing. In the case
of ink-jet printing, it is possible to change the pattern or
imagery without breaking vacuum. Advantageously, this allows
customized patterns to be created on the plastic roll without the
need for a roll on a printing station that requires a pre-imaged
print roller. Such patterning with an ink jet process would allow
sequential numbering of security labels and other security devices,
which is highly advantageous. Multi-layer patterning using a single
patterning roll or using different patterns in subsequent thin film
layers using the ink jet printing process may be used to create
complex graphics or even micro-electronics in the security thread.
In particular, a security thread with an optically variable feature
may be combined with a hidden magnetic bar code in either one
dimension, as in a standard bar code, or in a two dimensions, as in
a 2D bar code format. The magnetic layer is hidden between other
layers of the thin film design, as for example behind a reflective
layer or sandwiched between two highly reflective aluminum layers
as shown in FIGS. 18 and 19.
[0088] To insure good image fidelity, the printing station should
be situated on the cooled drum immediately before the deposition of
the first layer, typically aluminum, but may be any material with a
heat of condensation sufficient to vaporize the imaged oil. Other
substrates such as polyimide, polyhexadiene, polypropylene,
polyethylene, polystyrene, polycarbonate triacetate, biacetate, and
polynathphanate (PEN) may be used instead of the polyethylene
terephthalate (PET). With other substrates and other surfaces,
patterning oils based on the findamental surface energies
encountered and required low vapor pressures as described above
would be used.
[0089] Depositing the first layer that is to be imaged is the next
process step to be performed. In the case of an OVD security image
that is optically variable, either the reflector layer or the
absorber layer may be imaged. In general, any layer may be imaged
as long as the oil patterning process produces a discreet oil
image. For example, the imaging may occur in the dielectric layer
by placing the oil image on the prior-deposited layer. In other
words, the reflector layer or the absorber layer may be the layer
upon which the oil image is placed. Deposition of a metal layer
onto the patterned oil results in explosive evolution of liquid oil
into gas, causing the depositing layer to be ablated away. There
may be some residual oil (several monolayers of oil) remaining in
the patterned area which must be removed in order to this imaged
oil from transferring further down the web which would in turn
cause ghosting (another image pattern) of any subsequent deposition
layers.
[0090] In a typical case, the aluminum layer or the chromium layer
is imaged and then the rest of the design is added to complete a
Fabry-Perot structure, i.e. Al (opaque, patterned)/MgF.sub.2 1 QW @
400 nm to 8QW @ 700 nm/Cr 30% T. The low index MgF.sub.2 layer may
be substituted by any dielectric material that is highly
transmissive in the visible. High index dielectric materials will
result in an optically variable foil that is less shifting in color
than one that has a large optical shift where a low index
dielectric material is used. A partially aluminum layer that has a
thickness below the opaque point, for example, thickness in the
range 200-800 nm, will give a color shifting film that is partially
transparent so that information may be read through the optical
stack from the paper, or that is printed on the PET. All color
shifts move from long to shorter wavelengths, i.e. from
red-to-blue.
[0091] To remove residual oil in the patterned area, an oxygen glow
situated right after the deposition source on the cooled drum is
used. Glows may also be used on the backside of the web before and
after the deposition area. In this instance, the 02 glow will
remove any oil from the backside of the web that might have
transferred during the "inking process" or flash over during the
deposition process that could end up on the back side during
wind-up. Typically, the oxygen glow is run at 2,200 volts at 100 ma
for a 12'' wide glow system. Residual oil may be detected on the
final coated web by noting the variation in color, for example
blotches or ghost like images of the original images.
[0092] Resolution of the image using the flexographic printing
process has shown to be as low as 20 microns although 70 microns is
nominal. This is shown in FIG. 20. Besides text, a graphic image
can be made by processing a scanned image using a FloydSteinburg
technique as found in the software program COREL DRAW.TM.. This
program converts the image into square pixels, which have good
black (image) and white (no image) contrast. After coating, the web
is slit into ribbons between 1 and 5 mm wide wherein the text is
generally situated in the center of the ribbon. FIG. 21 show the
optically variable thread of this invention windowed into a bank
note and FIG. 22 shows the text symbols when viewed in
transmission.
[0093] Instead of a ribbon, the device may function as a security
stick-on label by applying adhesive 232 to one side of the PET and
laminating to a release layer 234 supported by paper carrier 236
and die cutting the label 230 as is shown in FIG. 23. The adhesive
can be a solvent based or a water-based adhesive. A suitable
adhesive is an acrylic adhesive, among many others. Instead of a
label, the product could be made into a hot-stamp security product
by inserting a release layer between the carrier web and the vacuum
deposited layer.
[0094] Of course numerous other embodiments may be envisaged
without departing from the spirit and scope of the invention.
* * * * *